Electrochemical Cell, More Particularly of a Redox Flow Battery, and Corresponding Cell Stack

Abstract

Described and illustrated is an electrochemical cell, in particular a redox flow battery, with at least one cell frame and at least one electrode. The cell frame circumferentially encloses a cell interior. The cell frame has at least one feed channel for feeding electrolyte into the cell interior and at least one discharge channel for discharging electrolyte from the cell interior. The at least one cell frame has at least one finger element projecting into the cell interior and wherein the electrode is arranged at least in regions in the cell interior and on opposite sides of the at least one finger element. In order to achieve a more appropriate flow through, which reliably allows for a lower pressure loss and a higher power density, it is provided that the at least one feed channel and/or the at least one discharge channel is provided at least in sections in the finger element and that the at least one finger element has at least one outlet opening into the cell interior for the electrolyte to be fed and/or at least one inlet opening from the cell interior for the electrolyte to be discharged.

Claims

1. A electrochemical cell, in particular of a redox flow battery, having at least one cell frame and at least one electrode, wherein the cell frame circumferentially encloses a cell interior, wherein the cell frame has at least one feed channel for feeding electrolyte into the cell interior and at least one discharge channel for discharging electrolyte from the cell interior, wherein the at least one cell frame has at least one finger element projecting into the cell interior and wherein the electrode is arranged at least in regions in the cell interior and on opposite sides of the at least one finger element, wherein the at least one feed channel and/or the at least one discharge channel is provided at least in sections in the finger element, and in that the at least one finger element has at least one outlet opening into the cell interior for the electrolyte to be fed and/or at least one inlet opening from the cell interior for the electrolyte to be discharged.

2. The electrochemical cell according to claim 1, wherein the electrode in the cell interior has a porosity for the flow through of the electrolyte at least partially from the at least one feed channel to the at least one discharge channel.

3. The electrochemical cell according to claim 2, wherein a non-porous section of the electrode, in particular in the form of a bipolar plate, which is electrically conductively connected to a porous section of the electrode, closes the cell interior on a side opposite of a semipermeable membrane.

4. The electrochemical cell according to claim 1, wherein the at least one finger element is formed as a continuous strut bridging the cell interior and separating two cell chambers of the cell interior from each other.

5. The electrochemical cell according to claim 1, wherein the height of the at least one finger element corresponds at least in sections at least substantially to the height of the cell interior and/or of the cell frame in the corresponding region of the finger element, and in that, preferably, the finger element bears on one side against a semipermeable membrane and on the opposite side against a non-porous section of the electrode.

6. The electrochemical cell according to claim 1, wherein at least one flow channel is inset into, in particular the porous section, of the electrode, and in that, preferably, the at least one flow channel adjoins an inlet opening and/or outlet opening of the at least one finger element.

7. The electrochemical cell according to claim 6, wherein at least one flow channel of the electrode adjoining an inlet opening and at least one flow channel of the electrode adjoining an outlet opening, in particular in each case, are spaced apart from one another via a porous section of the electrode for the flow through of electrolyte.

8. The electrochemical cell according to claim 6, wherein flow channels adjoining at least one inlet opening and flow channels adjoining at least one outlet opening are in at least one direction each provided alternately with respect to one another and/or in that the at least one flow channel of the electrode and the at least one finger element of the cell frame are arranged at least substantially perpendicular to one another.

9. The electrochemical cell according to claim 1, wherein a plurality of finger elements arranged at least substantially parallel to one another is provided and/or that a plurality of at least substantially parallel flow channels is provided in the electrode.

10. The electrochemical cell according to claim 1, wherein an odd number of finger elements is provided and in that, preferably, the finger elements alternately comprise in the order of their arrangement at least partially a feed channel and a discharge channel.

11. The electrochemical cell according to claim 1, wherein the at least one finger element forms a grid structure.

12. The electrochemical cell according to claim 3, wherein the at least one finger element is materially bonded to the semipermeable membrane and/or to the non-porous section of the electrode, in particular the bipolar plate, and in that, preferably, the materially bonded connection is joined by means of adhesive bonding or welding.

13. The electrochemical cell according to claim 3, wherein the non-porous section of the electrode, in particular the bipolar plate, and the porous section of the electrode are not firmly connected to one another, and in that, preferably, the non-porous section of the electrode, in particular the bipolar plate, and the porous section of the electrode engage in one another in a form-fitting manner.

