JP3208935B2 - Method for producing electrode for 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 molten carbonate fuel cell for producing a cathode electrode among electrodes of a molten carbonate fuel cell used in the energy sector which directly converts chemical energy of fuel into electric energy. The present invention relates to a method for manufacturing an electrode for use in a vehicle.

[0002]

2. Description of the Related Art Among the fuel cells proposed so far, a molten carbonate fuel cell uses an electrolyte plate (tile) formed by impregnating a molten porous material with a porous material as an electrolyte as a cathode (oxygen electrode). The anode and the anode (fuel electrode) are sandwiched from both sides, and an oxidizing gas is supplied to the cathode side and a fuel gas is supplied to the anode side to cause a reaction between the cathode side and the anode side, which is generated between the cathode and the anode. Power generation by the potential difference
Cells are formed, and each cell is stacked in multiple layers with a separator interposed therebetween to form a stack.

[0003] As a method of forming the electrode of the molten carbonate type fuel cell, the molding accuracy and the surface smoothness are excellent, and mass production is required.
In recent years, since it is possible to increase the size, the electrolyte plate has been manufactured by a tape forming method using a doctor blade method, which has been used as a method for manufacturing an electrolyte plate. A conventional method of manufacturing a cathode electrode using a tape forming method by such a doctor blade method is shown in FIG.
First, a simple substance of carbonyl Ni powder a as a raw material powder, a dispersant b and a solvent c are pulverized by a ball mill or the like (pulverization step d) to disperse the Ni powder a into primary particles, and then an organic binder f And a plasticizer g are added and mixed (mixing step e) to form a slurry h, which is formed into a tape (sheet) by a doctor blade device (tape forming step i).
Finally, use an electric furnace, reducing atmosphere furnace, vacuum furnace, etc.
By baking at a temperature of 900 ° C. (baking step j), a porous (porosity: 70 to 80%) cathode electrode is obtained.

The N manufactured by the above conventional manufacturing method
The cathode electrode, which is an i-porous body, is made of a single Ni powder a and is oxidized to NiO when assembled and operated as a battery. Although there is little creep deformation due to the clamping pressure the cathode electrode is once oxidized is confirmed, NiO ^{_{is, NiO + CO 2 → Ni ++}} + CO 3 - the reaction by eluting the slightly during carbonates go.

[0005] The dissolved Ni ⁺⁺ ions are reduced by hydrogen diffused from the anode side, and Ni
In the form of metal particles.

[0006] The Ni ⁺⁺ ions in the carbonate do not saturate in the carbonate;
The dissolution of i continues, which causes the collapse of the optimal microstructure (pore distribution, porosity) as the cathode electrode during the operation of the battery, and the short-circuit between the cathode and the anode due to Ni precipitated in the electrolyte plate. This has a significant effect on the performance of the battery, and is a factor influencing the life of the battery.

[0007] Therefore, conventionally, as a measure for preventing the above-mentioned NiO from dissolving in the carbonate to adversely affect the battery, changing the operating conditions of the battery by changing the temperature and gas composition, and changing the alkaline earth content. Addition to lower the basicity of the carbonate, etc.
Changing the composition of the carbonate, LiFeO ₂ , LiCoO ₂ , Li
Development of Mn ₂ O ₄ and the like have been considered.

[0008]

However, the above countermeasures are subject to restrictions on operating conditions. Also, regarding the above countermeasures, changes in the composition due to the diffusion and precipitation of alkaline earth in the carbonate bath due to the potential difference in the electrolyte plate. In addition, the alternative material has better stability than NiO, but has problems such as low electron conductivity and cannot be used as an electrode. As an alternative material, Ni × Fe ₃ -xO ₄
Although the use of is also proposed, this is excellent in stability in carbonate, but has a problem in electron conductivity and cannot be used as an electrode.

Accordingly, an object of the present invention is to provide a method of manufacturing a molten carbonate fuel cell electrode for manufacturing a cathode electrode having high solubility resistance so as to reduce the equilibrium solubility of NiO in a carbonate. is there.

