JP3003377B2 - 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 The structure of a conventional fuel cell of this type is as shown in the sectional view of FIG. For example, a molten carbonate fuel cell using an alkali metal carbonate as an electrolyte generally has an electrolyte layer 1 composed of an electrolyte and a substance held by the electrolyte.
And the fuel electrode 2 and the air electrode 3 provided so as to sandwich the electrolyte layer 1 are arranged in contact with each other.
It faces the current collector plate 4 on the fuel electrode 2 side, the fuel electrode side gas flow path plate 5, and the fuel electrode 2 of the separator 6 a for the purpose of flowing the reaction gas while physically supporting the battery member and these cell members. A fuel electrode side gas chamber 7 composed of a surface, a current collector plate 8 on the air electrode 3 side, an air electrode side gas flow path plate 9, and an air electrode side gas chamber 10 composed of a surface of the separator 6 b facing the air electrode 3. Have been.

FIG. 6 shows a schematic diagram of a cross section of an electrolyte layer and electrodes before heating a battery in a conventional cell. Numeral 14 denotes an organic substance made of, for example, a composition, polyvinyl alcohol, alkyl phthalate, or polyalkylene glycol added to impart flexibility to the electrolyte layer at the time of forming the electrolyte layer. 11 is an average particle size of 0.5 μm for holding the electrolyte.
Of LiAlO ₂ particles. The average pore size of this electrolyte layer 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 fills 80% by volume of the pores. L / K = 62/38
The eutectic electrolyte 17 (62 mol% lithium carbonate and 38 mol% potassium carbonate) was previously impregnated.

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

Next, as shown in FIG. 6, L / K = 62/38
Fuel electrode 2 which is a porous body of nickel alloy particles 12 containing eutectic electrolyte 15, electrolyte layer 1 containing LiAlO ₂ particles serving as an electrolyte holder and organic matter 14 such as a binder plasticizer, and L having the same composition as fuel electrode 2 side / K = 62/38 eutectic electrolyte 15
A conventional method for starting up a molten carbonate fuel cell including an air electrode 3 which is a porous body of nickel particles 13 containing nickel and a simultaneous oxidation of the air electrode will be described. FIG. 1 is an explanatory diagram showing the temperature rise pattern and the composition of the gas supplied to the fuel electrode and the air electrode in the process. The dashed line is the conventional heating pattern. Further, in the explanatory diagram of FIG. 2, the oxidation of the air electrode (the amount of nickel oxidation) is indicated by a broken line.

At room temperature, the air electrode, which is a porous body of the nickel particles 13, burns the organic substances 14 contained in the electrolyte layer 1 up to 380 ° C., which is 400 ° C. or less at which oxidation stops. Supply air. At this stage, the electrode does not shrink because of the strength of the porous body of the nickel particles 13 itself and because the L / K = 62/38 eutectic electrolyte 15 contained in the electrode is solid. The oxidation amount of nickel at this stage is about 3%.

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.) A mixed gas of nitrogen and carbon dioxide gas for preventing the decomposition of the electrolyte 15 is flowed until the pores in the electrolyte layer are filled to form gas partition walls (gas does not pass).

After confirming that the L / K = 62/38 eutectic electrolyte 15 has melted (about 500 ° C.), a mixed gas of hydrogen and carbon dioxide gas is provided on the fuel electrode side, and air, nitrogen and carbon dioxide gas are provided on the air electrode side. Pour the mixed gas. At this stage, the air electrode 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 on the fuel electrode side and a mixed gas of air and carbon dioxide on the air electrode side. And 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 2 kg / cm ² . Stage 3 in which air electrode 3 is not oxidized and L / K = 62/38 eutectic electrolyte 15 is melted
Although the air electrode 3 shrinks at 80 to 500 ° C., the surface pressure of the small-sized molten carbonate fuel cell stack is 2 kg / c.
m ² , the time required to raise the temperature, and the time required to oxidize the air electrode 3 are short, so that the shrinkage of the air electrode 3 at the time of raising the temperature is suppressed to 10% or less of the thickness before starting operation. Have been. (JP-A-2-299156, JP-A-2-2-2)
04971)

