Redox flow battery

Abstract

A redox flow battery includes a cell unit having a first chamber and a second chamber separated by a separator, a first tank storing a first electrolyte, a first circulation device circulating the first electrolyte between the first chamber and the first tank, a second tank storing a second electrolyte, and a second circulation device circulating the second electrolyte between the second chamber and the second tank, the first electrolyte and the second electrolyte each containing an active material, at least one of the active material contained in the first electrolyte or the active material contained in the second electrolyte being a quinone multimer in which a plurality of quinones are bonded via alkyl chains or a hydroquinone multimer in which a plurality of hydroquinones are bonded via alkyl chains.

Description

Technical Field

[0001] This invention relates to redox flow batteries.

[0002] This application claims priority based on Japanese Patent Application No. 2020-108615, filed with the Japan Patent Office on June 24, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] Redox flow batteries are a technology conceived by NASA in 1974. They consist of battery cells and a tank for storing electrolyte. A pump circulates the electrolyte between the battery cells and the tank for charging and discharging. Redox flow batteries can be freely designed to store large amounts of electricity based on the tank's capacity, making them suitable for storing large amounts of electricity and expected to be used to balance electricity demand, including natural energy sources.

[0004] In the current mainstream redox flow batteries, vanadium is used as the active material in the electrolyte. However, due to the soaring price of vanadium in recent years, the widespread adoption of redox flow batteries has not progressed. Nevertheless, research targeting vanadium alternatives is advancing worldwide, and in recent years, redox flow batteries using organic materials and metal complexes as active materials have been reported.

[0005] For example, Patent Document 1 discloses a redox flow battery that uses quinone / hydroquinone as active materials and performs charging and discharging through a redox reaction between the two. Furthermore, Non-Patent Document 1 discloses a redox flow battery that uses potassium ferrocyanide as the positive electrode active material and 2,5-dihydroxybenzoquinone (2,5-DHBQ) as the negative electrode active material.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2015-534708

[0009] Non-patent literature

[0010] Non-patent document 1: Z. Yang et al, "Alkaline Benzoquinone Aqueous Flow Battery for Large-Scale Storage of Electrical Energy", Advanced. Energy Materials, 2017 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Typically, redox flow batteries suffer from a capacity reduction problem with increasing charge-discharge cycles. In Non-Patent Literature 1, one of the main reasons for this capacity reduction is the cross-permeability of 2,5-DHBQ through the separator due to its small molecular weight.

[0013] In view of the above, at least one embodiment of the present invention aims to provide a redox flow battery that can suppress capacity reduction with increasing charge-discharge cycles.

[0014] Methods for solving problems

[0015] To achieve the above objectives, the redox flow battery of the present invention comprises: a battery cell having a first chamber and a second chamber separated by a membrane; a first tank for storing a first electrolyte; a first circulation device for circulating the first electrolyte between the first chamber and the first tank; a second tank for storing a second electrolyte; and a second circulation device for circulating the second electrolyte between the second chamber and the second tank. The first electrolyte and the second electrolyte each contain an active material, and at least one of the active material contained in the first electrolyte or the active material contained in the second electrolyte is a quinone polymer formed by multiple quinones bonded via alkyl chains or a hydroquinone polymer formed by multiple hydroquinones bonded via alkyl chains.

[0016] Invention Effects

[0017] The redox flow battery according to the present invention uses quinone polymers / hydroquinone polymers with a molecular weight larger than that of quinone / hydroquinone monomers as active materials, thereby suppressing the occurrence of cross-conversion phenomena compared to the case where quinone / hydroquinone monomers are used as active materials, and thus suppressing the capacity reduction that occurs with increasing charge-discharge cycles. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the configuration of a redox flow battery according to one embodiment of the present invention.

[0019] Figure 2 This is a graph showing the relationship between the number of quinone units in quinone polymers and the diffusion coefficient.

[0020] Figure 3 This is a schematic diagram illustrating the configuration of a redox flow battery according to another embodiment of the present invention.

[0021] Figure 4 This is the cyclic voltammogram of the hydroquinone pentamer prepared in Example 1. Detailed Implementation

[0022] Hereinafter, a redox flow battery according to an embodiment of the present invention will be described with reference to the accompanying drawings. This embodiment represents one aspect of the present invention and is not intended to limit the present invention; modifications can be made freely within the scope of the technical concept of the present invention.

