Lithium sulfide (Li₂S) delivers a high theoretical capacity of 1166 mAh g^-1 and can be paired with lithium-free anodes, which makes it a very promising cathode material for Li/S batteries. However, its low electronic and ionic conductivities contribute to a high activation voltage for Li/Li₂S cells. In order to reduce the activated voltage, we designed and prepared a Li₂S-C nanofiber cathode by electrospinning and a Li₂S-C nanoparticle composite cathode by sulfur assisted ball-milling method, respectively. The Li₂S-C nanofiber cathode with ultrafine Li₂S grains embedded in the mesopores of carbon nanofibers showed an activated voltage of 2.58V and a low charge potential of 2.51V, and delivered a discharge capacity of 510 mAh g^-1 after 100 cycles at 0.5C rate. The Li₂S-C nanoparticle composite cathodes prepared by ball-milling have a high Li₂S loading of about 82 wt.%, 76.3 wt.% amd 64wt.%, respectively, and showed a similar initial charge process and excellent cyclic performance as the Li₂S-C nanofiber. A specific capacity of 506 mAh g^-1 after 200 cycles at a rate of 0.5C can be obtained. These excellent properties could attributed to the formation of ultrafine grains size of Li₂S in highly porous and conductive carbon matrix.

In this work, alternative manufacturing methods are presented for the fabrication of sulfur composite cathodes. The high dispersion and homogeneity of the cathode layer result in high capacity Li/S batteries. Additional use of LiNO₃ as additive improved the energy density to 840 Wh kg_cathode^-1 (at 0.2 C) and 433 Wh kg_cathode^-1 (at 2 C) after 50 cycles. The shuttle mechanism is reduced and a coulombic efficiency of around 100% is reached and maintained constant until 1000 cycles. To understand more the degradation mechanisms of the battery, Thermogravimetry combined with gas analysis (TG/MS) as well X-ray diffraction (operando and mappings) were applied. The formation of an amorphous phase during cycling that remains nearly stable in the later cycles is considered to be one of the main factors affecting capacity decay. Moreover, others processes are identified as contributors of battery degradation like PVDF decomposition, structural changes of carbon black, and reduction of sulfur content on the bulk of the electrode. These new insights on the degradation processes may contribute to the further understanding, selection of materials, and improvement of this battery.

Lithium sulfur battery has attracted a huge amount of attention because of the extreme high theoretical capacity and low cost compare to other lithium battery. But the poor cycling life of lithium sulfur battery kept them from large scale usage. The relatively low electric conductivity of the charge and discharge product is another limitation for lithium sulfur battery. A lot of research work has focused on the improvement of electrode design, including the combination of porous carbon film, carbon paper, carbon nanotube, graphene or other conductive additive. The design of binder is another effect way to improved the battery performance. Since the binder covers up most of the inner surface of the electrode, it has a important effect in surface modification. In lithium sulfur battery, a notable feature of phase transformation will take place. During discharge, solid phase S₈/LiS₈ will change into soluble Li₂S₄, then precipitate into solid state Li₂S, while a combination of solid phase and liquid phase reaction will take place during charge. The surface effect of binder will have a much bigger influence on lithium sulfur battery performance because of this phase transformation. In this work, we will choose both conductive and non-conductive binder with different functional groups to study the effect of binder on surface modification and conductivity on battery performance. A huge difference is observed in charge and discharge behavior and final products between different binder. It indicates the surface modification effect of binder which might have a big influence in reaction mechanism. So, we suggest that the designing of binder with preferred physical and electrochemical properties are indeed crucial in further improving the performance of lithium sulfur battery.

The lithium-sulfur chemistry is a potential breakthrough solution to the enduring battery performance problem of inexpensive portable energy storage. A lithium-sulfur battery could achieve specific energy levels up to 800 Wh/kg, while lithium-ion cells today delivery only 250 Watt-hours per kilogram (Wh/kg), with potential improvement to 400 Wh/kg in the future. Lithium and sulfur are inexpensive raw materials, enabling lower cost batteries, and the cells can be produced in the same factories that are making lithium-ion cells today.
Although the operation principle of Li-S batteries has been known for decades, unfortunately they have not been commercialized on a large scale to date. The major problems connected with a fast capacity fading (stability) and low cycling efficiency are mainly due to a complicated reaction mechanism which involves different soluble lithium polysulfides.
It has been proposed that a high surface area, porous carbon materials enable confinement of sulfur and polysulfides and have an impact on the Li-S battery cycling properties (capacity and efficiency). However, some literature reports to have showed that the use of carbons with a designed morphology is insufficient for long cycling stability. Additional stability can be gained by utilizing a doped or optimized Li₃ClO-based glass electrolyte [1] as a barrier to halt the diffusion of polysulfides into the lithium.
In this study, we present our recent results on the role of LiRAP (lithium rich anti-perovskite) - as a solid state Li-S electrolyte. Besides using our doped or optimized Li₃ClO-based glass electrolyte, we have also prepared a highly efficient sulfur cathode which allows for an increased sulfur loading of up to 6.9 mgcm^-2. The use of the here reported electrolyte has resulted in a significant improvement in coloumbic efficiency and in a longer cycle life. The impact of an optimized electrolyte/cathode on the mechanisms proceeding in Li-S batteries were studied using 2.5 x (2.5 or 3.5) cm² cells and potentio - galvanostatic measurements.
[1] M.H. Braga, J.A. Ferreira, V. Stockhausen, J.E. Oliveira, A. El-Azab, Novel Li₃ClO based glasses with superionic properties for lithium batteries, J. Mater. Chem. A 2014, 2, 5470-5480.
[2] A. Murchison, J.A. Ferreira, M.H. Braga, Superionic solid electrolyte for Li-S batteries, in preparation.

The hybrid lithium-sulfur flow battery is a promising technology for grid-scale energy storage owing to its energy-dense character. Among the obstacles in developing a stable prototype has been the poor cycle life and rate performance currently possible with commercially available materials for the catholytes and membranes. For example, cross-over of soluble polysulfides from the catholyte to the lithium anode causes continuous and undesirable capacity fade over time. In that commercially available mesoporous separators do not adequately impede polysulfide cross-over, a paradigm shift is needed to advance the technology further. We will report our recent results in tailoring the pore structure and pore chemistry of polymer membranes for the specific task of reducing polysulfide cross-over. Our polymer platform is modular in this regard, and highlights the versatility of polymer design to address critical transport problems in this component of the energy storage device. We will discuss in detail their use in Li-S liquid cells employing lithium polysulfide catholytes in glymes as the electrolyte solvent and with Ketjen Black as the conductive additive.

Energy storage is an ubiquitous need in our modern society. To meet this need, a myriad of materials and device designs have been developed. A growing trend is the focus on the sustainability of these materials, such as the new NSF emphasis on Sustainable Chemistry, Engineering, and Materials (SusChEM). The work to be presented is the development of lithium battery components based on renewable resources such as cathodes based on lignin from woody biomass and alginate from marine plants as an electrode binder. Lithium sulfur batteries with high coulombic efficiency have been succesfully developed and will be used as a model system for the SusChEM initiative in the area of sustainable energy materials. Lignosulfonate can be thermally converted and annealed to yield a high-performance cathode material for use in Li-S batteries, with initial results showing reversible capacities in excess of 600 mAh/g, corresponding to an energy density of ~1300 Wh/kg and with Coulombic efficiencies greater than 99%. Fluorinated polymers were avoided and sodium alginate binder was succesfully employed to create electrodes through a slurry process.

Sulfur (S) and lithium sulfide (Li₂S) are prime candidates for next-generation rechargeable battery cathodes due to their much higher specific capacities compared to those used in lithium-ion batteries today. However, both S and Li₂S cathodes are plagued with the problems of low electronic conductivity and dissolution of intermediate lithium polysulfides into the electrolyte. Carbon-based materials are conventionally used to encapsulate these cathodes in an attempt to trap the lithium polysulfides, but the non-polar nature of carbon renders weak interaction with these polar lithium polysulfide species, hence weakening the trapping effect. Here we demonstrate the encapsulation of S and Li₂S cathodes using highly-polar TiO₂ and TiS₂ respectively, both of which bind strongly with lithium polysulfide species. Using S-TiO₂ yolk-shell nanostructures as cathode materials, we achieve a high specific capacity of 1,030 mAh/g_S, as well as unprecedented long cycle life of 1,000 cycles with a small 0.033% decay per cycle. Further, using the Li₂S-TiS₂ core-shell nanostructures, we achieve an unprecedented rate capability of 4 C with a specific capacity of 503 mAh/g_Li2S, as well as unprecedented areal capacity of 3.0 mAh/cm² with a high mass loading of 5.3 mg_Li2S/cm². This work opens up the new prospect of using transition metal oxides and sulfides instead of conventional carbon-based materials for effective encapsulation of S and Li₂S cathodes.

Porous carbons have been identified as excellent support materials for sulfur in lithium/sulfur batteries due to their good electrical conductivity, large surface area and low density. When made composites of these carbons with sulfur, they make the insulating sulfur electrochemically active. One of the major issues, though, of these C-S cathodes is getting less than theoretical capacity due to poor charge transfer kinetics. A variety of architectures of porous carbons have been designed so far to maximize sulfur utilization at higher charge/discharge rate. However, it is still not well established as to which textural parameter is more important than the rest for obtaining high specific capacities at fast C-rates, especially as the sulfur loading is increased. Moreover, no conclusive understanding of the effect of porosity on long cycle life (up to 1000 cycles) in relation to the amount of sulfur loading is present.
In this work, to address the aforementioned challenges, we systematically studied the effect of porosity characteristics like surface area, pore volume and pore size on sulfur utilization and long cycle life at high C-rates (1C) using highly tunable hierarchical porous carbons (HPCs) as the model system. All carbons were synthesized in the same way to eliminate any effects from other important parameters like electrical conductivity, surface chemistry etc. that may arise due to different synthesis techniques, carbon precursors and carbonization temperatures. A broad range of surface areas, pore volumes and pore sizes was present in the large set of carbons tested to get statistically accurate trends. The results obtained from this study on the correlation between individual structural parameter with specific capacity and cycle life, are conclusive and can be used as a useful guide for future development of carbon supports for Li/S batteries.

The lithium-sulfur system has been touted as one of the most promising next-generation battery technologies for achieving the significant weight and cost reductions required for efficient and pervasive vehicle electrification. However, the insulating nature of sulfur hinders the ability to create thick, high capacity cathodes which can be operated efficiently at the demanding power densities required by applications. In addition, the cycle-life of such batteries has been severely limited.
In this presentation, I will discuss the research and development efforts performed while working at Vorbeck Materials Corp. on an ARPA-E funded program with the goal of commercializing high performance lithium-sulfur batteries combining high-performance graphene-sulfur cathodes with a novel hybrid carbon/lithium anode system. I will first present a simple theoretical framework established to guide the optimization of various electrode formulations to maximize the full-cell specific energy.The impact of sulfur loading (in mg/cm²), graphene content, and the sulfur coating approach on capacity and cell-level energy density were determined at the extreme charge/discharge targets set by the ARPA-E program. The resulting batteries out-perform all other reports at the high targeted power densities.
The extreme charging currents required were found to result in extreme degradation of the lithium anode. To slow or even prevent this degradation a hybrid carbon/lithium anode system was developed. Throughout the talk I hope to emphasize the practical industrial perspective gained throughout this experience and emphasize the challenges associated with lithium-sulfur batteries exhibiting high areal capacity.

Low-dimensional sp² nanocarbon, such as carbon nanotubes (CNTs), graphene, and their hybrids, is of tremendous interest for advanced energy storage systems due to its extraordinary properties including outstanding electrical conductivity, excellent mechanical strength, and good chemical stability. Enormous efforts have been dedicated for attractive applications for sustainable energy harvest and storage. Among various energy storage systems, Li-S battery is highly considered as a promising candidate of next-generation rechargeable batteries for the extremely high theoretical energy density of 2600 Wh kg^-1, which is also benefited from the natural abundance, low cost, and environmental benignancy of cathode material S. However, several crucial problems should be addressed before its wide application: (1) Insulating nature of elemental S and its discharge products hinders full utilization of active materials, high-rate performance, and rechargeability. (2) Soluble polysulfide intermediates shuttle between cathode and anode, inducing severe parasitic reaction, depletion of Li anode, and capacity degradation. (3) Great volume fluctuation of S cathode causes electrode fracture and loss of electrical contact.
To circumvent above dilemma, low-dimensional sp² nanocarbon with tunable functionality and complex nanostructure was rationally designed as cathode scaffolds for high-performance Li-S batteries. Three major progresses on chemical vapor deposited (CVD) sp² nanocarbon aiming to conquer the major obstacles of Li-S battery would be presented: (1) Rational combination of graphene/single-walled CNT hybrids and chemically tailored porous carbon to obtain hierarchical nanocarbon with extraordinary powder conductivity of 55 S cm^-1 and high porosity, obtaining high S accommodation capability and outstanding high-rate performance of 810 mAh g^-1 at 10 C; (2) N-doped CNT for strongly-coupled C/S interfaces with enhanced chemical interaction between S species and N-doping sites, retarding dissolution of polysulfides and enabling 8-fold improvement of cycling life; (3) Hollow nanographene nanoshells with intriguing small size of 10-30 nm and single-/few-layer graphene walls to accommodate huge volume fluctuation, manifesting ultrahigh utilization of S as 91 % at 0.1 C and extensive long cycling life to 1000 cycles. This work would shed a new light on not only CVD synthesis of nanocarbon materials but also the comprehensive design of S composite cathode for high-performance Li-S batteries.

Lithium ion batteries have proven to be important energy storage devices. However, for certain domains like automotive transport, their storage capacities are too limited to serve as the primary energy source for general purpose applications.
The best candidates to overcome this limitation and, thus, replace the Li-ion systems are new battery types like lithium sulphur (Li-S) cells: Batteries based on this particular system already show better per-cycle performance than Li-ion.[1]
According to the current state of research, the efficiency of Li-S batteries is higher if the sulphur is confined in the cathode material.[2,3] So recently, hollow carbon spheres have attracted a lot of interest for application as cathode material in these types of batteries.[4,5] The cavity provides a large storage volume for sulphur while it can still be confined in the shell. But are they really the solution to the problems of Li-S batteries?
In this work hollow carbon spheres with mesoporous shell were synthesized by a hard templating approach employing silica spheres with a solid core and mesoporous shell. Impregnation of the template with a carbon precursor, carbonization under inert gas atmosphere and removal of the template by etching with hydrofluoric acid yielded hollow carbon spheres. The hollow spheres were characterized by nitrogen physisorption, scanning electron microscopy as well as transmission electron microscopy, powder X-ray diffraction and thermal analysis.
The carbon spheres were impregnated with sulfur via incipient wetness from solution and using melt impregnation at atmospheric pressure, enhanced pressure and under vacuum. The carbon/sulphur composites obtained through this procedure were then characterized by the same methods as the pure carbon.
The results of these analyses give strong hints that regardless of the impregnation method sulphur is only located in the shell while the cavity itself is not filled by sulphur. And to the best of our knowledge, none of the literature on hollow carbon spheres for Li-S batteries (e. g. [4,5]) does contain proof that sulphur diffused into the cavity of the particles.
Therefore, we strongly suspect that in the relevant literature, too, only the shell of hollow carbon spheres was filled by sulphur. This would make any other mesoporous carbon with a comparable pore volume an equally good cathode material.
[1] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J.-M. Tarascon, Nature Mater.2012, 11, 19-29.
[2] X. Ji, K. T. Lee, L. F. Nazar, Nature Mater.2009, 8, 500-506.
[3] S.-R. Chen, Y.-P. Zhai, G.-L. Xu, Y.-X. Jiang, D.-Y. Zhao, J.-T. Li, L. Huang, S.-G. Sun, Electrochim. Acta2011, 56, 9549-9555.
[4] N. Jayaprakash, J. Shen, S. S. Moganty, A. Corona, L. A. Archer, Angew. Chem. Int. Ed.2011, 50, 5904-5908.
[5] G. He, S. Evers, X. Liang, M. Cuisinier, A. Garsuch, L. F. Nazar, ACS Nano2013, 7, 10920-10930.

The development of reliable and efficient electrochemical energy storage systems that meet future demands is of great importance. Elemental sulfur is currently considered as one of the most promising cathode-active materials for rechargeable lithium batteries of the next generation. Reasons for this are, among others, the high theoretical energy density of the lithium-sulfur system and the abundance of sulfur. However, there are still many issues that prevent lithium-sulfur batteries from being used on a commercial scale, one of them being the poor capacity retention due to polysulfide dissolution. Several approaches to address the problem of the quasi-liquid cathode have been proposed and encapsulation strategies appear to be particularly promising.
Here we describe the hard templating synthesis of monolithic nitrogen-enriched carbons with high electrical conductivity and tailored porosity and their application as matrix material in high performance lithium-sulfur batteries. Electrochemical studies were carried out by cycling both coin and pouch cells, with areal mass loadings ranging from 1 to 4 mg(S₈) cm^-2. Low loaded cells exhibit very stable performance over hundreds of cycles (less than 5% capacity decay between the 5th and 1000th cycles at 1C). Highly loaded cells display good cyclability as well, with areal capacities approaching 3 mAh cm^-2 at C/5. Literature reports on sulfur cathodes showing similar capacity and durability are scarce. Apart from the sulfur loading, we also discuss the effect of the electrolyte-to-sulfur mass ratio on the cell characteristics and show data from in operando X-ray diffraction on 5×5 cm² pouch cells.
In the end, we present a route to fabricate 100-200 mu;m thick carbon discs with hierarchical pore structure for application as free-standing and binder-free electrodes in lithium-sulfur batteries. The latter are capable of delivering areal capacities exceeding 2 mAh cm^-2 over many cycles, at low C-rates.

Lithium-rich and manganese-rich composite cathode materials are promising candidates for use in the next generation of lithium-ion batteries. This class of materials is poised to be used for demanding vehicular applications due to the high capacities (~230 mAh/gm) that can be accessed during electrochemical cycling. However, major challenges remain that hamper actual cell performance. High voltage (> 4.5 V) cycling is necessary to extract the desired capacity, but it causes transition metal dissolution, large electrochemical hysteresis, possible oxygen loss, and the phenomenon of voltage fade. Once activated at high voltages during the first charge, further cycling leads to a continuous decay of the voltage profile and a concomitant decrease in energy output. Therefore, high voltage activation -- essential to access the high capacity of these materials -- induces the slow and progressive decay of voltage. In order to further develop these materials, it is of fundamental interest to understand the mechanistic details that lead to voltage fade. To this end, using a combination of electrochemical studies and characterization methods (x-ray spectroscopy and NMR), we seek to understand the structure-activity relationships of this class of materials. In this talk, we will present our recent findings related to the phenomenon of voltage fade in this class of materials. [1-4]
1. Croy, J. R.; Gallagher, K. G.; Balasubramanian, M.; Long, B. R.; Thackeray, M. M. Quantifying Hysteresis and Voltage Fade in xLi₂MnO₃bull;(1-x)LiMn_0.5Ni_0.5O₂ Electrodes as a Function of Li₂MnO₃ Content J. Electrochem. Soc. 161, A318 (2014).
2. Long, B. R.; Croy, J. R.; Dogan, F.; Suchomel, M. R.; Key, B.; Wen, J. G.; Miller, D. J.; Thackeray, M. M.; Balasubramanian, M. Effect of Cooling Rates on Phase Separation in 0.5Li₂MnO₃bull;0.5LiCoO₂ Electrode Materials for Li-Ion Batteries Chem. Mat. 26, 3565 (2014).
3. Gallagher, K. G.; Croy, J. R.; Balasubramanian, M.; Bettge, M.; Abraham, D. P.; Burrell, A. K.; Thackeray, M. M. Correlating hysteresis and voltage fade in lithium- and manganese-rich layered transition-metal oxide electrodes Electrochem. Commun. 33, 96 (2013).
4. Croy, J. R.; Gallagher, K. G.; Balasubramanian, M.; Chen, Z. H.; Ren, Y.; Kim, D.; Kang, S. H.; Dees, D. W.; Thackeray, M. M. Examining Hysteresis in Composite xLi₂MnO₃bull;(1-x)LiMO₂ Cathode Structures J. Phys. Chem. C 117, 6525 (2013).

Lithium-ion cathode materials have historically been limited to select crystal structures and cation orderings known to sustain facile lithium diffusion, such as the layered transition metal oxides. In layered materials (LiMO₂), anti-site disorder is undesired as cation mixed materials have smaller lithium slab spacing and consequently higher lithium diffusion barriers¹. Recently, however, Lee² and Urban³ showed that even disordered materials can cycle large amounts of lithium if the composition contains sufficient excess lithium (Li_1+xM_1-xO₂). In lithium excess chemistries, lithium sits in sites normally occupied by transition metals, creating low barrier lithium diffusion channels. These channels percolate across the particle at high lithium excess levels, creating a network of fast lithium diffusion pathways.
In this work, we validate the positive effect of lithium excess on electrochemical performance with a new series of Ni-based layered materials containing 0-15% lithium excess. We show that with increasing lithium content in this chemistry improves both discharge capacity and cyclability at 1C. Characterization on the lithium excess structures reveals a two domain microstructure in the transition metal layer, where the interface of the two domains forms the desired low barrier lithium diffusion channels.
The significance of this work is many-fold. First, we confirm the design principle of incorporating lithium excess to improve lithium diffusion in a new chemical system. Second, the distinct microstructure enables percolation of the low barrier lithium diffusion channels to be achieved at lower lithium excess levels. Finally, we demonstrate that percolation of these channels can be achieved in ordered materials, thus maintaining the high voltage advantage of ordered materials. These results point to an exciting strategy for future design of new lithium excess cathode materials.
Acknowledgment: This work was supported by Robert Bosch Corporation and Umicore Specialty Oxides and Chemicals. Research at sector 20-BM at the Advanced Photon Source was supported by U.S. DOE under Contract No. DE-AC02-06CH11357.
References
[1] Kang, K.; Ceder, G. Phys. Rev. B 2006, 74, 094105.
[2] Lee, J.; Urban, A.; Li, X.; Su, D.; Hautier, G.; Ceder, G. Science2014, 343, 519-22.
[3] Urban, A.; Lee, J.; Ceder, G. Adv. Energy Mater. 2014, 140078.

Standard lithium-ion porous battery electrodes contain active redox materials, binder, an electronically conductive carbon network, and are filled with a liquid electrolyte. While standard porous electrode models account for reaction and transport processes in the active material and electrolyte, they largely neglect the contribution of the conductive carbon network. Here, we control the degree of electronic connectivity in a porous LiFePO₄ electrode by varying the carbon content. Using nanoscale X-ray spectro-imaging, we determined the state-of-charge of ~1,000 particles in electrodes with various carbon loadings. We observed that smaller particles lithiate preferentially in electrodes with high carbon loading levels. At the same time, we do not observe significant particle size dependences in electrodes with lower carbon loading. These results reveal the intrinsic size dependence in the lithiation sequence of LiFePO₄ nanoparticles, as well as the strong connection between such sequence and the carbon loading level. This work highlights the importance of electronic connectivity in understanding size dependence and accurately modeling lithiation processes in battery electrodes.

In order to improve the electrochemical properties of LiFePO₄/C powder, a new grafting method for carbon coated cathode material was adopted in this study inspired from the previous studies of carbon modification ^[1]. The reduction of diazonium cations has been widely investigated during the past decades in order to functionalize surfaces ^[1-2]. Toupin and Bélanger ^[3] have undertaken detailed studies of the spontaneous reaction between Vulcan carbon black and aryldiazonium salts in aqueous solution. This method allows the attachment of various substituted aryl groups with a strongly C-C bond in order to change the surface properties.
This presentation will focus on the study of LiFePO₄/C cathodes for Li-ion batteries. More specifically, the aim of this work is to functionalize the carbon coating of LiFePO₄/C particles using diazonium chemistry. Bromophenyl groups were successfully grafted on carbon coating by reduction of in situ generated diazonium ions. An increase of specific capacity has been observed during cycling in coin-cell and more specifically at high rate.
The grafting reaction onto the carbon coating leads to a partial oxidation of LiFePO₄/C related to the amount of precursors used for the reaction. X-ray diffraction patterns show the presence of LiFePO₄/C and FePO₄ phases._. ICP analyses were performed in order to determine accurately the lithium content of the grafted samples. The ratios of LiFePO₄ and FePO₄ deduced from ICP analyses are consistent with those obtained with XRD measurements. Using XPS, the presence of grafted molecules on the carbon coating of LiFePO₄/C was confirmed.
Galvanostatic measurements at various current rates were carried out to further compare the electrochemical performances of LiFePO₄/C blank and grafted samples. At a 2C rate, the discharge capacity of the unmodified LiFePO₄/C is less (50 mAh.g^-1) than that of the bromophenyl (85 mAh.g^-1) modified LiFePO₄/C. At 5C, the specific capacity of the bromophenyl-modified electrode is estimated at 40 mAh.g^-1 while a very low capacity is achieved for the two others samples. It may be concluded that better electrochemical performance is obtained at higher cycling rate for the grafted LiFePO₄/C electrodes.From these results, the rate capability enhancement of the grafted samples can be explained by the presence of specific grafted groups onto the surface of the LiFePO₄/C particles that can “improve” the interfacial properties at the electrode particles/electrolyte interface. Future work will focus on the characterization of the surface of the grafted LiFePO₄/C.
References
[1] D. Belanger and J. Pinson, Chemical Society Reviews 2011, 40, 3995-4048.
[2] M. Delamar, R. Hitmi, J. Pinson and J. M. Saveant, Journal of the American Chemical Society 1992, 114, 5883-5884.
[3] M. Toupin and D. Belanger, Journal of Physical Chemistry C 2007, 111, 5394-5401.

LiMn_2-xM_xO₄ (M=Li, Al, Mg, Co, Ni, etc) have been considered as the most promising candidates for electric vehicles (EVs) and hybrid EVs (HEVs) because of advantages of low cost, abundance, good thermal stability and environmental affinity. The spinel material also has the advantages of fast lithium ions insertion/extraction resulting in high power performances because of a three-dimensional tunnel structure.^{1, 2} Lately, our group found that the electrically conductive carbon coated LiMn₂O₄ by using sucrose showed the outstanding power performance and from this study, the electron conductivity is considered as the rate determining step of the spinel LiMn₂O₄.³ However, this carbon coating methods always cause side effect of oxygen extortion from lattice during further heating treatment due to high concentration of oxygen in the lattice than in the air. Therefore, it is very difficult to optimize synthesis condition such as amount of sucrose, heating times and temperatures in order to conduct carbon coating without oxygen defects.
In this work, we synthesized the 20 micron-sized Li_1.01Al_0.06Mn_1.93O₄ and Super-P carbon black composite via simple spray drying process. This material showed the unprecedented rate capability. For example, the discharge capacity retention at 500 C-rate (60A g^-1) was 71.1% of its discharge capacity at 1 C and the charge capacity retention at 100 C-rate (12A g^-1) was 75.2% of its charge capacity at 1 C. The low temperature performance as another kinetic parameter was also greatly improved compared to bare material. Moreover, this material is the best candidate for Li-ion capacitors because not only is its power density comparable to supercapacitors and other Li-ion capacitors but also it shows much higher energy density than other capacitors.
1. N.-S. Choi, Z. Chen, S. A. Freunberger, X. Ji, Y.-K. Sun, K. Amine, G. Yushin, L. F. Nazar, J. Cho and P. G. Bruce, Angewandte Chemie International Edition, 2012, 51, 9994-10024.
2. M. S. Whittingham, Chem. Rev., 2004, 104, 4271-4302.
3. S. Lee, Y. Cho, H.-K. Song, K. T. Lee and J. Cho, Angewandte Chemie International Edition, 2012, 51, 8748-8752.

With concerns regarding the abundance and sustainability of lithium, the shift of much electrochemical research in batteries has been directed towards alternative systems using different charge carrying ions beyond Li, such as sodium and magnesium. Fortunately, Li-ion research has laid out an excellent platform to study and apply these alternative metal-ion systems due to the many similarities in the mechanism of intercalation-based charge storage. Systems beyond lithium require synthesis of cathode materials in the charged state in order to provide adequate amounts of charge carrying ions for energy storage. One method of preparing cathode materials in this state is chemical pre-intercalation, a simple and low cost method of inserting various charge-carrying ions into the crystal structure of a material. Additionally, post synthesis treatments, such as annealing and hydrothermal processes, can be performed on pre-intercalated materials to further improve their electrochemical properties. In this work, we synthesized lithium, sodium, magnesium, and potassium pre-intercalated vanadium pentoxide with nanostructured morphologies and explored the effects of post synthesis annealing and hydrothermal treatment on the electrochemical performance of Li/V₂O₅ system.
Chemical pre-intercalation was performed via a wet chemistry approach to successfully pre-insert charge carrying ions (K⁺, Li⁺, Na⁺, and Mg²⁺) into vanadium pentoxide. It was found that increasing the charge-carrier ion to vanadium molar ratio during synthesis from 1:1 to 5:1 resulted in a larger amount of pre-intercalated ions and thus a higher specific capacity (from 128 mAh/g to 182 mAh/g, respectively). Galvanostatic cycling of the materials in a Li-ion battery configurations was utilized to determine effects of the treatments on electrochemical performance. Annealing at 260°C for 24 hours under vacuum resulted in increased crystallinity of the vanadium pentoxides and improved electrochemical stability from 86.2% to 94.1% capacity retention over 20 cycles. Hydrothermal treatment at 180°C for 24 hours significantly increased the amount of pre-intercalated lithium ions. The initial specific capacity of the material was increased nearly twofold from 188 mAh/g for the untreated material to 368 mAh/g. Sodium pre-intercalated V₂O₅ annealed at 260°C for 24 hours under vacuum was galvanostatically cycled in a Na-ion configuration, and a first charge capacity of 170 mAh/g was achieved, indicating significant Na intercalation. On first discharge, this material exhibited a capacity of 270 mAh/g. In conclusion, we demonstrated how chemical pre-intercalation can be used in conjunction with post-synthesis treatments to enhance the electrochemical properties in a Li-ion battery system, and with successful pre-intercalation of ions beyond Li, this approach can be extended to emerging metal-ion systems such as Na-ion and Mg-ion batteries.

LiFePO₄ is very attractive as positive electrode material for lithium-ion batteries especially for its safety and low cost. However, its specific capacity is limited to 170 mAh/g. LiMBO₃ (M=Fe, Mn, Co) could be good alternatives to phosphates by having a higher theoretical specific capacity (>210 mAh/g) keeping the advantage of safety [1]. Moreover, borate compounds are expected to suffer from very low volume change upon cycling which is very interesting for the cycle life of the battery.Nevertheless, the lithium intercalation potentials in borate compounds are lower than in phosphates which will limit their energy density [2]. Theoretically, LiCoBO₃ is the most interesting borate compound in term of operating voltage and specific capacity; however, approaching its theoretical capacity seems difficult due to the structural/chemical instability of fully delithiated LiCoBO₃ [3].
In order to have both reversible capacity and relatively high voltage, new Li(Mn_1-xCo_x)BO₃ have been explored. These materials have been synthesized for the first time by a multiple-step process. This one includes the synthesis of two intermediates essential to prevent the formation of metallic cobalt and Mn³⁺ during the heat treatment.
Structural evolution of Li(Mn_1-xCo_x)BO₃ with the cobalt content has been followed by Powder X-Ray diffraction patterns and will be presented. TEM and neutron powder diffraction were carried out on these materials. Interestingly, ED patterns indicate that the C2/c space group previously reported for m-LiMnBO₃ [4] and LiCoBO₃ [5] cannot describe Li(Mn_1-xCo_x)BO₃ compounds. Neutron diffraction helps with the complete resolution of the structure and will be discussed during the presentation.
Electrochemical characterizations were also carried out on Li(Mn_1-xCo_x)BO₃ (0 le; x le; 1). Each material shows electrochemical activity, without in situ carbon coating. In order to improve performances of these compounds, an optimized synthesis has been developed and will be presented.
References:
[1] V. Legagneur et al., Solid State Ionics 139 (2001) 37
[2] D-H. Seo et al., Physical Review B 83, 205127 (2011)
[3] Y. Yamashita et al., ECS Electrochemistry Letters, 2 (8) A75-A77 (2013)
[4] O.S. Bondareva et al., Sov. Phys. Crystallogr. 23 (1978) 269
[5] Y. Piffard et al., Acta Cryst. (1998) C54, 1561-1563

Solid-state batteries have been developed rapidly due to their promising applications in safe, high-density energy storage technologies. Development of lithium superionic conductors with high conductivity and low activation energy is the most essential part in all solid-state lithium batteries. Significant progress has been made recently with discoveries of various superionic Li-ion solid electrolytes having ionic conductivity comparable with liquid electrolytes, but an in-depth understanding of the factors governing ionic diffusion properties in these materials are lacking. In this talk we will present our recent advances in revealing fundamental relationship between crystal structure and ionic transport in fast Li-ion conductors using first-principles modeling based on density functional theory. Our study highlights the critical influences of the anion-hosted matrix on the ionic conductivity. The findings not only provide valuable insights towards the understanding of ionic transport in discovered Li-ion conductors, but also serve as a design principle for the future discovery of new conducting materials for Li-ion batteries.

To design safe, high-energy, long-life and low cost batteries Li-air and Lithium sulfur (Li-S) are highly attracting technologies due to their high theoretical energy storage capacity. In case of Li-S battery, lithium metal is used instead of graphite as used in commercial batteries that has both electronic and ionic conductivity and work as sink and source. And the metal oxide is replaced by low weight and low cost sulfur that can bond to two lithium atoms yielding high energy density and low cost advantages for Li-S technology. The challenge for this technology to realize its full potential is essentially in the details of the reaction between lithium and sulfur. Polysulfides that are intermediately formed as the battery is charged and discharged, are soluble in the liquid organic electrolyte, causing capacity fading, self-discharge and degradation of the electrodes.
To prevent chemical reaction of the Li-S electrode materials with liquid electrolytes, here for the first time we use sulfide-based solid electrolytes (such as Agryrodites Li₆PS₅X, X=Cl, Br), Li₁₀GeP₂S₁₂ (LGPS)) as well as oxide-based solid electrolytes (Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP), Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLTZO)) instead of organic liquid electrolytes and combine them with organic catholytes. The use of fast ion conducting solid electrolyte membranes prevents that the polysulfides can reach the counter-electrode. The solid electrolytes need to exhibit a combination of fast lithium ionic conductivity of the order of 10^-3 Scm^-1 at room temperature with negligible electronic conductivity, electrochemical stability against reactions with the lithium anode or the cathode material, as well as suitability for industrial fabrication of dense solid membranes. Li-ion conducting argyrodites, LGPS, LAGP and LLTZO compounds were reported previously with ionic conductivity of the order of 10^-2 and 10^-4 Scm^-1 at room temperature.
We investigated the stability of all the above solid electrolytes when immersed in a solution of polysulfide, Li₂S₈, in tetrahydrofuran (THF) with the help of XRD, SEM and electrochemical impedance measurements. XRD and SEM indicated that an interface layer of (ion-conducting) thio-LISICON was formed on the surface of Li₆PS₅X and LGPS but the crystal structure was not changed inside the membrane material.
Li/solid electrolyte/Li₂S₈ (in THF) cells were assembled in a swagelok cell. Ni foam was used to enhance the electronic conductivity of the polysulfide cathodes. Li₂S₈/LAGP membrane/Li battery exhibited an initial specific capacity of 1289 mAh/g at a current of 0.1 mA/g minutely exceeding the theoretical specific capacity of 1254 mAh/g. Li₂S₈/LGPS/Li reached an initial specific capacity of 1444 mAh/g at 0.1 mA/g current.

Critical scientific and technical barriers for current battery technology center on safer operation, higher energy densities, and longer cycling lives. “Beyond Lithium-Ion” chemistries utilizing metallic lithium electrodes such as lithium/sulfur and lithium/air systems, have theoretical specific energies up to ten times greater than that of lithium-ion batteries. Safety concerns, due to the tendency for dendritic growth and mossy plating of lithium during prolonged cycling when conventional liquid or polymer electrolytes are used, are a formidable obstacle to their development. Solid ceramic electrolytes have been proposed as a promising solution. Cubic variants of the garnet phase Li₇La₃Zr₂O₁₂ (LLZO) are especially interesting because of their high ionic conductivities (>10^-4 S/cm) and apparent resistance to reduction by metallic lithium [1]. However, it has proven very challenging to process LLZO to simultaneously achieve high ionic conductivity, good chemical stability, and, most importantly, low resistance at solid electrolyte electrode interfaces.
We have addressed the difficulties in sintering LLZO by manipulating particle sizes of powders used to make green bodies, which are then densified. This has allowed us to lower the sintering temperature by 130° to 1100°C, while still using traditional low cost ceramics processing [2]. We are able to fabricate dense samples of different thicknesses with various interface microstructures; large-grained, small-grained, and hybrid structures [3], thus allowing us to study the effect of microstructure on electrochemical properties. We have learned that formation of very thin layers of Li₂CO₃ on LLZO pellet surfaces due to brief exposures to air [4] is often responsible for the high interfacial impedances observed in cells. The area specific impedance (ASR) is reduced by an order of magnitude when the layer of Li₂CO₃ on the pellet surface is removed. Lower interfacial impedances is also associated with smaller grain sizes and results in more stable DC cycling at higher critical current densities for Li/LLZO/Li symmetrical cells. A symmetrical lithium cell containing a dense small-grained sample of LLZO prepared in our laboratory exhibited the lowest ASR (37 W-cm²) ever reported for this material. Reasons for the improved performance of the small-grained LLZO samples will be discussed further during the presentation.
1.R. Murugan, V. Thangadurai, and W. Weppner, Angew. Chem., 119, 7925 (2007).
2.L. Cheng, J. Park, H. Hou, V. Zorba, G. Chen, T. J. Richardson, J. Cabana, R.E. Russo, and M. M. Doeff, J. Mater. Chem. A, 2, 172 (2014).
3.L. Cheng, W. Chen, M. Kunz, K. Persson, N. Tamura, G. Chen, and M. M. Doeff, Adv. Energy Mater., submitted.
4.L.Cheng, E. J. Crumlin, W.Chen, R. Qiao, H. Hou, S. F. Lux, V. Zorba, R. Russo, R. Kostecki, Z. Liu, K. Persson, W. Yang, J. Cabana, T. Richardson, G. Chen, and M. Doeff, Phys. Chem. Chem. Phys. DOI: 10.1039/c4cp02921f (2014).

Cubic Li₇La₃Zr₂O₁₂ (LLZO) garnets, especially Al and Ga doped LLZO, are receiving much scientific attention as fast lithium-ion conductor. [1,2] Superior chemical and thermal stability, electrochemical inertness in a wide potential window, and particularly its stability against Li metal, make LLZO an excellent candidate to be used as solid electrolyte in both lithium-ion and Li-oxygen batteries.
Much experimental as well as theoretical effort has been undertaken to collect information on the local coordination as well as the site preferences of dopant cations in LLZO. Finally, we could show that Al preferentially occupies the tetrahedrally coordinated 24d site and a distorted 4-fold coordinated 96h site in LLZO. [ 3] On the other hand, it turned out that Ga is solely located on the 96h site irrespective of the amount of Ga introduced. [4] Since the 24d site forms a junction between the loops of the Li-ion pathways in the fast lithium-ion conductor LLZO the occupation of the 24d sites by dopant cations is suspected to be more hindering the mobility of Li ions in contrast to the situation when only the 96h sites are occupied. Consequently, the location of Al and Ga is expected to strongly correlate with the Li-ion transport properties of LLZO.
In order to proof this assumption, we systematically varied the site occupation of 24d and 96h sites. This was done by synthesizing, for the first time, cubic mixed-doped Li_{7minus;3(x+y)}Ga_xAl_yLa₃Zr₂O₁₂ (AlGa-LLZO) garnet solid solutions with different portions of Al and Ga. We were able to show that phase pure AlGa-LLZO can be synthesized, with a higher solubility of Ga compared to Al. The evaluation of 42 different doping compositions clearly indicates an increase of the lattice parameter a₀ with increasing Ga content. High-field NMR studies carried out at 21 Tesla have shown that Ga occupies both the 24d and 96h sites; this is very similar to the behavior of Al. It is, however, in contrast to previous studies reporting on a single NMR line only. [2,4] The integrals of the NMR signals indicate that more 24d sites are occupied compared to 96h sites. ⁷Li NMR spectra show a decrease in line width with increasing Ga content; this points to an increasing Li diffusivity even though the overall occupation of the 24d sites increases. Finally, it seems that Li ion mobility seems to be more influenced by a₀ rather than by the site distribution of the dopants.
[1] Geiger, C. A.; Alekseev, E.; Lazic, B.; Fisch, M.; Armbruster, T.; Langner, R.; Fechtelkord, M.; Kim, N.; Pettke, T.; Weppner, W. Inorg. Chem. 2011, 50, 1089.
[2] Howard, M. A.; Clemens, O.; Kendrick, E.; Knight, K. S.; Apperly, P. A.; Anderson, P. A.; Slater, P. R. Dalton Trans. 2012, 41, 12048.
[3] Rettenwander, D.; Blaha, P.; Laskowski, R.; Schwarz, K.; Bottke, P.; Wilkening, M.; Geiger, C. A., Amthauer, G. Chem. Mater. 2014, 26, 2617.
[4] Rettenwander, D.; Geiger, C. A.; Tribus, M.; Tropper, P.; Amthauer, G. Inorg. Chem.2014, 53, 6264.

We report on a new family of fast ionic conductivity electrolytes based on the garnet LiLaZrO. Partial substitution of Zr by aliovalent atomic species through solid state solution synthesis results in ionic conductivities 2 orders of magnitude larger than the tetragonal phase of LiLaZrO and comparable to that of its cubic phase. The synthesis temperature is 400C lower than that required for the cubic stabilization of LiLaZrO. Ongoing impovements on microstructure and film density as well as optimization of the garnet stoichiometry are expected to yield ionic conductivities surpassing the highes values reported to-date on cubic doped LiLaZrMO (Ta, Al, W, Nb)

Li-ion batteries remain to be one of the primary choices in the portable electronics market by having the advantages of high energy density, variable long cycle life and variable charge-discharge rates compared to the other battery technologies. However, the current electrode materials are still not capable enough for the large energy density required for various applications (e.g. electric vehicles). Solid inorganic electrolytes become quite interesting at this point that can enable the use of high capacity electrode materials, which are otherwise not very stable and safe to be used in liquid electrolytes. They also provide additional advantages such as the elimination of the otherwise necessity for separators and usually better thermal and chemical stabilities. Here, Li₇La₃Zr₂O₁₂ garnets and doped variants are especially interesting solid electrolyte candidates with high Li-ion conductivities in the range of ~ 10^-4 S/cm at RT and offer also an enlarged thermal operation window. Despite the promises, processing of these ceramics based on conventional solid state synthesis and sintering was restricted to temperatures above 1000 °C to ensure the high Li-conducting cubic phase¹. We report a novel low temperature synthesis route for cubic Li_7-3x(Ga_x)La₃Zr₂O₁₂ through which we reduce the particle size, and the sintering temperature by more than 200 °C when compared to the state of art. Viz. nano-particles of the compounds could be obtained at a temperature of as low as ~ 600 ^oC by a modified sol-gel synthesis - combustion method utilizing mainly nitrate precursors. We also shed light on the conditions influencing the tetragonal to cubic phase transformation occurring at a very low temperature of ~ 100 ^oC.
Finally, we evaluate the newly synthesized Li_7-3x(Ga_x)La₃Zr₂O₁₂ in their near order structure-Li⁺ ionic transport interaction for low temperature processed All Solid State Li-ion Batteries towards various electrodes and performances. The new synthesis route and the utilization of nano c-Li_7-3x(Ga_x)La₃Zr₂O₁₂ open new pathways in terms of simplified solid electrolyte-electrode assembly and the prevention of Li-loss during synthesis and processing via strongly lowered temperatures and high sintering activity.
1. V. Thangadurai, S. Narayanan and D. Pinzaru, Chem Soc Rev, 2014, 43, 4714-4727.

