The effect of solvent on reactivity of the Li2S–P2S5 system in liquid-phase synthesis of Li7P3S11 solid electrolyte

Synthesis technology for sulfide-based solid electrolytes based on liquid-phase processing has attracted significant interest in relation to achieving the optimal design for all-solid-state batteries. Herein, guidelines to solvent selection for the liquid-phase synthesis of superionic conductor Li₇P₃S₁₁ are described through systematic examination. 70Li₂S-30P₂S₅ system, a source of Li₇P₃S₁₁, is treated via a wet chemical reaction using eight organic solvents with different physical and chemical properties (i.e., dielectric constant, molecule structure, and boiling point). We reveal that the solvent's polarity, characterized by the dielectric constant, plays an important role in the formation of crystalline Li₇P₃S₁₁ via wet chemical reaction. In addition, acetonitrile (ACN) solvent with a high dielectric constant was found to lead to high-purity crystalline Li₇P₃S₁₁ and intrinsically high ionic conductivity. Further, solvents with a high boiling point and ring structures that cause steric hindrance were found to be unfavorable for the wet chemical synthesis of Li₇P₃S₁₁ solid electrolyte. Overall, we demonstrate that ACN solvent is the most suitable for the liquid-phase synthesis of a crystalline Li₇P₃S₁₁ solid electrolyte with high purity based on its dielectric constant, molecular structure, and boiling point.