JPH0935730A - Molten carbonate fuel cell electrolyte matrix sheet and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte matrix with high breaking resistance, long life, and high productivity, and the manufacturing process of the electrolyte matrix. SOLUTION: Mixed slurry comprising an organic binder, a ceramic electrolyte holding material, and a solvent is impregnated in a fiber cloth made of ceramic fibers, and dried to form a ceramic fiber sheet 1. A mixed slurry comprising a ceramic fine powder holding material, an organic binder, a plasticizer is dried in a sheet to form an electrolyte green sheet 2. The ceramic fiber sheet 1 is interposed between two electrolyte green sheet 2, and they are integrally bonded with hot rollers 11a, 11b to form a three layer structure electrolyte matrix sheet 3.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrolyte matrix sheet for a molten carbonate fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art A unit cell of a molten carbonate fuel cell is a flat plate-like electrolyte matrix holding a molten carbonate salt, and a pair of flat plate-like porous gas diffusion electrodes arranged so as to sandwich the electrolyte matrix. That is, it is composed of a fuel electrode and an oxidant electrode, and a gas channel arranged outside these electrodes and serving as a supply path for the fuel gas and the oxidant gas and a conductive path. Usually, in order to obtain a large output, a plurality of these single cells are laminated with an electronically conductive separator plate in between to form a laminated battery.

At this time, an edge plate having an opening conforming to the planar shape of the electrode is provided, and the periphery of the edge plate and the separator plate are joined to form a closed gas flow path space. The electrolyte matrix is made larger than the electrode so as to cover the boundary line between the electrode and the edge plate.

Such an electrolyte matrix generally comprises an electrolyte holding material such as lithium aluminate powder,
Porous electrolytic matrix by heating and volatilizing the organic binder of the dried electrolyte green sheet, which is formed by a doctor blade method from a slurry obtained by mixing and kneading an organic binder such as polyvinyl butyral and an organic solvent. Obtained as.

In this case, in the step of volatilizing the binder by heating and volatilizing the organic binder contained in the electrolyte green sheet, the electrolyte matrix becomes a very brittle ceramic powder aggregate, and this aggregate forms an electrode edge plate and an electrode edge plate. Cracks are likely to occur at the boundary gaps or stepped portions.

When the matrix sheet after debinding is kept at a higher temperature and the electrolyte is impregnated with the electrolyte, the phase change of the electrolyte from the solid phase to the liquid layer and the temperature of the battery are lowered below the melting point of the electrolyte to stop or restart. When the temperature is raised, the same phase change and thermal deformation of the cell occur during the thermal cycle, and the cell is easily cracked.

[0007] Such cracking of the electrolyte matrix causes cross-mixing of the fuel gas and the oxidant gas, which leads to loss of the function of the battery. As a method of preventing cracking of the electrolyte plate, a reinforcing material such as ceramic fiber is used as a matrix sheet. It has been attempted to reinforce the matrix sheet by mixing it in the slurry. Alternatively, it has been attempted to construct an electrolyte plate by laminating a matrix sheet, a fiber sheet and an electrolyte sheet.

[0008]

As one of the methods for reinforcing the matrix sheet, for example, Japanese Patent Application Laid-Open No. 1-130.
No. 474, a thin sheet is formed from a slurry composed of ceramic fine powder and ceramic fibers, a plurality of the sheets are stacked, pressure-molded, and a binder is volatilized and then impregnated with an electrolyte. A method has been proposed. Further, Japanese Patent Laid-Open No. 1-132061 discloses an electrolyte plate in which gamma-lithium aluminate is mixed with ceramic fibers as a reinforcing material, wherein the ceramic fibers are high purity alumina fibers of 95% or more. Is proposed.

