JP2000345371A - Carbon thin film/metallic composite material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the electric conductivity and film strength at a low cost by coating a metallic structural body composed of a metallic fibrous or fine-wired or particulate material with a carbon thin film. SOLUTION: As the metallic material, e.g. a metallic fiber of about 1 to 50 μm is used and is previously subjected to shape working into a woven fabric or nonwoven fabric structural body, or the like. Next, the structural body of the metallic fiber, or the like, is coated with a carbon thin film. At first, a needle electrode composing the metallic structural body is dipped into an electrolytic soln. in which a monomer is dissolved into a solvent, voltage is applied on a space between it and a counter electrode, polymerization is executed, and a polymer is applied thereon. As the monomer, particularly, acrylonitrile, metaacrylonitrile or the like is preferable. By using coated electropolymerized polymer as a precursor, the structural body is subjected to heat treatment for imparting higher electric conductivity thereto. The heat treating temp. is preferably controlled to about 520 to 900 deg.C. In a carbonating stage to accompany the heat treatment, the content of carbon atoms in the carbon film is suitably controlled to >=90 wt.%. Furthermore, the thickness of the film is preferably controlled to <=1 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to energy-related materials such as electrode materials for fuel cells, secondary batteries, electric double-layer capacitors, supercapacitors, etc., as well as ion-adsorbing and harmful-gas-decomposing / desorbing materials, deodorization, and wastewater treatment. The present invention relates to a carbon thin film / metal composite material that can be effectively used in environmental purification-related technical fields such as water purification, medical purification, and air (water) purification filters.

[0002]

2. Description of the Related Art Conventional techniques for using activated carbon fiber (hereinafter referred to as ACF) for an electrode member for a capacitor include:
For example, Japanese Patent Application Laid-Open No. 3-85711 discloses a polyacrylonitrile-based (hereinafter referred to as PAN-based) ACF or an activated carbon fiber, and Japanese Patent Application Laid-Open No. 10-172870 discloses a device using a pitch-based ACF. JP-A-8-10704
No. 7 using a phenolic ACF, and JP-A-59-105312 discloses a product using a cellulose-based ACF. These are used as electrodes of high-performance capacitors, so to increase their surface area,
It is a porous body. Also, these electrodes are generally ACF
Is processed into cloth or felt.

[0003] Types of ACF include cellulose-based ACF, PAN-based ACF, phenol-based ACF, pitch-based ACF, and the like, depending on the raw materials. As a method for producing these ACFs, for example, JP-B-58-20883,
JP-B-58-25043, JP-B-58-3609
As disclosed in Japanese Unexamined Patent Publication No. 5 (2005) (although the steps are partially different depending on the type of raw material), first, from the synthesis of the raw material, it is spun into a fibrous form, and then subjected to a flame-resistant treatment (insolubilization treatment) (this Is referred to as a flame-resistant yarn), and then activation treatment is performed using steam, carbon dioxide gas or the like. This is further processed into a felt shape, and finally, an ACF felt is manufactured.

As a technique for improving the electrical conductivity of an electrode material, for example, Japanese Patent Application Laid-Open No. 10-509560 discloses a method in which aluminum is dispersed and mixed in a carbon material to form a composite electrode.

[0005] Further, regarding a carbon thin film / metal composite material,
J. Electrochem. Soc. , Vol. 13
7 (1990) p2499. Describes a primary structure of a polyacrylonitrile thin film formed by electrolytic polymerization on a Ni electrode and heat-treated at a temperature of 500 ° C. or less.

[0006]

In a conventional technique using ACF felt for an electrode member or the like, the manufacturing process includes a polymer synthesis process, a spinning process, a flame-proofing process, an activation process, and a felting process. Including, these series of steps are very complicated and lead to high cost of the electrode material.

[0007] Cellulose ACF has relatively low material cost but low strength. Phenol-based ACF does not require insolubilizing treatment and is easy to cross and felt, but the material cost is very high. The pitch-based ACF has problems such as being restricted by the shape of the molded product due to the characteristics of the raw material.

