Redox flow battery

Abstract

To provide a redox flow battery in which operating conditions are optimized and quinones are used as an active material.SOLUTION: A redox flow battery includes: a cell having a first chamber 3 and a second chamber 4 that are partitioned from each other by a barrier film; a first electrode 14 serving as a positive electrode during discharge; a second electrode 15 serving as a negative electrode during discharge; a first tank for storing a first electrolytic solution 12; a first circulation device 7 for circulating the first electrolytic solution between the first chamber and the first tank; a second tank for storing a second electrolytic solution 13; a second circulation device 9 for circulating the second electrolytic solution between the second chamber and the second tank. An active material is contained in each of the first electrolytic solution and the second electrolytic solution, and the active material contained in the second electrolytic solution is quinones. The redox flow battery further includes a power supply for causing an electrical current to flow between the first electrode and the second electrode during charge, a charging rate detection device 20 for measuring a charging rate, and a control unit 21. An upper limit for the charging rate is preset in the control unit, and, if a detection value by the charge rate detection device reaches the upper limit while the redox flow battery is being charged, the control unit stops the supply of a current from the power supply.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to redox flow batteries. [Background technology]

[0002] Redox flow batteries are suitable for storing large amounts of power because the amount of power stored can be freely designed according to the capacity of the electrolyte tank, and are expected to be used to level out power supply and demand, including natural energy. Redox flow batteries consist of cells that charge and discharge, and an electrolyte tank that stores power, and are characterized by charging and discharging by circulating the electrolyte with a pump.

[0003] Currently, redox flow batteries that use vanadium as the active material of the electrolyte are mainstream (see, for example, Patent Document 1), but due to the recent rise in the price of vanadium, redox flow batteries that use organic substances or metal complexes as the active material are being developed. For example, Patent Document 2 describes a redox flow battery that uses various quinones as the negative electrode active material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-157882 [Patent Document 2] Patent No. 6574382 Summary of the Invention [Problem to be solved by the invention]

[0005] In redox flow batteries that use vanadium as an active material in the electrolyte, precipitation of vanadium can occur depending on the vanadium concentration, operating temperature, etc., which can cause problems such as a decrease in battery capacity and voltage efficiency. Patent Document 1 proposes an operating method for a redox flow battery that can suppress the decrease in battery capacity and voltage efficiency caused by vanadium precipitation. However, a method for optimizing the operating conditions of a redox flow battery that uses quinones as the active material has not yet been established.

[0006] In view of the above circumstances, at least one embodiment of the present disclosure has an object to provide a redox flow battery that uses quinones as an active material and has optimized operating conditions. [Means for solving the problem]

[0007] In order to achieve the above object, the redox flow battery according to the present disclosure includes a cell having a first chamber and a second chamber separated by a diaphragm, a first electrode provided in the first chamber and serving as a positive electrode during discharge, a second electrode provided in the second chamber and serving as a negative electrode during discharge, a first tank for storing a first electrolytic solution, a first circulation device for circulating the first electrolytic solution between the first chamber and the first tank, a second tank for storing a second electrolytic solution, and a second circulation device for circulating the second electrolytic solution between the second chamber and the second tank, and the first electrolytic solution and the second electrolytic solution have respective a power source for causing a current to flow between the first electrode and the second electrode during charging; a charging rate detection device for measuring the charging rate of the redox flow battery; and a control device, wherein an upper limit value for the charging rate of the redox flow battery is set in advance in the control device, and when the value detected by the charging rate detection device reaches the upper limit value during charging of the redox flow battery, the control device stops the supply of current from the power source. The conversion rate R, which is the ratio of the active material reacted in the second chamber to the active material flowing into the second chamber, is defined by the following formula: R=I / (F×C×Q×n) where I is a current value flowing between the first electrode and the second electrode, F is a Faraday constant, C is a concentration of the active material in the second electrolytic solution, Q is a circulation flow rate of the second electrolytic solution, and n is a reaction charge, and the control device changes at least one of the current value or the circulation flow rate of the second electrolytic solution so that the conversion rate becomes equal to or less than a preset upper limit value during charging of the redox flow battery. do. [Effects of the Invention]

[0008] According to the redox flow battery of the present disclosure, by stopping the reception of power when the state of charge reaches a preset upper limit, the active material contained in the second electrolyte solution is not exposed to an excessively low potential environment while the redox flow battery is being charged or held, thereby suppressing decomposition of the active material contained in the second electrolyte solution, and as a result, the operating conditions of the redox flow battery using quinones as the active material can be optimized. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a redox flow battery according to a first embodiment of the present disclosure. [Figure 2] 1 shows cyclic voltammograms of a first electrolytic solution and a second electrolytic solution before and after the start of a charging cycle in a redox flow battery according to a first embodiment of the present disclosure. [Figure 3] 1 is a graph showing the relationship between the charge rate and the open circuit voltage measured during charging in a charge cycle in the redox flow battery according to the first embodiment of the present disclosure. [Figure 4] FIG. 1 is a schematic diagram illustrating the configuration of a redox flow battery according to a second embodiment of the present disclosure. [Figure 5] FIG. 1 is a schematic diagram illustrating the configuration of a redox flow battery according to a third embodiment of the present disclosure. [Figure 6] 10 is a graph showing changes in capacity with respect to charge / discharge cycles in a redox flow battery according to a third embodiment of the present disclosure. [Figure 7] FIG. 1 is a schematic diagram illustrating the configuration of a redox flow battery according to a fourth embodiment of the present disclosure. [Figure 8] FIG. 10 is a diagram showing simulation results by the inventors of the present disclosure. [Figure 9] FIG. 10 is a diagram showing simulation results by the inventors of the present disclosure. [Figure 10] FIG. 10 is a cross-sectional view of a cell of a redox flow battery according to a fourth embodiment of the present disclosure. [Figure 11]FIG. 10 is a schematic diagram illustrating the configuration of a redox flow battery according to a fifth embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a redox flow battery according to an embodiment of the present disclosure will be described with reference to the drawings. The embodiment described below shows one aspect of the present disclosure, but does not limit the present disclosure and can be modified as desired within the scope of the technical concept of the present disclosure.