[0012]

Since the conventional apparatus [0005] is constructed as described above, the surface pressure by the weight increase due the battery high lamination may not be a 2Kg / cm ² or less, electrolytic state that after the quality is dissolved, still air electrode is not oxidized
In this case, there is a problem that the air electrode shrinks by 10% or more, and the porosity of the air electrode decreases, thereby deteriorating the characteristics and making it impossible to perform power generation operation with the same efficiency as a small battery. Japanese Unexamined Patent Publication (Kokai) No. 2-299156 discloses that the use of an air electrode which is previously oxidized is effective in preventing the dimensional shrinkage of the air electrode. becomes difficult, and the oxidation process ing necessary before incorporation into the battery, there is a problem that the process causes increases cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and the remarkable shrinkage of the air electrode can be achieved even in a highly stacked fuel cell without adding a special step before assembling the cell. It is an object of the present invention to provide a method of manufacturing a molten carbonate fuel cell which can be avoided.

[0014]

According to a method of manufacturing a molten carbonate fuel cell according to the present invention, a porous material containing nickel is used for an air electrode, and nickel is used at the start-up of the cell (at the time of temperature rise). When the oxide porous body is formed by the oxidizing process, the porous body is oxidized at a temperature of 350 ° C. or more and the melting temperature of the electrolyte, and 5% or more of nickel in the air electrode is oxidized in advance before melting the electrolyte. It was made.

[0015]

When the temperature of the porous nickel becomes 350 ° C. or more in the air, the nickel starts oxidizing. However, since the reaction rate is small at this temperature, the actual oxidation temperature is preferably set to 400 ° C. or higher. Further, since the air electrode before oxidation is easily deformed when the electrolyte is melted, it is necessary to perform the oxidation at a temperature lower than the temperature at which the electrolyte starts to melt. Below this oxidation temperature, the electrode does not shrink because the nickel porous body constituting the air electrode contains a solid-state electrolyte. At this stage, nickel in the air electrode is oxidized by 5% or more, desirably 15% or more, and the temperature of the air electrode reinforced by the generation of nickel oxide is raised to melt the electrolyte, so that shrinkage of the air electrode can be prevented.

[0016]

【Example】

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG.
FIG. 2 is a schematic cross-sectional view of a laminate of the electrolyte layer 1, the air electrode 2, and the fuel electrode 3 before heating the battery according to the present embodiment.

Reference numeral 14 denotes an organic substance comprising polyvinyl alcohol, alkyl phthalate, and polyalkylene glycol, which is a composition added to impart flexibility to the electrolyte layer when the electrolyte layer is formed. 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 this electrolyte layer after degreasing is about 0.4 μm.

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 80% by volume of the pores. Which is previously impregnated with an electrolyte 15 (62 mol% of lithium carbonate and 38 mol% of potassium carbonate) just to fill the gap.

A porous body of nickel particles 13 (porosity 70%, average pore diameter 10 μm) is used for the air electrode 3, and an electrolyte (62 mol% lithium carbonate and 38 mol% Used beforehand is impregnated with potassium carbonate).

Next, a method for starting up the molten carbonate fuel cell of the embodiment and the simultaneous oxidation of the cathode are shown in FIG.
This will be described with reference to FIG. The solid line in FIG. 1 shows the operation start-up method (temperature rising pattern) of this embodiment, and the solid line in FIG. 2 shows the oxidation of the air electrode (nickel oxidation amount) in this embodiment.

