Methods for manufacturing a bipolar plate and bipolar plate

Abstract

Method for producing a bipolar plate (1) for an electrochemical system, comprising the following steps: - Provision of two half-plates (2, 3) made of a mainly non-metallic, electrically conductive material, - Applying an electrically insulating film (12) to both half-plates (2, 3), - Forming at least one of the half-plates (2, 3) together with the insulating film (12) in such a way that a channel-shaped structured surface is created, - Partial removal of the films (12) in areas of the half-plates (2, 3) where they rest on each other, before joining the half-plates (2, 3) or during joining the half-plates (2, 3) by thermal action, and - Connecting the two half-plates (2, 3) so that a channel (10) suitable for conducting a coolant is formed between the half-plates (2, 3) which is electrically insulated by means of the remaining foil (12).

Description

[0001] The invention relates to a method for producing a bipolar plate for an electrochemical system, in particular a fuel cell system. Furthermore, the invention relates to a bipolar plate.

[0002] A bipolar plate is known, for example, from DE 102 50 759 A1. This known bipolar plate has cooling channels provided with an electrically non-conductive coating, particularly made of ceramic. The coating of the bipolar plate according to DE 102 50 759 A1 is said to have good thermal conductivity. Thanks to this coating, it should be possible to use non-deionized water for cooling.

[0003] Another variant of a bipolar plate with coated cooling channels is known from DE 103 00 581 A1, a supplementary application to DE 102 50 759 A1. In this case, it is proposed to form an electrically non-conductive coating from a curing liquid medium that is conveyed in a circuit. To accelerate curing, heating the bipolar plates and / or the entire fuel cell assembly to a temperature that promotes the curing of the coating is provided.

[0004] DE 10 2019 007 298 A1 deals with the production of a partial plate of a bipolar plate. The partial plate is manufactured using a tool assembly comprising multiple dies. A first surface of the partial plate is formed by a flat gas diffusion layer. A metal foil, which forms the opposite surface of the partial plate, has curvatures that, together with surface structures of a second partial plate, form a cooling or media channel within the final product, i.e., the bipolar plate. A plastic matrix containing electrically conductive particles is located between the metal foil and the gas diffusion layer of each partial plate.

[0005] Details of a cooling system for a polymer electrolyte membrane fuel cell system are disclosed in DE 100 40 792 A1. The cooling system includes, among other things, cooling medium distribution chambers and cooling medium collection chambers. Possible materials for these chambers include polypropylene and polyvinylidene fluoride as non-conductive plastic materials. Furthermore, the possibility of using electrically conductive materials, such as stainless steel, aluminum, or titanium, when cooling with a non-conductive cooling medium is mentioned.

[0006] DE 101 28 836 A1 discloses an electrical insulation system for a fuel cell stack and a method for operating a fuel cell stack. It is assumed that the stack comprises several fuel cells connected in series and a cooling circuit. A liquid coolant with limited electrical conductivity is to be used for cooling, with water plus an antifreeze-based coolant being mentioned as a common liquid cooling agent. According to DE 101 28 836 A1, cooling passages can be connected in parallel and / or in series. The fuel cell stack is connected to a chassis, which has a chassis ground, and comprises several cooling passages. Electrically conductive components of the cooling circuit can be in the form of an outer boundary wall of the fuel cell stack, a cooler, and / or a pump. At least one of these components is connected to the chassis ground.Monitoring should be possible by using a measuring circuit to measure the resistance between a selected fuel cell and the chassis ground.

[0007] DE 200 16 734 U1 deals with the cooling of a fuel cell system featuring polymer electrolyte membranes, considering cooling by non-, weakly, or highly electrically conductive fluid media. According to DE 200 16 734 U1, the fuel cells are encased in electrically insulating and / or protective material.

[0008] US Pat. No. 3,969,145 A proposes a coating made of a dielectric material such as polytetrafluoroethylene for insulating cooling channels in fuel cell systems. A non-dielectric medium, namely water, is to be used as the coolant. Water can be present in liquid form or as water vapor.

[0009] DE 20 2007 016 862 U1 describes a bipolar plate of a fuel cell which contains at least one epoxy resin, a curing agent based on a metal-amine complex and a graphite filler.

[0010] DE 10 2018 211 982 A1 discloses a fuel cell comprising bipolar plates, which can be made of stainless steel, graphite, aluminum, titanium or graphite compound thermoplastic.

[0011] KR 10 2004 0 005 139 A1 describes a bipolar plate for a fuel cell stack that has a cooling water channel enclosed by insulating material. Suitable insulating materials include polymers or inorganic substances with hydrophobic properties.

[0012] The invention is based on the object of providing further developed possibilities for cooling electrochemical systems, in particular fuel cell systems, compared to the cited prior art, particularly from the point of view of manufacturing technology and energy as well as from the aspect of operational safety.

