JP3177768B2 - Method for producing molten carbonate fuel cell and sheet for electrolyte plate thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the internal resistance of a battery,
In particular, the present invention relates to a molten carbonate fuel cell in which resistance between an electrolyte plate and an electrode is reduced, and a method for manufacturing a sheet for an electrolyte plate of the battery.

[0002]

2. Description of the Related Art In a molten carbonate fuel cell, a fuel gas composed of hydrogen and an oxidizing gas composed of oxygen and carbon dioxide are electrochemically reacted to generate electric energy.
The fuel gas supplied to the anode and the oxidizing gas supplied to the cathode are separated by an electrolyte holder sandwiched between both electrodes, that is, an electrolyte plate. When the electrolyte plate is broken, each gas comes into direct contact. There has been a problem that battery performance is reduced due to gas cloth and gas leaks in which each gas is lost from the reaction system.

In order to solve this problem, if a plurality of electrolyte plates are laminated or the thickness of the electrolyte plate is increased per one sheet,
Although penetration cracks can be reduced, the distance between the electrodes is increased, which causes a problem that the conduction resistance of ions passing through the electrolyte plate increases. Therefore, for the purpose of improving the strength per unit thickness of the electrolyte plate, Japanese Patent Publication No. 2-58743 discloses that a ceramic fiber having a diameter of 1 to 6 μm and a length of 300 to 300 μm is used as a substrate structure.
Japanese Patent No. 58744 proposes using a potassium titanate fiber to prevent the electrolyte plate from cracking.

[0004]

An electrolyte plate in which alumina fibers and the like are added to a matrix composed of particles in order to improve the strength of the substrate generally has a larger surface roughness after firing than an electrolyte plate in which no fibers are added. I was While the electrolyte substrate had a diameter of 0.1 to 0.3 μm, the substrate surface of the electrolyte plate containing alumina fibers had relatively coarse pores of 1 μm or more in the major axis direction. Here, the volume-based central pore diameter indicates the distribution state of pores in the porous body, and divides large and small pores by size, sequentially accumulates the pore volume for each size, and calculates the cumulative value. When に な る becomes half (the center) of the total volume of all the pores, the size (diameter) of the pores is referred to as a volume-based central pore diameter.

[0005] Since a molten carbonate fuel cell has a basic structure in which an anode, an electrolyte plate, and a cathode are stacked, it is necessary to reduce the electric resistance at the interface between the members. However, in the case of using an electrolyte plate having a large surface roughness and having pores with a diameter of 1 μm or more in the major axis direction (for example, pores having an elliptical opening) on the surface, the adhesion at the interface between the members, particularly the cathode and the electrolyte plate And the adhesion at the interface with the polymer decreases. This is because the cathode is made of a metal oxide (NiO) made of a hard material and has fine irregularities on the surface. In addition, when the power generation time has elapsed and the mass of the electrolyte in the battery has decreased from the initial stage, the ion conduction resistance at the interface with poor adhesion increases, and there is a problem that the life of the battery is shortened.

[0006] An object of the present invention is to provide a molten carbonate fuel cell in which the internal resistance between an electrolyte plate and an electrode is reduced in order to solve the above problems. Another object of the present invention is to provide a method for producing the electrolyte sheet.

[0007]

In order to obtain a molten carbonate fuel cell exhibiting stable performance for a long period of time, it is necessary to use an electrolyte plate having no coarse pores on its surface and having excellent smoothness. It is valid. The present invention has a structure in which a rod-shaped or fibrous inorganic composite oxide which is larger in volume than the particles constituting the electrolyte plate is present inside the electrolyte plate. That is, the molten carbonate fuel cell of the present invention has an electrolyte plate, an anode made of a Ni-based porous plate sandwiching the electrolyte plate, and a cathode made of a NiO-based porous plate. Wherein the electrolyte plate has a volume-based central pore diameter of 0.1 to 0.1 at the surface in contact with both electrodes.
3 μm, and the maximum major axis diameter 1 μ existing on this surface
The area ratio occupied by pores of m or more is 0.1% or less of the entire surface.

