JPH07105955A - Electrode base material and its manufacture - Google Patents

Abstract

PURPOSE:To provide a base material for electrode which excels in the electrical conductivity in the direction of thickness of the electrode and the resistance against thermal oxidation and to offer a method for manufacturing the base material. CONSTITUTION:A base material for electrode consists of a composite of carbon fiber or graphite fiber and a carbon matrix. At least either of the boron and boric compound is included in the carbon fiber/graphite fiber solely or in both of the fiber and matrix in the content of 0.01-5.0wt.% in boron conversion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is widely applied to sodium-sulfur type secondary batteries, phosphoric acid type fuel cells, electrolysis of organic compounds, electrolysis synthesis, oxidation and reduction reactions, etc. The present invention relates to an electrode base material used and a method for manufacturing the same.

[0002]

2. Description of the Related Art Recently, a new type of secondary battery is used to store surplus power at night and to cope with the increase in demand during the daytime. The development of fuel cells is progressing, and both are in the stage of verification test. Carbon fiber is used for the electrode base material of any of these batteries because of its excellent high-temperature characteristics, electrical conductivity, chemical resistance, and thermal oxidation resistance, but the electrical conductivity of carbon fiber is certainly the axial direction of the fiber. However, it is not necessarily high in the cross-sectional direction. In addition, the molded product obtained by increasing the fiber length in relation to the strength was easily arranged in the plane direction, and the electrical conductivity in the thickness direction of the electrode base material was poor. On the other hand, the operating temperature of the secondary battery for power storage and the fuel cell for power generation is 200-
The temperature was as high as 400 ° C., and the thermal oxidation resistance with electrolytes was insufficient.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the conventional electrode base material and to provide an electrode base material excellent in electrical conductivity in the thickness direction of the electrode and thermal oxidation resistance and a method for producing the same. To do.

[0004]

The present invention adopts the following means in order to solve the above problems. That is, the first aspect of the present invention
The gist of is an electrode base material composed of a carbon fiber or a graphite fiber-carbon composite material. Only carbon fiber or graphite fiber in the electrode base material, or both of the matrix carbon, is 0.01 to 5 in terms of boron. In an electrode base material characterized by containing at least one of 0.0 wt% boron and a boron compound,

A second gist of the present invention is a short fiber of carbon fiber or graphite fiber containing boron, boron and a boron compound,
A thermosetting resin, a pore control agent, and optionally water or an organic solvent are kneaded, molded into a predetermined shape using a mold, desolvated, and then pressure-heated and cured, and further in an inert atmosphere. In a method for manufacturing an electrode base material, which is characterized by performing a heat treatment at a temperature of 1000 ° C. or higher at

The third gist is to impregnate a thermosetting resin solution containing boron and a boron compound with a sheet-like material composed of short fibers of carbon fiber or graphite fiber, remove the solvent, and then bring it to a predetermined thickness. Laminate and heat cure, then 10 in an inert atmosphere
There is a method for manufacturing an electrode base material, which is characterized by performing heat treatment at a temperature of 00 ° C. or higher,

Further, a fourth gist of the present invention relates to an electrode base material characterized in that a sheet-like material made of flame resistant fiber is impregnated with boron and a boron compound and further heat-treated at a temperature of 1000 ° C. or higher in an inert atmosphere. There is a manufacturing method.

The boron and the boron compound used in the present invention are not particularly limited as long as they contain boron, and boron fluoride,
Examples thereof include organic solvent-soluble compounds such as boron iodide, boron oxide, pentaborane, decaphorane, orthoboric acid, trimethylboron, triethylboron and triphenylboron. The electrodes contain boron oxide, boron carbide, and boron nitride. The amount of boron and / or the boron compound to be contained in the present invention is, in terms of boron, 0.01 to
It is 5.0 wt%.

If it is less than 0.01 wt%, it is difficult to achieve the intended effect, and if it exceeds 5.0 wt%, the effect is saturated and the resulting product becomes coarse and rigid, which is not preferable.

