Recent development of sulfide solid electrolytes and interfacial modification for all-solid-state rechargeable lithium batteries

A suitable theory is required to identify the electro-chemo-mechanical limits of Li-ion batteries performance in realistic electrode-electrolyte configurations. In all-solid cells, the battery life depends in larger measure on the mechanical integrity of the composite system[1]. The proposed fully coupled electro-chemo-mechanical model can contribute to the mesoscale optimization of such composite microstructures [2]. All-solid-state rechargeable lithium-ion batteries have attracted much interest because they have features partic- ularly favorable for large-scale application. The replacement of an organic liquid electrolyte with a non-flammable and more reliable inorganic solid electrolyte (SE) simplifies the battery design and improves safety and durability of the system[3]. However, the mechanical behavior of such electrodes will be considerably different than their liquid electrolyte counterparts. Direct stacking of solid-state cells enables the achievement of high operating voltages in a reduced volume. Furthermore, all-solid-state batteries allow the use of large-capacity electrode materials, for instance sulfur positive electrode paired with a lithium metal negative electrode, which are difficult to employ in conventional liquid electrolyte batteries. A key development to the success of all-solid-state batteries is a SE with high Li+ ion conductivity at room temperature[4, 5, 6]. In recent years, several solid electrolytes having level of conductivity comparable to organic liquid electrolytes have been discovered and tested with many active materials. The durability of a cohering solid- solid interface between electrode and electrolyte is likely to be important practical consideration. Notwithstanding the several techniques investigated to increase the contact area at the interface[7], interface cohesion and its effects on the rate capability and the overall performance throughout the expected life cycles needs to be maintained. The present research focuses on the development of a nonlinear continuum model able to account for the com- bined effects of Li diffusion and for the consequent volumetric expansion of the hosting material. The electrode and electrolyte are modeled as idealized as elastic materials, with elastic properties varying with lithium concentration. The complexity and the multi-physical nature of the problem requires numerical modeling strategies and poses several challenges. To address this, we have established a computational framework based on large deformation theory and in a thermodynamically consistent fashion. This is implemented in an in-house, object oriented C++ numerical code that incorporates three-dimensional finite element calculations. The numerical analysis allows for delamination at the interface between electrode particles and solid electrolyte. Crack formation and propagation is predicted by means of a cohesive zone model extended to include decreased Li flux across interfaces due to their loss of mechanical integrity. Our simulations indicate trends of mechanical reliability of all-solid state batteries realized with some of the most promising solid electrolyte materials (e.g. Li2S-P2S5 [1], LIPON [4], garnet SE [8]); our calculations are based on the mechanical properties available in literature. When physical values for the solid electrolyte’s mechanical behavior are not available, our calculations indicate trends of how mechanical reliability correlates with the battery design and operating conditions (i.e., charging rate). [1] Akitoshi Hayashi, Kousuke Noi, Atsushi Sakuda, and Masahiro Tatsumisago. Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries. Nature Communications, 3, 2012.[2] Giovanna Bucci, Yet-Ming Chaing, and W. Craig Carter. Formulation of the coupled electrochemical-mechanical boundary-value problem, with applications to transport of multiple charged species. Acta Materialia, 2015. (accepted). [3] KazunoriTakada.Progressandprospectiveofsolid-statelithiumbatteries.ActaMaterialia,61(3):759–770,2013. [4] J.B Bates, N.J Dudney, B Neudecker, A Ueda, and C.D Evans. Thin-film lithium and lithium-ion batteries. Solid State Ionics, 135(1 - 4):33 – 45, 2000.[5] Yoshikatsu Seino, Tsuyoshi Ota, Kazunori Takada, Akitoshi Hayashi, and Masahiro Tatsumisago. A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries. Energy Environ. Sci., 7:627–631, 2014. [6] Noriaki Kamaya, Kenji Homma, Yuichiro Yamakawa, Masaaki Hirayama, Ryoji Kanno, Masao Yonemura, Takashi Kamiyama, Yuki Kato, Shigenori Hama, Koji Kawamoto, and Akio Mitsui. A lithium superionic conductor. Nature materials, 10(9):682–6, September 2011.[7] Masahiro Tatsumisago, Motohiro Nagao, and Akitoshi Hayashi. Recent development of sulfide solid electrolytes and interfacial modification for all-solid-state rechargeable lithium batteries. Journal of Asian Ceramic Societies, 1(1):17 – 25, 2013.[8] Ezhiyl Rangasamy, Jeff Wolfenstine, and Jeffrey Sakamoto. The role of Al and Li concentration on the formation of cubic garnet solid electrolyte of nominal composition Li7La3Zr2O12. Solid State Ionics, 206(0):28 – 32, 2012.

