KR20040103706A - Process for the preparation of carbon nanotube or carbon nanofiber electrodes by using metal particles as a binder and electrode prepared thereby - Google Patents

Abstract

PURPOSE: Provided is a method for manufacturing a carbon nanotube or carbon nanofiber electrode that uses metal particles as an adhesive to reduce the internal resistance of a battery, to increase the durability, to minimize the resistance at adhesion surface, thereby significantly reducing ESR(Equivalent Series Resistance). CONSTITUTION: The carbon nanotube or carbon nanofiber electrode comprises a current collector, metal nanoparticles as an adhesive and carbon nanotubes or carbon nanofibers, wherein the metal nanoparticles are attached or fused to the surface of the carbon nanotubes or carbon nanofibers to accomplish the bonding of the carbon nanotubes or carbon nanofibers among themselves or the adhesion between the carbon nanotubes or carbon nanofibers and the current collector. The metal forming the metal nanoparticles is selected from the group consisting of alkali metals, alkaline earth metals, typical metals and transition metals.

Description

A method for manufacturing a carbon nanotube or carbon nanofiber electrode using metal particles as an adhesive, and an electrode manufactured by the same.

The present invention relates to a carbon nanotube or carbon nanofiber electrode using metal nanoparticles as an adhesive and a method of manufacturing the same. More particularly, the present invention provides bonding between electrode materials comprising carbon nanotubes or carbon nanofibers and bonding between these electrode materials and current collectors by applying heat and / or pressure using metal nanoparticles as adhesives. The present invention relates to a carbon nanotube or carbon nanofiber electrode and a method of manufacturing the same. The invention also relates to the use of such carbon nanotubes or carbon nanofiber electrodes in secondary batteries, supercapacitors, and fuel cells.

With the transition to the information society and the emergence of portable electronic devices, interest in energy storage devices is increasing.

Secondary batteries that store energy using electrochemical reactions have high energy density but low power density, which can be applied to systems requiring variable output such as electric vehicles or portable communication devices. Not only can not output high power, but also shorten the life and performance of the secondary battery, and the charge and discharge time is long, there is a limit to its use.

On the other hand, capacitors have very short charge and discharge times, long lifetimes, and high output densities. However, conventionally used electrical capacitors have very low energy density, which limits their use as storage devices. .

Electrochemical capacitors, on the other hand, have intermediate characteristics between an electric capacitor and a secondary battery. They have a long life and very short charge / discharge time, high output density, high power, and high energy density. Since it enables discharge, it is called a supercapacitor or an ultracapacitor (hereinafter, an electrochemical capacitor is called a supercapacitor).

An electric double-layer capacitor (EDLC), which stores energy using an electric double layer, is a supercapacitor, and is composed of an electrode, an electrolyte, and a separator that collect electricity. Among them, the electrode which constitutes the most important part of the supercapacitor requires characteristics such as high electron conductivity, large surface area, electrochemical inertness, easy forming and processability, and generally high porosity carbon material has high electric conductivity (e.g. Copper 5.88x10 ⁵ S / cm, graphite 1.25x10 ³ S / cm, semiconductor germanium 1.25x10 ^-2 S / cm), and is widely used because of its good formability and processability.

Porous carbon materials include activated carbon, activated carbon fibers, amorphous carbon, carbon aerogels, or carbon composite materials. The most commonly used materials for electrodes are made of activated carbon, which is woven into fibers by spinning with fibers. . However, activated carbon and activated carbon fibers have a large surface area of about 1000 to 3000 m 2 / g, but most of the micropores (<20 mm) which do not contribute to the electrode role, the effective pores are only 20 to 30% of the total The disadvantage is that.

Carbon nanotubes and carbon nanofibers, which were first synthesized in the early 1990s, have been attempted to be used as electrode materials because of their excellent physical properties. Graphitic Nano-Fiber is similar to carbon nanotubes in diameter and shape, but carbon nanotubes are literally shaped as tubes with empty centers, whereas carbon nanofibers are filled with carbon to the center. It is a fibrous carbon composite up to several hundred nanometers in diameter. Activated carbon fiber can be produced by spinning to a length of hundreds of meters in diameter by micrometer unit, whereas carbon nanofibers are catalytically synthesized like carbon nanotubes, and therefore have a diameter of several hundred nanometers or less Is tens of micrometers or less, and is synthesized by a method similar to the method of synthesizing carbon nanotubes.

Compared to other carbon materials, carbon nanotubes or carbon nanofibers have a uniform pore distribution in nanometer units, a large surface area to which ions of an electrolyte can reach, and a very small resistance of the electrode itself when used as an electrode. It is not only chemically stable but also has an electrical conductivity of up to 1.0x10 ⁴ S / cm, an effective utilization of a specific surface area of almost 100%, and a maximum specific surface area known to date is about 500 m ² / g. . This is perfect for the conditions that an electrode needs to make a supercapacitor with high energy and long lifetime.

On the other hand, the important factors that determine the output and frequency response of the supercapacitor are the resistance of the electrode material and the resistance of the electrolyte present in the pores of the electrode. Small pores result in a greater resistance in the process of the electrolyte moving into the pores, and thus the amount of energy that the activated carbon material can store despite the large surface area is not so high. In addition, the activated carbon material has a wide distribution of pores, so it can be used only for low frequency and direct current voltage of 100 mHz or less even when storing energy. This is the reason why supercapacitors composed of activated carbon are not easily generalized despite many improvements.

