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To overcome the challenges associated with the toxicity of the majority of organic solvents for the liquid phase synthesis of solid electrolytes toward the human body and environment, we demonstrate the synthesis of tin-based sulphide electrolytes using water, which is the most environmentally friendly solvent. ortho-Thiostannate, i.e., Li4SnS4, was obtained from a mixture of Li2S, Sn, and S using aqueous solution synthesis. Furthermore, Li10SnP2S12, a superionic conductor, was obtained by mixing an aqueous solution of Li4SnS4 and tetrahydrofuran suspension of Li3PS4, which exhibited the highest ionic conductivity (5.9 × 10−3 S cm−1 at 25 °C) in liquid-phase synthesis. This study successfully demonstrates that water can be efficiently used to synthesize sulphide electrolytes instead of conventional organic solvents. [ABSTRACT FROM AUTHOR]

The problem of lithium dendrites must be addressed for practical lithium metal all-solid-state batteries. Herein, three-dimensional morphological changes within Li3PS4 electrolyte away from the anode were observed using operando X-ray computed tomography. We revealed that the electronic conduction of decomposition and the electrolyte/void interface cause the lithium deposition within the Li3PS4. [ABSTRACT FROM AUTHOR]

The electrochemical window of solid electrolytes (SEs) plays a crucial role in designing active material–SE interfaces in high‐energy‐density all‐solid‐state batteries (ASSBs). However, the suitable electrochemical window for individual active materials is not yet investigated, as the electrochemical window of SEs is overestimated. In this study, the oxidation onset voltages (OOVs) of several SEs, namely those compatible with Li2S as a high‐capacity positive electrode material are determined. Results reveal that SEs with low OOVs decrease the capacity and increase the interfacial resistance of the corresponding ASSBs. The OOVs of SEs must exceed that of Li2S by more than 0.2 V to achieve high capacity, which in turn depends on SE ionic conductivity. Therefore, an Li2S positive electrode is combined with pseudobinary Li‐oxyacid salts as SEs, exhibiting high OOVs and ionic conductivities, to afford a high‐capacity (500 Wh kg−1) ASSB with high Li2S content. [ABSTRACT FROM AUTHOR]

Sulfide-based solid electrolytes (SEs) exhibiting high ionic conductivity are indispensable battery materials for next-generation all-solid-state batteries. However, sulfide-based SEs have a major drawback in their low chemical stability in air. When exposed to H2O or O2 gas, toxic H2S is generated, and their ionic conductivity considerably declines. However, their degradation mechanism caused by air exposure has not been understood yet. To clarify the degradation process, in this study, we developed a transmission electron microscope (TEM) system to evaluate the air stability of battery materials. Using a vacuum transfer double-tilt TEM holder with a gas-flow system, the in situ observation of the degradation process was conducted for a sulfide-based Li4SnS4 glass ceramic under an air-flow environment. Consequently, electron diffraction (ED) patterns and TEM images could clearly capture morphological changes and the amorphization process caused by air exposure. Moreover, based on the analysis of ED patterns, it is observed that Li4SnS4 is likely to decompose because of the reaction with H2O in air. Therefore, this airtight and air-flow TEM system should be effective in clarifying the process of the deterioration of sulfur-based SEs during exposure to air. [ABSTRACT FROM AUTHOR]

