High Energy Density Rechargeable Lithium Research Articles

Chemical Crossover Accelerates Degradation of Lithium Electrode in High Energy Density Rechargeable Lithium–Oxygen Batteries

AbstractLithium‐oxygen batteries (LOBs) are promising next‐generation rechargeable battery candidates due to theoretical energy densities that exceed those of conventional lithium‐ion batteries. Although LOB with high cell level energy density has been demonstrated under lean electrolyte and high areal capacity conditions, their cycle life is still poor, and the cell degradation mechanism remains unclear. In the present study, by use of a three‐electrode electrochemical setup and in situ MS analytical techniques, it is revealed that the reaction efficiency of the negative lithium electrode largely decreases due to chemical crossover from the positive oxygen electrode side, such as H2O and CO2. Based on this mechanistic understanding, a LOB with an ultra‐lightweight flexible ceramic‐based solid‐state separator with 6 µm thickness that effectively protects the lithium electrode against chemical crossover without diminishing the energy density of LOBs is fabricated. Notably, a 400 Wh kg−1class LOB exhibits a stable discharge/charged process for >20 cycles. The strategy demonstrated in this study sheds light on the direction for the practical implementation of LOBs with high energy densities and long cycle lives.

(Invited) A Micelle Electrolyte Enabled By Fluorinated Ether Additives for Polysulfide Suppression, High Voltage Cathode, and Li Metal Anode Stabilization

The Li-S battery is a promising next-generation technology due to its high theoretical energy density (2600 Wh/kg) and low active material cost. However, poor cycling stability and coulombic efficiency caused by polysulfide dissolution have proven to be major obstacles for a practical Li-S battery implementation. In this work, we develop a novel strategy to suppress polysulfide dissolution using hydrofluoroethers (HFEs) with bi-functional, amphiphlic surfactant-like design: a polar lithiophilic “head” attached to a fluorinated lithiophobic “tail.” A unique solvation mechanism is proposed for these solvents whereby dissociated lithium ions are readily coordinated with lithiophilic “head” to induce self-assembly into micelle-like complex structures. Complex formation is verified experimentally by changing the additive structure and concentration using small angle X-ray and neutron scattering. These HFE-based electrolytes are found to prevent polysulfide dissolution and to have excellent chemical compatibility with lithium metal: Li||Cu stripping/plating tests reveal high coulombic efficiency (>99.5%), modest polarization, and smooth surface morphology of the uniformly deposited lithium. Li-S cells are demonstrated with 1395 mAh/g initial capacity and 71.9% retention over 100 cycles at >99.5% efficiency—evidence that the micelle structure of the amphiphilic additives in HFEs can prohibit polysulfide dissolution while enabling facile Li+ transport and anode passivation. In addition, this type of electrolytes is also stable toward high voltage cathode to enable a lithium metal anode and high voltage cathode high-energy density rechargeable lithium battery.

(Invited) Insight into Interfacial Processes between Lithium-Rich Layered Oxide Cathode and High-Voltage Electrolyte

Lithium-rich layered oxide, xLi2MnO3·(1-x)LiMO2 (M = Mn/Ni/Co), is a promising high-capacity cathode active material for high-energy density rechargeable lithium batteries. While the capacity of lithium-rich layered oxide cathode can increase by increasing the charge cut-off voltage toward 5 V, it t relies on the anodic stability of electrolyte and the interface stability of charged cathode. We have been developing and suggesting fluorinated carbonates as effective high-voltage additives and solvents of new designed electrolytes, which provide a significant improvement in the stability of cathode-electrolyte interface, solid electrolyte interphase (SEI) layer and cycling performance, and longer life span of various high-capacity cathodes, with respect to commercial electrolyte system. Herein, we present our recent progress on the exploration of the limit of anodic stability of fluorinated carbonate-assisted electrolyte toward 5 V level and the capacity of a Li-rich cathode based full-cell, and the enhancement of battery safety. The mechanistic studies utilizing systematic spectroscopic analyses on the correlation among interfacial processes, the SEI formation and stabilization, and performance improvement would be discussed in the meeting. Acknowledgements This research was supported by the Ministry of Trade, Industry and Energy (A0022-00725) and the National Research Foundation grant (2019R1A2C1084024) funded by the Ministry of Science and ICT of Korea.

