JP2006110701A - Carbon fiber body, member having it, and their manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber body, which can be applied to various kinds of electrode materials, etc., and further to provide a member having the same and their manufacturing method. <P>SOLUTION: In the carbon fiber body, one end side of a plurality of carbon fibers is connected to the body portion of a carbon body elongated in one direction in the state that the carbon fibers are arranged in parallel. Such carbon fiber body can be manufactured by heating a catalyst in a liquid material in two steps. As for the materials, the material composed of a kind of liquid alcohol at an ordinary temperature and ordinary pressure, and a kind of hydrocarbon can be used. Furthermore particularly, a substrate having a catalyst on its surface is heated in the liquid material in two steps. By this manufacturing method, the member having the carbon fibers grown from the catalyst existing on the substrate can be obtained. This member can be used as various electrode materials without requiring any other treatments. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a carbon fiber body, a member having the same, and a method for manufacturing the same, and more particularly, to a carbon fiber body that can be used for an electric double layer capacitor, a secondary battery, and the like, and a member having the carbon fiber body.

  Carbon nanotubes, a form of carbon fiber body, can be applied to future nanotechnology such as field emission electron sources, nanoscale electronic devices, chemical storage systems, mechanical reinforcements, etc. due to their unique electrical and mechanical properties It is highly possible.

  In addition, electric double layer capacitors have come to be used in applications such as memory backup power supplies for personal computers, subsidizing and substituting secondary batteries, battery backup power supplies for electric vehicles or fuel cell vehicles, and power supplies for hybrid vehicles. ing.

  This electric double layer capacitor is composed of a conductor constituting an electrode and an electrolyte solution impregnated therein, and when a voltage is applied between both electrodes, the ionic species in the electrolyte is present at the interface of the polarizable electrode. Charges are accumulated in the electric double layer at the electrode-electrolyte interface that is adsorbed and generated by this, utilizing the fact that a pair of charge layers (electric double layers) with different signs are generated, and charging and discharging It has the characteristic that the deterioration accompanying this does not occur. Therefore, the electric double layer capacitor is connected in parallel with, for example, a power source (battery or a power source obtained by converting a commercial AC power source into a direct current), and charges are accumulated. By discharging, it is used in the form of backing up various electric / electronic devices (for example, D-RAM).

In the conventional electric double layer capacitor, activated carbon powder or the like is used as the electrode conductor (carbon fiber body). This is because the capacitance of the electric double layer capacitor is determined by the amount of charge stored in the electric double layer, and the amount of charge increases as the surface area of the electrode increases. Since activated carbon has a high specific surface area of 1000 m ² / g or more, it is a material suitable as an electrode material for an electric double layer capacitor that requires a large surface area.

As an electric double layer capacitor using activated carbon powder as a polarizable electrode, the activated carbon powder is mixed with a thermosetting resin such as a phenol resin to be solidified and used as a solid activated carbon electrode (see, for example, Patent Document 1). ).
Among electric double layer capacitors, those with particularly large capacities can be expected to be used as power sources for pulse power. However, the conventional electric double layer capacitor cannot supply a large current instantaneously and cannot perform a function required as a power source for pulse power. This is because the movement of ionic species is suppressed inside the fine pores with a diameter of several nm that the activated carbon powder has. More specifically, a solid activated carbon electrode using activated carbon powder has pores with a diameter of several nm that the activated carbon powder has and pores with a diameter of 100 nm or more that are formed when the phenol resin is carbonized (for example, patents). Reference 2).
Among these pores, the movement of ionic species is suppressed inside the fine pores with a diameter of several nm that the activated carbon powder has. Therefore, the conventional electric double layer capacitor has a problem that when discharging is performed with a large current, the capacity is apparently reduced and sufficient performance cannot be exhibited. Therefore, it is desired to realize an electrode having a fine structure that makes it easier to hold and move ionic species.

