Redox flow battery and operating method thereof

Abstract

The present application relates to a redox flow battery (11) comprising a battery device (12) and a measuring device for determining the state of charge wherein the measuring device comprises a hydraulic connection line (15) connecting a first tank (13) to a second tank (14) such that there is a permanent electrical connection between the electrolytes in the two tanks (13, 14), the measuring device comprises at least two electrodes (1, 2, 3, 4, 5, 6), a first electrode (3, 4, 6) being arranged directly in the positive electrolyte circuit and a second electrode (1, 2, 5) being arranged directly in the negative electrolyte circuit, the redox flow cell (11) comprising a control device (16) which is designed to detect a voltage difference between the two electrodes (1, 2, 3, 4, 5, 6).

Description

Technical Field

[0001] The present application relates to a redox flow battery including a state of charge measurement device and an operating method. The redox flow battery is preferably a vanadium-based battery, but batteries with different electrolyte compositions are also possible. Background Art

[0002] To determine the state of charge (SoC) of a redox flow battery, an electrochemical measuring cell is usually used to measure the open circuit voltage (OCV) of the battery. Specific application examples of such measuring cells have been disclosed, for example, in DE 10 2020 115 385 B3. Such a measuring cell comprises two chambers, which are separated from each other by a so-called partition or membrane. An electrode is arranged in each chamber, and the measurement signal is obtained between the electrodes. The chambers of the measuring cell are connected to the electrolyte circuit of the battery so that the electrolyte can flow through the chambers. Summary of the invention

[0003] The object of the present application is to provide an alternative means for at least approximately determining the SoC of a redox flow battery without the need for an electrochemical measuring cell.

[0004] The object of the present application is achieved by the embodiments in the independent claims. More advantageous embodiments of the present application can be found in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The invention is explained below with reference to the accompanying drawings, which show details.

[0006] Figure 1 A schematic diagram of a redox flow battery according to the present application is shown;

[0007] Figure 1a A variant schematic diagram of a hydraulic connecting pipeline according to the present application is shown;

[0008] Figure 2 A schematic diagram of an electrode layout according to the present application is shown;

[0009] Figure 3 A further schematic diagram of the electrode layout according to the present application is shown. DETAILED DESCRIPTION

[0010] Figure 1A redox flow battery 11 provided according to the present application is shown. The battery includes a battery assembly 12. The battery assembly 12 is an assembly consisting of multiple redox flow batteries and can be arranged in any arrangement. For example, the battery assembly 12 can be a single battery stack, a series structure of multiple battery stacks, a parallel structure of multiple battery stacks, or a series-parallel combination structure consisting of multiple battery stacks. The battery 11 includes two tanks for storing electrolytes. The two tanks are numbered 13 and 14. The + and - signs in the tanks 13 and 14 represent the polarity of the electrolytes in the respective tanks.

[0011] When the battery 11 is in operation, the electrolyte is supplied from the tank 13 and the tank 14 to the battery assembly 12, respectively. The tank 13 or the tank 14 and the piping system constitute an electrolyte supply system, and the piping system is located between the tanks 13, 14 and the inlets of their respective corresponding battery assemblies 12. Similarly, the piping system between the outlet of the battery assembly 12 and the tanks constitutes an electrolyte discharge system. Therefore, the battery 11 includes two electrolyte supply systems and two electrolyte discharge systems. Each supply system and its corresponding discharge system form an electrolyte circuit. To distinguish them, each circuit, system and circuit is named "negative" and "positive", referring to the polarity of the electrolyte in the element. A pump impeller is configured in each circuit to circulate the electrolyte. The direction of rotation of the pump impeller determines the flow direction of the electrolyte in each circuit. As Figure 1 As shown, the direction of rotation also depends on the following structural design: the pipeline opening of the supply system entering the tank is located at the lower part of the tank, and the opening of the discharge system entering the tank is located at the upper part of the tank.

