Unveiling high functional group utilization in trace-level electrolyte additives for stable zinc anodes in aqueous zinc-ion batteries

Aqueous zinc-ion batteries suffer from zinc dendrite formation, parasitic reactions, and interfacial corrosion, which greatly hinder cycling stability. Herein, a tiny amount of small-molecule glycolic acid (GA, 0.1 wt%) with multiple functional groups as a trace-level additive is proposed to promote stable cycling behavior of the zinc electrode through primarily modulating the inner Helmholtz layer and the zinc ion solvation structure, avoiding the drawbacks associated with a large amount of additives or macromolecular additives that may excessively disturb bulk electrolyte properties and hinder ion transport. The synergistic effect reduces the interfacial active water content at the zinc anode, thereby inhibiting unexpected side reactions and facilitating homogeneous, dense Zn plating. Specifically, the higher binding energy of GA towards Zn 2+ promotes the formation of a Zn 2+ solvation shell by removing certain water molecules, thereby suppressing undesirable reactions. Electron-transfer tendency from GA to the Zn anode also increases the electric double-layer capacitance. Therefore, an outstanding coulombic efficiency of 99.89% is maintained for 2500 cycles at 2 mA cm −2 and 1 mA h cm −2 for the Zn||Cu asymmetric cells with GA additive. Full cells coupled with MnO 2 and VO 2 cathodes exhibit remarkably prolonged cycling lifespan under different current densities. Such a high-functional-group utilization strategy delivers electrochemical performance improvements with only trace amounts of additives, highlighting a cost-efficient, practical pathway for applications.