Bipolar plate, method for manufacturing a bipolar plate and an electrochemical cell - Patents.com

Abstract

The present invention relates to a method for manufacturing a bipolar plate (1) comprising two individual conductive plates (1a, 1b), each made of a polymer-graphite composite material, the method comprising: providing two individual plates (1a, 1b); providing an annular sheet metal strip (2); placing the sheet metal strip (2) between the two individual plates (1a, 1b) in their peripheral regions; and fusing the sheet metal strip (2) to adjacent surfaces (3a, 3b) of the individual plates (1a, 1b), so that the two individual plates (1a, 1b) are fluid-tightly and electrically conductively connected to each other in the region of the sheet metal strip (2). The present 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 individual conductive plates, each formed from a polymer-graphite composite material. The present invention also relates to a bipolar plate comprising two individual conductive plates, each formed from a polymer-graphite composite material, connected to each other in a liquid-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 bipolar plate. [Background technology]

[0002] Bipolar plates of the first-mentioned type and methods for their manufacture are known: two individual plates made of a polymer-graphite composite material are joined in a liquid-tight and electrically conductive manner by laser welding or bonding.

[0003] German Patent Application Publication No. 102007058743 discloses a membrane electrode unit for a fuel cell. It describes a bipolar plate having a flow channel system and made of an electrically conductive material, including graphite-filled plastic, referred to herein as a "graphite bipolar plate," which can be modified by welding or bonding. Here, the bipolar plate comprises two plates joined together.

[0004] WO 2016 / 033147 describes a method for sealing a multi-component bipolar plate. The bipolar plate includes a first component and a second component, which are connected with a seal disposed therebetween. The seal is aligned with an area of ​​the first component and / or an area of ​​the second component having a protrusion. The protrusion is pressurized into the seal material, plastically deforming the seal, and a seal is formed between the first and second components. Additional spacers and joints may be used between the first and second components.

[0005] Laser welding is associated with high costs due to its low operating speed and is therefore considered inconvenient. A drawback of bonding is that the plates are electrically insulated from each other in the bonding gap. In electrochemical cells, the individual plates of bipolar plates made of polymer-graphite composites are typically in electrical contact with each other by contact pressure in non-bonded areas, such as the active surfaces, where the electrochemical reaction occurs. However, to increase the electrical conductivity of the plate surfaces, additional plasma ablation operations are required in these areas, thereby resulting in additional operating costs. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide an improved method for manufacturing a bipolar plate comprising two individual conductive plates, each formed from a polymer-graphite composite material. It is also an object of the present invention to provide such a bipolar plate and an electrochemical cell including such a bipolar plate. [Means for solving the problem]

[0007] This object is achieved with respect to a method for manufacturing a bipolar plate comprising two individual conductive plates each made of a polymer-graphite composite material, the method comprising: - Providing two separate plates; providing an annular sheet metal strip; - placing a sheet metal strip between two individual plates in the peripheral area of ​​the individual plates; - fusing sheet metal strips to adjacent surfaces of the individual plates, The two individual plates are joined together in a liquid-tight and electrically conductive manner in the area of ​​the sheet metal strip.

[0008] The sheet metal strips form mechanically strong and resilient connections between the individual plates, creating liquid-tight and electrically conductive connections. In addition, the sheet metal strips provide mechanical reinforcement to the formed bipolar plates, which has a positive effect on the handling and mechanical strength of the bipolar plates in the stack during stacking operations in constructing the electrochemical cell stack.

[0009] In particular, the individual plates have a channel system that allows the distribution and conduction of the medium entering the electrochemical cell in a manner known per se, and each individual plate preferably has a plate thickness in the range of 0.2 to 1 mm, in particular 0.3 mm.

[0010] Suitable polymer-graphite composites are preferably formed from a thermoplastic material, such as polypropylene (PP), filled with carbon particles in the form of graphite. The use of graphite particles with particle sizes less than 150 μm has proven successful. Additionally, small amounts of carbon black may also be added to the polymer-graphite composite. A polymer-graphite composite with a composition of about 20% by weight polymer, about 73% by weight graphite, and about 7% by weight carbon black has proven effective.

[0011] Suitable sheet metal strips preferably have a sheet metal strip thickness BD of 0.05 to 0.15 mm, in particular 0.1 mm. The sheet metal strip is preferably made of stainless steel, titanium, or steel plate, but other metals can also be used. The annular sheet metal strip is preferably produced by joining both ends of the sheet metal strip by spot welding. However, other known joining methods for joining both ends of a sheet metal strip to form an annular sheet metal strip can also be used, such as laser welding, soldering, bonding, crimping, etc.

