Redox flow battery system, and method for operating a redox flow battery

Abstract

A redox flow battery system comprising a battery cell that charges and discharges through supply of an electrolytic liquid, a monitor cell to which the electrolytic liquid is supplied, a voltmeter that measures the open voltage of the monitor cell, a thermometer that measures the liquid temperature of the electrolytic liquid, and a control unit that controls the charging and discharging of the battery cell on the basis of the open voltage, the control unit correcting the open voltage in accordance with the liquid temperature.

Description

[Technical Field]

[0001] This disclosure relates to a redox flow battery system and a method for operating a redox flow battery. This application claims priority under Japanese Patent Application No. 2020-164157, dated September 29, 2020, and incorporates all the provisions of the said Japanese application. [Background technology]

[0002] Patent documents 1 and 2 disclose a redox flow battery that includes a monitor cell supplied with the same electrolyte as the battery cells, separate from the battery cells that perform charging and discharging. This redox flow battery determines the state of charge (SOC) of the electrolyte by measuring the open circuit voltage (OCV) of the monitor cell. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2009-16217 [Patent Document 2] Japanese Patent Publication No. 2013-37857 [Overview of the project]

[0004] The redox flow battery system described herein is A battery cell that charges and discharges by supplying electrolyte, A monitor cell supplied with the aforementioned electrolyte, A voltmeter for measuring the open-circuit voltage of the monitor cell, A thermometer for measuring the liquid temperature of the electrolyte, The system includes a control unit that controls the charging and discharging of the battery cell based on the open-circuit voltage, The control unit corrects the open-circuit voltage according to the liquid temperature.

[0005] The operation method of the redox flow battery of the present disclosure is It is an operation method of a redox flow battery that supplies an electrolytic solution to a battery cell for charge and discharge, comprising a step of measuring the open circuit voltage of a monitor cell to which the electrolytic solution is supplied, a step of measuring the liquid temperature of the electrolytic solution, a step of correcting the open circuit voltage according to the liquid temperature, and a step of performing charge and discharge of the battery cell based on the corrected open circuit voltage.

Brief Description of the Drawings

[0006] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a redox flow battery system according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a cell stack. [Figure 3] FIG. 3 is a diagram for explaining an example of temperature correction of OCV in a redox flow battery system according to an embodiment. [Figure 4] FIG. 4 is a flowchart showing the processing procedure of the operation method of the redox flow battery according to an embodiment.

[0007] [Problems to be Solved by the Present Disclosure] In a redox flow battery, it is desirable to control so that the electrolytic solution does not become overcharged during operation.

[0008] When the electrolytic solution becomes overcharged, side reactions such as electrolysis of the electrolytic solution in the battery cell to generate gas and precipitation of active material ions occur in the battery cell. For example, by electrolysis of water in the electrolytic solution, oxygen is generated at the positive electrode and hydrogen is generated at the negative electrode. In addition, due to the precipitation of active material ions in the electrolytic solution, the active material ions decrease, which may lead to a decrease in the battery capacity.

[0009] Therefore, one of the objectives of the present disclosure is to provide a redox flow battery system and an operation method of a redox flow battery that can suppress overcharging of the electrolytic solution.

[0010] [Effects of this disclosure] The redox flow battery system and the method for operating the redox flow battery described herein can suppress overcharging of the electrolyte.

[0011] [Description of Embodiments in this Disclosure] A known method for operating redox flow batteries involves controlling the charging and discharging of the battery cells based on the open-circuit voltage of a monitor cell. The open-circuit voltage of the monitor cell is measured as the potential of the electrolyte, more specifically, the potential difference between the positive electrode electrolyte and the negative electrode electrolyte.

[0012] There is a correlation between the OCV of the monitor cell and the SOC of the electrolyte. In redox flow batteries, a limit range for OCV is predetermined to prevent the electrolyte from overcharging or over-discharging at a certain reference temperature, and charging and discharging are controlled so that the measured OCV remains within this limit range. For example, during charging, if the measured OCV exceeds the upper limit of the limit range, it is considered an overcharged state and charging is stopped. Similarly, during discharging, if the measured OCV falls below the lower limit of the limit range, it is considered an over-discharged state and discharging is stopped. When the electrolyte temperature rises, the reference potential of the electrolyte decreases, and therefore the OCV also decreases. In other words, OCV is temperature-dependent. If the electrolyte temperature is higher than the reference temperature, the measured OCV will appear lower than the OCV measured at the reference temperature. Therefore, when the electrolyte temperature is higher than the reference temperature, even if the measured OCV is within the limit range, the SOC of the electrolyte may fall outside the appropriate range. Therefore, if the electrolyte temperature differs from the reference temperature, the electrolyte may become overcharged or over-discharged.