Despite some progress performed, state-of-the-art lithium ion batteries still require improvements in energy and power to extend the range of electric vehicles and reduce charging time. In this domain, all-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium ion transport number, and no-liquid nature. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, allowing all-solid-state batteries to be easily prepared via simple mixing and cold-pressing processes, facilitating the scale-up.Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Indeed, lithium metal is believed to be the most promising negative electrode due to its specific large capacity (3862 mAh.g-1), low volumetric density (0.534 g.cm-3 at 20°C) and the lowest electrochemical potential (-3.03V vs ENH). Nevertheless, like most metal, lithium metal is morphologically dynamic. Its surface morphology is modified, since during the electrochemical cycling, a part of lithium migrates to the other electrode to react and is then plating on its surface heterogeneously, leading to a volume change and sometimes dendrite growth with potential internal short circuit and life-threatening accidents. Ceramic solid electrolytes have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. In the same time, the chemical nature and composition of ceramic solid electrolyte can affect the dendrite growth by the interfacial chemical and electrochemical stability with lithium metal forming solid electrolyte interphase as a passivating layer. Since the lithium dendrites have to grow through this layer, its composition should play an important role in the dendrite formation. Moreover, it is known that the stack can be easily deformed because lithium dendrite growth with a high shear modulus, indicating that the solid electrolyte and its interface with lithium metal should be sufficiently strong to endure the pressure originating from lithium dendrite growth. The oxide–based ceramic solid electrolytes can be shaped by sintering at high temperature, leading to a grain and grain-boundary microstructure with some porosity, facilitating the lithium dendrite growth through grain boundaries. Due to the low density and plasticity of sulfide based inorganic solid electrolyte, the dendrite growth through the particle-particle contact can be reduced but still present.Different parameters can influence the lithium dendrite growth and the critical current density in ceramic all-solid-state configuration, such as the solid electrolyte chemical composition, particle size, and the compactness of ceramic solid electrolyte. The pressure effect on the electrochemical performances of sulfide electrolytes was investigated. The pressure affects resistive grain boundaries, contact between lithium metal and solid electrolyte and lithium plating. As, the kinetics of reaction is derived from thermodynamic parameters, the temperature can affect the plating/stripping phenomena. These different parameters and the relationship between them will be presented and explained through complete studies based on sulfide solid electrolytes with the combination of various chemical and electrochemical techniques.

Review: [77 refs.

As lithium rechargeable batteries are considered a potential candidate for large‐scale energy storage applications in devices such as electric vehicles (EVs) and smart grids, their safety has become of prime concern. This calls for the need to replace the flammable organic liquid electrolyte (LE) with an inorganic solid electrolyte (SE), and thus, develop bulk‐type all‐solid‐state lithium batteries (ASLBs), fabricated using a scalable process. Sulfide SEs are considered the most competitive candidate owing to their high conductivity at room temperature (10−3–10−2 S cm−1), which is comparable to that of LEs, and their ductility, which enables the fabrication of ASLBs simply using cold pressing. In the present review, issues and challenges to be faced for the fabrication of bulk‐type ASLBs using sulfide SEs are presented and discussed, with a special focus on the development of SEs, compatibility of the electrode materials with SEs, and structure of the composite electrodes. Recent progress made with the aim of addressing the aforementioned issues and challenges is also presented, to provide an outlook on the future of SEs and ASLBs.

