A highly concentrated vanadium protic ionic liquid electrolyte for the vanadium redox flow battery

A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery. Despite being less conductive than standard aqueous electrolytes, it is thermally stable on a 100 degrees C temperature window, chemically stable for at least 60 days, equally viscous and dense with typical aqueous solvents and most importantly able to solubilize to 6 mol L-1 vanadium sulfate, thus increasing the VRFB energy density by a factor of 2.5. Electrochemical measurements revealed quasi-reversible redox transitions for both catholyte and anolyte at 25 degrees C while a proof-of-concept redox flow cell with the proposed electrolyte was tested for a total of 150 cycles at 25 degrees C, showing an open circuit potential of 1.39 V and energy and coulombic efficiencies of 65% and 93%, respectively. What's more, the battery can be equally cycled at 45 degrees C showing good thermal stability. This study underlines a new route to improve the energy-to-volume ratio of energy storage system. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.