[0013] This object is achieved according to the invention by a method for producing a bipolar plate according to claim 1. Furthermore, it is achieved by a bipolar plate according to claim 7. Embodiments and advantages of the invention explained below in connection with the production method also apply mutatis mutandis to the devices, that is to say the bipolar plate and the entire electrochemical system, and vice versa.

[0014] The method for producing a bipolar plate specified in claim 1 is based on the provision of two half-plates made of a mainly non-metallic, electrically conductive material and generally comprises the following steps: - Applying an electrically insulating foil to both half-plates, - forming at least one of the half-plates together with the insulating foil in such a way that a channel-shaped structured surface is created, - Partial removal of the films (12) in areas of the half-plates (2, 3) in which they rest on one another, before joining the half-plates (2, 3) or when joining the half-plates (2, 3) by thermal action, and - connecting the two half-plates so that a channel is formed between the half-plates which is electrically insulated by means of the remaining film (12) and is suitable for conducting coolant, in particular cooling water.

[0015] The bipolar plate according to the invention comprises, in a basic concept known per se, two half-plates made of an electrically conductive plate material as the base material, which contact each other in a central plane ME and are connected to each other by thermal action. At least one cooling channel is formed between the half-plates, which is electrically insulated from the plate material by an insulating material. According to claim 7, foils are provided as the insulating material. In the cooling channels, strip-shaped regions of displaced insulating material are located between the half-plates, such that the cooling channel is provided with an electrically insulating seal of increased wall thickness in the region of the central plane ME.

[0016] Thanks to these films, the electrochemical system, which comprises a plurality of such bipolar plates, can be operated with an electrically conductive coolant. If the electrochemical system is used in the form of a fuel cell system in a motor vehicle with a cooling system that uses water as a coolant, the same water can also be used to control the temperature of the electrochemical cells, i.e., fuel cells.

[0017] According to various possible designs, the main component of the plate material is non-metallic. In particular, the plate material is a thermoplastic material. The plate material may contain graphite, for example, to ensure sufficient electrical conductivity.

[0018] By adding additional material, particularly in powder form, the properties of the half-plates and thus of the entire bipolar plate can be specifically adjusted. In particular, the plate material can contain titanium. Overall, this allows for the production of half-plates that, when used in fuel cell stacks, allow only minimal hydrogen permeation into the cooling channels while simultaneously demonstrating excellent durability.

[0019] The foils can be removed in different ways in areas of the half-plates where they lie on top of each other within the finished bipolar plate: According to a first possible process variant, the foils are partially removed before joining the half-plates, which can be done, for example, by grinding.

[0020] An alternative process variant involves partially removing the foils during the joining of the half-sheets by thermal action. This is the same thermal action that also ensures the welding of the two half-sheets. In particular, the welding can be carried out by resistance welding.

[0021] Several embodiments of the invention are explained in more detail below with reference to a drawing. In the drawings: Fig. 1 a section of a bipolar plate of an electrochemical system in a sectional view, Fig. 2 a plan view of a half plate of the bipolar plate according to Fig. 1, Fig. 3 shows a section of a modified embodiment of a bipolar plate.

[0022] Unless otherwise stated, the following explanations refer to both embodiments. Corresponding or essentially equivalent parts are identified by the same reference numerals in all figures.

[0023] A bipolar plate, designated overall by reference numeral 1, is intended for use in an electrochemical system (not shown in detail), namely a fuel cell system. Within the fuel cell system, a plurality of bipolar plates 1 are arranged in a stack. Regarding the basic structure and function of a fuel cell system, reference is made to the prior art cited above.

[0024] The bipolar plate 1 comprises two half-plates 2, 3 that touch each other in a central plane ME. In this case, the half-plates 2, 3 are made of a thermoplastic base material as plate material 11. Titanium powder is distributed throughout the base material 11 as an electrically conductive filler material 15. Furthermore, the base material 11 contains graphite. Overall, this ensures that the electrical conductivity of the base material 11 is sufficient for the intended use.

[0025] Even before the half plates 2, 3 are assembled, they have an external structuring 4, which is located in an active field 8 of the later bipolar plate 1. In the embodiment according to Fig. 3, the structuring 4 is outside the displayed area.

[0026] The Fig. 2 shows a plan view of the side of the half-plate 2 which lies inside the later bipolar plate 1. The essentially identical plan of the half-plates 2, 3 is also shown in the embodiment according to Fig. 3. The half-plates 2, 3, like the entire bipolar plate 1, have a rectangular, not square, basic shape, with various ports 5, 6 located on the two narrow sides of the half-plates 2, 3. These are media ports 5, located at the corners of the half-plates 2, 3, and are intended for the passage of operating media of the electrochemical system.