[0010]

According to the present invention, in order to solve the above-mentioned problems, 1 to 10% of iron oxide or cobalt oxide powder is added to Ni powder, mixed, and further mixed with water and a binder. , A plasticizer and a dispersant, 200 g of water per 100 g of Ni powder,
A slurry is prepared by adding 10 g of a binder, 2 g of a plasticizer, and 0.5 g of a dispersant in a proportion, and after forming the slurry into a tape shape, 900-1050 ° C.
A method of manufacturing a porous cathode electrode by firing under firing conditions of 30 minutes.

Further, after adding lithium oxide or lithium carbonate to the above iron oxide or cobalt oxide and mixing the mixture, the mixture is calcined in the air and reacted to form a composite oxide, and the powder is mixed with the Ni powder. You may do so.

Alternatively, after adding and mixing an alkaline earth oxide with the above iron oxide or cobalt oxide, the mixture is calcined in the air and reacted to form a composite oxide powder.
You may make it mix with a powder.

Further, after mixing the above-mentioned iron oxide or cobalt oxide, lithium oxide and alkaline earth oxide, they are reacted by firing in the air to form a composite oxide, and the powder is mixed with Ni powder. You can also do so.

[0014]

[Function] A fine powder of iron oxide or cobalt oxide is added to Ni powder to form a slurry, formed into a tape shape, and then baked, the iron oxide or cobalt oxide forms a solid solution on the Ni surface to cover the Ni surface. Thus, an oxide film having excellent dissolution resistance is generated, and the elution of NiO can be suppressed by the oxide film.

[0015] When fine powder of a composite oxide obtained by firing a mixture of the above-mentioned iron oxide or cobalt oxide and lithium oxide or lithium carbonate and then pulverizing the mixture is added to Ni powder, the iron oxide or cobalt oxide becomes Ni. Is promoted, and the electron conductivity of the oxide generated on the Ni surface can be improved.

Further, when fine powder of a composite oxide obtained by calcining a mixture of the above-mentioned iron oxide or cobalt oxide and an alkaline earth oxide and then pulverizing the mixture is added to Ni powder,
The elution of iO can be suppressed, and the basicity of the carbonate impregnated in the electrode can be reduced.

Further, when fine powder of a composite oxide obtained by mixing lithium oxide and alkaline earth oxide with iron oxide or cobalt oxide is added to Ni powder, lithium The effect obtained when the oxide is added and the effect obtained when the alkaline earth oxide is added are obtained.

[0018]

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

FIG. 1 shows a process flow of an embodiment of the production method of the present invention.
Iron oxide (Fe ₂ O ₃ , iron hydroxide containing Fe ₃ O ₄ ) or cobalt oxide (CoO) 2 is added and mixed in the mixing step I. Water 3, binder 4, plasticizer 5, dispersant 6 is added and mixed to form a slurry 7. The slurry 7 is tape-formed in a tape forming step II, and the formed tape is fired in a firing step III to form a porous electrode (cathode electrode) 8. To get.

In the above method, the optimal addition amount of iron oxide or cobalt oxide 2 added to Ni powder 1 is 1 to 10%
/ Ni. The reason why the addition amount to Ni powder is set to 1 to 10% is that the expected effect cannot be expected if the addition amount is 1% or less, and 10%
This is because sintering of Ni or NiO is hindered and the strength as an electrode becomes insufficient.

1-10% of iron oxide or cobalt oxide 2 is added to Ni powder 1 and mixed in mixing step I, and appropriate amounts of water 3, binder 4, plasticizer 5, and dispersant 6 are added. After the slurry 7 is formed into a tape in a tape forming step II, the slurry 7 is fired in a weak reducing atmosphere at 900 to 1050 ° C. for 10 to 30 minutes in a firing step III. As a result, Fe or Co is reduced and activated, and iron oxide or cobalt oxide 2 is dissolved and diffused on the surface of the Ni powder 1, and Ni—
A film of Fe (or Co) oxide is produced, and only the surface of Ni can be wrapped with Fe ₂ O ₃ or CoO.

