Nonaqueous vanadium disproportionation flow batteries with porous separators cycle stably and tolerate high current density.

Abstract Vanadium acetylacetonate, or V(acac) 3 , provides a model chemistry for investigating the performance of nonaqueous disproportionation flow batteries. A flow reactor was developed to implement studies of efficiency, energy capacity, and power capability with respect to electrolyte flow rate and current density. Reactors incorporating a porous separator allowed V(acac) 3 to be cycled without appreciable capacity fade at current densities up to 100 mAcm−2. Experiments at the lowest flow rate, 12.5 mLmin–1, revealed limitations imposed by residence time within the reactor, which manifested as high charging overpotentials. These overpotentials vanish above 25 mLmin–1. A higher flow rate of 50 mLmin–1 yielded performance similar to cells at 25 mLmin–1, but could improve performance at current densities above 100 mAcm−2. Extrapolation of power density's dependence on current suggests a maximum power of 0.22 Wcm−2 for cells run at 206 mAcm−2. Energy efficiency passes through a maximum of 71% at 40 mAcm−2 and the corresponding energy density suggests that the chemistry can, in principle, deliver above 13 WhL−1 in acetonitrile solutions and above 24 WhL−1 in mixed-solvent solutions with higher V(acac) 3 solubility. A V(acac) 3 cell run at 40 mAcm−2 is shown to exhibit stable capacity and performance for more than 150 cycles. Highlights • A new reactor design resolves materials compatibility issues in nonaqueous RFBs. • Effects of flowrate and power on disproportionation electrochemistry are elucidated. • Vanadium acetylacetonate cycles stably, supporting charge/discharge for >150 cycles. • The nonaqueous support does not strictly limit power; cells tolerate 100 mAcm−2. [ABSTRACT FROM AUTHOR]