Zinc-Ferricyanide Flow Batteries Operating Stably under -10 °C

Alkaline ferri/ferro-cyanide-based flow batteries are well suited for energy storage because of their features of high electrochemical activity, good kinetics and low material cost. However, they suffer from low energy density and poor temperature adaptability. The ferri/ferro-cyanide catholyte exhibits low solubility (~0.4 M at 25 °C) in NaOH- or KOH-based supporting electrolyte and can easily form precipitates below room temperature. Here we report a lithium-based supporting electrolyte that significantly enhances the solubility of ferrocyanide. The use of LiOH intensifies the ion-dipole interaction between water molecules and solutes and cripples polarization among ferrocyanide ions. Thus, we have achieved a ferrocyanide-based catholyte of 1.7 M at 25 °C and of 0.8 M at -10 °C. A zinc-ferricyanide flow battery based on the lithium-based supporting electrolyte demonstrates a steady charge energy of ~72 Wh L^-1 _catholyte at 25 °C, and maintains stable for ~4200 cycles (~4200 hours). Furthermore, it remains stable for ~800 cycles (~800 hours) at -10 °C.