Flat-plate fuel cell stack

Abstract

To provide a flat-plate fuel cell stack that can achieve uniform temperature distribution in the in-plane direction and stacking direction of fuel cell cells without increasing the size of the fuel cell cells in the in-plane direction or complicating the structure in the flat-plate fuel cell stack, thereby improving power generation performance and durability and reliability through uniformity.SOLUTION: In a flat-plate fuel cell stack constructed by stacking a plurality of flat-plate-shaped fuel cells 3 in multiple stages via interconnectors 4 that electrically connect adjacent fuel cells 3, the thickness of the interconnectors 4 is varied depending on their arrangement in the stacking direction, such that the interconnector 4B arranged at the center of the stacking direction has a thickness t2 that is greater than the interconnectors 4A and 4C arranged at positions other than the center in the stacking direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a flat plate fuel cell stack configured by stacking a plurality of flat plate-shaped fuel cell units in multiple stages via interconnectors that electrically connect adjacent fuel cell units. [Background technology]

[0002] Compared to other stack structures such as cylindrical ones, flat-plate fuel cell stacks have the advantage of being easier to make compact and capable of increasing the power density per unit volume. Increasing the power output of flat-plate fuel cells is also effective in increasing the current density and cell size. However, increasing the current density increases the heat generation in the stack, which can lead to problems such as a wide temperature distribution in the in-plane direction and stacking direction of the fuel cell. Also, increasing the cell size of the fuel cell can easily cause heat to be trapped in the center of the in-plane direction of the fuel cell, which can easily increase the temperature difference in the in-plane direction of the fuel cell.

[0003] When the temperature difference in the in-plane direction of the fuel cell increases, the thermal stress on the fuel cell generally increases, increasing the risk of damage to the fuel cell. Furthermore, when the temperature distribution in the in-plane direction or stacking direction of the fuel cell increases due to the constraints of the material's upper temperature limit, it becomes necessary to lower the average temperature of the fuel cell, which results in the problem of not being able to fully utilize the power generation performance of the fuel cell. In particular, the problem of not being able to fully utilize the power generation performance of the fuel cell becomes more pronounced in the fuel cell stacked at both ends in the stacking direction, because their temperatures become relatively low.

[0004] From the above points, in order to improve the power generation performance and durability and reliability of a flat plate type fuel cell stack, it is necessary to make the temperature distribution uniform in the in-plane direction and stacking direction of the fuel cell.

[0005] Therefore, one technique for achieving uniform temperature distribution in the stacking direction of fuel cell cells is, for example, to provide a separator (interconnector) with a separator main body portion that contacts adjacent power generating bodies (fuel cell cells) and a heat dissipation portion that protrudes from the side edge of this separator main body portion, and the cross-sectional area and surface area of ​​the heat dissipation portion are increased as the separator stacking position becomes closer to the center, thereby increasing the amount of heat dissipation (see, for example, Patent Document 1).

[0006] In addition, at least one of the fuel cell cells arranged in the middle of the stacking direction is arranged to protrude beyond the row of the other fuel cell cells, thereby lowering the temperature of the middle of the stacking direction (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-273140 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-72199 Summary of the Invention [Problem to be solved by the invention]

[0008] According to the technology described in Patent Document 1, the presence of a heat dissipation portion protruding from the side edge of the separator main body not only results in an increase in cell size, but also in a significant increase in the size of the fuel cell cells in the in-plane direction in a flat-plate fuel cell stack.

[0009] According to the technology described in Patent Document 2, at least one of the fuel cell cells arranged in the middle of the stacking direction is arranged to protrude out of the row relative to the other fuel cell cells, which only results in a relatively small increase in cell size, but there is a risk of the structure, such as a gas manifold spanning multiple stacked fuel cell cells, becoming more complex, which may be inconvenient.

