A synergistic dual additive strategy for constructing gradient hydrophobic interfaces toward ultrastable aqueous zinc metal anodes

Abstract

Aqueous zinc-ion batteries (AZIBs) effectively address critical concerns of energy storage such as flammability risks, cost, and ionic conductivity. However, their practical deployment is severely hampered by water-induced parasitic reactions and inhomogeneous zinc deposition. Therefore, restricting the content and activity of water at the electrode interface is of paramount importance. Herein, we propose a novel synergistic hydrophobic-adsorption and competitive-coordination (H-C) strategy to in situ construct a functional gradient hydrophobic interface on the zinc anode, convincingly revealed by molecular dynamics simulations and sum-frequency generation vibrational spectroscopy. This is achieved by introducing trace amounts of benzylideneacetone (BZA) as the hydrophobic-adsorption unit (H) and ethanol as the competitive-coordination unit (C) into a 2 M ZnSO₄ electrolyte. The H-unit (BZA) preferentially adsorbs onto the zinc anode surface, forming a dense, waterproof inner layer that suppresses hydrogen evolution and corrosion reactions. Concurrently, the C unit (ethanol) modulates the outer solvation sheath of Zn²⁺ and disrupts the interfacial hydrogen-bond network, thereby facilitating Zn²⁺ desolvation and transport. Consequently, the engineered interphase enables a Zn‖Zn symmetric cell to achieve an extended cycling lifespan of up to 3000 hours at 1 mA cm⁻² and 1 mAh cm⁻², a high average Coulombic efficiency of 99.2% in Zn‖Cu half cells, and exceptional deep charge−discharge capability (85.4% DOD). Furthermore, when configured with δ-MnO₂, the full cell retains 84% capacity after 2000 cycles at 5C and exhibits remarkably suppressed self-discharge. This work demonstrates a rational design principle of synergistic functional additives for constructing advanced electrode–electrolyte interphases.