Studying conversion mechanism to broaden cathode options in aqueous Zn-ion batteries

Abstract

Aqueous Zn-ion batteries (ZIBs) are regarded as alternatives to Li-ion batteries benefiting from both improved safety and environmental impact in addition to being easy to manufacture at scale. 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 Cu₂S (336.7 mA h g⁻¹) and Cu₂O (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.