[0008] The yield of ACF obtained through a series of steps is reduced to about 30% of the raw material, for example, in the case of an acrylonitrile-based ACF by a flame-proofing or activation treatment step, which increases the cost of the acrylonitrile-based ACF. Is also connected.

From the viewpoint of performance, in the state of ACF fiber, although a large surface area can be obtained by making the fiber porous, when felting using a binder or the like, the area is drastically reduced. Is easily impaired.

Further, after the oxidized yarn is once felted,
There is also a method of obtaining an ACF felt by activation treatment. However, since the ACF density decreases due to activation spots and weight reduction during activation, and the felt strength decreases due to relaxation of fiber orientation, this step requires a long time. Since it is necessary to perform the process separately from the felt making process and the production of the ACF felt involves a discontinuous process, the cost is inevitably increased due to a decrease in productivity.

Further, it is necessary to reduce the internal resistance as a polarizing electrode or a battery electrode member of a high-performance capacitor, and it is desired that the electrode has a large surface area and high electric conductivity. In general, ACF felt is expected to be further improved in electrical conductivity due to the anisotropy of the graphite structure of ACF and insufficient carbonization.

To increase the electrical conductivity of the electrodes, for example,
Japanese Patent Application Laid-Open No. 10-509560 discloses a composite electrode or the like in which aluminum is simply mixed in carbon. However, although its conductivity is improved, its moldability is poor and there is a concern that the mechanical strength of the electrode may be reduced. You.

J. Electrochem. Soc. ,
Vol. 137 (1990) p2499. Heat-treats the polyacrylonitrile thin film formed on the Ni electrode at a temperature of 500 ° C. or less. However, in this temperature range, the graphite structure of the obtained carbon film is insufficiently developed, and is intended to be used as an electrode member. In some cases, the conductivity is poor. On the other hand, if the heat treatment is performed at a temperature of 500 ° C. for a sufficient time,
The conductivity improves to some extent with time, but causes a significant drop in productivity.

In the case of heat treatment at 500 ° C. or less, the development of the graphite structure in the plane of the film is basically insufficient.
The in-plane strength of the film is significantly reduced. At this time, there is a concern that the film may be damaged during the cooling process due to the difference in expansion coefficient between the metal and the pyrolyzed polyacrylonitrile. In particular, when a planar electrode is used, if the graphite structure in the film surface direction is not developed, the bonding of the polymer in the film surface direction is weak, and the thin film may fall off.

Further, a polyacrylonitrile thin film is directly
When heat treatment is performed at 00 ° C., due to the progress of graphitization,
The thermal decomposition reaction of the PAN thin film progresses remarkably, the decomposition loss of the polymer is large, and it is difficult to obtain a high quality film.

An object of the present invention is to solve the above-mentioned problems, and to provide a fuel cell, a secondary battery, and an electric double layer which are excellent in productivity, low in cost, and excellent in electric conductivity and film strength. Porous carbon thin films / metals used for capacitors, supercapacitor-electrode materials, filters for ion and harmful gas decomposition / desorption, deodorization, wastewater treatment, water purification, medical purification, air (water) purification, etc. It is to provide a composite material.

[0017]

SUMMARY OF THE INVENTION The present invention comprises the following. 1) A carbon thin film / metal composite material in which a metal fiber or a fine wire is coated with a carbon thin film. 2) A carbon thin film / metal composite material using a knitted, woven, or nonwoven fabric made of metal fibers or fine wires as the metal structure. 3) A carbon thin film / metal composite material using a porous structure obtained by sintering metal fine particles as the metal structure. 4) The carbon thin film / metal composite material according to 1) or 3), wherein the carbon atom content in the carbon thin film is 90 wt% or more. 5) The carbon thin film / metal composite according to 1) or 3), wherein the carbon thin film has a porous structure. 6) The carbon thin film / metal composite according to 1) or 3), wherein the thickness of the carbon thin film is 1 μm or less. 7) electrolytically polymerizing a monomer containing a nitrile group onto a metal surface having an arbitrary form by electrolytic polymerization, and then heat-treating the structure to which the polymer has been attached at least at a maximum temperature exceeding 500 ° C. A method for producing a carbon thin film / metal composite, comprising: 8) The method for producing a carbon thin film / metal composite according to 7), in which a metal structure having an acrylonitrile polymer thin film formed by electrolytic polymerization is first subjected to a low-temperature heat treatment at a temperature of 300 ° C. or lower, followed by a high-temperature treatment. 9) The monomer containing a nitrile group is at least one selected from acrylonitrile and methacrylonitrile. 10) A method for producing a carbon thin film / metal composite in which a metal structure on which a nitrile group-containing polymer thin film is formed is subjected to high-temperature heat treatment in a temperature range of 520 ° C to 900 ° C. 11) An electrode using a carbon thin film / metal composite material comprising 1) to 6). 12) An adsorbent or filter using a carbon thin film / metal composite comprising 1) to 6).

