A High‐Energy Aqueous All‐Sulfur Battery

Abstract Rechargeable aqueous batteries are promising energy storage devices because of their high safety and low cost. However, their energy densities are generally unsatisfactory due to the limited capacities of ion‐inserted electrode materials, prohibiting their widespread applications. Herein, a high‐energy aqueous all‐sulfur battery was constructed via matching S/Cu 2 S and S/CaS x redox couples. In such batteries, both cathodes and anodes undergo the conversion reaction between sulfur/metal sulfides redox couples, which display high specific capacities and rational electrode potential difference. Furthermore, during the charge/discharge process, the simultaneous redox of Cu 2+ ion charge‐carriers also takes place and contributes to a more two‐electron transfer, which doubles the capacity of cathodes. As a result, the assembled aqueous all‐sulfur batteries deliver a high discharge capacity of 447 mAh g −1 based on total mass of sulfur in cathode and anode at 0.1 A g −1 , contributing to an enhanced energy density of 393 Wh kg −1 . This work will widen the scope for the design of high‐energy aqueous batteries.