Ca-Preintercalated VO as a Dual-Function Cathode Additive for Polyiodide Anchoring in Zn-I Batteries.

Aqueous zinc-iodine (Zn-I) batteries have attracted considerable attention due to their abundant resources, high safety, and environmental friendliness. However, challenges inherent to conversion-type electrodes, including severe active material shuttling and suboptimal Coulombic efficiency, continue to limit their performance. Here, we present a high-performance Zn-I battery enabled by calcium-ion-preintercalated VO (CaVO) nanobelts as a cathode additive. By harnessing the synergistic effects of physical trapping (via activated carbon and interlayer confinement in CaVO) and chemical adsorption (through Ca binding sites), the hybrid host framework achieves superior immobilization of iodine species while simultaneously shortening Zn diffusion pathways, thereby facilitating efficient I/I redox kinetics. Furthermore, Ca-induced crystal structure modification enhances the Zn transport and provides additional capacity contributions. As a result, Zn-I cells employing I-loaded CaVO (CaVO/AC@I) composite cathodes deliver a high specific capacity of 244 mAh g at 0.2 A g, outstanding rate performance with 78.5% capacity retention at 5 A g, and an impressive energy density of 279 Wh kg, based on the combined mass of I and CaVO. This work presents a hybrid energy storage strategy for Zn-I systems, providing a feasible approach for the development of next-generation high-performance aqueous batteries.