Cell element for an electrochemical energy converter, and method and welding device for producing same

Abstract

The invention relates to a cell element (100, 200) for an electrochemical energy converter. The cell element (100, 200) comprises a transport layer (101) and a bipolar plate (103), wherein the bipolar plate (103) comprises a conductive structure (105) for conducting an operating medium, the conductive structure (105) has an at least partly embossed surface (107), and the transport layer (101) is directly welded to the conductive structure (105) in the region of the embossed surface (107) via a platinum-free connection in the form of a number of welding points (109).

Description

[0001] Description

[0002] title

[0003] Cell element for an electrochemical energy converter and method and welding device for its production

[0004] The invention presented relates to a cell element for an electrochemical energy converter as well as a manufacturing method for manufacturing a cell element for an electrochemical energy converter and a welding device for manufacturing a cell element for an electrochemical energy converter according to the appended claims.

[0005] State of the art

[0006] Particularly in electrolysis systems, bipolar plates with a precious metal coating are used to reduce contact resistance and prevent deterioration of the resistance due to a growing oxide layer over the lifetime of the bipolar plate.

[0007] Such precious metal coatings are complex to produce and cost-intensive.

[0008] Furthermore, bipolar plates are connected to transport layers, such as permeable, sponge-like structures, by resistance welding.

[0009] Laser welding is not used for this purpose because local gaps cannot be reliably avoided.

[0010] Disclosure of the invention

[0011] Within the scope of the invention presented, a cell element for an electrochemical energy converter, a manufacturing method for manufacturing the cell element, and a welding device for manufacturing the cell element are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the manufacturing method according to the invention or the welding device according to the invention naturally also apply in connection with the cell element according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0012] The invention presented serves in particular to provide a possibility for a cost-efficient cell element for an electrochemical energy converter.

[0013] Thus, according to a first aspect of the invention presented, a cell element for an electrochemical energy converter, such as an electrolysis system or a fuel cell system, is presented.

[0014] The presented cell element comprises a transport layer and a bipolar plate, wherein the bipolar plate comprises a conductive structure for conducting operating medium, wherein the conductive structure has a surface that is embossed at least in some areas, wherein the transport layer is directly welded to the conductive structure in the area of ​​the embossed surface via a platinum-free connection in the form of a number of welds.

[0015] The presented cell element can be, for example, a half-cell for a cell of a cell stack of an electrochemical energy converter.

[0016] In the context of the invention presented, a transport layer is understood to mean a porous transport layer or “Porous Transport Layer” (PTL).

[0017] In the context of the present invention, an embossed surface is understood to mean a surface shaped according to a three-dimensional or spatial pattern and comprising first regions and second regions, wherein the first regions differ in their height position from the height position of the second regions. Accordingly, for example, the first regions come into contact first or exclusively with a flat surface guided onto the embossed surface.

[0018] Furthermore, an embossed surface is flexible or resilient, so that the embossed surface is deformable, but pushes back into its original position with a spring force.

[0019] The presented invention is based on a welded connection between a conductive structure of a bipolar plate, such as a channel system or an embossed plate, and a porous transport layer.

[0020] The welded joint forms a platinum-free connection that connects the bipolar plate to the transport layer directly, i.e. without an intermediate layer.

[0021] Due to the deformability of the embossed surface of the conductive structure, a spring force is provided when the conductive structure is pressed onto the transport layer, which presses the respective raised areas of the conductive structure onto the transport layer and, as a result, compensates for material tolerances between the embossed surface or the conductive structure as the first joining partner and the transport layer as the second joining partner.

[0022] Due to the compensation of material tolerances, a secure and reliable contact between the conductive structure and the transport layer, i.e., a so-called “local zero gap”, is achieved, so that they can be welded together in a laser welding process.

[0023] The welding of the conductive structure and transport layer results in a particularly low contact resistance between the conductive structure or bipolar plate and the transport layer, so that a coating with precious metal, especially platinum, is unnecessary on the side facing the welding points of both the bipolar plate or conductive structure and the transport layer. The embossed surface can, for example, comprise a number of ring-shaped spring contours.

[0024] Due to the number of welding points provided according to the invention and the manufacturing method according to the invention, precious metal layers, in particular platinum layers, for reducing contact resistance between the bipolar plate and the transport layer can be dispensed with.

[0025] Accordingly, it can be provided that the transport layer has a precious metal layer only on one side facing away from the number of welding points.

[0026] It can be provided that the conductive structure comprises a number of channels formed on a base structure of the bipolar plate, wherein the number of welding points is formed on the bottom of at least one channel.

[0027] To form welds in a conductive structure comprising channels, the embossed surface can comprise a number of annular spring contours formed at a channel base. For example, the spring contours can have a spring height that lies within a height variance of a surface of the conductive structure. In particular, a spring contour can have a diameter of less than 500 μm and a spring height of greater than 50 μm.

