Cell frame, electrochemical cell, cell stack, and operating method

Abstract

A cell frame (4) for forming an electrochemical cell (2), particularly for a redox flow battery, is described and illustrated. The cell frame (4) circumscribes at least one cell interior (5) and includes at least one feed channel (13) for feeding electrolyte into the cell interior (5). The feed channel (13) has an inlet opening (18) separated from the cell interior (5) for the fed electrolyte and an outlet opening (19) adjacent to the cell interior (5) for allowing the fed electrolyte to flow out into the cell interior (5). To enable increased power density, the feed channel (13) has at least one transport channel (21) at least partially connecting the inlet opening (18) to the outlet opening (19) for transporting electrolyte into the cell interior (5) via the feed channel (13), and at least one return channel (22) for partially returning the fed electrolyte in a direction opposite to the transport direction (T) of the fed electrolyte in the transport channel (21). Each return channel (22) is in fluid contact with a transport channel (21) via at least one inlet opening (25) for the inflow of the returned electrolyte and an outlet opening (26) for the outflow of the returned electrolyte, said openings being spaced apart from one another in the transport direction (T) of the delivered electrolyte.

Description

Technical Field

[0001] The present invention relates to a self-frame for forming an electrochemical cell, particularly for a redox flow battery. The self-frame surrounds the perimeter inside at least one cell and includes at least one feed channel for feeding an electrolyte into the cell. The feed channel has an inlet opening separated from the inside of the cell for the electrolyte to be fed and an outlet opening adjacent to the inside of the cell for allowing the fed electrolyte to flow out into the cell. In addition, the present invention relates to an electrochemical cell and a cell stack having such a self-frame. Further, the present invention relates to a method of operating such an electrochemical cell or such a cell stack.

Background Art

[0002] Electrochemical cells are known in various designs and are sometimes referred to as electrochemical reactors because an electrochemical reaction occurs within the electrochemical cell. Electrochemical cells can be designed according to their intended use. For example, they can be designed as galvanic cells in the form of an electrochemical current source that supplies useful electrical energy through chemical reactions at different electrodes. However, alternatively, an electrochemical cell can be an electrolytic cell, which produces specific products by applying an external voltage. Or, a storage battery cell functions as a current source like a galvanic cell and further as a current storage unit as in the case of an electrolytic cell.

[0003] The present invention is applicable to all types of electrochemical cells. However, the present invention is particularly preferred in relation to battery cells, and here preferred in relation to redox flow batteries. Redox flow batteries themselves have been known for a long time in various designs. Such designs are described, for example, in Patent Documents 1 and 2. One important advantage of redox flow batteries is their suitability for storing extremely large amounts of electrical energy. The energy is stored in an electrolyte. The electrolyte can be kept in a space-saving manner in a very large tank. The electrolyte typically contains several metal ions, each in a different oxidation state. To extract electrical energy from the electrolyte, or to recharge the electrolyte, the electrolyte is passed through a so-called electrochemical cell.

[0004] An electrochemical cell is formed from two half-cells separated from each other by a semipermeable membrane. Each half-cell contains an electrolyte and an electrode. The semipermeable membrane serves to spatially and electrically separate the cathode and anode of the electrochemical cell from each other. Therefore, the semipermeable membrane must be permeable to ions. Ions convert the stored chemicals into electrical energy, or vice versa. Semipermeable membranes can be formed from, for example, microporous plastics, as well as nonwoven fabrics made of glass fiber or polyethylene, and so-called diaphragms. Redox reactions occur at both electrodes of the electrochemical cell. Electrons are released by the electrolyte at one electrode and accepted by the electrolyte at the other electrode. Metal and / or nonmetallic ions in the electrolyte form redox pairs, resulting in the generation of a redox potential. Examples of redox pairs include iron-chromium, polysulfide-bromide, or vanadium. These, or other, redox pairs can exist basically in aqueous or non-aqueous solutions.

[0005] The two electrodes of a cell, between which a potential difference is formed as a result of the redox potential, are electrically connected to each other outside the cell, for example, via an electrical charger. When electrons reach one half-cell from the other half-cell outside the cell, ions from both electrolytes pass directly from one half-cell to the other through a semipermeable membrane. To recharge a redox flow battery, a potential difference can be applied to the electrodes of both half-cells, rather than to the electrical charger, for example, by a charging device. This potential difference reverses the redox reactions occurring at the electrodes of both half-cells.

[0006] To form the described cell, a cell frame is used, in particular, to surround the inside of the cell. The cell frame generally does not completely surround the inside of the cell, but only along the narrower sides of the periphery. That is, the cell frame extends circumferentially around the inside of the cell, separating two opposing larger sides from each other. These sides are allocated to semipermeable membranes or electrodes. The thickness of the cell frame, formed by its edges, is generally significantly smaller than the width and height of the cell frame defining the opposing larger sides.

[0007] Each half-cell of an electrochemical cell comprises such a cell frame, manufactured, for example, from a thermoplastic material in an injection molding process. A semipermeable membrane is placed between the two cell frames. The semipermeable membrane separates the electrolytes of the two half-cells from each other in terms of convective mass exchange, but allows the diffusion of specific ions from one half-cell to the other. Furthermore, electrodes are positioned inside each cell so as to be in contact with the electrolyte flowing through the cell. The electrodes can, for example, seal the inside of each cell frame on the side opposite the semipermeable membrane. The inside of the cell can be left almost empty, and in any case, it can be filled with only one type of electrolyte. However, each electrode can also be provided at least partially inside the cell. In that case, the electrodes are generally designed so that the electrolyte can flow partially through the electrodes. Often, electrodes with a large specific surface area are considered, where the corresponding electrochemical reaction can occur relatively rapidly and / or over a wide area. This ultimately improves the performance per unit volume of the cell. However, even when electrodes extend into the cell, the cell interior is usually closed off by the electrodes on the side opposite to the semipermeable membrane. For example, a so-called bipolar plate, which may be covered with a reactor or another material, can also be considered a non-porous portion of the electrode.

