Evaluation of ionic liquids as electrolytes for vanadium redox flow batteries

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, [C(4)mim][NTF2], and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, [C(4)mpyr][NTF2], electrolytes. The electrochemical kinetics of the anodic and cathodic reactions was measured using cyclic voltammetry. The V-II/V-III and V-III/V-IV 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)/[C(4)mpyr][NTF2] cell. (c) 2020 Elsevier B.V. All rights reserved.