[0010] In view of this situation, the main object of the present invention is to provide a flat-plate fuel cell stack that can achieve uniform temperature distribution in the in-plane direction and stacking direction of the fuel cell without increasing the size of the fuel cell in the in-plane direction or complicating the structure of the fuel cell stack, thereby improving power generation performance and durability and reliability through this uniformity. [Means for solving the problem]

[0011] A first characteristic configuration of the present invention is a flat plate type fuel cell stack configured by stacking a plurality of flat plate-shaped fuel cell units in multiple stages via interconnectors that electrically connect adjacent fuel cell units, The thickness of the interconnectors is varied depending on the arrangement in the stacking direction so that the interconnectors arranged at the center of the stacking direction have a greater thickness than the interconnectors arranged other than at the center of the stacking direction.

[0012] According to this configuration, by making the thickness of the interconnector arranged at the center of the stacking direction in the planar fuel cell stack, where heat is likely to be trapped, greater than the thickness of the interconnector arranged at other locations, it is possible to increase the area of ​​the end face in the in-plane direction that serves as the heat dissipation surface. Accordingly, heat that tends to be trapped at the center of the planar fuel cell stack can be easily released to the outside through the interconnector, which has a relatively high thermal conductivity among the components of the planar fuel cell stack, with a large amount of heat dissipation from the heat dissipation surface.

[0013] This makes it less likely for heat to accumulate in the center of the flat fuel cell stack without changing the in-plane size or arrangement of the stacked fuel cell cells and interconnectors, thereby suppressing damage to the fuel cell cells and reduced power generation performance caused by this heat accumulation.

[0014] As a result, it is possible to provide a flat-plate fuel cell stack that can achieve uniform temperature distribution in the in-plane direction and stacking direction of the fuel cell cells in the flat-plate fuel cell stack, without increasing the size or complexity of the structure of the flat-plate fuel cell stack due to changes in the in-plane size or arrangement of the stacked fuel cell cells and interconnectors, and that can improve power generation performance and durability and reliability through this uniformity.

[0015] A second characteristic configuration of the present invention is that the interconnector arranged midway between the interconnector arranged at the center of the stacking direction and the interconnector arranged at both ends of the stacking direction has a thickness smaller than the interconnector arranged at the center of the stacking direction, and the interconnector arranged at both ends of the stacking direction has an even smaller thickness than the interconnector arranged in the middle.

[0016] According to this configuration, the thickness of the interconnector located in the center of the stacking direction in a flat-type fuel cell stack, where heat trapping is likely to occur, is made greater than the thickness of the interconnector located in the middle of the stacking direction as described above, making it less likely for heat trapping to occur in the center of the flat-type fuel cell stack, while the thickness of the interconnector located at both ends of the stacking direction in a flat-type fuel cell stack, where heat trapping is less likely to occur, is made smaller than the thickness of the interconnector located in the middle of the stacking direction as described above, thereby rationally suppressing the increase in size of the fuel cell cells in the stacking direction in a flat-type fuel cell stack. [Brief explanation of the drawings]

[0017] [Figure 1] A perspective view showing the configuration of a flat-plate fuel cell stack. [Figure 2] Vertical cross-sectional view of the main part showing the structure of the fuel cell [Figure 3] Vertical cross-section of the main part showing the thickness of the interconnector, which varies depending on the arrangement in the stacking direction. [Figure 4](A) is a perspective view showing the temperature distribution in the fuel cell stack of the embodiment, (B) is a perspective view showing the temperature distribution in the fuel cell stack of the comparative example, and (C) is a diagram comparing the simulation results of the fuel cell stack of the embodiment and the fuel cell stack of the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a flat plate fuel cell stack according to the present invention will now be described with reference to the accompanying drawings. Gas flow types that can be applied to the flat plate fuel cell stack of the present invention include, for example, a cross-flow type in which the flow directions of the fuel gas and the oxidant gas are crossing each other, a co-flow type in which the flow directions of the fuel gas and the oxidant gas are the same, and a counter-flow type in which the flow directions of the fuel gas and the oxidant gas are opposite to each other.

[0019] As shown in Figure 1, the flat fuel cell stack S exemplified in this embodiment is constructed by stacking a plurality of flat solid oxide fuel cell cells 3 (see Figures 2 and 3) between upper and lower flat end plates 1 and 2 in multiple stages (21 stages in this embodiment) via interconnectors 4 (see Figures 2 and 3) that electrically connect adjacent fuel cell cells 3, and then fixing them in a stacked state using bolts 5 and nuts 6. The interconnector 4 is made of a stainless steel material such as SUS430, and has a relatively high thermal conductivity among the stack constituent materials.