[0028] For example, the embossed surface can comprise a plurality of spring contours formed at a pitch of 1 mm or more, so that current carrying capacity is ensured by corresponding welds between the conductive structure and the transport layer.

[0029] It can further be provided that the conductive structure comprises an embossed plate which is welded onto a base structure of the bipolar plate, wherein the conductive structure comprises a plurality of connecting elements which are mutually welded to the base structure and the transport layer via a respective welding point.

[0030] By using an embossed plate, for example instead of a

[0031] Expanded metal is used to form the conductive structure of the bipolar plate, a predetermined connection geometry can be created, which requires welding points with a basic structure of the bipolar plate and with the transport layer at predetermined positions

[0032] For this purpose, the embossed plate can comprise a plurality of connecting elements, such as arms or webs, which extend in a predetermined height profile toward the base body of the bipolar plate or toward the transport layer. Accordingly, the respective connecting elements can be designed to be resilient or flexible in order to compensate for material tolerances between the embossed surface or the conductive structure as the first joining partner and the transport layer as the second joining partner or the basic structure of the bipolar plate as the third joining partner.

[0033] By using an embossed plate as a conductive structure, precious metal coatings for reducing contact resistance between the bipolar plate and the conductive structure, in particular on the base structure, a side of the conductive structure facing the base structure, a side of the conductive structure facing the transport layer and a side of the transport layer facing the conductive structure, can be dispensed with.

[0034] For example, the respective connecting elements can be arranged alternately upwards and downwards, as well as offset by 90°, or even in a star pattern. Such an offset design of the connecting elements creates a three-dimensional framework, which ensures good rigidity of the cell element for further processing, e.g., when connecting it to other cell elements to form a cell.

[0035] According to a second aspect, the presented invention relates to a manufacturing method for producing a cell element for an electrochemical energy converter.

[0036] The proposed manufacturing method comprises arranging a transport layer and a conductive structure of a bipolar plate on top of each other, the conductive structure having an embossed surface. Furthermore, the proposed manufacturing method comprises pressing the conductive structure onto the transport layer in such a way that the embossed surface is deformed and point contact between the conductive structure and the transport layer is ensured. Furthermore, the method comprises forming a number of welds at points where the embossed surface is in contact with the transport layer in order to directly weld the conductive structure to the transport layer via a platinum-free bond.

[0037] The number of welds can be created using a scanner and a fiber laser, for example, allowing welding times of just a few milliseconds per weld point and just a few seconds per cell element. Accordingly, a welding path speed of between 0.25 m / s and 0.75 m / s can be selected.

[0038] The presented manufacturing process is based on a pressing process in which the conductive structure is pressed or depressed onto the transport layer in such a way that the embossed surface is deformed and a punctual contact between the conductive structure and the transport layer is ensured.

[0039] An automatic hold-down device or handling robot, for example, can be used to press the conductive structure onto the transport layer. In particular, a predetermined weight can be placed on the conductive structure or the bipolar plate to provide a contact force that compresses the connecting elements.

[0040] It can be provided that the conductive structure comprises a number of channels formed on a basic structure of the bipolar plate and the number of welding points is formed at the bottom of at least one channel.

[0041] By forming the welds at the bottom of at least one channel as the lowest point of a guide structure, the channel or its bottom itself can act as a spring element and, for example, its cross-section can be changed by pressing. Alternatively or additionally, spring elements can be embossed into the bottom of a channel so that the bottom has a changing height profile and only comes into contact with a transport layer at a local minimum to form a weld.

[0042] It can further be provided that the conductive structure comprises an embossed plate which forms a plurality of connecting elements, wherein a first number of connecting elements are welded to a basic structure of the bipolar plate and a second number of connecting elements are welded to the transport layer, wherein respective connecting elements have a rounded contact region to which the connecting elements are spot-welded.

[0043] A rounded contact area defines the geometry of the welding point and ensures reliable contact between the conductive structure and the transport layer or base structure.

[0044] It can further be provided that respective welding points are formed automatically by means of a laser welding robot, wherein the laser welding robot determines a position of the welding points based on an image of the embossed surface determined by means of an optical sensor and an image recognition algorithm, wherein the image recognition algorithm determines as positions for welding points those points at which the embossed surface is in contact with the transport layer.

[0045] To select specific points for forming a weld, an automatic image recognition system can be used. This system detects, for example, local minima in a surface and selects these as points for forming a weld. Such an automatic image recognition system dynamically compensates for tolerances in the contact between a conductive structure and a transport layer or a base structure.