[0027] In addition, there are coolant ports 6, i.e. cooling water ports, which are each arranged between two media ports 5. The entire area bordering a narrow side of the half-plate 2, 3, in which the ports 5, 6 are arranged, is referred to as port area 7. The active field 8 lies between the port areas 7, which are arranged mirror-symmetrically to one another. Distribution areas, which are formed between the port areas 7 and the active field 8, are in Fig. 2 not shown for the sake of clarity.

[0028] In addition to the external structuring 4, each half-plate 2, 3 has an internal structuring 9, which defines the shape of cooling channels 10 in the bipolar plate 1. To enable the use of an electrically conductive coolant, the cooling channel 10 must be electrically insulated from the base material 11. For this purpose, the walls of the cooling channel 10 are formed by a foil 12 as electrical insulation. The foils 12 are arranged on the plate material 11 before the half-plates 2, 3 are joined and are also located in the port area 7.

[0029] During the production of the half-sheets 2, the sheet material 11 including the foil 12 can be deformed to form the internal structuring 9. Depending on the material selected, this can be done under the influence of temperature. Alternatively, the foil 12 is applied only after the structuring 9 has been produced. In principle, subtractive processes can also be used to create the structuring 9, just as in the case of the external structuring 4.

[0030] Within the finished bipolar plate 1 there is an electrically conductive connection between the half-plates 2, 3. This connection is made in the embodiment according to the Fig. 1 and Fig. 2 is produced by removing the film 12 from the half-plates 2, 3 before joining in those areas which are intended for contacting the other half-plate 3, 2, i.e. which are outside the channels 10.

[0031] In the embodiment according to Fig. 3, the half-plates 2, 3 initially remain completely covered by the film 12 on the side which has the internal structuring 9, i.e., which is formed in the form of the walls of the cooling channel 10. In this state, the half-plates 2, 3 are placed on top of each other and welded together. This is possible, for example, by resistance welding, whereby in Fig. 3, the conductivity of the bipolar plate 1 in the area between the channels 10 is symbolized by a lightning bolt. The resulting weld area, in which the half-plates 2, 3 are firmly bonded to each other, is designated 13.

[0032] Due to the energy supply during welding, the foils 12 are melted in the corresponding area and, under a pressure acting simultaneously between the half-plates 2, 3, are displaced into the adjacent cooling channels 10. In this way, strip-shaped areas of displaced insulating material 14 form in the cooling channels 10 between the half-plates 2, 3. Thus, in the transition area between the two half-plates 2, 3, i.e., in the area of ​​the center plane ME, the cooling channel 10 is provided with an electrically insulating seal of increased wall thickness. List of reference symbols 1 bipolar plate 2 half plates 3 half-plates 4 external structuring 5 Media port 6 Cooling water port 7 Port range 8 Active field 9 internal structuring 10 cooling channel 11 Base material, plate material 12 foil, insulation 13 Welding area 14 displaced insulation material 15 conductive additional material ME Middle Level

Claims

[1] Method for producing a bipolar plate (1) for an electrochemical system, comprising the following steps: - providing two half-plates (2, 3) made of a mainly non-metallic, electrically conductive material, - applying an electrically insulating foil (12) to both half-plates (2, 3), - forming at least one of the half-plates (2, 3) together with the insulating foil (12) in such a way that a channel-shaped structured surface is created, - Partial removal of the films (12) in areas of the half-plates (2, 3) in which they rest on one another, before joining the half-plates (2, 3) or when joining the half-plates (2, 3) by thermal action, and - connecting the two half-plates (2, 3) so that a channel (10) suitable for conducting a coolant is formed between the half-plates (2, 3) and is electrically insulated by means of the remaining film (12). [2] Method according to claim 1, wherein the partial removal of the foils (12) is carried out by grinding before joining the half-plates (2, 3). [3] Method according to claim 1 or 2, wherein half-plates (2, 3) made of a thermoplastic plate material (11) are used. [4] Method according to claim 3, wherein a graphite-containing plate material (11) is used as the plate material (11). [5] Method according to one of claims 3 or 4, wherein the plate material (11) used is one to which titanium is added as a powder. [6] Method according to one of claims 1 to 5, wherein resistance welding is used when joining the half-plates (2, 3) by thermal action, wherein the foils (12) are melted in the corresponding area and, under a pressure acting simultaneously between the half-plates (2, 3), are displaced into the adjacent cooling channels (10). [7] Bipolar plate (1) for an electrochemical system, in particular manufactured according to claim 6, comprising two half-plates (2, 3) made of an electrically conductive plate material (11) as the base material, which half-plates touch each other in a central plane ME and are connected to each other by means of thermal action, wherein at least one cooling channel (10) is formed between the half-plates (2, 3), which is electrically insulated from the plate material (11) by an insulating material (14), characterized by that foils (12) are provided as insulation material (14), and that in the cooling channels (10) there are strip-shaped areas of displaced insulation material (14) between the half-plates (2, 3), such that the cooling channel (10) is provided with an electrically insulating seal of increased wall thickness in the region of the central plane (ME).

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