JP2002025865A - Electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a large capacity of an electric double-layer capacitor. SOLUTION: A pair of polarizable electrodes is impregnated with an electrolyte and the electric double-layer capacitor is formed through the intermediary of a separator. At least one of the polarizable electrodes is a complex compound, made of a conductive polymer compound which is obtained on a porous carbonaceous material through a chemical oxidation polymerization method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electric double layer capacitor. More specifically, it is an electric double layer capacitor which can be charged and discharged at high speed and has a large capacity. For example, power supply for memory backup in mobile phones, IC cards, pagers, etc., emergency power supply in computers, data communication equipment, etc., energy storage devices that can be charged even at low voltage in solar power generation systems, etc., gasoline vehicles that can be charged and discharged at high speed The present invention relates to a power supply for an engine igniter, a device for storing regenerative braking energy in an electric vehicle, an electric-gasoline hybrid vehicle, and the like, and an electric double layer capacitor suitable for a power supply of a flashing indicator light embedded in a road which is difficult to replace.

[0002]

2. Description of the Related Art As is well known, an electric double layer capacitor is:
It is mainly composed of a pair of polarizable electrodes, current collecting electrodes of each polarizable electrode, and a porous separator interposed between the polarizable electrodes. Each polarizable electrode is impregnated with an electrolytic solution.

Conventionally, the polarizable electrode is usually made of activated carbon or fibrous activated carbon.
According to this, there is a disadvantage that the discharge capacity is small, so that it is impossible to maintain the discharge for a long time in actual use. Further, there is a disadvantage that a large current cannot be taken out due to a large internal resistance.

To solve this problem, Japanese Patent Laid-Open No. 6-104 discloses
No. 141 proposes a configuration in which a conductive polymer film produced by an electrolytic polymerization method is used as a polarizable electrode of an electric double layer capacitor. According to this, there is an advantage that the capacitance is larger and the internal resistance is smaller than when a conventional polarizable electrode is used, but this is not always satisfactory.

Japanese Patent Application Laid-Open No. 7-201676 proposes a configuration in which a conductive polymer film containing powdered or fibrous carbon produced by an electrolytic polymerization method is used as a polarizable electrode of an electric double layer capacitor. . According to this, the capacity is larger and the internal resistance is smaller than when only a conductive polymer film is used for the electrode, but the electrolytic polymerization method requires a conductor as the anode, so when the polarizable electrode is used as it is. However, there is a problem with the electrolyte resistance of the conductor, especially the stability with respect to the aqueous electrolyte. That is, gold, silver, platinum, stainless steel, titanium, tungsten and the like are stable with respect to the electrolytic solution but are expensive. Copper, nickel, tin and the like are inferior in electrolyte resistance. In addition, aluminum precedes or proceeds simultaneously with anodic oxidation, so that electrolytic polymerization hardly progresses and aluminum has poor electrolyte resistance. Further, the conductive polymer film can be used after being peeled off from the polymerized electrode, but it is difficult when the polymerized electrode is thin, and it becomes expensive when the polymerized electrode is thick.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric double-layer capacitor using a conductive polymer compound as a polarizable electrode, to achieve higher speed charging and discharging and a larger capacity.

[0007]

According to the present invention, there is provided an electric double layer capacitor comprising a pair of polarizable electrodes impregnated with an electrolytic solution and having a separator interposed therebetween, wherein at least one of the polarizable electrodes is provided. And a composite electrode having a conductive polymer compound obtained by a chemical oxidation polymerization method on a porous carbon-based material. The polarizable electrode used in the present invention is a conductive substance having a large surface area (for example, powdered or fibrous activated carbon), at least one of which is a porous carbon-based material and a conductive polymer obtained by chemical oxidation polymerization. A composite electrode comprising a compound. The porous carbon-based material used in the present invention is not particularly limited, and powdery,
Granular, fibrous, or compacted activated carbon is used. The conductive polymer compound obtained by the chemical oxidation polymerization used in the present invention is polypyrrole, polyaniline, polythiophene, polyfuran, polyselenophene, polyisothianaphthene, polyphenylene sulfide, polyphenylene oxide, polyazulene, or a derivative thereof, or These are copolymers.