[0008] Each cell frame has multiple openings and multiple channels. Through these, the corresponding electrolyte can flow from the supply line into the interior of each cell, from where it is withdrawn again and fed to the removal line. In this process, the electrolyte from each half-cell is sent from the storage container to the collection container via the supply and removal lines. This makes the electrolyte reusable. Therefore, there is no need to discard or replace the electrolyte.

[0009] If a redox flow battery consists of only a single cell, the supply line and the removal line for each half-cell are located outside the cell frame that forms the half-cell. Each cell frame has at least two openings. At least one of these openings is connected to the supply line, and at least one other opening is connected to the removal line. Inside the cell frame, each opening is connected to a fluid channel that opens into the cell. This allows the electrolyte to be supplied from the supply line to the cell through the supply channel, and the electrolyte that has flowed through the cell can be discharged through the discharge channel. To distribute the electrolyte more uniformly across the entire width of the cell and to remove the electrolyte more uniformly across the entire width of the cell, each supply channel and / or discharge channel can be branched once or several times between the outer opening and the cell interior, i.e., in the region of the frame shell of the cell frame. Alternatively, a series of separated supply channels and / or discharge channels for supplying or discharging the electrolyte may be provided in the cell frame. In both cases, the electrolyte enters the cell as uniformly as possible through the outlet opening of the supply channel on one side of the cell frame, and exits the cell as uniformly as possible through the discharge channel on the other side of the cell frame. This attempts to achieve the most uniform flow possible through the cell. Each supply channel is connected to the supply line at its other end via an inlet opening. This allows the electrolyte to reach the corresponding cell interior from the supply line through at least one supply channel in the cell frame of each half-cell.

[0010] If necessary, multiple electrochemical cells of the same type are combined in a single redox flow cell. For this purpose, these cells are usually stacked on top of each other. Therefore, the entire set of these cells is also called a cell stack. The electrolyte usually flows in parallel to each other in the individual cells, but these cells are usually connected in series electrically. Thus, these cells are usually connected in parallel fluidically and in series electrically. In this case, the charge state of the electrolyte is always the same in one of the half cells of each cell stack. Each half cell is connected to supply and removal lines in order to distribute the electrolyte to each half cell of the cell stack and to discharge the electrolyte from each half cell simultaneously. Since different electrolytes flow within each half cell or each cell of a single cell, these two electrolytes need to be separated from each other as they pass through the cell stack. Therefore, two separate supply lines and two separate removal lines are usually provided along the cell stack. Each of these channels is typically partially formed by the cell frame itself. For this purpose, the cell frame has four holes. These holes extend along the cell stack, are arranged in succession, and are separated from each other by sealing material if necessary, to form supply and removal lines.

[0011] As is known from various electrochemical cells, it is advantageous for increasing power density when at least one of the electrodes in one half-cell is at least partially fitted into the cell interior, is porous, and the corresponding electrolyte flows through the electrode. However, the increase in power density is often insufficient. This indicates that the surface provided by the electrode is not being fully utilized, or is not being utilized as effectively as possible. This can be explained by non-uniform flow through the electrode, as can also be observed in flows through porous solids. Since pressure loss depends largely on the respective free-flow cross-section and volumetric flow rate, even slight non-uniformity of porosity causes non-uniform flow. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] European Patent Application Publication No. 0051766(A1) [Patent Document 2] U.S. Patent Application Publication No. 2004 / 0170893(A1) [Overview of the project] [Means for solving the problem]

[0013] Therefore, the present invention is based on the challenge of designing and further developing the types of cell frames, electrochemical cells, cell stacks, and methods mentioned at the beginning and described in more detail above, so as to increase power density.

[0014] The problem is that in the cell frame described in the premise of claim 1, the supply channel includes at least one transport channel for transporting electrolyte into the cell via the supply channel, with an inlet opening at least partially connected to an outlet opening, and a channel for partially returning the supplied electrolyte in the opposite direction to the transport direction of the supplied electrolyte within the transport channel. 2 The system has two return channels, and the return channels are in fluid contact with the transport channel via at least one inlet opening for the inflow of the electrolyte to be returned and an outlet opening for the outflow of the electrolyte to be returned, and the inlet opening and the outlet opening are separated from each other in the transport direction of the electrolyte being supplied. The transport channel has at least a partial fluid chamber between at least one inlet opening and at least one outlet opening of the return channel, so that the supplied electrolyte can flow alternately through the fluid chamber toward the outlet opening in at least two different main streams, and as a result, it flows into the cell from the outlet opening in at least two different outlet directions. This will resolve the issue.

[0015] The aforementioned problem is, 8 In the electrochemical cell described in the premise section of the above, at least one cell frame is as described in claim 1 to 7 The problem is solved by designing according to one of the following terms.

[0016] The aforementioned problem is further addressed by claim 11 In the cell stack described in the premise section, the electrochemical cell is as claimed.8 ~ 10 It is solved by being designed according to any one of the following.

[0017] Furthermore, the above problem is solved by the method of operation of the electrochemical cell according to claim 12 According to, claim 8 ~ 10 Or the cell stack according to claim 11 It is solved by the method of operation described in. In this method, - The electrolytic solution is fed into at least one cell interior of at least one cell frame of at least one half cell via a feed channel, - The electrolytic solution flows through a transport channel, particularly a flow chamber ,of When flowing tree, At least two different main flows Temporarily alternating Direction of the outlet opening Shape Formed, and as a result, These mainstreams In at least two different outlet directions Alternately from the outlet opening Into the cell Inflow .

