JP2894377B2 - Method for manufacturing molten carbonate fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a molten carbonate fuel cell, and more particularly to a measure for preventing a reduction in the thickness of an air electrode, which is a problem at the time of starting operation of a high stack.

[0002]

2. Description of the Related Art FIG. 2 shows the structure of a conventional fuel cell of this type. For example, a molten carbonate fuel cell using an alkali metal carbonate as an electrolyte generally includes an electrolyte layer 1 made of an electrolyte and a substance holding the electrolyte, and a fuel electrode 2 provided so as to sandwich the electrolyte layer 1. A current collector plate 4 on the fuel electrode 2 side, which has a current collecting function and a purpose of physically supporting these battery members and flowing a reaction gas, and a fuel electrode side gas flow path plate; 5 and a fuel electrode side gas chamber 7 composed of a surface of the separator 6a facing the fuel electrode 2, and a current collector 8 on the air electrode 3 side, an air electrode side gas flow path plate 9 and the air electrode 3 of the separator 6b. It is composed of an air electrode side gas chamber 10 composed of a surface.

FIG. 3 is a schematic diagram showing a cross section of an electrolyte layer and electrodes of a conventional cell shown in, for example, Japanese Patent Application Laid-Open No. 2-299156 before the battery is heated for operation. In the figure, reference numeral 14 denotes an organic substance which is added for imparting flexibility to the electrolyte layer 1 at the time of forming the electrolyte layer 1 and comprises, for example, a composition, polyvinyl alcohol, alkyl phthalate, and polyalkylene glycol. Reference numeral 11 denotes LiAlO ₂ particles having an average particle size of 0.5 μm, which serves to hold an electrolyte. The average pore size of the electrolyte layer 1 after degreasing is about 0.4 μm.

The fuel electrode 2 is made of, for example, a sintered porous body (porosity: 60%, average pore diameter: 5 μm) of nickel alloy particles 12 containing 5 wt% of aluminum in Ni, and 80% by volume of the pores L / K = 62 just to fill
/ 38 eutectic electrolyte 17 (62 mol% lithium carbonate and 3
8 mol% of potassium carbonate).

Further, a porous body of nickel particles 13 (porosity 70%, average pore diameter 10 μm) is used for the air electrode 3, and an L / K = 62/38 eutectic electrolyte is used to fill 65% by volume of the pores. 17 (62 mol% lithium carbonate and 38 mol%
Which is previously impregnated with potassium carbonate).

Next, as shown in FIG. 3, L / K = 62/3
Fuel electrode 2 which is a porous body of nickel alloy particles 12 containing eutectic electrolyte 17, electrolyte layer 1 containing LiAlO ₂ particles 11 which are electrolyte holders and organic matter 14 such as a binder plasticizer, and the same composition as fuel electrode 2 side A conventional method for producing a molten carbonate fuel cell comprising the air electrode 3 which is a porous body of nickel particles 13 containing the L / K = 62/38 eutectic electrolyte 17 will be described. FIG. 4 shows the heating pattern and the composition of the gas supplied to the fuel electrode and the air electrode in the process, and FIG. 5 shows how the thickness of the nickel porous body having a porosity of 75% changes when the temperature is raised. In FIG. 5, the contact pressure is 5 kg / cm ² , the supply gas is N ₂ : CO ₂ = 70: 30, the solid line is the case where the electrolyte is not impregnated, and the broken line is the L / K = 62/38 eutectic electrolyte. When impregnated by volume%, the one-dot chain line is L / K = 80
This shows a case in which a / 20 eutectic electrolyte is impregnated with 65% by volume.

At room temperature, the air electrode 3, which is a porous body of the nickel particles 13, supplies air to both the fuel electrode and the air electrode until 380.degree. . At this stage, the strength of the porous body itself of the nickel particles 13 and the L / K
= 62/38 The eutectic electrolyte 17 is a solid, so that no shrinkage of the electrode occurs (see the broken line in FIG. 5).

