Bipolar plate for fuel cell, and method for manufacturing a bipolar plate

Abstract

To suppress warping associated with laser welding. [Solution] The bipolar plate 19 of the fuel cell is formed by welding an anode-side separator 14 and a cathode-side separator 14 that are stacked in the thickness direction. The bipolar plate 19 comprises a first weld 20, a second weld 21, and a rib 22. The first weld 20 is formed by partially tack-welding the anode-side separator 14 and the cathode-side separator 14. The second weld 21 is formed by laser welding the anode-side separator 14 and the cathode-side separator 14 over a predetermined length. The rib 22 is formed on at least one of the anode-side separator 14 and the cathode-side separator 14 and protrudes from around the first weld 20 in the thickness direction of the separator 14.

Description

Technical Field

[0001] The present invention relates to a bipolar plate of a fuel cell and a method for manufacturing the bipolar plate.

Background Art

[0002] As a fuel cell stack, a structure is known in which a membrane electrode gas diffusion layer laminate is sandwiched between bipolar plates and these bipolar plates and the membrane electrode gas diffusion layer laminate are laminated in the thickness direction. The bipolar plate is formed by welding a separator on the anode side and a separator on the cathode side. For such welding, for example, laser welding can be considered.

[0003] In the fuel cell stack, a separator on the anode side of the bipolar plate is disposed on the anode side of the membrane electrode gas diffusion layer laminate. Further, on the cathode side of the membrane electrode gas diffusion layer laminate, a separator on the cathode side of another bipolar plate that sandwiches the membrane electrode gas diffusion layer laminate with the bipolar plate is disposed. A fuel gas such as hydrogen is passed between the anode side of the membrane electrode gas diffusion layer laminate and the separator on the anode side, and an oxidizing gas such as air is passed between the membrane electrode gas diffusion layer laminate and the separator on the cathode side.

[0004] When the fuel gas and the oxidizing gas are passed through the anode side and the cathode side of the membrane electrode gas diffusion layer laminate in this way, power generation is performed based on the reaction of the fuel gas and the oxidizing gas in the membrane electrode gas diffusion layer laminate. The electric power based on the power generation in the fuel cell is collected through the bipolar plate and then output to the outside.

[0005] When laser welding the anode separator and the cathode separator to form the bipolar plate described above, the separators are stacked in the thickness direction, and the laser is irradiated from one separator towards the other. This causes one separator and the area of ​​the other separator closest to the first separator to melt. The separators are then joined together through the solidification of these molten areas.

[0006] In the above-mentioned separator, a large temperature difference tends to occur between the area melted by laser irradiation and the surrounding area. When such a large temperature difference occurs, the melted area rapidly cools down and solidifies and shrinks after laser irradiation, resulting in increased tension on the surrounding area due to the melted area. In the other separator, the interface between the melted area and its surrounding area becomes roughly arc-shaped, and the tensile force acts toward the center of the curvature of that interface. As a result of the tensile force acting on the other separator, warping occurs in both the other separator and the first separator.

[0007] As a countermeasure to this problem, for example, as shown in Patent Document 1, it is conceivable to temporarily fix the anode-side separator and the cathode-side separator by projection welding, and then laser weld them over a predetermined length. In this case, since the laser welding of the separators is performed while the anode-side separator and the cathode-side separator are temporarily fixed by projection welding, in other words, while their rigidity is increased, the aforementioned warping of the separators during welding becomes less likely to occur. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2024-85054 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, simply tack-fastening the anode and cathode separators with projection welding before laser welding may not be sufficient to suppress the warping of the separators caused by laser welding. In other words, projection welding the separators together may not increase their rigidity enough to suppress the warping caused by laser welding. [Means for solving the problem]

[0010] The following describes the means and effects of solving the above problems. The bipolar plate for a fuel cell that solves the above problems is formed by welding an anode-side separator and a cathode-side separator that are stacked in the thickness direction. The bipolar plate comprises a first weld, a second weld, and a rib. The first weld is formed by partially tack-welding the anode-side separator and the cathode-side separator. The second weld is formed by laser-welding the anode-side separator and the cathode-side separator over a predetermined length. The rib is formed on at least one of the anode-side separator and the cathode-side separator and protrudes from around the first weld in the thickness direction of the separator.