[0046] It can further be provided that the respective welds are formed automatically by means of a laser welding robot, whereby the laser welding robot forms the welds at fixed, predetermined positions. In particular, by using an embossed plate as a guide structure, the respective positions of the welds can be precisely specified, so that these positions can be stored in a memory and made available to a laser welding robot.

[0047] According to a third aspect, the presented invention relates to a welding device for producing a cell element for an electrochemical energy converter.

[0048] The presented welding device comprises a laser welding robot and a computing unit configured to carry out a possible embodiment of the presented manufacturing method.

[0049] In the context of the invention presented, a computing unit is understood to mean a computer, a processor, a control unit or any other programmable circuit.

[0050] Since a laser welding robot welds without contact, the risk of cell poisoning due to the transfer of metal ions is minimized.

[0051] It can be provided that the welding device has a surface made of titanium in the respective areas in which the welding device comes into contact with the transport layer and / or the conductive structure.

[0052] A surface made of titanium or titanium element in the respective areas where the welding device comes into contact with the transport layer and / or the conductive structure prevents poisoning of the cell element by transfer of metal ions.

[0053] Advantages described in detail for the cell element for an electrochemical energy converter according to the first aspect of the invention apply equally to the manufacturing method for manufacturing a cell element for an electrochemical energy converter according to the second aspect of the invention and to the welding device for manufacturing a cell element for an electrochemical energy converter according to the third aspect of the invention.

[0054] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0055] They show schematically:

[0056] Figure 1 shows a representation of a design of a cell element according to the prior art,

[0057] Figure 2 shows a first view of a possible design of the presented cell element,

[0058] Figure 3 shows a second view of the cell element according to Figure 2,

[0059] Figure 4 shows a first view of another possible embodiment of the presented cell element,

[0060] Figure 5 shows a second view of the cell element according to Figure 4,

[0061] Figure 6 shows a possible embodiment of the presented manufacturing process,

[0062] Figure 7 shows a possible design of the presented welding device, and

[0063] Figure 8 shows a possible design of hold-down devices for the welding device according to Figure 7.

[0064] Fig. 1 shows a cell element 1000 according to the prior art. The cell element 1000 comprises a bipolar plate 1100 on which a first noble metal layer 1110 is arranged, and a transport layer 1200 comprising a second noble metal layer 1210 and a third noble metal layer 1220 on a pore structure 1230.

[0065] Accordingly, the cell element 1000 comprises three precious metal layers 1110, 1210 and 1220.

[0066] The three precious metal layers 1110, 1210 and 1220 are necessary because the bipolar plate 1100 is welded to the transport layer 1200 over a large area in the area 1230 by resistance welding.

[0067] Fig. 2 shows a cell element 100. The cell element 100 comprises a transport layer 101 and a bipolar plate 103.

[0068] The bipolar plate 103 comprises a conductive structure 105 for conducting operating media.

[0069] The conductive structure 105 in turn comprises a surface 107 which is at least partially embossed.

[0070] The transport layer 101 is directly welded to the conductive structure 105 in the area of ​​the embossed surface 107 via a platinum-free connection in the form of a number of welds 109.

[0071] The cell element 100 has an optional precious metal layer 111 only on one side of the transport layer 101 facing away from the number of welding points 109.

[0072] Accordingly, the cell element 100 comprises two fewer precious metal layers than the cell element 1000 according to the prior art.

[0073] In Fig. 3, it can be seen that the conductive structure 105 forms a plurality of channels 113, at the respective bottom 115 of which a weld 109 in the form of a weld spot is formed. To provide the welds 109, the bipolar plate 103 is pressed down onto the transport layer 101, as indicated by arrows 119, so that local minima, i.e., particularly deep regions of the embossed surface 107, come into contact with the transport layer 101 and can be connected to it by a laser welding process.

[0074] The embossed surface 107 is designed to be resilient so that material tolerances of the transport layer 101 and the bipolar plate 103 are compensated when the embossed surface 107 is pressed down onto the transport layer 101.

[0075] Fig. 4 shows a cross-section through another cell element 200. Here, the bipolar plate 103 comprises a stamped plate 121 that forms resilient or flexible connecting elements 123. Accordingly, the stamped plate 121 is welded to the bipolar plate 103 via first connecting elements 123a and to the transport layer 101 via second connecting elements 123b.

[0076] For safe and easy spot welding, the connecting elements 123 are rounded or dome-shaped at their connection points before welding.

[0077] In Fig. 5, the cell element 200 is shown in a plan view, in which it can be seen that the connecting elements 123 are grouped radially offset from one another around a center point.

[0078] The connecting elements are welded at the welding points 109 with a transport layer 101 made of sintered titanium.

[0079] Fig. 6 shows a manufacturing method 300 for producing a cell element 100 for an electrochemical energy converter according to Fig. 1.