Li-ion batteries are finding wide applications in consumer products and are attractive for electrical vehicle applications. There have also been intensive efforts for materials and systems with much higher energy densities (beyond Li-ions). On the other hand, technologies like lead-acid batteries are still widely used and have the highest battery market share in the world because of the low cost and good safety records even though the energy density is low. There is a gap between the high energy density, high cost technologies and those with low energy density but low cost and good safety. This presentation will discuss the progress in developing alternative technologies, such as redox flow batteries and hybrid concepts to fill in the gap. In particular, systems using aqueous electrolytes will be emphasized. Several approaches will be discussed for increasing the energy density of such systems, including improving electrolytes, using novel redox couples, or totally new battery designs.

I will discuss our recent development of nanoscale planar batteries that allows us to investigate the materials properties during electrochemical processes. In-situ measurement of transport, optical properties, structure changes etc. are possible with such nanoscale planar devices. I will also discuss two types of applications: intercalation optoelectronics and high-performance metal-ion batteries batteries.

According to the increasing demand on the wearable and body-implanted devices, there has been extensive research on the stretchable electronics including the energy storage devices. In addition to the design of novel stretchable devices, efforts on development of more practical functionalities have been also made.
In this work, we report on the fabrication of waterproof stretchable electronics with embedded energy storage devices of planar microsupercapacitors (MSCs). MSC fabricated on a PET substrate consists of spray-coated multi-walled carbon nanotubes electrodes and ion-gel electrolyte of PEGDA/[EMIM][TFSI]. In order to increase the total capacitance, two MSCs are designed to form one piece. Those fabricated MSCs are dry-transferred onto a specially designed deformable substrate of Ecoflex to minimize the strain applied to active devices, where the MSCs are electrically connected via 300 mu;m thick embedded liquid metal interconnects of Galinstan. After integrating the MSCs with a switch and a mu;-LED, the whole device is encapsulated with a drop-coated thin Ecoflex film to have the total thickness of 3 mm.
The whole device can be uniaxially stretched up-to 80% to have the stable total capacitance within 3%. Strain distribution analyzed by finite element method also confirms that the strain applied to the active devices of MSC, switch, and mu;-LED is less than 0.1% under uniaxial strain of 80%. Due to the difference in Young&’s modulus between PET and Ecoflex, the strain applied to the active devices on PET film can be minimized under severe deformation such as bending, twisting, and stretching. Of particular importance is the stability of the stretchable device in water: The total capacitance of the MSC array remains the same and the mu;-LED remains lit for the same duration time even under stretching in water.
This work demonstrates the high application potential of our waterproof stretchable device in various wearable and body-attached electronics for everyday uses.

We have successfully designed a process that utilizes high-speed co-extrusion to simultaneously fabricate two layers of a functional battery structure (separator and interdigitated cathode) in a single deposition step. The use of our novel co-extrusion printhead technology enables structuring in battery electrodes - a new design tool that can improve battery energy density and power for a given application. Our multi-layered printhead architecture co-extrudes alternating slurries side by side to form a fine horizontally interdigitated cathode structure. Concurrently within the printhead, a thin layer of separator slurry is deposited on top of the interdigitated cathode electrode before exiting the printhead and contacting a current collector substrate. The relative thicknesses, widths, and lengths of the deposited features can be varied by altering the slurry parameters, printhead geometry, and process conditions. Our co-extrusion process removes multiple steps in a conventional battery coating process and has the potential to revolutionize battery manufacturing across most chemistries, significantly lowering end-product cost and shifting the underlying economics to make electric vehicles (EVs) and other battery applications a reality.
To date, we have realized a co-extruded integral battery structure with a silica-reinforced polymer separator and a heterogeneous LiNi_1/3Mn_1/3Co_1/3 O₂ (NMC) cathode fabricated in a single pass at print speeds comparable to conventional roll coating processes. The cathode consists of interdigitated regions of varying electrode porosity, enabling better active material utilization at higher C-rates. Separator and cathode slurry formulations were designed to be compatible with our co-extrusion process, which enables a range of layer thickness. We present electrochemical data for a series of samples with a final dried separator thickness of 16-21µm and cathode thicknesses in the range of 90-120µm. Our co-extruded integral battery, when paired with a conventional graphite anode, demonstrated a gravimetric and volumetric energy density of 267 Wh/kg and 436 Wh/L at a C/2 rate. Our co-extrusion printhead, constituent material formulations, and fabrication processes which enabled our proof-of-principle integral battery structure will be discussed.

Through mesoscale design of a 3D current collector, high power density and high energy density primary and secondary (rechargeable) batteries were fabricated. At the most fundamental level, mesostructuring enables optimization of the trade-off between energy and power density in energy storage systems due to unavoidable ohmic and other losses that occur during charge or discharge. Of course, it is at fast charge and discharge, where these effects are most important. By efficient design of the ion and electron transport pathways, we and others have shown it is possible to significantly improve the power-energy relationship. We have found a particularly effective way to provide these pathways is to use a colloidal-based template to form a mesostructured 3D current collector. The electrochemically active material is then deposited on this current collector. Using this approach, Li-ion batteries which could be discharged at up to 300C with 75% capacity retention were formed. The combination of a high surface area and short solid-state diffusion lengths offers a number of unique opportunities for both high energy and high power chemistries. As examples, we have formed conventional form-factor and microbattery high power cells based on a lithiated manganese oxide cathode and carbon or NiSn anodes, and high energy cells based on a silicon anode. Time permitting, I will also describe how such engineering can also provide benefits to supercapacitor systems.

The need to develop microbatteries parallels the fabrication of integrated and self-sufficient devices in which a computing processor, communicators, microsensors and on-board power sources are packed into a volume of 1-5 mm³. Ideally, these miniature devices can tap into energy sources existing in their surroundings such as solar, vibration and thermal energies, which are mostly intermittent. Thus, only microbatteries are well-suited for applications which require a sustained supply of power over a long period of time. Currently, either thin or thick film microbatteries are in common use; however, 2D geometries suffer from severe limitations in that they are unable to deliver high power and high energy densities simultaneously. Hence, it has become a matter of practical necessity to shift to 3D microbatteries which allow the use of an increased amount of active material while maintaining the footprint area as small as possible. In this context, a variety of electrode architectures has been considered including freestanding nano-pillars , 3D ordered macroporous (3DOM) materials, perforated or trenched silicon substrates, carbon foams and so on. Carbon foam preparation begins with the synthesis of high internal phase emulsion (HIPE) polymers. An HIPE consists chiefly of a polymerizable continuous phase and a much higher proportion of internal phase. Polymerization of the continuous phase and evaporation of the internal phase give rise to a highly porous and networked polymer that is functionalized and subsequently pyrolyzed to yield a carbon foam. Gas sorption and electron microscopy techniques reveal that emulsion-templated carbon foams are hierarchically porous. The BET specific surface areas, as evaluated by N₂ gas sorption, range from 400 to 600 m² g^-1. The large part of the surface area pertains to the micro/mesopores which are interspersed in the walls of the micro-sized voids (1 to 20 mu;m).
In my talk, I'll highlight the synthesis and use of emulsion-templated carbon foams as viable 3D current collectors for microbattery applications. Strategies for optimizing pore sizes and applying layers of electroactive materials on the carbon foams will be discussed along with a thorough characterization performed on the pristine and coated electrodes. Notably, we have employed electrodeposition and sol-gel methods to coat the carbon foams in layers of active materials (e.g.polyaniline, LiFePO₄, TiO₂ and other oxides). Areal capacities upwards of 1.5 mAhcm^-2 and excellent rate capabilities are observed for the monolithic 3D electrodes coated in LiFePO₄ . The performance of the carbon foams as freestanding anodes will also be presented in brief. Another novelty value in this approach is the feasibility of using the carbon foam current collector for a wide selection of active materials due to its stability in a wide voltage window (> 1 V). It can be used with all cathodes (LiCoO₂, Li₂FeSiO₄, MnO₂ etc.) and high-voltage anode materials such as Li₄Ti₅O₁₂.

The miniaturization of flying devices requires energy storage technology to be pushed to its technological limits. Given the energy density of available cells, miniature quadcoptors and smaller devices can often be run autonomously for only several minutes at a time. Designing for such applications thus requires lightweight electrode architectures capable of delivering high-rate discharge without sacrificing energy density. Reports of high-rate lithium-ion battery architectures featuring thin active material layers synthesized on metal nanostructures suggest a potential path to this goal. Here, we present a novel and highly tunable route to generate 3-dimensional metallic nanofoam current collectors using M13 bacteriophage virus as a template. To achieve this, genetically modified viruses are first cross-linked in order to form a hydrogel then an electroless deposition process is used to form biotemplated nanoscale metal networks. We demonstrate control over the geometry of these networks via genetic manipulation of the virus and through processing conditions, achieving tunable porosities and strut widths. These networks are shown to be highly conductive, to retain a nanoporous architecture following heat treatments in excess of 450°C, and to be mechanically flexible. Following the formation of biotemplated metal nanofoams, thin layers of active material were deposited via solution precipitation followed by thermal lithiation. The thickness of these materials was varied in the tens to hundreds of nanometers regime. Because the foam is composed of thin (~80 nm) struts it is possible to produce nanostructures with active material thicknesses in the 50-100 nm range but loading greater than 80% of the solid volume. This contrasts with other strategies, in which high volumes devoted to metallic or other conducting material limit active material loading. The resulting electrodes are inherently 3-dimensional, allowing for facile control over thickness and area specific capacity. Such a geometry minimizes polarization due to electron transport because of continuous metallic charge conduction pathways and a thin active material layer. The architecture also minimizes polarization due to charge transfer because of high surface area and a resulting low current density at the active/electrolyte interface. Biotemplated metal nanofoams thus provide an ideal platform for experimental investigation of the tradeoff between area specific capacity and rate capability necessary to enable next-generation autonomous robotic systems.

All-solid-state batteries using solid electrolyte materials provide intrinsic safety and high energy density. A variety of problems at the interfaces between the electrode and electrolyte materials are limiting the development of all-solid-state batteries. Computational modeling based on first principles methods can provide valuable insights into the fundamental mechanisms at the interfaces. In this talk, I will present our recent computational study about the solid-solid interfaces in all-solid-state Li-ion batteries. Our modeling study reveals the compatibility issues of the electrolyte that lead to the failure of garnet LLZO solid electrolyte materials. We will also discuss the first-principles atomistic modeling about the rate limiting factors at the solid interfaces.

Given the potential high energy density and intrinsic safety all-solid state lithium batteries hold the promise for the next-generation energy storage devices. The discovery of compatible material systems is crucial for the success of solid state batteries. Recently, the solid electrolyte of 3LiBH₄middot;LiI has gained increased attention because of its excellent compatibility with metallic lithium. Furthermore, this solid electrolyte can be cold pressed into dense pellet, rending a favorable processing property for solid lithium battery applications.[1] However, being a strong reducing reagent, the LiBH₄ has an inherent limitation caused by the interfacial reactions with the cathode materials that are oxidants. This research investigates the applicability of the 3LiBH₄middot;LiI in high power solid state batteries. The cathode of interest is titanium disulfide (TiS₂), which has been a demonstrated high-power cathode material for automobile batteries.[2] The research focuses on the compatibility of the cathode/electrolyte interface. Results showed that pristine TiS₂ cathode self-discharges through the chemical lithiation by LiBH₄ in the electrolyte composition. The interfacial reaction between TiS₂ and LiBH₄ is not self-limiting. Therefore, a significant low coulombic efficiency (CE) was observed in all cycles for the pristine TiS₂ cathode. A simple surface modification of TiS₂ has been developed to impart excellent interfacial compatibility of the cathode and electrolyte. The chemical modification preserves the ionic and electronic conductivity of TiS₂. The modified TiS₂ cathode showed 100% CE and extremely stable cycle performance. The details of the chemical modification, cell configuration, and cycling performance will be elaborated in this talk.
Acknowledgement:
This work was supported by the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility at Oak Ridge National Laboratory.
References:
[1] H. Maekawa, et al. Halide-Stabilized LiBH4, a Room-Temperature Lithium Fast-Ion Conductor, J. Am. Chem. Soc. 2009, 131, 894-895
[2] J. E. Trevey, C. R. Stoldt, S.-H. Lee, High Power Nanocomposite TiS₂ Cathodes for All-Solid-State Lithium Batteries, J. Electrochem. Soc., 2011, 158, A1282-A1289

A fundamental component in the global move towards clean, renewable energy is the electrification of the automobile. Current battery technology limits electric vehicles to a short travel range, slow recharge, and costly price tag. Li-ion batteries promise the high specific capacity required to replace the internal combustion engine with a number of possible earth abundant electrode materials; however, setbacks such as capacity fading hinder the full capability of these rechargeable batteries. In the search for better electrode materials, high resolution chemical imaging during typical battery operation is vital in understand and overcoming the failure mechanisms of these materials.
By combining X-ray absorption spectroscopy with high resolution hard X-ray transmission microscopy (TXM), we have tracked the chemical changes of electrode material in real time during typical battery operation. We will discuss recent results tracking electrochemical and morphological changes in cathode materials during cycling. We will show dramatic chemical and morphological changes during a deep discharges (< 1V) of LiCoO₂ and compare these to the changes seen during standard cycling and cycling above the 4.2 V limit consider “safe” for these materials. By pushing this standard cathode material beyond its typical operating voltage window, we are able to better understand its failure mechanisms and ensure the entire reversible capacity is utilized.

Organic liquid electrolytes are typically used in batteries due to their high Li-ion conductivity at room temperature; however, there are well-documented safety issues with these technologies, most notably fires due to electrical shorting. Solid-state electrolytes offer a solution to this problem, but the conductivity is two-orders of magnitude smaller, which limits the battery power. Recently, a solid-state, super-ionic conductor, Li₁₀GeP₂S₁₂, has been reported, which has an ion conductivity of 12 mS/cm at room temperature. This is the highest room temperature conductivity ever achieved for solid electrolyte and is comparable to the existing liquid electrolytes. This crystal family therefore holds great promise for application in high-power, high- safety Li-ion batteries.
First-principles, density functional theory methods are used to study the structural and dynamical properties of Li₁₀GeP₂S₁₂ and its Si counterpart Li₁₀SiP₂S₁₂. The ground-state structures, phonon density of states, and ionic conductivities are calculated. Multiple structures that are nearly equienergetic are identified for both Li₁₀GeP₂S₁₂ and Li₁₀SiP₂S₁₂. Soft-phonon modes are identified in the phonon density of states that is likely associated with the mobility of Li ions in the crystal. Using first-principles, molecular dynamics the room-temperature conductivity of Li₁₀GeP₂S₁₂ is determined to be 6.38 mS/com, which is in good agreement with previous studies, and the conductivity of Li₁₀SiP₂S₁₂ is 0.63 mS/com, which contradicts previously reported results.

Solid-state electrolytes have garnered significant attention for their potential to enable solid-state batteries for electric vehicles. However, the stability between solid-state electrolytes and metallic Li is not well understood. 75Li₂S-25P₂S₅ is a promising solid-electrolyte, because it exhibits high ionic conductivity (~1mS/cm) and can be consolidated to > 90% relative density at room temperature. In this work, the chemical, electrochemical, and mechanical stability of cold pressed 75Li₂S-25P₂S₅ (mol %) was investigated. AC impedance measurements were used to correlate the formation of a quasi-solid electrolyte interphase (SEI) that formed between lithium metal electrodes and 75Li₂S-25P₂S₅ pellets. The electrochemical performance of 75Li₂S-25P₂S₅ was analyzed between 0.01 and 1.0 mA/cm² followed by cross-sectional microstructural analysis. It will be shown that: i) below or equal to 0.05mA/cm² ohmic behavior is observed, ii) at 0.1mA/cm² a transition behavior occurs identified by an instability in polarization, and iii) above or equal to 0.5mA/cm², the potential decreases and is believed to be related to the formation of an electronically conducting phase. Nano indentation was used to characterize changes in the mechanical properties after DC cycling of Li-75Li₂S-25P₂S₅. Additionally, materials characterization such as Raman, XPS, and SEM will be presented to correlate the densification conditions with DC cycling stability. We believe this is one of the first studies to characterize the chemical, electrochemical, and mechanical stability of a Li-solid electrolyte interface. The methodology established in this work could be applied to other solid-state electrolytes as well.

Novel electrochemical energy storage systems with revolutionary energy density and power performance are needed to manage power grids based on intermittent renewable sources and to put urban mobility on a sustainable basis. For utility support cost-efficiency is of utmost importance, which means that low materials and processing costs in combination with long cycle-life, low operational costs and high capacity become the key figures of merit. Currently rechargeable all-solid-state lithium batteries are already attractive power sources for small scale applications and electrochemically stable Li⁺ fast ion conductors (FIC) can help to widen their application field to large-scale battery concepts (such as Li-air batteries with aqueous catholytes, Lithium-redox flow batteries etc.) that might be suitable to enhance the stability of power grids that have to manage substantial contributions from non-dispatchable renewable power sources.
Identifying and realizing stable FICs is crucial to make these concepts both technically and commercially viable. Here we will report on recent progress with respect to oxide and sulfide-based solid electrolytes. Our studies on thiophosphate-based solid electrolytes shed light on the role of disorder in the immobile sublattice as a crucial factor for maximizing their conductivity. This is exemplified both for argyrodite-type halide-doped thiophosphates Li₆PS₅X (where the S^2-/X^- disorder for X = Cl, Br opens up local paths for Li⁺ motion), Li₇P₃S₁₁, Li_9+xGe_xP_2-xS₁₂ (LGPS, where local P/Ge disorder limits the packing density) and isostructural compounds in comparison to a series of known and newly designed thiophosphates. While cost optimization makes it necessary to replace costly elements such as Ge, the main driving factor in the search for FIC sulfides is the enhancement of the stability against hydration. For the higher stability NASICON- and garnet-type oxide FICs, besides again finding low-cost alternatives, higher conductivity and enhanced processability are key factors for the design of new compounds, such as exemplified by low temperature routes to the garnet FICs.
Ab initio structure optimisations and bond-valence based atomistic simulations highlight the role of free volume for fast ion transport and the effect of the chemical bonding on the structural and electrochemical stability of the compounds. To reduce the synthesis costs, we designed low temperature or no heating routes for the preparation of various FICs. Electrochemical characterization of materials and tests of the solid electrolytes in a variety of batteries ranging from all-solid state cells to Li-air batteries will be presented.

Solid-state lithium ion electrolytes have the potential to improve the safety and reliability of lithium batteries, but they are typically several orders of magnitude lower in ionic conductivity than their liquid counterparts. Analyzing the transport of Li ions through solid state electrolytes may help enhance their conductivity.
Recently the crystalline solid electrolyte Li₁₀GeP₂S₁₂ (LGPS) achieved Li⁺ conductivities of up to 1.2x10^-2 Scm^-1, which is approximately equivalent to liquid electrolytes [1]. This increase in conductivity is attributed to site-to-site hopping of Li ions in the tetragonal LGPS solid [2]. Other LGPS-type electrolytes, like Li₁₁Si₂PS₁₂ have also exhibited fast Li ion hopping through tetrahedra in the bulk of the material [3]. Previous studies were conducted in the bulk of LGPS-type materials. We are investigating how sputtering thin films of LGPS-type electrolytes in order to reduce thickness, and thus improve manufacturability, affects the potential for high Li⁺ hopping rates. We chose to explore this potential through compositional mapping and analysis of a ternary LGPS system.
Initial work focused on sputtering of thin films, varying compositions of the unexplored Li-P-S ternary system. The sulfur and phosphorous in this material have vapor pressures that made stable plasmas during sputtering prohibitively difficult. To advance the development of the films, the PS₄ tetrahedra were replaced with SiO₄ tetrahedra in order to study the Li ion mobility in the similar Li-Si-O system. This system provides similar opportunity for Li ion hopping through tetragonal sites as other LGPS-type electrolytes. It can also serve as a model for thin film analysis of other high conductivity systems.
We explored the ternary phase diagram of Li-Si-O by sputtering a range of stoichiometric thin films. Through this mapping of the ternary phase diagram of the Li-Si-O system, the limits of deposition to which the tetrahedral coordination of Si can be preserved will be discussed. The stoichiometry of the thin film material was determined through ICP/AES and ellipsometry. The effect of composition on ion transport will be shown through impedance spectroscopy.
We have focused on understanding the lithium silicate compositional space and the effect of composition on ion transport through impedance measurements in blocking and non-blocking configurations. LGPS-type thin films have remained mostly unexplored and have the potential for high Li ion conductivity. Sputtering of a thin film LGPS-type electrolyte allows us to create these separator materials in a battery compatible and more scalabe/manufacturable thin film form. Data on the initial investigations into these chemistry/property relations in the sputtered films will be presented.
1. Kamaya, N. et al.Nat Mater10, 682-686 (2011).
2. Kuhn, A., Duppel, V. & Lotsch, B. V. Energy & Environmental Science6, 3548 (2013).
3. Kuhn, A. et al.Phys. Chem. Chem. Phys.16, 14669-14674 (2014).

Lithium batteries with increased energy density are required for the fast growing markets of mobile electronic devices, electric vehicles, and smart grids. High-voltage cathode, such as LiNi_0.5Mn_1.5O₄ with a working potential of ~4.7 V vs. Li/Li⁺, delivers increased energy with same amount of charge, and can be designed relatively easily by cation substitution in existing compound LiMn₂O₄, without altering much the crystal structures or the intercalation chemistry. However, the practical use of high-voltage Lithium batteries is hampered by the narrow electrochemical window of the liquid electrolyte in conventional batteries. A solid electrolyte with a sufficiently wide electrochemical window does not decompose when cycled to high voltage, and thus possibly enables the full utilization of high-voltage cathodes.
Here we demonstrate the possibility to realize the full utilization of high-voltage cathodes for lithium batteries in solid-state systems. The example consists of LiNi_0.5Mn_1.5O₄ cathode, Lipon solid electrolyte, and Li metal anode. Lipon is used as the model solid electrolyte mainly because of its wide voltage window (0~5.5 V) and excellent interfacial compatibility with both cathodes and anodes. The high coulombic efficiency of this solid-state battery exceeds 99.98%, indicating that the decomposition of solid electrolyte is minimal. The reversible capacity delivered by the solid-state lithium battery with LiNi_0.5Mn_1.5O₄ cathode is stable for 10,000 cycles with 90.6% capacity retention, corresponding to a decay of less than 0.001% per cycle. For most applications, such a battery has a cycle life longer than most devices, and can be used for a lifetime without maintenance. The round trip energy efficiency is greater than 97%. After the first cycle, the voltage-capacity profiles are almost identical for the subsequent cycles through at least 10,000 cycles. The issues of transition metal dissolution and electrode/electrolyte interfacial stability are naturally eliminated because there is no mobile solvent in the solid electrolyte. This work proves the excellent intrinsic stability of the high-voltage cathode LiNi_0.5Mn_1.5O₄.
Acknowledgement
This work was supported by the U.S. Department of Energy (DOE), Offi ce of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. Electron microscopy work was performed through a user project supported by ORNL&’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientifi c User Facilities Division, DOE-BES.
References
[1] J. Li, C. Ma, M. Chi, C. Liang, and N. J. Dudney. "Solid Electrolyte: the Key for High-Voltage Lithium Batteries," Adv. Energy Mater., 201401408.

Defects in crystals are an important factor governing the intrinsic properties of materials. While the concentration of defects in a crystal at a certain temperature and pressure is determined by thermodynamics, materials synthesized via non-equilibrium routes generally contain higher concentrations of defects. So, careful choices of synthesis conditions or post-treatment methods are needed to control the level of defects and to tune the properties of materials.[1]
Defects in a crystal can impede ion transport by blocking diffusion pathways in one- or two-dimensional ionic conductors; LiFePO₄ ,an important material in batteries, is a good example of this. While it has been considered a promising electrode material[2] due to its stability and high energy density, kinetic issues arising from the restrictive diffusion pathways for Li ions and the low electronic conductivity have been problematic.[3] In particular, Li ions can diffuse only through a 1-D tunnel in the crystal. Thus, this diffusion is susceptible to the presence of defects that may block the tunnel.[4] Since nano-sizing has been conducted widely for this material, the reduction in diffusion length and decreasing the effect of blocking of Li ion diffusion can partly resolve the low-power problem. However, the nano-sized LiFePO₄ shows low electrode tap density, which results in a significant reduction in the volumetric energy density. Also, most of the nano-size syntheses are more likely to generate surface defects on LiFePO₄. In this regards, it is increasingly important to develop a defect-less LiFePO₄ electrode material without particle size reduction that is capable of delivering satisfactory performance with reasonably high gravimetric/volumetric energy density.
In this presentation, we introduce a novel way to reduce anti-site defects in LiFePO₄ electrochemically at room temperature, which can be adapted regardless of particle size.[5] In this approach, we intentionally introduced a vacancy in the lithium channel by partial charging, and carried out a deep discharge below the conventional voltage cut#8209;off. As a result, we observed significant Fe_Li-defect annihilation, resulting in defect-less LiFePO₄ from a structural analysis. Furthermore, the electrochemical performance could be enhanced markedly in the ‘healed&’ sample. Density functional theory calculations suggest that Fe_Li-defect migration and annihilation could be facilitated by the introduction of vacancies near defects and the injection of excess electrons during over-discharge, which lowers the migration barrier for Fe defects.
1 Penn, R. L.; Banfield, J. F. Science1998, 281, 969.
2 Padhi, A. K.; Nanjundaswamy, K. S.; Goodenough, J. B. J. Electrochem. Soc.1997, 144, 1188.
3 Morgan, D.; Van der Ven, A.; Ceder, G. Electrochem. Solid-State Lett.2004, 7, A30.
4 Malik, R.; Burch, D.; Bazant, M.; Ceder, G. Nano Lett.2010, 10, 4123.
5 K-Y, Park; I. Pakr; H, Kim; H.-D. Lim; J. Hong;, J. Kim; K. Kang.- Chem. Mater., 2014, 26, 18

Increasing the energy density of secondary batteries is very important for their practical applications. The use of pure metal anodes has been regarded as the ideal case due to their high energy density and capacity. However, these secondary batteries are subjected to dendritic growth of metal at the anode upon cycling and end up with short circuiting of the batteries. Intensive researches have been focused on tailoring the composition of electrolyte so that dendrite formation could be alleviated. Whether dendrites could be suppressed by simply modifying the configuration of the anode still remains to be investigated. Here using a 3D colloidal templating strategy, we were able to deposit and etch metals smoothly. Specifically, the feasibility of this method in lithium and aluminum metal batteries were investigated. Colloidal templates of 450 nm SiO2 spheres on tungsten foil were first infiltrated with certain amount of metal. And these templates were directly used and cycled by applying alternative voltage or current. At a current density of 1 mAcm^-2 and depth of cycling of 33.3%, there was no obvious dendrite formation on these metal anodes after 100 cycles. At a high current density of 5 mAcm^-2 and 40% depth of cycling, these metal anodes were still able to be cycled without obvious dendrites after 50 cycles. The possible mechanism is probably the incorporation of the 3D colloidal template results in homogenization of electrical field in the templates during cycling of metals.

Recently, energy-storage or energy-conversion materials have taken a considerable attention due to our growing demands in special energy sources. New materials and novel molecular structures for energy storage and conversion devices are a key contributor to achieve a new version of energy sources. We introduce a novel energy storage material, which is optically transparent glass. Organically modified hybrid glasses have been actively investigated for optical device applications to create new optical properties by the incorporation of organic spacers. An organic /inorganic hybrid glass, alkylene-bridged sol-gel monomer, was synthesized. A sol-gel processable chromium precursor was also prepared for a co-polymerization. A green colored hybrid glass doped with chromium was prepared. The hybrid glass shows a high compressibility. In laser experiments, the optically transparent hybrid glass with the high compressibility revealed a strong ‘acoustic response&’ as much as a liquid. The diffraction efficiency and absorption light efficiency (45 %) of the Cr-dope glass was higher than that (25 %) of methanol; which means, the compressibility of the doped hybrid glass is as effective as liquid. Therefore, it can be served as a ‘HEAT GENERATOR (ENERGY- STORAGE MATERIAL)&’; as a result, the heat gets transferred into expansion or compression wave effectively. This is a new phenomenon that can develop a new energy-storage material.

Realization of next-generation energy storage systems necessitates exploration of not only new battery chemistries and device architectures but also innovative materials beyond carbon black for facilitating electronic charge transport. We will report our recent efforts towards the design and implementation of supramolecular polycyclic aromatic hydrocarbons as adaptive charge-transporting networks in a hybrid Li-S flow battery. Effects of concentration, state of charge, and molecular identity on performance characteristics - including rate behavior, storage-material utilization, and capacity fade - will be reported. These data will be presented alongside results obtained using a non-network forming polycyclic aromatic hydrocarbon of similar structure, which can only serve as molecular redox mediators. From these studies emerge the first structure-property relationships that will help guide the development of soft supramolecular materials for charge transport in energy storage devices.

In order to improve cell performance and to reduce safety concerns, a highly ordered hierarchical (HOH) graphite electrode was studied. Conventional graphite electrodes are widely used in lithium ion battery due to their long cycle life, and inexpensive precursors. However, they are hindered by poor power performance and safety concerns. Conversely, highly ordered hierarchical (HOH) graphite electrodes, which consist of linear channels, may improve power performance by reducing tortuosity of electrodes, while also mitigating safety concerns due to their linear channel. The HOH graphite electrodes were patterned using a laser, and Raman spectroscopy confirmed that there are no characteristics and structural changes after laser processing. Electrochemical performance was determined in half-cell against lithium foil electrode at various C-rates. High loading HOH graphite electrodes (5.5 mAh/cm²) showed higher capacity rate compared to conventional graphite electrodes by reducing tortuosity in porous electrodes up to 1/2 C-rate. To further understand the effects of tortuosity, potential interrupt tests and electrochemical impedance (EIS) tests were conducted. In addition, the results of intentional overcharged test related to safety issue showed lithium plating behavior on HOH electrode under the overcharge condition.

The effect of calcination atmosphere on the microstructure and ionic conductivity of garnet Li₇La₃Zr₂O₁₂ (LLZO) was studied. LLZO powder was doped with Al to stabilize the cubic phase and calcined in ambient and dry air and pure oxygen. After calcination, LLZO powders were densified to >96% relative density using induction hot pressing. The calcination conditions affected densification and thus the microstructure. Electrochemical Impedance Spectroscopy (EIS) showed that the grain boundary resistance is affected by the calcination conditions and likely results from the absence or presence of Li₂CO₃, LiOH and perhaps H⁺. Scanning electron microscopy, X-Ray diffraction, Raman spectroscopy and EIS data will be presented to correlate the effect of calcination atmosphere with the microstructure and ionic transport of induction hot pressed LLZO.

Over the last decades a progressive miniaturization of electronic components took place. As a result there is an increasing demand for micro-sized power sources, which drives the current research on thin-film batteries. Among the applications are sensors, RFID tags, and implantable medical devices. In this respect an all-solid-state thin-film Li-ion battery is desirable, since its excellent safety properties and easy integration in microelectronics are outstanding advantages. Furthermore, depending on the type of solid state electrolyte material, high voltage cathode materials and a lithium metal anode could be used in order to increase the energy density beyond commercially used Li-ion batteries.
Regarding fabrication, chemical vapor deposition (CVD) is a suitable method to grow functional thin-films for Li-ion batteries, since it allows for a homogeneous growth over large areas with high deposition rates and a very high purity. Unique is also the capability of conformal, directional deposition in order to realize three-dimensional architectures. However, with conventional CVD precursor delivery systems it is often difficult to ensure the correct composition throughout the entire deposition process, especially when dealing with multicomponent materials such as typically used for Li-ion batteries.
Recently, our group established a novel CVD precursor delivery system using CO₂-laser flash evaporation of solid precursors.^[1] A detailed characterization of (i) LiCoO₂ and (ii) Li₇La₃Zr₂O₁₂ thin-films shows that this novel CO₂-laser assisted chemical vapor deposition (LA-CVD) is a promising and versatile method. Microstructural features, such as the morphology, density and thickness of the films can be adjusted by tuning the process parameters. In addition, their electrochemical performance is already sufficient to operate an all-solid-state thin-film Li-ion battery, and has potential for further optimization.
References
[1] C. Loho, A. J. Darbandi, R. Djenadic, O. Clemens, H. Hahn, Chem. Vap. Deposition 2014, 20, 152-160 (DOI: 10.1002/cvde.201307089).

Prussian Blue analogues (PBAs) have demonstrated novel electrochemical properties that make them suitable for a variety of battery applications. The open framework structure plays an important yet poorly understood role in enabling the reversible insertion of ions in these materials. Understanding how the crystal structure affects electrochemical properties is key to furthering the development of PBAs for energy storage. In-depth X-ray diffraction (XRD) experiments show that small distortions in the lattice can improve specific capacity by allowing for the insertion of significantly more ions than previously thought possible in PBAs. In situ X-ray diffraction provides insight into the effects of different framework metal ions on structural stability, specific capacity, and electrochemical performance. Combining crystallography and electrochemistry provides a powerful approach to improving our understanding of PBAs and furthering their development.

We have developed a novel platform of planar micro-battery, which enables in situ studies of Li ion insertion in 2D materials. Optical, electrical, structural and electrochemical properties of individual flake 2D materials during lithiation/delithiation have been studied. In lithiated few-layer graphene, a simultaneous increase of optical transmittance and conductivity compared to pristine graphene is observed, lead to the final product (LiC₆) with sheet resistance of 3 ohms/sq and optical transmittance of 91.7%. In lithiated MoS₂, the conductivity of the final product is dependent on the charging method. By using a fast charging method, we obtained a higher specific capacity of MoS₂ than the standard charging method. More 2D materials with physical and chemical properties that are tunable by Li ion intercalation can be applied to this platform.

The role of aberration-corrected scanning transmission electron microscopy (STEM) in materials characterization is examined with respect to layered-oxide cathode materials for battery applications. STEM-based methods are quickly becoming the most promising characterization tools for these materials, owed largely to the wide-range of techniques available on advanced STEM instruments, including the direct imaging of both heavy and light elements, and both energy-dispersive X-ray (EDX) and electron energy loss (EEL) spectroscopies. The current talk will focus on multiple materials, including Li- and beyond Li-ion oxides, characterized via STEM methods, in pristine, cycled, and in-situ irradiated states. The latter allows for single particle tracking of the dynamic processes occuring upon Li and O loss from the material. Various imaging modes, including high/low angle annular dark field (H/LAADF) and annular bright field (ABF), in conjunction with EELS/EDX, will be used extensively for this analysis, while parameters such as Mn valence, O presence, and light element occupation will be discussed.

¹Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49933-1295, USA
²Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL60607-7059, USA
³Department of Physics, University of Illinois at Chicago, Chicago, IL60607-7059, USA
Using sodium as a potential charge carrier ion for rechargeable batteries has attracted attention of many researchers since Na-ion batteries are more eco-friendly and affordable due to much more abundance of sodium over lithium on earth. Another considerable issues are performance and cyclability of batteries. The anode materials usually experience large volume changes through the ion insertion and extraction. This volume change and lithium embrittlement causes cracks and loss of contact in the anode material, which ultimately causes the failure of battery. Here, we investigated and compared the structural and mechanical changes of ZnO nanowires during sodiation and lithiation by using in situ transmission electron microscopy. The cracks were created upon the first lithiation process of single crystalline ZnO nanowire. The lithiated ZnO nanowire shows multiple glassy domains, which has low strength and ductility. This results in poor cyclability of battery. On the other hand, ZnO nanowire after sodiation show dislocations on the surface of nanowire that results in more ductility of sodiated nanowire rather than lithiated one. This direct comparison demonstrates the critical role of anode material&’s mechanical properties on failure mechanism and cyclability of Li/Na-ion batteries.

Rechargeable lithium ion batteries (LIBs) are one of the key components for various portable electronic devices including mobile phones, laptops. LIBs are also promising energy storage and conversion devices such as electric vehicles (EVs) and hybrid electric vehicles (HEVs). In LIBs cathode material strongly influence the electrochemical performance. The phospho-olivine compound LiFePO₄ (LFP) is one of the most extensively studied active cathode material for high power performances because of low cost, low toxicity, high thermal stability, and excellent reversibility of electrochemistry [1]. However it&’s low electronic and ionic conductivity result in poor electrochemical performances in moderate and high rates which become a great challenge in order to use in EVs and HEVs [2]. In the recent years, anion doping has been considered as a suitable approach in order to improve the electrochemical performance of LiFePO₄ cathode material. Increase in the open circuit voltage influenced by the inductive effect of the PO₄^3- polyanion in LiVPO₄F has been reported by Barker et al.[3]
In the present work fluorine (F^-) doping at the PO₄^3- polyanion site has been exploited in an effort to increase the electrochemical performances of LFP. LiFe(PO₄)_1minus;xF_3x/C (x = 0 to 0.4) cathode materials were synthesized by sol-gel method using NH₄F as the dopant and lauric acid as the carbon source [4]. The effect of fluorine doping on the electrochemical performance of LiFePO₄/C cathode materials were studied in details on a CR2032 type coin cell in the half-cell configuration. We will present our studies on the reversible capacities of the LFP which shows an increase from 70 to 84 % of theoretical value for fluorine concentration of x up to 0.05. The capacity decrease to 30 % with further increase in the F concentration to x = 40 %. The capacity retention is very good at 0.1C rate (~90 to 96 %), however, decreases at higher C rates. In case of F doped samples the discharge capacity sharply drops down with increase in C rates. For LFP the discharge capacity decreases from 120 mAh/g at 0.1C rate to 6 mAh/g at 5C rate. The average discharge voltage decreased with increasing C rate from 3.4 V at 0.1 C to 2.8 V at 2 C. Under high current densities the voltage polarization became severe with F doping. We will present a detailed cyclic voltammograms and electrochemical impedance spectroscopic studies on these fluorine doped samples. The implication of fluorine doping in LFP for LIB applications will be further discussed.
C. Sudakar acknowledges Samsung GRO, SAIT (2013) and DST (grant # SR/S2/CMP-43/2011) for the funding.
References:
1. Padhi, A.K., K.S. Nanjundaswamy, and J.B. Goodenough, J.o Electrochem. Society,144 (1997)1188.
2. Sun, C.S., et al., J. Power Sources, 193 (2003) 841.
3. Barker, J., M.Y. Saidi, and J.L. Swoyer, J. Electrochem. Society, 150 (2003) A1394.
4. Radhamani, A.V., et al., Scripta Materialia,69 (2013) 96.

Due to the diffusion limitation of Li-ion, the thickness of electrodes using foil-type current collectors is much less than 100 µm for commercial Li-ion batteries. To overcome the issue, three dimensional Ni alloy foam current collectors are used in our study for ultra-thick Li-ion battery electrodes. Due to the unique structure of metal foam current collectors, the charge transfer ability is much higher than foil-type current collectors and the better kinetic performances of cell using metal foam allow the thickness of electrodes to become much thicker. In this study, design parameters effects on electrochemical performances are evaluated specifically such as the pore size of metal foam, thickness of electrodes, porosity of electrodes and content of carbon black and so on. Additionally, the electrochemical performances are evaluated and compared when the negative electrode is placed only one side or both side of positive electrode using metal foam current collector. The comprehensive results tell us which design parameter should be applied according to the specifications of Li-ion battery. Considering the power performance and capacity of the ultra-thick electrodes, the metal foam is one of the promising current collectors for high power and high capacity Li-ion batteries.

A number of cathode materials of interest to commercial Li-ion batteries function based on two-phase reaction mechanism.¹ Two-phase insertion/extraction process is typically associated with slow kinetics, large volume change and poor stability of the materials. Single-phase transformation, therefore, is considered kinetically advantageous compared to the two-phase process. In this presentation we report the synthesis, isolation, and characterization of room-temperature Li_xMn_1.5Ni_0.5O₄ solid solutions for the first time. Spinel LiMn_1.5Ni_0.5O₄ (LMNO) transforms through two topotactic two-phase reactions involving three cubic phases: (i) LiMn_1.5Ni_0.5O₄ (Phase I) →#127;_0.5Li_0.5Mn_1.5Ni_0.5O₄ (Phase II) (ii) #127;_0.5Li_0.5Mn_1.5Ni_0.5O₄ (Phase II) → #127;Mn_1.5Ni_0.5O₄ (Phase III) during charge/discharge. The volume changes of Phase I / II and Phase II / III are approximately 3% and 3.3%, respectively.² Several physical properties, including particle surface facets, particle size substitution and cation ordering, have large influence on phase transformations. Here we investigate the thermal behavior of Li_xMn_1.5Ni_0.5O₄ (0<x<1) by performing in situ thermal XRD studies on pristine and chemically-delithiated, micron-sized single crystals. We found that thermal treatment results in a reduction in the miscibility gap between Phase I and Phase II which led to the formation of single-phase solid solutions. The thermally-driven solid solutions were preserved at room temperature. A phase diagram revealing the structural changes as functions of both temperature and Li content was established. This work enables in-depth evaluation of the physical, electrochemical and kinetic properties of transient, intermediate phases and their role in battery electrode performance.
References
1. A. K. Padhi, K. Nanjundaswamy and J. B. d. Goodenough, Journal of the Electrochemical Society, 1997, 144, 1188-1194.
2. B. Hai, A. K. Shukla, H. Duncan and G. Chen, Journal of Materials Chemistry A, 2013, 1, 759-769.

A rationally designed three-dimensional (3D) nanostructured electrode is essential for the development of high-rate rechargeable batteries. The nanostructure also should provide mechanism to ensure the electrode charge/discharge cycling stability. Here we report that using 3D perpendicularly-oriented graphene network grown inside of nickel foam as template, VO₂(B) nanobelts can be self-assembled through hydrothermal growth to form a hierarchically, highly-ordered, and interconnected 3D nanostructure, called as VO₂(B)/graphene forest. Such a nanostructure can provide short diffusion length and large surface area to facilitate the ion intercalation/deintercalation, an ordered porous geometry to smooth ion migration in electrolyte and provide space for electrode material expansion, and a 3D interconnected network for structural stability and minimized electron transport resistance. When used as an electrode in the lithium ion battery, electrochemical measurements reveal that such a nanostructured electrode possess high-rate capability with a stable discharge capacity of 300 mAh/g at 0.5A/g and 178 mAh/g at a very high current density of 10A/g. It also exhibits a very long lifetime with capacity retention about 80% over 2000 cycles at a high current density of 2A/g.

Due to their unique properties together with the ease of synthesis and functionalization, graphene-based materials have been showing great potential in energy storage and conversion. Thus, careful attachment of nanostructures to graphene for maintaining the best synergism among two components has become an important methodology for the high performance energy conversion and storage devices. The amazingly fast progress of research about graphene and its modification methods to make its hybrids with other nanomaterials revolutionize its possible applications. These hybrid structures exhibit excellent material characteristics including high charge carrier mobility and long term stability because of excellent electrical conductivity, mechanical flexibility and electrochemical behavior of graphene. Besides, the versatile and fascinating properties of the nanostructures grown on graphene sheets make it possible to construct electrode materials with high performance and extraordinary stability for lithium ion battery (LIBs), supercapacitors (SC) and oxygen reduction reaction (ORR) in fuel cells. Among these, metal alloys, oxides, hydroxides, nitrides and sulfides are promising materials for energy storage and conversion devices. Here, we have synthesized different types of graphene (rGO, G, N/PG) and their composites with different kinds of metal alloys, oxides, hydroxides, nitrides and sulfides for their applications as electrode in LIBs, SC and ORR. It is found that the materials behave differently in their different composition and phase state. The aggregation is another critical factor that influence the electrochemical performance of the electrode materials thus a unique chemical interaction among the active materials and G substrate is built to utilize the maximum synergism among two components. Further enhancement in electrochemical properties of graphene is carried out by doping of heteroatom in graphitic planes of graphene. It is worth noting that Ni₃S₄-NG and Co₃Sn₂@Co-NG composites displayed 98.87% and 102% capacity retention with a discharge capacity of 1323.2 and 1615 mAh/g after 100^th cycle, respectively. Co(OH)₂ shows much higher energy density ~220 Wh/kg and stability of 10000 cycles as electrode of SC. Further FeN₃@3DNG shows much better performance than Pt/C as well as higher stability and excellent tolerance to fuel crossover effect. We believe that by tuning the composition, phase and chemical interaction of active material-graphene with highly stable structure will realize the utilization of these energy conversion and storage devices.
H. Yin, C. Zhang, F. Liu, Y. Hou, Adv. Funct. Mater., 2014, 24, 2930-2937.
Mahmood, N.; Zhang, C.; Yin, H.; Hou, Y., J. Mater. Chem. A 2014,2, 15-32.
Zhang, C.; Mahmood, N.; Yin, H.; Liu, F.; Hou, Y., Adv Mater 2013, 25, 4932-4937.
Mahmood, N.; Zhang, C.; Jiang, J.; Liu, F.; Hou, Y., Chem. Eur. J. 2013, 19, 5183-5190.
Zhang, C.; Hao, R.; Liao, H.; Nano Energy, 2013, 2, 88-97.

