Interhalogen Complexation Suppresses Hydrolysis–Corrosion Cross‐Talk Degradation in Aqueous Two‐Electron Zn–I 2 Batteries

Abstract

ABSTRACT Aqueous two‐electron Zn–I 2 (I ‒ /I 0 /I + ) batteries offer high theoretical energy density; however, their practical operation is limited by hydrolysis of iodine monochloride (ICl), which induces cathode irreversibility and Zn‐anode degradation. Here, we introduce an ether‐based complexation strategy that stabilizes interhalogen species and mitigates cross‐talk degradation in aqueous two‐electron Zn–I 2 batteries. Density functional theory calculations and spectroscopic analyses reveal the selective formation of an ICl–15‐crown‐5 (15C5) complex among various linear and cyclic ethers. The electron‐deficient iodine center in ICl is coordinated by electron‐rich oxygen atoms in 15C5 through lone‐pair donor–acceptor interactions. In situ UV–vis spectroscopy, distribution of relaxation times analysis, intrinsic reaction coordinate calculations, and real‐time pH monitoring collectively demonstrate that ICl–15C5 complexation effectively suppresses ICl hydrolysis. Consequently, the 15C5‐containing electrolyte shows stable capacity retention over 1000 cycles at 1000 mA g −1 with high Coulombic efficiency in coin cells, and sustains pouch‐type cell operation with a high discharge capacity of approximately 350 mA h g −1 over 150 cycles. This work identifies cross‐talk degradation driven by ICl hydrolysis as a critical bottleneck in two‐electron Zn–I 2 batteries and establishes interhalogen complexation as an effective electrolyte design strategy for high‐energy, long‐lifetime aqueous iodine‐based batteries.