Redox flow battery cell stack consisting of sub-cell stacks

Abstract

The aim of the invention is to reduce current losses in a cell stack of a redox flow battery. This is achieved by a cell stack (10) comprising a plurality of sub-cell stacks (101, 102, …, 10n), wherein a transition frame (40) is arranged between at least two sub-cell stacks (101, 102, …, 10n), which adjoin each other in the stacking direction (R), of the plurality n of sub-cell stacks (101, 102, …, 10n), and a first connecting group (41a, 41b, 42a, 42b) with a number m of connecting channels (43) is arranged in the transition frame (40). Each connecting channel (43) of the first connecting group (41a, 41b, 42a, 42b) passes through the respective transition frame (40) in the stacking direction (R), and one of the plurality of first electrolyte liquid channels (18a1, …, 18an, 18b1, …, 18bn, 19a1, …, 19an, 19b1, …, 19bn) of each first electrolyte group (36a, 36b, 37a, 37b) in each adjacent sub-cell stack (101, 102, …, 10n) of the transition frame (40) is closed by the transition frame (40) in the stacking direction (R), while the remaining electrolyte liquid channels (18a1, …, 18an, 18b1, …, 18bn, 19a1, …, 19an, 19b1, …, 19bn) of the sub-cell stack (101, 102, …, 10n) on one side of the transition frame (40) are each connected, via one of the number m of connecting channels (43) of the first connecting group (41a, 41b, 42a, 42b), to one of the remaining first electrolyte liquid channels (18a1, …, 18an, 18b1, …, 18bn, 19a1, …, 19an, 19b1, …, 19bn) of the sub-cell stack (101, 102, …, 10n) on the opposite side of the transition frame (40) in the stacking direction (R).

Description

[0001] Cell stack of a redox flow battery consisting of sub-cell stacks

[0002] The present invention relates to a cell stack of a redox flow battery having a plurality of sub-cell stacks arranged next to one another in a stack direction, wherein each sub-cell stack comprises at least one individual cell, and each individual cell is formed from a first half-cell and a second half-cell, and each first and second half-cell comprises a frame with a central recess extending through in the stack direction, and an electrode is arranged in each recess of a frame of each first and second half-cell, wherein the first and second half-cells of an individual cell are arranged next to one another in the stack direction, and the recesses and the electrodes arranged therein of the first and second half-cells of an individual cell are separated from one another in the stack direction by a semipermeable membrane,wherein in each sub-cell stack, a first electrolyte group is provided with a plurality of electrolyte fluid channels corresponding to the plurality of sub-cell stacks, and in each sub-cell stack, the plurality of first electrolyte fluid channels of the first electrolyte group pass through all frames of all individual cells of the respective sub-cell stack arranged side by side in the stack direction, wherein in each sub-cell stack, one of the electrolyte fluid channels of the first electrolyte group is connected to the recesses in the frames of the first half-cells via a respective first frame channel in the frames of the first half-cells of the individual cells of the respective sub-cell stack.

[0003] A redox flow battery is a well-known electrochemical energy storage device and typically consists of storage tanks for storing differently charged electrolyte fluids, such as positive and negative ones, as well as pumps and lines for circulating the electrolyte fluids (electrolytes) through one or more cell stacks, each containing a number of individual electrochemical 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, with the positive and negative half-cells of an individual cell separated from each other by a semipermeable membrane, typically an ion exchange membrane. The semipermeable membrane is, for example, a cation and / or anion exchange membrane, e.g., Nation®.The positive half-cell contains a positive electrode located in a frame through which the positive electrolyte flows. The negative half-cell contains a negative electrode located in a frame through which the negative electrolyte flows. The positive and negative electrolyte flows are circulated separately through the half-cells. The positive and negative electrodes are usually made of porous graphite felts through which the respective electrolyte flows. The half-cell frames are arranged side by side, and the resulting individual cells are connected to form a cell stack, with negative and positive half-cells alternating.Electrically conductive electrode plates, such as bipolar plates, are arranged as current collectors between adjacent individual cells of the cell stack. These plates are usually made of a composite material made of carbon and plastic. Current collectors are located on the axial outer sides of the axially outer individual cells of the cell stack. These current collectors provide electrical contact to the outside in order to tap an electrical voltage across the entire cell stack (discharging the redox flow battery) or to apply an electrical voltage to the cell stack (charging the redox flow battery). The cell stack is closed off on each of its axial outer sides by an end plate, which holds the cell stack together. Bolts are typically inserted through the end plates, and the end plates are pressed together onto the bolts using nuts.The nuts on at least one side are usually preloaded by a spring to compensate for any settling of the half-cell frames.

[0004] In a vanadium-based redox flow battery, the positive electrolyte fluid in the charged state consists of a redox pair in the form of vanadium with the oxidation number +4 (also known as V lv or V 4+ referred to) and vanadium with the oxidation number +5 (also known as V v or V 5+ The negative electrolyte fluid in the charged state consists of a redox pair in the form of vanadium with the oxidation number +2 (also known as V" or V 2+ referred to) and vanadium with the oxidation number +3 (also known as V 111 or V 3+(referred to as "redox flow batteries"), meaning that the negative electrolyte fluid has a more negative electrochemical potential than the positive electrolyte fluid. Redox flow batteries based on other redox pairs, for example, those based on the chemical elements Br, S, Fe, Ti, Mn, Cr, or organic compounds such as ferricyanide or quinone, are also known, all of which operate essentially according to the same principle.

[0005] A redox flow battery typically consists of several such cell stacks that are electrically connected to each other. The electrolyte fluids for all cell stacks are also usually supplied from the same storage tanks.

[0006] This structure and function of a redox flow battery is well known, for example from WO 2018 / 087220 A1 or WO 2014 / 131702 A1 .

[0007] To reduce the number of components required for a redox flow battery, cell stacks with a high number of individual cells are sought in order to achieve a higher cell stack voltage. This allows for fewer cell stacks to be required through appropriate electrical interconnection of the individual cell stacks. This reduces the number of cell stacks required in a redox flow battery and requires fewer components such as end plates, current collectors, cell connectors (bolts, nuts, preload springs, etc.), electrical connectors between the cell stacks, etc. This reduces the cost per kilowatt of battery power in a redox flow battery. However, the higher number of individual cells in a cell stack also increases the cell stack voltage. Since the electrolyte fluids are electrically conductive and represent an electrical resistance, a current flow inevitably occurs along the electrolyte fluid path.This current flow does not generate real work, but represents a loss. A higher cell stack voltage therefore causes a higher leakage current along the electrolyte fluid path, which reduces the efficiency of the redox flow battery. The leakage current increases with the cube of the number of individual cells in a cell stack. Therefore, the number of individual cells in a cell stack has previously been limited or long electrolyte channels have been provided, which increases the electrical resistance in the electrolyte circuit and thus reduces the leakage current. However, longer electrolyte channels increase the hydraulic resistance and require greater pumping power to circulate the electrolyte fluid in the cell stack. This, in turn, leads to more energy demand for the circulation of the electrolyte fluids, which in turn reduces the efficiency of the redox flow battery.

[0008] The design of a cell stack of a redox flow battery is therefore always a compromise between cost per kilowatt of battery power and losses or efficiency.

[0009] There are already approaches in the state of the art to improve, and ideally compensate for, the disadvantages mentioned above.

[0010] For example, there are approaches to arranging multiple cell stacks between two end plates in order to save on components holding the cell stacks together. Examples of this can be found in WO 2021 / 231777 A1 or KR 101791319 B1. Although this can save components, other problems such as leakage currents and limitations on the number of individual cells remain. Furthermore, these approaches result in different pressure drops of the electrolyte fluids across the individual cells due to different electrolyte fluid path lengths. This, in turn, leads to an inhomogeneous flow distribution of the electrolyte fluid in the cell stack, which limits the performance of a cell stack. WO 2014 / 145844 A1 proposes increasing the length of the electrolyte fluid paths to increase the electrical resistance and reduce the leakage current without excessively increasing the pumping losses.

