Stable cycling of Prussian blue/Zn battery in a nonflammable aqueous/organic hybrid electrolyte

Although rechargeable aqueous batteries are attracting increasing attention in recent years due to high safety, low cost, high power density and environmental friendliness, the aqueous batteries suffer from limited cycle life due to a narrow electrochemical window of the aqueous electrolytes, severe side reaction and instability of electrode materials in aqueous electrolytes. In this work, we propose a hybrid aqueous electrolyte with a mixed solvent of water and acetonitrile (ACN), which exhibits a wide electrochemical window, high ionic conductivity, and nonflammability. An aqueous battery with an iron hexacyanoferrate (FeHCF) cathode, Zn anode and H₂O/ACN hybrid electrolyte shows a high capacity of 69.1 mA h g^-1 at 10C (89.5% relative to that at 1C) and an extremely long cycle life with 51.4% capacity retention after 19 000 cycles at 10C. The excellent cycling performance of the aqueous FeHCF/Zn batteries can be attributed to the reduced water activity and extended electrochemical window because of the strong hydrogen-bonding interaction between ACN and H₂O. Besides, the large particle size and good crystallization of FeHCF can inhibit its dissolution in the aqueous electrolyte which further improves cycling performance. This work will shed light on the design of safe aqueous batteries for applications in large-scale energy storage.