Recent Development and Perspectives of Flexible Zinc-Air Batteries

In recent years, flexible and wearable electronic devices have attracted increasing research, industrial, and consumer attention. In particular, flexible zinc-air batteries (ZABs) are expected to become a promising power supply source for next-generation electronic products, especially the flexible and wearable ones, because of their high theoretical energy density, high specific capacity, high safety, and adaptability to uneven surfaces like human body. In the research field of flexible ZABs, a steady progress has been observed, and various ZAB preparation methods have been recently proposed. In this review, the main achievements and limitations of the recent research related to flexible ZABs are described. Firstly, the importance and applications of ZABs are discussed, followed by the working principle and configuration of typical ZABs. In the main text, the recent development of gel electrolytes, anodes, and cathodes is reviewed in detail. Currently, one of the most important limitations in the preparation of high-performance ZABs is the selection or preparation of a suitable gel electrolyte. A good gel electrolyte should have the ability of high-water holding capacity, high and low temperature resistance, high CO2-tolerance, excellent ionic conductivity, and good mechanical ductility. Several gel electrolytes with various functions have been developed. However, novel gel electrolytes with multifunctional properties have not been developed. In addition, interfaces between the gel electrolyte and air cathode and those between the gel electrolyte and metal anode must be investigated in detail for ZAB performance improvement. Till now, only the effects of physical compression on the electrolyte-air cathode and electrolyte-metal anode interfaces have been adopted and investigated. Moreover, the air cathode and metal anode must exhibit high flexibility to expand the application scope of ZABs as flexible power supplies. Carbon cloth has been typically used as the substrate of the air cathode; however, carbon corrosion occurs under high potential, which needs to be overcome. Meanwhile, the use of nickel mesh or copper foam as the substrate for the cathode will make the flexible ZABs too rigid and not bendable. For the metal anode, mostly zinc sheet or zinc spring have been used to meet the demand of flexibility. However, if novel strategies for the development of doped zinc anodes are investigated, such as those based on the utilization of zinc powder-metal combination, ZAB performance will be significantly improved. If the above-mentioned limitations are overcome, flexible ZABs will not be limited to laboratory use, and can be widely applied in commercial wearable electronic products. Furthermore, the challenges and future perspectives of ZABs are discussed in this review.