Fuel cell stack

Abstract

To provide a fuel cell stack with which it is possible to suppress a decrease in flow channel sectional area for input from the lamination direction.SOLUTION: Provided is a fuel cell stack formed by laminating fuel cell units, each having a power generation cell that is formed with a fuel electrode and an air electrode across an electrolyte layer, a fuel electrode current collector that is connected to the fuel electrode side face of the power generation cell, an air electrode current collector that is connected to the air electrode side face of the power generation cell, and a separator that is electrically connected to some of the current collectors, wherein either of the current collectors has a bottom part, a wall part, and a spring part, the spring part, in the laminated state, being joined to the separator of an adjacent fuel cell unit, the spring and the wall parts forming a plurality of flow channels between the electrode and the separator that extend in a direction orthogonal to the lamination direction and are parallel to each other, the arrangement of a plurality of wall parts and the extending direction of a plurality of spring parts being line symmetrical with respect to the middle flow channel among a plurality of flow channels.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a fuel cell stack.

Background Art

[0002] When stacking fuel cell units to form a fuel cell stack, it is necessary to assemble the components to be assembled in a state where they are in close contact with each other. Patent Document 1 discloses a configuration in which a first spring member that presses a separator and a second spring member that presses the separator independently of the first spring member are provided to bring the components into close contact with each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Both the first spring member and the second spring member in the above document are formed by standing up from a substrate so as to be a cantilever beam and having a plurality of elastically deformable spring portions (first standing piece, second standing piece). And the spring constants of the first spring member and the second spring member are different.

[0005] In such a configuration, when there is an input from the stacking direction, a bending moment that tries to knock down the spring portion occurs, and thereby a force directed in one direction within the joint surface with the cell acts on the substrate. That is, for example, when there is an input such as vibration during the operation of the fuel cell system, the first spring member and the second spring member may fall down and the substrate may sink. And when the substrate sinks, the flow path cross-sectional area of the gas flow path formed between the separator and the current collector decreases, and the pressure loss increases.

[0006] Therefore, the present invention aims to provide a fuel cell stack that can suppress the reduction of the flow channel cross-sectional area even when there is input from the stacking direction due to vibration or the like. [Means for solving the problem]

[0007] According to one aspect of the present invention, a fuel cell stack is provided, comprising stacked fuel cell units, each having a power generation cell formed by sandwiching an electrolyte between a fuel electrode and an air electrode, a fuel electrode current collector connected to the fuel electrode side of the power generation cell, an air electrode current collector connected to the air electrode side of the power generation cell, and a separator electrically connected to the fuel electrode current collector or the air electrode current collector. At least one of the fuel electrode current collector or the air electrode current collector has a bottom connected to the fuel electrode or the air electrode via a conductive joint, a plurality of wall portions protruding from the bottom, and a plurality of spring portions extending from the upper ends of the plurality of wall portions and deformable with respect to input from the stacking direction, with the upper ends of the wall portions as pivot points. With multiple fuel cell units stacked, the spring section is joined to the separator of an adjacent fuel cell unit. Multiple spring sections and walls form multiple parallel channels between the electrode, to which the bottom is connected, and the separator of an adjacent fuel cell unit, extending in a direction perpendicular to the stacking direction. The arrangement of the multiple walls and the direction in which the multiple spring sections extend are symmetrical with respect to the central channel among the multiple channels. One of the fuel electrode current collector or the air electrode current collector has a bottom, a wall, and a spring, while the other has multiple ribs. When viewed from the stacking direction, there is an overlapping portion between the joint between the spring and the separator of the adjacent fuel cell unit, and between the contact portion between the separator of the adjacent fuel cell unit and the electrode current collector of the adjacent fuel cell unit. The width of the joint between the spring and the separator of the adjacent fuel cell unit is greater than the width of the contact portion between the ribs and the separator. [Effects of the Invention]

