JP2003234254A - Electric double-layer capacitor using carbon nanotubes - Google Patents

Abstract

(57) [Problem] To provide a small electric double layer capacitor capable of storing a large capacity. SOLUTION: A pair of polarizable electrodes 1 impregnated with an electrolytic solution.
2 were placed facing each other in the container. Each polarizable electrode was composed of substrates 3, 4 serving as current collectors and brush-like carbon nanotubes 5, 6 grown on one surface thereof. The brush-like carbon nanotube of one electrode and the brush-like carbon nanotube of the other electrode faced each other in a non-contact state.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric double layer capacitor using carbon nanotubes capable of storing a large amount of electricity.

[0002]

2. Description of the Related Art Conventionally, in an electric double layer capacitor, a separator such as polypropylene nonwoven fabric is sandwiched between a pair of polarizable electrodes having a polarizable electrode layer composed mainly of activated carbon on a current collector to form an element. The layer is impregnated with an electrolytic solution, the element is housed in a metal container, and the structure is sealed in a metal container with a sealing plate and a gasket. These small electric double layer capacitors were mainly used for backup of IC memories.

Further, flat plate-like positive electrodes and negative electrodes each having an activated carbon-based electrode layer formed on a current collector are alternately laminated with a separator interposed therebetween, the laminated bodies are housed in a case, and an electrolytic solution is injected into the case. There has also been proposed a laminated electric double layer capacitor formed by infiltrating into the electrode layer (Japanese Patent Laid-Open No. 4-1541).
No. 06 publication). This was mainly used for large current and large capacity.

Conventionally, the polarizable electrodes constituting these electric double layer capacitors have mainly been activated carbon having a large specific surface area. Further, as the electrolytic solution, a polar solvent having a high dielectric constant such as water or carbonic acid ester has been used so that the electrolyte can be dissolved at a high concentration.

[0005]

However, activated carbon having a large specific surface area generally has a low electric conductivity, and the activated carbon alone cannot increase a large current because the internal resistance of the polarizable electrode becomes large. Therefore, in order to reduce the internal resistance, attempts have been made to increase the capacity by incorporating carbon nanotubes in the polarizable electrode to increase the electric conductivity (Japanese Patent Laid-Open No. 2000-124079). However, with this method, the conventional capacity was increased only about 1.7 times.

Further, the conventional electric double layer capacitor requires a separator such as PTFE in order to completely prevent ohmic contact between the positive and negative electrodes and to prevent the flow of ions, but the material and shape of the separator are There is a problem that the self-discharge characteristics of the electric double layer and internal resistance are greatly affected.

On the other hand, it is desired to realize an electric double layer capacitor having a larger capacity so that the time when the IC memory can be backed up can be further lengthened.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an electric double layer capacitor which is compact and can store a large capacity.

[0009]

The present inventor has made earnest efforts for the purpose of developing an electric double layer capacitor capable of realizing storage of a larger capacity. As a result, a pair of brush-like carbon nanotubes grown on the substrate are made to face each other without a separator at a required interval so as not to come into contact with each other, or the pair of brush-like carbon nanotubes are made to come into contact with each other without electrical contact so as to have a ferroelectric property. It has been found that by covering with a material of a high ratio and by making them bite into each other, it is possible to store electricity more than ten times that of conventional large-capacity electric double layer capacitors and to reduce the internal resistance to less than half. .

That is, in the first aspect of the invention, a pair of polarizable electrodes impregnated with an electrolytic solution are arranged in opposition to each other in a container, and each polarizable electrode is grown on a substrate serving as a current collector and one surface thereof. And a brush-like carbon nanotube, wherein the brush-like carbon nanotube of one electrode and the brush-like carbon nanotube of the other electrode face each other in a non-contact manner.

A second aspect of the invention is a brush in which a pair of polarizable electrodes impregnated with an electrolytic solution are arranged in a container so as to face each other, and each polarizable electrode is grown on a substrate serving as a current collector and one surface thereof. -Like carbon nanotubes and a coating layer having a ferroelectric constant that covers the surface of the brush-like carbon nanotubes, and the brush-like carbon nanotubes of one electrode and the brush-like carbon nanotubes of the other electrode are electrically non-contacting with each other. The present invention relates to an electric double layer capacitor using carbon nanotubes that is made to bite.

The structure of the carbon nanotube may be a single layer, that is, a single tube, or may be a multilayer, that is, a plurality of concentric tubes having different diameters. The diameter of the carbon nanotube is preferably 1 to 100 nm.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

The carbon nanotube is a substance in the form of an extremely fine tube (tube) having a hole diameter nanometer (one nanometer is one billionth) made by connecting carbon atoms in a mesh shape. The electrolyte ion diameter of a normal electrolyte is about 0.4-
Since it is 0.6 nm, carbon nanotubes having a hole diameter of 1 to 2 nm are preferable for adsorption and desorption of ions.

