Aqueous metal-sulfide battery with enhanced stability achieved by a four-electron Ag2S electrode with a Cu2+/Cu+ redox charge carrier

Sulfur with high specific capacity is a promising candidate for electrode material of aqueous/nonaqueous metal-sulfide batteries , however, it suffers from poor cycle stability due to its poor conductivity, large volume change and shuttle effect of polysulfide . For the first time, this work employs a semiconductor Ag 2 S with good electronic conductivity as cathode of aqueous metal-sulfide batteries, which gives a four-electron electrode reaction through a three-step all-solid-state conversion reaction of Ag 2 S→Ag 3 CuS 2 →AgCuS→Cu 2 S with a specific capacity of 432 mAh g −1 . Besides, low volume expansion and the elimination of shuttle effect due to the small K sp of Ag 2 S contribute to satisfactory cycle performance. The as-proposed Cu-Ag 2 S battery shows an extremely low overpotential of 50 mV and excellent cycle performance of 9000 cycles, which are the lowest and highest values respectively among all the reported metal-sulfide batteries. By pairing with Zn of lower potential, a cascade Zn-Ag 2 S battery is designed and achieves high working voltage up to1.22 V successfully. After Ag 2 S fully reducing into Cu 2 S in discharge process, Cu 2+ in the electrolyte can provide additional capacity for the battery, thus, the cascade battery design can achieve a higher energy density , representing a promising route to energy-dense aqueous batteries.