Redox flow battery

Abstract

For a modularly constructed redox flow battery (1), at least one positive and at least one negative intermediate tank (Za, Zb) are provided in the redox flow battery (1), wherein either a plurality of positive electrolyte tanks (13am) are connected to a positive intermediate tank (Za) and a plurality of negative electrolyte tanks (13bm) are connected to a negative intermediate tank (Zb), and / or a plurality of individual batteries (Bn) are connected to the positive and negative intermediate tanks (Za, Zb).

Description

[0001] Redox flow battery

[0002] The present invention relates to a redox flow battery comprising a number of individual batteries, each comprising at least one cell stack, wherein each cell stack comprises a plurality of individual cells, each individual cell comprising a positive half-cell with a positive cell electrode and a negative half-cell with a negative electrode, wherein the positive half-cell of an individual cell is supplied with a positive electrolyte during operation of the redox flow battery and the negative half-cell is supplied with a negative electrolyte during operation of the redox flow battery. The invention also relates to a method for operating such a redox flow battery.

[0003] The present invention relates to redox flow batteries. A redox flow battery is an electrochemical energy storage device and typically consists of electrolyte tanks for storing positive and negative electrolytes, as well as pumps and lines for circulating the electrolytes through one or more cell stacks, each comprising a number of individual cells. The individual cells of the cell stack are each formed by a positive half-cell and a negative half-cell arranged side by side. During operation of the redox flow battery, a positive half-cell of an individual cell is supplied with a positive electrolyte, and the negative half-cell with a negative electrolyte. The positive and negative half-cells of an individual cell are typically separated from each other by a semipermeable membrane, usually an ion exchange membrane.The semipermeable membrane is, for example, a cation and / or anion exchange membrane, e.g., based on a sulfonated fluoropolymer such as polytetrafluoroethylene (PTFE). The positive half-cell typically contains a positive electrode within a frame, through which the positive electrolyte flows. The negative half-cell typically contains a negative electrode within a frame, through which the negative electrolyte flows. The positive and negative electrolytes are circulated separately through the half-cells. The positive and negative electrodes are usually made of porous graphite felts that allow the electrolyte to flow through them. Electrode plates, such as bipolar plates, are arranged between adjacent cells of the cell stack to act as current collectors; these are usually made of a composite material of carbon and plastic.Current collectors can be located on the electrode plates of the axially outer surfaces of the individual cells of the cell stack. These collectors provide an external electrical contact, allowing an electrical voltage to be drawn across the entire cell stack (discharging the redox flow battery) or applied to the cell stack (charging the redox flow battery). The cell stack can be terminated on each axial outer surface by an end plate, which also holds the cell stack together.

[0004] The electrolyte of a redox flow battery is a liquid and essentially comprises an electrochemical redox couple (electroactive species) consisting of a first redox element and a second redox element, each in the form of a redox-active element or ion, or combinations of redox-active elements and / or ions with different electrical charges (oxidation states). The electrochemical redox couple is present in the liquid at a specific concentration. A wide variety of redox-active elements or ions, or combinations thereof, can be used as redox couples in a redox flow battery. The redox elements of a redox couple are typically dissolved in the electrolyte liquid. The electrolyte liquid is usually an aqueous acid, such as aqueous sulfuric acid. Redox flow batteries with a wide variety of redox couple combinations are known.Some non-exhaustive examples of known combinations of redox couples are V. 2+ / V 3+ vs. VO 2+ / VO2 + (in a vanadium redox flow battery), V 2+ / V 3+ vs. Br / CIBr2, Br2 / Br vs. S / S 2 ; Br / Br2vs. Zn 2+ / Zn, Ce 4+ / Ce 3+ vs. V 2+ / V 3+ , Fe 3+ / Fe 2+ vs. Br2 / Br, Fe 3+ / Fe 2+ vs. Cr 3 7Cr 2+ , Mn 2+ / Mn 3+ vs. Br2 / Br, Fe 3+ / Fe 2+ vs. Ti 2 7TiO 2+and others. The redox elements can be contained in the electrolyte in various chemical compounds, for example in the form of sulfates, such as vanadium sulfate, or chlorides, such as vanadium chloride. The vanadium-based redox flow battery is the most widely used, which is why the invention will be described below, but without limiting the generality of the invention, using a vanadium redox flow battery as an example.

[0005] In a vanadium-based redox flow battery, the positive electrolyte in the charged state consists of a redox couple in the form of vanadium with an oxidation number of +4 (also known as V(IV) or V). 4+ denoted) and vanadium with oxidation number +5 (also denoted as V(V) or V 5+ The negative electrolyte, in its charged state, consists of a redox couple in the form of vanadium with an oxidation number of +2 (also known as V(l I) or V). 2+ designated) and vanadium with oxidation number +3 (also designated V(III) or V3+ (designated) - meaning that the negative electrolyte has a more negative electrochemical potential than the positive electrolyte.

[0006] When a redox flow battery is operating, electrical energy is either delivered to a load or absorbed from an energy source. In the example of a vanadium-based redox flow battery, the well-known chemical reaction (redox reaction) 2H₂ takes place. + + VO2 + + V 2+ <-> VO 2+ + V 3+ + H2O during charging / discharging in a single cell of the redox flow battery. During the charging process, the reaction is triggered by an external current or voltage source, which applies an electrical voltage to a single cell (or the entire cell stack).

[0007] For the operation of the redox flow battery, the electrolytes are circulated through the cell stack, specifically through the individual cells of the cell stack, in an electrolyte circuit. Electrolyte pumps are used for this purpose.

[0008] The design and function of a redox flow battery is well known, for example from WO 2018 / 087220 A1 or WO 2014 / 131702 A1.

[0009] A redox flow battery is typically designed according to its electrical storage capacity (e.g., in Ah), as well as its electrical voltage or current, depending on the application. This necessitates redox flow batteries with varying electrolyte volumes (storage capacity) and / or different cell stacks, with varying numbers of cell stacks, which may also be electrically interconnected in different ways. Consequently, the piping system for distributing the electrolyte and the circulation pumps must also be adapted to the specific redox flow battery.

[0010] US 2008 / 0241643 A1 describes a vanadium redox flow battery with multiple positive and multiple negative electrolyte tanks that can be connected as needed to adapt the redox flow battery to different storage capacities. For this purpose, the electrolyte tanks are connected in series as required to increase the electrolyte volume. However, this requires additional electrolyte lines and switching valves, meaning the redox flow battery must be designed for the specific application in advance and is difficult to reconfigure later.

[0011] Therefore, a redox flow battery that can be designed in a modular fashion to enable and easily implement a wide variety of applications and configurations would be advantageous.

[0012] This is achieved with a redox flow battery, as mentioned above, with the features according to claim 1. The inventive design of the redox flow battery allows for the flexible provision of either multiple individual batteries, multiple positive and negative electrolyte tanks, or both, as needed. This allows for easy configuration of both the electrical voltage and current of the redox flow battery, as well as application-specific adjustment of the electrical storage capacity. This configuration and adjustment can also be carried out after the redox flow battery has been commissioned.If a positive return line from the first or second individual battery leads into the positive intermediate tank and from the positive intermediate tank leads on to the first positive electrolyte tank or the second positive electrolyte tank, or if a negative return line from the first or second individual battery leads into the negative intermediate tank and from the negative intermediate tank leads on to the first negative electrolyte tank or the second negative electrolyte tank, the mixing of the electrolyte in the intermediate tank can be improved, which can also reduce any stratification occurring in the electrolyte.

