Electrolyte solution for redox flow batteries, and redox flow battery provided with said electrolyte solution

Abstract

Disclosed is an electrolyte solution for redox flow batteries, the electrolyte solution including: a substance that contains metal ions; a water-soluble polymer that has a coordination part in a side chain; and an aqueous solvent. The coordination part forms a metal complex by coordinating with a metal ion.

Description

Electrolyte for redox flow battery and redox flow battery comprising the electrolyte

[0001] The present disclosure relates to an electrolyte for a redox flow battery and a redox flow battery including the electrolyte.

[0002] In recent years, redox flow batteries have been attracting attention as a way to efficiently use energy and reduce environmental impact. Redox flow batteries can be used as batteries (storage batteries) that store electricity generated in power generation units (e.g., power generation units that use solar, wind, ocean current, or geothermal energy, and power plants that use thermal, nuclear, or hydroelectric power). For example, a redox flow battery connected to a solar power generation unit can mainly store electricity during the day when sunlight is shining, and supply electricity to a demand unit (load unit) at night when sunlight is not shining.

[0003] For example, in the redox flow battery of Patent Document 1, the positive electrode electrolyte is an aqueous solution that contains a manganese redox substance as the active material on the positive electrode side and also contains polyethyleneimine.

[0004] International Publication No. 2013 / 164879

[0005] However, as a result of extensive research, the present inventors have found that the electrolyte solution of Patent Document 1 does not sufficiently improve the performance of redox flow batteries.

[0006] The present disclosure has been made in view of the above problems. That is, a primary object of the present disclosure is to provide an electrolyte for a redox flow battery that further improves the performance of the redox flow battery in which it is installed. Another object of the present disclosure is to provide a redox flow battery including such an electrolyte.

[0007] An electrolyte solution for a redox flow battery according to one embodiment of the present disclosure includes a substance containing a metal ion, a water-soluble polymer having a coordinating moiety in a side chain, and an aqueous solvent, wherein the coordinating moiety coordinates with the metal ion to form a metal complex.

[0008] A redox flow battery according to another embodiment of the present disclosure is a redox flow battery which circulates an electrolyte between an electric cell and an electrolyte tank and is charged and discharged by an oxidation-reduction reaction of an active substance, and which comprises: an electric cell having: a first chamber having a first electrode and a first aqueous electrolyte solution in contact with the first electrode; a second chamber having a second electrode and a second aqueous electrolyte solution in contact with the second electrode; and a diaphragm which separates the first chamber and the second chamber and electrically isolates the first aqueous electrolyte solution from the second aqueous electrolyte solution; and an electrolyte tank having: a first electrolyte tank connected to the first chamber and storing the first aqueous electrolyte solution; and a second electrolyte tank connected to the second chamber and storing the second aqueous electrolyte solution, wherein at least one of the first aqueous electrolyte solution and the second aqueous electrolyte solution is the above-mentioned electrolyte solution.

[0009] The present disclosure can provide an electrolyte for a redox flow battery that further improves the performance of the redox flow battery in which it is installed, and can also provide a redox flow battery including such an electrolyte.

[0010] Fig. 1 is a transparent perspective view schematically showing a redox flow battery according to a second embodiment. Fig. 2 is a schematic diagram showing a metal complex (water-soluble redox active polymer) formed of a water-soluble chelate polymer and a metal ion.

[0011] The "electrolyte for redox flow batteries" and "redox flow batteries" of the present disclosure will be described in detail below. While the description will be made with reference to drawings as necessary, the contents shown in the drawings are merely shown as schematic examples for the purpose of understanding the present disclosure, and the appearance and dimensional ratios may differ from the actual products.

[0012] Numerical ranges mentioned in this specification are intended to include the lower and upper limit values ​​themselves, unless otherwise specified, for example, by using terms such as "less than," "smaller," or "greater than." In other words, a numerical range such as 1 to 10 is interpreted as including the lower limit of 1 and the upper limit of 10.

[0013] In the present disclosure, the term "battery" refers to a device (secondary battery) that includes a pair of electrodes and an electrolyte, and in particular is charged and discharged through the movement of ions.

[0014] First Embodiment: Electrolyte for Redox Flow Battery The first embodiment relates to an electrolyte for a redox flow battery (hereinafter also simply referred to as "electrolyte"). The electrolyte according to the first embodiment comprises: a substance containing a metal ion (redox active substance), a water-soluble polymer having a coordinating moiety in a side chain (water-soluble chelate polymer), and an aqueous solvent, wherein the coordinating moiety coordinates with the metal ion to form a metal complex.

[0015] In this specification, the electrolyte solution according to the first embodiment is used in a redox flow battery. The "substance (containing a metal ion)" contained in the electrolyte solution is a substance responsible for the oxidation-reduction reaction that causes charging and discharging of the redox flow battery, and may be a substance capable of reversibly donating and receiving electrons to and from an electrode (hereinafter also referred to as a "redox active substance"). Furthermore, the water-soluble polymer contained in the electrolyte solution may incorporate the substance. This may be, for example, a metal complex, which may be capable of reversibly donating and receiving electrons to and from an electrode. In other words, the water-soluble polymer may incorporate the substance and reversibly donate and receive electrons to and from an electrode. Hereinafter, the water-soluble polymer is also referred to as a "water-soluble chelate polymer." Furthermore, a water-soluble polymer incorporating a substance (containing a metal ion) is also referred to as a "water-soluble redox active polymer."

[0016] [Mechanism of Action] The electrolyte solution according to the first embodiment can further improve the performance of a redox flow battery in which it is installed. The reason for this is presumed to be as follows. The electrolyte solution according to the first embodiment contains a water-soluble chelate polymer. The water-soluble chelate polymer has high solubility in the electrolyte solution, and can form a metal complex with metal ions, which are redox active substances, and can be incorporated. As a result, the metal complex can proceed with an oxidation-reduction reaction at the electrode in a state in which it is incorporated into the water-soluble chelate polymer. Therefore, the electrolyte solution according to the first embodiment can further improve the performance of a redox flow battery in which it is installed.

[0017] [Background to the Idea of ​​the Present Disclosure] As a result of intensively studying the prior art described in Patent Document 1, the present inventors have come to the technical finding that the solubility of polyethyleneimine in an electrolyte solution is not sufficiently high, and therefore a metal complex with a manganese redox substance in the electrolyte solution cannot be sufficiently formed, and as a result, the performance of a redox flow battery equipped with such an electrolyte solution cannot be sufficiently improved. As a result of continued research based on this technical finding, the present inventors have come to the idea of ​​the present disclosure, which further improves the performance of a redox flow battery by increasing the water solubility of a chelate polymer.

[0018] The electrolyte for the redox flow battery is preferably an alkaline aqueous solution from the viewpoints of suppressing the oxidation-reduction reaction of water and forming a significant potential difference. The pH of the electrolyte for the redox flow battery is, for example, greater than 7 and not greater than 13. The upper limit of this pH is preferably a pH at which the peptide derivative as the water-soluble chelate polymer is unlikely to undergo pH denaturation (alkali denaturation).

