JPS63264873A - Manufacture of electrolyte substrate for fuel cell - Google Patents

Abstract

PURPOSE:To make the pore size of a substrate small and to make the porosity large by preparing raw material slurry with fine powder obtained by crushing the hydrate of lithium aluminate formed by mixing gamma-lithium aluminate fine powder with water, and forming an electrolyte substrate with the slurry. CONSTITUTION:The hydrate of lithium aluminate prepared by mixing gamma-lithium aluminate fine powder with water is crushed to form fine powder, and an electrolyte substrate is formed with the fine hydrate particles. The crystal water in the hydrate is removed while a cell temperature is raised to operation temperature, and the portion where the crystal water was removed is converted into a micropore having a pore size of about 100Angstrom . Micropores 3 are formed in a lithium aluminate particle 1 in addition to a pore 2 formed between lithium aluminate particles 1. The electrolyte substrate having small pore size and large porosity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing an electrolyte substrate for a fuel cell.

[Conventional technology]

The required properties of an electrolyte substrate (electrolyte plate) that holds an electrolyte in its pores are that the material be stable with respect to the electrolyte and be an electronic nonconductor.

The electrolyte of a molten carbonate fuel cell consists of a ternary mixture of lithium carbonate, potassium carbonate, and sodium carbonate, or a binary mixture of two of these, and the cell is operated at a temperature above the melting point of the mixed salt. .

Generally, the operating temperature of a battery is as high as 600 to 700° C., and the electrolyte is highly corrosive, so the electrolyte substrate material must have heat resistance and corrosion resistance.

Furthermore, it is also necessary to have electrical insulation properties so that the generated potential does not short-circuit through the electrolyte substrate.

For the above reasons, lithium aluminate is used as the electrolyte substrate material.

Another required property of the electrolyte substrate is that the pores formed therein be small. An electrolyte substrate holding an electrolyte is sandwiched between a positive electrode and a negative electrode, and the positive electrode contains hydrogen as a fuel gas, and the negative electrode contains a mixed gas of oxygen and carbon dioxide as an oxidant gas. is supplied.

For this reason, the electrolyte substrate needs to have sealing properties to prevent the fuel gas and the oxidant gas from mixing and burning.

The electrolyte substrate uses the capillary force of the electrolyte to hold the electrolyte in the pores of the substrate, and the gas is sealed by the electrolyte, so the smaller the pore diameter of the substrate, the greater the ability to hold the electrolyte, which is desirable. . Furthermore, when the electrolyte holding power is large, electrolyte outflow can be prevented, and performance deterioration due to loss of electrolyte can also be prevented.

Furthermore, the electrolyte substrate needs to have a high porosity. In molten carbonate fuel cells, carbonate ions move through the electrolyte and electrochemical reactions proceed, so in order to improve cell performance it is necessary to reduce the ion conduction resistance of the electrolyte substrate. Ion conduction resistance is inversely proportional to the electrolyte mass in the electrolyte substrate, that is, the porosity of the substrate, if the area and thickness of the electrolyte substrate are constant. Therefore, it is desirable for the electrolyte substrate to have a large porosity in terms of performance.

In addition, since the electrolyte is consumed during battery operation due to evaporation due to corrosion of the battery components and reaction gases, it is desirable for the substrate to have a high porosity and hold a large amount of electrolyte from the viewpoint of longevity.

By the way, the conventional method for manufacturing an electrolyte substrate is disclosed in Japanese Patent Application Laid-Open No. 1986-
As described in Japanese Patent No. 72172, γ with a particle size of 1μ or less
- An aqueous slurry is made using lithium aluminate powder and wood pulp as raw materials, and the slurry is made into paper to form an electrolyte substrate. According to this method, the porosity can be sufficiently increased due to the formation of pores due to the burning of the pulp, but it is difficult to reduce the fiber diameter of the pulp, and no matter how small the raw material powder of γ-lithium aluminate is, the porosity can be sufficiently increased. However, while mixed with the aqueous slurry, lithium aluminate undergoes a hydration reaction and crystallizes, increasing the particle size, resulting in a problem in that the pore size of the completed electrolyte substrate becomes larger.

Furthermore, in JP-A-57-27569, fine powder of γ-lithium aluminate, crack-reducing particles of alumina, and electrolyte are mixed and molded by hot pressing.

In this case, since no water is used in the manufacturing process, the growth of particles due to hydration reactions is prevented, resulting in a substrate with a small pore size, but the reduction in porosity due to mixing particles with different particle sizes is not taken into account. First, there was a problem in that the porosity of the completed electrolyte substrate was reduced. Furthermore, in this case, the molded electrolyte substrate absorbs moisture from the air and undergoes a hydration reaction, resulting in deterioration in quality, making it difficult to store the substrate.

