JPH07307250A - Electric double-layer capacitor - Google Patents

Abstract

PURPOSE:To realize both large capacitance and low internal resistance at the same time by a method, wherein a polarized electrode contains active carbon and carbon whiskers, and the carbon whiskers and the particles of the active carbon are brought into electrical contact with each other. CONSTITUTION:Ethanol is added to the mixture which is composed of active carbon 0.1-20wt.% of carbon whiskers (an average diameter: not larger than 1.0mum, an average aspect ratio: not less than 20 and a graphitization rate: not less than 30%) and 0.5-20wt.% of polytetrafluoroethylene. The mixture is kneaded formed by rolling. Then the rolled sheet is dried to obtain a sheet polarized electrode. Polarized electrodes 1 and 8 which are punched out of the polarized electrode sheet are bonded to a stainless steel top cover 4 and a stainless steel case 5 with conductive adhesive 3 and 7. After the top cover 4 and the case 5 are dried, the polar electrodes 1 and 8 are impregnated with electrolyte solution composed of organic solvent and organic electrolyte. Then both electrodes 1 and 8 are made to face each other with a separator 2 therebetween.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electric double layer capacitor.

[0002]

2. Description of the Related Art A conventional electric double layer capacitor is, for example, an electric double layer capacitor element in which a separator is arranged between a pair of electrodes provided with an activated carbon electrode layer on a collector, together with an electrolytic solution, and a sealing plate in a metal case. And an electric double layer capacitor element that is sealed by a gasket that insulates both of them, or is wound by stacking a pair of electrodes and a separator, and the element is impregnated with an electrolytic solution and housed in an aluminum case. It is configured by sealing with a sealing member so that the electrolytic solution does not evaporate from the opening.

Further, a laminated flat plate type electric double layer capacitor for the purpose of large current and large capacity has been proposed (Japanese Patent Laid-Open No. Hei 4 (1998) -19984).
-154106, JP-A-3-203331, and JP-A-4-20311.
286108). In this laminated flat plate type electric double layer capacitor, a separator is arranged between a positive electrode and a negative electrode, which are usually formed in a rectangular shape, and they are laminated alternately to form an electric double layer capacitor laminated body. It is an element in which a positive electrode lead member and a negative electrode lead member are connected by caulking. The electric double layer capacitor laminated body element is housed in a case,
The electrolytic solution is impregnated and sealed with an upper lid.

[0004]

However, for power applications such as automobiles, electric double layer capacitors of high energy density and high output density which simultaneously satisfy a large capacity per unit volume and a low internal resistance are currently available. Is not known. Further, reduction in internal resistance is also desired for electric double layer capacitors for memory backup.

The conventional polarizable electrode has the following problems.

(B) When activated carbon powder or activated carbon short fibers are used, conductive carbon black and a binder are blended to impart strength to the polarizable electrode while reducing electrical resistance. However, in order to reduce the electric resistance, it is necessary to add a large amount of conductive carbon black, and the content of activated carbon in the polarizable electrode is reduced by this amount, so that the capacitance of the capacitor becomes small.

(B) When activated carbon long fibers are used for the polarizable electrode, the activated carbon fiber cloth has a low density and it is difficult to increase the capacity per unit volume. Further, since the current collector layer is in contact with only a part of the surface of the activated carbon fiber, the current collection of the entire activated carbon fiber becomes insufficient, and there is a problem that an electric double layer capacitor having a low internal resistance cannot be obtained. In order to overcome these problems, there is a proposal to use activated carbon fibers on the surface of which carbon has been deposited by a vapor phase growth method (JP-A-2-177525), but the manufacturing process is complicated and the cost is high. Therefore, the problem that the capacitance cannot be increased remains.

(C) Further, a metal-carbon composite material obtained by sintering stainless steel fiber (diameter about 2 μm), carbon fiber (diameter about 20 μm, specific surface area about 790 m ² / g) and cellulose fiber is used as a polarizable electrode. An electric double layer capacitor that has been proposed has also been proposed (J. Electroch
em. Soc. Vol. 137, P136-141, P
1750 to 1756, 1990), both the capacitance and the internal resistance are not specifications that can be satisfied.

