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

Abstract Four‐electron iodine conversion chemistry (I −/ I 2 /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 I 0 /I + conversion, even in the low‐concentrated ZnCl 2 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.