Transition metal dichalcogenides (TMD), analogue of graphene, could form various dimensionalities. Similar to carbon, one dimensional (1D) nanotube of TMD materials has wide application in hydrogen storage#65292;Li-ion batteries and super-capacitors due to their unique structure and properties. Here we demonstrate the feasibility of tungsten disulfide nanotubes (WS₂-NTs)/graphene (GS) sandwich-type architecture as anode for lithium-ion batteries for the first time. The graphene based hierarchical architecture plays vital roles in achieving fast electron/ion transfer, thus leading to good electrochemical performance. When evaluated as anode, WS₂-NTs /GS hybrid could maintain a capacity of 318.6 mA/g over 500 cycles at a current density of 1A/g. Besides, the hybrid anode does not require any additional polymetric binder, conductive additives or a separate metal current-collector. The relatively high density of this hybrid is beneficial for high capacity per unit volume. Those characteristics make it a potential anode material for light and high performance lithium-ion batteries.

Silicon, with a high specific capacity ~ 3,579 mAh/g, has been widely investigated as anode materials in lithium ion batteries [1]. There are few well know issues preventing the commercialization of silicon for this application, such as pulverization induced by volume expansion, low electrical conductivity, unstable solid electrolyte formation upon cycling. These issues have been addresses to some extent, although many of the proposed nanostructures that solve these problems are realized using slow and difficult to scale techniques. We propose a simple, scalable method to produce a metal-silicon nano-structure and we verify its applicability as anode material for lithium-ion batteries. NiO-Si core shell particles are synthesized utilizing a one-step spray pyrolysis method starting from a mixture of silicon nanoparticles and NiCl₂.6H₂O water based precursor. After coating, the core shell NiO-Si structure is annealed either at low temperature (<200°C) in a hydrogen atmosphere, or at 500°C in presence of polyvinylpirrolidone (PVP). These two procedures form either a Ni cage - Si core structure or a similar cage structure but covered with an amorphous carbon layer . Our preliminary results indicates that the latter structure has good electrical conductivity and prevents the direct contact between silicon nanoparticle and the electrolyte, resulting in an anode that maintains a high specific discharge capacity (>1240 mAh/g, silicon basis) for 110 cycles at 0.5 C discharge rate. The amorphous carbon coating successfully prevents the silicon nanoparticles inside the shell from directly contacting the electrolyte during cycling. We verified this by testing the battery performance with and without fluoroethylene carbonate (FEC) additive, finding little to no change in capacity and stability. In the case of silicon in direct contact with electrolyte, FEC additive helps forming thinner and more stable SEI on silicon surface improving the cycling performance [2]. In addition to its scalability, another advantage of this technique is its potential applicability to other material systems, such as NiO-Sn, NiO-SnO etc.
[1] M. N. Obrovac and L. Christensen, Electrochemical and Solid State Letters 2004, 7, A93-A96.
[2] C. C. Nguyen and B. L. Lucht, Journal of The Electrochemical Society 2014, 161(12), A1933-A1938.

As the leading battery technology, lithium-ion batteries (LIBs) have been widely used in consumer electronics. However, for future large-scale applications in electric or hybrid vehicles, further improvement would require concerning power and energy density demanded by such applications. Compared with the theoretical specific capacity of commercialized graphite (372 mAh/g) which is widely used as anode material in LIBs, the transition metal oxide shows great promise as they can provide much higher capacities and rate capabilities. For example, Zinc Ferrite (ZnFe₂O₄), which can be regarded as the replacement of one iron atom of Fe₃O₄ by zinc element, can provide an enhanced theoretical capacity of 1000mAh/g. To date, many efforts have been put on developing transition metal oxide based nanostructured-materials to enhance the rate performance. These nanostructures, such as nanoparticles, hollow nanospheres, nanotubes, etc., are effective in facilitating the Li ion diffusion due to a reduced diffusion length within the active materials and an increased electrolyte/electrode contact area. Moreover, carbon-based nanocomposites formed by carbon coating proved to enhance not only the ionic but also the electronic conductivity of electrode, which is very promising for high rate performances.
Here we propose a general method to synthesize carbon-coated ZnFe₂O₄ nanocrystals with various nanostructures templated by star-like poly (acrylic acid)-block-polystyrene (PAA-PS) diblock copolymer and polystyrene-block-poly(acrylic acid)-block-polystyrene (PS-PAA-PS) triblock copolymer. Through a strong coordination bonding between the metal moiety of inorganic precursors and the functional groups of PAA (-COOH), ZnFe₂O₄ nanocrystals can be selectively incorporated into the space formed by the PAA block in star-like block copolymer templates. As a result, ZnFe₂O₄ nanoparticles and hollow nanospheres can be synthesized guided by the star-like PAA-PS and PS-PAA-PS templates, respectively. In addition, the size of ZnFe₂O₄ nanocrystals could be easily changed by varying the molecular weight of templates. The soft template not only serves as an easy control over the size and shape of ZnFe₂O₄ nanocrystals, but also acts as carbon source when calcinated at high temperature at argon atmosphere. We demonstrated that the carbon-coated ZnFe₂O₄ nanoparticles and hollow nanospheres obtained by the templating method would be superior anode materials for LIBs.

The bronze polymorph of titanium dioxide (TiO₂-B) is interesting for many applications including high rate lithium ion batteries (LIBs), solar cells, photocatalysis, thermoelectrics and sensing, owing to its uniquely layered structure with open channels and highly asymmetric unit cell. However, such a metastable phase is extremely hard to obtain with high purity and crystallinity, significantly impeding its development in these fields. After more than 30 years since the first synthesis of TiO₂-B in 1980, hydrothermal methods are still the dominant route to produce this material in powder form, with limited purity, randomized crystal orientation and unavoidable presence of lattice water. Here we report the discovery of a waterless process to synthesize hetero-epitaxial crystalline thin films of TiO₂-B using pulsed laser deposition (PLD) onto its more stable variant, Ca:TiO₂-B (CaTi₅O₁₁), which serves as a template. The growth mechanism and various microstructures in the thin films are clearly shown at the atomic scale. By aligning the more open channels to out-of-plane directions, extremely high rates of lithium ion transport, up to 600C, with extraordinary structural stability can be achieved. As the methods and equipment required are readily accessible to the extended research community, we anticipate our report may stimulate further studies on and applications of these materials, which are attractive in realms that extend beyond LIBs.

During the past two decades, it has become clear that structural defects can greatly alter the behavior of nanoscale materials. With increased use of nanomaterials in the electrode architecture of Li-ion batteries, one should take into account how such defects can influence the electrochemical response of battery electrodes. In spite of this need, our fundamental understanding about the kinetics of lithium ions at microstructural defects is at its infancy. Here, we report, for the first time, the lithiation behavior of the individual SnO₂ nanowires containing twin boundary (TB). Comparing with the single crystal SnO₂ nanowire, in which the lithium ions preferred to diffusion along the [001] direction, our in situ TEM study indicates that the lithium transport pathway will totally change when the TB exists inside the SnO₂ nanowires. Direct atomic-scale imaging of the initial lithiation stage of the TB-SnO₂ nanowire and the DFT simulations prove that the lithium ions prefer to intercalate in the vicinity of the TB, which acts as a conduit for lithium ion diffusion inside the nanowires. Our results should lead to working out the great impact of interfaces on mass transfer, transport and storage and guide the development of high performance electrochemical devices that rely on ion transport by microstructure engineering.

The previous studies on SnO₂ as electrode materials convey a message that the inevitable pulverization of SnO₂ particles can be resolved by carbon-based materials. Since graphene has also proved effective for the harmful decrepitation of the particles with an advantage of electronic conductivity, wrapping SnO₂ by sufficient amount of graphene seems to be an answer to enhancing its cycle life. On the other hand, severe wrapping of SnO₂ by graphene is deleterious to its rate capability due to the sluggish motion of Li⁺ through the stacked graphene layers. Thus, in order to make graphene sheets favorable for Li-ion diffusion, they were modified to have large porosity with 3-D architectures, by a simple heating-rate control. The porous graphene-wrapped SnO₂, having direct diffusion channels for Li⁺, outperforms the SnO₂ with less-porous graphene. Consequently, the excellent performances are fulfilled, showing both stable cyclability (~1100 mAh g^-1 up to 100 cycles) and high rate capability (~690 mAh g^-1 under 3600 mA g^-1). This strategy using porosity-tuned graphene sheet furnishes a valuable insight into the effective encapsulation of active materials, especially for those undergoing pulverization during cycling.
[1] Y. Oh, S. Nam, S. Wi, J. Kang, T. Hwang, S. Lee, H. H. Park, J. Cabana, C. Kim and B. Park, J. Mater. Chem. A2, 2023 (2014).
[2] S. J. Yang, T. Kim, H. Jung, and C. R. Park, Carbon53, 73 (2013).
Corresponding Author: Byungwoo Park: [email protected]

Si based anode materials for lithium-ion batteries have gained much attention due to its high theoretical capacity (3,580 mAhg^-1). However, Si anode materials have critical limit to commercial use because of poor cycle performance associated with severe volume changes during cycling. To solve this problem, various approaches have been suggested. In particular, porous structure of Si materials would be helpful for improvement of cycle performance. In this work, C-coated mesoporous SiO_x nanoparticles were prepared as anode materials for lithium-ion batteries using a sol-gel reaction of Si precursor with oil templates. The hydrophobic oil, pore former, was uniformly distributed into the SiO_x precursor. After heat treatment under reducing atmosphere, the residual oil was contributed to form the carbon layer, which would be assisted to improve electrical conductivity of active materials, on the surface of SiO_x matrix. The C-coated mesoporous SiO_x nanoparticles showed a reversible capacity of 730 mAhg^-1 at current density of 200 mAg^-1 with stable cycle performance over 100 cycles and high rate capabilities. The microstructure and electrochemical properties of the C-coated mesoporous SiO_x nanoparticles will be discussed in more detail.

Technological improvements in lithium-ion batteries (LIBs) are being driven by an ever-increasing demand for portable electronic devices and electric vehicles applications. The main challenge remains developing electrode materials with high capacity, excellent rate performance and longer lifespan. The spinel-type transition metal oxides (AB₂O₄), particularly in the form of nanomaterials, have long been exploited as high capacity anode for LIBs; however, their poor Li⁺ and e^- conductivity and huge volume change upon cycling impede the high-rate and cyclability performance towards its practical application. Here we present a general and facile approach to fabricate flexible spinel/reduced graphene oxide (rGO) composite aerogels as a binder-free high-performance anode where the spinel nanocrystals are integrated within an interconnected rGO network. Benefitting from the hierarchical porosity of rGO aerogel and its mechanical stability, the hybrid system synergistically enhances the intrinsic properties of each component, yet robust and flexible. As a result, the spinel/rGO composite aerogel demonstrates superior electrochemical performance up to 60C (1C = 1 A g^-1) and long-term stability over 250 cycles at 1C rate (still ongoing). We believe the versatile strategy developed here can be easily extended to the co-assembly of rGO with other functional metal oxides/sulfides for diverse applications as e.g. supercapacitors or in catalysis.

Magnesium hydride MgH₂, which is a well-known compound for hydrogen storage, had been investigated as a novel anode material for lithium-ion batteries reported by Oumellal et al.^[1] The theoretical capacity of MgH₂ is 2038 mA h g^-1 if 2 Li⁺ incorporate into MgH₂, which is almost 6 times to that of graphite. However, the capacity fades rapidly and reduces to less than 200 mA h g^-1 after only 5 ~ 10 cycles ^[1,2], and no improvement had been done for years. In this study, we had successfully retained the reversible capacity of MgH₂ electrode by using LiBH₄ as a solid-state electrolyte. The result shows a stable reversible capacity of approximately 1230 mA h g^-1 can be obtained in the cycling test at a current density of 100 mA g^-1 between 0.3 and 1.0 V with nearly 100% capacity retention and 100% coulombic efficiency. The electrode evolution upon discharge-charge process at different stages had also been investigated in this study. This work opens a new way to look for high capacity anode materials for lithium-ion batteries. In addition, the electrochemical performance of numerous metal hydrides will be investigated by using LiBH₄ based solid-state electrolytes.
References:
[1] Y. Oumellal, A. Rougier, G. A. Nazri, J. M. Tarascon, L. Aymard, Nat. Mater.2008, 7, 916.
[2] S. Brutti, G. Mulas, E. Piciollo, S. Panero, P. Reale, J. Mater. Chem.2012, 22, 14531.

Size tunable SnO₂ nanocrystals (NCs) encapsulated in 3d macroporous carbon as anode materials for lithium-ion batteries (LIBs) have been synthesized via a rapid, scalable combustion method by using the biodegradable and recyclable polyvinyl alcohol (PVA) foam as the carbon source. The electrostatic forces between the copious hydroxyl groups of purified PVA sponge and tin precursor guaranteed the uniformly and intimate integration of tin oxide nanocrystals on the carbon matrix. The ultrafast combustion process carbonized the processed PVA molecules into a 3d carbon matrix, which not only encapsulated the SnO₂ nanocrystals to buffer the volume changes during the lithiation/delithiation process, but preserve the interconnected pore system for the facile electrolyte percolation. The best performing electrode based on the composite with optimized size range of SnO₂ NCs and graphitization degree of carbon delivered a remarkable rate performance up to 8 A g^-1 and long term cyclability up to 500 cycles for Li⁺ storage. Based on the detailed electrochemical analysis, in-situ technique and post-mortem morphological characterizations, we confirmed and quantitatively analyzed the contributions from traditional alloying/de-alloying mechanism and non-diffusion controlled pseudocapcitive behavior to the high rate Li⁺ storage.

In this work, the usage of TiNb₂O₇ (TNO) thin films as anode material is successfully demonstrated for the first time. The TNO thin films were deposited by pulsed laser deposition (PLD). The grazing incidence X-ray diffraction and high resolution transmission electron microscope analyses reveal the phase pure monoclinic crystal structure of TNO thin films grown on Pt (200)/TiO₂/SiO₂/Si (100) substrates. The field emission scanning electron microscopy and atomic force microscopy studies show that TNO films consist of pyramidal shape like morphology of 120 nm average grain sizes. The average RMS roughness was found to be 10.8 nm. The XPS studies confirm the chemical state of Nb, Ti as +5, +4 with good cation stochiometry. The galvanostatic charge/discharge cycle studies indicated the initial discharging specific capacity at 88 µAh µm^-1 cm^-2 and charging specific capacity at 91 µAh µm^-1 cm^-2 at 30 µA cm^-2 current density. Further, the structural and morphology analysis on TNO films after charge-discharge cycles reveal its excellent crystal structure stability and less volume expansion. The excellent columbic efficiency of 92 % is observed for first 12 cycles. The average Li insertion voltage was found to be at 1.65 V with excellent reversibility reaction and fast kinetics from cyclic voltamogram test. These non optimized preliminary results suggest TNO thin films can be used as new anode material for Li-ion rechargeable batteries with high specific capacity, good structural stability and excellent reversibility.

Here we report on the use of vertically aligned carbon nanotubes (VA-CNTs) with controlled length and artificially modified morphologies as an anode material for lithium-ion batteries. The lithium ion storage capacity of the CNTs modified physically by ion milling process is improved significantly compared to the non-modified case because their vertical alignment can increase the accessibility of Li ions, and Li ion diffusion into the CNTs through the surface defects can shorten the diffusion length. The irreversible discharge capacity of the modified VA-CNTs anode reaches up to 2350 mAh/g at 2C in the first cycle, and the reversible capacity is in the range of 1200 to 557 mAh/g for the 2nd to 20th cycles. These results suggest that the morphology of the CNTs with structural and surface defects play an important role in enhancing the capacity and make them excellent candidates for high performance electrode materials in Li ion batteries.