Even if the electrode thus manufactured is oxidized into NiO in the battery, the elution of NiO into the carbonate is suppressed because the oxide film 2a is formed on the surface as shown in FIG. In addition, the compression strength of the cathode electrode can be improved, and the microstructure of the electrode does not collapse.

Although Ni and oxide have low electron conductivity, they do not impair the performance as an electrode because of the thin film.

In the above, the firing temperature in the firing step III was set to 900 to 1050 ° C.
This is because sintering of the i-powder is insufficient, and if the temperature is 1050 ° C. or more, sintering proceeds excessively, the powder becomes dense, the porosity becomes small, and the electrode cannot be used.

Further, water 3, a binder (for example, polyvinyl butyral as an organic solvent) 4, a plasticizer (phthalic acid) 5, and a dispersant (for example, a nonionic surfactant) 6 are as follows. Add such amount.

To 100 g of the Ni powder, 200 g of water, 10 g of a binder, 2 g of a plasticizer, and 0.5 g of a dispersant are added in a proportion.

In the embodiment shown in FIG. 1, Fe,
Although it is possible to use a metal component of Co, the amount of solid solution in Ni increases during sintering, the thickness of the Ni-oxide layer having low electron conductivity increases, and the electric resistance of the electrode increases.

FIG. 3 shows another embodiment of the present invention.
In the same configuration as the process flow shown in FIG. 1, instead of adding iron oxide or cobalt oxide 2 alone to Ni powder 1 in mixing step I, iron oxide or cobalt oxide 2 and lithium oxide 9 or carbonate A composite oxide of lithium is prepared, and its fine powder is added to the Ni powder 1. Other configurations are the same as those in FIG.

More specifically, iron oxide (eg, Fe ₂ O)
₃ ) Lithium oxide (LiO) 9 is added to cobalt oxide (CoO) 2 in an optimal amount of 0.5 to 10% and mixed in mixing step IV. Oxide and Li oxide in air at 900-1
The mixture is reacted at a temperature of 100 ° C. for 30 to 60 minutes to produce a composite oxide (for example, Li ₂ Fe ₃ O ₅ ), which is pulverized in a fine crushing step VI to obtain a fine powder. The electrode (cathode electrode) 8 is manufactured through the same steps as those shown in FIG.

In the above method, the sintering condition in the sintering step V is that the temperature is 900 to 1100 ° C.
In the following, Li conversion of Fe ₂ O ₃ is insufficient, and 1100
If the temperature is higher than ℃, the grain growth of the oxide proceeds excessively.

The reason why the optimum addition amount of the lithium oxide 9 is 0.5 to 10% with respect to the iron oxide or the cobalt oxide 2 is that iron oxide Fe ₂ O ₃ and cobalt oxide CoO solid solution diffusion into Ni becomes insufficient and 10%
This is because sintering progresses when the composite oxide is produced by preheating, and the grain growth of the oxide progresses too much, which makes it difficult to perform the pulverization treatment in the subsequent pulverization step VI.

The pulverization in the pulverization step VI is performed by a crusher, a ball mill or the like.
m. The smaller the particle size, the better, but if the particle size is 15 μm or more, uniform mixing with the Ni powder 1 becomes difficult.
μm or less is desirable.

In the method shown in FIG. 3, the slurry 7 is mixed through the mixing step I without reacting the lithium oxide 9 with the iron oxide or the cobalt oxide 2 to form a composite oxide.
When the lithium oxide 9 is added alone at this time, it dissolves in water due to the aqueous slurry and increases the pH, and disperses the Ni powder poorly. Since the fine powder is used after the composite oxide composed of the lithium oxide 9 is generated, there is no problem that the dispersion of the Ni powder is deteriorated.