Highly safe all-solid-state batteries are constructed using oxide electrolytes because of their high chemical and electrochemical stabilities. Previously, we have developed various Li 3 BO 3 -based glass-ceramic electrolytes with high ductility and conductivity. In this study, we focus on the importance of electrode/electrolyte interfacial contacts in all-solid-state batteries. All-oxide solid-state cells (Li-In/LiNi 1/3 Mn 1/3 Co 1/3 O 2) with Li 3 BO 3 -based glass-ceramic electrolytes, are fabricated simply by pressing at room temperature. Furthermore, the effects of the ductility and ionic conductivity of glass-ceramic electrolytes on the charge-discharge properties of all-solid-state batteries are investigated. The 33Li 3 BO 3 ·33Li 2 SO 4 ·33Li 2 CO 3 (mol%) glass-ceramic electrolyte shows lower ionic conductivity and better ductility than the 90Li 3 BO 3 ·10Li 2 SO 4 electrolyte. The all-solid-state cells using these electrolytes operate as secondary batteries at 100 °C. However, better cycle performance is obtained with cells using the former electrolyte. Formation of well-contacted electrode/electrolyte interfaces when using highly ductile electrolytes leads to enhanced electrochemical performance of bulk-type all-solid-state batteries. • All-solid-state cells using Li 3 BO 3 -based glass-ceramic electrolytes are fabricated. • The cell with highly ductile electrolyte shows better charge-discharge performance. • Electrode-electrolyte interfacial formation is important for good cyclability. [ABSTRACT FROM AUTHOR]

Composite graphite negative electrodes were prepared by mixing graphite particles and 75Li 2 S·25P 2 S 5 (mol%) glass particles with weight ratios of x :100 −  x ( x  = 50, 60 and 70). The cell with the x  = 50 electrode showed the highest reversible capacity of more than 250 mAh g −1 . Optical microscopy was conducted for each composite electrode after electrochemical lithiation to investigate reaction distributions by color changes of graphite particles. In the x  = 50 electrodes, almost all the graphite particles changed to gold color, suggesting that the graphite particles were fully lithiated. In situ optical microscopy was also carried out for the composite graphite electrode to monitor color changes of graphite particles directly during charge-discharge tests. [ABSTRACT FROM AUTHOR]

• Room-temperature operating all-solid-state Na-S batteries are fabricated. • High reversible capacity of 1500 mAh g−1 is retained in the batteries for 50 cycles. • Coating of Na 3 SbS 4 on activated carbon–sulfur particles improves cell performance. The need for an effective design of composite electrodes in all-solid-state Na-S batteries is warranted because of their slow charge–discharge reactions. By employing a composite of activated carbon MSP20, sulfur, and Na 3 SbS 4 as the positive electrode material, we developed an effective all-solid-state Na-S battery that demonstrated the advantages of exhibiting a high capacity and good cyclability. Further, we discovered that filling the carbon micropores with sulfur and combining with highly conductive Na 3 SbS 4 , results in a reversible two-electron reaction between S and Na 2 S. This all-solid-state Na-S battery, operating at room temperature, demonstrates a high capacity of 1560 mAh per gram of sulfur (ca. 330 mAh per gram of positive electrode) and a capacity retention of 93% after 50 cycles. Decreasing the size of the S-MSP20 particles coated with Na 3 SbS 4 in a liquid phase process was observed to reduce the volume change of the particles during charge and discharge cycles, which resulted in an excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

All‐solid‐state lithium–sulfur batteries have attracted much attention because of their large capacity and long life. However, their rate capability is not sufficiently high, prompting a great demand for improvement. Herein, a sulfur‐based composite electrode is fabricated for the high‐rate operation of all‐solid‐state lithium–sulfur batteries. The electrode is made of a carbon material having a large number of "interconnected mesopores" with a diameter of 5 nm. The highly mesoporous structure is conducive to electrode reactions and the formation of conduction pathways. Consequently, the rate capability of the composite electrode is drastically improved compared with that of an electrode made of conventional conducting nanocarbon. The all‐solid‐state lithium–sulfur battery with this composite electrode shows a high capacity of 1100 mA h g−1 per sulfur after 400 cycles at a high current density of 1.3 mA cm−2 at 25 °C. These findings are expected to contribute toward the development of practical all‐solid‐state lithium–sulfur batteries. [ABSTRACT FROM AUTHOR]

