High-energy Li-ion Batteries Research Articles

Scenario-based prediction of Li-ion batteries fire-induced toxicity

The development of high energy Li-ion batteries with improved durability and increased safety mostly relies on the use of newly developed electrolytes. A detailed appraisal of fire-induced thermal and chemical threats on LiPF6- and LiFSI-based electrolytes by means of the so-called “fire propagation apparatus” had highlighted that the salt anion was responsible for the emission of a non negligible content of irritant gas as HF (PF6−) or HF and SO2 (FSI−). A more thorough comparative investigation of the toxicity threat in the case of larger-size 0.4 kWh Li-ion modules was thus undertaken.A modeling approach that consists in extrapolating the experimental data obtained from 1.3Ah LiFePO4/graphite pouch cells under fire conditions and in using the state-of-the-art fire safety international standards for the evaluation of fire toxicity was applied under two different real-scale simulating scenarios. The obtained results reveal that critical thresholds are highly dependent on the nature of the salt, LiPF6 or LiFSI, and on the cells state of charge. Hence, this approach can help define appropriate fire safety engineering measures for a given technology (different chemistry) or application (fully charged backup batteries or batteries subjected to deep discharge).

Dimensionally Stable and Fast Charging Graphite-Silicon Planar Composite Anode for Li-Ion Batteries

Advanced Li-ion batteries (LIBs) have been developed to have high capacity density, long cycle life, and high-rate performance for portable electronics, electric vehicles (EVs), and renewable energy storage. Graphite is currently the predominant anode material for commercial LIBs because it has a low cost, low charge/discharge plateau potential, satisfactory specific capacity (372 mAh g-1), and substantially high dimensional stability; its essential role in high-energy LIBs is expected to continue. Si is a potential Li-insertion anode material that has a substantially higher capacity than graphite but is susceptible to large (>300% when fully lithiated) volume expansion. The cyclic dimensional variations during charge/discharge cycles result in pulverization and electrical disconnection from the conductive paths of the Si active materials, leading to rapid capacity reduction during the cycles. In spite of a large amount of literature devoted to solving this issue in the past years, long-lasting Si anode up to now remains as a formidable challenge. On the other hand, composite anodes comprising graphite and limited amount of Si or Si oxide may be attractive transient products for advanced high-energy LIBs before viable Si-dominant anodes are realized. Moreover, improvement in the rate capability of Si-based anodes is needed for meeting the power requirements of various applications. In this presentation, a planar graphite-silicon composite Li-ion battery anode showing substantially higher capacities than graphite, fast-charging capability, and exceptional cycle stability will be described. The Si oxide-coated graphite flake (SGF) composite anode for Li-ion batteries (LIBs) synthesized by a unique microwave-heating process of graphite flakes (GFs) in a solution made of liquid polysiloxanes as the Si-containing precursor. Microwave-heating of the GFs induces the deposition of a conformal Si-containing conformal layer on the GF surfaces, which is subsequently turned into oxide-graphite-oxide sandwiched planar composite structure. The resulting SGF exhibits a reversible specific capacity of nearly 480 mAh g-1, 97% capacity retention at the current density of 2.5 A g-1 (~5C-rate), and 94% capacity retention after 500 cycles with an average Coulombic efficiency > 99.9%. Coating the composite with a thin layer of conducting polymer further enhance the overall specific capacity greater than 520 mAh g-1. The work suggest a new strategy for both designing and synthesizing high-performance anode materials for LIB applications. Figure 1

Improvement of Cycling Performance of Silicon-Graphite Composite Anode Using Blended Electrolyte Additives

Silicon-graphite composite anode materials are potential alternatives to graphite anode material for high-energy density Li-ion batteries, as the theoretical specific capacity of silicon is ten-fold larger than that of commercialized graphite.1,2 However, the major drawback of silicon-based anode material is a short cycle life caused by large volume change, low electrical conductivity and mechanical disintegration of particles. To overcome those issues, a variety of methods for improving cycle performance of silicon-based anodes have been researched, such as the use of composite with larger fraction of graphite,3,4 modification of surface property of silicon,4 and the use of new binder, nanostructured silicon, and functional electrolyte additives.3 Recently, the batteries with composite material containing very low fraction of silicon are being commercialized, which can accommodate the large volume change of silicon and obtain reasonable electrical conductivity. Another promising approach is the control of electrode-electrolyte interfacial reaction for the formation of a stable solid electrolyte interphase (SEI) utilizing functional electrolyte additives, which has to be based on a basic understanding of interfacial phenomena. In this presentation, we report the improved cycle performance and the interfacial phenomena of silicon-graphite composite anodes under the condition of various blended additives. Acknowledgements This research was supported by the Korean Ministry of Trade, Industry & Energy (10049609), National Research Foundation (2012026203), and Nano-Material Technology Development Program by the Ministry of Science, ICT and Future Planning (2009-0082580).

