High lithium ion conducting Li sub(2S-GeS) sub(2)-P sub(2S) sub(5) glass-ceramic solid electrolyte with sulfur additive for all solid-state lithium secondary batteries

Glass-ceramic Li sub(2S-GeS) sub(2)-P sub(2S) sub(5) electrolytes were prepared by a single step ball milling (SSBM) process. Various compositions of Li sub(4-xGe) sub(1)-xP sub(xS) sub(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 sub(2. All-solid-state LiCoO) sub(2)/Li cells were tested by constant-current constant-voltage (CCCV) charge-discharge cycling at a current density of 50 [micro]A cm[super]-2 between 2.5 and 4.3 V (vs. Li/Li[super]+). In spite of the high conductivity of the solid-state electrolyte (SSE), LiCoO sub(2/Li cells showed a large irreversible reaction especially during the first charging cycle. Limitation of instability of Li) sub(2)S-GeS sub(2-P) sub(2)S sub(5 in contact with Li was solved by using double layer electrolyte configuration: Li/(Li) sub(2)S-P sub(2S) sub(5)/Li sub(2S-GeS) sub(2)-P sub(2S) sub(5))/Li CoO sub(2. LiCoO) sub(2) with SSEs heat-treated with elemental sulfur at elevated temperature exhibited a discharge capacity of 129 mA h g[super]-1 at the second cycle and considerably improved cycling stability.