An object of the present invention is to solve these problems and provide an electric double layer capacitor which simultaneously satisfies a large capacity and a low internal resistance.

[0010]

In order to achieve the above object, the electric double layer capacitor of the present invention contains activated carbon and carbon whiskers, which are good conductive materials, in the polarizable electrode. The particles are electrically connected.

The polarizable electrode of the electric double layer capacitor of the present invention contains at least activated carbon and carbon whiskers having high conductivity, and the degree of graphitization of the carbon whiskers gives the polarizable electrode greater conductivity. Therefore, it is preferable to set it to 30% or more.

Such a carbon whisker can be manufactured by a vapor phase growth method, and its diameter is, for example, 0.1 to 2 μm.
m, the length is about 5 to 100 μm, and the aspect ratio is 1
It is in the range of 0 to 150, and the diameter is extremely fine compared to carbon fibers and the like. The density of carbon whiskers is usually 1.8 to 2.1 g / cm ³ , and the specific resistance is 7 × 10 ⁻⁵ to 1 ×.
10 ^-3 Ω · cm, specific surface area by BET method is 1-40 m
² / g.

Commercially available carbon whiskers include those having a graphitization degree in the range of 0 to 96%, which is determined by the Mering-Marie equation in the X-ray diffraction method, and generally have a high graphitization degree. The ones called graphite whiskers and the low ones called carbon whiskers are collectively referred to as carbon whiskers in the present invention. The same effect can be obtained by using any of the whiskers, but the carbon whisker having a graphitization degree of 30% or more has a low specific resistance of 1 × 10 ⁻³ Ω · cm or less, and thus is particularly preferably selected in the present invention. It

The carbon whiskers have an average diameter of 1
It is preferable to use those having an average length of 20 μm or more or an average aspect ratio of 20 or more and having an average length of 20 μm or more. When this carbon whisker is used as a conductivity improving material for a polarizable electrode, the apparent volume of the polarizable electrode is 1c.
The number of carbon whiskers present per m ³ is 1 × 1
It is preferable that the number is not less than ⁰⁹ .

The carbon fiber obtained by the solid-phase pyrolysis method of polyacrylonitrile fiber used in the conventional electric double layer capacitor has a diameter in the range of 5 to 20 μm, and has a density similar to that of carbon whiskers in the polarizable electrode. It cannot exist.

The polarizable electrode can be manufactured, for example, by the following method.

(A) A polarizable electrode composed of activated carbon and carbon whiskers can be produced by mixing carbon whiskers and a phenolic resin, followed by press molding and firing and activating in an inert gas atmosphere and a steam atmosphere.
An electrode can be obtained by joining this polarizable electrode to, for example, a current collector via a conductive adhesive or the like.

(B) Carbon whiskers, activated carbon powder and binder are mixed and kneaded in the presence of alcohol, molded into a sheet and dried to form a polarizable electrode. This polarizable electrode is bonded to the current collector via, for example, a conductive adhesive.

(C) Carbon whiskers, activated carbon powder, a binder and a solvent for the binder are mixed to form a slurry, which is coated on a metal foil serving as a current collector and dried to be integrated with the current collector. Obtain a polar electrode. As the binder, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, polyvinylpyrrolidone or the like can be used,
As the solvent for the binder, N-methylpyrrolidone, water or the like is appropriately selected.

In (b) or (c), if the polarizable electrode contains 1 to 10% by weight of conductive carbon black as a conductivity improving material in addition to carbon whiskers, the electric resistance of the polarizable electrode is further improved. Can be made smaller.

