Method for producing a half-plate of a bipolar plate, bipolar plate and electrochemical cell

Abstract

The invention relates to a method for producing a half-plate (1) of a bipolar plate (1'), comprising the steps of: - rolling (V1) a sheet-metal strip (B), - wherein the rolling is carried out in at least one first region (2) of the sheet-metal strip (B) to a uniform first sheet thickness (d1) and in at least one second region (3) of the sheet-metal strip (B) to a uniform second sheet thickness (d2), - wherein the first sheet thickness (d1) is greater than the second sheet thickness (d2) and the first region (2) and the second region (3) are each of a flat form, - introducing (V2) into the at least one first region (2) a surface structure (5) in the form of channels, - cutting the sheet-metal strip (B) to detach the half-plate (1) from the sheet-metal strip (B), wherein the half-plate (1) has at least one first region (2) and one second region (3). The invention also relates to a bipolar plate and to an electrochemical cell.

Description

[0001] Method for producing a half sheet of a bipolar plate, bipolar plate and electrochemical cell

[0002] The invention relates to a method for producing a half-sheet of a bipolar plate. Furthermore, the invention relates to a bipolar plate and an electrochemical device comprising at least one such bipolar plate.

[0003] In this context, an electrochemical cell is in particular a fuel cell, an electrolysis cell or a redox flow cell.

[0004] The heart of a fuel cell stack is the fuel cell. A fuel cell stack consists of several fuel cells and typically contains two bipolar plates per cell. Connecting several fuel cells into a fuel cell stack serves, among other things, to increase the output voltage.

[0005] Typically, a first and a second bipolar plate, placed one on top of the other and separated by a membrane, form the actual electrochemical cell. The anode is separated from the cathode by an MEA (membrane electrode assembly). A bipolar plate typically consists of two half-sheets that are bonded together, for example, by welding.

[0006] In order to distribute the reactants and fluids necessary for the operation of an electrochemical cell, such as a fuel cell, evenly over the electrochemically active area of ​​the membrane electrode assembly, distribution structures are often provided on the bipolar plate, which are designed as channels.

[0007] For the large-scale production of bipolar plates, it is common practice to roll a sheet metal strip to the desired thickness and subject it to heat treatment to ensure formability. However, heat treatment accounts for a large portion of the costs involved in producing bipolar plates, as it requires a lot of energy in the form of heat.

[0008] Therefore, the object of the present invention is to provide a method for producing a half-sheet of a bipolar plate that reduces the energy required to produce a bipolar plate compared to the prior art. This object is achieved by the features of the independent patent claims. Further advantageous developments are the subject of the dependent claims.

[0009] A first aspect of the present invention comprises a method for producing a half sheet of a bipolar plate.

[0010] The method comprises, as one method step, rolling a sheet metal strip, wherein at least one first region of the sheet metal strip is rolled to a uniform first sheet thickness and at least one second region of the sheet metal strip is rolled to a uniform second sheet thickness. The first sheet thickness is greater than the second sheet thickness, and the first region and the second region are each planar. Thus, the at least one first and the at least one second region have different sheet thicknesses and also different formability.

[0011] A channel-shaped surface structure for guiding reactants and fluids, such as hydrogen and / or oxygen, is then introduced into the at least one first region with a high degree of process reliability and without cracks forming in the sheet metal. For the at least one first region, a greater depth (also known as drawing depth) can thus be achieved when introducing the channel-shaped surface structure. Furthermore, this can save material; because where less formability is required, such as in the at least one second region, the sheet metal or sheet metal strip can be thinned further compared to locations where greater formability is required, such as in the at least one first region.

[0012] The step of rolling a sheet metal strip is carried out in such a way that the sheet metal strip is flat in at least one first region of the sheet metal strip and / or in at least one second region of the sheet metal strip and / or in at least one third region of the sheet metal strip and has a flat, mutually parallel surface as seen in a section through the sheet metal strip. This means that the surfaces of the sheet metal strip and / or of the at least one first region of the sheet metal strip and / or of the at least one second region of the sheet metal strip and / or of the at least one third region of the sheet metal strip are formed without a structure, i.e., flat, by the rolling process.In particular, the surfaces of the sheet metal strip and / or of the at least one first region of the sheet metal strip and / or of the at least one second region of the sheet metal strip and / or of the at least one third region of the sheet metal strip are formed by rolling without a depression or without a valley or without a peak or without a projection.

