Fuel cell

Abstract

The present invention provides a fuel cell in which a plurality of cells, in each of which a fuel electrode is formed on one surface of an electrolyte and an air electrode is formed on the other surface, are stacked. Between two adjacent cells, there are provided a separator which is provided at a distance from the cells, a fuel electrode current collector which is electrically connected to the separator and the fuel electrode of one cell, and an air electrode current collector which is electrically connected to the separator and the air electrode of the other cell. In addition, at least one of the fuel electrode current collector and the air electrode current collector is a spring-shaped current collector which has a plurality of first joint parts that are in area contact with the electrode of the cell, a plurality of second joint parts that are in area contact with the separator, and a plurality of spring parts that each connect a first joint part and a second joint part to each other and bend at a bending position that is positioned between the first joint part and the second joint part. In the spring part, a first portion between the first joint part and the bending position has a smaller spring constant in the stacking direction of the cells than a second portion between the bending position and the second joint part.

Description

fuel cell

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

[0002] JP2021-57109A discloses an electrochemical cell stack (fuel cell, etc.) in which multiple cells are stacked. This electrochemical cell stack includes separators between the cells and current collectors between the separators and the cells. The current collectors have convex portions that protrude in the stacking direction of the cells and concave portions that are recessed in the stacking direction of the cells, and the convex portions and concave portions of the current collectors are in contact with the electrodes or separators of the cells. As a result, the current collectors form gas flow paths between the separators and the cells, and also form conductive paths between the stacked cells.

[0003] In the electrochemical cell stack described in JP2021-57109A, when the current collectors are pressed in the stacking direction during cell stacking, a force is generated in the concave direction at the tops of the convex portions, which may cause the contact portions of the convex portions with the electrodes or separators to deform in the concave direction. When the convex portions of the current collectors deform in the concave direction, the contact area with the electrodes or separators decreases, increasing the electrical resistance in the stacking direction of the cells, which may result in a decrease in the power generation performance of the electrochemical cell stack (fuel cell).

[0004] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a fuel cell with improved power generation performance.

[0005] According to one aspect of the present invention, a fuel cell is provided in which multiple stacked cells are formed, each having an anode on one side of an electrolyte and an cathode on the other side. Between each cell, a separator is provided spaced apart from the cell, an anode current collector electrically connected to the anode and separator of one cell, and an cathode current collector electrically connected to the cathode and separator of the other cell. At least one of the anode current collector and the cathode current collector is a spring-type current collector having a first joint in surface contact with the cell electrode, a second joint in surface contact with the separator, and a plurality of spring portions connecting the first joint and the second joint and bending at bending portions located between the first joint and the second joint. The spring portions have a smaller spring constant in the stacking direction of the cells at a first portion between the first joint and the bending portion than at a second portion between the bending portion and the second joint.

[0006] FIG. 1 is a schematic diagram of a fuel cell stack according to a first embodiment. FIG. 2 is an enlarged view of a cell cross section. FIG. 3 is an enlarged view of a power generation unit. FIG. 4 is a schematic cross section of a current collector according to a comparative example. FIG. 5 is a schematic cross section of a power generation unit according to a comparative example. FIG. 6 is a schematic cross section of a power generation unit. FIG. 7 is a schematic cross section of a spring-type current collector according to a modified example. FIG. 8 is a schematic cross section of a spring-type current collector according to a modified example. FIG. 9 is a schematic cross section of both ends of a current collector. FIG. 10 is a schematic cross section of both ends of a current collector according to a modified example. FIG. 11 is a schematic cross section of both ends of a current collector according to a modified example. FIG. 12 is a schematic diagram of a fuel cell stack according to a modified example of the first embodiment. FIG. 13 is an enlarged cross section of a second joint in a fuel cell stack according to a second embodiment. FIG. 14 is an enlarged cross section of a second joint according to a comparative example. FIG. 15 is a schematic diagram of a fuel cell stack according to a third embodiment. FIG. 16 is a schematic diagram of a fuel cell stack according to a modified example.

[0007] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0008] First Embodiment FIG. 1 is a schematic diagram of a fuel cell stack (fuel cell) 100 according to a first embodiment, showing a partial cross-sectional view of two adjacent fuel cell cells (hereinafter simply referred to as cells) 1. The fuel cell stack 100 is configured by stacking a plurality of cells 1. More specifically, the cells 1, together with current collectors 3 (described below), constitute a power generation unit 10 (FIG. 3), and the fuel cell stack 100 is configured by stacking a plurality of power generation units 10 with separators 2 interposed therebetween. Each of the cells 1 constituting the fuel cell stack 100 is, for example, a solid oxide fuel cell (SOFC), and generates electricity by receiving a supply of anode gas and cathode gas. In this embodiment, the fuel cell stack 100 is intended to be installed in a mobile vehicle such as an electric vehicle or a hybrid vehicle, but may also be used as a power source for various electrical devices.

[0009] As shown in Figure 1, separators 2 and current collectors 3 are provided between each of the multiple stacked cells 1. Although Figure 1 shows only two adjacent power generation units 10 out of the multiple stacked power generation units 10, in reality, many more power generation units 10 can be stacked in the same manner. For simplicity, Figure 1 omits the outer edge of the fuel cell stack 100 (power generation units 10), and only shows a portion of the cross section of two adjacent power generation units 10.