[0019] The redox potential difference can be formed by selecting a redox active material and a water-soluble chelating polymer (or a coordination moiety contained therein) and by combining the first and second aqueous electrolyte solutions composed thereof, depending on the desired application and performance of the redox flow battery. For example, the combinations of iron ions and coordination moieties, in order of relatively low to high potential, are iron-polyalcohol-derived coordination moieties, iron-aminecarboxylic acid-derived coordination moieties, iron-cyano group-derived coordination moieties, and coordination moieties derived from compounds having iron-pyridine-derived coordination moieties.

[0020] (Redox-active substances) Redox-active substances are substances that undergo oxidation or reduction reactions. Redox-active substances include metal ions. Some metal ions can undergo oxidation reactions, increasing their valence. Other metal ions can also undergo reduction reactions, decreasing their valence.

[0021] The redox active substance forms a metal complex with the water-soluble chelating polymer. The metal ion contained in the redox active substance forms a coordinate bond with the coordination part of the water-soluble chelating polymer to form a metal complex. The metal ion is incorporated into the water-soluble chelating polymer in the form of a metal complex and exists in the electrolyte. The metal ion, while incorporated into the water-soluble chelating polymer, undergoes an oxidation reaction or a reduction reaction between the electrodes (see Figure 2 below).

[0022] In a preferred embodiment, if greater emphasis is placed on realizing various potentials of the electrolyte, the metal ion is an ion of one metal selected from the group consisting of Zn, Fe, Ti, Cu, Co, V, Ce, Cr, and Mn. The metal ion may be an ion of one metal selected from the group consisting of Zn, Fe, Ti, Cu, Co, Ce, Cr, and Mn. Among these, if greater emphasis is placed on reducing the production cost of the electrolyte, the metal ion is more preferably an ion of one metal selected from the group consisting of Zn, Fe, Ti, Cu, Cr, and Mn, and even more preferably an ion of one metal selected from the group consisting of Zn, Fe, Cr, and Mn. In a more preferred embodiment, the metal ion is an iron ion.

[0023] (Water-soluble chelate polymer) In this specification, the water solubility of a water-soluble chelate polymer refers to the mass of polymer that can be dissolved in an aqueous solvent per unit volume (solubility (g / L)). This solubility is measured as follows: a polymer material is mixed and dispersed in an aqueous solvent of a given volume, and the appearance is evaluated visually to determine the presence or absence of turbidity and / or precipitation. The higher the solubility of a material within the range in which turbidity or precipitation does not occur, the more excellent its water solubility. In this specification, the water solubility of a water-soluble chelate polymer refers to a solubility of 8 g / L or more, preferably 10 g / L.

[0024] The water-soluble chelate polymer has a coordination moiety in the side chain. In other words, the water-soluble chelate polymer has a (binding) moiety in the side chain. That is, the water-soluble chelate polymer can have a main chain and a moiety (side chain moiety) corresponding to a side chain relative to the main chain. The water-soluble chelate polymer can incorporate metal ions in the electrolyte. In an embodiment in which the water-soluble chelate polymer incorporates a metal ion, the metal ion and the coordination moiety of the water-soluble chelate polymer interact with each other (for example, electrostatic attraction). More specifically, the water-soluble chelate polymer forms a metal complex with the metal ion in the electrolyte. That is, the coordination moiety of the water-soluble chelate polymer coordinates with the metal ion to form a metal complex.

[0025] The water-soluble chelate polymer may have a repeating unit. In this case, the number of repeating units in the water-soluble chelate polymer is not particularly limited as long as the effects of the present disclosure are achieved. For example, the water-soluble chelate polymer may be an oligomer having two or more repeating units.

[0026] The water-soluble chelating polymer has multiple coordination moieties and forms a metal complex by monodentate or multidentate coordination with a metal ion. These multiple coordination moieties may be the same or different. When the water-soluble chelating polymer contains multiple different coordination moieties as coordination moieties, it is easy to modulate the redox potential.

[0027] The water-soluble chelate polymer captures metal ions in a state in which a metal complex is formed. The coordinating moiety forms a metal complex with the metal ion while being bound to the water-soluble chelate polymer. The mechanism of suppressing the diffusion of the coordinating moiety will be explained with reference to FIG. 2. FIG. 2 is a schematic diagram showing a metal complex (water-soluble redox active polymer) formed by a water-soluble chelate polymer and a redox active substance (metal ion) (in FIG. 2, a peptide derivative is given as an example of a water-soluble chelate polymer, and M representing a metal ion is shown). ｋ＋(where k represents a positive integer, e.g., the absolute value of the valence of a metal atom such as Zn, Fe, Ti, Cu, Ce, Cr, or Mn.) As shown in FIG. 2 , the molecular weight of the water-soluble chelate polymer containing the coordination moiety is much larger than that of the ligand (ligand alone), and it is therefore less likely to diffuse through the membrane. Therefore, in a redox flow battery incorporating the electrolyte solution according to the first embodiment, degradation of the performance of the redox flow battery due to diffusion of the coordination moiety is significantly suppressed.

[0028] The coordinating moiety may be, for example, at least one coordinating moiety derived from a ligand coordinated by a nitrogen atom, an oxygen atom, and a carbon atom, or a coordinating moiety containing a functional group coordinated by a nitrogen atom, an oxygen atom, and a carbon atom. Such a ligand may be a derivative of the following exemplary ligands (more specifically, a salt of the following ligand, an ion dissociated from its counterion, or a ligand having a reactive functional group introduced therein).

[0029] Examples of the ligand having a nitrogen atom and an oxygen atom coordinated thereto include aminopolycarboxylic acids and polyalcoholamines. Examples of aminopolycarboxylic acids include ethylenediaminetetraacetic acid (EDTA), ethylenediaminebis(2-hydroxyphenyl)acetic acid (EDDHA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA), triethylenetetramine-N,N,N',N'',N''',N'''-hexaacetic acid (TTHA), trimethylenediamine-N,N,N',N'-tetraacetic acid (PDTA), 1, Examples of the polyalcohol amines include 3-diamino-2-propanol-N,N,N',N'-tetraacetic acid (DPTA-OH), N-(2-hydroxyethyl)iminodiacetic acid (HIDA), N,N-bis(2-hydroxyethyl)glycine (DHEG), glycol ether diamine tetraacetic acid (GEDTA), glutamic acid diacetic acid (CMGA), ethylenediamine-N,N'-disuccinic acid (EDDS), N,N'-di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED), glycine, and sarcosinic acid.

[0030] Examples of the ligands with oxygen atoms include hydroxycarboxylic acids, polycarboxylic acids, and polyols. Examples of hydroxycarboxylic acids include citric acid, gluconic acid, glycolic acid, hydroxybutanoic acid, lactic acid, and salicylic acid. Examples of polycarboxylic acids include maleic acid and phthalic acid. Examples of polyols include glycol, catechol, and ascorbic acid.

[0031] Examples of the ligand having a nitrogen atom include pyridine, bipyridine, tripyridine, phenanthroline, polyethyleneimine (degree of polymerization from ethyleneimine: 2 to 5), and compounds having a cyano group (cyano compounds).

