Interhalogen Complexation Suppresses Hydrolysis-Corrosion Cross-Talk Degradation in Aqueous Two-Electron Zn-I2 Batteries.

Aqueous two-electron Zn-I2 (I‒/I0/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-I2 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-I2 batteries and establishes interhalogen complexation as an effective electrolyte design strategy for high-energy, long-lifetime aqueous iodine-based batteries.