Intercalation and Conversion Reactions of Nanosized β-MnO2 Cathode in the Secondary Zn/MnO2 Alkaline Battery

This work reports rechargeable Zn/beta-MnO2 alkaline batteries as promising stationary energy storage. Unlike commercial alkaline batteries with poor cyclic performance, the nanosized beta-MnO2 cathode in the mixture of LiOH and KOH electrolyte enables rechargeable reactions with high capacity. To unveil the underlying reaction mechanisms of nanosized beta-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 (beta-MnO2 -> gamma-MnOOH) and two-phase conversion reactions (gamma-MnOOH -> Mn-(OH)(2) -> lambda-MnO2) during the first cycle and Li and H cointercalation in the host structure of lambda-MnO2 spinel during the 100th cycle. It is remarkable that the addition of Bi2O3 in the nanosized beta-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/beta-MnO2 alkaline batteries.