Synergistic Construction of In Situ Self‐Polymerized Interface and Localized pH Buffer Zone for High‐Performance Aqueous Zinc–Iodine Batteries

Aqueous zinc–iodine (Zn–I 2 ) batteries are promising for large‐scale energy storage. However, their practical use is hindered by challenges such as Zn dendrite growth, hydrogen evolution reaction (HER), corrosion, and polyiodide shuttle effect. In this study, valerolactam (VL) is employed as an organic pH buffer to address these issues. Theoretical and experimental results demonstrate that VL can regulate the electrolyte local pH while in situ polymerizing on the electrode surface to form a mechanically stable solid electrolyte interphase (SEI) protection layer, effectively suppressing HER, corrosion, and dendrite growth. Furthermore, the introduction of VL significantly regulates the solvation structure of Zn 2+ , and disrupts the inherent hydrogen bonding network, which enhances the electrochemical performance. As a result, a symmetric cell with VL‐based electrolyte achieves impressive longevity under ultra‐high current density (4000 cycles at 40 mA cm −2 and 1 mAh cm −2 ), 4.3 times higher than the counterpart in the conventional ZnSO 4 electrolytes. Moreover, VL effectively suppresses polyiodide shuttle effect and improves electrochemical stability. Consequently, Zn–I 2 full battery exhibits exceptional cycling stability, sustaining 26 500 cycles with a high‐capacity retention of 86.4%. Therefore, organic pH buffering engineering has been proved to be a promising strategy for achieving dendrite‐free, shuttle‐free Zn–I 2 batteries.