Electrolyte additive screening for co-regulation of solvation and solid electrolyte interphase in aqueous zinc batteries

The development of aqueous zinc metal batteries is hindered by dendritic growth, parasitic side reactions, and unstable electrode-electrolyte interface, leading to rapid capacity fading. To address these issues, we rationally screen and identify a pair of complementary additives, methyl propionate and L-cysteine, to synergistically regulate zinc ion solvation structure and interfacial chemistry. Methyl propionate primarily lowers the energy barrier for zinc ion desolvation by weakening the interaction between zinc ions and water molecules, while L-cysteine stabilizes the interface by forming a protective and inorganic-rich solid electrolyte interphase through strong adsorption and preferential reduction. Besides, the incorporation of methyl propionate and L-cysteine reorganize the hydrogen-bond network, lower water activity, and suppress parasitic reactions. Consequently, the optimized electrolyte enables Zn||Zn symmetric cells to deliver stable plating/stripping over 500 h at 10 mA cm−2 and 10 mAh cm−2. This work demonstrates a molecular-level design strategy that integrates solvation regulation with solid electrolyte interphase engineering, providing insights into the rational design of aqueous zinc metal batteries. Aqueous zinc batteries suffer from unstable zinc interfaces and side reactions that limit their durability. Here, authors report a dual additive electrolyte design, based on methyl propionate and L-cysteine, that co-regulates zinc ion solvation and interfacial chemistry, enabling robust electrochemical performance.