[0013] Furthermore, the step of rolling along a conveying direction of the sheet metal strip can provide variable sheet thicknesses. The at least one first region and the at least one second region of the sheet metal strip and / or at least one third region of the sheet metal strip can be rolled alternately along the conveying direction of the sheet metal strip in order to realize a first and a second sheet thickness for the at least one first region and the at least one second region, respectively. This means that a first region can be rolled first and then a second region. However, it is also possible to produce both regions with one roll or in one rolling process.

[0014] Against this background, for example, heat treatment of the entire sheet metal strip, which could increase the formability of the entire sheet metal strip, e.g. uniformly, can be dispensed with, thereby saving energy. As a result, the presented method can reduce the manufacturing costs for a half-sheet of a bipolar plate. Furthermore, the presented method can enable more complex forming geometries or more complex geometries for the at least one first region. In other words, in regions with little forming for the production of the half-sheet, such as in the at least one second region and / or in at least one third region of the sheet metal strip, the sheet thickness can be reduced to a minimum by the rolling step.In at least one first region, which corresponds to an electrochemically active region in the electrochemical cell, the sheet thickness is selected to be higher during the rolling step than in the at least one second region and / or in the at least one third region in order to be able to realize complex forming geometries, such as for the channel-shaped surface structure, in the at least one first region.

[0015] In other words, the idea underlying the present invention is to provide the sheet or sheet metal strip for the production of half-sheets for bipolar plates with targeted local thickness differences in advance. The thinner the sheet metal strip is rolled in at least one second region and / or at least one third region, the greater the technical advantages, such as its lower thermal mass and weight. Conversely, the thicker the sheet metal strip is provided in at least one first region, the simpler and more cost-effective the forming process to introduce the channel-shaped surface structure into the at least one first region.

[0016] For the purposes of this invention, the term "formability" refers to the limit of plastic deformation that a material or sheet metal strip can endure without cracking. In other words, formability means the ability of a material or sheet metal strip to undergo plastic deformation before fracture.

[0017] Furthermore, in the rolling process step, a pair of rolls or a roll pairing can be used which roll the at least one first region and the at least one second region and / or at least one third region of the sheet metal strip. At least one roll of the pair or roll pairing can have at least one depression along its circumference. This depression serves to create or roll the at least one first region. Where the depression meets the sheet metal strip, more material of the rolled sheet metal strip can be accumulated. Thus, the at least one first region of the sheet metal strip can be rolled to a first sheet thickness. In contrast, where no depression is found, there is less material of the rolled sheet metal strip. Thus, the at least one second region of the sheet metal strip can be rolled to a smaller second sheet thickness.

[0018] Alternatively or additionally, it is also possible for the center distance of a pair of rolls or a roll pairing to be changed during the rolling process step. This is possible, for example, hydraulically and / or electromechanically. Thus, at least one roll of the pair or roll pairing can be changed in its relative position to the other roll of the pair or roll pairing in order to roll to a first sheet thickness in at least one first region of the sheet metal strip and to roll to a second sheet thickness in at least one second region of the sheet metal strip. In addition, the process comprises, as a further process step after rolling, the introduction of a channel-shaped surface structure into the at least one first region. The channel-shaped surface structure serves to homogeneously distribute reactants and fluids in the electrochemical cell.The channel-shaped surface structure can also be designed to conduct a first reactant, a second reactant, and / or a coolant from an inlet to an outlet. In this way, an electrochemical cell with at least one bipolar plate can be optimally supplied, thus maximizing efficiency. For example, a channel-shaped surface structure can be introduced into the at least one first region by embossing, punching, hydroforming, or rolling, for example, before the cutting step. The surface structure is embossed through the sheet metal so that both the top and bottom of the sheet metal reflect the structure.

[0019] Furthermore, the method comprises, as a further process step, cutting the sheet metal strip to separate the half-sheet from the sheet metal strip, wherein the half-sheet has at least a first region and a second region. Cutting the sheet metal strip thus produces individual half-sheets for the production of bipolar plates, which can be used in an electrochemical cell, such as a fuel cell or a fuel cell stack.

[0020] Furthermore, the cutting may comprise creating a fluid inflow or fluid outflow, in particular a coolant inflow and a coolant outflow and / or a hydrogen inflow and a hydrogen outflow and / or an oxygen inflow and an oxygen outflow.

