Liquid-phase synthesis of a Li3PS4 solid electrolyte using N-methylformamide for all-solid-state lithium batteries

Abstract

A Li₃PS₄ solid electrolyte was directly synthesized from Li₂S and P₂S₅ by a liquid-phase reaction using N-methylformamide (NMF) and n-hexane as reaction media. After the reaction of Li₂S and P₂S₅, a yellow NMF solution was obtained. The NMF solution was dried at 180 °C for 3 hours under vacuum to remove NMF and to obtain a powder. A crystalline phase of the obtained powder from the NMF solution was attributed to Li₃PS₄ crystals, and the ionic conductivity of the obtained powder was 2.3 × 10⁻⁶ S cm⁻¹ at 25 °C. Electrode–electrolyte composite materials for all-solid-state lithium batteries were prepared by coating the Li₃PS₄ solid electrolyte onto LiCoO₂ particles using the NMF solution. SEM and EDX analysis showed that LiCoO₂ particles were uniformly coated with the Li₃PS₄ solid electrolyte. An all-solid-state cell using the LiCoO₂ particles coated with the Li₃PS₄ solid electrolyte as a positive electrode operated as a secondary battery.