We demonstrate the first all-solid-state lithium secondary batteries that combine MoS₂ as the cathode material with lithium argyrodite Li₆PS₅Br solid electrolyte. On the first full discharge, the battery turns into an all-solid-state Li/S battery with Mo nanoparticles of a size of around 3 nm finely dispersed in the composite cathode. The cell achieves a competitive capacity retention of 85% over 700 cycles at rates in the range of C/5 to 1 C, retaining a reversible capacity of 270 mA h g⁻¹ at C/5 and 70 °C.