Understanding Interfacial Chemistry and Stability for Performance Enhancement of 4.55V Li-Ion Battery of LiNi0.5Co0.2Mn0.3O2//Silicon-Graphite Using FEC-Based Electrolyte

With increasing demand for electric and hybrid electric vehicles and energy storage systems, Li-ion batteries as their power sources are being required to store more than doubled energy density than currently used ones. Enabling the high-energy density Li-ion battery relies on high-voltage cathodes (e.g., multi-components layered oxides), high-capacity anodes (e.g., silicon (Si)-based materials) and advanced electrolyte.1 However, challenges of structural instability of cathode material, disastrous volume change and particle cracking and the instability of solid electrolyte interphase (SEI) layer of silicon anode material, and anodic instability of electrolyte at high voltage region remain. Surface coating and/or voltage control has been applied to high-voltage layered oxide cathode and silicon-based anode materials, respectively, to achieve their high-performance. Interfacial chemistry control using appropriate electrolyte composition and SEI stabilization for both cathode and anode are simpler, high impact and promising approaches for performance enhancement of a full-cell. We demonstrated that blended additives of methyl (2,2,2-trifluoroethyl)carbonate (FEMC) 2 and vinylene carbonate (VC) are effective in achieving the high-energy performance of LiNi0.5Co0.2Mn0.3O2 (NCM523)//silicon-graphite full-cells in fluoroethylene carbonate (FEC)-based electrolyte.3 Here we report the correlation of surface/SEI composition and stability to cycling performance of full-cell. The roles of solvent and additives in forming and stabilizing the surface film/SEI at cathode and anode are systematically studied using ex situ surface analysis techniques. The reasons for performance enhancement or fade are proposed in the aspects of interfacial chemistry and stability between cathode/anode and electrolyte, and interaction(s) between cathode and anode. Lithium 2016 coin full-cells, consisting of NCM523 cathode and silicon-graphite (30:70 wt%) anode, separator, were assembled in an argon-filled glove-box. The electrolyte was 1M LiPF6/FEC:DEC (50:50, vol%) with and without FEMC and VC additives. After 100 cycles between 3.0 and 4.55V at C/3 at room temperature, the SEI layer of both cathode and anode electrode were studied using ex situ Raman, FTIR and X-ray photoelectron spectroscopy. Figure 1 compares the cycling performance of NCM523//silicon-graphite full-cells in different electrolyte composition. With blended additives of FEMC and VC in FEC-based electrolyte, the full-cell shows a remarkable performance enhancement from EC-based one; the first discharge capacity is 168 mAh/g and initial coulombic efficiency of 86%, and capacity retention after 100 cycles is 71%. In contrast, the full-cell without additives exhibits inferior performance. Surface analyses of cathode and anode reveal that the use of blended additives induces to form a stable surface protective film/SEI at both cathode and anode, significantly reduces metal-dissolution phenomena and finally inhibits structural degradation. Further discussion would be presented in the meeting. Acknowledgements This research was supported by the Korean Ministry of Trade, Industry & Energy (A0022-00725 & 10049609), National Research Foundation (2012026203), Chungnam National University, and Nano-Material Technology Development Program by the Ministry of Science, ICT and Future Planning (2009-0082580).