[0020] The upper end plate 1 is provided with a fuel gas supply pipe 7 to which a fuel gas (such as hydrogen) is supplied, a fuel off-gas discharge pipe 8 to which a fuel off-gas is discharged, an oxidant gas supply pipe 9 to which an oxidant gas (air containing oxygen gas) is supplied, and an oxidant off-gas discharge pipe 10 to which an oxidant off-gas is discharged.

[0021] As shown in FIGS. 2 and 3, the fuel cell 3 includes a thin-film electrolyte 3A made of solid oxide, an anode 3B and an oxidant gas electrode 3C arranged on either side of the electrolyte 3A, an anode current collector 3D to which fuel gas is supplied from a fuel gas supply pipe 7, and an oxidant gas electrode current collector 3E to which oxidant gas is supplied from an oxidant gas supply pipe 9. The fuel cell 3 generates electricity through an electrochemical reaction between the fuel gas supplied to the anode current collector 3D and the oxidant gas supplied to the oxidant gas electrode current collector 3E. A plurality of fuel cell cells 3 are stacked and electrically connected in series via interconnectors 4. The anode current collector 3D and the oxidant gas electrode current collector 3E are made of porous materials such as metal mesh and porous metal, which have excellent electrical conductivity.

[0022] Although not shown, the fuel gas supplied to the fuel gas supply pipe 7 is distributed and supplied to the anode current collector 3D of each fuel cell 3 via a fuel gas supply manifold. The fuel off-gas from the anode current collector 3D of each fuel cell 3 is discharged from a fuel off-gas discharge pipe 8 via a fuel off-gas discharge manifold. The oxidant gas supplied to the oxidant gas supply pipe 9 is distributed and supplied to the oxidant gas electrode current collector 3E of each fuel cell 3 via an oxidant gas supply manifold. The oxidant off-gas from the oxidant gas electrode current collector 3E of each fuel cell 3 is discharged from an oxidant off-gas discharge pipe 10 via an oxidant off-gas discharge manifold.

[0023] As shown in Figure 3, the flat plate fuel cell stack S is equipped with, as interconnectors 4, a medium-thickness interconnector 4A having a standard intermediate thickness t1, a large-thickness interconnector 4B having a thickness t2 greater than that of the medium-thickness interconnector 4A (2.5 times t1 in this embodiment), and a small-thickness interconnector 4C having a thickness t3 smaller than that of the medium-thickness interconnector 4A (0.5 times t1 in this embodiment).

[0024] In the flat plate type fuel cell stack S, the thickness of the interconnectors 4 is varied depending on the arrangement in the stacking direction, so that the interconnectors 4 in a predetermined number of stages (the 5th to 6th stages and the 15th to 16th stages in this embodiment) arranged midway between the center and both ends in the stacking direction of the fuel cell cells 3 are medium-thickness interconnectors 4A, the interconnectors 4 in a predetermined number of stages (the 7th to 14th stages in this embodiment) arranged at the center in the stacking direction are large-thickness interconnectors 4B, and the interconnectors 4 in a predetermined number of stages (the 1st to 4th stages and the 17th to 20th stages in this embodiment) arranged at both the top and bottom ends in the stacking direction are small-thickness interconnectors 4C.

[0025] That is, in the flat plate type fuel cell stack S exemplified in this embodiment, by using a large thickness interconnector 4B having a thickness t2 larger than the thickness t1 of the medium thickness interconnector 4A as the interconnector 4 arranged in the center in the stacking direction where heat is likely to be trapped, it is possible to promote heat conduction in the in-plane direction via the interconnector 4 and increase the area of ​​the end face in the in-plane direction that serves as the heat dissipation surface. Accordingly, heat that is likely to be trapped in the center of the flat plate type fuel cell stack S can be easily released to the outside through the large thickness interconnector 4B, which has a relatively high thermal conductivity among the components of the flat plate type fuel cell stack S, with a large amount of heat dissipation from its heat dissipation surface.