According to a conductive polymer compound obtained by a chemical oxidation polymerization method on a porous carbon-based material, conductivity is improved, high-speed charge / discharge becomes possible, and capacity is increased.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A conductive polymer used in the present invention is prepared as follows. That is, a monomer and a dopant are dissolved in an organic solvent or water, and this solution is impregnated in a porous carbon-based material, and then immersed in an oxidizing agent solution to undergo chemical oxidative polymerization. Further, in a state where the porous carbon-based material is suspended in a solution of the monomer and the dopant, an oxidizing agent is added to perform polymerization. By this chemical oxidative polymerization, a conductive polymer compound is formed on the porous carbon-based material.

As the monomers used here, pyrrole,
Aniline, thiophene, furan, selenophene, isothianaphthene, phenylene sulfide, phenylene oxide, azulene, a derivative thereof, or a combination thereof (copolymer) can be used.
Among them, aniline and its derivatives are preferable from the viewpoint of high conductivity.

The dopant is added to impart conductivity to the conductive polymer, and is generally used as a sulfonate ion, a perchlorate ion, a hexafluorophosphate ion and a tetrafluorophosphate ion. Tetrafluoroborate ion,
Arsenic hexafluoride ion, hexafluoroantimonate ion, 4
Chloroaluminate ions, halogen ions, phosphate ions, sulfate ions, nitrate ions and the like can be used. In addition, polyvalent anions can also be used.

The porous carbon-based material used in the present invention comprises:
There is no particular limitation, and powdered, granular, fibrous, or shaped activated carbon is used, but those having a total acidic group content of 0.45 mmol / m ² or more based on the total surface area are preferred.
Here, the acidic group means a hydroxyl group or a carboxyl group on the surface of the carbon material. The total amount of the acidic groups is 0.45 mmol / m ² or more, preferably 0.5 to 4.0 mmo, based on the total surface area.
By using a l / m ² porous carbon-based material, the utilization factor of the surface area can be increased, and a large electric double layer capacity per unit surface area can be obtained.

The composite ratio of the conductive polymer and the porous carbon-based material in the conductive polymer composite electrode obtained in the present invention can take any value, but is preferably a conductive polymer / porous carbon-based material. Material = 5/95 to 50/50 (weight ratio), more preferably 10/90 to 25/75. If the amount of the conductive polymer is less than 5 wt%, a sufficient capacity increasing effect cannot be seen,
If the content exceeds wt%, it is not preferable because it is difficult to produce the composite by chemical oxidation polymerization.

As the bipolar electrodes forming a pair of the electric double layer capacitor, a conductive polymer composite electrode may be used, or only one of them may be used. In that case, the other polarizable electrode may use a conductive substance having a large surface area (for example, powdered or fibrous activated carbon). The porous carbon-based material used for producing the composite electrode can also be suitably used.

As the electrolytic solution to be impregnated into the polarizable electrode and the separator, a solution obtained by dissolving an electrolyte in water or an organic solvent (single or a mixture of carbonates, alcohols, nitriles, amides, ethers, etc.) can be used. .

The electrolyte includes one or more cations such as a proton, an alkali metal ion, a quaternary ammonium ion, and a quaternary phosphonium ion, a sulfonate ion, a perchlorate ion, an arsenic hexafluoride ion, a halogen ion, and a phosphorus ion. It is preferable to use an acid ion, a sulfate ion, or a nitrate ion alone or in combination of a plurality of anions.

The separator may be an insulating porous material that prevents electrical short circuit between the bipolar electrodes, is electrochemically stable, has high ion permeability, and has a certain mechanical strength. Specifically, a nonwoven fabric or a porous polypropylene film, polyethylene film, or the like can be used.

As a method for molding a polarizable electrode in the present invention, a generally known method can be applied. When the conductive polymer composite electrode is obtained in the form of a fibrous or molded body, it can be used as it is by punching it into an appropriate size. When the conductive polymer composite electrode is obtained in the form of powder or granules, the binder is added in an amount of 1 to several tens%, mixed well, and then placed in a mold and pressure-molded. It is also possible to apply heat during the pressing.

As the binder, polyvinylidene fluoride,
Fluoroolefin copolymer, carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol,
Either polyacrylic acid or polyimide is preferred.