[0018] The present invention has found that it is advantageous from the viewpoint of output density when the feed channel is divided into at least one transport channel and at least one return channel. In this case, the transport channel extends between an inlet opening for allowing the fed electrolytic solution to flow in and an outlet opening of the fed electrolytic solution for allowing the fed electrolytic solution to flow out into the cell. The inlet opening and the outlet opening of the feed channel and the transport channel may coincide. However, this is not essential. However, at least the inlet opening of the feed channel and the outlet opening of the feed channel will be at least partially connected to each other via the transport channel.

[0019] Furthermore, it may be appropriate that the inlet opening of at least one feed channel defines the transition portion of the electrolytic solution fed from the supply line to the feed channel, and the outlet opening of the feed channel defines the transition portion of the electrolytic solution into the cell interior. However, this is not essential either. In particular, a cell frame design is conceivable in which the exact end position of the supply line and the exact start position of the feed channel, or the exact end position of the feed channel and the exact start position inside the cell, cannot be absolutely and reliably determined. However, this is also of secondary importance for the present invention. The reason is that the specific extent of the feed channel is less important than the flow rate in the feed channel. Furthermore, the feed channel can be understood as a supply line when the periphery of the feed channel is completely accommodated within the cell frame. However, it may also be sufficient if the feed channel is incorporated into the cell frame as an open channel. This can simplify the production of the cell frame, for example, in an injection molding process. In this case, the feed channel is closed by a component adjacent to the corresponding side of the cell frame to form the supply line. Here, the same applies to the transport channel and the return channel.

[0020] The return channel branches off from the transport channel and guides the branched electrolytic solution back to the region of the transport channel provided upstream of the branch point into the return channel, as viewed in the flow direction of the electrolytic solution in the transport channel. Thus, a part of the electrolytic solution is returned. Or a part of the electrolytic solution is guided in a loop within the feed channel. Thus, the returned electrolytic solution enters the inlet opening of the return channel from the transport channel and re-enters the transport channel of the feed channel via the outlet opening, that is, in front of the inlet opening in the transport direction. Thus, the returned electrolytic solution interacts with the fed electrolytic solution flowing in the transport channel in the outflow region from the return channel to the transport channel.

[0021] This interaction depends, for example, on the angle between the flowing returned electrolyte and the supplied electrolyte flowing in the transport direction within the transport channel in this region. Furthermore, it is preferable that this angle is predetermined and fixed by the design of the supply channel. However, the corresponding interaction also depends on the volumetric flow rate and velocity of the electrolyte returned to the transport channel. Thus, the flow of the returned electrolyte can deflect the flow of the electrolyte supplied within the transport channel to varying degrees. The degree of deflection depends on the amount of returned electrolyte and / or the velocity of the returned electrolyte flowing out of the outlet opening of the return channel into the transport channel.

[0022] The supply channel can be designed such that the strength of the interaction between the returned electrolyte and the electrolyte being supplied in the region of the return channel's outlet opening affects the amount or proportion of supplied electrolyte entering the return channel through at least one inlet opening, without being supplied to the outlet opening of the transport channel or the supply channel. This is particularly advantageous when the large volumetric flow rate of electrolyte returning to the transport channel through the return channel's outlet opening affects the electrolyte flow in the transport channel, resulting in a smaller volumetric flow rate of returned electrolyte entering the return channel through the inlet opening. In this case, the influence of the returned electrolyte on the flow of supplied electrolyte in the region of the return channel's outlet opening is reduced. By utilizing this, if the supply channel is properly designed, the flow of supplied electrolyte can be directed into the transport channel in such a way that the volumetric flow rate or proportion of supplied electrolyte entering the return channel's inlet opening is larger.

[0023] Therefore, this allows the flow through the transport channel to be changed multiple times over time without further intervention, thereby ensuring that at least two flow states alternate. If the regions of the transport channel adjacent to the cell interior are designed such that, as a result of the two flow states, the supplied electrolyte alternately flows into the cell interior in at least nearly different directions and / or through different outlet openings, then a constant flow dispersion will not form inside the cell. Rather, at least a changing flow dispersion will occur inside the cell. This prevents the formation of dead spaces inside the cell, particularly around the electrodes, where the electrolyte does not flow at all or only a little, due to the constant flow dispersion. In this case, it is more likely that the dead spaces formed over time will be less or smaller, and / or the location of the dead spaces will change over time. What is ultimately achieved is that the inner surface provided by the electrodes can be used more effectively for electrochemical reactions.

[0024] In this context, the fundamental principle of fluid dynamics—that an expansion of the free-flow cross-section within a supply channel leads to the formation of a jet of electrolyte flowing into that expanded region, and that this jet tends to contact one side of the wall of the transport channel—can be used in the design of supply channels, and especially transport channels. A higher flow velocity exists in this region of the wall than on the opposite side. Depending on the extent to which the returned electrolyte affects the flow in this region, the flow will contact multiple different sides of the wall. Over longer distances, the flow, or its velocity, becomes more uniform again due to friction. Therefore, supply channels, or transport channels, should not be designed to be excessively long, but they still need to be long enough, as a certain distance of flow is required to contact multiple different sides of the wall.