By using carbon nanotubes or carbon nanofibers as electrode materials, it is also possible to manufacture supercapacitors that input and output high frequency energy. This is superior to any existing carbon material and proves that carbon nanotube is the most suitable material for the electrode of the supercapacitor.

In addition, one of the problems to be considered in manufacturing a carbon electrode used in a supercapacitor is to reduce the internal resistance of the electrode. This is because the internal resistance of the electrode is directly connected to the energy loss, which is a factor of deterioration of the capacitor.

In general, the maximum power density attainable in a supercapacitor is given by Equation 1 below:

Pmax = V _i ² / 4R

Where V _i is the initial voltage and R is the equivalent series resistance (ESR). BE Conway, Electrochemical Supercapacitors: Scientific fundamentals and technological applications, Kluwer Academic / Plenum Publishers New York 1999, Ch. 15.

Therefore, an important parameter that determines the output density of a supercapacitor is the internal resistance of the electrode itself. The internal resistance of the electrode itself is composed of first, the resistance between the carbon particles and the carbon particles as the electrode material, second, the resistance between the electrolyte and the electrode material, and third, the contact resistance between the electrode and the current collector. Among them, the improvement between the carbon and the carbon and the resistance between the electrode and the current collector can be improved in the process of manufacturing the electrode.

First, in order to improve the resistance between the carbon particles and the carbon particles as the electrode material, various types of electrode materials and manufacturing methods have been proposed.

When the electrode material is a conventional carbon material such as activated carbon or activated carbon fiber from the viewpoint of internal resistance improvement, the electrode may be compressed, bindered, matrixed or monolithic. type, cloth type, and film type.

The compression type is a case where the contact between particles is improved by applying pressure when the electrode material is particles, and most of them are used in parallel with other types. The binder type is a method of improving the contact characteristics between particles by using a binder (binder) such as PTFE. In matrix type, granular activated carbon is mixed with a polymer matrix and carbonized to prepare an electrode. In the above binder type, the binder itself does not serve as an electrode, whereas the polymer in the matrix type connects particles to particles and at the same time serves as an electrode. The integrated type includes carbon aerogels and carbon foams. These materials are porous monoliths and have a continuous carbon skeleton so that contact between the electrode materials does not have to be considered. The film type is a non-porous carbon material. There is no electrolyte in the electrode, and only the separator includes the electrolyte. Amorphous carbon falls in this case. The clad type corresponds to the case of activated carbon fibers and is the most widely used method for manufacturing electrodes.

As mentioned above, the types and methods of manufacturing the above-mentioned electrode materials have been attempted for the purpose of improving the resistance of the electrode itself, which is composed of carbon materials of activated carbon, which is the most studied so far among carbon materials, or the resistance between the electrolyte and the electrodes. Methods.

As an example of a method of reducing the contact resistance between carbon constituting the electrode and the carbon can be mentioned.

Kurabayashi et al. Disclose a preparation method of a supercapacitor in US Pat. No. 50,993,98. In the above patent, the electrode is made of activated carbon in a compression type, and the current collector uses a thin film made of metal, synthetic fiber, rubber, etc. As a method of bonding the electrode and the current collector, first, the current The solvent was dropped on the surface of the current collector to dissolve the surface, and the electrode was placed thereon, and the pressure was applied. Then, the solvent was blown out to prepare an electrode having a small bonding resistance between the carbon electrode and the current collector.

Kurayashi et al. (Kurabayashi et al. ) Is another method in the US Patent US 5072336 to reduce the contact resistance of the carbon electrode and the current collector to reduce the contact resistance between the gold, silver, nickel, platinum, copper A method of achieving adhesion between a carbon electrode and a current collector by depositing a metal such as by the evaporation method is disclosed. In addition, a method of bonding an electrode and a current collector in a manner similar to the above-described method using various methods of adhesive is disclosed (US Pat. No. 5,142,451, US Pat. No. 5,121,301).

Nishino et al. , In US Pat . No. 45,625,11, discloses a method of surface treating a surface of a carbon fiber or activated carbon fiber used as an electrode with a metal to be used as a current collector. There are various methods of coating metal thin films on the electrode surface (eg plasma spraying, arc-spraying, vacuum deposition, sputtering, non-electrolytic plating and conductive painting).

Tatarchuk et al. , In US Pat. No. 5,102,745, US 5304330, US Pat. The process of adhering the metal fiber used as the current collector and the carbon fiber used as the electrode is as follows. Stainless steel with a diameter of about 2 ㎛ and carbon fiber with a diameter of 1 ~ 5 ㎛ are cut to about 5 ㎜ in length, mixed well with cellulose and water, filtered and put into a mold to apply pressure in the form of a thin film. The disk thus formed was subjected to high temperature and pressure to bond the two fibers to each other to prepare an electrode having improved internal resistance. The document also refers to an adhesive that can assist in molding two or more fibers, and the shape of the fiber to be bonded is not particularly limited to metals, ceramics, carbon, and the like. Only adhesion is mentioned.

Farahmandi et al. , In US Pat . Nos. 5,777,428 and 60,847, disclose a preparation of electrodes fabricated from activated carbon fibers in the form of cloth. In particular, they were woven in the form of fibers together with activated carbon fibers using aluminum wires as current collectors. In order to improve the internal resistance of the electrode, the fiber woven with activated carbon fibers and aluminum wire was heat-treated below 600 ℃, the melting point of aluminum. Also disclosed is a method of bonding one side of the fiber by aluminum foil and heat treatment for a smoother current flow. The heat treatment here must be carried out below 600 ℃, which is explained as to suppress the reaction of carbon and aluminum.

