JP7552073B2 - solid oxide fuel cell - Google Patents

Description

The present invention relates to a solid oxide fuel cell.

So far, supported cells, in which a support layer is placed on a single cell having an electrolyte layer sandwiched between an anode layer and a cathode layer, have been used in solid oxide fuel cells (SOFCs, hereafter simply referred to as "SOFCs"). The support layer is made of ceramics or metal and has gas permeability. Metal-supported cells (MSCs), which have a support layer made of metal, have excellent mechanical strength, rapid start-up properties, etc.

The electrolyte layer, made of thin ceramics, is prone to damage due to stresses applied during manufacturing and operation. In addition, in SOFCs, anode gas and cathode gas must be distributed to the fuel pole (anode layer) and oxidizer pole (cathode layer) of the electrode layer, respectively, and sealing properties are required to prevent these gases from mixing.

The metal support cell assembly in an SOFC has a metal support cell and a cell frame that surrounds and holds the periphery of the metal support cell. For example, the following Patent Document 1 discloses a metal support cell assembly in which the support layer of the metal support cell is joined to the end of the cell frame. The support layer and the cell frame are joined by soldering, brazing, or a glass seal. In the metal support cell assembly of Patent Document 1, the electrolyte layer of the metal support cell is not in contact with the cell frame.

U.S. Pat. No. 8,287,673

In the metal support cell assembly described in Patent Document 1, the support layer is bonded to the end of the cell frame. Therefore, if the bond strength is insufficient, peeling may occur at the bonded portion, which may lead to gas leaks.

In addition, support cells are subject to heat treatments such as sintering during production, and there is a risk of deformation as a result of the heat treatment. In order to provide a solid oxide fuel cell with a highly reliable support cell, it is necessary to take into account the stress state associated with the shrinkage of the support cell during heat treatment.

The object of the present invention is to provide a solid oxide fuel cell with a highly reliable support cell.

In order to achieve the above object, the present invention provides a solid oxide fuel cell having a support cell in which an anode-side support layer and a cathode-side support layer are disposed on both sides of a unit cell having an electrolyte layer sandwiched between an anode layer and a cathode layer. The support cell has a cell outer periphery where a part of the electrolyte layer is exposed and a joining surface for joining a cell frame is formed, and a cell main body part located on the central side of the cell outer periphery. In a cross section in the thickness direction of the support cell, the cell main body part has a stacked structure symmetrical with respect to a center line (O2) of the thickness of the cell main body part, and the cell outer periphery part has a stacked structure symmetrical with respect to a center line (O1) of the thickness of the cell outer periphery part. The anode layer and the cathode layer are made of the same material, and the anode side support layer and the cathode side support layer are made of the same material. In the cell main body part, the anode layer and the cathode layer have the same thickness dimension, and the anode side support layer and the cathode side support layer have the same thickness dimension. The cell outer periphery is configured by laminating the electrolyte layer on which the bonding surface is formed, a first forming layer formed from the anode layer or the cathode layer, a second forming layer formed from the anode side support layer or the cathode side support layer, a third forming layer formed from the same material as the anode layer and the cathode layer, and a fourth forming layer formed from the same material as the electrolyte layer. In the cell outer periphery, the electrolyte layer and the fourth forming layer have the same thickness dimension, and the first forming layer and the third forming layer have the same thickness dimension .

According to the present invention, in the cross section of the support cell in the thickness direction, the cell body and the cell outer periphery have a laminated structure that is symmetrical with respect to the center line of their respective thicknesses, so that thermal contraction in the in-plane direction is controlled and bending deformation of the support cell is offset. Since the bonding surface that exposes the electrolyte layer is flattened, the bonding strength between the cell frame and the support cell can be improved, and a solid oxide fuel cell having a highly reliable support cell can be provided.

FIG. 2 is an exploded perspective view showing a fuel cell stack. FIG. 2 is an exploded perspective view of the cell unit shown in FIG. 1 . FIG. 3 is an exploded perspective view showing the support cell assembly shown in FIG. 2 . 1 is a cross-sectional view showing a fuel cell stack according to an embodiment. FIG. 3 is a partial cross-sectional view showing the support cell assembly taken along line AA in FIG. 2. FIG. 6 is a cross-sectional view showing the support cell shown in FIG. 5 . FIG. 6B is an enlarged cross-sectional view showing a main part of the support cell shown in FIG. 6A. FIG. 6B is a top view of the support cell shown in FIG. 6A. FIG. 6B is a bottom view of the support cell shown in FIG. 6A. FIG. 6B is a schematic diagram showing how bending acting on the support cell shown in FIG. 6A is offset. FIG. 11 is an enlarged cross-sectional view showing a main part of a support cell of a comparative example. FIG. 13 is a schematic diagram showing a state in which bending deformation occurs in a support cell according to a comparative example. FIG. 1 is an explanatory diagram used to explain stresses that occur when sintering a workpiece having two laminated layers made of different materials. 1 is a schematic diagram showing a state in which a workpiece has an asymmetric layered structure with respect to a center line of the thickness of the workpiece in a cross section in the thickness direction of the workpiece; 10C is a schematic diagram showing a state in which bending deformation occurs in the workpiece shown in FIG. 10B. 1 is an explanatory diagram used to explain the mechanism by which bending deformation is suppressed when the workpiece has a layered structure that is symmetrical with respect to the center line of the thickness of the workpiece in a cross section in the thickness direction of the workpiece. FIG. FIG. 11B is an explanatory diagram following FIG. 11A. This is an explanatory diagram following Figure 11B. FIG. 11C is an explanatory diagram following FIG. FIG. 11 is a cross-sectional view showing a fuel cell stack according to a first modified example. FIG. 13 is a partial cross-sectional view of the support cell assembly shown in FIG. 12. FIG. 14 is a cross-sectional view showing the support cell shown in FIG. 13 . 14B is an enlarged cross-sectional view showing a main part of the support cell shown in FIG. 14A. FIG. 14B is a top view of the support cell shown in FIG. 14A. FIG. 14B is a bottom view of the support cell shown in FIG. 14A. 13A and 13B are schematic diagrams showing how bending acts on a support cell of Modification 1. 13 is a schematic diagram illustrating the function of a support cell assembly to which the support cell of modified example 1 is applied. FIG. 13A and 13B are schematic diagrams showing how bending acts on a support cell of Modification 2. 13 is a schematic diagram illustrating the function of a support cell assembly to which the support cell of modified example 2 is applied. FIG.

