NOVELTY - A non-aqueous redox flow battery comprises positive/negative electrodes immersed in respective non-aqueous liquid positive/negative electrolyte and cation-permeable separator (126) between electrolytes. The electrodes are positioned within respective electrolyte chambers. The electrolytes have electrolyte salt, transition metal-free redox reactant and optionally electrochemically stable organic solvent. The redox reactant of the positive electrolyte comprises terafluorohydroquinone ether compound or tetrafluorocatechol ether compound.    USE - As non-aqueous redox flow battery (claimed) useful for large-scale electrochemical energy storage.    ADVANTAGE - The non-aqueous redox flow battery is more efficient. The non-aqueous redox flow battery based on oxidation and reduction of organic electroactive materials at the negative and positive electrodes and cation exchange involves transfer of cations such as alkali metal ions (e.g. lithium and sodium), and alkaline earth metal ions (e.g. magnesium and calcium) to balance charges resulting from the redox reactions.    DETAILED DESCRIPTION - A non-aqueous redox flow battery comprises negative electrode (102) immersed in non-aqueous liquid negative electrolyte, positive electrode (114) immersed in non-aqueous liquid positive electrolyte, and cation-permeable separator (126) between the electrolytes. The negative electrode is positioned within negative electrolyte (NE) chamber (104) defined by first housing (106) and containing the negative electrolyte. The NE chamber connecting with first NE reservoir (108) and second NE reservoir (110) such that the first NE reservoir, the NE chamber, and the second NE reservoir can be placed in fluid-flow communication and collectively define negative electrolyte circulation pathway. The first pump is operably positioned within the negative electrolyte circulation pathway to circulate the negative electrolyte back and forth between the first NE reservoir and the second NE reservoir over the negative electrode. The positive electrode is positioned within positive electrolyte (PE) chamber defined by second housing (116) and containing the PE. The PE chamber (118) connecting with first PE reservoir (120) and second PE reservoir (122) such that the first PE reservoir, the PE chamber, and the second PE reservoir can be placed in fluid-flow communication and collectively define positive electrolyte circulation pathway. The second pump is positioned within the PE circulation pathway to circulate the positive electrolyte back and forth between the first PE reservoir and the second PE reservoir over the positive electrode. The negative and positive electrolytes each independently comprise an electrolyte salt, transition metal-free redox reactant, and optionally an electrochemically stable organic solvent. The NE chamber and the PE chamber are separated from one another by the cation-permeable separator, such that cations from the electrolyte salt can flow back and forth between the NE chamber and the PE chamber to balance charges resulting from oxidation and reduction of the redox reactants during charging and discharging of the battery. The redox reactant of the positive electrolyte has higher redox potential than the redox reactant of the negative electrolyte, and the redox reactants are independently selected from organic compound comprising conjugated unsaturated moiety and/or boron cluster compound. The conjugated unsaturated moiety is aromatic and/or non-aromatic; and comprises carbon-carbon unsaturated bonds and/or carbon-heteroatom unsaturated bonds. The heteroatom of the carbon-heteroatom unsaturated bond is non-metallic heteroatom or metalloid heteroatom; where the redox reactant of the positive electrolyte comprises terafluorohydroquinone ether compound or tetrafluorocatechol ether compound selected from compound of formulae (I) and (II).    R15-R18 and X9-X12=F;    R19-R22=alkyl or alkoxyalkyl.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of redox flow battery.    Negative electrode (102)    Negative electrolyte chamber (104)    First housing (106)    First negative electrolyte reservoir (108)    Second negative electrolyte reservoir (110)    Positive electrode (114)    Second housing (116)    Positive electrolyte chamber (118)    First positive electrolyte reservoir (120)    Second positive electrolyte reservoir (122)    Cation-permeable separator (126)