JP2015088265A - Fuel battery unit cell with separator, fuel battery stack, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel battery unit cell with a separator which is increased in the strength by reducing cavities in a bonding portion; a fuel battery stack; and method for manufacturing such a fuel battery unit cell.SOLUTION: A fuel battery unit cell with a separator comprises: a fuel battery unit cell having an air electrode, a fuel electrode and a solid electrolytic layer disposed therebetween; a plate-like metal separator having a first principal face, a second principal face, and through-holes extending between the first and second principal faces and piercing the separator; and a bonding portion serving to bond the fuel battery unit cell to the first principal face of the metal separator, and including a silver-containing brazing filler metal. The bonding portion is divided into: an inner peripheral side region disposed on a through-hole side of the metal separator; an outer peripheral side region disposed outside the inner peripheral side region; and a middle region disposed between the inner peripheral side region and the outer peripheral side region. The distance between the fuel battery unit cell and the first principal face in the middle region is smaller than the distances between the fuel battery unit cell and the first principal face in the outer peripheral side region and the inner peripheral side region.

Description

  The present invention relates to a single cell with a separator, a fuel cell stack, and a method for manufacturing the same.

  A solid oxide fuel cell using a solid oxide as an electrolyte (hereinafter also referred to as “SOFC” or simply “fuel cell”) is known. The SOFC has, for example, a stack (fuel cell stack) in which a large number of fuel cell single cells each having a fuel electrode and an air electrode are stacked on each surface of a plate-like solid electrolyte layer. Electric power is generated by supplying a fuel gas (for example, hydrogen) and an oxidant gas (for example, oxygen in the air) to the fuel electrode and the air electrode, respectively, and causing a chemical reaction through the solid electrolyte layer.

  A single fuel cell is used by being joined to a separator that divides a section where fuel gas and oxidant gas are present. For this joining, a joining portion made of a brazing material such as Ag brazing is usually used.

A technique of brazing an alloy holding thin plate frame to a single fuel cell or sealing with a glass-based sealant is disclosed (see Patent Document 1).
In addition, since the characteristics of the air electrode change when brazed in a non-oxidizing atmosphere, a technique for brazing the separator and the fuel cell single cell in the atmosphere (atmospheric brazing) is disclosed (see Patent Document 2). .

JP 2000-331692 A JP 2010-21038 A

However, when the fuel cell single cell and the alloy holding thin plate frame (metal separator) are joined by brazing, bubbles may be involved. In this case, voids are formed in the joint, the strength of the joint is reduced, and the joint may be peeled off and gas leakage may occur.
It is an object of the present invention to provide a separator-equipped fuel cell unit cell, a fuel cell stack, and a method for manufacturing the same, in which pores in a joint portion are reduced and the strength is improved.

(1) A separator-equipped fuel cell unit cell according to the present invention includes:
A fuel cell single cell having an air electrode, a fuel electrode, and a solid electrolyte layer disposed between them;
A plate-shaped metal separator having a first main surface, a second main surface, and a through-hole penetrating between the first main surface and the second main surface;
A joining portion made of a brazing material containing Ag, joining the single fuel cell and the first main surface of the metal separator;
A separator-equipped fuel cell unit cell comprising:
An inner peripheral region disposed on the through-hole side of the metallic separator, an outer peripheral region disposed outside the inner peripheral region, and the inner peripheral region and the outer peripheral region. Is divided into intermediate areas arranged between
The distance between the single fuel cell and the first main surface in the intermediate region is smaller than the distance between the single fuel cell and the first main surface in the outer peripheral region and the inner peripheral region. It is characterized by.

  The distance in the intermediate area of the joint (the distance between the single fuel cell and the first main surface (lower surface) of the metal separator) is smaller than the distance between the outer peripheral area and the inner peripheral area. For this reason, bubbles entrained in the Ag brazing during brazing (manufacturing) can easily escape to the outside via the inner peripheral region or the outer peripheral region. As a result, the bonding strength of the bonded portion is ensured by reducing the ratio of pores (bubbles) in the bonded portion (Ag wax).

(2) You may have a dent in the said 2nd main surface side of the said metal separator in the location corresponding to the said intermediate | middle area | region.
For example, when the plate thickness of the metal separator is uniform, the metal separator has a dent on the second main surface side corresponding to the small interval in the intermediate region. That is, the use of a metal separator having a uniform plate thickness can reduce pores (bubbles) in the joint (Ag brazing).

(3) It is preferable that the said intermediate | middle area | region exists over the perimeter along the said through-hole.
Over the entire circumference of the through hole, holes in the joint (Ag brazing) are reduced, and the joint strength is improved.