The development of high voltage cathode materials for lithium ion batteries with good rate performance and charge capacity retention is currently a major challenge to the development of more efficient energy storage. One approach to the improvement of these metrics is to coat a high voltage cathode material with a protective layer to reduce electrolyte decomposition into a solid electrolyte interphase (SEI) which increases battery impedance and thus performance over the long term. To achieve this, the coating must suppress unwanted electro-oxidative and catalytic reactions at the electrode surface, while also avoiding the pitfall of hindering Li ion transport though the coating material.
We have investigated the growth of AlPO₃Me cathode coating materials by atomic layer deposition (ALD) onto LiNi_0.5Mn_0.3Co_0.2O₂ (NMC). These coatings have been targeted as a promising material as a result of phosphate coating performance with other coating techniques. The use of methyl phosphonate instead of phosphate was done with the intention of introducing disorder into the inorganic film to improve ionic transport.
We have explored a variety of ALD growth conditions which have allowed us to precisely tailor the elemental composition of the films. Variations in ALD pulse sequence and deposition temperature are explored as they relate to P/Al ratio, growth rate, and incorporation of organic component.
A fractional factorial designed experiment was performed to efficiently study the effects of this variety of film properties on NMC cathode performance. Coin cells were tested to investigate both charge capacity fade over time and capacity loss due to high rate. The best performing coatings of this set impart significant improvements to the NMC cathode material, and correlations between film structure and performance will be examined.

Lithium rich layered oxides significant attention as energy harvesting materials due to their large capacities, which are, however, consist of queries on the large irreversible loss in capacities for the first charge/discharge cycle with oxygen removal in lattices related to layered Li₂MnO₃. Herein we present detailed studies on the Li-rich Mn based layered oxides of 0.4Li₂MnO₃-0.6LiNi_1/3Co_1/3Mn_1/3O₂ that were electrochemically activated between 2.5 V and 4.3 or 4.7 V vs. Li⁺/Li. Electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) revealed unusual Mn reduction after first charging up to high voltage of 4.7 V. Moreover, its electronic structures are not fully recovered to original pristine of Mn⁴⁺ state when they were discharged again, interestingly, these phenomena was restricted to the surface of cathode particles. High-angle annular dark-field image in scanning transmission electron microscopy (HAADF-STEM) and electron dispersive spectra (EDS) also show dramatic decline of oxygen contents with many porous morphologies which associated with oxygen vacancies formation by following oxidation of O^2- ions to O₂. Our analysis suggests that unstable superficial Mn valence state with severe defects due to oxygen vacancies may lead the large irreversible capacity loss during the first charge/discharge cycle of Li-rich layered oxide.

Much progress has recently been made in the development of novel active materials, electrode morphologies and electrolytes for lithium ion batteries. Well-defined studies on size effects of the three-dimensional (3D) electrode architecture, however, remain to be rare due to the lack of suitable material platforms where the critical length scales (such as pore size and thickness of the active material) can be freely and deterministically adjusted over a wide range without affecting the overall 3D morphology of the electrode. Here, we report on a systematic study on length scale effects on the electrochemical performance of model 3D porous Au/TiO₂ core/shell electrodes. Bulk nanoporous gold provides deterministic control over the pore size and is used as a monolithic metallic scaffold and current collector. Extremely uniform and conformal TiO₂ films of controlled thickness were deposited on the current collector by employing atomic layer deposition (ALD). Our experiments demonstrate profound performance improvements by matching the Li⁺ diffusivity in the electrolyte and the solid state through adjusting pore size and thickness of the active coating which, for 200 mu;m thick porous electrodes, requires the presence of 100 nm pores. Decreasing the thickness of the TiO₂ coating generally improves the power performance of the electrode by reducing the Li⁺ diffusion pathway, enhancing the Li⁺ solid solubility, and minimizing the voltage drop across the electrode/electrolyte interface. Using the optimized electrode morphology, supercapacitor-like power performance with lithium-ion-battery energy densities was realized. Our results provide the much-needed fundamental insight for the rational design of the 3D architecture of lithium ion battery electrodes with improved power performance.

The reduced graphene oxide (RGO)/carbon double-coated 3-D porous LiMn_0.8Fe_0.2PO₄ aggregates (RGO/C/LMP) have been successfully synthesized as cathode materials for Li-ion batteries with excellent rate capability. The 3-D porous LMP aggregates prepared by a simple solvothermal method can take unique advantages of nanosized primary particles having short diffusion paths for Li, mesopores acting as electrolyte container for high-rate ion kinetics, and micron-sized secondary particles with high tap density for excellent volumetric energy density. Furthermore, the double coating of RGO and carbon simultaneously brings the advantages of conformal carbon layer on each nanoparticle surface, and soft RGO sheets connecting the aggregates to each other, thereby provides easy conduction pathways for the whole LMP aggregates. The RGO/C/LMP exhibits superior electrochemical performance, including excellent capacity and rate capability. Such improved performance may be attributed to the synergistic effect between the 3-D porous structure and RGO/C double coating.
[1] Y. Oh, S. Nam, S. Wi, J. Kang, T. Hwang, S. Lee, H. H. Park, J. Cabana, C. Kim and B. Park, J. Mater. Chem. A2, 2023 (2014).
[2] S. Yang, X. Feng, S. Ivanovici, and K. Müllen, Angew. Chem. Int. Ed.49, 8408 (2010).
Corresponding Author: Byungwoo Park: [email protected]

Nanoporous materials play a prominent role in the research and development of rechargeable lithium batteries [1]. Among these, ordered mesoporous carbon is promising as a conductive framework for lithium-sulfur battery electrodes [2]. Elemental sulfur, as a non-toxic and abundant cathode material, bears the advantage of a high theoretical capacity of 1675 mAh/g [3]. Sulfur-carbon electrodes require a high dispersity of sulfur, good contact between sulfur and carbon, and a high porosity of the entire composite for effective permeation of the electrolyte and short diffusion paths for Li ions.

We present advanced mesoporous carbon-sulfur composites by an optimized synthesis procedure relying on the nanocasting approach [4], using silica as a structural matrix. The materials are based on so-called CMK-5-type carbon [5] which consists of hollow, linear tubes, arranged in parallel orientation. As a result, two distinct modes of nanopores exist, intra-tubular and inter-tubular pores. We selectively fill the intra-tubular pores with sulfur while the second, extra-tubular pore system is not accessible due to the presence of the silica matrix. Subsequent matrix removal then yields an unfilled pore mode with a residual pore volume of 0.40 cm³/g at a sulfur loading of 60 %(wt). The surface of the 'empty' pores can be chemically modified by attachment of organic functions, which may be useful to prevent leaching of solute polysulfides. Thus, two large interfaces are generated in the carbon, namely (i) to the intra-tubular guest species (sulfur) and (ii) to the free space between the carbon tubes. The latter can be infiltrated by an electrolyte in a rechargeable cell and allows short diffusion paths for Li ions. Since Li ion diffusion is often the limiting factor in the charge/discharge kinetics [1], our materials are promising candidates for future lithium-sulfur battery design.

[1] P.G. Bruce, B. Scrosati, J.-M. Tarascon, Angew. Chem. Int. Ed. 47 (2008) 2930-2946.
[2] X. Ji, K. T. Lee, L. F. Nazar, Nature Mater. 8 (2009) 500-506.
[3] J. Shim, K. A. Striebel, E. J. Cairns, J. Electrochem. Soc. 149 (2002) A1321-A1325.
[4] T. Wagner, S. Haffer, C. Weinberger, D. Klaus, M. Tiemann, Chem. Soc. Rev. 42 (2013) 4036-4053.
[5] S.H. Joo, S.J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki, R. Ryoo, Nature 412 (2001) 169-172.

Lithium-sulfur (Li-S) batteries have been developed as one of promising energy storage systems because of high theoretical energy density and natural abundance. Despite considerable advances, there are significant hurdles such as cycle life and rate capability to be solved for practical implementation of Li-S batteries. To tackle these issues, a number of approaches have been introduced, including conducting material-sulfur composite concept. Current research trend is based on assumption of direct electron transfer between solid sulfur particles and carbons. We noticed that there is no conclusive evidence on such a reaction.
In this study, we reexamine electrochemical behaviors of sulfur cathodes and further suggest operating routes on charge and discharge process of Li-S cells.

Although the operational principles of Li-S batteries has been known for decades, these cells have not been commercialized on a large scale up to date. The two major problems connected with this cell chemistry are fast capacity fading (stability) and low cycling efficiency. Both problems are primarily due to a complicated reaction mechanism which involves different soluble lithium polysulfides.
In an attempt to confine polysulfides in the vicinity of their formation, a unique array of porous host matrixes have been used [1]. It has been proposed that in high surface area, porous carbon materials enable confinement of sulfur and polysulfides and have an impact on the Li-S battery cycling properties (capacity and efficiency). However, some literature reports have shown that the use of carbons with a designed morphology are insufficient to sustain long cycling stability. Additional stability can be gained by using a doped or modified Li₃ClO-based glass separator [2] that can stop polysulfide diffusion to the lithium.
In this study, we present our most recent results on the role of LiRAP (lithium rich anti-perovskite) - as a Li-S separator. Through different approaches we have optimized the surface of the separator with selected functional groups (materials) that can trap or repulse lithium polysulfides. The use of an optimized separator has resulted in Li-S battery cells with a significant improvement in coloumbic efficiency and in overall longer cycle life. The impact of an optimized separator on the mechanisms proceeding in Li-S batteries were studied using 2.5 x (2.5 or 3.5) cm² cells and potentio - galvanostatic measurements.
[1] A. Murchison, J.A. Ferreira, M.H. Braga, Superionic solid electrolyte for Li-S batteries, in preparation.
[2] M.H. Braga, J.A. Ferreira, V. Stockhausen, J.E. Oliveira, A. El-Azab, Novel Li₃ClO based glasses with superionic properties for lithium batteries, J. Mater. Chem. A 2014, 2, 5470-5480.

We present an approach to improve the stability of lithium-sulfur batteries using sulfur-doped ordered mesoporous carbons. An ordered mesoporous silica template was prepared and used for preparation of ordered mesoporous carbon-sulfur replica materials using a nanocasting strategy employing furfuryl alcohol and furfuryl mercaptan as carbon-sulfur precursor. The use of furfuryl mercaptan resulted in ordered mesoporous carbon materials of high quality. Less narrow pore size distribution and an increased sulfur content followed when increasing the concentration of furfuryl mercaptan used in the precursor solution. It was possible to control the sulfur content by the amount of furfuryl mercaptan used in the precursor solution and the sulfur content was found to be evenly distributed throughout the material. For the application in lithium-sulfur batteries, the material was additionally loaded with elemental sulfur following a melt-diffusion approach. The prepared electrodes showed very high capacity in the second cycle of 1497, 1211 and 1389 mAh/g for no sulfur doping, medium doping and high doping of the host, respectively. Sulfur doping especially increased capacity retention by a factor of 1.23 and 1.55 intermediate and high doping for the 50^th cycle compared to the non-doped host. We attribute this to a different bonding situation of the loaded sulfur inside the host indicated by cyclic voltammetry and X-ray photoelectron spectroscopy. Materials were characterized by a variety of methods including transmission electron microscopy, thermogravimetric analysis and battery cycling.

The fascinating advantages such as excellent electronic conductivity, high theoretical specific surface area, and good mechanical flexibility have enabled graphene as a promising scaffold to improve the conductivity of sulfur cathodes in lithium-sulfur (Li-S) batteries. However, graphene is not a good substrate to confine the polysulfides in cathodes and thus, stable the cycling. Herein, we designed a novel enclosed solid-gas reaction system and synthesized a unique graphene-sulfur composite with strong carbon-sulfur bonding as cathode for Li-S battery. In this composite, a thin layer of amorphous sulfur is highly dispersed on both surfaces of the graphene via strong chemical bonding. Therefore, the sandwiched graphene not only can achieve a high sulfur loading, but also can act as polysulfide reservoirs to alleviate the shuttle effect. Upon used as the cathode material in Li-S batteries, with the help of the designed structure, the as-synthesized material demonstrated a better electrochemical performance and cycle stability compared with those of previous graphene/sulfur composites.

Sulfur has been spotlighted as a promising cathode material due to its high theoretical capacity of 1672 mAh/g, environmental friendliness, and low cost. Even if it has many strong points in lithium sulfur(Li-S) batteries, it is still hard to be used in the commercial lithium ion batteries due to the low Coulombic efficiency and the capacity fading. Therefore, many approaches have been tried by inserting the carbon film such as carbon nanotubes, graphene, and carbon nanofiber between sulfur cathode and separator in order to block the diffusion of polysulfides to the Li metal and improve the electronic conductivity. However, it is not enough to prevent the migration of sulfur species to the anode. Here, we suggest anionic polymer coated-SWNT film to improve the electrochemical performance of Li-S batteries. This polymer modified film not only retards the diffusion of polysulfides to counter electrode with π-π interaction, but also enhances the conductivity of sulfur cathode by providing additional conductive path for the electrons. Our approach in inserting hydrophilic polymer modified SWNT between sulfur cathode and separator shows an improved cycle performance and high specific capacity, compared to pristine SWNT.

As the demand for density storage devices with high energy densities increases, the development of next generation energy-storage technology has been drawing significant attention over the past few decades. Among several candidates, lithium-sulfur (Li-S) batteries have been considered as one of the most promising energy storage systems (ESSs) on account of high theoretical capacity (1674 mAh/g), compared to 372 mAh/g of conventional lithium ion batteries (LIBs). In addition, sulfur is naturally abundant, environmentally sustainable and low-cost element. Despite aforementioned advantages of Li-S batteries, fast capacity fading within initial a few cycles owing to the dissolution of polysulfide intermediates into organic electrolytes and large volume changes during charge/discharge cycling have inhibited the development of practically viable batteries. In this study, we develop advanced Li-S batteries by synthesizing a series of organic crystals based on trithiocyanuric acid having two functional groups of thiol and amine. Two crystal structures were obtained from different crystallization solvents; a unique square tube with hierarchical pores, i.e., micron-scale hole in the tube and abundant micropores at the surfaces, and a splice plate with only micropores at the surfaces. Our study demonstrated that the tubular crystals with hierarchical pores serve as a model system for confining sulfur and accommodating the volumetric expansion during cycling, as shown by long-life and excellent capacity retention. Under optimized conditions, our Li-S cell can deliver reversible discharge capacity of 1100 mAh/g at 0.2C with stable cycling performance over 300 cycles, corresponding to capacity retention of 90% from the initial discharge capacity. In addition to the good capacity retention property of our Li-S cell, improved rate performance was also determined. The Li-S cell based on the tubular organic crystal/sulfur composite cathode was found to deliver a reversible capacity of 900 mAh/g at 2C. After cycling at various rates, further cycling at a low rate of 0.2C brings it back to a reversible capacity of 1100 mAh/g. The markedly improved cycling performance of our Li-S cell is attributed to the increased Li⁺-ion transport of the organic crystal/sulfur composite cathode along amine moieties of crystal frameworks, as determined by Randles-Sevcik analysis.

Lithium-Sulfur batteries called beyond Li-ion batteries have received tremendous attentions for its high theoretical capacity of 1672 mAh/g, natural abundance, and low cost. However, it has many critical issues to be solved such as shuttle effect and low Coulombic efficiency before commercialization. Also, low conductivity of sulfur itself restricts the full utilization of sulfur cathode, resulting in low specific capacity. Many approaches have been suggested by using sulfur coated single walled carbon nanotubes (S/SWNT) to solve the inherent problems of sulfur cathode. It exhibits good cycle performance and high specific capacity due to the good properties of SWNT as sulfur reservoir. But, it still shows a limitation in preventing the diffusion of polysulfides to the Li-metal and enhancing the conductivity of electrode. Here, we suggest a facile and effective coating method of encapsulating the freestanding S/SWNT film with polyaniline (PANI). The PANI not only can suppress the migration of polysulfide to counter electrode, but also improve the conductivity of the electrode by providing the additional conducting pathway for electrons. The S/SWNT covered with PANI exhibits a higher specific capacity, a better rate retention, and the more stable cycle performance than S/SWNT electrode.

The development of advanced batteries has been highly desired to meet the increasing demands of large-scale energy storage systems (ESSs). Lithium-sulfur (Li-S) battery is one of the most attractive battery system, owing to its high theoretical specific capacity (1675 mAh/g) and high energy density (2567 Wh/kg). Furthermore, sulfur presents benefits such as environmental friendly, low price, and natural abundance. Despite these advantages, practical application of the Li-S battery remains challenging. The major problem is rapid capacity fade, attributed to the dissolution of lithium polysulfide intermediates in the liquid electrolyte causing the loss of active mass. The polysulfide dissolution has also known to generate insoluble solid layers at the electrode surfaces during repeated charge/discharge cycles, leading to an increase in the impedance of the cell, decrease in the Coulombic efficiency, and the reduced specific capacity.
Herein, we have prepared new composite gel polymer electrolytes (CPEs) having dissimilar internal structures. Free-standing CPEs with ca. 80 mm thickness were prepared by mixing silica nanoparticles (SNPs), polyethylene glycol diacrylate (PEGDA), and lithium salt-doped tetraethylene glycol dimethyl ether (TEGDME), followed by UV irradiation. The SNPs showed a mean diameter of 220 nm and carried a high negative charge, offering the capability of impeding polysulfide dissolution into the electrolyte by electrostatic repulsion. To intensify the efficacy of the electrostatic repulsion, we have synthesized a CPE holding unique SNP density gradients in the thickness direction of the membrane (referred to as gCPE). We found several advantages from the gCPE, which can be summarized as follows: 1) high ionic conductivity over 1 mS/cm at room temperature, 2) generation of stable solid electrolyte interface layer on the cathode, and 3) prevention of polysulfide dissolution from the cathode into the electrolyte by effective charge-charge repulsion.
As a result, the Li-S batteries composed of the gCPE, the Li metal anode, and the sulfur cathode demonstrated the enhanced cycle lives, in which the Li-S cells still maintained a reversible specific discharge capacity of 970 mAh/g at 0.2 C rate after 100 cycles, which is equivalent to 85% capacity retention. This is in sharp contrast to the poor capacity retention < 50% of Li-S cells based on the conventional CPEs. The improved long-term cycle life of our Li-S battery is believed to be as a result of the strategic positioning of negatively charged SNPs near the cathode surfaces, in order to decelerate the dissolution of polysulfides during repeated charge-discharge process. To the best of our knowledge, this is the first work to unveil the important role played by the internal structure of the CPEs in determining the performance of Li-S cell.

The lithium-sulfur (Li-S) battery is a potential candidate for the next generation of lithium batteries with a high theoretical specific energy of 2600 Wh kg^-1 (based on active materials only) and a high theoretical capacity of 1675 mA h g^-1, assuming complete reduction of elemental sulfur to Li₂S. However, this capacity is rarely achieved for more than a few cycles, mainly due to a host of reactions associated with the discharge products of sulfur (the polysulfides ‘PS&’), which sets up a “redox shuttle” involving multistage redox reactions. The intermediate soluble discharge products, referred to as higher-order polysulfides, migrate to the anode and react with lithium, which leads to the corrosion/passivation of the anode, poor efficiency and short cycle-life. In addition, the final discharge products Li₂S and Li₂S₂ precipitate not only on the cathode surface, but also in the separator and in voids within the cell. This greatly lowers the rechargeability of the cell and effectively represents a loss of active mass [1, 2]. The electrolyte, as one of the main components of a battery, has a crucial impact on this behaviour. Ionic liquids (ILs) as room temperature molten salts have been considered as a new class of electrolyte materials for lithium-sulfur batteries in recent decades because of their wide potential electrochemical window, high chemical and electrochemical stability, low vapor pressure (consequently low flammability and negligible volatility), low solvation power toward ionic PSs compared to organic electrolytes due to weak Lewis acidic/basic nature which delays the onset of the mentioned shuttle effect [3, 4]. Another approach to suppress this shuttle effect is to modify the electrolyte with additives. It has been shown that LiNO₃ modifies the protective film on the Li anode (known as the solid electrolyte interphase, SEI), which can protect the Li anode from direct chemical reactions with PS [5]. We are studying the effect of LiNO₃ on the SEI layer in the Li-S system by using blended-ionic liquid electrolyte and comparing the results with those from equivalent cells with organic electrolytes. We find that the presence of LiNO₃ and IL in the electrolyte leads to higher initial capacity and better capacity retention (cycleability). We are investigating the surface chemistry of the anode with XPS, to gain a better understanding of how LiNO₃ and IL modify the SEI layer.
References:
1. Barghamadi, M., et al., J. Electrochem. Soc., 2013, 160(8), A12562.
2. Yuan, L.X., et al., Electroch. Commun., 2006, 8(4), 610.
3. Huang, J., and Hollenkamp, A.F. J. phys. chem. C, 2010, 114, 21840.
4. Park, J.-W., et al., J. Phys. Chem. C, 2013. 117(9),4431.
5. Zhang, S.S., J. Electrochem. Soc., 2012. 159(7), A920.

Recently, lithium-sulfur battery has become particularly attractive, due to their high theoretical capacity, high energy density and the natural abundance of element sulfur with a low cost. However, the cycling stability and coulombic efficiency of Li-S cells are limited. Developing hierarchical porous carbons to firmly confine the sulfur and the related polysulfides is one of the strategies for solving this problem. In this work, we developed an immobilizer host of sulfur from activated carbon aerogels (ACA-500) which were prepared by KOH activation of sime-carbonized aerogels (CA-500). The experimental results showed that the ACA-500 has not only high surface area and large pore volume, but also rational pore size distribution. It can hold a large amount of sulfur by infiltrating into nanopores. The discharge/charge curve of the ACA-500-S cells at 0.5C rate shows two plateaus at ~2.3 V and ~2.1 V, corresponding to reduction reaction from sulfur to long-chain polysulfides(Li₂S_x, 4< xle; 8) and the transformation of long-chain polysulfides to Li₂S₂ /Li₂S (Fig. 2A). The cells have high initial discharge capacity of 1130 mA h g ^-1 at 0.5C and 853 mA h g ^-1 at 1C, respectively. The reversible capacities are as high as 834 mA h g ^-1 at 0.5C and 806 mA h g ^-1 at 1C after 100 cycles, respectively. It can be concluded that the ACA-500 is a promising material for high-performance Li-S battery.

Due to a unique set of specificities (high surface area, large pore volume, chemical inertness addressed through good mechanical stability, good conductivity) open cell carbonaceous materials appear as outstanding candidates for a wide scope of applications ranging from water and air purification, adsorption, electro-catalysis and energy storage and conversion.
Here, Porous carbon foams were prepared by pyrolysis of phenolic resin from a dual template approach, using silica monoliths as hard templates and triblock copolymers as soft templating agents. Macroporosity of 50-80 % arose from the Si(HIPE) hard template, while soft templates generated micro- or mesoporosity, according to the operating procedure. The final materials exhibited BET specific surface areas of 400-900 m²middot;g^-1, depending on whether or not non ionic surfactants were used during the synthetic paths. Their performances as Li-sulfide battery positive electrodes were investigated and correlated with their hierarchical porosity. Triggering the porosity through an integrative chemistry-based rational design,[1] we found out that the novel 2P5HF carbon foam presents almost 1000 mAmiddot;hmiddot;g^-1 of remnant capacity after 50 cycles,[2] far from all the other electrodes seen in the literature, within the limit of our knowledge. Also we will show the effect of gold nanoparticles adding toward avoiding polysulfide leaching from the cathode, providing thereby stable remnant capacity when cycling.[3]
[1] Combining soft matter and soft chemistry: “Integrative Chemistry” toward designing novel and complex architectures. R. Backov.Soft Matter 2006, 2, 452.
[2] Carbonaceous multiscale-cellular foams as novel electrodes for stable efficient lithium-sulfur batteries. M. Depardieu, R. Janot, C. Sanchez, A. Bentaleb, C. Gervais-Stary, M. Birot, R. Demir-Cakan, M. Morcrette and R. Backov.RSC Advances2014, 4, 2397.
[3] Novel Au/Pd@carbon macrocellular foams as electrodes for lithium-sulfur batteries. M. Depardieu, R. Janot, C. Sanchez, A. Bentaleb, R. Demir-Cakan, C. Gervais, M. Birot, M. Morcrette and R. Backov, J. Mater. Chem. A, 2014, 2, 18047.

A polymer-coated sulfur electrode was prepared to block the soluble polysulfides via a surface-induced crosslinking polymerization onto sulfur electrode, and evaluated for rechargeable lithium sulfur batteries by electrochemical methods. The polymer coated sulfur composite electrode retained a specific capacity beyond 665 mA h g^-1 at high rates of 2 C after 100 cycles with an excellent coulombic efficiency of 100%.

The depletion of fossil fuels and the impacts of global warming add significant impetus to the ever-growing demand of renewable energy (i.e. solar, wind, waves, and geothermal heat). Battery technology plays a critical role on the practical applications of harnessing intermittent energy sources to a stable electricity supply. High energy density, low cost and reliable safety are basic requirements for the next-generation batteries. Solid-state batteries avert the flammable liquid electrolytes that used in conventional batteries and enable high energy battery chemistries. Therefore, they are promising candidates for future battery technologies of high-energy density and intrinsically safe.[1, 2] In this presentation, we will discuss the investigation of high energy density solid state batteries with transition metal sulfides as the cathode and metallic lithium as the anode. Thio-LiSICON has been used as the solid electrolyte.[3] Detailed research focuses on the development of mixed transition sulfides that include FeS₂, CoS₂, Ni₂S₃, and TiS₂. The research reveals the interplay of ionic and electronic conductivities of the cathode composites and their correlations with the cyclability and rate performance of the solid-state batteries.
Acknowledgement:
This work was supported by the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility at Oak Ridge National Laboratory.
References:
1. Li, J., et al., Solid Electrolyte: the Key for High#8208;Voltage Lithium Batteries. Advanced Energy Materials, 2014.
2. Lin, Z., et al., Lithium Polysulfidophosphates: A Family of Lithium#8208;Conducting Sulfur#8208;Rich Compounds for Lithium-Sulfur Batteries. Angewandte Chemie, 2013. 125(29): p. 7608-7611.
3. Liu, Z., et al., Anomalous high ionic conductivity of nanoporous β-Li3PS4. Journal of the American Chemical Society, 2013. 135(3): p. 975-978.

A facile hydrothermal method has been used for the synthesis of cobalt molybdate (CoMoO₄). The morphology of the CoMoO₄ was modified by varying growth parameters. The structural characterization of the synthesized CoMoO₄ was performed using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX). The XRD analysis confirmed the formation of phase pure CoMoO₄. It was observed that the morphology of the CoMoO₄ depends on growth conditions. Different morphologies such as cauliflower, brick and nano-sphere were observed. The EDX analysis further confirmed the formation of CoMoO₄. The potential use of the CoMoO₄ as an electrode material for supercapacitor applications was examined by investigating the electrochemical behavior using cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. The CV characteristics of the CoMoO₄ electrodes showed a typical pseudocapacitive behavior in 3M KOH solution. It was observed that the specific capacitance of the CoMoO₄ depends on its morphology. The highest specific capacitance of 168 F/g at the current of 1 mA was observed for the nano-sphered CoMoO₄. Furthermore, these electrodes showed excellent cyclic stability. The effect of electrolyte (LiOH, NaOH and KOH) on the electrochemical properties of the CoMoO₄ was investigated. It was observed the specific capacitance depend on the electrolytes and showed highest value in 3M LiOH electrolyte. The details of the synthesis methods, structural and electrochemical measurements will be presented. This work provides an ultimate facile method to synthesize morphologies controlled CoMoO₄ for the applications in next generation energy storage devices.

Li ion batteries are one of the most popular types of rechargeable batteries for portable electronics. One pressing issue for Li ion battery is the capacity loss and material degradation over repeated cycling. Study of battery failure mechanism requires proper tools with particular spatial resolving power.
Here we present an in-situ set-up for high resolution Raman mapping of Li ion batteries. The performance of the set-up is validated with LiNi_xMn_xCo_1-2xO₂ cathode material. Electrochemical cycling tests show that battery cell can be cycled for more than 20 times with columbic efficiency ~1. In-situ Raman mappings were collected to reconstruct the chemical composition of electrodes, as well as to differentiate chemical changes at different position. Our result showed that the in-situ Raman experiment successfully probed the inhomogeneous structural changes of NMC particles during cycling. The result indicated that Li de-intercalation/de-intercalation did not happen simultaneously for different particles. In addition, some particles showed larger degree of irreversible structural transition than others. The observation is in support of the idea that the degradation of battery material is inhomogeneous.
The in-situ mapping technique will serve as a high resolution probe for battery material surface in operando. It can be used to further understand battery failure mechanisms which are meaningful in developing long-lasting Li ion batteries.

Future rechargeable batteries will rely on both lithium-ion host materials and post-lithium-ion systems, such as Li-O₂. Regardless of the technology, further improvements in performance and safety of batteries require a fundamental understanding of the battery electrode materials and their electrochemical interfaces. In the talk, progress done in our group on the development and application of various in situ techniques will be presented.
Online Electrochemical Mass Spectrometry (OEMS) can qualitatively and quantitatively detect the formation of volatile species during operation of an electrochemical cell. Particularly for the Li-O₂ system, the ability to follow the O₂ consumption/evolution during cycling, e.g. to determine the cell rechargeability, is of critical importance. Several combinations of O₂-electrode substrates (Carbon, TiC) and electrolytes (Ethers, Nitriles) were investigated and the cell O₂ round-trip efficiencies determined during multiple cycles. Simultaneously, the influence of other volatile species (such as CO₂, H₂O, H₂, C₂H₄, etc.) that arise as a result of side-reactions with the electrolyte grows with cell voltage/cycle. Similarly, the stability of electrolytes based on carbonates and ionic liquids in cells containing both positive (e.g. NCM family) as well as negative (LTO, P, Sb, Sn, etc.) lithium-ion electrode materials were investigated. Results from complementary in situ techniques, namely IR spectrometry, combined IR/Raman microscopy and XPS will be presented with an emphasis on the critical role of interface-related electrochemical processes relevant for cell performance and safety.

Many in situ tools have been developed to aid the advancement of Li-ion battery for efficient and safe energy storage. The common limitation shared by all current technologies is the inability to directly observe phenomenon associated with lithium ion transportation, which may account for the unresolved challenging problems associated with short battery cycle life time and safety concerns for overheating. Neutron techniques stand out from many probing particles for its high penetration power and a highly probable nuclear reaction with ⁶Li. Given a proper nuclear instrument setup, the selective nature of this nuclear reaction between a neutron and a ⁶Li atom results in a spectrum that track and count lithium atoms directly. An in situ measurement of an electrochemical cell is presented in this work by using a neutron-based method, termed as neutron depth profiling (NDP). The in situ NDP instrumentation and methodology was developed at the 500 kW Research Reactor at The Ohio State University and the final data acquisition was performed using cold-neutron NDP facility at 20 MW Research Reactor at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). We have visualized and quantified the lithium atoms transportation in anode during battery charging and discharging. The developed in situ technique is also applicable to Li-ion batteries with thicker electrode and to study SEI dynamics.

The potential of Raman and UV-Vis diagnostics for spatially-resolved and in situ diagnostics of lithium-ion batteries is demonstrated. Focus is put on LiCoO₂ electrode materials, which were investigated in detail as composites of LiCoO₂ with binder (PVdF) and conductive (carbon) additives. In particular Raman spectroscopy allows to detect all components of the battery such as the LiCoO₂ and carbon active masses, carbon and PVdF additive-related bands as well as electrolyte bands [1].
Detailed wavelength-dependent analysis reveals the first observation of a resonance Raman effect for LiCoO₂-based materials for green (514 nm, 532 nm) laser excitation. The resonance effect is confirmed by a dependence of the A_1g and E_g phonon band intensity ratio on excitation wavelength and the occurrence of an overtone of the A_1g band for green excitation.
The resulting signal enhancement strongly facilitates the spatially-resolved and in situ analysis of LiCoO₂ composite electrodes. Spatially resolved analysis, i.e. Raman mapping of LiCoO₂ composite electrodes, shows a significant variation of chemical composition across the electrode surface and the presence of individual active mass particles, which are ~10-20 µm in size [2].
Raman spectra recorded under electrochemical conditions are largely invariant regarding the degree of lithium de-/intercalation indicating no significant structural changes on the surface of the active mass particles. To this end, Raman experiments are complementary to X-ray diffraction experiments. Interestingly, spatially resolved in situ Raman analysis (Raman mapping) of LiCoO₂ composite electrodes (85% LiCoO₂, 10% PVDF, 5% carbon black) demonstrates the chemical redistribution during electrochemical cycling. Our results indicate that the redistribution is correlated with changes in the LiCoO₂ phonon band intensities, which may be considered as a measure of the electronic structure of the active mass particles.
Besides Raman spectroscopy, the use of UV-Vis spectroscopy for LiCoO₂-based cathode and carbon-based anode materials has been explored. In case of carbon-based materials (SLP30) electrochemical cycling leads to significant absorption changes due to lithium de-/intercalation. In particular, for the fully lithiated graphite a strong increase of absorption at energies <2.5 eV is observed, which can be attributed to LiC₆ formation in agreement with reflectivity results from the literature.
Our results highlight the potential of Raman and UV-Vis analysis to contribute to the ongoing discussion on the mode of operation of lithium-ion batteries due to their ability to deliver spatially resolved and in situ information during battery operation.
References:
[1] T. Gross, L. Giebeler, C. Hess, Novel in situ cell for Raman diagnostics of lithium-ion batteries, Rev. Sci. Instrum. 2013, 84, 073109.
[2] T. Gross, C. Hess, Raman diagnostics of LiCoO₂ electrodes for lithium-ion batteries, J. Power Sources 2014, 256, 220.

The functionality of electrode and electrolyte materials depends strongly on their electronic structure, the determination of which is an important task for x-ray spectroscopy. For Li ion battery cathode manganese spinel studies I show a versatile transmission spectro-electrochemical operando cell with hard X-ray XANES studies, and some combinations of soft- and hard x-ray emission and absorption and Li X-ray Raman and NEXAFS spectra. For high temperature SOFC, I will show some sulfur K-edge spectra of anodes with unexpected traces of sulfate and thiophene on it and a number of oxygen and Fe L-edge spectra of cathode iron perovskites. We found a very interesting quantitative correlation between conductivity and relative spectral weight of electron hole transitions in the oxygen pre-edges of these iron perovskite cathodes. Further correlations between polaron conductivity and spectral weight near the Fermi energy was found in the high temperature valence band photoemission data recorded for high T. Our work includes operando high temperature - ambient pressure resonant photoemission spectroscopy on proton conducting ceramic electrolytes, which we performed parallel to electrochemical impedance studies. We did this with a novel AP PES/XPS end station. Our success with the correlation of performance or functionality of iron perovskites with the spectral weight of hole doping peaks in the oxygen pre-edges was transferred to the field of photo catalysis. Here we found a new transition in the t2g-eg doublet depending on the nitrogen doping of TiO2 which scales quite well with the nicotine degradation of TiON. Another material of interest is hematite a-Fe2O3, which can be used for solar photo-electrochemical water splitting with oxygen and hydrogen generation. The electronic structure of bulk and surface facing the electrolyte are important for functionality; positive bias of 600 mV creates a new transition in the upper Hubbard band. For microstructure characterization we use small angle scattering. Here I show examples for lithium batteries and solid oxide fuel cells.
[1] A. Braun, S. Seifert, P. Thiyagarajan, S.P. Cramer, E.J. Cairns. Electrochemistry Communications 2001, 3 (3) 136.
[2] A. Braun, S. Shrout, A. C. Fowlks, B. A. Osaisai, S. Seifert, E. Granlund, E. J. Cairns. J. Synchrotron Rad. (2003), 10, 320.
[3] A. Braun et al., Journal of Power Sources 2003, 112 (1) 231.
[4] A. Braun, H. Wang, S.S. Lee, EJ Cairns, JP Shim, Journal of Power Sources 170 (2007) 173.
[5] A. Braun, H. Wang, T. Funk, S. Seifert, E.J. Cairns, Journal of Power Sources 2010, 195 (22),7644.
[6] A. Braun et al., J. Power Sources 2008, 183, 2, 564.
[7] A. Braun et al., Applied Physics Letters, 95, 022107, 2009.
[8] A. Braun et al. J. Phys. Chem. C, 2010, 114 (1), 516.
[9] A. Braun, K. Sivula, D. K. Bora, J. Zhu, L. Zhang, M. Grätzel, J. Guo, E. C. Constable, J. Phys. Chem. C 2012, 116 (23) 16870.
[10] A. J. Allen, J. Ilavsky, P. R. Jemian, A. Braun, RSC Adv., 2014, 4, 4676.

Coherent x-ray diffractive imaging (CXDI), a lensless form of microscopy capable of discerning electron density and strain with 20 nm resolution, is used to map the strain evolution of a single cathode particle in a functional battery as it is cycled in-situ. The evolution of compressive/tensile strain reveals a number of interesting phenomena. For instance, a strain front nucleates and propagates inward/outward during discharge/charge. We demonstrate that CXDI is a powerful diagnostic tool to reveal correlation between strain and electrochemistry at the single particle level and offers valuable information for electrode/battery modeling and future battery design. Scanning electron microsocpy and electron energy loss spectroscopy (STEM/EELS) offers unprecendented spatial resolution, which has enabled nanoscale imaging and chemical anslysis of the interfaces, ground boundaries and phase boundaries. By combinign electron based and X-ray based novel imaging techniques, we demonstrate the state-of-the-art diagnostic tools developed for probling functional battery materials in operando.

The Solid Electrolyte Interphase (SEI) in lithium ion battery (LIB) negative electrodes is an intermediate layer between active materials (e.g., graphite, silicon) and the electrolyte. Formation of the SEI results from parasitic decomposition of the electrolyte, but ideally SEI passivates the surface as an electronic insulator while enabling ion conduction. Because of its unique role in transport behavior and because it is coupled to decomposition reactions that adversely effect battery cell performance, understanding the structure-function relationship of the SEI is central to extending cycle life and improving safety in LIBs. Additives (e.g., FEC) and coatings (e.g., alumina, titania, titanium nitride, carbon) have been shown to improve the cycle life of silicon active materials. Additionally, high concentration (~3 molar) electrolytes comprising large anion lithium salts and aprotic nonaquesous solvents traditionally thought to be unusable in battery applications (e.g., DMSO, DMF) show improved cycling behavior over ethylene carbonate and linear carbonates mixtures. The mechanisms leading to these improvements and how they relate to the SEI are very poorly understood. We investigate SEI formed on model systems (e.g., silicon wafer and amorphous silicon thin films) by anhydrous and anoxic UHV techniques (XPS, TOF-SIMS), as well as in situ spectroscopy (ellipsometry, ATR FTIR). By combining the information from these approaches and using statistical analysis of TOF-SIMS depth profiles we identify common structures across these approaches, suggesting the mechanisms and future engineering strategies that lead to the performance improvements.

Improvements in the energy density, rate capability, and safety of Li-ion batteries, as well as a reduction in cost, are needed for the wide-spread adoption of electric vehicles. Layered cathode materials with the general formula LiNi_yMn_yCo_1-2yO₂(0 < y le; 0.5) have attracted significant attention as an alternative to LiCoO₂ as they demonstrate higher capacity and increased thermal stability, along with a reduction in cost. However, the substitution of Co by Mn and Ni results in a decrease in the electronic conductivity and structural stability, thus limiting the rate capability and cycle life of these materials.
To overcome these issues, a LiNi_0.4Mn_0.4Co_0.2O₂ cathode with 5 wt.% single-walled carbon nanotubes [1] and an Al₂O₃ ALD surface coating [2] has been developed which has demonstrated cycling stability and high rate capability, even with cut-off voltages of 4.5 V and above. We have employed operando X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) to understand how the ALD coating affords this enhanced stability. Using the combination of element specific XAS recorded at the Mn, Co and Ni K edges and XRD, we can compare the evolution of the chemical state and structure of both uncoated and coated electrodes over a charge/discharge cycle. The results of this study will be presented, providing insight into the structural and electrochemical effects of ALD coating on these layered NMC cathodes. This knowledge will help to direct future developments to further improve the performance of this class of material.
1. C. Ban, et al., Advanced Energy Materials, 1 (2011) 58-62.
2. L. A. Riley, et al., Journal of Power Sources, 196 (2011) 3317-3324.

Lithium ion battery (LIBs) is considered as the best candidate for powering electrified automobiles such as electrical vehicle (EV). Although extensive efforts have been made on the development of LIBs, several related problems need to be overcome, such as the uneven distribution and price of lithium sources, which are an obstacle for the large scale application. Hence, sodium-ion batteries (SIBs) have drawn much interest as a power source for large scale energy storage, since sodium is much more in abundance and less cost resource than lithium for LIBs.
Layered alkali transition metal oxides (i.e., LiMO₂ and NaMO₂, M=transition metal) are the premier class of cathode materials in LIBs and SIBs. The safety characteristics of LiMO₂ cathode based LIBs are one of the most critical barriers to be overcome for the large scale application such as EV. One of the main reasons that might cause safety hazards of the LIB is associated with the thermal instability of LiMO₂ cathode materials, which is related to the occurrence of exothermic reactions between flammable electrolyte and liberating oxygen from charged LiMO₂ at high temperature. Based on the structural homology between the layered LiMO₂ and NaMO₂, we expect that the investigation of thermal stability of NaMO₂ cathode materials is also important for the practical use of SIBs. However, few attentions have been paid on safety issue of SIBs.
In this study, the thermal stability of charged NaMO₂ cathode materials is investigated by using combined in situ time-resolved X-ray diffraction and mass spectroscopy (TR-XRD/MS), which allows simultaneous observation of the structural changes and gas species that are evolved during thermal decomposition of charged cathode materials. In addition, ex situ/in situ X-ray absorption spectroscopy (XAS) has been also utilized to look at the local and electronic structural changes occurring during thermal decomposition in an elemental selective way. By utilizing these combined X-ray techniques, we are able to get better understanding of structural and electronic structure changes in charged cathode materials during thermal decomposition. In this presentation, the thermal decomposition behavior of charged NaMO₂ (M=Co, Cr) cathodes and the comparison with that of LiCoO₂ counterparts in LIB will be covered. The results obtained from this study will provide valuable guidance for developing new cathode materials with improved safety characteristics in both LIBs and SIBs.