All‐solid‐state batteries attract significant attention owing to their potential to realize an energy storage system with high safety and energy density. In this paper, a mechanochemical synthesis of novel amorphous positive electrode materials of the Ni‐rich LiNi1−x−yMnxCoyO2 (NMC)–Li2SO4 system suitable for oxide‐type all‐solid‐state batteries is reported. Through the mechanochemical treatment with Li2SO4, excellent formabilities of the electrode materials as those of ductile solid electrolytes are obtained. Owing to the deformability of the active material, a good electrode/electrolyte interface is provided simply by pressing at room temperature. In all‐oxide solid‐state cells using 80NMCs·20Li2SO4 (mol%) positive electrode materials, the cell capacity increases with the Ni content in the NMC. The all‐solid‐state cell using the 80NMC811·20Li2SO4 positive electrode active material exhibits a high capacity larger than 250 mAh g−1 in a voltage range of 1.6–4.8 V versus Li at 100 °C. Furthermore, bulk‐type all‐oxide solid‐state batteries (Li4Ti5O12/80NMC532·20Li2SO4 (mol%)) successfully function as secondary batteries with excellent cycle performances. [ABSTRACT FROM AUTHOR]

Solid electrolytes, such as sulfide glasses, are key materials to put all-solid-state Li-ion batteries into practical use. We evaluated the local structure of 75Li 2 S･25P 2 S 5 (mol%) Li 3 PS 4 glass with a structural phase transition from glass to crystal between 298 K and 523 K by X-ray total scattering data coupled with Reverse Monte Carlo (RMC) modeling. We have obtained structural models consistent with the observed structure factors (S obs (Q)) of Li 3 PS 4 at different temperatures with a low R -factor R p value within 2.0%. The RMC results suggest the PS 4 anion remains a tetrahedron over the wide range from glass to crystal based on the angular and distance distribution of intra-PS 4 S S pairs. On the other hand, the S S correlation of inter-PS 4 distances changes from a wider to a narrower distribution during crystallization. The angular distance distribution functions g (r , θ) indicate that the orientation of the PS 4 tetrahedra changes from random to long-range ordered as crystallization progresses. S Li partial correlation and the average spatial distribution of P and S show a wider distribution of Li-ions at a higher temperature of the glassy state and the distribution then narrows due to crystallization. The RMC results suggest that PS 4 libration plays an important role in Li-ion migration in Li 3 PS 4 solid electrolytes. • RMC can construct local structural model of Li 3 PS 4 over a wide range between glass to crystal. • The peak changes in G obs (r) at r = 3.3 Å and 4.0 Å are caused from narrowing S S correlation of inter-PS 4 anion with crystallization progresses. • The average spatial distribution of S atom and partial distribution function g Li-S (r) are indicated that Li-ion follows near S atom at any state. • The distribution of the angular histogram between the global z -axis and the orientational vector defined in PS 4 anion are narrower changing from glass to crystal. [ABSTRACT FROM AUTHOR]

Abstract All-solid-state batteries comprising sulfide solid electrolytes are promising for energy storage in electric vehicles because of their safety record. There is a high demand for batteries in the form of stackable compact sheets with high cell-based energy density that are mass fabricated in a scalable process. A slurry coating is advantageous for fabricating sheet-type batteries, improves productivity, and allows control of the layer thickness. Here we present a slurry-mixing method for fabricating homogeneously dispersed composite sheets containing micrometer-sized silicon particles. Subsequent removal of the volatile binder from the stacked-sheet cells is demonstrated to reduce their internal resistance. The silicon composite sheets exhibit high initial Coulombic efficiencies of 95%, with practical areal capacities of 2.0–4.4 mAh cm−2 at the 47th cycle under 0.30 mA cm−2, a reversible specific capacity of 2300 mAh g−1 after 100 cycles, and long-term cycling stability (specific capacity above 1700 mAh g−1 after 375 cycles). Cracks that are vertical to the silicon composite layer after cycling buffer the internal strain originating from silicon volume changes, providing excellent cycling stability. These results can assist the rational design of silicon anodes for high-cell-performance all-solid-state batteries. Graphical abstract Image 1 Highlights • Slurry mixing assisted by ZrO 2 balls forms good ionic/electronic conduction paths. • The binder is removed from the sheet-type cell to minimize its resistance. • The μm-Si-composite sheet with practical areal capacity has excellent performance. • Strain from Si volume changes is buffered by vertical cracks in the composite layer. • The slurry overcoating of solid electrolyte leads to high cell-based energy density. [ABSTRACT FROM AUTHOR]

