Membranes for zinc-air batteries: Recent progress, challenges and perspectives

Rechargeable Zinc (Zn)-air batteries are considered to be very attractive candidates for large-scale electricity storage due to their high volumetric energy density, high safety, economic feasibility and environmental friendliness. In Zn-air batteries, the membrane allows the transport of OH- ions between the air electrode and the Zn electrode while providing a physical barrier between the two electrodes in order to prevent electrical short circuits. The performance of this battery is greatly affected by the physicochemical properties of the employed membrane. However, the development of appropriate membranes has received insufficient attention. In this paper, an overview of recent developments and a critical discussion of the state-of-the-art studies focusing on membranes for Zn-air batteries are provided. The membranes are classified in seven categories, which are discussed in light of their structure, properties and performances in Zn-air battery. Moreover, membrane synthesis and modification strategies to minimize the crossover of zincate ions and formation/growth of Zn-dendrites are presented. Finally, the remaining key challenges related to the membranes and the most promising future research directions are provided. The main objective of this work is to provide guidance for researchers and industries for the selection and development of appropriate membranes with the ultimate goal of commercializing rechargeable Zn-air batteries.