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.