A Vanadium Redox Flow Battery based on a highly concentrated Protic Ionic Liquid Electrolyte

A protic ionic liquid is inctroduced for the first time as a solvent for a high energy density vanadium redox flow battery.  The proof-of-concept redox flow cell with a concentration of 3 mol L⁻¹ vandyl sulfate electrolyte was tested for a total of 30 cycles at 40°C, showing an open circuit potential of 1.38 V, a nominal capacity of 1900 mAh at a current density of 40 mA cm⁻¹ and energy and coulombic efficiencies of 64 and 90%, respectively. The continuous 16 hours of cycling suggest that the concentrated anolyte and catholyte are thermally stable and cycleable. This study underlines a new route to improve the energy-to-volume ratio of this promising energy storage system.