[0008] According to the above embodiment, even when there is input from the stacking direction, the reduction in the flow channel cross-sectional area can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a perspective view of a fuel cell unit according to an embodiment. [Figure 2] Figure 2 is a cross-sectional view along the line II-II in Figure 1. [Figure 3] Figure 3 is a diagram illustrating the dimensions of the wall and spring sections. [Figure 4]Figure 4 is a cross-sectional view of a fuel cell stack according to an embodiment. [Figure 5] Figure 5 is a cross-sectional view of a fuel cell stack when the separator has irregularities. [Figure 6] Figure 6 shows the forces generated in the wall and spring sections when input is applied from the stacking direction. [Figure 7] Figure 7 is a cross-sectional view of a modified fuel cell stack. [Figure 8A] Figure 8A shows the state when input is received from the stacking direction in the modified configuration. [Figure 8B] Figure 8B shows the state when input is received from the stacking direction in the configuration of the embodiment. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the attached drawings. Note that the size and proportions of each component in the drawings may differ from those of the actual components.

[0011] Figure 1 is a perspective view of the fuel cell unit 100 that forms the fuel cell stack 200. Figure 2 is a cross-sectional view along line II-II in Figure 21. In this embodiment, a solid oxide fuel cell mounted on a vehicle will be described as an example.

[0012] The fuel cell stack 200 of this embodiment is formed by stacking a plurality of fuel cell units 100 in the z-direction in the figure (hereinafter this direction is also referred to as the stacking direction) via a compression seal 10 and a non-compression seal 13.

[0013] The fuel cell unit 100 includes a power generation cell 1 formed by sandwiching an electrolyte 3 between a fuel electrode 5 and an air electrode 4, a fuel electrode current collector 7 connected to the fuel electrode 5 side of the power generation cell 1, an air electrode current collector 2 connected to the air electrode 4 side of the power generation cell 1, and a separator 6 electrically connected to the fuel electrode current collector 7.

[0014] The fuel electrode 5 and the air electrode 4 are provided with a metal porous layer. The fuel electrode current collector 7, the air electrode current collector 2, and the separator 6 are formed of a stainless material containing aluminum.

[0015] Further, the fuel cell unit 100 includes anode gas outlets 11A, 11B and anode gas inlets 12A, 12B. The anode gas flowing out from the anode gas outlets 11A, 11B passes through the anode flow path formed between the fuel electrode 5 and the separator 6 and flows into the anode gas inlets 12A, 12B.

[0016] The compression seal 10 is disposed on the surface of the air electrode 4 and is compressed and deformed by the restraint pressure applied from the stacking direction when stacked. The non-compression seal 13 is disposed on the surface of the fuel electrode 5 and is joined to the fuel electrode 5 and the separator 6.

[0017] The fuel electrode current collector 7 includes a plurality of ribs 7A that project in the stacking direction and extend in the y direction. The plurality of ribs 7A are arranged in parallel. Note that the ribs 7A are formed by press working or the like. The fuel electrode current collector 7 is joined to the fuel electrode 5 via a conductive joint portion 20B and is also joined to the separator 6 via a conductive joint portion 20C. The joint portions 20B and 20C are joined by a joining method capable of ensuring conductivity. As the joining method, welding, diffusion bonding, or the like can be used, but welding is desirable from the viewpoint of conductivity.

[0018] The air electrode current collector 2 includes a bottom portion 2A, a plurality of wall portions 2B, and spring portions 2C. The bottom portion 2A is connected to the air electrode via a conductive joint portion 20A. The wall portions 2B project from the bottom portion 2A. The spring portions 2C extend from the upper end portions of the wall portions 2B in a direction having a predetermined angle to be described later with respect to the protruding direction of the wall portions 2B and are deformable with the upper end portions of the wall portions 2B as fulcrums with respect to an input from the stacking direction. That is, the wall portions 2B and the spring portions 2C form a so-called cantilever beam. Note that the wall portions 2B and the spring portions 2C are formed by press working or the like.

[0019] Here, the dimensions of the wall portion 2B and the spring portion 2C will be described. As shown in FIG. 3, the stacking direction dimension (also referred to as height) of the wall portion 2B from the surface of the air electrode 4 is A, the height of the tip of the spring portion 2C is D, the height in the stacked state of the compression seal 10 is B, and the height of the non-compression seal 13 is C. Then, the relationship C≦A<B and D≧B holds.