[0025] Each cell frame can be used particularly advantageously when these cell frames form part of an electrochemical cell or part of a corresponding cell stack. Here, the advantages already mentioned above are realized. These advantages can be used particularly advantageously in relation to the electrochemical cell or cell stack of a redox flow battery. Each electrochemical cell preferably has two cell interiors; however, in special cases, three or more cell interiors may be provided. If necessary, it is preferable that the individual cell interiors be separated from each other by a semipermeable membrane. Furthermore, if the number of cell interiors is odd, the intermediate cell interiors can be designed as a kind of mixed cell interior, half of which belongs to one half of the electrochemical cell and the other half to the other half of the electrochemical cell.

[0026] From a methodological standpoint, the cell frame described above conveniently delivers electrolyte into the cells of at least one half-cell cell frame via at least one supply channel. As the electrolyte flows through the supply channel, it passes through a transport channel, preferably a fluid chamber of the transport channel. In the process, the delivered electrolyte forms at least two distinct main streams. A main stream should be understood as the part of the flow with the highest area-specific flow rate. In the region of the supply channel where the flow is non-uniform, there are areas with relatively strong flow and areas with relatively weak flow at the point in time when the flow is non-uniform. In this process, the areas with relatively strong flow form the main stream, while the areas with relatively weak flow do not contribute much to the volumetric flow rate of the electrolyte. If the flow in each region is represented by multiple flow lines, the multiple flow lines along the main stream will be close to each other, while the multiple flow lines in the region outside the main stream will be significantly far apart from each other. Multiple flowlines within a main flow will extend at least nearly, or at least substantially, parallel to one another, while multiple flowlines outside the main flow may extend independently of one another. This may occur, for example, when significant turbulence of the electrolyte occurs in the region outside the main flow. Such turbulence should be absent or at least significantly reduced within the main flow.

[0027] The main flow is not constant over time, and at least two different main flows may be observed at multiple different points in time. In addition, the time of one main flow alternates with the time of the other main flow. However, each of these main flows is directed toward the outlet opening. This is because, in all cases, the majority of the electrolyte supplied into the cell is supplied by the main flow. In accordance with the alternating switching of these main flows, the direction of the flow of these main flows into the cell of the cell frame through the outlet opening also alternates. Therefore, the flow of electrolyte flowing into the cell, preferably through the inside of the cell or through electrodes at least partially provided therein, also changes repeatedly, or continuously if necessary.

[0028] In the first particularly preferred cell frame, the transport channel has a fluid chamber at least partially between at least one inlet opening and at least one outlet opening of the return channel, so that the supplied electrolyte flows alternately through the fluid chamber toward the outlet opening in at least two different main streams, and as a result flows into the cell interior from the outlet opening in at least two different outlet directions. This enables a variable flow of electrolyte into the cell interior, and consequently a higher power density. In this context, it is particularly preferred if the fluid chamber is designed so that these main streams alternate at least at a nearly constant frequency. This makes the flow state more predictable, thus leading to an easier and more reliable increase in power density. It is even more advantageous if the fluid chamber is designed so that the frequency increases at least nearly linearly with increasing volumetric flow rate through the transport channel. The larger the volumetric flow rate, the greater the risk of non-uniform flow with a significant dead zone. Therefore, it is all the more important to increase the frequency of changes in the direction of electrolyte flow from the transport channel into the cell interior.

[0029] Alternatively, or in addition, the transport channel may have at least a portion of a fluid chamber between at least one inlet opening and at least one outlet opening of the return channel, the fluid chamber may at least partially form a free flow cross-section having a cross-sectional area corresponding to at least twice, preferably at least 2.5 times, and particularly at least 3 times, the cross-sectional area of ​​the free flow cross-section of the inlet opening and / or outlet opening of the supply channel and / or transport channel. This allows the supplied electrolyte to enter the larger cross-section of the fluid chamber like a free jet, and depending on the flow state, it may, for example, be more likely to come into contact with one side of the fluid chamber wall or the other side of the fluid chamber wall. This may form two alternating main streams within the fluid chamber. This results in two alternating main streams, on the one hand, and furthermore, alternating the direction in which the supplied electrolyte is guided from the supply channel into the cell interior.

[0030] If the cross-sectional area of ​​the free-flow cross-section at the outlet opening of the supply channel is greater than the cross-sectional area of ​​the free-flow cross-section at the outlet opening of the fluid chamber, an expansion of the supply channel can be brought about at the end of the supply channel. This allows the electrolyte to flow into the cell in multiple different directions in a simple manner without additional moving parts. This is particularly applicable when the transport channel expands in a funnel shape in this region. In this case, to simplify the supply channel, it is preferable that this expansion be located immediately after the fluid chamber in the direction of transport of the electrolyte being supplied. Similarly, it is structurally simple when the transport channel expands to merge with the outlet opening of the supply channel.

[0031] If a supply channel has at least two return channels for partially returning the supplied electrolyte in the opposite direction to the transport direction of the supplied electrolyte in the transport channel, the flow of the supplied electrolyte can be easily and reliably changed to at least two different main flows. This allows both return channels to continuously influence the deflection of the main flows in the region of the outlet opening of each return line. For simplification and reliability of the supply channel, it is useful when these return channels are located on the opposite side of the transport channel. In addition, easy and intentional return of the electrolyte can be achieved, especially when these return channels are not connected to each other.

[0032] To achieve the most uniform flow possible within the cell, particularly to the electrodes located therein, it may be reasonable to provide at least two, preferably at least four, and especially at least six, feeding channels per cell frame. For the same reason, it is useful to provide these feeding channels on the same side of the cell frame. Regardless of this, it is preferable that these feeding channels be provided independently of each other to avoid mutual interference. Nevertheless, various feeding channels can be connected to a common supply line on the inflow side. This can result in a relatively simple and functional design of the cell frame. In this case, in other respects, it is preferable that these feeding channels be provided continuously in parallel and separated from each other.