[0013] Furthermore, in order to expand the range of applications for the State of Charge (SOC) of the electrolyte, it is being considered to set the upper limit of the OCV limit as high as possible without causing the electrolyte to overcharge. In order to prevent the electrolyte from overcharging, it is necessary to consider the temperature dependence of the OCV. The inventors propose correcting the measured OCV value according to the electrolyte temperature so that the SOC of the electrolyte is within an appropriate range.

[0014] This disclosure has been made in light of the circumstances described above. First, the embodiments of this disclosure will be listed and described.

[0015] (1) The redox flow battery system according to the embodiments of this disclosure is A battery cell that charges and discharges by supplying electrolyte, A monitor cell supplied with the aforementioned electrolyte, A voltmeter for measuring the open-circuit voltage of the monitor cell, A thermometer for measuring the liquid temperature of the electrolyte, The system includes a control unit that controls the charging and discharging of the battery cell based on the open-circuit voltage, The control unit corrects the open-circuit voltage according to the liquid temperature.

[0016] The redox flow battery system of this disclosure can suppress electrolyte overcharging because it corrects the measured OCV according to the electrolyte temperature. By controlling the charging and discharging of the battery cells based on the corrected OCV, the state of charge (SOC) of the electrolyte can be maintained within an appropriate range.

[0017] (2) As one form of the redox flow battery system described above, The control unit may correct at least the upper limit of the open-circuit voltage.

[0018] The above configuration can suppress overcharging of the electrolyte.

[0019] (3) As one form of the redox flow battery system described above, The electrolyte may contain vanadium ions.

[0020] In the above configuration, both the positive and negative electrode electrolytes contain vanadium ions as active material ions. In redox flow batteries, repeated charging and discharging can cause active material ions in the electrolytes to move between the positive and negative electrode electrolytes through the diaphragm within the battery cell. In the above configuration, the active material ions in both the positive and negative electrode electrolytes are ions of the same element. Therefore, even if active material ions move between the positive and negative electrode electrolytes, it is easier to suppress the decrease in battery capacity. Furthermore, if the active material ions in the positive electrode electrolyte and the active material ions in the negative electrode electrolyte are ions of the same element, they can function as active material in both electrolytes.

[0021] (4) The method for operating a redox flow battery according to the embodiment of the present disclosure is: A method for operating a redox flow battery, which charges and discharges by supplying electrolyte to a battery cell, A step of measuring the open-circuit voltage of a monitor cell to which the electrolyte is supplied, A step of measuring the liquid temperature of the electrolyte, A step of correcting the open-circuit voltage according to the liquid temperature, The process includes a step of charging and discharging the battery cell based on the corrected open-circuit voltage.

[0022] The redox flow battery operation method described herein can suppress overcharging of the electrolyte. This is because the measured OCV is corrected according to the electrolyte temperature. By charging and discharging the battery cells based on the corrected OCV, the state of charge (SOC) of the electrolyte can be maintained within an appropriate range.

[0023] [Details of the embodiments of this disclosure] Specific examples of the redox flow battery system and the operation method of the redox flow battery described herein will be explained with reference to the drawings. Hereinafter, the redox flow battery may be referred to as the "RF battery". The same reference numerals in the drawings indicate the same or corresponding parts. However, the present invention is not limited to these examples, and is intended to include all modifications within the meaning and scope of the claims as shown, and equivalents thereof.

[0024] <Overview of the RF battery system> Referring to FIG. 1, the RF battery system 1 according to an embodiment will be described. The RF battery system 1 supplies a positive electrode electrolyte and a negative electrode electrolyte to the battery cell 10 to perform charge and discharge. The positive electrode electrolyte and the negative electrode electrolyte contain active material ions. In FIG. 1, as an example, a V-based RF battery in which both the positive electrode electrolyte and the negative electrode electrolyte contain vanadium (V) ions as active materials is shown. In FIG. 1, solid arrows indicate charge reactions, and dashed arrows indicate discharge reactions, respectively. The electrolyte used is not limited to a vanadium electrolyte, and those with known compositions can be used. Examples of the electrolyte include a Ti-Mn-based electrolyte in which the positive electrode electrolyte contains manganese (Mn) ions and the negative electrode electrolyte contains titanium (Ti) ions.

