Sustainable aqueous metal-air batteries: An insight into electrolyte system

To meet the growing demand for sustainable and endurable energy sources, various novel energy conversion and storage systems have emerged and been developed rapidly over the last decades. Aqueous metal-air batteries have aroused much interest owing to their superior energy density, exceptional reliability, and environmental benignity. Nevertheless, the practical discharge performance of aqueous metal-air batteries is far below that desired. In comparison to the electrode materials design with much effort, relatively minor attention has been paid to the development of electrolyte systems, which undoubtedly is crucial for battery properties. In order to stimulate and promote the development of electrolyte systems for high-performance aqueous metal-air batteries, in-depth insight into the working mechanism of aqueous metal-air batteries and recent advances on electrolytes development are presented in this work. The critical issues that conventional aqueous Zn-air, Al-air, and Mg-air batteries are confronted with are thoroughly discussed, whilst some facile solutions via electrolyte modification recently proposed in the literature are reviewed. An outlook on future research into electrolyte systems for aqueous metal-air batteries is proposed.