We demonstrate the synthesis of Cu-Li₂O@Si core-shell nanorod arrays via the lithiation of pre-synthesized CuO@Si core-shell nanorod arrays during the first cycle. When the voltage is set at the usual voltage range of Si anodes (0.01~2 V), the reaction between CuO and lithium is irreversible. Therefore, Cu-Li₂O@Si core-shell nanorod arrays are the actual anode materials of lithium-ion batteries after the first lithiation process, which show a high capacity of 1977 mAhg^-1 after 100 cycles and good cycling performance at 0.2 C. The core-shell structures can enhance the conductivity and accommodate the volume change during the lithiation/delithiation process, which may be responsible for the good performance. The morphology and structure of CuO@Si core-shell nanorod arrays after 5 cycles has been characterized by the TEM, HRTEM and SEAD pattern, confirming the lithiation/de-lithiation mechanism of the anodes. The synthetic process has been integrated in the electrochemical testing process via the voltage control, which can be extended to other core-shell structures as high-performance anodes of LIBs.

Novel lignin-based carbon composite materials consisting of amorphous and crystalline domains have been developed for use as anodes in lithium-ion batteries. The performance of these anodes is comparable to conventional anode materials at a significantly reduced manufacturing cost. However, the mechanism behind the performance of these novel materials is unknown. In this work, we develop an understanding of this mechanism through the use of reactive molecular dynamics simulations performed on computational models of the experimental systems. The nature of lithium-ion mobility in each domain and the degree of ion storage vs diffusion is ascertained as a function of ion-loading and related to structural properties of each composite system, including crystallite size, volume fraction of crystalline material, and composite density. Voltage profiles of the model systems are compared to those obtained from experiment. The molecular mechanism behind the performance of these systems is used to formulate a prediction of an ideal combination of material properties that would allow the development of even higher performing composite anodes.

Commercialization of electric vehicles (EV) is hindered due to the fact that present Li-ion batteries offer low rate capability performance. EVs require an energy storage system that can show potential in terms of all electrochemical parameters like high capacity, long cycle life, high coulombic efficiency and high power density. Presently used anodes in Li-ion batteries are stable and show long cycle life however some modifications are needed to enhance their rate capability performance. A comprehensive comparative study is conducted to study the parameters that can improve rate-capability of graphitic anodes. Five different graphite samples having different particle sizes, crystalline diameter, contact angle and surface area are used in comprehensive study. Electrochemical tests including rate-capability test, diffusivity test (GITT), hybrid pulse power characteristics are conducted to examine battery behavior at elevated C-rates. The results revealed rate-capability highly depends on different features of materials like wet-ability, porosity and surface area of material.

Flexible lithium-ion batteries (LIBs) is considered as most promising energy source for the next-generation flexible portable electronics devices. Flexible LIBs require a mechanical durability against repeated deformation that commonly occurs in flexible electronic devices. However, research on flexible LIBs is still in the nascent stage. In this study, we report the fabrication of a binder-free metal fibril mat-supported Si (Si@SFM) anode by a one-step process using a sputtering method. Fabrication of the Si@SFM anode was carried out using the radiofrequency (RF) magnetron sputtering method. In order to evaluate the electrochemical properties was fabricated by using the anode, 2032 coin-type half-cells were prepared and exhibited stable capacity retention. These results suggest that the Si@SFM electrode is readily suitable for use in rechargeable flexible LIBs.

Here we demonstrate a novel strategy for the preparation of graphene wrapped silicone@ polyaniline nanoparticles (Si@PANi/graphene). Si nanoparticles were covered by PANi via chemical polymerization, and the Si@PANi nanoparticles were wrapped by graphene under supercritical carbon dioxide fluid (scCO₂). Structure, composition, surface area and pore distribution of Si@PANi/graphene were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM) images, X-ray diffraction analysis (XRD), thermogravimetic analysis (TGA) and Brunauer-Emmett and Teller analysis (BET). The electrochemical properties as a Li-ion battery anode were also characterized by galvanostatic charge-discharge test, cyclic voltammetry and electrochemical impedance spectroscopy. With the aid of scCO₂, Si@PANi particles were homogeneously deposited between graphene sheets, providing a stable and efficient electrical contact between silicon particles during cycling, and consequently Si@PANi/graphene showed high capacity, cyclic stability and rate-capability.

The rapid development of the integrated circuit (IC) and Micro/Nano-Electro Mechanical System (M/NEMS) technologies are promoting the continued emergence or commercialization of the miniaturized autonomous devices such as wireless sensor networks (WSN) in smart grid.[1-4] In order to operate independently, the micro/nano autonomous electronic devices must have on-board power supply. However, the battery miniaturization still can not keep pace with the size scaling-down of the CMOS electronic technologies, due to the poor electrochemical performance of the micro/nano batteries or the un-compatible battery fabrication process with the IC technologies. Currently, the transition from two dimensional (2D) to three dimensional (3D) rechargeable LIBs with better electrochemical properties in a small areal footprint was found to cope well with state-of-the-art semiconductor technologies conceptually providing new opportunities for micro/nano power systems in the future. [5-7]
In this work, the electrochemical performances of 3D hexagonal match-like Si/Ge nanorod (NR) arrays buffered by TiN/Ti interlayer, which were fabricated on Si substrates by a cost-effective, wafer scale and Si-compatible process, were demonstrated and systematically investigated as the anode in lithium/sodium ion batteries (L/SIBs). The optimized Si/TiN/Ti/Ge composite NR array anode displays superior areal/specific capacities and cycling stability by reason of their favourable 3D nanostructures and the effective conductive layers of TiN/Ti thin films. Lithium/Sodium ion insertion behaviors were experimentally investigated in post-morphologies and elemental information of the cycled composite anode, and theoretically studied by the first principles calculations.
References:
[1]. Scott E. Thompson and Srivatsan Parthasarathy, materialstoday, 2006, 9, 20-25.
[2]. Yunhao Liu, Yuan He, Mo Li, IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS, 24, OCTOBER 2013.
[3]. Jeffrey W. Long, Bruce Dunn, Debra R. Rolison, and Henry S. White, Chem. Rev., 2004, 104, 4463-4492
[4]. Timothy S. Arthur, Daniel J. Bates, Nicolas Cirigliano, Derek C. Johnson , Peter Malati, James M. Mosby, Emilie Perre, Matthew T. Rawls, Amy L. Prieto, and Bruce Dunn, MRS Bull., 2011, 36, 523-531.
[5]. Loïc Baggetto, Harm C. M. Knoops, Rogier A. H. Niessen, Wilhelmus M. M. Kessels, and Peter H. L. Notten, J. Mater. Chem.,2010, 20, 3703-3708.
[6]. Alireza Kohandehghan, Peter Kalisvaart, Kai Cui, Martin Kupsta, Elmira Memarzadeha, and David Mitlin, J. Mater. Chem. A, 2013, 1, 12850-12861.
[7]. Peter H.L. Notten, Fred Roozeboom, Rogier A.H. Niessen, and Loïc Baggetto, Adv. Mater., 2007, 19, 4564-4567.

As the widespread emergence of modern technologies combined with human life, lithium ion battery (LIBs) has become one of the most important energy power sources focused on vehicles for transportation and stationary applications. However, the current LIBs provide a low energy density with reaching the theoretical limits, which emphasize the urgent need for new high energy density battery systems.
Herein, we have prepared the amorphous silicon nanolayer-embedded graphite/carbon hybrids by chemical vapor deposition (CVD) method with developing the cost-effective and scalable rotating furnace. This method broke out the fixed idea about the use of silane gas (SiH₄) on the uncompetitive prices. In addition, hybrid materials not only exhibit reversible specific capacity increases from 357 mAh g^-1 in accordance with natural graphite to 523 mAh g^-1 with the industrial electrode density (>1.6g cc^-1) but composite electrode allows for a high volumetric capacity (832mAh cm^-3) even with areal capacity loading of >3mAh cm^-2. Moreover, high coloumbic efficiency (92%) during the 1^st cycle and rapid increase of cycling efficiency reached 99.5% over only 6th cycles were confirmed, which is quite comparable to those of commercial graphite. These efficiencies have a decisive effect on full cell performance. Including silicon, there has not been reported on matching up the electrode density and composition same with those of commercial graphite (571mAh cm^-3) as of yet. In consequence, this successful hybrid anode could be extended to high-energy battery systems as a major breakthrough for electric vehicle or grid energy storage applications.

Recently, the technology of portable electronic equipment has been developed in various types. For example roll-up displays, wearable devices, and implanted medical devices. Therefore, Battery should possess appropriate form to meet with demands from various applications. In addition, high energy density battery such as lithium ion battery is required for current portable electronic equipment. Silicon offers one of the highest gravimetric capacities after lithium metal. Graphite is commonly used anodes in lithium ion battery due to its high reversible capacity and good cycling stability. Herein, we report a novel 3D structure anode based on combining graphite and silicon materials using soft lithography and RF-sputtering method.

Silicon has a great potential as anode material in lithium-ion batteries due to its high theoretical capacity. However, silicon undergoes a large volume change during cycling, causing stress to build up and eventually leading to fracturing of the electrode material. The most common approach to solve this issue is to use nanostructured silicon, like nanoparticles, wires, thin films and porous structures. While this limits the fracturing of the electrode, it also results in very high specific surface area structures, making silicon&’s inability to form a stable solid electrolyte interface (SEI) the primary issue. A number of factors influence the formation of the SEI, making it a difficult process to control, but also makes it possible to manipulate. Previously it has been shown that a coating of TiN and TiO enhances the cycling stability and Coulombic efficiency of silicon electrodes. In this project the effect of coating silicon in silicon nitride and silicon carbide is investigated using a thin film model system. Silicon nitride has been determined to function as a conversion electrode material while silicon carbide is regarded as electrochemically inactive. The hypothesis is that both of these coatings will take part in and affect the formation of the SEI, but by different mechanisms. These mechanisms and their effect on the electrode performance are analyzed using electrochemical characterization, as well as TEM and related spectroscopy techniques.
For this work, silicon thin films are deposited on copper and nickel substrates using PECVD with silane (SiH₄) as precursor. SiN and SiC coatings are obtained by adding ammonia and methane to the gas flow in the late stages of the deposition, respectively. Different coating stoichiometries are made by varying flow rate of the gasses. The pristine films are then characterized using spectroscopic ellipsometry and (S)TEM/EELS to determine their thickness and quality. Electrodes are then punched from the film, mounted in coin cells with lithium metal as counter electrode, and cycled at C/3 between 0.05 volts and 1 volt. Some cells are also run at increasing current rate to probe their high rate capability. Impedance spectroscopy is conducted at different steps during cycling to monitor the degradation mechanisms of the electrodes. Post mortem analysis of the cells, particularly with regard to SEI formation, is done using (S)TEM/EELS.
Early experiments have shown a dependency between capacity retention and nitrogen content of silicon nitride coated silicon thin film electrodes, with increasing nitrogen content resulting in increased capacity retention. The effect reaches a maximum for a slightly nitrogen deficient coating with respect to stoichiometric silicon nitride. These experiments also revealed an increased rate capability of the nitride coated electrodes compared to the non-coated electrodes, indicating that the hypothesized SEI-stabilizing effect did indeed occur.

Si based anode materials for lithium-ion batteries have gained much attention due to its high theoretical capacity (3,580 mAhg^-1). However, Si anode materials have critical limit for commercial use because of their poor cycle performance associated with severe volume changes during cycling. To solve this problem, various approaches have been suggested. In particular, SiO_x materials showed promising behaviors as anode materials for lithium ion battery. In this work, Si/SiO_x nanocomposite were prepared by heat treatment of hydorgen silsesquioxane (HSiO_1.5) through sol-gel reaction of triethoxysilane. Si/SiO_x nanocomposite materials showed stable cycle performance with reversible capacity of about 900 mAhg^-1. More detailed electrochemical performances and ex-situ analysis of Si/SiOx nanocomposite materials during cycling will be discussed in this presentation.

Although reducing graphene oxide (GO) is suitable for mass production of graphene, it is highly challengeable to obtain high quality reduced graphene oxide (RGO) with cost-effective, environmentally friendly, and safe methods. In this presentation, new reduction route of GO through mechanochemical process will be presented. RGOs with various degrees of graphitization were prepared from metal-assisted room temperature mechanochemical treatment of GO. Various analytical techniques including XRD, XPS, Raman, TGA, FT-IR, and TEM revealed that the mechanochemical treatment resulted in not only deoxygeneration of GO, but restoring the formation of graphitic carbon structure of GO. Furthermore, the relationship between the degree of graphitization of RGOs and their electrochemical properties was investigated as lithium storage materials. Electrochemical tests combined with physicochemical characterization on the RGOs showed that reversible capacity and rate capability of RGOs are highly dependent on the degree of graphitization of RGOs.

Theoretical capacity of Si is 3580mAh/g, which is much larger than that of graphite. However, Silicon has critical disadvantages, of low electrical conductivity and capacity fading caused by the drastic volume change that occurs during the charge-discharge cycle. The sol-gel process has several advantages e.g, considerably low working temperature and facile production of porous films and bulk materials with various shapes. In this study, silicon nanopowder was coated by TiO₂ layer which can play a buffer layer.
The ratios of silicon to TiO₂ were 10:90, 30:70, and 50:50. The samples were heated at 500#8451; and 700#8451; for 2 hours. The samples were analyzed with TGA(Thermogravimetric analysis), SEM(Scanning Electron Microscopy), and XRD(X-ray diffraction). Electrochemical properties were analyzed with Maccor series-4000.
The phase transition of TiO₂ starts at 500#8451; and weight increase at 800 #8451; due to silicon oxidation. Before heat treatment, TiO₂ phase was not observed by XRD because the phase was amorphous. But after heat treatment, the peaks were observed due to a transformation that occurred from the amorphous phase to the anatase or rutile phase. As more TiO₂ was added, the particle size increased. The capacity of the sample which was heated at 700 #8451; was better than that heated at 500 #8451;.

Birnessite is a layered manganese oxide with charge neutralizing alkali metal ions between the layers. Over the years, it has attracted interest for applications both within Li-ion batteries and supercapacitors, because it is an excellent precursor for low-temperature synthesis of manganese oxide-based materials such as LiMn₂O₄ - spinel and Hollandite. Most syntheses leading to highly crystalline Birnessite either requires hydrothermal conditions or a high temperature (400-500 C) post-treatment step for extended periods of time ranging from days to months. In a recent report, Fold von Bülow et al. described a fast synthesis leading to highly crystalline Birnessite within one hour at a synthesis temperature of only 65^oC.(Adv. Energy Mater. 2012, 2, 309) and we can now present a detailed kinetic study of a slight modification of this synthesis. We observe that small Birnessite crystals form virtually immediately upon mixing of the reactants, albeit initially of lower crystallinity. The size of the fully developed crystalline Birnessite platelets are in the micrometer-sized platelets with a thickness of about 20 nm after a reaction time of 30 min. Importantly, monovalent cations are entering the structure gradually, and, depending on the cation, this process takes anything from an hour to several hours until equilibrium is reached. The relative contents of Li⁺, Na⁺, and K⁺ also change continuously. Interestingly, this leads to structural changes in the manganese oxide layers, without affecting the interlayer. Furthermore, at short reaction times, simple metal salts precipitate in parallel with the Birnessite, but only Birnessite of high crystallinity can be observed after some hours of synthesis, which is in good agreement with the observed continuous electrochemical properties of the novel Birnessite materials when mixed with carbon, and show that the capacities are high, and that both the carbon as well as the Birnessite contributes to the total capacities. Importantly, we also show that while the capacity of Birnessite increases with the number of cycles do to enhanced ion-exchange, the opposite is observed for the carbon. This novel finding has important implications for further optimizations towards supercapacitors based on Birnessite.

