Zinc-Coordinated Imidazole-Based Ionic Liquid as Liquid Salt for All-Temperature Aqueous Zinc-Ion Batteries

Owing to the intrinsically high safety, low cost, natural abundance, and high energy density of Zn metal, aqueous Zn ion batteries (AZIBs) have become a promising candidate for large-scale energy conversion and storage. However, the practical application of AZIBs is hampered by the severe Zn dendrites growth and the poor low-temperature performance due to the elevated freezing point of aqueous electrolyte. Herein, the study proposes a new kind of room-temperature liquid Zn salt, which is called Zn coordinated ionic liquid (i.e., (EMIM) 5 Zn(OTF) 7 ), for all-temperature AZIBs. The aqueous electrolyte containing 0.261 mol kg −1 (EMIM) 5 Zn(OTF) 7 in Ethylene Glycol (EG) / H 2 O (6:4) exhibits ultralow freezing point below −100 °C. The liquid Zn salt and EG molecules not only modulate the solvation structure of Zn 2+ ion, reducing the coordinated H 2 O in the first solvation sheath, but also suppresses the parasitic side reaction. As a proof of concept, Zn || Zn symmetric cells and Zn || PANI full cells with the designed electrolyte achieve improved cycling stability and can operate under wide temperature (from −40 to 60 °C). Even with high Zn utilization ratio of 40%, long cycle life over 70 times with capacity retention of 80% is achieved.