JP4337587B2 - Interconnector and fuel cell stack - Google Patents

Description

  The present invention relates to an interconnector that can be used in a high-temperature environment, and a fuel cell stack that uses this interconnector to ensure electrical connection between a fuel cell and a current collector.

  Generally, in a fuel cell stack in which a plurality of fuel cells such as a solid oxide fuel cell (SOFC) are stacked, the exchange of electrons between the current collector and the fuel cell is the power generation of the entire fuel cell stack. In order to greatly affect the amount, it is very important to secure an electrical connection between the current collector and the fuel cell in a high temperature environment where the fuel cell undergoes thermal deformation in order to obtain a stable power generation amount. .

Against this background, in conventional fuel cell stacks, especially SOFC stacks with high operating temperatures, the current collector is electrically connected to the fuel cells uniformly over the entire surface of the fuel cell even when the operating temperature rises. In order to achieve this, a technique has been proposed in which pressure is applied to conductive ceramics, porous metal such as foam metal or metal fiber, or corrugated plates to bring the current collector into contact with the fuel cell (for example, Patent Document 1). reference).
JP 2000-36654 A

  However, the method in which pressure is applied to the conductive ceramics to bring the current collector into contact with the fuel cell has a high resistance to the conductive ceramics, so that the operating temperature is about 1000 [° C.]. Limited to application. Moreover, since the conductive ceramic body is generally expensive, the manufacturing cost of the fuel cell stack increases.

  On the other hand, when pressure is applied to the porous metal and the current collector is brought into contact with the fuel cell, the rigidity and elasticity of the porous metal are lost when the temperature rises to about 700 [° C.] or higher. In this case, the contact pressure between the fuel cell and the current collector cannot be maintained to ensure electrical connection. Similarly, when pressure is applied to the corrugated plate and the current collector is brought into contact with the fuel cell, the stiffness of the corrugated plate is lost when the corrugated plate becomes hot. An electrical connection cannot be ensured.

  One method of assembling a semiconductor device is a method of securing electrical connection in a high temperature environment using a resin interconnector having a conductive metal layer on the outer surface. Is not assumed to be applied to a system that handles a large current in a high-temperature environment containing high-temperature oxygen of 600 [° C.] or higher, such as SOFC, and is unreliable and cannot be directly applied to a SOFC stack. .

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a highly reliable interconnector that can ensure uniform electrical connection even in a high temperature environment without increasing the manufacturing cost. It is to provide.

  Another object of the present invention is a highly reliable fuel capable of ensuring uniform electrical connection between the fuel cell and the current collector over the entire surface of the fuel cell even in a high temperature environment without increasing the manufacturing cost. It is to provide a battery stack.

In order to solve the above-mentioned problem, the feature of the interconnector according to the present invention includes two metal plates whose ends are hermetically bonded to each other, and at least one of the metal plates has a gap formed between the plate surfaces. The inert gas is sealed in the gap, and at least one of the metal plates is formed in a corrugated shape .

  According to the interconnector and fuel cell stack according to the present invention, during high temperature operation, the interconnector expands due to an increase in internal pressure, so that electrical connection can be ensured uniformly.

  In addition, according to the interconnector and fuel cell stack according to the present invention, the interconnector is made of a metal plate, so that the manufacturing cost of the interconnector can be reduced.

  Further, according to the interconnector and the fuel cell stack according to the present invention, since the inert gas is sealed between the metal plates constituting the interconnector, the reliability of the interconnector can be ensured for a long time.

  The interconnector according to the present invention can be applied to, for example, a fuel cell stack in which a plurality of solid oxide fuel cells having a high operating temperature are stacked. Hereinafter, the configuration of a fuel cell stack according to the first to third embodiments of the present invention in which the interconnector according to the present invention is applied to the fuel cell stack will be described in detail with reference to the drawings.

  In each of the drawings used for the following description, the fuel cell stack is schematically shown for easy description, and each drawing does not show an accurate dimensional ratio. Further, the numerical values such as temperature in the description are one embodiment, and the present invention is of course not limited to this value.

[Configuration of fuel cell stack]
First, the configuration of the fuel cell stack according to the first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a partial cross-sectional view showing a configuration of a fuel cell stack according to a first embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing the configuration of the interconnector shown in FIG.