[0034] In the method shown in FIG. 3, the addition of the composite oxide by the addition of lithium oxide 9 on iron oxide or cobalt oxide 2 and then from the Ni powder 1, Fe ₂ O ₃ by firing in a firing step III , Can promote the solid solution of CoO into Ni, and can improve the electronic conductivity of the oxide generated on the surface of the Ni powder.

The present inventors have reported that LiO / Fe ₂ O ₃ = 5 /
When a composite oxide powder consisting of 95 (weight ratio) was added to Ni powder 1 at 5%, mixed, tape-formed and fired to produce an electrode, the microstructure of the produced electrode was changed. Did not.

In the manufactured electrode 8, the oxidation of Ni is promoted by the presence of Li.

The same effect as described above can be obtained by using Li ₂ CO ₃ or Li (OH) instead of LiO as the lithium oxide 9.

Since there are Li ions in the battery,
It is considered that the same effect can be expected by Li ions in the battery without adding LiO. However, if LiO is not added, solid solution diffusion of oxides into Ni becomes slow, and an oxide film is formed on the Ni surface. As a result, the battery tends to be compressed and deformed by the tightening stress of the battery inside the battery, so that the tightening stress needs to be adjusted.

Next, FIG. 4 shows another embodiment of the present invention. In place of the lithium oxide 9 in the embodiment of FIG. 3, an alkaline earth oxide 10 is replaced with iron oxide or cobalt oxide 2. To form a composite oxide and then add Ni powder 1
Is to be mixed.

Examples of the alkaline earth oxide 10 include Mg
Using O, CaO, SrO or the like, the optimal amount of iron oxide or cobalt oxide 2 to be added is 10 to 80%, and after mixing in mixing step IV, firing step V
Then, the iron oxide or the cobalt oxide 2 and the lithium oxide 9 are reacted under the same reaction conditions as shown in FIG. 3 to form a composite of the iron oxide or the cobalt oxide and the alkaline earth oxide. An oxide (for example, MgFe ₂ O ₃ ) is generated, and this composite oxide is pulverized using a ball mill or the like in a pulverization step VI, and added to the Ni powder 1 to form a slurry 7.
The electrode 8 is manufactured by forming into a tape in a tape forming step II and firing in a firing step III.

The reason why the addition amount of the alkaline earth oxide 10 to the iron oxide or cobalt oxide 2 is set to 10 to 80% is that the effect of the alkaline earth cannot be expected if it is 10% or less. This is because the effect is the same even if added.

According to this method, MgO is present around the oxide film 2a formed on the Ni surface as shown in FIG. 2 by the addition of the alkaline earth oxide 10, and the carbonate adheres to the NiO. This makes it difficult to elute NiO.

As shown in FIG. 4, the alkaline earth oxide 1
0 is added to the iron oxide or the cobalt oxide 2 to form a composite oxide, and when the alkaline earth oxide 10 is added alone during slurry production, the same as in the case of the lithium oxide 9, There is an effect on pH during slurry production.

FIG. 5 shows still another embodiment of the present invention, in which a lithium oxide 9 shown in FIG. 3 and an alkaline earth oxide 10 shown in FIG. The mixture is then mixed and fired to produce the composite oxide, and the electrode 8 is manufactured.

The mixing ratio (weight ratio) of the iron oxide or cobalt oxide 2, the lithium oxide 9, and the alkaline earth oxide 10 is, for example, LiO / MgO / Fe ₂ O ₃ = 2 /
After mixing in the mixing step IV as 48/50 (weight ratio),
An oxide of the above LiO / MgO / Fe ₂ O ₃ = 2/48/50 (weight ratio) was sintered in a firing step V to produce a composite oxide, and then pulverized in a pulverization step VI. The fine powder is added to the Ni powder 1 in the mixing step I and mixed to form a slurry 7, then formed into a tape in the tape forming step II, and fired in the firing step III to form an electrode (cathode electrode).
8 can be manufactured.