Background: Sleep Apnea is a common sleep disorder and Home Sleep Apnea Test (HSAT) is one of the relatively safe and convenient diagnostic screening tools of Sleep Apnea. Nowadays popular devices for HSAT suggesting to use AA batteries for power supply and disposable alkaline battery is recommended in the guideline of most devices. In 2019, a new type of rechargeable AA battery based on lithium-ion was successfully developed and put into the market. Here is the report of 2 years running, observing the performance of the new rechargeable lithium-ion AA battery, in order to proof the possibility and the advantage of the new lithium-ion battery replacing the existing battery. Method: Used Embla MPR PG with ST module to emulate an HSAT for 10 times and log the longest recording time of different battery. And analyze the voltage log of HSAT by Embla X100 in the past 3 years. Evaluate whether the new Rechargeable Lithium-ion battery is competent for HSAT by the longest recording time and the battery status during HSAT. Result: After 2 years of continuous use, the performance of Rechargeable lithium-ion battery was similar to that of Disposable alkaline battery. And Rechargeable lithium-ion battery had a constant voltage throughout the whole recording phase. Conclusion: The new rechargeable lithium-ion AA battery can perfectly replace the traditional disposable alkaline battery in the application of HSAT due to the un-obvious attenuation in 2 years. It also has great advantages in environmental protection and cost saving.

Rechargeable lithium-ion batteries (LIBs) involving lithium metal oxides, liquid electrolyte and graphite have been widely used in portable electronic devices due to their relatively high energy density and long cycle life. These desirable features make LIBs very attractive as the power source for electronic devices, hybrid electric vehicles (HEVs) and electric vehicles (EVs) applications [1, 2]. For future EV applications, higher energy density of LIBs up to 360 Wh kg-1 is required. Currently, the energy density of the state-of-the-art LIBs using conventional graphite anode, LiFePO4 (denoted as LFP) or LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes and 1-1.2 M LiPF6 in organic carbonate electrolytes provide practically achievable energy densities of up to around 200-260 Wh kg−1 [3]. When commercial graphite anodes are used, LiNi0.8Co0.15Al0.05O2 (NCA), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.5Mn1.5O4 (LNMO) and LiNiPO4 (LNP) cathode based batteries with high-voltage provide energy densities of 354, 338, 351 and 414 Wh kg-1, respectively. However, LIBs using these high-voltage cathode materials and the organic carbonate electrolytes exhibit quite low thermal stability and tend to catch fire or even explode when abnormal charge/discharge cycling or accidental penetration of cells occurs, which greatly limits the automotive applications. When replacing graphite with a Li metal anode, the energy densities of all battery systems can be enhanced significantly due to the highest theoretical specific energy density (3860 mAh g-1) among all anode materials for rechargeable LIBs. Nevertheless, commercial LIBs are prone to cause safety problems due to the safety concern arising from Li dendrite growth in liquid organic electrolytes [4-6].The promising solid-state LIBs offer high thermal stability (i.e., low risk in catching fire), high energy density, wide electrochemical stability window and less environmental impact. A competent electrolyte is the key component of solid-state LIBs. The solid-state electrolyte materials are mainly classified as solid polymer electrolytes (SPEs), inorganic solid electrolytes (ISEs), and organic/inorganic composite electrolytes. ISEs include oxide-based and sulfide-based materials [7, 8], which show very high ionic conductivity (10-2 – 10-3 S cm-1). Furthermore, the lithium ion transference number is close to 1. However, the major limitation factors of practical solid-state LIB applications are the large interfacial impedance between electrode and ISE and the difficulty of processing [9]. Considering processability, mechanical flexibility, interfacial compatibility and electrochemical stability, one prefers SPEs to the inorganic ceramic electrolytes. Nevertheless, SPEs have low ion conductivities (10−7 − 10−5 S cm−1 near room temperature) and most of the Li+ transference numbers are lower than 0.5 [10, 11]. The major requirements for SPEs include high ionic conductivity and transference number at room temperature, wide electrochemical potential window, high mechanical strength and excellent thermal stability. However, the ion conductivity is the most important (> 10-4 S cm-1 at room temperature desired) and should be considered first. The coordinating groups of a good polymeric host are expected to interact with Li+ and facilitate dissociation.In this study, we prepared various novel acrylonitrile-based polymers (e.g., acrylonitrile/acrylate copolymer and polymer with two pendant groups b-cyano ethyl ether (-O-CH2CH2-CN) sulfonate alkyl ether (-O-(CH2)3SO3Li). The corresponding SPEs comprising acrylonitrile-based polymer and ca. 50 wt.% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with high ionic conductivity (up to 10-3 S cm-1) at room temperature, high ion transfer number (up to 0.45) and large electrochemical potential window (oxidation stability > 5 V vs. Li+/Li) achieved. The selected SPEs were used as the separator in solid-state batteries with LiFePO4 as the cathode and Li foil as the anode; and long-term cycle stability of solid-state LIB was achieved. The polymers and corresponding SPEs were characterized by using DSC, SEM, XRD and FTIR measurements. Ionic conductivities of SPEs were determined from electrochemical impedance spectroscopy results. The linear sweep voltammetry technique was adopted to measure the oxidation stability window of SPE, and the Evans-Vincent-Bruce method was used to determined ion transfer number.

