We report that glass–ceramic Li 2S–P 2S 5 electrolytes can be prepared by a single step ball milling (SSBM) process. Mechanical ball milling of the xLi 2S·(100 − x)P 2S 5 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.