[0011] (Embodiment 1) <Configuration of redox flow battery according to embodiment 1 of the present disclosure> As shown in FIG. 1 , a redox flow battery 1 according to a first embodiment of the present disclosure includes a cell 2 having a first chamber 3 and a second chamber 4 separated by a diaphragm 5, a first tank 6 storing a first electrolytic solution 12 containing an active material, a first pump 7 serving as a first circulation device that circulates the first electrolytic solution 12 between the first chamber 3 and the first tank 6, a second tank 8 storing a second electrolytic solution 13 containing an active material, and a second pump 9 serving as a second circulation device that circulates the second electrolytic solution 13 between the second chamber 4 and the second tank 8.

[0012] The first tank 6 and the first pump 7 are provided in a first electrolyte circulation path 10, one end of which is connected to the first chamber 3. The second tank 8 and the second pump 9 are provided in a second electrolyte circulation path 11, one end of which is connected to the second chamber 4. A first electrode 14 is provided in the first chamber 3, and a second electrode 15 is provided in the second chamber 4. The first electrode 14 and the second electrode 15 are each 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 source 18, respectively. Note that if a DC power source is used instead of the AC power source 18 and the load 17 operates on DC current, the AC-DC converter 16 is not necessary.

[0013] Each of the first electrolytic solution 12 and the second electrolytic solution 13 is prepared by dissolving an active material in an aqueous solution containing a supporting electrolyte. The supporting electrolyte is not limited to, but may be, for example, potassium hydroxide, sodium hydroxide, potassium chloride, sodium chloride, tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, potassium acetate, sodium acetate, potassium sulfate, sodium sulfate, potassium sulfite, or sodium sulfite.

[0014] The active material dissolved in the first electrolytic solution 12 is not particularly limited, and may be a metal ion, a metal complex, air, a halogen, an organic molecule, or the like. In the following, potassium ferrocyanide will be described as an example of an active material dissolved in the first electrolytic solution 12. The active material dissolved in the second electrolytic solution 13 is a quinone. Here, the quinone refers to benzoquinone, naphthoquinone, anthraquinone, any carbon atom of these having any functional group or halogen bonded thereto, or a mixture thereof. Benzoquinones include 1,2-benzoquinone and 1,4-benzoquinone, naphthoquinones include 1,2-naphthoquinone, 1,4-naphthoquinone, 1,5-naphthoquinone, and 2,6-naphthoquinone, and anthraquinones include 1,2-anthraquinone, 1,4-anthraquinone, 1,5-anthraquinone, 2,3-anthraquinone, 2,6-anthraquinone, and 9,10-anthraquinone.

[0015] The redox flow battery 1 further includes a state-of-charge detection device 20 that measures the state-of-charge of the redox flow battery 1, and a control device 21. The control device 21 is electrically connected to the state-of-charge detection device 20 and a switching device 18a that switches the AC power supply 18 on and off. The configuration of the state-of-charge detection device 20 is not particularly limited and may have any configuration as long as it can measure the state-of-charge of the redox flow battery 1. In embodiment 1, however, a state-of-charge detection device having the following configuration will be described as an example. That is, the state-of-charge detection device 20 in embodiment 1 includes an oxidation-reduction potentiometer 20a that detects the oxidation-reduction potential (ORP) of the first electrolyte solution 12 in the first tank 6, and an oxidation-reduction potentiometer 20b that detects the ORP of the second electrolyte solution 13 in the second tank 8. The control device 21 can be realized, for example, by a computer incorporating a functional unit that operates the switching device 18a and a calculation unit that calculates the open circuit voltage (OCV), which is the absolute value of the difference between the detection values ​​of the oxidation-reduction potentiometers 20a and 20b, and calculates the charging rate from the OCV.

[0016] <Operation of the redox flow battery according to the first embodiment of the present disclosure> Next, the operation of the redox flow battery 1 according to the first embodiment of the present disclosure will be described. When the redox flow battery 1 discharges, the first chamber 3 serves as the positive electrode side, and the second chamber 4 serves as the negative electrode side. By operating the first pump 7, the first electrolytic solution 12 stored in the first tank 6 is supplied to the first chamber 3 via the first electrolytic solution circulation path 10. After the first chamber 3 is filled with the first electrolytic solution 12, the first electrolytic solution 12 flows out of the first chamber 3 and is returned to the first tank 6 via the first electrolytic solution circulation path 10. In this manner, the first electrolytic solution 12 circulates between the first chamber 3 and the first tank 6. Meanwhile, by operating the second pump 9, the second electrolytic solution 13 circulates between the second chamber 4 and the second tank 8 in a manner similar to that described above.

[0017] In the first chamber 3, the following half reaction (1) occurs, and trivalent iron ions (Fe 3+ ) receives electrons from the first electrode 14 and becomes divalent iron ions (Fe 2+ ) Fe 3+ +e- →Fe 2+ ···(1)

[0018] On the other hand, taking 1,4-benzoquinone as an example of the active material dissolved in the second electrolyte solution 13, the following half-reaction (2) occurs in the second chamber 4, causing electrons to move from 1,4-dihydroxybenzene, which is a reduced form of 1,4-benzoquinone, to the second electrode 15 and flow into the AC-DC converter 16.

[0019] [ka]

[0020] This generates a direct current in which the first electrode 14 is positive and the second electrode 15 is negative. This direct current is converted into an alternating current by an AC-DC converter 16 and supplied to a load 17.

[0021] When charging the redox flow battery 1, the control device 21 activates the switching device 18a to turn on the AC power supply 18. The AC current from the AC power supply 18 is converted to DC current by the AC-DC converter 16, and a current flows between the first electrode 14 and the second electrode 15. In the first chamber 3, the following half-reaction (3) occurs, causing electrons to move from divalent iron ions to the first electrode 14, resulting in trivalent iron ions. Fe 2+ →Fe 3+ +e - ···(3)

[0022] Meanwhile, in the second chamber 4, the following half-reaction (4) occurs, whereby 1,4-benzoquinone receives electrons from the second electrode 15 and becomes 1,4-dihydroxybenzene.

[0023] [ka]

[0024] During charging of the redox flow battery 1, the oxidation-reduction potentiometers 20a and 20b measure the ORP of the first electrolytic solution 12 in the first tank 6 and the ORP of the second electrolytic solution 13 in the second tank 8, respectively, and transmit these measurement results to the control device 21. The control device 21 calculates the state of charge (SOC) of the redox flow battery 1 from the transmitted ORP, and when the calculation result reaches a preset upper limit, it operates the switching device 18a to turn off the AC power supply 18, thereby stopping charging.