In (a), (b) and (c), 0.1 to 20% by weight of carbon whiskers are contained in the polarizable electrode.
It is preferable to include it. When it is less than 0.1% by weight, there is almost no effect of reducing the electric resistance of the polarizable electrode.
In addition, if the content exceeds 20% by weight, the content of activated carbon is reduced by this amount and the electrostatic capacity is reduced, which is not preferable. Particularly preferably, the polarizable electrode contains 0.5 to 10% by weight of carbon whiskers. In the present invention, the amount of each component in the polarizable electrode is a numerical value regarding the state before being impregnated with the electrolytic solution.

In (b) or (c), the binder is preferably contained in the polarizable electrode in an amount of 0.5 to 20% by weight. If the content is less than 0.5% by weight, the strength of the polarizable electrode is low, and if the content is more than 20% by weight, the binder is an insulating material, so that the electrical resistance increases and the capacitance increases. It is not preferable because it causes a decrease.

Activated carbon has a particle size of 20 μm or less and a specific surface area of 1
It is preferable to use one having a density of 500 to 3500 m ² / g because the capacity can be increased and the internal resistance can be reduced. The polarizable electrode may be in the form of a thin film, a sheet, a plate, or the like.

The current collector may be a conductive material that is electrochemically and chemically resistant to corrosion. When the electrolyte is an aqueous solution, conductive rubber, corrosion-resistant metal, graphite, etc. are used as the current collector, and when the electrolyte is a non-aqueous solution, stainless steel, aluminum, titanium, tantalum, etc. are used as the current collector. To be done. Of these, stainless steel and aluminum are preferred current collector materials in terms of both performance and price.

The main component of the polarizable electrode is activated carbon, and in addition to carbon whiskers, when carbon black such as acetylene black or Ketjen black, which is a conductive substance, or ruthenium oxide is mixed into the polarizable electrode, its electric resistance is further improved. Can be made smaller.

As the electrolytic solution, an aqueous solution of sulfuric acid, an aqueous solution of sodium sulfate, an aqueous solution of potassium hydroxide, a propylene carbonate solution of tetraalkylphosphonium tetrafluoroborate, a propylene carbonate solution of tetraalkylammonium tetrafluoroborate or a sulfolane solution can be used.

When a non-aqueous organic electrolyte is used, the withstand voltage is as high as 2.5 to 3.0 V and the withstand voltage is 1.0.
Compared with the case of using the V before and after the aqueous electrolyte solution, significantly energy density (E = CV ^2/2: where, E is the energy density, C is the capacitance, V is voltage) can be increased.

According to the present invention, the polarizable electrode contains activated carbon and carbon whiskers and has a rated voltage of 2.
It is possible to provide an electric double layer capacitor having an electrostatic capacity of 4000 F or more and an internal resistance of 12 m (millimeter) Ω or less at 8V.

[0029]

With the electric double layer capacitor of the present invention, it is possible to provide an electric double layer capacitor having a low internal resistance without reducing the electrostatic capacitance. INDUSTRIAL APPLICABILITY The present invention is effective for an electric double layer capacitor having a relatively small electrostatic capacity, but it is applicable to an electric double layer capacitor having a large electrostatic capacity of 100 to 10,000 F or a current of 3 A to 1000 A and for a large current. On the other hand, it is a particularly suitable configuration.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples, but these examples are examples of the present invention, and the present invention is not limited to these examples.

[Example 1] Activated carbon powder (specific surface area of about 18
00m ² / g, average particle size about 3 μm) 85% by weight, carbon whiskers (average diameter about 1.0 μm, normal length about 60)
μm, average aspect ratio about 60, degree of graphitization about 70%, specific resistance 1.5 × 10 ⁻⁴ Ω · cm, density 2.0 g / cm ³ )
Ethanol was added to a mixture of 5% by weight and 10% by weight of polytetrafluoroethylene, and the mixture was kneaded and rolled to form a sheet having a width of 10 cm, a length of 30 cm and a thickness of 0.65 mm. Then, it was dried at 130 ° C. for 2 hours to obtain a sheet-like polarizable electrode.

