JP2007317610A - Cell stack and fuel battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cell stack and a fuel battery which can improve bonding strength of a plate collector member to a fuel battery cell. <P>SOLUTION: In the cell stack, respective plate collector members 20 are placed in spaces between a plurality of fuel battery cells 1, in each of which a solid electrolyte layer 3 is sandwiched between an oxygen electrode layer 4 and a fuel electrode layer 2, and the plate collector member 20 is bonded to the oxygen electrode layer 4 of the fuel battery cell 1 for the fuel battery cell 1 and the plate collector member 20 to be electrically connected. The oxygen electrode layer 4 has a first oxygen electrode layer 4a placed on the solid electrolyte layer 3 and a second oxygen electrode layer 4b placed on the first oxygen electrode layer 4a. The first oxygen electrode layer 4a is made of conductive ceramic particles in an average size less than the particles of the second oxygen electrode layer 4b, one main side surface of the plate collector member 20 is bonded to the first oxygen electrode layer 4a, and a side surface of the plate collector member 20 is bonded to the second oxygen electrode layer 4b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cell stack and a fuel cell in which a plate current collecting member is disposed between a plurality of fuel cells, and the fuel cell and the plate current collecting member are electrically connected.

  In recent years, various fuel cells in which a cell stack of fuel cells is accommodated in a storage container have been proposed as next-generation energy. A solid oxide fuel cell is configured by storing a cell stack in which a plurality of fuel cells are electrically connected in a storage container, and flowing a fuel gas (hydrogen) to the fuel electrode layer side of the fuel cell, Electricity is generated at a high temperature of 600 to 900 ° C. by flowing air (oxygen) to the layer (also referred to as oxygen electrode layer) side. In order to electrically connect the fuel cells, a felt-like or plate-like current collecting member has been conventionally used.

Conventionally, as a cell stack, a plate-shaped current collecting member is disposed between fuel cells, the fuel cell and the plate-shaped current collecting member are joined with a conductive paste, and the space between the fuel cell and the current collecting member is What was electrically connected is known (for example, refer patent document 1).
JP 2005-19239 A

  However, in the conventional cell stack described in Patent Document 1, since the plate-like current collecting member is joined to the oxygen electrode layer of the fuel cell by a conductive paste, the plate-like current collecting member is joined to the oxygen electrode layer. There was a problem of low strength.

  That is, the oxygen electrode layer of the fuel cell is porous because oxygen needs to be supplied to the solid electrolyte layer, and the bonding strength of the oxygen electrode layer to the solid electrolyte layer is low. Since it is necessary to join the plate-like current collector member on the top, the bonding strength between the oxygen electrode layer and the plate-like current collector member is also reduced, and the plate-like current collector member is peeled off from the fuel cell, resulting in power generation. There was a problem that the output decreased.

  It is an object of the present invention to provide a cell stack and a fuel cell that can improve the bonding strength of a plate-like current collecting member to a fuel cell, reduce connection resistance, and achieve high output.

  In the cell stack of the present invention, a plate-shaped current collecting member is disposed between a plurality of fuel cells each having a solid electrolyte layer sandwiched between an oxygen electrode layer and a fuel electrode layer, and the oxygen of the fuel cell A cell stack formed by joining the plate current collector to an electrode layer and electrically connecting the fuel cell and the plate current collector, wherein the oxygen electrode layer is disposed on the solid electrolyte layer. And a second oxygen electrode layer provided on the first oxygen electrode layer, wherein the first oxygen electrode layer is formed from the second oxygen electrode layer. Are formed of conductive ceramic particles having a small average particle diameter, and one side main surface of the plate-like current collecting member is joined to the first oxygen electrode layer, and the side surface of the plate-like current collecting member is the second oxygen It is characterized by being bonded to the extreme layer. The first oxygen electrode layer is preferably made of conductive ceramic particles having an average particle size of 1 μm or less.

  In such a cell stack, the first oxygen electrode layer made of fine conductive ceramic particles is firmly bonded on the dense solid electrolyte layer, and further, the first oxygen electrode layer is made of fine conductive ceramic particles firmly bonded to each other. High strength due to bonding. Since the main surface of the plate-like current collecting member is joined on such a first oxygen electrode layer, the bonding strength of the first oxygen electrode layer to the solid electrolyte layer can be improved, and consequently the solid of the plate-like current collecting member. Bonding strength to the electrolyte layer can be improved.

  The cell stack of the present invention is characterized in that the first oxygen electrode layer is denser than the second oxygen electrode layer. In such a cell stack, the bonding strength of the first oxygen electrode layer to the solid electrolyte layer can be improved, and the bonding strength of the plate current collector to the first oxygen electrode layer can be improved. The bonding strength of the member to the solid electrolyte layer can be improved.

