Oxygen Defects in β-MnO₂ Enabling High-Performance Rechargeable Aqueous Zinc/Manganese Dioxide Battery

Rechargeable aqueous Zn/manganese dioxide (Zn/MnO₂) batteries are attractive energy storage technology owing to their merits of low cost, high safety, and environmental friendliness. However, the β-MnO₂ cathode is still plagued by the sluggish ion insertion kinetics due to the relatively narrow tunneled pathway. Furthermore, the energy storage mechanism is under debate as well. Here, β-MnO₂ cathode with enhanced ion insertion kinetics is introduced by the efficient oxygen defect engineering strategy. Density functional theory computations show that the β-MnO₂ host structure is more likely for H⁺ insertion rather than Zn²⁺, and the introduction of oxygen defects will facilitate the insertion of H⁺ into β-MnO₂. This theoretical conjecture is confirmed by the capacity of 302 mA h g^-1 and capacity retention of 94% after 300 cycles in the assembled aqueous Zn/β-MnO₂ cell. These results highlight the potentials of defect engineering as a strategy of improving the electrochemical performance of β-MnO₂ in aqueous rechargeable batteries.