Evaluation of ionic liquids as electrolytes for vanadium redox flow batteries

© 2020 Elsevier B.V. Non-aqueous redox flow batteries (NARFBs) are promising electrochemical energy storage devices due to their wide electrochemical potential windows, generally >2 V of organic solvents. This study aims to investigate the suitability of ionic liquids (ILs) as electrolytes for NARFBs containing a vanadium metal complex. The electrochemistry of a single-component NARFBs employing vanadium (III) acetylacetonate (V(acac)3) was studied in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C4mim][NTF2], and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, [C4mpyr][NTF2], electrolytes. The electrochemical kinetics of the anodic and cathodic reactions was measured using cyclic voltammetry. The VII/VIII and VIII/VIV couples were quasi-reversible and together yielded a cell potential of 2.2 V in both ILs. Charge/discharge characteristics show that a coulombic efficiency for cycles 1–50 ranged from 88 to 92% using a V(acac)3/[C4mpyr][NTF2] cell.