Formation of the high lithium ion conducting phase from mechanically milled amorphous Li2S–P2S5 system

The fast ionic conducting structure similar to thio-Lithium Super Ionic Conductor (LISICON) phase is synthesized in the Li2S–P2S5 system. The Li2S–P2S5 glass–ceramics with the composition of xLi2S·(100−x)P2S5 (75 ≤ x ≤ 80) are prepared by the heat-treatment of mechanically milled amorphous sulfide powders. In the binary Li2S–P2S5 system, 78.3Li2S·21.7P2S5 glass ceramic prepared by mechanical milling and subsequent heat-treatment at 260 °C for 3 h shows the highest conductivity of 6.3 × 10−4 S cm−1 at room temperature and the lowest activation energy for conduction of 30.5 kJ mol−1. The enhancement of conductivity with increasing x up to 78.3 is probably caused by the introduction of interstitial lithium ions at the Li sites which affects the Li ion distribution. The prepared electrolyte exhibits the lithium ion transport number of almost unity and voltage stability of 5 V vs. Li at room temperature.