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

Recently, mild aqueous rechargeable Zn-MnO 2 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 2 have been proposed as the cathodes in the literature, but the different reported performance and lack of a thorough understanding of reactions in MnO 2 cathodes greatly hinder the practical applications of mild aqueous Zn-MnO 2 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) 2 -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 2 cathodes through rational control of reaction mechanisms for high performance mild aqueous Zn-MnO 2 batteries.