[0032] Examples of the carbon atom-coordinated ligand include cyclopentadienyl.

[0033] Examples of functional groups coordinated by nitrogen atoms, oxygen atoms, and carbon atoms include hydroxy groups, carboxy groups, phosphate groups, sulfo groups, phenol groups, and pyridine groups.

[0034] Preferably, the coordinating moiety is at least one coordinating moiety derived from a ligand selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), ethylenediaminebis(2-hydroxyphenyl)acetic acid (EDDHA), diethylenetriaminepentaacetic acid (DTPA), and triethanolamine (TEOA), among others, and / or a coordinating moiety comprising at least one functional group selected from the group consisting of a hydroxy group, a carboxy group, a phosphate group, a sulfo group, a phenol group, and a pyridine group.

[0035] The coordination moieties contained in one molecule of the water-soluble chelate polymer may be different from each other. In this case, the redox potential of the electrolyte for the redox flow battery can be easily finely adjusted (i.e., the potential can be easily adjusted to a desired value) by adjusting the combination of the coordination moieties.

[0036] The water-soluble chelate polymer preferably contains a nitrogen atom and an oxygen atom. More specifically, the coordination moiety preferably contains a nitrogen atom and an oxygen atom. When the water-soluble chelate polymer is a polyamine derivative described below, if the coordination moiety of the polyamine derivative contains an oxygen atom, the solubility of the water-soluble chelate polymer can be further increased by the effects of both the cationic nitrogen atom constituting the polyamine derivative and the anionic oxygen atom contained in the coordination moiety (i.e., the effect of zwitterionicity).

[0037] When the water-soluble chelate polymer is a peptide derivative (described below) (the peptide derivative contains an amide bond (peptide bond) consisting of a nitrogen atom and an oxygen atom), the nitrogen and oxygen atoms contained in the amide bond are expected to provide high water solubility for the water-soluble chelate polymer main chain. Furthermore, when peptide derivatives derived from multiple amino acids are used as the water-soluble chelate polymer, it becomes easier to introduce different coordination moieties to the multiple functional groups possessed by the multiple amino acids. This allows for fine-tuning of the specifications of the redox flow battery according to its intended use.

[0038] In particular, when a peptide derivative contains a repeating unit derived from lysine, the terminal amino group of the side chain of the repeating unit derived from lysine can be utilized to introduce a coordinating moiety into the peptide while maintaining high water solubility, thereby preparing the peptide derivative. Furthermore, when the coordinating moiety introduced into the repeating unit derived from lysine in the peptide contains an oxygen atom, the water solubility of the water-soluble chelate polymer can be significantly increased not only by the nitrogen and oxygen atoms in the main chain but also by the nitrogen and oxygen atoms in the side chain.

[0039] Examples of water-soluble chelating polymers include peptide derivatives and polyamine derivatives.

[0040] -Polyamine Derivative- A polyamine derivative can be obtained by introducing a coordinating moiety to the terminal amino group of a polyamine. An example of such a coordinating moiety is the coordinating moiety in the water-soluble chelate polymer described above. A raw material for such a coordinating moiety is, for example, a ligand for forming the coordinating moiety in the water-soluble chelate polymer described above, which has a functional group reactive with the terminal amino group. The polyamine derivative allows for the introduction of a desired coordinating moiety while maintaining the dispersibility of the raw polymer (polyamine) and increasing its water solubility in a mild environment near neutral pH. An example of a polyamine derivative is a polyethyleneimine derivative.

[0041] - Peptide Derivative - The water-soluble chelating polymer is preferably a peptide derivative. A peptide derivative has a main chain composed of repeating units derived from amino acids and a side chain composed of a coordinating moiety. A peptide derivative is, for example, a compound in which a ligand is bound to the side chain of a peptide. A peptide derivative preferably contains a repeating unit derived from lysine. More specifically, the peptide derivative contains a main chain derived from lysine (α-poly-L-lysine and ε-poly-L-lysine), and more preferably has an ε-poly-L-lysine main chain.

[0042] The molecular weight of the water-soluble chelating polymer (peptide derivative) is, for example, 500 to 50000. The degree of polymerization is measured by size exclusion chromatography.

[0043] The water solubility of a peptide derivative is due to the amide bond (peptide bond) in the main chain, and may also be due to the side chain. The peptide derivative has a coordination moiety in the side chain, but may also have a water-soluble functional group in another side chain. Alternatively, the coordination moiety itself may be a water-soluble functional group.

[0044] The water solubility of a peptide derivative can be adjusted by introducing an amide bond (peptide bond) and a water-soluble functional group. For example, when a peptide derivative is synthesized using any of nine essential amino acids (valine, isoleucine, leucine, methionine, lysine (lysine), phenylalanine, threonine (threonine), and histidine) and eleven non-essential amino acids (arginine, glycine, alanine, serine, tyrosine, cysteine, asparagine, glutamine, proline, aspartic acid, and glutamic acid), a water-soluble functional group (more specifically, —OH, —COOH, NH ) that does not contribute to the formation of an amide bond of the peptide derivative can be introduced. ２ , -SH, or -CONH ２ Examples of amino acids that may be used include leucine, threonine, glutamic acid, aspartic acid, lysine, and cysteine.

[0045] The water solubility of the peptide derivative can be adjusted by the molar ratio of the amino acid having a water-soluble functional group to the amino acid having a hydrophobic functional group, which are used as raw materials for the peptide derivative. Examples of amino acids having a hydrophobic functional group include amino acids having an alkylene group (glycine, alanine, valine, leucine, and isoleucine).

[0046] These water-soluble functional groups also have reactivity and are therefore used to introduce ligands into the peptide derivatives. For example, when the water-soluble functional group is an amino group and the ligand has a carboxyl group, they react to form an amide bond, thereby introducing the ligand into the side chain of the peptide to form a peptide derivative.

[0047] -Method for synthesizing peptide derivatives- An example of a method for synthesizing peptide derivatives is shown below. A peptide is synthesized by condensation polymerization of amino acids. Here, the amino acids used as raw materials contain at least one amino group and one carboxyl group for synthesizing the peptide, as well as an amino group having a reactive functional group for introducing a ligand (e.g., leucine, threonine, glutamic acid, aspartic acid, lysine, cysteine, etc.). In addition to the amino acids used as raw materials, peptide synthesis may also contain a water-soluble condensing agent (more specifically, 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide, etc.) to promote the condensation polymerization reaction. Commercially available peptides may also be used.

[0048] At least some of the water-soluble functional groups in the side chain of the resulting peptide are reacted with a ligand to bond the ligand to the side chain of the peptide, thereby introducing a ligand moiety and synthesizing a peptide derivative. A reactive functional group capable of reacting with the water-soluble functional group in the side chain can be introduced into the ligand or a derivative thereof (more specifically, a salt of the ligand, etc.). In these reactions, the reaction time is, for example, 1 to 10 hours, and the reaction temperature is, for example, room temperature (25°C) to 30°C. The upper limit of the reaction temperature is a temperature at which the starting peptide and the resulting peptide derivative do not denature (thermally denature).