[0025] Typically, the RF battery system 1 is connected to the power grid 90 via an AC / DC converter 80 and substation equipment 81. The RF battery system 1 can charge the power generated by the power generation unit 91 or discharge the charged power to the load 92. The power generation unit 91 is a power generation facility that utilizes natural energy such as solar power generation or wind power generation, or other general power plants. The RF battery system 1 is used, for example, for load leveling applications, momentary low compensation, emergency power sources, etc., and for smoothing the output of natural energy power generation.

[0026] <Configuration of the RF battery system> The RF battery system 1 includes a battery cell 10, a positive electrode tank 12 for storing the positive electrode electrolyte, a negative electrode tank 13 for storing the negative electrode electrolyte, a positive electrode flow path 14 and a negative electrode flow path 15 for circulating each electrolyte between the tanks 12 and 13 and the battery cell 10. One of the features of the RF battery system 1 of the embodiment is that it includes a monitor cell 30, a voltmeter 30v, a thermometer 40, and a control unit 50.

[0027] (Battery cell) The battery cell 10 performs charging and discharging. The battery cell 10 has a positive electrode 104, a negative electrode 105, and a diaphragm 101 interposed between the positive electrode 104 and the negative electrode 105. The battery cell 10 is separated into a positive electrode cell 102 and a negative electrode cell 103 by the diaphragm 101. The diaphragm 101 is, for example, a cation membrane. The positive electrode cell 102 contains the positive electrode 104. The negative electrode cell 103 contains the negative electrode 105. The positive electrode cell 102 is supplied with positive electrolyte. The negative electrode cell 103 is supplied with negative electrolyte.

[0028] The positive electrode channel 14 and the negative electrode channel 15 have forward pipes 108, 109 and return pipes 110, 111. Each forward pipe 108, 109 delivers electrolyte from each tank 12, 13 to each cell 102, 103 that make up the battery cell 10. Each return pipe 110, 111 returns the electrolyte from each cell 102, 103 that make up the battery cell 10 to each tank 12, 13. Pumps 112, 113 are provided in the forward pipes 108, 109, respectively.

[0029] The RF battery system 1 typically uses a cell stack 100, as shown in Figure 2, in which multiple battery cells 10 are stacked. The cell stack 100 is constructed by sandwiching sub-stacks 200s between two end plates 210 and tightening them with a clamping mechanism 230. Figure 2 shows a cell stack 100 with multiple sub-stacks 200s. The sub-stacks 200s have a structure in which cell frames 120, positive electrodes 104, diaphragms 101, and negative electrodes 105 are repeatedly stacked in that order, with supply and discharge plates 220 positioned at both ends of the stack. The supply and discharge plates 220 are connected to the forward piping 108, 109 and return piping 110, 111 shown in Figure 1 above. The number of stacked battery cells 10 in the cell stack 100 can be selected as appropriate.

[0030] As shown in Figure 2, the cell frame 120 has a bipolar plate 121 and a frame 122. The bipolar plate 121 is positioned between the positive electrode 104 and the negative electrode 105. The frame 122 is provided around the bipolar plate 121. On the first side of the bipolar plate 121, the side facing the paper in Figure 2, the positive electrode 104 is positioned facing the negative electrode 105. On the second side of the bipolar plate 121, the side facing the paper in Figure 2, the negative electrode 105 is positioned facing the positive electrode 104. Inside the frame 122, the positive electrode 104 and the negative electrode 105 are housed, sandwiching the bipolar plate 121. A single battery cell 10 is formed by positioning the positive electrode 104 and the negative electrode 105 between the bipolar plates 121 of adjacent cell frames 120, with a diaphragm 101 in between. Between the frame bodies 122 of each cell frame 120, annular sealing members 127, such as O-rings, are placed to suppress leakage of electrolyte.

[0031] The cell frame 120 has a frame 122 with supply manifolds 123 and 124 and drain manifolds 125 and 126. In this example, the positive electrode electrolyte is supplied from the supply manifold 123 to the positive electrode 104 through a groove formed in the lower part of the first side of the frame 122. The positive electrode electrolyte supplied to the positive electrode 104 is discharged to the drain manifold 125 through a groove formed in the upper part of the first side of the frame 122. Similarly, the negative electrode electrolyte is supplied from the supply manifold 124 to the negative electrode 105 through a groove formed in the lower part of the second side of the frame 122. The negative electrode electrolyte supplied to the negative electrode 105 is discharged to the drain manifold 126 through a groove formed in the upper part of the second side of the frame 122. The fluid supply manifolds 123, 124 and the fluid drain manifolds 125, 126 are provided penetrating the frame 122, and the stacking of cell frames 120 constitutes the flow paths for each electrolyte. These flow paths are connected to the supply pipes 108, 109 and return pipes 110, 111 shown in Figure 1, respectively, via the supply and drain plates 220. The cell stack 100 is capable of circulating the positive electrode electrolyte and the negative electrode electrolyte to each battery cell 10 through these flow paths.