[0013] If a positive return line leads from the first individual battery or second individual battery to the first positive electrolyte tank or the second positive electrolyte tank (without going through the positive intermediate tank), or a negative return line leads from the first individual battery or second individual battery to the first negative electrolyte tank or the second negative electrolyte tank (without going through the negative intermediate tank), the electrolyte can be utilized better because there is no mixing of fresh electrolyte and used electrolyte in the respective intermediate tank.

[0014] The space requirement of a redox flow battery can be reduced if the positive intermediate tank is located above the first positive electrolyte tank or above the second positive electrolyte tank and the positive intermediate tank is connected to the first positive electrolyte tank or the second positive electrolyte tank via a positive downpipe, the positive downpipe forming an overflow in the positive intermediate tank, or if the negative intermediate tank is located above the first negative electrolyte tank or above the second negative electrolyte tank and the negative intermediate tank is connected to the first negative electrolyte tank or the second negative electrolyte tank via a negative downpipe, the negative downpipe forming an overflow in the negative intermediate tank.

[0015] In a particularly simple design, a positive return line from the first individual battery or from the second individual battery leads into the positive downpipe, or a negative return line from the first individual battery or from the second individual battery leads into the negative downpipe.

[0016] To reduce electrical short-circuit currents via the electrolytes, it is advantageously provided that a partition is provided in the positive intermediate tank or the negative intermediate tank, which separates the positive intermediate tank or the negative intermediate tank into a tank chamber and a battery chamber, wherein the tank chamber and the battery chamber are connected to each other via an overflow in the intermediate tank, and the positive tank line opens into the tank chamber of the positive intermediate tank or the negative tank line opens into the tank chamber of the negative intermediate tank, and the positive battery line is connected to the battery chamber of the positive intermediate tank or the negative battery line is connected to the battery chamber of the negative intermediate tank.Alternatively, a partition is provided in the positive or negative intermediate tank, separating it into a tank chamber and a battery chamber, with a positive return line from the first or second individual battery connected to the battery chamber of the positive intermediate tank, or a negative return line from the first or second individual battery connected to the battery chamber of the negative intermediate tank. The partition thus enables at least a temporary electrical interruption in the electrolyte.

[0017] In order to easily and efficiently temper an electrolyte, a temperature control unit is provided on or in the positive intermediate tank, or on or in the negative intermediate tank.

[0018] If the redox flow battery is equipped with a control unit configured to operate the positive tank pumps and the positive battery pumps independently, and the negative tank pumps and the negative battery pumps independently, operation can be easily optimized by decoupled tank and battery pumps. Furthermore, the required pumping power for transferring the electrolyte to the intermediate tanks can be reduced because the necessary flow resistance is low. This also allows an intermediate tank to be positioned above an electrolyte tank, which is advantageous for the footprint of the redox flow battery. Finally, this also allows for better control of electrolyte mixing, thus reducing electrolyte stratification.

[0019] Further advantages of the redox flow battery according to the invention will become apparent from the following description.

[0020] The present invention is explained in more detail below with reference to Figures 1 to 8, which show exemplary, schematic, and non-limiting advantageous embodiments of the invention.

[0021] Fig. 1 shows the basic operating principle of a redox flow battery,

[0022] Fig. 2 shows a redox flow battery with a cell stack,

[0023] Fig. 3 shows a structure of a cell stack of a redox flow battery, Fig. 4 shows an embodiment of a redox flow battery with several cell stacks, Fig. 5 shows an embodiment of a redox flow battery according to the invention with an intermediate tank.

[0024] Fig. 6 shows a possible implementation of a redox flow battery with an intermediate tank. Fig. 7 shows another possible implementation of a redox flow battery with an intermediate tank and

[0025] Fig. 8 shows a redox flow battery with an intermediate tank and a partition.

[0026] For a better understanding of the invention, the structure and function of a redox flow battery 1 will be briefly explained below with reference to Figs. 1 to 4, but without limiting the generality.

[0027] Fig. 1 shows a schematic diagram of a redox flow battery 1 using a single cell 2 of a cell stack 10 to illustrate the well-known operating principle of a redox flow battery 1. For clarity and illustration, Fig. 1 shows only a single cell 2 of a cell stack 10 of a redox flow battery 1, where a cell stack 10 will typically comprise a plurality of single cells 2 arranged side by side in the cell stack 10.

[0028] A single cell 2 consists of a positive and a negative half-cell 2a, 2b, which form a positive reaction chamber 3a and a negative reaction chamber 3b, wherein the two half-cells 2a, 2b, or the positive reaction chamber 3a and the negative reaction chamber 3b, are separated by a semipermeable, in particular ion-selective, membrane 4. The reaction chambers 3a, 3b are formed, for example, in recesses 6a, 6b of frames 5a, 5b. A cell electrode 7a, 7b is arranged in each of the frames 6a, 6b, or in the reaction chambers 3a, 3b, or in the recesses 6a, 6b, and is in contact with the respective electrolyte 15a, 15b located in the half-cell 2a, 2b. The recesses 6a, 6b and, if applicable, the cell electrodes 7a, 7b arranged therein of a single cell 2 are permeated by electrolytes 15a, 15b with different electrical charges or different redox potentials (positive electrolyte 15a and negative electrolyte 15b).Each of the electrolytes 15a, 15b contains a redox couple with specific, time-varying concentrations (depending on the state of charge) of redox elements. The semipermeable, in particular ion-selective, membrane 4 can, for example, be made of sulfonate-modified polytetrafluoroethylene (PTFE), trade name Nation™, and allows ions to equalize the charge between the positive reaction chamber 3a and the negative reaction chamber 3b (or between the electrolytes 15a, 15b contained therein). Current connections 11, 12 are also provided on a cell stack 10 of a redox flow battery 1 to tap off an electrical cell stack voltage Vz applied to the cell stack 10 via a load 14 (discharging the redox flow battery 1) or to apply an electrical cell stack voltage Vz to the cell stack 10 (charging the redox flow battery 1).

[0029] An electrical load 14 can have any shape. Based on the electrical voltage, current, or power requirements of the electrical load 14, a cell stack 10 can be configured in a redox flow battery 1 to provide the necessary electrical voltage and / or current. Redox flow batteries 1 are often used as stationary energy storage systems, for example, as emergency power systems for industrial plants, storage systems for renewable energy (photovoltaics, wind power), and similar applications. Consequently, depending on the application, a person skilled in the art can design or select a cell stack 10, or a parallel and / or series connection of several cell stacks 10, or cell strings consisting of several cell stacks 10, and redox pairs in a redox flow battery 1.

[0030] The electrolytes 15a, 15b are stored in electrolyte tanks 13a, 13b and are circulated from there through the cell stack 10, specifically through each half-cell 2a, 2b of a single cell 2 of the cell stack 10, by means of electrolyte pumps 9a, 9b. For this purpose, a supply line 16a, 16b and a discharge line 17a, 17b are provided for each electrolyte 15a, 15b, which are connected via electrolyte connections 22a, 22b, 23a, 23b to associated electrolyte channels 18a, 18b, 19a, 19b (see Fig. 3) in the cell stack 10.

