Proton-Switching Regulates Interfacial Iodine Chemistry for Long-Life Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I₂) batteries are promising candidates for safe and cost-effective energy storage, yet their practical application is limited by uncontrolled iodine speciation at electrified interfaces, driving severe polyiodide shuttling and parasitic reactions that cause rapid capacity fading. Existing strategies predominantly rely on static confinement or adsorption, which cannot adapt to evolving iodine speciation during charge-discharge, causing a trade-off between shuttle suppression and redox kinetics. In this study, we report a proton-switching strategy that regulates interfacial iodine chemistry via electrochemically driven protonation-deprotonation within an imine-linked two-dimensional polymer framework, thereby dynamically rewiring interfacial electrostatics during cycling. During discharge, protonation of imine generates positively polarized C═NH⁺ sites that stabilize I^- through electrostatic interactions, enabling controlled reduction of polyiodides without accumulation. Upon charging, deprotonation restores the neutral framework, favoring polyiodide stabilization and efficient iodine oxidation. As a result, the constructed Zn-I₂ battery delivers 51 000 cycles at 20 A g^-1 at 25°C and sustains over 70 000 cycles at -20°C. This durability is retained at a high iodine loading of 35.7 mg cm^-2, delivering an areal capacity of 5 mAh cm^-2 over 2000 cycles with negligible decay, placing this system among the most durable Zn-I₂ batteries.