The thermosetting resin used in the present invention is one which exhibits tackiness or fluidity at room temperature, and a phenol resin, furan resin or the like is preferably used. As the phenol resin, a resol type phenol resin obtained by reacting phenols and aldehydes in the presence of an alkali catalyst can be used. It is also possible to dissolve and mix a solid, heat-fusible ribolac-type phenol resin produced by the reaction of a phenol and an aldehyde under an acidic catalyst by a known method into a resol-type fluid phenol resin. But in this case a hardener,
For example, a self-crosslinking type containing hexamethylenediamine is preferable.

As the phenols, for example, phenol, resorcin, cresol, xylol, etc. are used, and as the aldehydes, formalin, paraformaldehyde, furfural, etc. are used. Also, these can be used as a mixture. It is also possible to use commercially available products as these phenolic resins.

A furan resin initial condensate is used as the furan resin. Furan resin is a furfuryl alcohol condensate or a furfuryl alcohol-furfural cocondensate. In this case, a furfuryl alcohol or a furfuryl alcohol-furfural mixture is mixed with an acidic catalyst and heated to a suitable viscosity. It is recommended to cool after use. It is also possible to eliminate the catalytic activity from these initial condensates at room temperature by means such as volatilization or neutralization.

Next, a method of manufacturing the electrode base material according to the second aspect of the present invention will be described. First, a carbon fiber or a graphite fiber containing boron is formed into a short fiber (preferably a fiber length of 0.0
1 to 10.0 mm), and a predetermined amount of boron and a boron compound, a predetermined amount of a thermosetting resin, and an organic polymer (preferably having a particle diameter of 200 to 20 μm) as a pore adjusting material are mixed and kneaded. . At this time, an organic solvent or water may be added to improve the fluidity of kneading. The kneaded product is poured into a mold to obtain an electrode having a predetermined shape, the solvent is removed, and pressure is applied to heat and cure. Further, the electrode base material of the present invention can be manufactured by firing at a temperature of 1000 ° C. or higher, preferably 2000 ° C. or higher in an inert atmosphere.

In this manufacturing method, it is necessary to select the mixing ratio according to the fiber length of carbon fiber or graphite fiber. As the fiber length increases, the bulk density of the fiber assembly increases, making it difficult to increase the fiber concentration. When the fiber length is short, the bulk density is small and the carbon fiber concentration during kneading can be increased, but the bulk density of the obtained electrode is also large and the voids are small,
The strength also tends to decrease. If the fiber length is long, the bulk density is large, and the carbon fiber concentration during kneading cannot be increased. The voids become too large and the strength also decreases. Therefore, it is preferable to mix fibers having different fiber lengths at an appropriate mixing ratio. The desirable mixing ratio of carbon fibers or graphite fibers to satisfy the appropriate porous structure and strength characteristics is 4 when the fiber length is 0.1 mm or less.
0 to 20 parts Fiber length 0.1 to 2.0 mm, 30 to 10 parts Fiber length 3.0 mm or more and 10 to 1 part are preferable.

The pore size controlling agent may have a particle size of 200 to 20.
A μm organic polymer is preferably used. When the particle size of the pore control agent is larger than 200 μm, the porosity increases and the bending strength tends to decrease. Particle size is 20
If it is less than μm, the gas permeability decreases. The organic polymer of the pore control agent is preferably an organic polymer that undergoes depolymerization by heating, typical examples of which are styrene, α-methylstyrene, vinyl aromatic monomers such as vinyltoluene, A homopolymer of a methacrylate-based monomer such as methyl methacrylate, ethyl methacrylate or n-butyl methacrylate, or 51 mol% or more of these monomer units and 49 mol% or less of another copolymerizable monomer. Examples thereof include copolymers. Particularly preferred are styrene polymers and methyl methacrylate polymers. Examples of other copolymerizable monomers include acrylate-based monomers such as methyl methacrylate, ethyl acrylate, and n-butyl acrylate, and acrylic acid and methacrylic acid.