[0023] <Construction of a redox flow battery according to an embodiment of the present invention>

[0024] like Figure 1 As shown, a redox flow battery 1 according to an embodiment of the present invention includes: a battery cell 2 having a first chamber 3 and a second chamber 4 separated by a separator 5; a first tank 6 storing a first electrolyte 12 containing active material; a first pump 7 serving as a first circulation device, which circulates the first electrolyte 12 between the first chamber 3 and the first tank 6; a second tank 8 storing a second electrolyte 13 containing active material; and a second pump 9 serving as a second circulation device, which circulates the second electrolyte 13 between the second chamber 4 and the second tank 8.

[0025] A first tank 6 and a first pump 7 are disposed in a first electrolyte circulation path 10 connected to a first chamber 3 at one end and the other end. A second tank 8 and a second pump 9 are disposed in a second electrolyte circulation path 11 connected to a second chamber 4 at one end and the other end. A first electrode 14 is disposed in the first chamber 3, and a second electrode 15 is disposed in the second chamber 4. The first electrode 14 and the second electrode 15 are electrically connected to an AC-DC converter 16. The AC-DC converter 16 can be electrically connected to a load 17 and an AC power supply 18, respectively. It should be noted that if a DC power supply is used instead of the AC power supply 18 and the load 17 operates with DC current, the AC-DC converter 16 is not required.

[0026] <First electrolyte and second electrolyte and active materials>

[0027] The first electrolyte 12 and the second electrolyte 13 are each prepared by dissolving the active material in an aqueous solution containing a supporting electrolyte. This aqueous solution can be an alkaline aqueous solution containing potassium hydroxide, sodium hydroxide, etc., a neutral aqueous solution containing potassium chloride, sodium chloride, etc., or an acidic aqueous solution containing hydrogen chloride, sulfuric acid, etc. The active material dissolved in either the first electrolyte 12 or the second electrolyte 13 can be a metal ion such as vanadium, a metal complex, air, halogens, organic molecules, etc., but at least one of the active materials dissolved in either the first electrolyte 12 or the second electrolyte 13 (i.e., both) is a quinone polymer or a hydroquinone polymer having the structure described later. The metal ions can be zinc or other metal ions that are deposited during reduction.

[0028] The quinone polymer used as the active material in the redox flow battery 1 is formed by multiple quinones bonded together via alkyl chains. Here, quinone refers to the substance shown in chemical formula (I) or (II) below, which has a structure in which oxygen atoms are bonded to two of the six carbon atoms forming a six-membered ring via double bonds, and R1 to R4 are bonded to the other four carbon atoms respectively. R1 to R4 can be any functional group or element such as hydrogen, C1-C6 alkyl, halogen, hydroxyl, C1-C6 alkoxy, sulfonyl, amino, nitro, carboxyl, phosphate, or thiol. Furthermore, for example, in chemical formula (I), the end of R1 can bond with the end of R2 to form a cyclic structure, or the end of R3 can bond with the end of R4 to form a cyclic structure; that is, multiple cyclic structures can be formed. Multiple cyclic structures can also be formed in chemical formula (II).

[0029] [Chemical Formula 1]

[0030]

[0031] As shown in chemical formula (III) below, the quinone polymer of the active material used in the redox flow battery 1 is formed by bonding two or more quinones of one or more types via alkyl chains R5 having one or more carbon atoms. In chemical formula (III), n is a natural number of 2 or more. Among the carbon atoms constituting the 6-membered ring, R6 and R7 are bonded to two carbon atoms other than the two carbon atoms bonded to oxygen atoms via double bonds and the two carbon atoms bonded to alkyl chains R5. R6 and R7, like R1 to R4, can be selected from any functional group and element. It should be noted that the quinone polymer shown in chemical formula (III) is formed by bonding two or more quinones as shown in chemical formula (I), but it can also be formed by bonding two or more quinones as shown in chemical formula (II).