Below, an embodiment of the present invention will be described with reference to the attached drawings. Note that the following description does not limit the technical scope or the meaning of the terms described in the claims. Also, the dimensional ratios in the drawings have been exaggerated for the convenience of explanation and may differ from the actual ratios.

A solid oxide fuel cell (SOFC) according to an embodiment of the present invention will be described with reference to the drawings. For ease of explanation, an XYZ Cartesian coordinate system is shown in the drawings. The X and Y axes are parallel to the horizontal direction, and the Z axis is parallel to the vertical direction.

Figure 1 is an exploded perspective view showing a fuel cell stack 1 according to an embodiment. As shown in Figure 1, the fuel cell stack 1 is configured by stacking a plurality of cell units 1U in the vertical direction. Hereinafter, the vertical direction of the fuel cell stack 1, indicated by the Z axis in the figure, will also be referred to as the "stacking direction." In addition, the surface direction of each layer constituting the cell unit 1U corresponds to the XY surface direction.

Figure 2 is an exploded perspective view of the cell unit 1U. As shown in Figure 2, the cell unit 1U is constructed by stacking a support cell assembly 1A and a separator 120 having a flow path portion 121 that defines a gas flow path.

Figure 3 is an exploded perspective view of the support cell assembly 1A. Figure 4 is a cross-sectional view showing the fuel cell stack 1, and Figure 5 is a partial cross-sectional view showing the support cell assembly 1A along line A-A in Figure 2. As shown in Figures 3, 4, and 5, the support cell assembly 1A has a support cell 10 and a cell frame 70 that surrounds and holds the periphery of the support cell 10.

Figure 6A is a cross-sectional view showing the support cell 10, and Figure 6B is a cross-sectional view showing an enlarged view of a main portion of the support cell 10. Figure 7A is a top view of the support cell 10, and Figure 7B is a bottom view of the support cell 10.

6A and 6B, the support cell 10 has a sandwich structure in which support layers (anode side support layer 61 and cathode side support layer 62) are arranged on both sides of the electrolyte electrode assembly 20 (corresponding to a single cell) in which the electrolyte layer 40 is sandwiched between the anode layer 30 and the cathode layer 50. The support cell 10 is configured by laminating the anode side support layer 61, the anode layer 30, the electrolyte layer 40, the cathode layer 50, and the cathode side support layer 62. The anode side support layer 61 and the cathode side support layer 62 have different lengths along the X direction and the Y direction. In the illustrated example, the length of the cathode side support layer 62 is shorter than the length of the anode side support layer 61. By making the lengths of the anode side support layer 61 and the cathode side support layer 62 different, a structure is formed in which a part of the electrolyte layer 40 is exposed. The exposed part of the electrolyte layer 40 forms a joining surface 94 that joins the cell frame 70. Hereinafter, the anode side support layer 61 and the cathode side support layer 62 may be referred to as a pair of support layers 61, 62. The anode layer 30 and the cathode layer 50 may be collectively referred to as the electrode layers 30, 50.

The electrolyte layer 40 is fixed to the anode side support layer 61 via the anode layer 30. The cathode side support layer 62 is fixed to the cathode layer 50. In the sandwich-structured support cell 10, a pair of support layers 61, 62 support the electrolyte electrode assembly 20. The support cell 10 is suitable for use in SOFCs because it has superior mechanical strength and rapid start-up performance compared to electrolyte-supported cells and electrode-supported cells.

The support cell 10 has a first bonding layer 81 with the cell frame 70 formed at the location where the electrolyte layer 40 is exposed. The support cell 10 further has a second bonding layer 82 that bonds the end 71 of the cell frame 70 to the end 63 of the cathode side support layer 62. The cell frame 70 and the electrolyte layer 40 are dense and have gas shielding properties. Therefore, by bonding the cell frame 70 and the electrolyte layer 40, a gas sealing function can be ensured.

Next, we will explain the cathode layer 50, electrolyte layer 40, anode layer 30, pair of support layers 61, 62, cell frame 70, separator 120, first bonding layer 81, and second bonding layer 82.

(Cathode Layer 50)
The cathode layer 50 is an oxidizer electrode that reacts with a cathode gas (e.g., oxygen contained in air) and electrons to convert oxygen molecules into oxide ions. The cathode layer 50 is resistant to an oxidizing atmosphere, and has high gas permeability that allows the cathode gas to pass through and high electrical (electron and ion) conductivity. Furthermore, the cathode layer 50 has a catalytic function that converts oxygen molecules into oxygen ions.

Examples of materials for forming the cathode layer 50 include oxides of lanthanum, strontium, manganese, cobalt, etc.

(Electrolyte layer 40)
The electrolyte layer 40 has a function of separating the anode gas and the cathode gas. The electrolyte layer 40 allows oxide ions to pass from the cathode layer 50 to the anode layer 30, but does not allow gas and electrons to pass through. When oxygen ions are the conductor for power generation, the electrolyte layer 40 is preferably formed from a material that has high conductivity for oxygen ions.

The electrolyte layer 40 is densely constructed to block anode gas and cathode gas and exhibit high ionic conductivity. The density of the electrolyte layer 40 is not particularly limited as long as it has gas blocking properties, but is preferably 90% or more, more preferably 96% or more, and particularly preferably 98% or more.

The material for forming the electrolyte layer 40 is not particularly limited, but examples thereof _{include solid oxide ceramics such as stabilized zirconia doped with rare earth oxides (e.g., one or more selected from Y2O3, Sc2O3, Gd2O3 , Sm2O3 , Yb2O3 , Nd2O3 , etc. ) ,} ceria-based solid solutions, and perovskite-type oxides (e.g., _{SrCeO3 , BaCeO3} , _CaZrO3 , _SrZrO3, etc.).

(Anode Layer 30)
The anode layer 30 is a fuel electrode that reacts an anode gas (e.g., hydrogen) with oxide ions to generate oxides of the anode gas and extract electrons. The anode layer 30 is resistant to a reducing atmosphere, and has high gas permeability and electrical (electron and ion) conductivity to allow the anode gas to pass through. Furthermore, the anode layer 30 has a catalytic function to cause the anode gas to react with oxide ions. Examples of materials for forming the anode layer 30 include metals such as Ni and Fe, and cermets of the metals and the ceramics listed as materials for forming the electrolyte layer 40.

