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

Mildly-acidic MnO-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 MnO with cycling still hinders the further development of the batteries. In this study, it is observed that the decrease in available capacity of MnO 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 MnO is suppressed and its cycle stability is improved with the addition of TiOSO as a facile electrolyte additive. As a result, under a current of 1200 mA g, the MnO electrode still gives a capacity of 230 mAh g for over 1500 cycles. Capacity retention is 75% after 10 000 cycles under a current rate of 4800 mA g. These findings provide fundamental insights on the degradation mechanism of MnO and a new strategy to improve the electrochemical performance of aqueous MnO-Zn batteries.