Zuckerbrod et al. , US Patent No. 4448856, prepared an electrode by mixing activated carbon powder and stainless steel powder with an adhesive as a means of reducing the contact resistance of the electrode. The particle size of each powder was limited to 25 to 450 mu m, and the electrode was manufactured by coating on a nickel wire or a metal plate, which is a current collector.

All of the above electrode manufacturing methods suggest various methods that can reduce the resistance of the current collector with activated carbon or activated carbon fibers. Since activated carbon can be made from fibers, various methods are available for processing into electrodes. However, since carbon nanotubes or carbon nanofibers are in the form of powder and cannot be manufactured in a fibrous form, there is a limitation in manufacturing the electrodes. The most common method is to produce a disk-shaped electrode which is compressed by mixing carbon nanotubes or carbon nanofibers with an adhesive.

Niu et al. Have prepared electrodes that change the surface functional groups of carbon nanotubes . See C. Niu et al., Appl. Phys. Lett. 70 (1997), 1480-1482. They oxidized carbon nanotubes with nitric acid, replacing about 10% of the surface functional groups with oxygen atoms. Electrodes made of surface-treated carbon nanotubes showed much better performance than those that did not. Especially, it was possible to improve the internal resistance between carbon nanotubes and carbon nanotubes by simply pressing them without using adhesives. Reported that it can be prepared.

Ma et al. Prepared an electrode using PF (Phenolic resin) powder as an adhesive on carbon nanotubes (RZ Ma, et al., J. of Power Sources, 84 (1999), 126). -129]. In particular, they produced an electrode carbonized by gluing acid by heat-treating an electrode prepared by adding an adhesive in order to reduce internal resistance between carbon nanotubes and carbon nanotubes. Was prepared to compare the performance. As a result of the comparative experiment, the resistance inside the electrode by the PF adhesive was relatively large, and the performance was excellent in the order of the carbonized electrode and the electrode treated with nitric acid.

An et al. Prepared a carbonized electrode that was pressed and bonded with PVdC (poly (vinyldent chloride)) as an adhesive to improve the contact resistance between carbon nanotubes [KH An, et al. , Adv. Mater., 13 (2001), 497. In particular, in this document, the surface is polished and nickel foam is used to improve the contact resistance between the electrode made of carbon nanotubes and the nickel foil used as the current collector. The electrode was used for the supercapacitor by compressing the carbon nanotube electrode using a form), and comparing the ESR (Equivalent Series Resistance) of the electrode showed that the polished nickel foil was more internal than the non-nickel foil. The resistance was cut in half, and the internal resistance of the electrode using nickel foam as the current collector was reduced to 1/4.

Emmenegger et al. Produced an electrode in which carbon nanotubes were grown directly on a metal plate that can be used as a current collector. Emmenegger, et al. , Appl. Surf. Sci., 162-163 (2000), 452-456]. After dispersing a metal capable of growing carbon nanotubes on a metal plate used as a current collector, an electrode was manufactured by a CVD method. The electrode thus manufactured is expected to be able to significantly reduce the internal resistance since the current collector and the individual carbon nanotubes are in contact with each other. However, the carbon nanotubes are easily separated because the bonding force between the carbon nanotubes and the current collector is weak, and the density of the carbon nanotubes is lower than that of the electrode manufactured by compressing the separately manufactured carbon nanotubes. The disadvantage is that it is difficult.

Looking at the above results, it can be seen that effectively reducing the internal resistance of the electrode can significantly improve the performance of the electrode. As can be seen from the above-mentioned documents, the most common method for manufacturing electrodes by processing carbon nanotubes in various ways is to use organic adhesives. However, when the organic adhesive is used, processing is easy, but there is a disadvantage of increasing the internal resistance of the electrode.

In addition, PF, PVdC, PTFE, etc., which are used as adhesives, have an excellent affinity with carbon nanotubes, so that when the carbon nanotubes are mixed with an adhesive and processed, most of the surfaces of the carbon nanotubes are covered. Therefore, instead of simply mixing and using organic adhesives, when the organic adhesive is added and carbonized, the entire electrode is derived from such organic adhesive and is wrapped with pyrolytic carbons having relatively high resistance.

MEANS TO SOLVE THE PROBLEM In the manufacture of a carbon nanotube or carbon nanofiber electrode which can be used for a secondary battery, a supercapacitor, or a fuel cell, this inventor uses nano size metal particle or a metal compound particle as an adhesive agent, and uses pressure and / or heat. By bonding and / or heat-treating to bond carbon nanotubes or carbon nanofibers and bonding carbon nanotubes or carbon nanofibers with a current collector, not only can the internal resistance in the electrode be significantly reduced, but also the durability is high. In addition, the present inventors have found that the resistance of the adhesive surface is almost minimized, and thus, an electrode body having a very low ESR (Equivalent Series Resistant) can be manufactured.

Figure 1 shows a Ragone plot of an electrode manufactured by annealing copper on the surface of carbon nanotubes.

An object of the present invention includes a current collector, metal nanoparticles, which are adhesives, and carbon nanotubes or carbon nanofibers, and the above-described metal nanoparticles are attached or fused to the surface of the above-described carbon nanotubes or carbon nanofibers, and thus carbon nanoparticles. The present invention provides an electrode composed of carbon nanotubes or carbon nanofibers that achieves bonding between a tube or carbon nanofibers and adhesion between a carbon nanotube or a carbon nanofiber and a current collector.

