In-situ amorphous transformation of VO in VO/VO for aqueous zinc ion batteries with high capacity and long cycles.

Rechargeable aqueous zinc-ion batteries (AZIBs) are attractive due to their superior safety, rich zinc resources, and cost-efficient. Vanadium-based oxides, as popular cathode materials, are inevitably subject to dissolution in aqueous solutions, and inherent low electrical conductivity and sluggish reaction kinetics, significantly impeding the performances in Zn storage. In this study, VO/VO composites are successfully prepared by a novel three-roll milling technique combined with high-temperature treatment to improve these shortcomings. The results demonstrate that the VO/VO electrode sustains excellent cycling (316.0 mAh g at 5 A g after 4000 cycles) and superior rate performance (186.69 mAh g at 20 A g). Ex-situ characterization reveals that the mechanism involves the co-intercalation of HO with Zn. It is found by testing in different electrolytes that VO is gradually amorphous in aqueous electrolyte during cycling, which greatly improves the structural stability and enhances the ability for capturing Zn. Moreover, it is demonstrated by calculations that a higher degree of amorphization promotes the adsorption of Zn. The present work provides a new idea for the development and mechanism explanation of high-performance AZIB materials.