Air electrode 3 which is a metallic nickel porous material at room temperature
Oxidation of the nickel porous body starts from 350 ° C., but the electrolyte layer 1
Air is supplied to both the fuel electrode atmosphere and the air atmosphere in order to burn off the organic substances 14 contained therein. At this stage, since the electrolyte contained in the electrode is solid, the electrode is unlikely to shrink. Although nickel oxidation starts, the reaction rate is low and temperature adjustment is easy. (3 after holding for 10 hours
% Of the nickel in the cathode was oxidized. )

The organic matter in the electrolyte layer is burned off at 380 ° C. in an air atmosphere and then heated to 430 ° C.
The air supply amount and the nitrogen supply amount are adjusted while monitoring the temperature so that the temperature does not exceed 0 ° C., and the air electrode is oxidized. (When controlled at 430 ° C. in 50% nitrogen and 50% air, holding for 10 hours oxidized about 40% of the nickel particles in the air electrode.) The oxidation amount can be estimated from the gas composition and flow rate at the entrance and exit of the stack. it can.

Thereafter, the temperature of the molten carbonate fuel cell was raised to about 500 ° C. and the air electrode was oxidized, and the mixed gas of hydrogen and carbon dioxide was supplied to the fuel electrode side, and air, nitrogen and carbon dioxide gas were supplied to the air electrode side. And the temperature is raised to the operating temperature of 650 ° C.

The surface pressure on the air electrode during the above series of heating processes is about 5 kg / cm ² . In this embodiment, the electrolyte in the air electrode is still in a solid state at the stage of 380 ° C. to 430 ° C. Since the unmelted electrolyte supports the nickel particles in the cathode, the cathode does not shrink even if the surface pressure is high. FIG. 3 is an explanatory diagram showing the shrinkage ratio of the air electrode in the example and the conventional example under a load of 5 kg / cm ² . The solid line indicates the shrinkage of the air electrode according to the conventional method, and the broken line indicates the shrinkage of the air electrode according to the conventional method.
From the figure, it can be seen that shrinkage is very slightly suppressed in this embodiment.

In the above embodiment, the case where the constituent material of the air electrode is nickel has been described. However, the air electrode constituting the molten carbonate type fuel cell and the gas flow path of the porous body integrated with the air electrode are provided. The porous metal used is from 450 ° C to 6
At about 50 ° C. , other than nickel alloys that cause problems in battery characteristics and the configuration of the battery stack due to a decrease in thickness under the conditions of the battery operating surface pressure, for example, even when being made of a copper alloy or an iron alloy, the same applies. Effect.

It is more desirable to mix nitrogen or hydrogen of 4% or less on the fuel electrode side at the temperature for oxidizing the air electrode from the viewpoint of preventing oxidation of the fuel electrode.

The impregnation amount of the electrolyte in the air electrode is 65% of the porosity of the nickel porous body in the above embodiment, but the ratio of the pores not occupied by nickel in the air electrode and the electrolyte in the air electrode is 65%. Should be 50% or less (26% in the case of the embodiment), and the same effect as that of the embodiment can be obtained with a surface pressure of about 2.5 kg / cm ² used in an actual stack. On the other hand, if the electrolyte is impregnated with an electrolyte of 80% or more of the porosity of the nickel porous body, the time required for oxidation becomes long. Therefore, it is desirable that the impregnation amount be 80% or less.

Further, in order to prevent significant oxidation of the fuel electrode is oxidized temperature before the electrolyte melt is desirably 450 ° C. or less, the air electrode after the oxidation treatment completion of the carbon dioxide gas mainly nitrogen or nitrogen It is desirable to flow a mixed gas or the like.
Oxidation of the air electrode starts at 350 ° C or higher, but in actual battery operation, 400 mm is required to reduce the startup time.
C or higher is desirable. If the temperature is lower than 350 ° C., it is considered that the oxidation reaction does not substantially proceed.

Although not shown in the above embodiment, if the pores of the anode contain 80% or more of the electrolyte in advance, the oxidation of the anode can be reduced, and the deterioration of the characteristics is not observed. I couldn't.