The brush-like carbon nanotubes constituting the polarizable electrode can be produced by a known method. For example, a Fe film is patterned on at least one surface of a silicon substrate by photolithography, and acetylene (C
General chemical vapor deposition (CVD method) using ₂ H ₂ ) gas
It can be produced by applying. This method gives a diameter of 12
Carbon nanotubes of ˜38 nm are vertically raised on the substrate in a multi-layer structure. In order to prevent the pair of opposed brush-like carbon nanotubes from electrically contacting each other, it is preferable to provide a non-conductive spacer such as Teflon (registered trademark) on the peripheral edge of the substrate. The gap between the brush tips of the pair of brush-like carbon nanotubes is preferably 5 to 30 μm.

In the second invention, in order to form a coating layer having a ferroelectric constant for covering the surface of the brush-like carbon nanotube, for example, the brush-like carbon nanotube grown on the substrate is made of Pd (Zr _0.5 Ti _0.5 ). A method of impregnating with a solution of O ₃ (High-Purity Chemical Laboratory “SYMETRIX”), taking out, and heat-treating in nitrogen is preferable.

A silicon flat plate is preferable as the substrate serving as a current collector, but a flat plate made of titanium, stainless steel, tantalum, graphite or the like can be used. Punching metal, expanded metal, metal net, etching foil of aluminum, etc. are also preferable in order to improve current collection efficiency.

The electrolytic solution of the electric double layer capacitor is prepared by using an aprotic solvent such as propylene carbonate, 1-butylene carbonate, sulfolane, acetonitrile, γ-butyl lactone or dimethylformamide in tetraethylammonium tetrafluoroborate or tetraethylammonium hexafluorophosphate. Organic solutes such as fert and tetrabutylammonium perchlorate, or cations such as lithium and quaternary phosphonium and BF ₄ ⁻ , P
F ₆ ⁻ , ClO ₄ ⁻ , CF ₂ SO ₂ ⁻ or the like in which an inorganic solute is dissolved, an aqueous electrolyte such as dilute sulfuric acid containing a salt of a lanthanoid element, or a polymer substance is added to these. Polymer type electrolytic solution or the like can be used.

Next, the present invention will be specifically described based on Examples.

Example 1 First Step A low-resistance N-type semiconductor silicon substrate having a thickness of 10 mm × 10 mm × 0.5 mm and a thickness of 60 μm on the entire periphery of one side thereof.
Then, a Teflon tape having a width of 1 mm was attached and covered. This Teflon tape serves as the spacer (8) in FIGS. 1 and 2. All of the drawings are schematic representations of coin-type electric double layer capacitors, and the dimensions of each member do not match the actual dimensions. Then, after patterning the Fe film on the one surface by photolithography, acetylene was added at a flow rate of 3
Brush-like carbon nanotubes were grown on the substrate by chemical vapor deposition at a flow rate of 0 ml / min at a temperature of 700 ° C. for 15 minutes. The carbon nanotubes thus produced had a multi-layered structure, a diameter of 12 nm and a length of 50 μm. Thus, a polarizable electrode composed of the substrate and the brush-like carbon nanotubes grown on one surface thereof was obtained.

Second Step FIG. 1 is a vertical sectional view showing a coin type electric double layer capacitor. In FIG. 1, a pair of upper and lower polarizable electrodes (1) and (2) each composed of a substrate (3) (4) serving as a current collector and brush-like carbon nanotubes (5) (6) The brush-like carbon nanotubes (5) of (1) and the brush-like carbon nanotubes (6) of the upper electrode (2) were placed in a stainless steel container (7) so as to face each other in a non-contact manner. . The gap (9) between the brush tips of the pair of brush-like carbon nanotubes (5) and (6) was set to 20 μm. Then, in a glove box under a dry nitrogen atmosphere, the electrolytic solution (a propylene carbonate solution of tetraethylammonium tetrafluoroborate (concentration = 1 mol / l)) was placed in a container (7).
It was injected into the inside and impregnated into the brush-like carbon nanotubes (5) and (6). Then, the polypropylene gasket (10) was used to caulk and seal the container (7) with a stainless steel lid (11). Thus, a coin type electric double layer capacitor was produced.

When the characteristics of this capacitor were measured,
The electric capacity per polarizable electrode weight was 15 F / g, and the internal resistance per polarizable electrode weight was 11Ω.

Example 2 First Process In Example 1, a low resistance N-type semiconductor silicon substrate was prepared.
A brush-like carbon nanotube was grown on the substrate by performing the same operation as in the first step of Example 1 except that it was coated with a Teflon tape having a thickness of 30 μm and a width of 1 mm.

