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 Li₂S, P₂S₅, LiCl, and Na₂S, 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 Li₁₀GeP₂S₁₂, Li₆PS₅Cl, and Na₁₁Sn₂PS₁₂ 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.