Rechargeable lithium ion batteries become an very important technology in the contemporary society. They are expanding their application in electric vehicles and power grids. However, current lithium ion batteries with liquid electrolyte have been suffering from potential safety crisis mainly due to their highly flammable organic liquid carbonate organic electrolyte and explosion hazards. These potential risks (combustion and explosion) would retard the commercialization of electric vehicles or hybrid electric vehicles. Thus, the safety issue of lithium ion battery merits further study. Solid electrolytes have attracted ever-increasing interest owing to their enhanced safety issue and higher energy density of lithium battery. Solid electrolyte materials mainly include inorganic solid electrolytes (ISEs) and solid polymer electrolytes (SPEs). The ISEs are classified into oxide-based, sulfide-based and etc. However, in spite of the presence of highly ion conductive ISEs, there are still many undergoing issues that limit the practical application at the present stage, like the large interface impedance between electrode and ISEs and the difficulty of processing. More attention has been paid to solid polymer electrolytes due to their superior flexibility and processability, which are also subjected to thermal expansion at elevated temperature. Poly(ethylene oxide) (PEO) solid polymer electrolyte has undergone a sort of renaissance in the past few decades. However, the quintessential frailty of PEO solid polymer electrolyte is low ionic conductivity (in the order of 10(-7) S cm(-1)) at room temperature with a relatively narrow electrochemical window. Hence, it is essential to develop new solid polymer electrolytes with comprehensive performance in terms of high ionic conductivity, wide electrochemical window, superior mechanical strength, excellent thermal stability as well as good interfacial compatibility. In this review, a series of polycarbonate-based solid polymer electrolytes (such as PEC, PPC, PTMC and PVC et al.) are summarized. In addition, we also present a brief review on preparation, electrochemical property, modification, ionic transportation mechanism and future development direction for each of these solid polymer electrolytes.

The application of rechargeable lithium batteries involves all aspects of our daily life, such as new energy vehicles, computers, watches and other electronic mobile devices, so it is becoming more and more important in contemporary society. However, commercial liquid rechargeable lithium batteries have safety hazards such as leakage or explosion, all-solid-state lithium rechargeable lithium batteries will become the best alternatives. But the biggest challenge we face at present is the large solid-solid interface contact resistance between the solid electrolyte and the electrode as well as the low ionic conductivity of the solid electrolyte. Due to the large relative molecular mass, polymers usually exhibit solid or gel state with good mechanical strength. The intermolecules are connected by covalent bonds, so that the chemical and physical stability, corrosion resistance, high temperature resistance and fire resistance are good. Many researchers have found that polymers play an important role in improving the performance of all-solid-state lithium rechargeable batteries. This review mainly describes the application of polymers in the fields of electrodes, electrolytes, electrolyte-electrode contact interfaces, and electrode binders in all-solid-state lithium rechargeable batteries, and how to improve battery performance. This review mainly introduces the recent applications of polymers in solid-state lithium battery electrodes, electrolytes, electrode binders, etc., and describes the performance of emerging porous polymer materials and materials based on traditional polymers in solid-state lithium batteries. The comparative analysis shows the application advantages and disadvantages of the emerging porous polymer materials in this field which provides valuable reference information for further development.