Second Step This brush-like carbon nanotube is treated with Pb (Zr _0.5
It was placed in a glass beaker containing 100 ml of a 0.5 mol / l aqueous solution of Ti _0.5 ) O ₃ (“SYMETRIX” manufactured by Kojundo Chemical Laboratory Co., Ltd.). The beaker is placed in a vacuum container, and the atmosphere in the container is evacuated to obtain Pb.
The (Zr _0.5 Ti _0.5 ) O ₃ aqueous solution was impregnated into the gaps between the carbon nanotubes. Next, the substrate with brush-like carbon nanotubes was taken out of the solution and heat-treated at a temperature of about 400 ° C. in a nitrogen atmosphere in an electric furnace. By this heat treatment, as shown in FIG. 3, the surface of the brush-like carbon nanotube was covered with a coating layer (12) made of a ferroelectric material. Thus, a polarizable electrode composed of the substrate and the brush-like carbon nanotubes grown on one surface thereof was obtained.

Third Process FIG. 2 is a vertical sectional view showing a coin type electric double layer capacitor. In FIG. 2, a pair of upper and lower polarizable electrodes (1) and (2) each composed of a substrate (3) (4) serving as a current collector and brush-like carbon nanotubes (5) (6) are attached to the lower electrode. The stainless steel container (7) so that the brush-like carbon nanotubes (5) of (1) and the brush-like carbon nanotubes (6) of the upper electrode (2) bite into each other in an electrically non-contact manner.
Placed inside. Then, the electrolytic solution was impregnated by the same operation as in the second step of Example 1 to produce a coin-type electric double layer capacitor.

When the characteristics of this capacitor were measured,
The electric capacity per polarizable electrode weight was 53 F / g, and the internal resistance per polarizable electrode weight was 8 Ω / g.

Comparative Example 1 Phenol resin-based activated KOH-enhancing treated activated carbon powder (specific surface area 2500 m ² / g, average particle size 5 μm) 60 wt
%, Carbon black (manufactured by Nippon Graphite Co., Ltd.) 30 wt%, and a tetrafluoroethylene-based binder 10 wt%. Ethanol was added to this mixture and kneaded, and the obtained kneaded product was rolled to obtain a sheet of 10 mm × 10 mm × 6 mm, which was dried at 250 ° C. for 2 hours. A pair of upper and lower electrodes (21) (22) thus obtained are provided with a spacer (23) between them.
As shown in FIG. 4, after being placed in a stainless steel container (7), a coin type electric double layer capacitor was manufactured in the same manner as in Example 1. In the figure, (24) is a graphite-based conductive adhesive layer.

When the characteristics of this capacitor were measured,
The electric capacity per polarizable electrode weight was 4.6 F / g, and the internal resistance per polarizable electrode weight was 16 Ω / g.

[0029]

The electric double layer capacitor according to the present invention is
Since it is configured as described above, a small size and a large capacity can be stored.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a coin type electric double layer capacitor according to a first embodiment.

FIG. 2 is a vertical sectional view showing a coin type electric double layer capacitor according to a second embodiment.

FIG. 3 is a vertical cross-sectional view showing a state where a brush-like carbon nanotube bites in a coin-type electric double-layer capacitor according to Example 2.

FIG. 4 is a vertical sectional view showing a conventional coin type electric double layer capacitor.

[Explanation of symbols]

(1) (2) Polarizable electrode (3) (4) PCB (5) (6) Brush-like carbon nanotubes (7) Container (8) Spacer (9) Gap (10) Gasket (11) Lid material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor K. Inazumi             1-89 Minami Kohoku 1-89, Suminoe-ku, Osaka             Standing Shipbuilding Co., Ltd. (72) Inventor Daisuke Fujita             1-89 Minami Kohoku 1-89, Suminoe-ku, Osaka             Standing Shipbuilding Co., Ltd. (72) Inventor Hideki Shiozaki             1-89 Minami Kohoku 1-89, Suminoe-ku, Osaka             Standing Shipbuilding Co., Ltd. (72) Inventor Kiman Nakayama             1-1-14 Karigaoka, Hirakata City, Osaka Prefecture Building 9               404 (72) Inventor Riichiro Saito             3-15-19 Iwatokita, Komae-shi, Tokyo

Claims (3)

[Claims] 1. A pair of polarizable electrodes impregnated with an electrolytic solution are arranged to face each other in a container, and each polarizable electrode is a substrate serving as a current collector and a brush-like carbon nanotube grown on one surface thereof. An electric double-layer capacitor using carbon nanotubes, which comprises a brush-like carbon nanotube of one electrode and a brush-like carbon nanotube of the other electrode facing each other in a non-contact manner. 2. A pair of polarizable electrodes impregnated with an electrolytic solution are arranged to face each other in a container, and each polarizable electrode is a substrate serving as a current collector and a brush-like carbon nanotube grown on one surface thereof. It is composed of a ferroelectric coating layer covering the surface of the brush-like carbon nanotube, and the brush-like carbon nanotube of one electrode and the brush-like carbon nanotube of the other electrode bite into each other in an electrically non-contact manner. , Electric double layer capacitor using carbon nanotube. 3. The electric double layer capacitor according to claim 1, wherein the carbon nanotube has a single-layer or multi-layer structure and a diameter of 1 to 100 nm.