Method for producing bipolar plate, bipolar plate and electrochemical cell

Abstract

The invention relates to a method for producing a bipolar plate (1), comprising two electrically conductive individual plates (1a, 1b), each of which is formed from a polymer-graphite composite material, comprising the following steps: providing the two individual plates (1a, 1b); providing an annular strip of metal sheet (2); placing a strip (2) of sheet metal between the two individual plates (1a, 1b) in the peripheral region of the individual plates (1a, 1b); and-fusing the sheet metal strip (2) into adjacent surfaces (3a, 3b) of the individual plates (1a, 1b), the two individual plates (1a, 1b) being connected to each other in the region of the sheet metal strip (2) in a fluid-tight and electrically conductive manner. The invention also relates to a bipolar plate (1) and an electrochemical cell (10).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a bipolar plate comprising two electrically conductive individual plates, each of which is formed from a polymer-graphite composite material. The present invention also relates to a bipolar plate comprising two electrically conductive individual plates, each of which is formed from a polymer-graphite composite material and connected to one another in a fluid-tight and electrically conductive manner. Finally, the present invention relates to an electrochemical cell, such as a polymer electrolyte fuel cell or an electrolyzer, comprising at least one such bipolar plate. Background Art

[0002] Bipolar plates of the type mentioned at the outset and methods for their production are known. Two individual plates made of a polymer-graphite composite are joined in a fluid-tight and electrically conductive manner by laser welding or bonding.

[0003] DE 10 2007 058 743 A1 discloses a membrane electrode unit for a fuel cell. It describes a bipolar plate having a flow channel system and formed from a conductive material, including a graphite-filled plastic. This plate, referred to herein as a "graphite bipolar plate," can be processed and modified by welding or bonding. The bipolar plate comprises two plates joined together.

[0004] WO 2016 / 033 147 A1 describes a method for sealing a multi-component bipolar plate. The bipolar plate comprises a first component and a second component, which are connected by a seal disposed between the first and second components. The seal is aligned with a region of the first and / or second component having a protrusion. The protrusion is pressed into the material of the seal, and the seal plastically deforms, thereby forming a seal between the first and second components. Additional spacers and bonds may be used between the first and second components.

[0005] Laser welding is associated with high costs due to its low processing speed and is therefore considered disadvantageous. A disadvantage of the bonding is that the plates are electrically insulated from each other in the bonding gap. The individual plates of a bipolar plate made of a polymer-graphite composite in an electrochemical cell are usually electrically contacted with each other by contact pressure in unbonded areas, such as the active surface, where the electrochemical reaction occurs. However, an additional plasma ablation process is required in these areas to increase the conductivity of the plate surface, which in turn leads to additional process costs. Summary of the Invention

[0006] The present invention aims to provide an improved method for producing a bipolar plate comprising two electrically conductive individual plates, each of which is formed from a polymer-graphite composite material. Furthermore, the present invention aims to provide such a bipolar plate and an electrochemical cell having such a bipolar plate.

[0007] This object is achieved by a method for producing a bipolar plate comprising two electrically conductive individual plates, each of which is formed from a polymer-graphite composite material, the method comprising the following steps:

[0008] - Two separate boards are provided,

[0009] - providing an endless metal sheet strip,

[0010] - placing a metal sheet strip between two separate plates in the peripheral region of the separate plates, and

[0011] - fusing a metal sheet strip into an adjacent surface of the individual plates, wherein the two individual plates are joined together in a fluid-tight and electrically conductive manner in the region of the metal sheet strip.

[0012] The sheet metal strips form a mechanically strong and resilient connection between the individual plates, resulting in a fluid-tight and electrically conductive connection. Furthermore, the sheet metal strips provide mechanical reinforcement for the resulting bipolar plates, which has a positive impact on the handling and mechanical strength of the bipolar plates in the stack during the stacking process when constructing an electrochemical cell stack.

[0013] In particular, the individual plates have a flow channel system which, in a manner known per se, enables the distribution and conduction of the influent medium in the electrochemical cell. The plate thickness of each individual plate is preferably in the range of 0.2 mm to 1 mm, in particular 0.3 mm.