All-solid-state rechargeable lithium-ion batteries have attracted much interest recently for applications of much larger scale than previous thin-film batteries. The replacement of an organic liquid electrolyte with a non-flammable inorganic solid electrolyte (SE) may simplify battery design and improve safety and durability [2]. However, in all-solid cells, the battery life depends in large measure on the mechanical integrity of the composite system [1]. A suitable theory to identify the electro-chemo-mechanical limits of Li-ion batteries performance in realistic electrode-electrolyte configurations is therefore required. In this work, a fully coupled electro-chemo-mechanical model is developed to facilitate the mesoscale optimization of such composite microstructures. A key development in all-solid-state batteries has been the discovery of solid electrolytes with high Li+ ion conductivity at room temperature comparable to that of organic liquid electrolytes [3, 4, 5]. These have been tested with numerous electrode active materials.The durability of a coherent solid-solid interface between electrode and electrolyte is likely to be an important consideration. Notwithstanding the several techniques investigated to increase the contact area at the interface [6], interface cohesion and its effects on the rate capability and the overall performance throughout the expected life cycles needs to be maintained. In the present research, we develop a nonlinear continuum model able to account for the combined effects of Li diffusion and for the consequent volumetric expansion of the hosting material. The electrode and electrolyte are idealized as elastic materials with elastic properties varying with lithium concentration. The complexity and the multi-physical nature of the problem require numerical modeling strategies and pose several challenges. To address this, we have established a computational framework based on large deformation kinematics and posed in a thermodynamically consistent fashion. The model is implemented in an in-house, object oriented C++ numerical code that incorporates three-dimensional finite element calculations. The numerical analysis allows for delamination at the interface between electrode particles and solid electrolyte. Crack formation and propagation is predicted by means of a cohesive zone model extended to include decreased Li flux across interfaces due to their loss of mechanical integrity. Our simulations indicate trends of mechanical reliability of all-solid state batteries realized with some of the most promising solid electrolyte materials (e.g. Li2S-P2S5 [1], LIPON [3], garnet SE [7]), using mechanical properties available in literature. When physical values for the solid electrolyte’s mechanical behavior are not available, the simulations indicate trends of how mechanical reliability correlates with the battery design and operating conditions (i.e., charging rate). Acknowledgments The work was supported by the grant DE-SC0002633 funded by the U.S. Department of Energy, Office of Science. Keywords Lithium ion batteries, All-solid-state batteries, Nonlinear continuum mechanics; Diffusion; Thermodynamics References [1] A. Hayashi, K. Noi, A. Sakuda, and M. Tatsumisago. Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries. Nature Communications, 3, 2012. [2] K. Takada. Progress and prospective of solid-state lithium batteries. Acta Materialia, 61(3):759 – 770, 2013. [3] J.B Bates, N.J. Dudney, B. Neudecker, A. Ueda, and C.D. Evans. Thin-film lithium and lithium-ion batteries. Solid State Ionics, 135(1 - 4):33 – 45, 2000. [4] Y. Seino, T. Ota, K. Takada, A. Hayashi, and M. Tatsumisago. A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries. Energy Environ. Sci., 7:627–631, 2014. [5] N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y. Kato, S. Hama, K. Kawamoto, and A. Mitsui. A lithium superionic conductor. Nature materials, 10(9):682–6, September 2011. [6] M. Tatsumisago, M. Nagao, and A. Hayashi. Recent development of sulfide solid electrolytes and interfacial modification for all-solid-state rechargeable lithium batteries. Journal of Asian Ceramic Societies, 1(1):17 – 25, 2013. [7] E. Rangasamy, J. Wolfenstine, and J. Sakamoto. The role of Al and Li concentration on the formation of cubic garnet solid electrolyte of nominal composition Li7La3Zr2O12. Solid State Ionics, 206(0):28 – 32, 2012. Figure 1: Simulation of a composite all-solid Li-ion battery microstructure upon lithiation. The diffusion fronts (white lines) appear perturbed due to partial delamination of the interface between electrode particles and solid electrolyte. Figure 1

Despite some progress performed, state-of-the-art lithium ion batteries still require improvements in energy and power to extend the range of electric vehicles and reduce charging time. In this domain, all-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium ion transport number, and no-liquid nature. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, allowing all-solid-state batteries to be easily prepared via simple mixing and cold-pressing processes, facilitating the scale-up.Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Indeed, lithium metal is believed to be the most promising negative electrode due to its specific large capacity (3862 mAh.g-1), low volumetric density (0.534 g.cm-3 at 20°C) and the lowest electrochemical potential (-3.03V vs ENH). Nevertheless, like most metal, lithium metal is morphologically dynamic. Its surface morphology is modified, since during the electrochemical cycling, a part of lithium migrates to the other electrode to react and is then plating on its surface heterogeneously, leading to a volume change and sometimes dendrite growth with potential internal short circuit and life-threatening accidents. Ceramic solid electrolytes have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. In the same time, the chemical nature and composition of ceramic solid electrolyte can affect its reactivity with lithium metal. In the same time, the electrochemical stability of solid electrolyte depending of its nature and composition is a key parameter to mix it with the different components of positive electrode as active materials and electronic conductors to ensure the better percolation and performances. The oxide–based ceramic solid electrolytes can be shaped by sintering at high temperature, leading to a grain and –grain boundary microstructure with some porosity, facilitating the lithium dendrite growth through grain boundaries. Due to the low density and plasticity of sulfide based inorganic solid electrolyte, the dendrite growth through the particle-particle contact can be reduced but still present.Hence different parameters can influence the performances and aging of all solid state ceramic battery. To explore them, various electrochemical technics and associated specific treatments can be developed to extract and identify each phenomena and ensure the better development of this technology. A specific sequential methodology will be presented with different examples from the materials, interfaces with lithium metal, pseudo-composites and temperature effects up to aging of total all-solid–state ceramic battery based on sulfide technology. The extracted different parameters and the relationship between them will be presented.

