Initiating a Reversible Aqueous Zn/Sulfur Battery through a “Liquid Film”

Sulfur cathodes have been under intensive study in various systems, such as Li/S, Na/S, Mg/S, and Al/S batteries. However, to date, Zn/S chemistry has never been reported. The first reliable aqueous Zn/polysulfide system activated by a “liquid film” comprising 4‐(3‐butyl‐1‐imidazolio)‐1‐butanesulfoni ionic liquid (IL) encapsulated within PEDOT:PSS. CF 3 SO 3 − anions in the IL operating as Zn 2+ ‐transfer channels is reported. Moreover, the PEDOT:PSS network retains the IL, which renders Zn 2+ ‐transfer channels and a polysulfide cathode with enhanced structural stability. The Zn/polysulfide system delivers extraordinary capacity of 1148 mAh g −1 and overwhelming energy density of 724.7 Wh kg −1 cathode at 0.3 Ag −1 . During the discharging phase, S 6 2− is dominantly reduced by Zn to S 2− (S 6   →  S 2− ). During the charging phase, these short chains are oxidized to form long‐chain Zn x Li y S 3‐6 . A further optimized high‐concentrated salt electrolyte is used to improve the reversibility of the battery, demonstrating an extended lifetime over 1600 cycles at 1 Ag −1 with a capacity retention of 204 mAh g −1 . This facile approach and the superior performance of the developed aqueous Zn/S chemistry provide a new platform for sulfur‐based battery and potentially solve the problems of other metal/sulfur batteries.