[0032] (electrolyte) The positive electrode electrolyte and the negative electrode electrolyte are typically aqueous solutions containing active material ions. As the aqueous solution, for example, an aqueous solution of sulfuric acid (H2SO4), an aqueous solution of phosphoric acid (H3PO4), nitric acid (HNO3) aqueous solution and the like can be used. The active material ions are ions of an element that functions as an active material in the electrolyte. Examples of the active material ions include ions of an element selected from the group consisting of vanadium (V), manganese (Mn), iron (Fe), chromium (Cr), titanium (Ti), and zinc (Zn). Representative examples of the active material ions in the positive electrode electrolyte include V ions, Fe ions, and Mn ions. Representative examples of the active material ions in the negative electrode electrolyte include V ions, Cr ions, Ti ions, and Zn ions. These active material ions may be used alone or in combination of a plurality. In the present embodiment, both the positive electrode electrolyte and the negative electrode electrolyte are aqueous sulfuric acid solutions containing V ions.

[0033] The active material ions in the positive electrode electrolyte and the active material ions in the negative electrode electrolyte may be ions of different elements or ions of the same element. Specific combinations of the respective active material ions used in the positive electrode electrolyte and the negative electrode electrolyte are shown below. (1) Positive electrode electrolyte: V ions (VO , 2+ , 3+ , 3+ , , 3+ , 3+ , 2+ , 3+ , , 2+ , 2+ , 2+ / VO2 + ), negative electrode electrolyte: V ions (V 3+ / V 2+ )<00002A3>(2) Positive electrode electrolyte: Fe ions (Fe 2+ / Fe 3+ ), negative electrode electrolyte: Cr ions (Cr 3+ / Cr 2+ ) (3) Positive electrode electrolyte: Mn ions (Mn 2+ / Mn 3+ ), negative electrode electrolyte: Ti ions (TiO 2+ / Ti 3+ ) (4) Positive electrode electrolyte: Fe ions (Fe 2+ / Fe 3+ ), negative electrode electrolyte: Ti ions (TiO 2+ / Ti 3+ ) (5) Positive electrode electrolyte: Mn ions (Mn2+ / Mn 3+ ), negative electrode electrolyte: Zn ions (Zn 2+ / Zn) The above VO 2+ This is a tetravalent V ion. (See above for VO2) + This is a pentavalent V ion. The above TiO 2+ This is a tetravalent Ti ion.

[0034] One characteristic is that the positive electrode electrolyte and the negative electrode electrolyte contain active material ions of the same element. Specifically, the active material ions contained in the positive electrode electrolyte and the active material ions contained in the negative electrode electrolyte are ions of the same element. Furthermore, all ions, including the active material ions contained in both the positive electrode electrolyte and the negative electrode electrolyte, are ions of the same element. Because the positive electrode electrolyte and the negative electrode electrolyte each contain active material ions of the same element, even if active material ions move between the positive electrode electrolyte and the negative electrode electrolyte due to repeated charging and discharging, the decrease in battery capacity is easily suppressed.

[0035] (Monitor cell) The monitor cell 30 is supplied with the same electrolyte as the battery cell 10. In other words, the positive electrode electrolyte supplied to the battery cell 10 and the positive electrode electrolyte supplied to the monitor cell 30 are each supplied from the positive electrode tank 12. The negative electrode electrolyte supplied to the battery cell 10 and the negative electrode electrolyte supplied to the monitor cell 30 are each supplied from the negative electrode tank 13. The state of charge (SOC) of the electrolyte supplied to the monitor cell 30 is the same as the SOC of the electrolyte supplied to the battery cell 10. The monitor cell 30 does not perform charging or discharging. The monitor cell 30 is located in the middle of the positive electrode flow path 14 and the negative electrode flow path 15. In this embodiment, the positive electrode electrolyte and the negative electrode electrolyte are supplied to the monitor cell 30 from the forward piping 108 of the positive electrode flow path 14 and the forward piping 109 of the negative electrode flow path 15, respectively.

[0036] The monitor cell 30 has the same configuration as the battery cell 10. The monitor cell 30 has a positive electrode 104, a negative electrode 105, and a diaphragm 101. The positive electrode cell 102 and the negative electrode cell 103, separated by the diaphragm 101, each contain the positive electrode 104 and the negative electrode 105, respectively.