Furthermore, the cell stack of the present invention is characterized in that the first oxygen electrode layer and the second oxygen electrode layer are made of a perovskite complex oxide containing La and Fe. In such a cell stack, a first oxygen electrode layer and a second oxygen electrode layer is a perovskite-type composite oxide containing La and Fe, for example, to become a LaSrCoFeO ₃ system, unlike the LaMnO ₃ system, the oxygen ion-conducting Even if it is the 1st oxygen electrode layer which has the mixed electroconductivity which has a property and electronic conductivity, and consists of a fine and dense electroconductive ceramic particle, the function as an oxygen electrode can be exhibited. Therefore, even if the denser first oxygen electrode layer is formed, the function as the oxygen electrode can be exhibited, and the bonding strength of the plate-like current collecting member to the solid electrolyte layer can be improved.

  In the cell stack of the present invention, the plate-like current collecting member has a Cr diffusion preventing layer containing Zn on the surface of a heat-resistant alloy containing Cr, and a perovskite type composite containing La and Fe or Mn. A coating layer containing an oxide and a zinc oxide is sequentially laminated.

  Further, the plate-like current collecting member contains at least part of components constituting the Cr diffusion preventing layer containing Zn and the oxygen electrode layer of the fuel cell on the surface of the heat-resistant alloy containing Cr. It is characterized by being sequentially laminated with a coating layer containing a perovskite complex oxide and zinc oxide.

  In such a cell stack, the Cr diffusion prevention layer can prevent Cr in the heat-resistant alloy from diffusing outside, and realizes a cell stack that can prevent so-called Cr poisoning of the fuel cell. can do. Moreover, even if it arrange | positions a current collection member between fuel cell and joins a current collection member and the oxygen electrode layer of a fuel cell, a coating layer contains at least one part of the component which comprises an oxygen electrode layer. Because it contains a complex oxide having a perovskite structure and a zinc oxide constituting a Cr diffusion preventing layer and a conductive layer, or because it contains a perovskite type complex oxide and zinc oxide containing La, Fe, or Mn The coating layer can have an intermediate thermal expansion coefficient between the oxygen electrode layer and the heat-resistant alloy, so that the difference in the coefficient of thermal expansion between the oxygen electrode layer and the heat-resistant alloy of the fuel cell can be reduced. The peeling between the layer and the plate-like current collecting member can be suppressed, and the electrical connection reliability between the fuel cells can be improved.

  That is, as the plate-like current collecting member, an alloy having a high conductivity is adopted, and since it is used at a high temperature, a heat-resistant alloy is preferably adopted. As such a heat-resistant alloy having a high conductivity, Cr is 10%. An alloy containing -30% by mass is generally used. However, when a current collecting member made of an alloy containing Cr is disposed between fuel cells and a plurality of fuel cells are electrically connected, if the fuel cell is operated for a long time, Cr in the current collecting member It diffuses outside the current collecting member, and the diffused Cr reaches the interface between the oxygen electrode layer and the solid electrolyte layer and degrades the activity. This phenomenon is referred to as so-called Cr poisoning, and causes a decrease in the power generation capacity of the fuel cell.

  In order to prevent such Cr poisoning, conventionally, the surface of an alloy containing Cr is coated with Mn, Fe, Co, and Ni (Japanese Patent Publication No. Hei 11-501764). When the surface of the containing alloy is coated with Mn, Fe, Co, and Ni, it is possible to suppress the diffusion of Cr in the Cr-containing alloy to the outside to some extent, but there is still much diffusion of Cr. In addition, a current collecting member is disposed between the fuel cells, and the current collecting member and the fuel cell member are joined to achieve electrical connection. The current collecting member is attached to the surface of the alloy containing Cr. When a coating layer of Mn, Fe, Co, Ni, etc. is provided, the current collector member is formed by the difference in thermal expansion coefficient between the coating layer on the surface of the alloy and the member of the fuel cell to which the coating layer is joined. There is a possibility that the fuel cells are peeled off and the fuel cells cannot be electrically connected. On the other hand, in the cell stack of the present invention, as described above, Cr in the heat-resistant alloy can be prevented from diffusing outside by the Cr diffusion preventing layer, and so-called Cr poisoning of the fuel cell is prevented. The cell stack can be realized, and the coating layer can have an intermediate thermal expansion coefficient between the oxygen electrode layer and the heat-resistant alloy. The difference in coefficient of thermal expansion can be reduced, peeling between the oxygen electrode layer and the plate current collector can be suppressed, and the reliability of electrical connection between fuel cells can be improved.