In one preferred embodiment of the present invention, the aforementioned metal nanoparticles are used in an amount of 0.01 to 3 times based on the weight of the carbon nanotubes or carbon nanofibers.

In one preferred embodiment of the present invention, the metal constituting the metal nanoparticles described above is selected from the group consisting of alkali metals, alkaline earth metals, typical metals, transition metals, the metal itself, metal sulfides, metal carbides, metal oxides And metal nitrides.

In one preferred embodiment of the present invention, the aforementioned metal nanoparticles have an average particle diameter of 1 μm or less.

In one preferred embodiment of the present invention, the current collector described above may be selected from the form of a plate, a net, or a form based on metal.

In one preferred embodiment of the present invention, the above-described metal nanoparticles are attached or fused to the carbon nanotubes by pressing at 1 to 500 atm or by heat treatment at a temperature of ± 500 ° C. of the metal or metal compound.

It is still another object of the present invention to provide a method for producing a carbon nanotube electrode comprising the following steps: (1) preparing an electrode material by mixing or supporting carbon nanotube or carbon nanofiber powder with a metal nanoparticle adhesive; (2) pressing the electrode material first to prepare a compressed electrode material, and (3) placing the first-compressed electrode material on a current collector and pressing or heat-treating secondly to obtain carbon nanotubes and carbon nano Bonding between the tubes and at the same time bonding the current collector and the electrode material.

In one preferred embodiment of the invention, in step (2), the above-described electrode material is uniformly dispersed on the current collector or simultaneously compressed at the same time as the dispersion, and the pressing may be performed under 1 to 500 atmospheres. have.

In one preferred embodiment of the present invention, in the step (3), the above-described metal nanoparticles are heat treated at a melting point ± 500 ° C. of the metal or metal compound pressed or used under 1 to 500 atm.

In one preferred embodiment of the present invention, in step (1), the carbon nanotubes and the metal nanoparticles are mixed by physical mixing, ultrasonic mixing, solvent mixing, carbon nanotubes or carbon nanofibers. It is carried out by a method selected from the group consisting of a method of uniformly dispersed on the surface of.

In one preferred embodiment of the present invention, the above-mentioned 'method of evenly dispersing the surface of the carbon nanotubes or carbon nanofibers' is carbon nanotubes or carbon nanoparticles by a supporting method such as a catalyst carrying method. It is carried out by a method selected from the group consisting of supporting on the fiber and then undergoing any oxidation or reduction, precipitation method, chemical vapor deposition method, electroplating, plasma spraying, and sputtering.

On the other hand, in the present invention, when the nanoparticles of the metal compound are attached to the carbon nanotubes or carbon nanofibers, the metal compound is completely or partially before or after the primary compression or the secondary compression / heat treatment. It may also be reduced. Reducing the metal compound particles to the metal particles completely or partially improves the electrical conductivity and increases the workability due to the ductility or malleability of the metal, thereby increasing the effect as an adhesive. There may be difficulties in reducing the metal compound as necessary. Reduction of such a metal compound may be carried out by a method commonly performed in the art, for example, a gaseous hydrogen reduction method or the like.

In one preferred embodiment of the present invention, the primary compression is carried out at a pressure sufficient to form carbon nanotubes or carbon nanofibers in the form of disks or thin films. This pressure is generally selected under a pressure of 1 to 100 atmospheres.

In one preferred embodiment of the invention, in step (3), the pressing and heat treatment can be carried out simultaneously or sequentially.

In one preferred embodiment of the invention, in step (3), the heat treatment is a group consisting of thermal heating, chemical vapor deposition, plasma, radio frequency (RF), microwave heating (microwave) Is performed in the manner selected.

Another object of the present invention relates to the use of a carbon nanotube or carbon nanofiber electrode according to the present invention in an electric double layer capacitor, a secondary cell or a fuel cell.

The present invention is explained in more detail below.

The problem to be achieved by the present invention is to stably bond the carbon nanotubes by using metal or metal compound nanoparticles to join the carbon nanotubes constituting the electrode at the melting point or above the temperature of the metal particles, thereby stably This is achieved by significantly improving the internal resistance of the electrode by joining with this almost stable metal and producing an electrode having higher durability in an electrode using an organic adhesive or a carbon adhesive.

In addition, the present invention is not a conventional simple method of physically attaching the current collector and the electrode material by applying pressure, but by minimizing ESR of the electrode by gluing using energy capable of inducing direct coupling between the current collector and the electrode material. It is to produce an electrode of high efficiency.

In the present invention, the current collector is used in the form of a metal plate, a net, a form that can be easily passed through the electricity, the electrode material of the electrode material of the carbon component, in particular the electrode material of carbon nanotubes This is used.

As described above, carbon nanotubes or carbon nanofibers have very excellent properties as electrode materials, but there are many problems to be solved in order to show high efficiency by being manufactured with real electrodes. Since activated carbon can be made of fibers, there is no great difficulty in application to electrodes. In addition, weaving activated carbon fibers together with metal fibers can solve some of the problems of bonding to current collectors. However, carbon nanotubes are in the form of particles which do not reach hundreds of nm in diameter and do not deviate from several to several tens of micrometers in length, and are not practically manufactured in fibrous form.

Therefore, in order to manufacture an electrode, it must be bonded to a current collector, and also bonded to carbon nanotubes or carbon nanofibers. As such, to use carbon nanotubes or carbon nanofibers as electrodes, they must be processed using adhesive.