In FIG. 1, polarizable electrodes 1 and 8 obtained by punching out a sheet of this polarizable electrode to a diameter of 12 mm.
Was bonded to the stainless steel upper lid 4 and the stainless steel case 5 with graphite-based conductive adhesives 3 and 7. The upper lid 4 to which the polarizable electrodes 1 and 8 were attached and the case 5 were dried in vacuum at 200 ° C. for 3 hours, and then the polarizable electrode was impregnated with a propylene carbonate solution containing 1 mol of tetraethylphosphonium tetrafluoroborate. . After that, both electrodes were opposed to each other with the separator 2 sandwiched therebetween, and the insulating gasket 6 made of propylene was used to caulk and seal the case. The coin type electric double layer capacitor has a diameter of 18.3 mm and a thickness of 2.0 mm.

[Example 2] Activated carbon powder (specific surface area of about 25
00 m ² / g, average particle size of about 6 μm) 85% by weight, carbon whiskers (average diameter of about 1.0 μm, average length of about 60)
μm, average aspect ratio about 60, graphitization degree about 94%, specific resistance about 7 × 10 ⁻⁵ Ω · cm, density about 2.1 g / cm ³ ).
A mixture of 5% by weight and 10% by weight of polyvinylidene fluoride was added with N-methylpyrrolidone in an amount of 4 times by weight, and the mixture was stirred and mixed while applying ultrasonic waves to obtain a slurry of activated carbon and carbon whiskers in which polyvinylidene fluoride was dissolved. It was
Width 10 cm, length 30 cm, thickness 30 μm
Coated on both sides of the aluminum etching foil of
After drying at ℃ for 3 hours, it was pressed by a roll.

This polarizable electrode with a current collector is attached to 58 mm × 1
The aluminum tab terminals 15 and 16 were welded to the portion of the current collector where the polarizable electrode layer was partly removed and cut into a size of 3 mm. As shown in FIG. 2, a separator 12 is wound between electrode pairs in which a polarizable electrode 10 made of activated carbon, carbon whiskers and polyvinylidene fluoride as a binder is formed on a current collector 11 made of an aluminum etching foil. After rotating and drying in vacuum at 130 ° C. for 5 hours, the polarizable electrode and the separator were impregnated with the electrolytic solution having the same composition as in Example 1,
It was inserted into the aluminum case 30 and curled and sealed through the sealing rubber 14. The dimensions of this electric double layer capacitor are 8 mm in diameter and 20 mm in length.

[Example 3] Activated carbon powder (specific surface area of about 22
00 m ² / g, average particle size of about 5 μm) 82% by weight, carbon whiskers (average diameter of about 0.7 μm, average length of about 30)
μm, average aspect ratio about 43, graphitization degree about 94%, specific resistance about 7 × 10 ⁻⁵ Ω · cm, density about 2.1 g / cm ³ ).
Ethanol was added to a mixture consisting of 5% by weight, 3% by weight of Ketjenblack and 10% by weight of polytetrafluoroethylene, and kneaded, and rolled to obtain a long sheet having a width of 10 cm and a thickness of 0.8 mm.

Then, this long sheet was dried at 130 ° C. for 2 hours to obtain a sheet-like polarizable electrode. This sheet electrode was cut into 10 cm squares, and as shown in FIG. 3, 2 cm × 4 c
Sheet-shaped polarizable electrodes of 10 cm square were adhered to both sides of a current collector of a roughened stainless steel foil having a thickness of 30 μm and having current collecting terminals 23 and 24 of m by using a graphite-based conductive adhesive.

Electrodes 20 and 2 to which polarizable electrodes are attached
1 are made to face each other via the separator 22, and similarly, a total of 13 positive electrodes and 13 negative electrodes are sequentially laminated via the separator, and the respective collector terminals 23 and 24 are crimped to the current collector leads 25 and 26. Connected by.

This electrode laminated body was dried in vacuum at 200 ° C. for 3 hours, then housed in an aluminum case 30, the positive electrode terminal 27, the negative electrode terminal 28 and the upper lid 29 were attached, and 1 mol was injected from a liquid injection port (not shown). A propylene carbonate solution of tetraethylphosphonium tetrafluoroborate having a concentration was injected, and the electrode laminate element was impregnated and sealed. The rectangular electric double layer capacitor has a height of 127 mm, a width of 114 mm and a thickness of 30 mm.