All-solid-state Li/S batteries with inorganic solid electrolytes have been studied because of their advantages of large energy density, good reversibility, and low cost. Preparation of sulfur composite electrodes using solid electrolyte and carbon additives is important for enhancing the utilization of sulfur and Li2S as an active material [1,2]. However, increasing sulfur or Li2S content in the composite electrodes tends to decrease reversible capacity because of their insulating nature. A melt diffusion process of sulfur into carbon pores is widely used for forming good sulfur-carbon contacts and inhibiting dissolution of polysulfide moieties into liquid electrolytes. We have prepared sulfur composite electrodes including 50 wt% sulfur by mechanical milling at 155oC, which is over the melting point of sulfur, and all-solid-state Li/S cells with the composite electrode showed the reversible capacity of over 1000 mAh g-1 at room temperature [3]. Alternative strategy to increase utilization of active materials is enhancing their lithium ion conductivity. Partial replacement of sulfide anions (S2-) in crystalline Li2S with iodide anions (I-) introduces lithium defects to Li2S and increases its lattice constant, and the structural modification will bring about conductivity enhancement. In this study, we have prepared Li2S-LiI solid solutions by mechanical milling [4]. The starting materials of crystalline Li2S and LiI were milled using a planetary ball mill apparatus. X-ray diffraction (XRD) for the (100-x)Li2S∙xLiI (mol%, 0 ≤ x ≤ 20) milled samples indicated that XRD peaks attributable to crystalline LiI disappeared and those attributable to Li2S shifted to the lower angle side with an increase in the LiI content. The lattice constant of Li2S increased with an increase in the LiI content, suggesting that solid solutions in the system Li2S-LiI were prepared by mechanical milling. The solid solution at the composition of x = 20 showed the highest Li+ ion conductivity of 2.2×10-6 S cm-1, which is two orders of magnitude higher than that of Li2S. An all-solid-state cell (Li-In/Li3PS4/Li2S-LiI) operated as a rechargeable battery at room temperature. The cell with the x=20 solid solution as an active material exhibited a stable reversible capacity of 930 mAh per gram of Li2S (80% utilization) for 50 cycles at 0.07C. Further conductivity enhancement was achieved in the ternary system Li2S-LiI-LiBr, and the highest conductivity was over 10-5 S cm-1at the composition with 40 mol% lithium halides. The concept of increasing ionic conductivity of sulfur-based active materials is effective in increasing their utilization and reversible capacity for Li/S cells. Acknowledgement This research was financially supported by ALCA-SPRING project.