(4) Between the fuel cell single cell and the first main surface on the side of the through hole with respect to the joint, the seal member is disposed over the entire circumference along the through hole and includes glass. It is preferable to further include a sealing part.

  In the absence of a seal, the joint (Ag wax) is exposed to both oxidant gas and fuel gas. In this case, oxygen and hydrogen diffuse and react in the Ag wax, so that voids are generated afterward and gas leakage may occur. Between the through-hole side fuel cell unit cell and the first main surface, the sealing portion is disposed over the entire circumference along the through-hole so that the joining portion (Ag wax) is exposed to the oxidant gas. Or only one of the fuel gases can be used. As a result, the reaction between oxygen and hydrogen in the joint (Ag wax) can be suppressed, and the generation of voids in the Ag wax can be reduced.

  Further, as described above, the bonding strength between the metal separator and the bonding portion (Ag brazing) is increased by reducing the ratio of the voids (bubbles) in the bonding portion (Ag brazing). For this reason, even if stress is applied to the separator-equipped fuel cell unit cell, the stress applied to the sealing portion by the bonding portion can be relaxed, and cracking of the sealing portion (including glass) can be prevented. Therefore, it is possible to prevent gas leakage at the joint more reliably.

(5) A fuel cell stack according to the present invention comprises a plurality of separator-attached fuel cell single cells according to (1) to (4).
It is possible to provide a fuel cell stack in which gas leakage at the joint is prevented.

(6) A method for producing a separator-equipped fuel cell unit cell according to the present invention includes:
A fuel cell single cell having an air electrode, a fuel electrode, and a solid electrolyte layer disposed between them, and the first main surface, the second main surface, and between the first main surface and the second main surface Preparing a plate-like metal separator having a through-hole,
Disposing a brazing material containing Ag on one or both of the single fuel cell and the metal separator;
Arranging the single fuel cell and the first main surface to face each other;
Joining the fuel cell single cell and the first main surface by melting the brazing material while applying a load,
In the step of disposing the brazing material, the brazing material is disposed in a brazing region, which is at least a part of a region facing the fuel cell single cell and the first main surface,
In the joining step, the load is applied from the second main surface of the metallic separator with a width narrower than the width of the brazing region.

  In the joining step, the metal separator is recessed by applying the load from the second main surface (upper surface) of the metal separator to a width narrower than the width of the brazing region. As a result, the Ag wax flows and it becomes easy to drive out the bubbles entrained in the Ag wax. In addition, since the metal separator is recessed, a slope is formed in the metal separator, so that the bubbles can be easily driven out.

  Thus, by applying a load with a width narrower than the width of the brazing region, the metallic separator is recessed, and the bubbles in the Ag braze are driven out, so that the bonding strength can be improved.

(7) It is preferable that the area | region which applies the said load exists over the perimeter along the said through-hole of the said metal separator.
Bubbles in the Ag solder are reduced over the entire circumference of the through hole, and the bonding strength is improved.

(8) In the bonding step, the brazing material is preferably melted in the atmosphere.
By melting the brazing material in the atmosphere, changes in the characteristics of the air electrode can be prevented.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell single cell with a separator, the fuel cell stack, and its manufacturing method which reduced the void | hole in a junction part and aimed at the strength improvement can be provided.

1 is a perspective view showing a solid oxide fuel cell 10. FIG. 1 is a schematic cross-sectional view of a solid oxide fuel cell 10. FIG. 3 is a cross-sectional view of a fuel cell 40. FIG. It is a top view of the fuel cell single cell 44 and the metal separator 53 (fuel cell single cell 50 with a separator). It is an expanded sectional view in the frame A of the fuel cell single cell 50 with a separator. It is an expanded sectional view of fuel cell single cell 50x with a separator concerning a comparative example. It is a cross-sectional photograph of the fuel cell single cell 50 with a separator which concerns on an Example. It is a cross-sectional photograph of the separator-equipped fuel cell unit cell 50x according to the comparative example. It is sectional drawing of the fuel cell 40a. It is an expanded sectional view in frame A of fuel cell single cell 50a with a separator. It is a figure showing the manufacturing process (application of a load) of the fuel cell single cell 50, 50a with a separator which concerns on the manufacturing method 1. FIG. It is a figure showing the manufacturing process (movement of the bubble in a joining process) of the fuel cell single cell 50, 50a with a separator which concerns on the manufacturing method 1. FIG. It is a figure showing the manufacturing process (sealing process) of the fuel cell single cell 50a with a separator which concerns on the manufacturing method 1. FIG. It is sectional drawing showing joining jig | tool Tp. It is a figure showing the manufacturing process of the fuel cell single cell 50, 50a with a separator which concerns on the manufacturing method 2. FIG. It is a figure showing the manufacturing method of the fuel cell single cell 50x with a separator which concerns on a comparative example. It is a graph which compares and represents the peel test result of the fuel cell single cell with separators 50 and 50a which concerns on an Example and a comparative example. It is a figure for demonstrating a peel test.

