JP2000243405A - Manufacture of solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a cathode having good adhesivity to an electrolyte layer and, sintered at a low temperature. SOLUTION: Sol containing alkoxide of the same composition and pure water are added to (LaSr)MnO3 as cathode powder, fully mixed and dried so as to gelate the sol, and are crushed. Then, polyvinyl butyral, diethylene glycol, and acetone are added, mixed, followed by deacetonizing treatment to obtain cathode slurry. The cathode slurry thus prepared is coated on an electrolyte layer formed on an anode to form a cathode, and the cathode is sintered by heating to an operation temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid oxide fuel cell which converts Gibbs energy into electrical energy by an electrochemical reaction using a solid electrolyte.

[0002]

2. Description of the Related Art A fuel cell using an oxide solid electrolyte such as yttria-stabilized zirconia, that is, a solid oxide fuel cell (hereinafter abbreviated as SOFC) has an operating temperature as high as 800 to 1000 ° C. Therefore, there is an advantage that the power generation efficiency is high and the reforming of the fuel gas is simplified. Also, since the electrolyte is solid,
It also has the advantages of easy handling and excellent long-term stability, and is expected as a next-generation fuel cell, and its development is being pursued by various organizations, both public and private.

[0003] SOFCs are roughly classified into a cylindrical type and a flat type.
The flat plate type is further roughly classified into two types in terms of the cell structure. One is a self-standing membrane SOFC in which a cell is formed by forming an anode and a cathode on both sides of a self-supporting electrolyte produced by a sintering method or the like, and the other is an anode, an electrolyte, This is a support film type SOFC in which a cathode is sequentially formed to constitute a cell. In addition, the SOF of the supporting film type
In C, the substrate may also serve as an anode or a cathode, in which case it is not necessary to form the electrode layer.

FIG. 5 is a cross-sectional view showing an example of a basic configuration of a supporting membrane type SOFC. As shown in the figure, in this configuration example, the cell substrate 11 also serving as the anode, the electrolyte 1
3, and the cathode 14 constitute an SOFC,
At a temperature of 800 to 1000 ° C., electric energy can be obtained by supplying hydrogen or fuel reforming gas to the anode side and oxygen or air to the cathode side.

[0005] The substrate material of the SOFC of the supporting film type is N in the anode substrate type which also serves as the anode as shown in FIG.
(LaSr) MnO ₃ is generally used for iO-YSZ and for a cathode substrate type also serving as a cathode. However, since these substrates also serve as (1) electrodes, they need to be formed porous so as to allow the reaction gas to permeate, and it is difficult to increase the strength as in a bulk body.

(2) Since it is a ceramic material, it is inherently low in toughness and brittle. Therefore, there has been a problem that cracks are easily generated by thermal shock at the time of starting and stopping.

On the other hand, as a substrate having no such disadvantages, recently, a configuration using a metal collector on the anode side as a substrate has been proposed by Fuji Electric Co., Ltd. or the Electronic Technology Research Laboratory of the Industrial Technology Institute. It was suggested that the use of a metal substrate constituted a cell that was resistant to thermal cycling.

[0008]

As described above, in the SOFC of the support film type, the use of a metal substrate makes it possible to manufacture a cell that is resistant to thermal cycling. However, with the use of a metal substrate, The following new problems have arisen. That is, in the case of a cell using a ceramic substrate, when forming a cathode, a method of coating a slurry and then sintering at a high temperature of 1200 ° C. or higher has been adopted, but metal is oxidized in a high-temperature oxidizing atmosphere. Then, an insulating film is formed. Therefore, when a metal substrate is used, a conventional cathode film forming method cannot be used, and it is necessary to form the cathode by another method.

Further, regardless of the material of the substrate, there is a problem in the high-temperature sintering method itself used in the conventional method of forming a cathode film. In other words, in order to improve the degree of adhesion between the cathode and the electrolyte by the high-temperature sintering method, the sintering temperature must be 1250 ° C. or higher.
There is a problem that (LaSr) MnO _{3 as} a cathode material and ZrO _{2 as an} electrolyte cause a chemical reaction to form lanthanum zirconate having a high electric resistance, thereby increasing the internal resistance of the cell.

