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

The new thio-LISICON (LIthium SuperTonic CONductor) found in the Li2S-GeS2, Li2S-GeS2-ZnS and Li2S-GeS2-Ga2S3 systems have structures related to the gamma-Li3PO4-type. Six new materials were found (Li2GeS3, Li4GeS4, Li2ZnGeS4, Li4-2xZnxGeS4, Li5GaS4 and Li4+x+delta(Ge1-delta'-xGax)S-4), and Li4+x+delta-(Ge1-delta'-xGax)S-4 showed the highest conductivity of 6.5 X 10(-5) S cm(-1) at room temperature. Our results on electrochemical measurements indicated that Li4+x+delta(Ge1-delta'-x-Ga-x)S-4 is stable up to approximate to 5 V vs. Li. An all-solid-state lithium cells using Li/Li4+x+delta-(Ge1-delta'-xGax)S-4/LiCoO2 was also examined. (C) 2000 Published by Elsevier Science B.V. All rights reserved.