Regulating the solvation structure and adsorption behavior in zinc anodes using polar organic molecules to achieve durable dendrite-free zinc metal anodes for aqueous zinc-ion batteries†

Aqueous zinc ion batteries (AZIBs) have attracted much attention because of their environmental friendliness, high theoretical capacity and low cost. However, zinc metal anodes face challenges of zinc dendrite formation and by-product generation during electrochemical reactions. Herein, the non-toxic cyclic organic compound 1,4,7,10-tetraazecyclododecane (Cy) was utilized as an additive to optimize a ZnSO₄ (ZS) electrolyte system, aiming to inhibit side reactions and dendrite growth on the zinc metal surface. Cy molecules could form coordination complexes with Zn²⁺ ions, thereby entering the solvated sheath of Zn²⁺ and reducing the activity of H₂O molecules. In addition, the contact between the active molecules of H₂O and the zinc metal anode was minimized, and hydrogen evolution potential was decreased as Cy adsorbed more preferentially to the surface of zinc metal than H₂O, thus avoiding local alkaline enhancement and effectively inhibiting side reactions. After incorporating 10 g L⁻¹ Cy into ZS electrolyte solution, a cycle life exceeding 4000 h was achieved for a Zn||Zn symmetric battery at 2 mA cm⁻²/1 mA h cm⁻². Additionally, stable cycling performance over 3000 cycles with an average CE of 99.45% was attained for a Zn||Cu asymmetric battery in the modified electrolyte system. Moreover, for a Zn||VO₂ full battery with the Cy-added ZS electrolyte, a capacity retention rate of 75.5% was obtained after 2000 cycles. This work proposes a high-efficiency electrolyte additive to suppress dendrite growth and side reactions on the surface of zinc metal by tailoring the solvated structure of Zn²⁺ and the interface between the Zn metal and the electrolyte.