[0012] According to the present application, the measuring device of the battery 11 includes at least two electrodes directly arranged in the electrolyte loop. The first electrode is directly arranged in the negative electrolyte loop, and the second electrode is directly arranged in the positive electrolyte loop. Therefore, the electrodes are in contact with the electrolyte, and a potential signal representing the state of the electrolyte can be obtained. Figure 1 A total of six such electrodes are shown: electrode 1 is arranged directly in the piping system of the negative supply system; electrode 2 is arranged directly in the piping system of the negative discharge system; electrode 3 is arranged directly in the piping system of the positive supply system; electrode 4 is arranged directly in the piping system of the positive discharge system; electrode 5 is arranged directly in the tank 14 of the negative supply system; electrode 6 is arranged directly in the tank 13 of the positive supply system. The word "directly" means that these electrodes are arranged directly in the element, rather than being independent measuring units connected to the electrolyte circuit through a branch as in the prior art.

[0013] As will be described in detail below, according to the present application, the measurement signal representing the state of charge of the battery 11 is formed by the voltage difference between the first electrode and the second electrode. For this purpose, a prerequisite is that there is a defined reference potential for the respective potentials of the two electrolyte circuits. That is, the two electrolyte circuits must not float electrically relative to each other. According to the present application, this is achieved by electrically connecting the two electrolyte circuits to each other via a hydraulic connecting line, which will be described in detail below.

[0014] According to an embodiment of the present application, the battery 11 includes a hydraulic connection line, which permanently electrically connects the electrolyte in the storage tank 13 and the electrolyte in the storage tank 14. Figure 1 In the figure, the hydraulic connection line is indicated by 15. Since the wall of the hydraulic connection line 15 is made of non-conductive material (the electrolyte delivery pipeline of such redox flow battery is usually designed in this way), its electrical connection function is realized by the electrolyte in the hydraulic connection line 15, that is, the hydraulic connection line 15 filled with electrolyte represents a salt bridge or an ion bridge. Therefore, such a hydraulic connection line 15 is an essential component of the measuring device in the present application. Figure 1a , Figure 1a Two variants of hydraulic connecting lines are described, by means of which the electrical connection of the electrolyte circuit required for the measuring device can be realized.

[0015] Hydraulic connecting lines between two tanks of a redox flow battery are known from the prior art. For example, WO 2022 / 033 750A1 discloses such a hydraulic connecting line (see FIG. 5 ). The disclosed hydraulic connecting line is in a tank above the electrolyte level and is used to enable the exchange of electrolyte between the two tanks when the amounts of electrolyte in the two tanks are different from each other. In WO 2022 / 033 750A1, when the electrolytes are mixed, different amounts of electrolyte appear in the two tanks. Even in normal operation of the redox flow battery, the so-called “crossover” in the battery assembly causes the amount of electrolyte in the two tanks to change over time. In this case, a hydraulic connecting line as disclosed in WO 2022 / 033750 A1 can also be used so that the liquid levels in the two tanks are rebalanced when the two tanks are displaced relative to each other by more than a predetermined amount. Therefore, this known hydraulic connecting line only allows the electrolyte circuit to be occasionally electrically connected, not permanently electrically connected. Since such an electrical connection would in principle lead to an abnormal discharge of the redox flow battery, conventional redox flow batteries are equipped with a shutoff valve in such a hydraulic connection line in order to be able to actively prevent such a discharge.

[0016] Figure 1a Two variants of the hydraulic connection line according to the present application are shown. Figure 1aIn the variant below, the two openings of the hydraulic connection line entering the tank are completely below the electrolyte level in the tank, so that the entire hydraulic connection line is always filled with electrolyte. In this variant, the diameter of the hydraulic connection line is kept small, which has the advantage that there is almost no exchange of electrolyte through the hydraulic connection line. Due to the high impedance characteristics of the electrical connection, the current flowing through the hydraulic connection line is also very small and can be ignored. Usually, the small diameter is also sufficient to compensate for the inhomogeneities of the electrolyte flow caused by the crossover. Figure 1a In the variant shown above, the two openings of the hydraulic connecting line into the tank are only partially below the liquid level. Therefore, the hydraulic connecting line is always only partially filled with electrolyte. It is also sufficient to partially fill the hydraulic connecting line with electrolyte to establish a permanent electrical connection. To this end, the hydraulic connecting line must extend in the horizontal direction with sufficient precision. In this variant, the hydraulic connecting line can have a larger diameter, because the hydraulic connecting line is only partially filled with electrolyte, so that a high-impedance electrical connection exists in this case as well. Therefore, as described in WO 2022 / 033750 A1, such a hydraulic connecting line can also be used advantageously for mixing electrolytes in the tank.

