JPH02162655A - Fuel cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a strong, flexible electrolyte retainer suitable for increasing the output and performance of a fuel cell by forming the electrolyte retainer with a porous metal plate. CONSTITUTION:An electrolyte retainer 1 which constitutes a molten carbonate type fuel cell together with a separator, an anode, a cathode, and an electric insulator is formed with a porous metal plate 8 including a core 9. This electrolyte retainer decreases the generation of cracks caused by the difference in thermal expansion coefficient compared with an electrolyte retainer formed by bonding ceramic and metal. The electrolyte retainer having high strength and high flexibility for increasing output and performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel cell, and particularly to constituent members suitable for increasing the performance and output of a battery.

[Conventional technology]

Molten carbonate fuel cells use carbonates of alkali metals such as lithium and potassium, which melt at high temperatures and exhibit carbonate ion conductivity, as electrolytes, and are normally operated at high temperatures of 600 to 800°C. This fuel cell has advantages such as a wide variety of fuel types that can be used and high energy efficiency.

In such a molten carbonate fuel cell, the electromotive force obtained by one unit cell is as low as about 1V, so it is necessary to stack a large number of unit cells in series to construct a high-output power generation plant. Therefore, this type of fuel cell has a structure as shown in FIG.

That is, electrolyte holding body 1 holding carbonate electrolyte
It is constructed by stacking a plurality of unit batteries each consisting of an anode 2 and a cathode 3 sandwiching and opposing each other with a separator 4 in between. To this fuel cell, H2 as a fuel gas is supplied to the anode 2 through the fuel gas flow path 5 in contact with the anode 2 of the separator 4, and carbonate ions of the molten carbonate electrolyte held in the electrolyte holder 1 reacts with H2+
The reaction C0,2-→H, O+CO, +2e occurs.

On the other hand, as an oxidizing agent, a mixed gas of 0□ and Co2 is supplied to the cathode 3 through the oxidizing gas flow path 6 in contact with the cathode 3 of the separator 4, causing a reaction of 1/202+CO2+28-4 CO,"-. , resulting in DC power.

Here, the separator 4 is generally used because it electrically connects the unit cells in series, prevents the fuel gas and oxidizer gas from mixing, and is stable against strong alkaline electrolytes. Stainless steel material is used.

The anode 2 forms a reaction field where fuel gas and liquid electrolyte coexist, and it is necessary to conduct electrons generated by the reaction to the separator 4. Therefore, the anode 2 is a conductive material that is stable with respect to the electrolyte in a reducing atmosphere. Generally, a porous plate of nickel is used.

For the same reason, the cathode 3 also uses a porous plate of lithiated nickel oxide as a conductive material that is stable with respect to the electrolyte in an oxidizing atmosphere.

On the other hand, the electrolyte holder 1 needs to have gas sealing properties to hold the molten salt electrolyte and prevent fuel gas and oxidant gas from mixing, and also to prevent electrical short-circuiting between the anode 2 and cathode 3. Since electrical insulation is required to prevent this, porous plates made of ceramics such as lithium aluminate and having micropores are generally used. In order to increase the output of a battery, the voltage of the battery is proportional to the number of stacked unit cells, and the current is proportional to the area of the battery, so it is necessary to increase the number of stacks and increase the area. The body is made of ceramic and breaks easily, making it difficult to achieve high output.

In other words, as the area becomes larger, handling during assembly not only deteriorates, but also temperature non-uniformity inside the electrolyte holder increases, thermal stress increases, and manufacturing accuracy decreases, making it easier to apply unbalanced loads. This makes it more likely to break, making it difficult to expand the area.

In addition, this electrolyte holder 1 contains a binder, etc., and is flexible in the state of a raw tape (green sheet), but after being heated to a temperature higher than the melting point of the electrolyte and impregnated with the electrolyte, the binder, etc. disappears, and the As a result, flexibility is lost and assembly of the battery becomes difficult, so it is necessary to employ a so-called internal battery impregnation method in which electrolyte is impregnated inside the battery during the process of raising the temperature of the battery. With this method, the height of the battery shrinks significantly during electrolyte impregnation, and the amount of shrinkage is proportional to the number of laminated layers.

This makes it difficult to increase the number of layers in terms of followability of the battery tightening structure, etc. Furthermore, in terms of battery performance, it is preferable for the electrolyte holder to be thin, but it cannot be made thin because of its low strength, making it difficult to improve performance.

In order to solve the above problems, it is necessary to increase the strength of the electrolyte holder 1.
As disclosed in Japanese Patent No. 4 and Japanese Patent Application Laid-Open No. 60-93760, a method has been adopted in which a metal mesh, expanded metal, etc. is provided inside or on the surface of the electrolyte holder 1, and the electrolyte holder 1 is reinforced with metal.