[0033] The advantages of the corresponding cell frames described above are particularly effective in increasing the power density of the electrochemical cell when a packing element with an open-pore structure is provided inside the cell. It is preferable that this packing element fills the inside of the cell at least almost completely. Further useful for simultaneously achieving good flow through the open-pore structure and good reactivity per unit volume may be when the packing element is designed as a graphite felt-like integrated packing element and / or as an electrode.

[0034] Regardless of this, if necessary, a more uniform flow can be brought into the cell by distributing at least substantially uniformly all outlet channels and / or all feed channels of at least one cell frame across one side of at least one cell frame. This ultimately allows for better utilization of the resulting free-flow cross-section and, consequently, a higher power density can be achieved.

[0035] In the first particularly preferred electrochemical cell, the interior of at least one cell is bounded around the cell frame on one side, bounded on one side to a semipermeable membrane, and bounded on the other side to an electrode or dipole plate. This enables a simple, cost-effective, and highly functional structure for the electrochemical cell. Alternatively, or in addition, the interior of the cell and the cell frame can be circumferentially arranged on the frame plane. This also simplifies the structure of the electrochemical cell, especially when many electrochemical cells are combined into a single cell stack.

[0036] If the feeding channels, transport channels, and / or return channels are aligned at least substantially parallel to the frame plane, proper conduction of the electrolyte into the cell is structurally easily achieved. This is especially true when the feeding channels, transport channels, and / or return channels are aligned to the frame plane along their entire longitudinal length.

[0037] In the first particularly preferred method, the electrolyte flow, while flowing through the transport channel, and especially while flowing through the fluid chamber, temporarily alternates between at least two main flows. This alternation should be understood as an automatic or forced change between at least two main flows during the operation of the supply channel. In this context, how rapid or abrupt these changes between the main flows are is not necessarily important. However, it is preferable that the changes in flow to at least two main flows alternate at a constant frequency. This is because, in principle, a more uniform and, consequently, more efficient flow can be achieved through the cell. In addition, it may be useful if the frequency at which the supplied electrolyte flow changes between at least two main flows is at least approximately proportional to the volumetric flow rate of the supplied electrolyte. In this case, as the volumetric flow rate increases, the electrolyte flow into the cell is temporarily and rapidly homogenized. This is preferable because, otherwise, as the volumetric flow rate increases, the flow differences when flowing through the cell become larger.

[0038] Achieving a uniform flow of electrolyte through the cell can also be done by assigning at least two main flows to opposing sides of the fluid chamber, and, if necessary, to opposing return channels. In this case, the desired flow state can be controlled more easily and reliably. To supply larger volumetric electrolyte into the cell in a structurally simple manner, it may be useful to distribute the supplied electrolyte from at least one common supply line to multiple supply channels in at least one cell frame, and to supply the supplied electrolyte into the cell in parallel through the multiple supply channels.

[0039] The present invention will be described in more detail below with reference to drawings that show only one exemplary embodiment. The drawings shown are as follows: [Brief explanation of the drawing]

[0040] [Figure 1A] This is a longitudinal cross-sectional view of a cell stack according to the present invention in the form of a redox flow battery. [Figure 1B]This is a longitudinal cross-sectional view of a cell stack according to the present invention in the form of a redox flow battery. [Figure 2] Figure 1 is a top view of the cell frame according to the present invention of the cell stack. [Figure 3] Figure 3 shows the details of the cell frame. [Figure 4A] Figure 3 shows a detail of the cell frame at a specific point in time during operation of the electrochemical cell according to the present invention, which has the cell frame shown in Figure 2. [Figure 4B] Figure 3 shows a detail of the cell frame at another point in time during operation of the electrochemical cell according to the present invention, which has the cell frame shown in Figure 2. [Figure 4C] Figure 3 shows a detail of the cell frame at another point in time during operation of the electrochemical cell according to the present invention, which has the cell frame shown in Figure 2. [Figure 4D] Figure 3 shows a detail of the cell frame at another point in time during operation of the electrochemical cell according to the present invention, which has the cell frame shown in Figure 2. [Modes for carrying out the invention]

[0041] Figures 1A and 1B show a cell stack 1, i.e., a cell stack of an electrochemical cell, particularly in the form of a redox flow cell, in a longitudinal cross-section. The cell stack 1 comprises three cells 2, each having two half-cells 3, and each of the two half-cells 3 has a corresponding electrolyte. Each half-cell 3 has a cell frame 4. The cell frame 4 has a cell interior 5 through which the electrolyte stored in a storage container can be conducted. An electrode 6 fits at least partially into the cell interior 5. The electrode 6 further seals and closes the cell interior 5 on one side. The electrolytes flowing through each cell interior 5 are different from each other. Each cell interior 5 is closed by a semipermeable membrane 7 provided between the cell frames 4 of the two half-cells 3, on the side opposite to the electrode 6 adjacent to the cell frame 4 of the second half-cell 3 of the same electrochemical cell 2. Thus, the two different electrolytes of the two half-cells 3 are prevented from convecting into the cell interior 5 of the cell frame 4 of the other half-cell 3. However, ions can pass from one electrolyte to the other by diffusion across the semipermeable membrane 7. This results in charge transport. Electrons are released or received due to redox reactions of redox pairs in the electrolyte at each electrode 6 of each half-cell 3 of one cell 2. The released electrons can flow from one electrode 6 to the other electrode 6 of one cell 2 via electrical connections, which are provided on the outside of the redox flow battery and have electrical demands if necessary. Which reaction occurs at which electrode 6 depends on whether the redox flow battery is being charged or discharged.

