High capacity all-solid-state Cu–Li2S/Li6PS5Br/In batteries

Inorganic lithium ion fast conductor Li6PS5Br has high ionic conductivity and consequently is promising as solid electrolyte in all-solid-state lithium secondary batteries. Here we fabricated Li6PS5Br by ball milling and subsequent heat treatment. The argyrodite phase already formed at 300 °C and is electrochemically stable between 0 and 4 V. Preparing Cu–Li2S–argyrodite composite cathode mixtures by ball milling increases the initial charge and discharge capacity of all-solid-state Cu–Li2S/Li6PS5Br/In batteries compared to mortar-ground composite cathode mixtures. A charge capacity of 500 mAh/g and discharge capacity of 445 mAh/g were achieved using composite cathode powder ball milled for 30 min. However, batteries using composite cathode prepared by either method show similar reversible discharge capacity for a range of C rates as the capacity is mainly limited by volume change of cathode material and the mixed mobile ion effect. Rietveld refinements after 20 cycles show an incomplete conversion stage with partial Cu+ for Li+ insertion both in the active material and the solid electrolyte.