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

Abstract 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 H 2 O‐H 2 O within EDL structure, lowering water activity and reducing the Zn 2+ desolvation energy barrier. When coupled with an I 2 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‐I 2 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.