[0049] (Aqueous Solvent) In this specification, the aqueous solvent contains 95% by weight or more, 97% by weight or more, 99% by weight or more, or 100% by weight of water. The aqueous solvent may contain a water-soluble solvent other than water. The water-soluble solvent is a solvent that is compatible with water. Examples of water-soluble solvents include alcohols (more specifically, monoalcohols such as methalcohol and glycols such as ethylene glycol) and ethers such as tetrahydrofuran.

[0050] Second Embodiment: Redox Flow Battery The second embodiment relates to a redox flow battery. In the redox flow battery according to the second embodiment, an aqueous electrolyte is circulated between an electric cell and an electrolyte tank, and charging and discharging are performed by an oxidation-reduction reaction of a redox active substance.

[0051] The second embodiment will be described in detail below, but portions that overlap with the disclosure of the first embodiment may be omitted. In addition, in the second embodiment, the members with the term "first" and the members with the reference numerals including "A" are applied to members related to a positive electrode (anode). On the other hand, the members with the term "second" and the members with the reference numerals including "B" are applied to members related to a negative electrode (cathode).

[0052] [Function] The redox flow battery according to the second embodiment will be described with reference to Fig. 1. Fig. 1 is a transparent perspective view showing the redox flow battery according to the second embodiment. The redox flow battery 1 according to the second embodiment is a secondary battery. As shown in Fig. 1, the redox flow battery 1 is electrically connected to a power generation unit 200 and a load unit 300 via a power converter (power conditioner (power conditioner), DC / AC converter) 100.

[0053] When the redox flow battery 1 is being charged, current flows as shown by the solid arrows indicated by Xs. The power generation unit 200 (for example, a power generation device that uses solar, wind, ocean currents, or geothermal energy, and a power plant that uses thermal, nuclear, or hydroelectric power) generates electric power. When electric power is generated by the power generation unit 200 that generates AC power, the AC current supplied from the power generation unit 200 is converted to DC current by the power converter 100. The converted DC current is supplied to the redox flow battery 1. This charges the redox flow battery 1. On the other hand, when electric power is generated by the power generation unit 200 that generates DC power (for example, a power generation device that uses solar power), the DC current supplied from the power generation unit 200 is supplied to the redox flow battery 1. This charges the redox flow battery 1.

[0054] When the redox flow battery 1 is discharging, a current flows as shown by the dashed arrow represented by Y. A load 300 (for example, a factory or a house) consumes power. The direct current supplied from the redox flow battery 1 is converted to alternating current by the power converter 100. The converted alternating current is supplied to the load 300. In this way, the redox flow battery 1 discharges.

[0055] [Configuration] As shown in Fig. 1 , the redox flow battery 1 includes an electric cell 2 and an electrolyte tank 3. The redox flow battery 1 is electrically connected to an external power generation unit 200 and a load unit 300 via a first electrode 211A and a second electrode 211B of the electric cell 2. The electric cell 2 is fluidly connected to the electrolyte tank 3, and an electrolyte 23 is circulated and supplied from the electrolyte tank 3 to the electric cell 2. The redox flow battery 1 also includes an electrolyte circulation path 4 and a pump 5.

[0056] (Electric Cell) The electric cell 2 has a first chamber 21A, a second chamber 21B, and a diaphragm 25. The electric cell 2 is partitioned by the diaphragm 25 into the first chamber 21A and the second chamber 21B.

[0057] First Chamber The first chamber (cathode chamber, anode chamber) 21A is a chamber partitioned by catholyte. The first chamber 21A is disposed opposite the second chamber 21B with respect to the diaphragm 25. The first chamber 21A contains a first electrode 211A and a first aqueous electrolyte (aqueous cathode electrolyte, aqueous catholyte) 213A. The first chamber 21A is fluidly connected to a first electrolyte tank 31A via a first electrolyte circulation path 41A. The first aqueous electrolyte 213A is circulated and supplied from the first electrolyte tank 31A to the first chamber 21A in the direction of arrow a1 by an electrolyte circulation pump 5 (first electrolyte circulation pump 51A).

[0058] =First Electrode= The first electrode 211A functions as a positive electrode during discharge of the redox flow battery 1, and a reaction takes place at the first electrode 211A according to half-reaction formula (1): A reduction reaction represented by the following half-reaction (1) occurs: [In half-reaction (1), O represents an oxidant, R represents a reductant, and m represents an integer of 1 or greater]. In this reduction reaction, electrons move in the direction represented by the dashed arrow y1 in FIG. 1. That is, first electrode 211A transfers electrons to the oxidant (metal ions of the positive electrode active material in first aqueous electrolyte solution 213A), and the oxidant is reduced to become the reductant.

[0059] The first electrode 211A functions as an anode during charging of the redox flow battery 1, and at the first electrode 211A, a reaction takes place according to half-reaction formula (2): [In half-reaction formula (2), O represents an oxidant, R represents a reductant, and m represents an integer of 1 or greater]. In this oxidation reaction, electrons move in the direction indicated by the solid arrow x1 in FIG. 1. That is, first electrode 211A receives electrons from the reductant (metal ions of the positive electrode active material in first aqueous electrolyte solution 213A), and the reductant is oxidized to become the oxidant.

[0060] The first electrode 211A may include a positive electrode active material. The positive electrode active material may include an element of the metal ions contained in the first aqueous electrolyte solution 213A.

[0061] =First aqueous electrolyte solution= The first aqueous electrolyte solution 213A may be the electrolyte solution for the redox flow battery according to Embodiment 1. However, at least one of the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B is the electrolyte solution for the redox flow battery according to Embodiment 1.

[0062] Second Chamber The second chamber (anode chamber, cathode chamber) 21B is an anolyte-separated chamber. The second chamber 21B faces the first chamber 21A across the diaphragm 25. The second chamber 21B contains a second electrode 211B and a second aqueous electrolyte (aqueous anode electrolyte, aqueous anolyte) 213B. The second chamber 21B is fluidly connected to the electrolyte tank 3 (second electrolyte tank 31B) via an electrolyte circulation path 4 (second electrolyte circulation path 41B). The second chamber 21B receives the second aqueous electrolyte 213B circulated from the electrolyte tank 3 (second electrolyte tank 31B) in the direction of arrow b1 by an electrolyte circulation pump 5 (second electrolyte circulation pump 51B).

[0063] =Second Electrode= The second electrode 211B functions as a negative electrode during discharge of the redox flow battery 1, and an oxidation reaction represented by the above half-reaction formula (2) occurs at the second electrode 211B. In this oxidation reaction, electrons move in the direction represented by the dashed arrow y2 in Figure 1. That is, the second electrode 211B receives electrons from the reductant (metal ions of the negative electrode active material in the first aqueous electrolyte solution 213A), and the reductant is oxidized to become an oxidant.

[0064] The second electrode 211B functions as a cathode when the redox flow battery 1 is charged, and a reduction reaction represented by the above half-reaction formula (1) occurs at the second electrode 211B. In this reduction reaction, electrons move in the direction represented by the solid arrow x2 in FIG. 1 . That is, the second electrode 211B transfers electrons to an oxidant (metal ions of the negative electrode active material in the second aqueous electrolyte solution 213B), and the oxidant is reduced to a reductant.