In the present invention, since the metal nanoparticles are used as the adhesive, they have various advantages as compared to the conventional organic adhesives and carbon-based adhesives, for example.

First, when the metal particles are used as an adhesive between carbon nanotubes or carbon nanofibers, unlike organic adhesives or carbonized carbon adhesives, there is almost no internal resistance by the adhesive. Second, since the metal particles are physically mixed or supported on the surface of carbon nanotubes or carbon nanofibers, and then bonded by heat treatment, carbon nanotubes, which can be generated by completely covering the surface of carbon nanotubes or carbon nanofibers, unlike other conventional adhesives It does not counteract the inherent advantages of tubes or carbon nanofibers. Third, in terms of durability, which has been pointed out as a disadvantage of organic adhesives and carbon adhesives, it is necessary to select a metal having corrosion resistance in a given electrolyte, and thus bonding by metal particles has much superior advantages. Fourth, organic adhesives are easily dissolved in the electrolyte components or easily react with strong corrosive electrolytes, and thus do not sufficiently serve as adhesives, whereas metal particles have almost no such disadvantages.

On the other hand, the above advantages make it possible to use the carbon nanotube or carbon nanofiber electrode according to the present invention very effectively as a cathode electrode of a secondary battery. The main reason for the decrease of lifespan or performance when using secondary batteries for a long time is that solid materials deposited during discharge form internal short-circuits or block the internal surface area of the electrode, thereby reducing the surface area of the electrode that the electrolyte can reach. do. This is commonly referred to as cathode clogging, which can be solved by using nanotubes or nanofiber electrodes that have no micropores and are structured to facilitate material transfer. In particular, a carbon nanotube or carbon nanofiber electrode having a very small internal resistance and excellent durability manufactured by the method devised in the present invention may exert an excellent effect as a cathode electrode of a secondary battery.

In addition, the carbon nanotube or carbon nanofiber electrode, which has a very small resistance of the electrode and a structure in which the diffusion of the reaction gas is very advantageous, can exhibit excellent performance even as a fuel cell electrode.

The production of carbon nanotubes or carbon nanofiber electrodes, which is another object of the present invention, will be described. As described above, the present invention mixes the metal nanoparticles with carbon nanotubes or carbon nanofibers or forms nanoparticles on the surface of the carbon nanofibers or carbon nanofibers using various supporting methods, followed by compression and / or heat treatment. It provides a method of manufacturing an electrode with a reduced internal resistance through the process.

At this time, when both crimping and heat treatment are applied, these may be performed sequentially or simultaneously. Specifically, there is a method of compressing carbon nanotubes or carbon nanofibers mixed with nanoparticles followed by heat treatment, or simultaneously heat-treating carbon nanotubes or carbon nanofibers mixed with nanoparticles. Bonding with the current collector may be performed sequentially by separating the compression and heat treatment as described above, or may be performed simultaneously.

According to a preferred embodiment of the present invention, in order to simplify the process, the carbon nanotubes or carbon nanofibers on which the metal particles, which are adhesives are supported or mixed, are evenly distributed and disposed on a current collector, and the compression and heat treatment are performed simultaneously. It is also possible to produce an electrode.

In the method of manufacturing a carbon nanotube or carbon nanofiber electrode according to the present invention, it is important to uniformly mix nanoparticles and nanotubes used as an adhesive, but uniformly mix metal nanoparticles and carbon nanotubes or carbon nanofibers. It will not specifically limit, if it is a method which can be mixed. As a method of uniformly mixing the metal nanoparticles with carbon nanotubes or carbon nanofibers, physical mixing, ultrasonic mixing, or the like may be mentioned. have.

In the specification of the present invention, the metal is not particularly limited as long as it has electrical conductivity as a dictionary meaning. For example, a base metal (O, group F, Cl, Br, I, VI of group VIII or group VIII) , S, Group N, and Group I, H) and semimetals (all elements except Group III B, Group IV C, Si, Ge, Se Group V, Se, Te, Po) . Specifically, in the present invention, the metal includes typical metals such as alkali metals and alkaline earth metals and transition metals, and can be easily passed through electricity, mixed with carbon nanotubes or carbon nanofibers, or carbon nanotubes or carbon nanofibers. If the surface is supported by the supporting method, pressed, and then heat-treated to bond the carbon nanotubes or the carbon nanofibers, the type is not greatly affected.

In the present invention, the metal of the metal nanoparticles can be used not only in the metal itself, but also in the form of alloys or other metal compounds with other metals, for example, metal oxides, metal sulfides, metal nitrides, metal carbides, and the like. Therefore, in the present specification, metal nanoparticles include not only metal nanoparticles but also nanoparticles of metal compounds. By nanoparticles is meant that the average diameter of the particles constituting the material has 1 μm or less, preferably 10 to 500 nm, more preferably 50 to 100 nm. In addition, the particle size distribution of the metal nanoparticles may be such that at least 50%, preferably at least 70%, more preferably at least 90% of the particles have a particle diameter of 1 μm or less.

In the present invention, the nanoparticle means that the particle size distribution of the particles constituting the material includes up to nanoscale, and if it can give microscopic adhesion between carbon nanotubes or carbon nanofiber particles, which are substantially electrode materials, The particles may be particles having an average particle diameter of several micrometers to several tens of micrometers.

