JP2000021423A - Separator for fuel cell and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for fuel cell, capable of improving battery performance by improving the adhesiveness between cells so as to lower the contact electrical resistance, and eliminating generation of cracks of a groove for gas passage at assembling of a battery so as to eliminate the troubles of gas leakage. SOLUTION: This separator 1 is formed with plural grooves 2 for gas passage in one surface or both surfaces thereof, and a bottom part of the groove for gas flow is preferably formed into a curved surface having a curvature at 1/10-1/100 of the groove width. This separator preferably has 0.5 mm or less of bow, 100 or less of Shore hardness, 200 kgf/mm2 or less of bending elastic modulus, and ±0.05 mm or less of thickness accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for a fuel cell, particularly for a polymer electrolyte fuel cell used for automobiles and small distributed power sources, and a method for producing the same.

[0002]

2. Description of the Related Art A fuel cell directly converts fuel energy into electric energy. Each cell of a polymer electrolyte fuel cell is, as shown in FIG. It is composed of a pair of electrodes 5 and 6 (anode 6 and cathode 5) arranged with an electrolyte membrane 7 made of a membrane interposed therebetween, and a separator 1 made of a dense carbon material sandwiching the electrodes 5 and 6 from both sides. The electrode is formed of a porous material made of short carbon fibers carrying a catalyst such as platinum or a material obtained by binding carbon black with a resin.

A plurality of grooves 2 extending linearly or in a lattice are formed in the separator 1, and a space formed between the grooves 2 and the surface of the cathode 5 is used as an oxygen-containing gas flow path. The space formed between the surfaces of the electrodes serves as a flow path for a fuel gas (for example, hydrogen gas or a mixed gas containing hydrogen gas as a main component) so that the chemical reaction that occurs when the oxygen-containing gas and the fuel gas come into contact with the electrode is performed. Utilization is used to extract electricity from between the electrodes.

In order to ensure the cell performance, the cells must be in close contact with each other. For this purpose, the dimensional accuracy of the separator is important. Insufficient adhesion between the electrodes causes an increase in contact electric resistance, which often causes a problem of a decrease in battery performance due to an increase in internal electric resistance.

[0005] A polymer electrolyte fuel cell is assembled by stacking each cell and bolting the periphery thereof with a tightening pressure of usually about 1 to 10 kg / cm ² .
It has also been experienced that due to factors such as poor dimensional accuracy of the separator, a biased load is generated at the time of tightening in cell assembly, cracks are generated at the bottom edge of the gas flow channel groove of the separator, and gas leakage is caused. When a gas leak occurs, the electrochemical reaction is inhibited, so that the performance of the battery is reduced. In addition, since hydrogen and oxygen are mixed, an explosion may occur.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a fuel cell,
In order to solve the above-mentioned conventional problems especially in polymer electrolyte fuel cells, we examined the relationship between the adhesion between cells and each factor such as the material properties, shape, and dimensions of the separator, and the relationship between separator production conditions. The purpose was to improve the adhesion between the cells, eliminate the problem of increased contact electric resistance, and eliminate the cracks in the gas flow channel grooves during battery assembly to reduce gas leakage. An object of the present invention is to provide a fuel cell separator capable of solving the problem and improving the cell performance, and a method for manufacturing the same.

[0007]

According to the present invention, there is provided a fuel cell separator according to the present invention, wherein a plurality of gas flow channel grooves are formed on one surface or both surfaces. A first feature is that the bottom of the distribution groove is curved.

In the above separator, the curvature of the curved bottom of the gas flow groove is 1/10 to 1 to 1 of the width of the groove.
/ 100 is a second feature.

Further, in the above separator, the warp is 0.5 mm or less, the Shore hardness (Hs) is 100 or less,
The flexural modulus is 2000 kgf / mm ² or less, the thickness accuracy is ± 0.05 mm or less, and the bending strength is 30
The third and fourth features of the present invention are that the pressure is 0 kgf / cm ² or more.