Amorphous active materials have been developed for high-performance lithium and sodium secondary batteries to achieve a higher capacity, higher rate performance, and longer cycle life than those of crystalline active materials. In this study, a new function of amorphous active materials was explored through the heat treatment of pseudobinary amorphous materials (for example, LiCoO 2 –Li 2 SO 4). Additionally, active materials with crystalline/amorphous nanoheterostructures, in which the nano-LiCoO 2 domains were dispersed in a Li 2 SO 4 -rich matrix, were demonstrated. In all-solid-state batteries with sulfide solid electrolytes (SEs), the crystalline/amorphous active materials reduced the interface resistance of the active material and SE when compared with that of Li. High electrochemical performance was achieved using the Li 2 SO 4 -rich matrix, which served as an interfacial stabilizer. In summary, this paper reports a new strategy based on annealing amorphous materials for developing active materials with nanoheterostructures for high-performance energy storage devices. [Display omitted] • Electrode active materials with crystalline/amorphous nanostructures were developed.. • The active materials showed high electrode performance in all-solid-state batteries. • This study offers a new strategy for high-performance secondary batteries.. [ABSTRACT FROM AUTHOR]

All-solid-state sodium-sulfur (Na/S) batteries are promising next-generation batteries with high safety and high energy density. Sodium sulfide (Na 2 S) has application as active material in positive electrodes owing to its advantages such as low cost, low toxicity, and a large theoretical capacity. However, the electronic and sodium ion conductivities of Na 2 S are significantly low, and ascertaining the entire contribution of the active materials to cell capacities is challenging. Therefore, facilitating an electronic and ionic conduction path in the positive electrode is essential. In this study, Na 2 S was mixed with sodium iodide (NaI) via a mechanochemical process and was used as an active material in an all-solid-state Na/S battery. Consequently, a Na 2 S–NaI solid solution was formed, and the ionic conductivity of Na 2 S–NaI increased by five orders of magnitude compared to that of Na 2 S. Na 2 S–NaI showed large charge–discharge capacities and cycle capability. In particular, 90Na 2 S·10NaI showed a large capacity and high cycle efficiency, and 94% of Na 2 S acted as an active material. The result of this study leads to the development of all-solid-state Na/S batteries with high capacities, high rates, and high cycles. • Na 2 S–NaI solid solution was synthesized via mechanochemical process. • Na 2 S–NaI showed five orders of magnitude higher ionic conductivity than that of Na 2 S. • Na 2 S–NaI showed large charge–discharge capacities and cycle capability. [ABSTRACT FROM AUTHOR]

All-solid-state sodium batteries are attracting attention as next-generation batteries, owing to their improved safety and abundance of sodium resources. To realize all-solid-state sodium batteries, solid electrolytes with high sodium-ion conductivities are required. In this study, Na 3 PS 4 electrolytes with partial substitution of P5+ with W6+ were investigated. The Na 3– x P 1– x W x S 4 sulfide-based solid electrolytes were prepared via a mechanochemical process and consecutive heat treatment. The Na 2.85 P 0.85 W 0.15 S 4 electrolyte with Na vacancies exhibited an ionic conductivity of 8.8 × 10−3 S cm−1 at 25 °C, which was higher than that of Na 3 PS 4 solid electrolyte. The all-solid-state batteries (Na-Sn/Na 2.85 P 0.85 W 0.15 S 4 /TiS 2) exhibited a reversible capacity of 140 mA h g−1 at a current density of 0.038 mA cm−2 and retained the capacity of 115 mAh g−1 for 40 cycles at 0.130 mA cm−2 at 25 °C. The Na 3– x P 1– x W x S 4 samples prepared via mechanochemistry are homogeneous electrolytes free of crystalline WS 2 impurities and are effective for application to all-solid-state sodium batteries. • Sulfide Na 3– x P 1– x W x S 4 electrolytes are prepared via a mechanochemical process. • Na 2.85 P 0.85 W 0.15 S 4 with Na vacancies shows a conductivity of 8.8 × 10−3 S cm−1. • All-solid-state cells exhibit a reversible capacity of 140 mAh g−1 of TiS 2 at 25 °C. [ABSTRACT FROM AUTHOR]