The method for producing nanoparticles used as an adhesive for carbon nanotubes or carbon nanofibers is not particularly limited, and generally, nanoparticles such as mechanical grinding, coprecipitation, spraying, sol-gel, electrolysis, emulsion, or reverse phase emulsion methods are generally used. It doesn't matter if it's manufactured in a way that can be made.

In addition, as a method of supporting the nanoparticles on the surface of the carbon nanotubes or carbon nanofibers, impregnation, precipitation, sol-gel method that can be commonly used when the catalyst is supported on the support gel), chemical vapor deposition (CVD), sputtering, evaporation, etc., which can be generally used when attaching a metal to a support, such as carbon nanotubes or carbon nanofibers. It will not specifically limit, if it is a method which can be supported on a surface.

In the present invention, the step of pressing the electrode material made of carbon nanotubes or a mixture of carbon nanofibers and metal nanoparticles may be carried out according to a conventional method, which is a mixture of carbon nanotubes or carbon nanofibers and metal nanoparticles. The electrode material can be primary-squeezed into any shape, for example disc shape, under any pressure, for example from 1 to 500 atm.

The disk-shaped compressed electrode material thus prepared is subjected to secondary compression and / or heat treatment under a pressure of 1 to 500 atm and / or at a temperature at which metal particles or metal compound particles used as an adhesive are melted or similarly formed. The metal nanoparticles attached to the carbon nanotubes or the carbon nanofibers by the second compression / heat treatment entangle or fusion the carbon nanotubes or the carbon nanofibers three-dimensionally. Seamlessly join the whole.

The method of heat-treating the metal nanoparticles attached to the carbon nanotubes or carbon nanofibers is not limited as long as it can heat the metal element or the metal compound. For example, thermal heating, CVD (chemical) vapor deposition, plasma, radio frequency (RF) heating, microwave heating, and the like.

In the heat treatment process, the heat treatment temperature and time vary depending on the type of metal used as the adhesive, but are not particularly limited as long as the metal nanoparticles can entangle or fusion between carbon nanotubes or carbon nanofibers. Is in the range of ± 500 ° C, preferably in the range of ± 100 ° C at the melting point of the metal nanoparticles. When the heat treatment is performed simultaneously with the pressing, the heat treatment temperature can be adjusted according to the pressing pressure. For example, the higher the pressing pressure, the lower the heat treatment temperature.

In addition, by the heat treatment, the surface of the current collector may be melted or made in a similar state to be bonded to the electrode.

The invention is described in more detail with reference to the following examples, but is not limited thereto.

[Production of Electrode]

Example 1

Copper nanoparticles are supported on carbon nanotubes, and copper nanoparticles prepared by reducing them are used as adhesives.

The carbon nanotubes used as the material of the electrode were a single wall carbon nanotube (SWCNT) prepared by a catalytic gas phase method (KH Chemicals Co.), having an average diameter of 6 nm and a surface area of 210 m 2 / g.

Cu (NO ₃ ) ₂ was supported by a supporting method with a carbon nanotube and copper at a weight ratio of 8: 2 (CNT: Cu). The carbon nanotubes carrying the copper compound nanoparticles were dried at 110 ° C. for one day, and reduced at 400 ° C. for 2 hours under a hydrogen atmosphere. The carbon nanotubes carrying the thus prepared copper nanoparticles were pressed at 10 atmospheres to form discs.

On the nickel foil having a thickness of 75 μm, which is a current collector, a carbon nanotube disk carrying copper nanoparticles prepared in the above step was placed, pressed at 10 atm under nitrogen atmosphere, and maintained at 900 ° C. for 10 minutes to prepare an electrode. The electrode thus prepared had a thickness of 150 to 300 µm.

Example 2

In the same manner as in Example 1, the carbon nanotube powder loaded with copper nanoparticles prepared by reducing the carbon nanotubes carrying the copper compound nanoparticles was uniformly dispersed on a nickel foil which is a current collector, and then under a nitrogen atmosphere. The electrode was manufactured by pressing while maintaining at 1100 ° C. The pressure applied was 10 atm and the compression time was 5 minutes.

Example 3

Copper nanoparticles prepared by the reversed phase emulsion method is an embodiment using an adhesive of carbon nanotubes.

Copper nanoparticles having an average diameter of 30 nm prepared separately from single wall carbon nanotube (SWCNT) as used in Example 1 were stirred under a nitrogen atmosphere at a weight ratio of 8: 2 (CNT: Cu). After mixing, the disk was pressed by 10 atm.

The electrode was prepared by placing a carbon nanotube disk on which the copper nanoparticles prepared in the above step were placed on a nickel foil having a thickness of 75 μm, which is a current collector, and compressed at 20 atm under nitrogen atmosphere for 10 minutes at 1000 ° C.

Example 4

The cobalt compound nanoparticles are supported on carbon nanotubes, and cobalt nanoparticles prepared by reducing them are used as adhesives.

Supporting Co (NO ₃ ) ₃ on a single wall carbon nanotube (SWCNT) as used in Example 1 (KH Chemicals Co.) with a weight ratio of carbon nanotubes to cobalt of 8: 2 (CNT: Co) It was. The carbon nanotubes carrying the cobalt compound nanoparticles were dried at 110 ° C. for one day, and reduced at 400 ° C. for 2 hours under a hydrogen atmosphere. The carbon nanotubes having the cobalt nanoparticles prepared as described above were pressed at 10 atmospheres to form discs.