[0025] <Operational Effects of the Redox Flow Battery According to the First Embodiment of the Present Disclosure> The inventors of the present disclosure repeated multiple charge-discharge cycles in the redox flow battery 1 described above, in which the active material dissolved in the second electrolyte solution 13 was 2-(3'-carboxypropyloxy)-6-hydroxy-9,10-anthraquinone (2,6-MHMBEAQ) (see chemical formula (5) below). Cyclic voltammetry was performed on the first electrolyte solution 12 and the second electrolyte solution 13 before the start of charge-discharge cycles and after 9,000 charge-discharge cycles. The obtained cyclic voltammograms are shown in FIG. 2.

[0026] [ka]

[0027] Comparing the peak current density before and after the charge-discharge cycle, the change in peak current density was small for the first electrolyte, but a significant decrease in peak current density after the second electrolyte was observed. The decrease in peak current density is thought to correspond to a decrease in the active material in the second electrolyte, and it is presumed that the active material, 2,6-MHMBEAQ, decomposed with repeated charge-discharge cycles.

[0028] The inventors of the present disclosure measured the potential difference between the electrodes at several different charge rates during the charging and discharging cycles, and defined this potential difference as the open circuit voltage (OCV). The results are shown in Figure 3. The OCV also increases as the charge rate increases. The increase in OCV indicates that the potential of the first electrolyte solution 12 increases while the potential of the second electrolyte solution 13 decreases. The rate of increase in OCV with increasing charge rate is not constant, but rather shows a curved relationship with inflection points at several charge rates. The inventors of the present disclosure suspected that the decomposition reaction of the active material would be promoted at a charge rate that shows such an inflection point. Therefore, they believed that the decomposition reaction of the active material could be suppressed by limiting the charge rate of the redox flow battery 1 to a value below the inflection point, rather than fully charging it.

[0029] Therefore, in the above-described explanation of the operation of the redox flow battery 1, if the upper limit of the state of charge preset in the control device 21 is set to 90%, preferably 75%, more preferably 60%, and most preferably 50% based on the curve relationship in Fig. 3, the state of charge of the redox flow battery 1 will always be maintained at or below the upper limit. This prevents the quinones, which are the active material, from being exposed to an excessively negative potential environment while the redox flow battery 1 is being charged or held, thereby suppressing decomposition of the active material. As a result, the operating conditions of a redox flow battery that uses quinones as the active material can be optimized.

[0030] Furthermore, by including a supporting electrolyte in the first electrolytic solution 12 and the second electrolytic solution 13, the electrical conductivity of the first electrolytic solution 12 and the second electrolytic solution 13 is improved, and the solution resistance is reduced. The reduced solution resistance reduces overvoltage, suppresses a decrease in the solution potential of the first electrolytic solution 12 and the second electrolytic solution 13, and inhibits decomposition of the active material contained in the first electrolytic solution 12 and the second electrolytic solution 13, thereby optimizing the operating conditions of a redox flow battery that uses quinones as the active material. The pH of the second electrolytic solution, in which the active material is a quinone, is preferably set to a pH range of 7 to 14, preferably 10 to 14, which is suitable for quinones. When the active material dissolved in the first electrolytic solution 12 is also a quinone, the pH of the first electrolytic solution is preferably set to a similar range. The pH is preferably adjusted by supplying an acid corresponding to the supporting electrolyte to the electrolytic solution. For example, if the supporting electrolyte is potassium carbonate (K2CO3), carbonic acid (or carbon dioxide) can be used as the corresponding acid, and if the supporting electrolyte is tripotassium phosphate (K3PO4), phosphoric acid (H3PO4) can be used as the corresponding acid.

[0031] (Embodiment 2) Next, a second embodiment of the present disclosure will be described. The redox flow battery according to the second embodiment is configured such that, independently of or in addition to the configuration of the first embodiment, charging of the redox flow battery is stopped when the voltage between the electrodes reaches a preset cutoff voltage. Hereinafter, the second embodiment having the above configuration will be described independently of the configuration of the first embodiment. In the second embodiment, the same components as those of the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0032] <Configuration of redox flow battery according to embodiment 2 of the present disclosure> As shown in Fig. 4, the redox flow battery 1 according to the second embodiment of the present disclosure includes a voltmeter 22, which is a voltage detection device that detects the voltage between the first electrode 14 and the second electrode 15. The voltmeter 22 is electrically connected to the control device 21. The other configurations are the same as those of the first embodiment, except that the redox flow battery 1 does not include the oxidation-reduction potentiometers 20a and 20b (see Fig. 1).

[0033] <Operation of the redox flow battery according to the second embodiment of the present disclosure> The discharge and charge operations of the redox flow battery 1 are the same as those in the first embodiment, except for the control of the charging rate. In the second embodiment, while the redox flow battery 1 is being charged, the voltmeter 22 detects the voltage between the first electrode 14 and the second electrode 15 and transmits the detected value to the control device 21. A cutoff voltage during charging of the redox flow battery 1 is preset in the control device 21, and when the value detected by the voltmeter 22 reaches the cutoff voltage, the control device 21 activates the switching device 18a to turn off the AC power supply 18, thereby stopping charging.

[0034] When quinones are used as the active material, the suitable cutoff voltage is 1.7 V, preferably 1.55 V, and more preferably 1.4 V. However, if the cutoff voltage is set low, the chargeable / dischargeable capacity range is limited, and therefore, in order to set the cutoff voltage low while maintaining the capacity range, it is effective to take measures such as reducing the current density or increasing the area of ​​the electrode.

[0035] By stopping charging when the voltage between first electrode 14 and second electrode 15 reaches a preset cutoff voltage during charging of redox flow battery 1, a decrease in the solution potential of second electrolyte solution 13 due to overvoltage during charging is suppressed, and decomposition of the active material contained in second electrolyte solution 13 is suppressed, making it possible to optimize the operating conditions of redox flow battery 1 that uses quinones as the active material.