Compressive pressure applied during the operation of all-solid-state batteries that employ a sulfide solid electrolyte (SE) assists particle contact, thereby maintaining the ionic and electronic conduction network. The relationship between compressive pressure and volume variation in active materials is critical for designing practical full-cells with enhanced cell-based energy densities. However, studies into these aspects are rare. Here, we systematically investigate the effects of volume change of active materials [silicon, graphite, and LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC)] at different pressures (75 and 50 MPa) on electrochemical performance, cell internal resistance, and microstructure of full-cells with a thin SE layer (approximately 75-μm-thick). Pressurization at 75 MPa and use of graphite with lower expansion ratios improves capacity and capacity retentions. Increasing variation in the negative electrode volume increases charge-transfer resistance and crack formation in the NMC-composite layer. This indicates that the buffering effect via the elastic deformation of the thin SE layer is insufficient. Pressure facilitates plastic deformation of Li x Si and SE, resulting in their improved contact, while perpendicular cracks appear throughout the Si-composite layer, effectively alleviating stress derived from variations in the volume of Si. This study provides important mechanistic insights into the design of advanced active materials and batteries required for industrial applications. Image 1 • Effects of volume variations in active materials under pressure on cells are studied. • High compressive pressure and low volume variation improve cell performance. • Volume variation of Si affects opposite electrode via thin solid electrolyte layer. • Pressure heals fine cracks and forms large perpendicular cracks in Si electrodes. • Pressure facilitates contact of Li x Si and solid electrolyte via plastic deformation. [ABSTRACT FROM AUTHOR]

Sulfide-based solid electrolytes have gained attention for application in solid-state lithium batteries, due to their high ionic conductivities, suitable mechanical properties, and wide electrochemical windows. However, the sulfide in these materials is very hygroscopic, and can react with traces of water, thus generating toxic H 2 S gas. This reduces the lithium-ion conductivity, which plays an important role in solid state batteries. On the contrary, it has also been found that the conductive performance of a sulfide solid electrolyte exposed to water can be partially recovered by a suitable heat treatment. In this study, multiple spectroscopic analyses using X-ray photoelectron spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, and diffuse reflectance infrared Fourier-transform spectroscopy were performed on an argyrodite-type sulfide solid electrolyte to elucidate the degradation mechanism under a small amount of moisture, as in a dry room, as well as the recovery mechanism of a degraded sample by vacuum heat treatment. We found that the degradation behavior of the PS 4 3− unit and the adsorption/desorption of water molecules on the surface of the electrolyte were correlated with the lithium-ion conductivity. [Display omitted] • Water durability of an argyrodite-type sulfide-based solid electrolyte in a low dew point air was investigated by using XPS, Raman, NMR, and DRIFTS. • The decomposed species and the adsorbed H 2 O were observed on the SE surface. • It was directly confirmed that the adsorbed H 2 O was desorbed by vacuum heating, and the conductivity recovered partially. [ABSTRACT FROM AUTHOR]