[0014] Suitable polymer-graphite composites are preferably formed from thermoplastics, such as polypropylene (PP), filled with carbon particles in the form of graphite. The use of graphite with a particle size of less than 150 μm has proven successful. Furthermore, small amounts of carbon black can also be added to the polymer-graphite composite. A polymer-graphite composite with a composition of approximately 20% by weight of polymer, approximately 73% by weight of graphite, and approximately 7% by weight of carbon black has proven successful.

[0015] The sheet metal strip preferably has a sheet metal strip thickness (BD) in the range of 0.05 mm to 0.15 mm, in particular 0.1 mm. The sheet metal strip is preferably made of stainless steel, titanium, or steel sheet, although other metals may also be used. The annular sheet metal strip is preferably produced by joining the ends of the sheet metal strip by spot welding. However, other known joining methods for joining the two ends of a sheet metal strip to form an annular sheet metal strip may also be used, such as laser welding, brazing, bonding, crimping, etc.

[0016] Preferably, a sheet metal strip is used for this purpose. The sheet metal strip, viewed in a cross-section along its longitudinal extension, has at least one bend. The sheet metal strip is angled in the bend, with an angle α in the range of 30° to 90° proving advantageous. This creates a positive connection between the two individual panels and the sheet metal strip. Due to the bent structure of the sheet metal strip, the individual panels are tightly connected and pressed together.

[0017] In order to be able to bend the sheet metal strip along its length, the sheet metal strip preferably has a sheet metal strip width BB of 1 mm to 2 mm.Roll forming the sheet metal strip has proven to be a suitable method for forming the at least one bend.

[0018] Alternatively or in combination therewith, it has proven useful to use a sheet metal strip which is designed as a perforated strip and has at least one row of holes.

[0019] In the context of the present invention, a perforated strip is understood to be a sheet metal strip having spaced-apart openings enclosed by the metal sheet and / or having spaced-apart openings arranged in the form of recesses at one edge of the sheet metal strip, the spaced-apart openings locally reducing the width of the metal sheet.

[0020] The openings in at least one row of holes surrounded by the metal sheet are filled with the polymer-graphite composite material from a single sheet or, depending on the arrangement, from two separate sheets when the metal sheet strip is fused and the bond between the metal sheet strip and the polymer-graphite composite material is improved. This also creates a positive-fit connection between the metal sheet strip and the polymer-graphite composite material. In particular, the metal sheet strip has a first row of holes and a second row of holes, wherein, when the metal sheet strip is fused, the first openings of the first row of holes are filled with the polymer-graphite composite material from the first of the two separate sheets, and, when the metal sheet strip is fused, the second openings of the second row of holes are filled with the polymer-graphite composite material from the second of the two separate sheets. Due to the openings, the interlocking of the polymer-graphite composite material and the metal sheet strip is even tighter, and the bond is particularly durable and strong mechanically.

[0021] The openings in the form of recesses arranged at the edge of the sheet metal strip and spaced apart from one another serve in particular to form the support foot so that, when the individual sheets are fused to the sheet metal strip, the underlying individual sheet cannot be circumferentially penetrated by the sheet metal strip. However, only a local, limited penetration of the lower individual sheet can occur in the region of the support foot.

[0022] In particular, the metal sheet strip is completely covered by the polymer-graphite composite material of the individual plates, but may be partially visible on the top or bottom of the bipolar plate assembled from the individual plates. For example, the edges of such supporting feet of the metal sheet strip may be visible on one or both sides of the bipolar plate.

[0023] Preferably, the metal sheet strip and / or at least one of the two individual plates are heated to a temperature above the softening temperature of the polymer-graphite composite material. The temperature must be high enough so that the surface of the metal sheet strip is wetted and surrounded by the polymer-graphite composite material.

