Communication—Redox Behavior of Cu2S in Li2S-Dissolving Aprotic Electrolyte for Sulfide-Ion Batteries

The redox behavior of Cu 2 S in a Li 2 S-dissolving aprotic electrolyte was investigated to examine the practical viability of rechargeable batteries using sulfide ions as carrier ions. We established aprotic electrolytes, dimethyl sulfoxide and dimethylformamide containing S 2− at over 0.10 M concentration by adding NH 4 NO 3 to increase the solubility of Li 2 S, which is hardly soluble in almost all aprotic solvents. Two redox reactions of Cu 2 S, Cu/Cu 2 S and Cu 2 S/CuS, were observed at −0.25 V and 0.60 V vs Mo, respectively. In addition, it was found that elemental S is electrodeposited/stripped at approximately 0.1 V vs Mo on graphite but not on platinum.