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 100th 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.