Progress in Iodine Host Materials for Aqueous Zinc-Iodine Batteries: From Physical Confinement, Chemical Adsorption to Electrocatalysis
Aqueous zinc-iodine (Zn-I2) batteries are promising for large-scale energy storage due to their intrinsic safety, low cost, and high theoretical capacity (211 mAh g−1 for iodine). However, their practical application is hindered by the poor electronic conductivity of iodine, sluggish redox kinetics, and the shuttle effect of polyiodides. This review systematically analyzes the reaction mechanisms of iodine cathodes, including two-electron (I−/I2) and multi-electron (I−/I2/I+ and I−/I2/I+/IO3−) pathways, and identifies key bottlenecks. It then comprehensively summarizes recent advances in iodine host materials, categorized into three strategies: physical confinement, chemical adsorption, and electrocatalysis. Representative host materials such as porous carbons, covalent organic frameworks (COFs), porous aromatic frameworks (PAFs), polymers, MXenes, and Prussian blue analogs (PBAs) are discussed, with emphasis on the structure–performance relationships. The review highlights that heteroatom doping (e.g., nitrogen) enhances chemical adsorption of iodine species, while single-atom catalysts (e.g., Co, Zn) provide electrocatalytic sites that accelerate conversion kinetics. Finally, future research directions are proposed, including exploration of multi-electron systems, mechanistic elucidation of iodine conversion, development of advanced host materials, and optimization of zinc anodes, to accelerate the commercialization of Zn-I2 batteries.