Local Electric Field Microenvironment‐Induced Dynamic Spatial Confinement to Stabilize I + Toward High‐Mass‐Loading and Stable Zinc–Iodine Batteries

Four-electron iodine conversion chemistry (I^-/I₂/I⁺) endows zinc-iodine batteries with competitive energy density. The stability of I⁺ conversion relies on its interaction with sufficient nucleophilic species (e.g., Cl^-, Br^-). However, under high iodine loading, nucleophilic species fail to afford sufficient coordination strength and number within thick iodine cathode to stabilize I⁺, thus compromising the high-voltage plateau and capacity. Here, we effectively spatially confine nucleophilic species (Cl^-) on the cathode by ─C─N⁺-induced localized electric field (LEF) microenvironment in polyquaternary ammonium iodide (PDDA-I). Spatial confinement maximizes Cl^- concentration on the cathode ensuring highly reversible I⁰/I⁺ conversion, even in the low-concentrated ZnCl₂ addition and high iodine loading. Importantly, the dynamically regulated Cl^- maintains a balance with iodine species at the ─C─N⁺ sites during cycling, effectively limiting the shuttling effect of polyiodides. Consequently, even adopting a high iodine loading of 16.03 mg cm^-2, the PDDA-I still maintains a distinct four-electron-conversion dual voltage plateau with a remarkable capacity of 4.97 mAh cm^-2. An impressive lifespan of 10 000 cycles is achieved at 12.6 mg cm^-2 with a capacity decay of 0.0012% per cycle, exceeding conventional iodine cathodes by 20-fold. This work provides an important reference for high-performance four-electron conversion zinc-iodine batteries at high iodine loading.