An Ether‐Chain‐Functionalized Zwitterion Enables Mild Zinc‐Ion Coordination and Dual‐Site Polyiodide Capture in Aqueous Zinc–Iodine Batteries

ABSTRACT

Aqueous zinc–iodine batteries are limited by zinc dendrite growth at the anode and polyiodide shuttling at the cathode. Conventional strongly coordinating additives can regulate Zn ²⁺ solvation, but the resulting high ligand‐dissociation barrier impedes interfacial charge transfer, creating an inherent trade‐off between solvation regulation and reaction kinetics. Here, we introduce ZEG, an ether‐chain‐functionalized imidazolium sulfonate zwitterion that combines mild Zn ²⁺ coordination with dual‐site polyiodide capture. In ZEG, the imidazolium cation reduces the donor strength of the ether oxygens through electron‐withdrawing and further weakens ether‐chain coordination by electrostatically repelling Zn ²⁺ , thereby lowering the ligand‐dissociation barrier while preserving solvation‐shell regulation. Meanwhile, at the iodine cathode, the imidazolium cation and ether chain provide complementary sites that reversibly capture polyiodides through electrostatic attraction and ion–dipole interactions, respectively, thereby suppressing polyiodide shuttling and improving iodine utilization. With ZEG, Zn–I ₂ full cells sustain over 35,000 cycles at 10 A g ⁻¹ , while 300 mAh pouch cells with a high iodine loading of 30 mg cm ⁻² operate stably for over 1200 cycles. By integrating mild Zn ²⁺ coordination with reversible dual‐site polyiodide capture, this design reconciles solvation regulation with rapid interfacial charge transfer and offers an innovative molecular design principle for multifunctional electrolyte additives.