[0010] FIG. 2 is an enlarged cross-sectional view of the cell 1. As shown in FIG. 2, the cell 1 is configured by forming an anode 12 on one surface of a solid electrolyte (electrolyte) 11 and an air electrode 13 on the other surface. The anode 12 includes an anode layer 121 disposed on one surface of the solid electrolyte 11 and a metal porous layer 122 provided to support the anode layer 121. The air electrode 13 includes a cathode layer 131 disposed on the other surface of the solid electrolyte 11 and a metal porous layer 132 provided to support the cathode layer 131. Known materials may be used to form the solid electrolyte 11, the anode layer 121, the cathode layer 131, and the metal porous layers 122 and 132.

[0011] The separator 2 is made of stainless steel containing aluminum, and is provided between two adjacent cells 1 at a distance from the cells 1, as shown in FIG.

[0012] The current collector 3 is made of stainless steel containing aluminum and electrically connects the electrodes 12, 13 of the cell 1 and the separator 2. The current collector 3, together with the cell 1, constitutes a power generation unit 10. The current collector 3 also forms gas flow paths 4, 5 between the separator 2 and the cell 1, as will be described later.

[0013] The current collectors 3 include an anode current collector 31 provided between the anode 12 and separator 2 of one of two adjacent cells 1, and an air cathode current collector 32 provided between the air cathode 13 and separator 2 of the other cell 1. The anode current collector 31 is electrically connected to the anode 12 and separator 2, and the air cathode current collector 32 is electrically connected to the air cathode 13 and separator 2. In this way, the current collectors 3 form a conductive path between the stacked cells 1.

[0014] The air electrode current collector 32 has a first joint 321 that is in surface contact with the air electrode (electrode) 13 of the cell 1, and a second joint 322 that is in surface contact with the separator 2. The air electrode current collector 32 is welded (metallicly bonded) to the air electrode 13 at the first joint 321, and is diffusion bonded (metallicly bonded) to the separator 2 at the second joint 322. The air electrode current collector 32 also has a spring portion 323 that connects the first joint 321 and the second joint 322, and bends at a bending portion 324 located between the first joint 321 and the second joint 322.

[0015] The first bonding portions 321 and the second bonding portions 322 are arranged alternately (in order) in a predetermined direction (the width direction of the air electrode current collector 32), and the first bonding portions 321 and the second bonding portions 322 are each connected by a spring portion 323. That is, the air electrode current collector 32 has a plurality of first bonding portions 321, second bonding portions 322, and spring portions 323 connecting these together, thereby forming a plurality of spaces between the separator 2 and the air electrode 13: spaces partitioned by the air electrode 13 and the air electrode current collector 32, and spaces partitioned by the separator 2 and the air electrode current collector 32. Of these, the space partitioned by the air electrode 13 and the air electrode current collector 32 forms an air flow path (gas flow path) 4 through which air (cathode gas) supplied to the cell 1 flows.

[0016] The anode current collector 31 has a third joint 311 that is in surface contact with the anode (electrode) 12 of the cell 1, and a fourth joint 312 that is in surface contact with the separator 2. The anode current collector 31 is welded (metallicly joined) to the anode 12 at the third joint 311, and is welded (metallicly joined) to the separator 2 at the fourth joint 312. The anode current collector 31 also has a connecting portion 313 that connects the third joint 311 and the fourth joint 312.

[0017] The third bonding portions 311 and the fourth bonding portions 312 are arranged alternately (in order) in a predetermined direction (the width direction of the anode current collector 31), and the third bonding portions 311 and the fourth bonding portions 312 are connected by connecting portions 313. That is, the anode current collector 31 is configured as an uneven member having a plurality of third bonding portions 311, fourth bonding portions 312, and connecting portions 313 connecting these portions, thereby forming a plurality of spaces between the separator 2 and the anode 12, including spaces partitioned by the anode 12 and the anode current collector 31 and spaces partitioned by the separator 2 and the anode current collector 31. Of these, the space partitioned by the anode 12 and the anode current collector 31 forms a fuel flow path (gas flow path) 5 through which fuel gas supplied to the cell 1 flows.

[0018] An insert material 21 made of copper, nickel, platinum, gold, or the like is interposed between the second bonding portion 322 and the separator 2 .

[0019] Fig. 3 is a perspective view of the power generation unit 10. As described above, the power generation unit 10 is composed of a cell 1 and a current collector 3, and the fuel cell stack 100 is formed by stacking the power generation units 10 with separators 2 interposed therebetween. As shown in Fig. 3, the periphery of the cell 1 is sealed with a sealing member 6, and stoppers 7 are provided on both ends of the current collector 3. Details of the stoppers 7 will be described later.

[0020] As described above, the fuel cell stack 100 includes separators 2 between the cells 1, and current collectors 3 between the separators 2 and the electrodes 12, 13 of the cells 1. The current collectors 3 and the electrodes 12, 13 also form gas flow paths 4, 5 through which gases to be supplied to the cells 1 flow.