[0026] This makes it possible to prevent heat buildup in the center of the flat fuel cell stack S without changing the in-plane size or arrangement of the stacked fuel cell cells 3 and interconnectors 4, thereby suppressing damage to the fuel cell cells 3 and deterioration of power generation performance caused by such heat buildup.

[0027] As a result, it is possible to provide a flat-plate fuel cell stack S in which the temperature distribution in the in-plane direction and stacking direction of the fuel cell 3 in the flat-plate fuel cell stack S can be made uniform, without incurring an increase in the size of the fuel cell 3 in the in-plane direction or a complex structure due to changes in the in-plane size and arrangement of the stacked fuel cell cells 3 and interconnectors 4, and which can thereby improve power generation performance and durability and reliability.

[0028] Furthermore, in the flat-type fuel cell stack S exemplified in this embodiment, the interconnectors 4 arranged at both ends in the stacking direction where heat is less likely to accumulate are small-thickness interconnectors 4C having a thickness t3 smaller than the thickness t1 of the medium-thickness interconnector 4A, thereby rationally suppressing the increase in size of the fuel cell cells 3 in the stacking direction in the flat-type fuel cell stack S.

[0029] Regarding the flat-type fuel cell stack S according to this embodiment, a stack power generation simulation was carried out to analyze the temperature distribution of heat generated during power generation within the flat-type fuel cell stack S, and the analysis results are shown in FIG. 4.

[0030] In this stack power generation simulation, the fuel cell stack to be analyzed is one in which fuel cell cells 3, each 15 cm on a side and 1.7 mm thick, are stacked in 21 layers between upper and lower end plates 1 and 2, each 5 mm thick, via interconnectors 4, with manifolds and other components omitted. Humidified hydrogen at a temperature of 600°C and a humidity of 3% is supplied to the fuel electrode 3B, and air at a temperature of 600°C is supplied to the oxidant gas electrode 3C.

[0031] In the fuel cell stack of the example to be analyzed, medium-thickness interconnectors 4A with a thickness of 2 mm (reference thickness) were used as the interconnectors 4 arranged in the 5th to 6th and 15th to 16th stages, large-thickness interconnectors 4B with a thickness of 5 mm, which is 2.5 times the reference thickness, were used as the interconnectors 4 arranged in the 7th to 14th stages, and small-thickness interconnectors 4C with a thickness of 1 mm, which is 0.5 times the reference thickness, were used as the interconnectors 4 arranged in the 1st to 4th and 17th to 20th stages, and the stacking height across the upper and lower end plates 1 and 2 was 101.7 mm. In contrast, in the fuel cell stack of the comparative example, medium-thickness interconnectors 4A with a thickness of 2 mm (reference thickness) were used as the interconnectors 4 regardless of the number of stages, and the stacking height across the upper and lower end plates 1 and 2 was 85.7 mm.

[0032] The heat dissipation conditions were as follows: the fuel cell stack was surrounded by 2 cm thick insulation, the heat dissipated from the outer surface of the insulation was radiant heat, and the inner surface temperature of the hot module was set to 600°C to exchange radiant heat.

[0033] As the analysis results of the stack power generation simulation, Figure 4(A) shows the temperature distribution in the fuel cell stack of the embodiment, Figure 4(B) shows the temperature distribution in the fuel cell stack of the comparative example, and Figure 4(C) shows the maximum cell temperatures in the fuel cell stack of the embodiment and the fuel cell stack of the comparative example. The temperature distribution of the fuel cell stack shown in Figures 4(A) and (B) is obtained by dividing the coflow type fuel cell stack being analyzed by a vertical symmetrical plane along the supply direction of the fuel gas and oxidant gas, with the lower left side of the paper being the supply side of the fuel gas and oxidant gas and the upper right side of the paper being the discharge side of the fuel gas and oxidant gas.

[0034] In the fuel cell stack of the comparative example, the maximum cell temperature was 724.5°C, the minimum cell temperature was 666.3°C, and the temperature difference between these was 58.2°C. In contrast, in the fuel cell stack of the example, the maximum cell temperature was 718.6°C, the minimum cell temperature was 665.2°C, and the temperature difference between these values ​​was 53.4°C. In other words, it was confirmed that the cell temperature difference in the fuel cell stack of the example was reduced by 4.8°C (8.2%) compared to the cell temperature difference in the fuel cell stack of the comparative example.

