Fuel cell and welding method

Abstract

To provide a fuel cell capable of reliably ensuring contact at the welding lines of a pair of metal separators.SOLUTION: In a fuel cell in which a membrane electrode assembly is disposed between a pair of bonded separators 12, bonded separator 12 is formed by welding a pair of metal separators 12a, 12b along welding lines 51, 52. A second metal separator 12b includes a protrusion 120 formed along welding lines 51, 52 that protrudes toward the opposing first metal separator 12a.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a fuel cell and a method for welding bonded separators for a fuel cell. [Background technology]

[0002] In recent years, technological developments related to fuel cells that contribute to energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. One known technology related to this type of fuel cell is a fuel cell stack, which is made by stacking multiple power-generating cells. Each power-generating cell includes a membrane electrode assembly (MEA) and a pair of metal separators arranged to sandwich the MEA. For example, the fuel cell described in Patent Document 1 uses bonded separators in which adjacent metal separators of adjacent power-generating cells are welded together to form a single unit.

[0003] Conventionally, when metal separators are welded together, the pair of metal separators is clamped with a clamping jig to prevent gaps from occurring at the welded portion due to waviness, etc. In this case, it is preferable to clamp the flat portions around both sides of the weld line to ensure contact between the metal separators at the weld line. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-150887 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when attempting to narrow the weld, there may be cases where there is not enough space to clamp the weld. For example, when a bead is provided close to the weld line, it is necessary to clamp the bead before welding due to space constraints. However, when clamping the bead, there is a problem in that it is difficult to ensure contact at the weld line. [Means for solving the problem]

[0006] A fuel cell according to one aspect of the present invention is characterized in that a membrane electrode assembly is disposed between a pair of bonded separators, the bonded separators being formed by welding a pair of metal separators together along a welding line, and one of the pair of metal separators has a first convex portion formed along the welding line that protrudes toward the other opposing metal separator. [Effects of the Invention]

[0007] According to the present invention, contact at the weld lines of a pair of metal separators can be reliably ensured. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an exploded perspective view showing one of the power generating cells that make up the fuel cell stack. [Figure 2] FIG. 2 is an enlarged view of the area surrounded by the dashed line C in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the AA cross section of FIG. [Figure 4] FIG. 4 is a diagram illustrating the shape of the welded region of the first and second metal separators. [Figure 5] FIG. 5 is a diagram illustrating a clamping method for laser welding. [Figure 6] FIG. 6 is a diagram illustrating a case where the bead portion is clamped. [Figure 7] FIG. 7 is a diagram illustrating the first modification. [Figure 8]FIG. 8 is a diagram showing another example of the first modification. [Figure 9] FIG. 9 is a diagram illustrating the second modification. [Figure 10] FIG. 10 is a diagram showing another example of the second modification. [Figure 11] FIG. 11 shows a pair of metal separators each having a protrusion formed thereon. [Figure 12] FIG. 12 is a diagram showing another example of an asymmetric convex shape. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and appropriate omissions and simplifications have been made for clarity of explanation. Furthermore, in the following description, identical or similar elements and processes are designated by the same reference numerals, and redundant explanations may be omitted. Note that the content described below merely shows an example of an embodiment of the present invention, and the present invention is not limited to the following embodiment, and can be implemented in various other forms.

[0010] Fig. 1 is an exploded perspective view showing one of the plurality of power-generating cells 10 that make up the fuel cell stack 1. In the example shown in Fig. 1, the plurality of power-generating cells 10 are stacked in the x-axis direction, and a clamping load (compression load) is applied in the stacking direction to the fuel cell stack 1. The fuel cell stack 1 is mounted, for example, as an on-board fuel cell stack in an electric vehicle that runs on fuel cell power.

[0011] The power-generating cell 10 includes a unitized electrode assembly (UEA) 11 and a first metal separator 12a and a second metal separator 12b arranged on either side of the UEA 11. The UEA 11 includes a membrane electrode assembly (MEA) 110 and a frame member 111 joined to the periphery of the MEA 110. The MEA 110 includes an electrolyte membrane 15, an anode electrode 16 provided on one side of the electrolyte membrane 15, and a cathode electrode 17 provided on the other side of the electrolyte membrane 15. The first metal separator 12a and the second metal separator 12b are formed by press-forming thin metal sheets and have a corrugated cross-sectional shape. Examples of the thin metal sheets that can be used include steel sheets, stainless steel sheets, aluminum sheets, titanium sheets, and thin metal sheets that have been subjected to a corrosion-resistant surface treatment.