  Hereinafter, a solid oxide fuel cell according to the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a perspective view showing a solid oxide fuel cell (fuel cell stack) 10 according to a first embodiment of the present invention. The solid oxide fuel cell 10 generates power by receiving supply of a fuel gas (for example, hydrogen) and an oxidant gas (for example, air (specifically, oxygen in the air)).

  In the solid oxide fuel cell 10, end plates 11 and 12 and fuel cells 40 (1) to 40 (4) are stacked, and bolts 21, 22 (22 a, 22 b), 23 (23 a, 23 b) and nuts 35 are stacked. It is fixed with.

  The bolts 22 (22a, 22b) and 23 (23a, 23b) have a cavity functioning as a flow path for fuel gas or oxidant gas (supply gas) inside or outside. Here, cavities functioning as flow paths for the supply gas are arranged inside the bolts 22 and 23. On the other hand, it is good also as a flow path of supply gas between the outer periphery of the volt | bolts 22 and 23 and the through-holes 32 and 33. FIG.

  Bolts 22a and 22b supply and discharge oxidant gas to and from the fuel cell 40, respectively. The bolts 23a and 23b supply and discharge the fuel gas to and from the fuel cell 40, respectively.

FIG. 2 is a schematic cross-sectional view of the solid oxide fuel cell 10.
The solid oxide fuel cell 10 is a fuel cell stack configured by stacking fuel cells 40 (1) to 40 (4). Here, for the sake of clarity, four fuel cells 40 (1) to 40 (4) are stacked, but in general, about 20 to 60 fuel cells 40 are often stacked. .

The end plates 11 and 12 and the fuel cells 40 (1) to 40 (4) have through holes 31 and 32 (32a and 32b) corresponding to the bolts 21 and 22 (22a and 22b) and 23 (23a and 23b), 33 (33a, 33b).
The end plates 11 and 12 are holding plates that press and hold the stacked fuel battery cells 40 (1) to 40 (4), and output current from the fuel battery cells 40 (1) to 40 (4). It is also a terminal.

  FIG. 3 is a cross-sectional view of the fuel battery cell 40. FIG. 4 is a top view of the single fuel cell 44 and the metal separator 53 (single fuel cell with separator). FIG. 5 is an enlarged cross-sectional view in the frame A of the separator-equipped fuel cell single cell 50.

  As shown in FIG. 3, the fuel cell 40 includes a so-called fuel electrode supporting membrane type fuel cell single cell 44, interconnectors 41 and 45, current collectors 42 a and 42 b, and a frame portion 43.

  The fuel cell single cell 44 is configured by sandwiching a solid electrolyte layer 56 between an air electrode (also referred to as a cathode or an air electrode layer) 55 and a fuel electrode (also referred to as an anode or a fuel electrode layer) 57. An air electrode 55 is disposed on the oxidant gas flow path 47 side of the solid electrolyte layer 56, and a fuel electrode 57 is disposed on the fuel gas flow path 48 side.

  The fuel gas flows into the fuel gas channel 48 through the fuel gas channel of the bolt 23a (a cavity disposed inside or outside the bolt 23a) and flows out into the fuel gas channel of the bolt 23b.

  The oxidant gas flows into the oxidant gas flow path 47 through the oxidant gas flow path of the bolt 22a (a cavity disposed inside or outside the bolt 22a), and flows out into the oxidant gas flow path of the bolt 22b. To do.

  As the air electrode 55, a perovskite oxide (for example, LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide) can be used.

  For the solid electrolyte layer 56, materials such as YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), SDC (samarium doped ceria), GDC (gadolinium doped ceria), and perovskite oxide can be used.

  The fuel electrode 57 is preferably a metal, and Ni, Ni-ceramic cermets or Ni-based alloys can be used.

  The interconnectors 41 and 45 are plates having conductivity (for example, a metal such as stainless steel) that can secure conduction between the fuel cell single cells 44 and prevent gas mixing between the fuel cell single cells 44. Shaped member.

  One interconnector (41 or 45) is arranged between the fuel cell single cells 44 (one interconnector is shared between two fuel cell single cells 44 connected in series). For). Further, in each of the uppermost and lowermost fuel cell single cells 44, conductive end plates 11 and 12 are arranged in place of the interconnectors 41 and 45, respectively.