In any of the above-mentioned electrolyte plates, it is necessary to evenly disperse the ceramic fibers in a kneading slurry composed of fine powder of an electrolyte holding material, an organic binder and a solvent. Usually, a defoaming mixer is used in such a dispersion mixing process, but even if ceramic fibers are added as it is to the raw material slurry of the matrix, the flocculation of the fibers, which is usually a cotton-like agglomerate, does not dissolve and is uniform. Difficult to disperse into. Further, when the mixture is forcibly mixed and dispersed by using a crushing mixer such as a ball mill, the fiber is disintegrated, and at the same time, the fiber itself is broken to shorten the fiber, and the fiber having the intended fiber length is uniformly dispersed. Becomes difficult.

On the other hand, as another method, Japanese Patent Laid-Open No. 4-115
Japanese Patent No. 464 proposes to construct an electrolyte plate in which a lithium aluminate matrix sheet, an alumina fiber sheet, and an electrolyte sheet are laminated in a three-layer structure.
In this method, the strength is remarkably improved because the ceramic fiber retains its original shape, but it is not integrated with the matrix sheet and is not sufficiently effective in improving the strength of the matrix sheet itself. Further, in this case, the fiber layer has a weak electrolyte retention property, the electrolyte leaks from the end of the fiber layer during the operation of the battery, which leads to a decrease in the battery performance, which is a problem for long-term operation while maintaining high performance. There is.

An object of the present invention is to provide an electrolyte matrix which has improved resistance to cracking of the electrolyte matrix, has a longer life, and has good productivity, and a method for producing the same.

[0012]

The present invention provides an electrolyte plate of a molten carbonate fuel cell in which a ceramic fiber is reinforced in an electrolyte matrix, and a ceramic fiber cloth comprises a ceramic electrolyte holding material, an organic binder and a solvent. The fibrous sheet impregnated with the mixed slurry and dried is sandwiched by a mixed slurry consisting of a ceramic fine powder electrolyte holding material, an organic binder, a plasticizer and a solvent, and dried electrolyte matrix green sheets to be integrated. Is characterized by.

Further, in the manufacturing method according to the present invention, a fiber cloth made of ceramic fibers is impregnated with a mixed slurry made of an organic binder, a ceramic electrolyte holding material and a solvent, and dried to form a ceramic fiber sheet. Based on a mixed slurry composed of ceramic fine powder electrolyte holding material, organic binder, plasticizer and solvent, this is dried into a sheet form to form an electrolyte matrix green sheet, and then a ceramic fiber sheet is placed between the two electrolyte green sheets. It is characterized in that it is sandwiched between two sheets and is fused and integrated as a sheet having a three-layer structure by using a heat roller or a heat press.

[0014]

[Function] When a ceramic fiber reinforced electrolyte matrix sheet is formed, a ceramic fiber cloth is used,
This fiber cloth is impregnated with a mixed slurry consisting of an organic binder, an electrolyte holding material and a solvent, and further laminated with an electrolyte matrix green sheet containing a conventional organic binder to facilitate fusion bonding inside or outside the battery. A solidified electrolyte matrix sheet is obtained. That is, according to this method using a fiber cloth, it is possible to easily obtain a ceramics fiber reinforced electrolyte matrix in which the original shape of the ceramics fiber is maintained without dispersing and mixing the ceramics fiber in the slurry for the electrolyte matrix.

Further, an electrolyte sheet having a composite integrated structure can be formed, and a homogeneous and high-strength electrolyte sheet can be obtained.

Further, the ceramic fiber cloth is impregnated and held with a slurry containing fine powder of an electrolyte holding material, which is mixed and adjusted, so that the central pore diameter of the ceramic fiber layer is the same as that of the electrolyte matrix sheet obtained from the conventional electrolyte matrix green sheet. It can be equal or less.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a manufacturing process of the composite electrolyte matrix sheet according to the present invention. The slurry for impregnating the ceramic fiber cloth is a mixture of a ceramic electrolyte retaining material powder represented by lithium aluminate, an organic binder, a plasticizer and a solvent in an appropriate amount, and a suitable condition for impregnating the slurry with a ball mill or the like. Disintegrate and mix with. At this time, the size, amount and mixing time of the mill balls are adjusted so that the particle size of the electrolyte holding material can penetrate into the fiber layer and an appropriate pore distribution can be obtained. After that, the slurry is adjusted to a viscosity suitable for impregnation with a vacuum stirring defoaming machine.