[0032] [Chemical Formula 2]

[0033]

[0034] As shown in the reversible reaction formula (1) below, the quinone polymer represented by chemical formula (III) becomes a hydroquinone polymer through electron and hydrogen atom donation and acceptance. When supplied to the chamber on the negative electrode side of battery cell 2, the quinone polymer is used as the active material in the state that requires charging for sufficient discharge (hereinafter referred to as the "discharge state"), and the hydroquinone polymer is used as the active material in the state that can discharge when fully charged (hereinafter referred to as the "charge state"). On the other hand, when supplied to the chamber on the positive electrode side of battery cell 2, the hydroquinone polymer is used as the active material in the discharge state, and the quinone polymer is used as the active material in the charge state. Regarding the quinone polymer and hydroquinone polymer shown in the reversible reaction formula (1), in this invention, the hydroquinone polymer is referred to as "the hydroquinone polymer corresponding to the quinone polymer", and the quinone polymer is referred to as "the quinone polymer corresponding to the hydroquinone polymer".

[0035] [Chemical Formula 3]

[0036]

[0037] The two or more quinones constituting a quinone polymer need not be a single quinone. For example, as shown in the following chemical formula (IV), two quinones can be bonded together via alkyl chains R5. R8 and R9, like R1 to R7, can be selected from any functional group and element. In the following chemical formula (IV), a compound consisting of x first quinones bonded to a 6-membered ring with R6 and R7 bonded together is depicted bonded to y second quinones bonded to a 6-membered ring with R8 and R9 bonded together. However, the first and second quinones can also be bonded alternately, in any order following any rules, or randomly. It should be noted that three or more quinones can also be bonded together via alkyl chains R5. The alkyl chain R5 is not limited to one type and can include multiple alkyl chains.

[0038] [Chemical Formula 4]

[0039]

[0040] In addition, as shown in the following chemical formula (V), the quinone polymer of the active material used in the redox flow battery 1 can be a pyranoquinone (Japanese original: ピラーキノン) obtained by synthesizing multiple quinones (which can be one quinone or two or more quinones) into a cyclic form via alkyl chain R5 bonds.

[0041] [Chemical Formula 5]

[0042]

[0043] As an example of such pyranoquinones, a benzoquinone pentamer obtained by cyclic synthesis of five benzoquinones via methylene bonds can be cited. The hydroquinone pentamer corresponding to this benzoquinone pentamer is shown in the following chemical formula (VI).

[0044] [Chemical Formula 6]

[0045]

[0046] <Operation of a redox flow battery according to an embodiment of the present invention>

[0047] Next, based on Figure 1 The operation of the redox flow cell 1 will be explained. It will be explained as follows: A quinone polymer represented by any of the chemical formulas (III) to (V) or a corresponding hydroquinone polymer is dissolved in the first electrolyte 12 as an active material. The active material dissolved in the second electrolyte 13 is a metal ion, a metal complex, or a quinone polymer different from the quinone polymer dissolved in the first electrolyte 12 or a corresponding hydroquinone polymer.

[0048] When the redox flow battery 1 is in a charging state, if chamber 3 is used as the positive electrode and chamber 4 as the negative electrode, the active material dissolved in the first electrolyte 12 is a quinone polymer. By operating the first pump 7, the first electrolyte 12 stored in the first tank 6 is supplied to chamber 3 via the first electrolyte circulation path 10. After chamber 3 is filled with the first electrolyte 12, the first electrolyte 12 flows out of chamber 3 and returns to the first tank 6 via the first electrolyte circulation path 10. In this way, the first electrolyte 12 circulates between chamber 3 and the first tank 6. On the other hand, by operating the second pump 9, the second electrolyte 13 circulates between chamber 4 and the second tank 8 using the same operation as described above.

[0049] Within chamber 3, through the forward reaction of reversible reaction formula (1), the quinone polymer accepts electrons from the first electrode 14 and is converted into a hydroquinone polymer. Conversely, electrons move from the active material dissolved in the second electrolyte 13 to the second electrode 15 and flow into the AC-DC converter 16. That is, when the redox flow battery 1 is in a charging state, the first electrode 14 is the positive electrode, and the second electrode 15 becomes the negative electrode, generating a direct current. This direct current is converted into an alternating current by the AC-DC converter 16 and supplied to the load 17.

