An analysis of the electrochemical mechanism of manganese oxides in aqueous zinc batteries

Abstract

Because of their high energy density, safety, eco-friendliness, and sustainability, aqueous rechargeable zinc batteries (ARZBs) have attracted burgeoning interests. Manganese oxide cathodes are particularly attractive because they are obtained from earth-abundant and non-toxic materials. However, the diversity of mechanisms that explain the electrochemistry with Zn metal anodes in mildly acidic media hinders ARZBs further development. In brief, a specific manganese oxide polymorph, typically MnO2, in mildly acidic elec-trolytes has been reported to exhibit different reaction mechanisms under similar electrochemical conditions. Moreover, the recently discussed dissolution/deposition process of MnO2 in both strong and mildly acidic electrolyte media has revolutionized the conven-tional intercalation chemistry. To this end, this perspective aims to clarify and seek possible convergence of the conflicting electro-chemical mechanisms for mildly acidic Zn-MnO2 batteries. We also suggest future research directions and opportunities for commer-cialization that may evolve from the recently researched acid-alka-line Zn-MnO2 battery technologies.