A ceramic fiber cloth prepared separately is impregnated with this viscosity-adjusted slurry to form a sheet.
The impregnated sheet is formed by using a vacuum impregnating device, a roller coater or the like to form the ceramic fiber sheet.

On the other hand, the molding of the electrolyte sheet is carried out in the same manner as the conventionally used method, that is, the electrolyte holding material powder, the organic binder, the plasticizer and the solvent are mixed in an appropriate amount, and the ball mill and the vacuum stirring defoaming are used. After crushing and mixing and adjusting the viscosity, the sheet is formed by a doctor blade method or the like and dried to form an electrolyte green sheet.

Each of the fibrous sheet and the electrolyte green sheet may be cut into a desired size as they are and used for battery lamination, but in this case, when the composite lamination is performed, it is necessary to perform an adjusting operation so that the respective sheets can be adhered to each other without voids. And

In order to save such troubles, it is more reliable to carry out the subsequent battery stacking work by forming the stacked body outside the battery in advance. Therefore, in this embodiment, the fiber sheet is sandwiched between the electrolyte green sheets and is pressed and integrated with a heating roller or the like. At this time, the gap between the upper and lower rollers and the rotation speed of the rollers are appropriately adjusted so that they adhere to each other without any gap. By this method, it is possible to form a composite matrix sheet in which the respective sheets are fused and integrated without any void. Next, the results of evaluation using the composite electrolyte matrix manufactured according to the present invention will be described. Lithium aluminate powder having a critical area of 10 m ² / g and olefinic copolymer resin were mixed at a ratio of 80:20, an organic solvent was added, and the mixture was crushed and mixed in a ball mill to form a slurry, which was then formed by a doctor blade method. A membrane was obtained to obtain an electrolyte matrix green sheet.

On the other hand, a purity of 95% or more, a thickness of 0.25 mm,
A slurry in which an alumina fiber cloth having a fiber diameter of 10 μm was mixed with a lithium aluminate powder having a critical surface area of 10 m ² / g and an olefin-based copolymer resin at a ratio of 80:20, an organic solvent was added, and the mixture was crushed and mixed with a ball meal. A roller-coating method was used to impregnate a compress to obtain an alumina fiber green sheet.

In order to obtain the composite matrix, as shown in FIG. 2, the laminated body in which the electrolyte green sheet 2 is sandwiched on both sides of the ceramic fiber green sheet 1 is heated by the heating rollers 11a and 11b adjusted to the temperature of 120 ° C. respectively. To obtain a composite electrolyte matrix green sheet 3 having a three-layer structure in which

A sample is cut out from this composite matrix green sheet, sandwiched between alumina plates, and about 0.2 kgf
・ A load of cm ² is applied, and Air: CO ₂ = 70: 30, 4
After the organic binder was diffused at 50 ° C. to 20 hr, the three-point bending was performed to measure the step strength. The result is the curve J in FIG.
Shown in As a comparative example, the measurement result of only the above-mentioned electrolyte matrix sheet is shown by the curve K in FIG. The measurement conditions are as shown in Table 1.

[0026]

[Table 1] The alumina fiber reinforced matrix had a residual stress value even after reaching the breaking strength, and showed a mild decrease tendency with an increase in the displacement amount, and the maximum stress value thereof was about 2.2 kgf · mm ² .

On the other hand, in the conventional electrolyte matrix plate, the stress value linearly increased up to a displacement of 0.22 mm, and the fracture strength was 0.3 kgf · mm ^2, and then fracture occurred.