[0021] Furthermore, the at least one first region and the at least one second region can be arranged alternately along a conveying direction of the sheet metal strip, or at least partially adjacent to one another in the conveying direction, or partially adjacent to one another or one behind the other in the conveying direction, or partially behind one another in the conveying direction. In this case, for example, a first region can be followed by a second region in the conveying direction of the sheet metal strip, which second region can then be followed by a first region. Thus, a second region can immediately follow a first region and / or vice versa. However, it is also possible for a further region to be arranged between a first and second region, which spaced the first region and second region apart from one another.

[0022] In addition, the sheet metal strip can have at least one third region. The sheet metal strip can also be rolled to a third sheet thickness in the at least one third region of the sheet metal strip. In other words, the at least one third region of the sheet metal strip can be rolled to a third sheet thickness. The at least one third region and the at least one second region can also at least partially delimit or at least partially border or at least partially confine or at least partially surround the at least one first region. The at least one third region can, for example, be shaped such that it can accommodate a seal. The at least one third region can thus be rolled to a third sheet thickness in order to obtain or create a plane for a seal.

[0023] Furthermore, the at least one second region and the at least one third region can be of equal thickness. In this case, the second sheet thickness and the third sheet thickness have the same value. The second sheet thickness and the third sheet thickness can also have essentially the same value. The expression "essentially the same value" can be understood in the present description to mean that the sheet thicknesses of the second region and third region are to be regarded as equal if they differ from each other by a maximum of + / - 5% in their sheet thicknesses. This means that with "essentially the same value", the third sheet thickness is, for example, the second sheet thickness + / - 5% of the second sheet thickness.

[0024] Furthermore, the second sheet thickness and / or the third sheet thickness can have a value that is at least 20% lower than the first sheet thickness. In other words, the first sheet thickness has a significantly higher value than the second and / or third sheet thickness.

[0025] Optionally, the method can further comprise the step of detecting a position of the channel-shaped surface structure relative to the sheet metal strip, for example, relative to the dimensions of the sheet metal strip, using a sensor as a starting point for cutting the sheet metal strip. This allows for compensation of manufacturing tolerances that may occur, for example, during the introduction of the channel-shaped surface structure. In this way, the cutting process can be adapted to the manufacturing tolerances, for example, to the position of the channel-shaped surface structure.

[0026] Before introducing a channel-shaped surface structure, the method can comprise, as a further method step, selective or partial annealing of the sheet metal strip, wherein during the annealing, at least the first region of the sheet metal strip is soft annealed in a targeted manner and / or by targeted application of heat and / or by targeted application of heat, and the at least one second region and / or the at least one third region of the sheet metal strip is / is excluded or left out therefrom. Alternatively or additionally, during the method step of selective annealing of the sheet metal strip, the at least one first region of the sheet metal strip and the at least one second region and / or third region of the sheet metal strip can be heat-treated differently or in different ways.In other words, during the process step of selectively soft annealing the sheet metal strip, more heat energy can be supplied to at least the first region of the sheet metal strip than to the at least one second region and / or third region of the sheet metal strip. The additional heat energy can, for example, comprise a longer annealing time and / or a greater heat intensity. As a result, the at least one first and at least one second region and / or the at least one third region of the sheet metal strip have different formability properties. The heat treatment of the sheet metal strip can therefore be concentrated on the at least one first region, into which a channel-shaped surface structure for conducting fluids or reactants can then be introduced with a high degree of process reliability without cracking occurring in the sheet metal. Heat treatment of the entire sheet metal strip can therefore be dispensed with, which saves energy for heating.Consequently, the presented method can reduce the manufacturing costs of a bipolar plate. Furthermore, the presented method can realize more complex forming geometries or more complex geometries for the at least one first region.

[0027] In selective annealing, energy is supplied predominantly to the at least one first region, with energy being supplied to a lesser extent or not at all to the at least one second region and / or third region. Thus, the heat treatment duration for treating the at least one second and / or third region and / or the heat intensity acting on the at least one second region and / or third region is shorter compared to the annealing duration for annealing the at least one first region and / or is less intense compared to the heat intensity acting on the at least one first region.

[0028] Soft annealing is generally used to, for example, reduce stresses in the material or in the sheet metal strip or in the at least one first region of the sheet metal strip and to increase the formability of the material or in the sheet metal strip or in the at least one first region. For example, in order to introduce a surface structure, the sheet metal strip requires a higher formability in the at least one first region than in the at least one second region and / or third region that is not to be formed or structured or into which no surface structure is to be introduced. Thus, the at least one second region and / or third region can have a lower degree of formability.