  The fuel cell of the present invention is characterized in that the cell stack is stored in a storage container. In such a fuel cell, the joining strength of the plate-like current collecting member to the fuel cell can be improved, and the long-term reliability of the fuel cell can be improved.

  In the cell stack of the present invention, the first oxygen electrode layer is firmly bonded onto the solid electrolyte layer, and the main surface of the plate current collector is firmly bonded to the first oxygen electrode layer. The bonding strength of the member to the solid electrolyte layer can be improved.

  FIG. 1 shows a cell stack according to the present invention. The cell stack is configured by arranging a plate-like current collecting member 20 between a plurality of fuel cells 1 and electrically connecting the plurality of fuel cells 1. ing.

  FIG. 2 is a perspective view showing the plate-like current collecting member 20, and FIGS. 3 and 4 are explanatory views showing a covering state of the surface layer 202 of the plate-like current collecting member 20 shown in FIG. 3 is a cross-sectional view taken along line AA shown in FIG. 2, and FIG. 4 is an enlarged cross-sectional view showing a joint structure with the fuel cell shown in FIG. As shown in FIG. 2, the plate-like current collecting member 20 is formed, for example, by processing a heat-resistant alloy plate into a comb blade shape and alternately bending adjacent blades to the opposite side.

  The current collecting member 20 is configured by providing a surface layer 202 made of a material containing Zn on the surface of a heat resistant alloy (hereinafter referred to as a current collecting base material) 201 made of an alloy containing Cr. Here, the surface layer 202 is configured such that the Cr diffusion preventing layer 202a and the covering layer 202b are laminated on the surface of the current collecting base material 201 in this order. Further, the current collecting member 20 is not limited to the shape shown in FIG. 2, and may be, for example, a cylindrical shape or a mesh shape.

As the current collecting base material 201, an alloy containing 10 to 30% by mass of Cr having high conductivity and heat resistance, for example, an Fe—Cr alloy, a Ni—Cr alloy, or the like is used. The Cr diffusion preventing layer 202a is a metal oxide having at least one of a spinel structure, a corundum structure, a wurtzite structure, and a rock salt structure, or a structure similar to these. In particular, the Cr diffusion preventing layer 202a is made of Zn—Mn spinel and may contain elements such as Fe and Cr. The Cr diffusion preventing layer 202a is formed from a Zn—Mn spinel, for example, (Zn, Mn) Mn ₂ O ₄ . Since the metal oxide containing Zn and Mn hardly dissolves Cr, it has the effect of suppressing the diffusion of Cr.

A conductive layer containing zinc as an element may be provided at the interface between the Cr diffusion preventing layer 202a and the coating layer 202b. This conductive layer contains ZnO, and pure ZnO is an insulator. However, Zn _{1 + δ} O becomes a cation-rich n-type semiconductor, and by adding a high-valence impurity element, n 1 Type impurity semiconductor. Here, since Zn in ZnO is a +2 valent ion, conductivity is imparted by dissolving a metal element that becomes +3 or higher ion. Al and Fe are particularly desirable as the metal element that becomes +3 or more ions. The conductive layer made of zinc oxide in which Al and Fe are solid-solved preferably has a conductivity of ¹ S · cm ⁻¹ or more at 550 ° C. to 900 ° C. near the power generation temperature in the atmosphere.

The coating layer 202b contains a composite oxide having a perovskite structure and zinc oxide containing at least a part of the components constituting the oxygen electrode layer of the fuel cell, and specifically includes La and Fe or Mn. It contains perovskite complex oxide and zinc oxide. More specifically, it can be composed of a perovskite complex oxide used for forming an oxygen electrode layer or the like, for example, LaFeO ₃ or LaMnO ₃ and ZnO.

Such a coating layer 202b contains LaFeO ₃ and LaMnO ₃ systems used for the oxygen electrode layer, a Cr diffusion prevention layer 202a, and ZnO used for the conductive layer. It has an intermediate thermal expansion coefficient between the Cr diffusion preventing layer 202a of the electric base material and the conductive layer, and can improve the reliability of bonding between the fuel cell and the current collecting member, and has excellent long-term reliability with little voltage drop. A fuel cell can be obtained.

  Since Cr in the current collecting base material 201 is vaporized and diffused to the outside, the Cr diffusion preventing layer 202a is preferably provided densely so as to cover at least the entire surface of the current collecting base material 201.

  If the Cr diffusion preventing layer 202a is 2 μm or less, particularly 1 μm or less, the conductivity as the current collecting member 20 is not affected even if it is insulating to some extent.

  In the case of dipping, the Cr diffusion preventing layer 202a of the present invention can be formed by immersing the current collecting base material 201 in a paste containing Zn or ZnO, and by heat treatment or heating during power generation.