[0031] In a cell stack 10 with several adjacent individual cells 2, an electrode plate 8, like a bipolar plate, is arranged between each pair of adjacent individual cells 2 (Fig. 3). At the outer ends of the cell stack 10, a current connection 11, 12 can be made on the outer electrode plates 8 or on the outer half-cells 2a, 2b (or cell electrodes 7a, 7b) of the cell stack 10, which can be electrically contacted from the outside.

[0032] The typical structure of a cell stack 10 of a redox flow battery 1 is explained in more detail with reference to Figs. 2 and Fig. 3.

[0033] A cell stack 10 of a redox flow battery 1 comprises at least one single cell 2, typically a plurality of single cells 2, each of which is in turn formed from two frames 5a, 5b of half-cells 2a, 2b. A frame 5a, 5b is preferably made of a plastic, such as an elastomer, e.g., a polyolefinic thermoplastic elastomer (TPE or TPO), such as Santoprene®, or a thermoplastic vulcanize (TPV), particularly by injection molding. In the stack direction R (in the direction in which the single cells 2a, 2b are arranged side by side) between two frames 5a, 5b of a single cell 2, a semipermeable membrane 4, typically an ion exchange membrane (either a cation or anion exchange membrane, e.g., Nation®), is arranged in the cell stack 10.The membrane 4 separates the reaction chambers 3a, 3b, recesses 6a, 6b of the half-cells 2a, 2b of a single cell 2, the cell electrodes 7a, 7b arranged therein, and the electrolytes 15a, 15b contained therein. Between two single cells 2 adjacent in the stack direction R, an electrode plate 8, e.g., a bipolar plate, is arranged in the cell stack 10. The electrode plate 8 is, as shown in Fig. 3, for example, inserted into mutually facing recesses 32 in the frames 5a, 5b. The frames 5a, 5b have central recesses 6a, 6b extending through the stack direction R, each forming a reaction chamber 3a, 3b, in which cell electrodes 7a, 7b, e.g., carbon fiber mats, are arranged, as shown in Fig. 3.

[0034] Through the recesses 6a, 6b in the frames 5a, 5b and the cell electrodes 7a, 7b arranged therein, the electrically differently charged electrolytes 15a, 15b are pumped through the respective half-cells 2a, 2b, whereby the cell electrode 7a, 7b of each half-cell 2a, 2b of a single cell 2 is permeated by an electrolyte 15a, 15b with a different electrical charge. The electrolytes 15a, 15b are supplied and discharged externally via electrolyte connections 22a, 22b, 23a, 23b and are then distributed internally via an electrolyte channel system with electrolyte channels 18a, 18b, 19a, 19b provided in the frames 5a, 5b. The electrolyte connections 22a, 22b, 23a, 23b are provided, for example, on an end plate 24 of the cell stack 10, as shown in Fig. 3, whereby other arrangements of the electrolyte connections 22a, 22b, 23a, 23b, for example on an end frame 20, and of the electrolyte channel system are also possible.

[0035] The cell stack 10 can be terminated at both axial ends in the stack direction R by an end frame 20. An electrically conductive current collector 21 is arranged in the end frame 20, for example, in a recess on one end face of the end frame 20, and is connected to an externally leading electrical current connection 11, 12. In the illustrated embodiment, the current collector 21 rests against the last electrode plate 8 of the last individual cell 2 to establish an electrical contact. However, the current collector 21 or a current connection 11, 12 could also be designed differently. Likewise, the end frame 20 could be omitted from the cell stack 10.

[0036] In the illustrated embodiment, the cell stack 10 is arranged between two rigid end plates 24 and pressed together by clamping means 25. The clamping means 25 are, for example, designed with through bolts 26, nuts 27, washers 28, and springs 29, as shown in Fig. 2. However, the cell stack 10 can also be held together in other ways; in particular, the clamping means 25 can be designed differently. The two end plates 24 can also be arranged between two pressure plates 30, which are pressed together by the clamping means 25, as shown in Fig. 2. To prevent the frames 5a, 5b from settling due to the clamping force of the clamping means 25, a spacer 31 can also be provided between the end plates 24.

[0037] The present invention is not limited to a specific embodiment of a half-cell 2a, 2b, a single cell 2, a cell stack 10, or the redox flow battery 1. Nor is the invention limited to a specific electrolyte 15a, 15b, or to specific redox elements in the electrolytes 15a, 15b. The above descriptions of a redox flow battery 1 serve only to illustrate the invention.

[0038] From the above description and the basic operating principle, it is also obvious that in a redox flow battery 1 there is a positive electrolyte 15a and a negative electrolyte 15b, as well as related to this a positive half-cell 2a and a negative half-cell 2b of a single cell 2 and a positive electrolyte circuit with a positive electrolyte pump 9a and a negative electrolyte circuit with a negative electrolyte pump 9b.

[0039] A redox flow battery 1 can also comprise several cell stacks 10, as illustrated in Fig. 4. In the embodiment shown in Fig. 4, two cell strings 40 are provided, each cell string 40 comprising a plurality of cell stacks 10, for example, as described above. However, a redox flow battery 1 can, of course, also have only one cell string 40. The cell stacks 10 in a cell string 40 can be electrically connected in series via the current terminals 11, 12 of the cell stacks 10 (not shown in Fig. 4 for clarity). However, other electrical connections of the cell stacks 10 in a cell string 40 are also possible, such as a parallel connection or a combination of series and parallel connections. The cell strings 40 can also be electrically connected in series or parallel, or as a combination of series and parallel connections.An arrangement of several electrically interconnected cell stacks 10 or cell strings 40 comprising several cell stacks 10 can also be called.

[0040] A single battery can be designated as Bn. A redox flow battery 1 can comprise several such single batteries Bn, whereby the single batteries Bn can in turn be electrically connected to each other by a series or parallel connection or a mixture of a series and parallel connection to form the redox flow battery 1. In this way, a redox flow battery 1 can be realized with the desired electrical output voltage and the desired electrical power.

[0041] Each cell stack 10 is supplied with a positive electrolyte 15a and a negative electrolyte 15b. For this purpose, an electrolyte tank 13a is provided for the positive electrolyte 15a and an electrolyte tank 13b for the negative electrolyte 15b. The positive electrolyte 15a is circulated through the cell stack 10 in the positive electrolyte circuit with a positive flow rate by a positive electrolyte pump 9a, and the negative electrolyte 15b is circulated in the negative electrolyte circuit with a negative flow rate by a negative electrolyte pump 9b, wherein the positive and negative flow rates are preferably approximately equal.

[0042] In the minimal configuration, a single battery Bn comprises at least one cell stack 10 consisting of a plurality of single cells 2, wherein each single cell 2 comprises a positive half-cell 2a with a positive cell electrode 7a and a negative half-cell 2b with a negative cell electrode 7b, wherein the positive half-cell 2a is supplied with the positive electrolyte 15a during operation of the redox flow battery 1 and the negative half-cell 2b is supplied with the negative electrolyte 15b during operation of the redox flow battery 1.