The method for producing a fuel cell separator according to the present invention is directed to a method for producing a fuel cell separator in which a mixture powder of a carbon powder and a binder resin is charged into a mold and press-molded. The ratio of 4
0% by weight or less, the mixture powder is pulverized to 40 mesh or less and sieved, and then the mixed powder is provided with a ridge for forming a groove, and the ridge is formed into a curved surface. After the preload, the mold is opened to remove volatile components and residual air after the preload, and then molded at a predetermined pressure. The temperature difference in the mold during the preload step and the molding step is within 10 ° C. The first feature is that after molding, an additional 1 g /
The second feature is that the heat treatment is performed under a pressure of ² cm ² or more.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, as shown in FIG. 1, in a fuel cell separator having a plurality of gas flow channel grooves formed on one or both surfaces, the bottom of the gas flow groove is illustrated. 1. Formed into a curved surface as shown in FIG.
FIG. 1 shows a configuration in which a curved portion 3 is provided so that the shape of a groove 2 is continuous with a straight portion 4, and FIG. 3 shows a configuration in which the curved portion 3 is provided without forming a straight portion. Any shape can achieve the effects of the present invention. It is desirable to set the curvature R of the curved surface portion to 1/10 to 1/100 of the width W of the groove. 1 and 2 illustrate only a separator having a gas flow groove formed on one surface.

The separator is a carbon plate-like body having a plurality of gas flow channel grooves formed on one or both sides. In order to improve the adhesion between cells, the warp is 0.5 mm or less. , Thickness accuracy (thickness variation) is ± 0.
When the warpage and the thickness accuracy exceed the above-mentioned ranges, the adhesion between cells becomes insufficient and gas leakage easily occurs.

[0013] Further, the characteristics of the carbon material constituting the separator include a flexural modulus of 2000 kgf / cm ² or less, a Shore hardness of 100 or less, and 300 kgf / cm ² or less.
/ Cm ² or more. When the flexural modulus and the Shore hardness exceed the above-mentioned values, and when the bending strength is less than the above-mentioned values, the adhesion between the cells may be insufficient at the time of assembling the cells by bolting.

Hereinafter, a method of manufacturing a fuel cell separator for obtaining the above characteristics will be described. The separator is manufactured by charging a mixture powder of the carbon powder and the binder resin into a mold and pressing the mixture. In the present invention, the ratio of the binder resin in the mixture powder is 40%.
% By weight or less. 40% by weight of binder resin
When the ratio exceeds the above, the flexural modulus and the Shore hardness of the obtained separator are increased.

As the carbon powder, artificial graphite, natural graphite,
Expanded graphite, coke powder, carbon black and a mixture thereof can be used. As the binder resin, a synthetic resin having excellent corrosion resistance such as a phenol resin, an epoxy resin, a polyimide resin, and a polysulfone resin can be used.

The mixing of the carbon powder and the binder resin is carried out using a device such as a pressure kneader, a twin screw kneader or a V-type mixer. When a binder resin containing a volatile component such as a solvent is used, a drying process of the mixture powder is performed as necessary.

The mixed powder contains a large amount of large-sized powder. In the present invention, it is necessary to pulverize the mixed powder to 40 mesh or less and to sieve the powder. For crushing, use an appropriate crusher such as a Nara crusher, jet mill,
Screen if necessary. Dense molding can be performed by setting the mesh size to 40 mesh or less.

The obtained mixed powder is charged into a mold and pre-pressed. After the pre-press, the mold is opened. By opening the mold after the preloading, the volatile components and residual air present therein are removed, the desired gas impermeability is obtained without the occurrence of intrinsic defects, and the occurrence of warpage is also prevented.

The mold is provided with a ridge for forming a groove, and in order to make the bottom of the groove a curved surface, a die having a curved surface is used. Next, the mold is closed and molding is performed at a predetermined pressure. The molding pressure and molding temperature are determined in consideration of the properties and moldability of the mixture powder.
Pressure of 00 to 3000 kgf / cm ² , room temperature to 250 ° C
Of temperature apply.

In the present invention, it is important to control the temperature difference in the mold within 10 ° C. during the molding step including the preloading step, and by this temperature control, a uniform cured state is achieved during molding. You. If the temperature difference exceeds 10 ° C., the cured state during molding is partially changed to cause thermal distortion, and the molded plate-like separator tends to be warped.

After molding, the mold is removed, and depending on the use conditions,
When strict flatness is required, the sheet is further sandwiched between flat plates having a smooth surface and good thermal conductivity, such as a graphite plate and an aluminum plate, under a pressure of 1 kgf / cm ² or more.
Heat treatment is performed in a temperature range of up to 250 ° C. Depending on design conditions, surface smoothing processing such as milling and surface processing, and peripheral processing are performed.

In the present invention, a mold provided with a ridge for forming a groove, and having a curved ridge in order to make the bottom of the groove a curved surface is used as the mold. However, the ridge for forming the groove has a taper angle of 10
It has been proposed to use a mold with a punching margin of more than degrees and a corner with a round corner of 0.2 mm or more at the edge of the ridge to prevent the occurrence of defects when releasing. (JP 10
In the case where molding is performed using this mold, a groove having a rounded portion at the bottom edge can be formed.

