Tailoring electrochemical interface to regulate competition between Zn deposition and hydrogen evolution in aqueous rechargeable batteries

Abstract

The practical implementation of aqueous Zn-ion batteries (AZIBs) is hindered by the irreversibility of Zn metal anodes, which suffer from heterogeneous electrodeposition coupled with parasitic hydrogen evolution reactions (HER). While substrate engineering is essential to address this issue, the HER activity of substrates and its modulation to achieve homogeneous Zn nucleation and growth have been largely overlooked. Here, we investigate the interplay between HER suppression and Zn deposition behavior by tailoring surface chemistry of Cu current collectors. Specifically, we introduce a deep eutectic solvent (DES) treatment that simultaneously removes native oxides and forms a choline-derived organic nanolayer on Cu surface as an alternative to conventional acid or thermal pretreatments. This unique interface not only inhibits proton reduction but also promotes conformal Cu–Zn alloy formation, thereby enhancing Zn binding and further suppressing HER. Such dynamic surface evolution collectively mitigates insulating byproducts formation and enables dense Zn growth with enlarged grains (>2 μm) and a thickness closely matching that of Zn foil (106 %). Consequently, Zn anodes deposited on DES-treated Cu deliver a cumulative capacity of 5.8 Ah cm-2 at 30 % depth of discharge (DOD) and retain 2.2 Ah cm-2 even at 50 % DOD, highlighting their potential for practical, high-performance AZIBs.