[0012] Preferably, a sheet metal strip is used for this purpose, which has at least one bent region in cross section in the direction of its longitudinal extension. The sheet metal strip is angled in the bent region; an angle α in the range of 30 to 90° has proven advantageous. This creates a form-fit connection between the two individual plates and the sheet metal strip. Due to the bent structure of the sheet metal strip, the individual plates are pressed together in close contact.

[0013] To allow the sheet metal strip to be bent along its length, the sheet metal strip preferably has a sheet metal strip width BB of 1-2 mm. Roll forming the sheet metal strip has proven to be a preferred method for creating at least one bend.

[0014] Alternatively, or in combination with this, it has proven useful to use a sheet metal strip configured as a perforated strip and having at least one row of holes.

[0015] In the context of the present invention, a perforated strip is understood to be a strip of sheet metal having spaced apart openings inclined by the sheet metal and / or having spaced apart openings arranged at one edge of the strip of sheet metal in the form of recesses that locally narrow the width of the sheet metal.

[0016] The openings of at least one row of holes surrounded by the sheet metal are filled with polymer-graphite composite material from an individual plate, or from both individual plates depending on the arrangement, when the sheet metal strip is fused, improving the bond between the sheet metal strip and the polymer-graphite composite. This also creates a form-fit connection between the sheet metal strip and the polymer-graphite composite. In particular, the sheet metal strip has a first row of holes and a second row of holes, and first openings of the first row of holes are filled with polymer-graphite composite material from a first individual plate of two individual plates when the sheet metal strip is fused, and second openings of the second row of holes are filled with polymer-graphite composite material from a second individual plate of two individual plates when the sheet metal strip is fused. The interlocking between the polymer-graphite composite and the sheet metal strip is even closer due to the openings, and the bond is mechanically very durable and strong.

[0017] Openings in the form of recesses, arranged on the edges of the sheet metal strip and spaced apart from one another, are used in particular to form the support legs so that when the individual plates are fused with the sheet metal strip, the lower individual plates cannot be penetrated annularly by the sheet metal strip, but only locally limited penetration of the lower individual plates can occur in the region of the support legs.

[0018] In particular, the sheet metal strips are completely covered by the polymer-graphite composite of the individual plates, but may be locally visible on the top or bottom of a bipolar plate assembled from the individual plates, e.g., the edges of such support legs of the sheet metal strips may be visible on one or both sides of the bipolar plate.

[0019] Preferably, the sheet metal strip and / or at least one of the two individual plates is heated to a temperature above the softening point of the polymer-graphite composite material. The temperature must be high enough so that the surface of the sheet metal strip is wetted and surrounded by the polymer-graphite composite material.

[0020] Heating is preferably achieved by induction heating of the sheet metal strip or by radiant heating in the peripheral areas of the individual plates.

[0021] A sheet metal strip can also be inserted into one of the individual plates during hot stamping of the polymer-graphite composite to form a single plate and be bonded thereto. To connect to a second individual plate, the sheet metal strip or strips are then heated together with the individual plate and / or the second individual plate that together already form a unit.

[0022] This object is achieved in particular for a bipolar plate formed by the method according to the invention, comprising two individual conductive plates, each formed from a polymer-graphite composite material, the individual plates being connected to one another in a liquid-tight and electrically conductive manner by means of an annular sheet metal strip fused to both of the individual conductive plates.

[0023] The individual plates are mechanically reinforced by sheet metal strips, which provides an advantage when stacking bipolar plates to form a cell stack.

[0024] The sheet metal strip preferably has at least one bent area in a cross section in the direction of its longitudinal extension. In particular, the sheet metal strip has a bent area in a cross section in the direction of its longitudinal extension that is fused to each individual plate in the area of ​​each individual plate. This allows the individual plates to interlock particularly well with the sheet metal strip and ensures that the individual plates are firmly connected to each other.

[0025] Alternatively or additionally, the sheet metal strip is configured as a perforated strip and has at least one row of holes. As already described above with respect to the method, the openings and / or recesses angled by the sheet metal may be present at the edges of the sheet metal strip. The openings of the at least one row of holes are filled with the polymer-graphite composite material of the individual plates when the sheet metal strip is fused, improving the bond between the sheet metal strip and the polymer-graphite composite material. In particular, the sheet metal strip has a first row of holes and a second row of holes, and first openings of the first row of holes are filled with the polymer-graphite composite material of a first individual plate of two individual plates when the sheet metal strip is fused, and second openings of the second row of holes are filled with the polymer-graphite composite material of a second individual plate of two individual plates when the sheet metal strip is fused.