[0024] Heating is preferably achieved by inductive heating of the metal sheet strip or by radiant heating in the peripheral region of the individual plates. During the hot stamping of the polymer-graphite composite material, the metal sheet strip can also be inserted into one of the individual plates to form a single plate and joined thereto. To connect to the second individual plate, the metal sheet strip or strips are then heated together with the individual plate and / or the second individual plate with which it has been formed into a unit.

[0025] This object is achieved by a bipolar plate, in particular a bipolar plate formed by the method according to the invention, comprising two electrically conductive individual plates, each of which is formed from a polymer-graphite composite material, wherein the individual plates are connected to one another in a fluid-tight and electrically conductive manner by means of an annular metal sheet strip fused into the two individual plates.

[0026] The individual plates are mechanically strengthened by the metal sheet strips, which provides advantages when the bipolar plates are stacked to form a battery stack.

[0027] Preferably, the sheet metal strip has at least one kink region, as viewed in a cross-section in the direction of its longitudinal extension. In particular, the sheet metal strip has a kink region in the region of each individual plate, as viewed in a cross-section in the direction of its longitudinal extension, and the sheet metal strip is fused to the region of each individual plate. This allows for particularly good interlocking of the individual plates with the sheet metal strip and ensures that the individual plates are securely connected to one another.

[0028] Alternatively or additionally, the metal sheet strip is designed as a perforated strip and has at least one row of holes. As already explained above with respect to the method, openings and / or recesses enclosed by the metal sheet can be present at the edges of the metal sheet strip. When the metal sheet strip is fused, the openings of the at least one row of holes are filled with the polymer-graphite composite material of the separate plates, and the bond between the metal sheet strip and the polymer-graphite composite material is improved. In particular, the metal sheet strip has a first row of holes and a second row of holes, wherein, when the metal sheet strip is fused, the first openings of the first row of holes are filled with the polymer-graphite composite material of the first of the two separate plates, and when the metal sheet strip is fused, the second openings of the second row of holes are filled with the polymer-graphite composite material of the second of the two separate plates.

[0029] This object is achieved by an electrochemical cell comprising at least one bipolar plate according to the present invention. The electrochemical cell is preferably a polymer electrolyte fuel cell, in particular a polymer electrolyte fuel cell for using hydrogen as fuel, or an electrolysis cell, in particular an electrolysis cell for splitting water into hydrogen and oxygen. However, the electrochemical cell may also be a redox flow battery or a battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figures 1 to 11 The present invention is intended to be explained by way of example. In the accompanying drawings:

[0031] Figure 1 shows a three-dimensional view of two separate plates with an annular metal sheet strip arranged between them,

[0032] Figure 2 Shown through Figure 1 The arrangement shown in section AA,

[0033] Figure 3 shows the metal sheet strips after fusion through the Figure 1 The cross section AA of the arrangement and the enlarged view of the fusion area,

[0034] Figure 4 Shown according to Figures 1 to 3 The metal sheet strip used is shown in a cross section in the direction of the longitudinal extension of the metal sheet strip on the left side of the figure, and perpendicular to the longitudinal extension of the metal sheet strip on the right side of the figure.

[0035] Figures 5 to 9 shows various possible cross sections of the sheet metal strip viewed in the direction of its longitudinal extension, and

[0036] Figure 10 The bipolar plates are shown in a three-dimensional view, and

[0037] Figure 11 A schematic diagram of an electrochemical cell is shown in three-dimensional view. DETAILED DESCRIPTION

[0038] Figure 1 A three-dimensional view of two individual plates 1a, 1b made of a polymer-graphite composite material is shown, wherein an annular metal sheet strip 2 is arranged between the two individual plates. Each individual plate 1a, 1b has medium flow openings 8, 9, which are arranged aligned one above the other. In addition, each individual plate 1a, 1b has an active field 7, with respect to which the electrodes of the polymer electrolyte membrane 11 are aligned in an electrochemical cell 10 (see FIG. 1 ). Figure 11 ). The electrochemical reaction of the electrochemical cell 10 takes place in the region of the active field 7. Furthermore, a large number of flow channels 6, which are only schematically shown, extend between the medium throughflow openings 8, 9 and can convey fluids such as coolant, fuel gas and oxidizing gas along the longitudinal extension of the individual plates 1a, 1b. The metal sheet strip 2 is placed between the two individual plates 1a, 1b in the peripheral region of the individual plates 1a, 1b. The metal sheet strip 2 is fused into the adjacent surfaces 3a, 3b of the individual plates 1a, 1b (see also Figure 2 ), wherein two individual plates 1a, 1b are joined together in a fluid-tight and electrically conductive manner in the region of a metal sheet strip 2 to form a bipolar plate 1 (see Figure 3 ).