[0035] Therefore, by increasing the thickness of the interconnector 4 located at the center in the stacking direction, heat buildup that tends to occur at the center of the flat-plate fuel cell stack S can be suppressed, while by reducing the thickness of the interconnector 4 located at both the upper and lower ends in the stacking direction, the size of the fuel cell cells 3 in the flat-plate fuel cell stack S can be suppressed from increasing in size in the stacking direction.

[0036] [Another embodiment] Another embodiment of the present invention will now be described. The configurations of the other embodiments described below are not limited to being applied alone, but can also be applied in combination with the configurations of the above-described embodiment or other other embodiments.

[0037] (1) In the above embodiment, the flat plate type fuel cell stack S is exemplified as one in which the number of stacked fuel cell cells 3 is set to 21, but this is not limited thereto, and the number of stacked fuel cell cells 3 may be set to 20 or less or 22 or more.

[0038] (2) In the above embodiment, examples of interconnectors 4 having different thicknesses include a medium-thickness interconnector 4A, a large-thickness interconnector 4B, and a small-thickness interconnector 4C, but this is not limited to this, and for example, the interconnector may include a medium-thickness interconnector 4A and a large-thickness interconnector 4B without including a small-thickness interconnector 4C.

[0039] (3) In the above embodiment, the fuel cell 3 is exemplified as one in which porous materials such as metal mesh or porous metal are used for the fuel electrode current collector 3D and the oxidizer gas electrode current collector 3E. However, this is not limited to this, and for example, the fuel electrode current collector 3D and the oxidizer gas electrode current collector 3E may be made of protrusion portions integrally formed with the interconnector 4. In this alternative embodiment, only the thickness of the substrate portion excluding the thickness of the protrusion portion in the interconnector 4 contributes to uniform temperature distribution, and the thickness of the substrate portion is made different depending on the arrangement in the stacking direction.

[0040] (4) In the above embodiment, the interconnectors 4 are made of materials having the same thermal conductivity regardless of their arrangement in the stacking direction. However, this is not limited to this. For example, a stainless steel material having a higher thermal conductivity than the other interconnectors 4 may be used for the large-thickness interconnector 4B arranged at the center of the stacking direction of the fuel cell 3, thereby preventing the flat-plate fuel cell stack S from becoming larger in the stacking direction of the fuel cell cell 3.

[0041] (5) The number of interconnectors 4A to 4C with different thicknesses provided in the flat plate type fuel cell stack S can be changed in various ways depending on the number of fuel cell cells 3 stacked. [Explanation of symbols]

[0042] 3 Fuel cell 4 Interconnector 4A Medium-thickness interconnector (interconnector in the middle of the stacking direction) 4B Large Thickness Interconnector (Interconnector at the center of the stacking direction) 4C Small thickness interconnector (interconnector on both ends in the stacking direction) t1 Thickness of the medium-thickness interconnector (interconnector in the middle of the stacking direction) t2 Thickness of the large interconnector (interconnector at the center of the stacking direction) t3 Thickness of the small interconnector (interconnector on both ends in the stacking direction)

Claims

1. A flat-plate fuel cell stack configured by stacking a plurality of flat-plate-shaped fuel cell units in multiple stages via interconnectors that electrically connect adjacent fuel cell units, A flat-plate fuel cell stack in which the thickness of the interconnectors is varied depending on their arrangement in the stacking direction, so that the interconnectors arranged in the center of the stacking direction have a greater thickness than the interconnectors arranged other than in the center of the stacking direction.

2. A flat-plate fuel cell stack as described in claim 1, wherein the interconnector arranged intermediately between the interconnector arranged at the center of the stacking direction and the interconnector arranged at both ends of the stacking direction has a thickness smaller than the interconnector arranged at the center of the stacking direction, and the interconnector arranged at both ends of the stacking direction has an even smaller thickness than the interconnector arranged in the middle.

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