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When activated carbon fiber (ACF) is used for an electrode member, an adsorption / desorption filter, etc., it plays a role in increasing the site of electric conduction carriers and adsorption sites of adsorbed molecules and the electrode surface area of a capacitor. It is a porous part. The term "porous" as used herein means a substance having a very small structure such as ultramicropores having a molecular size of 0.2 to 1 nm inside the carbon material, molecular defects, free volumes, voids, etc., which can contribute to low molecular adsorption sites. In addition, microstructures such as micropores of 1 to 10 nm, structural defects, crazes and cracks,
Further, it includes a relatively large macropore of about 10 nm to 100 nm, a destruction defect structure, and the like.

In the case of a normal ACF, a micropore structure of about 1 nm is formed, but the effective microstructure is only on the very surface of the ACF having a diameter of about 10 μmφ. Also, the imperfect graphite structure inside the ACF causes a decrease in the conductivity of the ACF in the fiber diameter direction.

In the present invention, first, means for solving the inefficient use of such a carbon material and the cause of a decrease in electric conductivity have been focused. In the case where the carbon membrane having the above-mentioned micropore size is functionally used, a membrane of 1 μm or less is sufficient, and furthermore, a thin or fine-particle metal material (electrode) is continuously disposed inside, thereby reducing the cost. Thus, a carbon thin film / metal composite material having excellent conductivity can be provided.

Examples of the metal electrode material include iron, stainless steel, nickel, aluminum, silver, platinum, zinc, cobalt, lithium, and mixtures thereof. In addition to materials other than metals, materials having (semi) conductivity such as silicon single crystal can be used. Among them, cheap iron, nickel,
Materials such as aluminum and stainless steel are preferred.

The metal material used in the present invention includes, for example,
Using a metal fiber of about 50 μm, the fiber is previously processed into a knit, a woven fabric, a non-woven fabric or any other shape suitable for the intended use, and then coated with a carbon thin film. This eliminates the need for a step of cutting fibers short and performing a felting process using a binder or the like, unlike the ACF, and there is no risk of crushing the micropores formed on the carbon material surface and reducing the surface area.

As a method of coating such a metal fiber structure with a carbon thin film, an electrolytic polymerization method is preferably used. First, a needle electrode constituting a metal structure is immersed in an electrolyte solution obtained by dissolving a monomer in a predetermined concentration in a solvent, a counter electrode is disposed, and polymerization is performed by controlling an applied voltage and a supply time thereof.
A polymer having a predetermined film thickness and film structure is coated. The time required for this is generally several seconds to several tens of seconds, the polymerization efficiency is very excellent, the system is simple and the production cost is extremely low.

As the monomer to be subjected to the above polymerization, those which can be expected to have a high conductivity having a π-electron conjugated system include:
For example, fluorancene, pyrene, pyrrole, thiophene, furan, phenol, aniline, 1-pyrenamine,
Acetylene, dimethylpyrrole perchlorate, N-methylpyrrole, vinyliferocene, N-methylaniline, o-
Phenylenediamine, 3-methylthiophene, 3,4-
Dimethylthiophene, dithiothiophene, azulene,
N, N-dimethylaniline, N, N-diethylaniline, 4,4′-diaminodiphenylether, L-valine, selenophene, paraphenylene, naphthylene, anthracene and its derivatives, fluorancene, carbazole, quinaldine, naphthalene, and a nitrile group (Meth) acrylonitrile (AN) and methacrylonitrile (MAN). In particular, acrylonitrile and methacrylonitrile-based polymers have good bondability to the nickel electrode and can form a durable composite film having excellent adhesion.

