Anhydrous deep eutectic electrolyte: Enabling dendrite-free and highly stable zinc anodes

Abstract

Zinc ion batteries (ZIBs) hold considerable theoretical promise due to their intrinsic advantages of cost-effectiveness and environmental sustainability. However, corrosion, hydrogen evolution reaction (HER) and dendrite problems associated with aqueous electrolytes severely limit the practical application of ZIBs. Here, we report a completely anhydrous deep eutectic electrolyte composed of choline chloride (ChCl), urea and ZnCl₂, achieving dendrite-free growth and ultra-long cycling stability. ChCl, urea, and ZnCl₂ are interconnected through hydrogen bonds to form the deep eutectic electrolyte, which broadens the electrochemical stability window (3.4 V vs. Ag/AgCl). In anhydrous deep eutectic electrolytes, the absence of water molecules results in the formation of a unique solvated structure of [ZnCl₄(urea)]²⁻. The higher nucleation overpotential due to the complex intermolecular interactions favor the deposition of Zn²⁺ as small nuclei, which promotes compact Zn nucleation behavior and inhibits the formation of Zn dendrites. In addition, the urea protective layer adsorbed on the surface of the Zn anode provides effective corrosion protection. Benefiting from these advantages, the assembled Zn//Zn symmetric cell demonstrates exceptional cycle stability of 11500 h. The Zn||AC hybrid capacitor with the anhydrous deep eutectic electrolyte displays remarkable stability of 8000 cycles, achieving high power and energy densities of 84.0 W kg⁻¹ at 34.1 Wh kg⁻¹. Additionally, it is noteworthy that the cells using the eutectic electrolyte demonstrate excellent performance at 50 °C.