Phosphorus-doped carbon sheets decorated with SeS2 as a cathode for aqueous Zn-SeS2 battery

SeS 2 @PCS exhibits high performance as cathode for aqueous Zn batteries based on the reversible conversion of SeS 2 to ZnSe and ZnS with I 2 as redox-mediator. • SeS 2 @PCS is firstly proposed as a conversional cathode for aqueous Zn batteries. • Electrolyte additive enhances the electrochemistry of SeS 2 @PCS. • SeS 2 @PCS exhibits ultrahigh energy density and excellent cycling. • Reversible conversion from SeS 2 to ZnSe and ZnS is demonstrated. • DFT calculations reveal the critical role of electrolyte additive. Intrinsically limited by the high dependence on the host framework structure, aqueous Zn-based batteries built on intercalated cathodes suffer unsatisfactory energy density. In this work, phosphorus-doped carbon sheets (PCS) encapsulated SeS 2 (SeS 2 @PCS) is proposed as a conversional cathode for aqueous Zn-SeS 2 battery. In the electrolyte of 1 M ZnSO 4 with I 2 as additive, the electrochemical performance of SeS 2 @PCS can be remarkably boosted. It delivers a reversible capacity of 1107 mAh g −1 with a flat discharge potential of 0.74 V (versus Zn 2+ /Zn) and small polarization of 0.41 V, corresponding to energy density up to 772 Wh kg −1 (based on SeS 2 ), which is one of the highest values reported in aqueous Zn-based batteries in mild electrolyte, and keeps a capacity retention of 85% after 1000 cycles. Moreover, the reaction mechanisms are demonstrated to be the reversible conversion between SeS 2 to ZnSe and ZnS. Experimental and theoretical calculations reveal that I 2 can function as redox mediator to enhance the reversible capacity and kinetics due to the improvement of material utilization ratio, electrode/electrolyte interface compatibility and adsorption of Zn 2+ ions. This work presents the design of high performance conversional cathodes and strategy to improve the kinetics for aqueous Zn-based batteries.