TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred System: In the redox flow battery system, the electro-active ions are lithium ions, sodium ions, magnesium ions, aluminum ions, silver ions, copper ions, protons, fluoride ions, hydroxide ions, or a combination. The energy reservoir is connected to the cathodic compartment, the electro-active material in it being a cathodic electro-active material and the redox mediator in it being a p-type redox mediator. The energy reservoir is connected to the anodic compartment, the electro-active material in it being an anodic electro-active material and the redox mediator in it being an n-type redox mediator. The electro-active ions are lithium ions. The energy reservoir is connected to the cathodic compartment, the electro-active material in it being a cathodic electro-active material and the redox mediator in it being a p-type redox mediator. The cathodic electro-active material is a metal fluoride, a metal oxide, Li1-x-zM1-zPO4, (Li1-yZy)MPO4, LiMO2, LiM2O4, Li2MSiO4, LiMPO4F, LiMSO4F, Li2MnO3, sulfur, oxygen, or a combination; the electrolyte is a solution in which one or more lithium salts are dissolved in a polar protic solvent, an aprotic solvent, or a combination; the p-type redox mediator is a metallocene derivative, a triarylamine derivative, a phenothiazine derivative, a phenoxazine derivative, a carbazole derivative, a transition metal complex, an aromatic derivative, a nitroxide radical, a disulfide, or a combination; and the separator is a lithium ion conducting membrane.M=Ti, V, Cr, Mn, Fe, Co, or Ni;Z=Ti, Zr, Nb, Al, or Mg;x=0 to 1;y=0 to 0.1; andz=-0.5 to 0.5.The cathodic electro-active material is lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), LiVPO4F, LiFeSO4F, LiNi0.5Mn0.5O2, LiCo1/3Ni1/3Mn1/3O2, LiMn2O4, LiNi0.5Mn1.5O4, or a combination; the electrolyte is a solution in which lithium chlorate (LiClO4), lithium hexafluoro phosphate (LiPF6), lithium tetrafluoro borate (LiBF4), lithium hexafluoro antimonate (LiSbF6), lithium trifluorocarbo sulfate (LiCF3SO3), LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2F)2, LiC(SO2CF3)3, Li(N(SO2C4F9)(SO2F)), lithium aluminate (LiAlO4), lithium aluminum chlorate (LiAlCl4), lithium chloride (LiCl), lithium iodide (LiI), lithium bis(oxalato)borate, or a combination is dissolved in water, a carbonate, an ether, an ester, a ketone, a nitrile, or a combination; the p-type redox mediator is a metallocene derivative; and the separator is a lithium phosphorus oxynitride glass, a lithium thiophosphate glass, a NASICON-type lithium conducting glass ceramic, a Garnet-type lithium conducting glass ceramic, a ceramic nano-filtration membrane, a lithium ion-exchange membrane, or a combination. The energy reservoir is connected to the anodic compartment, the electro-active material in it being an anodic electro-active material and the redox mediator in it being an n-type redox mediator. The anodic electro-active material is a carbonaceous material, a lithium titanate, a metal oxide, a metal, a metal alloy, a metalloid, a metalloid alloy, a conjugated dicarboxylate, or a combination; the electrolyte is a solution in which one or more lithium salts are dissolved in a polar protic solvent, an aprotic solvent, or a combination; the n-type redox mediator is a transition metal derivative, an aryl derivative, a conjugated carboxylate derivative, a rare earth metal cation, or a combination; and the separator is a lithium ion conducting membrane, provided that when the anodic electro-active material contains a lithium metal, the electrolyte is a solution in which one or more lithium salts are dissolved in an aprotic organic solvent. The anodic electro-active material is Li4Ti5O12, titanium dioxide (TiO2), silicon (Si), aluminum (Al), tin (Sn), antimony (Sb), a carbonaceous material, or a combination; the electrolyte is a solution in which lithium chlorate (LiClO4), LiPF4, (LiBF4), LiSbF6, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2F)2, LiC(SO2CF3)3, Li(N(SO2C4F9)(SO2F)), LiAlO4, LiAlCl4, LiCl, LiI, lithium bis(oxalato)borate, or a combination is dissolved in water, a carbonate, an ether, an ester, a ketone, a nitrile, or a combination; the n-type redox mediator is a transition metal derivative, an aryl derivative, or a combination; and the separator is a lithium phosphorus oxynitride glass, a lithium thiophosphate glass, a NASICON-type lithium conducting glass ceramic, a Garnet-type lithium conducting glass ceramic, a ceramic nano-filtration membrane, a lithium ion-exchange membrane, or a combination. The cathodic electrode is a carbon, a metal, or a combination; and the anodic electrode is a carbon, a metal, or a combination. The energy reservoir is connected to the cathodic compartment; the electrolyte is a solution in which one or more lithium salts are dissolved in a polar protic solvent, an aprotic solvent, or a combination; and the redox mediator in it is a p-type redox mediator. The energy reservoir is connected to the anodic compartment; the electro-active material in it is a carbonaceous material, a lithium titanate, a metal oxide, a conjugated dicarboxylate, a metal, a metal alloy, a metalloid, a metalloid alloy, a lithium metal, or a combination; the electrolyte is a solution in which one or more lithium salts dissolved in a polar protic solvent, an aprotic solvent, or a combination; and the redox mediator in it is an n-type redox mediator, provided that when the anodic electro-active material contains a lithium metal, the electrolyte is a solution in which one or more lithium salts are dissolved in an aprotic organic solvent. The battery system further comprises a second energy reservoir, where one of the two energy reservoirs is connected to the cathodic compartment, in which the electro-active material is a cathodic electro-active material and the redox mediator is a p-type redox mediator; and the other energy reservoir is connected to the anodic compartment, in which the electro-active material is an anodic electro-active material and the redox mediator is an n-type redox mediator. The electro-active ions are lithium ions, sodium ions, magnesium ions, aluminum ions, silver ions, copper ions, protons, fluoride ions, hydroxide ions, or a combination. The electro-active ions are lithium ions. The cathodic electrode is a carbon, a metal, or a combination; and the anodic electrode is a carbon, a metal, or a combination. The anodic electro-active material is a carbonaceous material, a lithium titanate, a metal oxide, a conjugated dicarboxylate, a metal, a metal alloy, a metalloid, a metalloid alloy, or a combination; the electrolyte is a solution in which one or more lithium salts are dissolved in a polar protic solvent, an aprotic solvent, or a combination; the p-type redox mediator is a metallocene derivative, a triarylamine derivative, a phenothiazine derivative, a phenoxazine derivative, a carbazole derivative, a transition metal complex, an aromatic derivative, a nitroxide radical, a disulfide, or a combination; the n-type redox mediator is a transition metal derivative, an aryl derivative, a conjugated carboxylate derivative, a rare earth metal cation, or a combination; and the separator is a lithium ion conducting membrane, provided that when the anodic electro-active material contains a lithium metal, the electrolyte is a solution in which one or more lithium salts are dissolved in an aprotic organic solvent. The battery system has a set of electrochemical cells, the cathodic electrode is connected to one or more other cells or to an external load, and the anodic electrode is connected to one or more other cells or to an external load.