Achieving High Energy Efficiency: Recent Advances in Zn-Air-Based Hybrid Battery Systems

Rechargeable Zn-air batteries (ZABs) are regarded as an attractive green energy storage technology, featured with large theoretical energy densities and intrinsic high safety factors. However, hindered by the sluggish kinetics of both oxygen reduction reaction and oxygen evolution reaction, rechargeable ZABs are confronted with some critical challenges such as low operating voltage, poor energy efficiency, and limited cycle life. Zn-air-based hybrid batteries (ZAHBs), integrating the advantages of a conventional ZAB with supplementary redox reactions, have emerged as a promising solution to address those challenges. Based on working principles, the hybrid batteries can be categorized into two groups: Zn-M/air hybrid batteries (M = Ni, Co, Ag, Cu, and Mn) and Zn-X/air hybrid batteries (X = KI, ethanol, and urea), which can achieve improved energy efficiency and density by optimizing charge-discharge voltage. Herein, a comprehensive overview of ZAHBs is provided, including the classification, latest progress, and electrochemical properties, as well as detailed discussion of relevant mechanisms. Moreover, the perspectives and opportunities for future research in the field of hybrid battery systems are also outlined. This review shall give helpful guidance on the design and application of ZAHBs, and provide important insights into the development of new electrochemical energy storage systems.