Mn-oxide cathode material for aqueous Zn-ion battery: structure, mechanism, and performance

The wide-scale expansion of renewable energy sources has triggered the demand for advanced energy storage technologies. Aqueous zinc ion batteries (AZIBs) have been widely noticed in recent years because of their intrinsic safety, abundant raw materials, and environmental friendliness. Among the reported cathode materials for ZIBs, Mn-oxide materials stand out as one of the most promising candidates with their diverse structures, high capacity, and cost-effectiveness. However, the complex energy storage mechanism and unstable electrochemical properties persistently obstruct the practical application of this technology. It has been realized that these disturbances are related to the structural evolution of Mn-oxide materials during the charge/discharge process, and considerable relevant research was carried out. In this review, we present an up-to-date review of the most recent advancements and challenges concerning Mn-oxide cathode materials for aqueous zinc ion batteries. Firstly, we offer a concise summary and categorization of several widely recognized energy storage mechanisms and crystal structures. Then, we focused on sorting out the structural evolution path of Mn-oxide materials, and explored the relevant influencing factors and the relationship between phase evolution and property fluctuations. Finally, we distill key optimization strategies and provide a forward-looking perspective on future research.