[0042] In the illustrated cell stack 1, each electrode 6 is positioned flat against the outer surface 8 of the cell frame 4. Therefore, these electrodes 6 form a frame surface in the contact area with the outer surface 8 of the cell frame 4. This frame surface functions as a sealing surface 9. A sealing material 10 exists between the mutually facing outer surfaces 8 of both cell frames 4 of one cell 2, and a semipermeable membrane 7 is contained therein in a sealing manner. The sealing material 10 is adjacent to the outer surfaces 8 of both adjacent cell frames 4, and thus forms a frame surface that functions as a sealing surface 9.

[0043] In the illustrated redox flow battery, four channels extend longitudinally to the cell stack 1. Two of these are supply lines 11 for supplying two electrolytes to the cell interiors 5 of each cell frame 4. The other two channels are removal lines 12 for draining the electrolyte from the cell interiors 5 of each cell frame 4. Figure 1A shows one supply line 11 and one removal line 12. Multiple supply channels 13 branch off from the supply line 11 in one half-cell 3 of each cell 2. The electrolyte can be supplied to the cell interiors 5 of each half-cell 3 via the supply channels 13. Discharge channels 14 are provided on the opposite side of each cell frame 4. The electrolyte can be discharged from the cell interiors 5 to the removal lines 12 via the discharge channels 14. The supply line 11 and the removal line 12, not shown in Figure 1A, allow the second electrolyte to flow through the cell interiors 5 of the other half-cell 3 via the same supply channels 13 and discharge channels 14.

[0044] Figure 2 shows a top view of the cell frame 4. Four holes 15 are provided at the corners of the cell frame 4. Each hole 15 forms part of a supply line 11 or a removal line 12. The supply channels 13 and discharge channels 14 are recessed into the illustrated outer surface 8 of the frame shell 16 of the cell frame 4 as recesses or open channels. The frame shell 16 surrounds the inside 5 of the cell. The supply channels 13 and discharge channels 14 are closed during assembly into the cell stack 1 to form a closed line around them. In the illustrated cell stack 1, this is done, for example, by a sealant 10 and electrodes 6. However, the electrodes 6 can also be spatially separated from the supply line 11 and removal line 12 by the sealant 10 and / or the electrical insulation of these sealants. Alternatively, or in addition, the sealant 10 adjacent to the semipermeable membrane 7, supply channels 13, and discharge channels 14 can be omitted.

[0045] In the illustrated embodiment, all discharge channels 14 are connected to one another in order to concentrate the electrolyte into the removal line 12. However, this is not mandatory. All supply channels 13 can also be started individually from the supply line 11. However, in the illustrated embodiment of the cell frame 4, branches are provided to distribute the electrolyte supplied via the supply line 11 to each supply channel 13 in stages. To ensure that the pressure drop across all supply channels 13, and consequently across the flow through all supply channels 13, is as uniform as possible, the electrolyte is supplied to the supply channels 13 via a collection line 17 having a large free cross-section. Thus, the pressure loss of the electrolyte flow supplied into the cell interior 5 is at least substantially determined by the pressure loss across all supply channels 13. In the illustrated embodiment of the cell frame 4, the supply channels 13 are designed differently from the discharge channels 14.

[0046] Figure 3 shows one of the similarly designed feeding channels 13 of the cell frame 4 of Figure 2. The illustrated feeding channel 13 has an inlet opening 18 and an outlet opening 19. In the illustrated feeding channel 13, the positions of the inlet opening 18 and the outlet opening 19 may be determined such that the outlet opening 19 defines a direct transition from the feeding channel 13 to the cell interior 5, and the inlet opening 18 is positioned at the beginning of the widening of the free-flowing cross-section. In the illustrated feeding channel 13, the inlet opening 18 may be assumed to be located at a constriction 20 of the free-flowing cross-section for the electrolyte. However, it is not usually necessary for each constriction 20 to be located where a narrowing free-flowing cross-section merges with a widening free-flowing cross-section. In the illustrated feeding channel 13, the inlet opening 18 for feeding the electrolyte into the cell interior 5 is also provided immediately before or adjacent to the region of the feeding channel 13 where the transport channel 21 and the two return channels 22 are connected to each other. The transport channel 21 is responsible for transporting the electrolyte solution to be supplied to the inside of the cell 5. Therefore, the transport channel 21 connects the inlet opening 18 and the outlet opening 19 of the supply channel 13 to each other, at least partially.

[0047] In this case, the inlet opening 23 of the transport channel 21 may coincide with the inlet opening 18 of the supply channel 13, as shown in the illustration for the supply channel 13. Alternatively, the inlet opening 23 of the transport channel 21 may be separated from the inlet opening 18 of the supply channel 13 in the transport direction T of the electrolyte supplied towards the inside of the cell 5. However, as a rule, there is no gap between the inlet openings 18 and 23. Similarly, the outlet opening 24 of the transport channel 21 may coincide with the outlet opening 19 of the supply channel 13. However, the outlet opening 24 of the transport channel 21 may be positioned in front of the outlet opening 19 of the supply channel 13 in the transport direction T of the electrolyte supplied towards the inside of the cell 5.

[0048] In this regard, a suitable illustrated supply channel 13 further comprises two return channels 22 in addition to the transport channel 21. These return channels 22 are located on the opposite side of the transport channel 21, and a portion of the supplied electrolyte is returned through these return channels 22 without being supplied into the cell interior 5. The returned electrolyte flows from the transport channel 21 into the return channels 22 through the inlet opening 25, returns along the return channels 22 in the opposite direction to the transport direction T of the electrolyte in the transport channel 21, and is then returned to the transport channel 21 again through the outlet opening 26.

