Regulating solvation structure and absorption behavior on zinc anode by polar organic molecules to achieve durable dendrite-free zinc metal anodes for aqueous zinc-ion batteries

Abstract

Aqueous zinc ion batteries (AZIBs) have attracted much attention because of their environmental friendliness, their high theoretical capacity and their low cost, but zinc metal anodes are faced with the problems of zinc dendrites and by-products during electrochemical reactions. Herein, the non-toxic cyclic organic compound of 1.4.7.10-tetraazecyclododecane (Cy) is utilized as an additive to optimize ZnSO4 (ZS) electrolyte system, aimed at inhibiting side reactions and dendrite growth on the zinc metal surface. The Cy molecules can form coordination complexes with Zn2+ ions, thereby entering the solvated sheath of Zn2+ and the reduction of the activity of the H2O molecule. In addition, the contact between the active molecules of the H2O and the zinc metal anode is minimized and hydrogen evolution potential is decreased due to the Cy adsorbs more preferably to the surface of zinc metal than H2O, thus avoiding local alkaline enhancement and effectively inhibiting side reactions. After incorporating 10 g/L Cy into the ZS electrolyte solution, a cycle life of exceeding 4,000 h for a Zn||Zn symmetric battery at 2 mA cm-2/1 mAh cm-2 is achieved, while a stable cycling performance over 3,000 cycles with an average CE of 99.45% is attainable for a Zn//Cu asymmetric battery in the modified electrolyte system. Moreover, for a Zn//VO2 full battery with Cy-added ZS electrolyte, a capacity retention rate of 75.5% is obtained after 2,000 cycles. This work proposes a high-efficiency electrolyte additive to suppress dendrite and side reactions on the surface of zinc metal by tailoring the solvated structure of Zn2+ and interface of Zn metal and electrolyte.