Further, a conductive agent may be added at the time of molding the electrode to lower the resistance of the electrode. This is to reduce the internal resistance of the polarizable electrode to efficiently extract electric charges.

As the conductive agent, carbon black, natural graphite, artificial graphite, metal fiber, titanium oxide, ruthenium oxide and the like can be used. In particular, ketjen black or acetylene black, which is a kind of carbon black, is preferable because it has a large effect even in a small amount.

[0022]

FIG. 1 shows the configuration of an electric double layer capacitor according to an embodiment of the present invention. Reference numerals 1 and 2 denote a pair of polarizable electrodes as a positive electrode and a negative electrode, 3 a separator interposed between the two polarizable electrodes 1 and 4, 4 a carbon plastic film for current collection, and 5 an insulating resin.

At least one of the bipolar electrodes 1 and 2 is constituted by the conductive polymer composite electrode according to the present invention. When one is a conductive polymer composite electrode, the other may use a layer of activated carbon.

Next, the materials used in the examples are shown.

<Porous carbon-based material 1> Surface area is 1150
activated carbon fiber cloth with m ² / g and total amount of acidic groups of 1.5 mmol / m ²

<Porous carbon-based material 2> The surface area is 900 m
² / g, powdered activated carbon having a total acidic group content of 2.2 mmol / m ²

<Porous carbon-based material 3> Powdered activated carbon BP-20 manufactured by Kuraray Chemical Co., Ltd.

<Conductive Polymer Composite Electrode 1> A porous carbon-based material 1 was added to 100 ml of a 0.2 (mol / liter) sulfuric acid aqueous solution containing 0.2 (mol / liter) aniline.
(50 × 50 mm, 0.466 g) was immersed at room temperature for 30 minutes to impregnate the monomer solution with 1.295 g.
2 (mol / liter) aqueous solution of ammonium persulfate 50
Then, the substrate was immersed in -1 ml at -1 ° C for 3 hours to carry out chemical oxidation polymerization.
Removed from the oxidant solution, washed with water and dried.
% Weight gain was observed.

<Conductive Polymer Composite Electrode 2> A porous carbon-based material 1 (5) was added to 25 ml of a 0.4 (mol / liter) sulfuric acid aqueous solution containing 0.4 (mol / liter) aniline.
0x50 mm, 0.475 g) was immersed at room temperature for 30 minutes to impregnate 1.406 g of the monomer solution.
(Mole / liter) aqueous solution of ammonium persulfate 50m
1 for 3 hours at -1 ° C to perform chemical oxidative polymerization. Removed from oxidant solution, washed and dried, 23%
Was found to have increased in weight.

<Conductive Polymer Composite Electrode 3> To 100 ml of a 0.2 (mol / l) aqueous sulfuric acid solution containing 0.2 (mol / l) aniline, 5.0 g of the porous carbon-based material 2 was added. After cooling to 0 ° C., 4.564 g of ammonium persulfate was added, and a chemical oxidation polymerization was carried out for 1 hour. After taking out from the polymerization solution, washing with water and drying, a weight increase of 22% was recognized.

<Conductive Polymer Composite Electrode 4> To 100 ml of a 0.2 (mol / l) sulfuric acid aqueous solution containing 0.2 (mol / l) aniline, 5.0 g of the porous carbon-based material 3 was added. After cooling to 0 ° C., 4.564 g of ammonium persulfate was added, and a chemical oxidation polymerization was carried out for 1 hour. It was taken out from the polymerization solution, washed with water and dried, and a weight increase of 37% was recognized.

<Conductive Agent> Ketjen Black EC-DJ-600 manufactured by Lion Corporation

<Binder> Polyvinylidene fluoride manufactured by Polysciences (MW120,000)

(Example 1) The conductive polymer composite electrode 1 was
A 13 mm diameter circle was punched out, and this was used as a positive electrode. A porous carbon-based material 1 (13 mm in diameter) was used as a negative electrode, and a polypropylene porous film was used as a separator. Then, an electric double layer capacitor as shown in FIG. 1 was formed by using a 2 (mol / liter) aqueous sulfuric acid solution as an electrolytic solution. 15m per electrode material weight using this
A constant current charge / discharge was performed at a current density of A / g, a DC capacitance was determined from a discharge curve, and a capacitance per electrode material weight was calculated. The specific capacitance of the obtained capacitor was 66 F /
g.

