Intercalation and conversion reactions of nanosized β-MnO₂ cathode in the secondary Zn/MnO₂ alkaline battery

This work reports rechargeable Zn/β-MnO₂ alkaline batteries as promising stationary energy storage. Unlike commercial alkaline batteries with poor cyclic performance, the nanosized β-MnO₂ cathode in the mixture of LiOH and KOH electrolyte enables rechargeable reactions with high capacity. To unveil the underlying reaction mechanisms of nanosized β-MnO₂, we combine thermodynamic frameworks with experimental characterization, including electrochemistry, X-ray diffraction, and X-ray photoelectron spectroscopy. The results demonstrate a series of proton intercalation reaction (β-MnO₂ → γ-MnOOH) and two-phase conversion reactions (γ-MnOOH → Mn(OH)₂ → λ-MnO₂) during the first cycle and Li and H cointercalation in the host structure of λ-MnO₂ spinel during the 100^th cycle. It is remarkable that the addition of Bi₂O₃ in the nanosized β-MnO₂ cathode exhibits outstanding capacity. After 100 dischargings, the battery demonstrates a capacity of 316 mA h g^-1. Our findings can serve in the tailored cathode design in high capacity and rechargeable Zn/β-MnO₂ alkaline batteries.