Capping Effect on High-Active Nucleated-Zn Toward Hydrogen Evolution-Free Zn Metal Batteries

Abstract

Aqueous Zn-ion batteries are promising for large-scale energy storage due to low cost and high safety. However, aqueous electrolyte induces severe side reactions at Zn anode, especially hydrogen evolution reaction (HER). Herein, it is first revealed that the freshly nucleated-Zn (FN-Zn) atoms during plating process show higher reactivity and stronger adsorption of proton than metallic Zn anode by X-ray absorption near edge structure (XANES) and corresponding extended X-ray absorption fine structure (EXAFS), and density functional theory simulations, promoting the decomposition of H₂O. Then, a universal and effective capping effect strategy is proposed to alleviate HER by electrostatically shielding FN-Zn activity. Specifically, sodium benzenesulfonate (SBS) is selected as a typical example by screening and comparing a series of electrolyte additives, in which sulfonate group with high coordination energy can be preferentially capped on FN-Zn to reduce its reactivity. Consequently, the symmetrical cell with SBS not only generates negligible amounts of H₂ by in situ electrochemical-gas chromatography but also can be up to 2550 h at 1 mA cm⁻². More importantly, the capping effect on HER-free Zn anode is verified by coin full cells exhibiting capacity retention of≈87.1% after 1000 cycles and large-area (4 × 6 cm²) pouch cells with desired performance.