[0011] WO 2014 / 039731 A1 describes the design of a cell stack of a redox flow battery with a plurality of sub-cell stacks between two end plates. The electrolyte fluids are passed through the adjacent frames of the half-cells of the individual cells of the cell stack. For this purpose, the frames have openings that are aligned to form a continuous electrolyte fluid path through the cell stack for each of the two electrolyte fluids. A number of openings corresponding to the number of sub-cell stacks is provided in each frame, so that a number of electrolyte fluid paths corresponding to the number of sub-cell stacks is formed for each of the two electrolyte fluids. Each of the electrolyte fluid paths thus formed supplies a sub-cell stack with the respective electrolyte fluid and bypasses the other sub-cell stacks.In each of the electrolyte fluid paths, only the voltage of the sub-cell stack is present, not the entire cell stack voltage. This reduces the resulting leakage currents in the sub-cell stacks and thus increases the efficiency of the cell stack. By making the length of the electrolyte fluid paths for the supply and discharge of the respective electrolyte fluid the same, uniform flow conditions across the individual cells can also be achieved. Although this type of cell stack design can eliminate or improve many of the problems mentioned above, it requires a number of different half-cell frames corresponding to the number of sub-cell stacks. This, in turn, increases the complexity of manufacturing the redox flow battery. It also makes the cell stack more prone to failure.Even a single incorrect frame would reduce the aforementioned advantages or even result in the failure of the cell stack.

[0012] It is an object of the present invention to provide a cell stack of a redox flow battery with which leakage currents can be reduced and with which the number of required components of the cell stack can be reduced, in particular the number of different frames required for the half-cells.

[0013] This object is achieved according to the invention in that a transition frame is arranged between at least two sub-cell stacks of the plurality of sub-cell stacks that are adjacent in the stack direction, a first connection group with a number of connection channels is provided in the transition frame and each connection channel of the first connection group passes through the respective transition frame in the stack direction, and one of the plurality of electrolyte liquid channels of the first electrolyte group of each adjacent sub-cell stack of the transition frame is closed in the stack direction by the transition frame and one of the remaining electrolyte liquid channels of the sub-cell stack on one side of the transition frame is connected via one of the number of connection channels of the first connection group to one of the remaining electrolyte liquid channels of the sub-cell stack on the opposite side of the transition frame in the stack direction.The transition frame separates the electrolyte paths in the individual sub-cell stacks, shortening the electrolyte fluid path length in the sub-cell stacks. This also reduces electrical leakage currents. Since multiple sub-cell stacks are provided in the cell stack, the number of required components and parts is also reduced. The use of such transition frames is particularly advantageous because the frames of the half-cells in the sub-cell stacks can all be designed identically.

[0014] It is advantageous if a transition frame according to the invention is arranged between all adjacent sub-cell stacks of the cell stack. This allows the cell stack to be easily scaled in terms of the number of sub-cell stacks. It also allows the number of required cell stack components to be further reduced.

[0015] Preferably, at least two electrolyte groups with a plurality of electrolyte fluid channels are provided in each sub-cell stack. This allows the electrolyte groups to be used, as needed, for the supply and removal of one electrolyte fluid, or for the supply and removal of different electrolyte fluids.

[0016] Particularly advantageously, four electrolyte groups with the majority of electrolyte fluid channels are provided in each sub-cell stack, whereby the advantages according to the invention can be utilized for the supply and removal of both electrolyte fluids.

[0017] For the cell stack, it is advantageous if the electrical connection between the sub-cell stacks is established internally within the cell stack. For this purpose, a central recess extending in the stack direction can be provided in at least one transition frame, in which an electrical connecting part is arranged, which electrically contacts the electrodes of the adjacent half-cells of the transition frame. If an electrode plate is arranged between the electrodes of the adjacent half-cells of the transition frame and the electrical connecting part, and each electrode plate rests against one of the electrodes and the connecting part, the connecting part can also be protected from the often aggressive electrolyte fluids.

[0018] It is also possible to form at least one transition frame from a first transition frame part and a second transition frame part, wherein the first transition frame part and second transition frame part are arranged next to one another and adjacent to one another in the stack direction. This enables a particularly advantageous embodiment in which the first transition frame part and the second transition frame part are designed as half-cells of a single cell of the cell stack, and the first transition frame part and the second transition frame part each form a single cell with an adjacent half-cell of an adjacent sub-cell stack, and at least one electrode plate is arranged between the first transition frame part and the second transition frame part. The transition frame is thus electrically integrated into the cell stack. A cell stack can thus be designed to be particularly compact.

[0019] If at least one connecting channel is configured with a through-channel and two bypass channels connected to the through-channel, wherein the through-channel passes through the transition frame in the stack direction and the bypass channels do not pass through the transition frame in the stack direction, and each bypass channel connects an electrolyte fluid channel of an adjacent sub-cell stack to the through-channel, the through-channels can be offset from an electrolyte fluid channel in an electrolyte group. This allows the through-channels to be aligned in the stack direction, simplifying the manufacture of the transition frame.

[0020] In a particularly advantageous embodiment, a sub-cell stack is designed with a single cell, with an electrical connection leading out of the cell stack at each half-cell of this single cell, and each electrical connection being electrically connected to one of the electrodes or to one of the electrolyte fluids or electrode plates in the single cell (2). Such a single cell can be used as a measuring cell to detect a cell voltage, which can be used for diagnostic purposes and to monitor the redox flow battery.

[0021] The present invention will be explained in more detail below with reference to Figures 1 to 13b, which show exemplary, schematic and non-limiting advantageous embodiments of the invention.

[0022] Fig.1 the basic operating principle of a redox flow battery,

[0023] Fig.2 a redox flow battery with a cell stack,

[0024] Fig.3 shows the structure of a cell stack of a redox flow battery,

[0025] Fig.4 a frame of a cell stack of a redox flow battery,

[0026] Fig.5 shows a cell stack according to the invention with sub-cell stacks and transition frames, Fig.6 shows a frame of a sub-cell stack according to the invention,

[0027] Fig.7a and 7b show the structure of a cell stack according to the invention with sub-cell stacks and transition frames. Fig.8 shows a further embodiment of the structure of a cell stack according to the invention with sub-cell stacks and transition frames.

[0028] Fig.9 and 10 each show a transition frame with electrical connection part,

[0029] Fig.11 and 12 an embodiment of a transition frame with first and second transition frame part and

[0030] Fig.13a and 13b show an embodiment of a first and second transition frame part as a half cell of a single cell of a sub-cell stack.

[0031] Fig. 1 shows a schematic structure of a redox flow battery 1 using a single cell 2 of a cell stack 10 in order to explain the well-known functional principle of a redox flow battery 1.

[0032] For better explanation and illustration, only one single cell 2 of a cell stack 10 of a redox flow battery 1 is shown in Fig. 1, wherein a cell stack 10 will generally have a plurality of single cells 2.

[0033] A single cell 2 consists of two half-cells 2a, 2b, which form a positive reaction chamber 3a and a negative reaction chamber 3b. 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. An electrode 7a, 7b is arranged in each of the reaction chambers 3a, 3b and in the recesses 6a, 6b. Electrolyte fluids 15a, 15b with different electrical charges (positive and negative electrolyte fluids) flow through the recesses 6a, 6b and the electrodes 7a, 7b arranged therein of a single cell 2. Each of the electrolyte liquids 15a, 15b contains a redox pair with specific, time-varying concentrations (depending on the state of charge) of redox elements.The semipermeable, particularly ion-selective, membrane 4 can be made, for example, of sulfonate-modified polytetrafluoroethylene (PTFE), with the trade name Nation™, and enables ions to achieve charge equalization between the positive reaction chamber 3a and the negative reaction chamber 3b (or between the electrolyte liquids 15a, 15b contained therein). The individual cell 2 is closed on both sides by an electrode plate 8. A redox flow battery 1 also includes power connections 11, 12 for tapping an electrical cell stack voltage Vz applied to the cell stack 10 via a consumer 14 (discharging the redox flow battery 1) or for applying an electrical cell stack voltage Vz to the cell stack 10 (charging the redox flow battery 1).

[0034] An electrical load 14 can take any form. Based on the 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 the necessary electrical current. Redox flow batteries 1 are often used as stationary energy storage devices, for example, to serve as emergency power systems for industrial plants, storage systems for renewable energy (photovoltaics, wind power), and the like. Consequently, depending on the application, a person skilled in the art can design a cell stack 10, or a parallel and / or serial connection of several cell stacks, and redox pairs in a redox flow battery 1.

[0035] The electrolyte fluids 15a, 15b are stored in storage tanks 13a, 13b and are circulated from there through the cell stack 10 by means of circulation pumps 9a, 9b, specifically through a half-cell 2a, 2b of a single cell 2 of the cell stack 10. For this purpose, a supply line 16a, 16b and a discharge line 17a, 17b are provided for each electrolyte fluid 15a, 15b, which are connected via electrolyte fluid connections 22a, 22b, 23a, 23b to corresponding electrolyte fluid channels 18a, 18b, 19a, 19b (see Fig. 4) in the cell stack 10.