However, this groove shape is not enough to prevent the generation of cracks in the grooves when stacking and tightening and assembling the cells of the fuel cell, and in order to reliably avoid the occurrence of cracks, As in the present invention, it is necessary to form the entire bottom into a curved surface.

[0024]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 A carbon powder having a true specific gravity of 2.18 and an average particle diameter of 45 μm, and a phenol resin methanol solution (PR manufactured by Sumitomo Durres Co., Ltd.)
940) was mixed using a twin-screw kneader while changing the mixing ratio of the two, and the resulting mixed powder was dried at room temperature in the air, pulverized using a Nara pulverizer, and then sieved. And powder having a size of 40 mesh or less was collected. Powders larger than 40 mesh were ground again and sieved.

The mold used is composed of an upper mold and a lower mold, and the molding section of the mold formed at the joint of the upper mold and the lower mold has a length of 15 mm.
0 mm, width 150 mm, thickness 3 mm, thickness variation is ± 0.04 mm, and a gas flow groove (width 1.5 mm, height 1 mm, bottom radius of curvature 0.
1 mm) is provided on each side of the separator to be formed, 33 lines on each side.

The resulting mixture powder having a mesh size of 40 mesh or less is filled in a mold, the molding temperature is set to 180 ° C., and the temperature difference (the difference between the maximum temperature and the minimum temperature) in the mold is adjusted to 8 ° C. Molding was performed. First, the mold was opened by preloading at 100 kgf / cm ² . Then, a pressure of 350 kgf / cm ² was applied and maintained for 3 minutes.

Separator obtained by die cutting (test material)
The following tests were conducted for (Contact electric resistance measurement test) Ten separators were laminated,
After fixing by applying a tightening pressure of 10 kgf / cm ² , a direct current of 10 A was applied, and the contact electric resistance between the stacked separators was measured.

(Gas leak test) After measuring the contact electric resistance,
The laminated separators were disassembled, and a pressure of 1 kgf / cm ² was applied to each separator with nitrogen gas to check for gas leak. Table 1 shows the results. All the test materials according to the present invention have low contact electric resistance and no gas leakage.

In Table 1, as for the amount of warpage, the separator was placed on the surface plate, the dial gauge was set to zero at the reference position, the amount of warpage was measured at nine points in total, and the maximum value was adopted. The thickness accuracy is obtained by measuring the thickness at nine locations of the separator with a micrometer and detecting the average value, the maximum value, and the minimum value to obtain the thickness accuracy. Flexural strength and flexural modulus were measured according to JIS K6911. The contact electric resistance was measured according to JIS R7202 by using a value obtained by subtracting a material component from the entire electric resistance as a contact electric resistance.

[0030]

[Table 1]

COMPARATIVE EXAMPLE 1 As in the example, carbon powder having a true specific gravity of 2.18 and an average particle size of 45 μm, and a phenol resin methanol solution (PR940, manufactured by Sumitomo Durres Co., Ltd.) were mixed at different mixing ratios. After mixing using an axis kneader and drying the resulting mixture powder in the air at room temperature, the mixture was pulverized using a Nara-type pulverizer and then sieved to collect powder having a size of 40 mesh or less. Powders larger than 40 mesh were ground again and sieved.

The mold used is composed of an upper mold and a lower mold, and the molding section of the mold formed at the joint of the upper mold and the lower mold has a length of 15 mm.
0 mm, 150 mm in width, 3 mm in thickness, the thickness variation is ± 0.05 to 0.08 mm, and the gas flow groove (width 1.5 mm, height 1 mm, bottom curvature in the shape shown in FIG. 2) A separator having a radius of 0.02 to 0.1 mm and having no curvature) is provided on each side of the separator to be formed, 33 pieces on each side.

The obtained mixture powder having a mesh size of 40 mesh or less was filled in a mold, molded under the same conditions as in Example 1, and the same test as in Example 1 was performed on the separator obtained after the die cutting. Table 2 shows the results.

