Local Electric Field Microenvironment‐Induced Dynamic Spatial Confinement to Stabilize I+ towards 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 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 impressing lifespan of 10000 cycles is achieved at 12.6 mg cm‐2 with a capacity decay of 0.0012% per cycles, exceeding conventional iodine cathode by 20‐fold. This work provides an important reference for high‐performance four‐electron conversion zinc‐iodine batteries at high iodine loading.