[0036] In a cell stack 10 with several adjacent individual cells 2, an electrode plate 8, such as a bipolar plate, is arranged between each two adjacent individual cells 2. At the outer ends of the cell stack 10, a power connection 11, 12 can be located on the outer electrode plates 8 or on the outer half-cells 2a, 2b of the cell stack 10, which can be electrically contacted from the outside.

[0037] 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 3.

[0038] A cell stack 10 of a redox flow battery 1 comprises at least one individual cell 2, generally a plurality of individual cells 2, which in turn are each formed from two frames 5a, 5b. A frame 5a, 5b is preferably made of a plastic, such as an elastomer, such as a polyolefinic thermoplastic elastomer (TPE or TPO), such as Santoprene®, or a thermoplastic vulcanate (TPV), in particular using an injection molding process. In the stack direction R, between two frames 5a, 5b of an individual 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 spaces 3a, 3b or recesses 6a, 6b of the half-cells 2a, 2b of a single cell 2 or the electrodes 7a, 7b arranged therein or the electrolyte liquids 15a, 15b located therein.An electrode plate 8, e.g., a bipolar plate, is arranged between each two adjacent individual cells 2 in the stack direction R in the cell stack 10. The electrode plate 8 can, as shown in Fig. 3, be inserted into mutually facing recesses in the frames 5a, 5b. The frames 5a, 5b can have central recesses extending in the stack direction R, each of which forms a reaction chamber 3a, 3b and in which electrodes 7a, 7b, e.g., carbon fiber mats, are arranged, as shown in Fig. 3.

[0039] The differently charged electrolyte fluids 15a, 15b are pumped through the recesses 6a, 6b in the frames 5a, 5b through the individual cells 2, with an electrolyte fluid 15a, 15b with a different electrical charge flowing through the electrode 7a, 7b of each half-cell 2a, 2b of an individual cell 2. The electrolyte fluids 15a, 15b are supplied and removed from the outside via electrolyte fluid connections 22a, 22b, 23a, 23b and are then distributed internally via an electrolyte fluid channel system provided in the frames 5a, 5b with electrolyte fluid channels 18, 19, as explained in more detail below.

[0040] The cell stack 10 can be closed off in the stacking direction R by an end frame 20 at each of its two axial ends. An electrically conductive current collector 21 is arranged in the end frame 20, e.g., in a recess on one end face of the end frame 20, and is connected to an externally routed electrical power 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 electrical contact. However, the current collector 21 or a power connection 11, 12 could also be designed differently. Likewise, the end frame 20 could be omitted.

[0041] 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 designed, for example, with through-passing 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.

[0042] In order to prevent the frames 5a, 5b from settling due to the contact pressure of the clamping device 25, a spacer 31 can also be provided between the end plates 24.

[0043] A typical structure of a conventional frame 5a, 5b of a half-cell 2a, 2b of a single cell 2 of a cell stack 10 of a redox flow battery 1 is described with reference to Fig. 4. The middle of Fig. 4 shows, as an example, the frame 5b of a negative half-cell 2b, through which a negative electrolyte liquid 15b is circulated. The electrolyte liquid flow is indicated by the arrows. In the frame 5b, a recess 6b is provided which runs through in the stack direction R and forms the reaction chamber 3b and in which the electrode 7b is arranged. In the frame 5b, an electrolyte liquid channel 18a for supplying a first (positive) electrolyte liquid 15a and an electrolyte liquid channel 18b for removing the first (positive) electrolyte liquid 15a are provided.Likewise, frame 5b each includes an electrolyte fluid channel 19a for supplying a second (negative) electrolyte fluid 15b and an electrolyte fluid channel 19b for discharging the second (negative) electrolyte fluid 15b. The electrolyte fluid channels 18a, 18b, 19a, 19b in frames 5a, 5b also extend through frames 5a, 5b in the stacking direction R. If the frames 5a, 5b of the half-cells 2a, 2b in a single cell 2 are arranged next to one another in the stacking direction R or if several single cells 2 are arranged next to one another in a cell stack 10 in the stacking direction R, then the respective electrolyte fluid channels 18a, 18b, 19a, 19b are arranged in alignment in the frames 5a, 5b, so that electrolyte fluid channels 18a, 18b, 19a, 19b are formed which run through the cell stack 10 in the stacking direction R.Thus, only electrolyte channel sections of the electrolyte channels 18a, 18b, 19a, 19b extending through the cell stack 10 are provided in the frames 5a, 5b, whereby these electrolyte channel sections are also referred to as electrolyte channels 18a, 18b, 19a, 19b for the sake of simplicity. The two electrolyte channels 15a, 15b are thus guided internally within the cell stack 10.

[0044] The electrolyte channel 19a for supplying the second (negative) electrolyte 15b is connected to the recess 6b of the frame 5b via a frame channel 35a for supplying the electrolyte 15b. The electrolyte 15b is supplied into the recess 6b via this frame channel 35a. The electrolyte channel 19b for discharging the second (negative) electrolyte 15b is connected to the recess 6b of the frame 5b via a frame channel 35b for discharging the electrolyte 15b. The electrolyte 15b is discharged from the recess 6b via this frame channel 35b. In this way, the electrolyte 15b is circulated through the recess 6b.

[0045] The frame 5a of a positive half-cell 2a can be designed in the same way as the frame 5b of a negative half-cell 2b, as indicated in Fig. 4 by the reference numerals in parentheses. However, the positive half-cell 2a is provided with frame channels 34a, 34b that connect the recess 6a in the frame 5a with the electrolyte channels 18a, 18b for the first (positive) electrolyte 15a.

[0046] Advantageously, a frame 5a, 5b is designed so that it can be used for both a positive half-cell 2a and a negative half-cell 2b. In the embodiment shown in Fig. 4, it is easily seen that by appropriately rotating the frame 5b of the negative half-cell 2b, a frame 5a of a positive half-cell 2a would be created. Thus, only one frame type would be required to construct the half-cells 2a, 2b of a cell stack 10.

[0047] Figure 4 also shows two sections through the frame 5b, which is incorporated into a cell stack 10. These show the electrolyte fluid channels 18a, 18b, 19a, 19b passing through the frames 5a, 5b of the individual cells 2 in the stack direction R. The electrode plates 8 between individual cells 2 and the semipermeable membranes 4 in an individual cell 2, as well as end plates 24 and other components of a redox flow battery 1, are not shown in Figure 4 for the sake of simplicity.

[0048] Based on this known structure of a cell stack 10 of a redox flow battery 1, the invention is described below.

[0049] Fig.5 shows a cell stack 10 according to the invention consisting of a plurality n>1 (at least two) of sub-cell stacks 10i, 102, ..., 10 n , which are arranged next to each other in the stack direction R. The upper limit for the plurality n of sub-cell stacks 10i, 102, ... , 10 ndepends on the design of the cell stack 10 and the sub-cell stacks 10i, IO2, ... , 10 n and is typically less than 15, preferably less than 10. The sub-cell stacks 10i, IO2, ... , 10 n are preferably arranged in the stack direction R between end plates 24 and are held together by the end plates 24, for example as described above with reference to Fig.2, wherein the cell stack 10 could of course also be held together in a different way.

[0050] Each sub-cell stack 10i, IO2, ... , 10 n comprises at least one single cell 2, preferably several single cells 2. In a sub-cell stack 10i, 102, ..., 10 nTypically, between one and forty individual cells 2 are provided. Each individual cell 2 is formed, as described above, from a first half-cell 2a and a second half-cell 2b. Each first half-cell 2a and second half-cell 2b comprises a frame 5a, 5b with a central recess 6a, 6b extending through in the stacking direction R to form the reaction spaces 3a, 3b. An electrode 7a, 7b is arranged in each recess 6a, 6b of a frame 5a, 5b of each first and second half-cell 2a, 2b (Fig. 6). The first and second half-cells 2a, 2b of an individual cell 2 are arranged next to one another in the stacking direction R, and the recesses 6a, 6b and the electrodes 7a, 7b arranged therein of the first and second half-cells 2a, 2b of an individual cell 2 are separated from one another in the stacking direction R by a semipermeable membrane 4. In stack direction R between two single cells 2 of a sub-cell stack 10i, IO2, ... , 10 nAn electrode plate 8 is arranged in each half-cell. Differently charged (positive and negative) electrolyte fluids 15a, 15b flow through the half-cells 2a, 2b. Thus far, the structure of a sub-cell stack 10i, 102, ..., 10 n that of a cell stack 10 of a conventional redox flow battery 1, as described above with reference to Figs. 2 and 3, for example. The cell stack 10 can be arranged between two end plates 24 as before. The cell stack 10 can also be held together as described with reference to Fig. 2.

