JPH02213055A - Molten carbonate fuel cell and electrolyte base plate and manufacture of electrolyte base plate - Google Patents

Abstract

PURPOSE:To retain a sufficient amount of molten carbonate electrolyte and to keep high cell performance for a long time by forming an electrolyte base plate so as to have a specified porosity and a specified mean pore size. CONSTITUTION:gamma-LiAlO2 powder which is the main material of a matrix for an electrolyte base plate is screened in a specified particle size or less with a vibrating screen and the powder on the screen is crushed, then repeatedly screened. Particles of the powder separated in each process are adjusted in a specified ratio and the powder is mixed with polyvinyl butyral and a pore forming agent in a dry process. The mixture is mixed with a solvent containing a plasticizer and fibers to form raw slurry. A green sheet is formed with the raw slurry. An electrolyte base plate having a porosity of 47% or more and a mean pore size of 0.5mum or less is obtained. By using this electrolyte base plate, the electrolyte impregnation amount is increased and cell performance is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a molten carbonate fuel cell, and in particular to an electrolyte substrate ( matrix) and its manufacturing method.

[Conventional technology]

JP-A-58-129781 and JP-A-62-237 regarding the conventional manufacturing method of electrolyte substrate (matrix)
For example, Publication No. 672 can be cited. These methods improve pore characteristics by mixing powders with different particle sizes (-particle sizes), but the factors that have a correlation with actual cell characteristics are not clear, and their limited range is unclear. The problem seems to be that it is not clear.

Molten carbonate fuel cells have attracted attention for their high power generation efficiency, large output, and excellent environmental protection.1 Their early development is highly desired not only in Japan but also around the world, and research and development is active. It is being done. However, there are still many problems that need to be solved before it can be put into practical use. Currently, at the development level, the electrode area is 3600 cm.
40 cells stacked, output 16kW, operating time 17
00h level, and in addition to improving output due to larger size, performance improvement (improvement of battery voltage at constant current density: target value of 0.85 V or more) and longer life (
Currently several thousand hours (target value of 20,000 hours or more) are required. The challenges to achieve this development goal are: 1) Forming an optimal reaction field 2) Maintaining an optimal reaction field 3) Improving the corrosion resistance of separator materials 4) Improving the corrosion resistance and durability of electrode (anode, cathode) materials etc. can be mentioned.

The electrochemical reaction that drives power generation occurs at the reaction field interface formed on the electrode surface. The interface situation of this reaction field is
The problem is how to create and maintain a state in which electrochemical reactions are most likely to occur. The state of this reaction field interface is also expressed by the term "wetting" of the electrode, which is determined by the surface structure of the electrode itself, the amount of electrolyte present, etc.

The amount of electrolyte present at the reaction field interface is determined by the correlation between the pore characteristics of the electrode and the electrolyte substrate and the amount of electrolyte impregnated. Therefore, the pore characteristics of the electrolyte substrate are.

It can be said that this is an important element for achieving good battery performance and maintaining it for a long time.

[Problem to be solved by the invention]

The following two items are listed as characteristics required for an electrolyte substrate.

1) Low liquid resistance (electrolyte ion movement resistance).

2) High electrolyte retention capacity.

Considering these two points as independent phenomena, it is considered that a larger porosity is desirable in order to lower liquid resistance, and a smaller pore diameter is desirable in order to improve electrolyte retention. However, these two
The two requirements are contradictory.

Increasing the porosity increases the amount of electrolyte that can be retained within the pores and lowers the movement resistance of electrolyte ions, but on the other hand, the ability to retain electrolytes decreases, resulting in less electrolyte flowing out and less transfer to the electrodes. This increase becomes a problem, and as a result, the amount retained in the electrolyte substrate becomes insufficient, causing crossover and an increase in internal resistance.

In addition, when the pore size is made smaller, the electrolyte retention force increases due to capillary force, but due to the proximity of particles, the porosity decreases and the electrolyte ion movement resistance increases, which increases the battery internal resistance and causes a decrease in battery performance. Taking these two contradictory phenomena into consideration, the challenge is how to control the pore characteristics of an electrolyte substrate to produce it.

SUMMARY OF THE INVENTION An object of the present invention is to provide a molten carbonate fuel cell having an electrolyte substrate with improved pore characteristics and a method for manufacturing the electrolyte substrate.

[Means for Solving the Problems] In order to achieve the above object, a molten carbonate fuel cell according to the present invention is provided, in which an electrolyte substrate holding the electrolyte is The porosity is 47% or more and the average pore diameter is 0.5 μm or less.