[0065] The second electrode 211B may include a negative electrode active material. The negative electrode active material may include an element of the metal ions contained in the second aqueous electrolyte solution 213B.

[0066] = Second aqueous electrolyte solution = The second aqueous electrolyte solution 213B may be the electrolyte solution for the redox flow battery according to Embodiment 1. However, at least one of the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B is the electrolyte solution for the redox flow battery according to Embodiment 1.

[0067] - Diaphragm - Diaphragm (separator) 25 separates first chamber 21A from second chamber 21B and electrically isolates first aqueous electrolyte solution 213A from second aqueous electrolyte solution 213B. Diaphragm 25 is interposed between positive electrode 21A and negative electrode 21B. Diaphragm 25 allows only specific chemical species (e.g., protons, hydroxide ions, and oxide ions) to pass through. Diaphragm 25 may be, for example, a porous membrane or an ion exchange membrane (more specifically, a cation exchange membrane, an anion exchange membrane, etc.).

[0068] (Electrolyte Tank) The electrolyte tank 3 stores the electrolyte and circulates and supplies the electrolyte to the electric cell 2. The electrolyte tank 3 has a first electrolyte tank 31A and a second electrolyte tank 31B. The electrolyte tank 3 has, for example, a two-layer structure composed of a first layer disposed on the inside thereof and a second layer disposed on the outside of the first layer. The first layer provides insulation to the inside of the electrolyte tank 3 and contains, for example, a resin. The second layer provides strength to the electrolyte tank 3 and contains, for example, a metal.

[0069] First Electrolyte Tank The first electrolyte tank 31A is a liquid storage tank that stores the first aqueous electrolyte 213A. The first electrolyte tank 31A is fluidly connected to the first chamber 21A and circulates the first aqueous electrolyte 213A to the first chamber 21A.

[0070] Second Electrolyte Tank The second electrolyte tank 31B is a liquid storage tank that stores the second aqueous electrolyte 213B. The second electrolyte tank 31B is fluidly connected to the second chamber 21B and circulates the second aqueous electrolyte 213B to the second chamber 21B.

[0071] (Electrolyte Circulation Path) The electrolyte circulation path 4 connects the electrolyte tank 3 and the electric cell 2 and is a path through which the electrolyte is circulated and supplied. The electrolyte circulation path 4 has, for example, a two-layer structure composed of a first layer disposed on the inside thereof and a second layer disposed on the outside of the first layer. The first layer is disposed on the inside thereof and provides insulation to the electrolyte circulation path 4, and contains, for example, a resin. The second layer provides strength to the electrolyte circulation path 4 and contains, for example, a metal.

[0072] The electrolyte circulation path 4 has a first electrolyte circulation path 41A and a second electrolyte circulation path 41B. The first electrolyte circulation path 41A connects the first chamber 21A and the first electrolyte tank 31A, and is a path through which the first aqueous electrolyte solution 213A is circulated and supplied. The second electrolyte circulation path 41B connects the second chamber 21B and the second electrolyte tank 31B, and is a path through which the second aqueous electrolyte solution 213B is circulated and supplied.

[0073] (Pump) The pump 5 is a circulation pump that circulates and supplies the electrolyte. The pump 5 has a first electrolyte circulation pump 51A and a second electrolyte circulation pump 51B. The first electrolyte circulation pump 51A circulates and supplies the first aqueous electrolyte solution 213A between the first chamber 21A and the first electrolyte solution tank 31A. The second electrolyte circulation pump 51B circulates and supplies the second aqueous electrolyte solution 213B between the second chamber 21B and the second electrolyte solution tank 31B.

[0074] [Preferred embodiment] In one preferred embodiment, the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B are the redox flow battery electrolyte solutions according to the first embodiment, and the redox active substance contained in both the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B is the same. In this embodiment, because the redox active substance is the same, even if the redox active substance permeates the diaphragm 25, it functions as a redox active substance on the permeated side. Therefore, in this embodiment, even if the redox active substance permeates, the function of the redox flow battery 1 is unlikely to deteriorate.

[0075] In another preferred embodiment, the coordination moieties of the water-soluble chelate polymers contained in first aqueous electrolyte solution 213A and second aqueous electrolyte solution 213B are different from each other. In this embodiment, even though first aqueous electrolyte solution 213A and second aqueous electrolyte solution 213B contain the same redox active substance, a significant potential difference can be formed by selecting and combining different coordination moieties of the water-soluble chelate polymers. In this manner, this embodiment can ensure design freedom while suppressing deterioration in the function of redox flow battery 1 due to permeation of the redox active substance.

[0076] In yet another preferred embodiment, the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B are the redox flow battery electrolyte solutions according to the first embodiment, the coordination moieties of the water-soluble chelate polymers contained in both the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B are the same, and the redox active substances contained in both the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B are ions of at least one metal selected from the group consisting of Zn, Fe, Ti, Cu, Co, Ce, Cr, and Mn, but are different from each other. In this embodiment, since the first aqueous electrolyte solution 213A and the second aqueous electrolyte solution 213B contain the same type of water-soluble chelate polymer, costs can be reduced. Meanwhile, a significant potential difference can be generated simply by selecting and combining different redox active substances. In this manner, this embodiment ensures design flexibility while reducing costs.