The degree of polymerization of the pore control material is not particularly limited,
In order to obtain powder or flake having an appropriate particle diameter, the specific viscosity is preferably 0.1 to 0.4, and more preferably 0.2 to 0.3. The mixing ratio of the pore control material is preferably in the range of 15 to 85 wt%. When the mixing ratio is less than 15 wt%, the porosity becomes small, and in the case of a fuel cell, the permeation of fuel gas becomes small. If the mixing ratio exceeds 85 wt%, the porosity increases and the strength of the electrode decreases, which is not preferable.

Carbon fiber or graphite fiber containing boron,
Boron and boron compounds, thermosetting resins, pore control materials,
And a kneading solution obtained by uniformly kneading any one or a mixed solvent of organic solvents such as methanol, ethanol, acetone and methyl ethyl ketone used as necessary to increase the fluidity into a single-sided rib shape or a double-sided rib shape mold. Pour or spread and shape into a flat plate. The solvent removal can be carried out at a normal temperature or a reduced pressure below the curing temperature of the thermosetting resin, preferably below 70 ° C. for phenol and below 60 ° C. for furan resin.

The subsequent pressure heating and curing is performed at a pressure of 3 to 20.
In 0 kg / cm ² preferably 5 to 100 kg / cm ^2,
The temperature is 80 to 300 ° C., preferably 80 to 200 ° C. for the phenol resin and 70 to 160 ° C. for the furan resin, and the heating time is usually 10 minutes to 10 hours. Then in an inert atmosphere, the temperature is 1000 ° C., preferably 2000
The electrode base material aimed at by the present invention can be produced by heat treatment at a temperature of ° C.

Next, a method of manufacturing the electrode base material according to the third aspect of the present invention will be described. This production method uses short fibers of carbon fibers or graphite fibers (preferably having a fiber length of 0.1 to 0.1).
A sheet-like material (sheet, paper, felt, woven fabric, knitted fabric, etc.) consisting of 30 mm) in a methanol solution of a thermosetting resin, for example, a phenol resin of 20 to 40 wt% and a boron compound in an amount of 0.01 to 0 of boron. After impregnating in a resin dipping liquid mixed with 0.5 wt%, the content is reduced to a predetermined amount, the solvent is removed under vacuum at low temperature, a desired number of the semi-cured carbon fiber products are laminated, and the temperature is 170 ° C. Above, pressure 5kg
/ Cm ² or more and pressurizing and heating to completely cure the matrix resin, and then the temperature is 1000 ° C in a non-oxidizing atmosphere.
This is the method of heat treatment for firing.

The concentration of the boron compound added is 0.01 to 0.5 wt% in terms of boron. The content of boron in the carbon fiber product is controlled by the concentration of boron in the impregnation liquid and the amount of impregnation after squeezing. The impregnation amount is about 300
The range of up to 1200% is preferable. The aperture ratio is defined by the following formula. Impregnation amount = (resin impregnation weight / carbon fiber sheet material weight) 1
00 That is, when the concentration of the boron compound is low and the amount of drawing is small, the content is small and the effect of the present invention is insufficient. Also, if the concentration is high and the squeezing amount is large, the content is large but the effect is 5.0.
Since it is saturated at wt%, it is wasteful and not preferable.

The concentration of the phenolic resin also affects the porosity of the electrode obtained by firing. That is, the resin concentration is 20 wt
If it is less than%, the porosity increases and the strength characteristics deteriorate. When the resin concentration is as high as 40 wt% or more, the strength characteristics are improved, but the porosity is reduced and the fuel permeability is reduced, which is not preferable. Preferred phenol resin concentration is 20
~ 40 wt%.

Desolvation was carried out under reduced pressure until the semi-cured state was reached.
Perform at a low temperature of ℃ or less. Several sheets of carbon fiber sheet material after resin impregnation are laminated so as to have a predetermined thickness, and the pressure is 5 to 30.
Hot-press molding is performed in the range of kg / cm ² and temperature of 120 to 200 ° C. to cure the resin. Then, heat treatment is performed at a temperature of 1000 ° C. or higher in an inert gas such as nitrogen gas.
By this heat treatment, the previously impregnated phenol resin is carbonized to become carbon and at the same time a glassy material is formed on the surface of the carbon fiber. Further, if necessary, heat treatment is performed at a high temperature of 2000 ° C. or higher to improve the conductivity and heat resistance of the present invention. Excellent in oxidization,
An electrode base material for a fuel cell is manufactured.