After burning off the organic substance 14 in the electrolyte layer 1 at 380 ° C. in an air atmosphere, the electrolyte is melted (488 ° C.) to fill the pores in the electrolyte layer 1 to form a gas partition (gas). It is not preferable to flow an oxidizing gas toward the air electrode 3 in order to prevent the oxidation of the fuel electrode 2 until the fuel electrode 2 does not pass through). Accordingly, nitrogen and carbon dioxide gas for preventing the decomposition of the L / K = 62/38 eutectic electrolyte 17 are flown to both sides of the fuel electrode 2 side and the air electrode 3 side.

After confirming that the L / K = 62/38 eutectic electrolyte 17 has melted (about 500 ° C.), a mixed gas of hydrogen and carbon dioxide is supplied to the fuel electrode 2 side, and air and carbon dioxide are supplied to the air electrode 3 side. A mixture of gases is flowed. At this stage, the air electrode 3 is oxidized to form a nickel oxide porous structure.

Then, the molten carbonate fuel cell, which has been subjected to the oxidation treatment of the air electrode 3 at about 500 ° C., is supplied with a mixed gas of hydrogen and carbon dioxide gas on the fuel electrode side and a mixed gas of air and carbon dioxide gas on the air electrode 3 side. To raise the temperature to the operating temperature of 650 ° C.

The surface pressure applied to the air electrode 3 during the above-described series of heating processes is about 2 kg / cm ² . Although the air electrode 3 is not oxidized and the L / K = 62/38 eutectic electrolyte 17 melts, the air electrode 3 shrinks at 380 to 500 ° C., but in a small-scale molten carbonate fuel cell stack, Since the surface pressure during this time is as low as ² kg / cm ² and the time required for temperature rise, that is, the time required for oxidizing the air electrode 3 is short, the shrinkage of the air electrode 3 at the time of temperature rise is before the start of temperature rise. Thickness of 10
% Or less.

[0012]

Since the conventional apparatus is manufactured as described above, if the surface pressure cannot be reduced to ² kg / cm ² or less due to the increase in weight due to the high stacking of the batteries, the initial operation of the apparatus will be reduced. Shrinkage of the cathode 3 occurs 10% or more while the electrolyte is melted but the cathode 3 is not yet oxidized, and the porosity of the cathode 3 is deteriorated so that the characteristics are deteriorated and the efficiency is equivalent to that of a small battery. There is a problem that power generation operation cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is intended to manufacture a molten carbonate fuel cell capable of avoiding remarkable shrinkage of an air electrode even in a highly stacked fuel cell. The aim is to get the way.

[0014]

A method of manufacturing a molten carbonate fuel cell according to the present invention comprises a porous body containing at least one metal of nickel, copper and iron and holding an electrolyte in a hole. An air electrode, and an electrolyte layer containing an organic substance, and a step of burning off the organic substance by raising the temperature;
A step of melting an electrolyte having a lower melting point than the electrolyte held by the air electrode to impregnate the organic substance traces, and the electrolyte layer does not allow gas to permeate due to the impregnation of the electrolyte, and the electrolyte of the air electrode is still completely dissolved. A step of flowing an oxidizing gas to the air electrode in a non-existent state to oxidize the metal of the air electrode.

[0015]

According to the present invention, the low-melting-point electrolyte melts at a lower temperature than the high-melting-point electrolyte in the air electrode 3 and fills the pores in the electrolyte layer to form a gas partition. At that time, the high melting point electrolyte in the air electrode is not completely dissolved. The unmelted high melting point electrolyte prevents the air electrode having the metal before oxidation from shrinking. At the stage when the gas partition is formed, a reducing gas is supplied to the fuel electrode to prevent deterioration of the cell characteristics due to oxidation of the fuel electrode, while an oxidizing gas is supplied to the air electrode to be held by the air electrode. The air electrode can be oxidized while preventing shrinkage before the high melting point electrolyte is completely dissolved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a laminate of an electrolyte layer, an air electrode, and a fuel electrode before heating a battery according to an embodiment of the present invention. In the figure, reference numerals 14 and 11 are the same as those in the conventional example shown in FIG.

The fuel electrode 2 of this embodiment is made of a sintered porous body (porosity: 60%, average pore diameter: 5 μm) of nickel alloy particles 12 containing 5 WT% of aluminum in Ni, and has a volume of 80 pores. % Of the low melting point electrolyte 15 (58.9 mol% of lithium carbonate and 36.1 mol%
Of potassium carbonate and 5 mol% of magnesium carbonate).