[0010] Further, the cells are laminated via a separator,
Conventionally, as a method of increasing the adhesion between the separator and the cathode when forming the stack, a method of applying a slurry made of the same component as the cathode on the cathode side or on the cathode of the separator during lamination to form a contact layer has been used. I have been. However, this kind of slurry is originally intended for high-temperature sintering, and S
There is also a disadvantage that the sintering is insufficient at the operating temperature of the OFC, and the development of a low-temperature sintering type slurry for the cathode-side contact layer has been demanded.

The present invention has been made in consideration of the problems of the prior art as described above, and an object of the present invention is to provide a method of manufacturing a cathode which can be sintered at a low temperature and has good adhesion to an electrolyte layer. In addition, the present invention provides a method for producing a contact layer which can be sintered at a low temperature and effectively adheres a cathode and a separator, can use a metal substrate, and can be used between an electrolyte and a cathode, and between a cathode and a cathode. An object of the present invention is to make it possible to manufacture an SOFC having a low interface resistance with a separator and excellent battery characteristics.

[0012]

According to the present invention, there is provided a method for manufacturing a solid oxide fuel cell comprising a cell having an oxide solid electrolyte and an anode and a cathode. ) The cathode powder is mixed with a sol composed of an alkoxide having the same composition as the cathode powder to form a cathode slurry, and the cathode slurry is used to form a cathode.

(2) In particular, the ratio of the solid component of the sol contained in the cathode slurry is selected to be 10 to 20 wt% of the cathode powder.

(3) In the above (1) and (2), the cathode powder and the sol are mixed, dried and gelled, and then a cathode slurry is formed.

(4) A cathode is formed on the solid oxide electrolyte by the slurry coating method or the screen printing method using the above-mentioned cathode slurry, and then the in-situ is formed at the operating temperature of the SOFC.
Sinter with tu.

(5) In the above (4), the cathode formed on the oxide solid electrolyte is sintered at the operating temperature of the SOFC, and when the gel in the cathode is crystallized, the gel and the electrolyte are mixed. During the process, a bond of MOM ′ (where M is a metal atom in the cathode, M ′ is a metal atom in the oxide solid electrolyte) is formed, and the cathode and the oxide solid electrolyte are brought into close contact with each other. It shall be.

(6) In a solid oxide fuel cell comprising a plurality of cells stacked with an airtight separator interposed therebetween, the above-mentioned cathode slurry is applied to the surface of the separator on the cathode side or the cathode of the cell. Is applied on the upper surface, and then laminated.

If the cathode is formed using the cathode slurry formed as in (2) or (3) as in (1) above, this cathode slurry can be sintered at the operating temperature of the SOFC. It is not necessary to pre-sinter in a high-temperature oxidizing atmosphere. Therefore, the number of heat cycles required for manufacturing the cell is reduced, and a metal material can be used as the substrate.

For this reason, a cathode is formed using the cathode slurry thus formed, and as described in the above (4), this is sintered in-situ at the operating temperature of the SOFC, so that the cathode and the oxide solid electrolyte are formed. Are obtained. Particularly, as shown in (5), if the gel is bonded to the electrolyte, particularly good adhesion can be obtained. Therefore, the generation of lanthanum zirconate which causes the deterioration of the cell characteristics is prevented, the contact resistance between the cathode and the solid oxide electrolyte is reduced, and the cell characteristics are improved.

As described in (6) above, when forming a stack by alternately stacking cells and separators, the above-mentioned cathode slurry is applied to the cathode side surface of the separator or the upper surface of the cathode of the cell. If this is used as a contact layer and the cell and the separator are closely laminated,
Sintering is performed at the operating temperature of the SOFC, good contact between the cell and the separator is obtained, and a high-performance SOFC can be obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <Embodiment 1> FIG.
FIG. 2 is a flowchart showing a method for producing a cathode slurry in a first example of a method for producing an OFC. A method for producing a cathode slurry will be described with reference to FIG.

