We report that glass-ceramic Li2S-P2S5 electrolytes can be prepared by a single step ball milling (SSBM) process. Mechanical ball milling of the xLi2S·(100 − x)P2S5 system at 55 °C produced crystalline glass-ceramic materials exhibiting high Li-ion conductivity over 10−3 S cm−1 at room temperature with a wide electrochemical stability window of 5 V. Silicon nanoparticles were evaluated as anode material in a solid-state Li battery employing the glass-ceramic electrolyte produced by the SSBM process and showed outstanding cycling stability.