[0051] In each sub-cell stack 10i, IO2, ... , 10 n In a preferred embodiment of the cell stack 10, an electrolyte group 36a is connected to one of the plurality n of sub-cell stacks 10i, IO2, ..., 10 n corresponding plurality n of electrolyte fluid channels 18ai, ... , 18a nfor the supply of the first (e.g. positive) electrolyte liquid 15a, an electrolyte group 36b with one of the plurality n of sub-cell stacks 10i, IO2, ..., 10 n corresponding plurality n of electrolyte fluid channels 18bi, ... , 18b n for the removal of the first (e.g. positive) electrolyte liquid 15a, an electrolyte group 37a with one of the plurality n of sub-cell stacks 101, IO2, ..., 10 n corresponding plurality n of electrolyte fluid channels 19ai, ... , 19a n for the supply of the second (e.g. negative) electrolyte liquid 15b and an electrolyte group 37b with one of the plurality n of sub-cell stacks 10i, IO2, ..., 10 n corresponding plurality n of electrolyte fluid channels 19bi, ... , 19b n for the removal of the second (e.g. negative) electrolyte liquid 15b, as shown in Fig.6 for a frame 5a, 5b.

[0052] However, for the invention it is sufficient if in the frame 5a, 5b of a sub-cell stack 10i, 102, ..., 10 n At least one such electrolyte group 36a, 36b, 37a, 37b is provided. Preferably, the electrolyte groups 36a, 36b or 37a, 37b are provided for at least the supply and discharge of one of the two electrolyte liquids 15a, 15b. For the supply or discharge of an electrolyte liquid for which no group 36a, 36b, 37a, 37b is provided, only one electrolyte liquid channel 18a, 18b, 19a, 19b is provided (as in Fig. 4). Preferably, all electrolyte groups 36a, 36b, 37a, 37b are provided.

[0053] For each provided electrolyte fluid channel 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n there is an electrolyte fluid connection 22ai, ... , 22a on the cell stack 10 n , 22bi, ... , 22b n , 23ai, ... , 23a n , 23bi, ... , 23bn provided to connect the corresponding supply line 16a, 16b or discharge line 17a, 17b for the electrolyte liquids 15a, 15b.

[0054] Fig. 6 shows a frame 5a, 5b of a single cell 2a, 2b in the preferred embodiment. In each frame 5a, 5b, the electrolyte groups 36a, 36b, 37a, 37b with the plurality n of electrolyte fluid channels 18ai, ..., 18a are arranged. n for the supply of the first (e.g. positive) electrolyte liquid 15a, the plurality n of electrolyte liquid channels 18bi, ... , 18b n for the discharge of the first (e.g. positive) electrolyte liquid 15a, the plurality n of electrolyte liquid channels 19ai, ... , 19a n for the supply of the second (e.g. negative) electrolyte liquid 15b and the plurality n of electrolyte liquid channels 19bi, ... , 19b nfor the removal of the second (e.g., negative) electrolyte 15b. In each frame 5a, 5b, only one section of these channels is provided. In the cells arranged in a sub-cell stack 10i, 102, 10 n adjacent frames 5a, 5b are the respective sections of the electrolyte fluid channels 18ai, 18a n , 18bi, 18b n , 19ai, 19a n , 19bi, 19b n aligned again to form the sub-cell stack 10i, IO2, ... , 10 n Electrolyte liquid channels 18ai, ... , 18a running in the stack direction R n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n to train.

[0055] According to the invention, in each frame 5a, 5b at least one of these electrolyte groups 36a, 36b, 37a, 37b is provided with several electrolyte fluid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b nprovided, preferably two electrolyte groups 36a, 36b or 37a, 37b for the supply and removal of one of the two electrolyte liquids 15a, 15b, preferably all electrolyte groups 36a, 36b, 37a, 37b for the supply and removal of the two electrolyte liquids 15a, 15b.

[0056] If an electrolyte group 36a, 36b, 37a, 37b of electrolyte liquid channels is provided for the supply of an electrolyte liquid 15a, 15b in a frame 5a, 5b, one of the plurality n of electrolyte liquid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b nin this group 36a, 36b, 37a, 37b are connected to the recess 6a, 6b via a frame channel 34a, 35a in order to supply the electrolyte liquid 15a, 15b to the recess 6a, 6b. If a group 36a, 36b, 37a, 37b of electrolyte liquid channels is provided for the removal of an electrolyte liquid 15a, 15b in a frame 5a, 5b, one of the plurality n of electrolyte liquid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n in this electrolyte group 36a, 36b, 37a, 37b via a frame channel 34b, 35b connected to the recess 6a, 6b in order to drain the electrolyte liquid 15a, 15b from the recess 6a, 6b.

[0057] In Fig.6, for example, the electrolyte group 36a serves to supply a (e.g. positive) electrolyte liquid 15a and the electrolyte group 36b serves to remove this electrolyte liquid 15a in this frame 5a. In each of these electrolyte groups 36a, 36b, one of the electrolyte liquid channels 18ai, ..., 18a provided therein is n , 18bi, ... , 18b n connected to the recess 7a via a frame channel 34a, 34b. In the adjacent frame 5b, the other electrolyte groups 37a, 37b can serve to supply and discharge the other (e.g., negative) electrolyte fluid 15b. In this case, one of the electrolyte fluid channels 19ai, ..., 19a provided in these electrolyte groups 37a, 37b n , 19bi, ... , 19b n connected via a frame channel 35a, 35b to the recess 7b in this frame 5b. The basic principle that in adjacent frames 5a, 5b of a sub-cell stack 10i, 102, ..., 10 nthe electrolyte liquids 15a, 15b are alternately carried out, thus naturally also remains in a sub-cell stack 10i, IO2, ... , 10 n upright. In order to operate in the sub-cell stacks 10i, IO2, 10 n In order to reduce electrical leakage currents, at least partially separate electrolyte liquid paths are formed according to the invention between at least two sub-cell stacks 10i, 102, 10 n a transition frame 40 is arranged, preferably between two adjacent sub-cell stacks 10i, 102, ..., 10 n (as shown in Fig.7a and 7b). For each electrolyte group 36a, 36b, 37a, 37b of electrolyte liquid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n in a sub-cell stack 10i, IO2, ... , 10 nIn the transition frame 40, there is a corresponding connection group 41a, 41b, 42a, 42b with a number m of used connection channels 43. The number m of used connection channels 43 is one smaller than the plurality n of electrolyte fluid channels in an electrolyte group 36a, 36b, 37a, 37b, i.e. m = n - 1. Each used connection channel 43 in a connection group 41a, 41b, 42a, 42b extends through the respective transition frame 40 in the stacking direction R, thus connecting the two end faces (in the stacking direction R) of the respective transition frame 40.

[0058] For each electrolyte group 36a, 36b, 37a, 37b on electrolyte liquid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n the transition frame 40 closes one of the plurality n of electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19bn each adjacent sub-cell stack 10i, IO2, ... , 10 n of the transition frame 40 in the stack direction R. One of the remaining electrolyte liquid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n for each electrolyte group 36a, 36b, 37a, 37b in a sub-cell stack 10i, IO2, ... , 10 n on one side of the transition frame 40, one of the number m of connecting channels 43 is connected to one of the remaining electrolyte liquid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n of the sub-cell stack 10i, IO2, ... , 10 n on the opposite side of the transition frame 40 in the stacking direction R.

[0059] Fig.7a shows this as an example for a cell stack 10 with three (n=3) sub-cell stacks 10i, 102, ... , 10 n. In each frame 5a, 5b of the half-cells 2a, 2b of individual cells 2, an electrolyte group 36a, 37a is provided on electrolyte fluid channels 18ai, ..., 18a for supplying the electrolyte fluids 15a, 15b. n , 19ai, ... , 19a n In the first (viewed in the flow direction of the electrolyte liquid) of the sub-cell stacks 10i, through each of the electrolyte liquid channels 18ai, ... , 18a n , 19ai, ... , 19a n the respective electrolyte fluid 15a, 15b (indicated by the arrows). In each sub-cell stack 10i, IO2, ... , 10 n one of these electrolyte fluid channels 18ai, ... , 18a n , 19ai, ... , 19a n in each electrolyte group 36a, 37a is closed by the adjacent transition frame 40 in the stack direction R.