[0011] According to the above configuration, it becomes possible to form the first and second welds as follows. Specifically, with the anode-side separator and the cathode-side separator overlapping in the thickness direction, the first weld is formed by partially tack welding the area surrounded by the ribs on these separators. Subsequently, the second weld is formed by laser welding the anode-side separator and the cathode-side separator over a predetermined length. By forming the first and second welds in this order, the rigidity of the separator can be increased by both tack welding and the ribs prior to laser welding. As a result, the rigidity of the separator can be increased to a level that can suppress warping associated with laser welding, thereby preventing such warping.

[0012] In the method for manufacturing a bipolar plate that solves the above problems, the anode separator and the cathode separator are stacked in the thickness direction, and then welded together. At least one of the anode separator and the cathode separator has a rib that protrudes in the thickness direction toward the opposite side of the other separator. The anode separator and the cathode separator are then tack-welded at the area surrounded by the rib. After the tack welding, the anode separator and the cathode separator are laser-welded over a predetermined length.

[0013] According to the method described above, the rigidity of the separator can be increased by both tack welding and ribs prior to laser welding. As a result, the rigidity of the separator can be increased to a level that suppresses warping associated with laser welding, thereby preventing such warping from occurring. [Brief explanation of the drawing]

[0014] [Figure 1] This is an exploded perspective view showing a fuel cell. [Figure 2] This is a front view showing the cathode-side separator of the fuel cell cell as seen from the direction of arrow A in Figure 1. [Figure 3] This is a schematic diagram showing the melting points of the separators when laser welding them together. [Figure 4] This is a cross-sectional view showing an enlarged view of the first weld between the anode-side separator and the cathode-side separator, and its surrounding area. [Figure 5] This is a plan view showing the first weld and its surrounding area as seen from above in Figure 4. [Figure 6] This is a plan view showing another example of a rib. [Figure 7] This is a plan view showing another example of a rib. [Figure 8] This is a cross-sectional view showing another example of contact between bipolar plates. [Figure 9]A cross-sectional view showing another example of contact between bipolar plates.

Embodiments for Carrying out the Invention

[0015] Hereinafter, an embodiment of a bipolar plate of a fuel cell and a method for manufacturing the bipolar plate will be described with reference to FIGS. 1 to 5. FIG. 1 shows a fuel cell 11 for forming a cell stack of a fuel cell. The fuel cell 11 includes a resin plate 12, a membrane electrode gas diffusion layer laminate 13, and a separator 14. The resin plate 12 is formed in a rectangular frame shape. The outer edge of the membrane electrode gas diffusion layer laminate 13 is joined to the resin plate 12. The resin plate 12 and the membrane electrode gas diffusion layer laminate 13 are sandwiched by the separator​​​​​​​The seal member 17 thermally welded to the separator 14 on the anode side, that is, the separator 14 on the right side in FIG. 1, surrounds a pair of two holes 16 located on one of the two diagonals in the resin plate 12 and the separator 14 and the anode side of the membrane electrode gas diffusion layer assembly 13. In the portion surrounded by the seal member 17 in the separator 14 on the anode side, a plurality of grooves 15 extending from one hole 16 side to the other hole 16 side of the pair of two holes 16 are formed. Thereby, it is possible to flow the fuel gas through the pair of the holes 16 and the plurality of grooves 15 to the anode side of the membrane electrode gas diffusion layer assembly 13.

