Symposium EN14 : Materials Science and Device Engineering for Safe and Long-Life Electrochemical Energy Storage

Severe safety concerns are currently impeding the large-scale employment of lithium/sodium batteries. Conventional electrolytes are highly flammable and volatile, which may cause catastrophic fires or explosions. Efforts to introduce flame-retardant solvents into the electrolytes have generally resulted in compromised battery performance because those solvents do not suitably passivate carbonaceous anodes. Here we report a salt-concentrated electrolyte design to resolve this dilemma via the formation of a robust inorganic passivation film on the anode. We demonstrate that a concentrated electrolyte using a salt and a popular flame-retardant solvent (trimethyl phosphate), without any additives or soft binders, allows stable charge–discharge cycling of both hard carbon and graphite anodes for more than 1000 cycles (over one year) with negligible degradation; this performance is comparable or superior to that of conventional flammable carbonate electrolytes. The unusual passivation character of the concentrated electrolyte coupled with its fire-extinguishing property contributes to developing safe and long-lasting batteries, unlocking the limit toward development of much higher energy-density batteries.

J. Wang, Y.i Yamada, K. Sodeyama, E. Watanabe, K. Takada, Y. Tateyama, and A. Yamada, Nature Energy (2017)

Developing a high-voltage enabling electrolyte is extremely critical for the success of the next generation high-energy density lithium-ion battery especially for electric vehicles. Material scientists have developed new cathode materials with improved specific capacity [1] and operating voltage (5 V vs. Li⁺/Li).[2] However, designed for a 4V-class lithium-ion chemistry, the conventional electrolyte suffers from oxidation instability on the charge cathode/electrolyte interface at high charging voltages which leads to severe transition metal (TM) dissolution and rapid capacity fading. The voltage instability of electrolyte becomes the bottleneck for the extensive application of the high voltage cathode materials. [2] Thus, new electrolytes with elevated voltage stability has been widely explored. [3]

Here we report a new class of fluorinated electrolyte comprising novel fluorinated sulfones including ((trifluoromethyl)sulfonyl)ethane (FMES), 1-((trifluoromethyl)sulfonyl)propane (FMPS) and 2-((trifluoromethyl)sulfonyl)propane (FMIS). [4] These compounds have been synthesized via new synthetic routes and evaluated as electrolyte materials under high voltage operation. The results indicate that sulfone with α-trifluoromethyl group possesses enhanced oxidative potential and reduced viscosity as compared to the non-fluorinated counterparts. The α-fluorinated sulfones also show enhanced wetting ability with polyolefin separator. A facile synthesis method for a reported sulfone 1,1,1-trifluoro-3-(methylsulfonyl)propane (FPMS) was also developed. With the new reaction method, large quantity of material was obtained and comprehensive evaluation of the properties of FPMS as high voltage electrolyte was performed. Unlike α-fluorinated sulfone, the γ-fluorinated sulfone resemble the property of the non-fluorinated one.
References:
[1] Nyten, A.; Abouimrance, A.; Armand, M.; Gustafsson, T.; Thomas, J. O. Electrochem. Commun., 2005, 7, 156-160; Ellis, B. L.; Makahnoul, R. M.; Makimura, Y.; Toghill, K.; Nazar, L. F. Nat. Mater., 2007, 6, 749-753.

[2] Hu, M.; Pang, X.; Zhou, Z. J. Power Sources, 2013, 237, 229-242; Santhanam, R.; Rambabu, B. J. Power Sources, 2010, 195, 5442-5451.

[3] Meinan He, Chi-Cheung Su, Zhenxing Feng, Li Zeng, Tianpin Wu, Michael J. Bedzyk, Paul Fenter, Yan Wang and Zhengcheng Zhang*. Adv. Energy Mater., 2017, 7, 1700109; Meinan He, Chi-Cheung Su, Cameron Peebles, Zhenxing Feng, Justin G. Connell, Chen Liao, Yan Wang, Ilya A. Shkrob, Zhengcheng Zhang. ACS Appl. Mater. Interface, 2016, 8(18), 11450-11458.Kunduraciz, M.; Amatucci, G.G. J Electrochem. Soc. 2006, 153, A1345-A1352; Wolfenstine, J.; Aleen, J. J. Power Sources, 2005, 142, 389-390.

[4] C-C. Su, M. He, P. C. Redfern, L. A. Curtiss, I. A. Shkrob and Z. Zhang. Energy Environ. Sci., 2017, 10, 900-904.

Aqueous rechargeable batteries provide the safety, robustness, affordability, and environmental friendliness necessary for grid storage and electric vehicle operations, but their adoption is plagued by poor cycle life due to the structural and chemical instability of the anode materials. In this talk I will present quinones as stable anode materials by exploiting their structurally stable ion-coordination charge storage mechanism and chemical inertness towards aqueous electrolytes. Upon rational selection/design of quinone structures, we demonstrate three systems that coupled with industrially established cathodes and electrolytes exhibit long cycle life (up to 3,000 cycles/3,500 h), fast kinetics (20C), high anode specific capacity (up to 200–395 mAh g⁻¹), and several examples of state-of-the-art specific energy/energy density (up to 76–92 Wh kg⁻¹/ 161–208 Wh l⁻¹) for several operational pH values (−1 to 15), charge carrier species (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺), temperature (−35 to 25 °C), and atmosphere (with/without O₂), making them a universal anode approach for any aqueous battery technology.

Although recent efforts have expanded the stability window of aqueous electrolytes from 1.23 V to >3 V, intrinsically safe aqueous batteries still deliver lower energy densities (200 Wh/Kg) when compared with state-of-the-art Li-ion batteries (~400 Wh/Kg). The essential origin for this gap comes from the location of their cathodic stability limit, which situates way above the hydrogen evolution potential at pH~7 (2.62 V vs. Li), thus excluding the use of the most ideal anode materials (graphite, Li metal).
In this work, we resolved this “cathodic challenge” by adopting an “inhomogeneous additive” approach, in which a fluorinated additive immiscible with aqueous electrolyte can be applied on anode surfaces as an interphase precursor coating. The strong hydrophobicity of the precursor minimizes the competitive water reduction during interphase formation, while its own reductive decomposition forms a unique composite interphase consisting of both organic and inorganic fluorides. The effective protection from such an interphase allows these high capacity/low-potential anode materials (graphite, Li metal) to couple with different cathode materials, leading to 4.0 V aqueous LIBs with high efficiency and reversibility. This new class of aqueous LIBs is expected to deliver energy densities approaching those of non-aqueous LIBs, but with extreme safety, environmental-friendliness and even the possibility of adopting flexible and open cell configurations, none of which is available from non-aqueous LIBs.

Conversion reaction that is beyond the intercalation in specific structures has the great potential to higher energy density with a variety of low cost materials. Nevertheless, several critical fundamental issues, such as poor reversibility and stability due to the ever-changing reaction interface, is far from being understood compared with the widely investigated intercalation reactions. How to understand and predict a stable conversion reaction that relays on the reaction interface is extremely important to the material physics and chemistry science and energy storage. In this poster, we will present a new concept of dynamic-equilibrium to stabilize the conversion reactions in rechargeable aqueous Zn battery systems. Our systematical studies in Zn-MnO₂ and Zn-I₂ electrochemical systems indicate that a well combination of appropriate active material and reaction media is important to enable a stable conversion reactions with a dynamic equilibrium of active species at the interface. (Nature Energy, 1, 16039, 2016; ACS Energy Lett, 2, 2674, 2017) In such conversion systems, active species can exchange between the electrode and the reaction media with manageable equilibrium. We believe that the principles for stabilizing the conversion Zn battery system could provide new insight into other conversion systems such as the widely investigated Li-S systems.

Aqueous sodium-ion batteries promise increased operational safety and lower manufacturing cost compared to current state-of-the-art lithium-ion batteries based on organic electrolytes. For large-scale stationary systems, which find increasing application in the grid integration of electricity generated from intermittent renewable sources, these advantages of aqueous electrolyte batteries could translate into lower total cost of ownership compared to organic electrolyte batteries. Sodium-ion batteries are of particular interest, considering that the economically accessible lithium reserves might not be sufficient for a worldwide large-scale adoption of lithium-ion batteries for electric mobility and stationary applications, while the sodium reserves are much larger.
The major disadvantage of water as electrolyte solvent for batteries is its intrinsically narrow electrochemical stability window (thermodynamically only 1.23 V) limiting maximum cell voltage and consequently the battery’s energy density. We recently discovered an aqueous sodium-ion electrolyte system with a much enhanced electrochemical stability window. The wide stability window of 2.6 V for 35m aqueous sodium bis(fluorosulfonyl)imide (NaFSI) solutions broadens the choice of suitable active materials for aqueous sodium-ion batteries. We demonstrate stable cycling of a NaTi₂(PO₄)₃ anode and a Na₃(VOPO₄)₂F cathode in this aqueous electrolyte enabling the fabrication of high-voltage rechargeable aqueous sodium-ion batteries.

R.-S. Kühnel, D. Reber, C. Battaglia, ACS Energy Letters 2017, 2, 2005

In order to keep pace with the increasing energy demands for advanced electronic devices and to achieve commercialization of electric vehicles (EVs) and energy storage systems (ESSs), improvements in high energy battery technology are required. Among the various types of the batteries, lithium ion batteries (LIBs) are considered to be among the most well-developed and commercialized energy storage systems. In this context, LIBs with Si anodes and Ni-rich cathodes have been receiving attention as one of the most promising alternative electrode materials for next-generation high energy batteries. Si-based anode and Ni-rich cathode materials exhibit high reversible capacities of < 2000 mAh/g and > 195 mAh/g, respectively. However, both of these materials have intrinsic drawbacks and practical limitations that prevent them from being utilized directly as active materials in high energy LIBs. Examples of such intrinsic drawbacks for the Ni-rich materials include particle pulverization during cycling and side reactions caused by the electrolyte at the surface, whereas in this case of Si, large volume changes during cycling and low conductivity are observed. Recent progress and some important approaches that have been adopted for overcoming and alleviating these drawbacks are systematically will be discussed.

Perovskites are versatile structures with an impressive range of applications due to their exotic physical properties including ferroelectric, dielectric, pyroelectric, and piezoelectric behaviors. This versatility is due to their robust framework, which allows multiple combinations of different cations and anions in the structure. Despite this, the use of perovskites in lithium-ion batteries has been very limited with only a few reports existing such as lithium lanthanum titanate as a fast lithium conductor and lithium lanthanum niobate as an insertion electrode. Introduction of a second cation on the B-site can produce complex structures containing two different B-site cations, and if these two cations on the B-site order along the crystal then the lattice parameter doubles in size giving rise to a so-called double perovskite structure. Here I will present our latest findings on a series of lithium-rich double perovskites as a new class of materials for all solid state lithium ion batteries, which display excellent stability and electrochemical performance. The perovskite structure is famously amenable to chemical and structural adjustment and by taking advantage of this we propose a new class of perovskite lithium cathode materials. I will present our comprehensive study of these materials using X-ray and neutron diffraction, total scattering, X-ray absorption analysis, impedance spectroscopy, muon spin relaxation measurements and their electrochemical evaluation in lithium ion battery cells. I will show that the combination of lithium mobility along with a redox active metal in a high oxidation state allows electrochemical deintercalation of lithium to provide a new class of electrode materials for lithium batteries.

Coating Al₂O₃ on the surface of cathodes can effectively prevent the chemical and structural evolutions during Li-ion battery operations, and therefore can improve the lifetime of cathode materials in Li-ion batteries. However, there is still a lack of systematic investigations of the cathode compositional effects on the Al₂O₃ coatings, which could bring very different interfacial structures and electrochemical performance to different cathode materials after coating. In this work, we used a wet-chemical method to synthesize a series of Al₂O₃-coated LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532), LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622), and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811), with various Al₂O₃ loadings and annealing conditions. Using nuclear magnetic resonance, electron microscopy and high-resolution X-ray diffraction techniques, we have shown that the structural and chemical evolutions of the surface coatings are highly dependent on annealing temperatures and cathode compositions. On all tested particles, higher annealing temperature leads to more homogeneous and more closely attached coating on cathode materials with the formation of LiAlO₂ phase. Meanwhile, we discovered that the decreasing Mn content facilitates the diffusion of surface aluminum into the bulk after high-temperature annealing, leading to a transfer from surface coating to bulk dopant, which is confirmed by local Al chemical environment evolution, local lattice distortion, and surface morphology change. Additionally, we observed the surface Co segregation in pristine NMC particles, which is found to have a critical influence on the chemical environment of the diffused aluminum. Density functional theory calculations indicate that the incompatibility between Mn and Al could be the reason of the composition dependence of surface Al insertion after the high-temperature annealing. Finally, we demonstrate that the diffusion of Al into the bulk leads to poor cyclability in the charging-discharging process, indicating the importance of the coating-cathode compatibility to the electrochemical performance of coated cathodes. This work is important to the development of better coating methods for the next generation cathode materials in Li-ion batteries with a longer lifetime.

Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis and long-term voltage fade, that currently prevent the commercial application of these promising electrode materials. Mitigating these behaviors requires an understanding of the anion redox mechanism and its role in governing the unique electrochemistry of lithium-rich materials. Here we reveal that in Li_1.17-xNi_0.21Co_0.08Mn_0.54O₂, these electrochemical properties arise from a strong coupling between anion redox and cation migration, which dynamically modulates the anion redox potential during cycling. We combine scanning transmission X-ray microscopy with resonant inelastic X-ray scattering to definitively show that a significant electronic state reshuffling occurs in the material bulk after states with predominantly O_2p character are depopulated during the first charge voltage plateau, while oxygen evolution occurs only at the primary particle surfaces. In conjunction with local and average structure probes we show that this reshuffling is linked to transition metal migration during the high voltage plateau, which decreases the potential of the bulk oxygen redox couple by > 1 V during subsequent discharge, leading to a novel switch in the relative anionic and cationic redox potentials. First-principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration, which shifts the depopulated O_2p states to higher energy relative to the transition metal 3d states. We propose the following anion redox mechanism: {O^2– + TM} → {O^– + TM_mig} + e^–, where TM and TM_mig indicate a transition metal before and after migration, respectively, which holistically explains the spectroscopic, structural, and electrochemical properties of anion redox in this material. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles. These insights provide opportunities to tune oxygen redox chemistry through control of the structural evolution of Li-rich materials.

Silicon has received significant attention as a viable alternative to graphitic carbon as the negative electrode in lithium-ion batteries due to its high capacity and availability. Significant problems exist in the utilization of silicon as an anode material. The common issues are volume change on cycling and the apparent inability to form a dense stabile solid electrolyte interphase, on silicon, have been issues many researchers have looked at in recent years. While significant advances have been made no universal solution to the stability of the silicon anode has developed. More recently it has become apparent that substantial lifetime issues exist in cells with silicon anodes even when not cycling. This raises major questions as to the parasitic reactions that occur at the silicon anode. This talk will focus on the challenges that are faced in the development of silicon anodes for lithium ion batteries and how the SEISta team, a consortium of researchers from 5 national labs (NREL, SNL, ANL,ORNL and LBNL) are approaching the problem.

Co-intercalation chemistry using sodium and potassium ions enable charge storage in graphite electrodes for alternative-ion battery chemistries. Using linear ether solvents (glymes) allows for reversible insertion and de-insertion of alkali ions coordinated by a glyme molecule into graphite electrodes. This unique chemistry boasts increased ion diffusivity in graphitic carbons while generating a large volume expansion (>250%). These unique features allow exploitation of this co-intercalation chemistry in systems ranging from low-power nano- and micro- actuators and energy harvesters to high rate batteries (>10 C with energy densities ~100 Wh/kg), which rival commercial supercapacitors. These results prove the viability of alternative-ion co-intercalation based batteries for use in low-cost, high-power applications.