That is, when the Cr diffusion prevention layer is made of a Zn—Mn spinel, for example, using a current collecting base material 201 containing Mn, this is made of, for example, Zn or ZnO and Fe ₂ O ₃ or Al ₂ O. ₃ is immersed in a paste containing ₃ and heat-treated to form a Cr diffusion preventing layer 202a made of Zn-Mn spinel on the surface of the current collecting base material 201, and ZnO on the surface of the Cr diffusion preventing layer 202a. A conductive layer containing Fe or Al can be formed.

In the case of using the current collector substrate 201 containing no Mn, it, for example, a Zn or ZnO, and _Fe 2 _{O 3} or _Al 2 _{O 3,} it was immersed in the paste in containing Mn, by heat treatment Further, a Cr diffusion preventing layer 202a made of Zn—Mn spinel is formed, and a conductive layer containing Fe or Al in ZnO can also be formed.

Furthermore, after forming the Cr diffusion prevention layer 202a made of Zn—Mn spinel on the current collection base material 201, the current collection base material 201 on which the Cr diffusion prevention layer 202a is formed is made of, for example, Zn or ZnO and Fe _2. A conductive layer containing Fe or Al in ZnO is formed on the Cr diffusion prevention layer 202a made of Zn-Mn spinel by dipping in a paste containing O ₃ or Al ₂ O ₃ and heat-treating. You can also

When the coating layer 202b is formed on the surface of the conductive layer, it is immersed in a paste containing a perovskite structure, a LaFeO ₃ system, a LaMnO ₃ system, and ZnO used for forming an oxygen electrode layer, etc., and heat-treated. Can be formed.

When forming the coating layer 202b on the surface of the Cr diffusion preventing layer 202a, the current collecting base material 201 is immersed in a paste containing Zn—Mn spinel and heat-treated to form the Cr diffusion preventing layer 202a. Then, it can be formed by dipping in a paste containing a perovskite structure, LaFeO ₃ system, LaMnO ₃ system, and ZnO used for forming an oxygen electrode layer and heat-treating.

  The Cr diffusion prevention layer 202a is formed by using a method such as plating or vapor deposition in addition to dipping (a dip coating method in which the current collecting base material is immersed in a liquid containing zinc for the Cr diffusion prevention layer). Dipping is desirable in terms of cost.

  Although the thickness of a conductive layer is based also on the lifetime of the current collection base material 201, in the case of dipping, 1-100 micrometers is preferable and 5-50 micrometers is more preferable. By setting the thickness to 5 μm or more, generation of voids due to air entrainment or the like can be prevented. Further, by setting the thickness to 50 μm or less, the internal stress due to the difference in thermal expansion from the current collecting base material 201 can be suppressed to the minimum, the decrease in conductivity can be suppressed, and the formation can be facilitated.

  As shown in FIG. 5, the fuel battery cell 1 is a hollow flat plate type, and includes a flat support substrate 10, a fuel electrode layer 2, a solid electrolyte layer 3, an oxygen provided around the flat support substrate 10. The electrode substrate 4, the interconnector 5, and the oxygen electrode material layer 14, and the support substrate 10 further includes a plurality of fuel gases extending in a direction (cell length direction) intersecting with the stacking direction of the fuel cells 1. It is configured to have a passage 16.

The support substrate 10 is made of, for example, a porous and conductive material, and has a flat cross section and arcuate portions at both ends of the flat portion as shown in FIG. A porous fuel electrode layer 2 is provided so as to cover one of the opposing surfaces of the flat portion and arc-shaped portions at both ends thereof, and a dense solid electrolyte layer 3 is laminated so as to cover the fuel electrode layer 2. Further, an oxygen electrode layer 4 made of a porous conductive ceramic is laminated on the solid electrolyte layer 3 so as to face the fuel electrode layer 2. A dense interconnector 5 is formed on the surface of the support substrate 10 that faces the surface on which the electrode layers 2 and 4 are provided. An oxygen electrode material layer 14 made of an oxygen electrode material is formed on the surface of the interconnector 5. Here, the oxygen electrode material is made of an oxide such as La (Fe, Mn) O ₃ or (La, Sr) (Co, Fe) O ₃ having a perovskite structure. However, the oxygen electrode material layer 14 is not necessarily formed. As shown in FIG. 5, the fuel electrode layer 2 and the solid electrolyte layer 3 are configured to extend to both sides of the interconnector 5 so that the surface of the support substrate 10 is not exposed to the outside.