Titanium carbide Ti₃C₂ is a member of the recently discovered family of two-dimensional materials known as MXenes. This material demonstrates a high storage capacity related to the rapid intercalation of ions within the structure, making this a promising electrode material for supercapacitors. However to date, the intercalation mechanism is still poorly understood and other techniques able to probe its dynamics are required.
Here, in-situ Atomic Force Microscopy (AFM) is used to monitor the strain developed in a Ti₃C₂ electrode during intercalation/extraction of monovalent and multivalent cations in a variety of aqueous electrolytes. The actuation mechanism is strongly dependent on the cation charge and ionic radius. When small cations such as Li⁺ or Mg²⁺ are inserted, electrostatic attraction between layers dominates, whereas intercalation of larger cations such as K⁺ or Ba²⁺ leads to a lattice expansion governed by steric effect. By using AFM as a high resolution probe, the strain measurements clearly evidences a 2-steps electrochemical intercalation in Ti₃C₂, corresponding to the 1^st and 2^nd adsorption layer between the MXene sheets with different kinetic response, in good agreement with the first principle simulations predictions.
We also show that the poor surface coverage and slow intercalation kinetics of Mg²⁺ and Al³⁺ cations are mainly explained by their large and strongly bonded hydration shell. Interestingly however, the capacitance can be doubled by preliminary opening the layers with smaller cations. Additionally, it is possible to replace the intercalated cation by another simply by switching the electrolyte, hence changing the actuation features of the same Ti₃C₂ electrode accordingly.
These results are interesting because they shed light on the cation intercalation mechanism in the 2D structure of the carbide, and show for the first time that the actuation of Ti₃C₂ can be finely controlled by a proper electrolyte selection. Moreover, the dynamics of interactions between cations and the layers can be efficiently probed with an AFM tip. Since a variety of 2D transition metal carbides can be synthesized, MXenes offer the promise of exciting discoveries for electrochemical capacitors and actuators.
The work was supported by the Fluid Interface Reactions, Structures and Transport (FIRST), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. . The facilities to perform the experiments were provided by the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Recently significant attention was focused on the development of rechargeable batteries with high energy densities in order to alleviate energy storage needs associated with the anticipated growth in renewable energy generation to satisfy a future carbon neutral environment. While Li-ion battery technology is prevalent throughout these emerging applications, the development of batteries implementing multivalent transporting ions such as magnesium (Mg) is an exciting opportunity because of their two-electron Mg/Mg²⁺ redox reaction that can lead to a high theoretical energy density (energy per unit weight) for the same amount of transporting ions, rivaling that of Li metal batteries. Moreover, as opposed to metallic lithium, magnesium is considered an environmentally friendly element with a high natural abundance in the Earth&’s crust (2.9% as compared to 0.002 % for Li). The main obstacles in using Mg in rechargeable batteries are i) kinetically hindered intercalation and diffusion of Mg ions within cathode materials most probably due to high charge to volume density of Mg ions resulting in large polarization effects and ii) incompatibility of Mg anode with high-voltage stable electrolytes. The current solution of these issues is attained by i) demonstrating reversible intercalation of Mg in cathodes based on Chevrel phases and ii) the development of Grignard/Ether Mg complex electrolyte solutions that allow reversibility of Mg electrodes. However, these systems exhibit relatively narrow electrochemical stability window (up to 2.2 V vs. Mg) limiting greatly the choice of cathodes for Mg batteries and ultimately, their potential specific energy. In this paper we describe development of full Mg cell, composed of nanostructured V₂O₅ cathode and Sn/C anode, which operates in the common electrolytes such as PC or acetonitrile. We demonstrate for the first time that a nanostructured bilayered V₂O₅ material can effectively intercalate Mg ions between V2O5 bilayers and can be discharged against Mg anode to create Mg-containing cathode in the discharged state. We show that the presence of small amount of water incorporated in the nanocrystalline environment of V2O5 is necessary for efficient reversible intercalation/deintercalation of Mg ions. We employ HRTEM and X-Ray fluorescence (XRF) imaging to understand the role of environment in the intercalation processes. This cathode was subsequently successfully coupled in a rebuilt full cell with a high-energy ball milled Sn/C composite anode to reach a considerable reversible capacity at elevated voltages. We show using HRTEM and XRF that reversible Mg intercalation is limited by anode capacity.

Rechargeable magnesium batteries have attracted wide attention for large scale energy storage. Currently, most studies focus on Mg metal as the anode, but this approach is still limited by the properties of the electrolyte and poor control of the Mg plating/stripping processes. Lessons learnt from lithium battery development history imply that alternative anode materials based on intercalation or conversion reactions may provide new opportunities for rechargeable Mg battery development. It is well known that kinetics of solid-state Mg ions transfer is extremely slow. Downsizing host materials has been very beneficial for ion transfer as shown in lithium/sodium battery chemistries. In this talk, we will discuss the synthesis and application of nanostructured materials such as Bi, Sn, and alloys as high-performance anode materials for rechargeable Mg ion batteries. These nanostructured anode materials deliver decent reversible specific capacity (>300 mAh/g), excellent stability, and high Coulombic efficiency (very close to 100% during cycling). The mechanisms behind this will be discussed. More importantly, these anode materials show compatibility with simple Mg salt electrolytes. The use of simple Mg salt electrolytes will expand materials choice for other components such as cathode, current collectors and open new opportunities to study Mg ion battery chemistry and further improve its properties.

Controlling the morphology of metal anodes is required for the energy storage community to push beyond the limiting energy density of Li ion battery technology. Lithium metal and its tendency to form dendrites is one example where the lack of morphological control restricts the replacement of the limiting graphite intercalation anode. Increased theoretical energy density and elimination of the dendrite problem are two often argued benefits for moving to a battery chemistry based on Mg as opposed to Li metal anode. Few accounts exist in the literature describing the morphology changes produced with cycling of Mg electrodes at relevant rates and capacities necessary for viable metal anode function.
We take on the challenge of describing morphology development and its impact at relevant electrodeposition and electrodissolution current densities during the first hundred cycles of a model Mg anode. In these studies, Mg electrodeposition is conducted onto Au and Pt electrodes of varying degree of orientation and texture in chloride containing ether-based electrolytes (chloroaluminate and MgCl₂ modified Mg complexes) to generate Mg surfaces with controlled facet populations exposed to the electrolyte. We demonstrate that substrate and electrolyte (anion and solvent) can be used to control the initial crystallographic orientation of these model anode films. First cycle galvanostatic stripping of a fraction of the anode film followed by atomic force microscopy and cross-sectional transmission Kikuchi diffraction allows measurement of the degree of anisotropy and orientation dependence of dissolution. Analytical electron microscopy (cross-section) methods show that high rate galvanostatic cycling yields continual re-nucleation and growth of the cycled layer that readily incorporates electrolyte constituents as filmed interfaces. The altered surface energetics due to these interfaces results in the formation of voids and eventual porosity within the cycled layer. This structural evolution imposes impedance changes for the cycled layer that show up in the chronopotentiometric traces generated during cycling. We use the orientation information learned to parameterize a phase field model that describes early stage evolution of both structure and electrochemical response. This work shows that morphology control extends to structural changes more subtle than dendrite formation. The ramification of performance limiting attributes such as porosity on lost metal capacity and lost mechanical integrity of cycled Mg will be discussed.
This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE&’s NNSA under contract DE-AC04-94AL85000

Li batteries have been used for power hybrid and electric vehicles (EV) but making EVs competitive would require much higher energy density of Li ion batteries. Thus, research in batteries need to make move on development of post Li ion batteries. Magnesium&’s thermodynamic properties makes it viable prospect as an anode.
The attractiveness of Mg metal anodes extends beyond the metal air chemistry (e.g. intercalation) due its low cost, non-dendritic environmentally benign, high theoretical specific charge capacity (2205 Ah/kg), and high theoretical energy density (3.8 Ah/cm³). However, technical limitations such as corrosion and surface passivation are hindering in achieving full potential of Mg anode. Especially surface passivation due to insulating blocking layer formed by reduction of electrolyte can severely inhibit Mg deposition. Thus for better understanding and eventually to overcome the limitation of Mg electrodes, one needs first to understand the interactions taking place at the electrolyte/Mg interface. Atom probe tomography (APT) and Transmission electron microscopy (TEM) are unique techniques to characterize material for obtain information on chemistry, 3-D distribution of elements, structure and morphology at small length scale (nanometers).
In this study, both these techniques are applied to study electrodeposited Mg to understand the deposition and stripping behavior. Mg layers were deposited using standard 3 electrode cyclic voltammogram (CV) cell with working electrode as Au coated-Si wafer, counter electrode as Mg⁰, and reference electrode as Mg⁰. Static and cyclic depositions were carried out using different electrolytes PhMgCl/AlCl₃ in THF and (PhMgCl)₄-Al(OPh)₃ to explore the effect of electrolyte chemistry. Also use of inorganic electrolyte for battery application remains to be relatively less explored area for Mg battery research. We plan to discuss functionality of Mg electrolytes like MgCl₂-AlCl₃ and MgTFSI₂ and its influence on the morphology, structure and chemistry of the deposited Mg layer.
Author would like to thanks JCESR for funding this project.

Rechargeable Mg batteries have been identified as a candidate storage system for the next-generation high energy density rechargeable batteries because of the possibility of pairing a non-dendrite forming Mg metal anode (~2.37 V vs. SHE) with high theoretical specific capacity (2205 A h kg^-1) [1] with a Mg intercalation-based cathode. However, several daunting problems still prevent the realization of Mg-battery: (i) the limited selectivity of electrolyte systems that display reversible Mg deposition, (ii) the narrow electrochemical window of the electrolyte, (iii) lack of high-voltage cathode materials, (iv) irremediable interruption of the battery functions by passivation of the anode material. While it is well established that Mg can be deposited reversibly from complex ethereal solutions of Mg-Chloro complex reagents, the stripping/deposition mechanism at the anode is still debated [2,3]. In this talk we present a detailed atomistic DFT study of the interaction of solvent molecules i.e. THF, and the salts (Mg-Chloro complex) when in contact with Mg-anode surfaces, focusing on the competitive absorption of these chemical species at the interface. Ab initio molecular dynamics results will complement adsorption calculations providing a better understanding of the morphology of the electrolyte/anode interface. These models are essential to clarify the challenging electron-transfer mechanism occurring at the electrode/solvent interface.
References:
[1] D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, and E. Levi, Nature407, 724-727 (2002).
[2] N. Pour, Y. Gofer, D. T Major, and D. Aurbach, J. Am. Chem. Soc. 133, 6270-6278 (2011).
[3] R. E. Doe, R. Han, J. Hwang, A. J. Gmitter, I. Shterenberg, H. D. Yoo, N. Pour, and D. Aurbach, Chem. Commun. 50, 243-245 (2014).

Although Li-ion batteries have been successful in various applications, their shortcomings with regard to high cost and global maldistribution of raw materials, as well as safety concerns have stimulated alternative rechargeable batteries based on other carrier ions represented by sodium and magnesium ions, targeting grid-scale energy storage systems (ESSs). However, many electrode materials in these emerging systems often suffer from sluggish kinetics due to the larger size or bivalency of carrier ions, limiting electrochemical performance particular in specific capacity and operation voltage. In this talk, I will introduce a new approach of engaging intercalated water in layered cathode materials. The intercalated water improves the performance of the given materials substantially by shielding electrostatic interactions or maintaining the crystal frameworks over repeated cycles. Detailed effects of intercalated water will also be described, along with promising potentials towards aqueous operations. Electron microscopy characterization for in-depth understanding of these materials will also be introduced.

Rechargeable magnesium batteries have recently gained more and more attention for a possible candidate of post lithium-ion batteries, because of i) potentially high energy density ((3.0V x 2e^- for Mg) / (4.0V x 1e^- for Li) = 1.5), ii) low cost (high clarke number; Mg (1.93) vs. Li(0.006)) and iii) intrinsic safety (no dendrite growth for Mg, while needle-like dendrite for Li). In 2000, a great success of Mg battery was achieved by Prof. Aurbach in the system comprising Mg metal anode, Chevrel phase Mo₆S₈ cathode and Grignard based electrolyte [1]. The prototype Mg battery can work very well over >2000 cycles. Guided by this discovery, intensive researches on anode, cathode and electrolyte materials have accelerated all over the world, to maximize the advantages of the Mg battery system.
A major challenge for high energy density Mg batteries is that there is still lack of practical cathode except for Chevrel phase Mo₆T₈ (T = S, Se). Although the Chevrel phases worked very well, the operated voltage is low (1.1 V vs. Mg) and the observed capacity is also low (110 mAh/g), resulting in low energy density as an entire battery system. To function as a post lithium-ion battery, new cathode materials with high energy density are strongly desired. One of the approaches to create the high energy density cathode is to utilize high capacity active materials such as sulfur [2] and oxygen [3]. On the other hand, high voltage operation is also another approach to realize high energy density of cathode. Here, V₂O₅ is well known to be a cathode material for Mg battery [4] which showed relatively high working voltage of 2.5 V vs. Mg. So far, unique approaches such as nanocrystalline material [5] and xerogel [6] have been reported to see the rechargeability of Mg battery cathode. We also discovered a new type of V₂O₅ materials on the basis of idea of amorphousization and recrystallization [7]. Interestingly, this idea gave us a new insight to tune the working voltage up to 3.0 V. A variety of approaches must be of significant importance to open a new door for high energy density Mg battery cathode.
In this presentation, we will discuss key findings of amorphous and metastable V₂O₅ and their cathode performances for Mg batteries.
References
[1] D. Aurbach et al., Nature, 407 (2000) 724.
[2] H. S. Kim et al., Nat. Commun., 2 (2011) 427.
[3] T. Shiga et al., Chem. Commun., 49 (2013) 9152.
[4] P. Novak et al., J. Electrochem. Soc., 140 (1993) 140.
[5] G.G. Amatucci et al., J. Electrochem. Soc., 148 (2001) A940.
[6] D. Imamura et al., J. Electrochem. Soc., 150 (2003) A753.
[7] T. Arthur et al., submitted for publication (2014).

Multi-valent (MV) ion intercalation batteries provide a realistic and compelling approach to meet the high energy density demanded by the next generation of electronics and vehicles. One of the challenges to achieve high energy density MV-ion systems is to develop a suitable cathode with a high enough voltage and diffusivity of the MV cation. Mg intercalation into V₂O₅ is one of the very few that has been shown to function reversibly at reasonable efficiency. In this study, we gain insight into the atomic mechanism and thermodynamics of Mg insertion into V₂O₅ from first-principles calculations. We have calculated the Mg composition - temperature phase diagram, equilibrium voltage curves and bulk solubility limits by building a cluster expansion model fit to energies from first-principles and subsequently performing Monte Carlo simulations. Preliminary results indicate that Mg in V₂O₅ is a “phase separating” system at room temperature. We believe that this study can be further used to estimate the practical levels of Mg intercalation that can be achieved with V₂O₅.

Rare-earth nickelates with a general formula Ln₂NiO_4+δ (Ln=La, Pr, Nd) retain attention as potential cathodes for energy production and storage systems such as fuel cells, electrolysers and CO₂ converters [1]. These mixed ionic electronic conductors (MIEC) are required to operate from intermediate to high temperature (400-800°C) under medium gas pressure. In order to offer a choice of the most pertinent composition for industrial applications with an important lifetime, three different well-densified Rare-Earth nickelate ceramics: La₂NiO_4+δ/ Pr₂NiO_4+δ/ Nd₂NiO_4+δ were exposed to medium and high water vapor pressure (20bar/40bar) at intermediate temperature (550°C) between 1 and 6 weeks in an autoclave device. CO₂-free and CO₂-saturated water were used. Eventual structural/chemical changes of the ceramic bulk and surface were characterized using various methods: weight mass control, microscopy, TGA, dilatometry, Raman/ATR FTIR microspectroscopy and X-ray diffraction. Raman mapping was performed on the surface of the ceramic exposed to the water vapor as well as on fresh ceramic fracture in order to follow the corrosion process. The compounds remain almost uncorroded (corroded film < 0.15 µm/week) under medium CO₂-free water pressure. On the contrary, under high pressure and/or CO₂-saturated water different second phases are detected, namely Ln(OH)₃, Ln₂O₃ and Ln₂O₂CO_3,. Nd₂NiO_4+δ ceramic exhibits the highest structural, mechanical and chemical stability (corroded film < 4.5 µm/week for 40 bar CO₂-saturated water, < 0.8 µm/week for 40 bar CO₂-free water and < 0.15 µm for 20 bar CO₂-free water), Pr₂NiO_4+δ shows the most important content of bulk protons, although it&’s significant surface hydroxylation. La₂NiO_4+δ sample seems to be the less stable in presence of CO₂-saturated water (~31 µm/week, 40 bar). As observed for earth-alkaline proton conducting perovskites [2,3], surface hydroxylation and carbonation competes with water/proton insertion.
1. J. Daily, S. Fourcade, A. Largeteau, F. Mauvy, J.C. Grenier, M. Marrony, Electrochimica Acta, 55 (2010) 5847.
2. A. Slodczyk, O. Zaafrani, M.D. Sharp, J.A. Kilner, B. Dabrowski, O. Lacroix, Ph. Colomban, Membranes, 3 (2013) 311.
3. Ph. Colomban, C. Tran, O. Zaafrani, A. Slodczyk, J. Raman Spectrosc. 44 (2013) 312.

One of the main limitations for sodium-ion batteries is the narrow choice of negative electrodes that provide good electrochemical stability and high rate performance. Recent work directed at intermetallic negative electrodes indicates that some of these systems offer better capacities and rate capabilities compared to hard carbon. However, at very high rate, the capacity of these intermetallics drops significantly. A contributing factor here is the high volume expansion that occurs upon sodiation which can cause irreversible damage to the negative electrode. Moreover, some of the metals that form intermetallics, such as antimony, are not particularly good electronic conductors.
Our work has focused on the synthesis of a composite structure based on forming antimony nanoparticles on reduced graphene oxide (RGO). The resulting composite exhibits high energy density at high rate. The material is prepared by chemical reduction at room temperature as 10 nm antimony nanoparticles are grown on the surface of the RGO sheets. The RGO component is flexible and provides excellent electronic conductivity. Furthermore, it is important to pay close attention to the electrode formulation because of the high volume expansion of antimony (310%). For this reason, carboxymethyl cellulose (CMC) and vapor grown carbon fibers (VGCF) were combined with the RGO/Sb composite in fabricating the electrode. At 1C, a capacity of 610 mAh.g^-1 is measured, while, at 20C (providing one mole of sodium in 3 minutes), 75% of the initial capacity is retained. Moreover, the system reversibility is very high as the coulombic efficiency is close to 99.9% at rates above 10C. Excellent reversibility is observed as no significant capacity loss is observed after 100 cycles. These antimony-based electrodes show great promise for developing a new generation of negative electrodes for sodium-ion batteries.

Na-ion batteries have attracted recent interest and start now to be counted as viable alternatives vs. Li ion technologies for specific applications. Indeed, recent works on phosphate-based Na-containing positive electrodes such as Na₃V₂(PO₄)₃ [1] and Na₃V₂(PO₄)₂F₃ [2] have demonstrated excellent performances and can be considered as a new step on the way of sodium-ion technology development. However, like for the Li-ion technology, safety issues related to the use of flammable liquid electrolytes remain, especially due to the high reactivity of sodium with moisture and oxygen. All-solid state batteries, which use non-flammable solid electrolytes instead of organic liquid ones, have been proposed as strong candidates for alternative energy storage devices.
Following a recent successful approach developed for Li-ion all-solid state batteries [3], we were able to assemble an all-solid state Na-ion battery using doped NaRAP (sodium rich anti-perovskite) - based as the solid electrolyte [4]. Thanks to a new experimental set-up, we report for the first time on Na-ion 2.5 x 2.5 cm² cells with a new formula cathode and carbon based anode.
[1] J. Liu, K. Tang, K. Song, P.A. van Aken, Y. Yu, J. Maier, Nanoscale, 2014, 6(10), 5081-6.
[2] T. Jiang, G. Chen, A. Li, C. Wang, Y. Wei, J. Alloys and Compounds, 478 (2009) 604-7.
[3] M.H. Braga, J.A. Ferreira, V. Stockhausen, J.E. Oliveira, A. El-Azab, Novel Li₃ClO based glasses with superionic properties for lithium batteries, J. Mater. Chem. A, 2014, 2, 5470-5480.
[4] M.H. Braga, J.A. Ferreira, A. Murchison, Superionic Glassy Electrolyte for Na-ion batteries, submitted.

Porous organic frameworks (POFs) with high surface area, permanent nano-/mesosized pores, and superior physiochemical stability have garnered extensive research interests in the past decade.¹ In particular, π-conjugated POFs are interesting because of their tailorable redox properties that can be adapted as a platform for electrochemical energy storage.² However, the use of POFs in energy storage has been rare. Here, we demonstrate the use of a redox-active, aza-based π-conjugated porous organic framework, Naph-aza-POF-1, as an efficient cathode material in Na-ion battery.³ Naph-aza-POF-1 was synthesized in melted ZnCl₂ by an ionothermal condensation reaction of 1,4,5,8-naphthalenetetramine with triquinoyl hydrate at 500 ^oC. The electrochemical properties of the Naph-aza-POF-1 were characterized in Na half cells. The Naph-aza-POF-1 exhibits a reversible capacity ~ 215 mAh/g between 1 - 4 V at a current density of 10 mA/g.
Reference:
1. J. X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, H. Niu, C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y Z. Khimyak, A. I. Cooper, Angew. Chem. Int. Ed., 2007, 46, 8574.
2. Xu, F.; Chen, X.; Tang, Z.; Wu, D.; Fu, R.; Jiang, D. Chem. Commun.2014, 50, 4788.
3. C. Deng; J. Lu; R Cutler; J. Mok; J. Zhang; H. Xiong, Manuscript in preparation.

In recent years, there has an emerging demand for the development of low-cost, efficient storage of off-peak electric power and electrical energy by using energy sources other than fossil fuels in the field of wind, solar and nuclear. Furthermore, all-solid-state batteries with inorganic solid electrolytes are promising power sources for a wide range of applications because of their safety, long-cycle lives and versatile geometries. Due to their abundant and ubiquitous sodium sources, rechargeable all-solid-state sodium batteries are more suitable than lithium-ion batteries for application of large-scale energy storage. A superior solid electrolyte is critical for realizing all-solid-state sodium battery. Herein, we reported that stabilization of a high-temperature phase by crystallization from a novel fluorphosphate glass (NTBPZ: Na₂O-TiO₂-B₂O₃-P₂O₅-ZrF₄-NaF) dramatically enhances the Na⁺ ion conductivity. Importantly, a room-temperature conductivity of over 10^-5 Scm^-1 was obtained in the NTBPZ glass-ceramic electrolyte, in which a NaZrPO₄ crystal with superionic conductivity was first realized. Last but not least, compared with chalcogenide glass-ceramic electrolyte reported previously, the NTBPZ glass-ceramic was prepared by melt-quench and double heating treatment process possessing low-cost and easy preparation properties, which was suitable for the large-scale all-solid-state Na-ion batteries.
References
[1] Hayashi A, Noi K, Sakuda A, Tatsumisago M. Nat. Commun., 2012, 3, 856
[2] Christensen R, Olson G, Martin S. J Phys. Chem. B, 2013, 117, 16577- 16586
[3] Slater M, Kim D, Lee E, Johnson C. Adv. Funct. Mater., 2013, 23, 947-958
Acknowledgement
This work was financially supported by the National Natural Science Foundation of China (Grant No. 61077070, 61177086).

In order to address recent concerns on the limited resources of lithium and the localized reserves, sodium secondary batteries have gained much attention as alternative power sources to replace lithium secondary batteries. Up to date, several types of Na rechargeable batteries have been investigated, such as, high-temperature Na-S (NAS) and Na-NiCl₂ (ZEBRA) batteries, room-temperature Na-ion and Na-O₂ batteries, and each system has the pros and cons. Here we introduce a new Na secondary battery system, i.e., a room-temperature Na-CuCl₂ secondary battery using an SO₂-based inorganic liquid electrolyte. The readily-synthesized CuCl₂/C nanocomposite delivered a high discharge capacity of 200 mAh/g with an operational voltage of 3.4 V, corresponding to a theoretical energy density of 580 Wh/kg. It also showed a high round-trip energy efficiency (>96%) and remarkable cycle-life over 1000 cycles. The outstanding battery performance can be obtained by the unique compatibility between a metal halide cathode and the inorganic electrolyte, and the related reaction mechanism will be also discussed in this presentation.

Although Li-ion is now the technology of choice for portable and automotive applications, concerns have been recently raised about the future availability and prize of lithium resources (1). Many alternatives are explored and a large amount of research is presently dedicated to the Na-ion technology, due to the fact that sodium is cheap, abundant and similar to lithium in terms intercalation chemistry. We focused our efforts on the vanadium polyanionic compound Na₃V₂(PO₄)₂F₃. Such a material presents an extraordinary theoretical capacity of 192.4 mAh/g for the extraction of 3 Na, although only the extraction of 2 of them has been experimentally demonstrated when the material is cycled vs. Na (2). The material is also extremely challenging from the crystal structure point of view, since the whole family of compositions Na₃V₂O_2x(PO₄)₂F_3-2x (0 le; x le; 1, with vanadium&’s oxidation state ranging from 3⁺ to 4⁺), shows an extremely rich phase diagram. In the case of Na₃V₂(PO₄)₂F₃ (x=0), the crystal structure was established in 1999 by Le Meins et al. (3), who assigned to it the tetragonal space group P4₂/mnm, used until now, although discrepancies in the reported cell parameters are found in literature. We recently reported on our finding of a small orthorhombic distortion in Na₃V₂(PO₄)₂F₃ (a=9.028Å, b=9.044Å), observed thanks to very high angular resolution synchrotron radiation diffraction (4). This led to a new structural determination in the Amam space group, preserving the structural framework but inducing a different arrangement of sodium ions. Interestingly, we also showed an orthorhombic-tetragonal transition determined by the disordering of sodium ions at high temperature. Regarding the sodium extraction mechanism, this has always been reported to be a simple solid solution of the tetragonal P4₂/mnm phase, consequence of the shrinkage of the unit cell. However, different facts suggest otherwise: firstly, the above-mentioned finding of a different space group for Na₃V₂(PO₄)₂F₃; secondly, a recent work where the phase diagram is calculated to be more complicated than a simple solid solution (5): finally, in-situ experiments performed on materials of the family Na₃V₂O_2x(PO₄)₂F_3-2x (x=0.8, 1), showing a complex behavior (6). We decided to re-investigate the phase diagram of Na₃V₂(PO₄)₂F₃, thanks to in-situ (operando) synchrotron radiation diffraction upon Na⁺ extraction. We observed for the first time an extremely complicated sequence of biphasic and monophasic reactions leading from Na₃V₂(PO₄)₂F₃ to NaV₂(PO₄)₂F₃, with several intermediate phases formed upon charge.
Ref: (1) J. M. Tarascon, Nat. Chem., (2010), 2, 510.
(2) R. K. B. Gover et al., Solid State Ionics, (2006), 177, 1495.
(3) J. M. Le Meins et al. J. Solid State Chem., (1999), 148(2), 260.
(4) M. Bianchini et al., Chem. Mat., (2014), 26(14), 4238.
(5) Young-Uk Park et al., Advanced Functional Materials, (2014), 24(29), 4603.
(6) N. Sharma et al., Chem. Mat., (2014), 26(11), 3391.

Energy storage is an indispensable need for increasing demands on numerous portable technologies. In this respect, rechargeable lithium (Li)-ion batteries (LIBs) have been considered as the most successful energy storage device due to their high energy densities and long cycle lives. The limited resource of Li, however, will face concerns of the future cost when LIBs are used for large-scale systems. As such, the sustainable supply of electrochemical energy storage devices is concerned, much effort is devoted in developments of non-lithium battery systems with multivalent charge carriers. Sodium (Na) super ionic conductor (NASICON) family with the general formula of A_xMM&’(XO₄)₃ provides extensive versatility toward chemical substitutions in the polyanionic framework. Importantly, large interstitial spaces can possibly accommodate 0 to 5 alkali cations, making NASICON structures promising candidates for energy storage applications. Recent studies have been invested in their interesting electrochemical properties as positive electrode materials in rechargeable sodium and lithium-ion batteries. However, no research on multivalent ion based-batteries using NASICON structures has been reported. Here we firstly demonstrate NASICON structured cathodes with multivalent ions such as Zn²⁺ as charge carriers, which can involve two or three electron transfers during the electrochemical charge/discharge processes. NASICON type structured cathode materials with different charge carrier cations are prepared via solid state and solution-based reactions and their crystal structures are determined by performing X-ray diffraction measurements. The synthesis conditions were determined based on the thermogravimetry analysis where the formation of desired structure is completed around 600^oC. Initial results indicate that phase pure materials can be synthesized by sintering the precursors at 600^oC for 10 hours. The synthesis procedures, characterization, and electrochemical test results will be presented in detail.

Sodium ion conducting solids continue to be explored for future electrochemical energy storage applications. In particular, Sodium Superionic Conductor (NASICON) materials are being actively pursued due to their known high ionic conductivity. The conductivity of NASICON-type materials is directly proportional to the Na⁺ carrier mobility (Na jumps), and is typically described as being controlled by structural restrictions along the conduction pathway, which is commonly referred to as the “bottleneck” region. It has been shown that for NASICON-type structures containing cations of different sizes, the PO₄ tetrahedra that bridge/link the MO₆ (M = Zr, Si) octahedra are distorted. These local PO₄ environments and distortions and not always clearly identified using XRD, yet can influence the Na cation conductivity. It has been suggested that while XRD may show an increase in the size of the bottleneck opening as a function of NASICON composition, local distortions can counteract this by modulating the Na⁺ jump pathway. Experimental techniques that can measure both the local molecular-level jump-motions and the local environments would provide additional insight into the role of structural distortions and phase impurities on the observed conductivity in NASICON materials. In this presentation, the multiple sodium and phosphate environments and structural distortions produced by different sol-gel syntheses and processing conditions were evaluated using ²⁹Si, ²³Na and ³¹P magic angle spinning (MAS) NMR spectroscopy. It was observed that the primary local structural distortion occurs in the PO₄ tetrahedra, while the SiO₆ octahedra showed relatively little variation. The impact of PO₄ distortions on the local Na dynamics were probed by variable temperature solid state ²³Na NMR spectroscopy, where the temperature dependence of the ²³Na spin-lattice relaxation rates (R₁ = 1/T₁) allowed the Na jump rates between different cation sites in lattice and the corresponding activation energies to be determined. It was found that for phases near the optimal conductive Na₃Zr₂PSi₂O₁₂ composition that slight changes in the synthesis and processing conditions produced large variations in the phosphate speciation and degree of structural distortions. These differences in the phosphate environment were shown to ultimately impact the Na jump dynamics. The NMR based Na⁺ jump rates are discussed with respect to conductivity results.

Sodium-ion batteries have recently attracted much attention for being an alternative economic selection for energy storage other than the lithium-ion batteries. Several materials have been used as the anode in sodium-ion batteries; among them, iron disulfide (pyrite) was recently found to exhibit high reversible capacity and cycling stability. Besides, iron disulfide is earth-abundant and environmental-friendly, being an excellent candidate incorporated with future development of renewable and sustainable energy. The operation of sodium-ion batteries is similar to lithium-ion batteries - by intercalation/deintercalation of sodium in the anode materials. Better understanding of the intercalation mechanism of sodium in iron disulfide anode is beneficial for designing sodium-ion batteries with higher capacity andhigh charge/discharge rates. We therefore use aberration-corrected scanning transmission electron microscopy (STEM) to characterize the structural evolution of iron disulfide with the intercalation of sodium atoms. We compare the structure of iron disulfide before and after intercalation of sodium by direct imaging of the light and heavy atoms using advanced STEM techniques, such as annular bright-field (ABF) and high-angle annular dark-field (HAADF) image modes, in combination of energy-dispersive X-ray and electron energy loss spectroscopy methods. The electrolyte used in this study is ethylene carbonate and propylene carbonate (EC:PC). Our preliminary results show that stability of the solid electrolyte interphase (SEI) layer formed on the surface of the iron disulfide anode plays a key role in the battery operations. Details of the structure of the SEI layer and its influence on the performance of this sodium-ion battery system will be discussed.

The development of rechargeable Mg batteries, driven by the desire to surpass the limiting specific energy density of Li ion batteries, is currently limited by the lack of stable, functional electrolytes compatible with high voltage cathodes. A functional electrolyte must deliver the Mg cation to the anode surface at nearly 100% Coulombic efficiency, requiring cation desolvation and accommodation without formation of a cation blocking film. Successful electrolytes have relied on Lewis acid - base reactions to form Mg cation-solvent complexes that include the traditional Grignard based and more recently reported inorganic MgCl₂ based complex electrolytes containing either BR₄^- or AlR_xCl_4-x^- species.¹ However, the stability of organometallic and chloroaluminate electrolytes against traditional current collectors and proposed oxide intercalation cathodes has been called into question. Novel Mg battery electrolytes based on the weakly coordinating trifluoromethylsulfonylimide (TFSI) anion have recently received much interest due to their wide electrochemical window and general chemical compatibility while maintaining the ability to deposit and strip Mg, a feature previously unknown for simple inorganic Mg salt solutions.^2,3,4 However, this process is typically characterized by low coulombic efficiency, and Mg surfaces tend to passivate in the absence of chloride additives.
We will demonstrate the role of Cl^- addition in modifying the bulk and interfacial speciation of Mg and in preserving Mg anode activity in TFSI-based electrolytes with the goal of understanding the attributes of inorganic Mg salt systems that govern the functionality of a Mg anode. Particular emphasis will be placed on the results of in-operando experiments, namely QCM, AFM, and X-ray absorption spectroscopy, which we employ in order to understand dynamic interfacial processes such as film formation and disruption on both Mg and non-Mg (e.g. Au) surfaces. Specifically, we will demonstrate that in the absence of Cl^-_, Mg surfaces rapidly passivate and unrecoverable material accumulates on the anode during cycling, whereas the presence of a moderate amount of Cl^- preserves the activity of deposited Mg and mitigates film buildup. The mechanism by which activity is preserved and its implications for novel Mg battery electrolyte development will be discussed.
This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE&’s NNSA under contract DE-AC04-94AL85000.
1. T. Liu, et al. J. Mater. Chem. A 2014, 2 3430
2. U.S. Patent #US 2013/0252112 A1
3. S.Y. Ha, et al. ACS Appl. Mater. Interfaces 2014, 6, 4063
4. Y. Orikasa, et al. Sci. Rep. 2014, 4, 5622

With the spread of renewable energy production and the electrification of transportation, the role of and requirements for batteries will expand in future years. An important technical requirement for batteries is that their energy density as a function of mass and/or volume must be high. One approach for achieving energy densities beyond that offered by lithium ion technology is to replace the monovalent Li¹⁺ ion with a multivalent ion, such as Mg²⁺. If the cathode material can accommodate the charge transfer from such a multivalent ion, this technology could ideally double the capacity from the cathode, given the same volume, as compared to lithium ions. While research on magnesium batteries has primarily focused on sulfide based cathodes combined with highly corrosive electrolytes, many scientific challenges remain as the field moves towards enabling oxide cathodes that may provide higher voltage and power. This work will describe the implementation of hybrid cells for studying multivalent cathodes, consisting of high surface area carbon anodes and a variety of electrolytes, such as Mg(TFSI)₂ in propylene carbonate, that are compatible with oxide intercalation electrodes. The importance of cathode-electrolyte capability and electrolyte-current collector compatibility will be discussed, as well as methods for enhancing the capacity of materials such as V₂O₅ through sol gel synthesis. By approaching multivalent batteries from the point of the view of the cathode, a new range of electrolytes has been investigated and provided a new approach to make the multivalent battery a commercial reality.

Lithium ion batteries (LIBs) are important energy storage system for many portable electronic devices and electronic vehicles. However, Li ion batteries are still unstable and expensive for the commercial market. For this reasons, next generation energy storage systems with non-Li ion batteries are interested. Regarding this, Mg is attractive candidate. Mg makes possible to store up to 2 electrons per one atom that can possess the higher volumetric energy comparable to LIBs. The atomic radius of Mg is comparable to Li that can provide high diffusion rate and rate capability. It is also abundant and inexpensive. In this study, we fabricated Si nanosheets for magnesium ion batteries. The Si nanosheets with thickness and diameter of < 5 nm and > 5 mm, were directly grown on graphite foil using chemical vapor deposition process. A half-cells tests were carried out using Si nanosheet as anode with various electrolytes. The half-cells tests showed cyclic performance and electrochemical properties. It demonstrate that SiNSs can be used as anode materials for magnesium ion batteries.

Next generation batteries based on divalent ions like magnesium (Mg) are very promising to increase performance and reduce cost of electrical storage as compared to Li ion batteries in use today. Mg, which exists several percent in seawater, has a history of being safely implemented as a consumable and replaceable electrode in emergency batteries that use aqueous electrolytes [1]. One major challenge with Mg is to find suitable cathode materials that would accommodate the insertion of the doubly charged ion [2]. Crown ethers 12-Crown-4, 15-Crown-5, and 18-Crown-6 were originally designed to capture and manipulate singly charged alkali ions Li+, Na+, and K+, respectively. Crown ethers can be used as hosts for divalent positive ions, as well. For example, an analysis of Mg++ placed inside the crown ethers mentioned above gives binding energies of 10-12 eV, which are about twice those of the mentioned singly charged ions [3]. In this research, derivatives of 18-Crown-6 are investigated as potential hosts for Mg ions. Materials chosen for the study are (a)1,4,10,13-Tetraoxa-7,16-diazacyclooctadecane (C12H26N2O4), which is also known as diaza-18-Crown-6, (b)1,4,10,13-Tetrathia-7,16-diazacyclooctadecane (C12H26N2S4) where oxygens of diaza-18-Crown-6 are replaced by sulfur atoms, and (c)4,7,13,16,21-Pentaoxa-1,10-diazabicyclo[8.8.5]tricosane (C16H32O5N2) which is a cryptand sold by the trade name Kryptofix 221. Insertion of Mg++ into the chosen host materials are analyzed by first principle quantum mechanical calculations using the DFT method with B3LYP functional and Pople type basis sets augmented with polarization functions. Atomic models consist of the mentioned hosts with and without the Mg ion. Calculated binding energy values of Mg++ are 9.8 eV for C12H26N2O4, 3.0 eV for C12H26N2S4, and 13.1 eV for C16H32O5N2. The cryptand which has the highest binding energy and also a cup like shape is a good cathode candidate for the Mg ion. C12H26N2S4 which gives a relatively low binding energy as compared to the other crown ethers might be useful as a transporter of Mg ions between the anode and the cathode. [1] See LED lantern (GH-LED10WBA-WH) from Green House (www.green-house.co.jp) [2] I. Shterenberg et al,“The challenge of developing rechargeable magnesium batteries,” MRS Bulletin Vol. 39, No. 5, p.453, May 2014 [3] H. Gokturk, “Molecular vesicles as battery electrodes,” ACS 248th National Meeting, August 2014

Grid-level energy storage demands a low-cost, safe, long cycle life battery chemistry. The Zn-MnO2 alkaline battery chemistry hits the first two targets. This type of battery has high energy density (comparable to that of a Li-ion battery) and low cost per kilowatt-hour. However, their rechargeability is limited by phase transformations which occur in the MnO2 cathode during discharge of close to one electron, which transforms it into an spinel phase, generally considered to be electrochemically inert. As a result, depth of discharge is limited to no more than 70% of the 1e- capacity of MnO2 at best, and in a large format cell typically no more than 0.5 e-.
We have extensively studied the MnO2 alkaline system and have developed a variety of techniques to extend this depth of discharge window, improving the capacity and cyclability of the cell dramatically. Using these techniques, we have achieved capacities of over 350 mAh/g (1.2 e-) for more than 150 cycles. In this presentation, we will discuss the various failure modes of the MnO2 alkaline system, and the techniques our group has developed to overcome them. We will describe the crystal structure and electrochemical performance of this material, as well as the structural changes occurring during its use as an electrode material as characterized via synchrotron radiation and other techniques.
With further development, this material, combined with either a zinc anode or an earth abundant, insoluble anode such as Fe or Cd, may allow for over 1000 cycles at a cost of less that $100/kWhr for a packed out cell.

An electrochemical direct injection (ECDI) cell involves the injection of solid cathode and anode materials into a small reactor, where the components are reacted and then ejected. This approach has the advantage of decoupling power and energy, while maximizing energy density. We investigate a zinc injection system, in which a small amount of zinc is injected into a small reactor containing an alkaline electrolyte. This approach raises some fundamental scientific challenges, including the utilization level of the electrochemical species as a function of power density, as well as practical issues such as clumping of reactive Zn particles when injected into the electrolyte.
The utilization level of zinc (i.e., percent of the theoretical maximum capacity that we are able to usefully extract) was found to decrease as discharge current increases. Despite the presence of competing reactions (passive H2 generation on Zn and galvanic corrosion) as well as diffusion limitations, we are able to achieve high utilization rates (>80% @ 0.25C and >40% @ 3C) using hyper-dendritic Zn. Nevertheless, we find that through an optimization of the electrolyte chemistry and concentration, we are able to achieve even greater utilization levels (> 70% @ 3C).
Clumping of the zinc particles in the alkaline electrolyte was also found to present some practical challenges during particle injection, and raises some interesting fundamental scientific questions on the agglomeration of reactive particles. These difficulties can be mitigated with the addition of ZnO to the electrolyte, however this may adversely impact the ability to effectively discharge Zn at the highest current and utilization rates. This talk will present highlights of some of these challenges.

The nitroxide radical polymer materials poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) has been successfully used to fabricate organic electrodes for energy storage applications. However the details of how electrons and ions are transported through these complex systems remain poorly understood. Here we describe results of molecular dynamics simulations of PTMA and related co-polymer films that we have utilized to investigate the solvent effects on electron transfer. To this end, PTMA films containing a range of of toluene and acetonitrile concentrations, consistent with experimental measures of solvent uptake, were generated using classical molecular dynamics simulations. Films were equilibrated and the packing of the individual groups was evaluated using radial distribution functions. Subsequently, sets of oligomer units were extracted and the inter- and intra-chain electronic coupling was calculated using the Corresponding Orbital Transformation. Based on the coupling values and distances between sites the electronic-coupling-weighted radial distribution function was calculated to give the effective electron transfer lengths as functions of polymer identity and solvent concentration. Implications of these results for transport within organic radical polymer materials will be discussed.

A Te/C composite, prepared by a simple high energy mechanical milling (HEMM) technique, was investigated as high-capacity cathode materials for a new rechargeable Li-Te battery system with redox potential of ~1.7 V (vs. Li/Li⁺). The Te/C was confirmed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). On the other hand, we designed an advanced mechanically reduced Te/C nanocomposites electrode material using a simple mechanical reduction of transforming TeO₂ into nanocrystalline Te by HEMM process. The mechanically reduced Te/C nanocomposites were comprised of nanocrystalline Te within amorphous carbon matrices, which were also thoroughly demonstrated by XRD and HRTEM. The mechanically reduced Te/C electrode shows good electrochemical performances, such as a high initial charge capacity of 740 mAh cm^-3, long capacity retention of 705 mAh cm^-3 after 100 cycles, good initial Coulombic efficiency of ca. 95%, and fast rate capability (5C: 550 mAh cm^-3).

Functional materials for various energy-related electrochemical applications require the delicate control over their compositions and nanostructures to achieve high performance. As a new family of porous materials, metal-organic frameworks (MOFs) have drawn much research interest due to their tunable structure/composition and widespread applications. Moreover, syntheses of functional materials from MOFs have drawn rapidly growing interests as well. The periodically porous and hybrid structure of MOFs offer unique benefits for the fabrication of nanostructured materials with various compositions for multiple purposes.
Starting from several common and well-studied MOFs, such as Prussian blue (PB) and ZIF-8, we have demonstrated the syntheses of functional materials with diverse chemical compositions and micro-/nanostructures. Specifically, using uniform PB microcubes as both the template and precursor, iron oxide-based complex hollow structures, including multi-shelled and multi-compositional microboxes can be realized. The possibility to control the hollow architecture and composition enables the optimization of performance for specific applications. As a demonstration, the Fe₂O₃ multi-shelled and Fe₂O₃/SnO₂ composite microboxes exhibit improved lithium storage properties as potential anode materials for lithium-ion batteries. By direct carbonization of ZIF-8 polyhedral particles in inert atmosphere, microporous carbon polyhedral particles with uniform porosity are obtained and served as a host material to encapsulate sulfur for lithium-sulfur batteries. The highly uniform microporous structure derived from the ordered architecture of ZIF-8 can be used as an ideal system to investigate the electrochemical behaviors of sulfur and/or polysulfides in microporous carbon. More recently, we have been working on the rational design and synthesis of metal/carbon nanocomposites and metal carbides from MOFs, which make use of both the metal and carbonaceous components in the pristine MOFs. These efforts broaden the spectrum of functional materials synthesized with the assistance of MOFs. Moreover, these metal/carbon nanocomposites and metal carbides are highly active electrocatalysts for water splitting, which efficiently convert electric energy into clean and sustainable H₂ fuel.
To sum up, MOF-assisted synthesis strategy has been adopted to construct a series of functional materials with diverse compositions (metal oxide, carbon, metal/carbon composite, metal carbide) and micro-/nanostructures (multi-shelled hollow structure, uniform porous structure). These functional materials play key roles in the development in many promising electrochemical energy storage and conversion technologies, including lithium-ion/lithium-sulfur batteries and electrochemical water splitting.
Reference
1. L. Zhang, H. B. Wu, X. W. Lou, J. Am. Chem. Soc. 2013, 135, (29), 10664.
2. H. B. Wu, S. Wei, L. Zhang, R. Xu, H. H. Hng, X. W. Lou, Chem. Eur. J. 2013, 19, (33), 10804.