In recent times, the research community engaged in significant efforts to explore the use of silicon-carbon nanoarchitectures as Li-ion battery anode active materials with the goal of overcoming the limited energy storage capacity of the state-of-the-art graphite-based devices. [1] The small size of the silicon -Si- structures tackles the large volume expansion undergone by the semiconductor upon lithiation, which causes pulverization of bulk Si electrodes, and promotes a robust cycling. The carbonaceous coatings, on the other hand, improves the electrical conductivity of the composite and prevent the direct interaction of Si with the electrolyte, which in turn assists the formation of a stable SEI. Although a wide range of different Si nanomaterial morphologies and their composites have been investigated, the use of commercial silicon nanoparticles -NPs- with a simple and high-quality carbon surface coating would be a highly-desirable solution for an immediate introduction into actual manufacturing. In this contribution, we describe a facile approach based on a chemical-vapor-deposition (CVD) process to address the problem. Commercial Si nanocrystals with an average size of 100 nm and low oxygen content (below 3% in weight) are introduced into a furnace with an alumina combustion boat. The particles are wrapped with a conformal coating of amorphous carbon resulting from the dissociation of acetylene - C₂H₂ - at 650 °C. After removing C₂H₂ from the reaction zone, the furnace is ramped up to 1000°C in Argon yielding a controlled graphitization of the carbon -C- shell. Correspondingly, the Raman analysis of the synthetized composite displays an increase in the ratio of intensity of the D an G peak from 0.7 to 1.4, while the onset of well-defined layered graphitic planes with no detectable silicon-carbide signature is observed from TEM and XRD analysis.[2] Notably, the presented approach does not deploy oxidizing agents during the thermal process, which are instead required for the formation of ordered graphitic shells in the case of a high-temperature methane CVD, hence preventing the detrimental formation of silicon oxide species. [2] The produced nanomaterials were introduced in slurry with no addition of conductive additives, coated onto a copper substrate and studied as anode material in a Li-ion battery half-cell assembly. The amorphous-carbon-coated Si particles, fabricated with the 650°C C₂H₂ CVD process, shows a first cycle coulombic efficiency – CE - of 85% and capacity of 1600 mAh g^-1. The graphitization of the NP carbon shell, achieved through the high-temperature step in Argon, further boosts the electrode performance, reaching a first cycle CE and capacity values of 88% and 2100 mAh g^-1 respectively, on a par with some of the best silicon-carbon architectures reported in the literature. [1]

[1] F. Luo et al, Journal of The Electrochemical Society, 162 (14) A2509-A2528, 2015
[2] I. H. Son et al., Small, 12 (5), 658–667, 2016

Silicon suboxide is one of the promising anode materials for lithium-ion batteries (LIBs) due to its high specific capacity, low operating voltage (less than 0.4 V) and rich abundance. The SiO_x electrode produces inert components (lithium oxide and lithium silicate) and nano-Si particles during initial lithiation/delithiation process. The former can act as buffer matrix to significantly reduce the volume change of nano-sized Si. Therefore, compared to pure Si, the SiO_x electrode shows relatively good cycling stability and thus appears promising for high energy density Li-ion batteries. Nevertheless, the poor intrinsic electronic and ionic conductivity of SiO_x often leads to a low specific capacity and inferior rate capability. In addition, the SiO_x electrode cannot withstand long-period cycling due to the inevitable volume variation of SiO_x.
In this work, we prepared SiO_x-TiO₂/C nanoparticles with unique watermelon-like structured by a simple sol-gel combined with a following carbon coating process. Ultrafine TiO₂ nanocrystals are homogeneously distributed inside SiO_x particles, forming SiO_x-TiO₂ dual-phase cores, which are coated with outer carbon shells. The incorporation of TiO₂ component can effectively enhance the electronic and lithium ionic conductivities, release the structure stress caused by alloying/dealloying of Si component and maximize the capacity utilization by decreasing the O/Si ratio (x value). The synergetic combination of these advantages enables the synthesized SiO_x-TiO₂@C nanocomposite to have outstanding electrochemical performances, including high specific capacity, excellent rate capability and stable long term cycleability. A stable specific capacity of ~910 mAh g^-1 is achieved after 200 cycles at the current density of 0.1 A g^-1 . These results suggest the synthesized SiO_x-TiO₂/C composite is a promising high performance anode material for lithium ion batteries.

The electrochemical performance of transition metal oxides (TMOs) electrodes for lithium-ion batteries (LIBs) has been hindered by their instability in electrochemical performance and lack of durability. In this research, a novel hierarchical micro-electrode for LIBs is successfully designed and fabricated. Anatase TiO₂ nanoparticles of ~100 nm are synthesized through a simple one-step wet-chemical method at elevated temperature. The Cu/Ni current collector with vertically-aligned Ni micro-channels is designed to support the TiO₂ active material. Electrochemical characterization revealed that such electrode has promising performance referring to enhanced capacity, reliable rate compatibility, and durable cyclic stability. The maximum insertion coefficient for the Li ion intercalation reaction is determined as ~0.85, which is one of the highest values for anatase anode of LIBs. Meanwhile, cross-sectional electron microscopic imaging along with X-ray energy dispersive spectroscopic elemental analysis validated the uniform spatial distribution of TiO₂ nanoparticles inside the Ni micro-channels throughout cycling. Synergistic effect between nano-TiO₂ active material and porous Cu/Ni current collector is the main cause. The favorable properties of the Cu/Ni/TiO₂ anode are improved electrochemical reactivity, reduced lithium ion diffusion pathways, great specific surface area, effective buffering of volume changes of TiO₂ nanoparticles, and the optimal paths for chargers transport.

Antimony is one of the most promising high-rate-capability Na- and Li-ion conversion electrode materials, demonstrating extraordinarily high rates of lithiation and sodiation, with small isotropic Sb nanocrystals exhibiting stable, reversible, long-term cycling at charge/discharge rates as fast as 20C without significant capacity loss. Herein, we investigate the effect of structural anisotropy on the lithiation and sodiation of high-capacity, high-power density Sb alloying electrodes fabricated from an engineered set of highly anisotropic Sb nanostructures recently developed by our laboratory. To our knowledge, none of these anisotropic structures have been previously reported in the literature, or evaluated as alloying electrode materials. In addition to describing the supercritical fluid-based synthesis of these anisotropic Sb nanostructures, we discuss how structural anisotropy, oxidation, and temperature influence the electrochemical alloying process, with an overarching goal of better understanding the transformations that take place during the high-rate electrochemical alloying of nanostructured antimony.

Increasing the energy density of the lithium-ion battery (LIB) is necessary to meet the demands for their expanding applications from portable electronics to large-scale emerging applications, such as renewable energy storage grids and electric vehicles that require acceptable driving distance upon a single charging. Among many candidates that can increase the energy density of anode, silicon (Si) is extremely compelling due to its high theoretical capacity (3579 mAh/g for Si compared to 372 mAh/g for commercial graphite anode), low operating potential, non-toxicity and worldwide abundance. However, the high specific capacity of the silicon-based electrode is typically observed only at the initial cycles, and cannot meet the long cycle life required for typical electric vehicle application. Utilization of polymeric material to hold active materials intact is a conventional approach, and the polymer binder plays even more significant role in the cell performance of the silicon-based electrodes because of their enormous volume changes during electrochemical cycling. In this presentation, two novel polymer binders for Si anode will be discussed. The first work investigated the architecture effect of synthetic polymers on the polymer binder performance for the high-mass loading silicon(15wt%)/graphite(73wt%) composite electrode (active materials > 2.5 mg/cm²). With the same chemical composition and functional-group ratio, the graft block copolymer reveals improved cycling performance in both capacity retention (495mAh/g vs 356 mAh/g at 100th cycle) and coulombic efficiency (90.3% vs 88.1% at 1^st cycle) than the physical mixing of glycol chitosan (GC) and lithium polyacrylate (LiPAA). Galvanostatic results also demonstrate the significant impacts of different architecture parameters of graft copolymers, including grafting density and side chain length, on their ultimate binder performance. By simply changing the side chain length of GC-g-LiPAA, the retaining de-lithiation capacity after 100 cycles varies from 347 mAh/g to 495 mAh/g. The second approach further tailored the functionality and architecture of the polymer binder. By incorporating catechol groups and balancing subsequent crosslinking of the chitosans, the polymer binder possesses both interaction with silicon materials and mechanical robustness to withstand the volume change during charging/discharging process. The degree of functionality and cross-link was systematically studied and optimized. The obtained polymer binders enable the Si-based anode to maintain the high long-term cycling stability, i.e., the retaining de-lithiation capacity after 100 cycles is 2269 mAh/g (90% capacity retaining). This presentation will discuss the design of polymer binders for Si-anode and the effect of various parameters including compositions, interactions, and mechanical properties.

Because of its lightweight, out-standing energy density, and well cycling stability, lithium-ion batteries (LIBs) are widely utilized in portable devices and electric vehicles (EVs). Researchers have intensively studied low-cost, high-storage capacity, and safe electrode materials for LIBs. Graphite is the most widely used commercial anode material, but its low theoretical capacity (372 mA h g^-1) restricts its application in high-energy-density devices. Lithium-titanium–based insertion materials possess excellent cycle life and high rate capability but suffer from low capacity (< 200 mA h g^-1) and high electrical resistivity. Silicon-based alloy materials and transition-metal-oxide-based conversion materials exhibit high capacity over 1000 mA h g^-1, but severe volume changes during charging/discharging processes lead to fast capacity fading.
Herein, we report a Mo-Fe-mixed Keplerate polyoxometalate (POM), a kind of Fullerene-like metal oxide clusters which was synthesized through a simple solution process as anode material for LIBs. Because of various oxidation states of Mo and Fe , the multiple redox centers within Mo-Fe-mixed POM during charge-discharge processes result in high capacity and excellent cycling stability. These results demonstrate that Fullerene-like Mo-Fe-mixed POM is a promising anode material for LIBs.

2D layered metal chalcogenides have displayed extraordinary properties that have put them on the forefront of various applications as promising catalysts, sensors, electrochromic devices, and electric actuators. Specifically, metal chalcogenides such as titanium (IV) sulfide (TiS₂), has been identified as a promising low cost cathode for rechargeable batteries. TiS₂ can exhibit specific capacities with a completely lithium-intercalated Li_xTiS₂ (x = 1) as high as 238 mAhg^-1. The electrochemical performance of bulk TiS₂ cathodes has been hindered by its low ion diffusion coefficient and moderate electrical conductivity. To overcome these challenges, bulk TiS₂ cathodes are mixed with conductive additives (typically carbon) and polymer binders (typically polyvinylidene fluoride -PVDF) to yield a paste that is finally cast onto a current collector. However, the electrochemical performance of the electrode is lowered due to the extra weight of all the inactive components (i.e., additives, polymer binder, and metal substrates) introduced during the fabrication. An alternative to the use of pasted electrodes is the direct growth of well-defined nanostructures on a conducting substrate. In this work, we report the synthesis, characterization, and electrochemical performance of carbon- and binder-free cathodes comprised of highly conducting TiS₂ nanobelts. The short ion diffusion paths, high electrical conductivity and absence of materials that hinder ion migration such as carbon and PVDF have led to Li-ion and Na-ion batteries exhibiting high capacity, less capacity fade, and resilience under higher cycling rates. Moreover, key to developing new secondary battery systems is multielectron reactions involving more than one electron transfer, which may lead to higher specific capacity and energy density. Herein, we will discuss our recent findings towards rechargeable aluminum batteries comprising carbon- and binder-free TiS₂ cathode electrodes. Finally, we will also discuss preliminary results that demonstrate high electrochemical performance of carbon- and binder-free TiS₂ electrodes in all-solid state ion batteries.

Lithium-ion batteries (LIBs) which have high energy density and light weight are widely used in portable devices such as cell phones, laptops, etc. However, the increasing price of lithium resources limits the applications of LIBs for large-scale energy storage systems. Sodium-ion batteries (NIBs) have been proposed as a promising candidate for large-scale energy storage systems because of the abundance and low cost of sodium resources. Several NIB cathode materials have been developed in recent years, and P2-type transition metal oxides (NaT_MO₂, T_M = Ti, V, Cr, Mn, Fe, Co, Ni) have attracted much attention because of their special layered structures which provide large space to storage Na ions thus lead to high specific capacity.
In this study, Na_0.5Mn_xFe_yNi_(1-x-y)O₂ was utilized as cathode material for NIBs because of the abundance and nontoxicity of those transition metals. Furthermore, effects of metal doping on Na_0.5Mn_xFe_yNi_(1-x-y)O₂ were also investigated. Na_0.5Mn_xFe_yNi_(1-x-y)O₂ and its metal doing were synthesized through a facile co-precipitation method followed by heat treatment. The metal-doped Na_0.5Mn_xFe_yNi_(1-x-y)O₂ exhibited high specific capacity as well as good cycling stability, demonstrating this NIB cathode material is suitable for large-scale energy storage applications.

Aluminum-based batteries hold great promise for low-cost and large-scale stationary storage of electricity. This notion has led a surge of reports on novel batteries comprising exclusively highly abundant chemical elements.^[1] In this work, we demonstrate that the synthetic kish graphite, a large-scale byproduct of steel-making, can be used as a cathode in such aluminum chloride−graphite batteries (AlCl₃−GBs), exhibiting high cathodic charge-storage capacities of up to 142 mAh g^-1.

Comprehensive characterization of kish graphite flakes and of other kinds of graphite by X-ray diffraction, Raman spectroscopy and BET surface area analysis led us to the conclusion that the superior performance of the kish graphite is rooted into a high structural perfection of such graphite, low level of defects and its unique “crater morphology”. In view of non-rocking chair mechanism of AlCl₃-GB and strong dependency of chloroaluminate ionic liquid composition on its energy density, in this work, we also demonstrate that kish graphite flakes enable to provide the density of 65 Wh kg^-1(highest so far for such Al-based batteries) by applying 2:1 (AlCl₃:EMIMCl) ionic liquid molar ratio, which compare very favorably with other battery electrochemistry suited for stationary storage of electricity (such as lead-acid or vanadium redox flow).^[2] In addition, kish graphite flakes show the unique ability for fast charge and discharge delivering a high power density of 4363 W kg^-1 for AlCl₃-GB, in this regard, they considerably surpass the natural graphite flakes.^{[3], [4]}

[1] M.-C. Lin, M. Gong, B. Lu, Y. Wu, D.-Y. Wang, M. Guan, M. Angell, C. Chen, J. Yang, B.-J. Hwang, H. Dai, Nature, 520, (2015)324-328.
[2] S. Wang, K. V. Kravchyk, F. Krumeich, M. V. Kovalenko, ACS Appl. Mater. Interfaces, 9, (2017)28478-28485.
[3] K. V. Kravchyk, S. Wang, L. Piveteau, M. V. Kovalenko, Chem. Mater., 29, (2017)4484-4492.
[4] D. Y. Wang, C. Y. Wei, M. C. Lin, C. J. Pan, H. L. Chou, H. A. Chen, M. Gong, Y. P. Wu, C. Z. Yuan, M. Angell, Y. J. Hsieh, Y. H. Chen, C. Y. Wen, C. W. Chen, B. J. Hwang, C. C. Chen, H. J. Dai, Nat. Commun., 8, (2017)7.

A layered SnS₂ /reduced graphene oxide (SnS₂/RGO) composite is prepared by a facile, one-step microwave-assisted method, and evaluated as an anode material for sodium-ion batteries (SIBs). The influence of the ratio of Sn4+ to RGO on the composition, micro-structure and morphology of products, doping effect of other atoms (e.g., cobalt), as well as its electrochemical performance as an anode material of Na-ion batteries was systematically investigated. The as-prepared SnS2/RGO composite exhibits an excellent reversible capacity of 703 mAh g-1 after 50 cycles under a current density of 50 mA g-1, whereas SnS2 particles show a capacity below 150 mAh g-1 after the 2nd cycle. The kinetics of the sodiation/desodiation for SnS2/RGO was also studied. The accelerated Na+ kinetics is believed to be beneficial to the electrochemical performance, especially the rate performance of the anode materials. When the current density is increased to 2A g-1, the SnS2/RGO still keeps a high capacity of 300 mAh g-1. This work demonstrates an efficient method to grow SnS₂ nanocrystals directly on graphene substrate, which can be used to prepare various kinds of layered metal dichalcogenides/RGO composites as high-performance anode materials for SIBs.