[0060] For electrolyte fluid channels 18ai, ... , 18a n , 19ai, ... , 19a n , which in the sub-cell stack 10i, IO2, ... , 10 nserve to supply electrolyte fluids 15a, 15b, is in each electrolyte group 36a, 37a in each sub-cell stack 10i, IO2, 10 n preferably the electrolyte fluid channel 18ai, 18a n , 19ai, 19a n closed by the transition frame 40, which is connected to the recess 6a, 6b in the frame 5a, 5b via the frame channel 34a, 35a. The flow of the respective electrolyte fluid 15a, 15b through this closed electrolyte fluid channel 18ai, ..., 18a n , 19ai, ... , 19a n thus ends at the transition frame 40. In the embodiment in Fig.7a, these are in each sub-cell stack 10i, IO2, ... , 10 n the electrolyte fluid channels 18ai, 19ai.

[0061] A sub-cell stack 10i, IO2, ... , 10 n is connected to the adjacent sub-cell stack 10i, IO2, ..., 10 in the stack direction R nvia the m connecting channels 43 in the transition frame 40 arranged therebetween, in the embodiment shown m = 2 (n - 1) connecting channels 43. For this purpose, the remaining (unclosed) electrolyte liquid channels 18a2, ... , 18a n , 19a2, ... , 19a n in each electrolyte group 36a, 37a each through a connecting channel 43 with one of the electrolyte liquid channels 18ai, ... , 18a n , 19ai, ... , 19a n in the electrolyte groups 36a, 37a in the adjacent sub-cell stack in stack direction R

[0062] 101, IO2, ... , 10 n In the embodiment according to Fig.7a, for example, the electrolyte fluid channels 18a2, 18a n , 19a2, 19a n in the first sub-cell stack 10i is connected to the electrolyte fluid channels 18ai, 18a2, 19ai, 19a2 in the adjacent second sub-cell stack 10i. After one of the supply electrolyte fluid channels 18ai, ..., 18a n, 19ai, ... , 19a n closed, are in the following sub-cell stack 10i, IO2, ... , 10 n fewer and fewer of the electrolyte fluid channels 18ai, ... , 18a n , 19ai, ... , 19a n by one of the electrolyte fluids 15a, 15b. In Fig.7a, for example, in the second sub-cell stack IO2, only two of the electrolyte fluid channels 18ai, ..., 18a are still present. n , 19ai, ... , 19a n flowing through electrolyte liquid 15a, 15b and in the last cell stack 10 n only one more.

[0063] For electrolyte fluid channels 18ai, ... , 18a n , 19ai, ... , 19a n , which are arranged in adjacent sub-cell stacks 10i, IO2, ..., 10 separated by a transition frame 40 n serve to supply electrolyte liquids 15a, 15b, is in each electrolyte group 36a, 37a in a sub-cell stack 10i, IO2, ... , 10 none of the remaining electrolyte fluid channels 18ai, ..., 18a (not closed by the transition frame 40) n , 19ai, ... , 19a n with the electrolyte fluid channel 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n in the adjacent sub-cell stack 10i, IO2, ... , 10 n connected to the adjacent sub-cell stack 10i,

[0064] 102, ... , 10 nvia the frame channel 34a, 35a with the recess 6a, 6b in the frame 5a, 5b. In Fig.7a, for example, the electrolyte fluid channels 18a2, 19b2 in the first sub-cell stack 10i are connected to the electrolyte fluid channels 18ai, 19bi in the adjacent second sub-cell stack 10i, wherein the electrolyte fluid channels 18ai, 19bi in the adjacent second sub-cell stack 10i are connected via the respective frame channel 34a, 35b with the respective recess 6a, 6b in the frame 5a, 5b of the half-cells 2a, 2b. In the last (seen in the flow direction of the electrolyte fluid 15a, 15b) sub-cell stack 10 n is therefore only one of the electrolyte fluid channels 18ai, ... , 18a serving to supply electrolyte fluid 15a, 15b n , 19ai, ... , 19a n through which the respective electrolyte liquid 15a, 15b flows.

[0065] For the supply of electrolyte liquid 15a, 15b serving electrolyte liquid channels 18ai, ... , 18an , 19ai, ... , 19a n It is therefore advantageous that in the flow direction of the electrolyte liquids 15a, 15b in the sub-cell stacks 10i, IO2, ... , 10 n fewer and fewer of the electrolyte fluid channels 18ai, ... , 18a n , 19ai, ... , 19a n flowed through by electrolyte liquid 15a, 15b.

[0066] Fig.7b shows the inventive design of a cell stack 10 with n sub-cell stacks 10i, 102, ..., 10 n for the electrolyte fluid channels 18bi, ... , 18b n , 19bi, ... , 19b n , which serve to drain the electrolyte fluids 15a, 15b. In each sub-cell stack 10i, IO2, ... , 10 n are again groups 36b, 37b with the majority n of sub-cell stacks 101 , 102, ... , 10 n corresponding plurality of electrolyte fluid channels 18bi, ... , 18b n , 19bi, ... , 19b nThe basic structure is the same as described above. Electrolyte channels 18bi, ..., 18b are provided for the removal of the electrolyte fluids 15a, 15b. n , 19bi, ... , 19b n is preferably the electrolyte liquid channel of a group 36b, 37b of electrolyte liquid channels 18bi, ..., 18b n , 19bi, ... , 19b n , which in a sub-cell stack 10i, IO2, ... , 10 n is connected via a frame channel 34b, 35b to the recess 6a, 6b in the frame 5a, 5b, via a connecting channel 43 in the transition frame 40 to one of the electrolyte fluid channels of an electrolyte group 36b, 37b on electrolyte fluid channels 18bi, ..., 18b n , 19bi, ... , 19b n in the adjacent sub-cell stack 10i, IO2, ... , 10 nconnected. In the embodiment of Fig. 7b, for example, the electrolyte fluid channel 19bi in the first sub-cell stack 101 is connected to the recess 6b in the frame 5b via a frame channel 35b. This electrolyte fluid channel 19bi in the first sub-cell stack 10i is connected to the electrolyte fluid channel 19b2 in the adjacent second sub-cell stack 102 via a connecting channel 43 in the transition frame 40 adjacent thereto in the stack direction R.

[0067] For the removal of electrolyte liquid 15a, 15b serving electrolyte liquid channels 18bi, ... , 18b n , 19bi, ... , 19b n It is therefore advantageous that in the flow direction of the electrolyte liquids 15a, 15b in the sub-cell stacks 10i, IO2, ... , 10 n more and more of the electrolyte fluid channels 18bi, ... , 18b n , 19bi, ... , 19b nare flowed through by electrolyte liquid 15a, 15b. Seen in the flow direction of the electrolyte liquid 15a, 15b, the last sub-cell stack 10i, 102, ..., 10 n Therefore, all electrolyte fluid channels 18bi, ... , 18b are advantageous n , 19bi, ... , 19b n of electrolyte fluid 15a, 15b. If in a sub-cell stack 10i , 102, ... , 10 n for the supply or removal of one of the two electrolyte liquids 15a, 15b no electrolyte group 36a, 36b, 37a, 37b on electrolyte liquid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n be provided, but only a single electrolyte liquid channel 18a, 18b, 19a, 19b, then the transition frame 40 connects the respective electrolyte liquid channels 18a, 18b, 19a, 19b in adjacent sub-cell stacks 10i, 102, ..., 10 nThis is shown as an example in Fig.8.

[0068] In Figs. 7a and 7b, only the frames 5b of one half-cell 2b are shown in plan view. The frames 5a of the other half-cell 2a of a single cell 2 are designed analogously.

[0069] There are, of course, various possibilities as to how the transition frame 40 can be connected via the connecting channels 43 to electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n neighboring sub-cell stacks 10i, IO2, ... , 10 n connects and which electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n be closed by the transition frame 40. However, it is advantageous if in each sub-cell stack 10i, IO2, ..., 10 n always the same electrolyte fluid channels 18ai, ... , 18a n, 18bi, ... , 18bn, 19ai, ... , 19a n , 19bi, ... , 19b n via frame channels 34a, 34b, 35a, 35b are connected to the respective recesses 6a, 6b, and the connection via the transition frames 40 always follows the same pattern. This means that one frame type is needed for the frames 5a, 5b and one type of transition frame 40. If the frames are additionally designed so that one frame can be used for both half-cells 2a, 2b by simply turning them (as in the embodiments of Figures 6, 7a, 7b), then even a single frame type is sufficient. If it is also ensured that the entire lengths of the electrolyte fluid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b nfor the supply and discharge of the electrolyte liquids 15a, 15b are the same (as in the embodiments of Figures 6, 7a, 7b) then the pressure loss in all sub-cell stacks 10i, IO2, ... , 10 n approximately the same, which improves the efficiency and operation of the redox flow battery 1.

