Dual‐Zone Chloride Engineering to Enable Ultra‐Stable Two‐Electron Zinc‐Iodine Batteries

Abstract

Abstract Zinc‐iodine batteries (ZIBs) with organic iodine hosts that harness the I − /I + conversion offer a promising route to high‐energy storage but remain limited by rapid capacity decay. Conventional approaches employing high‐concentration ZnCl 2 electrolytes effectively activate I − /I + conversion in carbon hosts but prove incompatible with organic systems. Here, its excess free Cl − is identified to displace polyiodide from organic iodine hosts, thereby triggering an irreversible I − /I + process. To address this, a dual‐zone chloride engineering strategy is introduced that spatially separates chloride environments into complementary domains. At the cathode, a non‐dissociative hydrophobic salt (trioctylmethylammonium chloride) establishes a confined Cl − ‐rich, water‐deficient environment, suppressing polyiodide desorption and preventing hydrolytic I⁺ decomposition. In the electrolyte, a chloride‐liberating salt (0.2 m ZnCl 2 ) dissolved in a glycerol‐water solvent replenishes free Cl − to fully activate I 0 /I⁺ conversion while enhancing high‐voltage tolerance. This cooperative design delivers an organic‐based two‐electron ZIB with 87.0% capacity retention over 11,000 cycles, and validates its universality in a carbon‐based ZIB retaining 87.2% capacity after 35,000 cycles. By uniting cathodic confinement with electrolyte liberation, dual‐zone chloride engineering establishes a generalizable framework for stabilizing two‐electron iodine redox chemistry, paving the way toward durable, high‐energy aqueous ZIBs.