[0029] In other words, the idea underlying the present invention is that not all regions of the sheet metal strip need to have the same formability. Furthermore, the at least one second region and / or third region, which is to be formed little or not at all, can be heat-treated to a lesser extent, for example, for a shorter time, or not at all. In this way, the energy required for annealing can be reduced, since the entire sheet metal strip no longer needs to be heated, but only the at least one first region. This allows energy and costs to be saved.

[0030] Furthermore, during selective annealing of the sheet metal strip, the at least one first region of the sheet metal strip can be annealed with a first annealing time and / or with a first heat intensity, and the at least one second and / or third region of the sheet metal strip can be annealed with a second heat treatment time and / or with a second heat intensity. The first annealing time or the first heat intensity can be different from the second heat treatment time or second heat intensity. Thus, each region can be heat-treated according to a desired formability, thereby saving energy overall. For example, the second heat treatment time can be shorter than the first annealing time. The second heat treatment time or the second heat intensity can also be half, 45%, or 40% of the first annealing time or the first heat intensity.Furthermore, the second heat intensity can be less intense than the first. This again demonstrates that energy can be saved.

[0031] The term "heat intensity" or "intensity" can be understood as "irradiance" (also radiation flux density, obsolete: radiation flux density). "Heat intensity" or "irradiance" can be the term for the total power of incoming electromagnetic energy that strikes a surface (e.g., the at least one first area and / or the at least one second area and / or the at least one third area), relative to the size of the area.

[0032] Selective annealing or local heat treatment can be performed, for example, in a continuous furnace. Annealing can locally improve the formability of the sheet metal strip.

[0033] Furthermore, during selective annealing, the first and / or second heat treatment durations and / or the first and second heat intensities in sections of a continuous furnace can be selectively controlled, for example, by a control device depending on the conveying speed and the position of the at least one first and the at least one second and / or third region. For this purpose, the continuous furnace can have a plurality of heating units, such as radiators that convert electrical energy into heat, for example, and / or nozzles that generate heat using gas, for example. The heating units can be arranged in a matrix or grid, for example, above and / or at a distance from the sheet metal strip.The control device can switch the heating units on and off according to the conveying speed and the position of the at least one first region and the at least one second region and / or third region, and / or can regulate their duration and / or intensity with regard to heat generation. The sheet metal strip is preferably made of stainless steel, which may be coated. Alternatively, the sheet metal strip can be made of titanium or a titanium alloy. Other metal alloys can also be used.

[0034] A second aspect of the present invention comprises a bipolar plate comprising two materially bonded half sheets produced by the method according to the invention.

[0035] The features relating to the method mentioned above under the first aspect of the invention can also be combined with further features under the second aspect of the invention.

[0036] The bipolar plate has an electrochemically active region on each of the half-sheets, which corresponds to the at least one first region of the two half-sheets. Furthermore, each half-sheet has, in particular, at least two distributor regions, which correspond to the at least one second region, for supplying and discharging fluids, such as reaction gases and / or reactants and / or coolants. Furthermore, the bipolar plate can be designed such that it has separate channels for fluids such as reaction gases and / or reactants and for a coolant.

[0037] In addition, connections for fluids, such as reaction gases and / or for reactants and / or for the coolant, can be connected to the distribution areas.

[0038] For example, the bipolar plate can comprise distribution structures for conducting fluids, such as coolants. In the case of a fuel cell, the coolant is typically conducted between two welded half-sheets of a bipolar plate. These distribution structures can be designed as channels, allowing the coolant to be conducted and cooling a fuel cell stack. The fuel (e.g., hydrogen) is distributed on the anode side of a bipolar plate of a fuel cell, and the air / oxygen is distributed on the cathode side.

[0039] The bipolar plate can have a channel-shaped surface structure, which can be designed as an open, groove-like channel structure. For example, the bipolar plate can include distribution structures for conducting fluids, such as coolants. These distribution structures can be designed as channels, allowing the coolant to be conducted and cooling a fuel cell stack. The anode side of a bipolar plate is used, in particular, for the distribution of the fuel (e.g., hydrogen), and the cathode side is used, in particular, for the distribution of air / oxygen.