This electrolyte plate has both front and back surfaces of 0.1 to 0.3.
It becomes the surface layer composed of a LiAlO ₂ particles μm diameter, inside of 0.1~0.3μm diameter LiAlO ₂ particles and L
It consists of a base layer composed of iAlO ₂ rods or fibers. Each of the surface layers is preferably 3 to 8% of the thickness of the electrolyte plate, and the porosity of the entire surface layer and base layer is 50%.
Preferably it is ~ 65%. As another electrolyte plate, at least one plate surface of this electrolyte plate was formed,
A surface layer composed of LiAlO ₂ particles having a diameter of 0.1 to 0.3 μm, and an L layer having a diameter of 0.1 to 0.3 μm covered with this surface layer.
A plurality of composite plates composed of a base layer composed of iAlO ₂ particles and LiAlO ₂ rods or fibers may be stacked. In this case, it is arranged so that the surface layer is in contact with each electrode.

As described above, the surface layer of the electrolyte plate has a thickness of 0.1 to 0.1.
Particles constituting 0.3 μm electrolyte plate (LiAlO ₂ particles)
Only, and the pores on the substrate surface are reduced in diameter.
Make uniform. Also, the absolute surface roughness decreases. Considering the case of a three-layer structure in which a particle layer constituting the electrolyte plate exists on the front and back of a layer to which a strength improving material (LiAlO ₂ fiber) such as a fiber is added, the surface layer having no fiber is the electrolyte plate. Since the thickness is 3% to 8% at the maximum (6 to 16% for the front and back surface layers), there is almost no effect on the substrate strength. The porosity of the electrolyte plate is preferably 50 to 65% from the experimental results. If the porosity is too small, the content of the electrolyte is small, and the battery efficiency becomes poor,
If it is too large, the characteristics of the electrolyte plate itself will change when tightened and pressurized in the fuel cell stack, and the cell performance will decrease.

A substrate strength improving material such as alumina fiber has a short fiber length of about 10 μm or more, which is larger than that of the electrolyte plate constituting particles of 0.1 to 0.3 μm. The electrolyte plate sheet produced by the doctor blade method has a structure in which an organic binder is buried between the substrate strength improving material and the particles constituting the electrolyte plate, so that the surface state is smooth. However, when the organic matter in the electrolyte plate sheet is thermally decomposed in the process of raising the temperature up to battery power generation conditions, the surface of the electrolyte plate where the volumetrically large substrate strength improving material is exposed loses its smoothness due to its shape. come.

[0011] The electrolyte plate of the present invention has improved smoothness as compared with the conventional one, since the fiber as the substrate strength improving material is not exposed on the surface. Moreover, uniform pores are formed in the surface layer of the electrolyte plate composed of only the particles constituting the electrolyte plate having a thickness of 0.1 to 0.3 μm.

In one cell of the fuel cell, there are two electrode / electrolyte plate interfaces and the number of electrolyte plate / electrolyte plate interfaces equal to the number of electrolyte sheet sheets constituting the electrolyte plate minus one.
Since the electrolyte plate is a material constituting both of the two types of interfaces, its surface state greatly affects the interfaces. Therefore, by improving the surface smoothness and using an electrolyte plate having uniform pores on the surface, voids existing at the electrode / electrolyte plate interface and the interface between the electrolyte plates can be miniaturized.

During operation of the molten carbonate fuel cell, a molten liquid electrolyte is distributed on the electrode / electrolyte plate portion. The distribution depends on the capillary force determined by the pore diameter of the electrode / electrolyte plate. At the beginning of the battery operation, the amount of electrolyte wear is small, so that the carbonate, that is, the electrolyte is distributed almost as set. However, when the operating time elapses and the electrolyte is worn due to the formation of a corrosive layer of the battery constituent material, the amount of the electrolyte decreases from a portion having a small capillary force, and the ionic conduction resistance increases. In a battery using an electrolyte plate with a large surface roughness, the interface,
In particular, since the resistance at the electrode / electrolyte interface increased with time, it can be inferred that the electrolyte at the interface decreased.

In the electrolyte plate according to the present invention, in which the substrate strength improving material is not exposed on the surface, the voids formed at the contact interface with the electrodes can be miniaturized because the surface smoothness is improved.
Adhesion can be improved. As a result, the influence of the electrode / electrolyte plate interface on the decrease in electrolyte due to long-term operation is small, and the increase in ionic conduction resistance of the electrolyte plate over time can be suppressed.

