Uncovering sulfur doping effect in MnO2 nanosheets as an efficient cathode for aqueous zinc ion battery

Manganese-based oxides are considered potential cathode materials for rechargeable aqueous zinc ion batteries (RAZIBs). However, structural instability and sluggish reaction kinetics are major limitations restricting their available capacity and cycle stability. Herein, sulfur doped MnO2 (S-MnO2) nanosheets is proposed as a high performance cathode for Zn-ion batteries, featuring large discharge capacity, high rate performance and long cycle life. Electrochemical measurements show a specific discharge capacity of 324 mAh g−1 at a current density of 200 mA g−1 and 205 mAh g−1 at a current density of 2000 mA g−1, which is 1.1 and 5.8 folds higher than that of pristine MnO2. The ex-situ X ray diffraction/absorption, electrochemical analysis and theoretical studies reveal that the doped sulfur atoms in oxygen sites with lower electronegativity can improve intrinsic electronic conductivity of MnO2 and weaken the electrostatic interactions with multivalent Zn2+cations, thus accelerating reaction kinetics. Moreover, sulfur doping induced amorphous surface with rich oxygen defects contributing to extra Zn storage sites with pseudocapacitve behavior. This study shines a new light on the anionic doping strategy in metal oxides for Zn ions storage and can be expanded to other cathode materials design for energy storage applications.