Sulfone-based high-voltage electrolytes for high energy density rechargeable lithium batteries: Progress and perspective

Further enhancement in the energy density of rechargeable lithium batteries calls for high-voltage cathode materials and stable anodes, as well as matched high-voltage electrolytes without compromising the overall property of batteries. Sulfone-based electrolytes have aroused great interest in recent years owing to their wide electrochemical window and high safety. However, significant challenges such as the complexity of synthesis, high melting point (typically above room temperature), high viscosity, and their poor compatibility with graphite-based anodes have drastically impeded their practical applications. In this review, recent progress of sulfone solvents in high energy density rechargeable lithium batteries is summarized theoretically and experimentally. More importantly, general improvement methods of sulfone-based electrolytes, such as adding additives and cosolvents, structural modifications of sulfone, superconcentrated salt strategy are briefly discussed. We expect that this review provides inspiration for the future developments of sulfone-based high-voltage electrolytes (SHVEs) and their widespread applications in high specific energy lithium batteries.

Selenium Nanocomposite Cathode with Long Cycle Life for Rechargeable Lithium‐Selenium Batteries

AbstractSelenium (Se) is a potential cathode material for high energy density rechargeable lithium batteries. In this study, a binder‐free Se‐carbon nanotube (CNT) composite electrode has been prepared by a facile chemical method. At initial state, Se is present in the form of branched nanowires with a diameter of <150 nm and a length of 1–2 μm, interwoven with CNTs. After discharge and re‐charge, the Se nanowires are converted to nanoparticles embedded in the CNT network. This synthesis method provides a path for fabricating the Se cathodes with controllable mass loading and thickness. By studying the composite electrodes with different Se loading and thickness, we found that the electrode thickness has a critical impact on the distribution of Se during repeated cycling. Promising cycling performance was achieved in thin electrodes with high Se loading. The composite electrode with 23 μm thickness and 60 % Se loading shows a high initial capacity of 537 mAh g−1 and stable cycling performance with a capacity of 401 mAh g−1 after 500 cycles at 1 C rate. This study reports a synthesis strategy to obtain Se/CNT composite cathode with long cycle life for rechargeable Li−Se batteries.

Flowable polymer electrolytes for lithium metal batteries

Solid polymer electrolytes (SPEs) are currently attracting extensive interest as Li-ion conducting materials for building safe and high energy density rechargeable lithium metal batteries due to their low flammability and ease in process. The structural design of polymer matrices could effectively regulate the physicochemical and electrochemical properties of SPEs, thereby enhancing the performance of rechargeable all solid-state lithium metal batteries (ASSLMBs). Herein, we report a new type of flowable polymer electrolyte (FPE), containing a liquid-like polymer with highly conductive polyether side chains and sulfonimide lithium salts [i.e., lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI)]. The high amorphicity and segmental mobility of the liquid-like polymer matrices facilitate fast ionic transport, thus leading to the highest ionic conductivity reported (6.6 × 10−4 S cm−1 at 70 °C and 1.4 × 10−4 S cm−1 at 30 °C). The introduction of FPE as a buffer layer between Li metal (Li°) electrode and poly(ethylene oxide)-based SPE decreases the interfacial resistivity of Li°/electrolyte and improves remarkably cyclability and coulombic efficiency of the Li° || LiFePO4 cell. These results suggest that the FPEs are promising candidates for lithium metal protection in ASSLMBs.

Novel synergistic coupling composite chelating copolymer/LAGP solid electrolyte with optimized interface for dendrite-free solid Li-metal battery

Solid electrolyte is one of the promising electrolytes to realize safe and high energy density rechargeable lithium metal battery. However, in view of the characteristics and defects of the solid inorganic and polymer electrolytes, the high-performance solid electrolyte is still a challenge for effective application in batteries. Herein, we report a novel inorganic-polymer flexible composite electrolyte prepared through synthetic of chelating copolymers. With synergistic coupling, the active filler-Li1.5Al0.5Ge1.5(PO4)3 can be uniformly distributed and maintains good composite with the polymer matrix. Thereby, this composite structure promotes the electrolyte with increased electrochemical stability and enhanced thermal stability. In our case, the larger volume fraction of continuous interface between the filler and gel polymer layer is helpful to increase ionic conductivity and Li+ ion transference number of composite electrolyte. Specifically, a large amount of fillers as a rigid part can block dendrites and provide effective pathways for lithium ion transfer, meanwhile, the uniform distribution of gel polymer layer on the surface of inorganic particles facilitates a soft contact to reduce the interface impedance and a substantial flexibility to adapt the volume change in electrode. For further illustration, the solid-state lithium battery of LiFePO4/Li using this composite electrolyte shows relatively satisfactory performance, indicating the considerable cycling performance and acceptable rate capability. Thus, owing to its easy processing and compelling characteristics, this type of electrolyte make promise to reshape the feasibility of the high safety, stable and high energy density rechargeable solid-state lithium metal batteries at room-temperature.