  The current collector 42 a is for ensuring electrical connection between the air electrode 55 of the fuel cell single cell 44 and the interconnector 41, and is, for example, a convex portion formed in the interconnector 41. The current collector 42b is for ensuring electrical continuity between the fuel electrode 57 of the fuel cell single cell 44 and the interconnector 41. For example, air-permeable nickel felt or nickel mesh can be used. .

  The frame portion 43 has an opening 46 through which an oxidant gas and a fuel gas flow. The inside of the opening 46 is divided into an oxidant gas flow path 47 through which oxidant gas flows and a fuel gas flow path 48 through which fuel gas flows. Further, the frame portion 43 of this embodiment includes an air electrode frame 51, an insulating frame 52, a metal separator 53, and a fuel electrode frame 54.

  The air electrode frame 51 is a metal frame disposed on the air electrode 55 side, and has an opening 46 at the center. An oxidant gas flow path 47 is defined by the opening 46.

The insulating frame 52 is a frame that electrically insulates between the interconnectors 41 and 45. For example, ceramics such as Al ₂ O ₃ , mica, vermiculite, and the like can be used, and an opening 46 is provided at the center. An oxidant gas flow path 47 is defined by the opening 46. Specifically, the insulating frame 52 is disposed between the interconnectors 41 and 45 such that one surface contacts the air electrode frame 51 and the other surface contacts the metal separator 53. As a result, the interconnectors 41 and 45 are electrically insulated by the insulating frame 52.

  The metal separator 53 is a frame-shaped metal thin plate (for example, thickness: 0.1 mm) having a through hole 58, is attached to the solid electrolyte layer 56 of the fuel cell single cell 44, and is formed of an oxidant gas. It is a metal frame that prevents mixing with fuel gas. The metal separator 53 divides the gap in the opening 46 of the frame portion 43 into an oxidant gas flow path 47 and a fuel gas flow path 48, thereby preventing mixing of the oxidant gas and the fuel gas.

  A through-hole 58 is formed in the metal separator 53 by a through-hole penetrating between the upper surface (second main surface) and the lower surface (first main surface) of the metal separator 53. The air electrode 55 of the fuel cell single cell 44 is disposed in the through hole 58. In addition, the fuel cell single cell 44 is joined and sealed around the through hole 58. The fuel cell single cell 44 to which the metal separator 53 is joined is referred to as a “fuel cell with separator”. Details of this will be described later.

  Like the insulating frame 52, the fuel electrode frame 54 is an insulating frame disposed on the fuel electrode 57 side, and has an opening 46 in the center. A fuel gas flow path 48 is defined by the opening 46.

  Bolts 21, 22 (22a, 22b), 23 (23a, 23b) are inserted into the air electrode frame 51, the insulating frame 52, the metal separator 53, and the fuel electrode frame 54, or an oxidant gas or a fuel gas is inserted. The through holes 31, 32 (32a, 32b), 33 (33a, 33b) that circulate are provided in the respective peripheral portions.

(Details of single cell 50 with separator)
The separator-equipped fuel cell unit cell 50 according to the present embodiment has a joint 61. A junction 61 is disposed between the single fuel cell 44 and the metal separator 53. Along the through hole 58, the lower surface (first surface) of the metallic separator 53 and the upper surface of the solid electrolyte layer 56 are joined at the joining portion 61.

  The joining portion 61 is made of a brazing material containing Ag, and joins the fuel cell single cell 44 and the lower surface (first main surface) of the metal separator 53 along the through hole 58 over the entire circumference.

As the material of the joining portion 61, various brazing materials mainly composed of Ag can be employed. For example, as a brazing material, a mixture of Ag and an oxide, for example, Ag-Al ₂ O ₃ (a mixture of Ag and Al ₂ O ₃ (alumina)) can be used. Examples of the mixture of Ag and oxide include Ag—CuO, Ag—TiO ₂ , Ag—Cr ₂ O ₃ , and Ag—SiO ₂ . Further, an alloy of Ag and another metal (for example, any one of Ag—Ge—Cr, Ag—Ti, and Ag—Al) can be used as the brazing material.

  The brazing material containing Ag (Ag brazing) is not easily oxidized at the brazing temperature even in an air atmosphere. For this reason, the fuel cell single cell 44 and the metal separator 53 can be joined in an air atmosphere using Ag wax, which is preferable in terms of process efficiency. If brazing is performed in a non-oxidizing atmosphere, the characteristics of the air electrode 55 may change.

  As shown in FIGS. 4 and 5, the joint 61 is divided into an inner peripheral area A1, an outer peripheral area A2, and an intermediate area A3. The inner peripheral region A1 is a region disposed on the through hole 58 side of the metallic separator 53. The outer peripheral side region A2 is a region disposed outside the inner peripheral side region A1. The intermediate area A3 is an area arranged between the inner peripheral area A1 and the outer peripheral area A2.

