JPH1021935A - Solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte fuel cell where the structure of an air electrode and a solid electrolytic film is improved and the cell output density and the yield at manufacture are improved. SOLUTION: In a solid electrolyte fuel cell, an air electrode, mixed layer, and solid electrolytic film are laminated in this order as follows. The air electrode is 28-40% in porosity, and 5-11μm in cavity diameter, and 70S/cm or over in conductivity, and 1.0-12.0m<2> /hr.atm in gas generation coefficient, and 2.5kgf/mm<2> or over in strength, and the mixed layer is 5-20% in porosity, and 0.5-3.0μm in gas cavity diameter, and 10S/cm<2> or over in surface conductivity, and the total thickness of the air electrode and the mixed layer is 1.0-3.0mm, and the thickness of the mixed layer is 0.5-5.0% of that total thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell characterized by the structure of an air electrode and a solid electrolyte membrane. In particular, the present invention relates to a solid oxide fuel cell having a suitable air electrode as a self-supporting type (the air electrode also serves as a support) and having high power generation performance.

[0002]

2. Description of the Related Art The prior art will be described by taking an air electrode of a cylindrical cell type solid oxide fuel cell (hereinafter also referred to as T-SOFC) as an example. T-SOFC is 1-59
705 is a type of solid oxide fuel cell (hereinafter also referred to as SOFC). T-SOFC
Has a cylindrical cell composed of a porous support tube, an air electrode, a solid electrolyte, a fuel electrode, and an interconnector. When oxygen (air) is flown to the air electrode side and gaseous fuel (H ₂ , CO, etc.) is flown to the fuel electrode side, O ²⁻ ions move in this cell, causing chemical combustion, and An electric potential is generated between the fuel electrodes to generate power. There is also a type in which the air electrode also serves as the support tube. The demonstration test of the T-SOFC was a 25 kw class (effective cell length 50
cm, 1152 cells).

[0003] At present, typical constituent materials of T-SOFC,
The thickness and manufacturing method are as follows (Proc. Of the
3rd Int. Symp. On SOFC, 1993). Support tube: ZrO ₂ (CaO), thickness 1.2 mm, extrusion Air electrode: La (Sr) MnO ₃ , thickness 1.4 mm, slurry coat Solid electrolyte: ZrO ₂ (Y ₂ O ₃ ), thickness 40 μm E
VD interconnector: LaCr (Mg) O ₃ , thickness 40
μm, EVD fuel electrode: Ni—ZrO ₂ (Y ₂ O ₃ ), thickness 100 μm
m, slurry coat-EVD

[0004] The characteristics required for the material for the air electrode (self-supporting type) of the T-SOFC are as follows. 1000 ° C (SOFC operating temperature), must be chemically stable in an oxidizing atmosphere. Be breathable. Conductivity (electronic conductivity). High ion dissociation catalytic action. Good compatibility with ZrO ₂ , which is considered to be the preferred material for solid electrolytes (similar thermal expansion coefficient, no reactivity). It can be formed into a thin (for example, 0.3 to 3.0 mm) pipe. High strength to some extent. It is economical.

To satisfy such characteristics as much as possible, Japanese Patent Publication No. 7-48378 discloses a "SOFC air electrode comprising a first layer and a second layer having a porosity of 25 to 57%. The pore size is 2.5 to 12 μm, the specific resistance is 0.22 Ω · cm or less, and the porosity of the second layer is 8 to 24.
%, The pore diameter is 0.2 to 3 μm, the ratio of the thickness of the air electrode of the second layer to the thickness of the air electrode is 2 to 28%, and the thickness of the air electrode is 0.7 to 3.0 mm. There should be a perovskite structure in which the cathode material is selected from the group consisting of lanthanum manganate, calcium manganate, lanthanum nickelate, lanthanum cobaltate, and lanthanum chromate. "
Has been proposed.

[0006]

However, when the porosity is set to 40% or more in the above characteristic value range, the strength is remarkably reduced, the reliability of the cell is reduced, the porosity is 28% or less, and the pore diameter is 5% or less. The present inventors have found that a gas permeability of not more than 0.0 μm significantly lowers the cell performance.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solid oxide fuel cell having an improved structure of an air electrode and a solid electrolyte membrane, improved cell output density and improved production yield.