For the past two decades since Li ion batteries were commercialized, graphitized carbon has been the dominant anode material. Efforts to change the anode to other group IV materials, like silicon, which might provide greater storage capacity are hindered by large volume changes which occur during intercalation/deintercalation of the Li ion [1]. Higher energy density is extremely desirable in demanding applications such as electric vehicles. An analysis of the optimal void space into which a Li ion would comfortably fit, gives a diameter of about 0.43 nm [2]. Such a spacing is difficult to obtain even with layered materials like graphite, let alone more densely packed materials like silicon. The objective of this research is to find cage shaped host materials which have large enough interior voids that can accommodate Li ions without excessive deformation. Host materials investigated include 2D cages such as 1,3,5,7-cyclooctatetraene (C8H8), trans,tran,cis-1,5,9-cyclododecatriene (C12H18), cyclopentadecane (C15H30) and 3D cages such as adamantane (C10H16), [2.2]paracyclophane (C16H16) and a new type of carbon ball which has a partially open surface (C76H52). Insertion of the Li ion into the selected host materials has been analyzed by first principle quantum mechanical calculations using the DFT method with B3LYP functional and Pople type basis sets augmented with polarization functions. Atomic models consist of the mentioned hosts with and without the Li ion. Interior dimensions of the chosen hosts as determined after optimizing the geometry are as follows: 0.37 nm for cyclooctatetraene, 0.40 nm for cyclododecatriene, 0.43 nm for cyclopentadecane, 0.36 nm for adamantane, 0.40 nm for paracyclophane, and 0.83 nm for the open carbon ball. All of the chosen materials have spacings greater than the interlayer distance of graphite, which is 0.335 nm. Energy of the host material with the Li ion located inside is compared with energy of the empty host plus energy of the Li ion. If the energy is lower when Li ion is inside the host, it can be expected to serve as a stable anode. Results of the calculations indicate that energy condition is satisfied for (a) 2D cages cyclododecatriene (1.3 eV lower), cyclopentadecane (1.3 eV lower), and (b) 3D cages paracyclophane (1.8 eV lower), open carbon ball (1.4 eV lower). On the other hand, cyclooctatetraene and adamantane are not spacious enough to serve as stable hosts for the Li ion. Because the chosen anode materials are single molecules, a monolayer of such molecules coated onto the copper current collector would make a very thin and light type of anode that has the potential to increase energy density. [1] K. Amine, et al., “Rechargeable lithium batteries and beyond: progress, challenges and future directions,” MRS Bulletin, Vol. 39, No. 5, p. 395, May 2014 [2] H. Gokturk, “Nanostructuring of graphite with noble gas atoms,” MRS Spring Meeting, April 2013

Sn-based intermetallic compound is general concept introducing second metal element to accommodate the inevitable internal strain caused by electrochemically induced volume change between tin and lithium-tin alloy during lithiation and delithiation processes. Particularly Co-Sn intermetallic compounds as an alternative anode material have been widely investigated during last decade due to the high capacity, cycle stability, and high rate performance. To the best of our knowledge, porous nanostructured intermetallic compound has not been investigated as anode for Li-ion battery because of the synthetic difficulty of controlling metal nucleation and sintering.
Ordered mesoporous CoSn intermetallic (Co_xSn_y) with various Co/Sn ratio is successfully synthesized through nano-replication technique as stable and high power anode materials for lithium ion battery. Especially, this is the first result for the synthesis of ordered mesoporous CoSn intermetallic through the direct template method. The electrochemical results show that mesoporous Co_xSn_y exhibits much better capacity than non-porous CoSn. Reversible capacity, coulombic efficiency, and cycle stability of mesoporous Co_xSn_y materials are dependent on their structures and compositions. Especially, 30 atomic % Co contained ordered mesoporous Co_0.3Sn_0.7 shows 83% capacity retention after 50 cycle, which means Co atoms effectively accommodate the volume strain associates with the lithiation-delithiation processes. The rate performance of mesoporous Co_0.3Sn_0.7 is significantly improved, which was deeply related to the kinetic behavior such as low charge transfer resistance, large diffusion coefficient (small Warburg factor) and low internal resistance. Sustainable ordered pore structure even after 50 cycle was also observed with TEM, which means Co atoms play a buffer role effectively to accommodate the volume strain associated with the lithiation-delithiation processes.

Silicon has been intensely studied as an anode material in Li batteries because of its high storage capacity. A major drawback is that Si suffers from mechanical degradation because of the ~400% volumetric expansion during lithiation. Nanostructured Si electrodes, such as nanowires and inverse opal lattices, have shown greatly improved mechanical robustness over bulk and thin film electrodes due to the size-induced ductility in nanometer-sized Si, and the incorporation of pores and open spaces to accommodate Si volume change during lithiation cycles. We address this loss of capacity due to mechanical deformation by creating nano-architected Si electrodes that combine the benefits of material size effects and mechanically robust structural geometries.
To fabricate architected electrodes, polymer nano-lattice scaffolds are made by 2-photon lithography, and a layer of Cu and another layer of amorphous Si are deposited by RF magnetron sputtering. The Cu layer is used to improve electrical conductivity across the nano-lattice. The Si layer is kept to hundreds of nanometers in thickness in order to take advantage of enhanced ductility in Si. In an alternative approach, free-standing solid Cu nano-lattices are fabricated by electroplating Cu into a polymer mold made from positive photoresist and removing the mold afterwards. Amorphous Si is then deposited over Cu by plasma-enhanced chemical vapor deposition (PECVD). The solid Cu lattice is mechanically stronger and PECVD provides more conformal Si coating.
For battery testing, an electrochemical cell is built inside of a SEM using a lithium electrode and the nano-architected Si electrode. The oxidized layer of Li2O on the Li electrode is first used as a solid electrolyte, and a constant voltage bias is applied during electrochemical cycling. In situ SEM observation shows that lithiation causes each lattice beam to expand in volume, and the overall structure to bow out slightly at locations of high lithiation. By the end of three lithiation cycles, the Si structures shows mechanical failure near the contact point between the Li and Si electrodes for the polymer-Cu-Si lattices. To provide better contact, an ionic liquid electrolyte is used to connect the Li electrode and the Si lattice. Preliminary galvanostatic cycling results in a first cycle capacity of 2200mAh/g and a capacity retention of ~80% after 16 cycles for the polymer-Cu-Si lattices. The mechanical robustness and cell cyclability are expected to improve significantly for the solid Cu lattices with PECVD-deposited Si because of structural strength and conformal coating. Nano-lattice geometries with different unit cell types, unit cell parameters, and Cu/Si thicknesses are tested and optimized for mechanical robustness, electrochemical capacity, and cell cyclability. In collaboration with Prof. Michael Ortiz, solid mechanics modeling is used to reveal the most favorable geometry to withstand dramatic volume expansion during lithiation.

Silicon based hollow nanostructures are receiving significant scientific attention as potential high energy density anodes for lithium ion batteries. However their cycling performance still requires further improvement. Here we explore the use of atomic layer deposition (ALD) of TiO₂, TiN and Al₂O₃ on the inner, the outer, or both surfaces of hollow Si nanotubes (SiNTs) for improving their cycling performance. We demonstrate that all three materials enhance the cycling performance, with optimum performance being achieved for SiNTs conformally coated on both sides with 1.5 nm of Li active TiO₂. Substantial improvements are achieved in the cycling capacity retention (1700 mAh/g vs. 1287 mAh/g for the uncoated baseline, after 200 cycles at 0.2C), steady-state coulombic efficiency (~100% vs. 97-98%), and high rate capability (capacity retention of 50% vs. 20%, going from 0.2C to 5C). TEM and other analytical techniques are employed to provide new insight into the lithiation cycling-induced failure mechanisms that turn out to be intimately linked to the microstructure and the location of these layers.

Silicon (Si) holds great promise for high-capacity lithium storage, but its poor cycling stability related to structure degradation remains to be solved. Nanostructured Si often improves cycling performance, however scalable synthesis remains challenging. Moreover, for practical applications, high areal-capacity loading above 3 mAh cm^-2 is needed. So far, this was demonstrated with only a few difficult-to-fabricate Si nanostructures. We have previously demonstrated improvement in cycling stability with Si microparticles using a self-healing polymer binder. However, high areal capacity, along with long cycling tolerance, has not been achieved. In this work, through a series of systematic studies regarding the interactions between self-healing polymer and Si particles and particle size control, we are able to achieve stable electrodes with high areal capacities of 3 to 4 mAh cm^-2 for low cost large Si particles (0.5 to 1.5 mu;m in diameter). These Si materials can easily be produced by existing mechanical milling processes

Silicon is a promising material for energy storage, both in electrochemical devices such as Li-ion batteries and in electrostatic devices such as micro-supercapacitors. Within Li-ion batteries it provides light weight and a potentially ten times higher capacity than carbon. Under the form of Si nanowires (SiNWs), the material can withstand the mechanical strains in lithiation/delithiation, allowing for long-term stability. In micro-supercapacitors SiNWs provide a high surface area with a low weight, a dielectric interface made of SiO2 due to SiNW surface oxidation and a high conductivity when SiNWs are doped. The supercapacitor devices then show a high power density in very short bursts (ms), and a long cycling stability over millions of galvanostatic cycles.
However, the classical CVD synthesis produces only small quantities of SiNWs as a thin film on substrate. Chemical routes have been described in the literature but they use highly pyrophoric reagents and/or high pressure conditions, which make SiNWs an expensive and scarce material. We propose a new way for the large scale/high yield synthesis of SiNWs using low cost conditions and reagents. The SiNWs produced show a thin, homogeneous diameter. Furthermore they can be doped p or n during the synthesis, as evidenced by Raman spectroscopy and electron-spin resonance (ESR). Assembled as drop-cast networks they provided efficient super-capacitor electrodes, with a power density at least 5 times higher than for micro-supercapacitors made of CVD grown SiNWs. Beside, first tests as Li intercalating material at the anode of Li batteries showed a high capacity and cycling stability.

The increasing share of intermittent renewable energy sources like PV and wind in the total electricity production leads to an increasing demand for storage of electricity. Li-ion batteries are a good candidate for this. But to meet the demands, an increase in energy density and power density of all the component of these batteries is needed.
For the anode material, the need for this “new generation” of batteries has led to the search for materials with higher capacity than those available today. Commonly used graphite anodes have significant drawbacks and for this reason, silicon has been proposed as one promising anode material. Silicon has low cost, high theoretical storage capacity and high volumetric capacity. However, planar solid-state thin film silicon anodes reveal several drawbacks of which the most important is the volume expansion upon Li insertion due to the formation of Li_xSi alloys which causes cracking and pulverization of Si electrodes, thereby leading to the loss of electrical contact and short cycle life.
In order to overcome this, we have made new nano-structured silicon material with large porosity and studied lithium insertion mechanisms, phase transitions and electrochemical cycle life.
Self-organized nano-structured silicon has been deposited by plasma-enhanced chemical vapor deposition (PECVD). On top of a c-Si wafer, a Li diffusion barrier layer was deposited , in this case a RF-magnetron sputtered TiN layer. All samples have been characterized by optical measurements (refractive index), FTIR (oxygen and carbon content) and Raman (crystal fraction). A selection of samples were also characterized by cross-sectional SEM. We performed electrochemical cycles vs a lithium electrode using Propylene Carbonate (PC) as electrolyte. The electrochemical techniques used were Cyclic Voltammetry (CV) and Galvanostatic Intermittent Titration Technique (GITT).
Based on the optical measurements we derive the porosity of the layers and found that we can vary the porosity over a wide range by tuning the deposition conditions.
We measured the capacity and the cyclic performance for layers with various thicknesses and found capacities close to the theoretical maximum for silicon and an excellent retention of the capacity after more than 100 cycles for thin layers. For a thicker layers we observed a lower capacity, but with an equally good cyclic stability.
We will discuss the various mechanisms which may be responsible for the different behavior of thinner and thicker silicon layers.

It is widely known that the forward and backward reaction rates for reversible electrochemical reactions are not necessarily identical. For lithium-ion batteries (LIBs), in most cases the rate performance of electrodes is evaluated using identical current for charge and discharge, and possible differences between the rate performances for lithiation and de-lithiation cannot be clearly revealed. Do lithiation and de-lithiation processes give the same rate performance for amorphous LIB anodes?
Here we report an observation of asymmetric rate performance in thin-film Si anodes. Rate performance during lithiation and de-lithiation was investigated independently by ensuring the same state of charge (SOC) before each charge/discharge. For a Si thin-film electrode under a high rate of 100C (420 A g^-1), 72% capacity can be delivered during lithiation in 22 seconds while only 1% capacity is observed for lithiation. A diffusion model for slab geometry is used to simulate the Li diffusion behavior in Si. The cause of this asymmetric rate performance is primarily the potential-concentration profile and voltage shift caused by ohmic resistance under high currents. Diffusion coefficients have a smaller effect on the asymmetric rate performance, where the chemical diffusion coefficient in de-lithiation is approximately 3 times lower than that in lithiation. Similar asymmetric rate performance is expected for other amorphous anodes, and rate-performance of LIB electrodes should be re-evaluated carefully to distinguish between charging and discharging.
Acknowledgement
The modeling of ionic conductivity and electrode kinetics was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. X. X. and Y.-T. C. acknowledge the support by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, subcontract No. 7056410 under the Batteries for Advanced Transportation Technologies (BATT) Program.
References
1. Juchuan Li, Nancy J. Dudney, Xingcheng Xiao, Yang-Tse Cheng, Chengdu Liang, and Mark W. Verbrugge, “Asymmetric Rate Behaviors of Si Anodes for Lithium-Ion Batteries: Ultrafast De-Lithiation vs. Sluggish Lithiation at high current densities,” Advanced Energy Materials, 201401627.

Group IV elements are promising materials for lithium storage which enables much higher energy density than commercialized graphite-based lithium ion battery (LIB). However, they suffer from tremendous volume change during lithiation (charging) and delithiation (discharging), resulting in fast capacity fading due to the pulverization of anode material during cycle. To overcome these problems, we propose a novel LIB anode structure where unlithiated core function as support frame for preventing pulverization of anode material, which can be achieved by fine control of Li⁺ ion diffusion from tailored atomic arrangement of anode material. To realize model system where electrochemical reaction can be controlled from the structure of anode material, we synthesized Ge dominant SiGe alloy nanowire (SiGe NW) where high population of Si is situated at the surface of SiGe nanowire (Type G-SiGe NW), which is easily obtained by annealing SiGe NW with uniform distribution of Si at high temperature in hydrogen environment. The high population of Si with low lithium diffusivity and electronic conductivity induce tardy diffusion of Li⁺ ion at the surface as confirmed in the galvanostatic intermittent titration technique (GITT) data, resulting in leaving unlithiated core which act as role of preventing pulverization of anode material. When the Type G-SiGe NWs are fabricated into Li half cells (2016R), it exhibits not only long cycle life with high capacity retention of 89 % at 0.2 C during 400 cycle, but also high columbic efficiency of average 98.8 % throughout 400 cycles. Although overpotential was increased slightly due to Si enrichment at the surface, high mole fraction of Ge guarantees high rate capability with 304.5 mAhg^-1 at 60 C. The mechanism of Si segregation at the surface and electrochemical characterization of each SiGe NW will be discussed in detail.

