Synthesis of New Lithium Ionic Conductor Thio-LISICON—Lithium Silicon Sulfides System

Abstract

The new lithium ionic conductors, thio-LISICON (LIthium SuperIonic CONductor), were found in the ternary Li 2S–SiS 2–Al 2S 3 and Li 2S–SiS 2–P 2S 5 systems. Their structures of new materials, Li 4+ x Si 1− x Al x S 4 and Li 4− x Si 1− x P x S 4 were determined by X-ray Rietveld analysis, and the electric and electrochemical properties were studied by electronic conductivity, ac conductivity and cyclic voltammogram measurements. The structure of the host material, Li 4SiS 4 is related to the γ-Li 3PO 4-type structure, and when the Li + interstitials or Li + vacancies were created by the partial substitutions of Al 3+ or P 5+ for Si 4+, large increases in conductivity occur. The solid solution member x=0.6 in Li 4− x Si 1− x P x S 4 showed high conductivity of 6.4×10 –4 S cm −1 at 27°C with negligible electronic conductivity. The new solid solution, Li 4− x Si 1− x P x S 4, also has high electrochemical stability up to ∼5 V vs Li at room temperature. All-solid-state lithium cells were investigated using the Li 3.4Si 0.4P 0.6S 4 electrolyte, LiCoO 2 cathode and In anode.