[0018] Also, the seal member 17 thermally welded to the separator 14 on the cathode side, that is, the separator 14 on the left side in FIG. 1, surrounds a pair of two holes 16 located on the other diagonal of the two diagonals in the resin plate 12 and the separator 14 and the cathode side of the membrane electrode gas diffusion layer assembly 13. In the portion surrounded by the seal member 17 in the separator 14 on the cathode side, a plurality of grooves 15 extending from one hole 16 side to the other hole 16 side of the pair of two holes 16 are formed. Thereby, it is possible to flow the oxidizing gas through the pair of the holes 16 and the plurality of grooves 15 to the cathode side of the membrane electrode gas diffusion layer assembly 13.

[0019] In the cell stack of the fuel cell 11, the fuel gas is flowed to the anode side of the membrane electrode gas diffusion layer assembly 13, and the oxidizing gas is flowed to the cathode side of the membrane electrode gas diffusion layer assembly 13. Thus, when the fuel gas and the oxidizing gas are flowed to the anode side and the cathode side of the membrane electrode gas diffusion layer assembly 13, power generation is performed based on the reaction between the fuel gas and the oxidizing gas in the membrane electrode gas diffusion layer assembly 13.

[0020] Figure 2 shows a separator 14 of the fuel cell cell 11, specifically the separator 14 located on the cathode side of the membrane electrode gas diffusion layer assembly 13, viewed from the direction of arrow A in Figure 1. This separator 14 is adjacent to the separator 14 on the anode side of another fuel cell cell 11 that is in contact with the aforementioned fuel cell cell 11. These adjacent separators 14 are welded together as shown by the dashed line.

[0021] More specifically, adjacent separators 14 are welded together so as to encircle two sets of holes 16 located diagonally opposite each other, and the entire outer edge of each separator 14 is also welded. This allows refrigerant to flow between adjacent separators 14 through the holes 16 located in the center of the short side of each separator 14. By allowing refrigerant to flow between the separators 14 of adjacent fuel cell cells 11 in this way, the cell stack can be cooled when its temperature rises during power generation.

[0022] <Bipolar plate for fuel cell> Figure 3 shows the anode-side separator 14 and the cathode-side separator 14, which are welded together as described above. The fuel cell is equipped with a bipolar plate 19 made up of the welded separators 14. The cell stack of the fuel cell is formed by alternately stacking the bipolar plate 19 and a resin plate 12 to which the membrane electrode gas diffusion layer assembly 13 shown in Figure 1 is joined, in the thickness direction. Laser welding can be used to weld the separators 14 together to form the bipolar plate 19.

[0023] In other words, a laser from the laser head 18 is irradiated from one separator 14 to the other in the direction of thickness between adjacent separators 14 that overlap in the thickness direction, as shown by the dashed line. In this example, the laser from the laser head 18 is irradiated from the upper separator 14 to the lower separator 14 in Figure 3. As a result, one separator 14 and the area of ​​the other separator 14 closer to the first separator 14 melt, as shown by the hatching in Figure 3. Then, the molten area solidifies, joining the separators 14 together.

[0024] In the separators 14 described above, a large temperature difference tends to occur between the areas indicated by hatching in Figure 3, i.e., the areas melted by laser irradiation and the surrounding areas. When the temperature difference between the melted areas and the surrounding areas is large, the tension on the surrounding areas by the melted areas, indicated by the arrows in Figure 3, becomes stronger as the melted areas rapidly cool down, solidify, and shrink after laser irradiation.

[0025] In one separator 14, i.e., the upper separator 14 in Figure 3, the tensile force acts almost parallel to the front and back surfaces of the separator 14. In contrast, in the other separator 14, i.e., the lower separator 14 in Figure 3, the interface between the molten area and its surroundings is roughly arc-shaped, so the tensile force acts toward the center of the curvature of that interface. As a result of the tensile force acting on the other separator 14, warping occurs in both the other separator 14 and the first separator 14.

[0026] To address these issues, the bipolar plate 19 is provided with a first weld 20, a second weld 21, and ribs 22, as shown in Figure 2. The first weld 20, the second weld 21, and the ribs 22 will be described individually below.