The present inventors used the electrode 8 produced by adding 5% of the fine powder of the composite oxide produced as the above weight ratio to Ni for the cathode, while using 8% Cr for Ni for the anode. When the power generation result of the used battery was examined, FIG.
The result as shown by the mark ○ was obtained. In FIG. 6, the mark ● indicates the power generation result when a conventional Ni-only electrode is used as the cathode.

As is apparent from FIG. 6, when the electrode 8 manufactured by the method of the present invention is used as a cathode, the initial performance of the battery is the same as that of the conventional cathode, and the initial performance is 20%.
Even after 00 hours, almost no decrease in performance was observed. Also, the amount of Ni in the carbonate after 2000 hours was about half that in the case where the conventional cathode was used. This gives N
It was found that a cathode having high dissolution resistance in which the elution of iO into the carbonate was suppressed was produced.

The above LiO / MgO / Fe ₂ O ₃ = 2
/ 48/50 (weight ratio) composite oxide powder
The microstructure of the electrode manufactured by mixing the powder at an addition amount of 5% was equivalent to the electrode manufactured by the method of FIG.

The above LiO / MgO / Fe ₂ O ₃ = 2/4
An electrode 8 manufactured using a composite oxide having a weight ratio of 8/50 was used as a cathode in a battery, and as a result of X-ray diffraction of the cathode electrode after power generation, the electrodes were NiO and Li ₂ Fe.
₃ O ₅ , NiFe ₂ O ₄ , Li ₂ NiFe ₂ O ₄ , Li
It consisted of Fe ₅ O ₈ .

In the embodiment shown in FIG. 5, Li ₂ CO ₃ is used as the lithium oxide 9 and Li ₂ CO ₃ / MgO
/ Fe ₂ O ₃ = 1/12/12 (weight ratio), and X-ray diffraction of a powder calcined at 1000 ° C. for 60 minutes in the air shows Li ₂ Fe ₃ O ₅ , LiFe ₅ O
₈ , MgFe ₂ O ₄ and Fe ₃ O ₄ were detected.

Further, the present inventors have reported that a Ni plate is made of LiO / M
A test piece coated with a composite oxide powder of gO / Fe ₂ O ₃ = 2/48/50 (weight ratio) and LiO / Fe ₂ O ₃ = 5/95 (weight ratio) according to the embodiment shown in FIG. The test piece obtained by applying the powder of the composite oxide of the above to a Ni plate is subjected to a firing step of electrode production.
After heating under the same conditions as in III to cause solid oxide diffusion of the composite oxide on the Ni surface, a corrosion test in a carbonate was performed.

6 in an atmosphere of air / CO ₂ = 80/20
In cross-sectional observation after heating at 50 ° C. for 20 hours, wall loss due to corrosion was as small as 2 to 4 μm in both of these test pieces. On the other hand, the Ni plate used as the comparative test piece had a thickness reduction of about 10 μm.

[0053]

As described above, according to the method of manufacturing an electrode for a molten carbonate fuel cell of the present invention, 1 to 10% of iron oxide or cobalt oxide powder is added to Ni powder and mixed. ,
In addition, water, a binder, a plasticizer, and a dispersant were added to Ni powder 100 g.
Of water, 10 g of a binder, 2 g of a plasticizer, and 0.5 g of a dispersant to obtain a slurry.
Since the porous cathode electrode is manufactured by firing under firing conditions of 1050 ° C. and 10 to 30 minutes, iron oxide or cobalt oxide is solid-solved and diffused on the surface of the Ni powder during firing to form an oxide film. To wrap the Ni surface to prevent the elution of NiO into the carbonate even if the electrode is
It is possible to obtain an electrode having high solubility resistance that can reduce the equilibrium solubility of iO in carbonate, and it is possible to improve the compression resistance of the electrode and not to change the microstructure of the electrode. In addition, a small amount of lithium oxide is mixed with the above iron oxide or cobalt oxide and calcined to obtain a composite oxide, and a powder of this composite oxide is added in a small amount to Ni powder. In the same manner as described above, by forming a tape and then sintering to produce an electrode, the addition of lithium oxide can promote the solid solution of iron oxide or cobalt oxide on the Ni surface, and can also oxidize the Ni surface. The effect that the electronic conductivity of the film can be improved can be obtained, and the powder of the composite oxide obtained by mixing the above-mentioned iron oxide or cobalt oxide with an alkaline earth oxide and calcining the same is used as Ni powder. Added to After mixing, tape forming and firing in the same manner as described above to produce an electrode, the alkaline earth exists around the iron oxide or cobalt oxide film on the Ni surface, and the carbonate becomes NiO. And has an effect of preventing the elution of NiO. Further, iron oxide or cobalt oxide, lithium oxide and alkaline earth oxide are mixed at a required mixing ratio and calcined to form a composite oxide, and the powder of this composite oxide is mixed with Ni powder. After forming the tape, it is fired to produce the electrode, which promotes solid solution of iron oxide or cobalt oxide on the Ni surface and prevents NiO from being dissolved. The effect is obtained.

