Preparation of Li₂S-P₂S₅ Based Glass-Ceramic Solid Electrolytesand their Application to All-Solid-State Lithium Secondary Batteries

Abstract

Glass-ceramics obtained by heating mechanically milled Li₂S-P₂S₅ glasses over crystallization temperature exhibited high lithium ion conductivity around 10^-3 S cm^-1 at room temperature. Crystals precipitated in the glass-ceramics largely changed with heat treatment temperature, and hence their conductivity also strongly depended on the temperature. In particular, the glass-ceramics obtained by heating at 230 ^oC had a crystal structure similar to highly conductive sulfide Li_3.25Ge_0.25P_0.75S₄, which exhibited the highest ambient conductivity in a series of thio-LISICON phases. Furthermore, Li₂S-P₂S₅ glass-ceramics added with small amounts of oxide such as P₂O₅ exhibited lower activation energy for conduction than pure sulfide glasses. All-solid-state In/LiCoO₂ cells using Li₂S-P₂S₅ glass-ceramics as solid electrolytes worked as lithium secondary batteries and the cell kept high discharge capacity around 100 mAh g^-1 over 200 cycles with charge-discharge efficiencies around 100 %.