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

Abstract

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.