LiNi_xMn_yCo_zO₂ (NMC) is the current choice of the cathode for high-performance Li-ion batteries. The structural and mechanical stability of NMC plays a vital role in determining the electrochemical performance of batteries. However, the dynamic mechanical properties of NMC during Li reactions are widely unknown because of the microscopic heterogeneity of composite electrodes as well as the challenge of mechanical measurement for air-sensitive battery materials. We employ instrumented nanoindentation in an inert environment to measure the elastic modulus, hardness, and interfacial fracture strength of The results are further compared with the properties of bulk NMC pellets. We perform first-principles theoretical modeling to understand the evolution of the elastic property of NMC on the basis of the electronic structure. This work presents the first time systematic mechanical measurement of NMC electrodes which characterizes damage accumulation in battery materials over cycles.

Vanadium Pentoxide (V₂O₅) has been identified as a potential cathode material owning to its high specific capacity, theoretically, 441 mAh g^-1 for 3Li⁺ ions insertion/extraction and 294 mAh g^-1 for 2Li⁺ ion insertion/extraction. However, the intrinsic drawbacks of V₂O₅, i.e. structural instability and poor electric and ionic conductivity, greatly inhibit the access of full capacity as well as the cycling and rate performance of this material. Here, we report a CTAB-assisted hydrothermal reaction to synthesize V₂O₅ clusters with nanofeatures. Unique porous fiber structure was obtained by assembly of tiny V₂O₅ nanoparticles, however, the fibers were aggregated into unfavorable bundles after thermal annealing. To achieve a dispersed structure and increase the conductivity, nitrogen-doped Graphene (NG) suspended in ethylene glycol was added to the reactant mixture. The obtained spherical V₂O₅ particles have similar assembled nanofeatures, and NG sheets are randomly intercalated into the matrix of V₂O₅ spheres. As cathode material in lithium ion battery, the V₂O₅/NG hybrids perform 2Li⁺ ion storage and demonstrate better cycling and rate performance compared to the bundle-like V₂O₅ fibers, delivering higher specific capacity of around 300 and 150 mAh g^-1 at a rate of C/10 and 5C, respectively. The enhanced performance in electrical energy storage are attributed to the synergistic effect of the nanostructured V₂O₅/NG composites.

Lithium-sulfur batteries represent a promising candidate for advanced rechargeable batteries with high energy density and long cycling lifetime. Although extensive efforts have been devoted to the research and development of mediators for sulfur cathodes to enhance its redox kinetics, their working mechanism is still a mystery. Further advancement in lithium-sulfur batteries requires a more fundamental understanding of its electrochemical properties and processes. We report herein some mechanistic insights into the electronic structures of active materials and various mediators (e.g., metal oxides, metal sulfides, metal carbides), as well as their interactions. This work offers not only an effective strategy to achieve fast redox kinetics in lithium-sulfur batteries, but also guidelines for future material design.

This study reports a high-performance tin (Sn)-coated vertically aligned carbon nanofiber array anode for lithium-ion batteries. The array electrodes has been prepared by coaxially sputter-coating of tin (Sn) shells on vertically aligned carbon nanofiber (VACNF) cores. The robust brush-like highly conductive VACNFs effectively connect high-capacity tin shells for lithium-ion storage. A high specific capacity of 800 mAh g^-1 of Sn was obtained at C/5 rate, reaching to the maximum value of amorphous Sn. However, the electrode shows poor cycling performance with conventional LiPF₆ based electrolyte. The addition of fluoroethylene carbonate (FEC) improve the performance significantly and Sn-coated VACNFs anode shows stable cycling performance. The Sn-coated VACNF array anodes exhibit outstanding capacity retention in the half-cell tests with electrolyte containing 10% of added FEC and could deliver a reversible capacity of 600 mAh g^-1 after 50 cycles at 0.5 C rate.

Lithium sulfide (Li₂S) is one of the most attractive cathode material for high energy density lithium batteries as it has high theoretical capacity of 1167 mA h g^-1. Also, this is a promising cathode material for the next-generation advanced lithium-ion batteries as it allows for the use of lithium-free metal-based high capacity Li-ion anodes (such as silicon anode etc.) and has large energy density to match with high capacity metal anodes. However, Li₂S suffers from poor rate performance and short cycle life due to its insulating nature and polysulfide shuttle during cycling. In this work, we reports a facile and viable approach to address these issues. We proposes a method to synthesize Li₂S based nanocomposite cathode material by dissolving Li₂S as the active material, polyvinylpyrrolidone (PVP) as the carbon precursor, and graphene oxide as matrix to enhance the conductivity, followed by a co-precipitation and high-temperature carbonization process. The Li₂S/rGO cathode yields an exceptionally high initial capacity of 858 mAh g^-1 based on Li₂S mass at 0.1C rate and also shows a stable cycling performance. The carbon coated Li₂S/rGO cathode demonstrates the capability of robust core-shell nanostructures for different rates and improved capacity retention, revealing carbon coated Li₂S/rGO designed as an outstanding system for high-performance lithium-sulfur batteries.

A carbon host capable of effectively and uniformly incorporating a high sulfur content is the key to the development of lithium-sulfur batteries (LSB). This study exhibits carbon nanotube microparticle as a sulfur host of a LSB cathode. Due to the macropores, our macroporous CNTPs achieved uniform sulfur infilteration without sulfur residue. Additionally, the macropores enhanced the micropore fraction and thereby improved the sulfur confinement. Our cathode showed a high reversible capacity of approximately 1300 m/g at a current density of 0.2 C even at a high sulfur content of 70 wt%. A high capacity retention of 74% was observed with a 10-fold current density increase.

Intercalation cathode materials are mature and the main commercialized cathodes for lithium-ion batteries in the market. However, presently only one Li ion is involved in the electrochemical reaction, which limits the accessible capacity to < 200 Ah kg^-1. This limits the application of lithium-ion batteries in a variety of applications, including electric vehicles. To get higher energy density, one way is using high-voltage cathode materials, but this generally requires a compatible stable high-voltage electrolyte to get the full capacity, which is very challenging. A feasible way to increase the capacity and energy density of Li-ion batteries is to find a material that can incorporate more than one lithium ion within the voltage window of current electrolyte systems. Li_xVOPO₄ is a strong candidate, which can reversibly react two lithiums at about 4.0V and 2.5 V and has a theoretical capacity > 300 Ah kg^-1 and energy density > 1000 Wh kg^-1. Our group has conducted many studies on this material and already proved that good electrochemical performance can be obtained for different LiVOPO₄ phases synthesized through various methods. However, these samples have large particles and high energy ball milling with carbon was required to decrease particle size and achieve good electrochemistry. Yet, the ball milling destroyed the crystallinity of the sample, creating highly sloped discharge curves which lowers the energy density. Consequently, direct nano-synthesis of LiVOPO₄ is needed to produce good electrochemistry and high energy density.
Here, a novel polyol-mediated synthesis was first proposed by us to synthesize nanocrystalline triclinic LiVOPO₄. This synthetic method is capable of producing particles smaller than 50nm in diameter without ball milling post treatment. Presently, a very good electrochemical performance was attained from our preliminary test: a reversible capacity above 300 Ah kg^-1 was obtained at 0.04C, close to the theoretical capacity of 318 Ah kg^-1; at 0.5C a capacity around 200 Ah kg^-1 was still obtained. More characterizations and further optimization is in progress, and will be presented in the meeting. This work is supported by NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012583.

Li-S batteries has a theoretic energy density of 2510 Wh/kg and 2740 Wh/L, which is one of the most promising candidates for the next generation rechargeable batteries ¹. Despite the great merits of the Li-S batteries such as high energy density and low cost, challenges, including polysulfide anions redox² and low lithium cycling efficiency, hinder its commercialization.
There has been great research effort devoted to the optimization of sulfur electrodes, the formulations of electrolytes as well as the ratios of electrolyte to sulfur. In this talk, we will address the impact of sulfur electrode porosity on the energy density of Li-S battery and the influence of electrolyte/sulfur ratio on the Li-S battery performance.
Based on our preliminary results, at sulfur loading of 3mAh/cm², when the porosity of sulfur electrode reduced from 70% to 50%, the energy density of Li-S battery (n/p=2) will increase from 380 Wh/kg and 400 Wh/L to 510 Wh/kg and 530 Wh/L, respectively.
Furthermore, the cycling efficiency of lithium will be discussed in this talk with different electrolyte formulations.

1) A. Manthiram, Y. Fu, S. Chung, C. Zu, Y. Su, Rechargeable Lithium–Sulfur Batteries, Chem. Rev., 2014, 114 (23), pp 11751–11787
2) SS Zhang, Improved Cyclability of Liquid Electrolyte Lithium/Sulfur Batteries by Optimizing Electrolyte/Sulfur Ratio, Energies 2012, 5, 5190-5197

Lithium-sulfur battery represents one of the most promising candidates for electric vehicles. However, its slow electrochemical kinetics and the shuttling of polysulfides between two electrodes have hindered its practical applications for years. Although numerous materials (e.g., metal oxides, metal sulfides, metal carbides) have been identified as efficient adsorbents or mediators for sulfur cathodes, the fundamental understanding of their working mechanisms is still missing. Based on the electronic structures, we thoroughly studied the interactions between various adsorbents and polysulfides, investigated the working principles of mediators, and rationally designed a hybrid sulfur cathode with fast redox kinetics. This work provides not only an effective strategy to achieve longer cycling lifetime and better rate performance, but also a clear design principle for advanced lithium-sulfur batteries.

Lithium–sulfur (Li–S) battery is one of the most promising candidates for next-generation secondary batteries. However, the practical application of Li–S battery is hindered by many scientific and technical obstacles. Many of them originate from the well-known shuttle effect induced by lithium polysulfides (LiPSs). LiPSs, as naturally produced intermediates, are prone to dissolve in organic electrolytes. Their polar nature prevents not only effective entrapment of LiPSs within the cathode but also efficient charge transfer between them and conductive scaffolds, which are normally nonpolar carbon. Thus, one of the most formidable challenges is the sluggish kinetics of LiPS redox reactions, which further results in low sulfur utilization and capacity fading.

To overcome the challenge, rational design of sulfur hosts emerges as one of the most effective approaches, which simultaneously enables strong LiPS adsorption, fast interfacial charge transfer, enhanced electrochemical kinetics, and/or efficient electrocatalysis. In this contribution, we start with a concept of self-healing Li–S batteries, by which the underlying mechanism based on solution–solid nucleation/growth theory and its correlation to spatial homogeneity of LiPS concentration are revealed. Guided by this understanding, we demonstrate a variety of nanocarbon (i.e., graphene and carbon nanotubes)-supported hybrid materials, including transition metal carbides, borates, hydroxides, and sulfides, as well as nanostructured polymer, to realize fast LiPS redox reactions and controlled nucleation/growth of solid products. These rationally designed sulfur hosts render Li–S batteries with superb electrochemical performance. We believe that the understanding of LiPS-involving reactions and design principles will create considerable opportunities to develop high-performance Li–S batteries.

References
[1] Peng, H. J.; Zhang, Q. Angew. Chem. Int. Ed. 2015, 54, 11018
[2] Peng, H. J.; Huang, J. Q.; Cheng, X. B.;et al. Adv. Energy Mater. 2017, 7, 201700260
[3] Peng, H. J.; Huang, J. Q.; Zhang, Q. Chem. Soc. Rev. 2017, 46, 5237
[4] Yuan, Z.;¹ Peng, H. J.;¹ Hou, T. Z.;¹ et al. Nano Lett. 2016, 16, 519
[5] Peng, H. J.;¹ Zhang, G.;¹ Chen, X.; et al. Angew. Chem. Int. Ed. 2016, 55, 12990
[6] Peng, H. J.;¹ Zhang, Z. W.;¹ Huang, J. Q.; et al. Adv. Mater. 2016, 28, 9551
[7] Peng, H. J.; Huang, J. Q.; Liu, X. Y.; et al. J. Am. Chem. Soc. 2017, 139, 8458
[8] Chen, C. Y.;¹ Peng, H. J.;¹ Hou, T. Z.;¹ et al. Adv. Mater. 2017, 29, 1606802
[9] Chen, X.;¹ Peng, H. J.;¹ Zhang, R.; et al. ACS Energy Lett. 2017, 2, 795
[10] Kong, L.;¹ Peng, H. J.;¹ Huang, J. Q.; et al. Energy Storage Mater. 2017, 8, 153

Emerging technologies are becoming increasingly advanced, requiring flexible components and their integration into various miniaturized interfaces such as for rollable displays, wearable technologies and e-textiles. As a result, there is a need for a fully flexible battery with high energy storage capacity that is simple and cost effective. In this work we demonstrate a simple route to producing flexible lithium-sulfur batteries. An adaptation to the well-established laser-scribing method to convert commercial polymer films into a patterned graphene-like electrode is used. The laser-induced graphene cathode and anode are patterned sequentially to create a 2D interdigitated structure. We show that, after the first laser pass, sulfur can be deposited selectively on the electrode through heterogeneous nucleation followed by melt imbibition. The other set of electrodes fingers are scribed to form the anode, followed by a deposition of silver nanoparticles to be used as seeds for lithium nucleation. A reverse pulse plating technique is adopted for the deposition of a smooth, dendrite-free lithium anode at a relatively high current density of 1 mA/cm². Lastly, an ionogel with a polysulfide-scavenger is applied onto the electrode fingers for the completion of a fully flexible device containing an electrolyte matrix rich with polar groups to capture and prevent the migration of polysulfides to the anode in order to maximize capacity retention over the life of the cell. Preliminary work shows that the novel method of sulfur deposition can yield uniform films of over the entire electrode and obtaining practical loadings of up to 3 mg/cm². Initial cycling shows that the battery can achieve an energy density as high as 196.9 mWh/cm³, which exceeds that of most published reports on lithium-ion microbatteries produced through nano-templating and microfabrication techniques.

Solid state electrolytes are known for non-flammability, dendrite blocking, and stability over large potential windows. Garnet-based solid-state electrolytes have attracted much attention for their high ionic conductivities and stability with lithium metal anodes. However, high interface resistance with lithium anodes hinders their application to lithium metal batteries. In this talk, I will discuss the following aspects of our advanced solid state batteries using garnet electrolyte:
Various interface engineering materials for Li metal and Garnet, including ALD Al₂O₃, PECVD Si, metals and alloys (Nature Materials 2016; JACS 2016; Advanced Materials 2017; Science Advances 2017);
Cathode-garnet interface engineering;
In-situ neutron depth profiling technique in understanding Li-garnet and CNT-garnet interfaces;
3D Li metal batteries using bilayer and trilayer Garnet 3D structures.

Li metal is considered as the “Holy Grail” of energy storage systems. The bright prospects give rise to worldwide interests in the metallic Li for the next generation energy storage systems, including highly considered rechargeable metallic Li batteries such as Li-O₂ and Li-sulfur (Li–S) batteries. However, the formation of Li dendrites induced by inhomogeneous distribution of current density on the Li metal anode and the concentration gradient of Li ions at the electrolyte/electrode interface is a crucial issue that hinders the practical demonstration of high-energy-density metallic Li batteries.
Free-standing graphene foam provides several promising features as underneath layer for Li anode, including (1) relative larger surface area than 2D substrates to lower the real specific surface current density and the possibility of dendrite growth, (2) interconnected framework to support and recycle dead Li, and (3) good flexibility to sustain the volume fluctuation during repeated incorporation/extraction of Li. The synergy between the LiNO₃ and polysulfides provides the feasibility to the formation of robust SEI in an ether-based electrolyte. The efficient in-situ formed SEI-coated graphene structure allows stable Li metal anode with the cycling Coulombic efficiency of ∼97 % with high safety and efficiency performance. These results indicated that interfacial engineering of nanostructured electrode were a promising strategy to handle the intrinsic problems of Li metal anodes, thus shed a new light toward LMBs, such as Li-S and Li-O₂ batteries with high energy density.
References
[1] Cheng XB, et al, Small 2014, 10, 4257.
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Lithium metal anode has become one of the most promising candidates for energy storage system due to the highest theoretical specific capacity and lowest electrochemical potential. Although substantial progress has been made in recent years, unstable behavior of lithium plating and stripping still prevents its successful transformation to commercialization. To address this issue, robust and conformal coatings directly on lithium surface by vapor deposition under ambient condition were designed and constructed. The resulted coatings not only possess hard inorganic moiety to block the growth of dendrites and soft organic moiety to improve the robustness, but also move dynamically with lithium surface regardless of the infinite volumetric change of lithium metal anodes. As examples, the coated lithium metal anodes were assembled with lithium ion phosphate and sulfur cathodes into rechargeable batteries. These batteries demonstrated double cycling lifetime, as well as dramatically decreased capacity degradation rates, as compared with batteries with pristine lithium anodes. Such a simple approach opens an avenue to stabilize lithium metal anodes for high performance rechargeable lithium metal batteries.