Novel Dendrite Resistant Composite Polymer Electrolyte (CPE) for High Energy Density Lithium Sulfur Batteries

Advances in energy storage (ES) devices have the potential to transform nearly every aspect of society, from transportation to communication to electricity delivery, national defense and domestic security. Among the various prevalent energy storage devices, the most prominent to date are related to electrochemical energy storage (EES) technologies. Several EES technologies are either in existence or have evolved over the years. Among the various systems studied, lithium battery technologies (LBs) have emerged in the forefront as a panacea to the high energy and high power problems facing portable electronics, electric powered vehicle, military applications as well as stand-alone stationary power systems integrated into the electric grid. Despite advances in the anode arena, lithium metal anodes due to the inherent dendrite formation limitations have never attained commercial status. Overcoming these barriers would be a major breakthrough in the search for high energy density anode systems due to its extremely high theoretical specific capacity (~3860 mAh/g) and the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode). Similarly, pursuit of high energy density rechargeable lithium metal battery (LMB) cathodes have led to sulfur (for a Li-S battery), air electrode (for a Li-air battery) or intercalation compounds (e.g. NbSe3, V2O5) to realize high voltage LMBs exhibiting high energy densities. Li-S batteries, owing to their high theoretical energy density (2600 Wh kg-1)1, is considered as one of the most promising Li metal-based batteries. However, the liquid organic electrolytes, S cathodes and Li metal in current LMBs could not be commercialized globally for high energy applications due to low cycle life and safety issues. The low cycle life, low coulombic efficiency (CE) and safety issue of rechargeable LMBs mainly arises due to the uncontrolled cellular and dendritic growth of Li metal during repeated lithium plating/stripping and formation of unstable solid electrolyte interphase (SEI) and the continuous growth of thick SEI during repeated cycling at the solid liquid interface of organic electrolyte based LMBs. In addition, the large volume expansion (~80%)3 of sulfur accompanying the electrochemical cycling, the low utilization of sulfur resulting from poor room-temperature electronic conductivity of sulfur (~10-15 S/cm) 4 , combined with the shuttle effect of highly soluble polysulfide species in the organic ether-based electrolytes has limited the use of Li-S batteries. To address these challenges facing sulfur cathodes, significant efforts have been made to demonstrate advanced composite cathodes using various carbon materials5, polymers6 and metal-organic framework (MOF) materials7. In addition, solid polymer electrolytes8 and electrolytes additives have also been studied to develop a viable Li-S battery system. Thin-film solid-polymer electrolyte batteries offer the potential for improved safety because of the reduced activity of lithium with the solid electrolyte, flexibility in design as the cell can be fabricated in various sizes and shapes, and high energy density. In this work, we demonstrate the use of a composite polymer electrolyte (CPE) with modified physical and chemical properties in Li-S batteries. These CPEs exhibits superior mechanical properties, excellent room-temperature lithium ion conductivity and low electrolyte: sulfur (E:S) ratio. These CPEs, when used as electrolytes for Li-S batteries, helps prevent both polysulfide dissolution and dendrite formation, in addition to providing very high energy density (~750 Wh/kg). Structural, chemical, physical and electrochemical characterization results validating these properties of the CPEs will be presented and discussed. Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0006825 and DE-EE-0008199, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM). References V. S. Kolosnitsyn and E. V. Karaseva, Russian Journal of Electrochemistry, 2008, 44, 506-509.Y. Sun, G. Li, Y. Lai, D. Zeng and H. Cheng, Scientific Reports, 2016, 6, 22048.B. Dunn, H. Kamath and J.-M. Tarascon, Science, 2011, 334, 928-935.M. Edeling, R. W. Schmutzler and F. Hensel, Philosophical Magazine Part B, 1979, 39, 547-550.J. Jin, Z. Wen, G. Ma, Y. Lu and K. Rui, Solid State Ionics, 2014, 262, 170-173.P. J. Hanumantha, B. Gattu, O. Velikokhatnyi, M. K. Datta, S. S. Damle and P. N. Kumta, Journal of The Electrochemical Society, 2014, 161, A1173-A1180.P. M. Shanthi, P. J. Hanumantha, B. Gattu, M. Sweeney, M. K. Datta and P. N. Kumta, Electrochimica Acta, 2017, 229, 208-218.B. A. Boukamp, I. D. Raistrick, C. Ho, Y.-W. Hu and R. A. Huggins, in Superionic Conductors, eds. G. D. Mahan and W. L. Roth, Springer US, Boston, MA, 1976, DOI: 10.1007/978-1-4615-8789-7_65, pp. 417-417.E. Peled, C. Menachem, D. Bar‐Tow and A. Melman, Journal of The Electrochemical Society, 1996, 143, L4-L7.