[0008]

SUMMARY OF THE INVENTION In the present invention, the problems have been solved from the following viewpoints. For the porosity, pore diameter, strength, and gas permeability coefficient of the air electrode (which can also serve as a cell support structure), optimal ranges were determined in order to balance air permeability and strength. Regarding the mixed layer, which is a boundary layer between the air electrode and the solid electrolyte membrane, the required electric resistance characteristics are defined not by the conductivity but by the interface conductivity. In addition, the relationship between the pore diameter and the air permeability was investigated from the viewpoint of ensuring the existing density of the three-phase interface between the air electrode, the solid electrolyte, and the air (oxidizing agent) and reducing the flow resistance of the air.

That is, the solid electrolyte fuel cell of the present invention comprises a solid electrolyte fuel cell having a layer structure in which an air electrode, a mixture layer of an air electrode material and a solid electrolyte, and a solid electrolyte membrane are laminated in this order. A fuel cell, wherein the air electrode has a conductivity of 70 S / cm or more. The reason why the conductivity of the air electrode is set to 70 S / cm or more is to secure the maximum output density of the cell of 0.1 W / cm ² or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the solid oxide fuel cell of the present invention, the interface conductivity of the mixed layer is preferably 10 S / cm ² or more in order to secure the cell output density. Further, in order to secure the cell output density, the gas permeability coefficient of the air electrode is preferably 1.0 to 12.0 m ² / hr · atm.
The strength of the air electrode is preferably 2.5 kgf / mm ² or more. This is for securing the strength as a self-supporting body.

In the solid oxide fuel cell of the present invention, the porosity of the air electrode is preferably 28 to 40%. If the porosity is less than 28%, the gas permeability coefficient decreases, and it is difficult to secure a certain cell performance (0.1 W / cm ² or more). If the porosity exceeds 40%, the conductivity decreases. This also makes it difficult to secure cell performance.

In the solid oxide fuel cell according to the present invention, the pore diameter of the air electrode is preferably 5 to 11 μm. If the pore diameter is less than 5 μm, the gas permeability coefficient decreases, and it is difficult to secure a constant cell performance (0.1 W / cm ² or more). If the pore diameter exceeds 11 μm, the strength becomes 2.5 kgf / cm ^2. This is because it is less than mm ² and becomes unsuitable as a self-supporting body (the air electrode itself plays the role of a strength member of the cell) (for example, the probability of breakage during the cell manufacturing process increases).

In the solid oxide fuel cell according to the present invention, the mixed layer has a porosity of 5 to 20% and a pore diameter of 0.5 to 0.5%.
It is preferably 3.0 μm. If the porosity is less than 5%, the resistance due to gas diffusion near the three-phase interface increases, and if the porosity exceeds 20%, the three-phase interface decreases and the interface conductivity decreases. . The reason why the pore diameter of the mixed layer is 0.5 to 3.0 μm is to secure the maximum output density of the cell.
If it is less than μm, the resistance due to gas diffusion will increase, and if the pore diameter exceeds 3.0 μm, the three-phase interface will decrease and the interface conductivity will decrease.

In the solid oxide fuel cell according to the present invention, the total thickness of the air electrode and the mixed layer is 1.0 to 3.0 mm. 5.0%
It is preferred that When the total thickness of the air electrode and the mixed layer is less than 1.0 mm, the resistance in the circumferential direction in the air electrode increases, so that it is difficult to secure the cell performance. This is because it is difficult to secure the cell performance because of the increase. When the thickness of the mixed layer is less than 0.5% of the total thickness, the three-phase interface is reduced and the interface conductivity is reduced, so that it is difficult to secure the cell performance. This is because it is difficult to secure cell performance because the voltage is lowered and the overvoltage is increased.

