Acetamide-Caprolactam Deep Eutectic Solvent-Based Electrolyte for Stable Zn-metal Batteries.

Aqueous Zn-ion batteries (AZIBs) are promising for grid-scale energy storage. However, conventional AZIBs face challenges including hydrogen evolution reaction (HER), leading to high local pH and by-product formation on the anode. Hereby we reconstruct the hydrogen bond network in the electrolyte using a deep eutectic solvent (DES) made of acetamide (H-bond donor) and caprolactam (H-bond acceptor), which effectively suppresses the reactivity of water and broadens the electrochemical voltage stability window. The coordination between Zn 2+ and acetamide-caprolactam in DES-based electrolytes produces a unique solvation structure that promotes the preferential growth of Zn crystals along the (002) plane. This will inhibit the formation of Zn dendrites and ensure the uniform deposition of Zn-ions on the anode surface. In addition, we found that this DES-based electrolyte can form a protective membrane on the anode surface, reducing the risks of Zn corrosion. Compared to conventional electrolytes, the DES-based electrolyte shows a long-term stable plating/stripping performance with a significantly improved Coulombic efficiency from 78.18% to 98.37%. We further demonstrate that a Zn||VS 2 full-cell with the DES-based electrolyte exhibits enhanced stability after 500 cycles with 85.4% capacity retention at 0.5 A g -1 . This article is protected by copyright. All rights reserved.