  In addition, the maximum current value that can be passed to the electrode per unit volume is proportional to the capacitance per unit volume of the electrode. Therefore, it is desirable that the capacitance per unit volume of the electrode is larger.

  A lithium secondary battery is used as an indispensable power source for information communication devices represented by mobile phones and notebook computers among various secondary batteries, and contributes to the reduction in size and weight of mobile devices. As an electrode material (additive) for such a lithium secondary battery, graphite or carbon fiber is used for the purpose of imparting strength and conductivity to the electrode. Both the positive electrode material and the negative electrode material of a lithium secondary battery have a layered structure, and during charging, lithium ions are extracted from the positive electrode and inserted between carbon hexagonal network layers of the negative electrode to form a lithium intercalation compound. Conversely, during discharge, a reaction occurs in which lithium ions move from the carbon negative electrode to the positive electrode. As described above, the carbon material of the electrode material has a function of occluding and releasing lithium ions, and the quality of the occluding and releasing functions greatly affects battery characteristics such as charge / discharge characteristics.

  Graphite, particularly anisotropic graphite, has a typical layered structure, and various atoms and molecules are introduced to form a graphite intercalation compound (GIC). When lithium ions are inserted between the graphite layers, the layers expand and the electrode material (particularly the negative electrode material) expands. If charging / discharging is repeated in such a state, the electrode is deformed or metal lithium is liable to be deposited, resulting in capacity deterioration and internal short circuit. Moreover, repeated expansion and contraction between layers causes destruction of the graphite crystal structure and adversely affects cycle characteristics (life). In addition, graphite has a problem of poor conductivity as an electrode material. On the other hand, a tubular carbon fiber manufactured by a vapor deposition method is also known as a carbon material. This carbon fiber has a tube shape in which a plurality of concentric carbon hexagonal network layers are formed, and when used as a negative electrode material, the insertion port of lithium ions is only the end face of the fiber, and a sufficient lithium intercalation compound is formed. However, there is a problem that the electric energy density is small and sufficient capacity cannot be obtained. Also, since the carbon hexagonal network layer is concentric, when lithium ions are inserted, the concentric carbon hexagonal network layer is forcibly spread and stress is generated, which also causes destruction of the crystal structure. is there.

Japanese Examined Patent Publication No. 4-44407 JP-A-4-288361

  An object of the present invention is to solve the above-mentioned problems by providing an electric structure that has a fine structure that facilitates the retention and movement of ionic species, has a large capacitance, and can instantaneously extract a large current. It is to provide a carbon fiber body applicable to a member of a double layer capacitor (electrode material) or a negative electrode material of a secondary battery which has excellent life performance and can also increase capacity, a member having the carbon fiber body, and a method for manufacturing the same. .

The above-mentioned subject is achieved by the following composition.
That is, the present invention is as follows.
(1) A carbon fiber body characterized in that one end side of a plurality of carbon fibers is bonded to a body portion of a carbon body extending in one direction so that the carbon fibers are arranged in parallel.
(2) One carbon fiber is 20-100 nm in diameter, The carbon fiber body as described in said (1) characterized by the above-mentioned.
(3) The carbon fiber body according to (1), wherein the length of one carbon fiber is 100 to 1000 nm.
(4) The carbon fiber body according to (1), wherein the distance between the carbon fibers is 5 to 100 nm.

(5) The carbon fiber body according to any one of (1) to (4) and a substrate having a catalyst on the surface thereof, and the carbon fiber body and the substrate are combined and integrated. A member characterized by that.

(6) A substrate having a catalyst on the surface is heated in a raw material that is liquid at normal temperature and pressure, the catalyst and the substrate are heated from normal temperature to 600 ° C. to 700 ° C., and after a predetermined time, further 800 ° C. to 900 ° C. The method for producing a carbon fiber body according to any one of (1) to (4), further comprising a step of raising the temperature to ° C.

