Rapid Synthesis of Li₁₀GeP₂S₁₂-type Li-Si-P-S-Cl Solid Electrolytes via a Solution Method (Supporting Information)

Owing to its high ionic conductivity, Li₁₀GeP₂S₁₂ (LGPS)-type Li-Si-P-S-Cl (LSiPSCl) solid electrolytes are promising candidates for all-solid-state batteries. This study introduces an LGPS-type LSiPSCl solid electrolyte synthesized rapidly via a solution method using excess sulfur and a solvent mixture of acetonitrile, tetrahydrofuran, and ethanol to enable large-scale production. X-ray diffraction patterns reveal an LGPS-type structure as the primary phase, while FE-SEM analysis confirms the presence of few large particles exceeding 5 µm. The LSiPSCl solid electrolyte synthesized via the solution method exhibits an ionic conductivity of 2.7 mS cm⁻¹, which is comparable to that of the sample synthesized using the mechanical milling method (3.1 mS cm⁻¹). In addition, the all-solid-state battery incorporating LSiPSCl synthesized using the solution method exhibits a slightly higher discharge capacity and similar cycle stability compared with the battery containing LSiPSCl synthesized using the mechanical milling method. These results confirm that the solution method successfully produces an LSiPSCl solid electrolyte. Raman and X-ray photoelectron spectroscopy analyses reveal a carbon surface layer on the particles originating from the solvent. This surface layer is identified as a key factor contributing to the higher discharge capacity of the all-solid-state battery containing the LSiPSCl solid electrolyte synthesized using the solution method. These findings suggest that the surface layer on the particles and/or particle characteristics are critical advantages of solution synthesis for improving battery performance.