[0070] For the redox flow battery 1, it is advantageous if the individual sub-cell stacks 10i , IO2, ... , 10 n are also electrically connected to form the cell stack 10. For this purpose, for each sub-cell stack 10i, IO2, ... , 10 n electrical contacts must be led outwards and the sub-cell stacks 10i, IO2, ... , 10 n could be electrically connected externally. However, it is simpler if the sub-cell stacks 10i, IO2, ... , 10 n are electrically connected internally in the cell stack 10.

[0071] Fig. 9 shows one embodiment of such an internal electrical connection. It shows a side view (for example, from the left in Fig. 7a) of a section of the cell stack 10 in cross section. Two sub-cell stacks 10i, 102 are shown, between which a transition frame 40 is arranged in the stack direction R. Individual cells 2 are shown in each sub-cell stack 10i, 102, as described with reference to Fig. 3. The frames 5a, 5b are connected to at least one electrolyte group 36a, 36b, 37a, 37b at electrolyte fluid channels 18ai, ..., 18a n , 18bi , ... , 18b n , 19ai , ... , 19a n , 19bi , ... , 19b nbut can also be designed with only one electrolyte fluid channel 18a, 18b, 19a, 19b. Adjacent individual cells 2 in a sub-cell stack 10i, 102 are separated from one another by electrode plates 8. A semipermeable membrane 4 is arranged between two half-cells 2a, 2b. The position of the cross-section is selected such that the electrolyte fluid channels 19ai for the electrolyte fluid 15a are visible. In the transition frame 40, a central recess 46 is provided which runs through in the stack direction R and in which an electrically conductive connecting part 45 is arranged. The electrical connecting part 45 is in electrical contact with the electrodes 7a, 7b of the half-cells 2a, 2b adjacent to the transition frame 40 in order to electrically connect the two sub-cell stacks 10i, 102 adjacent to the transition frame 40. In a cell stack 10, at least one transition frame 40 can be designed in this way; preferably, all transition frames 40 are designed in this way.

[0072] Fig. 10 shows a modification of the arrangement according to Fig. 9, in which additional bipolar plates 8 are arranged between the electrical connection part 45 and the adjacent electrodes 7a, 7b. This allows the use of an electrical connection part 45 that is not resistant to the electrolyte liquids 15a, 15b, because the connection part 45 is not in direct contact with the electrolyte liquid 15a, 15b. In a cell stack 10, at least one transition frame 40 can be designed in this way; preferably, all transition frames 40 are designed in this way.

[0073] Fig. 11 describes another embodiment of a transition frame 40 according to the invention. In this embodiment, the transition frame 40 is designed in two parts with a first transition frame part 40a and a second transition frame part 40b, wherein the first and second transition frame parts 40a, 40b are arranged next to one another and adjacent to one another in the stack direction R. The two transition frame parts 40a, 40b are designed like half-cells 2a, 2b of a single cell 2 (with frame, recess in the frame, electrode in the recess with electrolyte fluid channels and frame channels for the supply and removal of electrolyte fluid) and each form a half-cell 2a, 2b of a single cell 2 of a sub-cell stack 10i, 102, ..., 10 n Thus, each of the transition frame parts 40a, 40b forms with the adjacent half-cell 2a, 2b of a sub-cell stack 10i, 102, ..., 10 na single cell 2. In the stack direction R between these half-cells 2a, 2b, a semipermeable membrane 4 is arranged as usual. Thus, the transition frame 40 electrically becomes part of the sub-cell stacks 10i, 102, ..., 10 n and the cell stack 10. This allows the size of a cell stack 10 to be reduced. For this purpose, each of the transition frame parts 40a, 40b naturally has a recess 6a, 6b in which an electrode 7a, 7b is arranged. The electrodes 7a, 7b are separated by an electrode plate 8 arranged between them in the stack direction R, which simultaneously serves as an electrical connecting part 45 between the adjacent sub-cell stacks 10i, 102, ..., 10 n Likewise, the transition frame parts 40a, 40b have frame channels 34a, 34b, 35a, 35b to form one of the electrolyte fluid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b nto be connected to a recess 6a, 6b for supplying or discharging electrolyte fluid 15a, 15b. In a modification, as shown in Fig. 12, the electrical connection could again be made through a connecting part 45 and adjacent electrode plates 8.

[0074] In the case of a two-part design of the transition frame 40 with a first transition frame part 40a and a second transition frame part 40b, the first and second transition frame parts 40a, 40b do not have to be like half cells 2a, 2b of a single cell 2 of a sub-cell stack 10i, 102, ..., 10 n Instead of electrodes 7a, 7b, an electrical connecting part 45 could be arranged in the recesses 6a, 6b, electrically connecting the adjacent half-cells 2a, 2b of the transition frame 40. Such a configuration naturally also eliminates the need for frame channels 34a, 34b, 35a, 35b in the first and second transition frame parts 40a, 40b.

[0075] But also in an embodiment of the transition frame 40 with a first transition frame part 40a and a second transition frame part 40b as shown in Fig.11 or 12, there is at least one connection group 41a, 41b, 42a, 42b with connection channels 43, as described above, to the electrolyte liquid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n the neighboring sub-cell stacks 10i, IO2, ... , 10 n as described above. The basic principle here is that each electrolyte group 36a, 36b, 37a, 37b in a sub-cell stack 10i, IO2, ... , 10 na connecting group 41a, 41b, 42a, 42b with the connecting channels 43 in the transition frame 40. The relevant function of the transition frame 40 for separating the electrolyte fluid paths remains unchanged. This is explained using an exemplary embodiment shown in Figs. 13a and 13b. In this exemplary embodiment, which serves only as an illustration, Fig. 13a shows the supply side and Fig. 13b the discharge side of the electrolyte fluids 15a, 15b.

[0076] It can be seen that each of the transition frame parts 40a, 40b has a recess 6a, 6b in which an electrode 7a, 7b is arranged. Each transition frame part 40a, 40b has a frame channel 34a, 34b, 35a, 35b for the respective electrolyte fluid 15a, 15b.

[0077] The frame channels 34a, 34b, 35a, 35b are connected in a transition frame part 40a, 40b by a connecting channel 43 carrying electrolyte fluid 15a, 15b. Thus, each transition frame part 40a, 40b forms a half-cell 2a, 2b.

[0078] In the transition frame parts 40a, 40b, the connecting groups 41a, 41b, 42a, 42b with connecting channels 43 are provided to connect the electrolyte liquid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n the neighboring sub-cell stacks 10i, IO2, ... , 10 n to close or connect as described above.

[0079] The connecting channels 43 are designed somewhat differently in the embodiment according to Fig.13a, 13b, wherein according to the invention at least one connecting channel 43, preferably all connecting channels 43 of a connecting group 41a, 41b, 42a, 42b, particularly advantageously all connecting channels 43 of all connecting groups 41a, 41b, 42a, 42b, are designed as described below.

[0080] Inclined connecting channels 43, as shown in Figs. 7a, 7b, are more difficult to implement in practice with the two transition frame parts 40a, 40b; in particular, the aligned arrangement of such inclined connecting channel sections in the transition frame parts 40a, 40b would be more difficult to realize. Therefore, in the transition frame parts 40a, 40b, there are diversion channels 47 that do not pass through the respective transition frame part 40a, 40b in the stack direction R, and through-channels 48 that each pass through the transition frame part 40a, 40b, with two through-channels 48 each being arranged in alignment in the transition frame parts 40a, 40b. The diversion channels 47 are preferably formed in the end faces of the transition frame 40 and the respective adjacent sub-cell stacks 10i, 102, ..., 10 narranged facing each other. Two aligned through-channels 48 and the associated diversion channels 47 form a connecting channel 43. The diversion channels 47 allow the through-channels 48 to be separated from the electrolyte fluid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n be offset, so that the through-channels 48 no longer have to be arranged obliquely, but can be aligned, for example, in the stack direction R. A diversion channel 47 connects each of the electrolyte liquid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n in the adjacent frame 5a, 5b with a through-channel 48 in the transition frame parts 40a, 40b, whereby the connection of the electrolyte fluid channels 18ai, ..., 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b nis manufactured.

