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

Severe Zn dendrite and H 2 evolution reaction (HER) derived from high activity of free H 2 O hinder the commercialization of aqueous Zn-ion batteries (AZIBs). Regulating the Zn 2+ 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 Zn 2+ and H 2 O via the -C O group, conducing to reshape the Zn 2+ -solvation structure and interrupt the intrinsic hydrogen-bonds (H-bonds) of H 2 O. Furthermore, the steric-repulsion effect of -N(CH 3 ) 2 prevents H 2 O from entering the primary solvation structure. Such synergistic effects decrease the H 2 O 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||NH 4 V 4 O 10 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.