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Mechanical properties of Li10.35Ge1.35P1.65S12 (LGPS) solid electrolytes with different grain sizes were investigated via indentation tests. Hand-milled LGPS (HM LGPS, d50: 1.32 μm) and wet-milled LGPS (WM LGPS, d50: 0.46 μm) powders were uniaxially pressed to obtain pellet samples. The HM LGPS and WM LGPS pellets had a similar bulk density of 1.63 g cm-3. At the initial loading/unloading, the WM LPGS pellet showed a large deformation owing to a decrease in cavities compared with the HM LGPS. In the subsequent cycles, both pellets exhibited elastic deformation behavior in the pressure range up to 20 N. The elastic modulus and relative residual depth of HM LGPS and WM LGPS were 21.7 GPa and 15.0 GPa and 0.75 and 0.71, respectively. This result revealed that WM LGPS is more elastically deformable and less plastically deformable than HM LGPS, which could be associated with the grain boundary strengthening interpreted by the Hall-Petch relation. Based on these mechanical properties, the superior cycle stability at the In-Li electrode/WM LGPS electrolyte interface during charging/discharging was discussed. Controlling the mechanical properties of sulfide solid electrolytes by the grain size is important for suppressing physical degradation in all-solid-state batteries. [ABSTRACT FROM AUTHOR]

A machine learning method was developed, which predicts ionic conductivity based on chemical composition alone, aiming to develop an efficient method to search for lithium conductive oxides. Under the obtained guideline, the material search was focused on the Li2O-SiO2-MoO3 pseudo-ternary phase diagram, which is predicted to have high ionic conductivity (> 10-4 S·m-1). We investigated the formation range, ionic conductivity, and crystal structure of the lithium superionic conductor (LISICON) solid solution on the Li4SiO4-Li2MoO4 tie line. The ionic conductivity of the LISICON phases is about 10-7S·cm-1, which is higher than that of the end members; however, two orders of magnitude lower than that of the analogous LISICON materials. In addition, the experimental values were two or three orders of magnitude lower than the predicted conductivity values by machine learning. However, the developed prediction model can be used as an initial guideline for material exploration since the predicted values follow the trend of practical conductivity in the phase diagram. The crystal structure analysis indicated that the distance between the lithium sites and the occupancy of each lithium site in the crystal structure contributed to the decrease in ionic conductivity. This strong correlation between crystal structure and ionic conductivity was one of the reasons for the discrepancy between the predicted ionic conductivity based on chemical composition alone and the experimental value. [ABSTRACT FROM AUTHOR]

No design rules have yet been established for producing solid electrolytes with a lithium-ion conductivity high enough to replace liquid electrolytes and expand the performance and battery configuration limits of current lithium ion batteries. Taking advantage of the properties of high-entropy materials, we have designed a highly ion-conductive solid electrolyte by increasing the compositional complexity of a known lithium superionic conductor to eliminate ion migration barriers while maintaining the structural framework for superionic conduction. The synthesized phase with a compositional complexity showed an improved ion conductivity. We showed that the highly conductive solid electrolyte enables charge and discharge of a thick lithium-ion battery cathode at room temperature and thus has potential to change conventional battery configurations. [ABSTRACT FROM AUTHOR]

Solid solutions of Sn-Si derivatives with an LGPS (Li10GeP2S12)-type structure are synthesized by a solid-state reaction in the Li3PS4-Li4SnS4-Li4SiS4 quasi-ternary system. The monophasic region of the LGPS-type structure deviates from the tie line between Li10SiP2S12 and Li10SnP2S12, and the composition of the solid solution is determined to be -0.1 ≤ δ ≤ 0.5 and 0 ≤ y ≤ 1.0 in Li10+δ[SnySi1-y]1+δP2-δS12 (0.50 ≤ x ≤ 0.7 and 0 ≤ y ≤ 1.0 in Li4-x[SnySi1-y]1-xPxS4). The solid solution is formed by a double substitution that changes the Sn/Si ratio and the M4+ (Sn4+ and Si4+)/P5+ ratio, which adjusts the sizes of the lithium conduction tunnels and the lithium concentration, and contributes to the optimal conductivity value. The highest ionic conductivity value of 1.1 × 10-2 S cm-1 is achieved for the composition of Li10.35[Sn0.27Si1.08]P1.65S12 (Li3.45[Sn0.09Si0.36]P0.55S4) at 298 K, which is close to the value for the original LGPS compound (1.2 × 10-2 S cm-1). The Ge-free solid electrolyte could be suitable for practical applications in all-solid-state batteries. [ABSTRACT FROM AUTHOR]