[0020] The "predetermined angle" regarding the direction in which the spring portion 2C extends can be arbitrarily set within the range where the above relationship holds.

[0021] Also, when the angle formed by the surface of the air electrode 4 and the wall portion 2B is θ, the relationship θ≦90° holds.

[0022] FIG. 4 is a cross-sectional view of the stacked state of the above-described fuel cell unit 100.

[0023] In the stacked state, the compression seal 10 is compressed in the stacking direction, and the spring portion 2C is in a state of being bent and deformed in a direction approaching the bottom portion 2A with the upper end of the wall portion 2B as a fulcrum. In this state, the spring portion 2C and the separator 6 of the adjacent fuel cell unit 100 are joined via the joint portion 20E. Both the joint portion 20E and the joint portion 20A between the joint portion 20A and the air electrode 4 are joined by a joining method capable of ensuring conductivity. Welding is used for one of them and diffusion bonding is used for the other. From the perspective of conductivity, it is desirable to weld both, but in the stacking process, it is not possible to weld the other while one of them is welded.

[0024] Furthermore, in the stacked state, multiple cathode channels 21 are formed between the air electrode 4, to which the bottom 2A is connected, and the separator 6 of the adjacent fuel cell unit 100, by multiple spring sections 2C and multiple wall sections 2B, extending in a direction perpendicular to the stacking direction and parallel to each other. The arrangement of the multiple wall sections 2B and the direction in which the multiple spring sections 2C extend are symmetric with respect to the central cathode channel 21 among the multiple cathode channels 21. Although Figure 4 shows a pair of wall sections 2B and spring sections 2C extending in directions opposite to each other, in the actual fuel cell unit 100, multiple such pairs of wall sections 2B and spring sections 2C are arranged in the x direction.

[0025] Furthermore, when viewed from the stacking direction, there is an overlapping portion between the separator 6 of an adjacent fuel cell unit 100 and the joint 20E between the spring portion 2C and the separator 6 of an adjacent fuel cell unit 100 and the joint 20C between the fuel electrode current collector 7 of an adjacent fuel cell unit 100.

[0026] Next, we will explain the effects of configuring the fuel cell stack 200 as described above.

[0027] Figures 5 and 6 are cross-sectional views of a portion of the fuel cell stack 200 according to this embodiment.

[0028] The components that make up the fuel cell unit 100 may have variations in dimensions and shape within tolerances. For example, as shown in Figure 5, if there are variations in the height of the ribs 7A of the fuel electrode current collector 7, the separator 6 will deform when joined to the ribs 7A, resulting in unevenness. If a fuel cell unit 100 with such unevenness in the separator 6 is stacked on another fuel cell unit 100, a gap may form at the joint between the two fuel cell units 100 in areas where the height of the ribs 7A is lower than elsewhere, reducing the joining area and potentially increasing the resistance value of the current collector. Furthermore, in areas where the height of the ribs 7A is higher than elsewhere, excessive force may be applied to each current collector 2, 7 and the separator 6.

[0029] However, according to the configuration of this embodiment, the spring portion 2C can absorb the irregularities of the separator 6 by deforming. That is, as shown in Figure 5, when the height of the left rib 7A (i.e., the amount of downward protrusion in the figure) is lower than the height of the right rib 7A, the right spring portion 2C deforms more than the left spring portion 2C, thereby absorbing the irregularities of the separator 6, ensuring an appropriate contact area at both the left and right joints, and avoiding excessive input.

[0030] Furthermore, during operation, the fuel cell stack 200 for vehicles may be subjected to forces in the stacking direction due to vibrations, etc. In this case, as described above, a moment is generated in the spring portion 2C that approaches the bottom portion 2A with the upper end of the wall portion 2B as the pivot point, and a force acts on the spring portion 2C that tends to slide at the joint surface with the separator 6. If all the spring portions 2C are configured to extend in the same direction, if the joint strength of each part or the frictional force of the outer circumference is insufficient, all the spring portions 2C will sink in accordance with the above moment, and as a result, the cross-sectional area of ​​the cathode flow path 21 will decrease, and the pressure loss will increase.