[0043] In a state-of-the-art redox flow battery 1, a control unit 42 of the redox flow battery 1, for example, controls the electrolyte pumps 9a, 9b for circulating the respective electrolyte 15a, 15b. The control unit 42 can also acquire operating data of the redox flow battery 1, for example by means of suitable sensors such as voltage or current sensors.

[0044] An embodiment of a redox flow battery 1 according to the invention is shown in Fig. 5 and is described below with reference to it.

[0045] In the redox flow battery 1, a number n of individual batteries Bn are provided. In the embodiment according to Fig. 5, a first individual battery B1 and a second individual battery B2 are provided, where "n" is used as an index, with "n" being used when referring to a single individual battery in general. Otherwise, numbers are used to distinguish the individual batteries.

[0046] Each of the individual batteries Bn is configured as described above, i.e., with at least one cell stack 10, which is supplied with, specifically through which, electrolytes 15a, 15b are flowed. Each cell stack 10 comprises a plurality of individual cells 2, each individual cell 2 comprising a positive half-cell 2a with a positive cell electrode 7a and a negative half-cell 2b with a negative cell electrode 7b. During operation of the redox flow battery 1, the positive half-cell 2a of an individual cell 2 is supplied with a positive electrolyte 15a, and the negative half-cell 2b is supplied with a negative electrolyte 15b (as indicated, for example, in Fig. 4 for the individual battery Bn). For the sake of clarity, the corresponding piping for the electrolytes 15a, 15b in the cell stacks 10 and, if necessary, between cell stacks 10 is not shown in Fig. 5.

[0047] In the redox flow battery 1, at least one positive intermediate tank Za and at least one negative intermediate tank Zb are provided. These at least one positive intermediate tank Za and at least one negative intermediate tank Zb are in addition to at least one positive electrolyte tank 13a for holding the positive electrolyte 15a and at least one negative electrolyte tank 13b for holding the negative electrolyte 15b.

[0048] The available storage volume (for storing an electrolyte 15a, 15b) of the at least one positive intermediate tank Za and at least one negative intermediate tank Zb is preferably smaller than the storage volume of the at least one positive electrolyte tank 13a and the at least one negative electrolyte tank 13b. However, the available storage volume of the intermediate tanks Za, Zb can also be equal to or even larger than the storage volume of the electrolyte tanks 13a, 13b.

[0049] The at least one positive intermediate tank Za has a plurality of i inlet electrolyte connections EEai and a plurality of j outlet electrolyte connections AEaj. Likewise, the at least one negative intermediate tank Zb has a plurality of i inlet electrolyte connections EEbi and a plurality of j outlet electrolyte connections AEbj. However, the plurality of i inlet electrolyte connections EEai, EEbi at intermediate tanks Za and Zb need not be the same. Likewise, the plurality of j outlet electrolyte connections AEaj, AEbj at intermediate tanks Za and Zb need not be the same. Similarly, the number of inlet and outlet connections does not necessarily have to be the same.

[0050] “i” and “j” are each used as an index, with “i” and “j” being used when referring to components generally identified by them. Otherwise, numbers are used as indices to distinguish between multiple versions of the same component.

[0051] The intermediate tanks Za, Zb with the plural i at input electrolyte connections EEai and the plural j at output electrolyte connections AEaj make it possible to flexibly configure a redox flow battery 1.

[0052] In one possible configuration, at least two individual batteries B1 and B2 are provided, and each of the individual batteries B1 and B2 is connected to the positive intermediate tank Za and the negative intermediate tank Zb, respectively. For this purpose, a positive electrolyte input Ea1 of the first individual battery B1 is connected via a first positive battery line BLa1, in which a first positive battery pump BPa1 is located, to a first output electrolyte connection AEa1 of the positive intermediate tank Za. Likewise, a negative electrolyte input Eb1 of the first individual battery B1 is connected via a first negative battery line BLb1, in which a first negative battery pump BPb1 is located, to a first output electrolyte connection AEb1 of the negative intermediate tank Zb.Furthermore, a positive electrolyte input Ea2 of the second individual battery B2 is connected via a second positive battery line BLa2, in which a second positive battery pump BPa2 is located, to a second output electrolyte connection AEa2 of the positive intermediate tank Za. And a negative electrolyte input Eb2 of the second individual battery B2 is connected via a second negative battery line BLb2, in which a second negative battery pump BPb2 is located, to a second output electrolyte connection AEb2 of the negative intermediate tank Zb.

[0053] In general, each individual battery Bn is connected via a positive electrolyte input Ean and a negative electrolyte input Ebn and an associated battery line BLan, BLbn, in which a battery pump BPan, BPbn is arranged, to an associated output electrolyte connection AEan, AEbn of the positive intermediate tank Za or the negative intermediate tank Zb.

[0054] The multiple connections j at the output electrolyte ports AEaj, AEbj of the intermediate tanks Za, Zb thus allow several individual batteries Bn to be connected to the intermediate tanks Za, Zb. This enables flexible responses to various performance requirements of the redox flow battery 1 (electrical voltage, electrical current, electrical power), even during the operating time of the redox flow battery 1 and, above all, independently of the electrolyte tanks 13am, 13bm. An existing redox flow battery 1 can therefore be adapted accordingly, for which it is only necessary to add or replace individual batteries Bn, or to remove existing individual batteries Bn, or simply to disconnect them (for example, via the respective battery pumps).

[0055] In another possible configuration of the inventive redox flow battery 1, regardless of the intended number n of individual batteries Bn, a plurality of m (at least two) positive electrolyte tanks 13am and a plurality of m negative electrolyte tanks 13bm are provided, with "m" as a subscript, but "m" need not necessarily be the same for the positive and negative electrolyte tanks 13am and 13bm. In the embodiment shown, the redox flow battery provides a first positive electrolyte tank 13a1 and a second positive electrolyte tank 13a2, each connected to the positive intermediate tank Za. Likewise, a first negative electrolyte tank 13b1 and a second negative electrolyte tank 13b2 are provided, each connected to the negative intermediate tank Zb.For this purpose, the first positive electrolyte tank 13a1 is connected to a first positive tank line TLa1, in which a first positive tank pump TPa1 is arranged, and to a first inlet electrolyte port EEa1 of the positive intermediate tank Za. The second positive electrolyte tank 13a2 is connected to a second positive tank line TLa2, in which a second positive tank pump TPa2 is arranged, and to a second inlet electrolyte port EEa2 of the positive intermediate tank Za. Likewise, the first negative electrolyte tank 13b1 is connected to a first negative tank line TLb1, in which a first negative tank pump TPb1 is arranged, and to a first inlet electrolyte port EEb1 of the negative intermediate tank Zb. The second negative electrolyte tank 13b2 is connected to a second negative tank line TLb2, in which a second negative tank pump TPb2 is arranged, and to a second inlet electrolyte port EEb2 of the negative intermediate tank Zb.

[0056] In general, each electrolyte tank 13am, 13bm is connected to an associated tank line TLam, TLbm, in which a tank pump TPam, TPbm is arranged, to an associated inlet electrolyte connection EEam, EEbm (from the existing plurality i of inlet electrolyte connections EEai, EEbi) of the associated positive or negative intermediate tank Za, Zb.

