Because of the remarkably high theoretical energy output, metal–air batteries represent one class of promising power sources for applications in next-generation electronics, electrified transportation and energy storage of smart grids. The most prominent feature of a metal–air battery is the combination of a metal anode with high energy density and an air electrode with open structure to draw cathode active materials (i.e., oxygen) from air. In this critical review, we present the fundamentals and recent advances related to the fields of metal–air batteries, with a focus on the electrochemistry and materials chemistry of air electrodes. The battery electrochemistry and catalytic mechanism of oxygen reduction reactions are discussed on the basis of aqueous and organic electrolytes. Four groups of extensively studied catalysts for the cathode oxygen reduction/evolution are selectively surveyed from materials chemistry to electrode properties and battery application: Pt and Pt-based alloys (e.g., PtAu nanoparticles), carbonaceous materials (e.g., graphene nanosheets), transition-metal oxides (e.g., Mn-based spinels and perovskites), and inorganic–organic composites (e.g., metal macrocycle derivatives). The design and optimization of air-electrode structure are also outlined. Furthermore, remarks on the challenges and perspectives of research directions are proposed for further development of metal–air batteries (219 references).

Although alkaline zinc-manganese dioxide batteries have dominated the primary battery applications, it is challenging to make them rechargeable. Here we report a high-performance rechargeable zinc-manganese dioxide system with an aqueous mild-acidic zinc triflate electrolyte. We demonstrate that the tunnel structured manganese dioxide polymorphs undergo a phase transition to layered zinc-buserite on first discharging, thus allowing subsequent intercalation of zinc cations in the latter structure. Based on this electrode mechanism, we formulate an aqueous zinc/manganese triflate electrolyte that enables the formation of a protective porous manganese oxide layer. The cathode exhibits a high reversible capacity of 225 mAh g⁻¹ and long-term cyclability with 94% capacity retention over 2000 cycles. Remarkably, the pouch zinc-manganese dioxide battery delivers a total energy density of 75.2 Wh kg⁻¹. As a result of the superior battery performance, the high safety of aqueous electrolyte, the facile cell assembly and the cost benefit of the source materials, this zinc-manganese dioxide system is believed to be promising for large-scale energy storage applications.

This tutorial review presents an introduction to the fundamentals, challenges, recent advances and prospects of rechargeable zinc-ion batteries.