A Hydroxylated Zwitterion Enables Dual-Modal Synergy for Stable Zinc-Iodine Batteries

Abstract

Aqueous zinc-iodine(Zn-I₂) batteries face a universal challenge: soluble polyiodides formed at the cathode migrate to the zinc anode, causing severe active-material loss and Zn corrosion. Here, we report a hydroxylated betaine-type zwitterion that enables dual-modal interfacial control at both electrodes in Zn-I₂ batteries. At the zinc anode, the synergistic sulfonate-hydroxyl pair disrupts the Zn²⁺ hydration shell, decouples Zn²⁺-SO₄^2- interactions, increases the Zn²⁺ transference number, and promotes preferential (002) deposition below a compact, zwitterion-derived solid-electrolyte interphase. At the iodine cathode, the ammonium-hydroxyl pair captures polyiodides to suppress shuttling while maintaining an electrochemically beneficial polyiodide concentration. Owing to this adaptive regulation, Zn||Zn symmetric cells and Zn||Cu half-cells exhibit exceptional cycling stability (>8000 h) at 1 mA cm^-2 ; Zn-I₂ full cells deliver 50,000 cycles at 20 A g^-1 with an ultralow per-cycle capacity fade of 0.00012%; and pouch cells (42.9 mg cm^-2 of I₂) show only 0.026% capacity loss per cycle. This work establishes a paradigm of adaptive interfacial control that reconciles the distinct electrode processes in Zn-I₂ batteries.