14. The electrochemical cell according to claim 13, wherein ribs of the non-porous section of the electrode, in particular of the bipolar plate, engage in a form-fitting manner in the porous section of the electrode, and in that, preferably, the ribs of the non-porous section of the electrode, in particular of the bipolar plate, engage at least in sections in a form-fitting manner in the flow channels of the porous section of the electrode.

15. A cell stack, in particular of a redox flow battery, comprising a plurality of electrochemical cells according to claim 1.

16. The cell stack according to claim 15, wherein the finger elements are provided in each case in both half-cells of the plurality of electrochemical cells and/or in that the finger elements of at least mutually adjacent half-cells are arranged in each case at least in sections at least substantially aligned with one another in the stacking direction of the electrochemical cells.

17. The cell stack according to claim 15, wherein the height of the respectively aligned sections of the finger elements corresponds at least substantially to the height of the respective cell interior and/or of the respective cell frame in each case in the region of the aligned sections of the finger elements, and in that, preferably, the respectively aligned sections of the finger elements bear on one side against a semipermeable membrane and on the opposite side against a non-porous section of the electrode, in particular of the bipolar plate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention is explained in more detail below by means of a drawing which merely illustrates an example of an embodiment. The drawing shows in

[0039] FIG. 1A-B a first cell stack according to the invention in the form of a redox flow battery in a longitudinal sectional view,

[0040] FIG. 2A-D a cell frame of an electrochemical cell according to the invention of the cell stack of FIG. 1 together with an associated electrode in the cell interior of the cell frame in a plan view and in opposite sectional views along a sectional plane B-B or C-C perpendicular to the plane of the cell frame,

[0041] FIG. 3 a part of the electrode from FIG. 2 in a perspective view and

[0042] FIG. 4 a detail of a second cell stack according to the invention in a magnified view.

DESCRIPTION OF THE INVENTION

[0043] In FIGS. 1A and 1B, a cell stack 1, i.e. a cell pack of an electrochemical cell 2, in particular in the form of a redox flow battery, is shown in a longitudinal sectional view. The cell stack 1 comprises three cells 2, each having two half-cells 3 with corresponding electrolytes. Each half-cell 3 has a cell frame 4 which comprises a cell interior 5 through which an electrolyte stored in a receiver tank can be passed and in which an electrode 6 engages at least partially, which moreover completes and closes off the cell interior 5 to one side. The electrolytes flowing through the cell interiors 5 differ from one another. The respective cell interior 5 is closed on the side facing away from the electrode 6 adjacent to the cell frame 4 of the second half-cell 3 of the same electrochemical cell 2 by a semipermeable membrane 7 provided between the cell frames 4 of the two half-cells 3. Convective transfer of the two different electrolytes of the two half-cells 3 into the cell interior 5 of the cell frame 4 of the other half-cell 3 is thus prevented. However, ions can pass from one electrolyte to the other electrolyte by diffusion via the semipermeable membrane 7, resulting in charge transport

[0044] Redox reactions of the redox pairs of the electrolytes at the electrodes 6 of the half-cells 3 of a cell 2 either release or absorb electrons. The released electrons can flow from one electrode 6 to the other electrode 6 of a cell 2 via an electrical connection provided outside the redox flow battery and having an electrical load if required. Which reactions take place at which electrode 6 depends on whether the redox flow battery is being charged or discharged.

[0045] In the cell stack 1 shown, the electrodes 6 lie flat on an outer side 8 of the cell frame 4. The electrode 6 thus forms a frame surface in the contact area with the outer side 8 of the cell frame 4, which acts as a sealing surface 9. Between the facing outer sides 8 of the cell frames 4 of a cell 2 is a sealing material 10 in which the membrane 7 is sealingly received. The sealing material 10 lies flat against the outer sides 8 of the adjacent cell frames 4 and thus forms frame surfaces which act as sealing surfaces 9.

[0046] Four channels extend longitudinally to the cell stack 1 in the redox flow battery shown. Two of these are supply lines 11 for feeding the two electrolytes to the cell interiors 5 of the cell frames 4. The two other channels are disposal lines 12 for discharging the electrolytes from the cell interiors 5 of the cell frames 4. FIG. 1A shows a supply line 11 and a disposal line 12 in each case. A feed channel 13 branches off from the supply line 11 in respectively one half-cell 3 of each cell 2, via which the electrolyte can be fed to the corresponding cell interior 5 of the half-cell 3. A discharge channel 14 is provided at opposite sections of the corresponding cell frames 4, via which the electrolyte can be discharged from the cell interiors 5 into the disposal line 12. The supply line 11 not shown in FIG. 1A and disposal line 12 also not shown enable the second electrolyte to flow through the respective other cell interiors 5 of the other half-cells 3 via a similar feed channel 13 and discharge channel 14.