Iron Containing Li-Rich Materials As high Energy Cathodes for Li-Ion Batteries

Introduction As portable energy storage systems, Lithium-ion batteries are particularly attractive due to their high energy densities. Developing as well as improving appropriate cathode materials are important as the energy density of the commercial Li-ion batteries are limited mainly by the positive electrode materials. Several cathode material classes such as spinels (LiM xMn2-xO4, M = Mn, Ni, Co etc.)[1– 4], layered oxides (LiMO2, M = V, Cr, Co, Ni, Ni/Co/Mn, Al/Co/Mn etc.)[5], Li-rich layered oxides [xLi2MnO3 ∙(1-x)LiMO2, M = Mn, Co, Ni, Fe][5] and olivines (LiMPO4, M = Fe, Mn, Co, Ni etc.)[3] have been widely investigated in the recent years. Out of these materials, the layered Li-rich materials are particularly attractive for high energy Li-ion batteries as they offer high capacities (~200 mAh/g) in a voltage range 2.0-4.8 V. Up to now, layered Li-rich materials containing Co are broadly used as positive electrode materials in several commercial Li-ion batteries. Many literature reports show that these materials can exhibit a stable cycling stability and in addition, for some special compositions of the transition metals, a high rate capability[6] [7]. Nevertheless, Co is expensive and not environmentally friendly. Hence, keeping the advantages of Li-rich materials, together with reducing or eliminating Co from these Li-rich layered materials can be a big step to develop potential cathode materials for Li-ion batteries which are cost effective and environmentally friendly. The Li-rich materials containing Fe are particularly attractive as cathode materials for Li-ion batteries as they are more “green” and cost effective[8]. In 2002, Fe substituted Li2MnO3 was 1st synthesized as 4 V cathode materials. The material delivered only a very low specific capacity (~70 mAh/g) and a very severe capacity fading[8]. Later, it was found that the capacity retention of the above material can be improved by Ni or Al substitution. However, the reports on the long term cycling stability are scarce and those on high rate cycling stability (> 5C) and electrochemical mechanism are missing. Results and Discussion In the present work, Fe and Ni containing Li-rich materials with a general formula, xLi2MnO3. (1-x)LiNi0.4Mn0.4Fe0.2O2, were synthesized through a modified citric-acid assisted sol-gel process reported elsewhere[1 ]. The precursors obtained were subjected to final calcination temperatures of 800 °C, 850 °C, 900 °C, respectively. For a part of the material annealed at 900 °C, a quenching step with liquid N2 was applied. The annealing temperature was found to have an influence on the phase purity and morphology of the material. Rietveld refinement result based on the synchrotron diffraction experiments conducted at MSPD beamline, ALBA revealed that the amount of impurity phases increases with increase in annealing temperature. However, the quenching step was found to suppress the formation of impurity phase successfully, even after the high-temperature annealing. Moessbauer spectroscopy confirms the above observation and concludes the existence of Fe only in +3 oxidation state. After synthesis optimization, electrode optimization was done and the materials were investigated electrochemically using cyclic voltammetry and galvanostatic cycling. The details on the influence of annealing temperature on the morphology, cycling stability and rate capability will be discussed. In addition, a first insight into the electrochemical mechanism will be given. Acknowledgement: This research has benefitted from beamtime allocation at the Materials Science and Powder Diffraction Beam Line (MSPD) at ALBA (Barcelona, Spain). The kind support of the beamline scientist Dr. Francois Fauth is gratefully acknowledged.

Novel Cobalt-Rich Composite (CRC) Cathode and Siox Anodes for High-Energy Li-Ion Batteries

The increasing sophistication and functionality of mobile devices coupled with the human dependence for the devices leads to a strong demand for high performance batteries. Over the years, improvements in battery performance have taken place with minor enhancements resulting from improvement in cell design such as increasing the active material content, increasing the electrode density and reducing the weight and thickness of the inactive cell components. Further improvements by cell optimization are quickly reaching their limits creating a shift in focus to new active electrode material that are expected to result in the next leap in cell performance. In this work, Cobalt-Rich Composite (CRC) cathodes have been developed by modifying standard low voltage LiCoO2 (LCO) and stabilizing the structure by forming high Nickel and Manganese containing composites. The resulting CRC cathode shows surprisingly stable high voltage performance compared to LCO as shown in Figure 1. Traditionally the structure of LCO cathode falls apart at high charge voltages (>4.35V) when >0.5 moles of Li are extracted from the structure. The CRC cathode enables high electrode active content (>97%) and density (>4.0g/cc), high average voltage and high specific capacity required for high-energy cells. To complement the CRC cathode, a high capacity SiOx-based anode electrode has been developed. Current lithium ion cells continue to use graphite as the anode of choice. Si-based anodes have been widely studied as a possible replacement to graphite due to their high specific capacity (~4000mAh/g). Unfortunately Si-based materials suffer from large volume expansion resulting in pulverization and poor cycle life. However, by precise engineering the anode electrode formulation, binder and active material, high capacity SiOx-based anode electrodes with high percent active content (>80%) have been developed and shown to cycle well. Figure 2 shows 1Ah pouch cell data from cells integrating CRC cathode and SiOx anode, showing high specific energy of 285Wh/Kg and cycle life of ~450 cycles before reaching 80% capacity retention at C/5 rate. Swelling and abuse testing of the cells meet consumer electronics specifications and results will be presented. Figure 3 shows that by engineering the cell design and increasing the cell footprint, 10Ah capacity pouch cells integrating CRC cathode and SiOx anode with specific energy of ~350Wh/Kg have been made enabling automotive and drone applications. This presentation will also cover remaining challenges associated with CRC cathode and SiOx anode with respect to synthesis, performance and cell manufacturing to bring these materials and cell technology from prototypes to large-scale manufacturing. Figure 1