[0077] The embodiments of the redox flow battery electrolyte and redox flow battery according to the present disclosure are as follows. <1> An electrolyte for a redox flow battery comprising: a substance containing a metal ion; a water-soluble polymer having a coordinating moiety in a side chain; and an aqueous solvent, wherein the coordinating moiety coordinates with the metal ion to form a metal complex. <2> The electrolyte for a redox flow battery according to <1>, in which the water-soluble polymer is a polyamine derivative. <3> The electrolyte for a redox flow battery according to <1> or <2>, in which the water-soluble polymer contains a nitrogen atom and an oxygen atom. <4> The electrolyte for a redox flow battery according to any one of <1> to <3>, in which the water-soluble polymer is a peptide derivative. <5> The electrolyte for a redox flow battery according to <4>, in which the peptide derivative contains a repeating unit derived from lysine. <6> The electrolyte solution for a redox flow battery according to any one of <1> to <5>, wherein the metal ion is an ion of one metal selected from the group consisting of Zn, Fe, Ti, Cu, Ce, Cr, and Mn. <7> The electrolyte solution for a redox flow battery according to any one of <1> to <6>, wherein the metal ion is an iron ion. <8> The electrolyte solution for a redox flow battery according to any one of <1> to <7>, wherein the electrolyte solution is an alkaline aqueous solution. <9> The electrolyte solution for a redox flow battery according to any one of <1> to <8>, wherein the coordinating moiety is at least one coordinating moiety derived from a ligand selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), ethylenediaminebis(2-hydroxyphenyl)acetic acid (EDDHA), diethylenetriaminepentaacetic acid (DTPA), and triethanolamine (TEOA) and / or a coordinating moiety containing at least one functional group selected from the group consisting of a hydroxy group, a carboxy group, a phosphate group, a sulfo group, a phenol group, and a pyridine group. <10> The electrolyte solution for a redox flow battery according to any one of <1> to <9>, wherein the coordination moiety includes a plurality of different coordination moieties.<11> A redox flow battery that circulates an electrolyte between an electric cell and an electrolyte tank, and is charged and discharged by an oxidation-reduction reaction of an active substance, comprising: an electric cell having: a first chamber having a first electrode and a first aqueous electrolyte solution in contact with the first electrode; a second chamber having a second electrode and a second aqueous electrolyte solution in contact with the second electrode; and a diaphragm that separates the first chamber and the second chamber and electrically isolates the first aqueous electrolyte solution from the second aqueous electrolyte solution; and an electrolyte tank having: a first electrolyte tank connected to the first chamber and storing the first aqueous electrolyte solution; and a second electrolyte tank connected to the second chamber and storing the second aqueous electrolyte solution, wherein at least one of the first aqueous electrolyte solution and the second aqueous electrolyte solution is the electrolyte solution according to any one of <1> to <10>. <12> The redox flow battery according to <11>, wherein the first aqueous electrolytic solution and the second aqueous electrolytic solution are the redox flow battery electrolyte solutions according to any one of <1> to <10>, and the substance contained in both the first aqueous electrolytic solution and the second aqueous electrolytic solution is the same. <13> The redox flow battery according to <11> or <12>, wherein the substance is an iron ion. <14> The redox flow battery according to <12>, wherein the coordination moieties of the water-soluble polymers contained in both the first aqueous electrolytic solution and the second aqueous electrolytic solution are different. <15> The redox flow battery according to any one of <11> to <14>, wherein the first aqueous electrolytic solution and the second aqueous electrolytic solution are the redox battery electrolyte solutions according to any one of <1> to <10>, wherein the coordination moieties of the water-soluble polymers contained in both the first aqueous electrolytic solution and the second aqueous electrolytic solution are the same, and the substances contained in both the first aqueous electrolytic solution and the second aqueous electrolytic solution are ions of at least one metal selected from the group consisting of Zn, Fe, Ti, Cu, Ce, Cr, and Mn, and are different from each other. <16> The redox flow battery according to any one of <11> to <15>, wherein the coordination moieties contained in one molecule of the water-soluble polymer are different from each other.

[0078] The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to these examples.

[0079] Example 1 1. Preparation of Reagents The following reagents are used to prepare an aqueous electrolyte. (Amino acid) Lysine: manufactured by Tokyo Chemical Industry Co., Ltd. (Water-soluble condensing agent) 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide: manufactured by Tokyo Chemical Industry Co., Ltd. (Ligand) Ethylenediaminetetraacetic acid (EDTA) tetrasodium dihydrate: manufactured by Tokyo Chemical Industry Co., Ltd. N,N-bis(2-hydroxyethyl)glycine (DHEG): manufactured by Tokyo Chemical Industry Co., Ltd. (Redox active substance) Iron(III) chloride hexahydrate (iron salt): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Manganese(II) chloride tetrahydrate (manganese salt): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. (Solvent) Deionized water (Alkalinity adjuster) Sodium hydroxide: manufactured by Tokyo Chemical Industry Co., Ltd.

[0080] [2. Synthesis of Water-Soluble Chelate Polymer] Peptide derivative [1] is synthesized as a water-soluble chelate polymer. Lysine as an amino acid, 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide as an aqueous condensing agent, and deionized water are mixed and subjected to condensation polymerization. This forms an amide bond (peptide bond), synthesizing the peptide. The resulting peptide is purified using a column to obtain ε-poly-L-lysine as a peptide.

[0081] The resulting peptide, ε-poly-L-lysine, and ethylenediaminetetraacetic acid were mixed and stirred at a molar ratio (ε-poly-L-lysine:ethylenediaminetetraacetic acid) of 1:1 at room temperature (25° C.) for 5 hours. This reaction was carried out according to the following reaction formula: [In the above reaction formula, n represents the degree of polymerization and is a positive integer], the primary amino group (—NH ２ This is a dehydration condensation reaction in which an amide bond is formed between the carboxyl group (-COOH) of ethylenediaminetetraacetic acid and ε-poly-L-lysine. This results in the synthesis of peptide derivative [1], in which EDTA is bound to the side chain of ε-poly-L-lysine via an amide bond. The solubility of peptide derivative [1] is 10 g / L.

[0082] [3. Preparation of Electrolyte] (Catholite: First Aqueous Electrolyte) Iron chloride (iron salt) containing a redox active substance, deionized water (solvent) as a solvent, and sodium hydroxide as an alkalinity adjuster are stirred using a stirrer (mixer) to obtain an iron (III) aqueous electrolyte solution (pH = 8). The obtained electrolyte is designated as catholyte (first aqueous electrolyte).

[0083] (Anolyte: Second Aqueous Electrolyte) The resulting peptide derivative [1] as a redox-active polymer, iron chloride (iron salt) containing a redox-active substance, deionized water as a solvent, and sodium hydroxide as an alkalinity adjuster are stirred using a stirrer (mixer) to obtain an iron(II)-polylysine EDTA aqueous electrolyte (pH = 8). The resulting electrolyte is designated as anolyte (second aqueous electrolyte).

[0084] [4. Fabrication of Redox Flow Battery] (Preparation of Electric Cell) An electric cell as shown in FIG. 1 is fabricated. The electric cell has a substantially cubic shape and is composed of two connected substantially rectangular parallelepipeds. A diaphragm is sandwiched between the flanges (not shown) of two substantially rectangular parallelepiped glass containers, and the flanges are clamped and fixed with screws. This results in a substantially cubic container having two spaces separated by a diaphragm. The two substantially rectangular parallelepiped spaces in this substantially cubic container correspond to the first and second chambers, respectively. An electrode (carbon plate electrode) is provided on each of the inner wall surfaces of the two substantially rectangular parallelepiped spaces facing the partition. Furthermore, a first opening is provided on the upper surface of the substantially rectangular parallelepiped shape in each of the first and second chambers, and a second opening is provided on the lower surface of the substantially rectangular parallelepiped shape.

[0085] (Preparation of the circulation mechanism) A first cylindrical container having an internal volume approximately equal to that of the first chamber, a second cylindrical container having an internal volume approximately equal to that of the second chamber, and four rubber tubes are prepared. The first cylindrical container and the second cylindrical container have connection terminals on their top and bottom surfaces, respectively.

[0086] The first chamber of the approximately cubic container is connected to the first cylindrical container by two rubber tubes. Specifically, one end of one rubber tube is connected to the first opening of the first chamber and the other end is connected to a connection terminal on the top surface of the first cylindrical container. One end of another rubber tube is connected to the second opening of the first chamber and the other end is connected to a connection terminal on the bottom surface of the first cylindrical container. A pump for circulating catholyte is connected to this other rubber tube, thereby connecting the first chamber to the first cylindrical container. Similarly, two other rubber tubes connect the second chamber to the second cylindrical container. A pump for circulating anolyte is connected to the rubber tube connecting the second opening of the second chamber to the connection terminal on the bottom surface of the second cylindrical container.