[0021] In a fuel cell stack consisting of multiple stacked cells, if the current collector between the separator and the cell (electrode) has an uneven shape with protruding portions protruding in the cell stacking direction and recessed portions recessed in the cell stacking direction, when the current collector is pressed in the cell stacking direction, a force is generated at the top of the protruding portions in the recessed direction. This may cause the protruding portions to deform in the recessed direction, reducing the contact area between the current collector and the electrode or separator. A reduced contact area between the current collector and the electrode or separator increases electrical resistance in the cell stacking direction, potentially reducing the power generation performance of the fuel cell stack. For example, in a fuel cell in which the protruding portions 322' of the current collector 3' contact the separator 2', when the fuel cell is pressed in the cell stacking direction during stacking and crimping, as shown in FIG. 4 , the protruding portions 322' of the current collector 3' may deform in the recessed direction, reducing the contact area between the current collector 3' and the separator 2'.

[0022] On the other hand, when metal-bonding current collectors with uneven surfaces to cells (electrodes) and separators, gaps may occur at the joints between the current collectors and the cells (electrodes) and separators when the cells are stacked due to variations in component dimensions or the current collectors' inability to conform to the unevenness of the cell surfaces. This may result in a reduced contact area between the current collectors and the electrodes or separators. Furthermore, due to variations in component dimensions or the current collectors' inability to conform to the unevenness of the cell surfaces, if the clearance between the current collectors and the electrodes or separators is insufficient relative to the amount of compression of the sealing material around the cell periphery, excessive force may be applied to the cells and current collectors, potentially resulting in damage. For example, in the case of a fuel cell 100'' in which the anode current collector 31'' is welded (metallicly bonded) to the anode 12'' and separator 2'', and the cathode current collector 32'' is welded (metallicly bonded) to the cathode 13'', and diffusion-bonded (metallicly bonded) to the separator 2'', there is a risk that a gap (R) will occur between the separator 2'' and the cathode current collector 32'', as shown in Figure 5, due to variations in component dimensions and the inability of the current collectors 31'' and 32'' to conform to the irregularities on the cell surface. This increases the electrical resistance in the stacking direction of the cells, thereby reducing the power generation performance of the fuel cell stack.

[0023] Therefore, in this embodiment, the air electrode current collector 32 is a spring-shaped current collector that has a first joint portion 321 in surface contact with the air electrode 13, a second joint portion 322 in surface contact with the separator 2, and a plurality of spring portions 323 that connect the first joint portion 321 and the second joint portion 322 and bend at a bend portion 324 located between the first joint portion 321 and the second joint portion 322. The spring portions 323 are configured so that a first portion between the first joint portion 321 and the bend portion 324 has a smaller spring constant k in the stacking direction of the cell 1 than a second portion between the bend portion 324 and the second joint portion 322. As a result, when the cells 1 (power generating units 10) are stacked, the spring portions 323 absorb displacement of the separators 2 in the stacking direction of the cells 1, and suppress deformation of the joints (second joints) 322 with the separators 2, applying appropriate surface pressure to the joints (second joints) 322. This reduces electrical resistance in the stacking direction of the cells 1, improving the power generation performance of the fuel cell stack 100.

[0024] The current collector 3 (particularly the spring-type current collector 32) will be described in detail below.

[0025] First, a method for joining the current collector 3 to the electrodes 12, 13 and separator 2 of the cell 1 will be described.

[0026] FIG. 6 is a schematic cross-sectional view of the power generation unit 10, and is a partial cross-sectional view of two adjacent power generation units 10.

[0027] As described above, the cathode current collector (spring-type current collector) 32 has a first joint portion 321 in surface contact with the cathode (electrode) 13 of the cell 1, a second joint portion 322 in surface contact with the separator 2, and a spring portion 323 that connects the first joint portion 321 and the second joint portion 322 and bends at a bending portion 324. The anode current collector 31 has a third joint portion 311 in surface contact with the anode (electrode) 12 of the cell 1, a fourth joint portion 312 in surface contact with the separator 2, and a connecting portion 313 that connects the third joint portion 311 and the fourth joint portion 312.

[0028] 6 , the anode current collector 31 is welded (metallicly bonded) to the metal porous layer 122 of the anode 12 at a third joint 311, and the cathode current collector (spring-shaped current collector) 32 is welded (metallicly bonded) to the metal porous layer 132 of the cathode 13 at a first joint 321. In this way, since the electrodes 12 and 13 of the cell 1 have the metal porous layer 132, the electrodes 12 and 13 can be metallically bonded to the current collector 3.

[0029] Furthermore, the anode current collector 31 is welded (metallicly bonded) to the separator 2 at the fourth joint 312, and the cathode current collector (spring-type current collector) 32 is diffusion-bonded (metallicly bonded) to the separator 2 via the insert material 21 at the second joint 322. That is, the current collector 3 is metallically bonded to the electrodes 12 and 13 of the cell 1 and the separator 2. This reduces the resistance at the joints 311, 312, 321, and 322. This reduces the electrical resistance in the stacking direction of the cells 1, improving the power generation performance of the fuel cell stack 100. Note that welding is not used to bond the cathode current collector 32 to the separator 2 because, with the anode current collector 31 welded to the anode 12 and separator 2 and the cathode current collector 32 welded to the cathode 13, a welder cannot access the joint between the cathode current collector 32 and the separator 2.

