Suppressing Formation of Zn─Mn─O Phases by In Situ Ti Decoration of MnO₂ for Long Lifespan MnO₂-Zn Battery

Mildly-acidic MnO₂-Zn batteries are considered as a promising alternative for large-scale energy storage systems for their low toxicity, high safety, and low cost. Though, the degradation of MnO₂ with cycling still hinders the further development of the batteries. In this study, it is observed that the decrease in available capacity of MnO₂ with charge and discharge is accompanied by a structural transformation with the emergence of Zn─Mn─O phases. An electrodeposition test indicates that the Zn─Mn─O phase is formed from a co-precipitation of Zn and Mn during the charge process. Further, the structural change of MnO₂ is suppressed and its cycle stability is improved with the addition of TiOSO₄ as a facile electrolyte additive. As a result, under a current of 1200 mA g⁻¹, the MnO₂ electrode still gives a capacity of 230 mAh g⁻¹ for over 1500 cycles. Capacity retention is 75% after 10 000 cycles under a current rate of 4800 mA g⁻¹. These findings provide fundamental insights on the degradation mechanism of MnO₂ and a new strategy to improve the electrochemical performance of aqueous MnO₂-Zn batteries. © 2024 The Author(s). Small published by Wiley-VCH GmbH.