  In the fuel cell 1 having such a structure, the portion of the fuel electrode layer 2 facing the oxygen electrode layer 4 operates as a fuel electrode to generate electric power. That is, an oxygen-containing gas such as air is allowed to flow outside the oxygen electrode layer 4 and a fuel gas (hydrogen) is supplied to the gas passage 16 in the support substrate 10 and heated to a predetermined operating temperature. Then, an electrode reaction of the following formula (1) occurs, and power is generated by, for example, an electrode reaction of the following formula (2) occurring in the portion that becomes the fuel electrode of the fuel electrode layer 2.

Oxygen electrode: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte) (1)
Fuel electrode: O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻ (2)
The current generated by the electrode reaction is collected through the interconnector 5 attached to the support substrate 10.

  As shown in FIGS. 1 and 4, a current collecting member 20 is interposed and electrically connected between the plurality of fuel cells 1, thereby forming a cell stack. That is, the current collecting member 20 is joined to the oxygen electrode layer 4 of one fuel cell 1 and electrically connected to the interconnector 5 of the other fuel cell 1 adjacent thereto, thereby The fuel cells 1 are electrically connected in series to form a cell stack.

  The oxygen electrode layer 4 includes a first oxygen electrode layer 4a formed on the solid electrolyte layer 3 and a second oxygen electrode layer 4b provided on the first oxygen electrode layer 4a. The first oxygen electrode layer 4a and the second oxygen electrode layer 4b are made of conductive ceramic particles. The average particle diameter of the first oxygen electrode layer 4a is made of conductive ceramic particles smaller than the average particle diameter of the second oxygen electrode layer 4b, and the main surface on one side of the comb blade of the plate-like current collecting member 20 is the first one. The side surfaces of the comb blades of the plate-like current collecting member 20 are joined to the second oxygen electrode layer 4b.

  The first oxygen electrode layer 4a is formed using conductive ceramic particles having an average particle diameter (laser diffraction scattering method 50%) of 0.7 μm or less, and has a thickness of 20 μm or less. The second oxygen electrode layer 4b has an average value of The particle diameter (laser diffraction scattering method 50%) is formed using conductive ceramic particles having a thickness of 2 to 30 μm and has a thickness of 100 μm or more. The density of the first oxygen electrode layer 4a is set higher than that of the second oxygen electrode layer 4b. In other words, the porosity of the first oxygen electrode layer 4a is lower than that of the second oxygen electrode layer 4b. Has been.

  The first oxygen electrode layer 4a is formed using primary particles having an average particle diameter (laser diffraction scattering method 50%) of 0.7 μm or less, and the second oxygen electrode layer 4b is a primary particle of the first oxygen electrode layer 4a. Are formed using secondary particles (for example, prepared by spray-drying a slurry containing primary particles), whereby the average particle diameter of the first oxygen electrode layer 4a is the second oxygen electrode. The average particle diameter of the layer 4b is smaller, and the porosity of the first oxygen electrode layer 4a is smaller than that of the second oxygen electrode layer 4b and becomes dense.

  In such a cell stack, the first oxygen electrode layer 4a made of fine conductive ceramic particles is firmly bonded on the dense solid electrolyte layer 3, and the plate shape is formed on the first oxygen electrode layer 4a. Since the main surface of the current collecting member 20 is firmly joined, the joining strength of the plate-like current collecting member 20 to the solid electrolyte layer 3 can be improved. When the thickness of the oxygen electrode layer 4 is insufficient, an intermediate layer made of the same material as the second oxygen electrode layer 4b is formed between the first oxygen electrode layer 4a and the second oxygen electrode layer 4b. You can also

  Moreover, the side surface of the plate-shaped current collection member 20 is joined to the second oxygen electrode layer 4b, whereby the bonding strength of the plate-like current collection member 20 to the solid electrolyte layer 3 can be further improved. In addition, although the meniscus of the 2nd oxygen electrode layer 4b is formed in the side surface of the plate-shaped current collection member 20, it simplified and described in FIG. This meniscus can also improve the bonding strength of the plate-like current collecting member 20 to the oxygen electrode layer 4. In FIG. 4, the thickness of the current collecting member 20 is exaggerated for easy understanding.

As the first oxygen electrode layer 4a and the second oxygen electrode layer 4b, a perovskite complex oxide containing La and Fe, for example, (La, Sr) (Co, Fe) O ₃ having a perovskite structure can be used. By using this composite oxide, even if the first oxygen electrode layer 4a is somewhat dense, it can have a function as an oxygen electrode.

  Further, the current collecting member 20 is joined to the oxygen electrode layer 4 of one fuel battery cell 1, but is also joined to the interconnector 5 (oxygen electrode material layer 14) of the other fuel battery cell 1 adjacent thereto. . The current collecting member 20 is joined to the interconnector 5 by using a comb blade of the current collecting member 20 on the joining layer 25 similar to the second oxygen electrode layer 4b formed on the oxygen electrode material layer 14 on the surface of the interconnector 5. It is performed by embedding and bonding the side surface to the bonding layer 25.