Lithium (Li) metal anode holds great promises for the next-generation Li battery systems. Nevertheless, its dendritic growth, unstable SEI formation and poor cyclability severely impede the practical applications. Behind the above-mentioned problems, there are in fact more essential issues in play, and the infinite relative volume change of the “hostless” Li at cycling is a critical one that has been almost overlooked for decades. In this talk, I will first share our new findings and understandings of Li metal failure induced by the infinite volume change, followed by our materials design methodologies and several demonstrations of stable “hosts” for metallic Li to minimize the volume change issue. The main body of the talk will be our most recent advancements in Li metal anode by combining minimal volume change and conformal surface modification/protection. We will show that the both aspects of materials engineering are important and indispensable to the overall superior Li metal cycling stability. The talk will shed light on the integration of different aspects of materials development efforts into a single electrode towards viable Li metal technology, and also deliver more general insight to guide the future design of high-performance Li metal anode.

Solvent-in-salt electrolytes or solvates are proposed as possible candidates for improved safety and cycle life for lithium metal batteries, for example Li-S batteries. The electrolytes, composed of one or more aprotic, organic solvents coupled with a high concentration of salt, are structurally complex solutions that often exhibit reduced electrolyte consumption and coulombic efficiency only over a restricted rate and capacity range. The origin of this variability in performance is not sufficiently developed, but is essential in reducing the overall parasitic consumption of the necessarily small electrolyte volume fraction required for high energy density and extended cycle life. In this presentation, we attempt to correlate the limits of this enhanced behavior regime with the measured composition and structure of the solvate and the resulting compositional and morphological evolution of the lithium anode. Select solvates are characterized using a combination of Raman and NMR supported by molecular dynamics computation (both ab initio and classical). Lithium anode structural evolution is tracked in situ using EC-AFM and ex situ using electron microscopy methods coupled with well-defined lithium metal surfaces. Anode surface composition is characterized ex situ with XPS and ToF-SIMS. Our studies identify the properties required of a solvate to provide dimensional stability to the anode and limit electrolyte consumption, offering strategies for improved lithium metal batteries.

Li-ion batteries are the critical enabling technology for the portable devices, electric vehicles (EV), and renewable energy. However, the safety of current batteries still need to be improved to satisfy these requirements. We systematically investigated the electrochemical stability window, interface/interphase stability and resistance between electrodes and electrolytes, reversibility and robustness of the cells using these electrolytes. The critical issues limiting these safe electrolytes will be discussed.

Solid-state materials with extremely high ionic diffusion are necessary to many technologies including all-solid-state Li-ion batteries. Despite the strong efforts made towards the search for crystal structures leading high lithium diffusion, very limited number of compounds showing superionic diffusion are known and clear materials design principles are greatly sought for.
In this work, we demonstrate that LiTi2(PS4)3 exhibits the largest Li-ion diffusion coefficient ever measured in a solid. We use extensive characterisation (neutron, X-ray diffraction, impedance and NMR) as well as theoretical studies and rationalise the exceptional performances of this new superionic conductor through the concept of frustrated energy landscape. The absence of regular and undistorted lithium site to occupy leads to low energy barrier for diffusion as well as an exceptional pre-factor. Our work not only shines light on a new family of superionic conductors but offers a new design principle for discovering new ones.

Sulfide-based solid electrolytes have attracted much attention due to their high conductivities, which are far beyond those of oxide-based solid electrolytes.^[1,2] However, They (Li₂S-P₂S₅ system, i.e., LPS) have been normally synthesized by solid state synthesis such as mechanical ball milling. These methods require rigorous control of reaction environment as well as high temperature heat treatment and repeated pelletizing steps. In contrast, solution-based synthesis methods can induce chemical reaction among precursor particles (Li₂S and P₂S₅) at low temperatures resulting in the formation of conductive phases of β-Li₃PS₄ and Li₃P₇S₁₁ with only moderate thermal treatment.^[3,4] The method deserves great attention since it simplifies synthesis process, yields products of great purity, and may facilitate the fabrication of composite electrodes with improved interfaces.
In this work, we report a new liquid-based synthesis method supported by a strong nucleophile. Addition of the compound enables dissolution of P₂S₅ in common ether based solvents. Such a precursor solution was found to be highly effective in reacting with Li₂S to produce highly crystalline and conductive β-Li₃PS₄ under with moderate heat treatment (140 degrees celsius). Details of the solution reactions and postulated reaction pathways based on IR, NMR, and GC-MS will be discussed. The tuning of the liquid-based synthesis chemistry can open new research directions for solution-based synthesis of solid electrolytes.

[1] Kamaya, N. et al. A lithium superionic conductor. Nature Mater. 10, 682-686 (2011).
[2] Yamane, H. et al. Crystal structure of a superionic conductor, Li₇P₃S₁₁. Solid State Ion. 178, 1163-1167 (2007).
[3] Ito, S. et al. A synthesis of crystalline Li₇P₃S₁₁ solid electrolyte from 1,2-dimethoxyethane solvent. J. Power Sources 271, 342-345 (2014).
[4] Liu, Z. et al. Anomalous High Ionic Conductivity of Nanoporous β-Li₃PS₄. J. Am. Chem. Soc. 135, 975-978 (2013).

Li metal and Li-alloy based anode materials are the most promising anodes for next-generation Li batteries. The poor interfacial stability (unstable solid-electrolyte interphase (SEI)) in the battery has been the primary issue hindering their practical application. In this talk, I will present a strategy to reinforce the SEI with desired properties including good tolerance to the Li-based material volume change and efficient surface passivation against electrolyte penetration. The strategy works via introducing multiple functional components bonded to the Li-based material surface into the SEI. The SEI reinforced shows much better stability than the SEI reinforced by electrolyte additive strategy, which is the current state-of-art and commercially used solution to SEI stability issue.

Surface fluorination of reactive battery anode materials for enhanced stability
Jie Zhao^1,†, Lei Liao^1,†, Feifei Shi¹, Ting Lei², Guangxu Chen¹, Allen Pei¹, Jie Sun¹, Kai Yan¹, Jin Xie¹, Chong Liu¹, Yuzhang Li¹, Zheng Liang¹, Zhenan Bao², and Yi Cui^1,3*
¹ Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA.
² Department of Chemical Engineering, Stanford University, California 94305, USA.
³ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
^† These authors contributed equally.
Abstract
Significant increase in energy density of batteries must be achieved by exploring new materials and cell configurations. Lithium metal and lithiated silicon are two promising high-capacity anode materials. Unfortunately, both these anodes require reliable passivating layer to survive the serious environmental corrosion during handling and cycling. Here we developed a surface fluorination process to form a homogenous and dense LiF coating on reactive anode materials, with in situ generated fluorine gas by using a fluoropolymer, CYTOP, as the precursor. The process is effectively a “reaction in the beaker”, avoiding developing specialized equipment and handling highly-toxic fluorine gas. For lithium metal, this LiF coating serves as a chemically stable and mechanically strong interphase, which minimizes the corrosion reaction with carbonate electrolytes and suppresses dendrite formation, enabling dendrite-free and stable cycling over 300 cycles with current densities up to 5 mA/cm². Lithiated silicon can serve as either an anode prelithiation additive to compensate the initial lithium loss in existing lithium-ion batteries or a replacement for lithium metal in Li–O₂ and Li–S batteries. However, lithiated silicon reacts vigorously with the standard slurry solvent N-methyl-2-pyrrolidinone (NMP), indicating it is not compatible with the real battery fabrication process. With the protection of crystalline and dense LiF coating, Li_xSi can be processed in NMP with a high extraction capacity of 2504 mAh/g. With low solubility of LiF in water, this protection layer also enables the stability of Li_xSi in humid air (~40% relative humidity). Therefore, this environmental-friendly surface fluorination process brings huge benefit to both the existing lithium-ion batteries and next-generation lithium metal batteries.
[1] J. Zhao^†, L. Liao^†, F. Shi, T. Lei, Z. Bao, Y. Cui. et al, “Surface fluorination of reactive battery anode materials for enhanced stability”, JACS 139, 11550 (2017).

Solid-state Li-ion batteries are next-generation energy storage devices that could offer the tantalizing possibility of high energy density coupled with high safety. Increasingly, it is recognized that the performance of solid-state batteries is limited by the structure and composition of the solid interfaces, which are difficult to study with atomic resolution during electrochemical cycling. In-situ transmission electron microscopy (TEM) of energy storage materials allows for the detailed study of structure-property relationships near solid interfaces during electrochemical charge and discharge. This work focuses on the design and characterization of an in-situ TEM platform for investigating the structure-property relationships of a model energy storage oxide, V₂O₅, in contact with a commercially-available solid-state Li-ion oxide electrolyte (LATP, Li_1+x+3zAl_x(Ti,Ge)_2-xSi_3zP_3-zO₁). The V₂O₅ cathode was deposited by atomic layer deposition (ALD, ~ 50 nm thick) onto the electrolyte. Ex-situ characterization of the cathode and cathode/solid state electrolyte interface structure and composition was performed using Raman mapping and electron energy loss spectroscopy (EELS). Ex-situ Raman mapping showed homogeneous lithiation of V₂O₅ on the LATP. Ex-situ EELS of the V₂O₅/LATP interface indicated that lithiation occurred throughout the 50-nm layer of V₂O₅ and that no significant interphase was formed on the lithiated sample. The in-situ cell was fabricated by focused ion beam (FIB) milling and lift-out of a micron-long ‘wedge’ of V₂O₅ on LATP. The lithium metal anode was electrochemically deposited directly onto the gold electrode of an in-situ TEM chip. Assembly of the in-situ cell was performed in a scanning electron microscope (SEM) using a micromanipulator. Bright-field TEM and EELS showed that the deposited V₂O₅ layer formed a well-defined interface with LATP. Overall, this work demonstrates the ex situ characterization and fabrication of an in situ platform for the TEM study of oxide electrode/solid-state electrolyte interfaces that can readily be adapted to other types of solid-state battery chemistries.

Two-dimensional molybdenum disulfide (MoS₂) has been extensively investigated in applications for lithium (Li) storage material owing to its high theoretical capacity of ~670 mAh/g, while its low ionic and electrical conductivities and poor reversibility have tackled further development for battery applications.^[1] To mitigate these challenges, here we show incorporation of heteroatom with the same chalcogen group, selenium (Se), to MoS₂ and design tubular structure by coating on multi-walled carbon nanotube (MWCNT). The molybdenum sulfide selenide (MoSSe) shell on MWCNT structure was synthesized from one-pot hydrothermal reaction. Transmission electron microscopy (TEM) images exhibit bi- or tri-layers of MoSSe shell that coaxially coat the sidewall of MWCNT. Electron energy loss spectroscopy (EELS) analysis reveals 1: 0.7: 1 atomic ratio of Mo: S: Se for MoSSe shell. Notably, the presence of Se distorts total lattice structure, thus increasing the interlayer space to 6.6 Å, which is 0.4 Å larger than Se-free MoS₂. To evaluate electrochemical storage capability, few-layer MoSSe/MWCNT composites were prepared to binder-free and three-dimensional (3-D) structural electrode. The specific capacity for MoSSe/MWCNT electrode coupled with a counterpart of metallic Li electrode is ~1,900 mAh/g at a current density of 100 mA/g and ~95% of Coulombic efficiency is delivered. The 3-D electrode structure and few-layer MoSSe on MWCNT may allow for short diffusion distance of Li⁺ ion and fast electron transfer, respectively. The galvanostatic cell performance with MoSSe/CNT electrode was also compared with the similar structure of MoS₂/MWCNT electrode. With increasing a current density to 1,200 mA/g, the capacity of MoSSe/MWNT is a twofold increase in that of MoS₂/MWCNT, which indicates intrinsically higher lithium storage capability of MoSSe than MoS₂. The decreasing bandgap of MoS₂ by addition of Se can enhance electrical conductivity.^[2] In addition, the distorting atomic structure may signify the mobility of Li⁺ ion inside MoSSe shell.^[3] The few-layer MoSSe with MWCNT electrode is stably cycled in the measured 30 cycles, which is distinct from poor capacity retention of MoS₂/MWCNT electrode.

References
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[2] Nanoscale, 2015, 7, 10490.
[3] Nano Lett., 2017, 17, 3518.

The battery shape is critical limiting factor affecting foreseeable energy storage applications. In particular, deformable metal–air battery systems could offer a low cost, low flammability, and high capacity, but the fabrication of such metal–air batteries remains challenging. Here, we show that a shape-reconfigurable materials approach, in which the deformable components composed of micro- and nanoscale composites are assembled, is suitable for constructing polymorphic metal–air batteries. We adopt an aluminum–air battery cell as an ideal platform, which involves three-electron transfer during charging reactions; as a result, it provides a specific capacity that rivals that of a single-electron lithium-ion battery. This cell is a great platform to test a shape-reconfigurable design because of easier handling, greater safety, and lower reactivity. This architecture is simple and scalable and also addresses the fundamental limitations of aluminum–air batteries by allowing the use of deformable packing designs to increase the performance output. Further, this approach is technologically unique in that it a method that enables the realization of a 3D shape change, which has never been observed for aluminum–air batteries. This significant deformability results in a specific capacity of 128 mAh/g per cell; calculated from the total mass of anode (496 mAh/g per cell; based on the mass of consumed aluminum), and a high output voltage (10.3 V) with 16 unit battery cells connected in series. The resulting battery can endure significant geometrical distortion such as three-dimensional stretching and twisting while the electrochemical performance is preserved. This work represents an advancement in deformable aluminum–air batteries using the shape-reconfigurable materials concept, thus establishing a paradigm for shape-reconfigurable batteries with exceptional mechanical functionalities.

As the importance of renewable energy grows, Sodium/β”-alumina(BASE) cell has been recognized as one of the most effective energy storage device because of its high specific energy, high efficiency of charge/discharge and long cycle life. For better operation of Sodium-BASE cell, poor wettability, which is caused by moisture and impurity in the BASE such as calcium, of electrolyte on liquid sodium anode should be enhanced. However, the formation of the oxide film, which is related to moisture absorbed on the BASE surface, impedes sodium dissolution, thereby hindering an accurate determination of wetting behavior. In this study, the sessile drop technique under controlled moisture and O₂ environment is used as a type of an artificial Sodium-BASE cell system to study the issue of water interface formed onto the BASE. To separate water interface, BASE surface need to be coated by metal that can form an alloy with sodium and therefore completely isolate its surface in a way that emulate the sealed and complete real cell. Bi is chosen as protect layer and sodium alloy with Bi is impervious to water yet does not interfere with sodium conductivity. By the enhanced wettability, the Sodium-BASE batteries can be operated at lower temperature with solving the safety issues and to use low cost polymeric seals.

