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

ABSTRACT 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 − /I 0 /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.