The anode layer 30 is a porous body with multiple pores. The pores in the anode layer 30 are impregnated with a catalyst. The catalyst for the anode layer 30 can be, for example, a metal catalyst such as Ni or Cu.

(Support Layer (Anode Side Support Layer 61 and Cathode Side Support Layer 62))
3, 4, 5, 6A, and 6B, in the support cell 10 having a sandwich structure, the anode side support layer 61 supports the electrolyte electrode assembly 20 from the side of the anode layer 30, and the cathode side support layer 62 supports the electrolyte electrode assembly 20 from the side of the cathode layer 50. By the anode side support layer 61 and the cathode side support layer 62 supporting the electrolyte electrode assembly 20 in a sandwich structure, the mechanical strength of the electrolyte electrode assembly 20 can be improved and breakage can be suppressed.

As shown in Figures 4, 5, 6A, and 6B, the cathode-side support layer 62 has a cutout 68a on the upper outer periphery in the figures. The cutout 68a is formed by a support surface 68b that supports the cell frame 70 and a vertical wall 68c that rises upward in the figures from the inner end of the support surface 68b.

The support layer can be made of metal or ceramics. The material of the support layer can be selected with greater freedom depending on the required strength, etc. The support cell 10 can have a configuration in which the pair of support layers 61, 62 are both made of metal, or a configuration in which the pair of support layers 61, 62 are both made of ceramics. In the support cell 10 of the embodiment, the anode side support layer 61 and the cathode side support layer 62 are both made of metal.

The support layer made of metal (also called "metal support layer") is formed from a porous metal having gas permeability and electronic conductivity. The material for forming the metal support layer is not particularly limited as long as it is a metal material having high oxidation resistance and high heat resistance, but examples thereof include ferritic stainless steel. Ferritic stainless steel includes SUS400 series such as SUS410, SUS420, SUS430, and SUS440. In particular, Crofer (registered trademark) 22 alloy (manufactured by ThyssenKrupp-VDM), ZMG (registered trademark) 232G10 (manufactured by Hitachi Metals, Ltd.), ITM (manufactured by Plansee), SanergyHT (manufactured by Sandvik), etc. are preferably used.

The metal support layer is not limited to being made from the above materials, but can be made from, for example, an expanded metal with tiny through holes.

(Cell frame 70)
As shown in Figures 3, 4, and 5, the cell frame 70 supports the support cell 10 from the periphery. As shown in Figure 3, the cell frame 70 has an opening 70H. The support cell 10 is disposed in the opening 70H of the cell frame 70. As shown in Figures 4 and 5, the electrolyte layer 40 of the support cell 10 is surface-bonded to the lower surface of the cell frame 70 by a first bonding layer 81. The inner edge of the opening 70H of the cell frame 70 (the end 71 of the cell frame 70) is bonded to the end 63 of the cathode-side support layer 62 by a second bonding layer 82.

The cell frame 70 is formed from a dense metal material that does not allow gas to pass through, such as stainless steel. The density of the cell frame 70 is not particularly limited as long as it has gas shielding properties, but it is preferably 90% or more, more preferably 96% or more, and particularly preferably 98% or more. The surface of the cell frame 70 is subjected to an insulating treatment.

As shown in FIG. 3, the cell frame 70 has an anode gas inlet 70a and an anode gas outlet 70b through which the anode gas flows, and a cathode gas inlet 70c and a cathode gas outlet 70d through which the cathode gas flows.

(Separator 120)
2 and 4, the flow path portion 121 of the separator 120 is formed in a substantially linear shape such that the concave and convex shape extends in one direction (Y direction). Therefore, the flow direction of the gas flowing along the flow path portion 121 is the Y direction.

As shown in FIG. 2, the separator 120 has an anode gas inlet 125a and an anode gas outlet 125b through which the anode gas flows, and a cathode gas inlet 125c and a cathode gas outlet 125d through which the cathode gas flows.

(First bonding layer 81)
The first bonding layer 81 is disposed between the cell frame 70 supported by the support surface 68b of the cathode-side support layer 62 and the exposed electrolyte layer 40. The first bonding layer 81 is formed of a glass seal. This seals the end of the cathode layer 50 and ensures gas sealing properties.

(Second bonding layer 82)
The second bonding layer 82 is disposed between the cell frame 70 and the cathode-side support layer 62. The second bonding layer 82 further has a shape that extends toward the surface of the cell frame 70. The end 71 of the cell frame 70 is surrounded by the support surface 68b of the cathode-side support layer 62 and the second bonding layer 82. The material of the second bonding layer 82 can be a brazing material or glass. In the fourth modification, the material of the second bonding layer 82 is a brazing material. The main element of the brazing material is, for example, aluminum, copper, silver, or nickel.

[Layer structure of support cell 10]
6A, 6B, 7A, and 7B, the support cell 10 has a cell outer periphery 91 in which a part of the electrolyte layer 40 is exposed and a joining surface 94 for joining the cell frame 70 is formed, and a cell main body 92 located toward the center of the cell outer periphery 91. In a cross section in the thickness direction of the support cell 10, the cell main body 92 has a layered structure that is symmetrical with respect to a center line O2 of the thickness of the cell main body 92. Furthermore, in a cross section in the thickness direction of the support cell 10, the cell outer periphery 91 has a layered structure that is symmetrical with respect to a center line O1 of the thickness of the cell outer periphery 91.

The support cell 10 further has a cell intermediate portion 93 disposed between the cell main body portion 92 and the cell outer peripheral portion 91. In the cell intermediate portion 93, the support layer on the side where the joining surface 94 is formed has a notch portion 68a that joins the end portion 71 of the cell frame 70. In a cross section in the thickness direction of the support cell 10, the cell intermediate portion 93 has a layered structure that is symmetrical with respect to the center line O3 of the thickness of the cell intermediate portion 93.

The cell periphery 91 has an additional layer 95 arranged on the opposite electrode side to the anode layer 30 or cathode layer 50 on which the bonding surface 94 is formed. By arranging the additional layer 95, the cell periphery 91 can have a layered structure that is symmetrical with respect to the center line O1 of the thickness of the cell periphery 91.

