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

Abstract

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. CF₃ SO₃ ^- anions in the IL operating as Zn²⁺ -transfer channels is reported. Moreover, the PEDOT:PSS network retains the IL, which renders Zn²⁺ -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, S₆ ^2- is dominantly reduced by Zn to S^2- (S₆ → 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.