[0081] Such a design of a connecting channel 43 with a diversion channel 47 and the associated, offset through-channel 48 can of course also be provided in a one-piece transition frame 40, in which case there is a one-piece through-channel 48 instead of a two-piece through-channel 48. A cell stack 10 according to the invention with sub-cell stacks 10i, 102, 10 n and between adjacent sub-cell stacks 10i, 102, 10 n The transition frame 40 arranged in the cell stack can also be easily scaled, for example, to realize different cell stack voltages VR ZU. For this purpose, in each sub-cell stack 10i, IO2, 10 n a different number of single cells 2 can be used, as well as a different number n of sub-cell stacks 10i, 102, ... , 10 nThe invention thus makes it possible to optimize the structure of the cell stack 10 with regard to the leakage currents occurring in the electrolyte fluid paths.

[0082] It is also possible that each frame 5a, 5b and each sub-cell stack 101, 102, ..., 10 n at least one group 36a, 36b, 37a, 37b with a certain plurality n of electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19a-i, ... , 19a n , 19bi, ... , 19b n , but only a few of them are used in cell stack 10. Such a frame 5a, 5b and sub-cell stacks 10i, 102, ... , 10 n can be arranged in a cell stack 10 according to the invention with different numbers n of sub-cell stacks 10i, 102, ..., 10 n For the purposes of this application, the plurality n of electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19bn the number of cells actually in cell stack 10 or in the sub-cell stacks 10i, 102, ... , 10 n electrolyte fluid channels 18ai, ... , 18a in use n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n understood.

[0083] For example, frames 5a, 5b and sub-cell stack 10i, 102, ... , 10 n with a group 36a, 36b, 37a, 37b of five electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n If such a frame 5a, 5b and sub-cell stack

[0084] 101, IO2, ... , 10 n in a cell stack 10 with only two sub-cell stacks 10i, IO2, ... , 10 n used, then two of the five electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n ,

[0085] 19ai , ... , 19a n, 19bi , ... , 19b n in the group 36a, 36b, 37a, 37b are used and the remaining electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n would not be used. This corresponds to the use of frames 5a, 5b and sub-cell stacks 10i, 102, ... , 10 n with a group 36a, 36b, 37a, 37b with only two electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n , which for two sub-cell stacks 10i, IO2, ... , 10 n in the cell stack 10 would be sufficient. Analogously, more through-channels 48 could be provided in the transition frame 40 than are actually used in the cell stack 10.

[0086] It would also be conceivable to arrange the majority n of electrolyte fluid channels 18ai, ... , 18a in a cell stack 10 n , 18bi, ... , 18b n, 19ai, ... , 19a n , 19bi, ... , 19b n corresponding number of sub-cell stacks 10i, IO2, ... , 10 n to be provided, but less than these n sub-cell stacks 10i,

[0087] 102, ... , 10 n via the electrolyte fluid channels 18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n with electrolyte fluid. This means that the unsupplied sub-cell stacks 10i, IO2, 10 n electrically inactive, but present in the cell stack 10. In this embodiment, it must therefore be ensured that the electrically inactive sub-cell stacks 101, IO2, ..., 10 n can be electrically bridged in order to tap or apply an electrical voltage to the power terminals 11, 12. In a further advantageous embodiment of a cell stack 10, a sub-cell stack 10i, IO2, ..., 10 nas a measuring cell for measuring a cell voltage. The measuring cell can be designed as a single cell 2. A sub-cell stack 10i, 102, ... , 10 ncan therefore only have a single individual cell 2. The individual cell 2 serving as the measuring cell is supplied with electrolyte fluids 15a, 15b in the same way as the other individual cells 2 and as described above. However, one measuring cell has electrical connections leading to the outside, which are electrically connected in the measuring cell to the electrodes 7a, 7b or to the electrolyte fluids 15a, 15b or to electrode plates 8 in the half-cells 2a, 2b of the measuring cell. This allows a cell voltage to be measured between the electrodes 7a, 7b or the electrolyte fluids 15a, 15b, which can be used for diagnostic purposes or for monitoring the redox flow battery 1. The cell voltage at the redox flow battery 1 can be tapped as a measured value via the electrical connections leading to the outside.

Claims

Patent claims 1. Cell stack of a redox flow battery (1) with a plurality n of sub-cell stacks (10i, 1Ü2, 10 n ) arranged side by side in a stack direction (R), wherein each sub-cell stack (10i, 102, , 10 n) comprises at least one individual cell (2), wherein each individual cell (2) is formed from a first half-cell (2a) and a second half-cell (2b), and each first half-cell (2a) and second half-cell (2b) comprises a frame (5a, 5b) with a central recess (6a, 6b) extending in the stacking direction (R), and an electrode (7a, 7b) is arranged in each recess (6a, 6b) of a frame (5a, 5b) of each first half-cell (2a) and second half-cell (2b), wherein the first half-cell (2a) and second half-cell (2b) of an individual cell (2) are arranged next to one another in the stacking direction (R), and the recesses (6a, 6b) and the electrodes (7a, 7b) arranged therein of the first half-cell (2a) and second half-cell (2b) of an individual cell (2) are separated from one another in the stacking direction (R) by a semipermeable membrane (4) are, where in each sub-cell stack (101 , IO2, ... , 10 n) a first electrolyte group (36a, 36b, 37a, 37b) with one of the plurality n of sub-cell stacks (10i, IO2, ... , 10 n ) corresponding plurality n of first electrolyte liquid channels (18ai, ..., 18a n , 18bi , ... , 18b n , 19ai , ... , 19a n , 19bi , ... , 19b n ) and in each sub-cell stack (10i, IO2, ... , 10 n ) the plurality n of first electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the first electrolyte group (36a, 36b, 37a, 37b) in the stack direction (R) through all frames (5a, 5b) of all individual cells (2) of the respective sub-cell stack (10i, 102, ... , 10 n ), where in each sub-cell stack (10i, IO2, ... , 10 n ) one of the first electrolyte fluid channels (18ai, ... , 18a n , 18bi, ... , 18b n, 19ai, ... , 19a n , 19bi, ... , 19b n ) of the first electrolyte group (36a, 36b, 37a, 37b) via a respective first frame channel (34a, 34b) into the frame (5a) of the first half-cells (2a) of the individual cells (2) of the respective sub-cell stack (10i, 102, ... , 10 n ) is connected to the recesses (7a) in the frame (5a) of the first half-cells (2a), characterized in that between at least two sub-cell stacks (10i, 102, ... , 10 n ) of the plurality n of sub-cell stacks (10i, IO2, ... , 10 n) a transition frame (40) is arranged, that in the transition frame (40) a first connection group (41a, 41b, 42a, 42b) with a number m of connection channels (43) is provided and each connection channel (43) of the first connection group (41a, 41b, 42a, 42b) passes through the respective transition frame (40) in the stack direction (R), and that in each case one of the plurality of first electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the first electrolyte group (36a, 36b, 37a, 37b) of each adjacent sub-cell stack (10i, IO2, ... , 10 n ) of the transition frame (40) in the stacking direction (R) is closed by the transition frame (40) and one of the remaining electrolyte fluid channels (18ai, 18a n , 18bi, 18b n , 19ai, 19a n , 19bi, 19b n ) of the sub-cell stack (10i, IO2, 10 n ) on one side of the transition frame (40) via one of the number m of connecting channels (43) of the first connecting group (41a, 41b, 42a, 42b) with one of the remaining first electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the sub-cell stack (10i, IO2, ... , 10 n ) on the opposite side of the transition frame (40) in the stacking direction (R).

2. Cell stack according to claim 1, characterized in that between all adjacent sub-cell stacks (10i, 102, ..., 10 n) of the cell stack (10), a respective transition frame (40) is arranged, in that in each transition frame (40) a first connection group (41a, 41b, 42a, 42b) with a number m of connection channels (43) is provided and each connection channel (43) passes through the respective transition frame (40) in the stack direction (R), and in that in each case one of the plurality n of first electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the first electrolyte group (36a, 36b, 37a, 37b) of each adjacent sub-cell stack (10i, IO2, ... , 10 n ) of each transition frame (40) is closed in the stack direction (R) by the transition frame (40) and one of the remaining first electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the sub-cell stack (10i, IO2, ... , 10 n) on one side of each transition frame (40) via one of the number m of connecting channels (43) of the first connecting group (41a, 41b, 42a, 42b) with one of the remaining first electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the sub-cell stack (10i, IO2, ... , 10 n ) on the opposite side of each transition frame (40) in the stacking direction (R).