[0027] <First weld 20> The first weld 20 is formed by partially tack welding the anode-side separator 14 and the cathode-side separator 14. For such tack welding, spot welding can be used, for example. Alternatively, welding such as projection welding may be used instead of spot welding. The first weld 20 is formed in a position that avoids the holes 16 and grooves 15 in the anode-side separator 14 and the cathode-side separator 14.

[0028] <Second Weld 21> The second weld 21 is formed by laser welding the anode-side separator 14 and the cathode-side separator 14 over a predetermined length. This second weld 21 corresponds to the area shown by the dashed line in Figure 2, where the anode-side separator 14 and the cathode-side separator 14 are laser welded together.

[0029] <Rib 22> The rib 22 is formed on at least one of the anode-side separator 14 and the cathode-side separator 14. As shown in Figure 4, in this example, it is formed on both the anode-side separator 14 and the cathode-side separator 14. The rib 22 protrudes from around the first weld 20 in the thickness direction of the separator 14 and on the opposite side from the other separator 14. As shown in Figure 5, the rib 22 is formed to encircle the first weld 20.

[0030] More specifically, the rib 22 encircles the area around the first welded portion 20, as shown in Figure 2, so as to be the area where the holes 16 and grooves 15 etc. in the separator 14 are not formed and where the rib 22 can be formed. The shape of the encircling rib 22 can be, for example, a circle, a triangle, or a square, depending on the area.

[0031] The bipolar plate 19 described above can be formed by the following manufacturing method. Specifically, with the anode-side separator 14 and the cathode-side separator 14 stacked in the thickness direction, the area enclosed by the ribs 22 on the separators 14, as shown by the dashed line in Figure 4, is partially tack-welded. The first welded portion 20 is formed at the tack-welded portion in this way. Subsequently, the anode-side separator 14 and the cathode-side separator 14 are laser-welded over a length determined as shown by the dashed line in Figure 2. The second welded portion 21 is formed at the laser-welded portion in this way.

[0032] By forming the first weld 20 and the second weld 21 in this order, the rigidity of the separator 14 can be increased by both the tack weld and the rib 22 prior to laser welding. As a result, the rigidity of the separator 14 can be increased to a level that can suppress warping associated with laser welding, thereby preventing such warping from occurring.

[0033] According to the embodiment described in detail above, the following effects and advantages can be obtained. (1) Prior to laser welding the anode-side separator 14 and the cathode-side separator 14 to form the bipolar plate 19, the rigidity of the separator 14 can be increased by both tack welding and ribs 22. As a result, the rigidity of the separator 14 can be increased to a level that can suppress warping associated with laser welding, thereby suppressing the occurrence of such warping.

[0034] (2) The rib 22 is formed to encircle the first weld 20. Therefore, when the anode-side separator 14 and the cathode-side separator 14 are partially tack-welded to form the first weld 20, the rigidity of the separators 14 can be further increased.

[0035] (3) The rib 22 is formed to encircle the first welded portion 20 in a shape corresponding to the area around the first welded portion 20 in which the rib 22 can be formed. By forming the rib 22 on the separator 14 in this way, the empty area in the separator 14 that is not used for forming the holes 16 and grooves 15 can be effectively utilized to form the rib 22.

[0036] The above embodiment can also be modified as follows, for example. The above embodiment and the following modifications can be combined and implemented to the extent that they do not contradict each other technically. • For the shape of the rib 22 that goes all the way around, it is also possible to adopt the shape shown in Figures 6 and 7, for example.

[0037] The ribs 22 may be as shown in Figure 8. That is, when the cell stack of the fuel cell is formed, the tips of the ribs 22 protruding from the separator 14 that sandwiches the membrane electrode gas diffusion layer assembly 13 may be in contact with each other in the direction of protrusion. In this case, it is conceivable to form holes or notches in the resin plate 12 to which the membrane electrode gas diffusion layer assembly 13 is joined so as not to hinder contact between the tips of the ribs 22 in the direction of protrusion.