[0037] (Voltmeter) The voltmeter 30V measures the open-circuit voltage (OCV) of the monitor cell 30. The OCV represents the voltage between the positive electrode 104 and the negative electrode 105 in the monitor cell 30, i.e., the potential difference between the positive electrolyte and the negative electrolyte. By measuring the OCV of the monitor cell 30, the state of charge (SOC) of the electrolyte can be determined. The OCV value measured by the voltmeter 30V is transmitted to the control unit 50. The voltmeter 30V includes any measuring instrument capable of measuring voltage or any physical quantity convertible to voltage.

[0038] (thermometer) The thermometer 40 measures the liquid temperature of the electrolyte. In this embodiment, the thermometer 40 measures the liquid temperatures of the positive electrode electrolyte and the negative electrode electrolyte. The thermometer 40 includes a positive electrode thermometer 42 for measuring the liquid temperature of the positive electrode electrolyte and a negative electrode thermometer 43 for measuring the liquid temperature of the negative electrode electrolyte. The liquid temperature values ​​measured by each thermometer 42, 43 are transmitted to the control unit 50. The thermometer 40 includes any measuring instrument capable of measuring temperature or a physical quantity convertible to temperature.

[0039] The mounting position of the thermometer 40 is not particularly limited, as long as it can measure the liquid temperature of the electrolyte. In this embodiment, the positive electrode thermometer 42 is provided in the positive electrode tank 12. The negative electrode thermometer 43 is provided in the negative electrode tank 13. The positive electrode thermometer 42 may also be provided in the positive electrode flow path 14. The negative electrode thermometer 43 may also be provided in the negative electrode flow path 15. The positive electrode thermometer 42 and the negative electrode thermometer 43 may also be provided in the monitor cell 30.

[0040] (Control Unit) The control unit 50 not only controls the operation of the RF battery system 1, but also monitors the state of the RF battery system 1 and controls the operations necessary to improve it.

[0041] The control unit 50 is typically composed of a computer. The computer includes a processor, a memory, etc. The memory stores a program for causing the processor to execute the processing by the control unit 50. The processor reads and executes the program stored in the memory. The program includes a group of instructions regarding the processing by the control unit 50. The processing procedure by the control unit 50 will be described in detail in the section <Operating Method of RF Battery> described later.

[0042] The control unit 50 controls the charging and discharging of the battery cell 10 based on the OCV of the monitor cell 30 measured by the voltmeter 30v. The control unit 50 of the present embodiment corrects the OCV according to the electrolyte temperature measured by the thermometer 40. The control of charging and discharging by the control unit 50 uses the corrected OCV obtained by correcting the OCV.

[0043] 〈Charge and Discharge Control〉 The control of charging and discharging by the control unit 50 will be described. The memory of the control unit 50 stores the OCV limit range. The OCV limit range is the voltage range for performing charging and discharging. The upper limit value of the limit range is the upper limit voltage during charging. The lower limit value of the limit range is the lower limit voltage during discharging. The control unit 50 performs charging and discharging if the OCV is within the limit range, and stops charging and discharging when the OCV goes out of the limit range. The OCV limit range is a range of OCV set in advance so that the electrolyte does not overcharge or over-discharge at the reference temperature. In other words, the limit range is a range of appropriate SOC at the reference temperature. The reference temperature may be a temperature within the operating temperature range of the electrolyte. The reference temperature is, for example, 25°C.

[0044] 〈Temperature Correction of OCV〉 The temperature correction of the OCV by the control unit 50 will now be explained. The memory of the control unit 50 is pre-stored with information regarding the temperature characteristics of the electrolyte. The temperature characteristics of the electrolyte refer to the relationship between the potential and temperature of the electrolyte. The temperature characteristics of the electrolyte can be determined by testing. The temperature correction of the OCV by the control unit 50 involves obtaining or calculating the potential of the electrolyte according to the temperature of the electrolyte from the above information, and correcting the OCV based on that potential. This temperature correction allows the OCV of the monitor cell 30, measured by the voltmeter 30V, to be corrected to an OCV corresponding to the above-mentioned reference temperature. The charge and discharge control by the control unit 50 described above is performed based on the temperature-corrected OCV.