3. Cell stack according to claim 1 or 2, characterized in that in each sub-cell stack (10i, 102, ..., 10 n ) a second electrolyte group (36a, 36b, 37a, 37b) with one of the plurality n of sub-cell stacks (10i, IO2, ... , 10 n ) corresponding plurality of second electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) and in each sub-cell stack (10i, IO2, ... , 10n ) the plurality of second electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the second electrolyte group (36a, 36b, 37a, 37b) in the stack direction (R) through all frames (5a, 5b) of all individual cells (2) of the respective sub-cell stack (10i, 102, ... , 10 n ), where in each sub-cell stack (10i, IO2, ... , 10 n ) one of the second electrolyte fluid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the second electrolyte group (36a, 36b, 37a, 37b) via a second frame channel (34a, 34b, 35a, 35b) into the frame (5a, 5b) of the first half-cells (2a) or second half-cells (2b) of the individual cells (2) of the respective sub-cell stack (10i, IO2, 10 n) is connected to the recesses (6a, 6b) in the frames (5a, 5b) of the first half-cells (2a) or second half-cells (2b), that in each transition frame (40) a second connection group (41a, 41b, 42a, 42b) with a number m of connection channels (43) is provided and each connection channel (43) of the second connection group (41a, 41b, 42a, 42b) passes through the respective transition frame (40) in the stacking direction (R), and that in each case one of the plurality n of second electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the second electrolyte group (36a, 36b, 37a, 37b) of each adjacent sub-cell stack (10i, IO2, ... , 10 n ) of each transition frame (40) is closed in the stack direction (R) by the respective transition frame (40) and one of the remaining second electrolyte liquid channels (18ai, ..., 18a n , 18bi, ... , 18b n, 19ai, ... , 19a n , 19bi, ... , 19b n ) of the second electrolyte group (36a, 36b, 37a, 37b) of the sub-cell stack (10i, IO2, ... , 10 n ) on one side of each transition frame (40) via one of the number m of connecting channels (43) of the second connecting group (41a, 41b, 42a, 42b) with one of the remaining second electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the sub-cell stack (10i, IO2, ... , 10 n ) on the opposite side of this transition frame (40) in the stacking direction (R).

4. Cell stack according to claim 1 or 2, characterized in that in each sub-cell stack (10i, 102, ..., 10 n ) a second electrolyte group (36a, 36b, 37a, 37b) with one of the plurality n of sub-cell stacks (10i, IO2, ... , 10 n ) corresponding plurality n of second electrolyte liquid channels (18ai, ... , 18an , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ), a third electrolyte group (36a, 36b, 37a, 37b) with one of the plurality n of sub-cell stacks (10i, IO2, ... , 10 n ) corresponding plurality n of third electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) and a fourth electrolyte group (36a, 36b, 37a, 37b) with one of the plurality n of sub-cell stacks (10i, IO2, ... , 10 n ) corresponding plurality n of fourth electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) and the plurality n of second, third and fourth electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n) of the second, third and fourth electrolyte group (36a, 36b, 37a, 37b) in the stack direction (R) through all frames (5a, 5b) of all individual cells (2) of the respective sub-cell stack (10i, 102, ... , 10 n ), where in each sub-cell stack (10i, IO2, ... , 10 n ) each have an electrolyte fluid channel (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of two of the second, third and fourth electrolyte groups (36a, 36b, 37a, 37b) via a frame channel (34a, 34b, 35a, 35b) into the frame (5a, 5b) of the first half-cells (2a) of the individual cells (2) of the respective sub-cell stack (10i, 102, ... , 10 n ) is connected to the recesses (6a) in the frame (5a) of the first half-cells (2a) and in each sub-cell stack (10i , 102, ... , 10 n ) one each Electrolyte fluid channel (18ai, 18a n , 18bi, 18bn , 19ai, 19a n , 19bi, 19b n ) from the two remaining electrolyte groups (36a, 36b, 37a, 37b) via a frame channel (34a, 34b, 35a, 35b) into the frame (5b) of the second half-cells (2b) of the individual cells (2) of the respective sub-cell stack (10i, 102, ... , 10 n ) is connected to the recesses (6b) in the frame (5b) of the second half-cells (2b), that in each transition frame (40) a second connection group (41a, 41b, 42a, 42b) with a number of connection channels (43), a third connection group (41a, 41b, 42a, 42b) with a number of connection channels (43) and a fourth connection group (41a, 41b, 42a, 42b) with a number of connection channels (43) are provided and each connection channel (43) passes through the respective transition frame (R) in the stack direction (R), and that in each case one of the plurality n of electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19an , 19bi, ... , 19b n ) of the second, third and fourth electrolyte group (36a, 36b, 37a, 37b) of each adjacent sub-cell stack (10i, IO2, ... , 10 n ) of each transition frame (40) is closed in the stack direction (R) by the respective transition frame (40) and one of the remaining electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of the second, third and fourth electrolyte group of the sub-cell stack (10i, IO2, ... , 10 n ) on one side of each transition frame (40) via one of the number of connecting channels (43) of the second, third or fourth connecting group (41a, 41b, 42a, 42b) with one of the remaining electrolyte liquid channels (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n) of the second, third and fourth electrolyte group (36a, 36b, 37a, 37b) of the sub-cell stack (10i, IO2, ... , 10 n ) on the opposite side of this transition frame (40) in the stacking direction (R).

5. Cell stack according to one of claims 1 to 4, characterized in that in at least one transition frame (40) a recess (46) is provided which extends centrally in the stack direction (2) and in which an electrical connecting part (45) is arranged, wherein the connecting part (45) electrically contacts the electrodes (7a, 7b) of the adjacent half-cells (2a, 2b) of the transition frame (40).

6. Cell stack according to claim 5, characterized in that an electrode plate (8) is arranged between the electrodes (7a, 7b) of the adjacent half-cells (2a, 2b) of the transition frame (40) and the electrical connecting part (45), and each electrode plate (8) rests against one of the electrodes (7a, 7b) and the connecting part (45).

7. Cell stack according to one of claims 1 to 4, characterized in that at least one transition frame (40) consists of a first transition frame part (40a) and a second transition frame part (40b), wherein the first transition frame part (40a) and second transition frame part (40b) are arranged next to one another and adjacent to one another in the stack direction (R).

8. Cell stack according to claim 7, characterized in that in at least one transition frame (40) there is provided a recess (46) which extends centrally in the stack direction (R) through the first transition frame part (40a) and the second transition frame part (40b), in which recess an electrical connecting part (45) is arranged which electrically contacts the electrodes (7a, 7b) of the adjacent half-cells (2a, 2b) of the transition frame (40).

9. Cell stack according to claim 7, characterized in that the first transition frame part (40a) and the second transition frame part (40b) are each designed as a half-cell (2a, 2b) of a single cell (2) of the cell stack (10) and the first transition frame part (40a) and the second transition frame part (40b) are each connected to an adjacent half-cell (2a, 2b) of an adjacent sub-cell stack (10i, 102, ..., 10 n) forms a single cell (2) and at least one electrode plate (8) is arranged in the stack direction (R) between the first transition frame part (40a) and the second transition frame part (40b).

10. Cell stack according to one of claims 1 to 9, characterized in that at least one connecting channel (43) is designed with a through-channel (48) and two diversion channels (47) connected to the through-channel (48), wherein the through-channel (48) passes through the transition frame (40) in the stack direction (R) and the diversion channels (47) do not pass through the transition frame (40) in the stack direction (R), and that each diversion channel (47) has an electrolyte liquid channel (18ai, ... , 18a n , 18bi, ... , 18b n , 19ai, ... , 19a n , 19bi, ... , 19b n ) of a neighboring sub-cell stack (10i, IO2, ... , 10 n ) with the through channel (48).

11. Cell stack according to one of claims 1 to 10, characterized in that the sub-cell stacks (10i, 102, ..., 10 n ) are arranged in the stacking direction (R) between two end plates (24).

12. Cell stack according to one of claims 1 to 11, characterized in that a sub-cell stack (10i, 102, ..., 10 n ) is designed with a single single cell (2), wherein on each half cell (2a, 2b) of this single cell (2) an electrical connection from the cell stack (10) is led outwards and each electrical connection is electrically connected to one of the electrodes (7a, 7b) or to one of the electrolyte liquids (15a, 15b) or to an electrode plate (8) in the individual cell (2).

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