[0026] This object is achieved with an electrochemical cell comprising at least one bipolar plate according to the invention. Preferably, the electrochemical cell is a polymer electrolyte fuel cell, in particular for using hydrogen as fuel, or an electrolyzer, in particular for splitting water into hydrogen and oxygen. However, the electrochemical cell can also be a redox flow cell or a battery cell.

[0027] 1-11 are intended to illustrate the invention by way of example. [Brief explanation of the drawings]

[0028] [Figure 1] 1 shows a three-dimensional view of two individual plates with an annular sheet metal strip positioned between them. [Figure 2] 2 shows a cross section AA through the arrangement shown in FIG. 1. [Figure 3] 2 shows the cross section AA through the arrangement according to FIG. 1 after fusing of the sheet metal strips with an enlarged view of the fused area. [Figure 4] 1 to 3, shown in cross section in the direction of the longitudinal extension on the left side of the figure and in a direction perpendicular to the longitudinal extension on the right side of the figure. [Figure 5] 3 shows various possible cross sections of the sheet metal strip, viewed in the direction of the longitudinal extension. [Figure 6] 3 shows various possible cross sections of the sheet metal strip, viewed in the direction of the longitudinal extension. [Figure 7] 3 shows various possible cross sections of the sheet metal strip, viewed in the direction of the longitudinal extension. [Figure 8] 3 shows various possible cross sections of the sheet metal strip, viewed in the direction of the longitudinal extension. [Figure 9] 3 shows various possible cross sections of the sheet metal strip, viewed in the direction of the longitudinal extension. [Figure 10] 1 shows a bipolar plate in a three-dimensional view. [Figure 11] 1 shows a schematic three-dimensional view of an electrochemical cell. DETAILED DESCRIPTION OF THE INVENTION

[0029] FIG. 1 shows a three-dimensional view of two individual plates 1a, 1b made of a polymer-graphite composite material, with an annular sheet metal strip 2 disposed between them. Each individual plate 1a, 1b has medium flow-through openings 8, 9 aligned above and below. Furthermore, each individual plate 1a, 1b has an active field 7, in which electrodes of a polymer electrolyte membrane 11 in an electrochemical cell 10 are aligned (see FIG. 11 ). The electrochemical reaction of the electrochemical cell 10 occurs in the area of ​​the active field 7. Furthermore, numerous flow channels 6 (shown only diagrammatically) extend between the medium flow-through openings 8, 9, allowing the transport of fluids, such as coolant, fuel gas, and oxidizing gas, along the longitudinal extension of the individual plates 1a, 1b. The sheet metal strip 2 is disposed between the two individual plates 1a, 1b in the peripheral region of the individual plates 1a, 1b. The sheet metal strip 2 is fused to the adjacent surfaces 3a, 3b of the individual plates 1a, 1b (see also Figure 2), and the two individual plates 1a, 1b are joined together in a liquid-tight and electrically conductive manner in the area of ​​the sheet metal strip 2 to form a bipolar plate 1 (see Figure 3).

[0030] Figure 2 shows a cross section AA through the arrangement according to Figure 1. The existing flow channels 6 are clearly visible here. The same reference numerals as in Figure 1 denote identical elements.

[0031] Figure 3 shows a cross section AA through the arrangement according to Figure 1 after the sheet metal strip 2 has been fused to form the bipolar plate 1. The same reference numerals as in Figure 1 indicate the same elements. The fused area E can be seen in an enlarged view. The sheet metal strip 2 is fused in a form-fitting manner to both of the individual conductive plates 1a, 1b, connecting them to each other in a liquid-tight and conductive manner.

[0032] Figure 4 shows a sheet metal strip 2 used according to Figures 1 to 3, seen on the left side of the figure in a cross section BB in the direction of its longitudinal extension and on the right side of the figure in a direction perpendicular to its longitudinal extension. The right-hand view shows the sheet metal strip width BB. Furthermore, openings 5a are shown, which may optionally be present to form optional rows of holes 4, 4a. Furthermore, the openings 5a are provided in the form of recesses in the edges of the sheet metal strip 2 (here only one opening 5b is visible), and optionally a row of holes 4, 4b is also formed. The sheet metal strip 2, as seen on the left side of the figure, has a sheet metal strip thickness BD and two bending regions K1, K2.