First, (LaSr) MnO ₃ as a cathode powder
And an alkoxide of the same composition as this (LaSr) MnO
₃ Put the sol in a container and add pure water. At this time, if the amount of the sol is not added to some extent, the (LaSr) MnO ₃ powder will not uniformly adhere to the surface. On the other hand, if the amount of the sol is too large, the sol contains particles having a particle size in the order of nm, so that the binder may be absorbed when the slurry is formed, and the fluidity may not be obtained. For this reason,
Mixing ratio of solid component of sol to powder is 10 ~ 20wt%
By doing so, an optimum powder can be obtained. A ball is added to the mixture, and the mixture is mixed for about 6 to 24 hours. Thereafter, the mixture is dried at 100 to 120 ° C. until moisture is completely removed.
By this treatment, the sol uniformly attached to the surface of the (LaSr) MnO ₃ powder gels. Next, this is crushed, polyvinyl butyral, diethylene glycol, and acetone are added, and the mixture is again put in a container together with a ball, and mixed for about 6 to 24 hours. After that, deacetone treatment is performed by washing with hot water and vacuum degassing to obtain a cathode slurry.

Next, a method of manufacturing a cell having the structure shown in FIG. 2 using the cathode slurry manufactured as described above will be described.

First, an anode 2 having a thickness of about 50 μm is formed on a porous metal substrate 1 by the flame spraying method under the conditions shown in Table 1 below.

[0025]

[Table 1] Then, on the anode 2, using a plasma spray method,
The electrolyte layer 3 is formed to a thickness of about 150 μm under the conditions shown in Table 2 below.

[0026]

[Table 2] Next, the above-mentioned cathode slurry is applied to the electrolyte layer 3 by a screen printing method to a thickness of about 150 μm.
After drying at 120 ° C. for 1 hour, the cathode 4 is formed. After laminating the cells formed in this way with a separator,
When the temperature is raised to 950 ° C., when the temperature exceeds about 700 ° C., the gel in the cathode 4 starts to crystallize, and at this time, the aforementioned bonding of MOM ′ between the gel and the electrolyte occurs. Is formed,
The degree of adhesion of the cathode 4 to the electrolyte layer 3 is improved. Also,
The crystallized particles are fine and have high surface activity,
It is sufficiently sinterable at operating temperatures and acts as a sintering aid for other powders. Therefore, the present cathode can be sintered even at a temperature as low as the operating temperature of the SOFC.

FIG. 3 is a characteristic diagram showing characteristics of cells formed using the present slurry in comparison with characteristics of cells formed using a conventional slurry. As shown in the figure,
The electrode area of the cell used for the test was 200 cm ² , and the operating temperature was 9
At 50 ° C., H ₂ with 20% CO ₂ was used as the fuel gas, and air was used as the oxidant gas. As can be seen from the figure, the load characteristics are improved by using the slurry of the present invention as compared with the conventional one, and the rated current density of 0.3 Acm
^{At -2} , an improvement of about 30 mV is seen.

FIG. 4 is a cross-sectional SEM photograph in which a cell formed using the slurry was subjected to a characteristic test at an operating temperature of 950 ° C., and then cut to check the state of the cathode. FIG. 6 is a cross-sectional SEM photograph showing a state of a cathode of a cell formed using a conventional slurry. These cross-sectional SEM
As is clear from the comparison of the photographs, the section SE in FIG.
FIG. 4 shows that no sintering of the powder occurred in the M photograph.
In this example, sintering of the powder particles occurred, and it was confirmed that the cathode slurry of the present invention sintered at the operating temperature of the SOFC.

<Embodiment 2> This embodiment is an embodiment of a stack in which a number of cells manufactured by the same method as in Embodiment 1 are stacked, and the contact layer between the cathode and the separator is formed as described above. This is an example using a cathode slurry.

In this embodiment, similarly to the first embodiment, an anode is formed to a thickness of about 50 μm on a porous metal substrate by using a flame spraying method under the conditions shown in Table 1, and then a plasma is formed on the anode. The electrolyte layer 3 is formed to a thickness of about 150 μm by the thermal spraying method under the conditions shown in Table 2. Next, the cathode slurry prepared by the method shown in FIG. 1 was applied to the electrolyte layer by screen printing at about 150 μm, and then 100 to 12 μm.
Dry at 0 ° C. for 1 hour to form cells.