Bacteria-Assisted Synthesis of Electrode Materials for Li or Na Batteries

The production of materials for high-energy Li-ion batteries is generally associated with negative environmental footprints, due to high temperatures required and chemical toxicity of their components [1]. Our goal is to explore new bio-assisted low-temperature routes of synthesis in order to reduce this environmental impact and possibly improve their electrochemical performances. Bacteria are easy to grow; able to mineralize transition metals and other elements [2], with controlled morphology, crystal structure and texture; they also constitute a potential source of conductive carbon. For these reasons, bacteria assisted synthesis caught our attention, especially as exceptional power performances were already shown for biomineralized hollow shells of hematite (α-Fe2O3) [3] when compared to those of non-textured material. Hydrated amorphous ferric phosphate (a-FeIIIPO4·~3H2O) was precipitated from aqueous solution at 30°C under air at the contact of bacteria (Sporosarcina pasteurii). The resulting materials were investigated using various techniques (e.g. thermal analysis, mass spectrometry, infrared spectroscopy, electron microscopy) and consist of dead bacteria (2-3 µm x 0.5 µm) coated by a 70 nm thick layer of interconnected a-FeIIIPO4·~3H2O particles (40-80 nm), as presented by the following microscopy image. Surface chemistry of the bacterial cell wall plays a key role in the nucleation process thereby controlling particle size. After a mild temperature treatment, a 90 mAh/g capacity has been achieved versus Li (at 3.0 Volts mean voltage) with an excellent cyclability, constant coulombic efficiency (~100%) and interesting power performances. This approach allows overcoming the intrinsic poor conductivity of Fe phosphate without any use of harsh mixing treatments with conductive additive, or complex synthetic procedure. Bacteria are capable of many things and we are now applying this strategy for other materials and other metals like manganese. We will also address the positive attributes of these bio-assisted synthesis for application in Na-based batteries. [1] Samaras C., Meisterling K., Environmental Science & Technology. 42, 3170 (2008). [2] Dupraz S. et al., Chemical Geology. 265, 54 (2009). [3] Miot J. et al., Energy & Environmental Science. 7, 451 (2014). Figure 1

Revealing the Intrinsic Li Mobility in the Li2MnO3 Lithium-Excess Material

One of the most promising avenues for future high energy Li-ion batteries originate from the family of Li-rich layered cathodes. However, while exhibiting excellent initial capacity, these materials also suffer from voltage fade, high impedance, and poor rate capability, particularly in the Mn-rich, high Li excess concentration regime. Though it is clear that the Li2MnO3 component contributes to the high capacity as well as the chemical and structural degradation of the material, the inherent ionic conductivity of the material has not been clarified. In this work, we investigate the delithiation mechanism, involving coherent Li migration from two layers by first-principles density functional theory. Surprisingly, and contrary to expectations from available experimental results, we find that the pristine material exhibits excellent Li mobility enabling facile Li extraction from both the transition metal layer and Li-layer. Generally, the Li-extractions are highly accelerated by di- and trivacancy clusters,...

Microsphere LiFe0.5Mn0.5PO4/C composite as high rate and long-life cathode material for lithium-ion battery

LiFe0.5Mn0.5PO4/C composite material (denoted as SP-LFMP/C) with macro/nano hierarchical porous structure by adding the composite carbon source (i.e., 100 nm polystyrene sphere and 300 nm carbon sphere) is fabricated via a spray dry process. The SP-LFMP/C composite exhibits a 3D hierarchical structure with a high surface area (34.63 m2 g−1) and a wide pore size distribution (2–100 nm). The characteristic properties of the samples are examined using X-ray diffraction, micro-Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. The SP-LFMP/C composite achieves discharge capacities of 161, 160, 157, 146, 137, and 115 mAh g−1 at 0.2, 0.5, 1, 3, 5, and 10 C, respectively. Moreover, the SP-LFMP/C material also exhibits excellent cycling performance and stability at 55 °C during the 300 cycle test. These results indicate that the SP-LFMP/C cathode material is an excellent candidate for application in high-energy Li-ion batteries.