Example 2 A conductive polymer composite electrode 1 was
An experiment was performed in the same manner as in Example 1 except that the capacitor was used for both positive and negative electrodes. The specific capacitance of the obtained capacitor is 76
F / g.

Example 3 The conductive polymer composite electrode 2 was
An experiment was performed in the same manner as in Example 1 except that the positive electrode of the capacitor was used. The specific capacitance of the obtained capacitor is 71 F /
g.

Example 4 The conductive polymer composite electrode 2 was
An experiment was performed in the same manner as in Example 1 except that the capacitor was used for both positive and negative electrodes. The specific capacitance of the obtained capacitor is 82
F / g.

Example 5 A conductive polymer composite electrode 3 was mixed with a conductive agent and a binder at a weight ratio of 8: 1: 1.
0 mg was placed in a mold having a diameter of 13 mm and compacted at about 10 MPa. This was used as a positive electrode, and a porous carbon-based material 2, a conductive agent, and a binder were similarly compacted as a negative electrode, and a polypropylene porous membrane was used as a separator. Then, an electric double layer capacitor as shown in FIG. 1 was formed by using a 2 (mol / liter) aqueous sulfuric acid solution as an electrolytic solution. 15m per electrode material weight using this
A constant current charge / discharge was performed at a current density of A / g, a DC capacitance was determined from a discharge curve, and a capacitance per electrode material weight was calculated. The specific capacitance of the obtained capacitor was 49 F / g.
g.

Example 6 An experiment was conducted in the same manner as in Example 5 except that the conductive polymer composite electrode 3 was mixed and compacted in the same manner as in Example 5 and used as both positive and negative electrodes of a capacitor. The specific capacitance of the obtained capacitor was 69 F / g.

Example 7 An experiment was conducted in the same manner as in Example 5 except that the conductive polymer composite electrode 4 was mixed and compacted in the same manner as in Example 5 and used as the positive electrode of a capacitor.
The specific capacitance of the obtained capacitor was 45 F / g.

Example 8 An experiment was conducted in the same manner as in Example 5, except that the conductive polymer composite electrode 4 was mixed and compacted in the same manner as in Example 5 and used as both positive and negative electrodes of a capacitor. The specific capacitance of the obtained capacitor was 54 F / g.

Comparative Example 1 An experiment was conducted in the same manner as in Example 3 except that the porous carbon-based material 1 was used for both positive and negative electrodes of a capacitor. The specific capacitance of the obtained capacitor is 56F /
g.

Comparative Example 2 An experiment was carried out in the same manner as in Example 5, except that a mixture of the porous carbon-based material 2, a conductive agent and a binder was used for both positive and negative electrodes of a capacitor. The specific capacitance of the obtained capacitor was 44 F / g.

Comparative Example 3 An experiment was conducted in the same manner as in Example 5, except that a mixture of the porous carbon-based material 3, a conductive agent and a binder was used for both positive and negative electrodes of a capacitor. The specific capacitance of the obtained capacitor was 35 F / g.

Table 1 summarizes the above results.

[Table 1]

[0046]

As described above, according to the present invention, a composite electrode having a conductive polymer compound obtained by a chemical oxidation polymerization method on a porous carbon-based material is used. An effect is obtained that a large-capacity capacitor can be obtained by a simpler operation than an electric double-layer capacitor using a composite electrode having a conductive polymer compound obtained by an electrolytic polymerization method.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Explanation of symbols]

 1-polarity electrode 2 2-polarity electrode 3 Separator 4 Carbon plastic film for current collection 5 Insulating resin

Claims (3)

[Claims] An impregnated electrolytic solution is provided in a pair of polarizable electrodes,
In an electric double layer capacitor configured with a separator interposed therebetween, at least one of the polarizable electrodes is constituted by a composite electrode composed of a porous carbon-based material and a conductive polymer compound obtained by a chemical oxidation polymerization method. Electric double layer capacitor. 2. The electric double layer capacitor according to claim 1, wherein the conductive polymer compound obtained by the chemical oxidation polymerization method is polyaniline or a derivative thereof. 3. The electric double layer capacitor according to claim 1, wherein the conductive polymer compound is polymerized on the porous carbon-based material to form a composite.