[0036] (Embodiment 3) Next, a third embodiment of the present disclosure will be described. The redox flow battery according to the third embodiment is configured to control the temperature ranges of the first electrolytic solution 12 and the second electrolytic solution 13, independently of the configurations of the first and second embodiments or in addition to the configurations of at least one of the first and second embodiments. Hereinafter, the third embodiment, which has the above configuration independently of the configurations of the first and second embodiments, will be described. In the third embodiment, the same components as those of the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0037] <Configuration of redox flow battery according to embodiment 3 of the present disclosure> As shown in FIG. 5 , the redox flow battery 1 according to the third embodiment of the present disclosure includes a first temperature sensor 23 (first temperature detection device) and a second temperature sensor 24 (second temperature detection device) for detecting the temperatures of the first electrolytic solution 12 in the first chamber 3 and the second electrolytic solution 13 in the second chamber 4, respectively, and a first temperature adjustment device 25 and a second temperature adjustment device 26 for adjusting the temperatures of the first electrolytic solution 12 in the first chamber 3 and the second electrolytic solution 13 in the second chamber 4, respectively.

[0038] The configuration of the first temperature adjustment device 25 and the second temperature adjustment device 26 is not particularly limited, and any device may be used as long as it can adjust the temperatures of the first electrolytic solution 12 and the second electrolytic solution 13 to appropriate temperatures. In the third embodiment, however, the first temperature adjustment device 25 and the second temperature adjustment device 26 are described as heating devices whose heating function can be turned on and off. The heating device may be a heater that heats by supplying electric power, or may be a device that heats by circulating a heating fluid. In the former case, the heating function can be turned on and off by turning on and off the supply of electric power, and in the latter case, the heating function can be turned on and off by turning on and off the circulation of the heating fluid.

[0039] The first temperature sensor 23 and the second temperature sensor 24 are each electrically connected to the control device 21. The first temperature adjustment device 25 and the second temperature adjustment device 26 are each configured so that their heating functions are turned on and off by the control device 21. The other configurations are the same as those of the first embodiment, except that the oxidation-reduction potentiometers 20a and 20b (see FIG. 1) are not provided.

[0040] <Operation of the redox flow battery according to the third embodiment of the present disclosure> The discharge and charge operations of the redox flow battery 1 are the same as those of the first embodiment except for the control of the charging rate. In the third embodiment, a first temperature sensor 23 and a second temperature sensor 24 detect the temperatures of the first electrolytic solution 12 in the first chamber 3 and the second electrolytic solution 13 in the second chamber 4, respectively, and transmit these detected values ​​to a control device 21. A control range for the temperatures of the first electrolytic solution 12 and the second electrolytic solution 13 is preset in the control device 21. When the detected value of the first temperature sensor 23 or the second temperature sensor 24 falls below the lower limit of the control range, the control device 21 turns on the heating function of the first temperature adjustment device 25 or the second temperature adjustment device 26 to heat the first electrolytic solution 12 or the second electrolytic solution 13. When the detected value of the first temperature sensor 23 or the second temperature sensor 24 falls within the control range, the control device 21 turns off the heating function of the first temperature adjustment device 25 or the second temperature adjustment device 26.

[0041] When the active material is a quinone, if the temperature of the electrolyte is too high, the rate of the decomposition reaction of the active material may be accelerated. On the other hand, if the temperature of the electrolyte is too low, the reactivity of the active material may decrease and the ion exchange rate of the diaphragm 5 may decrease, resulting in an increase in overvoltage and a decrease in energy efficiency. Furthermore, if the temperature of the electrolyte is too low, the amount of active material that dissolves in the electrolyte may decrease, resulting in a decrease in the capacity density of the redox flow battery 1. In contrast, in the third embodiment, the temperatures of the first electrolyte solution 12 and the second electrolyte solution 13 are maintained within an appropriate range (the control range described above), so that the decomposition of the quinone active material can be suppressed, and decreases in energy efficiency and capacity density can be suppressed. As a result, the operating conditions of the redox flow battery 1 that uses quinones as the active material can be optimized.

[0042] <Consideration of control range> The inventors of the present disclosure performed charge-discharge cycles in which a charge operation and a discharge operation were repeated multiple times under conditions of a cutoff voltage of 1.4 V, a maximum charge capacity of 47% of the theoretical capacity, and temperatures of the first electrolytic solution 12 and the second electrolytic solution 13 of 30°C, 40°C, and 50°C in a redox flow battery 1 in which the active material dissolved in the first electrolytic solution 12 was potassium ferrocyanide and the active material dissolved in the second electrolytic solution 13 was 2,6-MHMBEAQ, and measured the capacity after each charge-discharge cycle. The results are shown in Figure 6. The vertical axis of the graph in Figure 6 represents the relative capacity, which is the ratio of the capacity after each cycle to the capacity after the first charge-discharge cycle.

[0043] In the early stages, when there is no degradation of the active material, the charging voltage does not reach the cutoff voltage of 1.4V, and the charging operation stops when the maximum charging capacity reaches 47%. In contrast, as the degradation of the active material progresses, the battery resistance increases, and the cutoff voltage of 1.4V is reached before the maximum charging capacity reaches 47%, and charging stops. As a result, the capacity starts to decrease at a certain number of cycles when the active material has deteriorated to a certain extent.

[0044] According to Figure 6, within the range of 30 to 50°C, the lower the electrolyte temperature, the greater the number of cycles at which capacity begins to decrease. In other words, the lower the electrolyte temperature, the greater the number of charge-discharge cycles at which capacity does not decrease. This is thought to be because the higher the electrolyte temperature, the more easily the active material 2,6-MHMBEAQ decomposes. Based on these results, the above-mentioned control range is preferably 30°C ± 15°C, and more preferably 30°C ± 10°C.

[0045] (Embodiment 4) Next, a fourth embodiment of the present disclosure will be described. The redox flow battery according to the fourth embodiment is configured to control the operating conditions during charging based on the conversion rate described below, independently of the configurations of the first to third embodiments or in addition to at least one of the configurations of the first to third embodiments. Hereinafter, the fourth embodiment having the above configuration will be described independently of the configurations of the first to third embodiments. In the fourth embodiment, the same components as those of the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0046] <Configuration of redox flow battery according to embodiment 4 of the present disclosure> As shown in Fig. 7, the redox flow battery 1 according to the fourth embodiment of the present disclosure includes a flow rate sensor 30 that detects the circulation flow rate of the second electrolytic solution 13 (for example, the flow rate of the second electrolytic solution 13 flowing through the second electrolytic solution circulation path 11), and the flow rate sensor 30 is electrically connected to a control device 21. The control device 21 is configured to be able to change the discharge flow rate of the second pump 9, and is configured to be able to change the value of the current flowing between the first electrode 14 and the second electrode 15 by changing the voltage of the AC power supply 18 when charging the redox flow battery 1. The other configurations are the same as those of the first embodiment, except that the sensor 20a (see Fig. 1) is not provided.