In the solid oxide fuel cell of the present invention, one criterion for achieving the maximum output density of the cell of 0.1 W / cm ² or more is as follows: the air electrode has a porosity of 2;
8 to 40%, a pore diameter of 5 to 11 μm, a conductivity of 70 S / cm or more, and a gas permeability coefficient of 1.0 to 1
2.0 m ² / hr · atm, and the mixed layer has a porosity of 5 to 20.
%, The pore diameter is 0.5 to 3.0 μm, the interface conductivity is 10 S / cm ² or more; the total thickness of the air electrode and the mixed layer is 1.0 to 3.0 mm; The thickness of the layer is between 0.5 and 5.0% of the total thickness.

In the solid oxide fuel cell of the present invention, one criterion for achieving the maximum output density of the cell of 0.2 W / cm ² or more is as follows: The air electrode has a porosity of 3;
0 to 39%, a pore diameter of 6 to 10 μm, an electric conductivity of 75 S / cm or more, and a gas permeability coefficient of 3.5 to 1
1.5 m ² / hr · atm, and the mixed layer has a porosity of 6-18.
%, The pore size is 0.7 to 2.7 μm, the interface conductivity is 15 S / cm ² or more; the total thickness of the air electrode and the mixed layer is 1.2 to 2.8 mm; The thickness of the layer is between 1.0 and 4.5% of the total thickness.

In the solid oxide fuel cell of the present invention, one criterion for achieving the maximum output density of the cell of 0.3 W / cm ² or more is as follows: the air electrode has a porosity of 3;
2 to 38%, a pore size of 6.5 to 9.5 μm, an electric conductivity of 80 S / cm or more, and a gas permeability coefficient of 5.
0 to 11.0 m ² / hr · atm, and the mixed layer has a porosity of 7
１７17%, the pore size is 1.0-2.2 μm,
The interface conductivity is 20 S / cm ² or more; the total thickness of the air electrode and the mixed layer is 1.3 to 2.6 mm; and the thickness of the mixed layer is 1.2 to 3.5 of the total thickness. %.

In the solid oxide fuel cell of the present invention, one criterion for achieving a maximum output density of the cell of 0.4 W / cm ² or more is as follows: the air electrode has a porosity of 3;
3 to 37%, a pore size of 7.0 to 9.0 μm, a conductivity of 90 S / cm or more, and a gas permeability coefficient of 6 to
10 m ² / hr · atm, and the mixed layer has a porosity of 8 to 15%.
The pore diameter is 1.2 to 1.8 μm, the interface conductivity is 40 S / cm ² or more; the total thickness of the air electrode and the mixed layer is 1.5 to 2.2 mm; Is 1.4 to 2.5% of the total thickness.

In the present invention, the mixed layer is preferably a sintered layer of powder produced by a coprecipitation method from a mixed aqueous solution of the air electrode composition and the solid electrolyte composition. In general, when the coprecipitated powder has a uniform composition and structure, the distribution of the three-phase interface between the gas phase, the air electrode material, and the solid electrolyte can be properly adjusted, and the cell resistance between the air electrode and the solid electrolyte membrane can be significantly reduced. There are many.

In the present invention, the air electrode is made of strontium dolantan manganite (LSM) or calcium-doped manganite (LCM), the solid electrolyte membrane is made of yttria-stabilized zirconia (YSZ), and the mixed layer is made of A solid oxide fuel cell comprising a mixture of both can be obtained. Here, the conductive ceramic of the present invention includes (La _1-x Sr _x ) _z MnO ₃ ,
It is preferable to have a composition of 0.22 ≦ x ≦ 0.28 and 0.96 ≦ z <1.0. Further, the range of x, z is more preferably 0.24 ≦ x ≦ 0.26, 0.97 ≦ z
≤ 0.99. This is because the above-mentioned required characteristics are all good in this range. (La _1-x Ca _x ) _z MnO ₃
In the case of 0.1 ≦ x ≦ 0.5, 0.96 ≦ z <1.0
It is preferable to have the following composition. Further, the range of x, z is more preferably 0.2 ≦ x ≦ 0.4, 0.97 ≦
z ≦ 0.99. This is because the above-mentioned required characteristics are all good in this range. On the other hand, the content of YSZ of Y ₂ O ₃ is preferably 8~12mol%.