Thin film energy storage systems offer the possibility of roll-to-roll processing on flexible substrates by use of different printing techniques, which enables cost-efficient large scale production. By the use of organic radical compounds as electrodes, such devices are able to combine a favorable environmental impact, since they do not rely on rare materials, with superior charging times and discharging power. Furthermore, an all-solid state device architecture is desirable for such devices, since that potentially increases safety and long-life operation significantly – leakage of liquid electrolytes is disabled by design a priori. Approaches for solid state electrolytes include different types of polymer electrolytes, such as dry polymer electrolytes, plasticized polymer salt complexes, gel polymer electrolytes, polymer-in-salt electrolytes and ceramic polymer electrolytes.
In this work we present an all-solid state thin film battery with electrodes based on polymers of organic radicals, such as TEMPO (2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl radical) [1] and TCAQ (tetracyano-9,10-anthraquinonedimethane) [2], and an ionic liquid gel electrolyte based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in a PMMA network [3, 4]. Electrodes and electrolyte were deposited out of liquid phase and dried thereafter resulting in a layer stack thickness in total of approximately 1 µm, including the charge collectors. Results on energy and power density as well as charging and discharging behavior will be presented.

[1] T. Janoschka et al.; Advanced Energy Materials 2013, 3, 1025
[2] B. Häupler et al.; Journal of Materials Chemistry A 2014, 2, 8999
[3] M.A. Susan et al., Journal of the American Chemical Society 2005, 127, 4976
[4] J. Jensen et al.; Journal of Polymer Science 2012, 50, 536

Sodium ion batteries (NIBs) are promising candidates for large-scale energy storage system applications. However, NIBs with organic liquid electrolytes suffer from the risk of flammability, leakage, and volatilization. All-solid-state NIBs with Na-ion-conducting solid electrolytes can prevent these safety issues mentioned above.
In this work, β"-alumina-based ceramic materials have been synthesized as electrolytes for all-solid-state NIBs. The β"-alumina-based ceramic materials were synthesized by using high temperature solid state reaction methods. The ionic conductivities of solid-state β"-alumina-based ceramic electrolytes were optimized by varying the concentration of precursors and additives, as well as the calcination and annealing temperatures. The calcination temperature affected the morphology and crystallinity of β"-alumina-based ceramic materials thus influenced the electrical properties. The morphology and structure of the β"-alumina-based ceramic electrolytes were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. The electrical properties of theβ" -alumina-based ceramic electrolytes were measured by using electrochemical impedance spectroscopy (EIS) and chronoamperometry measurement system in order to demonstrate its potential for all-solid-state NIB applications.

Oxygen evolution reaction (OER) in acid has been long considered a major obstacle in the generation and storage of renewable energy technology, such as regenerative fuel cells, metal-air batteries, and water electrolyzers¹. Because of the sluggish reaction kinetic, highly efficient electrocatalysts play a critical role in the advancement of above energy devices. Meanwhile, the low durability of OER catalysts in acid due to rapid catalysts dissolution has rendered the OER catalysts inactive under the high potential window in which OER occurs. Ruthenium oxide and iridium oxide are the only two known compounds to perform reasonable catalytic activity along with good stability in acid electrolyte². However, the scarceness of ruthenium and iridium metals builds up the cost of making these catalysts and thus limiting the implementation of water electrolyzer devices. To reduce the expensive metal content and increase the catalytic activity while retain stability of the catalyst are the objectives to make progression. We discovered a class of materials (pyrochlore-type ruthenate and iridium oxide) that show excellent OER catalytic activity while maintain acid stability.
Our recent results indicated the pyrochlore-type yttrium ruthenate (Y₂Ru₂O₇) outperformed RuO₂ in OER activity and stability. At 1.50 V vs. RHE, Y₂Ru₂O₇ exhibited more than 5 times higher current density than RuO₂. Moreover, after 10,000 consecutive cycles of cyclic voltammogram (CV) measurement, the OER activity loss of Y₂Ru₂O₇ was less than 10% of its initial value, while the loss of RuO₂ was more than 90%. X-ray absorption spectroscopy (XAS) analysis indicated a valence change of the Ru metal center in Y₂Ru₂O₇, suggesting that it is likely the structure related to the enhancement of activity. Density functional theory (DFT) calculations showed a stable Ru-O bond and thus increased the stability of catalyst. Pyrochlore-type yttrium iridium oxide (Y₂Ir₂O₇) was also synthesized and characterized, in comparison with IrO₂. At 1.55 V vs. RHE, the OER current density for Y₂Ir₂O₇ was about three times higher than IrO₂. The XAS analysis was applied to understand the structural origins for the observed high OER activity. A valance change in the center Ir atom was identified by while-line integration while Ir-O bond distance alteration was recognized in extended x-ray absorption fine structure (EXAFS) analysis.

References:
1. (a) Nocera, D. G., Acc. Chem. Res. 2012, 45 (5), 767-776; (b) Park, S.; Shao, Y.; Liu, J.; Wang, Y., Energy & Environ Sci 2012, 5 (11), 9331-9344.
2. (a) Kim, J.; Shih, P.-C.; Tsao, K.-C.; Pan, Y.-T.; Yin, X.; Sun, C.-J.; Yang, H., J Am Chem Soc 2017, 139 (34), 12076-12083; (b) Lebedev, D.; Povia, M.; Waltar, K.; Abdala, P. M.; Castelli, I. E.; Fabbri, E.; Blanco, M. V.; Fedorov, A.; Copéret, C.; Marzari, N.; Schmidt, T. J., Chem Mater 2017.

Lithium-sulfur (Li-S) is one of the most promising rechargeable batteries due to its high theoretical specific capacity, abundance, and low cost. Li-S batteries, however, suffer from detrimental volumetric changes, poor electrical conductivity, and polysulfide shuttling. To overcome these problems, current approaches mostly focus on chemical processes. Herein, we have developed two different physical strategies for suppressing the shuttle effect. The first method involves the deposition of metal thin films, such as Al and Ni, on sulfur cathodes by magnetron sputtering. In the second method, the Al sputtered filter papers with varying pore sizes are sandwiched between the cathode and the separator following the carbonization processes. Thin film coating on the cathode surface and the insertion of the protective interlayer can prevent the diffusion of polysulfides towards the anode, supressing the shuttle effect. The morphological and stuctural properties of the modified electrodes are comprehensively investigated through microscopic and spectroscopic characterization techniques. The electrochemical characterization of the half-cells with modified electrodes is also performed. This study introduces newly developed strategies to improve the cycling stability of Li-S batteries.

Nowadays, large-scale energy storage systems have attracted much attention because of the globe demand for renewable and sustainable energy. Lithium ion batteries (LIBs) have been widely used in portable electronics and electric cars owing to their high energy density. However, the high cost of lithium resource limits their application in large-scale energy storage systems. Recently, sodium-ion batteries (NIBs) have been considered as potential alternatives to LIBs due to the low cost of sodium resources. To develop the ability of NIBs in large-scale energy storage systems, researchers are focusing on developing low-cost raw materials as high-performance electrodes. Carbonaceous materials are the most promising anode materials owing to their low cost and sustainability. Hard carbon which has large interlayer distance and disordered orientation have been attracting much attention because of their high capacity among the carbonaceous materials.
In our study, we focus on biomass waste product derived hard carbons as anode materials for NIBs owing to their low cost and environmental friendly. Various biomass waste products were studied in this work, and several activation agents were carried out in order to prepare high-surface-area hard carbons. The surface area and microstructure of these biomass waste product derived hard carbons were characterized by Brunauer-Emmett-Teller (BET) surface area analyzer and scanning electron microscopy (SEM), respectively. The electrochemical properties were measured by cyclic voltammetry and galvanostatic charge/discharge cycle measurements. High capacity of around 300 mA h g^-1 was achieved with good cycling stability, indicating that biomass waste product derived hard carbons are promising anode materials for NIBs in large-scale energy storage applications.

Zinc-based batteries (e.g., Zn–air, Ag–Zn, Ni–Zn) have the potential to overcome some of the limitations of current Li-ion batteries: safety concerns associated with toxic and flammable electrolytes, high materials/manufacturing costs, and high single-cell specific energy decremented by weight and volume additions to control thermal events in Li-ion stacks. The key to realizing rechargeable aqueous zinc batteries lies in controlling the behavior of the zinc anode during cycling. Our team does this with an architectural redesign of the zinc anode to create an aperiodic monolith of interpenetrating, co-continuous networks of solid and void. Because the architecture ensures three-dimensionally (3D) wiring of all of the transporting reactants (electrons, ions, molecules), the entire volume of the 3D electrode becomes a more uniformly reacting phase, which lowers the kinetics of charge transfer, which minimizes the local current density, which thereby prevents any one region of the zinc electrode launching a dendrite, thereby physically ensuring more uniform charge–discharge reactions. Zinc sponges can now be cycled at high rate, to deep utilization of the *theoretical* zinc capacity, and to a specific energy competitive with lithium-ion batteries in prototype Ag–3D Zn, Ni–3D Zn, and 3D Zn–air cells. The road beyond the drama still too common with Li-based batteries is paved with zinc.

New generation of battery materials are accompanied by large volume and structure change and instability of interphase. Nanoscale materials design represents a new powerful paradigm shift and offers new solutions to address these challenges. Here I will present our recent progress on: 1) Nanoscale design of host and interface for Li metal anodes; 2) Discovery of sulfur cathode phase behavior, leading to new guidance to materials design; 3) The first successful example of cryogenic electron microcopy applied to battery materials research, leading atomic scale resolution of Li metal dendrite and solid electrolyte interphase.

One-dimensional nanomaterials can offer large surface area, facile strain relaxation upon cycling and efficient electron transport pathway to achieve high electrochemical performance. Hence, nanowires have attracted increasing interest in energy related fields. We designed the single nanowire electrochemical device for in situ probing the direct relationship between electrical transport, structure, and electrochemical properties of the single nanowire electrode to understand intrinsic reason of capacity fading. As the battery was charged and discharged repeatedly, lithium was progressively incorporated into the electrode, causing it to lose its crystalline structure and weakening its conductivity. Then, we designed the general synthesis of complex nanotubes by gradient electrospinning, including Li₃V₂(PO₄)₃, Na_0.7Fe_0.7Mn_0.3O₂ and Co₃O₄ mesoporous nanotubes, which exhibit ultrastable electrochemical performance when used in lithium-ion batteries, sodium-ion batteries and supercapacitors, respectively. Besides, we identified the exciting electrochemical properties (including high electric conductivity, small volume change and self-preserving effect) and superior sodium storage performance of alkaline earth metal vanadates through preparing CaV₄O₉ nanowires. We also constructed a new-type carbon coated K_0.7Fe_0.5Mn_0.5O₂ interconnected nanowires through a simply electrospinning method. The interconnected nanowires exhibit a discharge capacity of 101 mAh g^-1 after 60 cycles, when measured as a cathode for K-ion batteries. Our work presented here can inspire new thought in constructing novel one-dimensional structures and accelerate the development of energy storage applications.

Main references
[1] L. Q. Mai, Y. J. Dong, L. Xu, C. H. Han. Nano Lett. 2010, 10, 4273
[2] C. J. Niu, J. S. Meng, X. P. Wang, C. H. Han, M. Y. Yan, K. N. Zhao, X. M. Xu, W. H. Ren, Y. L. Zhao, L. Xu, Q. J. Zhang, D. Y. Zhao, L. Q. Mai. Nature Commun. 2015, 6, 7402
[3] L. Q. Mai, M. Y. Yan, Y. L. Zhao. Nature. 2017, 546, 469
[4] X. P. Wang, X. M. Xu, C. J. Niu, J. S. Meng, M. Huang, X. Liu, Z. A. Liu, L. Q. Mai. Nano Lett. 2017, 17, 544
[5] X. M. Xu, C. J. Niu, M. Y. Duan, X. P. Wang, L. Huang, J. H. Wang, L. T. Pu, W. H. Ren, C. W. Shi, J. S. Meng, B. Song, L. Q. Mai. Nature Commun. 2017, DOI: 10.1038/ s41467-017-00211-5

Polyimide shows great promises as the separator material in replacement of the commercial polyolefin counterparts. However, the polyimide nanoporous membranes have not yet been reported mainly due to the extremely poor processability of polyimides in dry and wet processes. In the past, only non-woven polyimide separators were demonstrated and fabricated, but exhibits low yield and mediocre mechanical strength. Here, we for the first time developed a facile solution-based synthesis of polyimide separators with outstanding mechanical strength (~1 GPa), high temperature resistance (>400 °C) and good electrolyte wettability. The method is low-cost and highly scalable for fast and large-scale fabrication, with great potential for industrial manufacturing. The batteries using the polyimide separators exhibited extraordinary rate capability, with ~30% higher capacity retention (~120 mAh/g) at a high rate of 10 C. We also demonstrated the cycling stability in the matched NMC532/Graphite full cells with commercial-level areal mass loading, which retains 91.2% of initial capacity after 200 cycles. Furthermore, we integrated dendrite detection function into the polyimide separator by a conductive interlayer inside the polyimide separator, which shows reliable early alarm of dendrite penetration. This innovation opens up the opportunity for safer batteries through separator engineering.

With the on-going thrust on sodium chemistry, owing to the huge abundance of sodium over lithium resources and similar electrochemical properties with that of lithium, sodium ion batteries (NIBs) are being projected as alternatives to lithium ion batteries (LIBs). Several intercalation materials have been studied as electrodes for NIB, most of which showed poor rate capabilities, owing to the huge size of sodium ions compared to lithium ions.^[1] Inorder to overcome these conventional power limitations, the concept of hybrid ion capacitors, which combines the advantages of both faradaic and non-faradaic processes, seems to be a promising approach. The cathode provides high power density, being a double layer capacitive electrode, while the anode imparts higher energy density.^[2,3,4] Thus a hybrid capacitor can achieve both the power and energy densities with very long cycle life. However, developing efficient sodium storage materials for the development of high performance Na-ion capacitor systems still remains a challenge. Herein, for the first time, we study the sodium-ion intercalation pseudocapacitance behavior of black TiO₂ nanotubes for their application as efficient anode material for Na-ion hybrid capacitor. Black TiO₂ nanotubes with a flower-like morphology, obtained through hydrothermal route, is characterized by several techniques such as X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), UV-absorbance, FTIR, Raman spectroscopy, etc. The presence of Ti³⁺ during TiO₂ reduction by foreign donor atoms or the oxygen deficiencies or defects created in the nanostructures, enhanced the conductivity due to the colossal bandgap narrowing (~1.51 eV). Black TiO₂ electrode exhibited excellent electrochemical properties revealing Na-ion intercalation pseudocapacitive behavior when cycled against Na-metal, with 57% of capacitive storage at 1.0 mV s^-1. Further, we carried out detailed studies on diffusion coefficient of Na-ions inside the black TiO₂ by using Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS) methods.^[5] A hybrid Na-ion capacitor is fabricated with black-TiO₂ as anode and activated carbon as cathode, and the device showed a high energy density of ~ 68 Wh kg^-1 and a high power density of ~12.5 kW kg^-1 with excellent cycling stability up to 10,000 cycles with ~ 80% capacitve retention. Thus the study reveals black TiO₂ as a promising candidate for sodium ion hybrid capacitors.

References
[1] M. D. Slater et al., Adv. Funct. Mater. 23, (2013), 947–958.
[2] K.Naoi et al., Energy Environ.Sci. 5, (2012), 9363-9373.
[3] B. Babu, P. G. Lashmi and M. M. Shaijumon, Electrochim. Acta 211, (2016), 289-296.
[4] Binson Babu and M. M. Shaijumon, J. Power Sources 353 (2017) 85-94
[5] M.V. Reddy et al., Electrochim. Acta, 128 (2014) 198-202.

Electrochemical devices, such as batteries, capacitors and fuel cells, are commonly used for storage and conversion of energy. Such devices are generally operated through simultaneous translocation of electrons and ions (e.g., protons, lithium ions, and sodium ions). Building devices with roust and effective transport pathways i the key towards high power performance and long cycling life. In this context, this presentation will discuss material synthesis and design towards electrochemical devices with improved performance, including 1) the design and synthesis of anode and cathode materials, 2) novel solid electrolytes and functional separators, and 3) design of novel hydrogen fuel cells with multifunctional anodes for enhanced transient power and prolonged lifetime.

