Metal-air batteries: progress and perspective

The metal-air batteries with the largest theoretical energy densities have been paid much more attention. However, metal-air batteries including Li-air/O2, Li-CO2, Na-air/O2, and Zn-air/O2 batteries, are complex systems that have their respective scientific problems, such as metal dendrite forming/deforming, the kinetics of redox mediators for oxygen reduction/evolution reactions, high overpotentials, desolution of CO2, H2O, etc. from the air and related side reactions on both anode and cathode. It should be the main direction to address these shortages to improve performance. Here, we summarized recently research progress in these metal-air/O2 batteries. Some perspectives are also provided for these research fields.