[0057] The multiple i connections at the inlet electrolyte ports EEai, EEbi of the intermediate tanks Za, Zb thus allow several electrolyte tanks 13am, 13bm to be connected to the intermediate tanks Za, Zb. This allows the electrical storage capacity of the redox flow battery 1, which is directly related to the available electrolyte volume, to be flexibly adjusted. For this purpose, additional electrolyte tanks 13am, 13bm can be connected to the intermediate tanks Za, Zb as needed, or electrolyte tanks 13am, 13bm can be removed or replaced, or even simply deactivated (for example, via the tank pumps).

[0058] It is possible that the redox flow battery 1 contains several individual batteries Bn, but only one positive electrolyte tank 13a and one negative electrolyte tank 13b, or that it contains only one individual battery B1, but several positive electrolyte tanks 13am and / or several negative electrolyte tanks 13bm. Of course, in another possible configuration of the redox flow battery 1, several individual batteries Bn and several positive and negative electrolyte tanks 13am, 13bm can be connected to the intermediate tanks Za, Zb simultaneously.

[0059] In another possible embodiment, it is also conceivable that several pairs of positive intermediate tank Za and negative intermediate tank Zb are provided in the redox flow battery 1, with the same configurations as shown above in Fig. 5 applying to each such pair of positive intermediate tank Za and negative intermediate tank Zb.

[0060] The electrolytes 15a, 15b returned from the individual batteries Bn can be returned to separate electrolyte tanks or to the electrolyte tanks 13am, 13bm from which the electrolytes 15a, 15b were taken.

[0061] For the return of the electrolytes 15a, 15b, a positive return line RLan and / or a negative return line RLbn can be routed from the existing individual batteries Bn to the intermediate tanks Za, Zb (as in the embodiment according to Fig. 5) and from the intermediate tanks Za, Zb further to the electrolyte tanks 13am, 13bm (or separate electrolyte tanks). However, it is also possible that a positive return line RLan and / or a negative return line RLbn from the existing individual batteries Bn is routed directly to the electrolyte tanks 13am, 13bm (or separate electrolyte tanks).

[0062] A direct return of the electrolyte 15a, 15b from the individual batteries Bn to the electrolyte tanks 13am, 13bm or to separate electrolyte tanks is more advantageous because it prevents a mixing of fresh electrolyte 15a, 15b from the electrolyte tanks 13am, 13bm and used electrolyte 15a, 15b from the individual batteries Bn in the intermediate tanks Za, Zb, which could, however, be compensated for if necessary by a higher volume flow of fresh electrolyte from the electrolyte tanks 13am, 13bm into the intermediate tanks Za, Zb.

[0063] The main advantage of an embodiment of a redox flow battery 1 according to the invention lies in the fact that the redox flow battery 1 can be equipped simply, flexibly, and modularly with the required number of individual batteries Bn and the required number of electrolyte tanks 13am, 13bm, which significantly simplifies the design and implementation of the redox flow battery 1. Furthermore, a redox flow battery 1 can also be easily expanded or reduced subsequently, depending on changing requirements.

[0064] Apart from this, the advantage arises that a low pressure drop occurs at the tank pumps TPam, TPbm because pumping only takes place in the respective intermediate tanks Za, Zb, and the flow resistance is low. In contrast, the flow resistance is considerably higher when circulating the electrolytes 15a, 15b through the cell stacks 10 of a single battery Bn. Consequently, with a comparatively low pumping capacity (compared to the battery pumps BPan, BPbn), the tank pumps TPam, TPbm can transfer a larger volume of electrolyte from the electrolyte tanks 13am, 13bm to the intermediate tanks Za, Zb. This also allows for a higher pumping head from the electrolyte tanks 13am, 13bm to the intermediate tanks Za, Zb.This also makes it easy to implement configurations with a height difference between the electrolyte level in the electrolyte tanks 13am, 13bm and the position of the intermediate tanks Za, Zb in the redox flow battery 1. This allows for the straightforward implementation of stacked electrolyte tanks 13am, 13bm and intermediate tanks Za, Zb or individual batteries Bn with low pumping power. Stacking them can help reduce the footprint of a redox flow battery 1. The pumping power is important because it is provided by the redox flow battery 1 itself, and the required pumping power therefore affects the efficiency of the redox flow battery 1.

[0065] A further advantage of the inventive design of the redox flow battery 1 is that the electrolytes 15a, 15b from the electrolyte tanks 13am, 13bm are mixed in the intermediate tanks Za, Zb, whereby all individual batteries Bn are supplied with the same resulting electrolyte 15a, 15b. Any differences occurring in the state of charge (SoC) or the concentrations of the electroactive species of the electrolytes 15a, 15b in the individual electrolyte tanks 13am, 13bm are therefore irrelevant. Thus, for example, it is unnecessary to adjust the states of charge of the electrolytes 15a, 15b during operation of the redox flow battery 1.

[0066] Furthermore, the inventive design of a redox flow battery 1 allows for an improved cooling concept. During charging / discharging of the redox flow battery 1, exothermic and endothermic chemical reactions occur in the electrolyte 15a, 15b, leading to a change in the temperature of the electrolyte 15a, 15b. Large temperature fluctuations can also occur due to external conditions in the environment of the redox flow battery 1. As is known, the electrolyte 15a, 15b of a redox flow battery 1 is temperature-sensitive, which is why the electrolyte 15a, 15b is preferably temperature-controlled during operation of the redox flow battery 1. For example, in a vanadium redox flow battery 1, the electroactive species V(V) in the positive electrolyte 15a can precipitate irreversibly at high temperature (e.g. >40°C), while the electroactive species V(l I) in the negative electrolyte 15b can precipitate irreversibly at sub-zero temperatures.Such a failure would reduce the electrical storage capacity. Due to the inventive design of the redox flow batteries 1 with the intermediate tanks Za, Zb, a single temperature control unit TE (Fig. 6) is sufficient for each intermediate tank Za, Zb, and it is not necessary to provide a separate temperature control unit for each individual battery Bn or each electrolyte tank 13am, 13bm. The temperature control unit TE can be arranged in or on the intermediate tank Za, Zb to temper the electrolyte 15a, 15b in the intermediate tank Za, Zb. The tempering of the electrolyte 15a, 15b can also be advantageously achieved or improved by preferably transferring electrolyte 15a, 15b from an electrolyte tank 13am, 13bm pair into the intermediate tank Za, Zb, in which the electrolyte 15a, 15b is cooler than in another electrolyte tank 13am, 13bm pair.This allows the cooling capacity required by the temperature control unit TE for temperature control of the electrolyte 15a, 15b to be reduced. Conversely, the same applies if the temperature of the electrolyte 15a, 15b is too low and the electrolyte needs to be heated. In this case, electrolyte is preferably drawn from an electrolyte tank 13am, 13bm pair containing electrolyte at a higher temperature than another electrolyte tank 13am, 13bm pair.

