The present disclosure relates to a heterocyclic compound represented by formula (1), (2) or (3), or a salt thereof. The present disclosure also relates to an active material containing at least one heterocyclic compound or a salt thereof described above, an electrolytic solution containing the active material, and a redox flow battery including the electrolytic solution.

Separators for zinc metal batteries, zinc metal batteries, and methods of fabricating a separator for use in a zinc metal battery are provided. The separator includes a hydrophilic membrane having a first side for facing a negative electrode when arranged in the zinc metal battery and a second side for facing a positive electrode when arranged in the zinc metal battery. The hydrophilic membrane includes a plurality of pores traversing the hydrophilic membrane from the first side to the second side enabling flow of zinc cations between the negative electrode and the positive electrode through the separator. Each of the pores may have a pore size ranging from about 0.1 to 1.3 μm.

The present invention provides an air battery using oxygen in air as a cathode active material, the air battery comprising: a cylindrical anode made of a metal; a cathode constituted by a co-continuous body having a three dimensional network structure formed by an integrated plurality of nanostructures having branches; and a separator that is arranged between the cathode and the anode and absorbs an electrolytic solution, wherein: the cathode is arranged inside the anode via the separator; and the anode has an open hole that reaches the separator and constitutes a housing of the air battery.

An aqueous secondary battery including: a positive electrode; a negative electrode; a separator; and an aqueous electrolytic solution including water and a metal salt represented by Chemical Formula 1 A.sub.xD.sub.y and having molality of about 5 M to about 40 M wherein in Chemical Formula 1, A is at least one metal ion selected from a sodium ion, a potassium ion, a magnesium ion, a calcium ion, a strontium ion, a zinc ion, or a barium ion, D is at least one type of atomic group ion selected from Cl.sup.−, SO.sub.4.sup.2−, NO.sub.3.sup.−, ClO.sub.4.sup.−, SCN.sup.−, CF.sub.3SO.sub.3.sup.−, C.sub.4F.sub.3SO.sub.3.sup.−, (CF.sub.3SO.sub.2).sub.2N.sup.−, AlO.sub.2.sup.−, AlCl.sub.4.sup.−, AsF.sub.6.sup.−, SbF.sub.6.sup.−, BR.sub.4.sup.−, and PO.sub.2F.sub.2.sup.−, and 0<x≤2, and 0<y≤2.

A redox flow battery system includes an anolyte having chromium ions in solution, wherein at least a portion of the chromium ions form a chromium complex with at least one of the following: NH.sub.3, NH.sub.4.sup.+, CO(NH.sub.2).sub.2, SCN.sup.−, or CS(NH.sub.2).sub.2; a catholyte having iron ions in solution; a first half-cell including a first electrode in contact with the anolyte; a second half-cell including a second electrode in contact with the catholyte; and a first separator separating the first half-cell from the second half-cell.

A method for determining an average oxidation state (AOS) of a redox flow battery system includes measuring a charge capacity for a low potential charging period starting from a discharged state of the redox flow battery system to a turning point of a charge voltage; and determining the AOS using the measured charge capacity and volumes of anolyte and catholyte of the redox flow battery system. Other methods can be used to determine the AOS for a redox flow battery system or use discharge voltage instead of charging voltage.

A solid state high voltage battery includes a cathode; an anode; a catholyte solution in contact with the cathode; an anolyte solution in contact with the anode, and a separator disposed between the cathode and the anode. At least one of the catholyte or the anolyte is gelled, and at least one of the catholyte or the anolyte comprises an organic electrolyte, an ionic liquid electrolyte, or water in salt electrolyte.

At least some embodiments herein disclose a vanadium-based solution formed by a combination of a vanadium compound, vanadium in metallic form and an appropriate reducing agent. A manufacturing process of the combination foregoes a need of using at least one among a relatively strong reducing agent that subsequently requires removal thereof and using an electrochemical reaction to achieve sufficient chemical reduction of vanadium that is needed for the vanadium-electrolyte solution to act as the liquid electrode in the vanadium-based battery. The liquid electrode, accommodated in a battery case, has an average oxidation state of within a range of +3.3 to +3.7, which is suitable for a catholyte and an anolyte in the battery.

The present invention relates to an energy storage device comprising a positive electrode, a negative electrode, and an aqueous polymer electrolyte disposed between the positive electrode and the negative electrode. At least one of the electrodes is an organic electrode. The aqueous polymer electrolyte comprises a metal ion component comprising a metal cation being Na.sup.+ or K.sup.+; a polymer or copolymer comprising at least one monomer unit being a carboxylic acid. At least 20 mol-% of a total amount of monomers in the polymer is monomers comprising carboxylic acid.

A method and systems are provided for utilizing black powder to form an electrolyte for a flow battery. In an exemplary method the black powder is heated under an inert atmosphere to form Fe.sub.3O.sub.4. The Fe.sub.3O.sub.4 is dissolved in an acid solution to form an electrolyte solution. A ratio of iron (II) to iron (III) is adjusted by a redox process.