[0012] In a pair of adjacent power generating cells 10, the first metal separator 12a of one power generating cell 10 and the second metal separator 12b of the other power generating cell 10 are joined together by welding. Hereinafter, the member in which the first metal separator 12a and the second metal separator 12b are welded together will be referred to as a joined separator 12. In other words, the fuel cell stack 1 is made up of a plurality of UEAs 11 and joined separators 12 stacked alternately.

[0013] 1, the power generating cell 10 is arranged so that its long sides are aligned with the y-axis and its short sides are aligned with the z-axis. The UEA 11, first metal separator 12a, and second metal separator 12b of the power generating cell 10 are each provided with an oxidant gas inlet manifold 20a, a refrigerant outlet manifold 21b, and a fuel gas outlet manifold 22b at their ends on the positive side in the y-axis direction. The oxidant gas inlet manifolds 20a, refrigerant outlet manifolds 21b, and fuel gas outlet manifolds 22b formed in the UEA 11, first metal separator 12a, and second metal separator 12b are all connected to one another in the stacking direction (x-axis direction).

[0014] The oxidant gas inlet manifold 20a, the refrigerant outlet manifold 21b, and the fuel gas outlet manifold 22b are aligned in the z-axis direction. The oxidant gas inlet manifold 20a is a manifold for supplying an oxidant gas (e.g., an oxygen-containing gas). The refrigerant outlet manifold 21b is a manifold for discharging a cooling medium (e.g., water). The fuel gas outlet manifold 22b is a manifold for discharging a fuel gas (e.g., a hydrogen-containing gas).

[0015] A fuel gas inlet manifold 22a, a refrigerant inlet manifold 21a, and an oxidant gas outlet manifold 20b are respectively provided at the negative y-axis end of the UEA 11, first metal separator 12a, and second metal separator 12b of the power generating cell 10. The fuel gas inlet manifolds 22a, the refrigerant inlet manifolds 21a, and the oxidant gas outlet manifolds 20b formed in the UEA 11, first metal separator 12a, and second metal separator 12b are all connected to one another in the stacking direction (x-axis direction).

[0016] The fuel gas inlet manifold 22a, the coolant inlet manifold 21a, and the oxidant gas outlet manifold 20b are aligned in the z-axis direction. The fuel gas inlet manifold 22a is a manifold for supplying the oxidant gas. The coolant inlet manifold 21a is a manifold for supplying the coolant. The oxidant gas outlet manifold 20b is a manifold for discharging the oxidant gas. In FIG. 1 , arrow F1 represents the flow of the oxidant gas, arrow F2 represents the flow of the fuel gas, and arrow F3 represents the flow of the coolant. The arrangement of the oxidant gas inlet manifold 20a, the oxidant gas outlet manifold 20b, and the fuel gas inlet manifold 22a and the fuel gas outlet manifold 22b is not limited to this embodiment and may be appropriately determined depending on the required specifications.

[0017] An oxidant gas flow field 24 extending in the longitudinal direction (y-axis direction) is formed on the surface of the first metal separator 12a facing the UEA 11. First bead portions 26, 28 formed by press molding are formed on the surface of the first metal separator 12a facing the UEA 11. The first bead portions 26, 28 are bank-shaped convex portions that protrude toward the UEA 11. Although not shown in the figures, a resin material is provided on the tops of the first bead portions 26, 28 and is fixed by printing, coating, or the like. The resin material improves adhesion between the first bead portions 26, 28 and the frame member 111 and functions as a sealant.

[0018] The first bead portions 26 are formed to individually surround each of the communication holes 20a, 20b, 21a, 21b, 22a, and 22b. The first bead portions 28 are formed to surround the region in which the oxidant gas flow field 24 and the communication holes 20a, 20b, 22a, and 22b are provided, the region being surrounded by the first bead portions 26. The oxidant gas flows from the oxidant gas inlet passage 20a into the oxidant gas flow field 24, flows through the oxidant gas flow field 24 toward the negative side of the y-axis, and is then discharged from the oxidant gas outlet passage 20b.

[0019] As shown by the two-dot chain line (imaginary line), a fuel gas flow path 25 extending in the longitudinal direction (y-axis direction) is formed on the surface of the second metal separator 12b facing the UEA 11. Second bead portions 27, 29 formed by press molding are formed on the surface of the second metal separator 12b facing the UEA 11. The second bead portions 27, 29 are bank-shaped convex portions that protrude toward the UEA 11. Although not shown in the figure, a resin material is provided on the tops of the second bead portions 27, 29 and is fixed by printing, coating, or the like. The resin material improves adhesion between the second bead portions 27, 29 and the frame member 111 and functions as a sealant.