All-solid-state batteries using sodium are promising candidates for next-generation rechargeable batteries due to the limited lithium resources. A practical sodium battery requires an electrolyte with high conductivity. Cubic Na 3 PS 4 exhibiting high conductivity of over 10−4 S cm−1 is obtained by crystallizing amorphous Na 3 PS 4 synthesized by ball milling. Amorphous Na 3 PS 4 crystallizes in a cubic structure and then is transformed into a tetragonal phase upon heating. In this study, in situ observation by transmission electron microscopy demonstrates that the crystallite size drastically increases during the transition from the cubic phase to the tetragonal phase. Moreover, an electron diffraction analysis reveals that amorphous domains and nano-sized crystallites coexist in the cubic Na 3 PS 4 specimen, while the tetragonal phase contains micro-sized crystallites. The nano-sized crystallites and the composite formed by crystallites and amorphous domains are most likely responsible for the increase in conductivity in the cubic Na 3 PS 4 specimens. • In situ heating observation in Amorphous Na 3 PS 4 prepared by ball milling. • Dark-field images reveal the crystallization behavior in Na 3 PS 4. • Microstructures of crystallites are observed in real space. • A mixture of amorphous domains and crystallites is confirmed. • Grain coarsening occurs during the transition from the cubic to tetragonal phases. [ABSTRACT FROM AUTHOR]

Liquid-phase synthesis for solid electrolytes has received considerable attention owing to its shape control, with the potential to produce particles easily on a large scale, and its low cost and energy consumption. However, solid electrolytes prepared through liquid-phase synthesis have been shown to have lower ionic conductivity than solid electrolytes prepared through the mechanical milling method. Recently, following various efforts, our group found that the crystallinity and remaining intermediate are the reasons for the low ionic conductivity of these materials. By using tetrahydrofuran (THF), we successfully improved the ionic conductivity of Li 3 PS 4 to 1.85 × 10−4 S cm−1 at 25 °C, higher than that afforded by ethyl propionate, which was reported to produce the highest ionic conductivity among the solvents used for liquid-phase synthesis. High-energy X-ray diffraction (XRD) measurements coupled with pair distribution function (PDF) analysis were employed to analyze the synthesized materials in order to determine why the ionic conductivity was higher than that of a sample prepared using ethyl propionate. The PDF analysis revealed that the crystallization of Li 3 PS 4 can be suppressed using THF, which has a lower boiling point than ethyl propionate. Moreover, it was revealed that the solvent could not be removed completely when the material has an amorphous structure, and thus, the ionic conductivity was lower than that of a material prepared using the solid-phase synthesis method. • By using tetrahydrofuran (THF) for liquid-phase synthesis, we prepared for Li3PS4 with relatively high ionic conductivity. • The Li 3 PS 4 structure was analyzed by high-energy X-ray diffraction coupled with pair distribution function (PDF) analysis. • The PDF analysis revealed that the crystallization of Li3PS4 can be suppressed using THF because of its low boiling point. • The THF could not be removed completely when the Li3PS4 has an amorphous structure, reducing the ionic conductivity. [ABSTRACT FROM AUTHOR]

Novel nitride glass electrolyte Li 3 BN 2 was prepared from Li 3 N and BN via a mechanochemical process using planetary ball milling. Raman and X-ray photoelectron spectroscopies revealed that the glass was composed of Li+ and BN 2 3− ions. The Li 3 BN 2 glass exhibited good ductility, and the powder-compressed pellet showed a relative density of 84%. The hot-pressed pellet of the Li 3 BN 2 glass showed a conductivity of 1.3 × 10−5 S cm−1 at 25 °C, which is much higher than that of oxide-based glass electrolytes such as Li 3 BO 3 glass and LiPON thin films. Moreover, Young's modulus of the Li 3 BN 2 glass was 51.1 GPa, which is an intermediate value between sulfides and oxides. The Li symmetric cell using the Li 3 BN 2 glass electrolyte was cycled stably at 100 °C without short-circuiting. Nitride glassy materials are promising electrolytes for all-solid-state batteries because of their high conductivity, good mechanical properties, and electrochemical stability. • Li 3 BN 2 glass electrolyte is prepared via a mechanochemical process. • The glass shows good ductility to be densified just by pressing at room temperature. • The glass electrolyte exhibits the conductivity of 1.3 × 10−5 S cm−1 at 25 °C. • The Li metal symmetric cell using the glass electrolyte is cycled stably at 100 °C. [ABSTRACT FROM AUTHOR]