Recent progress and perspectives on aqueous Zn-based rechargeable batteries with mild aqueous electrolytes

Aqueous rechargeable batteries are regarded as one of the ultimate solutions needed to solve the safety problems of conventional rechargeable batteries using organic electrolytes, but the challenge is to find suitable anode materials that will work well in the narrow electrochemical window of water with reasonable capacities. Aqueous Zn-based rechargeable batteries using Zn anode, a mild aqueous electrolyte, and Zn2+ or another monovalent/multivalent metal ion as charge carrier have been receiving extensive attention in recent years due to their low cost, high safety, environmental friendliness, and acceptable energy density. Although it is still a challenge to achieve high performance aqueous Zn-based rechargeable batteries with a long cycle life and a high energy density, considerable efforts have been devoted to overcoming the drawbacks associated with the Zn anode, electrolyte, and cathode materials. In this review, the recent advances on the aqueous Zn-based rechargeable batteries, including aqueous Zn ion batteries (AZIBs) and aqueous Zn hybrid batteries (AZHBs), are systematically reviewed. We first summarize and discuss the Zn anode behaviour and strategies to restrain the dendrite formation and improve the plating/stripping efficiency. Then, the cathode materials used in AZIBs and AZHBs are summarized in terms of their structures, electrochemical performance, and reaction mechanism, as well as the strategies used to improve their electrochemical performance. The electrolytes and their effects on the electrochemical performance of Zn anode and cathode materials are also discussed. Finally, the challenges for and perspectives on AZIBs and AZHBs are summarized to guide research directions in the future.