Acetamide‐Caprolactam Deep Eutectic Solvent‐Based Electrolyte for Stable Zn‐Metal Batteries

Abstract

AbstractAqueous 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 the hydrogen bonds in the aqueous electrolyte are reconstructed by using a deep eutectic co‐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 Zn2+ 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, it is 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%. It is further demonstrated that a Zn||VS2 full‐cell with the DES‐based electrolyte exhibits enhanced stability after 500 cycles with 85.4% capacity retention at 0.5 A g−1.