[0050] When the redox flow cell 1 is in a discharged state, the active material dissolved in the first electrolyte 12 is hydroquinone polymer. The alternating current from the AC power source 18 is converted into direct current by the AC-DC converter 16. In the first chamber 3, through the reverse reaction of the reversible reaction formula (1), the hydroquinone polymer is converted into a quinone polymer, and electrons move from the hydroquinone polymer to the first electrode 14 and flow into the AC-DC converter 16. On the other hand, electrons from the AC-DC converter 16 flow to the second electrode 15 and are accepted by the active material dissolved in the second electrolyte 13.

[0051] <Effects of a redox flow battery according to an embodiment of the present invention>

[0052] As mentioned above, redox flow batteries generally suffer from a significant capacity reduction with increasing charge-discharge cycles. Furthermore, as described above, Non-Patent Document 1 cites cross-contamination of the active material through the separator as one of the main reasons for this capacity reduction. While Non-Patent Document 1 uses quinone / hydroquinone monomers as the active material, the redox flow battery 1 of this invention uses quinone polymers / hydroquinone polymers as the active material dissolved in at least one of the first electrolyte 12 or the second electrolyte 13. Thus, by using quinone polymers / hydroquinone polymers with a larger molecular weight than quinone / hydroquinone monomers as the active material, the cross-contamination phenomenon can be suppressed compared to using quinone / hydroquinone monomers as the active material, thereby suppressing the capacity reduction with increasing charge-discharge cycles.

[0053] As an active substance, namely a quinone polymer / hydroquinone polymer, when using a substance having a structure obtained by cyclic synthesis of multiple quinones via alkyl chain bonds (e.g., chemical formula (V)) or a structure obtained by cyclic synthesis of multiple hydroquinones via alkyl chain bonds (e.g., chemical formula (VI)), there are no terminals in the active substance molecule. Therefore, each quinone unit or each hydroquinone unit constituting the active substance becomes equivalent, and thus the active substance molecule as a whole can be uniformly redox-induced. In addition, when using a quinone polymer / hydroquinone polymer containing two or more quinones / hydroquinones, the physical properties of the active substance can be easily adjusted by adjusting at least one of the types or ratios of quinones / hydroquinones.

[0054] In the redox flow battery 1, the quinone / hydroquinone polymers used as active materials contain multiple quinones / hydroquinones bonded via alkyl chains. In active materials formed by direct bonding of multiple quinones or hydroquinones, the conjugation of each quinone or hydroquinone extends to the entire active material molecule. Conversely, in active materials formed by alkyl chains, the conjugation of each quinone or hydroquinone is cleaved by the alkyl chains, and the conjugation does not extend to the entire active material molecule. In other words, in the former type of active material, the redox reaction of each quinone or hydroquinone is affected by the redox state of other quinones or hydroquinones due to the conjugation extending to the entire molecule. However, in the latter type of active material, the conjugation is cleaved, and the electronic properties of each quinone or hydroquinone are independent. Therefore, the redox reaction occurs uniformly within each quinone or hydroquinone. Consequently, battery performance is improved when using the latter type of active material compared to the former.

[0055] In the case of quinone polymers represented by chemical formulas (III) to (V), in each quinone, at least one of R6 and R7 (and the same applies to R8 and R9) bonded to carbons other than the carbon bonded to the alkyl chain R5 and the carbon bonded to oxygen via a double bond in the carbon constituting the 6-membered ring with a double bond is preferably not hydrogen, but an element or functional group other than hydrogen. In the case of hydroquinone polymers corresponding to the quinone polymers represented by chemical formulas (III) to (V), in each hydroquinone, it is preferable that at least one carbon other than hydrogen is bonded to the carbon constituting the 6-membered ring with a hydroxyl group, other than the carbon bonded to the alkyl chain and the carbon bonded to the hydroxyl group.

[0056] The preceding text described the tendency for capacity reduction in redox flow batteries with increasing charge-discharge cycles. Besides cross-linking, the main reasons for this are attributed to the decomposition of active materials caused by charge-discharge and heat. The decomposition of quinones occurs through the interaction of carbons in the quinone cyclic structure (excluding those bonded to alkyl chains and oxygen) with nucleophiles (OH groups) in the electrolyte. - The reaction proceeds as described above. If R6 and R7 (and R8 and R9) are elements or functional groups other than hydrogen, they react with nucleophiles (OH-) in the electrolyte. - The reaction is inhibited, thus inhibiting the decomposition of the active substance. It should be noted that this also applies to inhibiting the decomposition of hydroquinone.