Further, the electrolyte substrate according to the present invention has a porosity of 47% or more and an average pore diameter of 0.5 μm or less. Here, the electrolyte substrate preferably has two or more peak pore diameters. In addition, the electrolyte substrate has a peak pore diameter of 0.3 μm or more.

It is preferable to have a peak pore diameter of 0.1 μm or less.

Furthermore, if the range is limited, the electrolyte substrate has a volume of pores with a pore diameter of 0.3 μm or more and 3 μm or less, which is 20 vol% or more of the total pore volume, 0.1 μm or less, and 0.003 μm or more.
The volume of pores with a diameter of m or more is 20 vol relative to the total pore volume.
% or more is better.

Further, the method for manufacturing an electrolyte substrate according to the present invention includes a step of dry mixing a raw material powder, a binder, and a pore-forming agent, a step of adding and mixing a plasticizer and cellulose into a solvent mixture, and a step of adding and mixing a plasticizer and cellulose to a solvent mixture. The method includes a step of mixing the products of the step, a step of defoaming the mixed product under reduced pressure to obtain a raw material slurry for molding, and a step of molding a green sheet from the raw material slurry. Here, the raw material powder is γ-LiAΩO1.

After separating the powder with a predetermined particle size or less, the remaining raw materials are crushed and the powder with a predetermined particle size or less is separated again, and the crushing and powder separation steps are repeated as appropriate, and each powder separated in each step is It is preferable that the method includes a step of appropriately adjusting the usage ratio of .

In addition, in order to increase the strength of the electrolyte substrate, AQ
It is desirable to add Jim fibers 5 [Function] According to the present invention, since the electrolyte substrate has a porosity of 47% or less and an average pore diameter of 0.5 μm or less, the amount of electrolyte retained in the pores increases. Therefore, the movement resistance of electrolyte ions is reduced, and the electrolyte retention strength is increased. Therefore, a fuel cell equipped with such an electrolyte substrate can maintain its improved cell performance for a long time.

In addition, the electrolyte substrate has a peak pore diameter of 0.3 μm or more,
By having two beak pore diameters, one being 0.1 μm or less, the electrolyte ion transfer resistance and electrolyte retention are further improved.

〔Example〕

First, the material and manufacturing method of the electrolyte substrate will be described.

b) Matrix material As the main matrix material for the electrolyte substrate, use a material with a high specific surface area (
') y L x A Q Oz powder (specific surface area 23
m2/g) was used. In addition, in order to improve the strength and heat cycle resistance of the green sheet, we have added a spectral ratio of 7 (1
1/d, n: fiber length, d: fiber diameter) is about 100
2□O1 fiber was used.

Binder Low-temperature decomposable binder PVB (polyvinyl butyral resin 4000-Z, average degree of polymerization 1000°, manufactured by Denki Kagaku Kogyo mri) was used.

c) Pore forming agent Isobutylene maleic anhydride copolymer (isopane 04, K11 from Clareisobrene Chemical), which is an organic polymeric material that decomposes at low temperatures, was used.

2) Solvent To prepare a mixed slurry of powder and fibers.

trichlorethylene, tetrachlorethylene and n
- A mixture of butyl alcohol was used. The mixing ratio of the solvent mixture was 60 VOΩ% of trichlorethylene, 17% of tetrachlorethylene, and 23 von% of n-butyl alcohol.

Using the above materials, a slurry was prepared according to the raw material slurry preparation flow shown in FIG. PvB, γ-L
i A 1! After weighing O, powder, and pore-forming agent, they are mixed dry in a ball mill. On the other hand, plasticizer and A
Qzo3 fibers were added and mixed until the AQzO3 fibers were well loosened, and then mixed again with the former matrix material. The container is a polyethylene wide-mouth bottle (
2000 aa), and a resin ball was used.

The viscosity of the slurry at this time was adjusted by adjusting the amount of solvent to be around 5 voids based on the homogeneous mixability of the raw materials. 2 with ball mill
After mixing for 4 to 30 hours, the pressure was reduced using a vacuum pump, and at the same time as defoaming, the solvent was removed to adjust the viscosity to obtain a raw material slurry for molding.