  The distances (intervals) between the fuel cell single cell 44 and the lower surface (between the first main surfaces) of the inner peripheral region A1, the outer peripheral region A2, and the intermediate region A3 are defined as intervals G1, G2, G3. .

  As shown in FIG. 5, the gap G3 in the intermediate area A3 is smaller than the gaps G1 and G2 in the inner peripheral area A1 and the outer peripheral area A2. For this reason, bubbles entrained in Ag brazing at the time of manufacturing described later (at the time of brazing) can easily escape to the outside via the inner peripheral area A1 or the outer peripheral area A2. As a result, the bonding strength of the bonding portion 61 is ensured by reducing the ratio of pores (bubbles) Ha in the bonding portion 61 (Ag brazing).

  The width D0 of the joining portion 61 (brazing region) is, for example, 1.5 to 6 mm, and the widths D1, D2 of the inner peripheral side region A1 and the outer peripheral side region A2 are, for example, 0.5 mm or more. That is, the width D3 of the intermediate area A3 is, for example, 0.5 to 5 mm.

  Here, the metal separator 53 has a recess on the upper surface (second main surface) side at a location corresponding to the intermediate region A3. That is, since the thickness of the metal separator 53 is substantially uniform, the upper surface (second main surface) of the metal separator 53 has a dent corresponding to the small gap G3 in the intermediate region A3.

  On the other hand, when the metal separator 53 having a plate thickness in the intermediate region A3 larger than the plate thickness in the inner peripheral region A1 and the outer peripheral region A2, the upper surface (second main surface) of the metal separator 53 is used. ) Side may not have a dent.

  As shown in FIG. 4, the intermediate region A <b> 3 exists along the entire circumference along the through hole 58. For this reason, the void | hole Ha in the junction part (Ag brazing) 61 is reduced over the perimeter of the through-hole 58, and joining strength improves.

(Comparative example)
FIG. 6 corresponds to FIG. 5 and is an enlarged cross-sectional view of a separator-equipped fuel cell single cell 50x according to a comparative example.
In the separator-equipped fuel cell single cell 50x, the gap G at the junction 61 is uniform. That is, unlike the separator-equipped fuel cell unit cell 50, there is no difference in the gaps G1, G2, G3 in the inner peripheral area A1, the outer peripheral area A2, and the intermediate area A3. As a result, the bubbles entrained in the Ag solder at the time of manufacturing (at the time of brazing) are difficult to escape to the outside. As a result, the bonding strength of the bonding portion 61 is lowered by maintaining the holes (bubbles) Ha in the bonding portion 61 (Ag brazing).

  7 and 8 are cross-sectional photographs of the separator-equipped fuel cell unit cell 50 according to the example and the comparative example, respectively. It can be seen that in the comparative example, the proportion of the voids (bubbles) Ha in the joint portion 61 (Ag brazing) is larger in the comparative example than in the example. As a result, the bonding strength decreases. In FIGS. 7 and 8, the vertical direction is doubled from the horizontal direction for ease of viewing.

(Second Embodiment)
A second embodiment will be described. FIG. 9 is a cross-sectional view of a fuel battery cell 40a according to the second embodiment. FIG. 10 is an enlarged sectional view in the frame A of the separator-equipped fuel cell single cell 50a.

The separator-attached fuel cell single cell 50 a has a sealing portion 62 in addition to the joint portion 61.
The sealing portion 62 is disposed along the through hole 58 over the entire circumference on the side of the through hole 58 (inner peripheral side) from the joint portion 61, and the lower surfaces of the fuel cell single cell 44 and the metal separator 53 (the first side). 1 main surface) is sealed. Since the sealing portion 62 is disposed closer to the through hole 58 than the joint portion 61, the joint portion 61 is not in contact with the oxidant gas, and oxygen from the oxidant gas flow path 47 side to the joint portion 61 is eliminated. Movement is prevented. As a result, it is possible to prevent the occurrence of voids in the junction 61 due to the reaction between hydrogen and oxygen and gas leakage, and thus the reliability of the junction 61 can be further improved.

  When there is no sealing part 62, the junction part 61 (Ag wax) is exposed to both oxidant gas and fuel gas. In this case, oxygen and hydrogen diffuse in the junction 61 and react with each other, so that voids are generated later and gas leakage may occur. Between the fuel cell single cell 44 on the through hole 58 side and the first main surface, the sealing portion 62 is disposed over the entire circumference along the through hole 58, so that the joining portion 61 (Ag row) is exposed. It is possible to use only oxidant gas or fuel gas. As a result, the reaction between oxygen and hydrogen in the junction 61 (Ag solder) can be suppressed, and the generation of voids in the Ag solder can be reduced. Further, the sealing portion 62 may seal the joint portion 61 so as to cover a part of the upper surface (second main surface) of the metal separator 53.