[Problem that the invention seeks to solve]

The above two conventional technologies do not take into account the increase in particle size due to the hydration reaction of γ-lithium aluminate and the decrease in porosity due to the mixing of particles with different particle sizes, and the pore size of the electrolyte substrate is There was a problem in that it was not possible to satisfy both the requirements of reducing the size and increasing the porosity at the same time.

The present invention was made in view of the above points, and it is an object of the present invention to provide a method for manufacturing a conductive substrate for fuel cells that has a small pore diameter and a high porosity. be.

[Means for solving problems]

The above purpose is to create a fine powder made from lithium aluminate powder by pulverizing a lithium aluminate hydrate made by mixing γ-lithium aluminate fine powder and water. This is achieved by:

[Effect]

First, a hydrate LizAQz.7HzO is formed by reacting γ-lithium aluminate with water. At this point, the particle size is large, and even if the electrolyte substrate is molded in this state, the pore size will become large, so the formed hydrate is pulverized to form fine particles. Since the electrolyte substrate was formed using these hydrate fine particles as a raw material, the crystal water in the hydrate was scattered during the process of raising the temperature of the battery to the operating temperature, leaving about 100 wide-diameter fine pores with traces of scattered crystal water. becomes. As a result, in addition to the pores formed between the lithium aluminate particles, even finer pores are formed within the lithium aluminate particles.

An electrolyte substrate with small pore diameter and high porosity can be obtained.

〔Example〕

The present invention will be explained below based on the illustrated embodiments. FIG. 1 shows an embodiment of the invention. As shown in the figure, a raw material slurry is made using lithium aluminate powder as a raw material, and then this raw material slurry is made into a plate to form an electrolyte substrate.This is a method for manufacturing an electrolyte substrate for a fuel cell.

In this example, lithium aluminate powder was used as a raw material, and fine powder was formed by crushing a lithium aluminate hydrate made by mixing γ-lithium aluminate fine powder and water. . By doing this, the pore diameter of the electrolyte substrate becomes smaller and the porosity becomes larger.
It is possible to obtain a method for manufacturing an electrolyte substrate for a fuel cell, which allows the pore diameter to be small and the porosity to be large.

First, fine powder of γ-lithium aluminate was placed in water and reacted at room temperature for 150 to 200 hours to form a hydrate. The γ-lithium aluminate used had an average particle size of 0.1μ and a specific surface area of 23 rrr/g. Although it is possible to use particles with a large particle size and a small specific surface area, it is preferable to use particles with a large specific surface area because the hydration reaction time will be longer.1 The prepared hydrate has a scaly shape and is crystalline. Since a growth in particle size due to chemical reaction was observed, the powder was ground using a ball mill to a particle size of approximately 0.1 μm. An electrolyte substrate was molded using the fine powder of this hydrate according to the procedure described below.

First, trichlorethylene, tetrachloroethylene, and n-butyl alcohol were used as solvents, each at a volume ratio of 60.2.
:17. O: 1.8Q of solution mixed with 22.8
was placed in a ball mill, and 370 g of alumina fibers for reinforcing the electrolyte substrate were added and stirred to disperse the fibers. In this ball mill, 195% butyl phthalyl glycolate was added as a plasticizer to 4.8Q of a mixed solution having the same composition as the above-mentioned solvent.
mff1, polyvinyl butyral as a binder 6
05g was added and stirred and dissolved, and then mixed. Furthermore, 1.92 kg of lithium aluminate hydrate powder.

After adding 269 g of lithium carbonate for lithiumizing the above-mentioned alumina fibers and thoroughly kneading, deaeration was performed under reduced pressure to adjust the viscosity to obtain a raw material slurry.

This organic slurry was made into a plate by the doctor blade method to obtain an electrolyte substrate.

As described above, an organic slurry was used in this example, but since hydrate particles are used as a raw material, it is stable in water and can also be made into an aqueous slurry. The electrolyte substrate is coated with electrolyte after molding, is assembled into a battery, and as the temperature is raised to the operating temperature of the battery, the solvent, binder, and water of crystallization are removed, and the electrolyte soaks into the molded pores, completing the process. . Therefore, in order to investigate what kind of pore characteristics the formed electrolyte substrate exhibits at the battery operating temperature of 650°C, the formed sheet was fired at 650°C, and a solvent,
The binder and crystallization water were splashed off. Comparison of electrolyte substrates after firing with conventional electrolyte substrates using an electron microscope I
The results of this experiment are shown in Figure 2, and those of the conventional example are shown in Figure 3.

has been done.

As is clear from these two figures, when compared with the structure of the conventional electrolyte substrate molded from unhydrated lithium aluminate fine powder shown in Figure 3, it is approximately 0.1μ
The lithium aluminate particles 1 having a particle size of There are intraparticle pores 3 with sizes ranging from 0.005 to 0.01μ, which are thought to have been formed as a result of scattering of crystal water.
was recognized to exist.