[0047] <Operation of the redox flow battery according to the fourth embodiment of the present disclosure> Except for the control of the charging rate, the discharging and charging operations of the redox flow battery 1 are the same as those of Embodiment 1. In Embodiment 4, a conversion rate R is defined as the ratio of the active material that reacted in the second chamber 4 to the active material that flowed into the second chamber 4, and the operating conditions of the redox flow battery 1 are adjusted so that the conversion rate R is equal to or lower than a preset upper limit value when the redox flow battery 1 is being charged.

[0048] The conversion rate R is defined by the following formula (A).

number

[0049] Equation (A) includes the concentration C of the active material, which is determined when the operating conditions are set before the start of operation of the redox flow battery 1. For example, if the normal current value I and circulation flow rate Q during charging of the redox flow battery 1 are specified, it is possible to determine the concentration C that will make the conversion rate R a desired value. Furthermore, if there are constraints on the current value I and circulation flow rate Q due to external reasons or the like (they must be set to values ​​lower than normal), the concentration C can be increased to make the conversion rate R a desired value.

[0050] When switching the redox flow battery 1 from discharging operation to charging operation, the conversion rate R can be kept below a preset upper limit by changing the changeable current value I or the circulation flow rate Q, or both. In the above-described configuration of embodiment 4, the current value I can be changed by the control device 21 changing the voltage value of the AC power supply. Alternatively, a current adjustment device can be provided between the AC power supply 18 and the first electrode 14 and the second electrode 15, and the control device 21 can operate this current adjustment device to change the current value I. The circulation flow rate Q can be changed by the control device 21 changing the discharge flow rate of the second pump 9 based on the detection value of the flow rate sensor 30.

[0051] In redox flow battery 1, the position where the concentration of the active material in second electrolyte solution 13 is highest during charging is near the outlet of second chamber 4. For this reason, the solution potential of second electrolyte solution 13 near the outlet of second chamber 4 during charging is lowest, creating an environment where decomposition of quinones, which are the active material, is likely to proceed. To improve this environment where decomposition of quinones is likely to proceed, the conversion rate R can be reduced by reducing the current value I, increasing the circulation flow rate Q, or both.

[0052] The half-reaction of charging is expressed by half-reaction (4), and the concentration of quinones is C in equation (A). The initial setting concentration can be used for concentration C before charging begins, but as charging progresses, half-reaction (4) progresses and C decreases. The concentration of the reduced quinones produced by the progression of half-reaction (4) can be obtained from the charge capacity. Specifically, the concentration C' of the reduced quinones is calculated using equation (B) below.

number

[0053] The concentration C of quinones during charging can be calculated by the following formula (C), and therefore the conversion rate R during charging can be calculated by formula (A). C = (quinone concentration at the start of charging) - C' (C)

[0054] During charging, the current value I or the circulation flow rate Q, or both, are changed so that the conversion rate R calculated by formula (A) is equal to or less than a preset upper limit. This eliminates the high charging rate state near the outlet of the second chamber 4, and as a result, decomposition of the active material is suppressed, making it possible to optimize the operating conditions in the redox flow battery 1 that uses quinones as the active material. The inventors of the present disclosure have developed a redox flow battery with an electrode surface area of ​​25 cm, in which the electrolyte on the positive electrode side is a 0.4 M aqueous solution of potassium ferrocyanide and the electrolyte on the negative electrode side is a 0.5 M aqueous solution of quinone. 2 Each electrolyte was passed through the positive and negative electrodes of the redox flow battery at a rate of 65 ml / min, and the current density was set to 100 mA / cm. 2 The relationship between SOC and conversion rate was calculated when charging was performed under the above conditions. According to this calculation, the conversion rate increases as the SOC increases, but if the SOC is up to 95%, the conversion rate is 50% or less. From the results of this calculation, the upper limit of the conversion rate R is 50%, preferably 20%, and most preferably 10%.

[0055] <Simulations by the inventors of the present disclosure> The effects of different conversion rates were confirmed by simulation using COMSOL Multiphysics (registered trademark) version 5.2.0.166 (optional solvers: Tertiary Current Distribution, Secondary Current Distribution, Free and Porous flow), a multiphysics simulation software from COMSOL AB (Sweden).

[0056] In this simulation, the combination of the phenomenon to be simulated and the equation used to analyze the phenomenon is as follows: Reaction kinetics at electrode interfaces: Butler-Volmer equation Electrode equilibrium potential: Nernst equation Chemical species transport: Nernst-Planck equation Free flow: Navier-Stokes equation Flow in porous media: The Brinkman equation

[0057] In this simulation, the electrolyte on the positive electrode side is an aqueous solution containing two solutes, namely, chemical species 1A and 2A, and the electrolyte on the negative electrode side is an aqueous solution containing two solutes, namely, chemical species 1B and 2B. The physical properties of each electrolyte are summarized in Table 1 below, and the type, concentration, and diffusion coefficient of each chemical species are summarized in Table 2 below.

[0058] [Table 1]

[0059] [Table 2]

[0060] The flow path through which each electrolyte solution flows within the cell was a serpentine flow path having a unit flow path of 53 mm in length, 1 mm in width, and 1 mm in depth, folded back 13.5 times.

[0061] A simulation was performed to charge the redox flow battery by flowing a current of 0.5 A between the positive and negative electrodes for 60 seconds while flowing the negative electrode electrolyte at 25 mL / min and 100 mL / min under the condition of SOC = 50% (corresponding to a 1:1 concentration ratio of chemical species 2A and 2B) based on the negative electrode. From this simulation, contour plots of the concentration of chemical species 2B throughout the entire serpentine channel were obtained for the negative electrode electrolyte flow rates of 25 mL / min and 100 mL / min, respectively. These plots are shown in Figures 8 and 9.

[0062] The conversion rates for electrolyte flow rates of 25 ml / min and 100 ml / min are calculated from Equation (A) to be 2.49% and 0.62%, respectively. Because the only parameter that differs in Equation (A) between the two cases is the electrolyte flow rate Q, the conversion rate for the former, which has a lower electrolyte flow rate, is higher than that for the latter. In both Figures 8 and 9, the concentration of chemical species 2B is higher at the outlet than at the inlet of the flow channel, but this does not yet create an environment at the outlet that favors the decomposition of quinones. Comparing Figures 8 and 9, the concentration of chemical species 2B at the outlet is lower in the latter than in the former, suggesting that the lower the conversion rate, the more difficult the environment at the outlet for the decomposition of quinones becomes.