Here, the thermal expansion coefficient of each member will be described. At 750 ° C., the thermal expansion coefficient of a LaFeO ₃ system generally used as an oxygen electrode material of a fuel cell is 14 to 17 × 10 ⁻⁶ / ° C., and the LaMnO ₃ system is 10 to 11 × 10 ⁻⁶ / ° C., LaCrO ₃ system used as an interconnector is about 14 × 10 ⁻⁶ / ° C., and for the current collecting member 20, the current collecting substrate 201 is 11 × 10 ^−6. The Cr diffusion prevention layer 202a made of Zn—Mn spinel and the conductive layer containing Fe or Al in ZnO are 6 to 8 × 10 ⁻⁶ / ° C.

Therefore, when the fuel cell and the current collecting member are joined, stress based on the difference in thermal expansion is generated at the interface, but the coating layer 202b has a perovskite structure, LaFeO ₃ system used for forming an oxygen electrode layer or the like. In addition, since it contains LaMnO ₃ system and ZnO, it can have a desired coefficient of thermal expansion intermediate between the oxygen electrode layer and the current collecting base material 201 by changing the ratio thereof. Bonding reliability of the electric member can be improved.

A method for manufacturing the cell stack will be described. First, a slurry containing an air electrode material such as (La, Sr) (Co, Fe) O ₃ is applied to the surface of the solid electrolyte layer of the fuel cell by screen printing, and baked at a predetermined temperature to form the first oxygen The polar layer 4a is formed. Thereafter, a slurry containing an air electrode material such as (La, Sr) (Co, Fe) O ₃ is screen printed on the surface of the first oxygen electrode layer 4 a and the surface of the oxygen electrode material layer 14 of the interconnector 5. In this state, the current collecting member 20 is disposed between the plurality of fuel cells and pressed from both sides, whereby the comb blade of the current collecting member 20 comes into contact with the first oxygen electrode layer 4a, and the first The cell stack of the present invention is embedded in the coating film of the two oxygen electrode layer and the bonding layer, and in this state, the second oxygen electrode layer and the bonding layer are baked at a temperature lower than the baking temperature of the first oxygen electrode layer 4a. Can be formed.

  Although not shown, such a cell stack is arranged in a manifold to which fuel gas is supplied, and the fuel gas supplied into the manifold passes through the gas passage 16 of the fuel cell 1.

  In the fuel cell, the cell stack is accommodated in a storage container, and a fuel gas introduction pipe for supplying fuel gas such as city gas and an air introduction pipe for supplying air are disposed in the storage container. Composed.

First, 2 mol% of Fe ₂ O ₃ powder with an average particle diameter of 0.5 μm was converted into Fe in terms of Fe, and 1 mol% of Mn ₂ O ₃ powder with an average particle diameter of 0.4 μm was converted into Mn in terms of ZnO powder with an average particle diameter of 0.6 μm. A mixed powder prepared in a proportion, a solvent, a binder, and a dispersant were prepared to prepare a dipping liquid used for forming the Cr diffusion preventing layer 202a and the conductive layer.

  Next, a current collecting substrate made of an Fe—Cr heat resistant alloy plate (containing 75 mass% Fe, containing the remaining Cr, Mn, and Ni) having a thickness of 0.4 mm, a width of 20 mm, and a length of 120 mm is used as a dipping solution. In order to improve the wettability, the film was heat-treated in the atmosphere at 750 ° C., immersed in a dipping solution, applied to the entire surface of the current collecting substrate, and dried. Furthermore, a binder removal treatment was performed at a temperature of 100 ° C. for 1 hour, and subsequently at a temperature of 500 ° C. for 2 hours, followed by baking in a furnace at a temperature of 1050 ° C. for 2 hours to form a 10 μm thick conductive layer made of ZnO containing Fe. Then, a Cr diffusion preventing layer 202a made of Zn—Mn spinel and having a thickness of about 1 μm was formed between the conductive layer and the current collecting base material surface.

Next, ZnO powder having an average particle diameter of _0.6 μm and La _0.6 Sr _0.4 Co _0.4 Fe _0.6 O ₃ (LSCF) powder having an average particle diameter of 0.5 μm are in the ratio shown in Table 1. The mixture was mixed with a solvent (IPA) and a ZrO ₂ ball having a diameter of 15 mm and mixed in a rotary mill for 12 hours. The obtained mixed solution is dried at a temperature of 130 ° C., and the mixed powder is passed through 170 meshes. Furthermore, the mixed powder after the mesh pass, the acrylic binder, the solvent (mineral spirits), and the dispersant (DBP) were put in a polypot and mixed in a rotary mill for 12 hours. The mixed solution was dried at a temperature of 130 ° C., and a dipping solution for a coating layer was prepared using the mixed powder.

