High lithium ion conducting Li_2S-GeS_2-P_2S_5 glass-ceramic solid electrolyte with sulfur additive for all solid-state lithium secondary batteries

摘要

Glass-ceramic Li_2S-GeS_2-P_2S_5 electrolytes were prepared by a single step ball milling (SSBM) process. Various compositions of Li_(4-x)Ge_(1-x)P_xS_4 from x = 0.70 to x = 1.00 were systematically investigated. Structural analysis by X-ray diffraction (XRD) showed gradual increase of the lattice constant followed by significant phase change with increasing GeS_2. All-solid-state LiCoO_2/Li cells were tested by constant-current constant-voltage (CCCV) charge-discharge cycling at a current density of 50 μA cm~(-2) between 2.5 and 4.3 V (vs. Li/Li~+). In spite of the high conductivity of the solid-state electrolyte (SSE), LiCoO_2/Li cells showed a large irreversible reaction especially during the first charging cycle. Limitation of instability of Li_2S-GeS_2-P_2S_5 in contact with Li was solved by using double layer electrolyte configuration: Li/(Li_2S-P_2S_5/Li_2S-GeS_2-P_2S_5)/LiCoO_2. LiCoO_2 with SSEs heat-treated with elemental sulfur at elevated temperature exhibited a discharge capacity of 129 mA h g~(-1) at the second cycle and considerably improved cycling stability.