The method for producing a sheet for an electrolyte plate of a molten carbonate fuel cell according to the present invention comprises the steps of (1) LiAlO ₂ particles, L
a step of forming a base sheet by forming a first slurry formed by mixing rods or fibers of iAlO ₂ and a binder with a blade, and (2) a step of mixing LiAlO ₂ particles and a binder on the base layer. 2) a step of forming a surface layer sheet by forming a sheet of the slurry with a blade to form a composite sheet, and (3) a step of heating and drying the composite sheet. Instead of using the blade to sheet the second slurry on the base layer in the above step (2),
By spraying the slurry on a base layer or dipping into a slurry reservoir containing a second slurry.
A surface layer can be formed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1A schematically shows the surface and cross section of an electrolyte plate constituting a molten carbonate fuel cell as an embodiment of the present invention. This electrolyte plate is composed of a matrix composed of LiAlO ₂ powder having an average primary particle diameter of 0.1 μm and a LiAlO ₂ fiber 1a having a diameter of 0.8 μm and a length of 13 μm.
And a surface layer 2 which forms only the surface of the base layer 1 and is composed of only LiAlO ₂ powder having an average primary particle diameter of 0.1 μm. For comparison, FIG. 1B schematically shows the surface and cross section of an electrolyte plate composed of only the base layer 1 described above. The comparison material is LiA
Since the 10 ₂ fibers are almost uniformly dispersed in the electrolyte plate,
While the surface is also exposed, in the material of the present invention, LiAlO ₂ fibers are present inside the electrolyte plate, and
Only iAlO ₂ particles are present. After the green sheets of these two types of electrolyte plates were fired at 650 ° C. in air to thermally decompose organic substances such as binders, the surface of the fired electrolyte plates was measured with a contact-type surface roughness meter. The surface roughness of the comparative material was 2.5 μm, whereas the surface roughness of the material of the present invention was 0.3 μm, and the smoothness was improved. In addition, observation of the surface with an electron microscope confirmed that there were no pores having a diameter of 1 μm or more in the major axis direction on the surface of the material of the present invention.

Next, a specific production example will be described. (Embodiment 2) To a mixed organic solvent of ethyl alcohol: 1000 ml and butyl alcohol: 300 ml, 88 g of polyvinyl butyral was added as a binder (binder), and the mixture was stirred for 50 minutes and dissolved. After that, the electrolyte retainer, having a primary particle size of 0.1 to 0.3 μm and a specific surface area of about 20 m
² / g LiAlO ₂ powder: 335 g was added and mixed using a ball mill for 6 hours to obtain a slurry 3. Separately, the slurry 3 ′ prepared by using the same material and the same method as the slurry 3 was previously classified into a 0.8 μm diameter.
A slurry 4 was prepared by adding 55 g of LiAlO ₂ fiber having a length of 13 μm and mixing for about 4 hours. After that, degassing under reduced pressure and viscosity adjustment were performed on the slurries 3 and 4. FIG. 2 shows a doctor blade device used for producing a sheet for an electrolyte plate. According to this apparatus, a pipe-type blade 5 coats a slurry 4 on a film tape 12 conveyed in a predetermined direction on a base plate 11 to form a film 4A.
A (base layer) is prepared, and a blade 6 of the same shape coats the slurry 3 on the film 4A to form a film 3A (surface layer). The thus-produced laminated sheet is dried in a drying chamber 7. Thereafter, the laminated sheet is cut into a certain size or wound up into a roll. The laminated sheet produced by the apparatus shown in FIG.
It was subjected to a battery performance test.

(Embodiment 3) FIG. 3 is a schematic view of an apparatus combining a sheet producing apparatus using a doctor blade method and a spray coating method. In this apparatus, the film 4A of the slurry 4 formed into a sheet by the blade 6 is dried in the drying chamber 7, and then the coating film 3A is formed on the surface by the slurry 3 sprayed from the nozzle 8, and the surface is dried. It is dried in the chamber 7. Note that membrane 4
The film 3A can be formed by spraying without drying after the preparation of A. The laminated sheet thus produced was No. 2
The sheet was subjected to a strength test and a battery performance test described later.

(Embodiment 4) FIG. 4 is a schematic view of an apparatus combining a sheet producing apparatus using a doctor blade method and a dip coating method. After the film 4A of the slurry 4 formed into a sheet by the blade 6 is dried in the drying chamber 7, the film 4A is guided along a guide roller 9 to a slurry reservoir 10 filled with the slurry 3. A coating film of the slurry 3 is formed on the surface of the film 4A that has passed through the slurry reservoir 10, and the surface is dried in the drying chamber 7. The laminated sheet thus produced was subjected to a strength test and a battery performance test described below as No. 3 sheet.

According to this dip coating method, by coating not only the front surface but also the front and back surfaces simultaneously, a film 4A made of slurry 4 containing fine particles containing fibers as a central layer, and only fine particles on the front and back surfaces are formed. A sheet having a three-layer structure including a layer made of the slurry 3 containing the slurry 3 can be produced.

