JPH07240217A - Electrolyte substrate and flat cell manufacturing method - Google Patents

Abstract

PURPOSE:To provide a smooth electrolyte substrate suitable for a supporting body by baking a laminated body composed of an even number of green sheets formed by doctor blade method. CONSTITUTION:Green sheets 21 with 100-300mum thickness are formed of a slurry consisting of yttria-stabilized zirconia(YSZ) with 0.1mum particle size, a binder, a dispersant, a plastisizer, a dispersing solvent, etc., by a doctor blade method. Two green sheets 21 are stuck to each other by a dibutyl phthalate while the back sides thereof at the time of film formation are positioned face to face to obtain a laminated body 22. After being dried by hot air while sandwiched between glass plates, the laminated green sheets are baked at 1300 deg.C to obtain an electrolyte substrate with 300-600mum thickness. An electrolyte substrate with sufficient thickness and suitable for a supporting body for a self-standing film type cell is obtained by laminating the green sheets which have uniform thickness since they are formed by doctor blade method. The shrinkage anisotropy of green sheets in the film thickness direction at the time of firing is offset by layering the sheets while setting the back sides of the sheets face to face and warping is prevented.

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 an electrolyte substrate and a flat plate type cell, and not only for a flat plate type cell,
It can be applied as a method for producing a ceramic thin film or a plate member for general use.

[0002]

2. Description of the Related Art A flat plate type solid electrolyte fuel cell (hereinafter referred to as a flat plate SOFC) has a supporting structure, and a self-supporting membrane type cell (FIG. 1 (A)) in which an electrolyte layer 1 is a support and a fuel electrode ( Alternatively, the air electrode) 2 is classified as a support membrane type cell (FIG. 1B) that is a support. In addition, in FIG.
Reference numeral 3 indicates a fuel electrode (or an air electrode).

In order to manufacture the self-supporting membrane cell, a green sheet of an electrode material for a fuel electrode (or an air electrode) is further adhered to an electrolyte layer or a thin plate obtained by a sintering method, or a screen. A method of obtaining a film by firing after forming a film by printing or a slurry coating method is generally adopted.

[0004]

By the way, in the self-supporting membrane type cell, it is necessary to maintain the strength as a cell by thickening the electrolyte layer 1 as a support. However, the dense electrolyte layer 1 can be obtained by the sintering method. On the other hand, in the support membrane type cell, since the support is the fuel electrode (or the air electrode), the electrolyte layer 1 can be made thinner than the self-supporting membrane type cell. However, it is technically difficult to form a dense electrolyte layer, the support is a porous electrode layer, and it is necessary to make it relatively thick in order to maintain the strength as a cell. Therefore, gas diffusivity is impaired. Further, in the support membrane type cell, gas sealing is difficult and the stack structure becomes complicated.

Here, there are various methods for molding ceramics, but as a method for producing a thin film or a thin plate represented by a flat plate type SOFC cell, a doctor blade method is generally used. The advantage of this doctor blade method is that a thin film having a uniform thickness can be continuously formed. Therefore, also in the manufacturing method of the flat plate type SOFC cell, the film formation by the doctor blade method is the mainstream.

As a general cell manufacturing process, first, an electrolyte green sheet is formed by a doctor blade method, and this is fired to form an electrolyte thin film substrate. Continuing,
A cell can be obtained by directly coating the slurry of the fuel electrode or the air electrode on this, or by pasting a green sheet or the like and firing it.

[0007]

Generally, the doctor blade method is an excellent method for forming a film or a thin plate.
However, conversely, the film thickness of the obtained molded body is limited to 1 mm or less. This is because the doctor blade method uses a slurry to form a film on a non-absorptive polymer film, so if the film thickness is increased during film formation, cracks, warpage, etc. will occur during drying. It depends on what you cannot do.

Further, the obtained green sheets differ in the filling state and the like in the film thickness direction. Therefore, during firing, the shrinkage ratio in the film thickness direction is slightly different, and warpage or deformation occurs. Therefore, generally, a load is applied again at a high temperature to correct and smooth the surface. However, the size of the molded body is also limited, and if it is too large, sufficient smoothing is difficult.

However, in a flat plate type SOFC cell in which a self-supporting membrane type cell uses an electrolyte layer as a support, it is necessary to make the electrolyte membrane thick to some extent from the viewpoint of strength. In addition, sufficient smoothness is required even when the cell size is increased (area is increased).

