Synthesis and Electrochemical Properties of Li₃CuS₂ as a Positive Electrode Material for All-Solid-State Batteries

All-solid-state batteries using flame-retardant inorganic solid electrolytes boast of advantages such as safety and wide usable temperature ranges. Although Li2S with an antifluorite-type structure has a high theoretical capacity, it is challenging to use in all-solid-state batteries because of the insulating nature. Here, we report an antifluorite-type Li3CuS2 as a sulfide positive electrode active material with high electronic conductivity. All-solid-state batteries using Li3CuS2 were successfully operated without the addition of conductive additives to the positive electrode. The Li3CuS2 exhibited an initial charge–discharge capacity of 380 mAh g–1 with an average discharge voltage of 2.1 V vs Li+/Li.