[0067] Last but not least, the operation of the redox flow battery 1 can be optimized by decoupling the tank pumps TPam, TPbm and the battery pumps BPan, BPbn via the intermediate tanks Za, Zb. This also increases the degrees of freedom in controlling the operation of the redox flow battery 1. For example, the tank pumps TPam, TPbm do not need to run continuously, but could be operated intermittently to save pumping power, and can be configured to pump electrolyte 15a, 15b from the electrolyte tanks 13am, 13bm into the respective intermediate tanks Za, Zb only when needed. Likewise, the battery pumps BPan, BPbn can be operated independently of the tank pumps TPam, TPbm in order to operate the individual batteries Bn as optimally as possible, in particular in such a way that there is no overload of the cell stacks 10 or the individual cells 2 of the cell stacks 10 and also no depletion of electroactive species in the electrolyte 15a, 15b in the individual cells 2 of the cell stacks 10.For this purpose, the control unit 42 of the redox flow battery 1 (not shown in Fig. 5) can be configured to control the tank pumps TPam, TPbm and the battery pumps BPan, BPbn for optimal operation.

[0068] In a known manner, the necessary sensors for acquiring operating data of the redox flow battery 1 can also be used, such as for measuring the electrical cell voltage via a single cell 2 (also in the form of a separate measuring cell) or for measuring the electrical concentration potentials of the electrolytes 15a, 15b. The control unit 42 can then use the acquired measured values ​​of the operating data to control the redox flow battery 1, in particular the tank pumps TPam, TPbm and the battery pumps BPan, BPbn.

[0069] The decoupled battery pumps BPan, BPbn and tank pumps TPam, TPbm can also be used to improve the mixing of the electrolyte 15a, 15b in the intermediate tank Za, Zb and / or in the electrolyte tank 13am, 13bm. It is a known problem with redox flow batteries 1 that stratification of the electrolyte 15a, 15b can occur in the tanks (electrolyte tank 13am, 13bm and / or intermediate tanks Za, Zb) during operation. This is caused by density differences in the electrolyte 15a, 15b, which arise from water permeation or from the exchange of electroactive species across the semipermeable membrane in the individual cells 2 of a cell stack during battery operation. This effect is intensified by rapid load changes in the redox flow battery 1. Stratification may necessitate an increase in the volume flow of electrolytes 15a, 15b using the battery pumps BPan, BPbn to deliver more electroactive species through the cell stack 10.This can partially counteract a depletion of electroactive species in the individual cells 2 of the cell stack 10. However, the increased flow rate also increases the required pumping power, which in turn has a detrimental effect on the efficiency of the redox flow battery 1.

[0070] With an embodiment of a redox flow-through battery 1 according to the invention, stratification in the electrolyte 15a, 15b can be significantly improved. The mixing of the electrolyte 15a, 15b in the intermediate tank Za, Zb and also in the electrolyte tanks 13am, 13bm can be enhanced by increasing the flow rate through the tank pumps TPam, TPbm (continuously, intermittently, or pulsedly). This can be achieved with less pumping power, as already explained above. Completely independently, the battery pumps BPan, BPbn can be operated to optimally supply the individual batteries Bn with electrolyte 15a, 15b. The battery pumps BPan, BPbn can, for example, be operated at a constant rate over an extended period, while fresh electrolyte 15a, 15b is simultaneously pumped into the intermediate tanks Za, Zb via the tank pumps TPam, TPbm.

[0071] If the redox flow battery 1 has several pairs of positive intermediate tanks Za and negative intermediate tanks Zb, different charge states could occur between the electrolytes 15a, 15b present in the respective pairs of positive intermediate tanks Za and negative intermediate tanks Zb, which could impair the operation of the redox flow battery 1. This could be compensated for by controlling the flow rates of the positive and negative electrolytes 15a, 15b from the electrolyte tanks 13am, 13bm into the respective intermediate tanks Za, Zb.

[0072] It should be noted that it is possible, in a known manner, to fluidically connect a positive electrolyte tank 13am and a negative electrolyte tank 13bm to allow for equalization of the electrolyte levels. During operation of the redox flow battery 1, the electrolyte levels can shift through migration or (electro)osmosis of aqueous components of the electrolytes 15a, 15b through the semipermeable membranes in the individual cells. The gas spaces in a positive electrolyte tank 13am and an associated positive intermediate tank Za, or in a negative electrolyte tank 13bm and an associated negative intermediate tank Zb, could also be connected.

[0073] Fig. 6 shows an advantageous arrangement of an electrolyte tank 13am, 13bm and an associated intermediate tank Za, Zb. For simplicity, only one intermediate tank Za, Zb, one single battery Bn, and one electrolyte tank 13am, 13bm are shown here, as this is sufficient to explain the embodiment. The following descriptions apply equally to the positive electrolytes 15a and the negative electrolytes 15b.

[0074] In the embodiment shown in Fig. 6, the intermediate tank Za, Zb is arranged above the electrolyte tank 13am, 13bm. The intermediate tank Za, Zb is connected to the respective electrolyte tank 13am, 13bm via a downpipe 33a, 33b. The position of the downpipe 33a, 33b in the intermediate tank Za, Zb forms an overflow and thus determines the maximum fill level of the electrolyte 15a, 15b in the intermediate tank Za, Zb. In Fig. 6, the downpipe 33a, 33b opens below the electrolyte level in the electrolyte tank 13am, 13bm. The return line RLan, RLbn from the individual battery Bn opens into the intermediate tank Za, Zb. The tank line TLam, TLbm opens into the intermediate tank Za, Zb below the maximum fill level of the electrolyte 15a, 15b and is therefore designed as a dip tube. Furthermore, a gas space connection line 34 is provided, which connects the gas spaces above the electrolytes 15a, 15b in the electrolyte tank 13am, 13bm and in the intermediate tank Za, Zb. In Fig.6 is also indicated as a temperature control unit TE on the intermediate tank Za, Zb for temperature control of the electrolyte 15a, 15b.

[0075] In another possible embodiment according to Fig. 7, the downpipe 33a, 33b terminates above the electrolyte level in the electrolyte tank 13am, 13bm. Similarly, the tank line TLam, TLbm terminates in the intermediate tank Za, Zb above the maximum fill level of the electrolyte 15a, 15b in the intermediate tank Za, Zb. The return line RLan, RLbn from the individual battery Bn leads back to the electrolyte tank 13am, 13bm via the downpipe 33a, 33b, but could also lead directly into the electrolyte tank 13am, 13bm.

[0076] The arrangements according to Figs. 6 and 7 have different advantages and disadvantages. The tank line TLam, TLbm (Fig. 6), designed as a dip tube and opening, for example, near the bottom of the intermediate tank Za, Zb, results in active mixing of the electrolyte in the intermediate tank Za, Zb. Furthermore, good electrolyte utilization can be achieved, especially if the battery line BLan, BLbn is also located near the tank line TLam, TLbm in the intermediate tank Za, Zb, for example, also near the bottom. With an arrangement of the tank line TLam, TLbm and / or the downpipe 33a, 33b as in Fig. 7, a natural interruption of the unavoidable short-circuit currents flowing over the electrolytes 15a, 15b would result, at least during times when no electrolyte 15a, 15b is being pumped from the electrolyte tank 13am, 13bm into the intermediate tank Za, Zb.If the return line RLan, RLbn from the individual battery Bn leads into a downpipe 33a, 33b, further connections of individual batteries Bn can be provided easily and accessibly, because only several connections in the downpipe 33a, 33b, for example in the form of hose connections, would need to be provided for this purpose.