A porous body of nickel particles 13 (porosity: 70%, average pore diameter: 10 μm) is used for the air electrode 3, and a high melting point electrolyte 16 (80 mol% lithium carbonate and 80 mol%) is used to fill 65% by volume of the pores. 20 mol% of potassium carbonate) is used.

Next, a method for manufacturing a molten carbonate fuel cell, that is, an operation start-up method and simultaneous oxidation of an air electrode will be described.

At room temperature, the air electrode 3, which is a metallic nickel porous material, supplies air to both the fuel electrode atmosphere and the air electrode atmosphere to burn off the organic substances 14 contained in the electrolyte layer 1 until 380 ° C. at which oxidation starts. At this stage, since the electrolyte contained in the electrode is solid, the electrode is unlikely to shrink.

After burning off the organic matter 14 in the electrolyte layer 1 at 380 ° C. in an air atmosphere, the electrolyte is melted (4
88 ° C.) to prevent oxidation of the anode 2 until the pores in the matrix are filled to form gas barriers.
Flowing an oxidizing gas on the side is not preferred. Therefore, a carbon dioxide gas for preventing the decomposition of nitrogen and carbonate is supplied to both sides of the fuel electrode 2 and the air electrode 3.

It is confirmed that the electrolyte other than in the air electrode 3 is melted and the electrolyte layer 1 functions as a gas partition (about 500).
° C), a mixed gas of hydrogen and carbon dioxide gas is flown to the fuel electrode 2 side, and a mixed gas of air and carbon dioxide gas is flown to the air electrode 3 side. At this stage, the air electrode 3 is oxidized to form a nickel oxide porous structure.

Thereafter, the molten carbonate fuel cell, which has been subjected to the oxidation treatment of the air electrode 3 at about 500 ° C., is supplied with a mixed gas of hydrogen and carbon dioxide gas on the fuel electrode 2 side and with air and carbon dioxide gas on the air electrode 3 side. The mixed gas was flowed to raise the temperature to the operating temperature of 650 ° C.

The surface pressure on the air electrode 3 during the above-described series of heating processes is about 5 kg / cm ² . In this embodiment,
At the stage of 500 ° C., 50% or more of the electrolyte in the air electrode 3 is still in a solid state. That is, the ratio of the volume of the solid in the air electrode 3 due to the sum of the nickel particles and the unmelted electrolyte at this stage is about 50%. Since the unmelted electrolyte supports the nickel particles of the cathode 3, the cathode 3 does not shrink even if the surface pressure is high (see the dashed line in FIG. 5).
After confirming that the electrolyte from the portion other than the cathode 3 has filled the pores of the electrolyte layer 1, the oxidizing gas can flow only to the cathode 3, so that the oxidation of the anode 2 changes the pore structure. As a result, the deterioration of the cell characteristics can be prevented. FIG. 6 shows the shrinkage ratio of the air electrode in the example under the load of 5 kg / cm ² and the conventional example. From this figure, it can be seen that in the conventional example, the shrinkage was about 30%, but in this embodiment, it is several%.
It turns out that it is suppressed to.

In the above embodiment, the case where the fuel electrode 2 is used as a place for holding the electrolyte 15 having a lower melting point is described.
The present invention is not limited to this. For example, the current collector plate 4 on the fuel electrode side,
The fuel electrode side gas flow path plate 5, the current collector plate 8 on the air electrode 3 side, the air electrode side gas flow path plate 9, and the like may be used. It goes without saying that even if a low electrolyte is supplied into the cell from outside the cell, the same effect as in the above embodiment can be obtained.

In the above embodiment, nickel particles 13 are used as the porous structure of the air electrode 3. However, shrinkage becomes a problem at a temperature of 500 ° C. or more and a surface pressure of 3 kg / cm ² or more in a reducing atmosphere. The present invention can be applied to the case of a porous iron body, and has the same effects as those of the above embodiment.