[0020] The second bead portions 27 are formed so as to surround each of the communication holes 20a, 20b, 21a, 21b, 22a, and 22b individually. The second bead portions 29 are formed so as to surround the region in which the fuel gas flow field 25 and the communication holes 20a, 20b, 22a, and 22b are provided, which are surrounded by the second bead portions 27. The fuel gas flows from the fuel gas inlet passage 22a into the fuel gas flow field 25, flows through the fuel gas flow field 25 toward the positive side of the y-axis, and is then discharged from the fuel gas outlet passage 22b.

[0021] 2 is an enlarged view of the area surrounded by dashed line C of the bonded separator 12 shown in FIG. 1, viewed from the negative x-axis side. That is, FIG. 2 shows the surface of the second metal separator 12b facing the UEA 11. The fuel gas flow field 25 is formed by flow field grooves 25b between multiple protrusions 25a extending in the longitudinal direction (y-axis direction). Although not shown, the oxidant gas flow field 24 is also formed by flow field grooves between multiple protrusions extending in the y-axis direction, similar to the fuel gas flow field 25. The first metal separator 12a and the second metal separator 12b that constitute the bonded separator 12 are joined by laser welding, and are joined to each other along weld lines 51 and 52, which are indicated by dashed lines.

[0022] 2, the weld line 51 is set so as to surround the second bead portion 27 around the oxidant gas inlet passage 20a. The weld line 52 is set so as to surround the second bead portion 29. Around the oxidant gas inlet passage 20a, the second bead portion 27 and the second bead portion 29 are closely spaced apart and function as two rows of metal bead seals.

[0023] Fig. 3 is a cross-sectional view taken along the line AA in Fig. 2. The bonded separator 12 is formed of a first metal separator 12a, which is a component of the power generating cell 10A, and a second metal separator 12b, which is a component of the power generating cell 10B. The first bead portions 26 and 28 of the first metal separator 12a protrude toward the frame member 111 of the power generating cell 10A. The second bead portions 27 and 29 of the second metal separator 12b protrude toward the frame member 111 of the power generating cell 10B.

[0024] A clamping load (compression load) is applied in the stacking direction to the fuel cell stack 1. As a result, the first bead portions 26, 28 and the second bead portions 27, 29 are pressed against the frame members 111 of the UEAs 11 of the opposing power generation cells 10A, 10B. The first metal separator 12a and the second metal separator 12b are laser-welded at weld lines 51, 52.

[0025] 4 is a diagram illustrating the shapes of first metal separator 12a and second metal separator 12b at weld line 51 in FIG. 3, and is an enlarged view of the welded region including weld line 51. Fig. 4 shows the shapes of metal separators 12a and 12b before welding, with the dashed dotted line indicating the position of weld line 51. The welded region including weld line 51 of first metal separator 12a has a flat plate-like shape.

[0026] Meanwhile, protrusions 120 that protrude toward first metal separator 12a are formed by press working at weld line 51 of first metal separator 12a. Protrusions 120 are formed along weld line 51. In the example shown in Fig. 4, protrusions 120 are formed as arc-shaped protrusions with a radius r1 in a cross section perpendicular to weld line 51. Then, metal separators 12a and 12b are welded and joined by irradiating weld line 51 with a laser beam as indicated by the two-dot chain line LB.

[0027] When welding a pair of metal separators 12a, 12b, proper welding requires that the first metal separator 12a and the second metal separator 12b be in contact with each other without any gaps in the welding area. Therefore, when performing laser welding, flat areas on both sides of a welding line 51 are typically clamped with clamping jigs 40a, 40b, as shown in Fig. 5. With the metal separators 12a, 12b clamped in this manner, a laser beam is irradiated onto the welding line 51 as indicated by the two-dot chain line LB to weld and join the metal separators together.

[0028] However, in the weld line 51 in an area where the distance between the second bead portions 27 and 29 is narrow, such as around the oxidizer gas supply passage 20a in FIG. 2, it is difficult to secure clamping locations on the flat areas on both sides of the weld line 51. In such cases, welding must be performed by clamping the bead portions instead of the flat areas. However, because the metal separator is very thin, clamping the bead portions can easily deform the metal separator, creating gaps in the flat areas. This makes it difficult to ensure contact throughout the entire weld line, resulting in partial areas where contact is not ensured. As a result, welding performance varies, and proper welding cannot be performed throughout the entire weld line.

[0029] In this embodiment, as shown in Fig. 4, second metal separator 12b is formed with protrusions 120 that protrude toward first metal separator 12a. Therefore, even when bead portions 26, 28 and bead portions 27, 29 are clamped by clamping jigs 41a, 41b as shown in Fig. 6, contact between protrusions 120 of second metal separator 12b and the flat region of first metal separator 12a can be reliably ensured. In this way, forming protrusions 120 along weld lines 51 reliably prevents welding defects.