Next, the current collecting base material 201 on which the Cr diffusion preventing layer 202a and the conductive layer are formed is dipped in a dipping solution for a coating layer, and debinding is performed at a temperature of 130 ° C. for 30 minutes and subsequently at a temperature of 500 ° C. for 2 hours. Then, baking was carried out in a furnace at a temperature of 1050 ° C. for 2 hours to form a coating layer 202b having a thickness of 15 μm on the surface of the conductive layer, and a current collecting member was produced. Table 1 shows the coefficient of thermal expansion and conductivity at each weight composition ratio of ZnO and LSCF.

From Table 1, it can be seen that the coefficient of thermal expansion and the conductivity increase as the weight composition ratio of LSCF increases. Moreover, by optimizing the weight composition ratio of ZnO and LSCF, the thermal expansion coefficient of the oxygen electrode layer made of LSCF is 15 to 17 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the current collecting substrate is 6 to 8 ×. It has an intermediate coefficient of thermal expansion of 10 ⁻⁶ / ° C., and improves the reliability by suppressing peeling and voltage drop due to heat cycle when the fuel cell current collector and the fuel cell are joined. It becomes possible to do.

A cross section of a test piece having a weight composition ratio of 50:50 of ZnO and LSCF was confirmed by performing wavelength dispersion type EPMA (Electron Probe Micro-Analysis). JXA-8100 manufactured by JEOL Ltd. was used as the analyzer for EPMA, and the measurement conditions were an acceleration voltage of 15 kV, a probe current of 1.0 × 10 ⁻⁷ A, and an analysis area of 50 μm × 50 μm. Moreover, LiF was used for the spectroscopic crystal. As a result, it was confirmed that LSCF had no Cr diffusion.

Further, the air electrode material (primary particles) of (La, Sr) (Co, Fe) O ₃ having an average particle diameter (laser diffraction scattering method 50%) 0.4 μm is contained on the surface of the solid electrolyte layer of the fuel cell. The slurry to be applied was applied by screen printing and baked at 1150 ° C. to form a first oxygen electrode layer 4a having a thickness of 15 μm.

Thereafter, the surface of the first oxygen electrode layer 4a contains (La, Sr) (Co, Fe) O ₃ (secondary particles in which primary particles are aggregated) having an average particle diameter (laser diffraction scattering method 50%) of 3 μm. The second oxygen electrode layer slurry is applied by screen printing. In this state, the current collecting member 20 having a weight composition ratio of ZnO and LSCF of 50:50 is disposed as the coating layer, and the fuel cell side is disposed. By pressing, the comb blade of the current collecting member 20 is brought into contact with the first oxygen electrode layer 4a, embedded in the coating film of the second oxygen electrode layer, and the second oxygen electrode layer is bonded to the side surface of the comb blade. In this state, baking was performed at 1050 ° C., which is lower than the baking temperature of the first oxygen electrode layer 4a, to form a second oxygen electrode layer having a thickness of 150 μm.

When the particle diameters of the (La, Sr) (Co, Fe) O ₃ particles of the first oxygen electrode layer and the second oxygen electrode layer are compared by a scanning electron micrograph of the cross section of the oxygen electrode layer, the second oxygen electrode layer The (La, Sr) (Co, Fe) O ₃ particles of the first oxygen electrode layer are clearly larger, and the porosity of the first oxygen electrode layer is clearly smaller than that of the second oxygen electrode layer, It was confirmed that it was more precise. When the average particle diameter of the (La, Sr) (Co, Fe) O ₃ particles of the first oxygen electrode layer and the second oxygen electrode layer was measured by an intercept method using a scanning electron micrograph, the first oxygen electrode was measured. The average particle size of the layer was 0.6 μm, and the average particle size of the second oxygen electrode layer was 5.2 μm. Furthermore, when the porosity was measured by image processing using a scanning electron micrograph, the porosity of the first oxygen electrode layer was 3%, and the porosity of the second oxygen electrode layer was 33%. The oxygen electrode layer was denser than the second oxygen electrode layer.

  The interconnector of the fuel battery cell joined with the current collecting member produced for the peel test having a length of 1 cm and the current collecting member were joined with the tensile member, pulled on both sides, and the joining strength was measured. The oxygen electrode layer was peeled off, and the bonding strength at that time was 11N.

