Various compositions of Li2S-Li2O-P2S5 solid electrolytes were prepared by planetary ball milling and systematically investigated. Structural analysis by X-ray diffraction (XRD) and Raman spectroscopy showed phase changes in the electrolyte corresponding to changes in conductivity. All-solid-state LiCoO2/Li cells were tested by constant-current-constant-voltage (CCCV) charge-discharge cycling at a current density of 50 渭A cm鈭?#xA0;2 between 2.5 and 4.3 V (vs. Li/Li+). In spite of reduced conductivity from introducing oxide species into a sulfide based electrolyte, increased cycle stability is observed for increased concentrations of Li2O in the electrolyte.