Printed electronics are an ideal platform for the development of low-cost, flexible, ubiquitous electronics. There has been a parallel surge in interest in transient electronics, which are attractive for their ability to physically degrade or disappear after a period of functional operation. The combination of these two technologies appeals to a wide range of applications ranging from zero-waste electronics to temporary biomedical devices that are also cheap, lightweight and flexible. However, the realization of such electronic systems necessitates the development of a printed transient power source.
In this work, we report the development of a fully printed, transient silver-zinc primary battery. The battery stack consists of zinc and silver oxide electrodes, stencil printed separately onto silver ink current collectors, which are first printed onto PET. Various molecular weights of polyethylene oxide (PEO) are studied for use as a separator with alkaline KOH electrolyte. PEO is deposited onto the zinc electrode and saturated with KOH, forming a cross-linked gel upon which the silver oxide electrode can be laminated to complete the battery stack. Degradation of the various components and the discharged cell was measured in phosphate buffered saline over a range of temperatures.
The current densities and discharge capacities are on the order of 2mA/cm² and 4mAh/cm², respectively, with open circuit voltages of approximately 1.6V. Degradation times for the electrode materials varied from a few to several hours, but not more than a few days, while cross-linked PEO is known to slowly resorb in a saline environment. Degradation of the discharged cell occurred within a few days, at which point the films were brittle and broken, leaving behind primarily zinc oxide and silver powder. Overall, the performance of our battery is comparable to that of other printed microbatteries, with the added capability of being able to physically degrade over time, while still being sufficient for powering applications benefiting from printed transient electronic systems.

A flow battery has very unique and significant benefits due to its simple structure and flexible handling of its liquid active materials as ‘electrochemical fuels&’. In spite of this great ‘fueling&’ capability, which may enable the rapid charging of electric vehicles, the energy density of the regular catholytes and anolytes is lower (<100 Wh/l) than that of the solid-state active materials used in regular batteries. A non-aqueous system is a simple and effective method of improving the discharging voltage more than 2 V, which is the limit of the aqueous system, coupling with highly negative anodes. The concentration of redox species in organic solvents is, however, generally lower than that in aqueous solutions and difficult to reach over 2 M with, at least, the same molar of supporting salt. It is important to note that stoichiometric couples of redox species and an appropriate salt is the minimum requirement for the liquid active materials because the valence of the redox species must be changed during discharging and charging and compensating ions must be present in the system. Moreover, the liquids should have a stable fluidic property without freezing or precipitation even in a low temperature range.
In this study, we report an innovative strategy to prepare the liquid active materials in order to increase their energy density. Our technology focuses on the melting of pure redox compounds to maximize their concentration instead of dissolving them in solvents. This simple yet challenging approach has been successfully realized using supercooled liquid technology by the combination of a specific plasticizing salt and a low melting point redox active compound. Such a supercooled liquid can be obtained by mixing of 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-methoxy-TEMPO) and Li bis(trifluoromethanesulfonyl) imide (LiTFSI) and stabilizing the mixture further below their melting points. The redox-active supercooled liquid exists in a highly stable liquid state over a wide temperature range that extends to below its normal melting points. The special properties of this supercooled liquid are due to the scientifically unique and rare solvation state known as a ‘solvate ionic liquid&’, which is typified by a liquefied ion-pair stabilized by a neutral third compound. As a catholyte, the addition of an appropriate amount of solvent helps to enhance the electrochemical advantage while maintaining the liquid&’s supercooled nature, and a battery with a Li⁺ conducting architecture exhibits 93% electrochemical activity and 99% coulombic efficiency in the 1st cycle with an average discharge voltage of 3.6 V. The catholyte also performed an energy density of 200 Wh/l, which is one of the highest values for catholytes reported to date with an organic redox compound.

Novel materials and architectures for energy storage and conversion devices are critical to the advancement of the fields. Recent advances in dendritic nanotechnology have given rise to a myriad of applications in the areas of environment, biomedicine and energy. Our research offers the possibilities of using these nano-polymers in high energ-density applications such as in lithium-air (Li-O₂) and lithium-sulfur (Li-S) batteries. Recently, we showed that poly(amidoamine) (PAMAM) dendrimers - highly branched architectures with exceptional physicochemical and mechanical properties - could be used as hosts to encapsulate monodispersed ruthenium oxide (RuO₂) nanoparticles, and employed as catalysts in the air electrode for Li-O₂ batteries. The dendrimers stabilized the RuO₂ nanoparticles as well as ensured the availability of the entire nanoparticle surface for catalysis, thus reducing the amount of noble metal catalysts used in these systems by almost ten times than the state-of-the-art, yet achieving low overpotential for the oxygen evolution reaction and good cycling stability. Here, we will discuss the synthesis and characterization of dendrimer-encapsulated ruthenium nanoparticles (DEN-Ru) in both aqueous and organic (ethylene glycol) solvents. The complexation between the dendrimer and Ru³⁺ ions from the precursor solution was monitored using UV-vis spectroscopy. Further surface characterizations using XPS showed that the DEN-Ru exist in several oxidation states, in contrast to earlier reports by others of the formation of metallic nanoparticles. In addition, HRTEM also shows the presence of sub-nanometer clusters of Ru atoms, implying the formation of dendrimer-based superatoms. XAS investigations of the DEN-Ru provided further insight into the chemical coordination of the Ru atoms. The catalytic effect of these superatoms will also be discussed.
In the case of Li-S batteries, most research focus has been on improving the cycle life of the batteries by using thin electrodes (<2 mg/cm²). However, for practical applications, it is imperative to validate the different approaches on fabricating electrodes at a relevant scale. While challenges exist in the properties of the cathode materials themselves, the binder in the electrode is also critical in bonding the active materials together as well as maintaining a good electrical contact with the current collector. We have been able to obtain high loading (> 4 mg/cm²) of active sulfur using dendrimer-based functional binders with various surface functionalities. Here, we will discuss the structure-function relationships of dendrimer-based binders and cathode materials in enhancing the performance of high areal capacity Li-S batteries. By using novel dendrimer chemistry and assembly, our research provides new clues to embody the nanoscale properties of soft and porous dendritic nanostructures for improving the state#8208;of#8208;the#8208;art of sustainable, high energy density battery technology applications.

Biologically occurring redox centers hint at the design of a man-made energy storage system. Since the pioneering work by Tarascon et al.[1] towards a sustainable lithium rechargeable battery received significant resonance, organic materials such as carbonyl, carboxyl, or quinone-based compounds have been demonstrated to be bio-inspired organic electrodes.[2] The imitation of redox-active plastoquinone and ubiquinone cofactors through the utilization of redox active C=O functionalities in organic electrodes is a significant step-forward to biomimetic energy storage. However, the biological energy transduction is based on numerous redox centers of versatile functionalities available in nature, not limited to the simple redox active C=O functionalities.
In our continuing efforts to exploit new-type organic electrode materials containing N=C-C=N functionality from cellular energy transduction systems in sustainable rechargeable batteries,[3,4] herein we report a novel class of biological redox units as a high performance battery electrode, namely, pteridine redox centers, which are essential constituents in cellular energy metabolism, along with the novel strategy for tailoring these biological redox units to achieve better electrochemical performances available.[5]
Our work firstly exploits biological pteridine derivatives of alloxazine structures as high-performance electrodes in rechargeable batteries. Combined ex situ spectroscopic analyses and DFT calculations revealed that pteridine systems can store two Li ions and two electrons via a reversible tautomerism between alloxazine and isoalloxazine forms. To the best of our knowledge, this is the first demonstration of a reversible tautomerism of molecules during electrochemical reaction. By applying a molecular simplification strategy combined with in-depth analyses of the redox mechanism, the tailored pteridine electrodes showed outstanding performances, delivering 533 Wh kg^-1 of energy within 1 hour (236 mAh g^-1 asymp; 94.5% of theoretical capacity) and 348 Wh kg^-1 even within 1 minute with 96% capacity retention after 500 cycles, which is the best and longest cycling performance among the organic cathode materials reported at this time, and even comparable to conventional inorganic electrodes. Moreover, we demonstrate that redox cycling of the tailored pteridine electrodes is universally applicable to other energy storage systems with alternative carrier ions, e.g., sodium rechargeable batteries.
[1] H. Chen, M. Armand, G. Demailly, F. Dolhem, P. Poizot, J.M. Tarascon, ChemSusChem2008, 1, 348.
[2] M. Armand, S. Grugeon, H. Vezin, S. Laruelle, P. Ribière, P. Poizot, J.M. Tarascon, Nat. Mater.2009, 8, 120.
[3] M. Lee, J. Hong, D.-H. Seo, D.H. Nam, K.T. Nam, K. Kang, C.B. Park, Angew. Chem. Int. Ed. 2013, 32, 8322
[4] M. Lee, J. Hong, H. Kim, H.-D. Lim, S. B. Cho, K. Kang, C. B. Park, Adv. Mater.2014, 27, 2558
[5] J. Hong, M. Lee, B. Lee, D.-H. Seo, C. B. Park, K. Kang, Nat. Commun. 2014, Accepted

Lithium-ion batteries are playing an increasingly ubiquitous role in society, and the successful commercialization of battery technology has extended the use of lithium-ion chemistries to large-scale applications including electric and plug-in hybrid vehicles (EVs and PHEVs) [1]. Despite these technical accomplishments, large-scale vehicle electrification will require batteries with approximately three times the current energy densities. Therefore, further breakthroughs in scalable energy storage are necessary before the full benefits of vehicle electrification can be realized. One of barriers to the realization of such electrodes is the degradation of the surface due to irreversible reactions at electrode-electrolyte interface including electrolyte decomposition and corrosion of active materials in the acidic environments.
Coating the surface of electrodes in an effort to mitigate unfavorable side reactions has proved to be effective for improving the performance of Li-ion batteries, and atomic layer deposition (ALD) of ultrathin metal oxides such as Al₂O₃, LiAlO₂, and LiTaO₃ has been demonstrated to significantly enhance both stability and safety of electrodes [2,3]. However, metal oxide coatings are likely to be susceptible to hydrofluoric acid (HF) attack upon electrochemical cycling.
Metal fluoride can be alternative coating material due to its stability against HF attack, and strong bond between metal and fluorine. However, ALD of metal fluoride is complex and challenging because of the lack of suitable precursor for fluorine and/or high deposition temperature over 300°C [5-6]. Herein we report the deposition of ultrathin amorphous composite aluminum-tungsten-fluoride (AlW_xF_y) film on LiCoO₂ electrodes via ALD using trimethyaluminum (TMA) and tungsten hexafluoride (WF₆) at 200°C. We will discuss physical properties of 1 nm AlW_xF_y-based films, and electrochemical characterization of AlW_xF_y deposited LiCoO₂ electrodes
References
(1) Thackeray, M. M.; Wolverton, C.; Isaacs, E. D. Energy & Environmental Science2012, 5, 7854.
(2) Jung, Y. S.; Cavanagh, A. S.; Dillon, A. C.; Groner, M. D.; George, S. M.; Lee, S.-H. Journal of The Electrochemical Society2010, 157, A75.
(3) Park, J. S.; Meng, X.; Elam, J. W.; Hao, S.; Wolverton, C.; Kim, C.; Cabana, J. Chemistry of Materials2014.
(4) Li, X.; Liu, J.; Banis, M. N.; Lushington, A.; Li, R.; Cai, M.; Sun, X. Energy & Environmental Science2014, 7, 768.
(5) Ylilammi, M.; Ranta#8208;aho, T. Journal of The Electrochemical Society1994, 141, 1278.
(6) Pilvi, T.; Ritala, M.; Leskelä, M.; Bischoff, M.; Kaiser, U.; Kaiser, N. Applied optics 2008, 47, C271.

Recently, polyvalent cations such as Mg²⁺, Al³⁺, Pb²⁺ and Zn²⁺ have been intensively scrutinized as a feasible charge transport carrier for new battery systems with a high energy density and a commercial viability needed for electric vehicles and large-scale energy storage systems.^[1,2] As one of these kinds of early studies, a rechargeable Zn battery which is composed of α-MnO₂ cathode of 2 x 2 tunnel structure, zinc anode and an aqueous electrolyte has been reported. This battery is regarded as one of the most promising candidates due to its intrinsic safety, low price and eco-friendliness of component materials.^[3,4] This battery system shows a high reversible discharge capacity around 210 Ah kg^-1 with a nominal potential around 1.5 V, but the cycling performance still needs improving. To tackle this issue, it is important to uncover the exact electrochemical mechanism occurring on the cathode. Although some researchers proposed Zn²⁺ ion intercalates into the tunnel of α-MnO₂, not enough evidence was provided to support their claims. In this work, we will report the intercalation mechanism of zinc ions into the tunnels of α-MnO₂. To keep tracks of the change in the crystal structure during the discharge-charge process, in situ X-ray diffraction patterns were employed and the oxidation state of manganese was analyzed from Mn K-edge X-ray absorption spectra. The high-resolution transmission electron microscopic images were also taken to trace the morphological and crystallographic variations during cycling. The discharge product on the cathode was identified by analyzing the selected area electron diffraction patterns from the discharged electrode. From these observations, we concluded that as Zn²⁺ ion intercalates into the tunnel, manganese in α-MnO₂ undergoes a destructive disproportionation reaction (2Mn³⁺(s) → Mn⁴⁺(s) + Mn²⁺(aq)), where Mn²⁺ ions are dissolved into the electrolyte, turning the original tunnel structure of α-MnO₂ to the layered. Furthermore, during charge process, it is observed that the dissolved manganese ions return to incorporate into layers to form the original tunnel structure. During repeated cycling, however, the structure of α-MnO₂ partially collapses, gradually generating an amorphous phase of no internal tunnel, which results in gradational capacity fading. The large volume changes involved in the phase transitions is probably the main cause of this structural degradation. We believe that relieving this structural collapse is one of key factors for the improvement of the electrochemical performance and will present several solutions to overcome these challenges.
References
[1] D. Aurbach et al., Energy Environ. Sci., 6 (2013) 2265.
[2] L. A. Archer et al., Chem. Commun., 47 (2011) 12610.
[3] J. Lee et al., Electrochimica Acta 112 (2013) 143.
[4] B. Lee et al., Sci. Rep. 4, 6066: DOI:10.1038/srep06066 (2014).

Manganese oxides attract constant attention due to their excellent electrochemical performance combined with low cost and low toxicity. Manganese oxides with tunnel crystal structures form a special family of materials represented by the general formula A_xMnO₂, where “A” stands for a stabilizing cation (K, Na, Mg) residing inside the structural tunnels. These tunnels, formed by MnO₆ octahedra sharing edges and corners, provide excellent pathways for intercalation/deintercalation of charge-carrying ions. By matching the tunnel size of the host manganese oxide material with the radius of specific charge-carrying ions, it is possible to create intercalation-based electrodes for metal-ion energy storage systems beyond lithium, such as Na-ion and Mg-ion batteries. Electrochemical properties of manganese oxides can be improved by acid leaching of these materials. Acid leaching has been shown to partially remove the stabilizing cations, thus providing better access to the open tunnels for ions intercalation and more facile diffusion pathways. Additionally, acid leaching increases the average oxidation state of manganese, improves electrical and ionic conductivities, and results in the increased surface area of the materials. Although all these properties are important for battery electrodes, the systematic characterization of acid-leached tunnel manganese oxides has not been performed. In this work, we synthesized potassium-stabilized α-MnO₂ nanowires and demonstrated that acid leaching in nitric acid resulted in the increased specific capacities delivered by this material in both Li- and Na-ion batteries.
Potassium-stabilized α-MnO₂ (K_0.11MnO₂) nanowires were grown by a hydrothermal process, producing very high aspect ratio crystals with diameters of 20-200 nm and lengths of up to several microns. Acid leaching was performed in concentrated nitric acid for 24 hours at room temperature. Galvanostatic cycling of the Li-ion cells with both pristine and acid-leached α-MnO₂ nanowires showed that the acid-leached material exhibited much better electrochemical performance when compared to the pristine nanowires, with initial specific discharge capacities increasing from 96 mAh/g for pristine nanowires to 158 mAh/g for acid-leached nanowires. Galvanostatic cycling of the Na-ion cells with both pristine and acid-leached α-MnO₂ nanowires revealed that the specific discharge capacity increased from 106 mAh/g for pristine nanowires to 191 mAh/g for acid-leached nanowires. In summary, acid leaching is shown as an efficient post synthesis treatment leading to the increased electrochemical capacity of manganese oxide nanowires with tunnel crystal structures in intercalation based Li-ion and Na-ion batteries. Present work is focused on the characterization of acid-leached nanowires with tunnel crystal structures stabilized by sodium and magnesium ions (Na₄Mn₉O₁₈ and todorokite, respectively) and their performance in Na-ion and Mg-ion batteries.

Electrowinning of non-ferrous metals such as zinc, copper, nickel, and cobalt is an energy-intensive process and the reduction of electric energy consumption by improvement in the material, process, and operation is one of the key issues for next generation, where the cell voltage reduction is the promising approach to reduce the energy consumption. In electrowinning where oxygen evolution occurs as in case of zinc or copper electrowinning, the cell voltage strongly depends on the material and structure of the anode. Lead alloys are well known as the anode material in such cases, although the anode potential is much higher than that theoretically expected one due to its large overpotential for oxygen evolution. Therefore, an alternative anode with a high catalytic activity has been expected and the candidate is a coated titanium anode which is prepared by thermal decomposition of a precursor solution painted on a titanium substrate. In this paper, we report a novel anode technology for electrochemical energy conversion in electrowinning, which makes it possible to save the electric energy for metal production. The anode consisted of a mixture of amorphous ruthenium oxide (RuO₂) and tantalum oxide (Ta₂O₅) formed on a titanium substrate. The amorphous oxide coating was obtained by a low temperature thermal decomposition at 300 ^oC or less, compared to a traditional process being performed at 450 ^oC or more. SEM observation revealed that the oxide coating comprised nano particles of RuO₂ uniformly dispersed in amorphous Ta₂O₅ matrix. This unique structure of anode demonstrated that the cell voltage of copper or zinc electrowinning was reduced by 700 mV compared to lead alloy anode, which corresponds to 23 % voltage reduction for zinc electrowinning and 36 % for copper electrowinning. It was also found that some unwanted side reactions on anodes such as deposition of manganese oxide or lead oxide observed on lead alloy anodes were inhibited with the novel anode. Therefore, the anode with amorphous RuO₂-Ta₂O₅ catalytic coatings is expected to realize an environmentally friendly process for next generation of metal production.

Recently, Na ion batteries have garnered increasing research attention because of abundant Sodium (Na) resources, lower materials cost and identical ion transfer chemistries with Li ion batteries. However, most of the electrode materials used in Li ion batteries cannot be applied as electrode material for NIBs because Na ion is 55% larger than Li ion. Therefore, a great deal of research effort has been focused to develop novel electrode materials for NIBs.
In this project, we have studied two dimensional (2D) molybdenum sulfide (MoS₂) and molybdenum oxide (MoO₃) as a high capacity anode material for Na ion batteries. We demonstrate that hydrothermally synthesized 2D nanosheets of MoS₂ and MoO₃ offer superior performance than bulk MoS₂ and MoO₃ because of faster ion diffusion in layered structure. Moreover, the layered nature of electrode material facilitates ion intercalation/deintercalation during charge/discharge process. However, despite of initial high specific capacity, capacity faded quickly and cyclic performance of electrodes were not up to the mark.
To improve the stability of the batteries, we studied the performance degradation mechanism by ex-situ XRD, SEM and TEM, and used atomic layer deposition (ALD) to passivate the anode surface. We demonstrate that presence of an interfacial ultra-thin layer of protective coating at anode/electrolyte interface can significantly improves the stability during cycling. For instance, after 50 cycles, coated MoS₂ nanosheets electrodes retained 91% of its initial capacity while, on the other hand, bare MoS₂ anodes retained only 63%. The underlying mechanism of this capacity retention because of protective layer coating is studied and explained using various analytical methods

In the last few years, research to determine the most suitable anode and cathode materials for Na-ion batteries has gained an increased attention. It was a great surprise to discover that pure commercially available elements such as Sb, Sn, or P [1-3] can react electrochemically with Na, leading to sustainable reversible capacities as high as 500 mAh/g over more than 100 cycles when carboxymethyl cellulose (CMC) binder is used. These results were unexpected, especially if we compare them to the Li-ion systems. The most commonly used Li-ion binder, polyvinylidene difluoride (PVDF), was reported to not work in the sodium system but no further investigation was done to understand the chemical reasons. Recently, Dahbi et al. [4] reported on Na-CMC binder for hard carbon electrodes in Na-ion batteries. They demonstrated better electrochemical results with CMC binder than with PVDF. They also reported that fluoroethylene carbonate (FEC) was essential as an electrolyte additive to improve the cyclability of the PVDF-based electrode.
We were intrigued by the poor cycling performance shown by PVDF in Na-ion batteries, as well as by the role of the FEC additive. Sn-based materials were chosen as a model conversion system, to understand the relationship between the surface and bulk properties. Post-mortem scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) studies of the electrodes were performed to get an insight into the surface properties. In addition, electrochemical mass spectrometry (OEMS) analysis was used to detect the gas evolved in situ from the interface of the electrode, during the SEI formation in the 1^st cycle.
At the bulk level, as the structure details as a function of the composition are not easily accessible during the electrochemical cycles, the first-principles crystal structure prediction reveals an important theoretical tool to map the phase space of the binary system Na-Sn. [5] The total energy calculations of the identified stable structures enables the knowledge of the cell voltage-composition curve. By matching the theoretically suggested structures with the in situ X-ray diffraction (XRD) patterns we gain an insight into the phases formed upon sodiation and desodiation processes and hence, by complementing with molecular dynamics calculations, into the mechanism of reaction and the dynamics of Na atoms.
References:
[1] Kim, Y. et al., Adv. Mat.2013, 25, 3045.
[2] Baggetto, L. et al., Electrochem. Comm.2013, 27, 168.
[3] Baggetto, L. et al., Journal of Power Sources2013, 234, 48.
[4] Dahbi, M. et al., Electrochem. Comm.2014, 44, 66.
[5] Caputo, R. et al, RSC Advances 2013, 3, 10230
Support:
Swiss National Science Foundation is thanked for financial support (project no 200021_156597). This work is performed within the Swiss Competence Center of Energy Research Heat and Storage (SCCER) framework.

Germanium is a promising sodium ion battery (NIB, SIB) anode material that is held back by its extremely sluggish kinetics and poor cyclability. We are the first to demonstrate that activation by a single lithiation - delithiation cycle leads to a dramatic improvement in practically achievable capacity, in rate capability, and in cycling stability of Ge nanowires (GeNWs) and a Ge thin film (GeTF). TEM and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis shows that without activation, the initially single crystal GeNWs are effectively Na inactive, while the 100 nm amorphous GeTF sodiates only partially. Activation with Li induces amorphization (in GeNWs) reducing the barrier for nucleation of the Na_xGe phase(s). Introducing a dense distribution of nanopores via activation with Li at slower cycling rate, e.g. 0.1C, reduces the Na solid-state diffusion length by lowering the effective Ge thickness, and leads to improvement in cycling performance by buffering the sodiation stresses. The resultant kinetics are promising: Tested at 0.15C (1C = 369 mA/g, i.e. Na:Ge 1:1) for 50 cycles the GeNWs and GeTF maintain a reversible (desodiation) capacity of 346 mAh/g and 418 mAh/g, respectively. They also demonstrate a capacity of 355 and 360 mAh/g at 1C and 284 and 310 mAh/g at 4C. Even at a very high rate of 10C the GeTF delivers 169 mAh/g.

Hard carbon has been an integral part of the recent development of Na-Ion Batteries (NIBs) as its disordered structure of randomly aligned graphene domains and scattered nanovoids have imbued it with ideal Na⁺ ion storage properties. The specifics behind the storage mechanism were proposed by Dahn et al. in the early 2000&’s in a model that has since become known as the “falling cards model”. While this model has been an axiom of hard carbon research since its inception, recent experimental results by our group—as well as others—have shown some discrepancies with the model, which warrant further investigation. Herein, we conduct an in-depth study of the structural properties of amorphous carbons in relation to electrochemical properties in attempt to reconcile our experimental findings with the main tenets of the “falling cards model”. This task was done utilizing a combination of advanced characterization techniques, computational MD and DFT simulations along with traditional electrochemical measurements. The results of our investigations suggest that some parts of the “falling cards model” can be rationalized through alternate processes. Such findings represent a shift in the conventional knowledge attributed to hard carbon anodes used in NIBs, and thus should be shared—and evaluated—by the rest of the electrochemical energy storage community.

Energy storage is becoming of major importance in order to balance the intermittency of renewable energy sources which are needed to satisfy the increasing energy demand of current societies. Lithium ion batteries (LIB) have been studied for more than 30 years and are still the subject of numerous research works. Lower cost alternatives, such as sodium ion batteries (NIB) are an attractive solution for large scale stationary applications such as grid storage.^[1] To meet the low cost requirement our research effort is focused on organic based, “scalable” anode materials.
In the following presentation we will present and discuss our results related to the electrochemical activity of Schiff bases in NIB, until now unexplored for LIB. First we will show that the redox entity comprising two Schiff base groups attached to a phenyl ring (-N=CH-Ar-HC=N#8210;, Ar: aromatic) is active for sodium ion storage Electroactive polymeric Schiff bases are produced by reaction between non conjugated aliphatic or conjugated aromatic diamine block with terephthalaldehyde unit. Crystalline poly-Schiff bases are able to electrochemically store more than one sodium atom per azomethine group at potentials between 0 and 1.5 Volts vs. Na⁺/Na which make them suitable negative electrode materials. The redox potential is tuned through conjugation of the polymeric chain and by electron injection from donor substituents in the aromatic rings. Reversible capacities of up to 350mAh/g are achieved when the carbon mixture is optimized with Ketjen Black®. Interestingly, the “reverse” configuration (-CH=N-Ar-N=HC#8210;) is not electrochemically active, though isoelectronic. ^[2] Monomeric Schiff bases likewise show activity which is highly dependent on the number of aromatic rings and order of functionalities.^[3]
References:
[1] V. Palomares, P. Serras, I. Villaluenga, K. Hueso, J. Carretero-González, T. Rojo, Energy Envirom. Sci.5, 5884 (2012). V. Palomares, M. Casas-Cabanas, E. Castillo-Martínez, M.H. Han, T. Rojo, Energy Envirom. Sci.6, 2312 (2013).
[2] E. Castillo-Martínez, J. Carretero-González, M. Armand, “Poly-Schiff bases as low voltage redox centres for sodium ion batteries” Angewandte Chemie Int. Ed.,126, 5445-5449 (2014).
[3] M. Lopez-Herraiz et al. (in preparation)

Understanding how electrolyte formulation impacts the energetics and kinetics of ion-coupled electron transfer reactions and SEI formation mechanisms at electrode/electrolyte interfaces for rechargeable batteries will be crucial in taking the next step from small-scale (portable electronics) to medium- and large-scale (electric vehicles and grid storage) electrical energy storage devices. Here we present Raman spectroscopy and DFT calculations for a variety of Li⁺ and Na⁺ salts in common organic carbonate solvents at various concentrations that show a highly broadened background with overlapping vibrational structure. The broadened background is often attributed to fluorescence arising from degraded electrolyte products (SEI). Yet we propose an alternative mechanism, that the broaden background results from anharmonic coupling of high and low energy vibrational modes occurs within a solvated ion network. Our results suggest that concentration, anion identity and degree of cation solvation all influence the degree of interaction. These results are intriguing beyond a fundamental level as extended solute-solvent structure may play a key role in both the kinetics of lithiation or sodiation as well as SEI formation mechanisms and resulting composition.

Na-ion batteries have attracted recent interest and start now to be counted as viable alternatives vs. Li ion technologies for specific applications. Indeed, recent works on phosphate-based Na-containing positive electrodes such as Na₃V₂(PO₄)₃ [1] and Na₃V₂(PO₄)₂F₃ [2] have demonstrated excellent performances and can be considered as a new step on the way of sodium-ion technology development. However, like for the Li-ion technology, safety issues related to the use of flammable liquid electrolytes remain, especially due to the high reactivity of sodium with moisture and oxygen. All-solid state batteries, which use non-flammable solid electrolytes instead of organic liquid ones, have been proposed as strong candidates for alternative energy storage devices.
The Na₃ClO - based glass electrolyte exhibits a glass transition at T < 100 0C and in one of its variants presents ultrafast ionic conductivities of 50 mScm^-1 at 23 °C and electrochemical window of stability of ~4 V at room temperature which covers all the cathode/anode Na-ion known pairs.
Following a recent successful approach developed for Li-ion all-solid state batteries [3], we were able to assemble an all-solid state Na-ion battery using doped NaRAP (sodium rich anti-perovskite) - based as the solid electrolyte. Thanks to a new experimental set-up, we report for the first time on the electrochemical characteristics of NaRAP and doped NaRAP-based glassy electrolytes at temperatures from 23 0C up to 200°C [4] and of Na-ion 2.5 x 2.5 cm² cells.
[1] J. Liu, K. Tang, K. Song, P.A. van Aken, Y. Yu, J. Maier, Nanoscale, 2014, 6(10), 5081-6.
[2] T. Jiang, G. Chen, A. Li, C. Wang, Y. Wei, J. Alloys and Compounds, 478 (2009) 604-7.
[3] M.H. Braga, J.A. Ferreira, V. Stockhausen, J.E. Oliveira, A. El-Azab, Novel Li₃ClO based glasses with superionic properties for lithium batteries, J. Mater. Chem. A 2014, 2, 5470-80.
[4] M.H. Braga, J.A. Ferreira, A. Murchison, Superionic Glassy Electrolyte for Na-ion batteries, submitted.

Sodium ion batteries (SIBs) have received increasing attention as a viable alternative to lithium ion batteries (LIBs), especially for the large-scale energy storage systems. Nevertheless, electrochemical performance of most SIB materials is still insufficient for various practical applications. By this perception, we investigate both amorphous hydrate FePO₄#8729;xH₂O@C and anhydrate FePO₄@C as cathode materials for SIB. Galvanostatic measurement shows that higher discharge capacity of FePO₄#8729;xH₂O@C, 125.1 mA h g^-1, was achieved in contrast to FePO₄@C, 50.5 mAh g^-1, although hydrate FePO₄#8729;xH₂O@C has a theoretical capacity penalty as compared to FePO₄@C due to weight of crystal water and unprecedented rate performance of hydrate FePO₄#8729;xH₂O@C was observed. These phenomena imply that water molecules in the compound may act as a media to promote ionic conductivity enabling facile Na ion diffusion and amorphous composite has the advantage of unnecessary of structural transition during charging/discharging as compared to the intercalation compounds, so that facile accommodation of sodium ion possible. To the best our knowledge, this is the first time to report high performance of amorphous hydrated FePO₄#8729;xH₂O@C for SIBs with only simple carbon coating process. Our results demonstrate that structurally stable of amorphous FePO₄#8729;xH₂O@C is promising cathode candidate for next generation SIBs.

Batteries and electrochemical capacitors (ECs) represent the most widely used types of electrochemical energy storage devices. ECs are frequently overlooked as an energy storage technology despite the fact that these devices can deliver greater power, have much faster response times, and longer cycle life than batteries. Commercial technology uses carbon-based electrochemical capacitors in which energy storage by double layer processes leads to high power density, but low energy density. The interest in using pseudocapacitor-based materials for electrochemical capacitors is that the energy density associated with faradaic reactions is much greater, by at least an order of magnitude, than the electrical double layer capacitance of carbon electrodes.
Our recent work has focused on establishing the key criteria for pseudocapacitor materials. Fast faradaic reactions are required for a pseudocapacitive response and for this reason oxide pseudocapacitors have largely been those materials which exhibit surface or near surface redox reactions. However, our recent results with Nb₂O₅ show that this material undergoes fast faradaic reactions through an intercalation pseudocapacitance mechanism in which lithium ion insertion occurs in the bulk of the material. The principal benefit realized from this mechanism is that high levels of charge storage are achieved within short periods of time because there are no limitations from solid-state diffusion. Nb₂O₅ electrodes exhibit an energy density in excess of 100 mAh/g at a charging rate of 60C and hybrid electrochemical cells incorporating Nb₂O₅ display energy and power densities that surpass commercial carbon-based devices. We have identified some of the characteristics associated with intercalation pseudocapacitance and expect that other oxide systems are capable of achieving comparable levels of high rate energy storage.

Battery-based electrochemical storage is particularly attractive because of its high energy efficiency and ease of deployment, and lithium-ion batteries (LIBs) are one of the most well developed of these options. Sodium-ion batteries (SIBs), which replace lithium with abundant and inexpensive sodium, have received a great deal of attention recently. Similarities in manufacturing techniques between SIBs and LIBs may significantly accelerate their technological advance. Nevertheless, several scientific challenges still need to be resolved before the performance of SIBs becomes competitive with that of LIBs. In particular, the higher negative redox potential of Na compared to that of Li results in lower cell voltages and consequently lower energy densities. Moreover, the larger size of Na⁺ relative to Li⁺ causes slower solid-state diffusion in the active materials and leads to lower energy efficiencies when the batteries are rapidly charged or discharged. High capacity electrode materials with fast solid-state kinetics are therefore required in order to compensate for these intrinsic limitations.
In this presentation, I will introduce low-vacancy, sodium manganese hexacyanomanganate (MnHCMn) as a viable cathode material for SIBs. The as-synthesized MnHCMn shows a monoclinic crystal structure composed of nonlinear Mn-Nequiv;C-Mn bonds and containing eight large interstitial sites occupied by Na⁺ ions. Our experiments demonstrate a high specific capacity of 210 mAh g^-1 and excellent capacity retention at high rates in a propylene carbonate electrolyte. We discovered a novel mechanism wherein small lattice distortions allow for the unprecedented storage of 50% more sodium cations than in the undistorted case. These results represent a step forward in the development of sodium-ion batteries.

Na-ion batteries are considered as a very promising technology for large-scale energy storage because potentially they are safer, less expensive, and would have a lower environmental impact than the equivalent lithium-ion battery. With stable open-channel crystal structures and high theoretical capacity (~ 170 mAh/g), alluaudite compounds with the formula Na_xM₃(PO₄)₃, in which M stands for transition metals, have been investigated as intercalation materials for rechargeable batteries. In this study, a series of alluaudite compounds (e.g. Na_xFe₃(PO₄)₃, Na_xMn_0.5Fe_2.5(PO₄)₃, etc.) with the morphology of nanoplates were successfully synthesized using simple hydrothermal methods that easily scalable. By finely tuning the size of channels present in the crystal lattice with doping of different transition metals, and tuning the morphologies of the alluaudite products with different additives, high capacity with good cycling performance have been achieved. Phase transitions during charging and discharging are also studied in detail. And new compounds in the alluaudite class were obtained upon desodiation of the pristine materials. In-situ temperature-dependent X-ray diffraction analysis shows that both the pristine and partially desodiated states have excellent thermal stability. With high theoretical capacity, good thermal stability, low cost and environmentally benign composition, alluaudite compounds could be a very promising cathode material for Na-ion rechargeable batteries.

As a result of the high theoretical specific energy, the rechargeable aprotic Li-O₂ battery is under intense investigation worldwide.^1-5 One spin-off of the recent interest in rechargeable Li-O₂ batteries based on aprotic electrolytes is that it has highlighted the importance of understanding the fundamental mechanisms of O₂ reduction in such a medium.^6-15
Early mechanistic studies focused on two contrasting models of O₂ reduction in non-aqueous electrolytes. The first considered the process to be confined to the electrode surface while the second considered the process to occur principally in solution. We have combined a range of electrochemical, spectroscopic and microscopy methods to investigate the mechanism of electrochemical O₂ reduction in aprotic electrolytes and the growth mechanism of the discharge product, Li₂O₂. The results of these studies will be presented, as will the role of the electrolyte and electrode materials in controlling the Li₂O₂ formation mechanism.
(1) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nature materials2012, 11, 19.
(2) Lu, Y. C.; Gallant, B. M.; Kwabi, D. G.; Harding, J. R.; Mitchell, R. R.; Whittingham, M. S.; Shao-Horn, Y. Energy & Environmental Science2013, 6, 750.
(3) Black, R.; Adams, B.; Nazar, L. F. Advanced Energy Materials2012, 2, 801.
(4) Girishkumar, G.; McCloskey, B.; Luntz, A. C.; Swanson, S.; Wilcke, W. The Journal of Physical Chemistry Letters2010, 1, 2193.
(5) Li, F.; Zhang, T.; Zhou, H. Energy & Environmental Science2013, 6, 1125.
(6) Adams, B. D.; Radtke, C.; Black, R.; Trudeau, M. L.; Zaghib, K.; Nazar, L. F. Energy & Environmental Science2013, 6, 1772.
(7) Horstmann, B.; Gallant, B.; Mitchell, R.; Bessler, W. G.; Shao-Horn, Y.; Bazant, M. Z. J. Phys. Chem. Lett.2013, 4, 4217.
(8) Hummelshoj, J. S.; Luntz, A. C.; Norskov, J. K. J. Chem. Phys.2013, 138, 034703.
(9) McCloskey, B. D.; Scheffler, R.; Speidel, A.; Girishkumar, G.; Luntz, A. C. J. Phys. Chem. C2012, 116, 23897.
(10) Mitchell, R. R.; Gallant, B. M.; Shao-Horn, Y.; Thompson, C. V. J. Phys. Chem. Lett.2013, 4, 1060.
(11) Trahan, M. J.; Mukerjee, S.; Plichta, E. J.; Hendrickson, M. A.; Abraham, K. M. Journal of The Electrochemical Society2013, 160, A259.
(12) Sharon, D.; Etacheri, V.; Garsuch, A.; Afri, M.; Frimer, A. A.; Aurbach, D. The Journal of Physical Chemistry Letters2012, 4, 127.
(13) Jung, H. G.; Kim, H. S.; Park, J. B.; Oh, I. H.; Hassoun, J.; Yoon, C. S.; Scrosati, B.; Sun, Y. K. Nano Letters2012, 12, 4333.
(14) Peng, Z.; Freunberger, S. A.; Hardwick, L. J.; Chen, Y.; Giordani, V.; Barde, F.; Novak, P.; Graham, D.; Tarascon, J. M.; Bruce, P. G. Angewandte Chemie International Edition2011, 50, 6351.
(15) Zhai, D.; Wang, H. H.; Yang, J.; Lau, K. C.; Li, K.; Amine, K.; Curtiss, L. A. Journal of the American Chemical Society2013, 135, 15364.

Ever-increasing demand for high energy density rechargeable batteries in the automotive sector has stimulated substantial interest in developing aprotic rechargeable Li/O₂ cells due to the very high theoretical specific energy of this chemistry. The successful development of this technology is heavily dependent on the long-term stability of electrolyte compositions. Finding aprotic electrolytes that are stable toward both the O₂ electrode and the Li anode remains an elusive challenge.
Our group proposes and demonstrates a bold approach to enable the Li/O₂ cell chemistry through the use of molten salts, thereby eliminating the unstable organic electrolyte common to prior research. High capacity Li/O2 cells employing molten salt electrolytes comprising alkali metal cations and nitrate anions operate at an intermediate temperature ranging from 80 °C to 250 °C. Molten alkali metal nitrate electrolytes employed in O2 electrodes within this temperature range provide Li/O2 cells having significantly improved efficiency and rechargeability compared to prior art systems.

Li-O₂ battery is one of the most promising of alternatives among batteries with high theoretical energy densities beyond those possible with Li-ion batteries. However, Li₂O₂, the battery's primary discharge product is an electronic insulator and electrode passivation is a serious limitation. This not only limits the experimentally obtained discharge capacity to a small fraction of the theoretically predicted capacity, but also increases charge overpotentials which decreases the overall battery efficiency. Redox mediators have been proposed to mediate charge transfer for the oxidation of Li₂O₂ during the recharge step thereby favoring recharge at potentials much lower than is possible without their use. In this study, we report on the role of redox mediators such as LiI and LiNO₃ on improving the rechargeability of Li-O₂ batteries. Based on a combination of in-situ electrochemical mass spectroscopy and standard electrochemical measurements, we suggest that redox mediators could be key to demonstrating a highly rechargeable Li-O₂ battery. We compare the charge potentials of the Li-O₂ battery to the redox potentials of these mediators. We discuss our experimental results on the effectiveness of these redox mediators in several different aprotic solvents and suggest design rules for the selection of electrolyte-redox mediator combinations for Li-O₂ batteries. We also correlate our findings to the fundamental molecular electronic levels of the solvent.

Li-ion batteries suffer from low capacities while Li-O₂ batteries have high overpotentials and hence low energy efficiency. Taking as inspiration Li₅FeO₄, which when used as an electrocatalyst in Li-O₂ cells reduces overpotentials and demonstrates a high capacity unrelated to Li₂O₂ formation [1], we introduced the general concept of using lithium-metal-oxides with high Li₂O content as combination electrodes/electrocatalysts in hybrid Li-ion/Li-oxygen cells [2]. Using first principles density functional theory (DFT) calculations, we performed a high-throughput search for similar hybrid materials with high capacities and suitable properties [3].
While these materials exhibit promising capacities of up to 1000 mAh/g, their reaction mechanisms remain unknown. We performed DFT investigations of the reaction mechanisms in several of these materials, including Li₅FeO₄, Li₆MnO₄, and Li₆CoO₄. DFT calculations are performed to investigate the thermodynamics of Li and Li-O removal from these materials, in order to establish the details of the charge reaction. Atomistic and electronic structural changes in the materials are tracked during the reactions. Results on the energetics indicate a cross-over between pure lithium removal and concomitant oxygen loss, which is electronically shown to be correlated with development of the peroxide-like character of oxygen.
ACKNOWLEDGMENT
This research was supported as part of the Center for Electrical Energy Storage/Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Award Number DE-AC02-750 06CH11357). Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
REFERENCES
[1] L. Trahey, C. S. Johnson, J. T. Vaughey, S.-H. Kang, L. J. Hardwick, S. A. Freunberger, P. G. Bruce, M. M. Thackeray, Electrochemical and Solid-State Letters, 14, A64 (2011).
[2] M. M. Thackeray, M. K. Y. Chan, L. Trahey, S. Kirklin, and C. Wolverton, Journal of Physical Chemistry Letters, 4, 3607 (2013).
[3] S. Kirklin, M. K. Y. Chan, L. Trahey, M. M. Thackeray, and C. Wolverton, Physical Chemistry Chemical Physics, 16, 22073 (2014).

Rechargeable Li-air batteries (LAB) are promising high energy density alternatives for Li-ion batteries to meet the growing demand of the world for energy. Even though organic Li-air batteries theoretically offer higher energy density, high over-potentials during charge and discharge limit the efficiency leading to poor cyclic performance. In contrast to the insoluble discharge product in organic LABs the discharge products in aqueous LABs are highly soluble in the catholyte, which improves cycle efficiency, power performance and volumetric energy density. The safety concern here is the reaction between lithium anode and the catholyte. Hence, a direct contact has to be prevented by a fast lithium-ion conducting membrane.
Here we design hybrid inorganic-organic membranes and test their performance in a rechargeable aqueous Li-air battery. The membrane consists of NASICON-type Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) as the fast ion conducting ceramic in a matrix of a polymer electrolyte of polyshy;vinylidene fluoride (PVDF) : polyethylene oxide (PEO): LiBF₄. LAGP was prepared by melt quenching and subsequent thermal annealing. A room temperature total conductivity 5 × 10^-4 S cm^-1 was found for the composite membrane. Electrochemical stability of the membrane vs. Li/Li⁺ was evaluated by cyclic voltammetry. Cathodic deposition and anodic dissolution of lithium anode are the only two distinct peaks up to 4 V, confirming the wide electrochemical window of the membrane. Immersion of the membrane in LiCl solution for one month shows no sign of significant swelling or change in conductivity. This anode-protecting membrane is sandwiched between the lithium anode and the acidified aqueous LiCl (10 M; pHasymp;2.5) catholyte. The oxygen reduction and formation is catalyzed by finely dispersed Pt on multi-walled carbon nanotube arrays on a carbon fiber cloth.
Room temperature performance of the LAB when operated under open air conditions is tested by cycling between 1 V and 4.2 V at constant current density of 0.5 mAcm^-2. The cell retains its charge and discharge capacity for the first 10 cycles and shows low polarization between charge and discharge. The overpotential of the cell gradually increases with prolonged cycling resulting in the failure of the cell, due to the degradation of the polymer component of the composite membrane. To address this problem, we adjusted the initial acidity of the 10M LiCl solution to pH 4.7. With this catholyte the LAB retains its capacity for more than 50 cycles with an overpotential < 0.1 V.