(7) The liquid raw material is methanol, ethanol, propanol, isopropanol, butanol, pentanol or octanol as alcohols, and hexane, peptane, octane, benzene or toluene as hydrocarbons, The method for producing a carbon fiber body as described in (6) above, which is one or more elements selected from the group consisting of Fe, Co and Ni.

In the carbon fiber body of the present invention, one end side of a plurality of carbon fibers is bonded to the body of the carbon body extending in one direction so that the carbon fibers are juxtaposed, and the spacing between the carbon fibers is 5 To 100 nm geometric space exists, and sufficient space is secured to hold ionic species with a radius of 0.05 to 0.5 nm in the carbon fiber.
Examples of the ion species in the radius range include BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , and AsF ₆ ⁻ . Furthermore, the carbon fiber body obtained by the carbon fiber body manufacturing method of the present invention and the member having the carbon fiber body (one end of the carbon fiber body bonded to the substrate) are used as they are for the electrode of the electric double layer capacitor and the negative electrode of the secondary battery. It can be used for various purposes such as materials.

Hereinafter, the carbon fiber body of the present invention, members having the same, methods for producing the same, and applications thereof will be described in detail.
The carbon fiber in the present invention means a minimum unit fiber bonded at one end to the body of a carbon body extending in one direction, and the carbon fiber body is a carbon body that binds the plurality of carbon fibers to each other. It shall mean the structure comprised from the trunk | drum part.

The carbon fiber body according to the present invention is characterized in that one end side of a plurality of carbon fibers is bonded to a body of a carbon body extending in one direction so that the carbon fibers are juxtaposed.
The diameter of such carbon fibers is preferably in the range of 20 to 100 nm. When the thickness is 20 to 100 nm, it is possible to maintain a sufficient surface area for holding ions and strength as a structure.
The length of the carbon fiber constituting the carbon fiber body is preferably in the range of 100 to 1000 nm, and the balance between adsorption and desorption of ions to the carbon fiber is optimized.

  The carbon fiber body having the unique structure as described above has a large surface area. When this carbon fiber body is used as a polarizable electrode of an electric double layer capacitor or a carbon material of a negative electrode material of a secondary battery, the obtained polarizable electrode or negative electrode material is a collection of carbon fiber bodies. And many fine pores exist in those carbon fiber bodies. That is, a polarizable electrode using a carbon fiber body has a porous structure having pores having a larger diameter than activated carbon. As a result, the ion retention and mobility at this portion are higher than when activated carbon is used, and the apparent capacity is unlikely to decrease even during large current discharge. Thus, in this embodiment, the comb-like carbon fiber body having a unique structure is used for the polarizable electrode of the electric double layer capacitor or the negative electrode material of the secondary battery, thereby increasing the specific surface area and the capacitance. In addition, it is possible to form a fine structure that increases ion mobility.

Although it does not specifically limit as a manufacturing method of the carbon fiber body of this invention, For example, the method of heating the catalyst which accelerates | stimulates the production | generation of a carbon fiber body in a liquid raw material is mentioned.
More specifically, there is a method in which a catalyst is present on the surface of the substrate and the substrate is heated in the raw material (organic compound).
The raw material (organic compound) used in the carbon fiber body and the method for producing the member of the present invention is capable of generating carbon fiber by receiving the action of a catalyst and reacting with heat generated by heating.
The growth of the comb-like carbon fiber body of the present invention depends on the production method, and it is presumed that a characteristic comb-like structure was formed.
The liquid raw material in the manufacturing method of the carbon fiber body and its member of the present invention is as follows.

  The liquid raw material is not particularly limited, but alcohols include methanol, ethanol, propanol, isopropanol, butanol, pentanol, octanol and the like, and hydrocarbons include hexane, peptane, octane, benzene, toluene and the like. It is done.

