Revealing anion-evolution mediated superior bidirectional kinetics in Se-doped CuS1-xSex: a highly reversible conversion-type anode for zinc-ion battery

Anion doping has been regarded as a promising tactic for facilitating the redox reactions of conversion-type transition metal sulfide (TMS) anodes in rocking-chair zinc-ion battery (RCZIB). However, the evolution pathways of doped anion and the enhancement mechanisms of bidirectional reaction kinetics for anion-doped TMS anodes remain unrevealed during both the conversion and inverse-conversion processes. Herein, Se is selected as an appropriate anion to be doped into CuS (CuS_1-xSe_x x = 0.24) to design a highly reversible anode for RCZIB. Theoretical calculations and experimental results reveal that Se-doping significantly enhances the conversion kinetics of CuS_1-xSe_x through increased electrical conductivity, optimized Zn²⁺ adsorption behavior and reduced reaction energy barriers during discharging. Ex-situ characterizations demonstrate the dynamic evolution of Se anions, which are incorporated into the discharge product (ZnS_1-xSe_x) during the conversion process. The incorporated Se anions enhance inverse-conversion kinetics during charging via synergistic effects: boosted electrical conductivity, strengthened Cu adsorption capability and facile decomposition for ZnS_1-xSe_x. Subsequently, Se anions are reversibly re-doped into the regenerated charge product (CuS_1-xSe_x) upon reverse-conversion reaction. Benefiting from superior bidirectional reaction kinetics, CuS_1-xSe_x exhibits remarkable rate capability as well as long-term cycling stability in both half and full batteries. This exploration provides a new insight into the dynamic evolution of doped-Se and its synergistic enhancement mechanisms in bidirectional kinetics for highly reversible anion-doped TMS anodes in RCZIBs.