Lithium-ion batteries presently dominate the energy-storage landscape, but do so with the ever-present threat of thermal runaway and conflagration courtesy of flammable electrolytes and oxygen-releasing electrode materials. Fortunately, Zn-based batteries offer a compelling alternative grounded in the innate safety and cost advantages accompanying the use of aqueous electrolytes augmented by the high (domestic and worldwide) abundance of Zn and the high energy density of Zn-based batteries (comparable to or greater than Li-ion). The present performance, however, of traditional Zn-based batteries is hindered by suboptimal Zn utilization (typically <60% of theoretical capacity) and poor rechargeability—primarily attributed to the complex dissolution/precipitation processes that accompany Zn/Zn²⁺ cycling within the typical ad hoc structure of powdered-bed Zn electrodes. We address these limitations by redesigning the zinc anode as a highly conductive, porous, and 3D-wired “sponge” architecture; we achieve ease of manufacturability by fabricating the sponges using zinc-powder emulsions and select temperature/atmosphere treatment of the consolidated and shaped object. Our Zn sponge electrodes achieve >90% Zn utilization when discharged in primary Zn-air cells, retaining both the 3D framework of the Zn sponge and an impedance characteristic of the metal. Scanning electron microscopy demonstrates uniform deposition of charge/discharge products at the external and internal surfaces of a battery-cycled Zn sponge, even to deep depth-of-discharge. We further show that the structural characteristics of the Zn sponge promote greater rechargeability when cycled in prototype Ag-Zn and Ni-Zn cells. Our results show that all Zn-based chemistries can now be reformulated for next-generation, Li-free rechargeable batteries.
The information, data, or work presented herein was funded in part by the Office of Naval Research and by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR-0000391; the work has been Approved for Public Release, Distribution Unlimited.

The low cost, significant reducing potential, and relative safety of the zinc electrode is a common hope for a reductant in secondary batteries as a non-flammable alternative to the current popularity of lithium ion batteries, however, it is limited mainly to primary implementation due to shape change. In this work we exploit such shape change for the benefit of static electrodes through the in situ electrodeposition of hyper-dendritic nanoporous zinc foam at states beyond equilibrium.
The zinc foam proposed in this work is formed by a three-dimensional network of dendrites that is electrochemically active and electronically conductive, at the nanoscale. We find that the nanoporous zinc structure presents a modified activation energy for electrochemical cycling attributed by highly oriented crystals, high surface area and rapid kinetics. Conductive paths throughout the internal structure resulted in a more uniform current distribution: reducing non-uniform concentration gradients and anode polarization losses. The hyper-dendritic zinc electrode showed significant capacity retention over 100 cycles in flooded cells, and due to the electrochemical synthesis procedure can be reformed in situ if need be.
Most fascinating is that by operating mesoscale isotropic three-dimensional network of dendrites far from equilibrium densified the structure at standard battery operating conditions and suppressed initiation of dendrites. This is in contrast to most literature work with zinc which starts flat or packed which seeks to emulate the “equilibrium condition”. If hyper-dendritic structures can be recreated-locally in operando, a battery with a zinc anode capable of indefinite cycle life may be possible. Perhaps, if dendritic behavior can be maximized and controlled locally, it may deter system limiting short circuits globally, as the system will move towards more dense structures as opposed to more branched structures.

Here we show that the langasite structure is able to accommodate over 5% of extra oxygen by means of hypervalent doping via a facile Pechini method. The compositions studied were examined by EDX analysis in the TEM demonstrating the successfully incorporation of a hypervalent dopan with the consequent incorporation of extra oxygen, O_int. Dense pellets were prepared by fast Spark Plasma Sntering (SPS) of nano-sized powders at a high pressure of 600MPa and a low temperature of ~850°C, matching the synthetic temperature. Thus inhibiting GeO₂ volatilization or decomposition of the langasite phase. Doped pellets show an increase in the conductivity of two orders of magnitude (~ 4 10^-3 S cm^-1 at 700°C) when compared to the un-doped langasite ( ~ 1 10^-5 S cm^-1). In addition, the position of the extra O incorporated into the structure and the induced local deformation is been studied ¹⁷O Solid-State NMR and Neutron Powder Diffraction (NPD) techniques.

Energy storage has an important role in integrating variable renewable electricity generation technologies into the electric grid at large scale. The overall sustainability impact of any storage device, including an electrochemical energy storage device, depends on the energy cost of manufacturing it, as well as the service it provides during operation. These energy costs and benefits are systematically evaluated using net energy analysis, a life cycle approach to evaluating energy technologies. In this work, we apply net energy analysis to evaluate a solid oxide-based regenerative hydrogen fuel cell (RHFC) as a grid-scale energy storage system. We compare to our previous analysis of a different RHFC configuration, based on an alkaline water electrolyzer and a PEM fuel cell (AWE-PEMFC), and to various battery technologies. The key indicator for this comparison is the electrical energy stored on invested (ESOIe) ratio: the ratio of energy stored in the device over its lifetime to the energy required to build the device. A device with a higher ESOIe ratio provides the same service while consuming less manufacturing energy, leaving more energy available for other productive uses and producing less manufacturing-related emissions.
In our reference case solid oxide-based RHFC, the solid oxide electrolyzer (SOEC) and solid oxide fuel cell (SOFC) both contain Ni-YSZ at the hydrogen electrode; LSM at the oxygen electrode; and YSZ as the electrolyte. When operating as an electricity-only storage device, this SOEC-SOFC RHFC has a much lower ESOIe ratio than an analogous AWE-PEMFC RHFC. This is due to (1) the low electrical energy efficiency of a hydrogen-fed SOFC (30%) and (2) the SOEC&’s high energy intensity and short lifetime relative to an alkaline electrolyzer. The high energy intensity of the SOEC is due mostly to the use of an energy-intensive chromium-based interconnect alloy. Less energy intense alternatives such as nickel and steel could be used in a lower temperature environment. Lowering the operating temperature of the cell would therefore improve overall energy performance for the solid oxide based RHFC. If the SOFC is operated as a combined heat and power device (60% efficiency) instead of electricity only, the ESOIe ratio of the solid oxide-based RHFC is still modestly lower than the AWE-PEMFC RHFC.
The ESOIe ratio of the reference case solid oxide-based RHFC is similar to that of lithium ion batteries (ESOIe = 32; Energy Env. Sci., 2013, 6, 2804), though much lower than compressed air storage (ESOIe = 240). It is highly sensitive to the energy intensity and lifetime of the SOEC, as well as the efficiency of the SOFC. If the SOEC lifetime were doubled, or its energy intensity reduced by half, the solid oxide-based RHFC would achieve an ESOIe ratio similar to the AWE-PEMFC RHFC system.

Proton exchange membrane (PEM) fuel cells are being developed as alternative
energy sources for both residential and automotive application. In order for this technology to become fully
commercial, the reduction of cost and improvements in performance and durability of PEM fuel cells
membrane electrode assemblies (MEAs) are still required.
To address the requirement for further cost reduction the Pt loading of the cathode catalyst layer (CCL)
needs to be reduced to 0.2- 0.1 mg/cm² while maintaining high currents and efficiency. Consequently, it
becomes increasingly important to not only develop new catalyst materials, but also optimize the 3D
structural arrangement of the CCL components such as catalyst, ionomer and void space so that all critical
functionalities can be achieved simultaneously. In general terms this entails to provide sites catalytically
active for ORR, and to further provide transport to/from these sites for the reactants O₂, protons, electrons
and products H₂O and heat, respectively.
In order to be able to design CCL structures that meet the performance and durability requirements, it is
necessary to obtain a better understanding of structure versus performance relationships. This requires the
capability to fabricate different CCL structures, to characterize the spatial distribution of all components
within the catalyst layer (carbon, Pt, ionomer and void), to measure the physico-chemical properties (both
ex-situ and in-situ) and finally to use these experimental data as inputs for the development a model based
understanding of the relationship between CCL structure and CCL performance and durability.

We present a electrochemical direct injection (ECDI) reactor that uses nanostructured Zn particles for fast, efficient energy storage and conversion. Our design features an array of reactor cells, each of which require only a small amount of active material and electrolyte; such an architecture enables energy and power densities to be decoupled. In a single cycle, a small amount of Zn particles is co-injected with an alkaline electrolyte into each cell, and a redox potential is established as the particles contact the current collector. The cell is then discharged to completion, after which it is flushed and the cycle restarts.
The individual ECDI reactor cells can be parallelized and the co-injection, discharge, and evacuation of each cell can be actively controlled (as is the case with a standard internal combustion engine). In this manner, we are able to control the ratio of reactant to electrolyte on a per-cycle basis and achieve energy conversion efficiencies of >80% at 0.25C (~0.2 A/g). Furthermore, by optimizing mass loading and electrolyte chemistry, even at high discharge currents (3C or ~2.5 A/g) we are able to obtain conversion efficiencies of >70% with the nanostructured Zn (as compared to the >40% efficiencies that are typical for Zn particles). In addition to a demonstration of performance results, we also discuss important practical considerations for our cell design. While we demonstrate our ECDI reactor design using nanostructured Zn particles, future generations of this system can be extended and tailored to a variety of reductant/oxidant pairs

Recent work on the electrocatalytic reduction of CO₂ is presented. First, catalytic size effects on metallic nanoparticles in the 1 - 15 nm size range are discussed and their catalytic activity and selectivity are analyzed and compared to bulk electrodes. Thereafter, a novel family of nanostructured carbon-based catalyst for the electroreduction of CO2 to synthesis gas is discussed and compared to metal benchmark catalysts.

In the past decade, lithium ion batteries have played a dominant power source for items ranging from portable electronics to hybrid electric vehicles. However, they still do not offer enough energy density to meet the ever-increasing demands of many applications despite extensive research to explore ways to increase their charge-storage capability. As a new energy storage system to overcome this problem, Li-air batteries have attracted numerous attentions because they have the potential to provide several times higher capacity than commercial Li-ion cells [1, 2]. However, they are facing fundamental and practical challenges such as low rate capability, limited cycle life resulting from the instability of the electrode and electrolyte, and significant overpotential on charge due to slow kinetics of dissociation from reaction products (such as Li₂O₂). These critical issues are highly attributed to the air electrode, the reaction place between lithium ion and oxygen, and electrolyte directly contact with electrode. As one of the general components of the air electrode, carbon has played an important role in air electrode, because it provides reaction site and store place of the reaction products. However, unfortunately, it facilitates the unwanted side reaction such as formation of Li₂Co₃ and decomposition of electrolyte [3, 4], which deteriorate the cyclic performance of air cell. In this study, the suppression of unwanted reactions due to carbon during cycling is main issue. With aim to suppress that, the surface of carbon (graphene) was passivated by stable conducting material, PEDOT:PSS. We expected that the surface coated PEDOT:PSS layer can prevent from the direct contact between carbon and electrolyte (and/or Li₂O₂), which can suppress the unwanted side reaction and enhance the cyclic performance of the electrode. Moreover, the PEDOT:PSS could act as a conducting binder in the electrode, instead of general non-conducting polymer binder such as PVDF. In this work, the electrochemical performance of PEDOT:PSS coated carbon was characterized and compared with pristine carbon.
References
[1] Richard Padbury, Xiangwu Zhang, J.Power Source 196 (2011) 4436-4444
[2] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, Nature Materials 11(2011) 19-29
[3] P. G. Bruce, M. M. Ottakam Thotiyl, J. Am. Chem. Soc. 135(2013) 494-500
[4] Jun Lu, Yu Lei, Nature Communications DOI:10.1038/ncomms3383

The facet-dependent property has aroused great interest in the fields of catalyst, lithium ion battery and electrochemical sensor. The morphology with different well-defined crystal plans has a large impact on the performance of materials. Herein, Co₃O₄ cube and Co₃O₄ octahedron with well-defined crystal planes (001) and (111), respectively, are achieved by adjusting the amount of Co(NO₃)₂middot;6H₂O and NaOH reactants. The dependence of the electrochemical capacity and rate capability on the exposed facet of Co₃O₄ used as the cathode catalyst for Li-O₂ battery has been investigated for the first time. The Li-O₂ battery cathode catalyzed by Co₃O₄ octahedron with exposed (111) plane shows much higher specific capacity, cycling performance and rate capability than Co₃O₄ cube with exposed (001) plane. This can be largely attributed to the richer Co²⁺ on (111) plane of Co₃O₄ octahedron, which supplies more active sites for oxygen reduction (ORR) and oxygen evolution reaction (OER).

Ionic liquids are fascinating materials with properties unlike most organic solvents. They typically possess high ionic conductivities, wide electrochemical windows, and negligible vapor pressure.^1-4 These features make them ideally suited for various electrochemical applications; for example, as electrolytes in dye-sensitized solar cells, batteries, and supercapacitors.^4-6 Research in this field, however, has focused largely on a handful of cations and anions, with the imidazolium salts being the most well-known and thoroughly investigated. Here, we present a series of novel bicyclic 1,2,3-triazolium ionic liquids, which were synthesized via the copper-catalyzed azide alkyne click reaction in good yields, and demonstrate their utility for the electrochemical reduction of carbon dioxide. Our results show that this relatively new family of salts is indeed able to enhance electrocatalytic reduction of CO₂, and that in general, ionic liquids with a lower viscosity afford better performance. Although it is known that CO₂ has an unusually high solubility in ionic liquids,⁷ voltammetry studies performed on these triazolium ionic liquids indicate that the catalytic improvement is not merely a result of increased physical absorption of CO₂ in the reaction media. Rather, the ionic liquids appear to participate in the electron transfer processes taking place at the electrode surface. Furthermore, it is interesting to note that the triazolium-based ionic liquids exhibit markedly different voltammetric behavior from the imidazolium-based salts. This suggests that the reaction parameters may be further optimized through systematic modifications to the structure of the cations and anions of the ionic liquid employed. While the electrochemical reduction of carbon dioxide is thermodynamically very challenging, its successful and large-scale implementation is one way to simultaneously reduce CO₂ levels in the atmosphere and store solar energy in the form of hydrocarbon fuels.
References
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Zhang, S. J.; Sun, N.; He, X. Z.; Lu, X. M.; Zhang, X. P. J. Phys. Chem. Ref. Data2006, 35, 1475.
Wang, P.; Zakeeruddin, S. M.; Humphry-Baker, R.; Grätzel, M. Chem. Mater.2004, 16, 2694.
Zakeeruddin, S. M.; Graetzel, M. Adv. Funct. Mater.2009, 19, 2187.
Lau, G. P. S.; Tsao, H. N.; Zakeeruddin, S. M.; Grätzel, M.; Dyson, P. J. ACS Appl. Mater. Interfaces, 2014, 6, 13571.
MacFarlane, D. R.; Tachikawa, N.; Forsyth, M.; Pringle, J. M.; Howlett, P. C.; Elliott, G. D.; Davis, J. H.; Watanabe, M.; Simon, P.; Angell, C. A.; Energy Environ. Sci.2014, 7, 232.
Sun, L.; Ramesha, G. K.; Kamat, P. V.; Brennecke, J. F. Langmuir2014, 30, 6302.

The decreasing availability of easily accessible fossil fuels for the production of fuels and chemicals in combination with the accumulation of greenhouse gasses in the atmosphere have led to an increasing demand for renewable energy alternatives. One readily available source of renewable energy is sunlight. To ensure continuous availability of this energy, storage, for example in the form of high density transportation fuels is essential. Production of transportation fuels from captured CO₂ via electrochemical reduction is a process that allows for both storage of solar energy and leads to net neutral CO₂ emissions.
Although a number of different metals can be used for the electrochemical reduction of CO₂, Cu is the only one which is known to produce a high amount of hydrocarbons. [1] It was recently shown that a total of 16 different products can be formed during the electro reduction of CO₂ using Cu foil as the catalyst. [2] Among these products are a number of different C2 and C3 oxygenates, molecules that are potential renewable fuel candidates. Unfortunately, this reaction requires high overpotentials and suffers from low selectivities, to increase the efficiency, obtaining more mechanistic insight is therefore of great importance.
We have tested Cu particles supported on Carbon for the electrochemical reduction of CO and CO₂. The particles are synthesized in an ethylene glycol solution using the ‘so called&’ polyol method, leading to the formation of particles with a uniform and tunable particle size distribution. Carbon supported catalyst were prepared using particles of different sizes and applying different metal loadings. For electrochemical testing, the catalyst were supported on carbon paper gas diffusion electrodes. The effect of particle size and loading on the catalyst efficiency and selectivity towards different alcohols and hydrocarbons from CO₂ will be presented. To gain more insight in the reaction mechanism by suppression of the formation production, the most active catalyst were tested for the reduction of CO.
[1] Y. Hori, Handbook of Fuel Cells: Fundamentals, Technology and Applications, ed. A. L. W. Vielstich, H. A. Gasteiger, VHC-Wiley, Chickester, 2003, vol 2, pp. 720-733.
[2] K. P. Kuhl, E. R. Cave, D. N. Abram, T. F. Jaramillo, Energy Environ. Sci., 2012, 5, 7050.

CO/H₂ gas mixtures (“synthesis gas”) have long been used in industry to synthesize hydrocarbon fuels via the Fischer-Tropsch process; however, the development of this process for the production of other compounds has been slow. With the development of electrochemical pathways for the renewable production of CO and H₂ from CO₂ and water respectively, the Fischer-Tropsch process becomes increasingly interesting for the production of specialty chemicals. In particular, higher alcohols, those with two or more carbons, are of interest for their applications as both liquid fuels and synthetic feedstocks. This work seeks to develop selective catalysts for the renewable synthesis of higher alcohols via thermochemical CO hydrogenation.
In a collaboration with the Noslash;rskov group at Stanford University, micro-kinetic models were used to evaluate the optimal oxygen and carbon binding energies on transition metals which maximize alcohol selectivity. Density functional theory (DFT) calculations predicted that a Co₃Pt surface would lie high upon the selectivity volcano. To probe the relationships between composition and selectivity further, cobalt-platinum nanoparticles were prepared of varying atomic ratios via a liquid phase “polyol process”. This synthesis is thought to give greater control of particle size and composition than the more common co-precipitation techniques. Nanoparticle composition and structure were confirmed ex situ using a combination of transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). The catalysts were tested in a thermochemical reactor under Fischer-Tropsch conditions to evaluate their activity and selectivity.
Preliminary results have been gathered for CoPt₃, Co₄Pt, and Co₅₀Pt catalysts. The platinum-rich catalyst produced primarily C₁ products while the cobalt-rich catalysts showed reduced hydrocarbon and increased CO₂ selectivity when compared to previous reports on similar materials. Future work will investigate the role of our synthesis in these results and expand the examined phase space to determine which bulk composition yields the most selective surface.

Molybdenum Phosphide (MoP) sulfidized to produce a surface layer of Molybdenum Phosphosulfide (MoP|S) has been shown to exhibit one of the highest activities for the hydrogen evolution reaction (HER) of any non-noble metal in a strong acid. This enhanced performance can be explained by density functional theory (DFT) calculations which predict that nearest-neighbor S atoms potentially enhance the activity of the P atoms (the active sites) by shifting their hydrogen binding energies up the HER volcano. In this work, we further explore this theoretical prediction by synthesizing MoP|S catalysts with varying S concentrations and electrochemically measuring the resulting enhanced activity. The high activity of these non-noble catalysts makes them a promising candidate for replacing Pt, a rare and expensive metal, in many renewable energy hydrogen producing technologies such as proton exchange membrane (PEM) electrolyzers and photoelectrochemical (PEC) water splitting cells. These technologies are promising CO₂-emission free alternatives to hydrogen production, currently a 100 billion dollar industry that uses fossil fuels as its main feedstock.

The non-aqueous Li-air (O₂) battery is receiving a lot of attention for having much higher theoretical specific energy compared to state-of-the-art Li-ion battery technology. For future electric cars, high efficiency batteries with fast recharge are indispensable. In this work, we show that the rechargeablitiy of Li-O2 batteries is strongly dependent on the recharge rate and electrolyte composition. Four different electrolytes were prepared by using combinations of either bis(trifluoromethane)sulfonmide (LiTSFI) or lithium nitrate (LiNO₃) salts in dimethoxyethane, dimethylacetamide or dimethyl sulfoxide as solvents. We focus on the two main electrochemical steps in the Li-O2 battery: the electrochemical generation of O₂^- and the chemical formation and decomposition of Li₂O₂. Cyclic voltammetry was used to probe the former and electrochemical mass spectrometry was used to probe the latter. We correlate the electrolyte composition and solvent properties to the efficiency of the reduction and oxidation steps and to the rechargeability of the battery. The most efficient electrolyte system is identified and possible ways to increase the efficiency are suggested.

Recently, the emission of carbon dioxide is increasing due to the economic activity and the industrialization every year. Carbon dioxide, which is the largest contributor to the greenhouse effect, has been mentioned to reduce emission or convert. Additionally, carbon dioxide is attractive as a renewable carbon source and an environmentally friendly chemical reagent. The technique and process of conversion of carbon dioxide have become the frontier and hot issue in controlling the greenhouse effect.
In order to convert carbon dioxide, electrochemical reduction techniques and biological techniques are required. Electrochemical reduction method with low operating temperature, low operating pressure and easy process has been attracting attention to the pressurization operation. In electrochemical reduction, carbon dioxide is reduced to carbon monoxide, formic acid, and hydrocarbon on the electrode surface by applying the electric energy of outside. The type of products varied depending on the electrode material. The copper is known as a metal which can generate a selectivity of CO and hydrocarbon from carbon dioxide.
In this study, dendritic copper electrode is prepared on the copper mesh by electro-deposition applied high cathodic potential and accompanied hydrogen bubble reaction. It was confirmed according to the structure of the fabricated electrode in this manner, what effect the electrochemical reduction of carbon dioxide. The dendritic copper electrode was characterized by SEM and XRD. The products gas was confirmed by gas chromatograhy (GC) and fourier transform infrared spectroscopy (FTIR).

The design of new anion-conducting polymeric materials has been an active area due to anion exchange membranes application in alkaline fuel cells, which demonstrated significant advantages of higher cell efficiencies and low cost. The current challenge is that high conductivity is often accompanied by significant increase in water uptake, leading to uncontrolled dimensional swelling or even disintegration of the membrane. Herein, we report a unique design of cellulose nanocrystals-based membrane with superior dimensional stability and great water uptake. Cellulose nanocrystals, produced by acid or base hydrolysis of cellulose-rich sources, are nanosized particulates with exceptional mechanical properties. The nanocellulose hydrogels are known to exhibit high water absorption while maintaining excellent dimensional stability. In this study, cellulose nanocrystals were incorporated with different commercially available polymeric binder systems to prepare electrolyte membrane for alkaline fuel cells. The influence of cellulose nanocrystals content, binder formulations, and temperature in water absorption, swelling, and hydroxide conductivity was systematically studied. The resulting membrane exhibited improved dimensional stability (< 10% swelling) and great water uptake (>100%) compared to the polymer binders. The presence of cellulose nanocrystals did not compromise the hydroxide conductivity of the polymer binder system as demonstrated by electrochemical impedance spectroscopy (EIS). Compared to complex polymer synthesis route, the approach reported here is a facile and renewable strategy to prepared solid electrolytes with superior dimensional and structural stability without compromising on the high hydroxide conductivity, thus opening up a new opportunities in the area of solid electrolytes for alkaline fuel cells.

3D Inverse opal (IO) TiO₂ films and CdS nanoparticles were used in visible-light photoelectrochemical (PEC) cells. The CdS nanoparticles were deposited in-situ, onto the TiO₂ surface via a sonochemical synthesis. The interconnected macropores of TiO₂ IO films enabled the uniform deposition of CdS nanoparticles. The amount of CdS nanoparticles was dependent on the concentration of CdS precursor solution. Optimum quantity of CdS nanoparticles was showed at the maximum photocurrent density. Increasing amount of CdS nanoparticles enhanced the light absorption, but also increased the charge recombination with increasing CdS deposition. We showed a maximum photocurrent density of 7.29 mA/cm² at the optimum CdS deposition of 39.33 ms%. We also compared the PEC performance of CdS-deposited TiO₂ IO electrodes and that of CdS deposited-mesoporous TiO₂ electrodes. The PEC performance of CdS-deposited TiO₂ IO electrodes is 2 times higher than that of CdS-deposited mesoporous TiO₂ electrodes because of the uniform pores of the IO films.

Hydrogen is the energy source for fuel cells. The production of pure hydrogen at low cost will facilitate the realization of “hydrogen economy”. Pd-based metallic membranes are the bench-mark membranes in hydrogen separation. Researchers have investigated lower price crystalline alloys as potential candidates in hydrogen separation. Pd coatings are necessary to promote the hydrogen dissociation. Amorphous metals are candidate materials for hydrogen separation. S. Hara et al. [1] found that Ni₆₄Zr₃₆ without a Pd coating has hydrogen permeability only one order of magnitude lower than Pd₇₇Ag₂₃ at 673 K. Amorphous alloys, with their metastable structure, have drawn large interest because of their good mechanical properties. Amorphous metals which contain Zr usually have good glass forming ability. Also, Zr has strong affinity for binding with hydrogen, so amorphous alloys including Zr tend to have higher hydrogen permeability than alloys without Zr. We will present our experimental results on the hydrogen permeability of Zr₆₄Ni₃₆ that show good permeability at 573 K. We synthesized amorphous Zr₆₄Ni₃₆ membranes by splat quenching. We used X-ray diffraction to confirm the amorphous structure. We used differential scanning microscopy to investigate the thermal properties of Zr₆₄Ni₃₆ membranes. Because of the concern with crystallization, alloys with high glass transition temperatures (T_g) are preferable for hydrogen separation. We found that the thermal stability of amorphous metallic membranes in the presence of hydrogen demonstrates that the atmosphere is an important factor to consider in virtual applications.
References
[1] S. Hara, K. Sakaki, N. Itoh, H. Kimura, K. Asami, and A. Inoue, J. Memb. Sci. 164, 289 (2000)

Polymer electrolyte membrane fuel cells have been gaining significant interest over the past several years owing to their promise of clean energy and high scalability. The alkaline fuel cell (AFC) is considered to be promising energy conversion device due to its significant advantage of improved oxygen reduction kinetics and better fuel oxidation kinetics, which can lead to higher efficiencies and enable the use of non-precious metal catalysts, greatly reducing the cost of the device. However, AEM fuel cells continue to perform unfavorably compared to their PEM counterparts because of its performance gap of lower ionic conductivities and ineffective alkaline stability. Polyolefins are known to be highly stable in alkaline and electrochemical environments. Only few research were reported related to polyolefin-based AEMs probably due to chemistry problem. We have designed and synthesized “side-chain-type” polyolefin anion exchange membrane with high base stability using commercial heterogeneous catalyst mediated polymerization that provide multiple structural variations to allow tuning of the membrane properties. The side chain type polyolefin-based AEMs with one alkyl side chain or from trimethylamine exhibited comparable hydroxide conductivity to typical AEMs based on benzyltrimethyl ammonium motif in spite of their low water uptake. The polyolefin-based AEMs have similar alkaline stability and were stable up to 700 h in 5 M, even 10 M NaOH at 80 ^oC. The steric effects of the long alkyl chains in ‘side-chain-type&’ architecture surrounding the quaternary ammonium center are likely the cause of these mmembranes&’ good alkaline stability. The crosslinkable polyolefin-based AEMs were also obtained by introducing the thermally crosslinkable monomer during copolymerization simply. All of the crosslinked membranes shown better properties including lower water uptake, lower water swelling ratio, better mechanical properties, and lower methanol permeability, compared to those of the uncrosslinked counterpart. However, comparable hydroxide conductivities were observed for these crosslinked membranes. A combination of good thermal and chemical stability, excellent mechanical properties and excellent balance between hydroxide conductivity and swelling or methanol transport makes polyolefin-based membrane attractive as AEM materials for alkaline fuel cells applications. We consider that these ‘side-chain-type&’ polyolefin synthesized by commercial heterogeneous catalyst mediated polymerization could lead to new materials for the production of AEMs that meet the demanding challenges of alkaline fuel cells. The length of ‘side-chain-type&’ platform and cations are versatile, which may be further modified to address the various separations and energy-focused applications.

Proton exchange membrane (PEM) is a key component of proton exchange membrane fuel cell. Sulfonated polyimides (SPIs) are prepared by a novel sulfonated diamine, 1,4-bis(4- aminophenoxy -2- sulfonic acid) benzenesulfonic acid [pBABTS] to improve conductivity of PEM. SPIs are synthesized from sulfonated diamine pBABTS, a diamine, and an aromatic anhydride. Then SPI was doped with a protic ionic liquid (IL), 1-vinylimidazolium trifluoromethanesulfonate [VIm] [OTf], to improve PEM conductivity. We have prepared SPI/IL composite PEM using 40 weight % [VIm] [OTf], with a high conductivity of 10 mS/cm at 100^oC and anhydrous condition. pBABTS offered better conductivity, which can be attributed to its chemical structure that has more sulfonated groups attached to provide increased conductivity.

An exciting challenge in nanomaterials science is creation all-transparent and flexible electronic devices supported on plastic substrates. Already numerous such electrical device components have been demonstrated; transparent/flexible circuitry, capacitors, transistors, tactile and strain sensors, chem/bio sensors, heaters, displays and audiospeakers. However, to create a fully-integrated transparent/flexible device will also require energy storage and mangement systems. As for traditional electronic device, this role will almost certainly be played electrochemical charge storage systems such as batteries and supercapacitors.
In the absence of underlying current collectors, transparent supercapacitor electrodes based on disordered nanomaterial networks typically suffer from percolation effects, detrimental to both the resulting electrical and capactive properties. However, here we present transparent/flexible supercapacitors using PEDOT:PSS thin films, demonstrating a complete absence of percolation effects for film transmittance as high as T=99%. In doing so, we have achieved the highest energy storage/unit area for technologically relevant transmittance (T>90%).
Additionally, for a given charge storage material (with some volumetric capacitance), when the film thickness is constrained to provide some required transmittance, the only way to store more charge within the film is by increasing its lateral dimensions. We show that doing leads to a further, previously identified, property trade-off influencing the proportion of charge storage sites accessible as a function of film geometry and charge/discharge rate. In doing so, we demonstrate highest absolute capacitance in large area devices with technologically relevant transmittance (T<90%).

Development of renewable and efficient energy conversion and storage technologies has become essential for modern society because of the emerging ecological concerns. Amongst various energy storage systems, electrical double layer capacitors (EDLCs, supercapacitors) represent one of the most promising energy storage technologies because of their applicability in various novel device systems. They possess high power density and long cyclic stability as compared to pseudo-capacitors and other electrochemical energy storage devices such as batteries. However, their lower energy density is still limiting their large scale commercialization prospects. Carbon based materials such as activated carbon, CNT and graphene are being intensely investigated at the present time to overcome such limitations. The main disadvantages of the current methods of the synthesis of functional carbons are less yield, process complexity and cost for production. Developing carbon material from low cost precursors or waste products can reduce the cost considerably. The storage property can be further improved by tuning the porous structure.
In this work we demonstrate the use of waste office paper as the source for electrical double layer energy storage system. The carbon synthesized from the waste paper (WPC) by simple hydrothermal treatment followed by carbonization in inert atmosphere is shown to exhibit a high BET specific surface area of 2341 m2g-1 with a peculiar hierarchical pore distribution. The interesting 3D porous morphology which contains interconnected macroporous structure with the presence of micro as well as mesopores makes the material ideal for EDLC electrode application. This 3D macroporous structure helps with the penetration of electrolyte into the inner layers of the electrode and hence renders higher accessible surface area. The all solid state supercapacitor fabricated with WPC as the active material and ionic liquid gel electrolyte shows a specific capacitance of 179 Fg-1 and energy density of 56 Whkg-1 at a discharge current density of 1 Ag-1. The material exhibits a power density of 19000 Wkg-1 with an energy capability of 31 Whkg-1. Li ion hybrid capacitor (Li- HEC, the new generation charge storage device) lies in between the Li-ion battery and EDLCs in the Ragone plot and such Li-HEC fabricated with our WPC as the EDLC electrode shows a high energy storage capacity of 61 Whkg-1.

The relatively low cost, high surface area/mass ratio (>1000 m²/g), and ease of manufacture, of activated carbon (AC) makes it the prototypical material for electrochemical capacitor (EC) electrodes. However, the net obtainable capacitance is hampered by a space charge capacitance (C_sc), which adds in series with the expected double-layer capacitance (C_dl). We present a method to enhance the capacitance of AC electrodes based on plasma processing techniques previously used on few-layer graphene (FLG) and carbon nanotubes^[1], where a three-fold enhancement in the measured capacitance was obtained. We will indicate the development of a novel AC electrode that is of low pore size^[2], and which has been purposefully introduced with charged defects via Argon ion irradiation. Extensive characterization using electrochemical techniques such as cyclic voltammetry, impedance spectroscopy, as well as structural characterization through the use of Raman spectroscopy will be reported. Our work will show that the ion-irradiation would lead to a change (i) of the C_dl through modulating the effective charge storage surface area, as well as through (ii) a decrease of the C_sc through the addition of charged states^[3]. Additionally, we will probe the possible contribution to the net measured capacitance, due to the introduced charges, from a parallel pseudocapacitance, (C_p), composed of Faradaic charge-transfer or redox reactions^[4].
References:
[1] Narayanan, R., Yamada, H., Karakaya, M., Podila, R., Rao, A.M., and Bandaru, P.R. 2014
[2] Chmiola, J., Yushin, G., Gogotsi, Y., Portet, C., Simon, P., and Taberna, P.L. Science 313, 1760 (2006).
[3] Hoefer, M.A., and Bandaru, P.R. Journal of Applied Physics 108, 034308 (2010).
[4] Conway, B.E. J. Electrochem. Soc.1991, 1539-1548.

Pseudocapacitors based on metal oxides such as WO₃ are of higher capacitances by as much as an order of magnitude over that of traditional electric double layer capacitors. In this work, we synthesized porous hierarchically nanostructured tungsten trioxide successfully using a hydrothermal process at low temperature (95 °C) under atmospheric conditions. The as-prepared nanomaterials were used to fabricate symmetric/asymmetric supercapacitors. The WO₃ based electrodes were prepared by spreading over a FTO substrate a slurry containing nanostructured WO₃, acetylene black, PVDF and the N-methyl-2-pyrrolidone solvent. The composition of the materials in the electrodes was: 80% WO₃, 10% acetylene black and 10% PVDF. Our results show that WO₃ nanomaterials considerably enhanced the energy storage capacity of supercapacitor, over 10 times higher than a C-PVDF symmetric capacitor. Flexible WO₃ containing supercapacitors were also investigated.

Electricity storage is necessary to address the intermittency problem from renewable energy resources such as wind and solar energy. Supercapacitors are energy storage devices which are complimentary batteries in terms of power density are attractive for many applications. Developing high energy density supercapacitor with high power density remains a challenge. Here, we present a strategy for the synthesis of novel electrode materials based on one-dimensional (1D), two-dimensional (2D) nanostructures of V₂O₅ and reduced graphene oxide (rGO) electrodes for asymmetric supercapacitor applications. The 1D and 2D rGO/V₂O₅ nanostructures display superior electrochemical performance compared to the V₂O₅ nanostructure electrodes in aqueous electrolytes. The asymmetric supercapacitor devices show a working voltage window of 1.6 V. The energy and power density values are, to our knowledge, higher than any that have been previously reported for asymmetric supercapacitors using V₂O₅ electrodes.
References:
D. H. Nagaraju, Qingxiao Wang, P. Beaujuge and H. N. Alshareef J. Mater. Chem. A, 2014, 2, 17146-17152.

Converting CO₂ to valuable materials is attractive. Herein, we report using simple metallothermic reactions to reduce atmospheric CO₂ to dense nanoporous graphene. By using a Zn/Mg mixture as a reductant, the resulted nanoporous graphene exhibits highly desirable properties: high specific surface area of 1900 m²/g, a great conductivity of 1050 S/m and a tap density of 0.63 g/cm, comparable to activated carbon. The nanoporous graphene contains a fine mesoporous structure constructed by curved few-layer graphene nanosheets. The unique property ensemble enables one of the best high-rate performances reported for electrochemical capacitors: a specific capacitance of ~170 F/g obtained at 2000 mV/s and 40 F/g at a frequency of 120 Hz. This simple fabricating strategy conceptually provides opportunities for materials scientists to design and prepare novel carbon materials with metallothermic reactions.

Due to large variation of the solar energy availability in a day, energy storage is required in many applications when solar cells are used. However, application of external energy storage devices, such as batteries and supercapacitors, increases the cost of solar energy systems and requires additional charging circuitry. This combination is bulky and relatively expensive which is not ideal for many applications. In this work, a novel idea is presented for making two-terminal electrochemical devices with dual properties of solar energy harvesting and internal charge storage. The device is essentially a supercapacitor with a photoactive electrode. Energy harvesting occurs through light absorption at one of the electrodes made of a composite of a conducting polymer (i.e. PEDOT:PSS) and a Porphyrin dye. Upon exposure to AM1.0 solar irradiation, an open circuit voltage as large as 0.49 V was achieved across a cell with ~1 mF capacitance. The device showed a reasonable charge stability in dark when it took more than 30 min to drop the voltage. A short circuit current density of 0.12 mA/cm² was obtained under illumination. The device characteristics can be tuned to be more efficient in light absorption or enhance the capacitance by changing the ratio of the polymer and dye molecules in the composite film. Our study shows a great potential of this approach for concurrent solar energy harvesting and charge storage in a two-terminal device.

Combining carbon nanotube (CNTs) and graphene to assemble a 3D pillared graphene superstructure was recently proposed as the next generation novel carbon architecture for various energy storage devices, including supercapacitors, li-ion batteries and hydrogen storage systems among many. However, integration of graphene sheets, 2D nanoscale building blocks, and CNTs, 1D nanostructures, into 3D organized macroscopic pillared assembly and ultimately into bulk functional energy storage devices has been a challenge. This paper outlines our recent work in construction of a 3D carbon nanostructure with horizontal graphene sheets gridlocked with orthogonally aligned single wall carbon nanotubes. The structures show excellent electrical properties, mechanical strength, high porosity and enhanced energy density in an electrical double layer supercapacitor. Polarized Raman spectroscopy, optical ellipsometry and various microscopy characterizations were carried out to confirm the 3D architecture of these electrodes.
A three-dimensional gridlocked hierarchically nanostructured carbon electrode containing horizontal multilayer graphene sheets and magnetic field aligned vertical carbon nanotubes was constructed, and tested for the effectiveness of such electrodes in supercapacitor devices. Carbon slurry composed of activated charcoal, polyvinylidene fluoride (binder), graphene, and single-walled carbon nanotubes was dispersed in dimethylformamide (DMF) and coated upon carbon coated copper foil. Samples were then aligned within a magnetic field and DMF was subsequently evaporated to form the nanostructured electrodes. Fabricated electrodes were assembled into supercapacitor devices using a Swagelok Cell, and performance was tested and evaluated using various electrochemical methods. Our measurements confirm that electrodes containing carbon nanotubes aligned orthogonal to the graphene planes have significantly improved specific capacitance and energy density compared to unaligned samples. In a further advancement we have used purely metallic CNTs to further improve the performance of the supercapacitors. Polarized Raman spectroscopy was used to verify the contiguous alignment of CNTs and performance of supercapacitor devices with CNTs at different angles. Optical ellipsometry within 400 nm to 2 µm wavelength range was carried out to monitor and optimize horizontal alignment of graphene sheets. Detailed study on the fabrication of the 3D electrode, their performance in supercapacitor devices and as Li-ion battery anode, along with various characterization techniques used to optimize the 3D gridlocked nanostructure will be presented.

Electrochemical capacitors have attracted great attentions for various applications such as electrical vehicles and portable electronic devices. The electrochemical capacitors can be divided by three types according to electrochemical energy storage mechanism: electric double layer capacitor (EDLC), pseudo capacitor, and hybrid capacitor. Among these, EDLC has been widely used in practice due to its low cost and high performance, and generally employs carbon materials as electrode which is one of the most important components for high performance of capacitor. Conventionally, the carbon electrodes are modified by wet processes using acid, but they suffer from long processing time, low productivity, and toxic process. Here, we demonstrated an in-line plasma process for carbon material which improves not only the electrochemical performance but also the productivity.
We have developed an in-line plasma treatment system consisting of a linear ion source and a moving stage for sample loading which can be scaled up to continuous manufacturing such as roll-to-roll process. Plasma treatment was conducted on commercial activated carbon, and the electrochemical performances of the plasma-treated samples were evaluated using a potentiostat/galvanostat in conventional three-electrode system with 0.5 M H₂SO₄ aqueous solution. After plasma treatment, nano-hairy structure was uniformly formed at the whole surface of activated carbon and the ratio of oxygen bonding increased. The specific capacitance of the plasma-treated sample was 129.1 F/g, which is improved by about 35% compared to that of non-treated sample (95.3 F/g). This enhancement after plasma treatment is attributed to the increase of surface area by nanostructure formation and the functional group formation. The optimum condition of plasma process such as plasma reactive gas and plasma treatment time will be discussed.

Recently, there has been increasing interest in utilization of renewable biobased feedstock as advanced materials in energy storage and conversion systems. In this work, we report the synthesis of NiCo₂O₄@mesoporous carbon hybrid monolith as a promising electrode material for supercapacitor. The mesoporous carbon monolith is derived from lignin (the second most abundant biopolymer on earth), which explores routes of generating value-added products from main use as fuel. The 3D monolith serves as 3D scaffold for the growth of NiCo₂O₄ nanostructure, one of the most promising candidate for high performance electrode materials. From the angle of device design, the 3D hybrid monolith acts as both the electrode and current collector. This hybrid monolith exhibit remarkable electrochemical performance with high capacitance and desirable cycle life at high rates.

On-chip energy devices such as micro- supercapacitors have gained momentum in recent years as nanostructured (graphenic) electrode materials could finally be obtained using thin-film technologies [1]. From a system integration perspective, obtaining on -chip storage capabilities would be, of course, very useful to many systems, for example, for fully autonomous remote sensor applications. In particular, for autonomous micro-systems/sensors that need to be able to cope with harsh environment operation, graphene on silicon carbide (SiC) technologies would be preferred. Silicon carbide is known for its ability to act as a template for graphene growth as well as for its resilience in harsh conditions. However it has not been considered to date for supercapacitors as the creation and control of the porous morphology of SiC is extremely challenging. In this work, epitaxial SiC on silicon was investigated as both a template and source of nanostructured carbon electrodes through a catalytic method, and the obtained material was implemented as a micro-supercapacitor for the first time. Preliminary results indicate that the unpatterned porous-SiC based micro-supercapacitor results in specific capacitance of around 50 F/g. This is a very promising value for an on-chip storage device, as subsequent in-plane patterning of the porous SiC/graphene material can be expected to result in an additional several-fold increase. Such type of on-chip storage capability has numerous implications for fully integrated silicon -based electronic systems. The fabrication and evaluation of this novel SiC-based super capacitor will be presented.
[1] MF.El-Kady, R.B.Kaner, Scalable fabrication of high-power graphene micro-supercapacitors for flexible and on-chip energy storage”, Nature Communications, Feb.2013, DOI 10.1038/ncomms2446

Electrochemical supercapacitors based on graphene have gained much attention as they offer higher capacitance than the conventional ones based on active carbon. The solid-state supercapacitor with gelled electrolyte is of great interest due to the simple fabrication and the feasibility to make devices in thin film form [1, 2]. We fabricated high performance supercapacitors by using all carbon electrodes, with volume energy in the order of 10³ Wh/cm³, comparable to Li-ion batteries, and power densities in the range of 10 W/cm³, better than laser-scribed-graphene supercapacitors. All-carbon supercapacitor electrodes are made by solution processing and filtering electrochemically-exfoliated graphene sheets mixed with clusters of spontaneously entangled multiwall carbon nanotubes. We maximize the capacitance by using a 1:1 weight ratio of graphene to multi-wall carbon nanotubes and by controlling their packing in the electrode film so as to maximize accessible surface and further enhance the charge collection. This electrode is transferred onto a plastic-paper-supported double-wall carbon nanotube film used as current collector. These all-carbon thin films are combined with plastic paper and gelled electrolyte to produce solid-state bendable thin film supercapacitors. We assembled supercapacitor cells in series in a planar configuration to increase the operating voltage and find that the shape of our supercapacitor film strongly affects its capacitance. An in-line superposition of rectangular sheets is superior to a cross superposition in maintaining high capacitance when subject to fast charge/discharge cycles. The effect is explained by addressing the mechanism of ion diffusion into stacked graphene sheets.
References
[1] El-Kady, M.F., V. Strong, S. Dubin, and R.B. Kaner, Science, 2012. 335 (6074): p. 1326-1330.
[2] El-Kady, M.F. and R.B. Kaner, Nature Communications, 2013. 4: p. 1475.