A Deep Reduction and Partial Oxidation Strategy for Fabrication of Mesoporous Si Anode for Lithium Ion Batteries.

A deep reduction and partial oxidation strategy to convert low-cost SiO2 into mesoporous Si anode with the yield higher than 90% is provided. This strategy has advantage in efficient mesoporous silicon production and in situ formation of several nanometers SiO2 layer on the surface of silicon particles. Thus, the resulted silicon anode provides extremely high reversible capacity of 1772 mAh g(-1), superior cycling stability with more than 873 mAh g(-1) at 1.8 A g(-1) after 1400 cycles (corresponding to the capacity decay rate of 0.035% per cycle), and good rate capability (∼710 mAh g(-1) at 18A g(-1)). These promising results suggest that such strategy for mesoporous Si anode can be potentially commercialized for high energy Li-ion batteries.

Discovery of a surface protective layer: A new insight into countering capacity and voltage degradation for high-energy lithium-ion batteries

Capacity and voltage degradation is a crucial factor that restricts the commercialization of Li-rich layered cathode materials. Recently, it has been demonstrated that the degradation results from the structural evolution from layered to spinel-like phase, caused by the migration of transition metal (TM) ions. However, the direction and order of TM ions migration is hard to identify. In this study, a surface protective layer (SPL) is discovered for the first time at the outer edge of Li1.14Mn0.48Ni0.19Co0.19O2 nanoplate by the research on the surface condition of nanoplates after charge–discharge cycles. More importantly, by the detailed analysis for the SPL, we further reveal that the formation of SPL is active facet dependent, TM ions migrate toward the active facets, and Ni and Co ions hop more preferentially than Mn ions during the cycling. These discoveries can help to understand the fading mechanism of Li-rich layered cathode materials. In addition, electrochemical test indicates that the SPL greatly delays the corrosion of active surfaces in electrolyte and improves the cycling stability of Li-rich layered cathode materials. This insight provides a new thought for preparing long-life cathodes of high energy Li-ion batteries.

X-ray Photoemission Spectroscopy Study of Cationic and Anionic Redox Processes in High-Capacity Li-Ion Battery Layered-Oxide Electrodes

Electrode materials based on Li-rich layered oxides are of growing interest for high-energy Li-ion battery applications because of their staggering capacities associated with the emergence of a novel, reversible anionic process. However, the fundamental science at work behind this new process needs to be well understood for further optimization. Here we report on the redox mechanisms in high-capacity Li-rich materials Li2Ru1–xMxO3 and Li2Ir1–xMxO3, by combining X-ray photoemission spectroscopy (XPS) core peaks and valence intensity analyses. We fully confirm that these materials electrochemically react with Li via cumulative reversible cationic/anionic redox processes, but more importantly we reveal that, depending on the nature of the metal (Ru or Ir), there is a delicate balance between metal and oxygen contributions. For instance, we show a greater implication of oxide ions for Ir-based electrodes, consistent with the higher covalent character of Ir–O bonds compared to Ru–O bonds. We equally provide ev...

Micron-sized Fe–Cu–Si ternary composite anodes for high energy Li-ion batteries

To develop a practicable Si-based anode for high-energy LIBs, a FeCuSi composite was developed by properly building Si-metal alloys.

Editors' Choice—Practical Assessment of Anionic Redox in Li-Rich Layered Oxide Cathodes: A Mixed Blessing for High Energy Li-Ion Batteries

