Triggering High Capacity and Superior Reversibility of Manganese Oxides Cathode via Magnesium Modulation for Zn//MnO2 Batteries

Abstract Aqueous zinc‐ion batteries (ZIBs) have attracted extensive attention in recent years because of its high volumetric energy density, the abundance of zinc resources, and safety. However, ZIBs still suffer from poor reversibility and sluggish kinetics derived from the unstable cathodic structure and the strong electrostatic interactions between bivalent Zn 2+ and cathodes. Herein, magnesium doping into layered manganese dioxide (Mg–MnO 2 ) via a simple hydrothermal method as cathode materials for ZIBs is proposed. The interconnected nanoflakes of Mg–MnO 2 possess a larger specific surface area compared to pristine δ‐MnO 2 , providing more electroactive sites and boosting the capacity of batteries. The ion diffusion coefficients of Mg–MnO 2 can be enhanced due to the improved electrical conductivity by doped cations and oxygen vacancies in MnO 2 lattices. The assembled Zn//Mg–MnO 2 battery delivers a high specific capacity of 370 mAh g −1 at a current density of 0.6 A g −1 . Furthermore, the reaction mechanism confirms that Zn 2+ insertion occurred after a few cycles of activation reactions. Most important, the reversible redox reaction between Zn 2+ and MnOOH is found after several charge–discharge processes, promoting capacity and stability. It believes that this systematic research enlightens the design of high‐performance of ZIBs and facilitates the practical application of Zn//MnO 2 batteries.