[0030] Here, if the separator 2 or the current collector 3 were coated with an oxidation-resistant coating or the like, there is a risk that the current collector 3 would not be able to be metal-joined (e.g., welded) to the separator 2 and the electrodes 12, 13 due to the coating. In contrast, in this embodiment, as described above, the separator 2 and the current collector 3 are made of a stainless steel material containing aluminum. Aluminum has excellent oxidation resistance because it forms an alumina (aluminum oxide) film on its surface. Therefore, in this embodiment, there is no need to apply a coating to the separator 2 and the current collector 3. That is, in this embodiment, because the separator 2 and the current collector 3 are made of a stainless steel material containing aluminum, oxidation resistance during high-temperature operation of the fuel cell stack 100 is improved, and metal-joining (e.g., welding) to the current collector 3, the electrodes 12, 13 of the cell 1, and the separator 2 can be performed.

[0031] Next, the shape of the current collector 3 will be described.

[0032] As described above, the spring portion 323 of the cathode current collector (spring-type current collector) 32 connects the first joint 321 and the second joint 322 and is bent at the bent portion 324. That is, the spring portion 323 has a first portion 323A between the first joint 321 and the bent portion 324 and a second portion 323B between the bent portion 324 and the second joint 322. Also, as shown in FIG. 6 , both ends of the second joint 322 are connected to different spring portions 323. That is, the cathode current collector (spring-type current collector) 32 is configured as a so-called double-supported spring. As shown in FIG. 6 , the angle θ formed between the first portion 323A and the surface of the cell 1 (hereinafter also referred to as the inclination angle of the first portion 323A) １ is the angle θ between the second portion 323B and the surface of the cell 1 (hereinafter also referred to as the inclination angle of the second portion 323B). ２ is smaller than (i.e., θ １ <θ ２ ). The length L of the first portion 323A １ is the length L of the second portion 323B ２ longer than (i.e., L １ >L ２ As a result, the spring constant of the first portion 323A in the stacking direction of the cell 1 (hereinafter also referred to as the spring constant of the first portion 323A) k Ａ is the spring constant of the second portion 323B in the stacking direction of the cell 1 (hereinafter also referred to as the spring constant of the second portion 323B) k Ｂ (i.e., k Ａ <k Ｂ Between the separator 2 and the air electrode 13, the air electrode current collector (spring-shaped current collector) 32 and the air electrode 13 form an air flow path 4 having a cross-sectional shape resembling Mount Fuji (a shape with a convex top and a wide base) through which the cathode gas supplied to the air electrode 13 flows.

[0033] In this way, the spring portion 323 has an inclination angle θ of the second portion 323B adjacent to the second joint portion 322. ２ is the inclination angle θ of the first portion 323A. １ The length L of the second portion 323B adjacent to the second joint portion 322 is larger than the length L of the second portion 323B. ２is the length L of the first portion 323A １ This suppresses deformation of the second portion 323B and the second joint 322 when a load is applied in the stacking direction of the cells 1. Furthermore, because the air electrode current collector (spring-type current collector) 32 is configured as a doubly supported spring, when a load is applied to the second joint 322, the second joint 322 moves parallel to the stacking direction of the cells 1, suppressing deformation of the second joint 322.

[0034] On the other hand, the connecting portion 313 connecting the third joint portion 311 and the fourth joint portion 312 of the anode current collector 31 has a substantially linear shape. Therefore, the anode current collector 31 is configured as an uneven member having a plurality of third joint portions 311, fourth joint portions 312, and connecting portions 313 connecting these portions. As a result, a fuel flow path 5 having a trapezoidal cross section and through which fuel gas flows is formed by the anode current collector 31 and the anode 12 between the anode 12 and the separator 2. Note that, although the connecting portion 313 of the anode current collector 31 has a substantially linear shape in this embodiment, the present invention is not limited to this, and the connecting portion 313 may have a curved shape.

[0035] Next, the second moment of area of ​​the spring portion 323 of the spring-type current collector 32 will be described.

[0036] In this embodiment, the spring portion 323 of the air electrode current collector (spring-type current collector) 32 has a second moment of area of ​​the first portion 323A of I １ The second moment of area I of the second portion 323B is ２ is smaller than (i.e., I １ <I ２ Therefore, the spring constant k of the first portion 323A in the stacking direction of the cell 1 is Ａ is the spring constant k of the second portion 323B Ｂ Therefore, when a load is applied in the stacking direction of the cells 1, the load on the second portion 323B is reduced, and deformation of the second joint portion 322 is suppressed.

[0037] Here, the geometrical moment of inertia I of the spring portion 323 can be adjusted by changing the plate thickness of the spring portion 323, or by providing a slit in the longitudinal direction of the spring portion 323. For example, as shown in FIG. 7, by making the plate thickness t2 of the second portion 323B thicker than the plate thickness t1 of the first portion 323A of the spring portion 323, the geometrical moment of inertia I of the second portion 323B can be adjusted. ２ The second moment of area of ​​the first portion 323A is I １ 8, for example, by providing a slit S in the longitudinal direction in the first portion 323A of the spring portion 323, the moment of inertia I of the first portion 323A can be increased. １ The second moment of area I ２ However, the method for adjusting the second moment of area I of the spring portion 323 is not limited to the above, and any known method may be used.