An electrode was prepared by placing a carbon nanotube disk on which a cobalt nanoparticle prepared in the above step was mounted on a nickel foil having a thickness of 75 μm, which is a current collector, pressed at 10 atm under nitrogen atmosphere, and maintained at 1200 ° C. for 10 minutes.

Example 5

Copper particles are supported on carbon nanotubes by sputtering and used as an adhesive.

Single wall carbon nanotube (SWCNT) as used in Example 1 (KH Chemicals Co.) was pressed at 5 atmospheres to form a disc having a thickness of 100 to 300 μm.

Put the carbon nanotube disk prepared above into a sputter (thin film maker) and make a vacuum of about 10 ^-6 Torr, adjust the pressure to about 2x10 ^-2 Torr while flowing argon (Ar), and adjust the DC voltage To form an argon plasma, thereby sputtering copper for 5 minutes. The copper-sputtered carbon nanotube disks were taken out of the sputters, pulverized, mixed uniformly, and then pressed again at 5 atmospheres to form disks. The disk thus prepared was put back into the sputter as described above and sputtered copper.

The above sputtering-grinding-compression process was repeated 20 times to obtain carbon nanotube powder having copper particles uniformly supported on the surface of the carbon nanotubes, which was finally compressed to 10 atm to form a disc.

On the nickel foil having a thickness of 75 μm, which is a current collector, the carbon nanotube disc loaded with the copper nanoparticles prepared in the above step was placed, pressed at 10 atm under nitrogen atmosphere, and maintained at 1000 ° C. for 10 minutes to prepare an electrode.

Example 6

An example of manufacturing an electrode of a fuel cell by supporting platinum (Pt) on a carbon nanotube disk prepared in Example 1.

H ₂ PtCl ₆ was dissolved in water and supported on the carbon nanotube disk prepared in Example 1, dried at 110 ° C., and then reduced at 400 ^° C. for 2 hours while flowing hydrogen to prepare an electrode.

Example 7

In order to use as a fuel cell electrode, platinum nanoparticles prepared by supporting platinum compound nanoparticles in carbon nanotubes and reducing them are used as adhesives.

A single wall carbon nanotube (SWCNT) used in Example 1 (KH Chemicals Co.) was supported by H ₂ PtCl ₆ with a weight ratio of carbon nanotubes and platinum of 95: 5 (CNT: Pt). The carbon nanotubes carrying the platinum compound nanoparticles were dried at 110 ° C. for one day, and reduced at 400 ° C. for 2 hours under a hydrogen atmosphere. The carbon nanotubes loaded with the platinum nanoparticles thus prepared were pressed at 10 atmospheres to form discs.

An electrode was prepared by placing a carbon nanotube disk on which platinum nanoparticles prepared in the above step were loaded on a nickel foil having a thickness of 75 μm, which is a current collector, and pressing at 10 atm under nitrogen atmosphere for 10 minutes.

[Measurement of electrode performance]

The performance test of the electrode synthesized above was carried out as follows.

As the electrolyte of the electrode, 7M KOH aqueous solution was used. Each electrode manufactured above was processed to a diameter of 1.5 cm, and a separator of the electrode was used as a polymer separator (Celgard). The distance between the two electrodes was maintained at 300 μm. The resistivity of the electrode was measured using the Van der Pauw method.

Test Example 1

The resistivity measured by Van der Pauw method with respect to the electrode prepared in Example 1 was 9.1 mΩcm. The equivalent series resistance (ESR) inferred from the complex plane impedance plot was 35 m 35. Capacitance measured by constant current supply at DC voltage was 175 F / g. The calculated power density was 15 kW / kg and the energy density was 5.8 Wh / kg based on the total weight of the electrode. . The Ragone plot of the single cell electrode is shown in Figure 3.

Test Example 2

The resistivity of the electrode produced in Example 2 was 10 mPacm. The ESR inferred from the complex surface impedance plot was 41 m 41.

Test Example 3

The resistivity of the electrode produced in Example 3 was 25 mPacm. The ESR inferred from the complex surface impedance plot was 151 m151.

Test Example 4

The resistivity of the electrode produced in Example 4 was 15 mPacm. The ESR inferred from the complex surface impedance plot was 91 m 91.

Test Example 5

The resistivity of the electrode produced in Example 5 was 14.4 mPacm. The ESR inferred from the complex surface impedance plot was 88 m 88.

As a result of the experiment, it can be seen that the electrode manufactured by various methods using metal nanoparticles as an adhesive of carbon nanotubes is a very effective method for reducing internal resistance.

The values of internal resistance obtained in the above examples are much lower than those reported in the literature, which suggests that the use of metal nanoparticles to bond the carbon nanotubes can be achieved by the use of organic adhesives or carbon or carbon nanotubes. It is to prove that it is superior to existing methods such as adhesion after surface treatment.

Next, the capacitance of the carbon nanotube electrode manufactured by the method of the present invention is 175 F / g, which is a value close to the theoretical capacitance of 180 F / g, which is calculated to be generally obtained with an electrode using carbon nanotubes. .

In the results of Test Example 1, since the ESR of the electrode was very small, the output density of the electrode was very high. In addition, the change in energy density due to the power density is very small in the Ragone plot of Figure 3.

The electrodes with very low internal resistance are very useful as electrodes of secondary batteries, electrodes of supercapacitors, and electrodes of fuel cells, and are expected to produce stable products with much higher performance than those of conventional electrodes.