Li-rich layered oxides, e.g. Li[Li0.20Ni0.13Mn0.54Co0.13]O2 (LR-NMC), lead high energy density Li-ion battery cathodes, thanks to the reversible redox of oxygen anions that boost charge storage capacity. Unfortunately, their commercialization has been stalled by practical issues (i.e. voltage hysteresis, poor rate capability, and voltage fade) and hence it is necessary to investigate whether these problems are intrinsically inherent to anionic redox and its structural consequences. To this end, the ‘model’ Li-rich layered oxide Li2Ru0.75Sn0.25O3 (LRSO) is here used as a fertile test-bed for scrutinizing the effects of cationic and anionic redox independently since they are neatly isolated at low and high potentials, respectively. Through an arsenal of electrochemical techniques, we demonstrate that voltage hysteresis is triggered by anionic redox and grows progressively with deeper oxidation of oxygen in conjunction with the deterioration of both interfacial charge-transfer kinetics and bulk diffusion coefficient. We equally show that this anionic-driven poor kinetics keeps deteriorating further with cycling and we also find that voltage fades faster if oxygen is kept oxidized for longer. Our findings, which are in fact harsher for LR-NMC, convey caution that anionic redox risks practical problems; hence, when chasing larger capacities with this class of materials, we encourage considering real-world applications.

LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> ナノ粒子造粒体の機械的合成とその形成機構

LiNi0.5Mn1.5O4 is one of the promising cathode materials for high-energy Li-ion batteries. The development of a low-cost and environmental-friendly synthetic method of the LiNi0.5Mn1.5O4 powder is an important topic for large scale production. In this paper, we have prepared LiNi0.5Mn1.5O4 granules consisting of nanoparticles by a simple mechanical method using an attrition-type mill. The formation mechanism of LiNi0.5Mn1.5O4 granules was investigated from the powder properties of products prepared during the mechanical treatment of starting materials. The initial step of this formation reaction is a pulverization of starting materials. With increasing treatment time, the nano-sized LiNi0.5Mn1.5O4 particles are formed and then these particles are granulated with the size of few micrometers. The charge and discharge properties of cathodes made from the prepared LiNi0.5Mn1.5O4 granules were also tested. The present work may lead to the development of a scalable synthetic method of high-purity powders by the simple mechanical process at room temperature.

Understanding interfacial chemistry and stability for performance improvement and fade of high-energy Li-ion battery of LiNi0.5Co0.2Mn0.3O2//silicon-graphite

Understanding the chemical processes that occur at the electrode/electrolyte interface in a battery is crucial, as the interactions between anode/cathode and electrolyte and between cathode and anode of a full-cell determine the final battery performance. We have investigated the correlation among cycling performance, interfacial reaction behavior and the solid electrolyte interphase (SEI) stability of a LiNi0.5Co0.2Mn0.3O2//Si-graphite full-cell under an aggressive test condition between 3.0 and 4.55 V using fluoroethylene carbonate (FEC)-based electrolyte, and blended additives of methyl (2,2,2-trifluoroethyl)carbonate (FEMC) and vinylene carbonate (VC). Through the formation of a stable SEI at both high-voltage cathode and anode, metal dissolution from the cathode is inhibited and full-cell achieves enhanced cycling performance. Interfacially stabilized full-cell delivers a high energy of 622 Wh per kg of active material and improved capacity retention, whereas the cell in conventional electrolyte shows a rapid performance fade.

Scanning transmission electron microscopy analysis of Ge(O)/(graphitic carbon nitride) nanocomposite powder

Analytical electron microscopy has revealed the structure of particles that were synthesized by chemical reaction of GeO2 with NaBH4 in the basic solution including graphitic carbon nitride (g-C3N4) powders. The g-C3N4 was arranged by recrystallization of melamine at 600°C under N2 gas atmosphere. The samples were dried at 60°C or 180°C for 4h. The g-C3N4 was observed as lamellae of several ten nm or less in size and had an amorphous-like structure with a distorted lattice in an area as small as a few hundred pm in size. The reaction product was Ge(O) particles as fine as several nm in size and composed of Ge and O atoms. Most of the particles must be of GeO2−x with the amorphous-like structure that has also a distorted lattice in an area of a few hundred pm in size. In the sample dried at 60°C, the particles were found to be dispersed in a wide area on the g-C3N4 lamella. It is hard to recognize those particles in TEM images. The particles in the sample dried at 180°C became larger and were easily observed as isolated lumps. Hence, these powders can be regarded as GeO2/g-C3N4 or Ge/GeO2/g-C3N4 nanocomposites, and expected to be applicable to anode materials for high energy Li-ion batteries due to Ge catalysis effect, accordingly.