[0038] Next, the end portion 325 of the spring-type current collector 32 will be described.

[0039] 9 is a schematic cross-sectional view of both end portions 325 of the current collector 3. As shown in FIG. 9, stoppers 7 are provided at both end portions 325 of the air electrode current collector (spring-type current collector) 32.

[0040] Specifically, a stopper 7 is fixed to an end of the cell 1 in the width direction, and an end 325 of the cathode current collector (spring-type current collector) 32 is inserted between the stopper 7 and the cell 1. As a result, when the cells 1 are stacked, a load is applied to the second joint portion 322 of the cathode current collector 32 in the stacking direction of the cells 1, and the stopper 7 can withstand the shear force (direction of the arrow in FIG. 9 ) that occurs when the cathode current collector 32 is displaced. In this way, the shear force of the cathode current collector (spring-type current collector) 32 is supported by the stopper 7. This can mitigate the shear force acting on the second joint portion 322, and suppress deformation of the second joint portion 322.

[0041] The stopper 7 may be made of any material as long as it can be fixed to the cell 1 and can withstand the force of the current collector 3 in the shear direction.

[0042] 9, the stopper 7 is provided on the surface of the cell 1, but this is not limiting. For example, as shown in FIG. 10, the stopper 7 may be provided from the side surface of the widthwise end of the cell 1 to the surface. Furthermore, the stopper 7 may not be a separate member from the cell 1, but may be formed on the cell 1. For example, as shown in FIG. 11, a step may be provided on the widthwise end of the cell 1 when the cell 1 is molded, and this step portion may serve as the stopper 7.

[0043] As described above, the fuel cell stack 100 has a spring constant k Ａ is the spring constant k of the second portion 323B. Ｂ and both end portions 325 of the spring-shaped current collector 32 are supported by the stoppers 7. This prevents the second joint portion 322 from being deformed.

[0044] In this embodiment, the insert material 21 is interposed between the cathode current collector (spring-type current collector) 32 and the separator 2 to facilitate diffusion bonding, but this is not limiting. That is, in this embodiment, because deformation of the second bonding portion 322 is suppressed, the cathode current collector (spring-type current collector) 32 and the separator 2 may be diffusion bonded together without the insert material 21 interposed therebetween.

[0045] According to the fuel cell stack (fuel cell) 100 of the above embodiment, the following effects can be obtained.

[0046] In the fuel cell stack (fuel cell) 100, the cathode current collector 32 has a first joint 321 that is in surface contact with the cathode 13 of the cell 1, a second joint 322 that is in surface contact with the separator 2, and a plurality of spring portions 323 that connect the first joint 321 and the second joint 322 and are bent at bent portions 324 located between the first joint 321 and the second joint 322. The spring portions 323 have a first portion 323A between the first joint 321 and the bent portion 324 that has a smaller spring constant k in the stacking direction of the cell 1 than a second portion 323B between the bent portion 324 and the second joint 322. As a result, when the cells 1 (power generating units 10) are stacked, the spring portions 323 absorb displacement of the separators 2 in the stacking direction of the cells 1, and suppress deformation of the joints (second joints) 322 with the separators 2, applying appropriate surface pressure to the joints (second joints) 322. This reduces electrical resistance in the stacking direction of the cells 1, improving the power generation performance of the fuel cell stack 100.

[0047] Furthermore, because deformation of the joint (second joint) 322 with the separator 2 is suppressed, it is not necessary to interpose the insert material 21 between the cathode current collector 32 and the separator 2 to facilitate diffusion bonding. This allows for a reduction in the number of parts and steps, resulting in lower costs.

[0048] In the fuel cell stack (fuel cell) 100, both ends of the second joint portion 322 of the cathode current collector (spring-type current collector) 32 are connected to different spring portions 323. That is, the cathode current collector (spring-type current collector) 32 is configured as a so-called double-supported spring. As a result, when a load is applied to the second joint portion 322, the second joint portion 322 moves parallel to the stacking direction of the cells 1, thereby suppressing deformation of the second joint portion 322. This reduces the electrical resistance in the stacking direction of the cells 1, and improves the power generation performance of the fuel cell stack 100.

[0049] The fuel cell stack (fuel cell) 100 has an angle θ formed between the first portion 323A of the spring portion 323 and the surface of the cell 1. １ The angle θ between the second portion 323B and the surface of the cell 1 ２ As a result, the spring constant k of the first portion 323A in the stacking direction of the cell 1 is Ａis the spring constant k of the second portion 323B Ｂ Therefore, deformation of the second portion 323B and the second joint portion 322 when a load is applied in the stacking direction of the cells 1 is suppressed. This reduces the electrical resistance in the stacking direction of the cells 1, and improves the power generation performance of the fuel cell stack 100.

[0050] The fuel cell stack (fuel cell) 100 has a length L of the first portion 323A of the spring portion 323. １ The length L of the second portion 323B ２ As a result, the spring constant k Ａ is the spring constant k of the second portion 323B Ｂ Therefore, deformation of the second portion 323B and the second joint portion 322 when a load is applied in the stacking direction of the cells 1 is suppressed. This reduces the electrical resistance in the stacking direction of the cells 1, and improves the power generation performance of the fuel cell stack 100.

