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

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 H2O molecules to achieve higher ionization energy of H2O molecules. Simultaneously, these carboxylate groups of OAc- can serve as H-bond acceptors to construct H-bonds with H2O 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.

Automated summary

This study presents a binary hydrate-melt electrolyte as a solution to improve the cycling performance of zinc-ion batteries with metal zinc anodes. By adjusting the solvation structure of zinc ions, the side reactions on the anodes can be effectively suppressed, leading to higher coulombic efficiency. Experimental results demonstrate that the use of this electrolyte can achieve better cycling performance.