The secondary aqueous zinc-manganese battery

Secondary aqueous zinc-ion batteries have been widely investigated recently due to their high energy density, low-cost, and environmental friendliness, compared to organic batteries. Zinc based batteries still have unstable cycle performance, especially at a low current density, which usually presents severe declination of the specific capacity during cycling. Thus, it is important to improve the electrochemical performance of the secondary aqueous zinc-ion batteries in order to broaden their applications. The electrode materials are among the key factors that influence the electrochemical performance of batteries. On the cathode side, manganese oxides have been widely applied because they have a high theoretical specific capacity. Moreover, they can be conveniently prepared or obtained from natural minerals. However, the mechanism of these cathode materials in the aqueous electrolyte is still not clear, hindering the effective improvement of their electrochemical performance. The zinc anode of the zinc-ion batteries also suffers from the hydrogen evolution, the dendrite formation, and surface passivation. Plus, there are issues such as the decomposition of water, narrow operating temperature and electrochemical stable window, involved in the aqueous electrolyte due to the intrinsic properties of water. These drawbacks seriously affect the cycle stability and the service life of the battery. Herein, the application and the mechanism of different manganese oxides, the investigation of the zinc anode, the aqueous electrolyte, and the effect of separator in the secondary aqueous zinc batteries are reviewed. Furthermore, the future prospects of this system are elaborated.