Comparative Example 1 In Example 1, 5% by weight of Ketjen Black was used instead of the carbon whiskers.
A coin type electric double layer capacitor was assembled in the same manner as in Example 1 except that the components were blended.

Comparative Example 2 A coin-type electric double layer capacitor was assembled in the same manner as in Example 1 except that 10% by weight of acetylene black was added instead of the carbon whiskers.

Comparative Example 3 In Example 2, 5% by weight of Ketjen Black was used instead of the carbon whiskers.
A wound type electric double layer capacitor was assembled in the same manner as in Example 2 except that the components were blended.

[Comparative Example 4] A laminated electric double layer capacitor was assembled in the same manner as in Example 3 except that a total of 8% by weight of Ketjen black was blended in place of the carbon whiskers.

Table 1 shows the results of measuring the capacitance and the internal resistance of the electric double layer capacitors of Examples 1 to 3 and Comparative Examples 1 to 4 each having a rated voltage of 2.8V. From Table 1, it is clear that the electric double layer capacitor of the present invention can provide an electric double layer capacitor having a small internal resistance without sacrificing the capacitance.

[0044]

[Table 1]

[0045]

In the electric double layer capacitor of the present invention, the carbon whiskers which are thin and have excellent electric conductivity are contained in the polarizable electrode, and the activated carbon particles and the carbon whiskers are brought into electrical contact with each other. Thereby significantly reducing the electric resistance in the polarizable electrode. With an electric double layer capacitor adopting such a configuration, it is possible to easily manufacture a capacitor having a small internal resistance without sacrificing the electrostatic capacity, and therefore an electric capacitor having a large capacity and a low internal resistance of a level not known in the past. It has become possible to provide a double layer capacitor.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a button type electric double layer capacitor according to the present invention.

FIG. 2 is a cutaway perspective view showing an example of a wound electric double layer capacitor according to the present invention.

FIG. 3 is a cutaway perspective view showing an example of a laminated electric double layer capacitor according to the present invention.

[Explanation of Codes] 1, 10 ... Polarizable electrode 11 ... Current collector 20, 21 ... Polarizable electrode having current collector 2, 12, 22 ... Separator 3 ... Conductivity Adhesive 4 ... Metal top cover 5 ... Metal case 6 ... Insulation gasket 13 ... Aluminum case 14 ... Seal rubber 15, 16 ... Lead 23 ... Positive electrode current collector terminal 24 ... -Negative electrode current collecting terminal 25 ... Positive electrode current collecting lead member 26 ... Negative electrode current collecting lead member 27 ... Positive electrode terminal 28 ... Negative electrode terminal 29 ... Upper lid 30 ... Metal case

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuji Ikeda 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Central Research Laboratory, Asahi Glass Co., Ltd.

Claims (6)

[Claims] 1. An electric double layer capacitor, wherein a polarizable electrode contained therein contains activated carbon and carbon whiskers, and particles of activated carbon and the carbon whiskers are electrically connected. 2. The electric double layer capacitor according to claim 1, wherein the carbon whiskers have a degree of graphitization of 30% or more. 3. The electric double layer capacitor according to claim 1, wherein the carbon whiskers have an average diameter of 1 μm or less and an average aspect ratio of 20 or more. 4. A carbon whisker is provided in the polarizable electrode in an amount of 0.
The electric double layer capacitor according to claim 1, wherein the electric double layer capacitor is contained in an amount of 1 to 20% by weight. 5. The electric double layer capacitor according to claim 1, wherein the polarizable electrode contains 0.5 to 20% by weight of a binder. 6. An aluminum foil or a stainless steel foil is used as a collector of a polarizable electrode, and a separator impregnated with an electrolytic solution containing an organic solvent and an organic electrolyte is arranged between the polarizable electrodes. 5. The electric double layer capacitor according to any one of 5.