[Problem to be solved by the invention]

The above-mentioned conventional technology involves joining ceramics and metals, and does not take into account the difference in coefficient of linear expansion between the two. In other words, when a ceramic with a small coefficient of linear expansion and a metal with a large coefficient of linear expansion are bonded, thermal stress is generated due to the difference in the coefficient of linear expansion when the temperature of the battery rises and falls, and as a result, the ceramic electrolyte retention There was a problem that cracks occurred in the battery, making it impossible to operate due to so-called gas cross leak, which is a mixture of fuel gas and oxidizing gas.Furthermore, since the ceramic electrolyte holder itself is not flexible, it is difficult to store the electrolyte outside the battery. In the case of impregnation, there is also the problem that cracks occur when the weight of each member is applied during battery assembly.

An object of the present invention is to provide a high-strength and flexible electrolyte holder suitable for increasing the output and performance of fuel cells, and a method for manufacturing the same.

[Means to solve the problem]

The above object is to provide an electrolyte holder that holds a carbonate electrolyte and is made of a porous metal plate, an electrical insulator having electrical insulation properties that is in contact with at least one surface of the electrolyte holder, and the electrical insulator or the electrolyte holder. It has a pair of electrodes that sandwich the battery and take out the electromotive force generated by the battery reaction, and a flow path for gas to be supplied to the electrodes, and is in contact with the electrolyte holder or the electrical insulator at an end parallel to the flow path. A fuel comprising the electrolyte holder, a separator that connects in series a unit cell consisting of the electric #4AS body and the electrode, and the porous metal plate is impregnated with a carbonate electrolyte and then sandwiched between the electrodes and the separator. This is achieved by providing a method for manufacturing a battery.

[Effect]

When a porous metal plate is used as an electrolyte holder, it has high mechanical strength and flexibility, so even if the weight of each member is applied when the electrolyte holder is impregnated with carbonate electrolyte and assembled into a battery, the battery will Cracks do not occur even when thermal stress is applied when the temperature rises or falls. As a result, the fuel gas and oxidizing gas do not mix and burn and damage the battery.

Furthermore, since the electrolyte holder is a metal, it exhibits electrical conductivity, so it is necessary to separately provide a porous electrically insulating layer around it.
Gas sealing is not required, so even if cracks occur in the electrical insulation layer, the battery will not be damaged.

〔Example〕

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

Example 1 The structure of a fuel cell using the electrolyte holder of the present invention is shown in FIG.

An electrolyte holder 1 made of a porous metal plate is sandwiched in the center.
A unit battery is constituted by the electrically insulating plates 7, the anode 2, and the cathode 3, and the unit batteries are stacked with a separator 4 interposed therebetween having a gas flow path.

Here, the electrolyte holder 1 is N with an average particle size of 0.1 to 10 μm.
Thickness obtained by adding water and carboxymethylcellulose to i powder, kneading it, vacuum defoaming, forming the obtained slurry into a plate using the doctor blade method, and firing it at a temperature of 600 to 1300"C in a reducing atmosphere. is about 1 mm (about half of conventional), average pore diameter is 0.1 to 1.0 μm, and porosity is 30 to 70.
% nickel porous plate. Note that, as a method for forming the plate, a method may be used in which Ni powder is pressed and sintered using a hot press method.

The metal powder raw material may be any material that has good corrosion resistance against molten carbonate, and in addition to nickel, stainless steel, stainless steel with aluminum or yttrium added, copper, nickel-chromium steel, etc. can be used. Furthermore, if gold R* fibers are mixed in addition to these powders, the strength will further increase and a good electrolyte holder can be obtained.

Furthermore, since the metal sintered body alone is subject to large creep deformation due to the clamping surface pressure of the battery, in order to prevent this, L
iARO2, MgO, La20. .

1 to 20 at of metal oxides such as ZrO2, Cr, O, etc.
It is preferable to add om%.

The electrical insulating board 7 is made of a mixture of lithium aluminate powder with an average particle size of 1 to 2 μm and alumina fibers, trichlorethylene, tetrachloroethylene, and butyl alcohol.
A slurry obtained by mixing a mixture of a solvent, polyvinyl butyral, and butyl phthalyl glycolate in a ball mill and vacuum decuring was formed into a plate using a doctor blade method. This electric IIA edge plate 7
Incorporate the raw tape (green sheet) into the battery.
As the temperature of the battery rises, the binder and other substances in the green sheet scatter, eventually forming a porous ceramic plate.

