Implanted Zn²⁺-Conducting Hydrogel Interphase Enables Highly Compacted Thick Iodine Electrodes for Ah-Level Aqueous...

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 Zn²⁺-conducting (PAMPS-Zn, poly(zinc 2-acrylamido-2-methylpropane sulfonate)) hydrogel interphase via in situ ultraviolet-induced polymerization, which enables local Zn²⁺ buffering, enhanced Zn²⁺ 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 Zn²⁺ and provide a local Zn²⁺ reservoir, which mitigates interfacial Zn²⁺ depletion. Meanwhile, the interconnected Zn²⁺-conducting hydrogel network facilitates Zn²⁺ 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-I₂ 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-I₂ pouch cells (∼1.2 Ah) achieve stable operation for 850 cycles, providing compelling proof-of-concept validation of this strategy.