Recent advances in energy storage mechanism of aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion batteries (ZIBs) have recently attracted increasing research interest due to their unparalleled safety, fantastic cost competitiveness and promising capacity advantages compared with the commercial lithium ion batteries. However, the disputed energy storage mechanism has been a confusing issue restraining the development of ZIBs. Although a lot of efforts have been dedicated to the exploration in battery chemistry, a comprehensive review that focuses on summarizing the energy storage mechanisms of ZIBs is needed. Herein, the energy storage mechanisms of aqueous rechargeable ZIBs are systematically reviewed in detail and summarized as four types, which are traditional Zn2+ insertion chemistry, dual ions co-insertion, chemical conversion reaction and coordination reaction of Zn2+ with organic cathodes. Furthermore, the promising exploration directions and rational prospects are also proposed in this review.