  The catalyst used in the method for producing a carbon fiber body of the present invention is not particularly limited as long as it becomes an active point of a carbon fiber production reaction by heating with an organic compound that is a liquid raw material and accelerates the reaction. In addition, in the field of carbon fiber body production technology, it includes all those that are publicly known, those that can be used, and those that can be expected to be usable. Examples include metals and metal oxides. Of these metals, transition metals are preferred. Here, the transition metal refers to scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tantalum, tungsten, rhenium, iridium or platinum. Among them, particularly those belonging to Group VIII of the Periodic Table, among which iron, nickel and cobalt are particularly preferred, and iron is most preferred.

In the method for producing a carbon fiber body of the present invention, resistance heating or induction heating can be used as a heating method.
The heating temperature is resistance heating or induction heating so that the temperature of the catalyst existing on the surface of the substrate is in the range of 600 to 700 ° C. as the first stage and 800 to 900 ° C. as the second stage. Keep on.
A carbon fiber body having a unique temperature control in these two stages is formed.

  The resistance heating in the method for producing a carbon fiber body of the present invention is a system in which a substrate is heated by passing an electric current through a relatively high resistivity such as Si, and as described above, the catalytic metal is applied to the surface. An attached substrate is used.

Induction heating in the method for producing a carbon fiber body of the present invention is a principle of heating by an eddy current generated in an electrical conductor due to a change in electric field. This will be described in more detail as follows.
When AC electricity is passed through the conducting wire, lines of magnetic force are generated around it. When a conducting wire is wound in the shape of a coil and an electric conductor such as metal is placed in the center of the coil and the coil is energized, an induced current (eddy current) is generated in the electric conductor (metal, etc.) due to the influence of magnetic lines of force. Arise. This induced current loses energy due to the resistance of the electrical conductor (metal or the like) and generates heat. This exothermic phenomenon is used for heating as a heat source.
When the substrate to be heated is heated by this induction heating, the metal or carbon fiber substrate which is an electrical conductor is heated, and the substrate to be heated is brought into close contact therewith. Here, the close contact includes from the case where the surface is completely integrated to the case where an appropriate gap is provided as long as heat transfer is possible. Further, there is no need for an electrode portion for flowing current, the structure is simple, and the shape of the substrate to be heated increases the degree of freedom. Moreover, it is non-contact heating different from resistance heating, and temperature control is easy. In particular, even in the case of a heating object having a large area and a large capacity, the temperature can be precisely controlled without causing unevenness in the heating temperature.

  As the substrate used in the method for producing a carbon fiber body by induction heating, a Si substrate having a catalytic metal deposited on the surface is used. The surface on which the catalyst does not adhere is adhered to a metal or carbon fiber substrate that is directly heated by induction heating.

The carbon fiber body is formed by two-stage temperature control as described above. At normal temperature before heating, the surface of the Si substrate is present in a state where the metal catalyst is close or in a state where the whole is thinly covered. When the Si substrate and the metal catalyst are heated in the solution and the temperature is gradually raised, the catalyst starts to move, and the catalyst is formed in a substantially linear shape with an appropriate length along the crystal plane of silicon. Aggregate. The temperature at this point is 600 to 700 ° C. Here, once the temperature rise is stopped and the temperature of the Si substrate and the metal catalyst is maintained, carbon begins to deposit from the substantially linear catalyst surface, and the body of the carbon body Part is formed. This part has a semi-amorphous carbon body rather than a clear layer structure because of the low temperature.
Thereafter, when the temperature of the Si substrate and the metal catalyst is raised to a range of 800 to 900 ° C. as a second stage, a part of the substantially linear catalyst settles on the Si substrate and becomes granular and island-like. If the temperature is maintained, the granular and island-like portions will each be deposited independently to form a single carbon fiber. Then, the carbon fiber grows and forms a carbon fiber body with the body part deposited in the first stage on the upper part.