Currently widely used Lithium ion batteries are based on metal oxides or phosphates and carbon systems with theoretical specific capacity of about 400 Wh/Kg. However to meet the ever growing energy demand of modern society, specifically for extended range electric vehicles, high energy density batteries are required [1, 2]. From this viewpoint, the use of sulfur as a cathode material is highly beneficial since its theoretical specific capacity corresponding to 1675 mAh/g could generate high energy density of 2600 Wh/Kg which is 3x105 folds higher than the state-of-the art Lithium ion batteries [3]. However, research on lithium sulfur (Li/S) batteries using liquid electrolytes faces several problems such as the loss of the active material in the form of soluble polysulfide reaction products [4, 5]. Hence, for the development of next generation high performance power sources with high energy densities substantial emphasis has be laid on rechargeable all solid-state Li/S batteries. All solid state Li/S batteries include a solid electrolyte that offers several benefits such as good flexibility, potentially high electrochemical stability window and low flammability. The solid state nature could be very beneficial to Li/S batteries as they can prevent polysulfide dissolution and efficiently lessen dendrite penetration [6]. In this work, two kind of sulfur carbon composite electrodes were prepared by mechanical activation and thermal activation technique and the performance was evaluated by incorporating in a solid state battery. A composite solid polymer electrolyte prepared by dispersing the Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramic fillers in the blend of high and low molecular weights polymer matrix was used as a solid electrolyte. The solid state battery using thermally activated composite electrode showed good electrochemical performance and cycle stability due to intimate contact between the sulfur and the carbon. [1] Morris, R. Scott, et al. "High-energy, rechargeable Li-ion battery based on carbon nanotube technology." Journal of Power Sources 138.1 (2004): 277-280. [2] Thackeray, Michael M., Christopher Wolverton, and Eric D. Isaacs. "Electrical energy storage for transportation—approaching the limits of, and going beyond, lithium-ion batteries." Energy & Environmental Science 5.7 (2012): 7854-7863. [3] Aurbach, Doron, et al. "On the surface chemical aspects of very high energy density, rechargeable Li–sulfur batteries." Journal of the Electrochemical Society 156.8 (2009): A694-A702. [4] Hayashi, Akitoshi, et al. "All-solid-state Li/S batteries with highly conductive glass–ceramic electrolytes." Electrochemistry communications 5.8 (2003): 701-705. [5] Kobayashi, Takeshi, et al. "All solid-state battery with sulfur electrode and thio-LISICON electrolyte." Journal of Power Sources 182.2 (2008): 621-625. [6] Machida, Nobuya, et al. "Electrochemical properties of sulfur as cathode materials in a solid-state lithium battery with inorganic solid electrolytes." Solid State Ionics 175.1 (2004): 247-250.

Currently, electrolytes used in lithium-ion batteries are flammable and leaky, causing safety problems when used under high temperatures or extreme conditions. Solid electrolytes can fundamentally avoid the occurrence of such issues, at the same time, it can significantly increase the energy density of solid state lithium batteries. Solid electrolytes are classified into inorganic solid electrolytes and solid polymer electrolytes. Although inorganic solid electrolytes have the high mechanical strength and room temperature ionic conductivity, it has poor flexibility and complicated preparation process. In contrast, solid polymer electrolyte has good elasticity and good interface contact, which can overcome many disadvantages of the inorganic solid electrolyte. Among them, polyethylene oxide (PEO) is first proposed as a polymer electrolyte. Due to its excellent mechanical properties, electrochemical stability and thermal stability, it has been a hot topic for polymer solid electrolytes for decades. However, its low room temperature ionic conductivity limits practical application. Given the problems existing in PEO-based polymer electrolytes, several methods for improving ionic conductivity have been proposed. The primary methods include plasticization, the organic-inorganic composite, and polymer blending. Comparing these methods, it can be seen that adding plasticizers to the polymer can effectively increase the conductivity of the electrolyte, but at the same time it will cause a decrease in the mechanical properties, and the safety issues limit its application in lithium-ion batteries. Inorganic fillers can balance the problems of ionic conductivity and mechanical properties, but the construction of a good filler-polymer dispersion system is complicated in preparing such composite electrolytes, design a new type of multi-dimensional the ion transport network also face tremendous challenges. Undoubtedly, in the future research, inorganic fillers will be the dominant means in the modification of composite electrolytes. Compared with the former two modification methods, polymer blending is easy to operate and friendly to industry, but low ionic conductivity at room temperature still exist. To give full play to the advantages of polymer blending, using it as an auxiliary means to improve the performance of composite electrolytes will be the primary development direction of such modification methods. PEO is the most widely studied polymer electrolyte. Even though a large number of modification methods have emerged in its development history, the ionic conductivity at room temperature is still limited to a relatively low level. To meet the needs of the application in lithium-ion batteries, a high operating temperature (50−70℃) is still needed, the biggest problem remains exist. To solve the problems in polymer solid electrolytes, the research directions in the future may mainly focus on: Expanding the modification method of PEO to other polymer electrolyte host materials, broadening the scope of research, and finding the available polymer electrolytes at room temperature. Concerned about the preparation of ultra-thin polymer electrolytes, reducing the ion transmission path to increase the transmission efficiency of lithium ions between positive and negative electrodes. Effectively combines inorganic solid electrolytes and solid polymer electrolytes to give full play to their advantages. In addition, exploring the effect of inorganic filler morphology on the conductivity of the composite electrolyte will also deserve attention. Many one-dimensional, two-dimensional materials can build ion transport networks so that lithium ions can travel rapidly along the path. With the deepening of research, it is expected that PEO-based polymer electrolytes may replace liquid electrolytes and become an essential cornerstone for building the next generation of safe and reliable lithium-ion batteries.

