Ion‐Replenishing Interlayer and Tailored Electrolyte Jointly Activate Four‐Electron Zinc–Iodine Batteries

ABSTRACT Activating four‐electron iodine chemistry in zinc–iodine (Zn–I ₂ ) batteries promises higher energy density, yet remains challenged by polyiodide shuttling and the instability of high‐valence I ⁺ species. Here, we demonstrate that a customized NH ₄ Cl‐based aqueous electrolyte, coupled with an ion‐replenishing Cl‐functionalized covalent organic framework (COF–Cl) interlayer, enables long‐lived four‐electron Zn–I ₂ batteries. The optimized electrolyte promotes I ⁺ –Cl ⁻ complexation, while the COF–Cl interlayer immobilizes polyiodides and continuously releases Cl ⁻ to stabilize I ⁺ against hydrolysis, collectively ensuring reversible I ⁻ /I ⁰ /I ⁺ redox conversion. In situ spectroscopic and theoretical analyses reveal accelerated high‐valence redox kinetics and strong I ⁺ /polyiodide interactions. As a result, the optimized cell delivers high energy density (278 Wh kg ^{− 1} ), fast kinetics (128 mAh g ^{− 1} at 10 A g ^{− 1} ), and remarkable cycling durability over 45000 cycles at –5°C with an ultralow decay rate of 0.00039% per cycle, with the strategy further validated in pouch cells under low‐temperature conditions. This work establishes an effective ion‐replenishing interlayer–electrolyte strategy for robust, high‐energy aqueous Zn–I ₂ batteries.