Robust Pinhole-free Li3N Solid Electrolyte Grown from Molten Lithium.

Lithium metal is the ultimate anode choice for high energy density rechargeable lithium batteries. However, it suffers from inferior electrochemical performance and safety issues due to its high reactivity and the growth of lithium dendrites. It has long been desired to develop a materials coating on Li metal, which is pinhole-free, mechanically robust without fracture during Li metal deposition and stripping, and chemically stable against Li metal and liquid electrolytes, all while maintaining adequate ionic conductivity. However, such an ideal material coating has yet to be found. Here we report a novel synthesis method by reacting clean molten lithium foil directly with pure nitrogen gas to generate instantaneously a pinhole-free and ionically conductive α-Li3N film directly bonded onto Li metal foil. The film consists of highly textured large Li3N grains (tens of μm) with (001) crystalline planes parallel to the Li metal surface. The bonding between textured grains is strong, resulting in a mechanically robust film which does not crack even when bent to a 0.8 cm curvature radius and is found to maintain pinhole-free coverage during Li metal deposition and stripping. The measured ionic conductivity is up to 5.2 × 10–4 S cm–1, sufficient for maintaining regular current densities for controllable film thicknesses ranging from 2 to 30 μm. This Li3N coating is chemically stable, isolating the reactive metallic lithium from liquid electrolyte, prevents continuous electrolyte consumption during battery cycling, and promotes dendrite-free uniform lithium plating/stripping underneath. We demonstrated Li|Li4Ti5O12 cells with stable and flat potential profiles for 500 cycles without capacity decay or an increase in potential hysteresis.

Carbon-based silicon nanohybrid anode materials for rechargeable lithium ion batteries

Silicon has demonstrated great potential as anode materials for next-generation high-energy density rechargeable lithium ion batteries. However, its poor mechanical integrity needs to be improved to achieve the required cycling stability. Nano-structured silicon has been used to prevent the mechanical failure caused by large volume expansion of silicon. Unfortunately, pristine silicon nanostructures still suffer from quick capacity decay due to several reasons, such as formation of solid electrolyte interphase, poor electrical contact and agglomeration of nanostructures. Recently, increasing attention has been paid to exploring the possibilities of hybridization with carbonaceous nanostructures to solve these problems. In this review, the recent advances in the design of carbon-silicon nanohybrid anodes and existing challenges for the development of high-performance lithium battery anodes are briefly discussed.

High-Performance LiNi0.2Mn1.8O4 Spinel Cathode Material for Lithium Ion Batteries Obtained By Microwave-Assisted Synthesis