As shown in FIGS. 4 (a) and 4 (b), the composite electrolyte matrix green sheet 3 cut out to the same size as the cathode 4 has different thicknesses such that the anode 5 and the anode side alumina have different thicknesses so that a step is formed. From the frame 6 and the other side, a simulated cell 7 sandwiched by the cathode 4 from the other side was assembled, and a load of about 1 kgf · cm ² was applied to volatilize the organic binder to carry out a crack resistance confirmation test. A comparative test was also conducted using a conventional electrolyte matrix. The results are shown in Table 2.

[0029]

[Table 2] No cracking was observed when the composite matrices shown in Invention Sheets 1-6 were used, whereas the conventional matrix of Comparative Sheet 1 showed complete cracking.

Although the above-mentioned embodiment describes the procedure for obtaining the composite electrolyte matrix green sheet 3 having a three-layer structure outside the battery, it is also possible to construct the composite matrix inside the battery.

The structure of this battery is shown in the schematic diagram of FIG. The ceramic fiber green sheet 1 is assembled so as to be sandwiched between two electrolyte holding material green sheets 2.

A battery was constructed using the composite matrix of the materials shown in the above-mentioned invention sheet 1, a power generation test was carried out under the conditions shown in Table 3, and two thermal cycle tests were carried out during the power generation.

[0033]

[Table 3] The battery performance obtained as a result is shown in 1 of FIG. 6, and the battery performance of the battery using the conventional electrolyte matrix as a comparative example is shown in m of FIG. Note that n in FIG. 6 indicates the number of thermal cycles.

In the example using the conventional electrolyte matrix, the power generation was completely stopped by the gas cross-mixing caused by the crack of the electrolyte plate in the second heat cycle, but in the example using the ceramic fiber reinforced electrolyte matrix, the heat cycle was performed. After that, there was no deterioration in performance.

Generally, when electrolyte leakage occurs in the electrolyte matrix, the electromotive force of the battery tends to decrease at a constant rate. However, in the sheet of the present invention, this tendency is not observed and the loss of electrolyte occurs. It indirectly indicates that there is no.

In addition to the above examples, the same bending test was carried out using the composite matrix sheets of the invention sheets 2 to 6 in combination, and substantially the same results as in FIG. 3 were obtained. Other tests were conducted in the same manner as above using the materials shown in Table 4 with respect to the types of ceramic fiber cloths constituting the ceramic fiber sheet and the types of ceramic electrolyte holding materials impregnated into the ceramic fiber cloths, and similar results were obtained.

[Table 4] Also, as a method for obtaining a composite laminate of the electrolyte layer matrix green sheet and the ceramic fiber sheet, the results of the same test using the electrolyte matrix sheet manufactured by the method of externalizing outside the battery shown in FIG. 2 are also not shown. However, a similar effect was obtained. It became easy to handle by embodying it outside the battery.

In this embodiment, a ceramic fiber sheet was sandwiched between two electrolyte matrix green sheets to obtain an electrolyte matrix sheet having a three-layer structure, but the same effect can be obtained by further increasing the number and stacking the two layers alternately. Obtainable.

On the other hand, among the composite matrices of Table 2, invention sheet 1, invention sheet 3, invention sheet 4, invention sheet 5
FIG. 7 shows the results of pore distribution measurement by the mercury intrusion method for the composite electrolyte matrix of Invention Sheet 6 and. As a result, the micropores involved in electrolyte retention are all formed between 0.1 and 0.2 μm, and the electrolyte retention function shows a pore distribution equivalent to that of a conventional electrolyte matrix containing no ceramic fiber. I understand.

[0039]

INDUSTRIAL APPLICABILITY In an electrolyte matrix sheet for a molten carbonate fuel cell, a fiber sheet produced by using a ceramic fiber cloth as the electrolyte matrix sheet is sandwiched by two electrolyte matrix green sheets from both sides to be fused and integrated. The following effects can be obtained by using an electrolyte matrix sheet having a structure.

