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.