State-of-the-art Li-ion battery electrodes provide stable cycling performance at the cost of necessitating a host matrix to create interstitial sites for Li-ion insertion. Such intercalation mechanism essentially limits their energy density in terms of host to Li atom ratio. Next generation electrode materials based on alloying or conversion reactions could potentially overcome this limitation by allowing each host atom to accommodate multiple Li ions. However, these new reaction mechanisms generally lead to significant volume expansion after complete lithiation, which results in poor reversibility caused by mechanical disintegration, with the prominent example of Si anodes decrepitating after cycling. Nano-structuring Si can alleviate this problem for each nanoscale element but the traditional slurry-based electrode fabrication method does not provide efficient and reliable assembly of the nanoscale building blocks and leads to problems like capacity degradation, sluggish kinetics and low active material loading.

Recent advances in additive manufacturing present an opportunity to rationally design 3D electrode architecture with periodic lattice geometry and nanoscale feature sizes that could potentially resolve the volume expansion problem for high energy density electrode materials. We fabricate 3D-architected Si electrodes by depositing a conformal layer of 250nm a-Si on an interconnected polymer-Cu core-shell scaffold, where local mechanical stability is enabled by the enhanced ductility of nanoscale Si, and structural robustness of the electrode is reinforced by lattice architecture design. Good transport kinetics in these nano-architected electrodes is maintained by the conductive scaffold backbone and the low-tortuosity periodic structure immersed in liquid electrolyte. The high mechanical strain induced by the lithiation of Si stretches and elongates lattice beams with a relatively compliant polymer-Cu composite backbone, which results in unfavorable global expansion in the 3D-acrhitected electrodes. We demonstrate that by rationally designing the lattice architecture with built-in instability, buckling of the lattice beams could accommodate Si volume expansion and internalizes lattice beam elongation turning the square lattice into an auxetic lattice, as directly visualized by a custom-made in operando optical cell. We analyze this mechanical instability-driven mechanism using finite element modelling to reveal insights on the critical role of buckling for stress-relief and strain accommodation during Si lithiation. Special attention is paid to how the buckling orientation of each lattice beam interacts with its neighbors and how introducing artificial defects can control the buckling orientation collectively in the 3D-architected nanolattice electrode.

Lithium-ion batteries (LIBs) are highly important to mobile electronics, green-energy storage, and electric-vehicle technology. Commercial LIBs use relatively low-capacity graphite for anodes (372 mAh g-1). In contrast, the theoretical capacities of alloying anodes for LIBs are much higher (4200, 1600 and 990 mAh g-1 for Si, Ge and Sn, respectively). The drawback to using Si, Ge and Sn in anode construction is the roughly 300% volume change during the cycling process, which can lead to pulverization, unstable solid-electrolyte interphase, and rapid capacity loss. Herein we report the use of carbonized asymmetric membrane electrodes that contain silicon, germanium, tin dioxide or vanadium (V) oxide can significantly increase LIB electrode capacity while maintaining a long cycling life and an excellent rate performance. It is the first time that asymmetric membranes are proposed to be employed as lithium ion battery electrodes. These asymmetric membrane electrodes were fabricated using a novel adapted reverse-osmosis membrane technology, the phase-inversion method. The asymmetric membrane electrodes have a thin, nanoporous top layer (up to several µm) and a thick, macroporous bottom layer (100-200 µm). The top layer can prevent the leaching of fractured anodes, and the bottom layer provides solid mechanical support and void space that can efficiently accommodate the large volume changes driven by lithium insertions and extractions. It was demonstrated that 90% capacity of asymmetric membrane containing Si nanoparticles can be retained after 200 cycles with an initial capacity loss of ~ 30%. We also synthesized SnO2 and V2O5 asymmetric membranes using a unique combination of phase inversion and sol-gel chemistry. The resulting SnO2 electrode demonstrated a specific capacity of 500 mAh g-1 based on the overall electrode mass at a current density of 280 mA g-1 (~0.5C) with >96% capacity retention after 400 cycles. When the current density was increased from 28 to 560 mA g-1, its overall capacity was reduced by only 36%. The V2O5 electrode can be cycled at 0.5C with a capacity of 160 mAh g-1 for 380 times with ~100% capacity retention. Additionally the same method can be extended to stabilize micron-size Ge and Si alloying anodes with impressive cyclability. Finally, this method can be scaled up using a roll-to-roll process common in the membrane industry, breaking a huge barrier to the potential commercialization of the aforementioned electrode materials.

Titania (TiO₂) is a promising anode material in lithium-ion batteries due to its environmental friendliness, abundance, and safety. It has been previously reported that the generation of point defects, such as oxygen and cation vacancies, in TiO₂ has resulted in enhanced electrochemical performance^{1, 2}. In this study, we aim to induce point defects in TiO₂ nanotube electrodes through heat treatments in various atmospheres. Mott-Schottky analysis indicates that charge carrier density has increased due to oxygen-deficient atmospheres, suggesting oxygen vacancy formation. Crystallographic changes and defect production are also evident through decreases in peak intensity and peak shifts in the respective Raman spectra. The introduction of defects into the nanotube crystal structure results in changes in the charge storage behavior of the TiO₂ electrode observed via electrochemical characterization. The defects created through atmospheric treatments at elevated temperatures may then lead to enhanced battery functionalities of TiO₂ nanotube electrodes.

1. Swider-Lyons et al., (2002) Solid State Ionics, 152–153, 99–104.
2. Koo et al., (2012) Nano Letters, 12, 2429–2435.

To meet the challenge of discontinuity of the renewable energy flow, development of effective energy storage systems with high energy and high power density is necessary¹. We have pioneered the use of a new electroactive material i.e. BiVO₄ where faradaic behavior of Bi ion is recorded.² In the constant search for a better energy storage material it’s an attempt to move beyond the conventional Lithium and Sodium based battery materials. BiVO₄ is an n-type semiconductor which has shown excellent electrochemical behavior with specific capacitance of ca.1200 Fg^-1 at 1 Ag^-1. BiVO₄ in conjunction with SWCNTs has shown improved electrochemical performance and impressive cycling stability². To further improve its performance, BiVO₄ is combined with a few-layered nanostructured MoS₂ and has demonstrated much larger values of charge storage, longer discharge times and improved cycling stability in comparison to pristine BiVO₄, or graphene/BiVO₄ composites, and hence is considered a promising candidate for energy storage³. The area of merging energy capture and storage is still emerging especially in terms of evolving the conceptual idea of directly storing solar radiation as opposed to forming devices that consist of independent batteries/supercapacitors that are separately coupled with solar cells. Also, generating charge carriers that could be stored electrostatically or electrochemically, using photo assisted process is now being exploited using technologies involving DSSC (dye sensitized electron generation), photoelectrochemical or photochemical assisted production of high energy electrons and these are being interfaced with energy storage electrodes. WO₃/TiO₂ and Ni(OH)₂/TiO₂ are two of the most widely studied hybrid energy storage systems but unfortunately the devices show poor efficiencies mainly owing to multiple interfaces being involved. Therefore, we have adopted an alternate approach for coupling energy capture and storage in that the focus has been to create a strategy that minimizes interfaces and so in principle can lead to better performance and charge transport efficiency. We have studied BiVO₄ redox behavior in the presence and absence of light in order to provide insight into whether it is feasible for an electroactive component to be also photoactive in a single energy storage device⁴.

References
1. Guo, W., Xue, X., Wang, S., Lin, C. & Wang, Z. L. An Integrated Power Pack of Dye-Sensitized Solar Cell and Li Battery Based on Double-Sided TiO₂ Nanotube Arrays. Nano Lett. 2012, 12, 2520–2523.
2. Khan, Z., Bhattu, S., Haram, S. & Khushalani, D. SWCNT/BiVO₄ composites as anode materials for supercapacitor application. RSC Adv. 2014, 4, 17378–17381.
3. Arora, Y., Shah, A.P., Battu, S., Maliakkal, C.B., Haram, S., Bhattacharya, A., Khushalani, D. Nanostructured MoS₂/BiVO₄ Composites for Energy Storage Applications. Sci. Rep. 2016, 6, 36294.
4. Arora, Y., Khushalani, D. (Manusript under preparation).

Keywords: biological carbon, Lithium-sulfur battery, Ti₃C₂ MXene
With the rapid development of portable electronic devices and hybrid electric vehicles, rechargeable lithium-ion batteries with high storage capacity and cycling stability are considered to be the versatile, clean, and promising power source. However, the capacity of current cathode and anode materials was less than 400 mAh/g, which restricts the large-scale application. New cathode material sulfur and anode material stannum with theoretical capacity of 1675 mAh/g and 994 mAh/g were better electrode materials which could obtain 3-5 times higher capacity than traditional materials. But the shuttle effect, volumetric effect, low conductivity of sulfur and volumetric effect, electrode collapse of stannum have to be settled. Our group confirmed when sulfur and stannum are combined with carbon scaffolds, the performance of composites can be effectively improved. Our designs are based on the following three aspects:
(1) Biological genetic carbon materials. Our group maintained the morphology of biological materials and behaved the biological characteristics to synthesize a series of biological genetic carbon materials, which showed satisfactory performance in energy storage.
(2) Adsorption enhanced C/S composite materials. Our group used surface modification of green hierarchical porous carbon with conducting oxides Ti₄O₇, heteroatom, phosphides and nonconductive metal oxides to enhance chemisorption. And we firstly verified the monolayered chemisorptions behavior of Li₂S based on the adsorption test and DFT calculations. At the same time, we proposed the design principle based on the balance between surface adsorption and diffusion of Li₂S_x for adsorption enhanced C/S composites.
(3) Sn-based layered carbide composite anode materials. We proposed that using highly compact, electron conductive and lithium conductive Ti₃C₂ (MXene) instead of carbon to improve the volumetric capacity of composites anode. Notably, we found and confirmed the prepillaring and pillaring effect (Sn⁴⁺ used as the prepillaring agent, Li_xSn_y as pillaring agent) of this composite anode materials.
1. Y. Xia, W.K. Zhang,* X.Y. Tao et al,* ACS Nano, 7, 7083 (2013).
2. C.B. Jin, O.W. Sheng, X.Y. Tao et al,* Nano Energy, 37, 177-186 (2017).
3. O.W Sheng, C.B. Jin, X.Y. Tao et al,* J. Mater. Chem. A, 5, 12934-12942 (2017).
4. X.Y. Tao, Y. Cui et al,* Nat. Commun., 7, 11203 (2016).
5. X.Y. Tao, W.K. Zhang,* Y. Cui et al,* Nano Lett., 14, 5288-5294 (2014).
6. H.D. Yuan, X.Y. Tao et al,* ACS Energy Lett., 2, 1711-1719 (2017).
7. J.M. Luo, X.Y. Tao et al,* ACS Nano, 11, 2459-2469 (2017).
8. J.M. Luo, X.Y. Tao et al,* ACS Nano, 10, 2491-2499 (2016).

Research on two-dimensional (2D) nanomaterials is rising to an unprecedented height and continues to remain a very important topic in materials science. In parallel with the continuous discovery of new candidate materials and exploration of their unique characteristics, there are intensive interests to rationally control and tune the properties of 2D nanomaterials in a predictable manner. Attention has been focused on modifying these materials structurally or engineering them into designed architectures, driven by the requirements for specific applications. Recent advances in structural engineering strategies have demonstrated their ability to overcome current material and processing limitations, showing great promise for promoting device performance to a new level in many energy-related applications.
In this talk I will overview several important structural engineering strategies and their underlying mechanisms to significantly improve energy storage properties of 2D nanomaterials, and then focus on our recent progress in developing interlayer engineering and porosity engineering of 2D materials for efficient energy storage in Li-ion batteries, Na-ion batteries, and beyond.

In present scenario, most widely used electrochemical energy storage systems for consumer electronics are Li-ion batteries and supercapacitors. Conventional cathodes used in lithium ion rechargeable cells cannot meet the requirements of batteries required in electrical vehicles. Bi-material cathodes, comprise of battery and super-capacitors composites, yield high energy as well as high power density rechargeable cells. In this work, we demonstrated that microwave assisted hydrothermally grown carbon coated Na₃V₂(PO₄)₃@C (NVP@C) –activated carbon (AC) hybrid electrodes are excellent cathode material for lithium ion rechargeable cells. The as synthesized NVP@C (battery component) and commercially available AC (supercapacitor component) were mixed (40/60 weight ratio) to fabricate bi-material cathode. The electrochemical characteristics of NVP@C, AC and bi-material cathode (NVP@C/AC) were evaluated using 1(M) LiPF₆ in EC:DEC (3:7) in half cell configuration using lithium metal as counter and reference electrode. For selected cells full cell characteristics were also studied using Li₄Ti₅O₁₂ counter electrode. The cells were characterized by cyclic voltammograms, electrochemical impedance spectroscopy, rate capabilities and cycleability. At low specific currents (50 mAg^-1), the NVP@C, AC and NVP@C/AC deliver specific capacities of 105, 36 and 66 mAhg^-1 with 83%, 93% and 99% capacity retentions respectively after 100 cycles. At high specific currents (700 mAg^-1), the NVP@C/AC outperforms both and delivers specific capacity as high as 58 mAhg^-1 as compared to 35 and 27 mAhg^-1 for NVP@C and AC respectively. The synergistic effect of the bi-material cathode was confirmed by comparing cyclic voltammograms, electrochemical impedance spectra and galvanostatic charge–discharge profiles of these electrodes.

The layered nickel-rich materials have attracted extensive attention as a promising cathode candidate for high-energy density lithium-ion batteries (LIBs). However, they have been suffering from inherent structural and electrochemical degradation including severe capacity loss at high electrode loading density (>3.0 g cm⁻³) and high temperature cycling (>60°C). The structural issues originate from the phase transition (from layered to rock-salt like structure) of nickel-rich cathode upon electrochemical cycling. The ionic radius between lithium ion (0.76 Å) and divalent nickel ion (0.69 Å) is substantially similar, thus divalent nickel ion can easily migrate into lithium slabs.<span style="font-size:10.8333px"> </span>This cation mixing layer consisted of inactive NiO-like phase deteriorates the lithium ion transport and causes poor thermal stability. In terms of chemical stability, the residual lithium compounds such as LiOH and Li₂CO₃ in the nickel-rich cathode are strongly related to safety issues. The unstable trivalent nickel ions in host structure can increase these unwanted residual lithium compounds during synthesis process or storage period in air, resulting in electrochemical decomposition upon cycling and preventing lithium ion transport with the increase in charge transfer resistance.^[13-17] In addition, the electrocatalytic side reaction between cathode and electrolyte severely increases the non-conducting and unstable solid-electrolyte interphase (SEI) layer on the cathode surface for long-term cycles, thus resulting in poor cycle performance. In this regard, it is highly desired to construct the uniform SEI layer having high ionic conductivity and electrochemical/thermal stability on the cathode at early stage.
Herein, we report a high performance nickel-rich LiNi_0.84Co _0.14Al_0.02O₂ cathode with an artificial SEI layer. We discovered that initially formed SEI compounds effectively enhance the electrode wettability. Notably, these compounds were electrochemically rearranged by interacting with hydrolysis by-products, constructing homogeneous, artificial SEI layer along the grain boundaries of primary particle during the formation cycle. The prepared cathode with homogeneous Li_xPO_y layer and TM concentration gradient demonstrated extremely high thermal stability at 60°C with high structural and morphological integrity. When used at high electrode density of ~3.3 g cm⁻³, this cathode also outperforms in any nickel-rich cathodes (See Table S1). This work suggests that our strategy can simultaneously address two issues related to chemical and structural stability by the newly developed surface engineering method.

