Plate arrangement for a stack of electrochemical cells and method for manufacturing a plate arrangement

Abstract

A plate arrangement (1) for electrochemical cells (6) comprises a bipolar plate (3) made from at least one sheet metal part (4, 5) and a seal (9) connected to it, designed as an injection molded element, wherein a injection point (11) of the seal (9) is arranged in a recess (10) of the sheet metal part (4, 5) and is fully surrounded by a sealing lip (16) which is also located within the said recess (10).

Description

[0001] The invention relates to a plate arrangement suitable for use in a stack of electrochemical cells, in particular fuel cells. The invention further relates to a method for manufacturing such a plate arrangement.

[0002] DE 10 2022 110 834 B4 discloses a fuel cell system with a plurality of bipolar plates arranged in a stack, which separate electrochemical cells from one another. Frames are arranged between each pair of bipolar plates. Ports for conveying media to the active fields of the electrochemical cells are formed through the bipolar plates. Sealing arrangements exist for sealing flow spaces between the ports and the active fields; these arrangements each comprise two parallel sealing elements that partially overlap when viewed from above on the bipolar plates.

[0003] A fuel cell described in DE 11 2007 000 127 B4 comprises separators and membrane electrode units combined with seals, which are stacked alternately with the separators. The seals or separators form projections that extend in the stacking direction of a stack formed from the fuel cells and interact with contours of other components of the fuel cell stack.

[0004] DE 10 2016 212 718 A1 discloses a fuel cell separator with a seal. In particular, it addresses the increase of the contact pressure of an airtight line on the cooling surface side by additionally forming an airtight secondary line.

[0005] German patent DE 10 2014 220 529 A1 deals with the injection molding of an end plate for a fuel cell stack. Within this process, precautions are taken to prevent material from flowing into threaded holes.

[0006] The invention is based on the objective of achieving progress in the production of stacks of electrochemical cells compared to the prior art, particularly with regard to sealing technology.

[0007] This problem is solved according to the invention by a plate arrangement having the features of claim 1. According to claim 6, the plate arrangement can be used in a stack of electrochemical cells. Likewise, the problem is solved by a method designed according to claim 7 for manufacturing a plate arrangement for a stack of electrochemical cells, in particular fuel cells. The embodiments and advantages of the invention explained below in connection with the manufacturing method also apply mutatis mutandis to the devices, i.e., the plate arrangement and the entire cell stack, and vice versa.

[0008] The plate arrangement comprises at least one bipolar plate, and in particular a plurality of bipolar plates. Each bipolar plate is made from at least one sheet metal part. A seal, designed as an injection-molded element, is connected to the bipolar plate. An injection point of the seal is located in a recess of the sheet metal part and is completely surrounded by a sealing lip, which is at least partially also located within the aforementioned recess.

[0009] The invention is based on the premise that injection molding processes are fundamentally suitable for attaching seals to electrode plates, for example, bipolar plates. In the case of a bipolar plate, sealing material can be permanently applied to the top and bottom surfaces of the plate by injection molding. Injection points are located on the top and bottom surfaces of the plate.

[0010] To avoid injection points on the top and bottom of the plate, material can be fed from the side during injection molding, according to unclaimed methods, so that the injected material can be distributed evenly across the top and bottom of the plate to be fitted with a seal. This requires a mold geometry precisely matched to the thickness and any embossed geometry of the plate to be coated with sealing material, in which channels for feeding the sealing material are formed.

[0011] The patented solution departs from such known approaches, which have specific advantages and disadvantages, and instead proposes an injection molding process in which flowable material, in this case, sealing material, is injected into an area of ​​the plate assembly under production that is characterized by relatively low tolerance sensitivity. This area is in the form of a recess in the sheet metal part from which the bipolar plate, possibly together with other parts, is formed. To achieve precise interaction with adjacent parts of the cell stack despite the fact that the geometry of the injection point is not precisely defined in practice, the injection point is surrounded by a ring-shaped sealing lip. The injection point and sealing lip may visually give the impression of an enlarged injection point.In fact, the ring-shaped sealing lip, in the center of which the injection point is located, is characterized by a defined shape. Any potentially asymmetrical position of the injection point within the area enclosed by the sealing lip does not impair its function.