Much effort has been invested into research on developing catalysts for low temperature polymer electrolyte fuel cell over the last two decades. Platinum metal is a widely used material for electrodes, but due to high cost and insufficient availability, alternate catalysts are being developed. In this project Phosphorus (P) and Silicon (Si) doped carbons have been synthesized from lignin. Lignin is the second most abundant polymer on Earth, next to cellulose. A novel microwave assisted carbonization has been developed which is rapid and superior to other pyrolysis techniques. It also does not use any external gases during carbonization. The heteroatom-doped carbons can be used as cathodes for carrying out oxygen-reduction reaction (ORR) in fuel cells and can also function as electrodes in supercapacitors. The results of ORRs along with material characterizations (BET surface area, X-Ray Photoelectron spectroscopy (XPS), SEM imaging and Infrared Spectroscopy) will be presented.

Conventional Electrochemical double-layer capacitors (EDLCs) are well suited as power sources for devices that require large bursts of energy in short time periods. However, EDLCs suffer from low energy densities as compared to their battery counterparts, which restrict their applications in devices that require a simultaneous supply of high power and high energy. In the wake of improving the energy density of EDLCs, the concept of hybridization of lithium-ion batteries (LIBs) and EDLCs has attracted considerable attention in recent years. Such a hybrid known as a Lithium-ion capacitor (LIC) comprises a Li-ion intercalating anode and a fast charging-discharging EDLC cathode. Although quite ideal in theory, such a system poses major challenges, most of which are a result of the mismatch between the specific capacities and power densities of the LIB and EDLC electrodes.
Here we have fabricated a hybrid supercapacitor that utilizes a Li4Ti5O12 (LTO) based anode and a graphene and carbon nanotube (G-CNT) composite based cathode. LTO is an excellent candidate for LICs because the Li+ ions intercalate/de-intercalate at a redox potential of 1.55V v/s Li/Li+, which is well over the reductive decomposition of the electrolyte. Moreover LTO shows little or no volumetric changes with Li intercalation/de-intercalation, lending it an excellent cycling behavior. Graphene and CNTs, on the other hand are very well-known EDLC materials. Small amounts of CNT were added to graphene in order to prevent graphene sheet stacking and also improve conductivity. Both LTO and G-CNT composites were synthesized using electrostatic spray deposition (ESD) on copper and aluminum foils, respectively. The electrodes were tested as half cells for potential windows of 0.01-3V and 2-4V for anode and cathode, respectively vs Li/Li+. The full hybrid cell (LTO//G-CNT) was constructed using the previously fabricated anode and cathode and tested for a potential window of 0.01-4V. Full cells were assembled keeping in mind the capacity mismatch between the LTO and G-CNT electrodes. The electrodes were characterized using scanning electron microscopy and X-ray diffraction studies. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements were carried out to evaluate the electrochemical performance of the individual electrodes and the full hybrid cells.

Graphene has great potential for applications in capacitive energy storage devices. We show that the power density of carbon/carbon supercapacitor is enhanced by 50 % upon the addition of graphene. Graphene is also examined as conductive additive to substitute carbon black in supercapacitor electrode and our results demonstrate 10 % increase in energy density. Through morphological and electrochemical studies on the fabricated electrodes, these synergistic effects upon graphene addition are mainly ascribed to the “point-to-plane” interaction between activated carbon and graphene, and the better electrochemical performance of graphene compared to carbon black. In conclusion, adding graphene in conventional carbon electrode may have great practical impact for next-generation supercapacitors.

The creation of high efficiency energy storage systems with high dynamic characteristics and long life is the important task in different fields: photovoltaics, electromobiles, etc.
The paper deals with the study of a hybrid energy storage system based on an electric double layer capacitor (ultracapacitor) and accumulator for stand-alone photovoltaic power systems.
The use of electric double layer capacitors as energy storage components in PV systems allows to solve the following problems:
increase of output peak power of a PV generator;
operation optimization of MPPT devices;
smoothing of PV generator power at partial shadowing.
The carried out researches have the following results:
the structure of a stand-alone PV power system with energy storage systems on the basis of an accumulator and ultracapacitor has been developed;
the mathematical model of the offered energy storage system has been developed;
it is shown that the use of the offered energy storage systems decreases significantly the load on the storage battery and increases its life;
the optimum ratios of energy capacities of an ultracapacitor and accumulator are determined;
the possibility of the negative effect elimination of shadowing on PV station operation;
the algorithm of operation of the charge/discharge controller in a PV station with the hybrid energy storage system is developed.

As a promising hybrid energy storage system, lithium ion capacitors (LICs) have been intensively investigated regarding their practical use in various applications, ranging from portable electronics to grid support. The asymmetric LIC offers high-energy and high-power densities compared with conventional energy storage systems such as electrochemical double-layer capacitors (EDLCs) and lithium ion batteries (LIBs). To enable proper operation of the LIC, the negative electrode should be pre-lithiated prior to cell operation, which is regarded as a key technology for developing self-sustainable LICs. In this work, we have demonstrated the potential use of Li₆CoO₄ as an alternative lithium source to metallic lithium. A large amount of Li⁺ can be electrochemically extracted from the structure incorporated into the positive electrode via a highly irreversible process. Most of the extracted Li⁺ is available for pre-lithiation of the negative electrode during the first charge. This intriguing electrochemical behavior of Li₆CoO₄ is suitable for providing sufficient Li⁺ to the negative electrode. To obtain a fundamental understanding of this system, the electrochemical behavior and structural stability of Li₆CoO₄ is thoroughly investigated by means of electrochemical experiments and theoretical validation based on first principles calculations.

Nanowires have attracted increasing interests due to the one-dimensional nanomaterials can offer a range of unique advantages in many energy related fields. bulk materials made of nanowires were usually used as the electrodes. Although the electrochemical properties could be improved, the fast capacity fading is still one of the key issues and the intrinsic reasons are not clear until now. To understand intrinsic reason of capacity fading, we designed the single nanowire electrochemical devices for in situ probing the direct relationship between electrical transport, structure, and electrochemical properties of the single nanowire electrode. Our results show that conductivity of the nanowire electrode decreased during the electrochemical reaction, which limits the cycle life of the devices. Based on this conclusion, a series of hierarchical structures nanowires have been obtained, including hierarchical MnMoO₄/CoMoO₄ heterostructured nanowires and hierarchical mesoporous La_0.5Sr_0.5CoO_2.91 nanowires which show enhanced performance in Li-air batteries and supercapacitors. In our present work, a series of novel nanowire architecture have been designed and synthesized, including kinked hierarchical nanowires, hierarchical heterostructured nanowires and hierarchical scrolled nanowires which shows great electrochemical and biological probe performances. It is expected that our research may extend effective and helpful methods in directions that will solve the challenge of property degradation in energy storage and open new applications.

In this study, we report the synthesis of manganese oxide (MnO₂) microspheres by Ultrasonic Spray Pyrolysis process. A mixture solution of potassium permanganate and hydrochloric acid is nebulized into micro-size droplets, which are then carried by air flow and pass through a furnace tube. Each micro-droplet serves as one micro-reactor and upon heating, the precursor in the droplet is decomposed into MnO₂ (sub)microspheres. This synthetic process is very facile and can be easily scaled up. Thus synthesized MnO₂ microspheres are characterized by SEM, TEM, powder-XRD, Raman Spectroscopy, and XPS. Different morphologies of MnO₂ micropheres can be controlled by tuning precursor concentrations/ratios and furnace temperatures. Microspheres synthesized at 150 °C show amorphous MnO₂ while 500 °C gives rise to the crystalline α-MnO₂. The electrochemical properties is investigated by cyclic voltammetry and the specific capacitance is calculated as 325 F/g, demonstrating that they are promising electrode materials for supercapacitors. In addition, these microsphere can be directly sprayed on a conductive substrate such as indium tin oxide (ITO) glass and conductive carbon fiber paper, which may prove to be a useful technique for supercapacitor electrode coating. These microspheres can also be coated with a thin layer of conductive polymer, poly(3,4-ethylenedioxythiophene), which dramatically improves their capacitive properties at higher charge/discharge rates.

Electrochemical capacitors (ECs) are one of the most important electrical energy storage devices due to its high power performance, long cycle life and short charging time as compared to batteries. However, its energy density is rather low. The development of new EC electrode materials that are active to redox reactions, and hence have high energy storage capacity is of great significance for the implementation of EC technology. Transition metal oxides, especially manganese oxide, are considered as promising electrode materials for their favorable pseudocapacitive behavior, low cost and environmental friendliness. Here, we have reported the synthesis of monoclinic cobalt-manganese oxide nanostructured electrode material by a simple wet chemistry method followed by mild thermal treatment in the air. Cobalt-manganese oxide nanomaterials showed an average specific capacitance of 206 F g^-1 and energy density of 140 Wh kg^-1 at a scan rate of 5 mV s^-1 in 0.1 M Na₂SO₄ aqueous electrolyte via three electrode half-cell measurements. Synchrotron-based in situ X-ray diffraction (XRD) was used to study the charge storage mechanism during redox reactions, providing information about how crystalline structure changes upon the intercalation/de-intercalation of Na-ions. In situ X-ray absorption near edge spectroscopy (XANES) was used to study how electronic state of Mn changes during charge-discharge processes. These measurements showed the electronic and crystalline structure of cobalt-manganese nanomaterials remained stable during the redox reactions. Our results will contribute to the development of new type of manganese oxide-based electrodes for aqueous phase energy storage.

Shape-controlled MnCO₃ nanosphere and nanocube structures had been successfully synthesized by a facile precipitation method. In the sample preparation, NaHCO₃ solution and MnSO₄ solution were mixed in the presence of deionized water and ethylene glycol (EG). In different concentrations, uniform size well-dispersed MnCO₃ nanospheres or nanocubes were obtained. We proposed that the formation of these nanosphere and nanocube structures were owing to the selective piling of smaller aggregates onto the larger ones. The electrochemical properties of MnCO₃ samples were evaluated by using a three-electrode system. The samples were to be used as an electrode material for supercapacitor. The measurements were conducted in a 2M NaClO₄ aqueous electrolyte solution while a platinum foil served as counter electrode and a saturated calomel electrode served as the reference electrode. The working electrodes were prepared by mixing of the as-synthesized MnCO₃ materials with carbon black and polyvinylidene fluoride binder in a ratio of 70:20:10.The testing electrode was then inserted into a nickel foam current collector. The cyclic voltammetry test (CV) of MnCO₃ nanosphere and nanocube electrodes were measured at the voltage potential between 0 to 0.8V under various sweep rates from 5 to 100mV/s. The CV curves showed rectangular-like shapes under different scan rates, indicating that the MnCO₃ electrode materials exhibited superior supercapacitor characteristic. Moreover, the MnCO₃ nanosphere showed a specific capacitance of 129 Fg^-1 at 0.15 Ag^-1, while the nanocube electrode had a specific capacitance of 91 Fg^-1 at the same current density under charge-discharge. In order to estimate the long term stability of the MnCO₃ electrodes, we also measured their cycling performance. High retentions of 87% and 90% after 1000 cycles at current density of 0.3 A g^-1were obtained for the electrodes made with nanospheres and nanocubes, respectively. This suggested that they had prolonged electrochemical cycling life. To summarize, this study provides a facile precipitation method to synthesize mono-dispersed MnCO₃ as well as highlights the promising prospects of MnCO₃ being an electrode material for supercapacitor.

Asymmetric supercapacitors (ASCs) are emerging as a new class of high performance energy storage device. Carbon-based nanomaterials have been commonly used as anode for ASCs because of their large surface area, excellent electrical conductivity and large power density. Yet, the relatively low capacitance of carbon-based anodes limits the device energy density. Here we report a new pseudocapacitor anode, sulfur-doped V₆O_13-x (denoted as VOS), that achieves a benchmark capacitance of 1353 F/g (0.72 F/cm²) at the current density of 1.9 A/g (1 mA/cm²) in 5M LiCl solution. We find that the remarkable capacitance is attributed to the presence of multiple oxidation states (V³⁺, V⁴⁺ and V⁵⁺) in V₆O_13-x. Sulfur-doping also plays an important role in enhancing the charge transfer efficiency and Li ion mobility of the V₆O_13-x electrode. Significantly, the ASC device consists of a VOS anode and a MnO₂/graphene cathode achieves an excellent energy density of 45 Wh/kg (0.87 mWh/cm³). Our work shows that the capability of preparing anode with ultrahigh capacitance is critical for advancing the performance of ASCs.

Asymmetric supercapacitors (ASCs)#65292;also known as electrochemical hybrid supercapacitors, has attracted increasingly attention due to their potential applications in hybrid electric vehicles, portable electronics, microelectromechanical systems and sensors. ASCs typically consist of a battery-type Faradic electrode (cathode) as the energy source and a double layer-type electrode (anode) as the power source, and thus could be operate in a broader working voltage and deliver a substantial higher energy density. Electrode materials are well known to be essential to the property of the ASCs. With this in mind, considerable interests are inspired in exploring high-performance cathode and anode materials for ASCs. In recent year, we focused on the rational design and fabrication of functionally nanostructured materials as high-performance electrodes for ASCs. Several kinds of cathode and anode materials with enhanced capacitive performance such as MnO_2-x nanorods, 3D Ni@NiO, oxygen-deficient Fe₂O₃ nanorods, and 3D graphene nanoneworks have been successfully synthesized and used as electrodes in the fabrication of the ASC devices. Our results showed that the ASC devices based on these as-synthesized nanostructured electrodes possess high volumetric energy density (0.43-1.06 mWh/cm³) and long-term durability.

In order to enhance the performance of supercapacitors, advanced 3D Porous CNT/Ni(OH)₂ gel composite electrodes are developed in this work. Compared with previously reported graphene gel supercapacitors, in which ions have to bypass the 2D flakes, our electrodes using 1D CNTs have smaller diffusion resistance due to a shorter ion transport path. The developed 3D xerogel composite electrodes not only enhance significantly electrochemical performance but also demonstrate the success of a careful engineered guest/host materials interface.
Initially, the CNT gels are coated on the nickel foam to form a 3D scaffold, which serves as a microscopic electrical conductive network. Then Ni(OH)₂ are added into the CNT-coated nickel foam by using a traditional electrodeposition method. In this work, two types of the 3D CNT-coated nickel foams are investigated for the supercapacitor electrodes. They can be used as as-prepared hydrogels or dried in air to form xerogels. Both hydrogels and xerogels present 3D tangled CNT networks.
The experimental results show that the hydrogel composite electrodes having unbundled CNTs and Ni(OH)₂ have very high capacitances of 1400 F/g at low discharge rate, but possessing lower capacitances at higher discharge rate and poor cycling performance with only ~23% retention. In contrast, our developed xerogel composite electrodes can overcome the limitations of the hydrogel composite electrodes in terms of satisfied discharge performance of 1200 F/g and a good cycling retention more than 85% from a stronger Ni(OH)₂/CNT interface. The CNT bundles in the xerogel electrodes formed during the drying process can give a flatten surface with small curvature. While the unbundled CNTs in the hydrogel electrodes will hinder the Ni(OH)₂ nucleation and growth.

Hybrid nanomaterial architect are an interesting class of materials that can find applications in diverse fields owing to their multifunctionality tailored at the interface of the constituents. Graphene and carbon nanotubes (CNTs) within the family of multifunctional nanocarbons are the materials that exhibit excellent electrical conductivity and larger specific surface areas. Theory suggested that covalently bonded graphene/CNT hybrid conjoined material would extend those properties to three-dimensions, and be useful in energy storage and nanoelectronic technologies. We report on the synthesis and properties of electrostatic self-assembled graphene/carbon nanotube hybrid multilayer films as efficient energy storage ultracapacitor devices. Stable aqueous dispersion of polymer-modified graphene sheets were prepared in the presence of cationic poly(ethyleneimine) (PEI). The resultant water-soluble PEI-modified graphene (PEI-Gr) sheets were then used for sequential or layer-by-layer (LBL) electrostatic self-assembly with negatively charged acid-oxidized multiwalled carbon nanotubes (fMWCNT), forming hybrid multilayer 3D films (PEI-Gr/fMWCNT)_n architect as “all carbon” ultracapacitor, where n = 1,2,4,6,9,12 and 15. These hybrid films possess an interconnected network of nanocarbon mesoporous structures with well-defined interfaces and interphases to be promising for ultracapacitor electrodes. They exhibit a nearly rectangular cyclic voltammograms even at an exceedingly high scan rate of 1V/s with an average specific capacitance of ~ 220 F/g and specific energy density of 75.5 Wh/kg at room temperature (based on electrode weight), measured at a current density of 0.3 A/g, comparable to that of Ni metal hydride battery, but the supercapacitor can be charged/discharged within seconds or minute peaking at n = 4. We made an attempt to determine the relative contributions of the electric-double layer (EDL) capacitance (C_D) at the (PEI-Gr/fMWCNT)/electrolyte interface and the quantum capacitance (C_Q) of the PEI-Gr/fMWCNT hybrid. These successes are attributed to the effective utilization of the highest intrinsic surface capacitance and specific surface area by preventing re-aggregation of graphene sheets. The sort of curved morphology developed enables the mesorpores accessible to and wettable by aqueous electrolyte capable of operating beyond 1V. The work is supported by the author's start-up (SG) and NSF-KY EPSCoR (EPS-0814194 and 3048108525-l4-046) grants.

A hybrid multilayer electrode consisting of graphene nanosheets (supercapacitive) and conducting polymers i.e. polypyrrole (PPy) and polyaniline (PANi) [pseudocapacitive] processed electrochemically for intimate electronic contact and covalent interface exhibiting synergistic effect that yield excellent electrochemical performance for enhanced energy storage application. These multilayered supercapacitors are constructed layer-by-layer (LbL) in-situ via electrochemical anodic polymerization of polymers followed by electrochemical reduction of graphene oxide (ErGO) namely, (PPy/ErGO)_n and (PANi/ErGO)_n, where n = 1-5. These hybrid electrodes not only elucidated electronic conductivity through intimate contact, but also enhanced chemical / mechanical stability during the charge/discharge cycling processes. We investigated the electrochemical performance in terms of various parameters of LbL assembly including the number of bilayers (n) and chemical treatments that may affect the degree of reduction of GO on conducting polymers. The LbL-assembled hybrid multilayer electrodes exhibited excellent cyclic voltammogram behavior with gravimetric capacitance (C) of ~ 170 F g^-1 peaking at n = 4 and at a discharge current density of 0.15 A g^-1 that outperformed other hybrid supercapacitors based on conducting polymers and GO alone, especially if they were not electrochemically synthesized. The hybrid supercapacitors maintained 90% capacity over 500 cycles at a current density of 1.5 A g^-1. We have also conducted ac electrochemical impedance spectroscopy to determine interfacial capacitance (C_D) at the hybrid bilayer/aqueous electrolyte interface besides charge transfer resistance (R_ct). This study certainly opens up the possibility for large-scale production of graphene-based multilayered hybrid composites, promising for aerospace applications as well. The work is supported by the author's start-up (SG) and NSF-KY EPSCoR (EPS-0814194 and 3048108525-l4-046) grants.

Long lasting and fast charging energy storage devices have become increasingly important in many areas including portable electronics, transportation, and renewable energy applications. Graphitic porous materials with high specific surface area have been recognized as prominent candidates for high capacity/capacitance electrode for storage devices such as supercapacitors and rechargeable batteries. While it is known that their power and energy density are strongly dependent on pore density, pore size distribution, and on electrolyte confinement effects, a complete understanding of the influence of these factors on electric double-layer capacitance (EDLC) in nano/mesopores is still lacking. Here, to elucidate confinement effects on energy storage device performances, we have developed a well-defined cylindrical-pore platform made of vertically aligned single-walled carbon nanotubes (VACNTs) embedded in an insulating matrix. In this platform, only the inner-walls of well-graphitized nanotubes with known diameter and length are exposed to the electrolyte solution, thus enabling us to investigate the inner pore capacitance behavior. TEM, Raman, and x-ray scattering/attenuation measurements showed that the obtained VACNTs are single-walled carbon nanotubes with diameter distribution ranging from 1 to 5 nm, and a number density > 10¹¹/cm². Using cyclic voltammetry, galvanic charge-discharge measurements, and impedance spectroscopy, we have observed high capacitances of the inner CNT walls when in contact with aqueous electrolytes solutions, such as LiCl or KOH. The measured inner-wall of VACNTs capacitance approaches that reported for a single layer graphene. These novel results are expected to provide guidance toward improving Coulombic efficiency in rechargeable batteries and in designing supercapacitors with enhanced performances.
This work performed under the auspices of the US Department of Energy by Lawrence
Livermore National Laboratory under Contract DE-AC52-07NA27344.

Graphene aerogels are porous 3D materials that combine unique properties of high surface area, electrical conductivity, chemical inertness, and environmental compatibility. They have, therefore, received considerable attention for energy related applications such as supercapacitors, rechargeable batteries, capacitive deionization and catalysis. Polymer derived graphitic carbon aerogels were first developed at Lawrence Livermore National Laboratory (LLNL) in the late 1980s.[1] Since then, LLNL has developed methods to tailor synthesis, tune morphology and characterize these materials.[2, 3] Now LLNL is pioneering efforts to functionalize these materials. One current type of functionalization that is being investigated is the incorporation of nitrogen into the carbon lattice of the graphene aerogel for both its chemical and physical effects on the bulk material. Doping carbon aerogels with nitrogen may be advantageous for numerous energy related applications. Here, the successful incorporation of nitrogen into graphene-based bulk materials for electrical energy storage applications is reported.
To identify promising methods of incorporating nitrogen into the gel, a mix of both Pekala&’s and Baumann&’s methods was used. Rather than using resorcinol, nitrogen-containing analogues to the resorcinol monomer were used as the starting substrate and were cross-linked using formaldehyde and catalyzed by acetic acid to form nitrogen-doped carbon aerogels. Based on Pekala and Baumann et. al, moderate densities were targeted ranging from 0.10-0.30 g/cc. Using the described methods, the amount of nitrogen incorporated into a doped graphene aerogel can be control by changing starting substrate concentrations. Initial electrochemical results show a substantial increase in capacitance for the nitrogen-doped aerogels when compared to the un-doped carbon aerogel.
Work at LLNL was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. Funding was provided by the DOE Office of Energy Efficiency and Renewable Energy, and the Lawrence Livermore National Laboratory Directed Research and Development (LDRD) Grant 12-ERD-035.
1. Pekala, R.W., ORGANIC AEROGELS FROM THE POLYCONDENSATION OF RESORCINOL WITH FORMALDEHYDE. Journal of Materials Science, 1989. 24(9): p. 3221-3227.
2. Worsley, M.A., et al., Synthesis of Graphene Aerogel with High Electrical Conductivity. Journal of the American Chemical Society, 2010. 132(40): p. 14067-14069.
3. Baumann, T.F., et al., High surface area carbon aerogel monoliths with hierarchical porosity. Journal of Non-Crystalline Solids, 2008. 354(29): p. 3513-3515.

Preparation, multiscale modeling and partial characterization of novel, potentially low cost, high temperature and low humidity proton exchange membranes (PEMs) based on cross-linked, sulfonated poly(1,3-cyclohexadiene) (xsPCHD) blends and block copolymers with polyethylene glycol (PEG) are presented. These materials as membranes can have proton conductivities as high as 18 times that of current industry standard Nafion® even at low relative humidity (20%) and at 120 °C, which is critical for hot and dry fuel cell operation conditions. Nafion, and membranes of similar polymer chemistry, have shown a high correlation between charge transport and water transport. The xsPCHD/PEG polymer systems have shown the potential to decouple the charge transport and water transport, promoting increased proton conductivity at high temperatures and low relative humidity. For our modeling effort, we use classical molecular dynamics simulation, confined random walk theory, percolation theory and reactive molecular dynamics simulation modeling techniques to infer a mechanism for charge transport in order to understand the increase in charge transport and its weak correlation to water transport. Also, we aim to understand and predict what the structure, transport, and conductivity of these systems will be with varying xsPCHD and PEG concentration.

Alkaline electrolysis is a proven technology with several large scale facilities for hydrogen production realized and operated reliably for decades. Nevertheless, its broader deployment is hindered by the relatively high cost for hydrogen production. To overcome this obstacle, we need to improve cell efficiency, increase the production rate, and decrease capital cost. Since conventional alkaline electrolysis technology has reached maturation, only small incremental improvements can be expected. To achieve a drastic step forward, we have developed a new generation of alkaline electrolysis cells that can operate at elevated temperature and pressure, producing pressurized hydrogen at high rate (m³ H₂/h#158;m² cell area) and high electrical efficiency.
The concept relies on the development of corrosion resistant high temperature diaphragms, based on mesoporous ceramic membranes where aqueous KOH is immobilized by capillary forces, in combination with gas diffusion electrodes that overcome mass transport limitations at large production rates. Raising the operating temperature offers a means to drastically improve performance, as both ionic transport and reaction kinetics are exponentially activated with temperature. Indeed, we have demonstrated alkaline electrolysis cells operating at 200-250 °C and 20-50 bar at very high efficiencies and power densities. This enables high production rates near the thermoneutral voltage, thereby overcoming the need for cooling.
This work will provide an overview of the exploratory technical studies undertaken so far. Two electrochemical test stations have been established to carry our experiments at elevated pressures (up to 99 bar) and temperatures (up to 300 °C). The conductivity of aqueous KOH was investigated at elevated temperatures to establish the optimum concentration at 200-250 °C. An optimum value of 0.84 S cm^-1 was established at 200 °C for 45 wt% aqueous KOH immobilized in mesoporous SrTiO₃. Gas diffusion electrodes were developed using metal foams loaded with different non-precious metal electrocatalysts in order to reduce the overpotentials for oxygen and hydrogen evolution. Small cells have been fabricated and operated at temperatures up to 250 °C at 40 bar, yielding current densities of up to 1.1 A cm^-2 and 2.3 A cm^-2 at cell voltages of 1.5 V and 1.75 V, corresponding to electrical efficiencies of almost 99 % and 85 %, respectively. Long-term operation at 250 °C was successfully demonstrated for 350 h, suggesting relatively fast oxidation of the Ni foam at the anode. Efforts are currently directed towards the investigation of the intrinsic activity of mixed oxides and perovskites for the oxygen evolution reaction at elevated temperatures and pressures, aiming at identifying active and durable compositions that could potentially replace the Ni-foam. Finally, low-cost production methods have been utilized for a first scale-up of the cell size from 1 cm² to 25 cm².

We propose a new model for leakage current in a liquid-filled electrochemical capacitor (ECs) through electron tunneling between electrode and electrolyte. Previous studies of leakage current have focused on empirical values, and there have been no physics-based explanations to date. In our studies, we subjected few-layer graphene based electrodes to plasma processing [1], and modeled the resulting voltammetric and impedance spectroscopy characteristics through an equivalent circuit model comprised of double layer and Faradaic/redox capacitances as well as a shunt leakage resistance. The graphene samples were subject to 10 W, 20 W, and 50 W plasma powers, and the shunt resistance (as obtained from the Nyquist plots in electrochemical impedance spectroscopy) was found to decrease, six-fold, from 3.8 MOmega; (for the pristine sample) to 0.6 MOmega; (for the 20 W processed sample). We attribute such a decrease to an increased carrier density [2] in the graphene as a result of the plasma. It is discussed as to how the plasma processing leads to the introduction of associated charges in the graphene lattice, which is equivalent to doping and a carrier concentration increase. The predictions from our leakage model will be compared with the above experimental data. A comparison of current leakage mechanisms between various types of ECs will be made and characteristics unique to nanostructured electrodes will be delineated. [1] H. Yamada and P. R. Bandaru, Appl. Phys. Lett. 102, 173113 (2013). [2] H. Yamada and P.R. Bandaru, Appl. Phys. Lett. 104, 213901 (2014).

Formate is a valuable commodity chemical, a liquid H₂ carrier, and a promising fuel for fuel cells that could power portable electronics. Reducing CO₂ into formate is an attractive way to recycle CO₂ provided that the conversion can be performed with high energetic and material efficiency. Hydrogenating CO₂ to formate is energetically efficient yet high pressure of H₂ and high temperature is required. An electrochemical formate synthesis is advantageous because it would avoid handling H₂ and it could be powered directly by renewable electricity sources. Several materials are known that electrochemically reduce CO₂ to formate with good selectivity, but all require very large overpotentials (> 1V) to attain useful rates. This talk will describe metal catalysts recently developed in our lab that overcome this limitation. In CO₂-saturated aqueous HCO₃^- solutions at ambient temperature, these catalysts reach diffusion-limited current densities (5-10 mA/cm²) for CO₂ reduction to formate within 250 mV of overpotential and nearly quantitative Faradaic efficiency. These catalysts reach similar rates even in N₂-saturated HCO₃^- solutions. Under the latter conditions, the CO₂ is supplied by the dissociative reaction of HCO₃^- (HCO₃^- -> CO₂ + OH^-). Mechanistic studies support an electro-hydrogenation mechanism whereby the reduction is mediated by electrochemically produced surface hydrides.

This work reports a novel explanation and mechanism of the electrochemical reduction of CO₂ based on a thorough investigation of modified polycrystalline tin surfaces. This study was conducted with the use of an experimental methodology with unprecedented sensitivity for the identification and quantification of CO₂ electroreduction products. Polycrystalline tin electrodes were shown to produce formate, carbon monoxide and hydrogen across a range of potentials. Hydrogen is reported as the major product on Sn until -0.8V vs RHE, where formate production becomes favored. While CO* binding energy seems to be a good descriptor and key intermediate for CO production on several metals, it was determined that it is unlikely to be the key intermediate for formate production. A bidentate, oxygen-bound intermediate, OCHO*, is presented as the primary intermediate for formate production from CO₂ on metal surfaces. Furthermore, by using OCHO* as a descriptor for formate production, the high selectivity for formate on Sn can be explained, as Sn sits near the top of the formate volcano. Using this understanding, nanostructured tin electrodes with hypothesized tighter binding to CO* were synthesized and characterized. CO₂ and CO reduction on these electrodes yielded the production of methane, which is the first report of any > 2e^- reduced products generated on tin electrodes. These results suggest that oxygen bound intermediates are critical to understanding the mechanism of CO₂ reduction on metal surfaces, and emphasize how understanding the parameters that guide selectivity of this reaction can be utilized to design catalysts with novel behavior.

Hydrogen, the most abundant element in the universe, holds the promise to full fill the needs for a clean and sustainable future. However, to realise this potential of hydrogen, efficient methods of production is a prerequisite. Hydrogen can be generated using the hydrogen evolution reaction (HER) which requires the use of electrocatalysts to decrease the overpotential of the electrodes during the reaction. Identifying materials for electrocatalysts for HER has been a field of active research. Recently, non-noble catalysts, in particular chalcogenides derivatives, have shown potential towards HER. The identification of active edge sites for catalytic activity in MoS₂ nanostructures has paved way for the class for exploring MX₂ transition metal dichalcogenides (TMD).¹ WS₂ in exfoliated forms as electrocatalysts for HER has received interest recently but various other morphologies haven&’t been explored.²
In this work it has been established that 3D nanoflowers of WS₂ synthesized by a simple, fast, scalable and catalyst free chemical vapour deposition are composed of few layer WS2 along the edges of the petals.³ Few layer edges have been observed with atomic resolution using a double aberration corrected JEOL 2200 MCO operated at 200kV in Scanning Transmission Electron Microscopy (STEM) mode and a high angle annular dark field (HAADF) detector. These edges would serve as active sites for catalysis as established previously in literature. An experimental study to understand the evolution of these nanostructures shows the nucleation and growth along with the compositional changes they undergo.³ Having shed light on the structural evolution of these 3D nanoflowers and also studied their structure using high resolution microscopy, attempts were made to increase the number of active sites that would aid HER.⁴The activity of these nanostructures to commercially available materials and liquid exfoliated nanosheets will be presented.
References
1. Jaramillo, T. F. et al. Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts. Science 317, 100_102 (2007).- DOI:10.1126/science.1141483
2. Chowalla.M et al., Enhanced catalystic activity in strained chemically exfoliated WS2 nanosheets for hydrogen evolution, Nature, 12, 2013.- DOI:10.1038/NMAT3700.
3. Grobert .N et al., WS2 2D Nanosheets in 3D Nanoflowers, Chem. Commun.,50, 12360-12362, 2014.- DOI:10.1039/C4CC04218B
4. Jing et al., Enhanced hydrogen evolution catalysis from chemically exfoliated metallic MoS2 nanosheets, J. Am Chem. Soc, 2013.- dx.doi.org/10.1021/ja404523s

Research on electrochemical reduction of CO₂ has focused on establishing fundamental understanding of the catalytic process through investigations on a range of transition metals. These studies have resulted in the formulation of plots of CO₂ reduction reaction (CO₂RR) activities and onset potentials, which show a volcano-like trend when the CO binding strength (E_B[CO]) of catalysts is used as the descriptor. This helped identify E_B[CO] as an important descriptor in determining the effectiveness of a catalyst for CO₂RR. However, at the same time, these experiments showed that the production of products that require more than 2 electrons (> 2 e^- products) is restricted by high overpotentials regardless of the E_B[CO] of the catalysts. This requirement of high overpotentials was proposed to have originated from the unfavorable energetics between the surface bound intermediates. In an attempt to synthesize catalysts that overcome such unfavorable energetics, we looked to catalysts that may have surface sites that specifically stabilize one intermediate over the other.
The specific catalyst system that was investigated in this work was AgZn alloy, which was obtained as a polycrystalline foil. The activity of the alloy for CO₂RR was observed between that of polycrystalline Ag and Zn, which could be explained as a simple interpolation of the two monometallic systems. However, the activity of the alloy for the production of > 2 e^- products was enhanced above both of the monometallic systems, which can no longer be explained as a simple interpolation. We consider synergistic effects of the bimetallic system for the explanation.

Hydrogen (H₂) is a critical chemical feedstock for the fertilizer and petroleum processing industries, with an annual worldwide production of H₂ exceeding 50 million tons.[1] The development of low-cost hydrogen evolution reaction (HER) catalysts that can be readily integrated into electrolyzers is critical if renewable electricity-powered electrolysis were to compete cost effectively with steam reforming for H₂ production.[2] Herein, we report 3 distinct earth-abundant Mo-based catalysts, namely those based on MoS_x, [Mo₃S₁₃]^2- nanoclusters and sulfur-doped Mo phosphides (MoP|S), all loaded onto carbon black supports. These catalysts were synthesized via facile impregnation-sulfidization routes specifically designed for catalyst-device compatibility. Fundamental electrochemical studies demonstrate the excellent HER activity and stability of the Mo-based catalysts in an acidic environment; consequently, polymer electrolyte membrane (PEM) electrolyzers utilizing these catalysts, especially MoP|S, exhibit high performance throughout 24 hours of operation. This work is an important step towards the goal of replacing Pt for the HER in commercial PEM electrolyzers.
References
[1] N. Armaroli, V. Balzani, ChemSusChem 2011, 4, 21-36.
[2] J. A. Turner, Science 2004, 305, 972-974.

Optimal water management at low temperatures is one of the critical issues in commercializing polymer-electrolyte fuel cells (PEFCs), especially those with next-generation material sets. Recent studies have shown that liquid-water removal through the negative electrode is key to improving low-temperature PEFC performance¹. Achieving high rates of water removal requires optimizing the anode gas-diffusion layers (GDLs) for maximum water permeation. Compounding this optimization is the lack of understanding of water permeation, especially under in-situ conditions wherein the GDLs are compressed to provide good electrical contact with the current collector. In this study, we use synchrotron X-ray micro computed tomography (CT) to study the morphology of commercially available GDL materials under varied compressed state, and to correlate the morphological properties such as spatially-resolved porosity, pore-size distribution, and tortuosity to the GDL&’s water-transport capability measured in operating PEFCs.
Two sets of in-situ experiments were performed to quantify the above correlation. First, we study the morphology of the GDL samples through controlled compression, where levels of compression vary from 0 (uncompressed) to 60 % (highly compressed). A flat punch for uniform surface-area compression and a punch with a 1 mm groove for PEFC&’s inhomogeneous flow-field compression are used for this experiment. We observe decrease in porosity with increased levels of compression. A GDL exhibiting improved PEFC performance demonstrates a fiber-density modulation with a porosity difference of 0.06 to 0.08 depending on compression level; this spatial fiber density variation did not level out at higher compressions. Second, we simulated water movement through the GDLs by setting up a water column and using the punch with a groove. For the GDL exhibiting improved PEFC performance we observed a correlation between a liquid-water saturation and fiber-density modulation. We found that fiber-density-modulated GDLs provide efficient water removal pathways. X-ray micro CT imaging proved to be efficient, accurate and non-destructive method in resolving the relationship between liquid water saturation and local GDL morphological properties.
Acknowledgement
This work was funded by Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231. This work made use of facilities at the Advanced Light Source (ALS), supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy.
References
A. Steinbach, “High Performance, Durable, Low Cost Membrane Electrode Assemblies for Transportation Applications”, DOEAnnual Merit Review (2014).

The large demand in the use of portable electronics has been a strong driving force for development of high-performance energy storage devices with innovative properties such as lightweight, flexibility and stretchability. An indispensable component in every energy devices is a current collector, and R2R gravure printing method has received extensive attention for the preparation of the current collector on the flexible substrate due to its simple procedure and compatibility with various substrates. However, there is still plenty of room for further improvement particularly in conventional thermal post-process after R2R printing, which requires extensive annealing time and high temperature that could reduce productivity and substrate compatibility.
In this study, we have successfully fabricated Ag NP conductive film on flexible PET substrate by R2R gravure printing method followed by focused laser sintering post-process that can substitute conventional thermal annealing process. The laser annealing method suggested in this study restore the bulk state electrical conductivity of the printed Ag NP very rapidly without any noticeable substrate damage, and the resultant laser annealed Ag NP layer not only exhibits excellent electrical conductivity, but also demonstrates outstanding adhesion to the underlying polymer substrate which is essential for the fabrication of stable energy devices. After coated with activated carbon slurry, the prepared flexible electrodes with Ag NP current collector and active material are sandwiched with a polymer medium layer (PVA-H3PO4) as both electrolyte and separator, to assemble flexible all solid-state supercapacitors. The supercapacitor showed ideal capacitive behaviors in a number of electrochemical study (Cyclic voltammetry and Charge-discharge test) and retained its performance even in physical disturbance such as bending over 1000 operating cycles without any severe decrease of capacity, indicating that the laser annealing method could replace the conventional thermal method as an efficient post-processing for R2R printed metal NP electrode. So, by combining the proposed laser sintering method onto the existing R2R system, we expect that the productivity of flexible electronics could be improved to a great extent in terms of processing time and space.

Global dependence on fossil fuels as energy sources and the alarming increase of greenhouse gas emissions has necessitated the development of carbon-free and carbon-neutral renewable energy sources for the future. The sequestration of CO₂ emissions and the subsequent electrochemical reduction of CO₂ into fuel products, forms a carbon-neutral synthetic fuel cycle which could potentially be streamlined into existing fuel infrastructures. To date, only Cu has displayed any propensity as a catalyst to electrochemically reduce CO₂ into longer chain hydrocarbons, carboxylates, and alcohols. However, Cu generally requires a large overpotential to reduce CO₂ and has little product selectivity as a catalyst. Recent theoretical work indicates that scaling relations associated with reaction adsorbate binding energies could be limiting the CO₂ reduction activity of transition metal catalysts.[1] These studies suggest that alloying can improve the activity and selectivity of a CO₂ reduction catalyst by decoupling the binding energies of specific reaction intermediates.
We utilize physical vapor deposition (PVD) to synthesize a targeted library of binary alloy thin films for CO₂ reduction. X-ray diffraction and x-ray photoelectron spectroscopy characterization of AuPd thin films demonstrate that the bulk and surface composition can be rationally tuned with the source deposition rates. Analogous results with CuAu and PtCo demonstrate the compatibility and "plug and play" utility of PVD for the synthesis of a library of alloys. Alloys are screened for their CO₂ reduction activity and selectivity using electrochemical measurements in tandem with gas phase (gas chromatography) and liquid phase (nuclear magnetic resonance) product detection methods. Here, we will focus on synergistic effects observed for AuPd and PtIn alloys, demonstrating how alloying can engender new electrocatalytic properties beyond the sum of the components.
[1] Peterson, A.A.; Noslash;rskov, J.K., "Activity Descriptors for CO₂ Electroreduction to Methane on Transition-Metal Catalysts," J. Phys. Chem. Lett., 2012, 3, 251-258.

The development of efficient electrocatalysts is a major hurdle for the conversion of CO₂ and H₂O into carbon fuels using renewable electricity. Au is the most active polycrystalline metal catalyst for CO₂ reduction to CO [1]. Recently, we developed a catalyst called oxide-derived Au that has even higher selectivity for CO₂ reduction to CO at very low overpotentials [2]. Oxide-derived Au is a nanocrystalline, defect-rich material. Correlating activity to defect density in oxide-derived Au is challenging because extracting TEM samples from the oxide-derived Au films is inefficient. Here we report the synthesis of a vapor-deposited Au catalyst on a carbon nanotube film substrate. The as-deposited catalyst has high selectivity and activity for CO₂ reduction to CO (~95% Faradaic efficiency and ~15A/g mass activity at minus;0.5 V vs reversible hydrogen electrode). By comparison, catalysts prepared identically but annealed at 573~673K show much lower activity. The materials can be directly studied by TEM to compare their defect structures. The annealed samples show similar surface facets as the as-deposited one, but they have a lower density of grain boundaries, suggesting that grain boundaries are important determinants of CO₂ reduction activity on Au.
References:
(1) Hori, Y. In Modern Aspects of Electrochemistry; Vayenas, C. G., White, R. E., Gamboa-Aldeco, M. E., Eds.; Springer: New York, 2008; Vol. 42, p 89.
(2) Chen, Y.; Li, C. W.; Kanan, M. W. J. Am. Chem. Soc.2012, 134, 19969minus;19972.

Increasing fossil fuels consumption raises atmospheric concentration of greenhouse gases such as carbon dioxide (CO₂). As one of the active responses to slow down the overproduction of CO₂, utilization of CO₂ by converting into valuable carbon products including fuels has been investigated a lot recently. Electrochemical CO₂ reduction can offer the converting process in a mild condition which can be powered by a renewable energy source such as solar energy for the future energy source. Carbon monoxide (CO) can be produced from electrochemical CO₂ reduction and can be used as a gaseous reactant on Fischer-Tropsch process.
However, electrochemical CO₂ conversion has been challenged because of high overpotential, and various competitive reduction reactions. Especially, electrochemical CO₂ reduction in aqueous media often competes with hydrogen evolution reaction (HER) via water splitting. Therefore, development of electrocatalyst is critical to reduce overpotential (energy cost) and increase selectivity of CO₂ reduction.
Gold (Au) has been known to have high faradaic efficiency of electrochemical CO₂ reduction to CO over hydrogen generation. Herein, we investigated the gold nanoparticles deposited by e-beam evaporation method, a solvent-free method to reduce catalyst poisoning by impurities in solvent or in fabrication process. The morphologies of the gold nanostructures were controlled by the deposition condition varying thickness from 0.5 nm to 10 nm, which changed from few nanometer sized separated particles to their connected network ( few nm width and tens of nm length), and we demonstrate the influence of morphology on CO₂ reduction activities by monitoring cathodic current density and faradaic efficiency. We found that the faradaic efficiency of CO₂ to CO formation was strongly influenced by the formation of connected network. The nanosized gold catalysts performed the best total faradaic efficiency of CO₂ to CO around 80% in aqueous solution with 4nm Au thin film. From the high-resolution transmission electron microscope (HR-TEM) image, 4nm Au thin film shows mix morphology between nanoparticle and connected network nanoparticle. The mix morphology in 4nm Au thin film provides the high active surface area for the electrochemical CO₂ reduction to CO. From the ICP-MS results and CO partial current densities, we calculated the mass activity for every sample. The thickest film sample, 10nm Au thin film did not perform the highest mass activity for the CO₂ to CO formation although it has faradaic efficiency of CO₂ to CO almost 80%. There is possibility that the high faradaic efficiency of CO₂ to CO came from the high amount of gold on the 10nm Au thin film sample. From the HR-TEM image, 10nm Au thin film has only big connected network nanoparticle. Furthermore, the formation of big connected network nanoparticle opens the possibility for decreasing the active surface area on the CO₂ to CO formation that lowered the mass activity.