Next, a manufacturing method according to the fourth aspect of the present invention will be described. This method involves impregnating a sheet-like material made of flame-resistant fibers of short fibers or continuous long fibers having a fiber length of 3.0 mm or more into an alcohol solution of boron and a boron compound, squeezing it to a predetermined amount, and then drying it. This is a method of performing heat treatment at a temperature of 1000 ° C. or higher in an active gas atmosphere.

The resin is impregnated in the flame resistant fiber state to 1000
Heat treatment at a temperature of ℃ or more is not preferable, because the difference in heat shrinkage between the fiber and the matrix resin is too large, or the adhesiveness is lowered and the product becomes brittle. To produce an excellent electrode base material for a fuel cell by further impregnating with resin if necessary, followed by thermosetting using a hot press and heat treatment again at a temperature of 1000 ° C. or higher in an inert gas atmosphere. You can

[0025]

EXAMPLES The present invention will now be described in more detail with reference to examples. "Air permeability" of the electrode base material is JIS P8
117. The "specific resistance in the thickness direction" was obtained from the following equation by measuring the resistance value when the sample was sandwiched between copper plates and a current was applied. Specific resistance value (Ωcm) = measured resistance value (Ω) × sample area (c
m ² ) ÷ Sample thickness (cm) The “bending strength” was measured by a three-point bending method with a standard ratio of span (L) to thickness (t) of 32. As a measure of the heat-resistant oxidation resistance, the temperature at which the weight was halved by allowing it to stay in a high-temperature furnace in an air atmosphere for 30 minutes was shown as "weight half temperature". The "boron content wt% in the electrode substrate" was measured by the following method. 50 mg of sample and 1 g of sodium carbonate were gently heated and melted in a platinum crucible and then dissolved in distilled water to make 50 ml, and the whole was made into 50 ml, and the ICP emission spectrometer (ICP-575MK-
2) analysis wavelength 249.773nm output 1.6K
The boron content was measured with W.

(Example 1) A mixture of milled fibers having an average length of 160 μm and chopped fibers having a length of 6 mm composed of graphite fibers disclosed in JP-A-4-57926 at a ratio of 8: 2 was used. Parts by weight, 4 parts by weight of methyl methacrylate having a particle diameter of 60 μm as a pore control agent, 25 parts by weight of a phenol resin, and 1 part by weight of orthoboric acid are kneaded, spread in a flat plate mold, and then in a vacuum dryer. The solvent was removed.
After removing solvent, press pressure of 5kg / c using a press molding machine
It was heat-cured at m ^{2 at} a temperature of 170 ° C. for 1 hour. Next, the phenol resin intermediate material mixed with carbon fiber,
In a nitrogen atmosphere, the temperature was raised up to 2000 ° C. at a heating rate of 10 ° C./min, and further baked at 2000 ° C. for 1 hour to obtain an electrode base material. The boron content in the obtained electrode base material is 3.4 wt.
%Met. The electrode substrate has a thickness of 0.5 mm and a carbon content of 5
3%, porosity about 70%, bending strength 200kg / cm
² , the air permeability coefficient is 500 cc. mm / Hr. cm ² .
mmAq. The specific resistance value was 0.05 Ωcm, and the weight half-life temperature was 900 ° C, which was excellent as an electrode base material for phosphoric acid fuel cells.

(Comparative Example 1) Carbon fiber having an elastic modulus of 24 t
/ Mm ² type ordinary fiber, except that orthoboric acid was not mixed in, the electrode base material obtained by trial production in the same manner as in Example 1 has a thickness, carbon amount, void amount, air permeability coefficient, etc. The characteristics were at almost the same level as in Example 1. The bending strength was 120 kg / cm ² , the specific resistance was 0.13 μcm, and the weight half-life temperature was 750 ° C. The performance was lower than that of Example 1.