  As shown in FIG. 1, the fuel cell stack according to the first embodiment of the present invention is a disk-shaped (donut-shaped) solid oxide fuel cell (hereinafter abbreviated as a fuel cell) having an opening at the center. 1 has a configuration in which a plurality of fuel cells 1 are stacked in the vertical direction, and each fuel cell 1 is disposed so as to sandwich the electrolyte membrane 2 and the electrolyte membrane 2, and each air electrode functions as a cathode and an anode of the fuel cell 1. 3 and the fuel electrode 4.

  On both sides of the air electrode 3 and the fuel electrode 4, a current collector 5 made of a porous low-resistance conductor for taking out the electromotive force of the fuel cell 1 is provided. In the fuel cell stack having such a configuration, oxygen gas and hydrogen gas are supplied from the gas exchanger 6 to the air electrode 3 and the fuel electrode 4 through the opening of the fuel cell 1, respectively. Generates an electromotive force, and the electromotive force generated by the fuel cell 1 is taken out by the current collector 5.

  Further, in this fuel cell stack, a disk-shaped interconnector 7 having an opening at the center is provided between the opposing current collectors 5, and this interconnector 7 has airtightness as shown in FIG. It has two metal plates 11 and 12, a metal felt 13 inserted between the metal plates 11 and 12, and a brazing material 14 that fixes the metal felt 13 to the metal plates 11 and 12.

  Further, the end portions of the two metal plates 11 and 12, that is, the inner peripheral side and the outer peripheral side portions of the interconnector 7 are hermetically joined to each other by laser welding, and an inert gas Ar is interposed between the metal plates 11 and 12. (Argon) is enclosed. Then, the interconnector 7 having such a configuration expands and contracts in accordance with the function as a gas separator that prevents the mixing of the oxidizing gas and the hydrogen gas and the change in the internal pressure accompanying the change in the operating temperature. It also has a function as an air spring that ensures electrical connection between the electric body 5 and the air electrode 3 and the fuel electrode 4.

  In this embodiment, the metal plates 11 and 12 are formed of SUS430 having a thickness of 100 [μm], and the metal felt 13 is formed by compressing a thin wire of φ50 [μm] copper to a thickness of 0.3 [mm]. It is formed by what is entangled. The brazing material 14 is made of a Ni brazing material so that the fine copper wire forming the metal felt 13 is not sucked.

[Method of manufacturing interconnector]
Next, a method for manufacturing the interconnector 7 will be described with reference to FIG.

  FIG. 3 shows a plan sectional view of the interconnector.

  When manufacturing the interconnector 7, first, the brazing material 14 a is arranged in a lattice shape on the upper surface of the disk-shaped metal plate 12 having an opening in the center portion, and is then placed inside the outer periphery of the metal plate 12. Thus, the metal felt 13 is disposed on the brazing material 14a. Next, as shown in FIG. 3, the brazing material 14 b is arranged on the metal felt 13 in a lattice shape so as not to coincide with the lattice position of the brazing material 14 a formed on the metal plate 12, and then on the metal felt 13. The metal plate 11 having the same shape as that of the metal plate 12 is disposed on the brazing material 14b formed in the above. Note that the distance between the brazing material 14a and the brazing material 14b is actually closer than the state shown in FIG.

  Next, the metal plates 11 and 12 and the metal felt 13 are brazed and fixed by raising the temperature to a brazing temperature (melting temperature of the brazing materials 14a and 14b) in an inert gas or vacuum. Finally, with the gap between the metal plates 11 and 12 secured by the metal felt 13, the end surfaces of the metal plates 11 and 12 are aligned in an Ar atmosphere and hermetically joined by laser welding. Thereby, a series of manufacturing steps of the interconnector 7 is completed.

  In this embodiment, as shown in FIG. 3, the brazing materials 14a and 14b are arranged in a lattice shape. However, the present invention is not limited to this, and concentric circles of the disk-like metal plates 11 and 12 or the like. It may be arranged in other shapes. Further, when the interconnector 7 is manufactured, it is possible to adjust the amount of the brazing material 14a, 14b and the indentation pressure to the metal felt 13 so that the brazing material 14a, 14b does not wet the metal felt 13 and directly join it. desirable. Moreover, you may join the metal plates 11 and 12 and the metal felt 13 using other joining methods, such as ultrasonic joining, instead of a brazing process.