According to the method of the present invention, in manufacturing an electrode using carbon nanotubes or carbon nanofibers as an electrode material, which can be used in a secondary battery, a supercapacitor, or a fuel cell, a junction and a current between the carbon nanotubes or the carbon nanofibers are used. In bonding electrode material to metal constituting current collector, electrode is manufactured using existing organic adhesives by applying heat by using metal nanoparticles as an adhesive or by applying heat and pressure simultaneously. Compared to this, an effective electrode having a very small internal resistance and a very strong durability can be easily manufactured.

Claims (19)

A current collector, metal nanoparticles as an adhesive and carbon nanotubes or carbon nanofibers, and the above-described metal nanoparticles are attached or fused to the surface of the above-described carbon nanotubes or carbon nanofibers and are carbon nanotubes or carbon nanofibers. A carbon nanotube or carbon nanofiber electrode, characterized in that bonding between the carbon nanotubes or the carbon nanofibers and the current collector is achieved. The carbon nanotube or carbon nanofiber electrode according to claim 1, wherein the metal nanoparticle is used in an amount of 0.01 to 3 times based on the weight of the carbon nanotube or the carbon nanofiber. The carbon nanotube or carbon nanofiber electrode according to claim 1, wherein the metal constituting the metal nanoparticles is selected from the group consisting of alkali metals, alkaline earth metals, typical metals, and transition metals. According to any one of claims 1 to 3, the metal constituting the above-described metal nanoparticles are carbon nano, characterized in that in the form of the metal itself, metal alloys, metal sulfides, metal carbides, metal oxides or metal nitrides Tube or carbon nanofiber electrode. The carbon nanotube or carbon nanofiber electrode according to any one of claims 1 to 3, wherein the aforementioned metal nanoparticles have an average particle diameter of 1 µm or less. The carbon nanotube or carbon nanofiber electrode according to claim 1, wherein the current collector is selected from a plate, a net, and a form having a metal as a main component. [Claim 2] The carbon nanotubes according to claim 1, wherein the metal nanoparticles described above are attached or fused to the carbon nanotubes by pressing under a pressure of 1 to 500 atm or by heat treatment at a temperature of ± 500 ° C of the metal or metal compound. Or carbon nanofiber electrodes. Method of producing a carbon nanotube or carbon nanofiber electrode consisting of the following steps. (1) preparing an electrode material by mixing or supporting carbon nanotube or carbon nanofiber powder with metal nanoparticle adhesive; (2) first compressing the electrode material to produce a compressed electrode material; (3) By placing the first electrode material pressed on the current collector and pressing or heat treatment secondly, the carbon nanotubes and the carbon nanotubes or the carbon nanofibers and the carbon nanofibers are bonded to each other, and at the same time, the current collector and the electrode Bond the material. The method of manufacturing a carbon nanotube or a carbon nanofiber electrode according to claim 8, wherein in the step (2), the aforementioned electrode material is uniformly dispersed on the current collector or simultaneously compressed at the same time as the dispersion. . 10. The method according to claim 8 or 9, wherein in the step (2), the above-described metal nanoparticles are compressed under 1 to 500 atmospheres of carbon nanotubes or carbon nanofiber electrodes. 10. The carbon nanotubes according to claim 8 or 9, wherein in the step (3), the aforementioned metal nanoparticles are heat-treated at a temperature of melting point ± 500 ° C. of the metal or metal compound pressed or used under 1 to 500 atm. Or a method of producing a carbon nanofiber electrode. 10. The method according to claim 8 or 9, wherein in step (1), the carbon nanotubes or carbon nanofibers and the metal nanoparticles are mixed by physical mixing, ultrasonic mixing, solvent mixing, carbon nanotubes or carbon nanoparticles. A method for producing a carbon nanotube or a carbon nanofiber electrode, characterized in that it is carried out by a method selected from the group consisting of a method of uniformly dispersed on the surface of the fiber. The method according to claim 12, wherein the method of dispersing the carbon nanotubes or the carbon nanofibers evenly on the surface of the carbon nanotubes is carried on the carbon nanotubes or carbon nanofibers by a supporting method such as a catalyst carrying method. Next, the production of carbon nanotubes or carbon nanofiber electrodes, characterized in that carried out by a method selected from the group consisting of any oxidation or reduction, precipitation, chemical vapor deposition, electrodeposition, plasma spraying, and sputtering Way. 10. The method of manufacturing a carbon nanotube or a carbon nanofiber electrode according to claim 8 or 9, wherein the primary compression is made of a carbon nanotube or a carbon nanofiber in the form of a disk or a thin film. 10. The method for producing a carbon nanotube or carbon nanofiber electrode according to claim 8 or 9, wherein in step (3), pressing and heat treatment are performed simultaneously or sequentially. 10. The method according to claim 8 or 9, wherein in step (3), the heat treatment is performed in a group consisting of thermal heating, chemical vapor deposition, plasma, radio frequency (RF) heating, microwave heating. Characterized in that the method is carried out in a selected manner. An electric double layer capacitor using a carbon nanotube or carbon nanofiber electrode according to claim 1 or a carbon nanotube or carbon nanofiber electrode manufactured by the manufacturing method of claim 8 or 9. A secondary battery using a carbon nanotube or a carbon nanofiber electrode according to claim 1 or a carbon nanotube or carbon nanofiber electrode manufactured by the manufacturing method of claim 8 or 9. A fuel cell using a carbon nanotube or carbon nanofiber electrode according to claim 1 or a carbon nanotube or carbon nanofiber electrode manufactured by the manufacturing method of claim 8 or 9.