[0040] Furthermore, the bipolar plate can have two third regions. The two third regions can be arranged on two opposite sides of the at least one first region, so that, together with two second regions, they delimit the at least one first region. The third region can, for example, be shaped to accommodate a seal.

[0041] In general, the bipolar plate can be used, for example, in vehicles, to convert hydrogen (H2) with oxygen (O2) from the air to form water. The bipolar plate plays a central role in this process. It can serve as a structural support plate and form the two poles of the fuel cell – the anode plate for conducting H2 and the cathode plate for supplying O2.

[0042] The bipolar plate can perform various tasks, such as a uniform distribution of the fluids and reaction gases or reactants (H2 and O2), a supply of the gases to a catalyst layer, a removal of the resulting reaction water, a forwarding of the current resulting from the reaction and an efficient dissipation of the reaction heat.

[0043] The electrocatalytic conversion of hydrogen typically produces product water and, as already mentioned, heat. Both can be dissipated from a fuel cell via the bipolar plate.

[0044] A third aspect of the present invention comprises an electrochemical cell, in particular a fuel cell or an electrolysis cell, comprising at least one bipolar plate according to the invention.

[0045] It is expressly noted that the features of the method for producing a half-sheet of a bipolar plate and / or the features of the bipolar plate, as mentioned under the second aspect, can be used individually or in combination with one another in the electrochemical cell. In other words, the features mentioned above under the first and / or second aspect of the invention can also be combined with further features here under the third aspect of the invention.

[0046] In the following, the inventive concept presented above is expressed again and additionally in other words.

[0047] This idea concerns - in simplified terms - a method for producing a half sheet of a bipolar plate by introducing targeted thickness differences within a sheet used.

[0048] The thinner the starting material, for example, a sheet metal strip for a half-sheet of a bipolar plate, the lower the costs and the greater the technical advantages (e.g., in terms of thermal mass, etc.). The thicker the starting material, the easier and more cost-effective the sheet metal forming process.

[0049] The sheet metal for the production of half sheets for bipolar plates can be specifically provided in advance with thickness differences, i.e. at least with a uniform first sheet thickness in at least one first area and with a uniform second sheet thickness in at least one second area.

[0050] In areas that are to be subjected to minimal forming (e.g., in at least a second and / or third region of the sheet metal strip), the sheet thickness can be reduced. In an area that is to receive a complex channel structure or a channel-shaped surface structure (here, in at least a first region of the sheet metal strip), the sheet thickness is selected to be higher in order to be able to realize the more complex forming geometries without cracking.

[0051] Along a seal, for example in at least a third area of ​​the sheet metal strip, the material can also be thinned to obtain a plane for the seal.

[0052] The bipolar plate according to the invention can be used in an electrochemical cell, such as a fuel cell, an electrolyzer or a redox flow battery.

[0053] The invention will be explained in more detail below using an exemplary embodiment in conjunction with the accompanying drawings, in which: Fig. 1 shows a schematic flow diagram of a method for

[0054] Manufacturing a half sheet of a bipolar plate;

[0055] Fig. 2 is a schematic sectional view of a part of a

[0056] Sheet metal strip after process step V1;

[0057] Fig. 3 is a schematic plan view of a half sheet;

[0058] Fig. 4 is a three-dimensional view of a bipolar plate; and

[0059] Fig. 5 is a schematic view of an electrochemical cell.

[0060] In the following description, the same reference symbols are used for the same items.

[0061] Figure 1 shows a schematic flow diagram of a method for producing a half sheet 1 of a bipolar plate 1' (see Figure 4), with Figure 2 showing a schematic sectional view of a portion of a sheet metal strip B after process step V1. For the sake of simplicity and brevity, Figures 1 and 2 are described together below.

[0062] For example, Figure 1 shows that the method represents a continuous process, wherein a sheet metal strip B is conveyed along a conveying direction F.

[0063] Furthermore, Figure 1 shows that the method comprises, as a first process step, rolling V1 of a sheet metal strip B or a sheet metal plate. For example, the sheet metal strip is unwound from a sheet metal coil prior to rolling V1.

[0064] In this case, at least one first region 2 of the sheet metal strip B is rolled to a uniform first sheet thickness d1 and at least one second region 3 of the sheet metal strip B is rolled to a uniform second sheet thickness d2. In this case, flat regions are each rolled in such a way that a top and bottom side of the sheet metal strip run parallel in the respective region. According to Figure 2, the first sheet thickness d1 is greater than the second sheet thickness d2. Thus, the at least one first region 2 and the at least one second region 3 have different sheet thicknesses d1, d2 and also different formability. As a result, a channel-shaped surface structure 5 for conducting fluids and reactants, such as hydrogen and / or oxygen, can be introduced into the at least one first region 2 simply and with a high degree of process reliability without cracking occurring.

