Electrolyte Effect on the Electrochemical Performance of Mild Aqueous Zinc-Electrolytic Manganese Dioxide Batteries.

Recently, mild aqueous rechargeable Zn-MnO batteries have attracted increasing interest for energy storage due to the low cost of Zn and Mn resources, high safety, and environmental benignity. Extensive types of MnO have been proposed as the cathodes in the literature, but the different reported performance and lack of a thorough understanding of reactions in MnO cathodes greatly hinder the practical applications of mild aqueous Zn-MnO batteries. Here, we revealed the correlation between the reaction mechanisms and the used electrolytes for the mild aqueous zinc-electrolytic manganese dioxide (EMD) batteries. In optimal Zn(TFSI)-based electrolyte, the EMD cathode exhibits a mixed diffusion-controlled conversion reaction between EMD and H and diffusion-free "pseudocapacitance"-like reactions. This mechanism enables excellent cycling stability of an EMD cathode over 5000 cycles with a capacity retention of 94.6%. This study provides a useful insight into developing reversible MnO cathodes through rational control of reaction mechanisms for high performance mild aqueous Zn-MnO batteries.