  Further, in order to provide an extension allowance of the interconnector 7 when the internal pressure rises with an increase in the hand temperature, the metal plates 11 and 12 may be formed into a corrugated shape as shown in FIG. The waveform may be formed concentrically around the highest point when 11 and 12 expand to the outer periphery. Further, as shown in FIG. 5, instead of the metal felt 13, a bent thin metal plate 15 may be fixed to the metal plates 11 and 12. When the metal plates 11 and 12 are disk-shaped, the outer dimensions of the interconnector 7 do not change even if the metal plates 11 and 12 are formed into a corrugated shape.

  Furthermore, as shown in FIG. 6, only the end portion of the metal plate 11 may be formed into a waveform. In the example shown in FIG. 6, the metal felt 13 is brazed to the metal plates 11 and 12 at the convex portion of the metal plate 11, but the metal felt 13 is attached to the metal plate 11 at either the convex portion or the concave portion. May be brazed.

  Further, as shown in FIG. 7, both the metal plates 11 and 12 are formed into a corrugated shape, and the metal plate 11 and the metal plate 12 are aligned so that the concave portions of one metal plate and the convex portions of the other metal plate are aligned. You may arrange. According to such a configuration of the interconnector 7, the overall height of the interconnector 7 can be suppressed.

  In this embodiment, Ar, which is an inert gas, is used as the sealing gas. However, the present invention is not limited to this, and other inert gases, such as Ne (neon) and Xe (xenon), or A mixed gas of these inert gases may be used. However, He (helium), which is the same inert gas, is very easy to leak as apparent from being used for detecting a minute gas leak path, and is not suitable for ensuring long-term airtight maintenance.

N ₂ (nitrogen gas) may be classified as an inert gas, but it may cause a nitriding reaction with other materials in a high-temperature environment, so it is desirable not to use it as an enclosed gas. Since CO ₂ (carbon dioxide) is stable as a compound gas, it can be used as an enclosed gas.

[Ar pressure sealed in the interconnector]
By the way, in the interconnector 7 having the above-described configuration, the pressure of Ar sealed in the interconnector 7 increases as the temperature rises. For example, when the temperature rises to 650 [° C.]. Assuming that the volume of the interconnector 7 does not increase due to an increase in pressure, Boyle's law P1 · V1 / T1 = P2 · V2 / T2 (T1, T2, P1, P2, V1, V2 The internal pressure enclosed at atmospheric pressure of about 0.1 [mPa] during assembly is increased to about 0.34 [MPa] according to the following temperature, sealing pressure, pressure after change, sealing volume, and volume after change) .

At this time, since the spring force of the interconnector 7 functioning as an air spring is a value obtained by multiplying the internal pressure value by the planar area of the interconnector 7, the planar area of the interconnector 7 is 100 [cm ² ]. In this case, the spring force of the interconnector 7 is 3400 [N]. When both ends of the fuel cell stack are mechanically fixed and the whole fuel cell stack is not deformed in the stacking direction, the spring force of the interconnector 7 is applied to the plane of the current collector 5. The current collector 5 is pressed against the fuel cell 1.

  However, at this time, since the spring force of the interconnector 7 is too strong, it may cause damage to the fuel cell 1. Therefore, in order to adjust the spring force of the interconnector 7 when the temperature rises, It is desirable to adjust the pressure (filling pressure) P1 of Ar sealed in the connector 7 in consideration of the pressure P2 during use. Further, by adjusting the Ar sealing pressure P1 in this way, it is not necessary to perform operations such as crushing the interconnector 8 and inserting it between the fuel cells 1 when assembling the fuel cell stack. Can be easily manufactured.

  Specifically, the optimum pressure P2 at the time of high temperature is set, and the value of the set pressure P2 is substituted into the formula P1 = P2 · (V2 / V1) · (T1 / T2) derived from the above-mentioned Boyle's law. Therefore, it is desirable to determine the Ar sealing pressure P1. Ar filled in the interconnector 7 is filled with Ar with a specified pressure in a pressure vessel having a welding laser beam introduction window, and then the metal plates 11 and 12 are installed inside. It can be adjusted to the specified pressure by laser welding together.