The viscosity of the slurry during sheet forming was adjusted to 40 to 60 voids at room temperature (approximately 20° C.) in view of coating properties. The slurry thus obtained was poured into a slurry dam of a doctor blade machine to form a green sheet. The doctor blade machine was set to have a blade gap of 1.0 a+m and a drawing speed Q of a Mylar sheet (Lumirror manufactured by Toshi Co., Ltd., one side silicon coated) of 3 m/win. After completion of molding, the green sheet was air-dried for 4 hours, and after drying, the green sheet was cut into 400 mm square pieces and used as test materials.

In the present invention, further, in order to adjust the micropores,
A powder of γ-LiAQO□ was prepared.

The main equipment used for powder preparation is shown below.

b) Vibration mill: Central processing machine IJ, MB-3 type Port) Vibration sieve e DALTON fJI, 50ZA type One of the features of the present invention is the process of crushing secondary particles of γ-L i A Q Ox powder. Through one step, γ-L i A Q O,
By adjusting the secondary particle size, it becomes possible not only to ensure that the average pore size is micropores (0.5 μm) but also to control the porosity. Moreover, the ability of the electrolyte matrix substrate with this pore characteristic to be produced with good reproducibility is a function of the crushing process of the lithium aluminate powder.

Furthermore, by using electrolyte substrates with different porosities obtained by controlling the porosity in battery tests, it is possible to confirm how the porosity of the electrolyte substrate affects battery characteristics.

<Example 1> FIG. 3 shows the rIl'IB method by crushing secondary agglomerated particles of the raw material γ-L i A Q O and powder.

First, the raw material γ-L i A Q O2 powder.

Use a vibrating sieve to separate fine powder that passes through 100 meshes and other powders. Powder that has passed through 100 meshes is stored in A, while γ-LiAflO□ that has not passed through 100 meshes
The powder was placed in a dryer and dried at 150°C for 1.5 hours.

Next, the dried γ-LiAΩ02 powder and 10 kg of ceramic balls in diameter were placed in a 6Q vibrating mill bot. At this time, add 1w of ethanol to prevent agglomeration.
t% was added and crushed for 1 hour. The crushed powder was again treated with a vibrating sieve and sized using 100 meshes. This process was repeated four times, and the powder passed each time was stored separately in A-D.

Table 1 shows the relationship between the amount of powder and the bulk density of the powders A-D, which were crushed at different times. As a result, the bulk density of A and D is 1.
It was found to be 5 times (=D/A).

Table 1 It was also found that the porosity of the electrolyte substrate varied by changing the amount of powder used at different times of crushing. Table 2 summarizes changes in porosity due to differences in mixing amounts. A(1
It was found that the larger the amount of B (twice sieve) used and the smaller the amount of B (double sieve) used, the higher the porosity.

Table 2 The porosity was measured using green sheets fired at 650°C (
An electrolyte substrate) was immersed in n-propyl alcohol, the weight of the sample was measured before, during and after immersion, and the weight was calculated using the following equation (1).

t= (Wl-W,)/ (wz-wz)...
(1) [: Porosity (%) W,: Sample weight in air (g) W,: Sample weight after n-propyl alcohol impregnation (g) W,: Sample weight in n-propyl alcohol (g) Here, the SEMI of samples with different porosity, that is, lot size,
! The results of m are shown in 4th (a) to (c).

FIGS. 5(a) to 5(c) are diagrams corresponding to 4th (a) to (c), and are explanatory diagrams for explaining the relationship between raw material powder, cellulose, and porosity. From this result, the larger the porosity, the
It was found that there were many pores with large pore diameters.

<Example 2> The pore distribution of samples with different mixing ratios of powders subjected to secondary particle crushing at different times was measured using a porosimeter.

The results are shown in FIGS. 6 to 8.

Figure 6 shows the results for a sample with a porosity of 42.7%, which is 0.04%.
It is formed by two pore peaks centered at μm and 0.12 μm. Figure 7 shows the results for a sample with a porosity of 45.5%.
It can be seen that as the pores increase from μm to 0.12 μm, the maximum pore diameter increases to 1 μm. Figure 8 shows the results for a sample with a porosity of 50.5%, and it can be seen that a new porosity peak around 0.5 μm has been formed due to the increase in the number of crushing samples. Understood.

<Example 3> Electrolyte substrate (matrix) samples having different porosities were impregnated with electrolyte, and the resistance values thereof were measured. The results are shown in FIG. 9. The measurement method is as shown below. Two samples were stacked, and the electrolyte (mixed carbonate: Li) corresponded to 120% of the total pore volume.