As the solvent, benzonitrile, acetonitrile, water, nitrobenzene, dimethylformamide,
Methanol or the like can be used. Above all, when acetonitrile or dimethylformamide is used as a solvent for AN or MAN monomer, a polymer thin film having particularly excellent adhesive strength to a Ni electrode can be obtained.

Next, a heat treatment is performed at a temperature of 200 ° C. to 1200 ° C. for the purpose of further developing the π-electron conjugated system and imparting high conductivity to the precursor obtained by coating the thus-coated electropolymerized polymer. Further, if necessary, an activation treatment is performed using steam or the like. The heat treatment temperature is preferably lower from the viewpoint of manufacturing cost.

However, when the heat treatment is performed at a temperature of 500 ° C. or less, the graphite structure is insufficiently developed in this temperature range, and sufficient conductivity cannot be obtained. On the other hand, if the heat treatment is performed at a temperature of 500 ° C. for a sufficient time, the conductivity is improved with the processing time, but the productivity is remarkably reduced.

In addition, since the development of the graphite structure in the plane of the film is basically insufficient, the strength in the film surface is remarkably reduced. At this time, the difference in the coefficient of expansion between the metal and the thin film may cause damage to the film during the cooling process. In particular, if the graphite structure in the film surface direction is not developed, the bonding of the polymer in the film surface direction is weak. In some cases, the thin film is completely destroyed and falls off. For these reasons, the heat treatment temperature is between 520 ° C and 90 ° C.
About 0 ° C. is preferable. More preferably, 520 ° C to 70
0 ° C.

In the carbonization process accompanying the heat treatment,
In order to obtain sufficient conductivity, the content of carbon atoms in the carbon film is preferably at least 90 wt%, more preferably at least 99 wt%.

Here, a greater advantage is obtained by using metal fibers as the electrode base material than by using a plate-shaped metal electrode base material. When a polymer is coated by electrolytically polymerizing a monomer to a metal fiber, the polymer becomes a coating having a continuous surface on a cylinder. Also, when a similar coating is applied to a spherical metal or a spherical metal, a coating having a spherical continuous surface is formed. In the heat treatment process, the polymer thin film having these continuous surfaces grows a graphite structure within the thin film surface to some extent, thereby forming a film in which the entire carbon film is bonded (even if the bonding sites are sparse). Dropping from the base material hardly occurs.

When a carbon film is formed on a metal surface by heat treatment at a high temperature, and desorption or destruction occurs at the carbon thin film / metal interface due to a difference in expansion coefficient between the metal and the carbon thin film in the process of cooling to room temperature. In addition, it is possible to produce a stable carbon thin film / metal composite material in which the carbon thin film does not fall off from the composite material.

In the case of the AN and MAN monomers, a polymer film (PAN,
PMAN). Further, by performing a heat treatment on this, in a heat treatment at 520 ° C. or more, the polymer fixed locally on the surface of the metal electrode causes a decomposition oxidation reaction (dehydrogenation, denitrification), and the graphitization proceeds. At the same time as the conductivity increases, the micro-pores and / or
It has been found that micropores are formed inside and on the surface of the carbon membrane to form a porous body.

It has also been found that in such a porous microporous material, when the film is cooled from a high temperature after the heat treatment to a low temperature (room temperature), if the film is slowly cooled slowly, damage to the membrane is small. The slow cooling rate is 10 ° C./min or less, more preferably 10 ° C.
/ Min.