[0021] LiAlO ₂ (Comparative Example) LiAlO ₂ powder
A sheet prepared by the doctor blade method using only the slurry 4 to which No. 4 was added as a raw material was designated as No. 4 and subjected to strength tests and battery performance tests described later for comparison.

[0022]

【Example】

(Strength Test of Electrolyte Plate) The No. 1 to No. 3 sheets according to the present invention and the No. 4 sheet of the comparative material prepared above were subjected to binder removal calcination in air at 650 ° C. for 3 hours.
A sample of the electrolyte plate of o. was prepared. These samples were subjected to a three-point bending test. Table 1 shows the results. As a result, it was found that the electrolyte plates No. 1 to No. 3 of the present invention material had the same maximum bending strength as the electrolyte plate No. 4 of the comparative material. Therefore, No. 1 to No.
Even if an electrolyte plate obtained by firing three sheets is used for an actual battery, it is considered that the influence of gas crossing and gas leak due to crack generation is small as in the conventional case.

[0023]

[Table 1]

(Performance test of fuel cell) N according to the present invention
o.1 to No.3 sheets and a comparative material No.4 sheet are laminated in plurals, and a nickel (Ni) porous anode and nickel oxide are provided on both sides of each of the laminated sheets.
Various small single cells having a basic structure in which a cathode of a (NiO) -based porous body was arranged were assembled. A schematic diagram of the single cell is shown in FIG. The single cell 20 includes a plate-like anode 22, a current collector 23, a corrugated plate 24 having a fuel gas (hydrogen) flow path on one surface of a laminated sheet 21 formed by laminating electrolyte sheets,
And a separator 25 are sequentially stacked, and on the other surface of the laminated sheet 21, a plate-like cathode 26, a current collector 27, a corrugated plate 28 having a flow path of an oxidizing gas (oxygen, carbon dioxide), And the separator 29 are sequentially stacked and installed,
It is configured. No. 2 A single cell using the laminated sheet 21 sandwiching the No. 4 sheet with one sheet is referred to as a No. 1 cell, and a single cell using the laminated sheet sandwiching the No. 4 sheet with two No. 2 sheets is referred to as a No. 1 cell. .2 cells, 2 N
A single cell using a laminated sheet sandwiching a No. 4 sheet with an o.3 sheet is referred to as a No. 3 cell, and a single cell using a laminated sheet including three No. 4 sheets is referred to as a No. 4 cell. did. In each of the No. 1 to No. 3 laminated sheets, the surface layer composed only of the electrolyte plate component particles (LiAlO ₂ powder) has an electrode.
(Anode, cathode). A eutectic carbonate of lithium: potassium = 62: 38 (molar ratio) was used as an electrolyte, and the laminated sheet was debindered when the battery was heated, and the electrolyte was melted and impregnated into the debindered laminated sheet. Humidified hydrogen-carbon dioxide gas (fuel utilization rate 60%) as fuel gas and air and carbon dioxide gas (oxidizing agent utilization rate 40%) as oxidant gas are supplied to this single cell. Was set to 150 mA / cm ² to perform a power generation test.

FIG. 6 shows the time change of the cell voltage. In the No. 4 cell employing the No. 4 sheet of the comparative material, the cell voltage decreases with the passage of time.
No. 1, N using sheet No. 1, No. 2, No. 3
The voltage of the cells No. 2 and No. 3 hardly changes even after the operation time of 2000 hours has elapsed. This is presumably because the adhesion at the lamination interface between the battery members such as the electrolyte plate and the electrode was improved, and the increase in the ionic conduction resistance over time could be suppressed.
In each of the No. 1 to No. 3 cells, the No. 4 sheet was used together with the No. 1 to No. 3 sheets for the electrolyte plate. There is no.

[0026]

According to the present invention, the surface of the electrolyte plate in contact with both the anode and the cathode can be made smooth and uniform in pores by constituting each surface layer of powder. In addition, the adhesion at the contact surface between the electrolyte plate and the electrode is increased, the resistance at the electrode / electrolyte plate interface can be reduced, and the inside of the electrolyte plate is composed of powder and fibers for reinforcing the plate. Even if the electrolyte plate is given a high strength, the characteristics of the electrolyte plate can be maintained even when the electrolyte plate is fastened in the fuel cell stack, so that the life of the fuel cell can be extended.