Here, the reason for having a laminated structure that is symmetrical with respect to the center lines O1, O2 of the thickness is to cause stress to act in the same manner on each of the two imaginary layers separated by the center lines O1, O2 of the thickness.

Specifically, the additional layer 95 can be formed from a first layer 95a (corresponding to a third forming layer) that is the same as the cathode layer 50 or the anode layer 30, and a second layer 95b (corresponding to a fourth forming layer) that is the same as the electrolyte layer 40. The cell peripheral portion 91 has a symmetrical laminated structure with respect to the anode-side support layer 61. By configuring in this manner, it is possible to easily construct the cell peripheral portion 91 having a laminated structure that is symmetrical with respect to the center line O1 of the thickness.

The bonding surface 94, which is an exposed portion of the electrolyte layer 40, can be disposed on either the anode layer 30 side or the cathode layer 50 side, and is not limited thereto. In the embodiment of the support cell 10, the bonding surface 94 is disposed on the cathode layer 50 side. Therefore, the additional layer 95 is disposed on the anode layer 30 side, which is the opposite polarity side to the cathode layer 50 on which the bonding surface 94 is formed.

The cell body 92 is a laminate of a cathode side support layer 62, a cathode layer 50, an electrolyte layer 40, an anode layer 30, and an anode side support layer 61. The thickness dimensions of the cathode layer 50 and the anode layer 30 are approximately equal. The thickness dimensions of the cathode side support layer 62 and the anode side support layer 61 in the cell body 92 are approximately equal. The center line O2 of the thickness in the cell body 92 is the center line of the electrolyte layer 40.

The cell intermediate portion 93, like the cell main body portion 92, is a laminate of the cathode side support layer 62, the cathode layer 50, the electrolyte layer 40, the anode layer 30, and the anode side support layer 61. However, since the cell intermediate portion 93 has a cutout portion 68a, the thickness of the cathode side support layer 62 in the cell intermediate portion 93 is smaller than the thickness of the cathode side support layer 62 in the cell main body portion 92. The thickness dimensions of the cathode side support layer 62 in the cell intermediate portion 93 and the anode side support layer 61 in the cell intermediate portion 93 and the cell outer peripheral portion 91 are approximately equal. The center line O3 of the thickness in the cell intermediate portion 93 is the center line of the electrolyte layer 40.

The cell outer periphery 91 is formed by laminating the exposed electrolyte layer 40, the anode layer 30 (corresponding to the first forming layer) , the anode side support layer 61 (corresponding to the second forming layer) , and an additional layer 95. The additional layer 95 is formed by laminating, from the anode side support layer 61 side, a first layer 95a (corresponding to the third forming layer) which is the same as the anode layer 30, and a second layer 95b (corresponding to the fourth forming layer) which is the same as the electrolyte layer 40. The center line O1 of the thickness of the cell outer periphery 91 is the center line of the anode side support layer 61.

In manufacturing the support cell 10, a green sheet is first prepared. The green sheet is a sheet in which the ink for each layer is applied to a laminate film and then the laminate film is laminated. Each layer in the green sheet is only connected by a binder and a solvent.

Next, the green sheet is degreased. Before firing, the temperature is raised in the air (e.g., to 600°C) to remove the binder and solvent contained in each layer. During the degreasing process, significant chemical shrinkage occurs.

Next, reduction firing is performed. After degreasing, the product is heated in a reducing atmosphere (e.g., 1250°C) and sintered. During the reduction firing process, significant thermal shrinkage occurs. After reduction firing, the anode layer 30 is impregnated with a catalyst solution.

Figure 8 is a schematic diagram showing how bending acting on the support cell 10 of the embodiment is offset. Figure 9A is an enlarged cross-sectional view showing a main part of the support cell 200 of the comparative example, and Figure 9B is a schematic diagram showing a state in which bending deformation occurs in the support cell 200 of the comparative example.

As shown in FIG. 9A, in the cross section of the thickness direction of the support cell 200, the cell main body 292 of the comparative support cell 200 has a stacked structure that is symmetrical with respect to the center line O2 of the thickness of the cell main body 292. The cell peripheral portion 291 has a structure in which the electrolyte layer 40, the anode layer 30, and the anode side support layer 61 are stacked. Therefore, in the cross section of the thickness direction of the support cell 200, the cell peripheral portion 291 has an asymmetric stacked structure with respect to the center line O1 of the thickness of the cell peripheral portion 291.

As shown in FIG. 9B, in the comparative support cell 200, bending (arrow 201) occurs in the cell outer periphery 291 of the asymmetric laminated structure as a result of heat treatment such as sintering. For this reason, bending stress is concentrated in the electrolyte layer 40 at the portion indicated by the reference symbol 202. As a result, the bonding surface 294 where the electrolyte layer 40 is exposed does not become flat, and the bonding strength between the cell frame 70 and the support cell 200 decreases, which may lead to a decrease in gas sealing performance.

On the other hand, as shown in FIG. 8, in the support cell 10 of the embodiment, in the cross section in the thickness direction of the support cell 10, the cell main body 92, the cell intermediate part 93, and the cell outer peripheral part 91 have a stacked structure that is symmetrical with respect to the center lines O2, O3, and O1 of the thickness of the support cell 10. In each of the cell main body 92, the cell intermediate part 93, and the cell outer peripheral part 91, the thermal contraction in the in-plane direction is controlled, and the bending deformation (arrows 96, 97) of the support cell 10 is offset. As a result, the joint surface 94 exposing the electrolyte layer 40 is flattened, improving the joint strength between the cell frame 70 and the support cell 10 and improving the gas sealing performance. This makes it possible to provide a solid oxide fuel cell having a highly reliable support cell 10.

Next, the phenomenon of bending occurring in a workpiece having a layered structure asymmetric with respect to the center line of the thickness will be explained with reference to schematic diagrams. Figure 10A is an explanatory diagram used to explain the stress that occurs when sintering workpiece 300, which is made of two layers 301 and 302 made of different materials, Figure 10B is a schematic diagram showing a state in which workpiece 300 has a layered structure asymmetric with respect to the center line of the thickness in a cross section in the thickness direction of workpiece 300, and Figure 10C is a schematic diagram showing a state in which bending deformation occurs in workpiece 300 shown in Figure 10B.