[0057] As mentioned above, while cross-linking can be suppressed by increasing the molecular weight through the polymerization of quinones or hydroquinones, if the molecular weight of the active material is too large, the blockage of membrane ion channels due to the attachment of the active material and the decrease in the diffusion coefficient of the active material may lead to increased resistance and decreased current density. To suppress this decrease in current density, it is considered necessary to determine an upper limit for the molecular weight of the active material, i.e., the number of quinone or hydroquinone units contained in the active material. However, to determine the upper limit for the number of units, the relationship between the number of units and the diffusion coefficient is needed. Therefore, the relationship between the number of units and the diffusion coefficient will be investigated below.

[0058] Prior to this application, a prior art document (T. Janoschka, et al., “An aqueous, polymer-based redox-flow battery using non-corrosive, safe, and low-cost materials”, Nature vol. 527, pp. 78-81, 5, Nov., 2015) described an example of a redox flow battery using a substance formed by polymerizing redox-active molecules as the active material, the diffusion coefficient of which is (7.0 ± 0.5) × 10⁻⁶. -8 cm 2 / sec. Therefore, it is assumed that if a diffusion coefficient of at least 1×10 is used... -7 cm 2 Molecules with a density of 1 / sec or higher, when used as active materials, can suppress the decrease in current density in redox flow batteries.

[0059] The diffusion coefficient can be calculated from the particle radius (molecular radius) by using the Stokes-Einstein equation (A) in the well-known document 2 (JTEdward, “Molecular Volumes and the Stokes-Einstein Equation”, J.Chem.Edu., vol.47(4), p261-270, Apr., 1970), which was known prior to this application.

[0060] D=kT / (nπηr)···(A)

[0061] Here, D is the diffusion coefficient, k is the Boltzmann constant, T is the absolute temperature, n is an empirical value, η is the viscosity of the solvent, and r is the particle radius (molecular radius).

[0062] In prior art document 2, the radius based on van der Waals volume was used as the particle radius (molecular radius) r. Using the van der Waals volume calculation method disclosed in prior art document 2, the molecular radius r of each quinone unit in the benzoquinone pentamer obtained by synthesizing five benzoquinones into a cyclic form via methylene bonds was calculated. Table 1 below summarizes the volume increment of each segmented structure (segmented structure) and the number of segmented structures when the structure of each quinone unit is divided. By adding them together, the molecular volume r of the quinone unit was obtained as r = 99.6 cubic angstroms.

[0063] [Table 1]

[0064]

[0065] When using the Stokes-Einstein equation (A), the molecular radius *r* of the quinone unit is calculated by assuming the quinone unit is a perfect sphere and based on the van der Waals volume. The viscosity of the solvent is the viscosity of water at 25°C, the temperature is 298 K, and *n* is an empirical value of 6. The relationship between the number of quinone units and the diffusion coefficient is calculated within the range of 2 to 1000. The results are presented in… Figure 2 .

[0066] According to prior art document 3 (B. Yang et al., “An Inexpensive Aqueous Flow Battery for Large-Scale Electrical Energy Storage Based on Water-Soluble Organic Redox Couples”, J. Electrochemical Society, 161(9)A1371-A1380, 2014), in systems using water as a solvent, the diffusion coefficient decreases by approximately one order of magnitude due to hydrogen bonding. Therefore, in Figure 2 In addition to the relation (solid line) calculated using Stokes-Einstein equation (A), the relation (dashed line) obtained by multiplying the relation (solid line) by 0.1 is also illustrated.

[0067] Based on the relationship between the number of quinone units and the diffusion coefficient obtained in this way, depicted by the dashed line, the diffusion coefficient can be estimated to be 1 × 10⁻⁶. -7 cm 2 The upper limit for the number of quinone units per second is approximately 600. According to such a method, for example in the quinone polymer shown in chemical formula (III), the upper limit for the number of quinone units can be determined by changing the alkyl chain R5, or by changing the substituents R6 and R7 (and R8 and R9 as well).

[0068] It should be noted that by making the alkyl chain R5 the methylene group with the smallest molecular weight, the number of quinone units contained in the active substance can be increased without increasing the molecular weight to the necessary level or excessively reducing the diffusion coefficient.