[0065] The rolling V1 thus provides different sheet thicknesses d1, d2 along the conveying direction F of the sheet metal strip B. The at least one first region 2 and the at least one second region 3 are rolled alternately along the conveying direction F of the sheet metal strip B in order to realize a first sheet thickness d1 and a second sheet thickness d2 for the at least one first region 2 and the at least one second region 3, respectively. This means that a first region 2 can be rolled first, followed by a second region 3. However, it is also possible to produce both regions 2, 3 with one roll or in one rolling process.

[0066] As Figure 1 further shows, the at least one first region 2 and the at least one second region 3 are arranged alternately along the conveying direction F of the sheet metal strip B or in sections one behind the other in the conveying direction. Thus, for example, in the conveying direction F of the sheet metal strip B, a first region 2 is followed by a second region 3, which is then followed by a first region 2. Thus, a second region 3 immediately follows a first region 2 and vice versa.

[0067] With reference to the half-sheet 1 in Figure 3, it can be seen that the sheet metal strip B has at least one third region 4. The at least one third region 4 of the sheet metal strip B is rolled to a third sheet thickness d3. Specifically, two third regions 4 and two second regions 3 delimit or surround a first region 2. The at least one third region 4 or the two third regions 4 is / are further shaped such that it can accommodate a seal. Thus, the at least one third region 4 or the two third regions 4 are rolled to a third sheet thickness d3 in order to create a plane for a seal.

[0068] The second sheet thickness d2 and the third sheet thickness d3 have essentially the same value. This means that the sheet thicknesses d2, d3 of the second region 3 and the third region 4 are considered equal if they differ from each other by a maximum of + / - 5%. Furthermore, the second sheet thickness d2 and the third sheet thickness d3 have a lower value than the first sheet thickness d1. In other words, the first sheet thickness d1 has a higher value than the second and third sheet thicknesses d2, d3.

[0069] In addition, the method according to Figure 1 comprises, after rolling, as a further method step V2, the introduction of a channel-shaped surface structure 5 into the at least one first region 2. The channel-shaped surface structure 5 serves to homogeneously distribute fluids. Strictly speaking, the channel-shaped surface structure 5 is designed to guide a first reactant, a second reactant, and a coolant from an inlet to an outlet. In this way, an electrochemical cell, such as a fuel cell, comprising one or more bipolar plates 1', produced from two materially bonded half-sheets 1, which were formed according to the method presented here, can be optimally supplied with reactants and / or coolant, so that the efficiency of the electrochemical cell can be maximized.For example, the introduction V2 of a channel-shaped surface structure 5 into the at least one first region 2 can be achieved by embossing, punching, hydroforming, or rolling. Due to the typically small sheet thickness of the sheet metal strip of less than 1 mm, the channel structure is formed on the top and bottom sides of the sheet metal strip.

[0070] The method may include, as an optional step, detecting a position of the channel-shaped surface structure 5 in relation to the dimensions of the sheet metal strip B by means of a sensor as a starting point for cutting the sheet metal strip B. Thus, manufacturing tolerances that occur, for example, during the introduction V2 of the channel-shaped surface structure 5 can be compensated.

[0071] During cutting, a half-sheet 1 is separated from the sheet metal strip B, wherein the half-sheet 1 comprises at least a first and a second region 2, 3. Cutting the sheet metal strip B thus results in individual half-sheets 1.

[0072] In addition, the cutting comprises creating a fluid inflow and fluid outflow, in particular a coolant inflow 6 and coolant outflow 7, a hydrogen inflow 8 and hydrogen outflow 11 as well as an oxygen inflow 9 and oxygen outflow 10. As a result, the presented method can reduce the manufacturing costs of a half-sheet 1 of a bipolar plate 1'. Furthermore, the presented method can enable the realization of more complex forming geometries or more complex geometries in the first region 2. In other words, in regions in which little forming is carried out, such as in the second regions 3, the sheet thickness d2 can be reduced to a minimum by the rolling step V1. In the first region 2, the sheet thickness d1 is selected to be higher during the rolling step than in the second regions 3 in order to achieve complex forming geometries, such asfor a channel-shaped surface structure 5, in the first area 2 to be able to be realized without cracks.

