Studying the Conversion Mechanism to Broaden Cathode Options in Aqueous Zinc-Ion Batteries.

Aqueous Zn-ion batteries (ZIBs) are regarded as alternatives to Li-ion batteries benefiting from both improved safety and environmental impact. The widespread application of ZIBs, however, is compromised by the lack of high-performance cathodes. Currently, only the intercalation mechanism is widely reported in aqueous ZIBs, which significantly limits cathode options. Beyond Zn-ion intercalation, we comprehensively study the conversion mechanism for Zn2+ storage and its diffusion pathway in a CuI cathode, indicating that CuI occurs a direct conversion reaction without Zn2+ intercalation due to the high energy barrier for Zn2+ intercalation and migration. Importantly, this direct conversion reaction mechanism can be readily generalized to other high-capacity cathodes, such as Cu2 S (336.7 mA h g-1 ) and Cu2 O (374.5 mA h g-1 ), indicating its practical universality. Our work enriches the Zn-ion storage mechanism and significantly broadens the cathode horizons towards next-generation ZIBs.