Glycine as a Bi-functional Electrolyte Additive for Favorable Zn Deposition

Aqueous zinc-ion batteries (ZIBs) with advantages of low cost, high safety, and eco-friendliness hold immense potential as large-scale energy storage devices. Nevertheless, the uncontrollable side reactions and Zn dendrites severely compromise the reversibility and stability of zinc anodes, hindering the practical application of ZIBs. In this study, glycine is introduced as a bi-functional additive into the ZnSO₄ electrolyte to address these challenges. Experimental results and theoretical calculations demonstrate that the glycine can effectively modulate the solvation structure of Zn²⁺, thereby suppressing the hydrogen evolution reaction (HER) and the formation of by-products. Additionally, glycine molecules preferentially adsorb onto the zinc anode, altering the interface between the Zn anode and the electrolyte. This increases the nucleation overpotential and inhibits the 2D diffusion of Zn²⁺, promoting the homogeneous deposition of Zn. As a result, the Zn||Zn symmetric cell with glycine additive displays a stable cycling performance for over 1500 h at 5 mA cm⁻² and 1 mA h cm⁻², and the Zn||Cu asymmetric cell exhibits a reversible plating/stripping process with the high stable coulombic efficiency (CE) of 98.4% over 600 cycles. This study offers a low-cost, efficient, and environmentally benign electrolyte additive for favorable Zn deposition.