[0069] <Another embodiment of the present invention: a modified redox flow battery>

[0070] like Figure 3 As shown, another embodiment of the redox flow battery 1 of the present invention may further include an inactive gas supply unit 20 for supplying inactive gases to the first tank 6 and the second tank 8, respectively. The inactive gas supply unit 20 includes an inactive gas supply source 21, inactive gas supply paths 22 and 23 connected at one end to the supply source 21 and at the other end to the first tank 6 and the second tank 8, respectively, and compressors 24 and 25 respectively disposed on the inactive gas supply paths 22 and 23. Here, rare gases such as nitrogen and argon can be used as the inactive gas. It should be noted that when compressed gas is used in the inactive gas supply source 21, the compressors 24 and 25 can be omitted.

[0071] The supply of inactive gas to the first tank 6 and the second tank 8 can be carried out at any time, and can be continuous or intermittent. In particular, it is preferable to supply the inactive gas before the start of operation of the redox flow battery 1. In addition, as a method of supplying inactive gas, it can be bubbled into the first electrolyte 12 and the second electrolyte 13, or it can be supplied into the gas phase in the first tank 6 and the second tank 8.

[0072] By supplying inactive gases to tanks 6 and 8 respectively, the possibility of unintended oxidation and side reactions occurring due to contact between the active substances in electrolyte 12 and electrolyte 13 and oxygen can be reduced. It should be noted that... Figure 3 In this process, inactive gas is supplied to both the first tank 6 and the second tank 8, but it is also possible to supply inactive gas to only either the first tank 6 or the second tank 8. In this manner, if the active substance in either the first electrolyte 12 or the second electrolyte 13 is a quinone polymer or a hydroquinone polymer, it is preferable to supply inactive gas to the tank storing that electrolyte.

[0073] Example

[0074] Example 1

[0075] An example of preparing the hydroquinone pentamer of formula (VI) is described. 13.8 g of 1,4-dimethoxybenzene and 9.3 g of oligooxymethylene were dissolved in 200 ml of 1,2-dichloroethane, and 12.5 ml of a boron trifluoride diethyl ether complex was added dropwise. The mixture was stirred at room temperature for 30 minutes. The reaction solution was diluted with 1 L of methanol, and the precipitate was filtered to obtain the crude product. This solid was washed with chloroform-acetone (80 ml: 80 ml) to generate 17.6 g of the cyclic pentamer. Due to the contamination of the washing solvent, the yield (117%) exceeded the theoretical value, but it was used directly in the subsequent reaction. 8.8 g of the cyclic pentamer was dissolved in 375 ml of chloroform, and 210 ml of a 1 mol / L boron tribromide solution in dichloromethane was added to allow the reaction to proceed. The reaction solution was stopped by injecting it into ice water. The precipitated solid was filtered and washed with 0.5N hydrochloric acid, acetone, and chloroform. A pale brown solid precipitated from the acetone and chloroform washings; this was filtered to obtain 1.65 g of hydroquinone pentamer. The yield was 27%.

[0076] Cyclic voltammetry of the resulting hydroquinone pentamer was obtained. In the determination, a 5 mm glassy carbon electrode was used as the working electrode, Ag / AgCl (3 M sodium chloride aqueous solution) as the reference electrode, and platinum wire as the counter electrode. The scan rate was set to 25 mV / sec. The results are shown below. Figure 4 The results show that the redox potential of the hydroquinone pentamer is -0.75 (V vs. SHE), and the solubility of the hydroquinone pentamer is 1.8 M per hydroquinone unit. Therefore, it shows sufficient performance as an active material for redox flow batteries.

[0077] The contents described in the above embodiments are as follows.

[0078] [1] One type of redox flow battery has the following characteristics:

[0079] The battery cell (2) has a first chamber (3) and a second chamber (4) separated by a separator (5);

[0080] The first tank (6) stores the first electrolyte (12);

[0081] The first circulation device (first pump 7) circulates the first electrolyte (12) between the first chamber (3) and the first tank (6);

[0082] The second tank (8) stores the second electrolyte (13);

[0083] The second circulation device (second pump 9) circulates the second electrolyte (13) between the second chamber (4) and the second tank (8).