High energy density rechargeable lithium ion batteries are considered as more efficient energy storage devices for use from portable consumer electronics to large-scale applications. Apparently, the high voltage spinel and olivine lithium iron phosphate cathode materials are being considered as the target materials to achieve sustainable development, particularly for large-scale utility with energetic (energy and power density) and economic aspects. Obviously, the spinel materials are abruptly beginning to attract owing to its high electrochemical performance at room temperature. Unfortunately, the above material remains inferior due to its large capacity loss observed when operating at higher temperature. Obviously, the spinel, LiNi0.5Mn1.5O4 with a potential plateau of~4.7V is abruptly beginning to attract owing to its high electrochemical performance at room temperature. Unfortunately, the specific composition of above material remains inferior due to its high operation potential which cause the electrolyte oxidation, especially a large capacity loss observed when operating at higher temperature [1, 2]. Considering the above aspects, the commercial lithium manganese oxide spinel, LiMn2O4 (LMO) cathode can become preferable candidate particularly with regard to costs, environmental and efficiency perspectives. However, the LMO also suffer from the rapid capacity fading with cycling due to the manganese dissolution at an elevated temperature which limits the practical use of this material for large-scale applications. Numerous efforts have been proposed to overcome this issue. Recently, researchers demonstrated the excellent performance of octahedral LMO and attributed it to their surface facets, especially {111} which allow for thinner SEI formation than {110} facets [3, 4]. LMO chemistry can be improved by doping with very small amount of the nickel, e.g., LiNi0.2Mn1.8O4 [5]. As part our continuing investigations on the impact of microwave chemistry on the electrochemical performance of battery materials [6], we report the preparation of nickel-doped LMO (i.e., LiNi0.2Mn1.8O4) with microwave irradiation as an essential step to achieve enhanced electrochemistry. As-prepared active Mn3O4 with well-shaped octahedral {011} facets morphology was doped with lithium and very low amount of Ni to give LiNi0.2Mn1.8O4 spinel with exposed {111} facets (Fig.1a) that allowed for structural and cycle stability. In addition, the 6,7Li MAS NMR shows the two isotropic Li resonance of nearly 528.4 - 604.7 ppm and 528-596.3 ppm for LMNO and LMNO-mic results the multiple Li environments by the distribution of Mn and Ni atoms. Interestingly, the microwave irradiated spinel delivered a better cycle stability, rate capability, low impedance, and improved lithium diffusivity at different temperatures compared to the untreated one. In this presentation, we will discuss in detail our findings on the impact of microwave irradiation on the electrochemical performance of the LiNi0.2Mn1.8O4 spinel at ambient and high temperature (60oC). Fig.1: (a) SEM image of LMNO-mic with {111} facets, and (b) Cycle stability of LMNO and LMNO-mic at 60oC References 1) O. K. Park, Y. Cho, S. Lee, H. C. Yoo, H. K. Song, J. Cho, Energy Environ. Sci. 2011, 4, 1621-1633. 2) S. T. Myung, K. S. Lee, D. W. Kim, B. Scrosati, Y. K. Sun, Energy Environ. Sci. 2011, 4, 935-939. 3) K. R. Chemelewski, E. S. Lee, W. Li, A. Manthiram, Chem. Mater. 2013, 25, 2890-2897. 4) B. Hai, A. K. Shukla, H. Duncan, G. Chen, J. Mater. Chem. A, 2013, 1, 759-769 5) M.A. Kebede, N. Kunjuzwa, C.J. Jafta, M.K. Mathe, K.I. Ozoemena, Electrochim. Acta 2014, 128, 172 - 177 6) C.J. Jafta , M. K. Mathe , N. Manyala , W.D. Roos, K.I. Ozoemena, ACS Appl. Mater. Interfaces, 2013, 5, 7592−7598 Figure 1

Failure Mode of Lithium Metal Batteries with a Block Copolymer Electrolyte Analyzed by X-Ray Microtomography

Solid block polymer electrolytes are promising candidates for the development of high energy density rechargeable lithium metal based batteries. All solid-state batteries comprising lithium metal negative electrode and lithium iron phosphate (LiFePO4) composite positive electrode were assembled. A polystyrene-b-poly(ethylene oxide) (SEO) copolymer doped with a lithium salt was used as the electrolyte. After cycling the batteries, the reason for capacity fade and failure was determined by imaging the batteries using synchrotron hard X-ray microtomography. These experiments revealed partial delamination of the lithium foil and the block copolymer electrolyte layer. The void volume between the foil and electrolyte layer obtained after 40 to 90 cycles is comparable to volume change in the battery during one cycle. A simple model to account for the effect of delamination on current density in the battery is presented. Capacity fade and battery failures observed in our experiments are consistent with this model. No evidence of lithium dendrite formation was found. In contrast, cycled lithium-lithium symmetric cells with the same polymer electrolyte at the same current density failed due to dendrite formation. No evidence of delamination was found in these cells.