[0073] Optionally, a selective soft annealing of the sheet metal strip B can be carried out as a further process step before the introduction of V2.

[0074] During selective annealing, the at least one first region 2 of the sheet metal strip B can be annealed selectively or by selectively applying heat. The at least one second region 3 and the at least one third region 4 of the sheet metal strip B can be excluded or omitted. This allows different formability to be generated in the regions 2, 3, and 4. Thus, the heat treatment of the sheet metal strip B can be concentrated on the at least one first region 2, into which a channel-shaped surface structure 5 for conducting fluids can be introduced easily and with high process reliability.

[0075] As a result, heat treatment of the entire sheet metal strip B can be omitted, thus saving energy for heating. Consequently, the presented method can reduce the manufacturing costs of a half-sheet 1 of a bipolar plate 1'. Furthermore, the presented method can be used to realize more complex forming geometries or more complex geometries in the at least one first region 2.

[0076] Specifically, during selective annealing of sheet metal strip B, the at least one first region 2 can be annealed for a first annealing time or at a first heat intensity, and the at least one second region 3 and third region 4 can be subjected to a second heat treatment time or at a second heat intensity. The first annealing time or the first heat intensity is different from the second heat treatment time or the second heat intensity. Thus, each region can be heat-treated according to a desired formability, thereby saving energy overall. In this case, the second heat treatment time is shorter than the first annealing time, or the second heat intensity is less intense than the first heat intensity.

[0077] Selective soft annealing can be performed in a continuous furnace. Soft annealing can locally improve the formability of sheet metal strip B.

[0078] Furthermore, during selective annealing, a control device (not shown) can selectively control the first annealing time and second heat treatment time or the first and second heat intensities in sections of the continuous furnace depending on the conveying speed and the position of the at least one first region 2 and the at least one second region 3 and third region 4. For this purpose, the continuous furnace can have several heating units, such as radiators that convert electrical energy into heat, for example, and / or nozzles that generate heat using gas, for example. The heating units can be arranged in a matrix or in a grid.The control device can switch the heating units on and off according to the conveying speed and the position of the at least one first region 2 and the at least one second region 3 and the at least one third region 4 or can regulate their duration and intensity with regard to the generation of heat.

[0079] Figure 2 shows a schematic sectional view of the sheet metal strip B after process step V1 with a cutting direction parallel to the conveying direction F.

[0080] The rolled sheet metal strip B comprises a first region 2 and two second regions 3. The first region 2 has a first sheet thickness d1, and each second region 3 has a second sheet thickness d2. As indicated in Figure 2, the second sheet thickness d2 is less than the first sheet thickness d1.

[0081] Figure 3 shows a schematic plan view of the half sheet 1 from Figure 1 .

[0082] It can be seen that the half-sheet 1 has two third regions 4. The third regions 4 have a third sheet thickness d3. The third sheet thickness d3 is equal to the second sheet thickness d2. The first region 2 is arranged centrally with respect to the half-sheet 1 and forms an electrochemically active region in an electrochemical cell. For example, two second regions 3 and two third regions 4 are arranged on opposite sides of the first region 2. The channel-shaped surface structure 5 extends between the two second regions 3 and the two third regions 4.

[0083] Described differently, Figure 3 shows that the half-sheet 1 has two third regions 4. The two third regions 4 are arranged on two opposite sides of the first region 2, so that, together with the two second regions 3, they delimit the first region 2. The third regions 4 are shaped, for example, such that they can each accommodate a seal. The third regions 4 have a third sheet thickness d3, which here has the same value as the second sheet thickness d2.

[0084] Furthermore, Figure 3 shows fluid inflows and fluid outflows, here a coolant inflow 6, a coolant outflow 7, a hydrogen inflow 8, a hydrogen outflow 11, an oxygen inflow 9, and an oxygen outflow 10 in the two second regions 3. Other arrangements or combinations of the inflows and outflows are also conceivable.

[0085] Thus, the half-sheet 1 is designed in such a way that it has channels for reaction gases and / or for reactants and / or for a coolant.

[0086] As already explained, the half-sheet 1 has a channel-shaped surface structure 5, which is designed as an open, groove-like channel structure. To form a bipolar plate 1' (see Figure 4), two half-sheets 1 are arranged one above the other and bonded together in such a way that coolant channels are formed through the channel structures or through the channel-shaped surface structure 5 between the two half-sheets 1.