[0012] The sealing lip, viewed from above on the bipolar plate, has, for example, an oval shape, particularly an elliptical one. The sealing lip can also be circular. In principle, other closed shapes for the sealing lip are also possible, such as a polygonal shape, for example, in the form of a hexagon or octagon. In various sealing lip shapes, the smallest diameter of the sealing lip can be less than the smallest width of the entire seal – measured from above on the bipolar plate.

[0013] A bipolar plate is particularly suitable if it is constructed from two half-sheets. The two half-sheets are not necessarily completely mirror images of each other. Flow channels, especially for a coolant, can be formed between the half-sheets. Simultaneously, flow-guiding structures for operating fluids can be formed on the outer surfaces of the half-sheets.

[0014] According to various possible embodiments, a sealing lip of the described type, that is, an annular sealing lip enclosing a injection point, is located only on one side of the bipolar plate, i.e., on a side that can arbitrarily be designated as the top or bottom, whereas on the opposite side, also within the plan view of the recess formed in the sheet metal part, a flat section of the seal is formed. Thus, a lip geometry defined by the seal is combined with a flat contact surface on the opposite side, for example, on the underside of the seal.

[0015] The flat gasket side opposite the sealing lip is particularly wide, ensuring that within the fully assembled cell stack, even with tolerable positioning errors, the flat gasket side always interacts with an annular sealing lip. This means that the minimum width of the flat gasket side is greater than the diameter of the annular sealing lip. The small diameter of the annular seal, which is particularly evident from the fact that the area enclosed by the annular seal is largely filled by the injection point, allows for space-saving placement of the seal within the cell stack, despite the tolerance-insensitive, manufacturable design of the plate arrangement. This is a good prerequisite for a high volumetric power density of the entire electrochemical system, of which the cell stack is the main component.

[0016] The recess formed in the bipolar plate, in which the injection point is located, can be configured in various ways, for example as a hole in the sheet metal part or in the overlapping sheet metal parts, which is completely filled with sealing material. This hole can function as a through-hole. The through-hole is, in particular, located centrally beneath the seal, and has a diameter of no more than half the width of the seal.

[0017] Similarly, designs are possible in which the recess, where the injection point is created during manufacturing, is a bulge in a contour that defines an edge or opening of the bipolar plate. This opening could, for example, be a port used for the supply or discharge of operating fluids to the electrochemical system. Through-holes of the type described above, which are completely enclosed by the metallic material of a bipolar plate, can also be located in the edge region of a port. In this case, too, sealing material can extend to the edge of the port.

[0018] The patented method for manufacturing a plate arrangement for a stack of electrochemical cells begins with the provision of a bipolar plate which has at least one recess configured in one of the described ways, i.e., either closed or open. In the course of the method, a seal is simultaneously injection-molded onto the bipolar plate, wherein a injection point is placed in the aforementioned recess and sealing areas are created on both the top and bottom surfaces of the bipolar plate such that a sealing lip is formed within the aforementioned recess, enclosing the injection point in a ring-like manner when viewed from above.

[0019] In this process, the seal is not necessarily formed symmetrically with respect to a mirror plane placed centrally through the bipolar plate. Regardless of any potential mirror symmetry, in injection molding, the sealing material is fed in, in particular, orthogonally to the plane in which the bipolar plate lies. It is sufficient to feed the injection-moldable sealing material, especially a thermoplastic, through a single mold component.

[0020] Several embodiments of the invention are explained in more detail below with reference to a drawing. This drawing shows: Fig. 1 Partially a first embodiment of a plate arrangement comprising a seal for a stack of electrochemical cells, namely fuel cells, Fig. 2. Another design option for a seal within a fuel cell stack, Fig. 3 components of a fuel cell stack in top view, Fig. 4. Partially shown in a schematic representation of the fuel cell stack. Fig. 3 in a sectional view.

[0021] Unless otherwise stated, the following explanations apply to all embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0022] A plate arrangement 1 is part of a cell stack designated by reference numeral 2, which in the present cases is configured as a fuel cell stack. The cell stack 2 comprises a plurality of metallic bipolar plates 3. Regarding the fundamental function of the fuel cell system, which includes the fuel cell stack 2 as its core component, reference is made to the prior art cited above.