(1) By using a ceramic fiber cloth, it is not necessary to go through the complicated step of uniformly dispersing and mixing the ceramic fibers in the slurry for the electrolyte matrix sheet, and the fiber sheet can be easily manufactured, and the productivity is improved. A high sheet can be obtained. Further, in particular, the one integrated outside the battery can be easily handled and can be easily assembled even when the battery is assembled. (2) The integrated electrolyte matrix sheet exhibits high cracking resistance, prevents thermal shock and cracking in the gap between the edge and the electrode, and greatly improves battery reliability.
(3) By impregnating the ceramic fiber layer with the electrolyte retaining material, the electrolyte retaining property can be maintained and the life can be extended.

[Brief description of drawings]

FIG. 1 is a process drawing showing a manufacturing procedure of an electrolyte matrix sheet according to the present invention.

FIG. 2 is a schematic diagram showing a state of producing an electrolyte matrix sheet having a three-layer structure.

FIG. 3 is a diagram showing a relationship between bending stress and displacement of an electrolyte matrix sheet.

4A and 4B are configuration diagrams of a simulated cell used in a crack test.

FIG. 5 is a schematic diagram showing an arrangement of electrodes and an electrolyte assembled outside the battery.

FIG. 6 is a characteristic diagram showing changes over time in the output voltage of the fuel cell including thermal cycles.

FIG. 7 is a pore distribution diagram of the electrolyte matrix sheet according to the present invention.

[Explanation of symbols]

 1 Ceramic Fiber Green Sheet 2 Electrolyte Green Sheet 3 Electrolyte Matrix Green Sheet 4 Cathode 5 Anode 6 Alumina Frame

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Seta 4-4, 2 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Stock company Toshiba Keihin Office (72) Inventor Yasushi Shimizu 4-4, Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Stock company Toshiba Keihin office (72) Inventor Katsumi Sato 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Stock company Toshiba Keihin office

Claims (5)

[Claims] 1. A molten carbonate fuel cell comprising an electrolyte plate holding molten carbonate between a pair of positive and negative gas diffusion electrodes made of a porous body, wherein a fiber cloth made of ceramic fibers and an organic binder, Ceramic electrolyte holding material,
A ceramic fiber sheet impregnated with a mixed slurry composed of a solvent and dried is sandwiched between a ceramic fine powder electrolyte holding material, an organic binder, a plasticizer, and a solvent-containing mixed slurry composed of a solvent, which is sandwiched between the electrolyte green sheets to form an integrated body. An electrolyte matrix sheet for a molten carbonate fuel cell, characterized in that 2. A ceramic fiber made of one or more materials selected from alumina, titania, zirconia, metal titanate, metal zirconate and lithium aluminate is used as a fiber cloth. 2. An electrolyte matrix sheet for a molten carbonate fuel cell according to 1. 3. The electrolyte matrix sheet for a molten carbonate fuel cell according to claim 1, wherein any one selected from lithium aluminate and lithium titanate is used as a holding material for the electrolyte matrix green sheet. 4. An organic binder containing an organic binder prepared by mixing one or more selected from an olefin-based copolymer resin, an olefin-acrylic-based polymer resin, and an olefin-vinyl-based copolymer resin, an electrolyte matrix green sheet and fibers. The electrolyte matrix sheet for a molten carbonate fuel cell according to claim 1, which is used as a binder for the sheet. 5. A fiber cloth made of ceramic fibers is impregnated with a mixed slurry made of an organic binder, a ceramic electrolyte holding material, and a solvent, and dried to form a ceramic fiber sheet, while a ceramic fine powder electrolyte holding material, Based on a mixed slurry composed of an organic binder, a plasticizer and a solvent, this is dried into a sheet form to form an electrolyte matrix green sheet, and then the ceramic fiber sheet is sandwiched between two electrolyte green sheets, A method for producing an electrolyte matrix sheet for a molten carbonate fuel cell, characterized in that the sheet is fused and integrated as a sheet having a three-layer structure using a hot roller or a hot press.