[0051] The fuel cell stack (fuel cell) 100 has a second moment of area of ​​the first portion 323A of the spring portion 323 of I １ The second moment of area I of the second portion 323B is ２ As a result, the spring constant k of the first portion 323A in the stacking direction of the cell 1 is Ａ is the spring constant k of the second portion 323B Ｂ Therefore, when a load is applied to the cells 1 in the stacking direction, the load on the second portion 323B is reduced, suppressing deformation of the second joint portion 322. This reduces the electrical resistance in the stacking direction of the cells 1, improving the power generation performance of the fuel cell stack 100.

[0052] In the fuel cell stack (fuel cell) 100, the electrodes (anode 12 and cathode 13) of the cell 1 include metal porous layers 122 and 132, and the current collectors 3 (anode current collector 31 and cathode current collector 32) are metal-bonded to the electrode metal porous layers 122 and 132 and separator 2 of the cell 1. Because the electrodes 12 and 13 of the cell 1 have the metal porous layers 132, the electrodes 12 and 13 can be metal-bonded to the current collectors 3. Furthermore, because the current collectors 3 are metal-bonded to the electrodes 12 and 13 and separator 2 of the cell 1, the resistance at joints 311, 312, 321, and 322 between the current collectors 3 and the electrodes 12 and 13 and separator 2 of the cell 1 is suppressed. This reduces electrical resistance in the stacking direction of the cells 1, improving the power generation performance of the fuel cell stack 100.

[0053] In the fuel cell stack (fuel cell) 100, the separators 2 and current collectors 3 are made of stainless steel containing aluminum. This improves oxidation resistance during high-temperature operation of the fuel cell stack 100. Furthermore, because of the improved oxidation resistance, there is no need to coat the separators 2 and current collectors 3, and the current collectors 3 can be metallically joined (by welding, for example) to the electrodes 12, 13 of the cells 1 and the separators 2. This reduces electrical resistance in the stacking direction of the cells 1, improving the power generation performance of the fuel cell stack 100.

[0054] In the fuel cell stack (fuel cell) 100, stoppers 7 are provided at both end portions 325 of the air electrode current collector (spring-type current collector) 32 to support the shearing force of the air electrode current collector (spring-type current collector) 32. This can mitigate the shearing force acting on the second joint portion 322, and suppress deformation of the second joint portion 322.

[0055] In this embodiment, the inclination angle θ of the first portion 323A of the spring portion 323 １ The inclination angle θ of the second portion 323B ２ and the length L of the first portion 323A is smaller than １ The length L of the second portion 323B ２ and the second moment of area of ​​the first portion 323A is I １ The second moment of area I of the second portion 323B is ２In other words, the spring constant k of the first portion 323A of the spring portion 323 in the stacking direction of the cells 1 is smaller than Ａ is the spring constant k of the second portion 323B. Ｂ If it is configured to be smaller than θ １ <θ ２ , L １ >L ２ , I １ <I ２ For example, the length L of the first portion 323A does not need to be satisfied. １ , the length L of the second portion 323B ２ , the second moment of area of ​​the first portion 323A is I １ , the second moment of area I of the second portion 323B ２ is configured to satisfy the relationship of the following formula (1), L １ >L ２ , I １ <I ２ In this case, the spring constant k Ａ is the spring constant k of the second portion 323B. Ｂ will be smaller than

[0056] In this embodiment, the cathode current collector 32 is a spring-type current collector having a spring portion 323 that bends at a bending point 324, but this is not necessarily limited to this. For example, the anode current collector 31 may be a spring-type current collector having a spring portion, or both the cathode current collector 32 and the anode current collector 31 may be spring-type current collectors having spring portions (see FIG. 16 ). That is, it is sufficient that at least one of the cathode current collector 32 and the anode current collector 31 is a spring-type current collector having a spring portion.

[0057] Furthermore, as in this embodiment, the spring-type current collector 32 is preferably configured as a double-arm spring in which both ends of the second joint portion 322 are connected to different spring portions 323, but this is not necessarily limited to this and the current collector 32 may also be configured as a cantilever spring.

[0058] Furthermore, as in this embodiment, it is preferable that the anode 12 and the cathode 13 include the metal porous layers 122 and 132, and that the anode current collector 31 and the cathode current collector 32 are metal-bonded to the metal porous layers 122 and 132, respectively, but this is not necessarily limited to this. For example, only the electrode that is in surface contact with the spring-shaped current collector having a spring portion may include a metal porous layer, and the spring-shaped current collector may be metal-bonded to the metal porous layer.

[0059] Furthermore, as in this embodiment, it is preferable that the current collector 3 is metallically bonded to the electrodes 12, 13 and the separator 2, but this is not necessarily limited to this, and the current collector 3 may be bonded to the electrodes 12, 13 and the separator 2 by a method other than metallic bonding. Furthermore, in this embodiment, the metallic bonding method is welding or diffusion bonding, but it is not limited to this, and may be, for example, brazing.