[0077] Typically, the individual battery Bn, or a cell stack 10 of the individual battery Bn, will be located at least partially below the electrolyte level in the electrolyte tank 13am, 13bm (as in Fig. 6 or Fig. 7) to facilitate access to the individual batteries Bn, for example, for maintenance personnel. In such an arrangement, in the event of damage to the individual battery Bn, for example, a leak in a cell stack 10, a siphon effect can occur, through which electrolyte 15a, 15b can be drawn from the intermediate tank Za, Zb and possibly also from the electrolyte tank 13am, 13bm via the return line RLan, RLbn. This can lead to significant leakage of electrolyte 15a, 15b, which should preferably be avoided.

[0078] To passively interrupt the siphon effect via the return line RLan, RLbn, the downpipe 33a, 33b is shown in Fig. 7 in combination with the tank line TLam, TLbm, which terminates above the fill level in the intermediate tank Za, Zb. This allows only a small volume of electrolyte to be lost through the siphon effect until sufficient air is drawn in via the downpipe 33a, 33b to interrupt the siphon effect. In the embodiment according to Fig. 6, electrolyte 15a, 15b would be drawn from the electrolyte tank 13am, 13bm due to the siphon effect. To prevent this, the gas space connection line 34 is provided in Fig. 6, which ensures pressure equalization. This also ensures in the embodiment according to Fig. 6 that the siphon effect is interrupted as soon as sufficient air is drawn in via the downpipe 33a, 33b.

[0079] Losses due to short-circuit currents could also be reduced in a known manner by providing so-called shunt killers (essentially an electrical interruption between charged electrolyte and uncharged electrolyte), for example in the form of paddle wheels, by locally introducing gas bubbles into the electrolyte 15a, 15b or by providing longer conductor sections at suitable points in the electrolyte circuit.

[0080] Another way to reduce short-circuit currents in a redox flow battery 1 according to the invention is explained with reference to Fig. 8. In this embodiment, the intermediate tank Za, Zb is divided by a partition 35 into a tank chamber 36 and a battery chamber 37. The tank line TLam, TLbm opens into the tank chamber 36, and electrolyte 15a, 15b is drawn from the intermediate tank Za, Zb into the battery chamber 37 via the battery line BLan, BLbn. The tank chamber 36 and the battery chamber 37 are connected to each other via an overflow 38. To fill the intermediate tank Za, Zb with electrolyte 15a, 15b, electrolyte 15a, 15b is first pumped into tank chamber 36 via the tank line TLam, TLbm and the respective tank pump TPam, TPbm until tank chamber 36 overflows and electrolyte 15a, 15b enters battery chamber 37.The fill levels in tank chamber 36 and battery chamber 37 can be monitored and controlled by corresponding level sensors, for example by the control unit 42. In another possible embodiment, the electrolyte 15a, 15b is also drawn from the intermediate tank Za, Zb in tank chamber 36 via the battery line BLan, BLbn. In this embodiment, the return line RLan, RLbn from the individual battery Bn terminates in the intermediate tank in battery chamber 37. The electrolyte 15a, 15b is then pumped from battery chamber 37 into the electrolyte tank 13am, 13bm, for example via a downpipe 33a, 33b as shown in Fig. 6 or Fig. 7. In both versions, an electrical separation is achieved between the electrolyte 15a, 15b pumped from the electrolyte tank 13am, 13bm and the electrolyte 15a, 15b pumped back into the electrolyte tank 13am, 13bm.For this purpose, the downpipe 33a, 33b or a return line RLan, RLbn should of course not end in the electrolyte 15a, 15b in the electrolyte tank 13am, 13bm (as for example in the embodiment according to Fig.6), but at a distance from the electrolyte 15a, 15b (as for example in the embodiment according to Fig.7 and Fig.8).

Claims

Patent claims 1. Redox flow battery with a number of individual batteries (Bn) comprising at least one cell stack (10), wherein each cell stack (10) comprises a plurality of individual cells (2), wherein each individual cell (2) comprises a positive half-cell (2a) with a positive cell electrode (7a) and a negative half-cell (2b) with a negative cell electrode (7b), wherein the positive half-cell (2a) of an individual cell (2) is supplied with a positive electrolyte (15a) during operation of the redox flow battery (1) and the negative half-cell (2b) is supplied with a negative electrolyte (15b) during operation of the redox flow battery (1), characterized in that at least one positive intermediate tank (Za) for receiving the positive electrolyte (15a) and at least one negative intermediate tank (Zb) for receiving the negative electrolyte (15b) are provided in the redox flow battery (1).wherein the at least one positive intermediate tank (Za) has a plurality of input electrolyte connections (EEa1, EEa2, EEam) and a plurality of output electrolyte connections (AEa1, AEa2, AEam) and the at least one negative intermediate tank (Zb) has a plurality of input electrolyte connections (EEb1, EEb2, EEbm) and a plurality of output electrolyte connections (AEb1, AEb2, AEbm), and that in the redox flow battery (1) with the at least one positive intermediate tank (Za) and with the at least one negative intermediate tank (Zb) a first individual battery (B1) and a second individual battery (B2) are provided, which are each connected to the positive intermediate tank (Za) and the negative intermediate tank (Zb) by a positive electrolyte input (Ea1) of the first individual battery (B1) via a first positive battery line (BLa1) in which a first positive Battery pump (BPa1) is arrangeda first output electrolyte connection (AEa1) of the positive intermediate tank (Za) is connected, and a negative electrolyte input (Eb1) of the first individual battery (B1) is connected via a first negative battery line (BLb1) in which a first negative battery pump (BPb1) is arranged, to a first output electrolyte connection (AEb1) of the negative intermediate tank (Zb), and by connecting a positive electrolyte input (Ea2) of the second individual battery (B2) via a second positive battery line (BLa2) in which a second positive battery pump (BPa1) is arranged, to a second output electrolyte connection (AEb2) of the positive intermediate tank (Za), and a negative electrolyte input (Eb2) of the second individual battery (B2) via a second negative battery line (BLb2) in which a second negative battery pump (BPb2) is arranged,with a second output electrolyte connection (AEb2) of the negative intermediate tank (Zb) and / or that in the redox flow battery (1) with the at least one positive intermediate tank (Za) and with the at least one negative intermediate tank (Zb) a first positive electrolyte tank (13a1) for receiving a positive electrolyte (15a) and a second positive electrolyte tank (13a2) for receiving a positive electrolyte (15a) are provided, each of which is connected to the positive intermediate tank (Za), and a first negative electrolyte tank (13b1) for receiving a negative electrolyte (15b) and a second negative electrolyte tank (13b2) for receiving a negative electrolyte (15b) are provided, each of which is connected to the negative intermediate tank (Zb) by connecting the first positive electrolyte tank (13a1) to a first positive tank line (TLa1) in which a first positive tank pump (TPa1) is arranged is,with a first inlet electrolyte port (EEa1) of the positive intermediate tank (Za), and the second positive electrolyte tank (13a2) with a second positive tank line (TLa2), in which a second positive tank pump (TPa2) is arranged, with a second inlet electrolyte port (EEa2) of the positive intermediate tank (Za), and by connecting the first negative electrolyte tank (13b1) with a first negative tank line (TLb1), in which a first negative tank pump (TPb1) is arranged, with a first inlet electrolyte port (EEb1) of the negative intermediate tank (Zb), and the second negative electrolyte tank (13b2) with a second negative tank line (TLb2), in which a second negative tank pump (TPb2) is arranged, with a second inlet electrolyte port (EEb2) of the negative intermediate tank (Zb).