Engineering a stable Solid Electrolyte Interphase (SEI) layer on high capacity Si electrodes is a critical issue to reduce the continuous capacity loss of Li-ion batteries. A hypothesis that an ideal SEI component shall be an ionic conductor and electronic insulator has been postulated based on the study of graphite electrode. In order to help design an artificial SEI for Si, it is necessary to have a detailed understanding of the properties of SEI components coated on Si electrode.
We developed a computational method based on Density Functional Theory to study ionic and electronic conduction in SEI components on Si electrodes. In our model, both ionic (e.g., Li vacancy and Li interstitial) and electronic defects (e.g., polaron) are considered to study the total electrical conduction. We apply this method to study fluorides, oxides and carbonates, which are important components in the naturally formed SEI on Si. We found that the ionic conduction was low in fluorides compared with other SEI components (e.g., carbonates). However, due to the low ionic conduction and low concentration of free carriers, fluorides on Si can help block electron leakage from the electrode and prevent further degradation of electrolyte molecules. In addition, by relating the material properties on Si electrodes and their electrochemical performance, balancing different SEI properties to design artificial SEIs on Si electrodes becomes possible.

One-dimensional (1D) silicon (Si) based anode nanostructures is one of the promising anode materials in lithium-ion battery because of high specific capacity and lateral relaxation leading to long cycling stability. It is well know that a solid-electrolyte-interphase (SEI) layer forms on the surfaces of the anode materials and act as a passivation layer during the Li-ion cycling. Although the SEI layer acts as a passivation layer, the formation of the SEI layer consumes Si anode materials and reduces silicon nanowire (SiNW) diameter, leading to fading of their capacity retention during cycling. In order to investigate the effect of the formation of the SEI layer with respect to the capacity retention, we directly measured the reduction in silicon nanowire diameter and volume with number of cycles. Based on the measurements, Si consumption rates versus the number of battery cycles were measured. Moreover, from the change in silicon nanowire volume, specific capacity reduction for silicon nanowire half cells was predicted and the predicted specific capacity shows a very good agreement with measurement.

Silicon-based materials are an emerging anode technology for the use in the next generation electrochemical enegy storage, because it is cheap, widely distributed on our planet and non-toxic to the environment [1]. However, the development of commercial silicon-based anode progresses slowly due to the properties inherent to pure silicon, such as safety and capacity limiting volume expansions during cycling and poor conductive nature [2]. Functionalization of the nanostructured silicon oxide with conductive carbon coating is one of the possible strategies to overcome these problems. Moreover, oxide matrix of silicon benefits to alleviate large volume changes [3-4]. The present work is aimed to develop a novel simple preparation technique of SiO_x/C nanocomposite through mechanochemically activated sol-gel process combined with dry-ball milling (DBM) process.
In this synthesis, tetraethyl orthosilicate (TEOS), aqueous ammonia and acetylene black(AB) were mixed by a high-energy ball milling at 800 rpm for 4 hours. The resulting slurry was dried at 110 ^oC for 2 hour in an air oven and then annealed at 600 ^oC for 2 hours in N₂ atmosphere. The obtained sample could be identified as amorphous SiO_x/C composite by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis. It could be also seen a field emission scanning electron microscopy (FE-SEM) observation that the SiO_x/C composite was composed of large agglomerated micro-sized particles. In order to reduce the particle size, the composite was mechanically milled at 800 rpm for 4 hours by high-energy DBM with additional AB as an additive. The as-milled sample was the SiO_x/C nanocomposite consisting of highly dispersed carbon nanoparticles on fine amorphous SiO_x particles. Electrochemical properties of the SiO_x/C nanocomposite were evaluated by assembling a CR2032 coin-type cell. The galvanostatic charge-discharge test was performed on multichannel battery testers (Hokuto Denko,HJ1010mSM8A) between 0.01 and 3.0 V versus Li/Li⁺ at a current density of 50 mA g^-1. The cell exhibited a highly stable reversible capacity of 620 mAh g^-1 at a current density of 50 mA g^-1 after 30 cycles with no capacity fading. The SiO_x/C nanocomposite was also annealed at different temperatures for in 3%H₂+N₂ atmosphere and then evaluated its battery performance.
References
1) Chang et.al., Enengy Environ. Sci, 5(2012)6895.
2) Yao et al., J. Power Sources, 196(2011)10240.
3) Yan et. al., Sci. Rep. (2013)1568.
4) Guo et al., Electrochim. Acta, 74(2012)271.

Emerging application of Li-ion batteries for electric vehicles requires LIBs with higher energy density. Developing new anode materials with high specific capacity is an effective way to increase the energy density of LIBs. Due to its high theoretical capacity (3579 mAh/g) and abundance, silicon has been regarded as one of most promising alternatives to the currently-used graphite anode. However, there is a major barrier to the practical application Si: its large volume change during charge/discharge causes to severe pulverization of Si particles and degradation of Si electrodes, leading to poor cycling stability. Extensive efforts have been devoted to improving the cyclability of Si-based anodes with encouraging results, including development of various Si nanostructures/nanocomposites, novel binders and electrolyte additives.
In this talk, I will present development of micro-sized mesoporous Si-C composite composed of interconnected Si nanoscale building blocks and carbon conductive network. The effect of Si nanoscale building blocks (size and doping composition) and carbon coating are studied on the electrochemical performance. We also engineered to produce graphene enabled dual conductive network on the micro-sized porous Si-C composite for high areal capacity electrodes toward practical application. New interpenetrated polymer gel binder for the Si anode materials will be also studied for improving efficiency and cycling stability of Si anodes. High temperature electrochemical performance of the Si anode material and related safety issues will be also discussed and correlated with the surface properties of Si materials.

Here we describe a class of electric-conducting polymers that conduct electron via the side chain π-π stacking. These polymers can be designed and synthesized with different chemical moieties to perform different functions, extremely suitable as conductive polymer binder for lithium battery electrode. A class of methacrylate polymers based on a polycyclic aromatic hydrocarbon side moiety was synthesized and applied as an electrode binder to fabricate a silicon (Si) electrode. The electron mobilities of these polymers are characterized as 1.9e-4 cm²V^-1s^-1. These electric conductive polymeric binders can maintain the electrode mechanical integrity and Si interface stability over a thousand cycles of charge and discharge. The as-assembled batteries exhibit a high capacity and excellent rate performance due to the self-assembled solid-state nanostructures of the conductive polymer binders. This new generation of conductive polymer binders also enhance the stability of Solid Electrolyte Interphase (SEI) of a Si electrode over long-term cycling. The physical properties of this polymer are further tailored by incorporating ethylene oxide moieties at the side chains to enhance the adhesion and adjust swelling to improve the stability of the high loading Si electrode.

Lithium-ion batteries (LIBs) have been considered as one of the most promising electric energy storage systems due to the various merits of high voltage, high capacity, low cost and environmental friendliness. However, there are still several challenging issues in LIBs to be overcome in order to fulfil the requirements as high-performance power sources in future market, including higher capacity, lower cost, longer cycle life and better rate performance. Nanostructure engineering has been demonstrated as a powerful and effective strategy in the rational design of new electrode materials with optimized performance through both morphological and compositional solutions. For example, various nanostructures with controlled morphologies including hollow spheres/cubes, nanowires/rods as well as nanoplates could achieve significantly enhanced lithium storage properties due to the size and shape effects. However, the intrinsic properties including low electrical conductivity and poor mechanical stability of most oxide electrode materials, leading to unsatisfactory cycling stability and rate performance, still seriously limit their applications. Recently, an emerging concept of hybrid nanostructures has attracted tremendous attention since better performance could be expected in such architectures. Coaxial nanocables, as one of the most interesting hybrid nanostructures, hold the great potential for simultaneously resolving the problems of poor electrical conductivity and weak mechanical stability with rational design and careful choice of core and shell components. However, there are not too many such reports showing the attractive properties of nanocable structures for lithium storage, probably due to the lack of appropriate synthesis methods.
In this work, we have successfully synthesized CNF@MnO and CNF@CoMn₂O₄ coaxial nanocables with considerably enhanced lithium storage performance through a facile two-step strategy. The method involves the polyol process for the synthesis of metal-glycolate layer on the surface of the CNFs and the subsequent thermal ennealing treatment undr N₂ protection. These two nanocable electrodes exhibit remarkable lithium storage properties in terms of high specific capacity, long cycle life and superior rate performance. For example, at a high charge/discharge current density of 1000 mA/g, the CNF@CoMn₂O₄ nanocable electrode can deliver a high capacity of about 655 mAh/g and can last for at least 300 cycles, which is remarkable. The enhanced electrochemical performance could be attributed to several advantages of the smart coaxial nanocable configuration, which can effectively alleviate the volume change, prohibit the nanoparticle aggregation and facilitate the electron transport. Such high-performance nanosctructures with large-scale production might hold great potential for the fabrication of high energy and power density lithium-ion batteries.

Stress originated from volumetric expansion (~300 %) during cycling is notorious in metal alloy based anode materials including Sn (994 mAh/g). Nanoscale Sn embedded buffer matrix is an ideal structure for high performance anode of solid state Li-ion batteries. There were previous attempts to utilize 1D carbon (C) structures as a buffer matrix with transition metal alloying or atomic layer deposition (ALD) coating. However, the drawbacks of them were requirement of electrochemically unreactive materials related with low capacity and additional post treatments. Here, we developed a novel fabrication method of ideal Sn/C 1D hybrid nanostructures via porosity controlled C nanofibers. For precise modulation of Sn size and dispersion, we considered Sn diffusion originated from thermal expansion coefficient (CTE) difference between Sn (23.5×10^-6 /°C) and C (1.5×10^-6 /°C) during calcination. Through this fabrication method, superior anode performance was realized without current collector, binder and conducting additives.
Electrospinning proceeded with a solution of Sn acetate (SnAc) as metal precursor and polyacrylonitrile (PAN) as polymer matrix. Calcination proceeded at 700 ^oC, 5 h with the ambient controlled by high vacuum (HV) and Ar gas. The porosity was evaluated by BET specific surface area (SSA) and total pore volume of N₂ adsorption/desorption isotherm. Structures were analyzed by FE-SEM and TEM. Electrochemical performance of Sn/C nanofibers was measured in all solid-state Li-ion cell.
We modulated Sn diffusion by controlling the porosity of C nanofiber matrix and designed 3 calcination schemes as stabilization + Ar (SA) calcination, HV calcination, and Ar calcination. Stabilization accelerated the decomposition of polymer matrix via dehydration. Furthermore, HV and Ar calcination showed differences in gas-solid reactions between CO (g), CO₂ (g) and C nanofibers. In porosity measurement, SA calcination showed the highest BET SSA as 98.97 m²/g and Ar calcination showed the lowest as 10.46 m²/g. In accordance with the porosity tendency, Sn size and dispersion were controlled well. SA calcination with highest porosity formed a structure of all Sn agglomerates outside C nanofibers. HV calcination with moderate porosity induced coexistence of outside Sn agglomerates and inside Sn nanoparticles. Finally, Ar calcination with lowest porosity induced 15 nm sized Sn nanoparticles fully embedded C nanofibers. For the first time, we successfully revealed a key parameter of controlling the structures of Sn/C nanofibers. Interestingly, all Sn/C nanofibers showed ohmic contact behavior, and we demonstrated all solid-state Li-ion cell with Sn/C nanofibers as an anode without current collector. In charge/discharge cycling performance, Sn fully-embedded C nanofibers showed superior capacity of 762 mAh/g with Coulombinc efficiency over 99.5 % during 50 cycles. Intimate relationship between Sn structures and electrochemical performances is discussed.

Li metal is the ultimate anodic material for secondary Li batteries; however, two major problems prohibit its practical application: growth of lithium metal dendrites during anodic stripping/plating cycles, which may cause serious safety hazards, and the low Coulombic efficiency due to repeated reaction between Li anode and the electrolyte. [1] Much effort has been exerted in recent years with modest success to control the surface electrochemistry on Li to promote uniform Li+ dissolution/ Li deposition and to prevent side reactions with electrolyte. [2-4]
Here we present a novel Li-C composite material, in which nanostructured carbon backbone serves to disperse Li metal in order to achieve high specific surface area. The resulting electrodes show much-prolonged dendrite forming time and high Coulombic efficiency in stripping/plating tests. The Li-C composite is also paired with different cathodic materials to assemble into full batteries. LiFePO4 and Li-S batteries using the Li-C composite anode with balanced anodic and cathodic capacity exhibit good performance. This novel anodic material will be highly promising for future energy storage technologies, especially those non-lithiated cathodic systems such as Li-S and Li-air batteries.
[1] Li Z., Huang J., Liawb B., Metzler V., Zhang J. Journal of Power Sources 254 (2014) 168 - 182.
[2] Zheng G., Lee S. W., Liang Z., Lee H.-Y., Yan K., Yao H., Wang H., Li W., Chu S., Cui Y. Nature Nanotechnology 9 (2014) 618 - 623.
[3] Lu Y., Tu Z., Archer L. A. Nature Materials 13 (2014) 961- 969
[4] Lu Y., Korf K., Kambe Y., Tu Z., Archer L. A. Angew. Chem. 126, (2014) 498 - 502

We study electrochemical sodium and lithium cycling, and tensile testing behavior of graphene oxide (GO) self-standing paper electrode thermally reduced at varying temperatures in Ar atmospheres. The annealed papers were directly utilized as both the working electrode and current collector in Li (LIB) or Na half-cells (NIB) and their electrochemical performance was studied for up to 1050 cycles. We find strong dependence of annealing temperature and gas environment on the electrical conductivity, electrochemical capacity, and rate capability of the electrodes. The effect however was opposing for the two cell types; electrode&’s Li capacity increased with increasing annealing temperature reaching stable ~325 mAh.g_anode^-1 at 100 mAh.g^-1 (or ~100 mAh.cm_anode^-3 at ~48 mu;A.cm^-2 w.r.t. total volume of the electrode) at 900 °C while maximum Na charge capacity was observed at 500 °C at stable ~110 mAh.g_anode^-1 at 100 mA.g^-1 (or ~77 mAh.cm_anode^-3 at 70 mu;A.cm^-2) highest reported for GO paper electrode and saw a sharp decline for temperatures above 500 °C. Further, uni-axial tensile tests and videography highlighted the high elasticity and strain to failure in crumpled paper electrodes.

Novel carbon composite materials have been developed from low cost lignin for use as anodes in lithium-ion batteries. The composite systems consist of two interwoven domains consisting of amorphous and crystalline carbon, with edge-terminating hydrogens. In this work, we have developed atomistic models of the experimental systems, and via the use of reactive molecular dynamics simulations, we reveal the discovery of a new mechanism of lithium-ion storage as a function of ion loading and local carbon structure. The pair correlation functions and electrostatic profiles for the resulting lithium-ion distributions, computed for both favorable and unfavorable energy states, are then analyzed in order to develop an understanding of this unique type of ion localization.