As shown in FIG. 10A, the workpiece 300 is made up of a laminate of an A layer 301 made of a first material and a B layer 302 made of a second material. Here, the amount of shrinkage of the second material is assumed to be greater than the amount of shrinkage of the first material. The amount of shrinkage is the sum of shrinkage due to chemical changes during firing and thermal shrinkage due to temperature changes. Since the first material is subject to strong shrinkage from the second material, a compressive stress (arrow 303) acts on the A layer 301. On the other hand, since the second material is subject to a reaction force from the first material, a tensile stress (arrow 304) acts on the B layer 302.

As shown in Figures 10B and 10C, when the stress state of the two layers 301 and 302 is not symmetrical in the thickness direction, deformation (bending) occurs in a direction that relieves each stress (compressive stress (arrow 303) in layer A 301, and tensile stress (arrow 304) in layer B 302) (arrow 305 in Figure 10C).

Next, the mechanism by which a workpiece having a layered structure symmetrical with respect to the center line of the thickness suppresses bending deformation will be described with reference to schematic diagrams. Figures 11A, 11B, 11C, and 11D are explanatory diagrams used to explain the mechanism by which bending deformation is suppressed when the workpiece 310 has a layered structure symmetrical with respect to the center line O4 of the thickness in a cross section in the thickness direction of the workpiece 310.

As shown in Fig. 11A, the stress state accompanying the shrinkage of the first material and the second material is not symmetrical. As shown in Fig. 11B, when the material is divided into two layers, upper and lower, bending deformation occurs in each layer as described above (arrows 311, 312). As shown in Fig. 11C, since the material is actually joined, the deformations cancel each other out. The deformations indicated by the arrows 311, 312 on the right side of the workpiece 310 cancel each other out, and the deformations indicated by the arrows 311, 312 on the left side cancel each other out. As shown in Fig. 11D, only shrinkage in the in-plane direction occurs, and no bending deformation occurs.

As described above, the solid oxide fuel cell of the embodiment has a support cell 10 in which support layers 61, 62 are arranged on both sides of an electrolyte electrode assembly 20 (single cell) in which an electrolyte layer 40 is sandwiched between an anode layer 30 and a cathode layer 50. The support cell 10 has a cell outer periphery 91 in which a part of the electrolyte layer 40 is exposed and a joining surface 94 for joining the cell frame 70 is formed, and a cell main body 92 located on the central side of the cell outer periphery 91. In a cross section in the thickness direction of the support cell 10, the cell main body 92 has a stacked structure symmetrical with respect to a center line O2 of the thickness of the cell main body 92, and the cell outer periphery 91 has a stacked structure symmetrical with respect to a center line O1 of the thickness of the cell outer periphery 91.

By configuring in this manner, the thermal contraction in the in-plane direction is controlled in each of the cell main body 92 and the cell outer periphery 91, and the bending deformation of the support cell 10 is offset. As a result, the joint surface 94 exposing the electrolyte layer 40 is flattened, improving the joint strength between the cell frame 70 and the support cell 10 and improving the gas sealing performance. This makes it possible to provide a solid oxide fuel cell having a highly reliable support cell 10.

The support cell 10 further has a cell intermediate portion 93 disposed between the cell main body portion 92 and the cell outer peripheral portion 91. The cell intermediate portion 93 has a notch portion 68a where the support layer 62 on the side where the joining surface 94 is formed joins the end portion 71 of the cell frame 70. In a cross section in the thickness direction of the support cell 10, the cell intermediate portion 93 has a laminated structure that is symmetrical with respect to the center line O3 of the thickness of the cell intermediate portion 93. By configuring in this manner, the thermal contraction in the in-plane direction is also controlled in the cell intermediate portion 93, and the bending deformation of the support cell 10 is offset. As a result, the flatness of the joining surface 94 is maintained, and a solid oxide fuel cell having a highly reliable support cell 10 can be provided.

The cell periphery 91 has an additional layer 95 arranged on the opposite electrode side to the anode layer 30 or cathode layer 50 on which the bonding surface 94 is formed. By arranging the additional layer 95 in this manner, the cell periphery 91 can have a layered structure that is symmetrical with respect to the center line O1 of the thickness of the cell periphery 91.

The additional layer 95 can be formed from the same layers (anode layer 30, electrolyte layer 40, cathode layer 50) that make up the electrolyte electrode assembly 20 (single cell). By configuring it in this way, it is easy to construct a cell outer periphery 91 that has a stacked structure that is symmetrical with respect to the center line O1 of the thickness.

The additional layer 95 is formed from a first layer 95a that is the same as the cathode layer 50 or the anode layer 30, and a second layer 95b that is the same as the electrolyte layer 40, and the cell peripheral portion 91 has a symmetrical laminate structure with the anode side support layer 61 at the center. By configuring it in this way, it is easy to construct a cell peripheral portion 91 that has a symmetrical laminate structure with respect to the center line O1 of the thickness.

The bonding surface 94 is disposed on the cathode layer 50 side, and the additional layer 95 is disposed on the anode layer 30 side. By configuring it in this way, it is possible to provide a solid oxide fuel cell having a highly reliable support cell 10 in which the cell frame 70 is bonded to the cathode layer 50 side.

(Variation 1)
FIG. 12 is a cross-sectional view showing a fuel cell stack 1 according to the first modification, and FIG. 13 is a partial cross-sectional view showing a support cell assembly 1A. FIG. 14A is a cross-sectional view showing a support cell 11, and FIG. 14B is a cross-sectional view showing an enlarged main part of the support cell 11. FIG. 15A is a top view of the support cell 11, and FIG. 15B is a bottom view of the support cell 11. FIG. 16A is a schematic diagram showing a state in which bending acts on the support cell 11 of the first modification, and FIG. 16B is a schematic diagram for explaining the operation of the support cell assembly 1A to which the support cell 11 of the first modification is applied. Note that the same reference numerals are used to designate members common to the above-mentioned embodiment, and explanations thereof will be omitted.

As shown in FIG. 14B, variant 1 differs from the support cell 10 of the above-described embodiment in that, in a cross section in the thickness direction of the support cell 11, the cell middle portion 103 has an asymmetric layered structure with respect to the center line O3 of the thickness of the cell middle portion 103.

As shown in FIG. 12, in the fuel cell stack 1 according to the first modification, a current collection auxiliary layer 130 is laminated between the support cell assembly 1A and the separator 120. The current collection auxiliary layer 130 forms a space through which gas can pass while equalizing the surface pressure, thereby assisting in electrical contact between the support cell 11 and the separator 120. The current collection auxiliary layer 130 can be formed, for example, from a wire mesh-like expanded metal.