[0034]

[Table 2] << Table Note >> Gas Leakage: Number of test materials with gas leak out of 10 test materials

As shown in Table 2, the test material No. Sample No. 3 had a large amount of warpage and a small curvature at the bottom of the groove, so that the contact electric resistance was large and gas leakage occurred. Test material No. 4 is
Test material No. 3, the mixing ratio of the carbon powder and the methanol solution of the phenol resin is the same, and the molded test material is
The amount of warpage was reduced by heat treatment at a temperature of 200 ° C. under a pressure of 1 kgf / cm ² or more, sandwiched between graphite plates with smooth surfaces, and the curvature of the groove bottom was sufficiently large. Although not recognized, the contact electric resistance was improved, but the contact electric resistance was not sufficiently reduced due to low bending strength.

Test material No. No. 5 has large contact electric resistance because of large thickness variation. Test material No. Sample No. 6 has a large flexural modulus, so that the adhesion of the laminated test materials is poor and the contact electric resistance is large. Test material No. 7, N
o. In No. 8, a gas leak occurred because the groove bottom was not curved and a crack occurred at the edge of the groove bottom during lamination. Test material No. 9 has a high hardness, and thus has a large contact electric resistance.

[0037]

According to the present invention, the adhesion between cells is improved, the contact electric resistance is low, the crack of the gas flow channel groove during battery assembly is eliminated, and the problem of gas leakage is eliminated, and the battery performance is improved. Provided are a fuel cell separator that can be improved and a method of manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a structure of a polymer electrolyte fuel cell.

FIG. 2 is a cross-sectional view showing one embodiment of a groove shape of the separator of the present invention.

FIG. 3 is a sectional view showing another embodiment of the groove shape of the separator of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 2 Gas channel groove part 3 Curved surface part 4 Linear part 5 Cathode 6 Anode 7 Electrolyte membrane R Curvature radius of curvature part W Width of groove part

[Procedure amendment]

[Submission date] July 27, 1999 (July 7, 1999
7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

After molding, the mold is removed, and depending on the use conditions,
When strict flatness is required, it is further sandwiched between flat plates having a smooth surface and good thermal conductivity, such as a graphite plate and an aluminum plate, and placed under a pressure of 1 g / cm ² or more under a pressure of 150 to ² g / cm ^2.
Heat treatment is performed in a temperature range of 50 ° C. Depending on design conditions, surface smoothing processing such as milling and surface processing, and peripheral processing are performed.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction contents]

As shown in Table 2, the test material No. Sample No. 3 had a large amount of warpage and a small curvature at the bottom of the groove, so that the contact electric resistance was large and gas leakage occurred. Test material No. 4 is
Test material No. 3, the mixing ratio of the carbon powder and the methanol solution of the phenol resin is the same, and the molded test material is
The amount of warpage was reduced by performing a heat treatment at a temperature of 200 ° C. under a pressure of 1 g / cm ² or more, sandwiched between graphite plates having a smooth surface, and the curvature at the bottom of the groove was sufficiently large. Although not recognized, the contact electric resistance was improved, but the contact electric resistance was not sufficiently reduced due to low bending strength.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG. 1 is a sectional view showing one embodiment of a groove shape of a separator of the present invention.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2 is a sectional view showing another embodiment of the groove shape of the separator of the present invention.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3 is a partial cross-sectional view showing a structure of a polymer electrolyte fuel cell.

Claims (6)

[Claims] 1. A fuel cell separator having a plurality of gas flow channel grooves formed on one or both surfaces thereof, wherein the bottom of the gas flow groove is curved. 2. The fuel cell separator according to claim 1, wherein the curvature of the curved bottom of the gas flow groove is 1/10 to 1/100 of the width of the groove. 3. A warp of 0.5 mm or less and a Shore hardness of 1
00 or less, flexural modulus 2000 kgf / mm ² or less,
3. The fuel cell separator according to claim 1, wherein the thickness accuracy is ± 0.05 mm or less. 4. The fuel cell separator according to claim 1, wherein the separator has a bending strength of 300 kgf / cm ² or more. 5. A method for producing a separator for a fuel cell, wherein a mixture powder of carbon powder and a binder resin is charged into a mold and press-molded, wherein the proportion of the binder resin in the mixture powder is set to 40% by weight or less. After pulverizing and sieving the powder to 40 mesh or less, the mixed powder is provided with a ridge for forming a groove, and the ridge is charged into a mold having a curved surface and pre-pressed. After the pre-press, the mold is opened to remove volatile components and residual air, and then molded at a predetermined pressure, and the temperature difference in the mold during the pre-press step and the molding step is reduced by 10 ° C.
A method for producing a fuel cell separator, characterized in that the control is performed within the following range. 6. The method for producing a fuel cell separator according to claim 5, wherein heat treatment is performed after molding under a pressure of 1 g / cm ² or more.