(Example 2 and Comparative Example 2) A carbon fiber having a modulus of elasticity of 24 t / mm ^{2 and} a normal fiber having a fiber length of 12 m
Paper is made by a known method using m chopped fiber and has a basis weight of 3
0 g / m ² of carbon fiber paper was produced. Phenolic resin (Phenolite 5900, made by Dainippon Ink KK) 2
Trimethylborate 2.5 in 0 wt% methanol solution
Resin impregnation liquid 1 was prepared by mixing wt%. For comparison, Resin Impregnation Solution 2 was prepared by removing boron oxide from the above impregnation solution. The carbon fiber paper is treated with each resin impregnating solution 1.2. 60%
The solvent was removed with a dryer of No. 1 to prepare prepreg 1.2. Cut the above prepreg into 50 cm x 50 cm and stack 5
Each sheet was heat-cured at a pressing pressure of 5 kg / cm ^{2 and a} temperature of 180 ° C. Furthermore, in a nitrogen atmosphere, the temperature is 24
The electrode base material was manufactured by firing at 00 ° C. The performance of each electrode substrate is shown in Table 1. As can be seen from the table, the boron-containing electrode base material of the present invention, as compared with the boron-free electrode base material of the comparative example, has a heat-resistant oxidation resistance and a specific resistance in the thickness direction which are represented by a weight half-life temperature. The value was small and the electrical conductivity was excellent.

[0029]

[Table 1]

(Examples 3 to 6 and Comparative Example 3) As raw materials, 98% of acrylonitrile and 2% of other copolymer components were used.
Acrylonitrile fiber in air atmosphere, temperature 240-2
Heat treatment was performed at 80 ° C. to obtain a flame resistant fiber having a density of 1.40 g / cm ³ . This fiber was crimped by a known method and cut into a stable fiber. The web was made by carding in a known manner. Next, several webs are piled up and needle punched to obtain a basis weight of 10 mm and a basis weight of 1000 g / m ^3.
Created the felt. The felt was immersed in various concentrations of a trimethylborate methanol solution for immersion to remove the solvent, and then heated up to 600 ° C. at a rate of 20 ° C./min in a nitrogen gas atmosphere. Then, the temperature was raised to 2400 ° C. at a rate of 10 ° C./minute and kept at 2400 ° C. for 10 minutes. After that, the temperature was lowered and the sample was taken out after the temperature became 50 ° C. or lower. The performance of the obtained felt-like electrode is shown in Table 2. The electrode base material of this embodiment exhibits high performance when used in a sodium-sulfur battery.

[0031]

[Table 2]

[0032]

According to the present invention, by containing boron, the specific resistance value in the thickness direction is small, and the weight loss at oxygen atmosphere and high temperature is small, which is excellent in electrical conductivity and thermal oxidation resistance. A substrate can be provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01M 4/86 B 10/39 Z

Claims (4)

[Claims] 1. An electrode substrate made of carbon fiber or graphite fiber-carbon composite material, wherein the carbon substrate or graphite fiber alone in the electrode substrate, or both of the matrix carbons, is converted into boron in an amount of 0.01 to. An electrode substrate containing 5.0 wt% of at least one of boron and a boron compound. 2. A short fiber such as a carbon fiber or a graphite fiber containing boron, a boron and a boron compound, a thermosetting resin and a pore control agent, and optionally water or an organic solvent are kneaded to obtain gold. Molded into a predetermined shape using a mold, after removing the solvent,
A method for producing an electrode base material, which comprises heat-curing under pressure, and heat treatment at a temperature of 1000 ° C. or higher in an inert atmosphere. 3. A thermosetting resin solution containing boron and a boron compound is impregnated with a sheet-like material composed of short fibers of carbon fiber or graphite fiber, desolvated, and then laminated to a predetermined thickness and thermoset. And a heat treatment at a temperature of 1000 ° C. or higher in an inert atmosphere. 4. A sheet-shaped material made of flame resistant fiber is impregnated with boron and a boron compound, and further in an inert atmosphere.
A method for producing an electrode base material, which comprises performing a heat treatment at a temperature of 000 ° C. or higher.