The present invention has been made in consideration of such circumstances, and has a sufficient film thickness and a sufficient smoothness even when a cell has a large area when a cell is manufactured by the doctor blade method. It is an object of the present invention to provide a method for manufacturing a flat plate type cell having an electrolyte substrate, a fuel electrode or an air electrode.

[0011]

The first invention of the present application is characterized in that it is obtained by firing a laminate obtained by laminating several electrolyte green sheets formed by the doctor blade method. It is an electrolyte substrate.

A second invention of the present application is a method of manufacturing a flat plate type cell, wherein green sheets of a fuel electrode and an air electrode are bonded to the front surface and the back surface of the laminated body and integrally fired.

Specifically, the present invention has an electrolyte film thickness necessary for maintaining sufficient strength for producing a self-supporting membrane type cell by the doctor blade method and a sufficient smoothness in firing. Therefore, the thickness of the film is increased by laminating several electrolyte green sheets formed by the doctor blade method. Further, at this time, the number of laminated green sheets is set to an even number, and the green sheets are attached so as to be vertically symmetrical as shown in FIG. Use as electrolyte membrane. At this time, an electrolyte membrane having an arbitrary thickness can be obtained depending on the thickness of one green sheet or the number of laminated green sheets. In addition, by stacking the green sheets of the fuel electrode and the air electrode having the shrinkage ratios on the front and back sides of the laminated body of green sheets and firing them together, a flat plate cell having sufficient strength and smoothness is obtained. .

[0014]

[Function] In order to obtain sufficient strength as a self-supporting membrane type cell for producing an electrolyte membrane by the doctor blade method, it is possible to easily increase the thickness by laminating and stacking several electrolyte green sheets. The film thickness can be freely controlled by the number of sheets. Regarding the shrinkage anisotropy during firing due to the difference in the filling state in the film thickness direction that occurs during the production of green sheets, the number of sheets to be laminated is an even number as a method of laminating green sheets, and the front and back surfaces of the sheets are laminated. By laminating the green sheets so as to be vertically symmetrical, the shrinkage anisotropy in the film thickness direction of each green sheet is canceled out, and the stack as a whole becomes isotropic. Therefore, warpage or cracking, which is likely to occur in the green sheet single-layer film during firing, hardly occurs in the laminate, and an electrolyte membrane having good smoothness can be obtained. In addition, since the manufacturing yield is significantly improved, the manufacturing cost can be reduced.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (Example 1) FIGS. 2A, 2B and 3A,
Refer to (B).

Electrolyte raw material powder [yttria-stabilized zirconia (YSZ): particle size 0.1 μm], polyethyl methacrylate as an organic binder, amine as a dispersant, dibutyl phthalate as a plasticizer, and thinner as a dispersant are described below. It is put in a 1 liter magnetic pot together with 10 mmφ magnetic balls in the ratio shown in Table 1 and kneaded on a mill roller at 72 rpm for 12 hours to obtain a slurry suspension.

Table 1 Electrolyte raw material powder 200 g Binder 43.3 g Dispersant 3.6 g Plasticizer 17.3 g Dispersion solvent 215 g The slurry obtained in water was taken out and allowed to stand still overnight in a sealed container, and then the slurry was about 50 ° C. Vacuum degassing is performed while heating to 0, and the slurry is adjusted to have a slurry viscosity of 5 to 60,000 cp. Subsequently, a doctor blade film forming machine was used to form a film having a thickness of 100 to 300 μm to obtain a green sheet.

Subsequently, the above-mentioned green sheet is length 2
After cutting to about 00 mm (sheet width 180 mm),
As shown in (A), the back surfaces of electrolyte green sheets 21 (the surfaces in contact with the film at the time of film formation) are bonded together using dibutyl phthalate as an adhesive, and two layers of green sheets are laminated as shown in FIG. 2 (B). Item 22

Further, as shown in FIG. 3 (A), the back surface of the green sheet is attached to both sides of the two-layer laminated product by using dibutyl phthalate as shown in FIG. 3 (B) four-layer laminated product. 31 was also made. These laminated products were sandwiched between glass plates, dried with hot air at 100 ° C. for about 1 hour, taken out, and then punched into a predetermined size using a mold.

For the two-layer or four-layer electrolyte green sheet laminate obtained by the above method, 500 ° C.
After degreasing, baking at 1300 ° C, thickness 300-60
The electrolyte membrane was 0 μm. With respect to these electrolyte membranes, warpage or waviness as shown in FIG. 5 was measured.
The following “Table 2” shows the measurement results.