Lithium ion batteries (LIBs) are the most popular types of rechargeable battery with their superior gravimetric and volumetric capacities for electric and hybrid vehicles. But more than energy density, cost, lifetime or recyclability, safety issues is the most challenging parameter to investigate especially after ageing. Even if separator is considered as electrochemically inert, it play a major role in all of these properties. It is so crucial to evaluate its evolution in time, to observe its degradation and its impact on safety and performances of LIBs.
The aim of this study is to determine the evolution of chemical, morphological and mechanical properties of a polyethylene separator under two different ageing conditions: calendar ageing and fast charge cycling in 18650 LFP/G batteries systems. Its porosity is evaluated by Helium pycnometry, its mechanical properties by tensile test. Surface chemical composition is also investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Surface state is observed by scanning electronic microscopy (SEM) and by atomic-force microscopy (AFM). Electrochemical performances are analyzed by impedance spectroscopy and C-rate tests to investigate the consequences of the separator ageing. Safety tests are also performed by overcharge in an Accelerating Rate Calorimeter (ARC) and by in-situ dendrites growing in coin cells.
First results show a decrease of the separators porosity which causes a decrease of the cell performances at high capacity rate. A deposit is observed on the extreme surface. A mechanistic model of ageing will be proposed which integrate a porosity gradient and an evolution in time.

The inferior cycling stability critically impedes the development of potassium-ion batteries (KIBs). The solid electrolyte interface (SEI) for nitrogen doped graphite foam (NGF) was studied in both KPF₆ and KN(SO₂F)₂ (KFSI)-based organic electrolytes, aiming to unravel the SEI effect on K⁺ ion storage mechanism. Electrochemical characterizations disclose that the KN(SO₂F)₂-based cells deliver improved electrochemical performance in terms of reversibility and cycling stability, compared to KPF₆ based cells. Experimental results including depth-profiling XPS and FTIR spectra, together with the theoretical calculations, reveal that (CH₂OCO₂K)₂, C₂H₅OCO₂K, KF and K₂CO₃ are the dominant components of SEI layers in both electrolytes. Particularly, the amount of K₂CO₃ in KPF₆-based electrolyte is much more than that in KFSI-based electrolyte, resulting in inferior stability. Moreover, the depth-profile XPS results indicate that the SEI formed in KFSI based electrolyte is much more stable, compact and thinner than that in KPF₆ based electrolyte. All these features, together, ensure good stability and high reversibility in KFSI-based electrolyte.
The nitrogen doping effect on K⁺ ion storage was also explored. Enhanced electrochemical performance was identified upon increasing the nitrogen content, due to i) the enrichment of active sites for K⁺ ion storage and ii) the improved electronic conductivity. Moreover, the electrochemical performance is strongly dependent on N-doping types. Specifically, the pyridinic nitrogen dominates the reversible capacity, as identified by the presence of critical point at 4.29 at. %. In which, the atomic ratio of pyridinic N in NGF is 2.53 at. %, which is higher than that of 7.03 at. %, with only 2.16 at. % pyridinic N. The result is consistent with the theoretical study, which verifies that the charge transferred from K ions to NGF increases with the pyridinic nitrogen doping. Our results promote better understanding of K⁺ ion storage mechanism in graphite and provide invaluable guidance for optimized carbon-based electrode design for high-performance KIBs.

Li_XFePO₄ is a model phase-separating material for Li-ion batteries. While its tendency to phase-separate between particles at the electrode length scale is well-documented, the phase separation mechanism within individual particles has been highly controversial, with experimental observations of both intra-particle phase separation and solid solution. Phase separation not only creates large elastic strains that degrade the material, but also prevents us from accessing and studying a large lithium composition space in the miscibility gap. Understanding the phase transformation mechanisms are therefore crucial for developing safe and long-life batteries.

To understand whether LiFePO₄ undergoes intra-particle phase separation, we developed a microfluidic liquid platform that enables us to track in real time the migration of lithium within individual particles during lithiation and delithiation. We directly visualize phase separation at low cycling rates and solid solution behavior at high rates of cycling, with a spatial resolution as low as 10 nm. To explain this behavior, we use both experiment and simulations to identify lithium surface diffusion at the particle/electrolyte interface as the dominant pathway by which lithium migrates within individual particles during phase separation. Thus, solid solution arises at high rates when the rate of lithium insertion is faster than the rate of surface diffusion. Stabilizing solid solution within individual particles not only reduces elastic strain during charge and discharge, but also provides new avenues towards the study of the defect-chemical properties in the previously-inaccessible miscibility gap.

A 3D multiphysics phase-field model is developed to study phase segregation in LiFePO₄ nanoparticles, of interest due to their high (dis)charge rates. Spinodal decomposition into Li-rich and –poor phases is modified and can be suppressed by mesoscopic effects, which influences the kinetic and mechanical performance of this material as a battery electrode. Elastic and structural constants, diffusivity, and surface energy are highly anisotropic and concentration dependent, necessitating a 3D treatment. Previous work has shown the ability of surface wetting to stabilize minority phases, modifying the (dis)charge voltage profile [1].

The model includes spinodal decomposition, anisotropic, concentration-dependent elastic moduli, misfit strain, and facet dependant surface wetting within a Cahn-Hilliard framework. Simulations are carried out on realistic, plate-like particles of varying sizes in 3D in order to examine modification to phase segregation. The stability of a phase at an intermediate composition, sometimes seen experimentally, is also examined.

[1] Welland, M.J., Karpeyev, D., O’Connor, D.T., Heinonen, O, “Miscibility gap closure, interface morphology and phase microstructure of 3D Li_xFePO₄ nanoparticles from surface wetting and coherency strain”, Submitted to ACS Nano, 2015.

A cathode based on micron-sized LiFePO4 (LFP) was used to highlight the possible improvements in the intrinsic limitations of poor electrical and ionic conductivity. So, these problems were overcomed to surface coating machanism that has provided a major breakthrough in high-performance electrodes of lithium-ion batteries (LIBs). This method with conductive materials at the level of single active particles has been used to challenge poor conductivity in electrodes. Nevertheless, the resulting decrease in the volumetric capacity and the complexity of the required manufacturing conditions are problematic for particle-scale coating techniques. Here, we report a facile alternative route to coating conformal thin-layer conducting poly(3,4-ethylenedioxythiophene) (PEDOT) through vapour reaction printing (VRP) on prepared LFP electrodes. The PEDOT coated LFP electrodes exhibited outstanding improvements in cycling stability and their rate capability compared with the uncoated pristine LFP electrode. These results were attributed to the conformal PEDOT layer, which offers improved conduction pathways and ion diffusion. Therefore, this new method of coating prepared LFP electrodes with a conductive conformal thin layer is providing for the design of electrodes for high-performance LIBs.

Carbon materials are proving to hold the key to substantial advances in today’s energy storage technologies. Naturally abundant biomass, such as cotton and wheat flour, and even currently wasted resources, such as banana peels and recycled papers, have been successfully converted to produce renewable carbon materials for energy storage systems via a low-cost and high throughput manufacturing process. Excitingly, these biomass-derived renewable activated carbon scaffolds usually possess hierarchically porous structures which are beyond the synthetic materials, making them ideal backbones for depositing active materials with higher capacity for supercapacitors, and for hosting sulfur in lithium-sulfur batteries to manipulate the “shuttle effects” of polysulfides. Specifically, biomass-derived activated cotton textile (ACT) has been demonstrated an excellent flexible conductive substrate to fabricate flexible power sources, such as flexible supercapacitors with enhanced capacity and flexible lithium-sulfur (Li-S) batteries with prolonged lifespan. When the with magnetic Fe/Fe₃C nanoparticles embedded ACT was used as a sulfur host, an obviously increased lifespan of the assembled Li-S cell can be ascribed to a new proposed magnetic field-assisted polysulfides trapping mechanism. Besides flexible ACT, carbon nanotubes (CNTs) have also successfully derived from the natural yeast-fermented wheat dough without using any extra-catalysts or additional carbon sources. Yeast-derived carbon nanotubes from the fermented wheat dough not only provide an ideal sulfur host for Li-S batteries with a record lifespan of 5000 cycles but also expand our current understanding of the synthesis of carbon nanotubes. Using biomasses is definitely the right track towards making renewable carbon materials for future energy storage devices.

Silicon has been focused as a promising anode material due to its high theoretical capacity (3579 mAh g^-1). However, it suffers from capacity degradation due to the evolution of fractures in the electrode caused by the volume expansion of Si (~300%) during cycling [1]. To overcome this problem, water-soluble polymers have been suggested as alternatives of a traditional PVDF-binder system for improving the mechanical stability and electrochemical properties of Si through their strong interaction capabilities between active materials and binder [2-4]. Herein, we first introduce the polyacrylamide (PAM) hydrogel as a new binder system, which has a good capacity for preserving their mechanical strength and shape with abundant polar-functional groups in their structure. For the 3D-polymer network in the electrode, we applied in situ polymerization method during the electrode fabrication. Through this 3D PAM network, the composite electrode exhibited a great capacity retention of ~2000 mAh g^-1 after 300 cycles. Accordingly, the effect of the chemical/mechanical properties of PAM gel on the electrochemical properties of Si is adequately elucidated, and these results are properly applied for the design as a novel binder system in the Si anode.

[1] U. Kasavajjula, C. Wang, and A. J. Appleby, J. Power Sources 163, 1003 (2007).
[2] J. Li, R. B. Lewis, and J. R. Dahn, Electrochem. Solid-State Lett. 10, A17 (2007).
[3] A. Magasinski, B. Zdyrko, I. Kobalenko, B. Hertzberg, R. Burtovyy, C. F. Huebner, T. F. Fuller, I. Luzinov, and G. Yushin, ACS Appl. Mater. Interfaces 11, 3004 (2010).
[4] I. Kovalenko, B. Zdyrko, A. Magasinski, B. Hertzberg, Z. Milicev, R. Burtovyy, I. Luzinov, and G. Yushin, Science 334, 75 (2011).

A facile, efficient, environmentally benign route has been reported to synthesize toast-like porous carbon (TPC) materials via one-step solid reaction between LiH and CaCO₃ powder mixture at 600 ^oC. The release of gas from the reaction process plays a key role in the formation of toast-like micro-/meso- porous structure. As an anode material for Li ion batteries, the as-synthesized TPC exhibits ultrahigh specific capacity of 1016 mAh g^-1 (after 300 cycles at 200 mA g^-1), superior rate capability (730 mAh g^-1 at 1000 mA g^-1), and excellent cycling ability (up to 1400 cycles at 4000 mA g^-1). The exceptional lithium storage performance of TPC could be attributed to its novel hierarchical structure and good structural stability, which not only provide high accessible surface area for charge storage, but also act as reservoirs for lithium storage. This chemical reaction route opens new avenues for synthesizing porous carbon materials for energy storage application.

Lithium sulfur battery represents an advanced energy storage system because of its environmental benignity, high theoretical energy density (2600 Wh kg^-1) and natural abundance of sulfur. However, the low conductivity of sulfur, polysulfides dissolution, and sulfur volumetric expansion during lithiation/delithiation process will decrease the reaction kinetics of polysulfides and sulfur utilization, leading to low capacity, limited rate capability and inferior cycling stability. To solve these problems, there have been intensive efforts in choosing highly conductive carbon materials to design porous or hollow structures for secure sulfur hosts. Although these materials can effectively alleviate polysulfides dissolution during short-time cycling, the weak interaction with polar polysulfides will inevitably results in increase of charge transfer and dissolution of polysulfides over long-time electrochemical reaction.

Here, we first grew ZIF-67 nanoparticles (~450 nm) uniformly within a three-dimensional carbon nanotube sponge, and after carbonization and sulfuration, we finally fabricated a hybrid network with numerous carbon nanotubes penetrating hierarchically porous graphitic carbon polyhedrons uniformly dispersing Co₃S₄ nanoparticles (from ZIF-67) to host sulfur. Co₃S₄ has been reported to have strong affinity to polysulfides, and can act as a catalyst to accelerate the conversion of polysulfides to Li₂S₂/Li₂S (insoluble discharged products), which are beneficial for improving battery cycling stability (polysulfide stabilization) and rate capability (increased reaction kinetics). In our system, highly dispersed Co₃S₄ nanoparticles can provide sufficient sites to trap polysulfides and catalyze the conversion reaction smoothly, additionally the outer wrapping porous graphitic carbons (physical barriers) can further protect polysulfides from dissolving into the electrolyte. Moreover, the highly three-dimensional conductive CNT and graphitic carbon hybrid network acting as a self-standing electrode can not only facilitate electrolyte infiltration and charge transport, but also improve sulfur loading and utilization. Our novel 3D hybrid electrodes exhibit a much superior ultralong Li-S battery performance than previously reported MOF-based electrodes in recent literature.

Lithium-sulfur batteries are considered to be the most promising energy-storage solution to meet the future energy demand. However, both anode and cathode suffer from fatal drawbacks which hinder the practical application of Li-S batteries. Especially in the anode, dendrite growth, infinite volume expansion and unstable solid electrolyte interphase greatly trigger the safety hazard and capacity fading. Herein we provide a facile approach via designing a nonwoven fiber separator of polyethyleneimine-grafted polyacrylonitrile nanofibers to regulate lithium deposition and mitigate the shuttle of lithium polysulfides. Through the precise process of electrospinning, the diameter of PAN fibers could be decreased to hundreds of nanometers, which provides uniform pathway for lithium ions transportation. The branched PEI group effectively increase the nitrogen content of the whole separator, which could chemically anchor Li ions. In comparison with the traditional PE/PP separator the PEI-g-PAN separator possesses better affinity and larger uptake of ether-based electrolyte. As a result, the lithium metal anode with PEI-g-PAN separator show better cycling stability and longer lifespan with a high Coulombic efficiency of 97% after 200^th cycle. Even more noteworthy is that the PEI functional group with positive charge could catch the troublesome polysulfides during charge/discharge of the Li-S batteries. Consequently, this bifunctional PEI-g-PAN separator is beneficial to both anode and cathode of Li-S batteries, and reveal a new avenue for the next-generation energy storage.

Graphene-wrapped porous spherical MnCO₃ is synthesized via a facile process combining the homogeneous precipitation and the hydrothermal method. This composite material, applied as a lithium-ion battery anode, shows a superior lithium storage capacity and remarkable long cycling performance due to its special nanostructure. It delivers a reversible capacity of 1168.5 mA h g^-1 at a current density of 500 mA g^-1 after 200 cycles. After 1000 cycles at high rate of 3000 mA g^-1, a stable capacity of 594.7 mA h g^-1 can be maintained with the capacity retention of 86.3%. Full cells with the composite anode and the commercial NCM523 cathode are assembled and show good cycling stability over 100 cycles. Furthermore, a series of composite materials with different content of graphene are prepared to identify the role of graphene in electrodes during the charge/discharge process. Kinetics-analysis based on cyclic voltammograms (CVs) reveals that the presence of graphene can promote Li⁺ transportation at electrode/electrolyte interface, which increases its surface capacitive contribution and results in superior electrochemical performance than other MnCO₃ samples.

Commercial application of Li-S battery is hampered by a series of complicated problems: (1) low active materials utilization and limited rate capability because of insulating nature of sulfur and its discharge product lithium sulfide(Li₂S); (2) rapid capacity decay caused by dissolution and shuttle of intermediate products (Li₂S_n, 2<n<8). Herein, we fabricated a novel carbon as the host for sulfur cathode for effective trapping of polysulfides. The novel nanostructure has the following characteristics: (1) the interior void space for higher sulfur-loading and relieving sulfur expansion; (2) the partially mesoporous shell allow fast ion transportation and thus a superior rate capability; (3) the outermost surface of hollow carbon nanosphere cluster (HCNC)with inadequate pore structure enable minimized lithium polysulfide dissolution during long cycle; (4) the agglomerate primary hollow nanosphere enable a high tapped density; and (5) the integral conductive carbon framework facilitate good electrons transfer. Due to the unique architecture of HCNC with good electrical conductivity, large void space, radialized mesoporous pathway, and outmost compacted carbon layer, they could deliver a high initial capacity of 1302 mA h g^-1 at 0.2C with a reversible capacity of 803 mA h g^-1 after 500 cycles. The sulfur cathode demonstrated a good rate capability with 721 mA h g^-1 at 5C. Optimization and integration of different pore structures and morphologies can be the effective way for future development of high-rate and long-cycle Li–S batteries.