[0017] Figure 2 The electrode layout is shown in detail. Figure 2 In the upper part, the electrodes are arranged in the tank and penetrate the tank wall; Figure 2 In the lower part of the apparatus, the electrodes are arranged in the pipe system and penetrate the pipe wall. The pipe wall is a non-conductive material. As an alternative, the electrodes can also be completely placed inside the corresponding element (tank or pipe system). In this case, the wires lead from the electrodes through the wall of the corresponding element to the outside space.

[0018] Preferably, the electrodes in the positive and negative circuits are arranged in substantially the same manner. Figure 1 , if the first electrode in the negative circuit is arranged as electrode 1, the second electrode in the positive circuit should be arranged as electrode 3; if the first electrode in the negative circuit is arranged as electrode 2, the second electrode in the positive circuit should be arranged as electrode 4; if the first electrode in the negative circuit is arranged as electrode 5, the second electrode in the positive circuit should be arranged as electrode 6. However, small deviations from the most optimal arrangement are not decisive.

[0019] The first electrode and the second electrode are used to provide a measurement signal representing the state of charge SoC of the battery 11. The measurement signal is formed by the voltage difference between the first electrode and the second electrode. Figure 1 The reference numeral 16 is a control device for detecting the voltage difference. Figure 1As shown, although the control device 16 can be arranged separately from the battery 11, it is still considered to be an integral part of the battery 11. The control device 16 can also be integrated into the battery 11. If the battery 11 is part of a larger energy storage system, the control device 16 can be integrated into a higher-level control system. In any case, the control device 16 is always connected to at least two electrodes (electrode 1, electrode 2, electrode 3, electrode 4, electrode 5 and / or electrode 6, if present) arranged in the electrolyte circuit.

[0020] Depending on the position of the two electrodes, their voltage difference can reflect different state of charge parameters. Figure 1 The voltage difference between electrode 1 and electrode 3 is V 13 represents the charge state of the electrolyte before entering the battery assembly 12; accordingly, the voltage difference V between electrode 2 and electrode 4 24 represents the charge state of the electrolyte after passing through the battery assembly 12; accordingly, the voltage difference V between the electrode 5 and the electrode 6 56 It indicates the charge state of the electrolyte in tank 13 and tank 14.

[0021] If the battery 11 includes more than one electrode in each electrolyte circuit, additional voltage differences may be formed. The voltage differences may provide additional information about the state of the battery 11. Figure 1 The information that can be obtained is particularly interesting when the voltage difference (V 13 -V 24 ) can reflect the difference in charge state before and after the electrolyte flows through the battery assembly 12. The difference can also represent a measure of the flow rate of the electrolyte flowing through the battery assembly 12. Therefore, the difference can be used as a control signal for the pump delivery rate. This eliminates the need for a pressure sensor in the electrolyte loop, which is usually used to provide a control signal for the pump delivery rate. In addition, the voltage difference V between electrode 2 and electrode 1 21 is a measure of the negative half-area conversion rate of the battery assembly 12. Similarly, the voltage difference between electrode 4 and electrode 3 is a measure of the positive half-area conversion rate of the battery assembly 12. These quantities can be used to detect abnormal side reactions in the battery assembly 12 and obtain information about the remaining state of health (SoH) of the battery, while also estimating the Coulomb efficiency (CE) of the battery assembly 12.

[0022] If more than two electrodes are arranged in each electrolyte circuit, it is also possible to detect the imbalance between the negative electrolyte and the positive electrolyte with respect to their respective states of charge. Figure 3 The conditions for carrying out the detection method will be described in detail. Figure 3The upper part shows part of the negative electrode electrolyte circuit, and the lower part shows part of the positive electrode electrolyte circuit. The arrows in the figure indicate the flow direction of the electrolyte. In each of the upper and lower parts, two electrodes are set, one of which is arranged at an upstream position along the flow direction, and the other electrode is arranged at a downstream position along the flow direction. The hydraulic path length between the two electrodes is defined as the distance traveled by the electrolyte when flowing from the upstream electrode to the downstream electrode. The corresponding voltages are measured between the two electrodes belonging to the same circuit: V- and V+ (negative electrode circuit voltage V-, positive electrode circuit voltage V+). If V- is inconsistent with V+, it indicates that the charge state of the positive and negative electrolytes is unbalanced. However, in this case, the hydraulic path length between the two electrodes in the two circuits must be as equal as possible. In addition, the battery assembly 12 cannot be arranged in the hydraulic path between the two electrodes. Combined with Figure 1 , which means that an electrode combination of electrode 5, electrode 1, electrode 6 and electrode 3, or an electrode group of electrode 2, electrode 5, electrode 4 and electrode 6 can be used for the evaluation. However, it is not possible to use electrode 1 and electrode 2 as well as electrode 3 and electrode 4, because in this case the battery array 12 is arranged in the hydraulic path between the electrode pairs. The condition of the same hydraulic path length between the electrode pairs can be met particularly easily if all participating electrodes are arranged in a tank.

