Cation‐Mediated Water Activity Balance Enables High‐Rate Four‐Electron Zn‐I 2 Batteries

ABSTRACT High‐rate 4e − aqueous zinc‐iodine (Zn‐I 2 ) batteries are promising for large‐scale storage, yet they face a fundamental trade‐off: high water activity triggers hydrolysis, while conventional water‐suppression strategies severely impede kinetics. To solve this, we selected CHA‐HBr and HA‐HBr as additives to investigate the structural modulation effects on the Zn‐I 2 chemistry. Compared to its flexible linear counterpart, the rigid cyclic framework in CHA‐HBr not only enriches local electron density at the amino group via a pronounced electron‐donating inductive effect, but also imposes superior steric hindrance with restricted conformational degrees of freedom. Comparative testing and theoretical calculations prove that these synergistic structural and electronic features of CHA‐HBr facilitate a water‐depleted solvation sheath, diminishing the nucleophilic reactivity of iodine species and inhibiting the I + hydrolysis while simultaneously ensuring superior high‐rate kinetics by significantly lowering desolvation energy barriers. Consequently, the Zn‐I 2 (CHA‐HBr) battery exhibits a high capacity of 250 mAh g −1 at 20 A g −1 , maintaining stability over 20 000 cycles with a 99.8% coulombic efficiency. Furthermore, a pouch cell with a high mass loading of 14.0 mg cm −2 delivers a capacity of 0.56 Ah, validating the potential for constructing highly stable 4e − Zn‐I 2 batteries.