During operation, the active materials within lithium ion batteries break down and degrade. This is one of the limiting factors of a promising high energy density, low cost, and low toxicity electrode material - lithium manganese oxide (LiMnO₂). LiMnO₂ degrades at a much faster rate than other popular electrodes and, consequently, its main use is restricted to primary (single use) lithium cells. This accelerated degradation is mostly due to dissolution of Mn into the electrolyte and subsequently depositing on the surface of the graphitic negative electrode, altering the composition of the solid electrolyte interphase (SEI) layer and accelerating the consumption of available lithium. An understanding of the influence of operating conditions on the spatial and temporal dynamics of Mn remains elusive. Developing a spatial high-resolution chemical map of positive and negative electrodes from LiMnO2 cells at different stages during their lifetime presents an important step towards uncovering the relationship between the rate of degradation and the transport of Mn. High-resolution X-ray fluorescence (XRF) holds the potential to elucidate this link by identifying and quantifying the presence of Mn on the surfaces of electrodes.

While X-ray imaging techniques, such as X-ray microscopy and computed tomography, have grown in popularity in recent years for spatial analysis of lithium-ion batteries, those techniques suffer from spatial resolutions that can be, at best, down to the tens to hundreds of nanometers. As the Mn migration results in very thin coatings of Mn on the negative electrode (tens to single nanometers), X-ray imaging techniques are not well-suited for this type of investigation. Recent developments in micro-XRF, however, have enabled trace element analysis down to the parts-per-billion (attogram) regime. This is due, in part, to a switchable X-ray target that allows the spectrometer to be optimized for the material under investigation, as well as a significantly brighter X-ray source that enhances weak detection signals. This state-of-the-art laboratory micro-XRF system has been employed to study the negative electrodes of fresh and cycled LiMnO₂ batteries, with the system tuned to identify any regions of Mn in each specimen. In our comparison, we have found that this laboratory micro-XRF spectrometer is fully capable of detecting trace levels of Mn in the graphite negative electrode, and have shown that a significant quantity of Mn may be found in the aged electrode while not being detected in the fresh electrode. This technique has thus demonstrated substantial promise for studying the migration of transition metal oxides (e.g., manganese oxide) in lithium-ion batteries, paving the way for enhanced development of commercial battery devices.

We created a unique sodium ion battery (NIB, SIB) cathode based on selenium in cellulose-derived carbon nanosheets (CCN), termed Se-CCN. The elastically compliant two-dimensional CCN host incorporates a high mass loading of amorphous Se (53wt.%), which is primarily impregnated into the 1 cm³g^-1 of the nanopores. This results in facile sodiation kinetics due to short solid-state diffusion distances and large charge transfer area of the nanosheets. The architecture also leads to an intrinsic resistance to polyselenide shuttle and to disintegration/coarsening. As a Na half-cell, the Se-CCN cathode delivers a reversible capacity of 613 mAh g^-1 with 88% retention over 500 cycles. The exceptional stability is achieved employing a standard electrolyte (1M NaClO₄ EC-DMC), without secondary additives or high salt concentrations. The rate capability is also superb, achieving 300 mAhg^-1 at 10C. Compared to recent state-of-the-art literature, the Se-CCN is the most cyclically stable and offers the highest rate performance. As a Se-Na battery, the system achieves 992 Wh/kg at 68 W/kg and 384 Wh/kg at 10144 W/kg (by active mass in cathode). We are the first to fabricate and test a Se-based full NIB, which is based on Se-CCN coupled to a Na intercalating pseudographitic carbon anode (PGC). It is demonstrated that the PGC anode increases its structural order in addition to dilating as a result of Na intercalation at voltages below 0.2 V vs. Na/Na⁺. The {110} Na reflections are distinctly absent from the XRD patterns of PGC sodiated down to 0.001 V, indicating that Na metal pore filling is not significant for pseudographitic carbons. The battery delivers highly promising Ragone chart characteristics, for example yielding 203 and 50 Wh kg^-1 at 70 and 14000 W kg^-1 (by total material mass in anode and cathode).

Vanadium oxides are among the most promising materials that can be used as electrodes in multivalent rechargeable batteries. Specifically, they can be used as cathodes in Al ion batteries, but voltages reported so far are low, limiting energy density. We use amorphization as a strategy to increase voltage and compare the energetics of Al insertion in crystalline and amorphous vanadium dioxide (VO₂). We start by developing and optimizing the force-field model for vanadium oxide phases, which are then used in generating the amorphous structure of VO₂. The Al insertion sites in both amorphous and crystalline phases are then systematically investigated by first-principles calculations. We show that Al insertion in amorphous VO₂ can occur with well-dispersed insertion energies, with a lowest energy site more thermodynamically favourable than any insertion site in the crystalline VO₂. We compute the voltage-composition profile for amorphous VO₂ and show that amorphization increases the average voltage of the VO₂ cathode by about 0.85 V, as compared to crystalline material. We also suggest that the stability of the amorphous VO₂ cathode is improved by reducing volume expansion during Al insertion, potentially leading to longer cycle life in practical applications. Overall, the demonstrated improvements suggest a high potential of amorphous VO₂ electrodes for multivalent batteries.

Due to limited natural abundance of lithium, novel battery technologies are needed for large-scale, stationary storage of electricity.¹ Such batteries can then be combined with renewable sources of electricity, for the best integration of a variety of sources into electrical grid. We will discuss the utility of graphite as cathode material in non-aqueous aluminum batteries as a highly promising post-Li-ion technology for low cost and/or large scale storage of electricity.^{2, 3} In particular, the focus will be on a balance between structural perfection of the graphite, its electrochemical performance and material’s synthesis costs. In this regard, we provide a balanced analysis of the overall cell-level energy density of graphite based aluminum batteries. In view of its non-rocking chair operation mechanism, we show the achievable energy densities as a function of the composition of chloroaluminate ionic liquid (AlCl₃ content) and compare it with other battery electrochemistries suited for stationary storage of electricity (such as lead-acid or vanadium redox flow). We will discuss also other issues associated with this technology, one being the incompatibility of most metallic current collectors with the corrosive AlCl₃-based ionic liquids. Finally, we will present a novel concept of flexible aluminum-graphite battery using current collectors from earth-abundant elements and point to further avenues to commercialization of aluminum-graphite batteries as a potential grid-level energy storage technology.⁴

References

[1] M.-C. Lin, et al. Nature 2015, 520, 324-328.
[2] K. V. Kravchyk, et al. Chem. Mater. 2017, 29, 4484-4492.
[3] S. Wang, et al. ACS Appl. Mater. Interfaces. 2017, 9, 28478-28485.
[4] S. Wang, et al. Advanced Science 2017, submitted.

Renewable energy technologies, such as regenerative fuel cells, metal-air batteries, and water electrolyzers had attracted many attentions to researchers in years¹. However, sluggish reaction kinetic of the oxygen evolution reaction (OER) has set a great challenge on the device implementation. Highly efficient electrocatalysts play a critical role in the advancement of these new energy devices. In acidic media, unsatisfactory durability of OER catalysts due to rapid catalysts dissolution has rendered the OER catalysts inactive under the high potential window in which OER occurs. Ruthenate and iridium oxide are the only two known compounds to have reasonable catalytic activity with high stability in acid electrolyte². Recently, pyrochlore-type yttrium ruthenate (Y₂Ru₂O₇) was reported to show great OER catalytic activity in acidic media^2a, but a good understanding of the structural factors that governs the OER activity is still severely lacking. A systematic study on the structural and electronic properties is essential for better material design.

To this end, we synthesized a series of pyrochlore-type ruthenate and iridium oxide by substituting the A-site with lanthanide series elements (Ln₂M₂O₇, M = Ru, Ir). With different ionic radii of the lanthanide elements, the unit cell size, MO₆ local geometry, M-O bond distance can all be systematically adjusted, making them ideal candidates to study the structural and electronic/catalytic property relationship based on our established approach^2a. Our results show OER activity of a dozen of Ln₂Ru₂O₇ electrocatalysts correlates with very well with structural parameters, such as M-O bond distance. The x-ray absorption spectroscopy (XAS) analysis, together with other techniques, provide important details that likely account for the observed performance trend.



References:
1. (a) Nocera, D. G., The artificial leaf. Acc. Chem. Res. 2012, 45 (5), 767-776; (b) Park, S.; Shao, Y.; Liu, J.; Wang, Y., Oxygen electrocatalysts for water electrolyzers and reversible fuel cells: status and perspective. Energy & Environmental Science 2012, 5 (11), 9331-9344.
2. (a) Kim, J.; Shih, P.-C.; Tsao, K.-C.; Pan, Y.-T.; Yin, X.; Sun, C.-J.; Yang, H., High-Performance Pyrochlore-Type Yttrium Ruthenate Electrocatalyst for Oxygen Evolution Reaction in Acidic Media. Journal of the American Chemical Society 2017, 139 (34), 12076-12083; (b) Seitz, L. C.; Dickens, C. F.; Nishio, K.; Hikita, Y.; Montoya, J.; Doyle, A.; Kirk, C.; Vojvodic, A.; Hwang, H. Y.; Norskov, J. K.; Jaramillo, T. F., A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction. Science 2016, 353 (6303), 1011-1014.

With the development of electric vehicles on the rise, what will be the fate of the over 250 million combustion engine vehicles in the United States? Recycling the elemental lead from the lead-acid batteries in our vehicles for use in low cost sodium-lead batteries may be a promising route for large scale energy storage. Additionally, the infrastrucutre for recycling these batteries is already in place, with over 95% of lead-acid battery waste currently being recycled. Previous sodium-lead anode chemistries have shown high volumetric energy densities at the cost of poor cycling performance due to the high volumetric expansion associated with sodium lead alloying. This work highlights the use of diethylene glycol dimethyl ether (diglyme) as an electrolyte solvent to improve the cyclic stability of sodium-lead alloying at the anode. Diglyme molecules are hypothesized to form weak coordinations with sodium cations, and these freely moving complexes enhance the diffusion of sodium through the SEI layer without damaging the layer, which preserves its protective properties throughout cycling. This novel chemistry allows the fabrication of sodium-lead batteries with high capacity per unit volume, while retaining the capacity through hundreds of cycles. Relative to its lithium-ion counterparts, the abundance and cost of the raw materials for this device are the highlights of its potential impact on the future of energy storage. If the lead-acid battery from every vehicle in the United States were recycled, the resulting quantity of sodium-lead grid energy storage would exceed 700 GW, which would enable the storage of 70% of the nation's current energy production (~1000 GW).

The development of inexpensive, reliable, and environmentally benign energy storage technologies will enable renewable energy sources like wind and solar at the energy grid level. Alkaline Zn/MnO₂ batteries have traditionally been limited to ~ 30 rechargeable cycles; however, recent studies have achieved hundreds to thousands of cycles by utilizing chemical additives or novel cycling protocols. These results, coupled with the batteries’ existing supply chain, low manufacturing costs, environmental compatibility, and non-flammability, have made the Zn/MnO₂ battery chemistry a promising candidate for grid-level energy storage applications.

Recent results have shown that Zn/MnO₂ batteries can be cycled over 3000 times when only a fraction of the cathode’s theoretical capacity is accessed during each cycle. These limited depth of discharge (DOD) systems have demonstrated costs of $100 to $150 per kWh delivered. The effects of battery additives, however, have not yet been studied in a Zn/MnO₂ battery cycled in this fashion. Here, we demonstrate an improvement in alkaline Zn/MnO₂ battery cycle-ability under limited DOD conditions in the presence of an electrolyte additive, triethanolamine (TEA). In addition to studies on full cells, the effect of TEA on each battery component (cathode, anode, and separators) was investigated by cyclic voltammetry, real-time stripping voltammetry, x-ray diffraction measurements, and scanning electron microscopy.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Dr. Imre Gyuk, Energy Storage Program Manager, Office of Electricity Delivery and Energy Reliability is also thanked for his financial support of this project.

Two-dimensional (2D) layered transition-metal dichalcogenides has been regarded as highly useful electrode materials for rechargeable lithium-ion and sodium-ion batteries. However, their metal ion storage mechanism (conversion reaction or intercalation) and cyclic stability depends on the potential region as well as nanostructure design. In this talk, we will present our detailed investigation on ultrathin MoS_2-xSe_x nanoflakes vertically aligned on the 3D lightweight graphene foam (MoS_2-xSe_x/GF) in Na-ion storage. Sample is fabricated by a hydrothermal reaction followed by a selenization process. As a freestanding electrode, the MoS_2-xSe_x/GF demonstrates high-rate reversible Na-ion storage, where both the capacity and rate-performance are enhanced by the selenium substitution. We show that by adjusting the potential range it is possible to maintain the 2D layered structure and improve the capacitance retention by the intercalation mechanism. The irreversible conversion reaction has been verified with in-situ Raman spectroscopy and ex-situ X-ray diffraction measurements. This study shed new light on better understanding the electrochemical performance of 2D transition metal chalcogenides in batteries.

Aqueous zinc ion batteries (ZIBs) have received incremental attention because of cost effectiveness and abundance of Zn source. MnO₂ is a most promising cathode material for ZIBs due to its high capacity, abundant material supply, and excellent safety. However, it suffers from low electronic conductivity, which results in sacrificed capacity and low rate performance of the cathode. Conventionally, introducing conducting additives (such as carbon black, super P, carbon nanotube, or poly(3,4-ethylenedioxythiophene) with mass ratio ranging from 20%-33%) would help to improve the electronic conductivity of the MnO₂-based electrode. On the other hand, binders (such as polyvinylidene fluoride or carboxymethyl cellulose with mass ratio around 10%) are required to construct a workable cell. Finding efficient additives that enhances the electronic conductivity of MnO₂, while at the same time minimizing the content of both additives and binders, become a tempting goal as it would lead to high performance electrode with high packing density. In the present work, we demonstrate a binder free composite electrode of MnO₂/reduced graphene oxide (rGO) with high MnO₂ mass ratio (80 wt% of MnO₂) using vacuum filtration. No additional additives (other than rGO) is introduced. The MnO₂ nanosheets are homogeneously distributed on the surface of rGO sheets. Enhanced capacity, improved rate capability and cyclability are achieved in the MnO₂/rGO composite electrodes, when compared to the conventional MnO₂ electrodes. The MnO₂/rGO composite electrodes have manifested the merits of an ideal electrode material: high capacity (301.4 mAh g^-1 at 0.15 A g^-1), fantastic rate capability (172.3 mAh g^-1 at 6 A g^-1), and cycling stability (the capacity retention remains 97.8% after 500 charge/discharge cycles at 6 A g^-1). Our work demonstrates that the MnO₂/rGO composite electrodes are one of the most attractive cathodes in zinc storage applications.

Potassium (K) is an element almost as abundant as sodium and with a low standard redox potential comparable to Li/Li⁺, which makes the investigation of K-based batteries a field which has been gaining interest lately. A group of possible cathode materials which has not been studied in detail yet are crystalline vanadium oxides, although their excellent metal insertion properties are known for a variety of other alkali and alkaline earth elements. In this study, four promising vanadium oxide phases (layered α-V₂O₅ and β-V₂O₅, non-layered bronze- and rutile-type VO₂) are investigated from first principles as potential electrode materials for K ion batteries. Insertion energetics and diffusion barriers at the dilute limit were computed and changes in electronic structure upon K insertion (densities of states, charge density distributions) analyzed. We investigated the influence of dispersion corrections on the potassiated layered and non-layered vanadium oxides in order to choose an appropriate computational setup for all phases. Our results show that the metastable β-V₂O₅ provides the lowest (strongest) insertion energies for K and the lowest diffusion barriers compared to orthorhombic α-V₂O₅, bronze- and rutile VO₂. While three of these phases show an energetically favorable potassiation and relatively small diffusion barriers, VO₂(R) is predicted to be incapable of electrochemical K incorporation.

Recently, sodium-ion batteries have received a renewed interest due to the cheap a