Steric Coordination Modulated Iodine Chemistry With Four-Electron Conversion for Zinc-Iodine Batteries

The advancement of high-voltage aqueous zinc-iodine batteries is impeded by the instability of I⁺ intermediates during the conversion process, which suffers from hydrolysis and poor reversibility in conventional electrolytes. To overcome these challenges, we propose a steric coordination strategy employing Cl^- and sulfonate-rich TES^- ions to modulate the coordination environment of I⁺ ions. Cl^- ions activate I⁺ ions through halide coordination, while the steric-hindrance effect of TES^- within the TES-I-Cl coordination structure effectively shields I⁺ ions from nucleophilic attacks by water-derived hydroxyl groups, collectively facilitating the reversible I^-/I⁰/I⁺ four-electron conversion. Concurrently, adsorbed ions (TES^-, Ch⁺, Cl^-) establish an electrostatic shielding layer to homogenize zinc deposition and form a dehydrated electric double layer to mitigate zinc corrosion. Moreover, the disruption of H-bond networks between the water molecules induced by the additives reduces the water activity, further suppressing I⁺ hydrolysis and water dissociation. Benefiting from these synergetic effects, the zinc-iodine battery achieves highly reversible and stable iodine chemistry, including a high-rate capability and long-term cycling stability over 42 000 cycles (capacity retention: ∼70%). This work provides fundamental insights into ion coordination chemistry for designing high-energy-density aqueous iodine storage.