As shown in Figures 13, 14A, 14B, 15A, and 15B, the support cell 11 according to the first modification has a cell outer periphery 91 in which a portion of the electrolyte layer 40 is exposed and a joining surface 94 for joining the cell frame 70 is formed, and a cell main body 92 located toward the center of the cell outer periphery 91, similar to the support cell 10 according to the embodiment. In a cross section of the support cell 11 in the thickness direction, the cell main body 92 has a layered structure that is symmetrical with respect to a center line O2 of the thickness of the cell main body 92. Furthermore, in a cross section of the support cell 11 in the thickness direction, the cell outer periphery 91 has a layered structure that is symmetrical with respect to a center line O1 of the thickness of the cell outer periphery 91.

The support cell 11 of the first modification further has a cell intermediate portion 103 disposed between the cell main body portion 92 and the cell outer peripheral portion 91. The cell intermediate portion 103 has a cutout portion 68a where the support layer on the side where the joining surface 94 is formed joins the end portion 71 of the cell frame 70. In the cross section in the thickness direction of the support cell 11, the cell intermediate portion 103 has an asymmetric layered structure with respect to the center line O3 of the thickness of the cell intermediate portion 103.

The cell outer periphery 91 and the cell middle portion 103 have an additional layer 95 arranged on the opposite electrode side to the anode layer 30 or cathode layer 50 on which the bonding surface 94 is formed. In the support cell 11 of the first modified example, the bonding surface 94 is arranged on the cathode layer 50 side, and the additional layer 95 is arranged on the anode layer 30 side, similar to the support cell 10 of the embodiment.

The cell body 92 is a laminate of a cathode side support layer 62, a cathode layer 50, an electrolyte layer 40, an anode layer 30, and an anode side support layer 61. The thickness dimensions of the cathode layer 50 and the anode layer 30 are approximately equal. The thickness dimensions of the cathode side support layer 62 and the anode side support layer 61 in the cell body 92 are approximately equal. The center line O2 of the thickness in the cell body 92 is the center line of the electrolyte layer 40.

The cell intermediate portion 103 is formed by stacking the cathode side support layer 62, the cathode layer 50, the electrolyte layer 40, the anode layer 30, the anode side support layer 61, and the additional layer 95. The additional layer 95 is formed by stacking the first layer 95a, which is the same as the anode layer 30, and the second layer 95b, which is the same as the electrolyte layer 40, from the anode side support layer 61 side. Since the cell intermediate portion 103 has a cutout portion 68a, the thickness of the cathode side support layer 62 in the cell intermediate portion 103 is smaller than the thickness of the cathode side support layer 62 in the cell main body portion 92. The thickness dimension of the anode side support layer 61 is approximately equal in all regions of the cell main body portion 92, the cell intermediate portion 103, and the cell outer periphery portion 91. Thus, in the cross section in the thickness direction of the support cell 11, the cell intermediate portion 103 has an asymmetric stacking structure with respect to the center line O3 of the thickness in the cell intermediate portion 103. In the illustrated example, the center line O3 of the thickness of the cell middle portion 103 is near the interface between the anode layer 30 and the anode side support layer 61.

The cell outer periphery 91 is formed by laminating the exposed electrolyte layer 40, the anode layer 30, the anode side support layer 61, and the additional layer 95. The additional layer 95 is formed by laminating, from the anode side support layer 61 side, a first layer 95a identical to the anode layer 30, and a second layer 95b identical to the electrolyte layer 40. The center line O1 of the thickness of the cell outer periphery 91 is the center line of the anode side support layer 61.

In the support cell 11 of the first modified example, the thickness of the anode side support layer 61 is not reduced in the cell middle portion 103. Therefore, the support cell 11 of the first modified example can improve the mechanical strength of the cell middle portion 103 compared to the support cell 10 of the embodiment.

As shown in Figures 14A, 14B, and 16A, the cell middle portion 103 has a structure in which the laminated structure of the cell outer periphery portion 91 is offset from the outer periphery end on the cathode side toward the center of the support cell 11 to the vertical wall 68c in the cutout portion 68a of the cathode side support layer 62. Arrow 104 shown in Figure 14A represents the outer periphery length (active area) on the cathode side, and arrow 105 shown in Figures 14A and 14B represents the offset length.

The cell middle part 103 has an asymmetric stacked structure as a whole (FIG. 14B), but can be seen as a structure in which a part 106 having a symmetric stacked structure and a part 107 having an asymmetric stacked structure are stacked (FIG. 16A). The part 106 having a symmetric stacked structure offsets the stacked structure of the cell outer peripheral part 91, so that, like the cell outer peripheral part 91, the electrolyte layer 40, the anode layer 30, the anode side support layer 61, the first layer 95a (same as the anode layer 30) of the additional layer 95, and the second layer 95b (same as the electrolyte layer 40) of the additional layer 95 are stacked. The part 107 having an asymmetric stacked structure has a cathode side support layer 62 and a cathode layer 50 stacked. The part 107 having an asymmetric stacked structure shrinks relatively more than the part 106 having a symmetric stacked structure. Tensile stress acts on the part with large shrinkage, and compressive stress acts on the part with small shrinkage.

As shown in FIG. 16A, in the support cell 11 of the first modified example, in the cross section of the thickness direction of the support cell 11, the cell middle part 103 has a laminated structure that is asymmetric with respect to the center line O3 of the thickness of the cell middle part 103. Therefore, a bending moment occurs in the direction indicated by the arrow 108 in the figure. In the cross section of the thickness direction of the support cell 11, the cell main body part 92 and the cell outer peripheral part 91 have laminated structures that are symmetric with respect to the center lines O2 and O1 of the thickness, respectively. In each of the cell main body part 92 and the cell outer peripheral part 91, the thermal contraction in the in-plane direction is controlled, and the bending deformation is offset. As a result, the joint surface 94 that exposes the electrolyte layer 40 is flattened, improving the joint strength between the cell frame 70 and the support cell 11 and improving the gas sealability.

