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

Abstract 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)5Zn(OTF)7), for all‐temperature AZIBs. The aqueous electrolyte containing 0.261 mol kg−1 (EMIM)5Zn(OTF)7 in Ethylene Glycol (EG) / H2O (6:4) exhibits ultralow freezing point below −100 °C. The liquid Zn salt and EG molecules not only modulate the solvation structure of Zn2+ ion, reducing the coordinated H2O 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.