  Moreover, the internal volume of the interconnector 7 can be adjusted by the compression thickness of the metal felt 13 accommodated in the inside and the corrugated height of the metal plates 11 and 12. Further, when the metal felt 13 is not used, a step may be formed around the periphery by a technique such as pressing so that the internal volume between the metal plates 11 and 12 can be secured.

  As is clear from the above description, in the fuel cell stack according to the first embodiment of the present invention, the interconnector 7 that expands and contracts according to the operating temperature is inserted between the fuel cell 1 and the current collector 5. The connector 7 is formed by sealing Ar between the two metal plates 11 and 12 and hermetically sealing the ends of the metal plates 11 and 12. According to such a configuration, during high temperature operation in which thermal deformation of the fuel cell 1 occurs, the interconnector 7 functions as an air spring by expanding with a change in internal pressure. The electric connection between the fuel cell 1 and the current collector 5 can be ensured.

  Further, since the interconnector 7 can be made of a material satisfying only the tensile strength without using expensive super heat resistant special steel, ceramics, graphite, or the like, the manufacturing cost of the interconnector 7 can be reduced. it can. In addition, since Ar that hardly leaks gas is enclosed between the metal plates 11 and 12, the reliability of the interconnector 7 can be ensured for a long time.

  Further, in the fuel cell stack according to the first embodiment of the present invention, at least one of the metal plates 11 and 12 constituting the interconnector 7 is formed into a corrugated shape, so that the fuel cell 1 is thermally deformed at a high temperature. In some cases, the allowance of the interconnector 7 can be secured and the thermal deformation of the fuel cell 1 can be followed.

  Further, in the fuel cell stack according to the first embodiment of the present invention, the Ar sealing pressure is adjusted based on the internal pressure at the time of expansion. Therefore, when the fuel cell stack is assembled, the interconnector 7 is crushed and the fuel is stacked. There is no need to perform an operation such as insertion between the batteries 1, and the fuel cell stack can be easily manufactured. In addition, it is possible to prevent the fuel cell 1 from being damaged by the spring force of the interconnector 7 being too strong at a high temperature.

  In the fuel cell stack according to the first embodiment of the present invention, the metal felt 13 is inserted between the metal plates 11 and 12, and the metal felt 13 is fixed to the metal plates 11 and 12. Even when the thickness of the interconnector 7 changes during high-temperature operation in which the battery 1 is thermally deformed, the metal felt 13 moves following the metal plates 11 and 12, and conducts electrical conduction between the current collectors 5. Can be maintained.

  At this time, since Ar is enclosed between the metal plates 11 and 12, a copper fine wire having a low electrical resistance but low environmental resistance such as oxidation, or an Ag material weak in a high-temperature oxidizing atmosphere is used as the metal felt 13. Even if the electrical conductor is used, the electrical conductor is protected without deterioration, and the reliability of the interconnector 7 can be ensured for a long period of time. Further, the current uniformity can be improved by conducting the electromotive force of the fuel cell 1 in a matrix.

  Further, in the fuel cell stack according to the first embodiment of the present invention, the metal felt 13 is fixed to the metal plates 11 and 12 by the brazing process, thereby reducing the cost and labor required for manufacturing the interconnector 7. In addition, the interconnector 7 can be configured to have a low resistance.

  Furthermore, in the fuel cell stack according to the first embodiment of the present invention, the metal plates 11 and 12 are formed into a corrugated shape, and at the same time, the positions of the convex portions of one metal plate and the concave portions of the other metal plate coincide. Thus, since the metal plates 11 and 12 are arranged, the overall height of the interconnector 7 can be suppressed while maintaining the function of the interconnector 7, and the fuel cell stack can be made compact.

  In the fuel cell stack according to the first embodiment of the present invention, the interconnector 7 is configured in the same shape as the fuel cell 1 and Ar is sealed in one air chamber, so that the internal pressure is Evenly distributed pressure is applied uniformly, and the fuel cell 1 and the current collector 5 are electrically connected across the entire surface of the fuel cell 1 without causing damage to the fuel cell 1. Can be secured.

  Next, the structure of the interconnector in the fuel cell stack according to the second embodiment of the present invention will be described with reference to FIG.