[Brief description of the drawings]

FIG. 1 is a process flow showing one embodiment of a method for producing an electrode for a molten carbonate fuel cell of the present invention.

FIG. 2 is a schematic view showing a part of a crystal structure of an electrode manufactured by the manufacturing method of FIG.

FIG. 3 is a process flow showing another embodiment of the manufacturing method of the present invention.

FIG. 4 is a process flow showing another embodiment of the manufacturing method of the present invention.

FIG. 5 is a process flow showing still another embodiment of the manufacturing method of the present invention.

FIG. 6 is a diagram of a power generation result comparing an electrode manufactured by the manufacturing method of FIG. 5 with a conventional electrode.

FIG. 7 is a process flow showing an example of a conventional method for manufacturing a cathode electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ni powder 2 Iron oxide or cobalt oxide 3 Water 4 Binder 5 Plasticizer 6 Dispersant 7 Slurry 8 Electrode 9 Lithium oxide 10 Alkaline earth oxide I Mixing process II Tape forming process III Firing process IV Mixing process V Firing process VI Crushing process

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinichiro Sakai 3-1-1-15 Toyosu, Koto-ku, Tokyo Ishikawa Shima-Harima Heavy Industries Co., Ltd. (56) References JP-A-2-253562 (JP, A) JP-A-3-238764 (JP, A) JP-A-1-112665 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/88 H01M 4/86

Claims (4)

(57) [Claims] 1. An iron oxide or cobalt oxide powder is added to Ni powder in an amount of 1 to 10% and mixed, and water, a binder, a plasticizer, and a dispersant are further added to 200 g of water with respect to 100 g of Ni powder. ,
A slurry is prepared by adding 10 g of a binder, 2 g of a plasticizer, and 0.5 g of a dispersant in a proportion, and after forming the slurry into a tape shape, 900-1050 ° C.
A method for producing an electrode for a molten carbonate fuel cell, comprising producing a porous cathode electrode by firing under firing conditions for 30 minutes. 2. A small amount of lithium oxide or lithium carbonate is added to iron oxide or cobalt oxide, mixed, and then calcined in the air to cause a reaction between the two to form a composite oxide. The method for producing an electrode for a molten carbonate fuel cell according to claim 1, wherein Ni is added to Ni powder and mixed. 3. An alkaline earth oxide is added to and mixed with iron oxide or cobalt oxide, and the mixture is calcined in the air to cause a reaction between the two to form a composite oxide. 2. The method for producing an electrode for a molten carbonate fuel cell according to claim 1, wherein the mixture is added to Ni powder and mixed. 4. A mixture of iron oxide or cobalt oxide, lithium oxide and alkaline earth oxide, and calcined in air,
The method for producing an electrode for a molten carbonate fuel cell according to claim 1, wherein these are reacted to form a composite oxide, and the powder of the composite oxide is added to the Ni powder and mixed.