[0031] However, in this embodiment, since multiple pairs of spring portions 2C extending in opposing directions are provided, as shown in Figure 6, the sliding forces acting on the spring portions 2C (P1L and P1R in the figure) cancel each other out, leaving only the stacking forces acting on the wall portion 2B (P2L and P2R in the figure). Furthermore, the wall portion 2B and the compression seal 10 can withstand the stacking forces. Therefore, the situation in which the flow path cross-sectional area decreases and pressure loss increases due to the aforementioned sinking does not occur.

[0032] Next, a modified example of this embodiment will be described. This modified example also falls within the scope of the present invention, similar to the embodiment described above.

[0033] Figure 7 is a cross-sectional view of a part of the fuel cell stack 200 according to this modified example. Figure 8A is an enlarged view of the portion of the fuel cell stack 200 according to this modified example in which the rib 7A and the spring portion 2C face each other via the separator 6. Figure 8B is an enlarged view of the portion of the fuel cell stack 200 shown in Figure 4 in which the rib 7A and the spring portion 2C face each other via the separator 6.

[0034] The difference between the fuel cell stack 200 shown in Figure 7 and the fuel cell stack 200 shown in Figure 4 is that, when viewed from the stacking direction, the width of the joint 20E (D2 in the figure) between the spring portion 2C of one fuel cell unit 100 and the separator 6 of the adjacent fuel cell unit 100 is greater than the width of the portion where the rib 7A of the fuel electrode current collector 7 and the separator 6 come into contact (D1 in the figure). Here, "width" refers to the dimension in the z direction, which is perpendicular to the stacking direction (z direction) and perpendicular to the direction of gas flow in the cathode gas flow path (y direction).

[0035] When an input P1 is received from the stacking direction, this input P1 is transmitted to the separator 6 via the rib 7A (P2, P3, and P4 in Figures 8A and 8B), and further transmitted from the separator 6 to the spring section 2C. In this case, as shown in Figure 8A, if the width D2 of the joint 20E is greater than the width D1 of the part where the rib 7A and the separator 6 are in contact, then the entire portion of the separator 6 that receives the input P4 is joined to the spring section 2C. Therefore, the entire input P4 can be received by the spring section 2C.

[0036] In contrast, as shown in Figure 8B, if the width D1 of the contact area between the rib 7A and the separator 6 is greater than the width D2 of the joint 20E, then a portion of the separator 6 that receives the input P4 is not joined to the spring portion 2C. Therefore, the portion of the separator 6 that is not joined to the spring portion 2C will experience greater stress than the joined portion. Even in this case, a portion of the input P4 can be received by the spring portion 2C, so a strength problem does not immediately arise.

[0037] As described above, the configuration shown in Figure 8B does not cause any strength problems, but from the standpoint of durability, the modified configuration shown in Figure 8A is more advantageous because it reduces the stress on the separator 6. In other words, this modified configuration can further improve the durability of the fuel cell stack 200.

[0038] In the above description, a configuration was described in which a pair of wall portions 2B and spring portions 2C, each extending in a direction opposite to the other, are arranged in the x-direction. However, the arrangement of the wall portions 2B and spring portions 2C and the direction in which the spring portions 2C extend are not limited to this, and any configuration in which the sliding forces P1L and P1R shown in Figure 6 cancel each other out as a whole unit is acceptable. For example, with respect to the central flow path among the multiple cathode flow paths 21, all the spring portions 2C on one side may extend in the same direction, while all the spring portions 2C on the other side may extend in the opposite direction to the spring portions 2C on the other side.

[0039] Furthermore, although the above description described a configuration in which the separator 6 is joined to the fuel electrode current collector 7 in the state of the fuel cell unit 100, the separator 6 may also be joined to the air electrode current collector 2 in the state of the fuel cell unit 100. In this case, the air electrode current collector 2 will have a shape having multiple ribs, similar to the fuel electrode current collector 7 in the above description, and the fuel electrode current collector 7 will have a shape having a bottom, multiple walls, and a spring, similar to the air electrode current collector 2 in the above description.

