Formation Mechanism of Thiophosphate Anions in the Liquid-Phase Synthesis of Sulfide Solid Electrolytes Using Polar Aprotic Solvents

摘要

Preparation of sulfide-based Li-ion conductive solid electrolytes by a liquid-phase process has been proposed as an effective route for industrial scaling-up. However, reaction mechanisms in the liquid-phase synthesis or the role of solvents in the reactions is not yet well understood. Here, the reaction between Li_(2)S and P_(2)S_(5) in the composition of 50:50 mol mediated by a polar aprotic solvent (acetonitrile) was investigated. The study of the crystal and local structure of the 50Li_(2)S·50P_(2)S_(5) sample revealed large chemical changes upon crystallization, highlighting the initial formation of a polymer-like (PS_(3)~(–))_(n ) intermediate. On the basis of the (PS_(3)~(–))_(n ) intermediate, the reaction pathways for the formation of P_(2)S_(6)~(2–), PS_(4)~(3–), and P_(2)S_(7)~(4–) anions are elucidated. These findings give a deeper insight into the reaction mechanisms governing the liquid-phase synthesis of sulfide solid electrolytes and provide more specific criteria for designing novel materials with superior characteristics through this liquid-phase approach.