2. Redox flow battery according to claim 1, characterized in that a positive return line (RLa1, RLa2) from the first individual battery (B1) or second individual battery (B2) leads into the positive intermediate tank (Za) and from the positive intermediate tank (Za) leads further into the first positive electrolyte tank (13a1) or the second positive electrolyte tank (13a2), or that a negative return line (RLb1, RLb2) from the first individual battery (B1) or second individual battery (B2) leads into the negative intermediate tank (Zb) and from the negative intermediate tank (Zb) leads further into the first negative electrolyte tank (13b1) or the second negative electrolyte tank (13b1).

3. Redox flow battery according to claim 1, characterized in that a positive return line (RLa1, RLa2) leads from the first individual battery (B1) or second individual battery (B2) into the first positive electrolyte tank (13a1) or the second positive electrolyte tank (13a2), or that a negative return line (RLb1, RLb2) leads from the first individual battery (B1) or second individual battery (B2) into the first negative electrolyte tank (13b1) or the second negative electrolyte tank (13b2).

4. Redox flow battery according to one of claims 1 to 3, characterized in that the positive intermediate tank (Za) is arranged above the first positive electrolyte tank (13a1) or above the second positive electrolyte tank (13a2) and the positive intermediate tank (Za) is connected to the first positive electrolyte tank (13a1) or the second positive electrolyte tank (13a2) via a positive downpipe (33a), wherein the positive downpipe (33a) forms an overflow in the positive intermediate tank (Za), or that the negative intermediate tank (Zb) is arranged above the first negative electrolyte tank (13b1) or above the second negative electrolyte tank (13b2) and the negative intermediate tank (Zb) is connected to the first negative electrolyte tank (13b1) or the second negative electrolyte tank (13b2) via a negative downpipe (33b), wherein the negative downpipe (33b) forms an overflow in the negative intermediate tank (Zb).

5. Redox flow battery according to claims 3 and 4, characterized in that a positive return line (RLan) from the first single battery (B1) or the second single battery (B2) opens into the positive downpipe (33a), or that a negative return line (RLbn) from the first single battery (B1) or the second single battery (B2) opens into the negative downpipe (33b).

6. Redox flow battery according to one of claims 1 to 5, characterized in that a partition (38) is provided in the positive intermediate tank (Za) or in the negative intermediate tank (Zb), which separates the positive intermediate tank (Za) or the negative intermediate tank (Zb) into a tank chamber (36) and a battery chamber (37), wherein the tank chamber (36) and the battery chamber (37) are connected to each other via an overflow in the intermediate tank (Za, Zb), and that the positive tank line (TLam) opens into the tank chamber (36) of the positive intermediate tank (Za) or the negative tank line (TLbm) opens into the tank chamber (36) of the negative intermediate tank (Zb), and that the positive battery line (BLan) is connected to the battery chamber (37) of the positive intermediate tank (Za) or the negative battery line (BLbn) is connected to the battery chamber (37) of the negative intermediate tank (Zb).

7. Redox flow battery according to one of claims 1 to 5, characterized in that a partition (38) is provided in the positive intermediate tank (Za) or in the negative intermediate tank (Zb) which separates the positive intermediate tank (Za) or the negative intermediate tank (Zb) into a tank chamber (36) and into a battery chamber (37), and that a positive return line (RLan) from the first individual battery (B1) or from the second individual battery (B2) is connected to the battery chamber (37) of the positive intermediate tank (Za) or a negative return line (RLbn) from the first individual battery (B1) or from the second individual battery (B2) is connected to the battery chamber (37) of the negative intermediate tank (Zb).

8. Redox flow battery according to one of claims 1 to 7, characterized in that a temperature control unit (TE) is provided on or in the positive intermediate tank (Za) or a temperature control unit (TE) is provided on or in the negative intermediate tank (Zb).

9. Redox flow battery according to one of claims 1 to 8, characterized in that a control unit (42) is provided in the redox flow battery (1) which is configured to operate the positive tank pumps (TPam) and the positive battery pumps (BPan) independently of each other and to operate the negative tank pumps (TPbm) and the negative battery pumps (BPbn) independently of each other.

10. Method for operating a redox flow battery (1) with a number of individual batteries (Bn) comprising at least one cell stack (10), wherein each cell stack (10) comprises a plurality of individual cells (2), wherein each individual cell (2) comprises a positive half-cell (2a) with a positive cell electrode (7a) and a negative half-cell (2b) with a negative cell electrode (7b), wherein the positive half-cell (2a) of an individual cell (2) is supplied with a positive electrolyte (15a) during operation of the redox flow battery (1) and the negative half-cell (2b) is supplied with a negative electrolyte (15b) during operation of the redox flow battery (1), characterized in thatthat a positive electrolyte (15a) is pumped from at least one positive electrolyte tank (13am) via a positive tank line (TLam) with a positive tank pump (TPam) into a positive intermediate tank (Za) and the positive electrolyte (15a) in the positive intermediate tank (Za) is pumped into a plurality of individual batteries (Bn), wherein the positive electrolyte (15a) for each of the plurality of individual batteries (Bn) is pumped via a positive battery line (BLan) connected to the positive intermediate tank (Za) with a positive battery pump (BPan), and a negative electrolyte (15b) is pumped from at least one negative electrolyte tank (13bm) via a negative tank line (TLbm) with a negative tank pump (TPbm) into a negative intermediate tank (Zb) and the negative electrolyte (15b) in the negative intermediate tank (Zb) is pumped into a plurality of individual batteries (Bn), wherein the negative electrolyte (15b) for each of the plural, Individual batteries (Bn) are each supplied via a negative battery line (BLbn) connected to the negative intermediate tank (Zb) with a negative battery pump (BPbn), and / or that a positive electrolyte (15a) is supplied from a plurality of positive electrolyte tanks (13am) via a positive tank line (TLam) with a positive tank pump (TPam) into a positive intermediate tank (Za) and the positive electrolyte (15a) in the positive intermediate tank (Za) is supplied via a positive battery line (BLan) connected to the positive intermediate tank (Za) with a positive battery pump (BPan) into at least one individual battery (Bn),and a negative electrolyte (15b) is pumped from a plurality of negative electrolyte tanks (13bm) via a negative tank line (TLbm) with a negative tank pump (TPbm) into a negative intermediate tank (Zb) and the negative electrolyte (15b) in the negative intermediate tank (Zb) is pumped via a negative battery line (BLbn) connected to the negative intermediate tank (Zb) with a negative battery pump (BPbn) into at least one individual battery (Bn).

11. Method according to claim 10, characterized in that the positive tank pumps (TPam) and the positive battery pumps (BPan) are operated independently of each other and / or that the negative tank pumps (TPbm) and the negative battery pumps (BPbn) are operated independently of each other.

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