[0040] As described above, in this embodiment, a fuel cell stack 200 is provided, which is formed by stacking fuel cell units 100 having a power generation cell 1 formed by sandwiching an electrolyte 3 between a fuel electrode 5 and an air electrode 4, a fuel electrode current collector 7 connected to the fuel electrode 5 side surface of the power generation cell 1, an air electrode current collector 2 connected to the air electrode 4 side surface of the power generation cell 1, and a separator 6 electrically connected to the fuel electrode current collector 7 or the air electrode current collector 2. In this fuel cell stack 200, at least one of the fuel electrode current collector 7 or the air electrode current collector 2 has a bottom portion 2A connected to the fuel electrode 5 or the air electrode 4 via a conductive joint, a plurality of wall portions 2B protruding from the bottom portion 2A, and a plurality of spring portions 2C extending from the upper ends of the plurality of wall portions 2B and deformable with respect to input from the stacking direction, with the upper ends of the wall portions 2B as pivot points. With multiple fuel cell units 100 stacked, the spring portion 2C is joined to the separator 6 of an adjacent fuel cell unit 100, and the multiple spring portions 2C and multiple wall portions 2B form multiple flow channels 21 that extend in a direction perpendicular to the stacking direction and are parallel to each other between the electrode to which the bottom portion 2A is connected and the separator 6 of an adjacent fuel cell unit 100, and the arrangement of the multiple wall portions 2B and the direction in which the multiple spring portions 2C extend are symmetrical with respect to the central flow channel 21 among the multiple flow channels 21.

[0041] As a result, in the stacked state, the sliding force (x-direction) generated by input from the stacking direction is canceled out, improving the strength against stress and creep force in the stacking direction, thus suppressing the reduction in the flow path cross-sectional area of ​​the gas flow path due to input from the stacking direction. In addition, since the spring portion 2C absorbs the displacement of the separator 6 in the stacking direction during stacking, the reduction in the contact area is suppressed even if irregularities occur on the separator 6. In other words, contact resistance can be reduced.

[0042] In this embodiment, at least one of the fuel electrode 5 and the air electrode 4 has a porous metal layer. This allows for the use of metal bonding (e.g., welding, diffusion bonding, brazing, etc.) for joining with the current collector, thereby further reducing contact resistance.

[0043] In this embodiment, the angle formed between the surface on the side where the spring portion 2C of the wall portion 2B extends and the bottom portion 2A is 90 degrees or less. Thereby, it is possible to improve the strength in the stacking direction after joining with the separator 6. In addition, it is possible to provide the draw gradient required in press working.

[0044] In this embodiment, when viewed from the stacking direction, there is an overlapping portion between the spring portion 2C, the joint portion 20E between the spring portion 2C and the separator 6 of the adjacent fuel cell unit 100, the separator 6 of the adjacent fuel cell unit 100, and the portion where the separator 6 of the adjacent fuel cell unit 100 contacts the electrode current collector. Thereby, an input from the stacking direction during the stacking process or during operation can be transmitted to the spring portion 2C. Also, the conductive path can be made shorter.

[0045] In this embodiment, one of the fuel electrode current collector 7 or the air electrode current collector 2 has the bottom portion 2A, the wall portion 2B, and the spring portion 2C, and the other has a plurality of ribs 7A forming a flow path. And when viewed from the stacking direction, the width D2 of the joint portion 20E between the spring portion 2C and the separator 6 of the adjacent fuel cell unit 100 is larger than the width D1 of the portion where the rib 7A contacts the separator 6. Thereby, the stress applied to the portion other than the spring portion 2C can be reduced, and the durability can be improved.

[0046] In this embodiment, a compression seal 10 having compressibility in the stacking direction is disposed on the same plane as one current collector (in the embodiment, the air electrode current collector 2), and a non-compressible seal 13 having non-compressibility is disposed on the same plane as the other current collector (in the embodiment, the fuel electrode current collector 7). When the stacking direction dimension of the wall portion 2B is A, the stacking direction dimension of the compression seal 10 after stacking is B, the stacking direction dimension of the non-compressible seal 13 after stacking is C, and the height from the surface to which the bottom portion 2A at the tip of the spring portion 2C is connected before stacking is D, the relationship C ≦ A < B and D ≧ B holds. Thereby, it is possible to prevent the deformation amount of the spring portion 2C from becoming excessive when absorbing displacement in the stacking direction.