[0030] (Variation 1) FIG. 7 is a diagram showing Modification 1 of the above-described embodiment. Similar to the case of FIG. 4, FIG. 7 is an enlarged view of a welding region including the welding line 51 in FIG. 3, and shows the shapes of the respective metal separators 12a and 12b before welding. The welding region of the first metal separator 12a has a flat plate shape as in the case of the above-described embodiment. On the other hand, the convex portion 120 of the second metal separator 12b includes a first arc region 121 including the tip of the convex portion and second arc regions 122a and 122b continuously provided at both ends of the first arc region 121. The radius r1 of the first arc region 121 and the radii r2 of the second arc regions 122a and 122b are set such that r1 < r2. Note that the convex portion 120 of Modification 1 may be formed in a part including the welding region within the flat region between the bead portions 27 and 29, or may be formed in the entire flat region. That is, the entire flat region is the second arc region 122 having a radius r2, and the central portion thereof is the first arc region 121 having a radius r1.

[0031] As described above, when a plurality of power generation cells 10 are stacked to form the fuel cell stack 1, the plurality of power generation cells 10 are compressed in the stacking direction. By providing the second arc regions 122a and 122b having a larger radius so as to be continuous with the first arc region 121, the spring constant with respect to compressive deformation can be increased, and the sealing performance (pressing force improvement) in the bead portions 26 to 29 can be improved. Further, since the radii r1 and r2 are set such that r1 < r2, the second arc regions 122a and 122b are more easily deformed than the first arc region 121. Therefore, when compressed, the second arc regions 122a and 122b are deformed, so that deformation of the first arc region 121, which is the welded portion, can be suppressed. As a result, it is possible to prevent the welded portion from peeling off.

[0032] In FIG. 7, the second arc regions 122a and 122b are set to have the same radius r2. However, as shown in FIG. 8, the radius r2a of the second arc region 122a and the radius r2b of the second arc region 122b may be set to different values. In the example shown in FIG. 8, they are set such that r2a < r2b. Therefore, the rigidity when the bead portion is compressed is greater in the second arc region 122a than in the second arc region 122b. By setting the radius r2a and the radius r2b to different values in this way, the rigidity of the left and right bead portions with respect to compression can be individually corrected. In the case of the arc-shaped convex portion 120 with the radius r1 shown in FIG. 4, it may also be an asymmetric convex portion 120 composed of an arc surface 120(r1) with the radius r1 and an arc surface 120(r2) with the radius r2 (< r1) as shown in FIG. 1十二. The arc surface 120(r1) is continuously formed on the inclined surface of the bead portion 29, and the arc surface 120(r2) is continuously formed on the inclined surface of the bead portion 27. Also in this case, the rigidity of the left and right bead portions with respect to compression can be individually corrected.

[0033] (Modification Example 2) FIG. 9 is a diagram for explaining Modification Example 2. In Modification Example 2, the shape of the convex portion 120 of the second metal separator 12b is the same as that shown in FIG. 4, but the shape in the welding region of the first metal separator 12a is different. In the first metal separator 12a of Modification Example 2, a concave portion 123 that is recessed with respect to the convex portion 120 of the second metal separator 12b is formed. The concave portion 123 is formed along the welding line 51 and is formed as an arc-shaped concave portion in a cross section orthogonal to the welding line 51. The radius r3 of the concave portion 123 is set such that r1 < r3 so that the tip of the convex portion 120 with the radius r1 contacts the bottom of the concave portion 123 at the welding line 51. Also in the case of Modification Example 2, the contact between the convex portion 120 of the second metal separator 12b and the concave portion 123 of the first metal separator 12a can be surely ensured, and welding defects can be surely prevented. Furthermore, since it is a structure in which the convex portion contacts the concave portion, the separators can be prevented from being displaced laterally.

[0034] Note that, as shown in FIG. 10, the shape of the recess 123 of the first metal separator 12a may be configured by two arc regions with different radii, similar to the convex portion 120 in the first modification. In FIG. 10, the central region of the bottom of the recess 123 is composed of a first arc region 123a with a radius r3a, and second arc regions 123b and 123c with a radius r3b are provided so as to be continuous with both ends of the first arc region 123a. The radii r3a and r3b are set such that r3a < r3b. In this case, the second arc regions 123b and 123c are more likely to deform than the first arc region 123a, and when the bead portion is compressed, deformation of the first arc region 121, which is the welded portion, is suppressed. As a result, it is possible to prevent the welded portion from peeling off.