The sealing part 62 has a width of 0.2 to 4 mm and a thickness of 10 to 80 μm, for example.
Specifically, the sealing part 62 can be comprised from sealing materials, such as glass, glass ceramics (crystallized glass), and the composite of glass and ceramics.

Further, as described above, the bonding strength between the metallic separator 53 and the bonding portion (Ag brazing) 61 is increased by reducing the ratio of pores (bubbles) in the bonding portion 61 (Ag brazing). Yes. For this reason, even if stress is applied to the separator-attached fuel cell single cell 50, the joint 61 can relieve the stress applied to the sealing portion 62 and prevent the sealing portion (including glass) 62 from cracking. Therefore, it can prevent that the junction part 61 is exposed to oxidizing gas or fuel gas, and can prevent a gas leak more reliably.

  Further, due to the difference in the thermal expansion coefficient between the single fuel cell 44 and the metal separator 53, the thermal stress in the fuel cell stack, etc., the metal separator 53 and the sealing portion 62 (glass) at position P in FIG. ) Is applied to the interface, but since the tensile stress is absorbed by improving the bonding strength of the bonding portion 61, the sealing portion 62 (glass) is difficult to break.

(Manufacturing method of separator-equipped fuel cell unit cell 50, 50a according to the embodiment)
The separator-equipped fuel cell unit cell 50a can be manufactured by the following manufacturing methods 1 and 2.
A. Manufacturing method 1
11-13 is a figure showing the manufacturing process of the fuel cell single cell 50, 50a with a separator which concerns on the manufacturing method 1. FIG.

(1) Preparation of single fuel cell 44 and metallic separator 53 The single fuel cell 44 and metallic separator 53 are prepared. As described above, the fuel cell single cell 44 is configured by sandwiching the solid electrolyte layer 56 between the air electrode 55 and the fuel electrode 57. Here, unlike the manufacturing method 2, the original metal separator 53 does not have a dent.

(2) Arrangement of brazing material (see FIG. 11)
A brazing material containing Ag is disposed on one or both of the single fuel cell 44 and the metal separator 53. Here, the brazing material 611 is disposed on both the fuel cell single cell 44 and the metal separator 53, but it is also possible to dispose only one of them.

  Here, the brazing material 611 is disposed in a brazing region (region of width D0), which is at least part of a region where the fuel cell single cell 44 and the lower surface (first main surface) of the metal separator 53 face each other. .

(3) Load application (see Fig. 11)
The fuel cell single cell 44 and the first main surface of the metal separator 53 are arranged to face each other and a load is applied. Here, the load is applied prior to the melting (heating) of the brazing material 611, but the load may be applied after the heating and before the brazing material is cured.

FIG. 14 is a cross-sectional view showing a cross-sectional shape in the XY plane of a joining jig (heavy stone) Tp for applying a load. The joining jig Tp has a cylindrical shape and applies a load to the intermediate region A3. That is, a load is applied from the upper surface (second main surface) of the metal separator 53 with a width D3 narrower than the width D0 of the brazing region. The widths D0 and D1 to D3 mean lengths in the direction from the through hole 58 of the metal separator 53 toward the outer periphery C of the metal separator 53. That is, it is the length in the X direction shown in FIGS.
Here, since the joining jig Tp has a cylindrical shape, a load is applied over the entire circumference along the through hole 58 of the metallic separator 53.

(4) Joining (see Fig. 12)
The joining portion 61 is formed by melting the brazing material 611 while applying a load, and the fuel cell single cell 44 and the first main surface of the metallic separator 53 are joined.

  Here, the brazing material is melted in the atmosphere (atmospheric brazing). This is to prevent a change in the characteristics of the air electrode 55. In air brazing, an oxide film is formed at the brazing interface, so that the contact angle of the brazing portion is larger than in brazing in a vacuum or reducing atmosphere. For this reason, it becomes easy for the brazing part to entrap bubbles, and the strength of the joining part 61 (brazing) decreases due to the holes Ha (bubbles), and the joining may peel off and gas leaks.