[0047] In this embodiment, the air electrode current collector 2, the fuel electrode current collector 7, and the separator 6 are made of stainless steel containing aluminum. This improves oxidation resistance when operating at high temperatures, such as in solid oxide fuel cells.

[0048] In this embodiment, either the joint 20E between the spring portion 2C and the separator 6 of the adjacent fuel cell unit 100, or the joint 20A between the bottom portion 2A and the electrode (air electrode 4 in this embodiment) that the bottom portion 2A is connected to, is a welded joint, while the other is a diffusion joint. By using metal joints in this way, the resistance value of the joint can be reduced to that of the base material.

[0049] It goes without saying that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical idea described in the claims. [Explanation of Symbols]

[0050] 1. Generating cell, 2. Air electrode current collector, 3. Electrolyte, 4. Air electrode, 5. Fuel electrode, 6. Separator, 7. Fuel electrode current collector, 10. Compression seal, 13. Non-compression seal

Claims

1. A power generation cell formed by sandwiching an electrolyte between a fuel electrode and an air electrode, A fuel electrode current collector connected to the fuel electrode side surface of the aforementioned power generation cell, An air electrode current collector connected to the air electrode side surface of the aforementioned power generation cell, A separator electrically connected to the fuel electrode current collector or the air electrode current collector, In a fuel cell stack comprising stacked fuel cell units having, At least one of the fuel electrode current collector or the air electrode current collector is A bottom portion connected to the fuel electrode or the air electrode via a conductive joint, Multiple wall portions protruding from the bottom, Multiple spring portions extending from the upper ends of the multiple wall portions and capable of deforming with respect to input from the stacking direction, with the upper ends of the wall portions as pivot points, It has, With multiple fuel cell units stacked, the spring portion is joined to the separator of an adjacent fuel cell unit, and multiple flow channels extending in a direction perpendicular to the stacking direction and parallel to each other are formed between the electrode to which the bottom portion is connected and the separator of the adjacent fuel cell unit by the multiple spring portions and the multiple wall portions. The arrangement of the multiple wall portions and the direction in which the multiple spring portions extend are symmetrical with respect to the central flow path among the multiple flow paths. One of the fuel electrode current collector or the air electrode current collector has the bottom portion, the wall portion and the spring portion, and the other has a plurality of ribs. When viewed from the aforementioned stacking direction, There is an overlapping portion between the joint between the spring portion and the separator of the adjacent fuel cell unit, and the portion where the separator of the adjacent fuel cell unit and the electrode current collector of the adjacent fuel cell unit come into contact. A fuel cell stack characterized in that the width of the joint between the spring portion and the separator of the adjacent fuel cell unit is greater than the width of the portion where the rib and the separator come into contact.

2. In the fuel cell stack according to claim 1, A fuel cell stack in which at least one of the fuel electrode and the air electrode has a porous metal layer.

3. In the fuel cell stack according to claim 1, A fuel cell stack in which the angle between the side of the wall from which the spring portion extends and the bottom portion is 90 degrees or less.

4. In the fuel cell stack according to Claim 1, A compression seal having compressibility in the stacking direction is arranged on the same plane as one of the current collectors, and a non-compressible seal having non-compressibility is arranged on the same plane as the other current collector. A fuel cell stack such that, when the dimension of the wall portion in the stacking direction is A, the dimension of the compression seal after stacking is B, the dimension of the non-compression seal after stacking is C, and the height of the tip of the spring portion before stacking from the surface to which the bottom portion is connected is D, the relationship C ≤ A < B and D ≥ B holds.

5. In the fuel cell stack according to claim 1, A fuel cell stack in which the air electrode current collector, the fuel electrode current collector, and the separator are formed of stainless steel containing aluminum.

6. In the fuel cell stack according to claim 1, A fuel cell stack in which either the joint between the spring portion and the separator of the adjacent fuel cell unit, or the joint between the bottom portion and the electrode to which the bottom portion is connected, is a welded joint, and the other is a diffusion joint.

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