[0080] The manufacturing method 300 comprises an arrangement step 301, in which a transport layer and a conductive structure of a bipolar plate are arranged one above the other, the conductive structure having an embossed surface. Furthermore, the manufacturing method 300 comprises a pressing step 303, in which the conductive structure is pressed onto the transport layer in such a way that the embossed surface is deformed and a point-like contact between the conductive structure and the transport layer is ensured.

[0081] Furthermore, the manufacturing method 300 comprises a forming step 305 in which a number of welds are formed at points where the embossed surface is in contact with the transport layer in order to weld the conductive structure to the transport layer.

[0082] The transport layer only has a precious metal layer on one side facing away from the number of welding points.

[0083] Fig. 7 shows a welding device 400 for producing a cell element 100 for an electrochemical energy converter according to Fig. 1.

[0084] The welding device 400 comprises a laser welding robot 401 and a computing unit 403 configured to carry out the manufacturing method 300 according to Fig. 6.

[0085] To hold down the connecting elements, the welding device can comprise a number of hold-down devices 405, shown in Fig. 8, which are configured to bend or hold down the connecting elements 123. Accordingly, the hold-down devices 405 can be made of titanium or include a contact area made of titanium to prevent poisoning of the transport layer 101 with metal ions.

Claims

Claims 1 . Cell element (100, 200) for an electrochemical energy converter, wherein the cell element (100, 200) comprises: a transport layer (101), a bipolar plate (103), wherein the bipolar plate (103) comprises a conductive structure (105) for conducting operating medium, wherein the conductive structure (105) has a surface (107) that is embossed at least in some areas, wherein the transport layer (101) is directly welded to the conductive structure (105) in the area of the embossed surface (107) via a platinum-free connection in the form of a number of welds (109).

2. Cell element (100, 200) according to claim 1, characterized in that the conductive structure (105) comprises a number of channels (113) formed on a basic structure of the bipolar plate (101), wherein the number of welding points (109) is formed on the bottom (115) of at least one channel (113).

3. Cell element (100, 200) according to claim 1 or 2, characterized in that the conductive structure (105) comprises an embossed plate (121) which is welded onto a base structure of the bipolar plate (103), wherein the conductive structure (105) comprises a plurality of connecting elements (123) which are alternately welded to the base structure and the transport layer (101) via a respective welding point (109).

4. Manufacturing method (300) for producing a cell element (100, 200) for an electrochemical energy converter, the manufacturing method (300) comprising: Arranging (301) a transport layer (101) and a conductive structure (105) of a bipolar plate (103) one above the other, wherein the conductive structure (105) has an embossed surface (107), pressing (303) the conductive structure (105) onto the transport layer (101) such that the embossed surface (107) is deformed and a punctiform contact between the conductive structure (105) and the transport layer (101) is ensured, Forming (305) a number of welds (109) at points where the embossed surface (107) is in contact with the transport layer (101) in order to directly weld the conductive structure (105) to the transport layer (101) via a platinum-free connection.

5. Manufacturing method (300) according to claim 4, characterized in that the conductive structure (105) comprises a number of channels (113) formed on a base structure of the bipolar plate (103) and the number of welding points (109) is formed on the bottom (115) of at least one channel (113).

6. Manufacturing method (300) according to claim 4 or 5, characterized in that the conductive structure (105) comprises an embossed plate (121) which forms a plurality of connecting elements (123), wherein a first number of connecting elements (123a) are welded to a basic structure of the bipolar plate (103) and a second number of connecting elements (123b) are welded to the transport layer (101), wherein respective connecting elements (123) have a rounded contact region to which the connecting elements (123) are spot-welded.

7. Manufacturing method (300) according to one of claims 4 to 6, characterized in that that respective welding points (109) are formed automatically by means of a laser welding robot (401), wherein the laser welding robot (401) determines a position of the welding points based on an image of the embossed surface (107) determined by an optical sensor and an image recognition algorithm, wherein the image recognition algorithm determines as positions for welding points those points at which the embossed surface (107) is in contact with the transport layer (101).

8. Manufacturing method (300) according to one of claims 4 to 6, characterized in that respective welding points (109) are formed automatically by means of a laser welding robot (401), wherein the laser welding robot (401) forms the welding points (109) at fixed predetermined positions.

9. Welding device (400) for producing a cell element (100, 200) for an electrochemical energy converter, the welding device (400) comprising: a laser welding robot (401), a computing unit (403) configured to carry out a manufacturing method (300) according to one of claims 4 to 8.

10. Welding device (400) according to claim 9, characterized in that the welding device (400) has a surface made of titanium in respective regions in which the welding device (400) comes into contact with the transport layer (101) and / or the conductive structure (105).

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