[0049] The transport channel 21 comprises a fluid chamber 27. The fluid chamber 27 is at least partially located between the outlet opening 26 and the inlet opening 25 of the return channel 22. The fluid chamber 27 has a larger cross-sectional area of ​​free flow cross-section than the inlet opening 18 of the supply channel 13 and / or the inlet opening 23 of the transport channel 21. This allows for the formation of several significantly different flow states within the fluid chamber 27. In the case of the illustrated supply channel 13, which is preferred in this regard, the cross-sectional area of ​​the free flow cross-section of the outlet opening 19 of the supply channel 13 is larger than the cross-sectional area of ​​the free flow cross-section of the outlet opening 28 of the fluid chamber 27, so that the supply channel 13 expands after the fluid chamber 27 toward the cell interior 5, allowing the electrolyte supplied to the cell interior 5 to flow into the cell interior 5 in several different directions. This is also facilitated by the merging of the supply channel 13 toward the cell interior 5 adjacent to the corresponding expansion of the free flow cross-section. Since the transport channel 21 or supply channel 13 is located immediately after the fluid chamber 27 and spreads out in a funnel shape in the transport direction T of the electrolyte being supplied, it is preferable that the supply channel 13 be designed to be relatively short.

[0050] Figures 4A to 4D show different points in time in the supply channel 13 through which the supplied electrolyte flows. First, Figure 4A shows the basic flow state within the supply channel 13. For clarification, please refer to the reference numerals in Figure 3 below. The supplied electrolyte flows into the supply channel 13 through the inlet opening 18 and then into the fluid chamber 27 of the transport channel 21. The cross-sectional area of ​​the free flow cross-section is approximately three or four times the cross-sectional area of ​​the transport channel 21 or the fluid chamber 27 in the region of the inlet openings 23 and 29. Therefore, a kind of free jet is formed in the region of the fluid chamber 27 after the inlet opening 23. Consequently, the flow within the fluid chamber 27 is not uniform, and a main flow is formed that contains at least the majority of the volumetric flow rate of the supplied electrolyte. In contrast, outside the main flow within the fluid chamber 27 of the transport channel 21, the flow velocity is significantly lower. Therefore, significantly less electrolyte flows through that area. In addition, the electrolyte flowing through it swirls violently.

[0051] Due to the fundamental principles of fluid dynamics, the flow of electrolyte entering the fluid chamber 27 like a free jet will likely come into contact with the walls of the fluid chamber 27. As shown in the explanatory diagram in Figure 4A, the main flow of electrolyte in the fluid chamber 27 comes into contact with the left side of the fluid chamber 27 and spreads out on this side toward the end of the fluid chamber 27 allocated to the cell interior 5, and consequently spreads toward the outlet openings 19 and 24 of the transport channel 21 and therefore the supply channel 13. As the main flow flows along the left side of the fluid chamber 27, the main flow enters the region of the constriction 30 at a constant angle toward the end of the fluid chamber 27. At the constriction 30, or the leading edge of the fluid chamber 27, the cross-sectional area of ​​the free flow cross-section is approximately one-third or one-quarter of that of the central part of the fluid chamber 27. After the end of the fluid chamber 27, or the constriction 30, the transport channel 21 or supply channel 13 widens, and the free flow cross-section becomes larger. For this reason, the main flow of electrolyte from the fluid chamber 27 can enter the cell interior 5 from the outlet openings 19 and 24 of the transport channel 21 or the supply channel 13 at the same angle as when the main flow enters the constricted section 30.

[0052] However, a portion of the main flow of electrolyte does not pass through the constricted section 30, but is pushed into the return channel 22 from the inlet opening 25 located in front of the end of the fluid chamber 27 in the electrolyte transport direction T. The returned electrolyte is guided along the return channel 22 in the opposite direction to the electrolyte transport direction T within the fluid chamber 27, through the outlet opening 26 in the region of the starting end of the fluid chamber 27 or the starting end of the transport channel 21, and returned to the fluid chamber 27 or the transport channel 21. There, the returned electrolyte interacts with the free jet of electrolyte being supplied into the fluid chamber 27.

[0053] In the case shown in Figure 4A, the volumetric flow rates of the electrolyte returned through the two return channels 22 are not the same. Since the main flow of electrolyte flows along the left side of the fluid chamber 27, the amount of electrolyte pushed into the left return channel 22 is much greater than the amount pushed into the opposite right return channel 22. As a result, much more electrolyte flows out of the outlet opening of the left return channel 22. In the case of the illustrated feeding channel 13, which is preferable in this respect, the returned electrolyte flows out of the outlet opening 26 almost perpendicular to the original direction of the free jet, so the free jet is deflected to the right toward the wall of the fluid chamber 27 by the returned electrolyte, as shown in the sequence in Figure 4B. Therefore, the main flow of the supplied electrolyte changes after a certain period of time and then flows along the right side of the fluid chamber 27 toward the inside of the cell 5.