High performance rechargeable batteries are essential for meeting the demand for new energy storage application. Lithium metal is considered as the “Holy Grail” of battery technologies, as a result of its low gravimetric density, lowest redox potential and highest theoretical specific capacity, compared to any other lithium ion battery anode materials. However, uncontrolled lithium dendrite growth still remains as the single most critical blockade of widespread production and commercialization of lithium metal based cells. The mossy and dendritic lithium poses a potential safety hazard and leads to a low Coulombic efficiency in galvanostatic cycling. Here, we demonstrate that stable cycling of lithium metal anodes could be achieved by using a chemically inert and electronically insulating oxidized polymer nanofiber mat. The polymer network allows homogeneous lithium deposition confined inside the fiber layer via attraction forces between the polar functional groups and lithium ions. The resulting Coulombic efficiency could reach 97.4% up to a practical current density of 3 mAh/cm^-1 and with an areal capacity of 1 mAh/cm^-1 over more than 120 cycles. This simple approach to tackle the intrinsic problems of lithium metal would enable a series of lithium metal based energy storage technologies.

All-solid-state Li-ion batteries are a promising alternative for the rapidly growing power sources for mobile devices. However, the mechanisms of lithiation/delithiation in all-solid-state batteries are still an open question, and the ‘holy grail&’ to engineer devices with extended lifetime. Here, we combine real-time scanning electron microscopy in ultra-high vacuum with electrochemical cycling and confocal Raman spectroscopy to investigate the mechanism of lithiation in all-solid-state thin film batteries with Al anodes. We find that a Li-Al-O thin layer forms at the top surface of the anode, confirmed by the emerging Raman peaks after cycling at 1380, 1585 cm^-1. This oxide layer covers stable LiAl alloy mounds that are formed by a surface driven reaction (with Fd3m phase, Raman shift at 2890 cm^-1). A simple thermodynamic model for the lithiation of Al suggests that LiAlO₂ and Li₅AlO₄ are expected to form at 3.35 V and 0.17 V, respectively, indicating that different Li-Al-O phases co-exist at the surface of the anode. The rapid capacity loss in these batteries is due to the blockage of Li and Al diffusion pathways necessary for the decomposition of AlLi at room temperature and which occurs as a result of Li-Al-O formation on exposed Li-Al surfaces [1]. The addition of a thin and inert metallic cap layer could prevent the surface driven reactions observed, and the design of new device architectures will be presented.
[1] M. S. Leite et al. “Insights into capacity loss mechanisms of all-solid-state Li-ion batteries with Al anodes”. J. Mat. Chem. A, in press, 2014. DOI: 10.1039/c4ta90112f. Inside Cover.

Graphite, the most commonly used commercial anode material, encounters some disadvantages such as low theoretical specific capacity (372 mAhg^{minus; 1}) and limited rate capability. Thus, intense efforts have been devoted to searching for new carbon-based anode materials with enhanced Li+-ion storage capacity. The carbon materials, such as graphene oxide, carbon nanotubes and amorphous carbon have shown the outstanding cycle-performance in LIBs due to fairly inert electrochemistry, high electrical conductivity, and high specific surface area. However, the first and second one might have poor electrical conductivity due to plenty of structure defects and oxygen groups. Generally, even after the reduction of graphene oxide, the prepared reduced graphene oxide show still poor electrical conductivity compared to the intrinsic graphene. The last one has relatively small surface area and non-interconnected structures, resulting in poorer electrochemical performance.
Herein, we report the synthesis of hierarchical 3D-nano-structured graphenes (H-3DNGs) via precursor-assisted CVD technique which show high surface area (~1,100 m²g^-1) and conductivity (50 Scm^-2). Since the H-3DNGs can provide highly efficient electronic pathways and surface area during the charge/discharge cycles of LIBs, the fabricated LIB exhibits high capacity and good cycling performance. Also, we employed a facile solvothermal method for deposition of MoS₂ on the surface of the H-3DNGs. Typically, many researches have mainly focused on MoS₂ in the composite of MoS₂ and carbon. However, we developed the MoS₂-assisted H-3DNGs (MA-H-3DNGs), using MoS₂ as supporting material for H-3DNGs.
MA-H-3DNGs showed superior cycling performance and rate capability to H-3DNGs. MA-H-3DNGs revealed 1491 mAhg^-1 of specific capacity even after 500 cycles at a rate of 1.0 C. Furthermore, it showed 515 mAhg^-1 even at a rate of 10 C. Anomalously, MoS₂ on graphene was observed to be reversible, during charge/discharge. Namely, MoS₂ sheets were confirmed even after electrochemical cycling. To prove this phenomenon, we successfully calculated and simulated mutual dependence between carbon layer and MoS₂ layer through Ab initio quantum chemistry methods. We found that MoS₂ layer influenced carbon layer to get good Li-ion mobility and that carbon layer also had effect on MoS₂ layer. In other word, we proved that synergy effect between carbon and MoS₂. We will discuss details later.

Despite of high theoretical capacity of silicon based materials, their poor cycle performance caused by severe volume expansion of silicon and low initial efficiency hinder their commercial use for lithium ion battery. Silicon embedded in metal alloy matrix material is one of the promising candidates to solve these problems. Silicon nanocrystals with the size of ~200 nm embedded Al-Cu-Fe alloy materials were prepared by melt spinning process and investigated their lithium storage characteristics for lithium ion battery. Si/Al-Cu-Fe alloy materials showed stable cycle performance over 50 cycles. In order to characterize microstructure of these materials and understand their electrochemical performance, various analytical techniques including XRD, SEM and TEM were carried out. More detailed electrochemical performances and ex-situ analysis of Si/Al-Cu-Fe nanocomposite materials during cycling will be discussed in this presentation.

MoO₂ has received much attention as a lithium storage anode material due to its higher energy density and higher theoretical capacity (209 mAh g^-1) than LTO. However, previous studies showed that MoO₂ has poor cycle performance caused by phase transition from monoclinic to orthorhombic phase during lithium intercalation and de-intercalation. In this work, nanostructured MoO₂ were prepared by simple solid state synthesis and investigated as an anode material for lithium rechargeable battery. Nanostructured MoO₂ showed a highly reversible capacity retention as high as 84% of the initial capacity over 100 cycles, indicating that highly stable lithium ion intercalation and de-intercalation into MoO₂ lattice. More detailed electrochemical performances of MoO₂ and ex-situ analysis of lithium intercalated MoO₂ anode will be discussed in this presentation.

Silicon based electrode materials for Li-ion battery have attracted great attention due to the high theoretical capacity of 4212 mAh/g (3.75 moles of Li per mole of Si) compared to graphite (1 mol Li per 6 mol C) used in commercial LIBs. Unfortunately, practical applications of silicon as an anode material exhibit the huge volume change (>300%) during the alloying / dealloying process with Li, which would result in the loss of electrical conductivity, dramatic pulverization of silicon, and consequently a rapid capacity fading in the cycling. To alleviate this problem, silicon nanosized or nanostructures materials have been suggested, which can increase the transport of electron and lithium ion and reduce mechanical stress during cycling, resulting in improved electrochemical performance. Among these nanostructures, the combination with carbon is becoming attractive and important material because it improves the electric conductivity and plays a role of a buffer of volume expansion.
In this research, a novel composite electrode material consisting of nano-sized silicon core and nanoporous hollow carbon has been developed as an anode candidate for Li storage. The two type of amorphous silicon oxide layer (dense SiO₂ and nanoporous SiO₂) is coated onto silicon nanoparticle to form a nanoporous carbon shell with a void space between the silicon nanoparticle core and carbon shell. Subsequently nanoporous carbon is formed through nanocasting pathway.
The composite material, silicon nanoparticle encapsulated within pod-like nanoporous carbon, involves 50 wt% of carbon species and has 1002 m²/g of high surface area with 2 nm of pores. When the composite material uses as anode electrode material for Li storage, the high reversible capacity with improved cycle stability are exhibited compared with pristine silicon. The reversible capacity of the composite material is 1007 mAh/g after 50 cycle at 400 mA/g of current density (81 mAh/g of pristine silicon nanoparticle).
These improvements are attributed to the nanoporous carbon shell, which reduces the cell impedance, prevents the aggregation of silicon nanoparticle, accommodates the volume change, and stabilizes reaction with Li during the electrochemical Li-alloying process.

For decades, many intensive researches have been conducted on Li-ion batteries. However, it still remains challenging to develop batteries with higher energy density. TiNb₂O₇ has recently been studied as an attractive anode material for lithium ion batteries due to its practical capacity of ~ 280 mAh g^-1 much higher than those of well-known anode materials such as TiO₂ (~ 150 mAh g^-1) and Li₄Ti₅O₁₂ (~ 160 mAh g^-1). However, low electronic conductivity and poor lithium diffusivity limits its practical use as an active material. Porous TiNb₂O₇ nanofibers were prepared via simple electro-spinning and functionalized its surface by subsequent ammonia gas treatment. As-prepared sample has porous structure with the pore diameter of ~ 20 nm and nanocrystalite extremely reducing the diffusion pathway for lithium ion. In addition, conductive transition metal nitride (Ti_1-xNb_xN) on the surface of nanofibers can prompt fast electron transport along the surface. The sample shows a lithium storage capacity of ~ 250 mAh g^-1 at 1C and a high rate capability of ~ 180 mAh g^-1 at 100 C. These drastic achievements are attributed to enhanced kinetics related to lithium ion and electron due to the unique porous and one dimensional geometry with conductive material.

Lithium-ion batteries have been widely used as a power source of micro-devices due to their high capacity, no memory effect, and a long cycle life. However, lithium-ion batteries with liquid electrolytes have some problems about size, safety, reliability, cost, and energy density. All-solid-state Li-ion batteries can solve such problems because their solid electrolytes exhibit no leaking themselves and releasing toxic gases when the batteries are broken down. Among many anode materials such as carbon, germanium, and silicon and so on, silicon as an anode material is promising owing to its high theoretical capacity (4200 mAh/g) and no lithium metal dendrite formation after cycling. Anodes based on silicon have some limitation of fast capacity fadedness of the electrode and 400% volume increase after lithiation. To overcome the limitation, Al-Si anodes are researched as an alternative using the electrical and structural property of Al. In this work, Al-Si anode films are deposited by RF magnetron sputtering on four types of valley structured Si(100) substrates with different depths according to four intervals (10, 20, 30 and 40 of lines by means of photolithography. As depths of valleys increase, the capacities of the batteries are much higher than that of a planar type lithium ion battery, which correlate with the corresponding increase in the surface area to deposit an anode electrode. The morphology of Al-Si anodes before and after lithiation is investigated by the scanning electron microscope (SEM) images and X-ray diffraction (XRD), and the electrochemical properties of the Si-Al anode thin films are measured by WBCS 3000. We designed an all-solid-state Li-ion thin film battery with Al-Si anodes in order to obtain improved electrochemical properties and safety.

The disproportionated SnO and its nanocomposite (Sn/SnO₂/C), prepared by a simple high energy mechanical milling technique, was investigated as high-capacity anode materials for rechargeable Li-ion batteries. The disproportionated SnO was comprised of nanocrystalline-Sn and -SnO₂, which was confirmed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). On the other hand, the disproportionated Sn/SnO₂/C nanocomposites were comprised of disporportionated Sn and SnO₂ within amorphous carbon matrices, which were also thoroughly demonstrated by XRD, HRTEM, and extended X-ray absorption fine structure. The disproportionated Sn/SnO₂/C nanocomposite electrode shows good electrochemical performances, such as a high initial charge capacity of 891 mAh g^-1, long capacity retention of 642 mAh g^-1 after 300 cycles, good initial Coulombic efficiency of ca. 72%, and fast rate capability (2C: 628 mAh g^-1, 3C: 582 mAh g^-1).

Silica(Si) has been projected as one of the most promising anode materials of lithium-ion batteries in substitution of the graphitic carbon anode owing to its abundance in nature, low Li insertion potential and large theoretical capacity (Li_4.4Si: 4200 mAh g^-1). However, large volume changes of Si upon insertion and extraction of lithium can cause pulverization and breakdown of the electrical conductive network, which results in rapid capacity fading. Thus far, several approaches have been reported to overcome this issue by decreasing the particle size [1], using thin-films [2], or selecting an optimized binder [3]. Wang et al. [4] have also reported that nano-sized silicon oxide(SiO_x)/C composite showed a good cyclic performance.
Recently, Taniguchi and Tussupbayev [5] developed a novel and simple processing technique for the preparation of LiFePO_4/C nanocomposites using a fluidized bed reactor and investigated the effect of a wide range of process parameters on the physical and electrochemical properties of obtained materials. In this study, we investigated the synthesis and characterization of SiO_x/C nanocomposites using the same processing technique, i.e. a drip combustion in fluidized bed.
The starting solution was prepared by mixing tetraethyl orthosilicate (TEOS) and kerosene with a 2:3 volume ratio. It was supplied to a drip nozzle and dripped into a fluidized bed reactor [5], which is operated at 900#8451; and a fluidization number of U₀ (superficial velocity) / U_mf (minimum fluidized velocity) = 5. The solid particles obtained from the reactor exit were collected using a cyclone and a bag filter. The obtained sample could be identified as amorphous SiO_x by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis. It could be also seen from a field-emission scanning electron microscopy (FE-SEM) observation that the sample consisted of SiO_x/C composite with several tens nanometer in size. Furthermore, we could confirm from an elemental mapping analysis by FE-SEM with energy-dispersive spectroscopy (EDS) that nano-sized silica particles were well distributed into a soft agglomeration of nano-sized carbon particles. The electrochemical performance of the nano-sized SiO_x/C composite was characterized using Li|1 M LiPF₆ in EC:DMC = 1:1| SiO_x/C cells in the potential range from 0.01 to 3.0 V versus Li/Li⁺. The results of electrochemical characterization will be detailed on the conference.
Reference
1) A. Magasinski et al., Nat. Mater. 9 (2010) 353.
2) R. Lv et al., J. Power Sources 196 (2011) 3868.
3) J. Li et al., Electrochem. Solid-State Lett. 10 (2007) A17.
4) J. Wang et al., J. Power Sources 196(2011)4811.
5) I. Taniguchi ,R. Tussupbayev, Chem. Eng. J.,192(2012)334.

