Recent Development of Mn-based Oxides as Zinc-Ion Battery Cathode

Manganese-based oxide is arguably one of the most well-studied cathode materials for zinc-ion battery (ZIB) due to its wide oxidation states, cost-effectiveness, and matured synthesis process. As a result, there are numerous reports that show significant strides in the progress of Mn-based oxides as ZIB cathode. However, ironically, due to the sheer number of Mn-based oxides that have been published in recent years, there remain certain contemplations with regards to the electrochemical performance of each type of Mn-based oxides and their performance comparison among various Mn polymorphs and oxidation states. Thus, to provide a clearer indication of the development of Mn-based oxides, the recent progress in Mn-based oxides as ZIB cathode was summarized systematically in this Review. More specifically, (1) the classification of Mn-based oxides based on the oxidation states (i. e., MnO2, Mn3O4, Mn2O3, and MnO), (2) their respective polymorphs (i. e., alpha-MnO2 and delta-MnO2) as ZIB cathode, (3) the modification strategies commonly employed to enhance the performance, and (4) the effects of these modification strategies on the performance enhancement were reviewed. Lastly, perspectives and outlook of Mn-based oxides as ZIB cathode were discussed at the end of this Review.