  In the carbon fiber body manufacturing method of the present invention, undesired oxygen is by-produced during the carbon fiber body formation reaction, causing combustion of the raw organic compound. In order to avoid the problem, it is preferable to discharge oxygen generated in the reaction system by the induction heating by introducing an inert gas.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.
[Example 1]
Methanol was used as a liquid raw material. A substrate having a volume resistivity of 0.02 Ωcm and a Si (100) plane orientation of 10 × 20 × 0.5 mm ³ was used. The Si substrate was ultrasonically cleaned in acetone. An Fe thin film having an average thickness of 5 nm was deposited on the Si (100) substrate surface by sputtering with Ar gas. This Si substrate was placed in a substrate holder and immersed in methanol placed in a separable flask, and then nitrogen gas was introduced to flow a direct current and heated to 700 ° C. The surface of the Si substrate was covered with alcohol vapor (bubbles), and the temperature of the liquid in the flask rose to about 60 ° C. In order to lower the boiling point of the raw material methanol, the flask containing the liquid was placed in a cooling tank filled with cold water. A Liebig condenser was attached to collect the evaporated methanol. The Si substrate temperature was measured by using an optical radiation thermometer and focusing on the substrate surface. The current passed through the Si substrate was kept constant during growth. After maintaining in this state for about 1 minute, the temperature was raised to 850 ° C. and further heated for 4 minutes.

FIG. 1 is a diagram illustrating an example of a configuration of a synthesis apparatus for generating a carbon fiber body. This synthesizer includes a water cooling means 2 for cooling the liquid tank 1 outside the liquid tank 1, a substrate holder 5 that holds the substrate 3 and has an electrode 4 for passing a current through the substrate 3, a liquid A lid 9 holding a condensing means 7 comprising a water-cooled pipe 6 that cools and condenses the organic liquid vapor evaporating from the tank 1 and returns it to the liquid tank 1, a substrate holder 5, the condensing means 7, and a valve 8 for introducing N ₂ gas. The organic liquid 10 is hermetically sealed and held by the liquid tank 1 and the lid 9.
FIG. 2 is an SEM (electron microscope) image of the synthesized carbon fiber body. It was observed that the comb-like carbon fiber was growing on the substrate surface.

  The carbon fiber body of the present invention or a member having the same includes an electric double layer capacitor member (electrode material), a negative electrode material for a secondary battery, an FED / emitter, an electrode for a fuel cell, an electrochemical electrode, a catalyst carrier, a solar cell It can be applied to battery electrodes and the like.

1 is a diagram illustrating a configuration of a synthesis apparatus used in Example 1. FIG. 2 is an electron microscope (SEM) image of a carbon fiber body grown on a substrate obtained in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid tank 2 Water cooling means 3 Substrate 4 Electrode 5 Substrate holder 6 Water cooling tube 7 Condensing means 8 Valve 9 Lid 10 Organic liquid

Claims (7)

  A carbon fiber body, wherein one end side of a plurality of carbon fibers is bonded to a body of a carbon body extending in one direction so that the carbon fibers are juxtaposed.   The carbon fiber body according to claim 1, wherein the carbon fiber has a diameter of 20 to 100 nm.   The carbon fiber body according to claim 1, wherein the carbon fiber has a length of 100 to 1000 nm.   The carbon fiber body according to claim 1, wherein an interval between the carbon fibers is 5 to 100 nm.   A member comprising the carbon fiber body according to any one of claims 1 to 4 and a substrate having a catalyst on a surface thereof, wherein the carbon fiber body and the substrate are combined and integrated. .   A substrate having a catalyst on the surface is heated in a raw material that is liquid at normal temperature and pressure, and the temperature of the catalyst and the substrate is increased from normal temperature to 600 ° C. to 700 ° C. After a predetermined time, the temperature is further increased to 800 ° C. to 900 ° C. The method for producing a carbon fiber body according to any one of claims 1 to 4, further comprising a step of heating.   The liquid raw material is methanol, ethanol, propanol, isopropanol, butanol, pentanol or octanol as alcohols, and hexane, peptane, octane, benzene or toluene as hydrocarbons, and the catalyst is Fe, Co The method for producing a carbon fiber body according to claim 6, wherein the carbon fiber body is one or a plurality of elements selected from the group consisting of Ni and Ni.