Through the pores of the electrically insulating plate 7, the electrodes (anode 2 and cathode 3) and the electrolyte holder 1 are communicated with the electrolyte, and a battery reaction occurs. Electrical insulation board 7 of this embodiment
The thickness was about 0.2 mm and the pore diameter was about 1 μm. This electric insulating plate 7 is made of ceramic and is easily broken, but even if cracks occur, the electrolyte holder 1 does not have to worry about cracks, so there is no risk of cross leakage. The materials that can be used for plate 7 are:
Various metal oxides, nitrides, etc. that are stable to the electrolyte and have high electrical resistance can be used.

Furthermore, in this embodiment, the electrical insulating plate 7 is
Although it is provided on both the upper and lower surfaces of the , it is also possible to use only one of them.

As a method for impregnating the electrolyte holder 1 made of porous metal with an electrolyte, a mixed carbonate (lithium carbonate 6
2 mol%, potassium carbonate 38 mol%) is applied to the surface of the electrolyte holder 1 in an amount corresponding to the pore volume of the electrolyte holder, and heated to the melting point of the mixed carbonate (approximately 490°C) or higher in an electric furnace. A so-called external impregnation method was used in which the pores of the electrolyte holder 1 were impregnated with molten carbonate.

After the electrolyte holder 1 was impregnated with carbonate, it was held between electrodes and separators.

The electrolyte holder 1 of the present invention maintains a good condition without cracking during assembly even when externally impregnated, and almost no shrinkage in battery height is observed during temperature rise. In terms of performance, the load current density is 150 mA.
The unit cell voltage at /c rri increased by about 5%.

Example 2 An electrolyte holder 1 whose structure is shown in FIGS. 2a and 2b of this example is composed of a porous metal plate 8 and a core material 9.

This core material 9 is made of nickel and has a diameter of 0.2 mm.

A 40-mesh wire mesh that had been flattened by roll pressing was used. A slurry obtained by adding water and carboxymethylcellulose to the same nickel powder as in Example 1 and degassing it under vacuum was applied to the surface of this core material 9, and then it was fired and produced. According to this embodiment, the effect of the action of the core material 9 is to further increase the mechanical strength of the electrolyte holder 1.

Note that expanded metal may be used as the core material instead of wire mesh. Further, in this embodiment, the core material 9 is provided inside the porous metal plate 8, but the same effect can be obtained even if the core material 9 is provided on the surface of the porous metal plate 8.

As the material for the porous metal plate 8 and the core material 9, various metals with good corrosion resistance can be used, as in the first embodiment, but it is preferable that there is no difference in linear expansion coefficient, since thermal stress will be reduced.

Example 3 The structure of a battery using the electrolyte holder of this example is shown in FIG.

In this embodiment, the electrolyte holder 1 has a structure in which an electrical insulating layer 10 is provided on the surface of a porous metal plate 8.

First, a porous metal plate 8 was created using the manufacturing method shown in Example 1. Next, alumina was sprayed onto the surface of the porous metal plate 8 to form an electrically insulating layer 10 with a thickness of about 0.1 mm.

This electrical isolation nre1o can be used as alumina, but it reacts with the electrolyte inside the battery to become lithium aluminate and consumes the electrolyte, so it was previously lithiated using lithium hydroxide. .

The material of the electrical insulating layer 10 of this embodiment can be made of oxides and nitrides of various metals that are stable with respect to the electrolyte, similar to the electrical insulating plate shown in the first embodiment.

Alternatively, it is also possible to form the film by thermally spraying the entire bend itself and then oxidizing it.

In addition, in FIG. 3, electricity #! is applied to both sides of the porous metal plate 8. tA
Although nine layers are provided, only one side may be used.

In the third embodiment, since the electrical insulating layer 10 is integrated with the porous metal plate 8, the number of parts is reduced compared to the first embodiment, making assembly easier.
can be made as thin as about 10μm, and the product! This also has the effect of making the FFI pond more compact and reducing the internal resistance of the battery.

Example 4 FIG. 4 shows the battery structure of this example.

An electrical insulating layer 10 is provided at the portions of the separator 4 and the electrodes (anode 2, cathode 3) that are in contact with the electrolyte holder 1.

The electrical insulating layer 10 provided on the anode 2 and cathode 3 is
Since it is necessary to communicate the electrolyte, it must be porous. Therefore, in the same manner as described in Example 3, alumina was sprayed and molded.

On the other hand, the electrical insulating layer 10 provided on the separator 4.

Since it does not need to be porous, aluminum was diffused onto the surface of the separator and then oxidized to form the separator, but a method in which aluminum is plated and then oxidized may also be used.