[0084] The first electrolyte (12) and the second electrolyte (13) contain active substances respectively. At least one of the active substances contained in the first electrolyte (12) or the active substances contained in the second electrolyte (13) is a quinone polymer formed by multiple quinones bonded by alkyl chains or a hydroquinone polymer formed by multiple hydroquinones bonded by alkyl chains.

[0085] The redox flow battery according to the present invention uses quinone polymers / hydroquinone polymers with a molecular weight larger than that of quinone / hydroquinone monomers as active materials, thereby suppressing the occurrence of cross-conversion phenomena compared to the case where quinone / hydroquinone monomers are used as active materials, and thus suppressing the capacity reduction that occurs with increasing charge-discharge cycles.

[0086] [2] Another type of redox flow battery is the redox flow battery of [1].

[0087] The above-mentioned active substances have a structure obtained by cyclic synthesis of multiple quinones via the above-mentioned alkyl chain bonds or a structure obtained by cyclic synthesis of multiple hydroquinones via the above-mentioned alkyl chain bonds.

[0088] Based on this structure, there are no terminals in the active substance, so the quinone units or hydroquinone units that make up the active substance become equivalent, and thus the active substance molecule as a whole can be uniformly oxidized and reduced.

[0089] [3] Another type of redox flow battery is the redox flow battery of [1] or [2].

[0090] The diffusion coefficient of the above-mentioned quinone polymer or the above-mentioned hydroquinone polymer is 1×10⁻⁶. -7 cm 2 / sec or more.

[0091] Although cross-linking can be suppressed by increasing the molecular weight through the polymerization of quinones or hydroquinones, if the molecular weight of the active material is too large, the membrane ion channels may be blocked due to the attachment of the active material, and the diffusion coefficient of the active material may decrease, leading to increased resistance and decreased current density. In contrast, according to the above [3] configuration, by using an active material with a diffusion coefficient of 1×10 -7 cm 2 Setting an upper limit on molecular volume using a method of above / sec can suppress the increase in resistance associated with the blockage of membrane ion channels and the decrease in diffusion coefficient, thus suppressing the decrease in current density.

[0092] [4] Another type of redox flow battery is any one of [1] to [3],

[0093] Each quinone constituting the above quinone polymers contains a six-membered ring with oxygen attached by a double bond.

[0094] In the carbons constituting the above-mentioned 6-membered ring, at least one carbon other than hydrogen is bonded to the carbons bonded by the alkyl chain and the carbons bonded by the double bond.

[0095] Another major reason for the capacity reduction with increasing charge-discharge cycles is considered to be the decomposition of active materials caused by charge-discharge and heat. The decomposition of quinones occurs through the interaction of carbons in the 6-membered ring of quinone (excluding those bonded by alkyl chains and carbons bonded by double bonds) with nucleophiles (OH groups) in the electrolyte. - The reaction proceeds. In contrast, according to the above [4] structure, it reacts with the nucleophile (OH) in the electrolyte. - The reaction is inhibited, thus inhibiting the decomposition of active substances.

[0096] [5] Another type of redox flow battery is any one of [1] to [3],

[0097] Each hydroquinone that makes up the above-mentioned hydroquinone polymer contains a 6-membered ring bonded with a hydroxyl group.

[0098] In the carbons constituting the above-mentioned 6-membered ring, at least one carbon other than the carbons bonded to the alkyl chain and the carbons bonded to the hydroxyl group is bonded to an element or functional group other than hydrogen.

[0099] Another major reason for the capacity reduction with increasing charge-discharge cycles is considered to be the decomposition of the active material caused by charge-discharge and heat. The decomposition of hydroquinone occurs through the reaction of carbons in the 6-membered ring of hydroquinone (excluding the carbons bonded to the alkyl chain and the hydroxyl group) with nucleophiles (OH groups) in the electrolyte. - The reaction proceeds. In contrast, according to the above [5] structure, it reacts with the nucleophile (OH) in the electrolyte. - The reaction is inhibited, thus inhibiting the decomposition of active substances.

[0100] [6] Another type of redox flow battery is any one of [1] to [5],

[0101] The aforementioned quinone polymers or hydroquinone polymers contain at least two quinones or at least two hydroquinones.

[0102] Based on this composition, the physical properties of quinone polymers or hydroquinone polymers can be easily adjusted by including two or more quinones or two or more hydroquinones.