  FIG. 8 is a partial cross-sectional view showing the configuration of the interconnector in the fuel cell stack according to the second embodiment of the present invention.

  In the fuel cell stack according to the first embodiment, the interconnector 7 is configured so that Ar forms one air chamber in order to make the pressure applied to the current collector 5 and the fuel cell 1 uniform. In the fuel cell stack according to the second embodiment of the present invention, as shown in FIG. 8, the interconnector 7 is provided with a metal plate 22 that forms a protrusion between the opposing metal plates 21 a and 21 b, and the metal plate 22. Is formed by a plurality of air chambers sealed with Ar. And according to the structure of such an interconnector 7, while being able to accelerate | stimulate the heat exchange between ambient gas and Ar, the manufacturing process of the interconnector 7 can be simplified.

  Finally, with reference to FIG. 9, the structure of the interconnector in the fuel cell stack according to the third embodiment of the present invention will be described.

  FIG. 9 is a partial cross-sectional view showing the configuration of the interconnector in the fuel cell stack according to the third embodiment of the present invention.

  In the above embodiment, emphasis was placed on ensuring the electrical connection between the fuel cell 1 and the current collector 5, but in the fuel cell stack according to the third embodiment of the present invention, an inert gas was sealed inside. A plurality of air springs formed by the metal plates 31 and 32 are joined, and the plurality of air springs are sandwiched between the high-strength structural members 33a and 33b to form the interconnector 7. And according to the structure of such an interconnector 7, since the spring constant of the interconnector 7 does not fall even in the high temperature environment which a thermal deformation produces, the function as an air spring of the interconnector 7 is securable.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

It is a fragmentary sectional view which shows the structure of the fuel cell stack used as the 1st Embodiment of this invention. It is a fragmentary sectional view which shows the structure of the interconnector in the fuel cell stack shown in FIG. FIG. 2 is a plan sectional view showing a configuration of an interconnector in the fuel cell stack shown in FIG. 1. It is a fragmentary sectional view which shows the structure of the application example of the interconnector shown in FIG. It is a fragmentary sectional view which shows the structure of the application example of the interconnector shown in FIG. It is a fragmentary sectional view which shows the structure of the application example of the interconnector shown in FIG. It is a fragmentary sectional view which shows the structure of the application example of the interconnector shown in FIG. It is a fragmentary sectional view which shows the structure of the interconnector in the fuel cell stack used as the 2nd Embodiment of this invention. It is a fragmentary sectional view which shows the structure of the interconnector in the fuel cell stack which becomes the 3rd Embodiment of this invention.

Explanation of symbols

1: solid oxide fuel cell 2: electrolyte membrane 3: air electrode 4: fuel electrode 5: current collector 6: gas exchanger 7: interconnector 11, 12, 21a, 21b, 22, 31, 32: metal plate 13: Metal felt 14: Brazing material 15: Metal plate 33a, 33b: Structural member

Claims (9)

Two metal plates whose ends are hermetically bonded to each other are provided, at least one of the metal plates is formed so that a gap is formed between the plate surfaces, and an inert gas is sealed in the gap, and the metal An interconnector characterized in that at least one of the plates is formed into a corrugated shape. The interconnector according to claim 1, wherein at least one end of the metal plate is formed into a corrugated shape.   The inert gas is any one of argon, neon, and xenon, or a mixed gas of at least two of these gases. Interconnector.   The interconnector according to any one of claims 1 to 3, wherein the pressure of the inert gas sealed in the gap is determined based on an internal pressure during expansion.   The metal piece having flexibility is inserted into the gap, and the two metal plate surfaces are mechanically and electrically joined to each other by the metal piece. 5. The interconnector according to any one of items 4.   The interconnector according to claim 5, wherein the metal piece and the metal plate are joined by brazing.   The two metal plates are formed into a corrugated shape so that the concave portion of one metal plate coincides with the convex portion of the other metal plate. The interconnector according to claim 1.   The position of brazing the said metal piece and the said metal plate is arrange | positioned so that it may not become the same position between two metal plate surfaces, The interface of Claim 6 or Claim 7 characterized by the above-mentioned. connector. A fuel cell stack comprising the interconnector according to any one of claims 1 to 8.

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