As shown in FIG. 16B, in the support cell 11 of the first modified example, a bending moment (arrow 108) is generated by the cell middle portion 103 having an asymmetric stacked structure. This bending moment acts in a direction (arrow 109) that tightens the cell outer periphery 91 toward the cell frame 70. Therefore, the cell outer periphery 91 can be compressed against the cell frame 70 while maintaining the flatness of the joint surface 94 that exposes the electrolyte layer 40. This makes it possible to provide a solid oxide fuel cell having a support cell 11 with higher reliability.

As shown in Figures 12 and 13, in the support cell assembly 1A according to the first modification, an insulating layer 140 is arranged so as to straddle and cover the sides of the first bonding layer 81, the electrolyte layer 40, the anode layer 30, the anode-side support layer 61, and the additional layer 95. The insulating layer 140 is formed by coating, for example, with alumina, zirconia, or silica as the main material. The insulating layer 140 is connected to the same second layer 95b as the dense electrolyte layer 40 in the additional layer 95, so that the insulation distance between the anode side end and the cathode side end is longer. This can improve the insulation reliability.

As described above, the support cell 11 of the solid oxide fuel cell of the first modified example further has a cell intermediate portion 103 disposed between the cell main body portion 92 and the cell outer peripheral portion 91. The cell intermediate portion 103 has a cutout portion 68a where the support layer 62 on the side where the joining surface 94 is formed joins the end portion 71 of the cell frame 70. In a cross section in the thickness direction of the support cell 11, the cell intermediate portion 103 has an asymmetric stacked structure with respect to the center line O3 of the thickness of the cell intermediate portion 103.

By configuring in this way, the mechanical strength of the cell intermediate portion 103 can be improved compared to a case where the cell intermediate portion 93 has a stacked structure symmetrical with respect to the center line O3 of the thickness of the cell intermediate portion 93. In the cross section in the thickness direction of the support cell 11, the cell main body portion 92 and the cell outer peripheral portion 91 have stacked structures symmetrical with respect to the center lines O2 and O1 of the thickness, respectively. In each of the cell main body portion 92 and the cell outer peripheral portion 91, the thermal contraction in the in-plane direction is controlled, and bending deformation is offset. As a result, the joint surface 94 exposing the electrolyte layer 40 is flattened, improving the joint strength between the cell frame 70 and the support cell 11 and improving the gas sealing performance. This makes it possible to provide a solid oxide fuel cell having a highly reliable support cell 11.

The cell outer periphery 91 and the cell middle part 103 have an additional layer 95 arranged on the opposite pole side to the anode layer 30 or the cathode layer 50 on which the joint surface 94 is formed. By configuring in this way, a portion 106 having a symmetrical stack structure in which the stack structure of the cell outer periphery 91 is offset is formed in the cell middle part 103. A bending moment is generated by the cell middle part 103 having an asymmetric stack structure, but this bending moment can act in a direction that tightens the cell outer periphery 91 toward the cell frame 70. Therefore, the cell outer periphery 91 can be compressed to the cell frame 70 while maintaining the flatness of the joint surface 94 that exposes the electrolyte layer 40. This makes it possible to provide a solid oxide fuel cell having a support cell 11 with higher reliability.

(Variation 2)
Fig. 17A is a schematic diagram showing how bending acts on the support cell 12 of Modification 2, and Fig. 17B is a schematic diagram for explaining the operation of the support cell assembly 1A to which the support cell 12 of Modification 2 is applied. Note that the same reference numerals are used to designate members common to the above-described embodiment and Modification 1, and explanations thereof will be omitted.

In the second modification, similar to the first modification, in the cross section of the thickness direction of the support cell 12, the cell middle portion 113 has an asymmetric stacking structure with respect to the center line O3 of the thickness of the cell middle portion 113. The second modification differs from the support cell 11 of the first modification described above in that the cell middle portion 113 does not have a symmetric stacking structure in which the stacking structure of the cell outer periphery portion 91 is offset.

In the support cell 12 of the modified example 2, as in the modified example 1, the thickness of the anode side support layer 61 is not reduced in the cell middle portion 113. Therefore, the support cell 12 of the modified example 2 can also improve the mechanical strength of the cell middle portion 113 compared to the support cell 10 of the embodiment.

The cell intermediate portion 113 has an asymmetric stacked structure as a whole, but can be considered to have a structure in which a portion 116 having a symmetric stacked structure and a portion 117 having an asymmetric stacked structure are stacked (FIG. 17A). The portion 116 having a symmetric stacked structure is a stack of the thin cathode side support layer 62 on which the joint surface 94 is formed, the cathode layer 50, the electrolyte layer 40, the anode layer 30, and the portion of the anode side support layer 61 corresponding to the depth of the notch portion 68a, as in the cell intermediate portion 93 of the embodiment. The portion 117 having an asymmetric stacked structure is the remaining portion of the anode side support layer 61 excluding the portion corresponding to the depth of the notch portion 68a. The portion 117 having an asymmetric stacked structure shrinks relatively more than the portion 116 having a symmetric stacked structure. Tensile stress acts on the portion with large shrinkage, and compressive stress acts on the portion with small shrinkage.

As shown in FIG. 17A, in the support cell 12 of the second modified example, in the cross section of the thickness direction of the support cell 12, the cell middle part 113 has a stacked structure that is asymmetric with respect to the center line O3 of the thickness of the cell middle part 113. Therefore, a bending moment occurs in the direction indicated by the arrow 118 in the figure. In the cross section of the thickness direction of the support cell 12, the cell main body part 92 and the cell outer peripheral part 91 have stacked structures that are symmetric with respect to the center lines O2 and O1 of the thickness, respectively. In each of the cell main body part 92 and the cell outer peripheral part 91, the thermal contraction in the in-plane direction is controlled, and the bending deformation is offset. As a result, the joint surface 94 that exposes the electrolyte layer 40 is flattened, improving the joint strength between the cell frame 70 and the support cell 11 and improving the gas sealing property. This makes it possible to provide a solid oxide fuel cell having a highly reliable support cell 11.

As shown in FIG. 17B, in the support cell 12 of the second modification, a bending moment (arrow 118) is generated by the cell middle portion 113, which has an asymmetric stacked structure. This bending moment acts in a direction (arrow 119) that moves the cell outer periphery 91 away from the cell frame 70. Therefore, compared to the first modification, the effect of suppressing damage to the electrolyte layer 40 of the cell outer periphery 91 is slightly reduced.