[0103] [7] Another type of redox flow battery is any one of [1] to [6],

[0104] The alkyl chain mentioned above is methylene.

[0105] In active materials composed of multiple quinones or multiple hydroquinones directly bonded together, the conjugation of each quinone or hydroquinone is dispersed throughout the active material molecule. In contrast, in active materials composed of multiple quinones or multiple hydroquinones bonded together via alkyl chains, the conjugation of each quinone or hydroquinone is cleaved by the alkyl chain, and the conjugation does not extend to the active material molecule. In the former type of active material, the redox reaction of each quinone or hydroquinone is affected by the redox state of other quinones or other hydroquinones due to the conjugation extending to the molecule. However, in the latter type of active material, the conjugation is cleaved, and the redox reaction occurs uniformly in each quinone or hydroquinone. Thus, the battery performance is improved when using the latter type of active material compared to the former type. According to the above [6] configuration, by using the alkyl chain with the smallest molecular weight, namely the methylene chain, which plays this role, it is possible to suppress the molecular weight from increasing to the necessary level and the diffusion coefficient from excessively decreasing when increasing the number of quinone units or hydroquinones contained in the active material.

[0106] [8] Another type of redox flow battery is any one of [1] to [7],

[0107] It also has an inactive gas supply unit (20) that supplies inactive gas to at least one of the first tank (6) or the second tank (8).

[0108] Based on this structure, it is possible to suppress the unintentional oxidation and side reactions of active substances caused by contact with oxygen.

[0109] Explanation of reference numerals in the attached figures

[0110] 1: Redox flow battery

[0111] 2: Battery Unit

[0112] 3: Room 1

[0113] 4: Room 2

[0114] 5: Diaphragm

[0115] 6: The first can

[0116] 7: Pump 1 (Circulation Unit 1)

[0117] 8: The second can

[0118] 9: Pump No. 2 (Second Circulation Unit)

[0119] 12: First electrolyte

[0120] 13: Second electrolyte

[0121] 20: Inactive Gas Supply Department

Claims

1. A redox flow battery comprising: a cell unit having a first chamber and a second chamber separated by a separator; a first tank storing a first electrolyte; a first circulation device that circulates the first electrolyte between the first chamber and the first tank; a second tank storing a second electrolyte; and a second circulation device that circulates the second electrolyte between the second chamber and the second tank, the first electrolyte and the second electrolyte each containing an active material, at least one of the active material contained in the first electrolyte or the active material contained in the second electrolyte being a quinone multimer in which a plurality of quinones are bonded via an alkyl chain or a hydroquinone multimer in which a plurality of hydroquinones are bonded via an alkyl chain, the number of units of the quinone multimer or the hydroquinone multimer being less than 600. The active material has a structure in which a plurality of quinones are bonded in a ring shape via the alkyl chain or a structure in which a plurality of hydroquinones are bonded in a ring shape via the alkyl chain. Each quinone constituting the quinone multimer includes a 6-membered ring to which oxygen is bonded via a double bond, Among carbons constituting the 6-membered ring, at least one carbon other than a carbon to which the alkyl chain is bonded and a carbon to which oxygen is bonded via the double bond is bonded to an element other than hydrogen or a functional group. Each hydroquinone constituting the hydroquinone multimer includes a 6-membered ring to which a hydroxyl group is bonded, Among carbons constituting the 6-membered ring, at least one carbon other than a carbon to which the alkyl chain is bonded and a carbon to which the hydroxyl group is bonded is bonded to an element other than hydrogen or a functional group. The quinone multimer or the hydroquinone multimer includes at least two kinds of quinones or at least two kinds of hydroquinones. The diffusion coefficient of the quinone multimer or the hydroquinone multimer is 1 x 10 -7 cm 2 / sec or more. The alkyl chain is a methylene group.

2. The redox flow battery of claim 1, wherein, 7. The redox flow battery according to claim 1 or 2, further comprising a non-active gas supply portion that supplies a non-active gas to at least one of the first tank or the second tank.

3. The redox flow battery of claim 1 or 2, wherein, ​ ​ 4. The redox flow battery of either claim 1 or 2, wherein, ​ ​ 5. The redox flow battery of either claim 1 or 2, wherein, ​ 6. The redox flow battery of either claim 1 or 2, wherein, ​ ​

Images