[0087] Generally speaking, a bipolar plate 1' can fulfill various tasks, such as uniform distribution of the fluids in an electrochemical cell, supplying the fluids to a catalyst layer, transporting the resulting reaction water, conducting the current resulting from the reaction, and efficiently dissipating the reaction heat. Figure 4 shows a three-dimensional schematic view of a bipolar plate 1' comprising two integrally bonded half-sheets 1. The same reference numerals as in Figure 3 denote the same elements. Figure 5 shows a schematic three-dimensional view of an electrochemical cell, in particular a fuel cell 20, comprising two bipolar plates 1' according to Figure 4 and a membrane-electrode unit 13 arranged between the two bipolar plates 1'.By stacking further membrane electrode units 13 and bipolar plates 1', a fuel cell stack 100 comprising a plurality of fuel cells 20 is created.

[0088] List of reference symbols

[0089] 1 half sheet r bipolar plate

[0090] 2 first area

[0091] 3 second area

[0092] 4 third area

[0093] 5 channel-shaped surface structure

[0094] 6 Coolant inlet

[0095] 7 Coolant drain

[0096] 8 Hydrogen inflow

[0097] 9 Oxygen inflow

[0098] 10 Oxygen outflow

[0099] 11 Hydrogen outflow

[0100] 13 Membrane electrode assembly

[0101] 20 fuel cells

[0102] 100 Fuel cell stack d1 first sheet thickness d2 second sheet thickness d3 third sheet thickness

[0103] V1 rollers

[0104] V2 Introduction of a channel-shaped surface structure

Claims

Patent claims 1 . A method for producing a half sheet (1 ) of a bipolar plate (1 '), comprising the steps: - rolling (V1) of a sheet metal strip (B), - wherein in at least one first region (2) of the sheet metal strip (B) it is rolled to a uniform first sheet thickness (d1) and in at least one second region (3) of the sheet metal strip (B) it is rolled to a uniform second sheet thickness (d2), - wherein the first sheet thickness (d1) is formed greater than the second sheet thickness (d2) and the first region (2) and the second region (3) are each formed flat, - introducing (V2) a channel-shaped surface structure (5) into the at least one first region (2), - Cutting the sheet metal strip (B) to separate the half-sheet (1) from the sheet metal strip (B), wherein the half-sheet (1) has at least a first region (2) and a second region (3).

2. Method according to claim 1, - wherein the at least one first region (2) and the at least one second region (3) are arranged alternately or in sections one behind the other along a conveying direction (F) of the sheet metal strip (B).

3. Method according to claim 1 or 2, - wherein the second sheet thickness (d2) has a value at least 20% lower than the first sheet thickness (d1).

4. Method according to one of the preceding claims, - wherein the sheet metal strip (B) has at least one third region (4), - wherein the sheet metal strip (B) is rolled to a third sheet thickness (d3) in the at least one third region (4) of the sheet metal strip (B), and wherein the at least one third region (4) and the at least one second region (3) at least partially delimit the at least one first region (2).

5. Method according to claim 4, - wherein the second sheet thickness (d2) and the third sheet thickness (d3) have substantially the same value.

6. Method according to one of the preceding claims, - wherein the introduction (V2) of the channel-shaped surface structure (5) into the at least one first region (2) is carried out by embossing, punching, hydroforming or rolling.

7. Method according to one of the preceding claims, - wherein the cutting comprises creating a fluid inflow and a fluid outflow, in particular a coolant inflow (6) and a coolant outflow (7) and / or a hydrogen inflow (8) and a hydrogen outflow (11) and / or an oxygen inflow (9) and an oxygen outflow (10).

8. Method according to one of the preceding claims, - wherein the method comprises, as a further method step, a selective annealing of the sheet metal strip (B) prior to the introduction (V2) of the channel-shaped surface structure (5), in which the at least one first region (2) of the sheet metal strip (B) is specifically annealed and at least the second region (3) of the sheet metal strip (B) is excluded from the targeted annealing, so that the at least one first region (2) and the at least one second region (3) have different deformability capacities from one another.

9. Bipolar plate (1') comprising two materially bonded half-sheets (1'), produced by a method according to one of the preceding claims.

10. Electrochemical cell, in particular fuel cell (20), with at least one bipolar plate (1') according to claim 9.

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