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

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 ZnCl₂ 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 ZnCl₂) dissolved in a glycerol-water solvent replenishes free Cl^- to fully activate I⁰/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.