[0054] This is shown in Figure 4C. Subsequently, the main flow enters the constricted section 30 at the end of the fluid chamber 27 at the opposite angle, and due to the design of the supply channel 13, also enters the cell interior 5 from the supply channel 13 at a similar angle. However, because the main flow moves within the fluid chamber 27, more electrolyte is returned by the right return channel 22 than by the left return channel 22, so the returned electrolyte flowing out from the right outlet opening 26 of the right return channel 22 pushes the free jet in this region back to the left, as shown in Figure 4D. As a result, the main flow of supplied electrolyte returns to the left again, and the above cycle is repeated. In this process, if the volumetric flow rate of supplied electrolyte is at least approximately constant, the cycle time, and therefore the corresponding frequency, is maintained at least approximately constant. [Explanation of symbols]

[0055] 1 Cell Stack 2 cells 3 Half Cells 4-cell frame 5 cells inside 6 electrodes 7 Semi-permeable membrane 8 External surface 9 Sealing surface 10. Sealing material 11 Supply Line 12 Removal Lines 13 Supply Channels 14 Emission Channels 15 holes 16 Frame Shell 17 Collection lines 18 Entrance opening 19 Exit opening 20 Stenosis 21 Transportation Channels 22 branch channels 23 Entrance opening 24 Exit opening 25 Inflow opening 26 Outlet opening 27 Fluid chamber 28 Exit opening 29 Entrance opening 30 Stenosis T Transport direction

Claims

1. A cell frame (4) for forming an electrochemical cell (2), wherein the cell frame (4) surrounds the periphery of at least one cell interior (5) and comprises at least one supply channel (13) for supplying an electrolyte to the cell interior (5), the supply channel (13) having an inlet opening (18) separated from the cell interior (5) for the electrolyte to be supplied and an outlet opening (19) adjacent to the cell interior (5) for allowing the supplied electrolyte to flow out into the cell interior (5), in the cell frame (4), The supply channel (13) has at least one transport channel (21) connecting the inlet opening (18) to the outlet opening (19) for transporting the electrolyte into the cell interior (5) via the supply channel (13), and two return channels (22) for partially returning the supplied electrolyte in the opposite direction (T) to the transport direction of the supplied electrolyte within the transport channel (21), and the return channels (22) have at least one inlet opening (25) for letting the returned electrolyte in and an outlet opening (26) for letting the returned electrolyte out, through the transport channel The fluid is in contact with the channel (21), the inlet opening and the outlet opening are separated from each other in the transport direction (T) of the electrolyte being supplied, and the transport channel (21) has at least a portion of a fluid chamber (27) between the at least one inlet opening (25) and the at least one outlet opening (26) of the return channel, so that the electrolyte being supplied can flow alternately through the fluid chamber (27) in the direction of the outlet opening (19) in at least two different main streams, and as a result, it flows from the outlet opening (19) into the cell interior (5) in at least two different outlet directions. A cell frame characterized by the following features.

2. The cell frame according to claim 1, wherein the transport channel (21) has at least a portion of a fluid chamber (27) between the at least one inlet opening (25) and the at least one outlet opening (26) of the return channel (22), and the fluid chamber (27) at least partially forms a free flow cross section having a cross section area equivalent to at least twice the cross section area of ​​the free flow cross section of the inlet openings (18, 23) and / or outlet openings (19, 24) of the supply channel (13) and / or the transport channel (21).

3. The cell frame according to claim 2, characterized in that the cross-sectional area of ​​the free flow cross-section of the outlet opening (19) of the supply channel (13) is greater than the cross-sectional area of ​​the free flow cross-section of the outlet opening (28) of the fluid chamber (27).

4. The cell frame according to any one of claims 1 to 3, characterized in that the two return channels (22) are arranged on opposite sides of the transport channel (21).

5. A cell frame according to any one of claims 1 to 4, characterized in that a packing element having an open pore structure is provided inside the cell (5).

6. A cell frame according to any one of claims 1 to 5, characterized in that it is provided with at least two feeding channels (13).

7. The cell frame according to claim 6, characterized in that all of the outlet channels (14) and / or the plurality of feed channels (13) of at least one cell frame (4) are uniformly distributed across the entire side of the at least one cell frame (4).

8. An electrochemical cell (2) having two half-cells (3), wherein the two half-cells are separated from each other by at least one semipermeable membrane (7), and each half-cell has at least one cell frame (4) surrounding at least one cell interior (5) for flowing an electrolyte, wherein at least one cell frame (4) is designed according to any one of claims 1 to 7.

9. The electrochemical cell according to claim 8, characterized in that the interior of at least one cell (5) is bounded around the cell frame (4) on one side, bounded on one side to the semipermeable membrane (7), and bounded on the opposite side to an electrode (6) or a bipolar plate, and / or the interior of the cell (5) and the cell frame (4) are arranged circumferentially on the frame plane.

10. The electrochemical cell according to claim 9, characterized in that the feeding channel (13), the transport channel (21), and / or the return channel (22) are aligned parallel to the frame plane.

11. A cell stack (1) comprising a plurality of electrochemical cells (2) that are adjacent to each other and firmly connected to each other, wherein the plurality of electrochemical cells (2) are designed according to any one of claims 8 to 10.

12. A method for operating an electrochemical cell (2) according to any one of claims 8 to 10, or a cell stack according to claim 11, - The electrolyte is supplied via the supply channel (13) to at least one cell interior (5) of at least one cell frame (4) of at least one half cell (3), - As the electrolyte flows through the transport channel (21), it temporarily and alternately forms at least two different main streams toward the outlet opening (19), and as a result, it alternately flows from the outlet opening (19) toward the inside of the cell (5) in at least two different outlet directions. A method of operation characterized by the following features.

13. The method according to claim 12, wherein the flow of the electrolyte being supplied temporarily alternates between the at least two main channels as it flows through the transport channel (21).

14. - The at least two main streams are assigned to opposite sides of the fluid chamber (27), and / or - The electrolyte to be supplied is distributed from at least one common supply line (11) to a plurality of supply channels (13) of at least one cell frame (4), and supplied parallel to the inside of the cell (5) via the plurality of supply channels (13). The method according to claim 12 or 13.

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