[0035] In the above-described embodiments and the first and second modifications, the convex portion 120 is formed on the side of the second metal separator 12b, but the convex portion 120 may be formed on the side of the first metal separator 12a. Further, in the second modification, a convex portion is formed on one metal separator and a concave portion is formed on the other metal separator. However, as shown in FIG. 11, a convex portion may also be formed on the other metal separator. In FIG. 11, the second metal separator 12b is formed with a convex portion 120 including a first arc region 121 and second arc regions 122a and 122b similar to those of the second metal separator 12b shown in FIG. 7. On the other hand, on the first metal separator 12a, a convex portion 130 protruding in the direction of the second metal separator 12b is formed at the position of the welding line 51. Note that the shape of the convex portion 120 on the side of the second metal separator 12b may be the same as the shape of the convex portion 120 shown in FIG. 4.

[0036] In the above-described embodiments and the first and second modifications, the shapes of the metal separators 12a and 12b at the welding line 51 have been described. Although illustration and description are omitted, the shapes of the metal separators 12a and 12b at the welding line 52 are also configured in the same manner as the metal separators 12a and 12b at the welding line 51.

[0037] The various embodiments and modifications described above are merely examples, and the present invention is not limited to these unless the features of the invention are impaired. Other embodiments that are conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0038] 1... fuel cell stack, 10, 10A, 10B... power generation cell, 11... UEA, 12... bonded separator, 12a... first metal separator, 12b... second metal separator, 15... electrolyte membrane, 16... anode electrode, 17... cathode electrode, 20a... oxidant gas inlet passage, 20b... oxidant gas outlet passage, 21a... refrigerant inlet passage, 21b... refrigerant outlet passage, 22a... fuel gas inlet passage, 22b... fuel Fuel gas outlet communication hole, 24...oxidizer gas flow path, 25...fuel gas flow path, 26, 28...first bead portion, 27, 29...second bead portion, 40a, 40b, 41a, 41b...clamping jig, 51, 52...welding line, 110...MEA (membrane electrode assembly), 111...frame member, 120, 130...convex portion, 121, 123a...first arc region, 122a, 122b, 123b, 123c...second arc region, 123...recess

Claims

1. In a fuel cell in which a membrane electrode assembly is disposed between a pair of bonded separators, The bonded separator is formed by welding a pair of metal separators together along a welding line, A fuel cell, characterized in that one of the pair of metal separators has a first protrusion formed along a welding line that protrudes toward the other opposing metal separator.

2. 2. The fuel cell according to claim 1, a shape of the first convex portion in a cross section perpendicular to the welding line is composed of a first arc-shaped region having a radius r1 including the tip of the convex portion, and a second arc-shaped region having a radius r2 provided continuously from each end of the first arc-shaped region, A fuel cell characterized in that the radius r2 is set to be larger than the radius r1.

3. 2. The fuel cell according to claim 1, a first recessed portion recessed relative to the first protruding portion is formed at the welding line of the other metal separator, a cross section of the first protrusion perpendicular to the welding line has an arc shape with a radius r1; The first recess has an arc shape with a radius r2 in a cross section perpendicular to the welding line, A fuel cell, wherein the radius r2 is set to be larger than the radius r1.

4. 4. The fuel cell according to claim 3, a shape of the first recess in a cross section perpendicular to the weld line is composed of a first arc-shaped region having a radius r2 including a recess bottom region, and second arc-shaped regions having a radius r3 provided at each end of the first arc-shaped region, A fuel cell, wherein the radius r3 is set to be larger than the radius r2.

5. 2. The fuel cell according to claim 1, a shape of the first convex portion in a cross section perpendicular to the welding line is a first arc-shaped region having a radius r1 on one side of the welding line and a second arc-shaped region having a radius r2 on the other side of the welding line; The fuel cell, wherein the radius r1 and the radius r2 are set to different values.

6. 2. The fuel cell according to claim 1, a shape of the first convex portion in a cross section perpendicular to the weld line is composed of a first arc-shaped region of radius r1 including a tip of the convex portion, a second arc-shaped region of radius r2 continuing from one end of the first arc-shaped region, and a third arc-shaped region of radius r3 continuing from the other end of the first arc-shaped region, The radius r2 and the radius r3 are set to different values.

7. 2. A method for welding the bonded separators in the fuel cell according to claim 1, comprising: Each of the pair of metal separators constituting the joined separator includes a pair of bead portions on both sides of the weld line, the bead portions protruding in a direction away from the opposing metal separator, A welding method comprising: welding the weld line while holding at least one of the pair of opposing bead portions of the pair of opposing metal separators with a holding jig.

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