Ca2+-Preintercalated V2O5 as a Dual-Function Cathode Additive for Polyiodide Anchoring in Zn–I2 Batteries

Aqueous zinc-iodine (Zn-I2) 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-I2 battery enabled by calcium-ion-preintercalated V2O5 (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 Ca2+ binding sites), the hybrid host framework achieves superior immobilization of iodine species while simultaneously shortening Zn2+ diffusion pathways, thereby facilitating efficient I0/I- redox kinetics. Furthermore, Ca-induced crystal structure modification enhances the Zn2+ transport and provides additional capacity contributions. As a result, Zn-I2 cells employing I2-loaded CaVO (CaVO/AC@I2) composite cathodes deliver a high specific capacity of 244 mAh g-1 at 0.2 A g-1, outstanding rate performance with 78.5% capacity retention at 5 A g-1, and an impressive energy density of 279 Wh kg-1, based on the combined mass of I2 and CaVO. This work presents a hybrid energy storage strategy for Zn-I2 systems, providing a feasible approach for the development of next-generation high-performance aqueous batteries.