[0033] 5 to 9 show various possible cross sections of the sheet metal strip 2, viewed in the direction of its longitudinal extension. The same reference numerals as in FIG. 3 denote the same elements.

[0034] FIG. 5 shows a cross section of a sheet metal strip 2 in which the sheet metal strip 2 only has a bent region K in the middle, where the sheet metal strip 2 is bent by 90°.

[0035] FIG. 6 shows a cross section of a sheet metal strip 2, in which the sheet metal strip 2 has two bent regions K1, K2 in which the sheet metal strip 2 is bent by 90° in the same direction.

[0036] FIG. 7 shows a cross section of a sheet metal strip 2 having two bending regions K1, K2 in which the sheet metal strip 2 is bent at an acute angle in the same direction.

[0037] FIG. 8 shows a cross section of a sheet metal strip 2 having two bending regions K1, K2 in which the sheet metal strip 2 is bent at an acute angle in different directions.

[0038] Figure 9 shows a cross-section of a sheet metal strip 2 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. See also Figure 4, row of holes 4a; two parallel rows of holes 4a, 4c are provided as shown in Figure 9. The openings 5a, 5c in the sheet metal strip 2 are filled with a polymer-graphite composite material, forming a mechanically very intimate and strong connection between the individual plates 1a, 1b. Optionally, the sheet metal strip 2 according to Figure 9 also has at least one bending region K (see Figure 4).

[0039] Figure 10 shows a bipolar plate 1 in a three-dimensional view. The same reference numerals as in Figures 1 and 3 indicate the same elements. In contrast to the individual plates 1a, 1b shown in Figure 1, here there are individual plates 1a, 1b with circular medium-through-flow openings 8, 9. The location of the fusion zone E is shown, but is not visible from the outside of the bipolar plate 1. In the area of ​​the shown fusion zone E, there would normally be sealing structures (not shown separately) on both sides of the bipolar plate 1 to seal the bipolar plate 1 against the adjacent polymer electrolyte membrane 11 (see Figure 11).

[0040] FIG. 11 shows a schematic three-dimensional view of an electrochemical cell 10. The electrochemical cell 10 comprises two bipolar plates 1, 1′ and a polymer electrolyte membrane 11 arranged between them (shown only diagrammatically). The polymer electrolyte membrane 11 is shown as representative of a membrane electrode unit, which comprises a plastic membrane with electrodes, catalyst layers, and gas diffusion layers arranged on both sides. Several electrochemical cells 10 can be stacked to form a cell stack 100. The electrochemical cell 10 here is a polymer electrolyte fuel cell. However, the electrochemical cell 10 could also be an electrolyzer or another type of electrochemical cell. [Explanation of symbols]

[0041] 1, 1' Bipolar Plate 1a, 1b individual plates 2 sheet metal strips 3a, 3b surface 4, 4a, 4b, 4c rows of holes 5a, 5b, 5c opening 6 Flow path 7. Active Space 8 Media flow opening 9 Media flow opening 10 Electrochemical Cell 11, 11' Polymer electrolyte membrane 100 cell stacks K, K1, K2 bending area E Fusion area BD sheet metal strip thickness BB sheet metal strip width

Claims

1. A method for manufacturing a bipolar plate (1) comprising two individual conductive plates (1a, 1b) each made of a polymer-graphite composite material, said method comprising: - providing said two individual plates (1a, 1b); - providing an annular strip of sheet metal (2); - placing a sheet metal strip (2) between the two individual plates (1a, 1b) in the peripheral area of ​​the individual plates (1a, 1b); - fusing said sheet metal strip (2) to the adjacent surfaces (3a, 3b) of said individual plates (1a, 1b), The method, wherein the two individual plates (1a, 1b) are connected to each other in a liquid-tight and electrically conductive manner in the area of ​​the sheet metal strip (2).

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

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

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

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

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

7. 7. Bipolar plate (1) according to claim 6, wherein said sheet metal strip (2) has at least one bent region (K) seen in cross section in the direction of its longitudinal extension.

8. The sheet metal strip (2) has, in the area of ​​each individual plate (1a, 1b), a bent area (K) fused to each individual plate, which is seen in a cross section in the direction of the longitudinal extension of the sheet metal strip. １ , K. ２ 8. The bipolar plate (1) according to claim 7, having a

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

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

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