[0045] In this embodiment, the potential-temperature coefficient of the active material ions is used as the temperature characteristic of the electrolyte. The potential-temperature coefficient indicates the rate at which the standard electrode potential of the active material ions changes when the temperature of the electrolyte rises by 1°C. The unit is [mV / K]. A sign of "-" for the potential-temperature coefficient means that the above potential decreases with increasing temperature. The potential-temperature coefficients for each type of active material ion are shown below.

[0046] (Potential-temperature coefficient of active material ions) V ion (VO) 2+ / VO2 + ) :-0.901[mV / K] V ion (V 3+ / V 2+ ): 1.5 [mV / K] Fe ions (Fe 2+ / Fe 3+ ): 1.175 [mV / K] Cr ions (Cr 3+ / Cr 2+ ): 1.4 [mV / K] Mn ions (Mn 2+ / Mn 3+ ): 1.8 [mV / K] Ti ions (TiO 2+ / Ti 3+ ): -2.7 [mV / K] Zn ions (Zn 2+ / Zn): 0.119 [mV / K]

[0047] (Method of temperature compensation) The OCV temperature correction calculation process is performed as follows: Calculate the temperature difference between the measured electrolyte temperature and the reference temperature. Referencing the potential-temperature coefficient of the active material ions, calculate the change in the reference potential relative to the OCV at the reference temperature from the potential-temperature coefficient and the temperature difference. Correct the OCV by adding the change in the reference potential to the measured OCV of the monitor cell. The specific calculation method for temperature correction is explained below. Let the reference temperature be Tb [°C], the measured OCV be X [V], the positive electrode electrolyte temperature be Tp [°C], the negative electrode electrolyte temperature be Tn [°C], the potential-temperature coefficient of the active material ions in the positive electrode electrolyte be αp [mV / K], and the potential-temperature coefficient of the active material ions in the negative electrode electrolyte be αn [mV / K]. The unit of the potential-temperature coefficient is [mV / K]. The unit of the electrolyte temperature is [°C]. In the unit of the potential-temperature coefficient, "K" represents absolute temperature. The unit of the liquid temperature, "°C," represents Celsius temperature. Absolute temperature and Celsius temperature differ only in their reference temperature; their units are the same. That is, 1K = 1°C. The unit of the potential-temperature coefficient [mV / K] is the same as [mV / °C]. The change in reference potential A can be calculated using [(αp × (Tp - Tb)) - (αn × (Tn - Tb))]. Then, by setting [X + A], the OCV is corrected. Correcting at least the upper limit of the OCV can suppress overcharging.

[0048] A specific example of temperature compensation will be explained using Figure 3. The active material ions in the positive electrode electrolyte are tetravalent or pentavalent V ions (VO2). 2+ / VO2 + The active material ions in the negative electrode electrolyte are trivalent or divalent V ions (V 3+ / V 2+ ) The reference temperature is 25°C. The OCV limit range at the reference temperature of 25°C is 1.33V to 1.60V. In the example shown in Figure 3, the hydrogen generation potential is used as the reference, and the active material ions (VO2) of the positive electrode electrolyte at 25°C are used. 2+ / VO2 + Assume that the potential of (V) is 1.001V. Also, the active material ions (V) of the negative electrode electrolyte at 25°C. 3+ / V2+ ) is assumed to have a potential of -0.255V. In this case, the difference between the reference potential of the positive electrode electrolyte and the reference potential of the negative electrode electrolyte at 25°C, that is, the reference potential of OCV, is 1.256V. The liquid temperature of each of the positive electrode electrolyte and the negative electrode electrolyte is 50°C. That is, it is assumed that the liquid temperature of the electrolyte has risen by 25°C from the reference temperature. When the temperature of the electrolyte rises by 1°C, the reference potential of the positive electrode electrolyte shifts by -0.901mV, that is, it decreases by 0.901mV. Also, the reference potential of the negative electrode electrolyte shifts by 1.5mV, that is, it increases by 1.5mV. As shown in Figure 3, when the liquid temperature of the positive electrode electrolyte rises from 25°C to 50°C, the potential of the active substance ions (VO 2+ / VO2 + ) decreases by [0.901×25]mV compared to that at 25°C, so it becomes 0.9785V. When the liquid temperature of the negative electrode electrolyte rises from 25°C to 50°C, the potential of the active substance ions (V 3+ / V 2+ ) increases by [1.5×25]mV compared to that at 25°C, so it becomes -0.2175V. In this case, the reference potential of OCV at 50°C becomes 1.196V. Therefore, for a temperature rise of 25°C, the reference potential of OCV decreases by approximately 60mV according to [(0.901 + 1.5)×25]. That is, the reference potential of OCV at a liquid temperature of 50°C for the electrolyte decreases by 60mV compared to the reference potential of OCV at the reference temperature. This means that the OCV measured when the liquid temperature of the electrolyte is 50°C is 60mV lower than the OCV measured at 25°C. Therefore, if the OCV is charged to a state of 1.6V under the condition that the liquid temperature of the electrolyte is 50°C, it means that it is charged to a state of 1.66V under the condition of 25°C. Therefore, under the condition that the liquid temperature of the electrolyte is 50°C, the measured OCV is corrected by adding 60mV, which is the amount of change in the reference potential, to the measured OCV by the above-described temperature correction. This correction is synonymous with correcting the limit range of OCV to 1.27V or more and 1.54V or less under the condition that the liquid temperature of the electrolyte is 50°C.