Dimensionally Stable and Fast-Charging Graphite-Silicon Planar Composite Anode for Li-Ion Batteries

Advanced Li-ion batteries (LIBs) have been developed to have high capacity density, long cycle life, and high-rate performance for portable electronics, electric vehicles (EVs), and renewable energy storage. Graphite is currently the predominant anode material for commercial LIBs because it has a low cost, low charge/discharge plateau potential, satisfactory specific capacity (372 mAh/g), and substantially high dimensional stability; its essential role in high-energy LIBs is expected to continue. Si is a potential Li-insertion anode material that has a substantially higher capacity than graphite but is susceptible to large (>300% when fully lithiated) volume expansion. The cyclic dimensional variations during charge/discharge cycles result in pulverization and electrical disconnection from the conductive paths of the Si active materials, leading to rapid capacity reduction during the cycles. In spite of a large amount of literature devoted to solving this issue in the past years, long-lasting Si anode up to now remains as a formidable challenge. On the other hand, composite anodes comprising graphite and limited amount of Si or Si oxide may be attractive transient products for advanced high-energy LIBs before viable Si-dominant anodes are realized. Moreover, improvement in the rate capability of Si-based anodes is needed for meeting the power requirements of various applications. In this presentation, a planar graphite-silicon composite Li-ion battery anode showing substantially higher capacities than graphite, fast-charging capability, and exceptional cycle stability will be described. The Si oxide-coated graphite flake (SGF) composite anode for Li-ion batteries (LIBs) synthesized by a unique microwave-heating process of graphite flakes (GFs) in a solution made of liquid polysiloxanes as the Si-containing precursor. Microwave-heating of the GFs induces the deposition of a conformal Si-containing conformal layer on the GF surfaces, which subsequently turns into oxide-graphite-oxide sandwiched planar composite structure. The resulting SGF exhibits a reversible specific capacity of nearly 480 mAh/g, 97% capacity retention at the current density of 2.5 A/g (~5C-rate), and 95% capacity retention after 400 cycles with an average Coulombic efficiency > 99.9%. The data suggest new strategies for both designing and synthesizing high-performance anode materials for LIB applications. Figure 1

Improved Electrochemical Performance of Multi-Phase Layered-Spinel Cathodes for Li-Ion Batteries