When PAN or PMAN is subjected to a heat treatment, the temperature is, for example, 200 to 300 ° C. for the purpose of preventing an excessive decomposition reaction and oxidative heat generation and obtaining a stable film and a carbon film having a well-developed graphite structure. After a low-temperature heat treatment to allow the cyclization reaction of the nitrile group to proceed sufficiently,
It is desirable to change the temperature stepwise, such as re-heat treatment at a temperature of at least ° C. The time required for the low-temperature treatment is 30 minutes to 90 minutes. The temperature of the low-temperature treatment depends on the film thickness and the molecular weight of the polymer, but is preferably 200 ° C. or higher, more preferably 250 ° C. or higher, in order to cause a sufficient cyclization reaction in a short time. For the purpose of suppressing the rapid decomposition and oxidation reaction, the temperature is preferably 300 ° C. or lower, more preferably 250 ° C. or lower.

Further, as the thickness of the precursor polymer to be subjected to the heat treatment becomes smaller, the decomposition oxidation reaction such as denitrification proceeds more efficiently at a lower heat treatment temperature, the π-electron conjugate system develops, and the conductivity improves. So desirable. The thickness of the film is desirably 1 μm or less, preferably 0.1 μm or less, and more preferably 0.05 μm or less. Further, in order to further improve the performance of the film thus produced, an electrolytic polymerization process and / or
Alternatively, ions that become conductive carriers after the heat treatment are chemically injected, or after obtaining a predetermined carbon thin film / metal composite material, the conductive carriers are injected using a physical method such as an ion beam, A method for improving the conductivity of the composite material is also possible.

Further, as a method for achieving high functionality, for example, a substance having a (photo) catalytic action such as platinum or titanium oxide is carried in a carbon film, thereby adsorbing and decomposing toxic gas, sterilizing function and the like. A carbon film having a new functionality can also be manufactured.

As a method for controlling the porous structure of the membrane, for example, a polymer such as PMMA, which is thermally decomposed by high-temperature treatment, is adjusted in its amount and blended and / or co-polymerized in the electrolytic polymerization process. At the stage where the polymer is polymerized and then the polymer is heat-treated at a high temperature of 300 ° C. or higher, a method of removing the material by thermal decomposition and making the polymer porous may be considered.

So far, a carbon thin film / metal composite material using a metal fiber as an electrode has been basically described, but the shape of the metal electrode may be a material freely processed and shaped according to the purpose of use. For example, using a porous structure obtained by sintering metal fine particles, a carbon thin film / metal composite material in which the surface of fine particles forming a porous wall is coated with a carbon thin film by the above-described electrolytic polymerization method and a series of heat treatment techniques is also available. It can also be manufactured. With this composite material, a material having a larger surface area and excellent strength can be produced.

The carbon thin film / metal composite material according to the present invention is used as an electrode material for a fuel cell, a secondary battery, an electric double layer capacitor, a large-capacity capacitor, an ion and harmful gas decomposing / desorbing material, or a deodorizing / drainage treatment. , Water purification, medical purification, air (water) purification filters and the like.

As described above, the porous carbon thin film / metal composite material has a simple process in a series of production processes, is capable of continuous production, and has high productivity. Further, the energy cost for the production is low, and the raw material used for the carbon film is much smaller than that of the conventional ACF, so that the cost can be reduced. In addition, since a metal electrode is basically used as a skeleton, it is possible to provide an electrode member, an adsorbent, a filter, and the like, which have high conductivity equivalent to that of a metal and excellent strength.

[0041]

The present invention will be described in more detail with reference to the following examples.

A nickel fiber having a diameter of 2 μm was immersed in a mixed solution of acetonitrile, tetraethylammonium, and acrylonitrile (concentration: 0.03 g / cm ³ ), and subjected to electrolytic polymerization for 30 seconds. At this time, a potential of -2.0 V was applied using the nickel needle wire as a cathode. Then, the polyacrylonitrile (PA
N) Dry the coated needle wire at 150 ° C for 3 minutes, then
Heat treatment was performed at 0 ° C. for 60 minutes. At this time, yellow coloration of the sample surface occurred, which was considered to be due to the PAN cyclization reaction. When this was further heat-treated at 700 ° C. for 60 minutes in a nitrogen atmosphere, a black carbon thin film / metal composite material was finally obtained. For the purpose of observing the film thickness and surface of the carbon thin film / metal composite material, for simplicity, 2 cm × 5 c
The monomer was electrolytically polymerized on the m-side nickel plate in the same manner as above, and the thickness of the PAN thin film formed on the electrode plate was measured using an atomic force microscope (AFM). Although there are surface irregularities, the average thickness is about 80 nm.
About PAN thin film was obtained. Furthermore, the surface of the carbonized and blackened one under the same conditions as described above was observed using an AFM or an electron microscope, and as a result, porosity such as many defects was confirmed. When the electrical conductivity of the carbon thin film / metal composite material was compared with that of a carbon fiber produced from a PAN fiber having a diameter of 10 μm under the same heat treatment conditions, an electrical conductivity larger by one digit or more was confirmed. Further, the content of carbon atoms in the carbon film was measured by elemental analysis and found to be 99% by mass.