Also, by adding an oxidation-resistant film-forming element such as aluminum, chromium, or zirconium to the fuel electrode, it is possible to prevent deterioration of the battery characteristics due to oxidation of the fuel electrode during oxidation of the air electrode.

Further, in the above embodiment, the oxidation amount of nickel before dissolving the electrolyte at the start of the operation was 40%. However, as shown in FIG.
% Or less, which is effective for starting under a surface pressure of 5 kg / cm ² . FIG. 4 shows a surface pressure of 5 kgf / cm ² at 525 ° C.
5 is a graph showing the effect of the amount of oxidation on the change in thickness (shrinkage of the air electrode) of a nickel porous body having a porosity of 75% when the temperature is increased, when held in a nitrogen atmosphere. In the case of a surface pressure of about 2.5 kg / cm ² used in an actual stack, if the oxidation amount of nickel before dissolving the electrolyte is 5% or more, the same effect as in the embodiment can be obtained. The amount may be 5% or more, preferably 15% or more.
The shrinkage of the air electrode also depends on the load applied, the porosity of the nickel porous body constituting the air electrode, and the like. It is good to set so that it may be 10% or less which is considered to be no.

However, considering the leakage of the wet seal due to the increase in thickness due to oxidation at the start of operation, it is desirable that the increase in volume due to oxidation of nickel is smaller than the pore volume in the electrode before oxidation.

[0033]

As described above, in the present invention, the porous oxide material is formed by the process of oxidizing nickel at the start-up (at the time of temperature rise) of the battery using the porous material containing nickel for the air electrode. At the time of formation, an oxidation treatment was performed at a temperature of 350 ° C. or higher and a temperature lower than the melting temperature of the electrolyte, and a part of nickel of the air electrode was oxidized in advance before melting the electrolyte. Since the nickel porous body is partially oxidized while containing the solid state electrolyte, the electrode does not shrink, and the temperature of the air electrode strengthened by the generation of nickel oxide is raised to melt the electrolyte. Can be prevented from shrinking. Even if a special process is not performed before assembling the cell, there is an effect that a method for manufacturing a molten carbonate fuel cell which can avoid remarkable shrinkage of the air electrode even in a highly stacked fuel cell can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a temperature rising pattern and a composition of a supply gas when a molten carbonate fuel cell according to an embodiment of the present invention is started, together with a conventional example.

FIG. 2 is an explanatory view showing an embodiment of the present invention and oxidation of a cathode (oxidation amount of nickel) at the time of startup of a molten carbonate fuel cell together with a conventional example.

FIG. 3 is an explanatory view showing an embodiment of the present invention and shrinkage when starting up a molten carbonate fuel cell together with a conventional example.

FIG. 4 is a graph showing the effect of the amount of oxidation on the change in thickness of a porous nickel body having a porosity of 75% according to the present invention when the temperature is increased.

FIG. 5 is a sectional view showing a general molten carbonate fuel cell.

FIG. 6 is a schematic cross-sectional view showing an electrolyte layer and electrodes of a general molten carbonate fuel cell.

[Explanation of symbols]

 Reference Signs List 1 electrolyte layer 2 fuel electrode 3 air electrode 12 nickel alloy particles 13 nickel particles 15 L / K = 62/38 eutectic electrolyte

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazunori Sato 8-1-1, Tsukaguchi-Honmachi, Amagasaki-shi Mitsubishi Electric Corporation Materials and Devices Laboratory (56) References JP-A-63-66858 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 8/00-8/24 H01M 4/86-4/98

Claims (1)

(57) [Claims] 1. A molten carbonate fuel in which a porous oxide material is formed by a process of oxidizing nickel at the start of operation of a battery using a porous material containing nickel containing carbonate as an electrolyte for an air electrode. In the battery manufacturing method, 3
A molten carbonate fuel cell characterized in that it is oxidized at a temperature not lower than 50 ° C. and not higher than the melting temperature of the electrolyte to oxidize at least 5% of nickel in the air electrode before melting the electrolyte. Production method.