A Binary Hydrate-Melt Electrolyte with Acetate-Oriented Cross-Linking Solvation Shells for Stable Zinc Anodes.

Abstract

Aqueous zinc-ion batteries (ZIBs) with low cost and high safety are promising energy-storage devices. However, ZIBs with metal Zn anodes usually suffer from low coulombic efficiency and poor cycling performance due to the occurrence of side reactions on the Zn anodes. Here, a binary hydrate-melt ZnCl₂ /Zn(OAc)₂ electrolyte is designed to suppress the hydrogen evolution reaction and by-product formation on Zn anodes by adjusting the Zn²⁺ solvation structure. In the solvation structure of the hydrate-melt ZnCl₂ /Zn(OAc)₂ electrolyte, the carboxylate group in OAc^- will coordinate with the Zn²⁺ , which will weaken the interaction between Zn²⁺ and H₂ O molecules to achieve higher ionization energy of H₂ O molecules. Simultaneously, these carboxylate groups of OAc^- can serve as H-bond acceptors to construct H-bonds with H₂ O molecules in their neighboring solvation structures, forming a cross-linking H-bond network. Such a cross-linking H-bond network further suppresses the water activity in ZnCl₂ /Zn(OAc)₂ electrolyte. As a result, in such an electrolyte, the side reactions are effectively restricted on Zn anodes and thus Zn anodes can achieve a high coulombic efficiency of 99.59% even after cycling. To illustrate the feasibility of the ZnCl₂ /Zn(OAc)₂ electrolyte in aqueous ZIBs, Zn||p-chloranil cells are assembled based on the ZnCl₂ /Zn(OAc)₂ electrolyte. The resultant Zn||p-chloranil cells exhibit enhanced cycling performance compared with the cases with a conventional ZnSO₄ electrolyte.