According to this embodiment, since the electric IAS layer of the separator 4 can be made dense, the separator 4 does not come into direct contact with the electrolyte, and the corrosion resistance of the separator 4 is improved.

〔Effect of the invention〕

According to the present invention, when a porous metal plate is used as an electrolyte holder, it has high mechanical strength and flexibility, so that cracks do not occur in the electrolyte holder, and the reliability and durability of the battery are improved. .

In addition, since it is possible to externally impregnate the electrolyte, shrinkage of the battery during the temperature rising process can be prevented, and the structure can be made high-rise, which has the effect of obtaining high output.

Furthermore, since the electrolyte holder can be made thinner, the ionic conduction resistance can be reduced, resulting in improved power generation efficiency and higher performance.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a battery according to Example 1 of the present invention, FIG. 2a is a plan view of an electrolyte holder according to Example 2 of the present invention, FIG. 2b is a vertical cross-sectional view of FIG. 2a, and FIG. FIG. 4 is a vertical cross-sectional view of a battery according to Example 4 of the present invention, and FIG. 5 is a perspective view of a conventional battery. 1... Electrolyte holder, 2... Anode, 3...
Cathode, 4... Separator, 5... Fuel gas channel, 6... Oxidizing gas channel, 7... Electrical insulating plate, 8... Porous metal plate. 9... Core material, 10... Electrical insulation layer.

Claims (1)

[Scope of Claims] 1. An electrolyte holder that holds a carbonate electrolyte and is made of a porous metal plate, an electrical insulator having electrical insulation properties that is in contact with at least one surface of the electrolyte holder, and the electrical insulator or A pair of electrodes that sandwich the electrolyte holder and take out the electromotive force generated by the battery reaction, and a flow path for gas to be supplied to the electrodes, and an end parallel to the flow path of the electrolyte holder or the electrical insulator. 1. A fuel cell comprising: a separator that contacts a body and connects in series a unit cell consisting of the electrolyte holder, the electric insulator, and the electrode. 2. The average pore diameter of the porous metal plate is 0.1 to 1.0μ
The fuel cell according to claim 1, wherein the fuel cell has a porosity of 30 to 70%. 3. The porous metal plate is made of Ni, Cr, Cu, Fe, Al.
, Y. The fuel cell according to claim 1, comprising at least one type of ,Y. 4. Claim 1, wherein a metal oxide is added to the porous metal plate.
The fuel cell described in . 5. The fuel cell according to claim 1, further comprising an electrically insulating layer provided on or inside the porous metal plate. 6. The fuel cell according to claim 1, further comprising a mesh or expanded metal made of a metal having substantially the same linear expansion coefficient as the porous metal plate on the surface or inside of the porous metal plate. 7. The fuel cell according to claim 1, wherein the electrical insulator is a porous body of metal oxide or metal nitride. The fuel cell described. 9. The fuel cell according to claim 1, wherein an electrically insulating layer is provided on the surface of the separator that comes into contact with the electrolyte holder. 10. The fuel cell according to claim 8 or 9, wherein the electrical insulating layer is formed by spraying a metal oxide or a metal nitride. 11. The fuel cell according to claim 8 or 9, wherein the electrical insulating layer is formed by spraying, diffusing, or plating a metal and then oxidizing it. 12. A fuel cell manufacturing method in which a plurality of unit cells each consisting of an electric insulator and an electrode facing each other while sandwiching an electrolyte holder holding a carbonate electrolyte are stacked via a separator having a gas flow path, A slurry obtained by adding a solvent and a binder to a metal powder having an average particle size of 0.1 to 10 μm or a mixture of the metal powder and metal fibers and kneading the electrolyte holder is formed into a plate, and the slurry is kneaded at a temperature below the melting point of the metal. A method for manufacturing a fuel cell, which comprises firing. 13. A fuel cell manufacturing method in which a plurality of unit cells each consisting of an electric insulator and an electrode facing each other while sandwiching an electrolyte holding body holding a carbonate electrolyte are stacked via a separator having a gas flow path, A method for manufacturing a fuel cell, characterized in that the electrolyte holder is formed into a plate by hot pressing a metal powder having an average particle size of 0.1 to 10 μm or a mixture of the metal powder and metal fibers. 14. A fuel produced by stacking a plurality of unit cells, each consisting of an electrical insulator and an electrode facing each other with an electrolyte holding body made of a porous metal plate holding a carbonate electrolyte interposed therebetween, with a separator having a gas flow path interposed therebetween. A method for manufacturing a fuel cell, wherein the porous metal plate is impregnated with a carbonate electrolyte and then sandwiched between electrodes and a separator.