Co, K, Coj = 62:38 mofl ratio) is kneaded with approximately 20% of its weight of water to form a paste, which is applied between two samples and dried. This is sandwiched between two cathodes, and gold wire (diameter 0
, 3 mm) was installed as a measurement terminal.

With this as one block, blocks were made for each sample with a different porosity, and an insulating plate (artificial mica plate) was sandwiched between each block, and they were stacked together, tightened with the same pressure, heated to 650°C, and measured with a milliohmmeter. The resistance value was measured.

From the results in Figure 9, it can be seen that the larger the porosity, the higher the liquid resistance (
It was found that the transfer resistance value of carbonate electrolyte ions) decreased.

<Example 4> Assemble single cells using samples with different porosity.

Their performance was compared. All cell members and other assembly conditions were the same except for the electrolyte substrate sample.

The results are shown in Figure 1. When the porosity is 47voQ% or more, the battery performance shown by the solid line is at a load current density of 150raA/
It was found that the value of the internal resistance was 0.8 V when the temperature was 41 voQ% or more and the value of the internal resistance indicated by the broken line was 13 mΩ or less when the porosity was 41 voQ% or more.

The electrode area is 64cm'', and the measurement conditions are a temperature of 650℃ and an anode gas composition of 80%H2-20%CO.
,,Cathode gas composition is 70%Air-30%CO,,
The reaction gas utilization rate is based on standard conditions of 40%.

〔Effect of the invention〕

According to the present invention, an electrolyte substrate (
This is a desirable condition for the pore characteristics of the matrix).
Therefore, it is possible to hold a sufficient amount of carbonate electrolyte as an electrolyte substrate, improving battery performance and
It has a long-lasting effect.

Further, according to the manufacturing method according to the present invention, the electrolyte substrate described above can be easily manufactured.

[Brief Description of the Drawings] Figure 1 is a characteristic diagram of a battery using electrolyte plates with different porosities produced according to the embodiments of the present invention, and Figure 2 is a diagram of the characteristics of a battery using electrolyte plates with different porosities produced according to the embodiments of the present invention. The manufacturing flow diagram, Figure 3 is a flow diagram of the process of crushing and sizing the raw material powder, and Figure 4 shows the porosity and surface condition of the sample (SEMfR
Figures 5(a) to (C) are explanatory diagrams corresponding to Figures 4(a) to (c), and Figures 6, 7, and 8 are porosity diagrams. FIG. 9 is a diagram showing the results of measuring the pore distribution of samples with different porosity using a porosimeter, and FIG. 9 is a diagram showing the relationship between resistance value and porosity of samples with different porosity.

Claims (1)

[Claims] 1. In a molten carbonate fuel cell using carbonate as an electrolyte, an electrolyte substrate holding the electrolyte has a porosity of 4.
A molten carbonate fuel cell having an average pore diameter of 7% or more and 0.5 μm or less. 2. An electrolyte substrate for a molten carbonate fuel cell, which has a porosity of 47% or more and an average pore diameter of 0.5 μm or less. 3. In claim 2, the electrolyte substrate has a thickness of 0.3 μm or more3
The volume of pores with a pore diameter of μm or less is 20% of the total pore volume.
An electrolyte substrate for a molten carbonate fuel cell, in which the volume of pores with a diameter of vol% or more, 0.1 μm or less, and 0.003 μm or more is present in a volume of 20 vol% or more based on the total pore volume. 4. A step of dry mixing the raw material powder, a binder, and a pore-forming agent, a step of adding and mixing a plasticizer and cellulose into the solvent mixture, a step of mixing the products of both of the above steps, and a step of reducing pressure. 3. The method for manufacturing an electrolyte substrate according to claim 2, comprising the steps of: defoaming the mixed product to obtain a raw material slurry for molding; and molding a green sheet from the raw material slurry. 5. In claim 4, the raw material powder is γ-LiAlO_2
After separating the powder with a predetermined particle size or less, the remaining raw materials are crushed and the powder with a predetermined particle size or less is separated again, and the crushing and powder separation steps are repeated as appropriate, and the powder separated in each step is Claim 1 comprising the step of appropriately adjusting the proportion of each powder used.
A method of manufacturing the electrolyte substrate described above. 6. A method for producing an electrolyte substrate for a molten carbonate fuel cell, characterized in that Al_2O_3 fibers are added to the γ-LiAlO_2 raw material powder according to claim 5. 7. The method of manufacturing an electrolyte substrate for a molten carbonate fuel cell according to claim 4, wherein an isobutylene maleic anhydride copolymer is used as the pore-forming agent.