Eutectic Electrolytes with Doubly‐Bound Water for High‐Stability Zinc Anodes

The aqueous zinc-ion battery has the advantages of environmental friendliness, safety, and reliability, which is expected to be used for large-scale energy storage. However, due to the high activity of water, the hydrogen evolution reaction (HER) easily occurs on the surface of the zinc anode during the charge-discharge process, which is accompanied by corrosion, by-products, and dendrite formation. Herein, a new-type eutectic electrolyte consisting of ZnCl2, tetramethylurea (TMU), and H2O with the optimal molar ratio of 1:3:1 (ZT-1) is developed for the high-stability zinc anodes. The H2O in this system is doubly bound through the coordination with Zn2+ and the hydrogen bonding with TMU, thus leading to the greatly inhibited activity of H2O. In addition, the H2O and TMU are successively stripped during the desolvation process of ZnCl2(TMU)(H2O), followed by the deposition of [ZnCl2] at the zinc interface. In this way, the tendency of HER, corrosion, dendrites, and by-products induced by the decomposition of H2O molecules at the zinc interface is minimized, enabling a much more stable plating/stripping process of Zn2+. Consequently, the Zn//Zn symmetric cell can stably cycle for >2000 h, while the Zn//Cu half cell can stably cycle 800 times with an average Coulombic efficiency of 99.5%.