[Brief description of the drawings]

FIG. 1 is a schematic view of a surface and a cross section of an electrolyte plate constituting a molten carbonate fuel cell of the present invention and a comparative material thereof.

FIG. 2 is a schematic view of an apparatus for producing a sheet for an electrolyte plate according to the present invention by a doctor blade method.

FIG. 3 is a schematic view of an apparatus for producing a sheet for an electrolyte plate according to the present invention by a combination of a doctor blade method and a spray coating method.

FIG. 4 is a schematic view of an apparatus for producing a sheet for an electrolyte plate according to the present invention by a doctor blade method and a dip coating method.

FIG. 5 is a schematic view of a molten carbonate fuel cell provided with an electrolyte plate according to the present invention.

FIG. 6 is a graph showing changes over time in performance of a molten carbonate fuel cell using various electrolyte plates according to the present invention.

[Explanation of symbols]

Reference Signs List 1 base layer 1a LiAlO ₂ fiber 2 surface layer (LiAlO ₂ particle layer) 3 slurry (LiAlO ₂ particle) 4 slurry (LiAlO ₂ particle / fiber) 5, 6 blade 7 sheet drying room 8 spray nozzle 9 guide roller 10 slurry reservoir 11 units Plate 12 Film tape 20 Single cell 21 Laminated sheet 22 Anode 23 Collector plate 24 Corrugated plate 25 Separator 26 Cathode 27 Collector plate 28 Corrugated plate 29 Separator

────────────────────────────────────────────────── (5) References JP-A-8-55628 (JP, A) JP-A-56-91376 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8/02

Claims (6)

(57) [Claims] 1. An electrolyte plate, and an anode composed of a Ni-based porous plate and a cathode composed of a NiO-based porous plate sandwiching the electrolyte plate, and a reaction gas supplied from both poles of the anode and the cathode In the molten carbonate fuel cell that generates power by the electrochemical reaction of the above, the electrolyte plate,
The volume-based central pore diameter on the surface in contact with both the cathode and anode electrodes is 0.1 to 0.3 μm, and the area ratio of pores having a maximum major axis diameter of 1 μm or more present on the surface is as follows: 0.1% or less with respect to the entire surface,
LiAlO ₂ having a diameter of 0.1 to 0.3 μm formed on both front and back surfaces
A surface layer composed of particles, and 0.1 to 0.1
A molten carbonate fuel cell comprising: a 0.3 μm-diameter LiAlO ₂ particle and a base layer composed of LiAlO ₂ rods or fibers. 2. The method according to claim 1, wherein each of the surface layers has a thickness of 3 to 8% of a thickness of the electrolyte plate, and a porosity of the entire surface layer and the base layer is 50 to 65%. Molten carbonate fuel cell. 3. The molten carbonate fuel cell according to claim 1, wherein the electrolyte plate is formed by stacking a plurality of composite plates each including the surface layer and the base layer. 4. The electrolyte plate according to claim 1, wherein the electrolyte plate is LiAlO ₂ particles,
A first slurry formed by mixing a rod or fiber of LiAlO ₂ and a binder is used to form the base layer by using a blade, and a second slurry formed by mixing LiAlO ₂ particles and a binder is formed on the base layer by using a blade. to form a surface layer to prepare a composite sheet, and dried by heating the composite sheet
The molten carbonate fuel cell according to claim 1, wherein the molten carbonate fuel cell is formed by combining a plurality of the fuel cells. 5. The electrolyte plate according to claim 1, wherein the electrolyte plate is LiAlO ₂ particles,
A first slurry formed by mixing a LiAlO ₂ rod or fiber and a binder is used to form the base layer using a blade, and a second slurry formed by mixing the LiAlO ₂ particles and a binder on the base layer is sprayed onto the base layer. to form a surface layer to prepare a composite sheet, and dried by heating the composite sheet
The molten carbonate fuel cell according to claim 1, wherein the molten carbonate fuel cell is formed by combining a plurality of the fuel cells. 6. The electrolyte plate according to claim 1, wherein the electrolyte plate is LiAlO ₂ particles,
A first slurry formed by mixing a rod or fiber of LiAlO ₂ and a binder is sheeted with a blade to form the base layer, the base sheet is dried, and the dried base sheet is mixed with LiAlO ₂ particles and a binder. By immersing in a slurry reservoir containing a second slurry obtained by mixing and pulling up to form the surface layer on the base layer sheet surface to form a composite sheet, and heating and drying the composite sheet. 2. The molten carbonate fuel cell according to claim 1, wherein the molten carbonate fuel cell is made.