[0087] (Adding the Electrolyte) The substantially cubic container is placed so that the first opening faces vertically upward. The first cylindrical container and the second cylindrical container are placed so that they face vertically downward from top to bottom. The rubber tube is removed from the first opening of the first chamber, and catholyte is added through the first opening of the first chamber. The volume of the catholyte fills approximately 80% of the total volume of the first chamber and the first cylindrical container. The first opening of the first chamber is connected to the removed rubber tube. This brings the catholyte into contact with the electrode placed inside the first chamber in the first chamber. Similarly, anolyte is added to the second chamber. This brings the anolyte into contact with the electrode placed inside the second chamber in the second chamber. This completes the redox flow battery of Example 1.

[0088] The redox flow battery of Example 1 includes an iron(III) aqueous solution-based electrolyte as the catholyte (first aqueous electrolyte) and an iron(II)-polylysine EDTA aqueous solution-based electrolyte as the anolyte (second aqueous electrolyte). In the redox flow battery of Example 1, one of the catholyte and the anolyte is an electrolyte that falls within the scope of the invention according to claim 1.

[0089] In the redox flow battery of Example 1, the coordination moiety derived from ethylenediaminetetraacetic acid is contained in the water-soluble chelate polymer and bound thereto. Therefore, in the anolyte (second aqueous electrolyte), the coordination moiety is less likely to diffuse through the membrane. Because the diffusion of the coordination moiety is suppressed in this manner, the redox flow battery of Example 1 is less likely to experience deterioration in battery performance.

[0090] Example 2 A redox flow battery of Example 2 is fabricated in the same manner as Example 1, except that the catholyte (first aqueous electrolyte) and the anolyte (second aqueous electrolyte) are different.

[0091] (Catholite: First Aqueous Electrolyte) The obtained peptide derivative [1] as a water-soluble chelating polymer, iron chloride (iron salt) containing a redox active substance, deionized water as a solvent, and sodium hydroxide as an alkalinity adjuster are stirred using a stirrer (mixer) to obtain an iron(III)-polylysine EDTA aqueous solution electrolyte (pH = 12). The obtained electrolyte is designated as catholyte (first aqueous electrolyte).

[0092] (Anolyte: Second Aqueous Electrolyte) The peptide derivative [2] as a water-soluble chelating polymer, iron chloride (iron salt) containing a redox-active substance, deionized water as a solvent, and sodium hydroxide as an alkalinity regulator are stirred using a stirrer (mixer) to obtain an iron(II)-polylysine DHEG aqueous electrolyte (pH = 12). The resulting electrolyte is designated as anolyte (second aqueous electrolyte).

[0093] The peptide derivative [2] is synthesized by mixing and stirring ε-poly-L-lysine as a peptide and N,N-bis(2-hydroxyethyl)glycine (DHEG) in a molar ratio (ε-poly-L-lysine:DHEG) of 1:1 at room temperature (25°C) for 5 hours to form an amide bond (peptide bond). This reaction is represented by the following reaction formula: [In the above reaction formula, n represents the degree of polymerization and is a positive integer], the primary amino group (—NH ２This is a dehydration condensation reaction in which DHEG is bound to the side chain of ε-poly-L-lysine via an amide bond. The solubility of the peptide derivative [2] is 10 g / L.

[0094] The redox flow battery of Example 2 includes an iron(III)-polylysine EDTA aqueous solution-based electrolyte as the catholyte (first aqueous electrolyte), and an iron(II)-polylysine TEOA aqueous solution-based electrolyte as the anolyte (second aqueous electrolyte).

[0095] In the redox flow battery of Example 2, both catholyte and anolyte are electrolytes encompassed within the scope of the invention according to claim 1. Compared to Example 1, the coordination moieties in the anolyte (second aqueous electrolyte) are less likely to diffuse through the diaphragm, and the coordination moieties in the catholyte (first aqueous electrolyte) are also less likely to diffuse through the diaphragm. Because the diffusion of the coordination moieties is further suppressed in this way, the redox flow battery of Example 2 is even less susceptible to deterioration in battery performance.

[0096] Furthermore, in the redox flow battery of Example 2, when comparing catholyte and anolyte, only the coordination moiety of the water-soluble chelate polymer is different. By changing only the coordination moiety in both electrolytes, a significant potential difference can be created. In other words, by changing the coordination moiety of the water-soluble chelate polymer, it is possible to modulate the redox potential of the redox flow battery and the potential difference between them, for example, depending on the desired application and performance.

[0097] Furthermore, the redox flow battery of Example 2 has in common the redox active material being iron ions. Therefore, although the membrane does not allow the permeation of only a specific chemical species (e.g., hydroxide ions), even if small amounts of redox active materials permeate each other, the performance of the redox flow battery is unlikely to deteriorate because only the valence differs.

[0098] Example 3 A redox flow battery of Example 3 was fabricated in the same manner as in Example 1, except that the catholyte (first aqueous electrolyte solution) was different.

[0099] (Catholite: First Aqueous Electrolyte) The resulting peptide derivative [1] as a water-soluble chelating polymer, manganese chloride (manganese salt) containing a redox active substance, deionized water as a solvent, and sodium hydroxide as an alkalinity adjuster are stirred using a stirrer (mixer) to obtain a manganese(III)-polylysine EDTA aqueous electrolyte solution (pH = 8). The resulting electrolyte is designated as catholyte (first aqueous electrolyte).

[0100] In the redox flow battery of Example 3, both catholyte and anolyte are electrolytes encompassed within the scope of the invention according to claim 1. Compared to Example 1, the coordination moieties in the anolyte (second aqueous electrolyte) are less likely to diffuse through the diaphragm, and the coordination moieties in the catholyte (first aqueous electrolyte) are also less likely to diffuse through the diaphragm. Because the diffusion of the coordination moieties is further suppressed in this way, the redox flow battery of Example 3 is even less susceptible to deterioration in battery performance.

[0101] Furthermore, in the redox flow battery of Example 3, when comparing catholyte and anolyte, only the redox active material is different. In this way, by changing only the redox active material in both electrolytes, a significant potential difference can be created. In other words, by changing the redox active material, it is possible to modulate the redox potential of the redox flow battery and the potential difference between them depending on, for example, the desired application and performance.

[0102] Example 4 A redox flow battery of Example 4 is fabricated in the same manner as in Example 1, except that the anolyte (second aqueous electrolyte) is different.

[0103] (Anolyte: Second Aqueous Electrolyte) The peptide derivative [3] as a water-soluble chelating polymer, iron chloride (iron salt) containing a redox-active substance, deionized water as a solvent, and sodium hydroxide as an alkalinity regulator are stirred using a stirrer (mixer) to obtain an iron(II)-polylysine EDTA / DHEG aqueous electrolyte (pH = 8). The resulting electrolyte is designated as anolyte (second aqueous electrolyte).