The prepared cell and the separator are coated alternately with the cathode slurry prepared by the same method as described above on the cathode side of the separator, and the separator and the cathode are brought into close contact with each other by the contact layer made of the cathode slurry. .

When the temperature of the stack thus stacked is raised to an operating temperature of about 950 ° C., when the temperature exceeds about 700 ° C., the gel in the contact layer starts to crystallize, and at the operating temperature, Sintering results in good contact between the separator and the cathode.

In this embodiment, the cathode slurry is applied to the cathode side of the separator and alternately laminated with the cell. Alternatively, the cathode slurry is applied to the cell cathode and the separator is applied. Obviously, the same effect can be obtained by alternately laminating with.

[0034]

As described above, according to the present invention, (1) Since the SOFC is manufactured by the manufacturing method according to any one of claims 1 to 5, the electrolyte and the cathode are SOF.
At the operating temperature of C, adhesion was sufficiently effective. Therefore, a metal substrate can be used, and the interface resistance between the electrolyte and the cathode can be kept low, so that a highly reliable SO with excellent battery characteristics can be used.
FC can be manufactured.

(2) If the cathode is manufactured by the manufacturing method according to the sixth aspect, the cathode and the separator are sufficiently and effectively adhered to each other at the operating temperature of the SOFC, and the interfacial resistance therebetween can be suppressed low. Thus, a highly reliable SOFC having more excellent battery characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for producing a cathode slurry in a production method of the present invention.

FIG. 2 is a basic structural diagram of a cell manufactured in a first embodiment of the manufacturing method of the present invention.

FIG. 3 is a characteristic diagram showing the characteristics of a cell formed by the first embodiment of the manufacturing method of the present invention in comparison with the characteristics of a cell formed by the conventional manufacturing method.

FIG. 4 is a cross-sectional SEM photograph of a cathode of a cell formed and tested according to the first embodiment of the manufacturing method of the present invention.

FIG. 5 is a cross-sectional view illustrating an example of a basic configuration of a supporting film type SOFC.

FIG. 6 is a cross-sectional SEM photograph of a cathode of a cell formed and tested by a conventional manufacturing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal substrate 2 Anode 3 Electrolyte layer 4 Cathode

Claims (6)

[Claims] 1. A method for manufacturing a solid oxide fuel cell comprising a cell having an oxide solid electrolyte, an anode and a cathode, wherein a cathode powder is mixed with a sol comprising an alkoxide having the same composition as the cathode powder. A method for manufacturing a solid oxide fuel cell, comprising: forming a cathode slurry; and forming a cathode using the cathode slurry. 2. The method according to claim 1, wherein the ratio of the solid component of the sol contained in the cathode slurry is 10 to 20 wt.
%. The method for producing a solid oxide fuel cell according to claim 1, wherein the percentage is selected as%. 3. The solid electrolyte fuel according to claim 1, wherein the cathode slurry is formed by mixing the cathode powder and the sol, and then drying and gelling the sol. Battery manufacturing method. 4. The cathode is formed on the solid oxide electrolyte by a slurry coating method or a screen printing method using the cathode slurry, and then formed at the operating temperature of the solid oxide fuel cell.
The method for producing a solid oxide fuel cell according to any one of claims 1 to 3, wherein sintering is performed in n-situ. 5. Sintering a cathode formed on an oxide solid electrolyte at an operating temperature of a solid oxide fuel cell,
When crystallizing the gel in the cathode, bonding of MOM ′ (where M is a metal atom in the cathode and M ′ is a metal atom in the oxide solid electrolyte) between the gel and the electrolyte. The method for producing a solid oxide fuel cell according to claim 4, wherein the cathode is brought into close contact with the solid oxide electrolyte. 6. A solid oxide fuel cell comprising a plurality of cells each having an oxide solid electrolyte, an anode and a cathode interposed via a separator made of an airtight material, wherein the cathode slurry is used as a cathode of a separator. 6. The method for manufacturing a solid oxide fuel cell according to any one of claims 1 to 5, wherein the method is applied to a side surface or an upper surface of a cathode of a cell, and then laminated.