[0039] Figure 2 Shown through the Figure 1 The existing flow channel 6 is clearly visible here. Figure 1 The same reference numerals in the drawings represent the same elements.

[0040] Figure 3 The metal sheet strips 2 are shown after they have been fused to form the bipolar plate 1 . Figure 1 The arrangement of the structure of the cross section AA. Figure 1Identical reference numerals denote identical elements. The fusion region E can be seen in the enlarged view. The metal sheet strip 2 is fused in a form-fitting manner into the two individual plates 1 a, 1 b and connects the two individual plates to one another in a fluid-tight and electrically conductive manner.

[0041] Figure 4 Shown according to Figures 1 to 3 The sheet metal strip 2 used is shown on the left side of the image in a cross-section BB in the direction of its longitudinal extension, and on the right side perpendicular to the longitudinal extension. The right side of the figure shows the sheet metal strip width BB. Furthermore, openings 5a are indicated, which may optionally be present and form an optional row of holes 4, 4a. Furthermore, the openings 5a are provided in the form of recesses at the edge of the sheet metal strip 2 (only one opening 5b is visible here), which may also optionally form a row of holes 4, 4b. The sheet metal strip 2 has a sheet metal strip thickness BD and two bending regions K1, K2, as can be seen on the left side of the figure.

[0042] Figures 5 to 9 Various possible cross sections of the sheet metal strip are shown, viewed in the direction of the longitudinal extension of the sheet metal strip 2. Figure 3 The same reference numerals in the drawings represent the same elements.

[0043] Figure 5 A cross section of the sheet metal strip 2 is shown with only a bending region K, in which the sheet metal strip 2 is bent by 90° in the middle.

[0044] Figure 6 A cross section of a sheet metal strip 2 is shown having two bending regions K1 , K2 , in which the sheet metal strip 2 is bent by 90° in the same direction.

[0045] Figure 7 A cross section of a sheet metal strip 2 is shown having two bending regions K1 , K2 , in which the sheet metal strip 2 is bent at an acute angle in the same direction.

[0046] Figure 8 A cross section of a sheet metal strip 2 is shown having two bending regions K1 , K2 , in which the sheet metal strip 2 is bent at acute angles in different directions.

[0047] Figure 9 A cross section of a sheet metal strip 2 is shown having openings 5a in the form of a first row of holes 4, 4a and openings 5c in the form of a further row of holes 4, 4c. Figure 4 , a row of holes 4a, wherein, as Figure 9As shown in FIG, two parallel rows of holes 4a, 4c are provided. The openings 5a, 5c in the metal sheet strip 2 are filled with a polymer-graphite composite material and form a particularly mechanically tight and strong connection between the individual plates 1a, 1b. Optionally, according to Figure 9 The metal sheet strip 2 may also have at least one bending region K, see Figure 4 .

[0048] Figure 10 The bipolar plate 1 is shown in a three-dimensional view. Figure 1 and Figure 3 The same reference numerals in the figures denote the same elements. Figure 1 In contrast to the individual plates 1a, 1b shown in FIG, there are individual plates 1a, 1b with circular medium flow openings 8, 9. The position of the fusion region E is indicated, but it is not visible on the outside of the bipolar plate 1. In the region of the indicated fusion region E, sealing structures (not shown separately) are usually present on both sides of the bipolar plate 1 to seal the bipolar plate 1 against the adjacent polymer electrolyte membrane 11 (see FIG. Figure 11 ).