１． Purpose Rechargeable batteries using inorganic solid electrolytes are currently attracting attention from many quarters as next-generation rechargeable batteries because they can use lithium metal (3860 mAh g-1), which has a large theoretical capacity, as the negative electrode due to its ability to suppress dendrites, and can operate at high temperatures. MoS2, a transition metal dichalcogenite, has a layered structure consisting of sheets of MoS2, which has been studied as a cathode active material because of its extremely high theoretical capacity (670 mAh g-1 , 3390 mAh cm-3) and relatively low cost. In the case of liquid electrolytes, electrodes with MoS2 crystals grown on graphene by a hydrothermal method have been developed to prevent re-lamination of MoS2 and to ensure conductivity(1), but there were problems such as a small bulk density of active material and a very complicated electrode fabrication method. In contrast, we thought that the issues of preventing re-lamination and ensuring conductivity could be solved by using an inorganic solid electrolyte with a structure in which solid electrolyte and conductivity aids are sandwiched between single to several layers of MoS2 and MoS2 particles. In this method, the bulk density of the active material can be freely selected, and electrode fabrication becomes relatively easy. Therefore, in this study, electrodes were fabricated using single~several layers of MoS2 solvated in a solvent in order to fabricate electrodes while preventing re-lamination. The solid electrolyte (Li3PS4) used for mixing was also synthesized by the liquid-phase method, and the electrodes were prepared only by liquid-phase mixing, which is advantageous for industrialization. ２． experiment MoS2 (1.0 g) and butyl lithium-hexane solution (2.0 M, 25 mL) were mixed, and MoS2@Li powder was obtained by inserting lithium atoms between layers of MoS2 by irradiating with bath-type ultrasound for 3 hours. MoS2@Li was then exfoliated and dispersed by ultrasonic homogenization in butyl acetate solvent for 20 minutes to prepare MoS2 dispersion.For electrode preparation, MoS2 dispersion, conductive auxiliary material (vapor-grown carbon fiber), solid electrolyte (Li3PS4 dispersion solution), and zirconia balls (φ4 mm, 20 g) were mixed by shaking at 1500 rpm for 10 minutes. The solvent was then removed by centrifugation and decantation, vacuum dried for 48 hours, and annealed at 100 °C for 2 hours. The Li3PS4 dispersion solution was synthesized in advance by a liquid-phase method using butyl acetate as solvent. The cell was fabricated using amorphous Li3PS4 synthesized by a mechanochemical method as the electrolyte and a Li/In alloy as the reference electrode and anode, and combined with the above cathode to form a two-pole cell. ３． Results and discussion Transmission electron microscope images of the MoS2 dispersion used to fabricate the electrode are shown in Fig. 1. As a result, it was confirmed that MoS2 of about several hundred nm was present in the dispersion solution in a single to several layer state, and that single to several layers of MoS2 were dispersed in the solvent.The charge-discharge curves of electrodes with exfoliated and untreated MoS2 are shown in Fig. 2. A charge plateau was observed at approximately 2.2 V for both electrodes. Multiple plateaus were observed during the discharge process, confirming that several types of reactions were occurring in a multi-step manner. No reduction reaction was observed at 2.5 to 4.5 V. The electrode made of untreated MoS2 had a discharge capacity of about 500 mAh g-1, whereas the electrode made of exfoliated MoS2 showed a very high discharge capacity of 1105 mAh g-1, more than twice the maximum. The Cyclic voltammograms of electrodes with exfoliated and untreated MoS2 are shown in Fig. 3. The CV measurements have peaks at similar positions for these electrodes, and the electrodes with exfoliated MoS2 showed higher current values overall. These results suggest that the reaction mechanism is almost the same for these electrodes, and that the utilization of MoS2 was improved by using stripped MoS2.(References)(1) Liu , K.Jia , J.Yang , S.He , Z.Liu , X.Wang , J.Qiu Chem.Eng.J 475,146181(2023) Figure 1

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