Synchronous Interfacial Chemistry via a Fluorine‐Free Bifunctional Additive for Ultrastable Aqueous Zinc‐Iodine Batteries

The simultaneous interfacial instability at both electrodes of aqueous zinc‐iodine (Zn‐I 2 ) batteries remains a fundamental challenge, as conventional compartmentalized strategies often overlook their shared electrolyte environment. Here, maltol is employed as a fluorine‐free bifunctional additive to synchronize interfacial chemistry. At the zinc anode, maltol associates with water and preferentially adsorbs on the surface in a planar, cooperative configuration, reconstructing the inner Helmholtz plane (IHP) to suppress water‐/sulfate‐induced side reactions and regulate Zn nucleation/growth. At the iodine cathode, its multidentate oxygen sites anchor and destabilize I 3 − , restricting polyiodide migration and promoting reversible I 2 /I − conversion. The strategy is validated in two complementary Zn‐I 2 models. An I − catholyte cell achieved over 35,000 cycles with only 0.0007% capacity decay per cycle. In the solid iodine‐loaded porous carbon (I 2 @PC) model, a high‐loading cell delivered an areal capacity of approximately 2 mAh cm −2 and retained 83.8% capacity after 11,000 cycles. Moreover, a 0.54 Ah pouch cell provided over 250 Ah cumulative output at 5.4 mAh cm −2 and an N/P ratio of 5.37. This work demonstrates a sustainable molecular‐design strategy that synchronously stabilizes both electrodes, offering a holistic solution beyond conventional single‐electrode approaches for long‐lived, high‐performance aqueous Zn‐I 2 batteries.