[0104] The peptide derivative [3] was prepared by mixing and stirring ε-poly-L-lysine as a peptide, ethylenediaminetetraacetic acid (EDTA), and N,N-bis(2-hydroxyethyl)glycine (DHEG) (molar ratio: EDTA / DHEG = 1 / 1) at a molar ratio (ε-poly-L-lysine:[EDTA+DHEG]) of 1:1 at room temperature (25°C) for 5 hours. This reaction is represented by the following reaction formula: [In the above reaction formula, n represents the degree of polymerization and is a positive integer], the primary amino group (—NH ２ This is a dehydration condensation reaction in which amide bonds (peptide bonds) are formed between ε-poly-L-lysine (ε-poly-L-lysine) and ethylenediaminetetraacetic acid (EDTA) and the carboxyl groups (-COOH) of N,N-bis(2-hydroxyethyl)glycine (DHEG). This results in the synthesis of peptide derivative [3], in which EDTA and DHEG are bound to the side chains of ε-poly-L-lysine via amide bonds. The solubility of peptide derivative [3] is 10 g / L.

[0105] The redox flow battery of Example 4 includes an iron(II)-polylysine EDTA / DHEG aqueous electrolyte as the anolyte (second aqueous electrolyte), and an iron(III) aqueous electrolyte as the catholyte. In the redox flow battery of Example 4, one of the catholyte and the anolyte is an electrolyte within the scope of the invention according to claim 1.

[0106] In the redox flow battery of Example 4, the coordination moieties derived from ethylenediaminetetraacetic acid and N,N-bis(2-hydroxyethyl)glycine are contained and bound within the water-soluble chelate polymer. Therefore, in the anolyte (second aqueous electrolyte), the coordination moieties are less likely to diffuse through the membrane. Because the diffusion of the coordination moieties is suppressed in this manner, the redox flow battery of Example 1 is less likely to experience degradation in battery performance.

[0107] Furthermore, in the redox flow battery of Example 4, the multiple coordination moieties contained in one molecule of peptide derivative [3] are derived from ethylenediaminetetraacetic acid (EDTA) and N,N-bis(2-hydroxyethyl)glycine (DHEG). Therefore, the multiple coordination moieties contained in one molecule of peptide derivative [3] are different. By varying the types of the multiple coordination moieties in one molecule of the water-soluble chelate polymer, the redox potential of the electrolyte can be finely adjusted.

[0108] The redox flow battery electrolyte according to the present disclosure can be used in a redox flow battery, and the redox flow battery according to the present disclosure can be used as a storage battery for electricity generated in a power plant or a power generation device.

[0109] DESCRIPTION OF SYMBOLS 1... Redox flow battery 2... Electric cell 21A... First chamber 211A... First electrode 213A... First aqueous electrolyte 21B... Second chamber 211B... Second electrode 213B... Second aqueous electrolyte 25... Diaphragm 3... Electrolyte tank 31A... First electrolyte tank 31B... Second electrolyte tank 4... Electrolyte circulation path 41A... First electrolyte circulation path 41B... Second electrolyte circulation path 5... Pump 51A... First electrolyte circulation pump 51B... Second electrolyte circulation pump 100... Power converter (power conditioner, DC / AC converter) 200... Power generation unit 300... Load unit

Claims

1. An electrolyte for a redox flow battery comprising: a substance containing a metal ion; a water-soluble polymer having a coordinating moiety in a side chain; and an aqueous solvent, wherein the coordinating moiety coordinates to the metal ion to form a metal complex.

2. The electrolyte for a redox flow battery according to claim 1, wherein the water-soluble polymer is a polyamine derivative.

3. The electrolyte for a redox flow battery according to claim 1 or 2, wherein the water-soluble polymer contains a nitrogen atom and an oxygen atom.

4. The electrolyte for a redox flow battery according to any one of claims 1 to 3, wherein the water-soluble polymer is a peptide derivative.

5. The electrolyte for a redox flow battery according to claim 4, wherein the peptide derivative contains a repeating unit derived from lysine.

6. The electrolyte for a redox flow battery according to any one of claims 1 to 5, wherein the metal ion is an ion of one metal selected from the group consisting of Zn, Fe, Ti, Cu, Co, Ce, Cr, and Mn.

7. The electrolyte for a redox flow battery according to any one of claims 1 to 6, wherein the metal ion is an iron ion.

8. The electrolyte for a redox flow battery according to any one of claims 1 to 7, which is an alkaline aqueous solution.

9. The redox flow battery electrolyte according to any one of claims 1 to 8, wherein the coordinating moiety is at least one coordinating moiety derived from a ligand selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), ethylenediaminebis(2-hydroxyphenyl)acetic acid (EDDHA), diethylenetriaminepentaacetic acid (DTPA), and triethanolamine (TEOA), and / or a coordinating moiety including at least one functional group selected from the group consisting of a hydroxy group, a carboxy group, a phosphate group, a sulfo group, a phenol group, and a pyridine group.

10. The electrolyte for a redox flow battery according to any one of claims 1 to 9, wherein the coordination moiety includes a plurality of different coordination moieties.

11. A redox flow battery in which an electrolyte is circulated between an electric cell and an electrolyte tank, and which is charged and discharged by an oxidation-reduction reaction of an active substance, comprising: an electric cell having: a first chamber having a first electrode and a first aqueous electrolyte in contact with the first electrode; a second chamber having a second electrode and a second aqueous electrolyte in contact with the second electrode; and a diaphragm which separates the first chamber and the second chamber and electrically isolates the first aqueous electrolyte from the second aqueous electrolyte; and an electrolyte tank having: a first electrolyte tank connected to the first chamber and storing the first aqueous electrolyte; and a second electrolyte tank connected to the second chamber and storing the second aqueous electrolyte, wherein at least one of the first aqueous electrolyte and the second aqueous electrolyte is the electrolyte according to any one of claims 1 to 10.

12. The redox flow battery according to claim 11, wherein the first aqueous electrolyte solution and the second aqueous electrolyte solution are electrolyte solutions for redox flow batteries according to any one of claims 1 to 10, and the substance contained in both the first aqueous electrolyte solution and the second aqueous electrolyte solution is the same.

13. The redox flow battery according to claim 11 or 12, wherein the substance is an iron ion.

14. The redox flow battery of claim 12, wherein the coordination moieties of the water-soluble polymer contained in both the first aqueous electrolyte solution and the second aqueous electrolyte solution are different.

15. The redox flow battery according to any one of claims 11 to 14, wherein the first aqueous electrolyte solution and the second aqueous electrolyte solution are the electrolyte solutions for redox batteries according to any one of claims 1 to 10, the coordination moieties of the water-soluble polymer contained in both the first aqueous electrolyte solution and the second aqueous electrolyte solution are the same, and the substances contained in both the first aqueous electrolyte solution and the second aqueous electrolyte solution are ions of at least one metal selected from the group consisting of Zn, Fe, Ti, Cu, Co, Ce, Cr, and Mn, and are different from each other.

16. The redox flow battery according to any one of claims 11 to 15, wherein a plurality of coordination moieties contained in one molecule of the water-soluble polymer are different.

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