[0060] In addition, as in this embodiment, the separator 2 and the current collector 3 are preferably made of stainless steel containing aluminum, but this is not necessarily limited to this. For example, part or all of the separator 2 and the current collector 3 may be made of other materials.

[0061] Furthermore, as in this embodiment, it is preferable to provide stoppers 7 at both ends 325 of the spring-type current collector 32 to support the shear force of the spring-type current collector 32, but this is not necessarily limited to this, and the stoppers 7 do not necessarily have to be provided.

[0062] [Modification of First Embodiment] A fuel cell stack (fuel cell) 100 according to a modification of the first embodiment will be described with reference to Fig. 12. Note that elements similar to those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0063] 12 is a schematic diagram of a fuel cell stack (fuel cell) 100 according to a modification of the first embodiment, and is a partial cross-sectional view of two adjacent power generation units 10. This embodiment differs from the first embodiment in that the first joint portion 321 of the spring-type current collector 32 has an opening 326.

[0064] As shown in FIG. 12 , the air electrode current collector (spring-type current collector) 32 has an opening 326 at a first joint 321 that comes into surface contact with the air electrode 13 of the cell 1. That is, the space defined by the air electrode current collector 32 and the separator 2, which is formed between the air electrode 13 and the separator 2, communicates with the metal porous layer 132 of the air electrode 13 via the opening 326. Therefore, air (cathode gas) can be supplied to the air electrode 13 from the space defined by the air electrode current collector 32 and the separator 2 via the opening 326. That is, the space defined by the air electrode current collector 32 and the separator 2 can also be used as an air flow path (gas flow path) 4. The air in the air flow path 4 that enters the cell 1 from the opening 326 diffuses to the air electrode via the metal porous layer 132. This allows for a larger reaction area at the air electrode 13, improving the power generation performance of the fuel cell stack 100.

[0065] In this modified example, only the first joint portion 321 of the cathode current collector 32 has the opening 326, but the present invention is not limited to this, and an opening may also be provided in the third joint portion 311 of the anode current collector 31. This allows the space partitioned by the anode current collector 31 and the separator 2 to be used as the fuel flow path 5 through which the fuel gas supplied to the cell 1 flows, and the fuel gas can be supplied from the fuel flow path 5 to the anode 12 via the opening 326. This allows the reaction area of ​​the anode 12 to be increased, improving the power generation performance of the fuel cell stack 100.

[0066] Also in this modified example, the air electrode current collector 32 is a spring-type current collector 32 having a spring portion 323, but this is not limited to this, and the fuel electrode current collector 31 may also be a spring-type current collector having a spring portion.

[0067] Second Embodiment A fuel cell stack (fuel cell) 100 according to a second embodiment will be described with reference to Figure 13. Elements similar to those in the other embodiments are given the same reference numerals, and descriptions thereof will be omitted.

[0068] 13 is an enlarged cross-sectional view of the second joint 322 in the fuel cell stack (fuel cell) 100 according to the second embodiment. This embodiment differs from the other embodiments in that the pitch width X of the second joint 322 is larger than the pitch width Y of the fourth joint 312.

[0069] 13 , the second bonding portions 322 of the cathode current collector (spring-type current collector) 32, which come into surface contact with the separator 2, are formed at positions facing the fourth bonding portions 312 of the anode current collector 31, which come into surface contact with the separator 2, when viewed in the cross-sectional direction of the cell 1. The pitch width X of the second bonding portions 322 is larger than the pitch width Y of the fourth bonding portions 312.

[0070] 14 , if the pitch width X′ of the second joints 322 is smaller than the pitch width Y′ of the fourth joints 312, when the fuel cell stack 100 is pressed in the stacking direction of the cells 1, the spring portion 323 of the air electrode current collector (spring-type current collector) 32 cannot withstand the force in the stacking direction of the cells 1 in the portion outside the second joints 322 (the portion where the fourth joints 312 and the second joints 322 do not overlap when viewed in the cross-sectional direction of the cells 1). Therefore, a pressing stress is applied to the separator 2, which may cause the separator 2 to break.

[0071] In contrast, in this embodiment, the pitch width X of the second joint portions 322 is larger than the pitch width Y of the fourth joint portions 312, so that the force in the stacking direction of the cells 1 can be received entirely by the spring portions 323. Therefore, damage to the separators 2 and the current collectors 3 can be prevented.

[0072] Third Embodiment A fuel cell stack (fuel cell) 100 according to a third embodiment will be described with reference to Figure 15. Elements similar to those in the other embodiments are given the same reference numerals, and descriptions thereof will be omitted.

[0073] 15 is a schematic diagram of a fuel cell stack (fuel cell) 100 according to a third embodiment, showing a partial cross-sectional view of two adjacent power generation units 10. This embodiment differs from the other embodiments in that the first joint 321 is formed at a position opposite the third joint 311.

[0074] 15 , in this embodiment, first bonding portions 321 of the cathode current collector (spring-type current collector) 32 that come into surface contact with the cathode 13 are formed at positions facing the third bonding portions 311 of the anode current collector 31 that come into surface contact with the anode 12, when viewed in the cross-sectional direction of the cell 1. Furthermore, second bonding portions 322 of the cathode current collector (spring-type current collector) 32 that come into surface contact with the separator 2 are formed at positions facing the fourth bonding portions 312 of the anode current collector 31 that come into surface contact with the separator 2, when viewed in the cross-sectional direction of the cell 1. Preferably, as in the second embodiment, the pitch width of the second bonding portions 322 is greater than the pitch width of the fourth bonding portions 312.

