Recent advances and challenges in divalent and multivalent metal electrodes for metal-air batteries

Metal-air batteries (MABs), which possess exceptionally high energy density and exhibit other ideal features such as low cost, environmental benignity and safety, are regarded as promising candidates for the next generation of power sources. The performance of MABs and the challenges involved in these systems are primarily related to metal electrodes. In the present work, different types of MABs are overviewed from the perspective of the metal electrodes. Most metal electrodes that have been studied in recent years are reviewed, among which Zn, Al, Mg and Fe are highlighted. The advantages and disadvantages of each system are presented, and recent advances that address challenges such as corrosion, passivation and dendrite growth are introduced. In addition, investigations focused on revealing interactions between the metal electrodes and electrolytes or exploring electrolytes to improve the performance of metal electrodes are also discussed. Finally, a general perspective on the current situation of this field and on future research directions is provided.