Cation-Engineered Gradient Interfacial Structure Toward Dendrite-Free and Shuttle-Free Aqueous Zn-Iodine Batteries

Uncontrolled dendrite growth, water-induced side reactions, and polyiodide shuttling remain critical in aqueous Zn-iodine batteries (AZIBs). Herein, an "electric double layer (EDL)-directed regulator" strategy utilizing amphiphilic acetylcholine cation (ACh⁺) as interfacial modifiers is proposed. The directed adsorption of ACh⁺ on the Zn anode surface assembles a hydrophobic-hydrophilic gradient interfacial structure. The hydrophobic inner layer establishes a water-poor EDL structure, reducing direct Zn-electrolyte contact and suppressing side reactions. Meanwhile, the hydrophilic outer layer disrupts the original H₂O-H₂O within EDL structure, lowering water activity and reducing the Zn²⁺ desolvation energy barrier. When coupled with an I₂ cathode, dissolvable polyiodide anions are captured by ACh⁺ via electrostatic interactions, effectively inhibiting the polyiodide shuttles. Consequently, the Zn anode with optimized EDL delivers a high Coulombic efficiency (CE) of 99.82%, with remarkable stability over 3700 h at 1.0 mA cm^-2/1.0 mAh cm^-2 and 1500 h at 10 mA cm^-2/1.0 mAh cm^-2. Moreover, the Zn-I₂ full cell exhibits an ultralow capacity decay rate of merely 0.000512% per cycle over 25000 cycles at 2.0 A g^-1. This work provides an effective EDL regulation strategy for optimizing the Zn anode interfacial chemistry toward the advanced AZIBs.