[0038] As described above, by bringing the tips of the ribs 22 into contact with each other, the rigidity of each bipolar plate 19 in the cell stack is increased, and consequently, the rigidity of the entire cell stack is also increased.

[0039] When the cell stack of the fuel cell is formed, as shown in Figure 9, the tip of the rib 22 in the protruding direction may be in contact with the adjacent separator 14 that sandwiches the membrane electrode gas diffusion layer assembly 13 between itself and the separator 14 on which the rib 22 is formed. In this case, it is conceivable to form holes or notches in the resin plate 12 to which the membrane electrode gas diffusion layer assembly 13 is joined, in order to allow the rib 22 to pass toward the adjacent separator 14.

[0040] As described above, by bringing the tip of the rib 22 into contact with the adjacent separator 14, the contact area between the separators 14 in the cell stack can be increased. As a result, the power collection efficiency from the cell stack via the separators 14 can be improved. Furthermore, by utilizing the elasticity of the separator 14 in the warping direction and bringing the tip of the rib 22 in the protruding direction into contact with the separator 14 as described above, the stacking of the bipolar plate 19 and the membrane electrode gas diffusion layer assembly 13 in the cell stack can be made more secure.

[0041] The rib 22 does not necessarily have to encircle the separator 14 in a shape corresponding to the area where the rib 22 can be formed. In other words, the rib 22 may encircle the separator 14 in a shape other than the one described above.

[0042] Rib 22 does not necessarily have to be a circular shape. [Explanation of Symbols]

[0043] 11… Fuel cell 12… Resin plate 13…Membrane electrode gas diffusion layer assembly 14... Separator 15...Groove 16...hole 17...Sealing material 18… Laser head 19… Bipolar plate 20…First weld 21...Second weld 22... Rib

Claims

1. In a bipolar plate for a fuel cell, in which an anode-side separator and a cathode-side separator, which are stacked in the thickness direction, are welded together, A first welded section is formed by partially tack-welding the anode-side separator and the cathode-side separator, A second welded section formed by laser welding the anode-side separator and the cathode-side separator over a predetermined length, A rib is formed on at least one of the anode-side separator and the cathode-side separator, and protrudes from around the first weld in the thickness direction of the separator, A bipolar plate for a fuel cell equipped with [a specific feature / feature].

2. The rib is formed to encircle the first welded portion, as described in claim 1, for the bipolar plate of a fuel cell.

3. The bipolar plate for a fuel cell according to claim 2, wherein the rib encircles the first welded portion in a shape corresponding to the region where the rib can be formed.

4. The bipolar plate for a fuel cell according to any one of claims 1 to 3, wherein when a cell stack of a fuel cell is formed by stacking the ribs in the thickness direction with a membrane electrode gas diffusion layer assembly sandwiched between separators welded to each other, the tip of the rib in the protruding direction contacts the adjacent separator that sandwiches the membrane electrode gas diffusion layer assembly between the separator on which the rib is formed.

5. The bipolar plate for a fuel cell according to any one of claims 1 to 3, wherein when a cell stack of a fuel cell is formed by stacking membrane electrode gas diffusion layer assemblies in the thickness direction with separators welded to each other, the ribs are in contact with each other at the tips of the ribs in the direction of protrusion that protrude from the separators sandwiching the membrane electrode gas diffusion layer assemblies.

6. In a method for manufacturing a bipolar plate, in which an anode-side separator and a cathode-side separator are stacked in the thickness direction, and then these separators are welded together, At least one of the separators, the anode-side separator and the cathode-side separator, has a rib formed on it that protrudes in the thickness direction in the direction opposite to the other separator. The anode-side separator and the cathode-side separator are tack-welded together at the location surrounded by the rib. A method for manufacturing a bipolar plate, comprising laser welding the anode-side separator and the cathode-side separator over a predetermined length after the aforementioned tack welding.

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