By applying a load with a width D3 that is narrower than the width D0 of the brazing region, it is possible to prevent the holes Ha caught in the joint 61 from staying. That is, the metal separator 53 is recessed by applying a load from the upper surface (second main surface) of the metal separator 53 with a width narrower than the width D3 of the brazing region. For this reason, the Ag wax flows and it becomes easy to expel the air holes Ha caught in the Ag wax to the outside. That is, in accordance with the flow of Ag wax, the bubbles Ha move from the center to the end and are pushed out (see FIG. 12).
Further, since the metal separator 53 is recessed, a slope is formed in the metal separator 53, so that the bubbles Ha can be easily driven out from the end (see FIG. 12).

  The width D0 of the brazing region is, for example, 1.5 to 6 mm, and the width D3 of the region to which the load is applied is narrower by the widths D1 and D2 (0.5 mm or more) than the width of the brazing region. 0.5-5 mm.

  As described above, a region to which a load is applied exists along the entire circumference along the through hole 58 of the metal separator 53. For this reason, the void | hole Ha in the junction part 61 (Ag brazing | wax) is reduced over the perimeter of the through-hole 58, and joining strength improves.

(5) Sealing (see FIG. 13)
The sealing part 62 is formed using the sealing material containing glass, and the 1st main surface of the fuel cell single cell 44 and the metal separator 53 is sealed. Along the through hole 58, the entire circumference is disposed on the through hole 58 side (inner peripheral side) with respect to the joint portion 61, and the space between the fuel cell single cell 44 and the lower surface (first main surface) of the metal separator 53 is between. Seal.
In the case of the separator-equipped fuel cell unit cell 50, this sealing step is omitted.

  As described above, the separator-attached fuel cell single cells 50 and 50a shown in FIGS. 4, 5, 7 and 10 are produced. In the separator-equipped fuel cell unit cell 50 or the like, by applying a load with a width D3 narrower than the width D0 of the brazing region, the joint portion 61 is formed in the inner peripheral region A1, the outer peripheral region A2, and the intermediate region A3. It is divided. That is, basically, the region where the load is applied corresponds to the intermediate region A3.

  However, this correspondence does not necessarily mean that the boundary between the region to which the load is applied and the intermediate region A3 completely coincide. This is because the slope shape of the metallic separator 53 differs depending on the magnitude of the applied load and the material (rigidity, etc.) of the metallic separator 53. That is, for the sake of easy understanding of the correspondence, the same symbol G3 or the like is used for the width of the area to which the load is applied and the width of the intermediate area A3.

In the above description, the case of air brazing is described as an example. In air brazing, an oxide film is formed at the brazing interface. Therefore, compared to brazing in a vacuum or reducing atmosphere, the contact angle of the brazing part is large, and bubbles are easily involved. That is, in atmospheric brazing, it is significant to prevent the generation of holes Ha by applying a load with a width D3 narrower than the width D0 of the brazing region.
On the other hand, even when brazing is performed in a vacuum or a reducing atmosphere, there is a considerable possibility that holes Ha are generated. Atmospheric gas (or gas generated from the constituent material of the separator-equipped fuel cell unit cell 50) may be caught in the joint 61 (brazing). That is, even in brazing in a vacuum or a reducing atmosphere, it is meaningful to prevent the generation of voids Ha in the joint 61 by applying a load with a width D3 narrower than the width D0 of the brazing region. .

B. Manufacturing method 2
FIG. 15 is a diagram showing a manufacturing process of the separator-equipped fuel cell unit cell 50 a according to the manufacturing method 2.

(1) Preparation of single fuel cell 44 and metal separator 53 (see FIG. 15)
A single fuel cell 44 and a metal separator 53 are prepared. Here, unlike the manufacturing method 1, a metal separator 53 having a recess R is used.

(2) Arrangement of brazing material (see FIG. 15)
(3) Load application (see Fig. 15)
(4) Joining Thereafter, the brazing material is arranged, a load is applied, and joining is performed in the same process as in manufacturing method 1. The slope of the metal separator 53 corresponding to the dent R facilitates the expulsion of bubbles to the outside, prevents the occurrence of holes Ha in the joint 61, and improves the joint strength.
Even in this case, it is preferable to apply the load with a width D3 narrower than the width D0 of the brazing region. Moreover, it is preferable that the shape of the dent R corresponds to the area to which the load is applied.

  As described above, the separator-attached fuel cell single cells 50 and 50a shown in FIGS. 4, 5, 7, 10 and the like can be produced as in the case of the production method 1.

(Manufacturing method of separator-equipped fuel cell unit cell 50x according to a comparative example)
FIG. 16 corresponds to FIG. 11 and is a diagram illustrating a manufacturing process of the separator-equipped fuel cell unit cell 50x according to the comparative example. Here, a load is applied from the upper surface (second main surface) of the metal separator 53 with a width D3x wider than the width of the brazing region, using a joining jig (heavy stone) Tpx.

