Abstract
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.
Highlights
The ever-increasing global concerns over environmental and energy issues, such as air pollution, climate change and fossil fuel depletion has triggered substantial development of renewable energy technologies, electrochemical reactions of oxygen reduction at the cathode and Zn oxidation at the anode under alkaline condition
The poly(vinyl alcohol) (PVA) and poly(vinyl chloride) (PVC) polymers were dissolved in water, and the dried composite PVA/PVC film was immersed in THF in order to form a macroporous structure via a partial dissolution process
The syndiotactic polypropylene (syn-PP) nanofibers-based Zn-air battery was found to exhibit more than 40% discharge capacity improvement compared to the Whatman filter paper-based battery
Summary
The ever-increasing global concerns over environmental and energy issues, such as air pollution, climate change and fossil fuel depletion has triggered substantial development of renewable energy technologies, electrochemical reactions of oxygen reduction at the cathode and Zn oxidation at the anode under alkaline condition. Despite the relatively good chemical stability and low costs of these commercial membranes, such as Celgard® 4560 and Celgard® 5550 (Celgard LLC), a crossover of significant amounts of Zn(OH)42− species from the Zn elec trode to the air one has been reported to increase cell polarization and resulting in capacity fading of the battery (section 2.3) [83,86,87] This indicates the need for designing and developing dedicated membranes that can block zincate permeation in order to achieve a highly-effective rechargeable Zn-air flow battery [83,84,86]. The existing research gaps and strategies proposed to solve the problems associated with the currently used membranes are discussed
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