The construction of a “hydrophilic-hydrophobic-zinc-affinitive” gradient structure in the solid electrolyte interphase layer to achieve long-term stable cycling of zinc electrode

Aqueous zinc-ion batteries (AZIBs) have gained significant attention due to their excellent safety and high energy density. However, uncontrolled dendrite growth and side reactions on the zinc electrode severely limit their practical application. In this study, 2-Mercaptoethane sulfonate sodium (Mesna) was introduced as an electrolyte additive to address these issues. Mesna anchors to the surface of the zinc electrode, forming a unique “hydrophilic-hydrophobic-zinc-affinitive” three-gradient structure in the solid electrolyte interphase (SEI) layer. The outer layer, consisting of SO₃⁻, forms a hydrophilic interface through electrostatic interactions, effectively reducing the interfacial reaction energy barrier and enhancing the migration kinetics of Zn²⁺. The intermediate layer, composed of alkyl and thiol groups, works together to create a hydrophobic barrier, thereby inhibiting water-induced side reactions. The inner layer, made up of thiol groups, forms chemically stable Zn-S bonds through strong coordination, providing long-term stable interfacial protection and regulating zinc deposition. This multi-level synergistic mechanism enables the modified Zn||Zn half-cell to achieve a cycling life of 3500 h at 1 mA cm⁻² and maintain stable cycling for 400 h at 51.2 % depth of discharge. The molecular interface engineering strategy proposed in this study offers a novel approach for the design of high-stability AZIBs.