  In this case, as shown in FIG. 6, the metal separator 53 of the separator-equipped fuel cell single cell 50x does not have a recess. That is, the gap G between the joint portions 61 is uniform. As a result, the bubbles entrained in the Ag solder at the time of manufacturing (at the time of brazing) are difficult to escape to the outside, and the bubbles in the joint 61 (Ag braze) are held, so that the joint strength of the joint 61 is maintained. Decreases.

FIG. 17 is a graph comparing the peel test results of the separator-equipped fuel cell unit cell 50 according to the example and the comparative example.
FIG. 18 is a diagram for explaining the peel test. A cut Lc is made in the metal separator 53, and the metal separator 53 is pulled therefrom to be peeled off from the single fuel cell 44 at the joint 61.

  As shown in FIG. 17, in the example and the comparative example, at the displacement amount Ms (= 4.5 mm), the stresses F1 (= 49 N) and F0 (= 29 N) are started, and the peeling at the joint portion 61 is started. It was. Thus, it can be seen that the bonding strength at the bonding portion 61 is higher in the example than in the comparative example.

(Other embodiments)
Embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and modified. The expanded and modified embodiments are also included in the technical scope of the present invention.

10 Solid oxide fuel cells 11, 12 End plates 21, 22 (22a, 22b), 23 (23a, 23b) Bolts 31, 32, 33 Through hole 35 Nut 40 Fuel cell 41, 45 Interconnector 42a, 42b, Current collector 43 Frame portion 44 Fuel cell single cell 46 Opening 47 Oxidant gas flow path 48 Fuel gas flow path 50 Fuel cell single cell with separator 51 Air electrode frame 52 Insulating frame 53 Metal separator 54 Fuel electrode frame 55 Air electrode 56 Solid electrolyte layer 57 Fuel electrode 58 Through hole 61 Joining portion 62 Sealing portion 611 Brazing material A1 Inner peripheral region A2 Outer peripheral region A3 Intermediate region Ha Hole (bubble)
Tp joining jig

Claims (8)

A fuel cell single cell having an air electrode, a fuel electrode, and a solid electrolyte layer disposed between them;
A plate-shaped metal separator having a first main surface, a second main surface, and a through-hole penetrating between the first main surface and the second main surface;
A joining portion made of a brazing material containing Ag, joining the single fuel cell and the first main surface of the metal separator;
A separator-equipped fuel cell unit cell comprising:
An inner peripheral region disposed on the through-hole side of the metallic separator, an outer peripheral region disposed outside the inner peripheral region, and the inner peripheral region and the outer peripheral region. Is divided into intermediate areas arranged between
The distance between the single fuel cell and the first main surface in the intermediate region is smaller than the distance between the single fuel cell and the first main surface in the outer peripheral region and the inner peripheral region. A separator-equipped fuel cell single cell. The separator-equipped fuel cell unit cell according to claim 1, wherein a recess corresponding to the second main surface side of the metallic separator is provided at a location corresponding to the intermediate region. The separator-equipped fuel cell unit cell according to claim 1, wherein the intermediate region exists along the entire circumference along the through hole. A sealing member that is disposed over the entire circumference along the through hole between the single unit cell of the fuel cell and the first main surface on the side of the through hole with respect to the joint, and has a sealing material including glass The fuel cell single cell with a separator according to any one of claims 1 to 3, further comprising a section. A fuel cell single cell with a separator according to any one of claims 1 to 4,
A fuel cell stack comprising a plurality of the fuel cell stacks. A method of manufacturing a separator-equipped fuel cell unit cell,
A fuel cell single cell having an air electrode, a fuel electrode, and a solid electrolyte layer disposed between them, and the first main surface, the second main surface, and between the first main surface and the second main surface Preparing a plate-like metal separator having a through-hole,
Disposing a brazing material containing Ag on one or both of the single fuel cell and the metal separator;
Arranging the single fuel cell and the first main surface to face each other;
Joining the fuel cell single cell and the first main surface by melting the brazing material while applying a load,
In the step of disposing the brazing material, the brazing material is disposed in a brazing region, which is at least a part of a region facing the fuel cell single cell and the first main surface,
In the bonding step, the load is applied with a width narrower than the width of the brazing region from the second main surface of the metallic separator.
A method for producing a separator-equipped fuel cell unit cell. The region to which the load is applied exists over the entire circumference along the through hole of the metal separator.
The manufacturing method of the fuel cell single cell with a separator of Claim 6 characterized by the above-mentioned. In the joining step, the brazing material is melted in the atmosphere.
A method for producing a separator-equipped fuel cell unit cell according to claim 6 or 7.

Images