[0021]

EXAMPLES Overview of Tests The following four types of tests were performed to clarify the optimum characteristic value range for the structure around the air electrode. (1) Relationship between gas permeability coefficient and conductivity of air electrode and power generation performance: In order to improve power generation performance, it is desirable that both gas permeability coefficient and conductivity are high. However, both have basically contradictory characteristics, so it is necessary to balance them. In this test, a range in which both were well balanced was determined.

Specifically, the gas permeability coefficient is 0.5 to 1
5.0 m ² / hr · atm, SOFC air electrode (conductivity support) with conductivity in the range of 40 to 120 S / cm is formed by extrusion molding method.
It was produced by firing. The control of gas permeability and conductivity was performed by changing the particle size of the raw material powder and the firing temperature.
An interconnector is formed on an air electrode support by a slurry coating method, baked, and a mixed layer is formed by a slurry coating method using powder by a coprecipitation method, and then a YSZ film is formed by a slurry coating method and fired. did. Further, the fuel electrode was formed into a film by the slurry coating method and fired to prepare an evaluation cell, and the power generation was evaluated. For efficient operation, it is desirable that the maximum output density is at least 0.1 W / cm ² or more. Gas permeability coefficient is less than 1.0m ² / hr · atm, greater than 12m ² / hr · atm, conductivity maximum power density of less than 70S / cm is less than 0.1 W / cm ^2.

(2) The relationship between the strength of the cathode and the probability of cell breakage (reverse yield) during the manufacturing process: In a cathode self-supporting cell, the cathode functions as a structure for maintaining the cell shape To fulfill. Then, during the manufacturing process of the cell (the process of firing the solid electrolyte membrane, the fuel electrode, etc.), the maximum load is applied to the air electrode as this structure. At that time, if the strength of the air electrode is weak, the cell is damaged (cracked or broken). Here, a production test was performed with a total of 300 test cells to be described later and an air electrode strength of 0.2 to 3.2 kgf / mm ² . As a result, as described above, it was found that when the strength of the air electrode (support) is 2.5 kgf / mm ² or more, the probability of breakage during the cell manufacturing process can be suppressed to 5% or less.

(3) Relationship between porosity and pore diameter of the air electrode, gas permeability coefficient, conductivity and strength: These generally have the following relationships. Large porosity → large porosity, large gas permeability coefficient, small strength Large porosity → large gas permeability coefficient, small conductivity, small strength Therefore, in order to put the gas permeability coefficient, conductivity and strength in appropriate ranges, It is necessary to control the pore diameter and porosity of the cathode in a certain range. Here, the test was performed in the range of an average pore diameter of 3.5 to 13.5 μm and a porosity of 24 to 45%. As a result, it was found that the porosity needs to be 40% or less because the conductivity is 70 S / cm or more. Since the gas permeability coefficient was 1.0 m ² / hr · atm or more, it was found that the porosity needs to be 28% or more and the pore diameter needs to be 5 μm or more. Support strength is 2.5
It has been found that the pore diameter needs to be 11 μm or less in order to be kgf / mm ² or more.

(4) Relationship between mixed layer and cell power generation performance: The following test cells were prepared and their power generation performance was measured. (A) Cell without mixed layer (B) The mixed layer has the same composition as the air electrode, but the structure (crystal,
(C) A cell in which a mixed layer is formed using a solid phase mixed powder of an air electrode (LSM) and YSZ as a raw material (calcination temperatures 1, 3).
(D) A cell in which the mixed layer is formed from a solid phase mixed powder of an air electrode (LSM) and YSZ (calcination temperature 900
(C) (E) A cell in which the mixed layer is formed using a coprecipitated powder of the air electrode (LSM) and YSZ as a raw material. As a result, since the maximum output density is 0.1 W / cm ² or more, the interface The conductivity is 10 S / cm or more, and the porosity of the mixed layer is 5 to 5.
It has been found that the pore size needs to be 20% and the pore size must be in the range of 0.5 to 3.0 μm.

Test cell preparation method and test method (1) Air electrode raw material powder: prepared by a liquid phase mixing method (La
_0.75 Sr _0.25 ) _0.99 MnO ₃ powder (hereinafter simply referred to as LSM powder) was pulverized and classified into the following six average particle sizes. They were mixed in the following ratio. Coarse powder: 5 μm, 10 μm, 20 μm, 30 μm, 40 μ
m Fine powder: 0.5 μm Fine powder addition amount: 0, 5, 10 wt% In the test of the relation of the mixed layer and the strength of the air electrode (support),
Only 20 μm of the air electrode coarse powder was used.

