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

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.