Environmental concerns and limiting oil resources constitute a huge driving force for developing advanced lithium batteries for the use in electric vehicles [1]. The greatest challenge for the scientist is to build high power and safe batteries from inexpensive and sustainable raw materials. As a result, this challenge gave a rise to the interest in silicon oxide (SiO_x) as a promising candidate for the next generation anode materials [2-3]. However, same as pure silicon, SiO_x is a poor conductor and suffers from volume changes during lithium ion migration, and these problems could be possibly overcome by nanostructured SiO_x with a conductive carbon layer [4-5]. In this study, a combination of spray pyrolysis and dry ball milling was used as a novel approach to prepare SiO_x/C composite anode material.
A precursor solution containing tetraethyl orthosilicate (TEOS) and aqueous nitric acid (HNO₃, 0.1 M) was atomized by an ultrasonic nebulizer at a frequency of 1.7 MHz. The sprayed droplets were carried into a reactor by nitrogen gas with a gas flow rate of 2 dm³ min^-1. Under high reaction temperature (400-800 0C) the droplets were transformed into solid spherical particles and collected by an electrostatic precipitator at the reactor exit. The obtained samples were spherical particles with a geometric mean diameter of 0.8 mu;m and could be identified as amorphous SiO_x by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis. The amorphous SiO_x particles prepared at 600 0C were then mixed with acetylene black(AB) by high energy dry ball milling at 800 rpm for 2 hour. The ball-milled sample was confirmed as amourphose SiO_x/C composites by XRD and FT-IR analysis. As a result, we could conclude that the SiO_x/C composite were successfully synthesized by the combination of spray pyrolysis and dry ball milling. The morphology and structure of the SiO_x/C composite were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with energy-dispersive spectroscopy (EDS). Electrochemical performance of SiO_x/C composites was studied by using coin-type cells (CR2032). The cells were tested galvanostatically between 0.01 and 3.0 V versus Li/Li⁺ on multichannel battery testers at a current density of 50 mA g^-1. The results of electrochemical characterization will be detailed on the conference.
References
[1] Yan et., Al. Sci. Rep. (2013)1568.
[2] Chang et.al., Enengy Environ. Sci., 5(2012) 6895.
[3] Guo et al., Electrochim. Acta, 74(2012)271.
[4] Wang et al., Electrochim. Acta, 93(2013) 213.

Silicon nanowires (SiNWs) were conformally coated with ultrananocrystalline diamond (UNCD) by a novel route using candle wax as seeding source, which is more effective in the diamond nucleation than traditional methods. These one-dimensional UNCD decorated SiNWs (UNCD/SiNWs) exhibit diameters in the range of 100 to 150 nm and a UNCD grain size of ~5 nm. Bare SiNWs and UNCD/SiNWs were used in lithium-ion battery (LIB) anodes, where UNCD coating provide effective conduction channels for both electrons and Li-ions and protects the integrity of SiNWs by featuring electrochemical inertness and mechanical strength. The cyclic voltammetry studies show redox peaks for Si consistent with lithium insertion/extraction, indicating good reversibility over extensive cycling. Charge-Discharge tests showed that bare SiNWS can deliver an initial discharge capacity of ~740 mAh/g and stable capacity of 255 mAh/g, however the UNCD/SiNWs electrodes supply an initial high discharge capacity of ~1270 mAh/g and a reversible capacity of ~450 mAh/g over 50 cycles. No visible cracks were found on the UNCD/SiNWs anode material after extensive Li alloying/dealloying, the anode retained its good contact with the current collector, and no anode paring was observed. Thereby, the performance of LIBs based on silicon can be enhanced by implementing the UNCD/SiNWs hybrid structure grown directly on current collector (Cu), which represents a promising anode material with high energy density and long cycling stability.

Structures and porosity including interconnectivity of micro- and meso-porosity play an important role in the performance of porous electrode materials. The information obtained on structural and porosity changes in electrode materials during a charge-discharge cycle provides insights to a better understanding of chemical and mechanical degradation mechanisms and a better design of electrodes.
The pore geometry in most porous materials, even in the ordered mesoporous silica, is complex with interconnected cages, channels and micropores. It is challenging to directly characterize the interconnectivity of the pores in nano or meso-porous materials. The techniques such as small angle x-ray or neutron scattering and gas absorption do not provide direct information on how channels and cages are connected. In this presentation, we will demonstrate that hyperpolarized (HP) ¹²⁹Xe NMR is a powerful and unique tool in probing porosity and interconnectivity in porous materials.
Hyperpolarized (HP) ¹²⁹Xe NMR techniques have been applied to probe the changes in structures and porosity of silicon anode materials in Li ion batteries. A newly constructed state of art HP ¹²⁹Xe NMR polarizer has enabled us to examine the changes in structures and porosity of practical silicon anodes as a result of electrochemical cycles in Li ion batteries. The influence of binders and growth of SEI layers on the porosity of an anode made of silicon, carbon black and polymer binders before and after electrochemical reactions have also been investigated using (HP) ¹²⁹Xe NMR. Our initial results indicate that ¹²⁹Xe NMR is a powerful diagnostic tool to any changes in porosity or surface compositions during the electrochemical reactions.

Rapid progress has been made in realizing battery electrode materials with high capacity and long-term cyclability in the past decade. However, low 1^st cycle Coulombic efficiency as a result of the formation of solid electrolyte interphase and Li trapping at the anodes, remains unresolved. Here we report Li_xSi-Li₂O core-shell nanoparticles as an excellent prelithiation reagent with high specific capacity to compensate the first cycle capacity loss. These nanoparticles are produced via a one-step thermal alloying process. Li_xSi-Li₂O core-shell nanoparticles are processible in a slurry and exhibit high capacity under dry air conditions with the protection of a Li₂O passivation shell, indicating that these nanoparticles are potentially compatible with industrial battery fabrication processes. Both Si and graphite anodes are successfully prelithiated with these nanoparticles to achieve high 1^st cycle Coulombic efficiencies of 94% to >100%. It suppresses the undesired consumption of Li from cathode materials during SEI formation. The approach is generally applicable to various anode materials involving complex nanostructures. The Li_xSi-Li₂O core-shell nanoparticles enable the practical implementation of high-performance electrode materials in lithium-ion batteries. In addition, Li_xSi alloy also serves as a new anode material with the potential to pair with all high capacity lithium-free cathodes for next generation high-energy-density lithium-ion batteries.

Synthesis and understanding of nanomaterials with improved properties are critical in the development of high capacity electrochemical cells for application in lithium ion batteries. Nanostructured materials have shown to have exceptional storage capabilities. In this project, we have prepared nanostructured columnar self-assembled ruthenium oxide (RuO₂) directly on stainless steel current collectors using low pressure chemical vapor deposition. The as-prepared materials were examined by powder X-ray diffraction. 3D pyramidal structure ranging from 50 to 80 nm was self-assembled. Galvanostatic charge-discharge experiments versus Li/Li⁺ in the range of 4 to 0.1 V have demonstrated that these nanostructures are reversible at extremely high capacity (~1150 mAh g-1, 5.70Li per mol of RuO₂). The capacity retention was approximately 100% from the first to second cycle and 87% after 60 cycles. The origin of the excess capacity was probing using cyclic voltammetry (CV), which was performed at various different voltage ranges. The CV results will be discussed.

The phenomenal growth of modern electronics has motivated us to look for more efficient energy storage solutions, e.g. lithium-ion batteries. The current generation of Li-ion batteries uses graphite in the anode, but in recent years there has been an increased focus to replace graphite with silicon, which has approximately ten times the theoretical charge capacity of graphite. Apart from personal electronic devices, such an increase in capacity could have a significant effect on a number of proposed applications, e.g. electric cars, wearable devices, etc. However, there are significant challenges to be addressed to make it a viable technology. The main challenge of using silicon as an anode material is its significant volume expansion during the charging cycle, which is caused by the larger specific volume of lithium-silicon alloys. Previously, these issues have been solved by exploiting different morphologies of silicon nanoparticles (SiNPs), such as nanoribbons and nanowires. Although such methodologies are effective and relatively successful, they are not yet economically viable.
Here, we propose to use an alternate route of soft and hard material integration by using silicon nanoparticles encapsulated with conductive hydrogels. Novel hydrogels based on natural monomers, such as chlorophyllin, are used by applying the technique of in-situ polymerization. The hydrogel used here has multiple functionalities; first, due to the low mechanical property of the hydrogel, it serves as a soft enclosure for the relative free expansion of silicon. Secondly, it helps to increase the conductivity by utilizing electrically conductive monomers in the hydrogel preparation. The Polypyrrole and phytic acid that are used also create better binding in the polymeric hydrogel. Such a method is very promising, as it alleviates the two major concerns of silicon usage in the anode of an Li-ion battery - fracture of silicon due to repeated charge cycles, and enhancement of electrical conductivity of the silicon anode. The improved binding would allow for increased adhesion energy between the SiNPs and binder materials. Furthermore, we believe such an approach would make anode fabrication based on silicon less process-intensive and overall more cost-efficient.

We demonstrate synthesis and electrochemical performance of novel molecular precursor-derived ceramic (PDC)/carbon nanotube embedded graphene self-supporting composite papers as Li-ion battery electrode. The papers were prepared through vacuum filtration of various PDC-graphene oxide (GO) dispersions in DI water followed by thermal reduction at elevated temperatures that resulted in a homogenous PDC/reduced GO papers that were highly crumpled, mechanically robust and consisted of a 3-D electrically conducting network. These electrodes showed electrochemical capacities as much as approx. 300 mAh.g^-1 with respect to total weight of the electrode (approx. 500 mAh.g^-1 w.r.t. active material), with negligible capacity loss for more than 1000 cycles. Boron-doped silicon carbon nitride (Si(B)CN/graphene) outperformed its un-doped counterparts (SiCN/graphene), both in terms of electrochemical capacity, cycling stability and coulombic efficiency.

We report synthesis of a sheet-like composite composed of hexagonal boron nitride (or BN) functionalized with polysilazane-derived silicon carbonitride (SiCN) ceramic. The composite powder shows high electrical conductivity, is stable against oxidation up to at least 1000 °C in flowing air, and has higher Li electrochemical capacity with superior cyclic stability even at very high C-rates not observed in un-doped or boron doped SiCN. The SiCN/BN composite electrodes showed stable charge capacity of 517 mAh g^-1 at 100 mA g^-1 and 283 mAh g^-1 even at high current density of 2400 mA g^-1 at the electrode level which is almost 3 times higher than SiCN electrode prepared and tested under similar conditions. Also, the anode showed a stable Li cycling with a high charge capacity of 401 mA g^-1 at 100 mA g^-1 after 1000 cycles at 1600 mA g^-1. Chemical characterization of the composite suggests that addition of BN to polysilazane in moderate amounts (10 wt%) followed by the pyrolysis of polysilazane/BN composite resulted in a higher free-carbon content in the SiCN matrix, which exceeded the percolation limit and improved the electrical conductivity and Li-reversible capacity.

Huge progress has been made in developing silicon anodes for high-energy lithium ion battery. With powerful nano-engineering, cycle life of silicon anodes has been highly extended while unstable SEI formation has been efficiently suppressed. However, three major problems, including severe side reactions, poor scalability and low tap density, highly hinder its further industrial application. Here, these three problems are altogether resolved by a mechanical-based strategy. Rather than the solution-based chemical reactions and assembly widely used before, industrially-mature mechanical techniques are introduced here to fabricate nanostructured silicon secondary clusters (SC). With the mature techniques, >20 g of final product per batch can be easily produced even under lab scale, with >95% yield. Furthermore, since no surface property needs to be considered in mechanical techniques, they can be simply applied to a broad range of materials beyond silicon. In this work, near-ultimate packing density (up to 1.375 g cm^-3) is produced. This enables tight connection between silicon and carbon conducting frameworks. As a consequence, more than 95% of initial capacity is retained after 1400 cycles at 1C, with average specific capacity ~1250 mAh g^-1. Noticeably, thanks to the improved electron conductance and tap density, no carbon nanotube (CNT) additive is needed here for high mass loading any more. Stable cycling with >2 mg cm^-2 loading of active matierals is achieved without CNT. In contrast to other solvent-based counterparts for SC fabrication, the mechanical-based techniques provide more opportunities for modifying SC structure. Here, as a demonstration, CNT was uniformly integrated into SC, further improving intra-cluster electron conductance. Consequently, notable enhanced rate capability can be attained, with high reversible specific capacity ~1140 mAh g^-1 and ~880 mAh g^-1 at 2C and 4C, respectively.

The synthesis cobalt oxide has great importance but is quite challenging due to the complexity of its chemical formation. A one step synthesis for the growth of CoO nanoparticles and their performance as anode for rechargeable lithium ion batteries are described. Low-pressure chemical vapor deposition was used to deposit CoO directly on stainless steel current collector from cobalt acetylacetonate precursor. CoO nanoparticles were synthesized at a temperature around 400° C and 3 torr. The crystal structured was characterized by X-ray diffraction and the morphology was studied by field-emission scanning electron microscopy. Electrochemical measurements were performed and the nanoparticles electrode exhibited high discharge capacity and good cycling performance with >95% Coulombic efficiency. The nanoparticle shows excellent cyclability. The enhancement of the electrochemical performance is attributed to the high specific surface are excellent contact between the nanoparticles and the current collector. This work is promising in that it provides a reproducible method for the synthesis of cobalt oxide.

2D-dimensional nickel oxide (NiO) nanoplates were prepared using a low pressure chemical vapor deposition (LPCVD) producing metallic Ni directly on stainless steel current collectors followed by annealing under ambient oxygen atmosphere. The structural identities of the as-deposited nanomaterials were examined by X-ray diffraction, which revealed the formation of NiO (111 preferred orientation) after annealing. The morphology was examined by field emission scanning microscopy, which displayed the uniform arrangement of NiO nanoplates. The electrochemical properties of the as-deposited NiO nanoplates were investigated galvanostatic discharge-charge experiments in the range of 4.0 to 0.1 V versus Li/Li⁺ at a constant current of 100 mA for the first 10 cycles. A capacity of 1377 mAh g^-1 was observed during the first discharge process. The rate was increased to 200 mA which displayed a capacity 1291 mAh g^-1. After 70 cycles at 100 mA a capacity of 1542 mAh g^-1 was calculated. A capacity of 1723 mAh g^-1 was shown at a constant current reading of 500 mA after 110 cycles. The as-deposited NiO nanoplates stabilize around 1650 mAh g^-1 after 140 cycles at 500 mA. The NiO nanoplates exhibited better reversibility and higher capacity than previously synthesized NiO anodes. It is interesting that the NiO nanoplates held the extra capacity even after 150 cycles. The origin of the extra capacity in the NiO nanoplates will be discussed.

High capacity anodes are important materials to enable next generation of high energy batteries for portable electronics, electrical transportation and grid scale storage. However, these materials also present significant challenges due to their complete bonding and structure changes, large volume expansion, instability of solid electrolyte interphase and dendritic metal protrusion. In this talk, I will present our nanomaterials design approach to address these challenges. In the past seven years, my group has made exciting progress in Si anodes through multiple generations of materials design and invention of novel concepts including nanowires, core-shells, hollow particles, yolk-shells, double-walled hollow tubes, pomegranates, conducting hydrogel and self-healing. In addition, we have exploited the nanomaterials design concepts for other promising anodes including phosphorus and Li metals and produced exciting performance.