[0049] Figure 11 A schematic three-dimensional view of an electrochemical cell 10 is shown. The electrochemical cell 10 comprises two bipolar plates 1, 1' and a polymer electrolyte membrane 11 (shown only schematically) arranged between the two bipolar plates. The polymer electrolyte membrane 11 is shown as a representative of a membrane electrode unit, which comprises a plastic film with electrodes, catalyst layers, and gas diffusion layers arranged on both sides of the plastic film. Several electrochemical cells 10 can be stacked to form a cell stack 100. Here, the electrochemical cell 10 is a polymer electrolyte fuel cell. However, it can also be an electrolytic cell or another type of electrochemical cell.

[0050] Reference Signs List

[0051] 1. 1' bipolar plate

[0052] 1a, 1b separate boards

[0053] 2 metal sheet strips

[0054] 3a, 3b surfaces

[0055] 4, 4a, 4b, 4c a row of holes

[0056] 5a, 5b, 5c openings

[0057] 6 Flow channels

[0058] 7 Effective Field

[0059] 8 Medium flow openings

[0060] 9 Medium flow opening

[0061] 10 Electrochemical Cells

[0062] 11, 11' polymer electrolyte membrane

[0063] 100 battery stack

[0064] K, K1, K2 bending areas

[0065] E Fusion area

[0066] BD Metal sheet strip thickness

[0067] BB Sheet metal strip width.

Claims

1. A method for producing a bipolar plate (1), comprising two electrically conductive individual plates (1a, 1b), each of which is formed from a polymer-graphite composite material, the method comprising the following steps: - providing two separate plates (1a, 1b); - providing an annular metal sheet strip (2); - placing the metal sheet strip (2) between the two separate plates (1a, 1b) in the peripheral region of the separate plates (1a, 1b); and - fusing the metal sheet strip (2) into adjacent surfaces (3a, 3b) of the separate plates (1a, 1b), the two separate plates (1a, 1b) being connected to one another in the region of the metal sheet strip (2) in a fluid-tight and electrically conductive manner.

2. The method according to claim 1, wherein A sheet metal strip (2) is used which, viewed in cross section in the direction of its longitudinal extension, has at least one kink region (K).

3. The method according to claim 1 or claim 2, wherein: A sheet metal strip (2) is used which is designed as a perforated strip and has at least one row of holes (4).

4. The method according to claim 3, wherein: The metal sheet strip (2) has a first row of holes (4a) and a second row of holes (4b), wherein, when the metal sheet strip (2) is fused, the first openings (5a) of the first row of holes (4a) are filled with the polymer-graphite composite material of the first individual plate (1a) of the two individual plates (1a, 1b), and when the metal sheet strip (2) is fused, the second openings (5b) of the second row of holes (4b) are filled with the polymer-graphite composite material of the second individual plate (1b) of the two individual plates (1a, 1b).

5. The method according to any one of claims 1 to 4, wherein: The metal sheet strip (2) and / or at least one of the two separate plates (1a, 1b) is heated to a temperature above the softening temperature of the polymer-graphite composite material.

6. A bipolar plate (1) comprising two electrically conductive individual plates (1a, 1b), each of which is formed from a polymer-graphite composite material, the individual plates (1a, 1b) being connected to one another in a fluid-tight and electrically conductive manner by means of an annular metal sheet strip (2) fused into the two individual plates (1a, 1b).

7. The bipolar plate (1) according to claim 6, wherein: The sheet metal strip (2) has at least one bending region (K) when viewed in cross section in the direction of its longitudinal extension.

8. The bipolar plate (1) according to claim 7, wherein: The sheet metal strip (2) has a bending region (K1, K2) in the region of each individual plate (1a, 1b) when viewed in cross section in the direction of its longitudinal extension and is fused into the region of each individual plate.

9. The bipolar plate (1) according to any one of claims 6 to 8, wherein: The sheet metal strip (2) is designed as a perforated strip and has at least one row of holes (4, 4a, 4b).

10. An electrochemical cell (10), in particular a polymer electrolyte fuel cell or an electrolyzer, comprising at least one bipolar plate (1) according to one of claims 6 to 9.

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