(2) Preparation of a compound for extrusion: 100 parts by weight of the above LSM powder (the same applies hereinafter) and an organic binder 10
, 3 parts of glycerin and 10 parts of water were added and kneaded to obtain a compound for extrusion. (3) Extrusion molding: The above compound was extruded at an extrusion pressure of 30 kgf / cm ² to obtain a green pipe. (4) Drying / degreasing: Place a green pipe in a hot air circulating drier, first time 40 ° C x 24 hours, second time 175 ° C x 2
Drying and degreasing were performed for 4 hours.

(5) Air electrode firing: gas furnace (oxidizing atmosphere,
The dried and degreased green pipe was fired using an oxygen partial pressure of 2 × 10 ⁻³ atm). The firing conditions are 1,350 to 1,450 ° C. × 10 hours in the test on the characteristics of the air electrode, 1,450 ° C. × 10 hours in the test on the characteristics of the mixed layer, and 1,250 to 1,450 ° C. in the test on the strength of the air electrode. X 10 hours.
During firing, shelves were assembled so that the periphery of the sample (cell) was sealed with a muffle. This is to prevent the Mn component from scattering during firing. When such closed firing is not performed, the strength of the air electrode (support) is 50 to 7
0%. Observation of such a sample by SEM / EDX revealed that the Mn component on the sample surface was reduced to about 60% of the theoretical value.

(6) Dimensions after calcining the cathode: In the tests for the relationship between the characteristics of the cathode and the characteristics of the mixed layer, the dimensions of the cathode pipe were 16 mm in outer diameter × 1.7 mm in thickness × length in the stage after calcination. Those having a length of 200 mm were used. For the air electrode strength test only, one having an outer diameter of 20 mm, a thickness of 3.0 mm and a length of 200 mm was used. In each case, one end was sealed. The reason why the latter was made larger in diameter and thicker was that it was necessary to cut out a test piece for a three-point bending test having a width of 4.0 mm × a thickness of 2.5 mm and a length of 40 mm.

(7) Evaluation of air electrode gas permeability: 0.1 kgf / cm ^{2 of} N ₂ gas was applied to the air electrode (support) pipe of the above dimensions.
The gas permeation amount was measured by applying a differential pressure. (8) Electrode conductivity evaluation: The above-mentioned air electrode pipe (length 50
mm) is cut out and its conductivity is set to 1,0
It was measured at 00 ° C. by a four-terminal method. (9) Evaluation of air electrode strength: A three-point bending test was performed at room temperature (however, the strength did not decrease even at 1,000 ° C in the atmosphere) using the test piece.

(10) Interconnector film formation: 7.0 mm wide × 50 mm long × 50 thick on the outer periphery of the air electrode pipe.
A μm (axial, linear) interconnector film was formed by slurry coating. The material used was La _0.75 C
a _0.25 CrO ₃ , and the firing temperature was 1,400 ° C. × 2 hours.

(11) Mixed layer film formation: Mixed layer films were formed for the types (B), (C), (D) and (E) (described above) as follows. In the air electrode characteristics and strength-related tests, only the following D type (coprecipitated powder) was used. At the time of mixed layer film formation, masking was performed on the interconnector. (B) LSM powder 100 having the same composition as the air electrode and having a particle size of 3 μm
In parts, 4.4 parts of an organic binder (ethyl cellulose),
367 parts of ethyl alcohol and 1 part of α-terpineol
21 parts, 3.8 parts of polyoxyethylene alkyl phosphate, and 3.8 parts of sorbitan sesquiolate were mixed to obtain a slurry for film formation. This was coated on the air electrode by a dipping method and fired at 1,500 ° C. for 5 hours.