Polymeric binders has been shown to be critical for retaining capacity and cyclability of silicon (Si) anodes in lithium-ion batteries mainly due to their capability of maintaining structural integrity of electrode against ~300 % volume change of Si during cell operation. Despite the persistent efforts to develop superior binders so far, the research in this area focused on only a specific binder property, which is sporadically claimed to be most critical in each case. In order to present guideline on the design of binders for next generation Si anodes, we have investigated various binder properties, including crosslinking, self-healing, and mechanical properties by taking advantage of simple chemistry of Meldrum`s acid in a systematic fashion. We have classified our polymeric binders into three categories. First one is the binder with no/weak interactions, polyvinylidene fluoride (PVDF) featuring van der Waals between polymer chains. In agreement with the previous literature reports, the capacity of PVDF decayed fast and showed the worst cycling performance. Second one is the binder with covalent attachment/crosslinking. To profoundly examine these types of binders, polymers/copolymers were synthesized starting from monomers with distinct properties - namely, styrene (S) for stiffness; methyl methacrylate (M) for flexibility; 5-methyl-5-(4-vinylbenzyl)Meldrum&’s acid (K) for crosslinking. It is noteworthy that Meldrum&’s acid, K, can be pyrolyzed to form ketene intermediates which can undergo [2+2] dimerization and react with native hydroxyl on the Si surface. The comparison of the cycling performance between relative stiff KSM binder and flexible KM binder at the same K ratio (15%) showed that stiff binder has slightly better capacity retention than flexible binder. Moreover, as the K ratio increases in KM binders, the capacity retention also drastically increases, indicating that crosslinking is more dominant factor than stiffness. The third one is the binders with supramolecular interactions (self-healing binder). Lithium 2-methyl-2-(4-vinylbenzyl)malonate (C) for self-healing monomer was obtained upon hydrolysis of K unit under basic conditions. Self-healing capability originates from strong ion-dipole interactions between lithium carboxylate moieties of binders and native oxides of Si and Cu foil. Thus, the ion-dipole interactions can recover the electrode cracks formed during Si volume expansion, which was clearly observed by scanning electron microscopy (SEM) analysis. The self-healing effect of C₁₀₀ binder results in the electrode surface without large cracks and the best cycling performance with 51 % capacity retention compared to other binders studied even after 500 cycles. Investigation of series of binders with distinct properties clearly show that while crosslinking and initial covalent attachment can improve the performance, the self-healing effect is more critical for high-performance Si anodes.

Presently, LIBs have got tremendous attention due to their high energy densities and have been considered as promising power source for future EV. In this regard, metallic Si, Ge and Sn are considered as potential substitute to the conventional graphite (372 mAh/g) due to their high theoretical capacities 4200, 1600 and 992 mAh/g, respectively and thermal stability. However, structural disintegration, limited access to redox sites and loss of electrical contact have long been identified as primary reasons for capacity loss and poor cyclic life of these materials. Although nanotechnology plays critical role by developing nanostructures but simple reduction in size introduce new fundamental issues like side reactions and thermally less stable. Furthermore, formations of unstable SEI film due to the decomposition of the organic electrolyte at #706;0.5 V vs. Li/Li⁺. Thus, a careful design that can inhibit the side reaction by surface protection, make all redox sites accessible by increasing the intrinsic conductivity, maintain a continues network for ionic and electronic flow and keeps the structural integrity, resulting improved performance and excellent capacity retention with long cyclic life to meet the requirements set by USABC for LIBs use in EVs. Here, we have developed hybrid structures of Si and Sn using two strategies to overcome the aforementioned problems. The encapsulation of the NPs/NTs in the shell of inactive metal and dual protection was provided by the overcoat of NG. The second strategy accounts the surface protection by C shell and dual protection by soft matrix of porous carbon (PC). The intrinsic conductivity is increased by the backbone of highly conductive metal that efficiently transfers the electron to all redox sites inside the nanostructure and acts as stress relaxer due to its hard nature. Furthermore, these hybrids also took the advantages of Li⁺ storage at the grain boundaries that brings additional capacity. The high performance of the composite based on the synergistic effect of several components in the nanodesign. Moreover, NG/PC increases the contact area between electrolyte and electrode for better performance because of their high surface area. In addition, due to the high conductivity and fast ions transfer mobility, graphene/porous carbon maintains the fast electrical flow of the composites. As a result these hybrids possess extraordinary performance with capacity retention of ~100% after long cyclic life of 2000 cycles. These strategies to combine the different property enhancing factors in one composite with engineered structures will bring the realization of the LIBs in EVs.
Li, Q.; Mahmood, N.; Jinghan, Z.; Hou, Y., Sun, S., Nonotoday, 2014, DOI:10.1016/j.nantod.2014.09.002.
Mahmood, N.; Zhang, C.; Liu, F.; Jinghan, Z.; Hou, Y., ACS Nano 2013, 7, 10307-10318.
Zhang, C.; Mahmood, N.; Yin, H.; Liu, F.; Hou, Y., Adv Mater 2013, 25, 4932-4937.
Mahmood, N.; Zhang, C.; Hou, Y., Small 2013, 9, 1321-1328.

In recent work, our group has demonstrated improved cycling performance of silicon (Si) negative electrodes for lithium ion (Li-ion) batteries though the use of a self-healing polymer (SHP) binder. Our work was successful in utilizing commercially available micron sized particles to produce cells that were stable for over 100 cycles¹. This work details further investigation into the effects of increased crosslinking on the performance of the SHP in the Si electrodes.
Crosslinking was varied using a combination of difunctional and trifunctional molecules as the starting materials for the supramolecular SHPs. Additionally, a covalent crosslinker was used in some samples to examine the effects of static crosslinks as compared to the dynamic hydrogen bonding of the SHP. Standard mechanical tensile measurements were performed in addition to creep and stress relaxation experiments used to determine characteristic relaxation times for each material from viscoelastic theory. Cell cycling performance was correlated to this data and a relationship between mechanical characteristics, Li-ion conductivity, and cycling stability was seen. This work represents a step toward understanding the reasons behind performance improvements seen in the Si electrodes with SHP and will allow us to begin to tailor molecular structures of self-healing polymer binders specifically for battery applications.
1. Wang, C. et al. Self-healing chemistry enables the stable operation of silicon microparticle anodes for high-energy lithium-ion batteries. Nat Chem5, 1042-1048 (2013).

Many high-energy-density lithium ion battery electrode materials have been studied to meet the requirements for smaller weight and longer battery life. For example, silicon is able to deliver 3600 mAh/g by forming Li₁₄Si₄, which is higher than the specific capacity of other known negative-electrode materials. However, Li-Si has poor cycle life and low cycle efficiency due to coupled mechanical and chemical degradation, which leads to quick capacity fade upon cycling. One of the most important degradation mechanisms is the failure of solid electrolyte interphase (SEI). When SEI fails, it will cause irreversible lithium consumption in the lithium ion battery system.
The SEI is a passivation layer formed between the electrolyte (liquid) and electrode surface (solid) to enable the long-term cyclability. From studying of the naturally formed SEIs under different conditions, relationships between the properties of SEI and cycling stabilities have been revealed. We hypothesize that an ideal SEI should be electronic insulating, ionic conducting, mechanically “strong,” and chemically stable. We have tested the hypothesis by studying ceramic coatings, such as Al₂O₃ and LiF that are ionic conducting and electric insulating, transition metal oxide coatings that are electronic insulating and chemically stable, and ionic conductive polymers (ionic conducting and mechanically “strong”). We envision that this work can provide a general guideline in the design of artificial SEIs to improve the current efficiency and increase the life of lithium ion batteries.

Toward the development of portable energy storage and electric vehicle applications, flexible Li-ion batteries have naturally received much attention. From a practical viewpoint, flexible storage devices must have (1) higher electrode capacities, (2) mechanical flexibility, and (3) better active materials-substrate contact. Herein, we attempt to provide novel integration well-aligned Cu_xZn_ySn_zS (CZTS) nanostructures for electrodes onto a bendable substrate via a simple solvothermal method with proper growth condition. The lithium ion battery utilizing such CZTS nanostrucutres as anode showed a promising initial capacity of 1250 mA h g^-1 at 10000 mA g^-1 current density, and stabilized to 1115 mA h g^-1 after 150 cycles. Furthermore, a flexible CZTS //LiNi_0.7Co_0.3O₂ lithium ion full cell is fabricated, with an output voltage of >3 V, exhibiting high flexibility, excellent electrical stability, and superior electrochemical performances. Our direct integration well-aligned Cu_xZn_ySn_zS (CZTS) nanostructures will help pave the way not only for Tin-base but also for polymer substrate-based bendable Li-ion batteries.

Stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. Here, we demonstrate a promising novel electrode design by growing two-dimensional (2D) atomic crystal layers including hexagonal boron nitride (h-BN) and graphene directly on Cu metal current collectors. Lithium ions were able to penetrate through the point and line defects of the 2D layers during the electrochemical deposition, leading to sandwiched lithium metal between ultrathin 2D layers and Cu. The 2D layers afford an excellent interfacial protection of Li metal due to their remarkable chemical stability as well as mechanical strength and flexibility, resulting from the strong intralayer bonds and ultrathin thickness. Smooth Li metal deposition without dendritic and mossy Li formation was realized. We showed stable cycling over 50 cycles with Coulombic efficiency sim;97% in organic carbonate electrolyte with current density and areal capacity up to the practical value of 2.0 mA/cm2and 5.0 mAh/cm2, respectively, which is a significant improvement over the unprotected electrodes in the same electrolyte.

Many living things in nature often provide inspiration for advantageous properties that are actually informative for practical technologies. Specifically, millipedes, myriapodous arthropods, show stong adhesion ability onto diverse rugged surfaces. The excellent adhesion of millipedes is supported by a synergetic effect between many contacting points based on continuous pairs of legs and several micron-sized adhesive pads placed on each leg. In this talk, this millipedes&’ adhesion mechanism in real world was shifted to polysaccharide binder in nanoscale world to determine superior binder for silicon (Si) electrodes in lithium rechargeable batteries. Comparative battery cycling measurements based on a variety of polysaccharide binders indicate that native xanthan gum is outperforming other polysaccharide binders. The exceptional performance of native xanthan gum can be rationalized by its structural advantage corresponding to millipedes in both physical and chemical perspectives: Physically, series of side chains from superstructure of xanthan gum mimic millipedes&’ series of legs, while, chemically, ion-dipole interactions from charged functional groups mimic millipedes&’ micron-sized adhesive pads. The systematic investigation offers structural binder design rules in Si electrodes, and provides thorough understanding on how important it is to introduce electrostatic charges and superstructures as a Si electrode binder.

Silicon alloys have the highest specific capacity when used as anode material for lithium-ion batteries, however, the drastic volume change inherent in their use causes formidable challenges toward achieving stable cycling performance. Large quantities of binders and conductive additives are typically necessary to maintain good cell performance. In this report, an only 2% (by weight) functional conductive polymer binder without any conductive additives was successfully used with a micron-size silicon monoxide (SiO) anode material, demonstrating stable and high gravimetric capacity (> 1000 mAh/g) for ~500 cycles and more than 90% capacity retention. Prelithiation of this anode using stabilized lithium metal powder (SLMP®) improves the first cycle Coulombic efficiency of a SiO/NMC full cell from ~48% to ~90%. The combination enables good capacity retention of more than 80% after 100 cycles at C/3 in a lithium-ion full cell.

A class of new functional conductive polymers is developed for electrochemical energy storage applications. Contrasting other polymer binders, these binders has tailored electronic structure, adhesive functional groups, and controlled polarity for ion transport. This class of materials is suitable as binders for high capacity alloy anode materials. Materials with high lithium storage capacity, such as Si and Sn based alloys, have recently been extensively studied for their applications as lithium-ion battery anodes. However, the large-volume change associated with lithiation and delithiation of these materials severely hinders the practical application. The functional conductive polymer binders maintain conductivity and mechanical integrity during the battery operation, implementing the conceptual idea of combining binding, electron conducting and ion conducting into one material to significantly improve the electrode cycling performance.
We will cover the theory to develop the functional conductive polymer binders for Si and Sn alloy, generations of the conductive polymer binders from our laboratory, and discuss the electric conductivity, adhesion and ion transport functionalities in these binders. Different Si based materials such as Si nanomaterial and SiO micron size materials are also used with these binders to fabricate electrode, and their performance characteristics reported. Electrode architectures are also very important for functional binders and alloy materials. The talk will also cover develop Si and conductive polymer electrode architectures including Si/binder composite particles, and in situ formation of Si network in the electrode. Conductive polymers with Sn materials system in lithium and Sodium ion batteries will also be discussed.

Given the large surface area and unique channels, metal-organic frameworks (MOFs),¹ have served as a “generalist” in the fields of clean energy,² such as adsorbents for hydrogen,³ electrolytes for fuel cells,⁴ electrode materials for supercapacitors⁵ and so on. However, only a few immature applications of MOFs as electrodes for lithium ion batteries (LIBs) or micro-LIBs have been researched.^6-9 To the contrary, Si anode, with the highest theoretical capacity, low working potential and feasible integration with other micro- or nano-electronic devices, has been intensively investigated experimentally and theoretically to address the volume expansion issue during discharge/charge processes. But, fully addressing the deterioration of the electrode structures caused by the volume expansion, which would generally results in performance fading and safety issues, is still challenging.
In this work, a novel class of MOFs, was initially proposed to composite/network with Si nanorod (NR) arrays as anodes for LIBs employing the modified nanosphere lithography (NSL) and inductive coupled plasma (ICP) dry etching followed by a method of solution growth. An over 20 times higher capacity was accomplished in the MOFs/Si nanocomposite electrode compare with that in the only Si NR anodes. In addition, with the employment of a buffer layer of Ti/TiN to modify the electronic conductivity of the interfaces between Si inner core and outer MOFs, a further enhanced capacity was realized accompanied with the high Coulombic Efficiency (CE). First principles calculations were performed to verify the favorable lithium diffusion in this kind of MOFs structure.
References:
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The bronze polymorph of titanium dioxide, known as TiO₂(B), has shown promising properties for Li-ion batteries, including high charge rates, high capacity (<300 mAhg^-1), and overall chemical stability . In contrast to previous studies performed with powder examples, here highly crystalline TiO₂(B) epitaxial films were grown on strontium-titanate-buffered silicon substrates. The structural quality of the films was confirmed by XRD and atomic resolution transmission electron microscopy. Polarization-dependent Raman spectroscopy was collected from these samples and compared to nanopowder results reported in the literature. Our measurements were coupled with density functional theory calculations to analyze the atomic displacements associated with each Raman-active vibrational mode. These results provide a reference for the investigation of crystallinity, structure, composition, and properties of TiO₂(B) materials with Raman spectroscopy, and a basis for optical study of these materials for application in batteries.

Intensive efforts are dedicated to improve the rate capability and capacity retention of the electrodes through emerging nanotechnologies and optimum designs. However, the leading mechanisms at the intrinsic scales that govern the rate dependent capacity of electrodes are much less illuminated. Through the use of electron microscopy, synchrotron X-ray methods and ab initio calculations, in an example of conversion electrode NiO, we found that a dominance in slow NS mode during high-rate discharge leads to a loss in the deliverable capacity. The near-surface capacity for lithiation can be drawn very quickly, it encounters unexpected difficulty when trying to propagate into the interior (I). We found that the interior capacity for lithiation and Ni²⁺/Ni⁰ can be activated expeditiously after the nucleation and growth of a lithiation “wedge”, with an incubation time on the order of 100 seconds. Due to this finite incubation time, the interior redox capacity of NiO nanoparticles cannot be drawn if the charging rate is too high, which intrinsically limits the rate capability (power) of NiO anode. The discovered heterogeneous reaction nature and its correlation to the rate capability in the present work provides guidance for the further design of battery materials that favors high-rate charging.