On the other hand, a test piece as a comparative example was produced as follows. A slurry of the first oxygen electrode layer containing an air electrode material (primary particles) of (La, Sr) (Co, Fe) O _{3 having} an average particle diameter (laser diffraction scattering method of 50%) of 0.4 μm is screen-printed, A slurry of the second oxygen electrode layer containing (La, Sr) (Co, Fe) O ₃ (secondary particles in which primary particles are aggregated) having an average particle size (laser diffraction scattering method 50%) of 3 μm on the surface is screened The first oxygen electrode layer and the second oxygen electrode layer were baked at 1150 ° C. at the same time to form a first oxygen electrode layer having a thickness of 15 μm and a second oxygen electrode layer having a thickness of 150 μm.

A slurry containing (La, Sr) (Co, Fe) O ₃ (secondary particles in which primary particles are aggregated) of 3 μm (laser diffraction scattering method 50%) as a bonding material on the second oxygen electrode layer. Is printed, and the current collecting member 20 is disposed and pressed to the fuel cell side, whereby the comb blade of the current collecting member 20 is brought into contact with the second oxygen electrode layer and embedded in the coating film of the bonding material. In this state, baking was performed at 1050 ° C., which is lower than the baking temperature of the first and second oxygen electrode layers.

When the particle diameters of the (La, Sr) (Co, Fe) O ₃ particles of the second oxygen electrode layer and the bonding material are compared by a scanning electron micrograph of the cross section of the oxygen electrode layer, the second oxygen electrode layer and the bonding material are compared. Were substantially the same, and the porosity of the second oxygen electrode layer and the bonding material was substantially the same. As in the above example, the average particle size and porosity of the second oxygen electrode layer and the bonding material were measured. The average particle size of the second oxygen electrode layer was 5.5 μm, and the porosity was 25%. The average particle diameter of the material was 5.2 μm, and the porosity was 32%.

  The fuel cell interconnector and the current collecting member were joined with a tensile member, pulled on both sides, and the joint strength was measured. The current collecting member and the oxygen electrode layer were peeled off. 2.5N.

  In the comparative example, since the current collecting member is bonded onto the second oxygen electrode layer having a large average particle size (high porosity), the bonding strength is as small as 2.5 N. Since the current collecting member is bonded on the first oxygen electrode layer, it can be seen that the bonding strength is 11 N larger than that of the comparative example.

It is sectional drawing which shows the cell stack of this invention. It is a perspective view which shows the current collection member of FIG. It is sectional drawing of the current collection member along the AA line shown in FIG. It is sectional drawing which expands and shows a part of FIG. It is a cross-sectional perspective view of a fuel battery cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Fuel electrode layer 3 Solid electrolyte layer 4 Oxygen electrode layer 4a 1st oxygen electrode layer 4b 2nd oxygen electrode layer 5 Interconnector 20 Plate-shaped current collection member 201 Current collection base material 202 Surface layer 202a Cr diffusion prevention layer 202b coating layer

Claims (6)

A plate-shaped current collecting member is disposed between each of the plurality of fuel cells formed by sandwiching the solid electrolyte layer between the oxygen electrode layer and the fuel electrode layer, and the plate-shaped current collector is disposed on the oxygen electrode layer of the fuel cell. A cell stack formed by joining electric members and electrically connecting the fuel cell and the plate-like current collecting member, wherein the oxygen electrode layer is a first oxygen provided on the solid electrolyte layer A conductive layer having a polar layer and a second oxygen electrode layer provided on the first oxygen electrode layer, the first oxygen electrode layer having a smaller average particle diameter than the second oxygen electrode layer Made of conductive ceramic particles, one main surface of the plate-shaped current collector is bonded to the first oxygen electrode layer, and a side surface of the plate-shaped current collector is bonded to the second oxygen electrode layer A cell stack characterized by that. The cell stack according to claim 1, wherein the first oxygen electrode layer is denser than the second oxygen electrode layer. 3. The cell stack according to claim 1, wherein the first oxygen electrode layer and the second oxygen electrode layer are made of a perovskite complex oxide containing La and Fe. The plate-like current collecting member contains a Cr diffusion preventing layer containing Zn, a perovskite complex oxide containing La, Fe, or Mn and zinc oxide on the surface of a heat-resistant alloy containing Cr. The cell stack according to any one of claims 1 to 3, wherein a coating layer is sequentially laminated. The plate-like current collecting member has a perovskite type containing a Cr diffusion preventing layer containing Zn and at least a part of components constituting the oxygen electrode layer of the fuel cell on the surface of a heat-resistant alloy containing Cr. The cell stack according to any one of claims 1 to 3, wherein a composite oxide and a coating layer containing zinc oxide are sequentially laminated.   6. A fuel cell comprising the cell stack according to claim 1 stored in a storage container.

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