(C) and (D) The LSM powder having a particle size of 0.5 μm and the 8 mol% YSZ powder having a particle size of 0.3 μm were mixed in a solid phase using a ball mill to obtain a raw material powder. Using this raw material powder, a film was formed in the same manner as in (B). (E) Co-precipitated powder (weight ratio of 50:50 in terms of oxide) of 8 mol% YSZ and LSM (same composition as described above)
No. 73739 (the same applicant as the present application). Thereafter, a film was formed using this coprecipitated powder in the same manner as in (B).

(12) Solid electrolyte membrane formation: particle size 0.3 μm
A mixture of 4.4 parts of an organic binder (ethyl cellulose), 3.8 parts of a surfactant, 367 parts of ethyl alcohol, 121 parts of α-terpineol, and 3.8 parts of sorbitan sesquiolate was mixed with 100 parts of 8 mol% YSZ of m. Obtained. This slurry was coated on the mixed layer or the air electrode by a dipping method, and fired at 1,500 ° C. for 5 hours. The thickness of the fired solid electrolyte membrane was 20 μm.

Fuel electrode membrane: NiO /
100 parts of YSZ powder (weight ratio after reducing Ni: 60:40) is mixed with 250 parts of an organic solvent (ethanol, xylene), 10 parts of an organic binder (ethyl cellulose), 3 parts of a surfactant (antifoaming agent), and 3 parts of a deflocculant. Mix to obtain a slurry. This slurry was coated on a solid electrolyte membrane by a dipping method and fired at 1,400 ° C. for 2 hours. The thickness of the fuel electrode after firing was 100 μm. Next, 3% H ₂ , 97%
The fuel electrode was reduced at 1,000 ° C. in a N ₂ atmosphere.

Power generation performance evaluation: Using the cell prepared as described above (having an air electrode outer diameter of 13 mm), air was used as an oxidizing agent, H ₂ + 11% H ₂ O was used as a fuel, and a fuel utilization rate was 80%. %, The maximum power density was measured by performing a power generation performance evaluation operation.

Test Results (1) Relationship between air electrode gas permeability coefficient and maximum output density: FIG. 1 is a graph showing the relationship between the air electrode gas permeability coefficient and the maximum output density. At a stage where the gas permeability coefficient is low, the maximum power density increases as the gas permeability coefficient increases. However, when the gas permeability coefficient is approximately 8 m ² / hr · atm or more, the maximum output density is reduced due to the effect of lowering the conductivity of the air electrode. When the gas permeability coefficient was examined in the range of 0.5 to 14 m ² / hr · atm,
In order for the maximum output density to be 0.1 W / cm ² , a gas permeability coefficient in the range of 1 to 12 m ² / hr · atm was appropriate. Particularly, the maximum output density was high (approximately 0.4 W / cm ² or more) in the gas permeability coefficient range of 6 to 10 m ² / hr · atm.

(2) Relationship between air electrode conductivity and maximum output density: FIG. 2 is a graph showing the relationship between air electrode conductivity and maximum output density. The higher the electrical conductivity, the higher the maximum output density. On the other hand, the higher the electrical conductivity, the lower the gas permeability coefficient. Therefore, the maximum output density decreases when the electrical conductivity is 100 S / cm or more. When the conductivity was examined in the range of 55 to 110 S / cm, it was found that the conductivity was more than 70 S / cm in order for the maximum output density to be 0.1 W / cm ² . Particularly, the maximum output density was high (approximately 0.4 W / cm ² or more) in the conductivity range of 90 to 110 S / cm.

(3) Relationship between the strength of the air electrode (support) and the probability of breakage in the cell manufacturing process: FIG. 3 is a graph showing the relationship between the strength of the air electrode (support) and the probability of breakage in the cell manufacturing process. The failure probability has a clear inverse correlation with the cathode intensity. When the air electrode strength was 2.5 kgf / mm ² or more, the probability of breakage could be reduced to 5% or less.

(4) Relationship between porosity of air electrode and gas permeability coefficient: FIG. 4 is a graph showing the relationship between porosity of the air electrode and gas permeability coefficient. The gas permeability coefficient increases almost linearly as the porosity increases. Gas permeability coefficient of 1-1
In order to obtain 2 m ² / hr · atm, the porosity needs to be 28 to 40%. In order to achieve a gas permeability coefficient of 6 to 10 m ² / hr · atm, the porosity needs to be 33 to 37%.