In the above embodiment, the low-melting-point electrolyte 15 is a mixed salt of 58.9 mol% of lithium carbonate, 36.1 mol% of potassium carbonate and 5 mol% of magnesium carbonate, and the high-melting-point electrolyte 16 is 80 mol%. % Of lithium carbonate and 20 mol% of potassium carbonate were used. Basically, if the difference between the temperatures at which the high-melting electrolyte and the low-melting electrolyte completely dissolve was 30 ° C. or more, the above procedure was performed. The effect according to the example is obtained. For example, as the low melting point electrolyte 15, 4
When a mixed salt of 3.5 mol% of lithium carbonate, 31.5 mol% of potassium carbonate and 5 mol% of sodium carbonate is used, the melting point is 397 ° C.
It is possible to use electrolytes of many compositions, including a mixed salt of 62 mol% lithium carbonate and 38 mol% potassium carbonate at 88 ° C.

In the above embodiment, at the temperature of 500 ° C., 50% or more of the electrolyte 16 in the air electrode 3 is still in a solid state, and the air electrode is formed by the sum of nickel particles and unmelted electrolyte at this stage. The volume fraction of solids in 3 is about 50
%Met. Even if the unmelted electrolyte in the cathode 3 is small, it is effective to prevent the electrode from shrinking, but the sum of the volume of the nickel particles in the cathode 3 and the volume of the unmelted electrolyte is 35.
% Or more, it is more effective to prevent the air electrode 3 from shrinking.

In the above embodiment, the case where the constituent material of the air electrode 3 is nickel has been described. However, the air electrode 3 constituting the molten carbonate type fuel cell and the gas of the porous material integrated with the air electrode 3 have been described. 500 ° C porous metal used for flow channel
To the extent that the thickness is reduced under the conditions of the battery operating surface pressure, the battery characteristics, other than the nickel alloy that causes a problem in the configuration of the battery stack, such as a copper alloy or an iron alloy, the same effect. To play.

[0030]

As described above, according to the present invention, an air electrode made of a porous material containing at least one metal of nickel, copper and iron and holding an electrolyte in a hole portion, and an electrolyte containing an organic substance a layer, by heating, the step of burn off the organics and melt the electrolyte of the low melting point than the electrolyte held in the air electrode is impregnated with the organic trace Engineering
Degree, and a step of oxidizing the metal of the air electrode the electrolyte layer by flowing an oxidizing gas into the air electrode in a state where the electrolyte of the addition the air electrode does not transmit gas insoluble still completely by impregnation of the electrolyte Therefore, there is an effect that a method for manufacturing a molten carbonate fuel cell which can prevent the shrinkage of the air electrode and the oxidation of the fuel electrode can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional side view showing an electrolyte layer and electrodes according to a method for manufacturing a molten carbonate fuel cell according to one embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a conventional molten carbonate fuel cell.

FIG. 3 is a sectional side view showing an electrolyte layer and electrodes according to a conventional method for manufacturing a molten carbonate fuel cell.

FIG. 4 is an explanatory diagram showing a temperature pattern and a gas composition flowing to an electrode in a process of raising the temperature of a conventional molten carbonate fuel cell.

FIG. 5 is a characteristic diagram showing the effect of various electrolyte impregnations on the change in thickness of a porous nickel body having a porosity of 75% when the temperature is raised.

FIG. 6 is a graph showing a comparison of the shrinkage of an air electrode between a conventional example and an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte layer 2 Fuel electrode 3 Air electrode 12 Nickel alloy particle 13 Nickel particle 14 Organic matter 15 Low melting point electrolyte 16 High melting point electrolyte 17 L / K = 62/38 eutectic electrolyte

Continuation of the front page (56) References JP-A-63-6754 (JP, A) JP-A-1-183069 (JP, A) JP-A-3-238764 (JP, A) JP-A-62-24571 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01M 8/00-8/24 H01M 4/86-4/98

Claims (1)

(57) [Claims] 1. An air electrode comprising at least one metal selected from the group consisting of nickel, copper, and iron and comprising a porous body for holding an electrolyte in a hole, and an electrolyte layer containing an organic substance. the burn off process, the step of from the electrolyte held in the air electrode to melt the electrolyte having a low melting point is impregnated into the organic material remains, and the electrolyte layer is an electrolyte in addition the air electrode does not transmit gas by impregnation of the electrolyte A method for producing a molten carbonate fuel cell, comprising the step of flowing an oxidizing gas through the air electrode in a state where the metal is not completely melted yet to oxidize the metal of the air electrode.