Universal Solution Synthesis of Sulfide Solid Electrolytes Using Alkahest for All‐Solid‐State Batteries

The wet-chemical processability of sulfide solid electrolytes (SEs) provides intriguing opportunities for all-solid-state batteries. Thus far, sulfide SEs are wet-prepared either from solid precursors suspended in solvents (suspension synthesis) or from homogeneous solutions using SEs (solution process) with restricted composition spaces. Here, a universal solution synthesis method for preparing sulfide SEs from precursors, not only Li2 S, P2 S5 , LiCl, and Na2 S, but also metal sulfides (e.g., GeS2 and SnS2 ), fully dissolved in an alkahest: a mixture solvent of 1,2-ethylenediamine (EDA) and 1,2-ethanedithiol (EDT) (or ethanethiol). Raman spectroscopy and theoretical calculations reveal that the exceptional dissolving power of EDA-EDT toward GeS2 is due to the nucleophilicity of the thiolate anions that is strong enough to dissociate the GeS bonds. Solution-synthesized Li10 GeP2 S12 , Li6 PS5 Cl, and Na11 Sn2 PS12 exhibit high ionic conductivities (0.74, 1.3, and 0.10 mS cm-1 at 30 °C, respectively), and their application for all-solid-state batteries is successfully demonstrated.