Implanted Zn 2+ ‐Conducting Hydrogel Interphase Enables Highly Compacted Thick Iodine Electrodes for Ah‐Level Aqueous Zinc–Iodine Pouch Batteries

Increasing the compaction density of dry‐processed thick iodine cathodes is essential for enhancing energy density, yet remains hindered by sluggish reaction kinetics and aggravated polyiodide shuttling. Herein, we report an implanted Zn 2+ ‐conducting (PAMPS‐Zn, poly(zinc 2‐acrylamido‐2‐methylpropane sulfonate)) hydrogel interphase via in situ ultraviolet‐induced polymerization, which enables local Zn 2+ buffering, enhanced Zn 2+ transport, and suppression of polyiodide migration in highly compacted dry‐processed iodine cathodes. Abundant sulfonate groups in polymeric chains serve as immobilized anionic sites that coordinate Zn 2+ and provide a local Zn 2+ reservoir, which mitigates interfacial Zn 2+ depletion. Meanwhile, the interconnected Zn 2+ ‐conducting hydrogel network facilitates Zn 2+ transport through the thick electrode, reducing reliance on conventional electrolyte‐permeation‐mediated ion transport in dry‐processed electrodes, which is intrinsically limited by the hydrophobic nature of the PTFE binder and high ionic tortuosity. Importantly, the negatively charged, water‐regulated hydrogel interphase also suppresses polyiodide diffusion through electrostatic repulsion and reduced water‐driven dissolution. Consequently, under high compaction conditions (∼0.5 g cm −3 ), Zn–I 2 batteries incorporating PAMPS‐Zn interphase achieve a high areal capacity of 9.6 mAh cm −2 at 0.5 C and an ultralong lifespan exceeding 4400 cycles at 5 C. Notably, Ah‐level Zn‐I 2 pouch cells (∼1.2 Ah) achieve stable operation for 850 cycles, providing compelling proof‐of‐concept validation of this strategy.