[0049] <Operating Method of RF Battery> Referring to Figure 4, the operation method of the RF battery according to the embodiment will be described. The operation method of the RF battery involves supplying positive electrode electrolyte and negative electrode electrolyte to the battery cell 10 using the RF battery system 1 described above to perform charging and discharging. One of the features of the operation method of the RF battery according to the embodiment is that it comprises a first step S11, a second step S12, a third step S13, and a fourth step S14, as shown in Figure 4. Contents similar to those described in the RF battery system 1 described above may be omitted.

[0050] (First step) The first step, S11, is the step of measuring the OCV of the monitor cell 30. The OCV of the monitor cell 30 is measured using a voltmeter 30V.

[0051] (Second step) The second step, S12, is the step of measuring the electrolyte temperature. Specifically, the electrolyte temperature Tp of the positive electrode and the electrolyte temperature Tn of the negative electrode are measured. Each electrolyte temperature Tp and Tn are measured using the thermometers 42 and 43 described above.

[0052] (Third step) The third step S13 is a step in which the OCV measured in the first step S11 is corrected according to the electrolyte temperature measured in the second step S12. The third step S13 corrects the measured value of OCV by the calculation process described in the (Temperature Correction Method) section above. The third step S13 is a process executed by the control unit 50 described above.

[0053] (Fourth step) The fourth step, S14, charges and discharges the battery cell 10 based on the OCV corrected in the third step, S13. Specifically, if the corrected OCV is within the aforementioned limit range, charging and discharging are performed. If the corrected OCV is outside the aforementioned limit range, charging and discharging are paused. In other words, during charging, if the corrected OCV exceeds the upper limit voltage of the limit range, charging is paused. Also, during discharging, if the corrected OCV falls below the lower limit voltage of the limit range, discharging is paused.

[0054] Effects and Benefits The RF battery system 1 and the method of operating the RF battery according to the above embodiment have the following effects.

[0055] This prevents overcharging of the electrolyte because the OCV measurement is corrected according to the electrolyte temperature. By controlling charging and discharging based on the corrected OCV, the state of charge (SOC) of the electrolyte can be maintained within an appropriate range.

[0056] [Test Example 1] A prototype RF battery system with a configuration similar to the embodiment described above was fabricated. Using this RF battery system, the system was evaluated with and without OCV temperature compensation.

[0057] The positive electrode electrolyte and the negative electrode electrolyte use an aqueous sulfuric acid solution containing V ions. This electrolyte is prepared by dissolving 0.5 M V ions in an aqueous sulfuric acid solution with a concentration of 1 M. The V ions in the positive electrode electrolyte are tetravalent or pentavalent (VO2). 2+ / VO2 + ) The V ions in the negative electrode electrolyte are trivalent or divalent (V 3+ / V 2+ )

[0058] In the RF battery system using the above electrolyte, the OCV limit range at the reference temperature of 25°C is 1.33V to 1.60V.

[0059] (Sample No. 10) Sample No. 10 is an RF battery system without temperature compensation. For Sample No. 10, charge-discharge cycle tests of the RF battery system were performed while maintaining the electrolyte temperatures of both the positive and negative electrodes at 50°C. Both charging and discharging were performed at a current density of 50 mA / cm². 2 The process is carried out with a constant current. Charging is performed until the OCV measurement reaches 1.60V, the same as the upper limit of the above limit range. Discharging is performed until the OCV measurement reaches 1.33V, the same as the lower limit of the above limit range. In other words, during charging, the control switches to discharging when the OCV measurement reaches 1.6V, and during discharging, the control switches to charging when the OCV measurement reaches 1.33V.