[0021]

[Table 1]

(Example 2) Air electrode raw material powder (LaSrMn)
O ₃ : particle size 0.5 to 2 μm, or fuel electrode raw material powder (Ni
(O / YSZ: particle size 0.1 to 1.0 μm), polyethyl methacrylate as an organic binder, amine as a dispersant, dibutyl phthalate as a plasticizer, and thinner as a dispersion solvent are shown in Tables 3 and 4 below. 4 ”in the same manner as in Example 1 to obtain air electrode and fuel electrode green sheets having a thickness of 100 to 150 μm.

Table 3 (air electrode slurry mixing conditions) Air electrode raw material powder 110 g Binder 26.5 g Dispersant 4.1 g Plasticizer 8.0 g Dispersing solvent 80 g Table 4 (fuel electrode slurry mixing conditions) Fuel electrode raw material powder 160 g Binder 47 0.2 g dispersant 7.4 g plasticizer 14.2 g dispersing solvent 105 g, followed by 2 of the electrolyte obtained by the procedure of Example 1.
As shown in FIG. 4 (A), the back surface (the surface in contact with the film at the time of film formation) of the green sheets 41 and 42 of the air electrode and the fuel electrode is used as an adhesive for both surfaces of the one-layer or four-layer green sheet laminated product. It was attached using dibutyl furarate to obtain an air electrode / electrolyte / fuel electrode green sheet laminate 43 (illustrated in FIG. 4 (B)). These laminated products were also sandwiched between glass plates in the same manner as in Example 1 and dried, and then punched into a predetermined size.
Degreasing was performed at 0 ° C, firing was performed at 1300 ° C, and warpage and waviness were measured. The measurement results are shown in Table 2 described above.

(Comparative Example 1) Regarding Comparative Example 1, Example 1
Similarly to the above, an electrolyte green sheet having a thickness of 300 to 600 μm was formed, and after firing as a single film, warpage and waviness were measured. The measurement results are shown in Table 2 above.

(Comparative Example 2) Also, in Comparative Example 2, the electrolyte green sheet single film having the green sheets for the air electrode and the fuel electrode adhered thereto in the same manner as in Example 2 had no warpage or waviness after firing. Measurement was performed. The measurement results are shown in Table 2 above.

According to the present invention, a flat plate type SOFC having sufficient strength as a thick film electrolyte membrane or a self-supporting membrane type cell in which this and an air electrode and a fuel electrode are integrally fired, which has been difficult in the conventional doctor blade method. Can be manufactured. In addition, the electrolyte or cell obtained by the present invention is greatly reduced in warpage and undulation, and cracks or cracks in the firing process are reduced, so that improvement in manufacturing yield can be expected. Further, according to the present invention, a flat plate type SOF
It can be applied to general ceramic thin films or plate materials other than C cells.

[0027]

As described above in detail, according to the present invention,
Method of manufacturing flat plate cell having electrolyte substrate or fuel electrode, air electrode having sufficient film thickness and sufficient smoothness even in increasing cell area when manufacturing cells by doctor blade method Can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory view of a conventional flat-plate SOFC cell,
1A is a cross-sectional area of a self-supporting membrane cell, and FIG. 1B is a cross-sectional view of a supporting membrane cell.

FIG. 2 is an explanatory view of a green sheet two-layer laminated product according to the first embodiment of the present invention, and FIG.
(B) shows the state after bonding.

FIG. 3 is an explanatory diagram of a green sheet four-layer laminated product according to the first embodiment of the present invention, and FIG.
(B) shows the state after bonding.

FIG. 4 is an explanatory view of an air electrode / electrolyte / fuel electrode green sheet laminated product according to Example 2 of the present invention, and FIG.
Shows the state before bonding and FIG. 4B shows the state after bonding.

FIG. 5 is an explanatory view of warpage and waviness of an electrolyte membrane or a cell.

[Explanation of symbols]

21 ... Electrolyte green sheet, 22 ... Green sheet 2-layer laminated product, 31 ... Green sheet 4-layer laminated product,
41 ... Fuel electrode green sheet, 42 ... Air electrode green sheet, 43 ... Air electrode / electrolyte / fuel electrode green sheet laminated product.

Claims (3)

[Claims] 1. An electrolyte substrate, which is obtained by firing a laminate obtained by laminating several electrolyte green sheets formed by a doctor blade method. 2. An electrolyte substrate, comprising an even number of the laminates according to claim 1, which are laminated so as to be vertically symmetrical. 3. A method of manufacturing a flat plate cell, comprising bonding green sheets of a fuel electrode and an air electrode to the front surface and the back surface of the laminated body and firing them integrally.