Nanocomposite electrode materials for high energy density rechargeable lithium batteries

The manganese and chromium oxide nanocomposite electrode materials were synthesized by redox reactions using transition metal powders in solutions. The layered Li[CrxLi(1/3 − x/3)Mn(2/3 − 2x/3)] O2 (x= 0.054, 0.0142, 0.147 and 0.311) materials having α-NaFeO2 (R-3 m) structure were prepared by solid-state reactions with LiOH and the pre-prepared manganese and chromium precursors. The amount of chromium, after removing the traces of Li2CrO4 from the prepared samples, is found to increase with temperature. The Li[CrxLi(1/3 − x/3)Mn(2/3 − 2x/3)] O2 material with x = 0.147 exhibits a high discharge capacity of 280 mAh g− 1 in the first cycle and a good reversible capacity of about 250 mAh g− 1 when cycled in the voltage range 2.0–4.9 V. Whereas, the Li[CrxLi(1/3 − x/3)Mn(2/3 − 2x/3)]O2 material with x = 0.311 delivers a very low initial discharge capacity of 98 mAh g−1, which is found to be increased up to a discharge capacity of about 260 mAh g− 1 at the 30th cycling. This drastic increase in capacity is attributed to the redox couples of Cr+ 4/Cr+ 6 and Cr+3/Cr+4.

Gel polymer electrolyte lithium-ion cells with improved low temperature performance

For a number of NASA's future planetary and terrestrial applications, high energy density rechargeable lithium batteries that can operate at very low temperature are desired. In the pursuit of developing Li-ion batteries with improved low temperature performance, we have also focused on assessing the viability of using gel polymer systems, due to their desirable form factor and enhanced safety characteristics. In the present study we have evaluated three classes of promising liquid low-temperature electrolytes that have been impregnated into gel polymer electrolyte carbon-LiMn 2O 4-based Li-ion cells (manufactured by LG Chem. Inc.), consisting of: (a) binary EC + EMC mixtures with very low EC-content (10%), (b) quaternary carbonate mixtures with low EC-content (16–20%), and (c) ternary electrolytes with very low EC-content (10%) and high proportions of ester co-solvents (i.e., 80%). These electrolytes have been compared with a baseline formulation (i.e., 1.0 M LiPF 6 in EC + DEC + DMC (1:1:1%, v/v/v), where EC, ethylene carbonate, DEC, diethyl carbonate, and DMC, dimethyl carbonate). We have performed a number of characterization tests on these cells, including: determining the rate capacity as a function of temperature (with preceding charge at room temperature and also at low temperature), the cycle life performance (both 100% DOD and 30% DOD low earth orbit cycling), the pulse capability, and the impedance characteristics at different temperatures. We have obtained excellent performance at low temperatures with ester-based electrolytes, including the demonstration of >80% of the room temperature capacity at −60 °C using a C/20 discharge rate with cells containing 1.0 M LiPF 6 in EC + EMC + MB (1:1:8%, v/v/v) (MB, methyl butyrate) and 1.0 M LiPF 6 in EC + EMC + EB (1:1:8%, v/v/v) (EB, ethyl butyrate) electrolytes. In addition, cells containing the ester-based electrolytes were observed to support 5 C pulses at −40 °C, while still maintaining a voltage >2.5 V at 100 and 80% state-of-charge (SOC).

Multinary alloy electrodes for solid state batteries II. A new LiSiMg alloy negative electrode material for use in high energy density rechargeable lithium cells

Electrochemical coulometric titration has been used to explore the electrode properties of a ternary LiSiMg alloy composition. The measured electrode potential and lithium capacity for this system are comparable to those estimated from consideration of the isothermal Gibbs triangle for the ternary system. These measured values are far higher than those of the state-of-the-art binary systems currently employed in thermal batteries. For example, measured electrode potentials for the ternary alloy at 440 °C were about 90 mV more negative than those for the conventional 44 wt.% LiSi binary alloy, translating to a loss of only about 70 mV compared to pure lithium. Consequently, the maximum specific energy (considering active materials only) of a cell employing this material as the negative electrode component with a hypothetical cathode (say, one lithium in 60 g of active material) which is 2.0 V positive of pure lithium should be about 35% higher than that of a comparable cell using the 44 wt.% LiSi binary alloy.

Capacity—cycle life behavior in secondary lithium cells

The practical utilization of high energy density rechargeable lithium cells is dependent upon maintaining high capacity for the duration of the required cycle life. However, a critical, yet generic problem with room temperature lithium systems is that the capacity often declines considerably during the early stages of cycling. We report the results of our studies on electrolyte degradation which we observe after cells have undergone 300 and 700 deep cycles with 3-methylsulfolane- and 2-methyltetrahydrofuran—LiAsF 6 electrolytes, respectively.