Synthesis of a new lithium ionic conductor, thio-LISICON–lithium germanium sulfide system

The new thio-LISICON (LIthium SuperIonic CONductor) found in the Li2S–GeS2, Li2S–GeS2–ZnS and Li2S–GeS2–Ga2S3 systems have structures related to the γ-Li3PO4-type. Six new materials were found (Li2GeS3, Li4GeS4, Li2ZnGeS4, Li4−2xZnxGeS4, Li5GaS4 and Li4+x+δ(Ge1−δ′−xGax)S4), and Li4+x+δ–(Ge1−δ′−xGax)S4 showed the highest conductivity of 6.5×10−5 S cm−1 at room temperature. Our results on electrochemical measurements indicated that Li4+x+δ(Ge1−δ′−x–Gax)S4 is stable up to ≈5 V vs. Li. An all-solid-state lithium cells using Li/Li4+x+δ–(Ge1−δ′−xGax)S4/LiCoO2 was also examined.