[0023] Each bipolar plate 3 is composed of two half-sheets 4, 5, which are generally referred to as sheet metal parts 4, 5, and separates a half-cell 7 of a first fuel cell 6, i.e., electrochemical cell, from a half-cell 7 of another fuel cell 6. Each fuel cell 6 has a membrane electrode assembly 8, which includes, among other things, a frame also referred to as a subgasket. The membrane electrode assembly 8 is located in the center of each cell 6. The half-sheets 4, 5 are steel sheets, which may be coated in a manner known per se. Continuous and / or batch processes can be used to manufacture the half-sheets 4, 5.

[0024] In the fuel cell stack 2, several ports 10 are formed by the bipolar plates 3, which generally represent recesses in the bipolar plates 3. The ports 10 serve to convey cooling or operating media of the fuel cell stack 2. Further means for supplying or removing media, in particular hydrogen and air, located outside the fuel cell stack 2 are not shown.

[0025] In a top view of the bipolar plate 3, a distribution field 12 and an active field 13 are visible, in which the desired electrochemical reactions that generate electric current take place. Embossed structures are generally designated 14, and flow channels in which a service or cooling medium flows are designated 15. In particular, spaces between the half-sheets 4, 5 are designed as flow channels 15 for a cooling medium.

[0026] To seal flow channels 15 or other spaces that need to be fluidically separated, seals 9 are provided. These seals are injection-molded onto the half-sheets 4 and 5 and thus permanently bonded to them. Each seal 9 contacts the same bipolar plate 3 on both sides, i.e., on its upper and lower surfaces. The terms "upper surface" and "lower surface" refer only to the figures and do not imply anything about the spatial orientation of the components of the fuel cell stack 2. In particular, a vertical orientation of the bipolar plates 3 is possible.

[0027] A injection point of the injection-molded seal 9 is designated 11. The injection point 11 lies – in a top view of the plate arrangement 1 – outside the metallic material of the bipolar plate 3, that is, within the recess 10. Generally, the recess 10 can be either an opening with a closed rim or a protrusion open on one side.

[0028] As from the Fig. As shown in figures 1 to 4, an annular sealing lip 16 is formed, which surrounds the injection point 11. In the exemplary embodiment according to Fig. In the top view, the sealing lip 16 has an oval shape; in the other embodiments, it has an at least approximately circular shape. In all cases, the minimum diameter of the sealing lip 16, measured at its highest elevations, is designated DL. The total width of the seal 9 is designated BD. As can be seen from the Fig. 2 and Fig. As can be seen from Figure 4, a flat section 17 of the seal 9 lies opposite the sealing lip 16 on the side of the bipolar plate 3 – in the illustrated arrangements, on its underside. The section 17 is also located mostly within the recess 10, which contains no material from the half-sheets 4, 5. Within the fully assembled cell stack, forces are transmitted between the flat section 17 and a sealing lip 16 positioned above it.

[0029] In the injection molding process for the seal 9, the material from which the seal 9 is constructed is fed in a direction normal to the plane in which the bipolar plate 3 lies. Feeding is only provided from one side of the mold. Looking at the seal 9 in cross-section, as shown in the Fig. 2 and Fig. As sketched in Figure 4, sections of the sealing lip 16 appear as a double-lipped seal. Reference symbol list 1. Plate arrangement 2 stacks of electrochemical cells, fuel cell stacks 3 Bipolar plate 4 half-sheet, sheet metal part 5 Half sheet metal, sheet metal part 6 Fuel cell, electrochemical cell 7 half-cell 8 Membrane electrode arrangement 9 Seal 10 Port, recess 11 Injection point 12 distribution panel 13 Active field 14 Embossing structure 15 Flow channel 16 Sealing lip 17 level section BD Width of the seal DL diameter of the sealing lip QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 110 834 B4

[0002] DE 11 2007 000 127 B4

[0003] DE 10 2016 212 718 A1

[0004] DE 10 2014 220 529 A1

[0005]

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