[0063] <Modification of the redox flow battery according to the fourth embodiment of the present disclosure> In the fourth embodiment, only the conversion rate R of the second chamber 4 is controlled, but this is not limiting. When the active material dissolved in the first electrolytic solution 12 is also a quinone, the high charging rate state near the outlet of the first chamber 3 can be eliminated by controlling the conversion rate R of the first chamber 3 in the same manner as described above, and as a result, decomposition of the active material can be suppressed.

[0064] When the conversion rate R is controlled only by the circulation flow rate Q, the flow rate of second electrolyte solution 13 in second chamber 4 is increased compared to when the conversion rate R is controlled together with the current value I. This increases the flow rate of second electrolyte solution 13 near the surface of second electrode 15 in second chamber 4, reduces the boundary thickness on the surface of second electrode 15, and promotes mass transfer, thereby suppressing concentration overpotential. This reduction in overpotential suppresses a decrease in the solution potential of second electrolyte solution 13 and suppresses decomposition of the active material contained in the second electrolyte, thereby optimizing the operating conditions of redox flow battery 1 that uses quinones as the active material.

[0065] FIG. 7 shows a schematic configuration of the cell 2 in which a first electrode 14 and a second electrode 15 are disposed inside a first chamber 3 and a second chamber 4, respectively, which are filled with a first electrolytic solution 12 and a second electrolytic solution 13. However, in reality, each of the first chamber 3 and the second chamber 4 has a flow path through which the first electrolytic solution 12 and the second electrolytic solution 13 flow. FIG. 10 shows an example of such a configuration. The plate-shaped first electrode 14 and the second electrode 15 are disposed to sandwich the diaphragm 5, and plate-shaped bipolar plates 31 made of a conductive material are provided on the opposite side of the diaphragm 5 from the first electrode 14 and the second electrode 15. The bipolar plate 31 has a flow path 32 through which the first electrolytic solution 12 and the second electrolytic solution 13 flow so as to contact the first electrode 14 and the second electrode 15, respectively.

[0066] The flow rates of the first electrolytic solution 12 and the second electrolytic solution 13 can be increased by, for example, reducing the pressure loss of the electrolytic solutions. To achieve this, it is effective to employ a comb-like flow path structure for the flow path 32. The comb-like flow path is a structure in which the flow path 32 includes an inlet-side flow path 32a that introduces the electrolytic solution into the electrode and a discharge-side flow path 32b that discharges the electrolytic solution from the electrode, and the inlet-side flow path 32a and the discharge-side flow path 32b are arranged to mesh with each other and face each other.

[0067] (Embodiment 5) Next, a fifth embodiment of the present disclosure will be described. The redox flow battery according to the fifth embodiment is configured to adjust the pH of the second electrolytic solution 13 (and the first electrolytic solution 12) independently of the configurations of the first to fourth embodiments or in addition to the configurations of at least one of the first to fourth embodiments. Hereinafter, the fifth embodiment having the above configuration will be described independently of the configurations of the first to fourth embodiments. In the fifth embodiment, the same components as those of the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0068] 11 , the redox flow battery 1 according to the fifth embodiment of the present disclosure includes a supply device 40 that supplies an acid or alkali corresponding to the supporting electrolyte (the same as the supporting electrolyte) to the second tank 8. The supply device 40 includes a storage tank 41 that stores the acid or alkali to be supplied to the second tank 8, a supply pipe 42 that connects the storage tank 41 with the second tank 8, and a supply pump 43 provided in the supply pipe 42. The supply pump 43 is configured so that its start and stop are controlled by the control device 21. When carbon dioxide gas is used as the acid to be supplied, a carbon dioxide cylinder is used instead of the storage tank 41, and a compressor or a blower is used instead of the supply pump 43.

[0069] When the active material dissolved in the first electrolytic solution 12 is also a quinone, the supply device 40 may include a storage tank 46 that stores an acid or alkali to be supplied to the first tank 6, a supply pipe 47 that connects the storage tank 46 to the first tank 6, and a supply pump 48 provided on the supply pipe 47. Furthermore, the configuration is not limited to supplying an acid or alkali into the second tank 8 (and the first tank 6), and may be configured to supply an acid or alkali to the second electrolytic solution circulation path 11 (and the first electrolytic solution circulation path 10), or may be configured to supply an acid or alkali to the second chamber 4 (and the first chamber 3).

[0070] Also provided is a pH sensor 50 (pH detection device) that detects the pH of second electrolytic solution 13. If the active material dissolved in first electrolytic solution 12 is also a quinone, a pH sensor 51 (pH detection device) that detects the pH of first electrolytic solution 12 may be provided. pH sensor 50 (and pH sensor 51) are electrically connected to control device 21. The other configurations are the same as those of embodiment 1, except that sensor 20a (see FIG. 1) is not provided.

[0071] <Operation of the redox flow battery according to the fifth embodiment of the present disclosure> The discharge and charge operations of the redox flow battery 1 are the same as those of the first embodiment except for the control of the charging rate. In the fifth embodiment, the pH sensor 50 (and the pH sensor 51) detects the pH of the second electrolytic solution 13 (and the first electrolytic solution 12) during the discharge and charge operations of the redox flow battery 1 and transmits the detection result to the control device 21. For example, when the detected value of the pH sensor 50 (and the pH sensor 51) exceeds the upper limit of the pH suitable for quinones, or when the detected value is within the pH range suitable for quinones but is close to the upper limit or shows an increasing trend toward the upper limit, the control device 21 operates the supply device 40, specifically the supply pump 43 (and the supply pump 48), to supply acid into the second tank 8 (and the first tank 6). The amount of acid supplied is adjusted based on the detected value of the pH sensor 50 (and the pH sensor 51). Conversely, when the pH of the second electrolytic solution 13 (and the first electrolytic solution 12) falls below the lower limit, the control device 21 operates the supply device 40 to supply alkali into the second tank 8 (and the first tank 6). As a result, even if the pH of the second electrolytic solution 13 (and the first electrolytic solution 12) fluctuates during operation of the redox flow battery 1, the pH can be adjusted to a value suitable for quinones.