In addition, the pore characteristics of the fired electrolyte substrate of this example were compared with those of the conventional electrolyte substrate using a mercury porosimeter.
The measurement results of the conventional example are shown in FIG. 4, and those of the present example are shown in FIG. Both of these figures show the relationship between pore diameter, cumulative pore volume, and differential pore volume, with cumulative pore engraftment and differential pore volume plotted on the vertical axis, and pore diameter plotted on the horizontal axis. It is something.

As is clear from both of these figures, in the conventional substrate shown in Figure 4, which uses non-hydrated particles, the peak of the differential pore volume only exists around the pore diameter of 103 mm (0.1μ). However, the electrolyte substrate of this example shown in FIG. 5 using a hydrate is as follows.
It was observed that two peaks existed near the pore diameters of 103mm and 10"mm. Also, the maximum value of cumulative pore volume, which is closely related to the porosity of the electrolyte substrate, was determined by hydration. It was observed that the porosity was approximately 0.5 cc/g for the conventional substrate without hydration, and approximately 7 cc/g for the hydrated substrate of this example. It was confirmed that the electrolyte substrate of this example using a hydrate had good pore characteristics with the same ratio (30 to 40%).

In this way, according to this embodiment, the pore diameter of the electrolyte substrate can be made small and the porosity can be made large, so that the electrolyte holding power is increased, the separation of fuel gas and oxidant gas is improved, and the electrolyte The amount of loss of fi! This is effective in improving the reliability and extending the life of the pond. Also, 1! Since the amount of electrolyte retained increases, battery performance can be improved by reducing the ionic conduction resistance of the electrolyte, and battery life can be extended due to electrolyte disappearance. Furthermore, the electrolyte substrate becomes stable against water and does not need to be stored in a dehumidified atmosphere, making storage easier. Since the removal of crystallized water in the lithium aluminate hydrate is also performed at the same time as raising the temperature of the battery, the number of manufacturing steps can be reduced.

Other embodiments of the invention will now be described. A fine powder of hydrate prepared in the same manner as in the above-mentioned example was fired to obtain a powder from which water of crystallization had been removed, and an electrolyte substrate was formed using the powder as a raw material in the same manner as in the above-mentioned example.

The crystal water removal temperature of the raw material powder was set to 650℃, 800"C, 9
When the temperature was changed to three different temperatures at 00°C, there was a change in pore volume when the molded electrolyte substrate was fired at 650°C.

When the pore volume of pores with a pore diameter of around 100 pores, that is, the pore volume due to particle pores, is 650°C, O, 1 is almost the same as in the above example.
6cc/g, 0.10cc/g at 800℃, 90
The pore volume decreased to 0.07 ω/g at 0°C as the crystal water removal temperature increased. In the case of the above embodiment, the removal temperature is limited to 65'O ℃, which is the battery operating temperature, because the crystal water is removed during the battery temperature rising process, but according to this embodiment, the crystal water removal temperature is The temperature can be arbitrarily selected and the pore volume of around 100 pores in diameter can be controlled thereby. This is effective when it is necessary to reduce the porosity depending on the creep characteristics of the electrolyte substrate and the combination with constituent members such as electrodes.

〔Effect of the invention〕

As described above, the present invention provides a method for producing an electrolyte substrate for a fuel cell, in which the pore size of the electrolyte substrate is small and the porosity is large, thereby making it possible to have a small pore size and a large porosity. Can be done.

[Brief explanation of drawings]

FIG. 1 is a flowchart of an embodiment of the method for manufacturing an electrolyte substrate for fuel cells according to the present invention, FIG. 2 is an explanatory diagram showing the structure of an electrolyte substrate according to an embodiment, and FIG. An explanatory diagram showing the structure of an electrolyte substrate produced by the electrolyte base manufacturing method, and FIG. 4 are the same. FIG. 5 is a characteristic diagram showing the relationship between the pore diameter, cumulative pore volume, and differential pore volume of an electrolyte substrate according to an embodiment of the method for manufacturing an electrolyte substrate for a fuel cell according to the present invention. 1... Lithium aluminate particles, 2... Interparticle pores, ID Fig. 2 3-Q Konai Kurumada J and Fig. 4 N8 hole direct scratch [A1 5g Procedural amendment (voluntary) 1988 September 2 pigeons

Claims (1)

[Scope of Claims] 1. A method for manufacturing an electrolyte substrate for a fuel cell, in which a raw material slurry is prepared using lithium aluminate powder as a raw material, and then this raw material slurry is made into a plate to form an electrolyte substrate. A fuel characterized in that the raw material is a fine powder formed by pulverizing a lithium aluminate hydrate made by mixing a fine powder of γ-lithium aluminate and water. A method for manufacturing an electrolyte substrate for a battery. 2. The fine powder formed by pulverizing the hydrate of lithium aluminate is a pulverized hydrate obtained by firing the hydrate and removing at least a part of the crystal water. A method for producing an electrolyte substrate for a fuel cell according to item 1.