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-I2) 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 I3 -, restricting polyiodide migration and promoting reversible I2/I- conversion. The strategy is validated in two complementary Zn-I2 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 (I2@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-I2 batteries.