[0023] like Figure 3 In the arrangement shown, one electrode in each electrolyte circuit can be considered the so-called working electrode and the other electrode the reference electrode. V- and V+ represent the potential difference between the working and reference electrodes. This is particularly important when more than two electrodes are used per electrolyte circuit. Thus, each electrolyte circuit has exactly one reference electrode and one or more working electrodes, and the potential difference is developed from the working electrode to the reference electrode. It is obvious that the electrodes are arranged in equivalent positions in each electrolyte circuit.

[0024] In summary, it can be said that with one electrode per electrolyte loop, a measurement parameter characterizing the state of charge (SoC) of the battery can be obtained. In addition, with multiple electrodes per electrolyte loop, further characteristics of the battery can be determined or estimated.

[0025] Carbon element can be used as the material of the electrode. For example, the material of the electrode can be graphite or glassy carbon. In addition, the material of the electrode can also be a conductive plastic. If the redox flow battery is a vanadium-based battery, the electrode material should preferably be a vanadium-based material. It can be a vanadium oxide (such as vanadium pentoxide V 2 O 5 ) and carbon as the active material in plastics.

[0026] According to the present application, the method for determining the state of charge SoC of the battery 11 comprises the following steps:

[0027] - Detecting the voltage on the first electrode.

[0028] - Detecting the voltage on the second electrode.

[0029] - Calculate the voltage difference between the voltages on the first electrode and the second electrode detected in the previous two steps.

[0030] As described above, the first electrode is arranged in the negative electrolyte loop, and the second electrode is arranged in the positive electrolyte loop.

[0031] In order to determine further characteristics of the redox flow battery 11, the redox flow battery 11 comprises at least four electrodes, at least two of which are arranged in the negative electrolyte loop, and at least two of which are arranged in the positive electrolyte loop. According to the present application, the method further comprises the following steps:

[0032] - Detect the voltage at the two electrodes of the negative electrolyte loop.

[0033] - Detect the voltage at the two electrodes of the positive electrolyte circuit.

[0034] - Calculate the voltage difference for each electrolyte loop voltage measured in the first two steps respectively.

[0035] The inventors have found that by combining several methods for determining SoC, the reliability of determining the SoC of the redox flow battery 11 can be statistically improved. Therefore, by determining the state of charge SoC of the respective electrolyte circuit from the voltage difference V- and / or V+, the value of the state of charge SoC determined according to the present application can be made more accurate. Another possible combination is to estimate the state of charge of the redox flow battery 11 by using the terminal voltage of the redox flow battery 11. Therefore, if Figure 1 As shown, optionally, the redox flow battery 11 comprises a measuring device 17 for measuring the terminal voltage. In order to estimate the state of charge SoC using the terminal voltage, the following steps need to be performed:

[0036] - Turn off power to the battery pack.

[0037] - After a predetermined period of time has passed, the terminal voltage is detected.

[0038] - Divide the terminal voltage by the number of batteries arranged consecutively in the battery assembly 12.

[0039] Turning off the power to the battery assembly 12 means that the redox flow battery 11 will not be charged or discharged from this step. The predetermined length of time that must pass in this state depends on the flow rate of the pump at the current operation and the electrolyte volume of the battery assembly 12. If the volume of the battery assembly 12 is completely filled with electrolyte, the terminal voltage is equal to the product of the number of series-connected cells in the battery assembly 12 and the open circuit voltage.

[0040] The reliability can be further increased by combining other known methods for determining the state of charge, for example, coulomb counting or optical sensor determination methods for determining the state of charge (see DE 10 2016 117 604 A1 for details).