[0072] The contents described in each of the above embodiments can be understood, for example, as follows.

[0073] [1] A redox flow battery according to one embodiment includes: A cell (2) having a first chamber (3) and a second chamber (4) separated by a diaphragm (5); a first electrode (14) provided in the first chamber (3) and serving as a positive electrode during discharge; a second electrode (15) provided in the second chamber (4) and serving as a negative electrode during discharge; a first tank (6) for storing a first electrolyte (12); a first circulation device (first pump 7) that circulates the first electrolytic solution (12) between the first chamber (3) and the first tank (6); a second tank (8) for storing a second electrolytic solution (13); a second circulation device (second pump 9) that circulates the second electrolytic solution (13) between the second chamber (4) and the second tank (8); Equipped with a redox flow battery (1) comprising: the first electrolytic solution (12) and the second electrolytic solution (13) each containing an active material; and the active material contained in the second electrolytic solution (13) being a quinone; The redox flow battery (1) a power supply (AC power supply 18) that applies current between the first electrode (14) and the second electrode (15) during charging; a charging rate detection device (20) that measures the charging rate of the redox flow battery (1); A control device (21) and Furthermore, An upper limit value of the charging rate of the redox flow battery (1) is set in advance in the control device (21), and when the value detected by the charging rate detection device (20) reaches the upper limit value during charging of the redox flow battery (1), the control device (21) stops the supply of current from the power source (18).

[0074] According to the redox flow battery of the present disclosure, by stopping the reception of power when the state of charge reaches a preset upper limit, the active material contained in the second electrolyte solution is not exposed to an excessively low potential environment while the redox flow battery is being charged or held, thereby suppressing decomposition of the active material contained in the second electrolyte solution, and as a result, the operating conditions of the redox flow battery using quinones as the active material can be optimized.

[0075] [2] A redox flow battery according to another embodiment is the redox flow battery according to [1], The upper limit of the charging rate is 90%.

[0076] According to this configuration, similar to the configuration [1] above, it is possible to optimize the operating conditions in a redox flow battery that uses quinones as the active material.

[0077] [3] A redox flow battery according to yet another embodiment is the redox flow battery according to [1] or [2], The device further includes a voltage detection device (voltmeter 22) that detects the voltage between the first electrode (14) and the second electrode (15), A cut-off voltage for charging the redox flow battery (1) is preset in the control device (21), and when the value detected by the voltage detection device (22) reaches the cut-off voltage during charging of the redox flow battery (1), the control device (21) stops the supply of current from the power source (18).

[0078] According to this configuration, a decrease in the solution potential of the second electrolytic solution due to overvoltage during charging is suppressed, and decomposition of the active material contained in the second electrolytic solution is suppressed, so that the operating conditions can be optimized in a redox flow battery that uses quinones as the active material.

[0079] [4] A redox flow battery according to yet another embodiment is the redox flow battery according to [3], The cutoff voltage is 1.7V.

[0080] According to this configuration, similar to the configuration [3] above, it is possible to optimize the operating conditions in a redox flow battery that uses quinones as the active material.

[0081] [5] A redox flow battery according to yet another embodiment is the redox flow battery according to any one of [1] to [4], a first temperature detection device (first temperature sensor 23) that detects the temperature of the first electrolytic solution (12); a second temperature detection device (second temperature sensor 24) that detects the temperature of the second electrolytic solution (13); a first temperature controller (25) for heating or cooling the first electrolytic solution (12); a second temperature control device (26) for heating or cooling the second electrolytic solution (13); Furthermore, The control device (21) operates the first temperature adjustment device (25) and the second temperature adjustment device (26) to adjust the temperatures of the first electrolytic solution (12) and the second electrolytic solution (13), respectively, so that the detected values ​​of the first temperature detection device (25) and the second temperature detection device (26) are within a range of 30°C±15°C.

[0082] When the active material is a quinone, if the temperature of the electrolyte is too high, the rate of the decomposition reaction of the active material may be accelerated. On the other hand, if the temperature of the electrolyte is too low, the reactivity of the active material may decrease and the ion exchange rate of the diaphragm may decrease, resulting in an increase in overvoltage and a decrease in energy efficiency. Furthermore, if the temperature of the electrolyte is too low, the amount of active material that dissolves in the electrolyte may decrease, resulting in a decrease in the capacity density of the redox flow battery. In contrast, with the above configuration, the temperature of the electrolyte is maintained within an appropriate range, thereby suppressing decomposition of the active material and suppressing decreases in energy efficiency and capacity density. As a result, the operating conditions of a redox flow battery that uses a quinone as the active material may be optimized.

[0083] [6] A redox flow battery according to yet another embodiment is the redox flow battery according to any one of [1] to [5], The conversion rate R, which is the ratio of the active material reacted in the second chamber (4) to the active material flowing into the second chamber (4), is defined by the following formula: R=I / (F×C×Q×n) I is the value of the current flowing between the first electrode (14) and the second electrode (15), F is Faraday's constant, C is the concentration of the active material in the second electrolytic solution (13), Q is the circulation flow rate of the second electrolytic solution (13), and n is the reaction charge, The control device (21) changes at least one of the current value and the circulation flow rate of the second electrolytic solution (13) so that the conversion rate becomes equal to or less than a preset upper limit value during charging of the redox flow battery (1).

[0084] With this configuration, it is possible to eliminate a high charge rate state near the outlet of the second chamber, thereby suppressing decomposition of the active material, thereby optimizing the operating conditions of a redox flow battery that uses quinones as the active material.

[0085] [7] A redox flow battery according to yet another embodiment is the redox flow battery according to [6], The control device (21) changes the circulation flow rate of the second electrolytic solution (13) so that the conversion rate becomes equal to or less than a preset upper limit value.

[0086] According to this configuration, the circulation flow rate of the second electrolyte solution is increased to set R equal to or less than the upper limit. This reduces the boundary thickness on the surface of the second electrode, promoting mass transfer and suppressing concentration overpotential. This reduction in overpotential also suppresses a decrease in the solution potential of the second electrolyte solution, thereby suppressing decomposition of the active material contained in the second electrolyte solution. This allows for optimization of operating conditions in a redox flow battery that uses quinones as the active material.

[0087] [8] A redox flow battery according to yet another embodiment is the redox flow battery according to [6] or [7], The upper limit of the conversion rate is 50%.

