Suppressing Formation of Zn─Mn─O Phases by In Situ Ti Decoration of MnO 2 for Long Lifespan MnO 2 -Zn Battery.

Mildly-acidic MnO 2 -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 2 with cycling still hinders the further development of the batteries. In this study, it is observed that the decrease in available capacity of MnO 2 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 2 is suppressed and its cycle stability is improved with the addition of TiOSO 4 as a facile electrolyte additive. As a result, under a current of 1200 mA g -1 , the MnO 2 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 MnO 2 and a new strategy to improve the electrochemical performance of aqueous MnO 2 -Zn batteries.