[0041] Reference Symbols List

[0042] 1 Electrode

[0043] 2 Electrodes

[0044] 3 Electrodes

[0045] 4 Electrodes

[0046] 5 Electrodes

[0047] 6 Electrodes

[0048] 11 Redox Flow Battery

[0049] 12 Battery Components

[0050] 13 Storage Tanks

[0051] 14 Storage Tanks

[0052] 15 Hydraulic connection lines

[0053] 16 Control Devices

[0054] 17 Measurement device for detecting terminal voltage

Claims

1. A redox flow battery (11), comprising a battery assembly (12) having two electrolyte inlets and two electrolyte outlets, a first tank (13) for storing a positive electrolyte, a second tank (14) for storing a negative electrolyte, two first pipe systems located between the tanks (13, 14) and the inlet of the battery assembly (12), and two second pipe systems located between the tanks (13, 14) and the outlet of the battery assembly (12), wherein the tanks (13, 14) and the first pipe systems constitute two supply systems, and the second pipe systems constitute two discharge systems, and the corresponding supply systems and discharge systems respectively form a negative electrolyte circuit and a positive electrolyte circuit, and a pump impeller for circulating the electrolyte is arranged in each electrolyte circuit, and the redox flow battery (11) comprises a measuring device for determining a state of charge, It is characterized in that The measuring device for determining the state of charge comprises a hydraulic connection line (15) which connects a first tank (13) to a second tank (14) so ​​that there is a permanent electrical connection between the electrolytes in the two tanks (13, 14), the electrical connection being established by the electrolyte in the hydraulic connection line (15), and the measuring device comprises at least two electrodes (1, 2, 3, 4, 5, 6), wherein the first electrode (3, 4, 6) is arranged in a positive electrolyte circuit and the second electrode (1, 2, 5) is arranged in a negative electrolyte circuit, and the redox flow battery (11) comprises a control device (16) which is capable of detecting a voltage difference between the two electrodes (1, 2, 3, 4, 5, 6).

2. The redox flow battery (11) according to claim 1, wherein the electrodes (1, 3, 5, 6) are arranged directly in the supply system.

3. Redox flow battery (11) according to claim 2, wherein the electrodes (1, 3) are arranged directly in the pipe system of the supply system.

4. The redox flow battery (11) according to claim 2, wherein the electrodes (5, 6) are arranged directly in the tank (13, 14).

5. The redox flow battery (11) according to claim 1, wherein the electrodes (1, 3, 5, 6) are arranged directly in the exhaust system.

6. A redox flow battery (11) according to any preceding claim, wherein the redox flow battery (11) comprises more than one electrode (1, 2, 3, 4, 5, 6) in each electrolyte circuit.

7. The redox flow battery (11) according to claim 6, wherein one electrode (1, 3, 5, 6) is arranged directly in the supply system and one electrode (2, 4) is arranged directly in the discharge system.

8. The redox flow battery (11) according to claim 7, wherein one electrode (1, 3) is arranged directly in the pipeline system of the supply system.

9. The redox flow battery (11) according to any one of claims 6 to 8, wherein the control device (16) is capable of detecting a voltage difference between two electrodes (1, 2, 3, 4, 5, 6) arranged in the same electrolyte circuit.

10. A redox flow battery (11) according to any preceding claim, wherein the redox flow battery (11) comprises a measuring device (17) for detecting the terminal voltage.

11. A method of operating a redox flow battery (11) according to any one of claims 1 to 5, The following steps are involved: detecting an electrical voltage at the first electrode (3, 4, 6); detecting an electrical voltage at a second electrode (1, 2, 5); Calculate the voltage difference detected in the first two steps; The voltage difference is a measure of the battery's state of charge.

12. A method of operating a redox flow battery (11) according to any one of claims 6 to 10, The following steps are involved: Detecting the voltage of two electrodes in the negative electrolyte loop; Detecting the voltage of two electrodes in the positive electrolyte loop; Calculate the voltage differences detected in the first two steps respectively.

13. A method of operating a redox flow battery (11) according to claim 11, the battery according to claim 10, comprising the steps of: Turning off the power supply of the battery assembly (12); detecting the terminal voltage after a predefined period of time; Dividing the terminal voltage by the number of batteries arranged in series in the battery assembly (12); The quotient obtained in the last step is a measure of the battery's state of charge.

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