(5) Relationship between pore diameter of air electrode and gas permeability coefficient: FIG. 5 is a graph showing the relationship between pore diameter of the air electrode and gas permeability coefficient. The gas permeability coefficient increases almost linearly as the pore diameter increases. Gas permeability coefficient of 1-1
In order to make it 2 m ² / hr · atm, the pore diameter needs to be 5 to 11 μm. In order to achieve a gas permeability coefficient of 6 to 10 m ² / hr · atm, the pore diameter needs to be 7 to 9 μm.

(6) Relationship between porosity and conductivity of air electrode:
FIG. 6 is a graph showing the relationship between the porosity of the air electrode and the conductivity. The conductivity usually has an inverse correlation with the porosity, which is clearly shown in FIG. Conductivity 70S /
In order to attain cm or more, the porosity must be 40% or less. In order to make the conductivity 90 to 110 S / cm, the porosity must be 32 to 37%.

(7) Relationship between pore diameter and strength of air electrode: FIG. 7 is a graph showing the relationship between pore diameter and strength of the air electrode. The strength decreases linearly as the pore diameter increases. In order for the strength to be 2.5 kgf / mm ² or more, the pore diameter must be 11 μm or less.

(8) Relationship between porosity of mixed layer and maximum output density: FIG. 8 is a graph showing the relationship between porosity of the mixed layer and maximum output density. When the porosity of the mixed layer is low, the maximum power density increases as the porosity increases. However, when the porosity is approximately 10% or more, the maximum output density decreases due to the effect of lowering the interface conductivity of the mixed layer. In order to have a maximum power density of 0.1 W / cm ² or more, the porosity must be 5 to 20%. In order to achieve a maximum power density of 0.4 W / cm ² or more, the porosity should be 8-15.
%Must.

(9) Relationship between pore diameter of mixed layer and maximum output density: FIG. 9 is a graph showing the relationship between pore diameter of the mixed layer and maximum output density. As for the maximum output density, at the stage where the pore diameter of the mixed layer is low, the maximum output density increases as the pore diameter increases. However, when the pore diameter is approximately 1.2 μm or more, the maximum output density decreases due to the effect of lowering the interface conductivity of the mixed layer. In order to have a maximum output density of 0.1 W / cm ² or more,
The pore size must be between 0.5 and 3.0 μm. In order to have a maximum output density of 0.4 W / cm ² or more, the pore size is
It must be between 1.2 and 1.8 μm.

(10) Relationship between interface conductivity of mixed layer and maximum output density: FIG. 10 is a graph showing a relationship between interface conductivity of the mixed layer and maximum output density. The maximum power density increases as the interfacial conductivity increases. Maximum power density 0.
To be 1 W / cm ² or more, the interface conductivity is 10 S / cm ²
Must be at least. In order to have a maximum power density of 0.4 or more, the interface conductivity must be 40 S / cm ² . The data indicated by the black dots in the graph are from the test cells A to E from left to right.

(11) Relationship between air electrode thickness and maximum output density: FIG. 11 is a graph showing the relationship between the air electrode thickness (including the thickness of the mixed layer) and the maximum output density. If the cathode is too thin, the electrical resistance (when electricity travels along the circumference of the cell) will increase and the maximum power density will decrease, while if the cathode is too thick, the gas permeability will decrease and the maximum power density will decrease. Therefore, there is an optimum range for the thickness of the cathode. In FIG.
This is clearly shown. In order for the maximum output density to be 0.1 W / cm ² or more, the thickness of the air electrode must be 1.0 to 3.0 μm. In order for the maximum output density to be 0.4 W / cm ² or more, the thickness of the air electrode must be 1.5 to 2.2 μm.

(12) Relationship between mixed layer thickness ratio and maximum output density: FIG. 12 is a graph showing the relationship between the mixed layer thickness ratio and the maximum output density. If the mixed layer is too thin, the interface conductivity increases and the maximum output density decreases. If the mixed layer is too thick, the gas permeability decreases and the maximum output density decreases.
Therefore, there is an optimal range for the thickness of the mixed layer. FIG.
This is clearly shown in FIG. Maximum power density 0.1
In order to be W / cm ² or more, the ratio of the thickness of the mixed layer (based on the thickness of the air electrode and the mixed layer) must be 0.5 to 5.0%. In order for the maximum output density to be 0.4 W / cm ² or more, the ratio of the thickness of the mixed layer must be 1.4 to 2.5%.

