A co-solvent in aqueous electrolyte towards ultralong-life rechargeable zinc-ion batteries

Abstract

Severe Zn dendrite and H2 evolution reaction (HER) derived from high activity of free H2O hinder the commercialization of aqueous Zn-ion batteries (AZIBs). Regulating the Zn2+ solvation structure is a straightforward way to solve the above issues. Herein, a polar solvent, tetramethylurea (TMU), is designed as a co-solvent in the aqueous electrolyte, which can form strong interactions with Zn2+ and H2O via the -CO group, conducing to reshape the Zn2+-solvation structure and interrupt the intrinsic hydrogen-bonds (H-bonds) of H2O. Furthermore, the steric-repulsion effect of -N(CH3)2 prevents H2O from entering the primary solvation structure. Such synergistic effects decrease the H2O activity, and hence suppress Zn dendrite and HER. As a result, Zn||Cu cells with TMU-based electrolyte can stably run over 6000 cycles with 99.8% Columbic efficiency at a current density of 10 mA cm−2, and the cumulative capacity of Zn||Zn cell reaches up to 5 Ah cm−2, exceeding most of the reported works involving co-solvent. The Zn||NH4V4O10 battery, under an N/P ratio of 4, can run for 300 cycles with 68% capacity retention, much better than that without TMU (3.9%). Our work reveals that rationally designing the electrolyte components at the molecular level is essential in stabilizing the Zn anode and achieving high-performance AZIBs.