[0043]

The carbon thin film / metal composite material of the present invention does not require a discontinuous polymer synthesizing step, a felting step, or the like in its manufacturing process, and a series of manufacturing processes is simplified. In addition to this reason, since a carbon thin film / metal composite having a carbon film with a developed graphite structure can be constructed in a short time with a relatively small amount of monomer material, the production efficiency is excellent.
A low cost porous carbon thin film / metal composite can be obtained. In addition, since the metal material forms the basic skeleton, a carbon thin film / metal composite material having extremely low internal resistance, high electrical conductivity, and relatively excellent strength can be obtained as an electrode member.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/58 H01M 4/58 4L033 // C01B 31/02 101 C01B 31/02 101Z 5H003 D06M 15/70 D06M 15/70 F-term (reference) 4C080 AA07 BB02 JJ03 JJ04 JJ05 KK08 LL10 MM05 MM07 QQ03 QQ20 4D019 AA01 AA03 BA02 BA03 BA18 BA20 BB02 BB03 BB06 BC20 BD01 4G046 CA04 CB03 CB09 CC03 CC05 A04B06A06 A02B BA22 BA50 CA02 DA02 DA03 FA07 FA12 FA22 FA37 4K044 AA01 AA02 AA03 AA06 AB01 AB04 AB08 AB10 BA18 BB01 BC14 CA62 4L033 AB01 AB05 AB06 AB07 AC15 CA26 CA69 CA70 5H003 AA01 BA01 BB01 BC01 BC02 BC05 BD01 BD02 BD04

Claims (12)

[Claims] 1. A carbon thin film / metal composite material obtained by coating a metal structure made of metal fibers, fine wires or fine particles with a carbon thin film. 2. The carbon thin film / metal composite material according to claim 1, wherein a knitted, woven or non-woven structure of a fibrous or fine metal wire is used as the metal structure. 3. The carbon thin film / metal composite material according to claim 1, wherein a porous structure obtained by sintering metal fine particles is used as the metal structure. 4. A carbon thin film having a carbon atom content of 90% by mass.
The carbon thin film / metal composite material according to any one of claims 1 to 3, which is the above. 5. The carbon thin film / metal composite according to claim 4, wherein the carbon thin film has a porous structure. 6. The carbon thin film / metal composite according to claim 4, wherein the thickness of the carbon thin film is 1 μm or less. 7. A polymer containing a nitrile group is electropolymerized on a metal surface of a fine-line, fibrous, or fine-particle-shaped metal structure by electrolytic polymerization. A method for producing a carbon thin film / metal composite, which comprises heat-treating to a maximum temperature of 500 ° C. 8. The carbon thin film / metal composite according to claim 7, wherein the metal structure on which the nitrile group-containing polymer thin film is formed is subjected to a low-temperature heat treatment at a temperature of 300 ° C. or less before the high-temperature heat treatment. Manufacturing method. 9. The carbon thin film / metal composite according to claim 7, wherein at least one monomer selected from acrylonitrile and methacrylonitrile is used as the monomer containing a nitrile group. Production method. 10. A method for producing a carbon thin film / metal composite in which a metal structure on which a nitrile group-containing polymer thin film is formed is heat-treated at a high temperature in a temperature range of 520 ° C. to 900 ° C. 11. An electrode using the carbon thin film / metal composite according to any one of claims 1 to 6. 12. An adsorbent or a filter using the carbon thin film / metal composite material according to any one of claims 1 to 6.