In both Modification 1 and Modification 2, the cell intermediate portions 103, 113 have an asymmetric stacked structure with respect to the center line O3 of the thickness of the cell intermediate portions 103, 113. However, the direction of the generated bending moment can be reversed by offsetting the stacked structure of the cell peripheral portion 91 (Modification 1, FIG. 16A) or not offsetting the stacked structure of the cell peripheral portion 91 (Modification 2, FIG. 17A). In other words, the cell intermediate portions 103, 113 having an asymmetric stacked structure and capable of generating a bending moment in a specific direction can be interposed between the cell main body portion 92 and the cell peripheral portion 91. Depending on how the bending moment is applied, it is possible to select whether or not to offset the stacked structure of the cell peripheral portion 91.

As described above, in the support cell 12 of the solid oxide fuel cell of the second modification, as in the first modification, in the cross section in the thickness direction of the support cell 12, the cell intermediate portion 113 having the notch portion 68a has an asymmetric stack structure with respect to the center line O3 of the thickness of the cell intermediate portion 113. By configuring in this way, the mechanical strength of the cell intermediate portion 113 can be improved compared to the case where the cell intermediate portion 93 has a stack structure symmetric with respect to the center line O3 of the thickness of the cell intermediate portion 93. In the cross section in the thickness direction of the support cell 12, the cell main body portion 92 and the cell outer peripheral portion 91 have stack structures symmetric with respect to the center line of their respective thicknesses. In each of the cell main body portion 92 and the cell outer peripheral portion 91, the thermal contraction in the in-plane direction is controlled, and the bending deformation is offset. As a result, the joint surface 94 exposing the electrolyte layer 40 is flattened, so that the joint strength between the cell frame 70 and the support cell 11 is improved, and the gas sealing property is improved. This makes it possible to provide a solid oxide fuel cell having a highly reliable support cell 11.

In addition, as is clear from variants 1 and 2, a cell intermediate portion 103, 113 having an asymmetric laminated structure and capable of generating a bending moment in a specific direction can be interposed between the cell main body portion 92 and the cell outer peripheral portion 91.

1 fuel cell stack,
1A Support cell assembly,
1U cell unit,
10, 11, 12 Support cell,
20 Electrolyte electrode assembly (single cell),
30 anode layer,
40 electrolyte layer,
50 cathode layer,
61 anode side support layer,
62 cathode side support layer,
68a notch portion,
68b support surface;
68c vertical wall,
70 cell frames,
81 First bonding layer,
82 second bonding layer,
91 Cell outer periphery,
92 Cell body portion,
93 Cell middle part,
94 Joint surface,
95 additional layer,
95a first layer,
95b second layer,
103 cell middle part,
106 A portion having a symmetrical laminate structure in the middle of the cell;
107 A portion having an asymmetric laminated structure in a middle part of the cell;
113 Cell middle part,
116 A portion having a symmetrical laminate structure in the middle of the cell;
117 A portion having an asymmetric laminated structure in the middle part of the cell;
120 Separator,
140 insulating layer,
O1: center line of thickness at the outer periphery of the cell;
O2: Center line of thickness in cell body;
O3: Centerline of thickness at mid-cell.

Claims (5)

A solid oxide fuel cell having a support cell in which an anode-side support layer and a cathode-side support layer are disposed on both sides of a single cell having an electrolyte layer sandwiched between an anode layer and a cathode layer,
the support cell has a cell outer periphery where a part of the electrolyte layer is exposed and a joining surface for joining a cell frame is formed, and a cell main body part located closer to the center than the cell outer periphery ,
In a cross section in the thickness direction of the support cell, the cell main body has a laminated structure symmetrical with respect to a center line (O2) of the thickness of the cell main body, and the cell outer periphery has a laminated structure symmetrical with respect to a center line (O1) of the thickness of the cell outer periphery ,
the anode layer and the cathode layer are made of the same material, the anode side support layer and the cathode side support layer are made of the same material,
In the cell main body, the anode layer and the cathode layer have the same thickness dimension, and the anode side support layer and the cathode side support layer have the same thickness dimension,
the cell outer periphery is configured by laminating the electrolyte layer on which the bonding surface is formed, a first forming layer formed from the anode layer or the cathode layer, a second forming layer formed from the anode side support layer or the cathode side support layer, a third forming layer formed from the same material as the anode layer and the cathode layer, and a fourth forming layer formed from the same material as the electrolyte layer;
A solid oxide fuel cell , wherein, at the outer periphery of the cell, the electrolyte layer and the fourth formation layer have the same thickness dimension, and the first formation layer and the third formation layer have the same thickness dimension . The support cell further includes a cell intermediate portion disposed between the cell main body portion and the cell outer periphery portion,
the cell intermediate portion has a cutout portion where the anode side support layer or the cathode side support layer on the side where the joining surface is formed is joined to an end portion of the cell frame,
In a cross section of the support cell in the thickness direction, the cell intermediate portion has a laminated structure that is symmetrical with respect to a center line (O3) of the thickness of the cell intermediate portion ,
2. The solid oxide fuel cell according to claim 1, wherein, in the cell intermediate portion, the anode layer and the cathode layer have the same thickness dimension, and the anode side support layer or the cathode side support layer on the side where the joining surface is formed and the cathode side support layer or the anode side support layer on the opposite side have the same thickness dimension . The support cell further includes a cell intermediate portion disposed between the cell main body portion and the cell outer periphery portion,
the cell intermediate portion has a cutout portion where the anode side support layer or the cathode side support layer on the side where the joining surface is formed is joined to an end portion of the cell frame,
In a cross section of the support cell in the thickness direction, the cell intermediate portion has an asymmetric laminate structure with respect to a center line (O3) of the thickness of the cell intermediate portion ,
2. The solid oxide fuel cell according to claim 1, wherein in the cell intermediate portion, the anode layer and the cathode layer have the same thickness dimension, and the cathode side support layer or the anode side support layer on the side opposite to the side on which the joining surface is formed and the cathode side support layer or the anode side support layer in the cell main body portion have the same thickness dimension . 4. The solid oxide fuel cell according to claim 3, wherein the cell intermediate portion is configured by further laminating a layer identical to the third formation layer of the cell outer periphery and a layer identical to the fourth formation layer on the cathode side support layer or the anode side support layer opposite to the side on which the joining surface is formed. The solid oxide fuel cell according to any one of claims 1 to 4, wherein the bonding surface is disposed on the cathode layer side.