[0049]

As is apparent from the above description, the present invention can provide a solid oxide fuel cell having improved cell output density and improved production yield.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a gas permeability coefficient of an air electrode and a maximum output density.

FIG. 2 is a graph showing the relationship between the conductivity of the air electrode and the maximum output density.

FIG. 3 is a graph showing the relationship between the strength of an air electrode (support) and the probability of breakage in a cell manufacturing process.

FIG. 4 is a graph showing a relationship between a porosity of an air electrode and a gas permeability coefficient.

FIG. 5 is a graph showing a relationship between a pore diameter of an air electrode and a gas permeability coefficient.

FIG. 6 is a graph showing the relationship between the porosity of the air electrode and the conductivity.

FIG. 7 is a graph showing a relationship between a pore diameter of an air electrode and strength.

FIG. 8 is a graph showing a relationship between a porosity of a mixed layer and a maximum output density.

FIG. 9 is a graph showing the relationship between the pore diameter of the mixed layer and the maximum output density.

FIG. 10 is a graph showing the relationship between the interface conductivity of the mixed layer and the maximum output density.

FIG. 11 is a graph showing the relationship between the thickness of the air electrode and the maximum output density.

FIG. 12 is a graph showing a relationship between a thickness ratio of a mixed layer and a maximum output density.

Claims (10)

[Claims] 1. A solid electrolyte fuel cell having an air electrode, a mixed layer comprising a mixture of an air electrode material and a solid electrolyte, and a layered structure in which solid electrolyte membranes are laminated in this order. A solid oxide fuel cell having a conductivity of 70 S / cm or more. 2. The solid oxide fuel cell according to claim 1, wherein the mixed layer has an interface conductivity of 10 S / cm ² or more. 3. The gas permeability coefficient of the air electrode is 1.0-1.
Was 2.0m ² / hr · atm, the solid electrolyte fuel cell according to claim 1 or 2, wherein strength of 2.5 kgf / mm ² or more. 4. The solid oxide fuel cell according to claim 3, wherein the air electrode has a porosity of 28 to 40%. 5. The solid oxide fuel cell according to claim 3, wherein the air electrode has a pore diameter of 5 to 11 μm. 6. The solid oxide fuel cell according to claim 1, wherein the mixed layer has a porosity of 5 to 20% and a pore size of 0.5 to 3.0 μm. 7. A total thickness of the air electrode and the mixed layer is 1.0.
３3.0 mm: the thickness of the mixed layer is 0.3 mm of the total thickness.
The solid oxide fuel cell according to any one of claims 1 to 6, wherein the content is 5 to 5.0%. 8. A solid electrolyte fuel cell having an air electrode, a mixed layer made of a mixture of an air electrode material and a solid electrolyte, and a layered structure in which solid electrolyte membranes are laminated in this order: The porosity is 28 to 40%, the pore size is 5 to 11 μm, the conductivity is 70 S / cm or more, the gas permeability coefficient is 1.0 to 12.0 m ² / hr · atm, and the mixed layer Has a porosity of 5 to 20%, a pore diameter of 0.5 to 3.0 μm, an interface conductivity of 10 S / cm ² or more; and a total thickness of the air electrode and the mixed layer of 1.0 to 1.0 S / cm ^2. A solid oxide fuel cell, wherein the thickness of the mixed layer is 0.5 to 5.0% of the total thickness. 9. The solid electrolyte fuel according to claim 1, wherein the mixed layer is a sintered layer of powder produced by a coprecipitation method from a mixed aqueous solution of an air electrode composition and a solid electrolyte composition. battery. 10. The air electrode is made of strontium dolantan manganite (LSM) or calcium dolantan manganite (LCM), the solid electrolyte membrane is made of yttria-stabilized zirconia (YSZ), and the mixed layer is made of both. The solid oxide fuel cell according to any one of claims 1 to 9, comprising a mixture.