[0060] (Sample No. 1) Sample No. 1 is an RF battery system with temperature compensation. Except for a change in the OCV limit range, Sample No. 1 is tested in the same way as Sample No. 10, with the positive and negative electrode electrolyte temperatures maintained at 50°C during the charge-discharge cycle test of the RF battery system. Charging and discharging are performed at a current density of 50 mA / cm², the same as in Sample No. 10. 2 This is done with a constant current. For sample No. 1, during charging, the control switches to discharging when the corrected OCV value (described later) reaches 1.6V, and during discharging, the control switches to charging when the corrected OCV value reaches 1.33V.

[0061] In Sample No. 1, the corrected OCV is obtained by adding the change in the reference potential for OCV at 25°C to the measured OCV value. The change in the reference potential can be calculated from the temperature difference between the reference temperature and the potential-temperature coefficients of the active material ions in the positive electrode electrolyte and the active material ions in the negative electrode electrolyte. Under the condition that the electrolyte temperature in Sample No. 1 is 50°C, the reference potential of the OCV decreases by 60mV for a temperature increase of 25°C. Therefore, in Sample No. 1, charging and discharging are performed with a value obtained by adding 60mV to the measured OCV value. In other words, in Sample No. 1, the OCV limit range is changed to 1.27V or more and 1.54V or less. Specifically, during charging, the control switches to discharging when the measured OCV value reaches 1.54V, and during discharging, the control switches to charging when the measured OCV value reaches 1.27V.

[0062] For each of the above samples, the presence or absence of gas generation was investigated after repeating the charge-discharge cycle more than 100 times. As a result, no gas generation was detected in sample No. 1. In contrast, gas generation was detected in sample No. 10. Furthermore, when the battery capacity of each sample was compared after the charge-discharge cycle test, the battery capacity of sample No. 1 was higher than that of sample No. 10. Therefore, it is considered that overcharging was suppressed in sample No. 1. [Explanation of symbols]

[0063] 1. Redox flow battery system (RF battery system) 10 battery cells 101 Diaphragm, 102 Positive electrode cell, 103 Negative electrode cell 104 Positive electrode, 105 Negative electrode 12 Positive electrode tank, 13 Negative electrode tank 14 Positive electrode channel, 15 Negative electrode channel 108,109 Outbound piping, 110,111 Return piping 112,113 pumps 30 monitor cells 30V voltmeter 40 thermometer 42 Positive electrode thermometer, 43 Negative electrode thermometer 50 Control Unit 80 AC / DC converters, 81 Substation equipment 90 Power system, 91 Power generation unit, 92 Load 100-cell stack 200s substack 120 Cell Frame 121 Bipolar plate, 122 Frame 123,124 Fluid supply manifold, 125,126 Drainage manifold 127 Sealing member 210 End plate, 220 Intake / exhaust plate, 230 Tightening mechanism

Claims

1. A battery cell that charges and discharges by supplying electrolyte, A monitor cell supplied with the aforementioned electrolyte, A voltmeter for measuring the open-circuit voltage of the monitor cell, A thermometer for measuring the liquid temperature of the electrolyte, The system includes a control unit that controls the charging and discharging of the battery cell based on the open-circuit voltage, The control unit corrects the open-circuit voltage according to the liquid temperature. Redox flow battery system.

2. The redox flow battery system according to claim 1, wherein the control unit corrects at least the upper limit of the open-circuit voltage.

3. The redox flow battery system according to claim 1 or claim 2, wherein the electrolyte contains vanadium ions.

4. The control unit is The temperature difference between the electrolyte solution temperature and the reference temperature is calculated. Based on the potential-temperature coefficient of the active material ions contained in the electrolyte and the temperature difference, the change in the reference potential is calculated. A redox flow battery system according to any one of claims 1 to 3, wherein the open-circuit voltage is corrected by adding the amount of change in the reference potential to the measured open-circuit voltage.

5. A method for operating a redox flow battery, which charges and discharges by supplying electrolyte to a battery cell, A step of measuring the open-circuit voltage of a monitor cell to which the electrolyte is supplied, A step of measuring the liquid temperature of the electrolyte, A step of correcting the open-circuit voltage according to the liquid temperature, The process includes a step of charging and discharging the battery cell based on the corrected open-circuit voltage. How to operate a redox flow battery.

6. The step of correcting the open-circuit voltage is: A process for calculating the temperature difference between the electrolyte solution temperature and a reference temperature, A process for calculating the change in reference potential based on the potential-temperature coefficient of the active material ions contained in the electrolyte and the temperature difference, A method for operating a redox flow battery according to claim 5, comprising the process of adding the amount of change in the reference potential to the measured open-circuit voltage.

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