Although the vast majority of fuels and hydrocarbon products are presently derived from petroleum, there is immense interest in the development of alternate routes for synthesizing these products by hydrogenating carbon oxygenates. Electrochemical methods of reducing carbon dioxide could serve as a method of storing electrical energy derived from intermittent sources like solar and wind if efficient catalysts with high hydrocarbon selectivity are developed. Although metals in the form of foils are increasingly well-characterized as electrocatalysts for carbon dioxide reduction, the activity and stability of their nanoscale counterparts remain poorly understood. We present an understanding of the electrochemical conditions and ligands that afford control over the stability of gold and copper nanoparticles for electrochemical carbon dioxide reduction. Random walk simulations reveal the mechanism by which the nanoparticles lose surface area and assemble into dendrites under polarization conditions. In addition, we have found that the gold and copper nanoparticles exhibit selectivities for electrochemical carbon dioxide reduction that are distinctly different from that of their foil counterparts. The changes in hydrocarbon selectivity for the copper nanoparticles are due to an underlying difference in the mechanism by which electrochemical carbon dioxide reduction proceeds on the nanoparticle surface. Our improved understanding of the activity and stability of gold and copper nanoparticles for electrochemical carbon dioxide reduction is a first step towards their incorporation into membrane electrode assemblies for electrolyzers.

Photocatalytic reduction of carbon dioxide to yield hydrocarbons on the surface of semiconductor catalyst has the potential to become a viable and sustainable alternative energy source to fossil fuel. This is one of the most anticipated solutions for the simultaneous solar energy harvesting and CO₂ reduction, two birds with one stone for the energy and environmental issues. In our previous study, the result shows that the graphene oxide with the tuning bandgap is a promising photocatalyst for CO₂ reduction to methanol under visible-light irradiation¹. The CO₂ photoreduction reaction usually suffers from limited solar fuel conversion efficiency of photocatalyst that is due to the fast recombination and instability of the photo-generated electrons-holes pair.
In this study, GO decorated with copper nanoparticles (Cu/GO), has been used to enhance photocatalytic CO₂ reduction under visible-light. A rapid one-pot microwave process was used to prepare the Cu/GO hybrids with various Cu contents. The attributes of metallic copper nanoparticles (~4-5 nm in size) in GO hybrid are shown to significantly enhance the photocatalytic activity of GO, primarily through the suppression of electron-hole pair recombination, further reduction of GO&’s bandgap, and modification of its work function. X-ray photoemission spectroscopy studies indicate a charge transfer from GO to Cu. A strong interaction is observed between the metal content of the Cu/GO hybrids and the rates of formation and selectivity of the products. The photocatalytic activity of the Cu/GO hybrids was measured in the gas-phase CO₂ photoreduction under visible light irradiation. Methanol and acetaldehyde have been found to be the major product and hydrogen as a minor product from the photocatalytic reduction of CO₂ on Cu/GO. The Cu/GO-2 composite containing 10 wt.% Cu exhibited the highest solar fuel formation rate of 6.84 mu;mol g-cat^-1 h^-1 for photocatalytic CO₂ reduction under visible light irradiation. This photocatalytic CO₂ reduction rate observed in this study is 60 times higher than that obtained by the pristine GO and 240 times higher than that by commercial P-25 under visible light. The size and density of Cu nanoparticles on graphene oxide basal plane highly influenced the photocatalytic CO₂ reduction efficiency and selectivity of solar fuel formation. Detailed investigations on the optimum co-catalyst (Cu) content, its size distribution, and possible mechanism for the selective solar fuel generation will be discussed.
References
1. H.C. Hsu, I. Shown, H. Y. Wei, Y. C. Chang, H. Y. Du, Y. G. Lin,C. A. Tseng,C. H. Wang, L. C.Chen, Y. C. Lin, K. H. Chen, Nanoscale, 5, 262 (2013).

The development of a cost-effective process for electrochemical reduction of CO₂ could enable a shift to a sustainable energy economy and chemical industry. A key technological development is a catalyst that is active to reduce CO₂ at low overpotentials, selective to generate desirable products without the formation of unwanted byproducts, and stable to obtain high current densities over long period of time. Here, we electrochemically deposit Cu nanoparticles on nitrogen-doped carbon nanospike (CNS) electrode, which was prepared via plasma enhanced chemical vapor deposition (PECVD) in the presence of acetylene (C₂H₂) and ammonia (NH₃).¹
Cu is an efficient metal catalyst for formation of significant amounts of hydrocarbon at high reaction rates.² Nanosized Cu particles introduce defects-favorable active sites for reaction of adsorbed hydrogen atoms, which is an important step in the reduction of CO₂ in protic media.³ Additionally, density functional theory plus dispersion (DFT-D) calculations revealed highly selective adsorption of CO₂ by pyridinic nitrogen-doped carbon.⁴ The combination of nitrogen-doped CNS with nanosized Cu is expected to synergistically improve activity and selectivity for CO₂ reduction reaction.
Acknowledgement: This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Oxidic metallate clusters promote the Oxygen Evolution Reaction (OER). The mechanism of OER is rooted in proton-coupled electron transfer. Using electrokinetics measurements together with the results of Differential Electrohemical Mass Spectrometery (DEMS), a cohesive PCET mechanism for OER by oxidic Mn, Ni and Co catalysts has been constructed. Moreover, the effect of metal ion promoters such as iron on the activity of these films, especially on Ni oxidic clusters has been defined.

There has been an increasing interest in the design of ordered mesoporous transition metal oxides due to their fascinating properties such as high surface areas, large pore volumes, uniform and narrow pore size distributions, making them highly valuable model systems for various research areas including energy conversion and storage.¹ Mesostructured cobalt oxide based materials have been shown to be promising electrocatalyst for water oxidation, which is widely considered to be a major barrier for utilizing solar energy in artificial photosynthesis. ^2,3. Herein, we demonstrated the design of a series of mixed binary and ternary non-noble metal oxides for electrochemical water splitting. Among the composite oxides, ordered mesoporous Co₃O₄-CuCo₂O₄ and iron doped cobalt oxide show a significant enhancement for electro-catalytic water splitting with a lower overpotential and higher current density.^4,5
(1) Tüysüz, H.; Schüth, F. Advances in Catalysis2012, 55, 127.
(2) Deng, X.; Tüysüz, H. ACS Catal.2014, 4, 3701.
(3) Tüysüz, H.; Hwang, Y. J.; Khan, S. B.; Asiri, A. M.; Yang, P. D. Nano Research2013, 6, 47.
(4) Grewe, T.; Deng, X. H.; Weidenthaler, C.; Schüth, F.; Tüysüz, H. Chem .Mater.2013, 25, 4926.
(5) Grewe, T.; Deng, X. H.; Tüysüz, H. Chem. Mater.2014, 26, 3162.

Hydrogen evolution reaction (HER) catalysis is vital for sustainable hydrogen fuel production from water. Photoelectrochemical (PEC) water splitting devices and polymer electrolyte membrane (PEM) electrolyzers rely on HER catalysts to efficiently generate hydrogen.^1-3 Platinum and its alloys are the most active HER catalysts but platinum is an expensive precious metal.⁴ There is a need to replace platinum with a non-precious metal earth-abundant alternative.⁵
Transition metal phosphides have recently been reported to have extremely high activity for the HER in acidic conditions, many of which also show exceptional stability on titanium substrates.^6-9 Nanoparticales of nickel phosphide, molybdenum phosphide, cobalt phosphide, and iron phosphide have been shown to reach current densities of 20 mA/cm² between 61 mV and 130 mV overpotential. Though extremely active, it is difficult to compare the intrinsic activity of the transition metal phosphides due to uncertainty in the catalyst surface area.
We discuss our progress in synthesizing transition metal catalysts in equivalent geometries to enable accurate comparison of turnover frequencies. In so doing, we are able to compare the intrinsic activity of the transition metal phosphides for HER and compare their activity with other highly active HER catalysts such as molybdenum sulfide (MoS₂) and platinum. Based on our findings, we propose strategies for synthesizing highly active electrodes and incorporating transition metal phosphides into devices.
1. Walter, M. G., et. al., Chemical reviews2010, 110, 6446-6473.
2. Carmo, M., et. al., International Journal of Hydrogen Energy2013, 38, 4901-4934.
3. Seitz, L. C. et. al. ChemSusChem2014, 7, 1372-1385.
4. Greeley, J., et. al., Nature Chemistry2009, 1, 552-556.
5. Vesborg, P. C., et. al., RSC Advances2012, 2, 7933-7947.
6. Callejas, J. F., et. al. ACS nano2014.
7. McEnaney, J. M., et. al. Chemistry of Materials2014, 26, 4826-4831.
8. Popczun, E. J., et. al. Journal of the American Chemical Society2013, 135, 9267-9270.
9. Popczun, E. J. et. al. Angewandte Chemie2014, 126, 5531-5534.

Exploring the chemical reactivity of different atomic sites on crystal surface and controlling their exposures are important for catalysis and renewable energy storage. Here, we use two-dimensional (2D) layered molybdenum disulfide (MoS₂) to demonstrate the electrochemical selectivity of edge versus terrace sites for Li-S batteries and hydrogen evolution reaction (HER). Lithium sulfide (Li₂S) nanoparticles decorates along the edges of the MoS₂ nanosheet versus terrace, confirming the strong binding energies between Li₂S and the edge sites and guiding the improved electrode design for Li-S batteries. We also provided clear comparison of HER activity between edge and terrace sites of MoS₂ beyond the previous theoretical prediction and experimental proof.

WSe₂ thin films have been deposited onto a conductive substrate (tungsten foil) using a relatively simple chemical-vapor-transport technique. X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy indicated that the films consisted of micron-sized single crystals of WSe_2 that were oriented perpendicular to the surface of the tungsten foil substrate. Linear sweep voltammetry was used to assess the ability of the WSe_2 films to catalyze the hydrogen-evolution reaction and chronopotentiometry was used to gauge the temporal stability of the catalytic performance of the films under cathodic conditions. A 350 mV overpotential (eta;) was required to drive the hydrogen-evolution reaction at a current density of minus;10 mA cm² in aqueous 0.5 M H₂SO₄, representing a significant improvement in catalytic performance relative to the behavior of macroscopic WSe₂ single crystals. The WSe₂ thin films were relatively stable under catalytic conditions, with the overpotential changing by only sim;10 mV after one hour and exhibiting an additional change of sim;5mV after another hour of operation.
In addition, thin films of molybdenum diselenide have been synthesized using a two-step wet-chemical method, in which excess sodium selenide was first added to a solution of ammonium heptamolydbate in aqueous sulfuric acid, resulting in the spontaneous formation of a black precipitate that contained molybdenum triselenide (MoSe₃), molybdenum trioxide (MoO₃), and elemental selenium. After purification and after the film had been drop cast onto a glassy carbon electrode, a reductive potential was applied to the precipitate-coated electrode. Hydrogen evolution occurred within the range of potentials applied to the electrode, but during the initial voltammetric cycle, an overpotential of sim;400 mV was required to drive the hydrogen-evolution reaction at a benchmark current density of minus;10 mA cm^-2. The overpotential required to evolve hydrogen at the benchmark rate progressively decreased with subsequent voltammetry cycles, until a steady state was reached at which only sim;250 mV of overpotential was required to pass minus;10 mA cm^-2 of current density. During the electrocatalysis, the catalytically inactive components in the as-prepared film were (reductively) converted to MoSe₂ through an operando method of synthesis of the hydrogen-evolution catalyst. The initial film prepared from the precipitate was smooth, but the converted film was completely covered with pores sim;200 nm in diameter. The porous MoSe₂ film was stable while being assessed by cyclic voltammetry for 48 h, and the overpotential required to sustain 10 mA cm^-2 of hydrogen evolution increased by <50 mV over this period of operation.

Prussian Blue analogues (PBAs) have shown promise as electrode materials for grid-scale batteries because of their high cycle life and rapid kinetics in aqueous-based electrolytes (1,2). However, these materials suffer from relatively low specific capacity, which may limit their practical applications. Here, we investigate strategies to improve the specific capacity of these materials while maintaining their cycling stability and elucidate mechanisms that enhance their electrochemical properties. In particular, we have studied the electrochemical and structural properties of manganese hexacyanoferrate (MnHCFe) and cobalt hexacyanoferrate (CoHCFe) in an aqueous, sodium-ion electrolyte. We also studied hybrid manganese-cobalt hexacyanoferrates (Mn-CoHCFe) with different Mn/Co ratios that combine properties of both MnHCFe and CoHCFe. The materials have the characteristic open-framework crystal structure of PBAs, and their specific capacities can be significantly improved by electrochemically cycling both the carbon-coordinated Fe and the nitrogen-coordinated Co and Mn ions. In situ synchrotron X-ray diffraction studies combined with in-depth cyclic voltammetry and electrochemical impedance spectroscopy provide insight into the different electrochemical properties associated with the Fe, Co, and Mn redox couples. We show that the C-coordinated Fe exhibits a diffusionless kinetic regime with a stable crystal structure during cycling that enables the outstanding kinetics and cycle life previously displayed by PBAs in aqueous electrolytes. On the other hand, the N-coordinated Co and Mn ions exhibit a slower, diffusion-controlled kinetic regime with more structural distortion, but they still contribute significantly towards increasing the specific capacity of the materials. These results provide the understanding needed to drive development of PBAs for grid-scale applications that require extremely high cycle life and kinetics.
References
(1) Pasta, M.; Wessells, C. D.; Huggins, R. A.; Cui, Y. Nat. Commun.2012, 3, 1149.
(2) Pasta, M.; Wessells, C. D.; Liu, N.; Nelson, J.; McDowell, M. T.; Huggins, R. a; Toney, M. F.; Cui, Y.; Huggins, A. Nat. Commun.2014, 5, 3007.

Supercapacitors are a type of electrochemical energy storage devices, which have attracted much attention due to their high power delivery ability. In order to achieve enhanced energy density of supercapacitor, elevated operation potential window is highly demanded. Although numerous efforts have been spent on developing aqueous electrolyte based hybrid supercapacitor device, the water decomposition still limit the operation window of device to be less than 2 V. Therefore, organic electrolyte based non aqueous hybrid supercapacitor is of great interest for its large operation window (>2.5 V).
Orthorhombic phase Nb₂O₅ (T-Nb₂O₅) nanocrystals are found to exhibit fast pseudocapacitive Li⁺ storage based on an unique intercalation pseudocapacitance (theoretical value: 200 mAh g^-1).² The Li⁺ diffusion is proved to have fast kinetics in the bulk material without inducing any phase change.^2a However, the latest report showed capacities of T-Nb₂O₅ nanocrystals are only around 140~150 mAh g^-1 despite the high surface area.² Meanwhile, the fast fading of capacity is still haunting the T-Nb₂O₅ material.
In this work, we introduce a strategy to enhance the capacity and stability of T-Nb₂O₅ and the corresponding application for realizing a hybrid supercapacitor. In the first step, we develop a facile method to synthesize ultrathin T-Nb₂O₅ nanowires to increase the electrolyte accessbility as well as shorten the ion diffusion length. Subsequently, a few nanometer carbon coating derived from polydopamine is applied to tailor the electrode/electrolyte interface in order to achieve high cycling stability. The capacity reaches 186.8 mAh g^-1 @ 0.5 C, while it preserves 140.1 mAh g^-1 @ 25 C. Meanwhile, the capacity maintains 82 % after 1000 cycles at 5 C.
3V hybrid supercapacitor devices are assembled using the T-Nb₂O₅ based electrodes with further optimization. Activated carbon and polyaniline (PANI) are used as the counter electrode, delivering energy densities of 43.4 Wh kg^-1 and 110 Wh kg^-1, respectively. The results show that the T-Nb₂O₅ is promising for developing the next generation hybrid supercapacitor device.
Reference
1. Burke, A., R&D considerations for the performance and application of electrochemical capacitors. Electrochimica Acta 2007,53 (3), 1083-1091.
2. (a) Augustyn, V.; Come, J.; Lowe, M. A.; Kim, J. W.; Taberna, P.-L.; Tolbert, S. H.; Abruña, H. D.; Simon, P.; Dunn, B., High-rate electrochemical energy storage through Li+ intercalation pseudocapacitance. Nature Materials 2013,12 (6), 518-522; (b) Kim, J. W.; Augustyn, V.; Dunn, B., The Effect of Crystallinity on the Rapid Pseudocapacitive Response of Nb₂O₅. Advanced Energy Materials 2012,2 (1), 141-148.

Electrochemical capacitors have attracted great attention as energy storage devices for a wide range of applications due to high power density and high cyclability; however the low energy density of electrochemical capacitors has inhibited their implementation. Materials with layered structures possess favorable characteristics for improving the energy density of electrochemical capacitors by promoting the transportation and the intercalation-deintercalation processes of alkaline cations within the layers of the crystal structure due to the large layer-layer distance. In this study, layered potassium doped vanadium (V) oxide (K_XV₂O₅) nano-sheets were successfully synthesized at room temperature in aqueous solution and followed by simple annealing process. Ideal pseudocapacitive behavior was demonstrated via cyclic voltammetry measurements in a three-electrode half cell using an aqueous 1M KCl electrolyte solution with 1.0 V potential window. The resulting specific capacitance of 600 F/g at a sweep rate of 5 mV/s is the highest reported specific capacitance of a vanadium oxide material to the best knowledge of the authors, in addition was able to retain a specific capacitance 300 F/g at a sweep rate of 200 mV/s with distinct redox peaks remaining present even at high sweep rates. Through in-situ x-ray diffraction using synchrotron radiation, the reversible expansion and contraction of the vanadium oxide layers was observed during the charge-discharge electrochemical processes. The development of a novel K_XV₂O₅ layered nano-structure provides new insights into the development of energy storage devices utilizing aqueous electrolytes and pseudocapacitive materials.

Electrochemical capacitors (supercapacitors) have attracted intense attention due to their high power density, fast charge-discharge process, long cycle life and used in many practical applications. Ni-Co composites, also known as ternary metal composites, have excited great interest in recent years because of their high-performance in supercapacitors. Owing to the coupling of two metal species, these materials could render the composites with rich redox reactions and improved electronic conductivity. In particular, the tunable compositions in the Ni-Co oxides provide vast opportunities to manipulate the crystal structure and its physical/chemical properties.
Here we report the interesting formation of Ni-Co oxides and Ni-Co sulfide nanowire arrys (NWAs) with Ni/Co molar ratio at 1: 1 and their derived free standing structure on different substrates for ECs. Ni-Co oxides NWAs were synthesized on ordered TiO₂ nanotubes and Ni foam respectively by a facile hydrothermal method. Ni-Co sulfides NWAs were fabricated through S^2- ion exchange using synthesized Ni-Co oxides nanowires as precursor. The electrochemistry testes showed that this self-supported electrode is able to deliver ultrahigh specific capacitance. To raise the cell voltage and thereby boost the energy density more effectively, we use the Ni-Co sulfides NWAs for the battery-like Faradic electrode and activated carbon for the capacitive electrode to compose an asymmetric cell, and this has extended the cell voltage to 1.8 V in an aqueous electrolyte, resulting in high energy density, high power density and good cycling stability all together. To the best of our knowledge, such a prototype device has not been fabricated and explored before.
As we all know, dimensionality and rational design of electrode architectures plays a crucial role in determining materials' fundamental properties and the electrochemical performance of supercapacitor. For a proof-of-concept, Ni-Co layered double hydroxides (LDH), NiCo₂O₄ and NiCo₂S₄ nanosheets supported on carbon fiber paper (CFP) substrate are prepared in our next work. When tested as the pseudo-capacitor positive electrode, the self-support nanosheets on CFP demonstrate good performance and rate capability as well as excellent cycling life, which contribute to the unique 2D nanosheets structure supported on 3D conductive CFP substrate with open permeable channels, facilitating electrolyte penetration and ensuring more efficient ion diffusion and faster electron transport. The asymmetric supercapacitor based on pseudocapacitance of both electrodes is further first realized by using NiCo₂S₄ nanosheets and FeOOH nanorods as positive and negative materials, respectively. And it exhibits high energy density and power density as well as outstanding cycling life.

In the last few years, a lot of interest has been shown in 2-D materials that present exotic and/or enhanced properties when compared to their bulk counterparts. Several techniques can be sued to prepare this two dimensional “flakes”, being micromechanical exfoliation the most commonly used. However it is suitable only for fundamental research as it provides a very low yield¹. V. Nicolosi et al^2,3 were able to increase this yield by non-chemical, solution-phase exfoliation of layered materials in water or organic solvents. Thought it was initially applied for the production of monolayer, high surface area graphene, liquid phase exfoliation can be used to process any kind of two dimensional materials from a layered bulk sample^1,2,3.
In the present work, 2D materials prepared by liquid phase exfoliation are presented as good candidates for supercapacitor or battery electrodes. In the specific case of energy storage, two-dimensional materials are beneficial, as they present a higher electrode/electrolyte contact area per unit mass, thus optimizing the active material utilization. These materials can be mixed with conductive additives, such as carbon nanotubes and graphene, which enhance the overall electrode performance. Several methods can be used to prepare these composites, however in this work we give special attention to a single step preparation of MnO2/Graphene composite. In a typical procedure, a high-surface area, porous MnO₂ powder is produced through the oxidation of Mn(NO₃)₂ by KMnO₄. Subsequently, the material is exfoliated in isopropanol at 37kHz for 3 hours, resulting in MnO₂ nanolayers. Following a novel approach, the MnO₂ powder is also exfoliated simultaneously with graphite resulting in a MnO₂ layers/Graphene hybrid (GMOH).
The obtained dispersions are then sprayed onto ITO electrodes, following a cost-effective spray deposition technology, suitable for the fabrication of both semi-industrial scale and laboratory size film supercapacitor electrodes. By testing electrodes with different thicknesses it was found out that the electrochemical utilization is enhanced for GMOH. A capacitance as high as 300 F.cm^-3 was also achieved with GMOH thin electrodes followed by 225 F.cm^-3 for simple MnO₂ layers.
(1) Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Science2013, 340.
(2) Coleman, J. N.; Lotya, M.; O&’Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V. Science2011, 331, 568.
(3) Higgins, T. M.; McAteer, D.; Coelho, J. C. M.; Sanchez, B. M.; Gholamvand, Z.; Moriarty, G.; McEvoy, N.; Berner, N. C.; Duesberg, G. S.; Nicolosi, V.; Coleman, J. N. ACS Nano2014.

We recently produced a new 2-D material, viz. Ti₃C₂, by selective HF etching of aluminium from a MAX phase Ti₃AlC₂ and labelled it MXene. Here we report improved synthesis procedure which allows to avoid HF during synthesis. MXenes represent a large family of transition metal carbides and carbonitrides, not just a single phase. Unlike graphene, whose chemistry is restricted to carbon, MXenes allow a variety of chemical compositions and are establishing themselves as a new class of two-dimensional materials. MXenes possess good in-plane conductivity, which in combination with the rich surface chemistry makes them attractive for electrical energy storage applications.
We studied MXene potential as electrode material for electrochemical capacitors. We report on the intercalation of Li⁺, Na⁺, Mg²⁺, K⁺, NH₄⁺, and Al³⁺ ions between the 2D Ti₃C₂T_x layers. In most cases, the cations intercalated spontaneously. We show high capacitance up to 900 farads per cubic centimeter (much higher than that of porous carbons) of flexible Ti₃C₂T_x paper electrodes in aqueous electrolytes. We found that tuning of material surface chemistry can improve MXene capacitive performance. Several different electrochemical techniques were employed to understand the mechanism of charge storage. Cyclic voltammetry measurements showed a high rate handling ability for MXene. Galvanostatic cycling showed no degradation of the capacitive properties after more than 10,000 cycles.
References
M. Ghidiu*, M. R. Lukatskaya*, M.Q. Zhao, Y. Gogotsi, M. W. Barsoum, “Conductive two-dimensional titanium carbide clay with high volumetric capacitance” Nature, 2014, DOI 10.1038/nature13970
M. R. Lukatskaya, O. Mashtalir, C.E. Ren, Y. Dall&’Agnese, P. Rozier, P. L. Taberna, M. Naguib, P. Simon, M.W. Barsoum, Y. Gogotsi, “Cation Intercalation and High Volumetric Capacib tance of Two-dimensional Titanium Carbide” Science, 2013, 341 (6153), pp. 1502-1505
Y. Dall'Agnese, M. R. Lukatskaya, K. M. Cook, P. L. Taberna, Y. Gogotsi, P. Simon, “High capacitance of surface-modified 2D titanium carbide in acidic electrolyte” Electrochemistry Communications, 2014, 48, pp. 118-122
M. D. Levi, M. R. Lukatskaya, S. Sigalov, M. Beidaghi, N. Shpigel, L. Daikhin, D. Aurbach, M. W. Barsoum, Y. Gogotsi, “Solving the Capacitive Paradox of 2D MXene by Electrochemical Quartz-Crystal Admittance and in situ Electronic Conductance Measurements” Advanced Energy Materials, DOI: 10.1002/aenm.201400815

Electrochemical capacitors, namely supercapacitors (SCs), combined with exceptionally long cycle life, fast charging rate, high safety, high power density, and enhancing energy density, provide a potential approach to solve energy storage problems. Although MnO₂ is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. In a series of studies, we have developed several kinds of MnO₂ based materials on flexible substrates and applied them as supercapacitor electrodes, including worm-like nanoporous amorphous MnO₂ nanowires, carbon nanotube/MnO2 nanotube hybrid porous films, hydrogenated single-crystal-ZnO @amorphous-ZnO-doped-MnO₂ core-shell nanocables, MnO₂/carbon nanotube alternate nanostructures, etc [1-7]. The assembled symmetric and asymmetric flexible SC devices exhibit excellent electrochemical performance, demonstrating their broad potential applications as effective power sources for portable/wearable electronics.
References:
1. ACS Nano, 7 (2013) 2617-2626.
2. Nano Lett. 14 (2014) 731-736
3. Nano Energy, 8 (2014) 274-290
4. Nano Energy, 10 (2014) 108-116
5. Angew Chem Int Ed. (2014) DOI: 10.1002/anie.201407365
6. J. Mater. Chem. A, 2 (2014) 595-599.
7. J. Mater. Chem. A, 2 (2014) 17561-17567

As an emerging #64257;eld, stretchable electronics that can sustain large mechanical strain without degradation in their electronic performance have large potential to be widely applied in bio-implantable system, wearable system, wireless sensors and so on. Over the past few years, various kinds of stretchable devices such as organic light-emitting diode devices, radio frequency devices, #64257;eld effect transistors, pressure and strain sensors, temperature sensors, and arti#64257;cial skin sensors have been developed. To power the stretchable electronics and achieve a fully power-independent and stretchable system, it is urged to explore new power source devices with high stretchability. In recent years, extensive efforts have been devoted to studying stretchable conversion or storage devices like solar cells, photovoltaic cells, Li-ion batteries and supercapacitors (SCs). Among these power source devices, SCs are perceived as one of the most promising energy storage devices due to their high power density, modest energy density, fast charge-discharge capability and long cycle life. The key point for fabricating stretchable SCs is the design of stretchable SCs electrodes. The realization of low-cost, stretchable SC device with high energy and power density is still highly desirable.
Recently, we present a simple and large-scale water surface assisted synthesis of multiwall carbon nanotube (MWCNT) based stretchable #64257;lm. Taking advantage of extremely #64258;at surface of water, uniform #64257;lms were formed which combined the excellent conductivity of MWCNTs with the high stretchability of PDMS. The MWCNT/PDMS #64257;lm containing 10% MWCNTs exhibited a high conductivity of 4.19 S cm^minus;1 and could be stretched to a high strain of 50% without damaging its conductivity and structure. In addition, the size and shape of the #64257;lm can be easily tuned by changing the area and shape of water surface. More importantly, the prepared MWCNT/PDMS #64257;lm is an excellent conductive and mechanical substrate to support electrochemically active materials. When a layer of polyaniline (PANI) nano#64257;bers was deposited on the MWCNT/PDMS #64257;lm, the PANI/MWCNT/PDMS #64257;lm electrode exhibited a benchmark speci#64257;c capacitance of 1023 F g^minus;1 and areal capacitance of 481 mF cm^minus;2 at a scan rate of 5 mV s^minus;1. A solid-state symmetric supercapacitor (SSC) device with remarkable stretchability and outstanding electrochemical properties was also assembled for demo by the PANI/MWCNT/PDMS #64257;lms as stretchable electrodes. The as-fabricated SSCs possessed good and stable capacitive behavior even under dynamic stretching conditions, with more than 95% capacitance retention after 500 cycles during the dynamic stretching and releasing process. Moreover, this device was able to deliver a maximum energy density of 0.15 mWh cm^minus;3 (11 Wh kg^minus;1), which is considerably higher than most of SSCs reported recently.

Recently, there has been extensive research on flexible/ stretchable electronic devices according to the increasing demand for wearable or bio-implanted devices. Simultaneously, the requirement of flexible/stretchable power system has been enhanced. Among the energy storage devices, supercapacitor has been considered as a promising candidate for the next-generation energy storage devices due to its high power density, stability, long cycle life, fast charge/discharge rate, and relatively simple structure. Carbon based materials, such as graphene, carbon nanotube (CNT), and activated carbon, are widely used as electrodes for supercapacitors due to their high electrical conductivity, light weight, and large electrochemical surface area. In particular, CNTs have been investigated as filler for the polymeric composites owing to their strength, stiffness, and pliability. Adopting CNTs to the polymer matrix could improve the electrical conductivity as well as the mechanical strength of pristine polymer.
In this work, we report on the fabrication of biaxially stretchable micro-supercapacitor (MSC) array using composite electrodes of polymer and multi-walled carbon nanotubes (MWNTs). The deformable substrate consists of soft Ecoflex with locally implanted stiff platforms of negative photoresist, SU-8, so that the strain on the surface region just above the SU-8 can be suppressed. The narrow and long serpentine interconnection of Ti/Au encapsulated with polyimide film accommodates the strain under deformation, minimizing the strain applied to MSCs mounted on the strain suppressed area. The planar MSC is fabricated with electrodes of polyaniline nanowire (PAni NW) grown on the spray-coated MWNT-COOH film by potentiodynamical deposition method, and patterned ionogel electrolyte of PEGDA/[EMIM][TFSI]. The fabricated MSC array operates in the potential range from -1.2 V to 1.2 V and shows extremely high volumetric capacitance of 278 F/cm³ at a scan rate of 100 mV/s. The MSC array shows stable performance retaining 80% of initial capacitance after 5000 charge/discharge cycles at a current density of 100 mu;A/cm². Furthermore, there is no noticeable change in the charge/discharge characteristics and capacitance under uniaxial strain of 70% and biaxial strain of 50%. This work demonstrates the potential application of our stretchable MSC array as an energy storage device in the wearable computer, electronic paper, and bio-implantable electronics.

Investigation of high performance energy storage devices has been extensively done in accordance with the increasing demands for energies. Supercapacitors, receiving attention as the next-generation energy storage devices, have advantages such as relatively simple structure, fast response time, long cycle life and high instantaneous power compared to batteries although its low energy density. In order to enhance the energy density, many groups made efforts via application of new electrode materials, improvement of electrode design and investigation of various kinds of electrolytes etc. The energy density is proportional to the specific capacitance and square of the potential window. With aqueous electrolytes, however, enhancement of energy density is restricted due to their potential range limited to approximately 1 V, decomposition voltage of water.
In this work, we report on the dramatically improved electrochemical performance of maicro-supercapacitors (MSCs) via use of gel type electrolyte made of poly(methyl methacrylate) and organic solvent of propylene carbonate, whose stable potential window is between -1.2 and 1.2 V. As electrodes, layer-by-layer assembled thin film of multi-walled carbon nanotubes with top layer Mn₃O₄ nanoparticles was used. Fabricated MSC exhibited a volumetric capacitance of 45 F/cm³ at a scan rate of 10 mV/s and a maximum volumetric energy density and power density of 36 mWh/cm³ and 445 W/cm³, respectively. After repetitive operation up to 30,000 cycles, the capacitance maintained at ~92 % of the original value. Furthermore, the performance of MSC was stable in air for more than 2 weeks to keep more than 80 % of initial capacitance. Such fabricated MSCs can be dry transferred on our specially designed deformable polymer substrate to form an integrated circuit with controlled total capacitance and output voltages. Under deformation of bending, twisting, and stretching, the electrochemical performance of MSCs remained stable. In addition, we protected integrated devices from external impact via encapsulation and confirmed that the deformable MSCs array directly attached onto the skin or cloth operated stably regardless of various human motions. This work demonstrates that our deformable MSCs array can be widely applied as embedded energy storage devices of flexible/stretchable electronic devices such as skin-attachable and wearable computers.

Energy harvesting device enables to convert ambient energy into electricty, and provides sustainable power source for various sensors. Mechanical vibriations are ubiquitous in ambient environment and have relative high power density (Human: 10-100 µW/cm², industry: 1-10 mW/cm²). It is necessary to store the instaneous electricity converted from mechanical vibrations into an energy storage device. The integration of energy harvesting and storage device requires high integration level to minimize the unnecessary energy loss in power-management circuit, and high durability in intensively mechanical vibrations. ^{1, 2} Recently, the self-charging power cell for one-step energy conversion storage has been demonstrated with the integration of piezoelectric separator and Li-ion battery.^{3, 4} However, the battery is limited by the slow charging rate, poor cyclibility and low power-density. In our work, we integrate the piezoelectric polyvinylidene fluoride (PVDF) into a supercapacitor as the separator to overcome the above issues. The double-sides of the polarized PVDF were coated with H₃PO₄/poly(vinyl alcohol) (PVA) gel. Porous graphene was stuck with PVA as both anode and cathode, forming an all-solid-state supercapacitor. Externally mechanical vibrations establish a piezoelectric potential across the PVDF, and drive the ion to migrate towards the interface of graphene sueprcapacitor electrode, establishing an electric-double layer at the interface and storing the electricity in the form of electrochemical energy. We successfully lighted a 12.5 mW LED by connecting with this self-powered supercapacitor. Our hybrid energy harvesting and storage device can be further extended for providing sustainable power source of various types of sensors.
References
(1) Xie, Y.; Liu, Y.; Zhao, Y.; Tsang, Y. H.; Lau, S. P.; Huang, H.; Chai, Y. J. Mater. Chem. A 2014, 2, 9142-9149.
(2) Zeng, W.; Tao, X.; Chen, S.; Shang, S.; Chan, H. L. W.; Choy, S. H. Energy Environ. Sci. 2013, 6, 2631-2638.
(3) Xue, X.; Deng, P.; He, B.; Nie, Y.; Xing, L.; Zhang, Y.; Wang, Z. L. Advanced Energy Materials 2014, 4, DOI: 10.1002/aenm.201301329.
(4) Xue, X.; Wang, S.; Guo, W.; Zhang, Y.; Wang, Z. L. Nano Lett. 2012, 12, 5048-5054.

Increasing power and energy demand for next-generation portable and flexible electronics has stimulated intensive efforts to explore various electrochemically active materials for energy storage devices. In this talk, I will present our latest results in exploration of carbon based materials for electrochemical capacitors. The discussion will focus on the two functions of carbon based materials. First, carbon is a promising electrode material for electric double layer capacitors. Recently, we report an effective strategy to activate carbon cloth for charge storage via chemical exfoliation. The activated carbon cloth showed a maximum areal capacitance of 88 mF/cm2 without loading any other active capacitive materials. Second, carbonaceous materials can function as a protective layer for pseudocapacitive electrode. Our recent studies showed that carbonaceous shell-coated polyaniline and polypyrrole electrodes achieved remarkable capacitance retentions of sim;95 and sim;85% after 10thinsp;000 cycles.

In this communication we will show a brief view of three different nanostructured carbons that we have developed for energy storage applications. The first one was prepared from an in situ generated growth catalyst that produces highly oriented graphitic nanowiggles (GNWs). GNWs are a new form of disordered nanocarbons with graphite domains stacked perpendicular to the filament axis.¹ They had been prepared by acetylene decomposition at 525 C on Al-Mg mesh coated with iron-based nanoparticles. During CVD, inter-diffusion of Mg, Fe, and O between the electrodeposited Fe particles and the mesh generate flakes which become the active site for nanowiggle growth. The properties of this unique form of carbon were evaluated by TEM, HRTEM, SEM, Raman spectroscopy, XPS and cyclic voltammetry. The second one is a lignin-derived nanoporous carbon with narrow and tuneable pore-sizes and few-layer graphene in their microstructure produced by the activation of lignin with KOH. For different contents of KOH relative to carbon, the pore size and specific surface area are highly influenced by the in-plane crystal size of few-layer graphene. The results also manifest the competition between the oxidation of carbon by KOH and the intriguing C#8210;C re-organization provoked by the chemical activation.² In order to assess the influence of material properties on the capacitive response, the carbons better suited to electrolyte characteristics in terms of pore- and ion-sizes were electrochemically characterized in symmetric cells. The third one provides a new procedure for making nanotube electrodes for energy storage applications by using a biscrolling procedure of nanotube sheets from spinnable nanotube forests.³ Generically applicable biscrolling methods are demonstrated for producing yarns comprising up to 99 wt % of otherwise unspinnable nanopowders or nanofibers that remain highly functional. These methods utilize the strength and electronic connectivity of down to 1 wt % of carbon nanotube sheet that is helically scrolled in the yarn. This new technology is used to make yarns of graphene ribbons, high performance battery materials and catalytic nanofibers for fuel cells.
References
1. In-situ generation of metal-metal oxide catalysts for the growth of highly oriented graphitic nanowiggles, Javier Carretero-González, et al. Carbon Volume 68, March 2014, Pages 821-825.
2. Nanoporous carbons from natural lignin: study of structural-textural properties and application to organic-based supercapacitors, Adriana M. Navarro-Suárez, et al. RSC Adv., 2014, 4, 48336-48343.
3. Oriented Graphene Nanoribbon Yarn and Sheet from Aligned Multi-Walled Carbon Nanotube Sheets, Javier Carretero-Gonzalez et al., Adv. Mater. 8 November, 2012, 5695-5701.

High performance and low-cost energy storage devices are the key requirements in the development of a more sustainable energy future. Supercapacitors have been predicted to occupy a larger market share than that of Li-ion rechargeable batteries in the next 10 years, mostly due to superior cycling ability and longer operational life. However, several disadvantages, including much lower energy density, quicker self-discharge and higher cost are threatening their potential commercial usage. Herein, we focus on preparing three-dimensional gridlocked nanostructured carbon electrodes containing single wall carbon nanotubes and graphene sheets, aligned orthogonal to each other, to facilitate both conductivity and improved ion-movement towards enabling high performance electrical double layer capacitor with improved energy densities. The performance is also monitored as a function of various alignment directions that enables tunable porosity and interconnectivity thereby controlling the ensuing electrochemical performances.
Recently, we have developed a three-dimensional gridlocked hierarchical nanostructured carbon electrode containing horizontal multilayer graphene sheets and magnetic field aligned vertical carbon nanotubes, and tested the effectiveness of such electrodes in supercapacitor devices. Carbon slurry composed of activated charcoal, polyvinylidene fluoride (binder), graphene, and single-walled carbon nanotubes was dispersed in dimethylformamide (DMF) and coated upon carbon coated copper foil. Samples were then aligned within a magnetic field and DMF was subsequently evaporated to form the nanostructured electrodes. Fabricated electrodes were assembled into supercapacitor devices using a Swagelok Cell, and performance was tested and evaluated using various electrochemical methods. Our measurements confirm that electrodes containing carbon nanotubes aligned orthogonal to the graphene planes have significantly improved specific capacitance and energy density compared to unaligned samples. The alignment technique also improves columbic efficiency and power density. SEM images and polarized Raman spectra analysis verify the strategically aligned nanoarchitecture design of the carbon electrodes. The aligned carbon nanotubes connect and stitch together horizontal graphene layers creating a grid locked three dimensional network of conductive pathways. The highly porous structure, in combination with enhanced conductivity in the electrodes, has 4x - 10x larger active surface area and superior supercapacitor performance compared to devices with electrodes without the aligned carbon nanotubes.
The electrode alignment technique can also be used for other device applications such as in Li-ion battery, sorbents, catalyst supports for fuel cells, and hydrogen storage systems to improve their performance. Detailed study on the fabrication of the 3D electrode and their performance in supercapacitor devices and as Li-ion battery anode will be presented.

We propose an analytical equivalent circuit model, comprised of both active and passive elements, for nanostructured electrochemical capacitors, (ECs) which can be applied directly to experimental data. Nanostructures are typically considered for ECs in order to increase the surface area of the electrodes (i.e., through the double-layer capacitance, C_dl) and to allow internal and external Faradaic and redox reactions (pseudocapacitance, C_p) [1]. However, the nanostructures also introduce a small density of states (quantum capacitance, C_Q) [2] and a long screening length (space charge capacitance, C_sc). In order to compare with cyclic voltammetry (CV) experiments, we also must consider resistive elements: contact and electrolyte resistance (series resistance, R_se) and leakage resistance (shunt resistance, R_sh), in addition to diffusion associated Warburg impedance. Using a combination of such circuit elements, we describe CV measurements for graphene electrodes subject to plasma processing. We observe that total capacitance C_tot increases and R_sh decreases with plasma processing and attribute these changes to an increased carrier density, which influences almost all of the previously mentioned circuit elements. Consequently, a theoretically postulated C_dl of ~ 20 mu;F/cm² will be shown to be diminished by an order of magnitude to ~ 2 mu;F/cm². However, plasma processing yet serves to enhance the capacitance of the graphene electrodes three-fold, to ~ 5 mu;F/cm². This study thus seeks to divide the relatively complex EC action into several simpler elements dependent on controllable nanostructure properties. [1] H. Yamada and P.R. Bandaru, Appl. Phys. Lett. 104, 213901 (2014). [2] H. Yamada and P. R. Bandaru, Appl. Phys. Lett. 102, 173113 (2013).

Porous carbon materials have attracted tremendous attention due to their high surface area, large pore volume, high electrical conductivity and diverse surface functions. These features are desired for a broad range of applications, such as water purification, gas absorption, catalysts immobilization and energy storage. A major recent interest has been enhancing energy efficiency and reducing fossil fuel dependence by electrochemical energy storage. Although a vast number of porous carbons have been developed for electrode applications, these devices performance are still limited by their moderate energy or power density, mainly due to the lack of effective carbon architecture. Traditional carbon materials, such as activated carbons (ACs) have high surface area but poor control of porosity and pore connectivity, which leads to decreased energy density at high rates due to large diffusion resistance. Carbon nanotubes (CNTs) networks have large open pores for high-rate charge/discharge but their surface area is insufficient to ensure large capacitance. Although other novel carbons were made that show higher specific capacitance than normal ACs through pore size control under sub-nanometer range, the relatively slow ion diffusion in small pores restricts the power performance.
It has been shown that porous carbons having hierarchical pore structure is a viable design to achieve both high surface area and facile transport kinetics. Herein, we report a new type of microporous carbon made through a low temperature pyrolysis process of an intrinsic 3D hierarchical nanostructured polymeric molecular sieve without any sacrificing template. A conducting polymer molecular sieve was converted into porous carbon by thermal annealing; subsequent chemical activation to further increase the carbon surface area and microporosity without structural collapse, which leads to 3D hierarchical porous carbon (HPC). The microporous carbon shows 3D porous network connected by coral-like nanofibers with diameters of ~100 nm. This polymeric molecular sieve template approach offers several advantages over other previously reported synthetic methodology. With the use of specific crosslinker, the porous network structure is easily tuned; moreover, the raw materials are of low cost, together with the simple synthetic technique, this technique offer wide range of tunability, including pore volume and surface area, in addition to heteroatom doping of nitrogen and other types of metal ions, showing promising electrochemical performance of above 200F/g in aqueous electrolyte and comparable gravimetric capacitance in organic electrolyte.