[0088] According to this configuration, similar to the configurations [6] and [7] above, it is possible to optimize the operating conditions of a redox flow battery that uses quinones as the active material.

[0089] [9] A redox flow battery according to yet another embodiment is the redox flow battery according to any one of [1] to [8], the second chamber (4) includes a flow path (32) through which the second electrolytic solution (13) flows; The flow passage (32) is a comb-shaped flow passage.

[0090] This configuration reduces the pressure loss of the second electrolytic solution flowing through the flow path, allowing the flow rate of the second electrolytic solution to be increased. This reduces the boundary thickness on the surface of the second electrode, promoting mass transfer and suppressing concentration overpotential. This reduction in overpotential also suppresses a decrease in the solution potential of the second electrolytic solution, thereby suppressing decomposition of the active material contained in the second electrolytic solution. This allows for optimization of operating conditions in redox flow batteries that use quinones as the active material.

[0091]

[10] A redox flow battery according to yet another embodiment is the redox flow battery according to any one of [1] to [9], the second electrolytic solution (13) contains a supporting electrolyte, The second electrolytic solution (13) has a pH of 7 to 14.

[0092] According to this configuration, the second electrolytic solution contains a supporting electrolyte, which improves the electrical conductivity of the second electrolytic solution and reduces its solution resistance. The reduced solution resistance reduces overvoltage, suppresses a decrease in the solution potential of the second electrolytic solution, and inhibits decomposition of the active material contained in the second electrolytic solution, thereby optimizing the operating conditions of a redox flow battery that uses quinones as the active material. Furthermore, the second electrolytic solution has a pH of 7 to 14, which is suitable for quinones.

[0093]

[11] A redox flow battery according to yet another embodiment is the redox flow battery according to

[10] , a pH detector (50) for detecting the pH of the second electrolytic solution (13); a supply device (40) for supplying an acid or alkali to the second electrolytic solution (13); Equipped with The control device (21) operates the supply device (40) based on the value detected by the pH detection device (50) to supply the acid or alkali to the second electrolytic solution (13).

[0094] With this configuration, even if the pH of the second electrolytic solution fluctuates during operation of the redox flow battery, the pH can be adjusted to a value suitable for quinones. [Explanation of symbols]

[0095] 1. Redox flow battery 2 cells 3 Room 1 4 Room 2 5 Diaphragm 6. First Tank 7. First pump (first circulation device) 8. Second Tank 9. Second pump (second circulation device) 12 First electrolyte 13 Second electrolyte 14 1st electrode 15 2nd electrode 18 AC power supply (power supply) 20. Charge rate detection device 21 Control device 22 Voltmeter (voltage detection device) 23 First temperature sensor (first temperature detection device) 24 Second temperature sensor (second temperature detection device) 25 1st temperature control device 26 Second temperature control device 32 Flow path 40 Feeding device 50 pH detector

Claims

1. a cell having a first chamber and a second chamber separated by a diaphragm; a first electrode provided in the first chamber and serving as a positive electrode during discharge; a second electrode provided in the second chamber and serving as a negative electrode during discharge; a first tank for storing a first electrolytic solution; a first circulation device that circulates the first electrolytic solution between the first chamber and the first tank; a second tank for storing a second electrolyte; a second circulation device that circulates the second electrolytic solution between the second chamber and the second tank; Equipped with a redox flow battery in which the first electrolytic solution and the second electrolytic solution each contain an active material, and the active material contained in the second electrolytic solution is a quinone; The redox flow battery comprises: a power source that flows a current between the first electrode and the second electrode during charging; a charging rate detection device for measuring the charging rate of the redox flow battery; Control device and Furthermore, an upper limit value of the charging rate of the redox flow battery is set in advance in the control device, and when the value detected by the charging rate detection device reaches the upper limit value during charging of the redox flow battery, the control device stops the supply of current from the power source; A conversion rate R, which is a ratio of the active material reacted in the second chamber to the active material flowing into the second chamber, is defined by the following formula: R=I / (F×C×Q×n) I is a value of a current flowing between the first electrode and the second electrode, F is a Faraday constant, C is a concentration of the active material in the second electrolytic solution, Q is a circulating flow rate of the second electrolytic solution, and n is a reaction charge, the control device changes at least one of the current value or the circulation flow rate of the second electrolytic solution so that the conversion rate becomes equal to or less than a preset upper limit value during charging of the redox flow battery.

2. 2. The redox flow battery according to claim 1, wherein the upper limit of the charging rate is 90%.

3. a voltage detection device for detecting a voltage between the first electrode and the second electrode; 3. The redox flow battery according to claim 1, wherein a cutoff voltage during charging of the redox flow battery is preset in the control device, and when a value detected by the voltage detection device reaches the cutoff voltage during charging of the redox flow battery, the control device stops supply of current from the power source.

4. 4. The redox flow battery according to claim 3, wherein the cutoff voltage is 1.7 V.

5. a first temperature detection device that detects the temperature of the first electrolytic solution; a second temperature detection device that detects the temperature of the second electrolytic solution; a first temperature control device that heats or cools the first electrolytic solution; a second temperature control device that heats or cools the second electrolytic solution; Furthermore, 5. The redox flow battery according to claim 1, wherein the control device operates the first temperature adjustment device and the second temperature adjustment device to adjust the temperatures of the first electrolytic solution and the second electrolytic solution, respectively, so that the detected values ​​by the first temperature detection device and the second temperature detection device are within a range of 30°C±15°C.

6. 6. The redox flow battery according to claim 1, wherein the control device changes the circulating flow rate of the second electrolytic solution so that the conversion rate is equal to or less than a preset upper limit value.

7. The redox flow battery according to any one of claims 1 to 6, wherein the upper limit of the conversion rate is 50%.

8. the second chamber includes a flow path through which the second electrolytic solution flows; The redox flow battery according to any one of claims 1 to 7, wherein the flow path is a comb-teeth flow path.

9. the second electrolytic solution includes a supporting electrolyte; 9. The redox flow battery according to claim 1, wherein the second electrolytic solution has a pH of 7 to 14.

10. a pH detection device for detecting the pH of the second electrolytic solution; a supply device for supplying an acid or alkali to the second electrolytic solution; Equipped with 10. The redox flow battery according to claim 9, wherein the control device supplies the acid or alkali to the second electrolytic solution by operating the supply device based on the value detected by the pH detection device.

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