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Polyoxometalates have been explored as multi-electron active species in both aqueous and non-aqueous redox flow batteries.Although non-aqueous systems in principle offer a wider voltage window for redox flow battery operation,realization of this potential requires a judicious choice of solvent as well as polyoxometalate properties.We demonstrate here the superior performance of N,N-dimethylformamide (DMF) compared to acetonitrile as a solvent for redox flow batteries based on Li3PMo12O40.This compound displays two 1-electron transfers in acetonitrile but can access an extra quasi-reversible 2-electron redox process in DMF.A cell containing 10 mM solution of Li3PMo12O40 in DMF produced a cell voltage of 0.7 V with 2-electron transfers (State of Charge =60％) and showed a good cyclability.As a means to boost energy density,operation of the redox flow battery at a higher concentration of 0.1 M Li3PMo12O40 produced cells with cell voltage of 0.6 V in acetonitrile and a cell voltage of 1.0 V in DMF;both showed excellent coulombic efficiencies of more than 90％ over the course of 30 cycles.Energy density was also increased by employing an asymmetric cell with different polyoxometalates on each side to extend cell voltage.Li6P2W18O62 exhibited 3 quasi-reversible 2-electron transfers in the potential range between-2.05 V and -0.5 V vs.Ag/Ag+.10 mM Li6P2W18O62/Li3PMo12O40 in DMF produced a cell with cell voltage of 1.3 V involving 4-electron transfers (State of Charge =50％) with coulombic efficiency of nearly 100％ and energy efficiency of nearly 70％ throughout the test with more than 20 cycles.These promising results demonstrate proof-of-concept approaches to improving the performance of polyoxometalates in non-aqueous redox flow batteries.