[0047] FIGS. 2A-B show plan views of a cell frame 4 and sectional views along a common sectional plane but in opposite viewing directions. For the sake of clarity, FIG. 2A shows the cell frame without electrode and FIG. 2B shows the same cell frame with inserted electrode. In the sectional views according to FIG. 2C-D, the electrodes are also shown inserted. Four openings 15 are provided in the corners of the cell frame 3, each opening 15 forming part of a supply line 11 or a disposal line 12. The feed channel 13 and the discharge channel 14 are recessed as recesses or open channels in the shown outer side 8 of the frame casing 16 of the cell frame 4, which surrounds the cell interior 5. The feed channel 13 and the discharge channel 14 are closed to form circumferentially closed lines when assembled into a cell stack 1. In the cell stack 1 shown, this is done, for example and in sections, by the sealing materials 10 and the electrodes 6. However, the electrodes 6 could also be spatially separated from the supply lines 11 and the disposal lines 12 by sealing materials 10 and/or the electrical insulation of these materials. Alternatively or additionally, the sealing material 10 adjacent to the semipermeable membrane 7, the feed channels 13 and the discharge channels 14 could also be omitted.

[0048] The feed channel 13 and the discharge channel 14 are branched in the embodiment shown, so that the electrolyte can be fed distributed via the cell interior 5 via the feed channel 13 and discharged distributed via the discharge channel 14. However, this is not necessary. Thus, feed channels 13 branching off separately from the supply line 11 could also be provided. Likewise, discharge channels 14 connected separately to a disposal line 12 could also be provided.

[0049] The cell frame 4 shown, which is preferred in this respect, is provided circumferentially to the cell interior 5 and also has three finger elements 17 formed as struts, which extend transversely through the cell interior 5 and thus divide the cell interior 5 into four cell chambers 18, which are completely separated from one another in the cell frame 4 shown. Moreover, the finger elements 17 extend parallel to the plane of the cell frame 4 and parallel to each other as well as parallel to the longitudinal extension of the cell frame 4. Furthermore, the finger elements 17 are spaced at least substantially equidistant from the adjacent finger element 17 or the lateral edge 19 of the cell interior 5. In this way, cell chambers 18 of equal size are provided. In the cell frame 4 shown and preferred in this respect, two finger elements 17 each have a part of the feed channel 13 which is also formed as an open channel in the region of the finger elements 17 and is closed by the semipermeable membrane 7 or the electrode 6. The third and middle finger element 17, on the other hand, has a part of the discharge channel 14, which is also formed as an open channel, which is closed by the semipermeable membrane 7 or the electrode 6 when the cell 2 is assembled. In the cell frame 4 shown, parts of the discharge channel 14 are also still provided in the lateral edges 19, into which electrolyte can flow from the cell interior 5. However, parts of the feed channel 13 could also be provided in the sides of the cell frame 4. Then, however, finger elements 17 would preferably each follow inwardly with a part of the discharge channel 14. In this way, for example, the electrolyte is passed from the feed channel 13 to the discharge channel 14 via a cell chamber 18 in each case.

[0050] The electrolyte flows into the cell interior 5 via outlet openings 20, which are distributed along the longitudinal extent of the finger element 17. The electrolyte flows out of the cell interior 5 or the cell chambers 18 via inlet openings 21 into the discharge channel 14. In the cell frame 4 shown and preferred in this respect, the inlet openings 21 are provided in the finger element 17 and in the lateral edges 19 of the cell frame 4. If a feed channel 13 is provided in the lateral edges 19 of the cell frame 4, outlet openings 20 are preferably also provided there in order to allow the electrolyte to flow from there into the cell interior 5.

[0051] The outlet openings 20 and the inlet openings 21 are shown in FIGS. 2C-D. It is also shown that the finger elements 17 extend over at least substantially the entire height of the cell frame 4. However, a part of the height of the cell frame 4 in the region of the finger elements 17 is provided by the electrode 6. This section of the electrode 6 constitutes the non-porous section 22 of the electrode 6 in the form of a bipolar plate. The porous section 23 of the electrode 6 extends into the cell chambers 18 of the cell interior 5 and is provided in electrically conductive contact with the non-porous section 22 of the electrode 6. The porous section 23 of the electrode 6 has flow channels 24, one end of each of which connects to an outlet opening 20 of the feed channel 13 or an inlet opening 21 of the discharge channel 14. The flow channels 24 run parallel to one another and at an at least substantially equal distance from one another. Along the flow channels 24, ribs 26 are provided in the non-porous section 22 of the electrode 6, which ribs engage in a form-fitting manner in the flow channels 24 of the porous section 23 of the electrode 6.