Li-ion batteries are implemented as the major power source for portable electronic devices because of their high energy density and long cycle-life. High capacity cathode materials are essential to increase the energy density of Li-ion batteries within the stability of standard electrolyte solutions. Layered LiNi1/3Mn1/3Co1/3O2 and high voltage spinel LiNi0.5Mn1.5O4 are promising cathode materials as these can provide specific capacities of 160 and 130 mAh g-1, respectively. It is known that LiNi1/3Mn1/3Co1/3O2 exhibits good cycling stability when cycled in the potential range of 2.5-4.3 V vs. Li/Li+ [1-3] and undergoes severe capacity fading upon cycling to potentials ≥ 4.5 V [4, 5]. Similarly, spinel LiNi0.5Mn1.5O4 is usually cycled in the potential range of 3.5-4.9 V [6, 7]. When cycled to potential lower than 3.5 V in order to increase the specific capacity, it also undergoes capacity fading upon cycling, due to structural instability arising from a well-known Jahn-Teller effect [8, 9]. Recently, Li and Mn-rich layered compounds with a general composition xLi2MnO3.(1-x)LiMO2 (M=Mn, Co and Ni) are considered as attractive cathode materials for high energy Li-ion batteries as these materials can provide capacities ≥ 250 mAh g-1. Li-rich layered-spinel composites are also explored as high capacity cathodes which can exhibit capacities ≥ 200 mAh g-1 within a wide potential range of 2.0-5.0 V [10-12]. Thus, multiphase cathodes may be found advantageous as compared to single phase, i.e., either layered or spinel cathode materials. In the present study, we have synthesized layered-spinel composite cathode materials LiNi1/3Mn2/3O2 and LiNi0.33Mn0.54Co0.13O2 involving Li2MnO3 (monoclinic), LiNiO2 (rhombohedral) and LiNi0.5Mn1.5O4 (spinel) by self-combustion reaction (SCR). The Reitveld analysis and TEM study clearly indicates the presence of these phases. Interestingly, these cathode materials exhibited superior cycling stability when cycled in a wide potential range of 2.3-4.9 V vs. Li (Fig. 1). LiNi1/3Mn2/3O2 exhibited an initial specific capacity of 80 mAh g-1 which increased to about 220 mAh g-1 after 20 cycles and then a stable capacity is observed even after 100 cycles. On the other hand, the specific capacity decreases from 190 to 150 mAh g-1 with 79 % capacity retention for the spinel LiNi0.5Mn1.5O4. Also, LiNi0.33Mn0.54Co0.13O2 exhibited a stable specific capacity of about 170 mAh g-1 after 100 cycles when cycled in the potential range of 2.3-4.9 V. On the other hand, the specific capacity of LiNi0.33Mn0.33Co0.33O2 decreased from 208 mAh g-1 to a value of 130 mAh g-1 after only 50 cycles. The structural studies of cycled electrodes indicate that the spinel content in the active mass increases upon cycling due to structural layered-to-spinel transformation. However, the presence of untransformed Li2MnO3 in the active mass stabilizes the structure even after cycling in a wide potential range. These results indicate that neither layered nor spinel can be cycled in a too wide potential range while multiphase layered-spinel cathode materials can be cycled in a wide potential range with a stable high specific capacity in Li-ion batteries. Thus, the order of stability of these cathode materials can be presented as layered-spinel> spinel > layered. References T. Ohzuku, Y. Makimura, Chem. Lett., 7, 642 (2001).H. Sclar, D. Kovacheva, E. Zhecheva, R. Stoyanova, R. Lavi, G. Kimmel, J. Grinblat, O. Girshevitz, F. Amalraj, O. Haik, E. Zinigrad, B. markovsky, D. Aurbach, J. Electrochem. Soc., 156, A938 (2009).S.K. Martha, H. Sclar, Z.S. Framowitz, D. Kovacheva, N. Saliyski, Y. Gofer, P. Sharon, E. Golik, B. Markovsky, D. Aurbach, J. Power Sources, 189, 248 (2009).X. Li, Y.J. Wei, H. Ehrenberg, F. Du, C.Z. Wang, G. Chen, Solid State Ionics, 178, 1969 (2008).P.K. Nayak, J. Grinblat, M. Levi, Y. Wu, B. Powell, D. Aurbach, J. Electroanal. Chem., 733, 6 (2014).Y. Xue, Z. Wang, F. Yu, Y. Zhang, G. Yin, J. Mater. Chem. A, 2, 4185 (2014).Y. Talyosef, B. Markovsky, G. Salitra, D. Aurbach, H.-J. Kim, S. Choi, J. Power Sources, 146, 664 (2005).M. Okubo, Y. Mizuno, H. Yamada, J. Kim, E. Hosono, H. Zhou, T. Kudo, I. Honma, ACS Nano, 4, 741 (2010).C.Y. Ouyang, S.Q. Shi, M.S. Lei, J. Alloys Compd., 474, 370 (2009).E.-S. Lee, A. Hug, H.-U. Chang, A. Manthiram, Chem. Mater., 24, 600 (2012). S.-H. Park, S.-H. Kang, C.S. Johnson, K. Amine, M.M. Thackeray, Electrochem. Commun., 9, 262 (2007).D. Luo, G. Li, C. Fu, J. Zheng, J. Fan, Q. Li, L. Li, Adv. Energy Mater., 4, 1400062 (2014). Figure 1

Use of Swcnts to Increase the Energy Density of Li-Ion Batteries

New advances in synthesis of single wall carbon nanotubes (SWCNTs) allowed for the first time to produce multi-ton quantities of this unique material while significantly reducing its cost, opening up many commercial applications in energy storage. One of the applications is the use of SWCNTs as a conductive additive for high energy Li-ion batteries. It was found, that electrical properties of SWCNTs allow to reduce the amount of it in cathode and anode formulations to below 0.1% versus typical 2-5% of carbon black, maximizing the percentage of active materials and increasing the energy density of the Li-ion cells. Investigation of the electrode formulations revealed uniform distribution of SWCNT throughout the electrode structures, reinforcement of the electrode structure resulting in improved mechanical properties and electrochemical performance with both cathode and anode materials. In this presentation we will discuss the properties of commercially made SWCNTs and their comparison to MWCNTs and typical conductive carbons. Technical challenges facing application of SWCNTs in batteries include preparation of stable dispersions and formulation of electrodes with good electrical and mechanical properties. The results on various polymer dispersants will be presented along with ways of accommodating low concentration dispersions into the material mixing process and battery manufacturing. Test data was generated with LCO, LFP and NCM cathode materials and Si anode material will be discussed in detail with short term rate capability and long term cycle life and storage results.