Molecular Tailoring of Helmholtz Plane by a Cyclic Imino Additive: Inhibiting Hydrogen Evolution Reaction and Enabling Dendrite‐Free Zn Anodes for High‐Performance Hybrid Zn/Na Aqueous Batteries

Abstract Aqueous zinc‐sodium (Zn/Na) hybrid ion batteries (AZSIBs) combine the high energy density of aqueous Zn‐ion batteries and the high safety of aqueous Na‐ion batteries. However, AZSIBs suffer from rapid performance degradation​ because of unregulated zinc deposition and unwanted chemical reactions. To address these challenges, this study introduces a new type of additive, 5,5‐dimethylhydantoin (DMH), which has a cyclic structure and an imine group. It can reconstruct the Helmholtz plane of the anode while inhibiting the hydrogen evolution reaction and promoting the epitaxial growth of the zinc (002) plane. Theoretical and experimental results reveal that DMH molecules preferentially adsorbed on the anode surface, displacing active H ₂ O from the inner Helmholtz Plane (IHP), and Zn ²⁺ is deposited in a compact and dense manner along the Zn (002) plane. As a result, Zn//Zn symmetric cell demonstrates stable cycling for 2400 h without a short circuit. Moreover, Zn//V ₂ O ₅ full cell cycles stably for over 3,000 cycles at a current density of 3 A g ⁻¹ . This work establishes a paradigm of additive engineering for developing high‐performance AZSIBs.