[0075] As described above, in this embodiment, the first bonding portion 321 and the third bonding portion 311, and the second bonding portion 322 and the fourth bonding portion 312 are arranged in series in the stacking direction of the cells 1. As a result, the load in the stacking direction of the cells 1 is transmitted in series from the first bonding portion 321 to the third bonding portion 311 and from the second bonding portion 322 to the fourth bonding portion 312, and the cells 1 and the separators 2 are not subjected to bending input. Therefore, damage to the cells 1 and the separators 2 is prevented.

[0076] In this embodiment, the cathode current collector 32 is a spring-type current collector 32 having a spring portion 323. However, this is not limiting, and the anode current collector 31 may also be a spring-type current collector having a spring portion. Furthermore, as shown in FIG. 16 , both the cathode current collector 32 and the anode current collector 31 may be spring-type current collectors having spring portions. In either case, a first bonding portion 321 in the cathode current collector 32 that is in surface contact with the cathode 13 and a third bonding portion 311 in the anode current collector 31 that is in surface contact with the anode 12 are formed at opposing positions when viewed in the cross-sectional direction of the cell 1. Furthermore, a second bonding portion 322 in the cathode current collector 32 that is in surface contact with the separator 2 and a fourth bonding portion 312 in the anode current collector 31 that is in surface contact with the separator 2 are formed at opposing positions when viewed in the cross-sectional direction of the cell 1. As a result, the cells 1 and separators 2 are not subjected to bending input when a load is applied in the stacking direction of the cells 1, and damage to the cells 1 and separators 2 is prevented.

[0077] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0078] Although the above-described embodiments have been described as separate embodiments, they may be combined as appropriate.

Claims

1. A fuel cell in which a plurality of cells are stacked, each having an anode on one side of an electrolyte and an cathode on the other side, wherein a separator spaced apart from the cell is provided between each cell, an anode current collector electrically connecting the anode and separator of one cell, and an cathode current collector electrically connecting the cathode and separator of the other cell, wherein at least one of the anode current collector and the cathode current collector is a spring-type current collector having a first joint in surface contact with the electrode of the cell, a second joint in surface contact with the separator, and a plurality of spring portions connecting the first joint and the second joint and bending at a bending portion located between the first joint and the second joint, wherein a first portion of the spring portion between the first joint and the bending portion has a smaller spring constant in the stacking direction of the cells than a second portion between the bending portion and the second joint.

2. A fuel cell according to claim 1, wherein the second joint portion of the spring-shaped current collector has both ends connected to different spring portions.

3. A fuel cell according to claim 1, wherein the angle between the first portion and the surface of the cell of the spring portion is smaller than the angle between the second portion and the surface of the cell.

4. A fuel cell according to claim 1, wherein the first portion of the spring portion is longer than the second portion.

5. A fuel cell according to claim 1, wherein the second moment of area of ​​the first portion of the spring portion is smaller than the second moment of area of ​​the second portion.

6. A fuel cell according to claim 5, wherein the second moment of area of ​​the first portion is I １ , the length of the first portion is L １ , the second moment of area of ​​the second portion is I ２ , the length of the second portion is L ２ In this case, This is called a fuel cell.

7. A fuel cell as described in claim 2, wherein one of the fuel electrode collector and the air electrode collector has a third joint portion in surface contact with the electrode of the cell, a fourth joint portion in surface contact with the separator, and a connecting portion connecting the third joint portion and the fourth joint portion, the second joint portion is formed at a position opposite the fourth joint portion when viewed in the cross-sectional direction of the cell, and the pitch width of the second joint portion is larger than the pitch width of the fourth joint portion.

8. A fuel cell as described in claim 2, wherein one of the fuel electrode collector and the air electrode collector has a third joint portion in surface contact with the electrode of the cell, a fourth joint portion in surface contact with the separator, and a connecting portion connecting the third joint portion and the fourth joint portion, the first joint portion being formed at a position facing the third joint portion when viewed in the cross-sectional direction of the cell, and the second joint portion being formed at a position facing the fourth joint portion when viewed in the cross-sectional direction of the cell.

9. The fuel cell according to claim 1, wherein the first joint portion has an opening.

10. A fuel cell as described in claim 1, wherein at least one of the fuel electrode and the air electrode is provided with a metal porous layer, and the current collector in face-to-face contact with the electrode having the metal porous layer is metal-bonded to the metal porous layer and the separator.

11. A fuel cell according to claim 10, wherein the cell comprises at least an electrode having a metal porous layer in surface contact with the spring-type current collector, and the spring-type current collector and the metal porous layer are metal-jointed at the first joint.

12. A fuel cell according to claim 10, wherein the separator and the current collector metallurgically bonded to the metal porous layer and the separator are made of stainless steel material containing aluminum.

13. A fuel cell according to any one of claims 1 to 12, wherein both ends of the spring-type current collector are provided with stoppers for supporting a force in the shear direction of the spring-type current collector.

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