[0052] This form fit is also shown in FIG. 3. However, as an alternative to the form fit shown, another form fit could also be provided between the porous section 23 and the non-porous section 22 of the electrode 6. In this case, the flow channels 24 are provided with a free end 25 so that the flow channels 24 are not in direct contact with each other. The flow channels 24 are each spaced apart from each other via porous sections of the electrode 6. In addition, the flow channels 24 extend over the predominant width of the cell chamber 18. The length of the flow channels 24 being approximately equal in this case. In this regard, it makes no difference whether the flow channels 24 connect to a feed channel 13 or a discharge channel 14. In the case of the electrode 6 shown, the flow channels 24 are cut out of the porous material of the electrode 6. The porous material of the electrode 6 is a kind of felt made of graphite fibers. In contrast, the non-porous section 22 of the electrode 6 is in the form of a solid plate of graphite, from which the ribs 26 for the form fit with the porous section 23 of the electrode 6 project. In this case, the thickness of the porous section 23 of the electrode 6 is significantly greater than the height of the ribs 26. In many cases, it is convenient if the thickness of the porous section 23 of the electrode 6 is at least twice as great as the height of the ribs 26 of the non-porous section 22 of the electrode 6. In the present case, the thickness of the porous section 23 of the electrode 6 is at least three times as great as the height of the ribs 26.

[0053] FIG. 4 shows a detail of a section through a cell stack 1 extending over several half-cells 3. Here, each of the half-cells 3 comprises a cell frame 4, with a semipermeable membrane 7 or a non-porous section 22 of the electrode 6 provided between each two cell frames 4. Here, the semipermeable membrane 7 and the non-porous section 22 of the electrode 6 are connected to the associated cell frames 4 without a sealant. In this case, the connection has been joined materially bonding and by way of welding the cell frames 4 formed from a thermoplastic and the semipermeable membranes 7 or electrodes 6, which are also at least partially made from a thermoplastic. However, the cell stack 1 could in principle also be designed in a different way.

[0054] Between a semipermeable membrane 7 and a non-porous section 22 of the electrode 6, a finger element 17 is provided in each case, in which a feed channel 13 or discharge channel 14 is provided in the form of an open channel closed in each case by the semipermeable membrane 7. In the case of the cell stack 1 shown, the finger elements 17 are connected, in particular welded, to the non-porous sections 22 of the electrodes 6 via materially bonded connections 27. Furthermore, the finger elements 17 extend from the porous section 23 of the electrode 6 to the adjacent semipermeable membrane 7, thus over the entire height of the cell interior 5, so that two adjacent cell chambers 18 are separated from each other. Furthermore, the corresponding finger elements 17 of the successive half-cells 3 are each arranged aligned with one another in the stacking direction of the half-cells 3. In this way, a form-fitting, indirect force transmission from one finger element 17 to the next finger element 17 can take place, whereby the forces between two finger elements 17 in each case can be transmitted via a semipermeable membrane 7 or a non-porous section 22 of an electrode 6. Consequently, the corresponding forces do not lead to a compression of the porous sections 23 of the electrodes 6 in the cell interior 5 or the cell chambers 18.

LIST OF REFERENCE SIGNS

[0055] 1 Cell stack [0056] 2 Cell [0057] 3 Half-cell [0058] 4 Cell frame [0059] 5 Cell interior [0060] 6 Electrode [0061] 7 Semipermeable membrane [0062] 8 Outer side [0063] 9 Sealing surface [0064] 10 Sealing material [0065] 11 Supply line [0066] 12 Disposal line [0067] 13 Feed channel [0068] 14 Discharge channel [0069] 15 Openings [0070] 16 Frame casing [0071] 17 Finger element [0072] 18 Cell chamber [0073] 19 Lateral edge [0074] 20 Outlet opening [0075] 21 Inlet opening [0076] 22 Non-porous section [0077] 23 Porous section [0078] 24 Flow channel [0079] 25 Free end [0080] 26 Rib [0081] 27 Connection