Increasing demand of high-performance portable energy storage devices boosts the development of lithium-ion battery technologies [1]. Transition metal oxides have attracted tremendous attention as promising anode materials for Li-ion batteries due to their ability to deliver much higher specific capacities than commercial graphitic anodes. This class of electrode materials shows a peculiar lithium storage avenue through the electrochemically driven phase conversion, in contrast to other prevailing mechanisms such as intercalation and alloying [2]. It is generally believed that conversion reactions will give rise to severe structure modifications of the electrode materials, for example, breaking large pristine crystals into small nanoparticle composites, which may improve electronic and ionic transport at a price of cyclability. It is of great importance to understand the structure evolution during a conversion process and thus precisely control the reaction pathways to regulate the phases with desired structures and morphologies. For such purpose, we need to utilize in situ transmission electron microscopy (TEM) and spectroscopy [3,4], which have sufficient spatial resolution and chemical detectability, to build up direct correlations between microstructure and electrochemistry.
In this study, we choose spinel iron oxide (Fe₃O₄) nanoparticles as a model system for lithium conversion and implement the in situ dry-cell setup for real-time observation of electrochemical lithiation inside a TEM, where the composite electrode containing Fe₃O₄ nanoparticles and the amorphous carbon support will be lithiated, while extra side reactions are eliminated with no participation of liquid electrolyte [5]. A series of comprehensive characterizations have been performed using complementary in situ imaging, diffraction, and spectroscopy methods, which revealed the morphological, structural, and chemical evolutions with respect to the progress of lithiation. With further performance tests using coin-cells and ex situ microscopy analysis, we are able to explicitly establish the full panorama that crosslinks the dimensionality effects, structure alteration, electrochemical properties, and the reaction pathways on the atomic level. Our findings provide insights into understanding conversion mechanisms in spinel structures, and also show implications for improving performance in future design of battery electrodes.
References
[1] J. M. Tarascon and M. Armand, Nature 414, 359 (2001).
[2] J. Cabana, et al. Adv. Mater. 22, E170 (2010).
[3] C.M. Wang, et al. Nano Lett. 11, 1874 (2011).
[4] A. Nie, et al. ACS Nano 7, 6203 (2013).
[5] K. He, et al. ACS Nano 8, 7251 (2014).

Manganese dioxide (MnO₂) is widely known to possess various allotropic forms such as α-, β- and γ-phases, which are constructed by combination of octahedral [MnO₆] building blocks to form different tunneled structures. These special structures are believed to account for the various characteristics of MnO₂ when it is employed as electrode material in lithium (ion) batteries. There is, however, lack of direct proof demonstrating the role of tunneled structure during electrochemical lithiation/delithiation of MnO₂.
In this work, by applying high resolution scanning transmission electron microscopy (HRSTEM) to single α-MnO₂ nanowire along both axial and radial directions, the tunneled structure is clearly shown and characterized. The α-MnO₂ nanowire is proved to be single crystalline and grow along [001] direction. Cross-sectional HRSTEM images have shown that the nanowire has a squared cross section and 2x2 tunnels align parallelly along its growth direction [001], matching very well with simulated crystal structure. An in-situ TEM setup for study of MnO₂&’s dynamic lithiation/delithiation process is also designed and demonstrated. It is found that upon lithiation, the α-MnO₂ nanowire shows different orientation-sensitive morphologies. That is, α-MnO₂ unit cell expands asynchronously along [100] and [010] directions, resulting in macroscopic difference under [010] and [100] zone axes observations. DFT simulation demonstrates that such an asynchronous expansion originates from the specific Li-occupancy sequence at Whckoff 8h sites inside α-MnO₂&’s 2×2 tunnels.

Various nanostructured transition metal oxides as alternative candidates for Li-ion battery have been widely investigated to overcome current capacity limitation. Particularly, manganese oxides are widely utilized as anode for Li-ion battery due to the high electrochemical capacity, good capacity retention, and high rate performance. Unfortunately, the complicated oxidation states of manganese (Mn(II), Mn(III), and Mn(IV)) and interference from factors such as surface chemistry and morphology of the material make it more difficult to reveal the lithium-storage mechanisms clearly.
In this research, ordered mesoporous MnO₂, Mn₂O₃, Mn₃O₄, and MnO materials with 3-D pore structure were successfully synthesized via a nano-replication method by using ordered mesoporous silica of KIT-6 (Cubic Ia3d space group mesostructure) as the template under specific oxidation and reduction conditions. All of the ordered mesoporous manganese oxides with different crystal structures and oxidation states demonstrated almost the same spherical-like morphology with several hundred nanometers of particles.
Four representative ordered mesoporous manganese oxides, MnO₂, Mn₂O₃, Mn₃O₄, and MnO, are utilized as electrode materials for Li-ion battery within the potential window of 0.0 and 3.0 V vs. Li⁺/Li. If various manganese oxides utillize the same conversion reaction, the theoretical capacity will be 1233 mAh/g for MnO₂, 1019 mAh/g for Mn₂O₃, 937 mAh/g for Mn₃O₄, and 756 mAh/g for MnO, respectively. All of ordered mesoporous manganese oxide materials show reversible capacity of about 800 mAh/g with the average charging voltage of 1.3V.
This work includes the study of reaction mechanism for Li storage using synchrotron radiation (in-situ XRD and XAFS) and also observation of pore structure transition to clarify the effectivity of pore structure to accommodate the volume change for lithiation-delithiation processes.

Li-ion batteries revolutionized the today&’s e-society as these are working successfully in portable commercial electronic devices like cell phones and lab-top computers. Due to their high energy density and light weight, Li-ion batteries are promising to extend their applications like surgical tools, drilling bits along with much awaited electric vehicles. However, safety, stability and compatibility of electrodes/electrolyte are concern since batteries have to work in extreme temperatures (100 C) to extend their applicatons. Current commercial Li-ion batteries use polar organic solvents with a dissolved lithium salt as electrolytes. These solvents have a major inherent limitations in terms of safety especially at high temperatures (>60 C) due to their high vapor pressure and the chemical reactions between the dissolved lithium salts and electrolyte solvents. Alternatively, room temperature ionic liquids (RTILs) based electrolytes are gained paramount importance due to negligible vapor pressure, wide electrochemical window and structural stability, especially for high temperature applications (up to 150 °C). Hence, RTIL-based Li-ion batteries provide safety with much reduced explosion or pressure risks due to their admirable physicochemical properties compared to Li-ion cells with conventional organic electrolytes. Many RTILs are promising to use in Li-ion batteries, but no single IL to achieve the all the requirements to be a successful electrolyte from room temperature to 120 ^oC. Also, identifying electrode materials for 120 ⁰C are challenging due to their structural and thermal stability limitations and incompatibility with ILs. In particular, piperidinium based ILs has thermal and electrochemical stability at high temperatures but poor electrochemical properties at RT. Similarly, immadazoilum based ILs exhibits better electrochemical properties at RT, so tailoring both these systems would leads to design better electrolyte for Li-ion batteries to work from RT to 120 ^oC. With this background, we systematically monitored and tailored the RTILs based electrolytes by tuning their cation, functionality, viscosity, conductivity with Li-salt along with thermal stability intern Li-ion battery applications from RT to 120 ^oC by choosing stable electrode materials, for instance Si based materials.

A new concept of Si microwire anodes for Li ion batteries, which consists of an array of Si microwires embedded at one end in a Cu current collector, has been lately developed [1]. The process for the production of the wires is fully scalable, allowing the production of anodes as large as a silicon wafer, with wires as long as the thickness of the wafer [2]. The method is based in the electrochemical etching of macropores and a chemical over-etching step, what makes it very economical.
The capacity of the anodes is very stable over 100 cycles [3], and breaks all the records when considering the capacity per area (mAh/cm²), with wires of 70 micron in length [4]. This capacity can be even larger when preparing longer wires. Nevertheless, it is not known which may be the limit for scaling up the wires.
In the paper for this conference, an electrical and mechanical description of the wires will be given, explaining which are the charging rate limits of the wires. A model based on the series resistance, aging and state of charge will be discussed. Comments of the future development of the wires will be given.
[1] E. Quiroga-González, E. Ossei-Wusu, J. Carstensen, H. Föll, J. Electrochem. Soc., 158 (2011) E119.
[2] E. Quiroga-González, E. Ossei-Wusu, J. Carstensen, H. Föll, Nanoscale Res. Lett. 9 (2014) 417.
[3] E. Quiroga-González, J. Carstensen, H. Föll, Electrochim. Acta, 101 (2013) 93.
[4] E. Quiroga-González, J. Carstensen, H. Föll, Energies, 6 (2013) 5145.

Although silicon (Si) exhibits very high theoretical capacity (4200 mAh/g) as an anode for Li-ion batteries, it suffers fast capacity fade because of the large volume expansion during lithiation/de-lithiation processes. Although various nano-structured Si and their composite have been developed to minimize the pulverization of Si particles during the cycling process, most of these approaches worked well only at relatively low loading conditions (<1 mAh/cm²). Here, we will discuss how the porous structured Si and rigid skeleton supported Si composite affect the electrode performance at a high loading of ~3 mAh/cm². The performance of porous Si materials from electrochemical etching and Mg thermal reduction will be compared. Good cycling stability of electrochemical etched Si was demonstrated with >90% capacity retention at the loading of ~ 3 mAh/cm². Both ex situ and in situ TEM have been used to characterize the Si electrode before and after cycling. The effect of various binders, including self-healing binders on the performance of thick electrode will also be discussed.
Acknowledgement:
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technology of DOE, projects on Batteries for Advanced Transportation Technologies.

ABO₃ compounds have drawn much attention due to their large lattice space for large ions and its high conversion capacity. However, the structural evolution and atomic detail of the conversion reaction are still unknown. In this work, we present the microscopic detail of the conversion reaction in WO₃ based on in situ transmission electron microscopy studies. With atomic imaging, nanobeam diffraction and electron energy loss spectroscopy, intercalation prelude conversion reaction is explicitly revealed in WO₃ during lithium, sodium and calcium insertion. This step effectively catalyzed subsequent conversion reaction. The conversion reaction happens via structure distortion and collapse into pseudo-amorphous structure. This study provides atomic structure evolution during ion insertion in ABO₃ compounds and new insight to the conversion reaction mechanism in various ion batteries.

The ability to spontaneously repair damage, which is termed as self-healing, is an important survival feature in nature because it increases the lifetime of most living creatures. This feature is highly desirable for rechargeable batteries because the lifetime of high-capacity electrodes, such as silicon anodes, has been shortened by the mechanical fractures generated during the cycling process. Here, inspired by nature, we apply self-healing chemistry to silicon microparticle anodes to overcome their short cycle life. Coating Si anodes with a room temperature repeatable self-healing polymer, we show that the low-cost native Si microparticles (~3-8 micro), for which stable deep galvanostatic cycling was previously impossible, can now have an excellent cycle life. We attain a cycle life of 10 times longer than state-of-art anodes made from Si microparticles while retaining a high capacity (up to >3,000 mAh/g)^[1]. Cracks and damage in the coating during cycling can be spontaneously healed due to the presence of the self-healing polymers rationally designed to have features, such as room-temperature reversible healing due to the hydrogen bonding chemistry, the amorphous structure, its low glass transition temperature and the high stretchability. By further modifications of the battery structures, we can achieved stable Si electrodes with high areal capacities of 3 to 4 mAh cm^-2.^[2]
[1] C. Wang, H. Wu, Z. Chen, M. T. McDowell, Y. Cui, Z. Bao, Nat. Chem. 2013, 5, 1042.
[2] Z. Chen, C. Wang, J. Lopez, Z. Lu, Y. Cui, Z. Bao, Adv. Ener. Mater. 2014, submitted

We have performed a number of experiments to examine the mechanical behavior of high capacity anodes. In particular, using two separate techniques, we have measured the fracture energy of lithiated silicon thin-film electrodes as a function of lithium concentration. The fracture energy is found to be similar to that of pure silicon and essentially independent of the concentration of lithium. Thus, while lithiated silicon can flow plastically, it appears to fracture in a brittle manner. Additionally, we have measured stresses that develop during lithiation/delithiation of germanium electrodes. We have performed complementary XRD experiments to determine the phases that develop during lithiation/delithiation. These measurements demonstrate plastic flow in germanium, which limits the stresses, thus reducing the driving force for crack propagation. Overall, these experiments provide key insight into the development of high-capacity anode systems that avoid fracture and thereby enable long cycle life.

Composite Li-ion anode can be fabricated using silicon nanopowders synthesized by induced plasma atomization. Properties of such nanopowder were characterized by physical and electrochemical methods. Primary particles were crystalline with spherical shape and the typical diameter ranging from 50 to 200 nm. The Si nanopowder showed a high gravimetric capacity (4900 mAh/g) at first discharge and around 12% irreversible loss of lithium. In addition, observations of a single silicon particle made by in situ TEM permitted to compare the volume change during lithiation with other silicon anode nanomaterials.

Electrodes in rechargeable batteries undergo complex electrochemically-driven phase transformations upon driving Li ions into their structure. Such phase transitions in turn affect the reversibility and stability of the battery. It is of prime importance to better understand how Li ions transport within the host electrodes and what phase transitions are triggered during such interaction. This presentation gives an overview of the PI&’s research program on in situ transmission electron microscopy (TEM) of battery materials. Various anode materials including SnO₂, Zn-Sb were subjected to lithiation process and the transport of Li ions was visualized within their atomic structure. For SnO₂ nanowires, it was observed that the Li ion transport preferably happens along (200) or (020) plans and [001] crystallographic directions. Zn-Sb alloys also exhibit a new cubic alloying phase Li₂ZnSb that form by intermixing of the ABAB atomic ordering in hexagonal LiZnSb due to Li inclusion in their lattices.

High capacity material candidates for lithium-ion batteries, such as Silicon, experience extreme, unavoidable expansion and contraction during the lithiation and delithiation processes. These volumetric changes lead to rapid morphology deterioration of the electrode materials (cracks, electrical isolation of particles, pulverization, etc), which dramatically reduces the battery lifetime to a few charge-discharge cycles. While the use of nanoparticles or complicated anode structures can avoid this volumetric deterioration, these strategies tend to be expensive and limit mass loadings. Therefore, lessons from nature suggests instead of avoid the deterioration, applying a self-healing motif may provide the answer to stable battery operation. The idea of self-healing has recently been demonstrated to improve anodic cycling performance of low cost micron-sized silicon particles (SiMPs) by simple application of a Self-Healing Polymer (SHP) binder. This novel concept has shown to greatly increase the cycle life, as compared to traditional polymer binders.
While the SHP-binder is a great step towards using silicon in next-generation LIBs, the function of self-healing within the battery anode under operation is not well understood. In this study, transmission x-ray microscopy (TXM) is used to monitor SHP-SiMPs anodes in-operando. Tracking of contrast and structural changes of individual SiMPs at various points along the first charge/discharge cycle give key insights into the effects of the SHP. The effects of particle size and charge rate are quantitatively examined. The data gathered from this study provide a mechanistic understanding of the self-healing process occurring within the operating battery.

Sn, which offers large theoretical capacity (994 mAh/g), is a potentially useful anode material in lithium-ion batteries. Similar to Si anodes, Sn anodes also experience large volume changes (~260%), which induce capacity loss through mechanical degradation. Unlike Si, during lithiation, Sn forms several lithiated phases at different states of charge.
This work was performed on electroplated Sn films deposited on elastic substrates. Potentiostatic electrochemical lithiation at specific potentials was used to induce selective phase transformations. A Multi-beam Optical Stress Sensor (MOSS) was used to measure the stress evolution in situ during lithiation. X-ray diffraction (XRD) and Focused ion beam (FIB) were used to characterize the samples after lithiation. From the measured stress evolution, the yield stress of different phases was obtained. A kinetic model was applied to analyze the phase progression measured in the experiments, and to extract kinetic parameters, such as the mobility of the Li ion and the reaction rate coefficients of different phase transformations.