JP2002025868A - 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 with an active carbon material and through electrolytic polymerization.

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.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric double layer capacitor using a conductive polymer obtained by an electrolytic polymerization method as a polarizable electrode, to achieve a higher speed charge / discharge and a larger capacity. I do.

[0006]

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. , Characterized in that the conductive polymer is formed by compounding a conductive polymer on a powdered or fibrous activated carbon by an electrolytic polymerization method.

[0007] The use of a composite of a conductive polymer on a powdered or fibrous activated carbon by an electrolytic polymerization method improves conductivity, enables high-speed charge and discharge, and increases capacity.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive polymer used here is prepared as follows. That is, dissolve the monomer,
In addition, the monomer and the dopant are dissolved in an organic solvent or water that is stable without being oxidized even at the potential at which the electrolytic oxidation reaction of the monomer occurs, and the powdered activated carbon is suspended in the solution and electrolytically polymerized. In the case of fibrous activated carbon, it can be used as it is as a polymerization electrode (anode).

As the polymerization electrode used in the electrolytic polymerization, any conductor can be used as long as it is stable at the used potential. For example, metals such as gold, silver, copper, platinum, stainless steel, titanium, nickel, lead, tin, aluminum and tungsten, or alloys thereof, or graphite (polyacrylonitrile, pitch, phenol, etc.) can be used. Further, any object may be provided with conductivity by plating or the like.

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 also be used.

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 activated carbon to be suspended may be powdery or fibrous, but those which settle in the polymerization solution are not preferred. However, when the solution settles, the solution may be stirred to prevent the solution from settling.

[0013] The activated carbon material used in the present invention is not particularly limited, and powdered, granular, fibrous, or shaped activated carbon is used. m ² or more at which is preferable. Here, the acidic group means a hydroxyl group or a carboxyl group on the surface of the carbon material. This total amount of acidic groups is 0.4 to the total surface area.
5 mmol / m ² or more, preferably 0.5 to 4.0 mmol / m ²
By using this 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.

As described above, the conductive polymer composite formed on the surface of the polymerization electrode during electrolytic polymerization is used as a polarizable electrode, or the conductive polymer composite peeled from the polymerization electrode is used as a polarizable electrode. Use as As the bipolar electrodes forming a pair of the electric double layer capacitor, a conductive polymer composite may be used together, 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 composite ratio of the conductive polymer and the activated carbon material in the conductive polymer composite obtained in the present invention can take any value, but preferably, the ratio of the conductive polymer / activated carbon material = 5 /
95 to 90/10 (weight ratio), more preferably 10/9
0 to 70/30. If the amount of the conductive polymer is less than 5% by weight, no sufficient capacity increasing effect is obtained, and if the amount is more than 90% by weight, the internal resistance increases, which is not preferable.

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 of molding the 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, at the time of forming the electrode, a conductive agent may be added 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.

[0023]

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 made of the conductive polymer composite according to the present invention. If one is a conductive polymer composite, the other may utilize a layer of activated carbon.

Next, the materials used in the examples are shown.

<Activated carbon material 1> The surface area is 1150 m ² /
g, activated carbon fiber cloth having a total acidic group content of 1.5 mmol / m ²

<Activated carbon 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

<Conductive polymer composite 1> 0.5 (mol /
2.0 (mol / liter)
Activated carbon material 1 (30 × 30
mm, 0.162 g) and a carbon plastic sheet were heat-sealed, and immersed in the solution.
(mV vs SSCE) to form a composite of polyaniline (polymerization charge: 5 C / cm ² ). When the carbon plastic sheet was peeled off, washed with water and dried, a weight increase of 19% was observed.

<Conductive polymer composite 2> From a solution in which 3.0 g of activated carbon material 2 was added to 100 ml of a 50 (mmol / liter) sulfuric acid aqueous solution containing 25 (mmol / liter) aniline, potentiostatic electrolysis was performed. Polymerization method (800
(mV vs SSCE) to form a polyaniline film on the platinum electrode (polymerization charge: 60 coulombs / cm 2). Peel the polyaniline film from the platinum electrode,
Drying yielded 0.276 mg of the composite.
The composite contained 15% polyaniline as calculated from activated carbon material not incorporated into the membrane.

<Conductive polymer composite 3> From a solution obtained by adding 0.4 g of activated carbon material 2 to 50 ml of a 50 (mmol / liter) sulfuric acid aqueous solution containing 25 (mmol / liter) aniline, a potentiostatic electrolysis was performed. Polymerization method (800m
VvsSSCE) to form a polyaniline film on a platinum electrode (polymerization charge: 60 coulombs / cm 2). The polyaniline film was peeled off from the platinum electrode, washed with water and dried to obtain 0.266 mg of a composite. When calculated from the activated carbon material that was not incorporated into the membrane,
The composite contained 62% polyaniline.

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

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

Example 1 A conductive polymer composite 1 was punched into a circle having a diameter of 13 mm, and this was used as a positive electrode. Activated carbon material 1 (diameter 13 mm) was used as a negative electrode, and a polypropylene porous membrane was used as a separator. did. 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. When a constant current charge / discharge was performed at a current density of 15 mA / g per electrode material weight using this, a DC capacitance was obtained from a discharge curve, and a capacity per electrode material weight was calculated.
The specific capacitance of the obtained capacitor was 64 F / g.

Example 2 An experiment was performed in the same manner as in Example 1 except that the conductive polymer composite 1 was used for both positive and negative electrodes of a capacitor. The specific capacitance of the obtained capacitor is 75F
/ G.

Example 3 A conductive polymer composite 2 was mixed with a conductive agent and a binder at a weight ratio of 8: 1: 1.
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 the negative electrode was formed by similarly compacting activated carbon material 2, a conductive agent, and a binder, 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. Using this, constant current charge / discharge was performed at a current density of 15 mA / g per electrode material weight, a DC capacitance was obtained from a discharge curve, and a capacity per electrode material weight was calculated. The capacitance was 58 F / g.

Example 4 An experiment was carried out in the same manner as in Example 3 except that the conductive polymer composite 2 was mixed and compacted in the same manner as in Example 3 and used as both positive and negative electrodes of a capacitor. The specific capacitance of the obtained capacitor was 96 F / g.

Example 5 An experiment was conducted in the same manner as in Example 3 except that the conductive polymer composite 3 was mixed and compacted in the same manner as in Example 3 and used as the positive electrode of a capacitor. The specific capacitance of the obtained capacitor was 59 F / g.

Example 6 An experiment was conducted in the same manner as in Example 3 except that the conductive polymer composite 3 was mixed and compacted in the same manner as in Example 3 and used for both the positive and negative electrodes of the capacitor. The specific capacitance of the obtained capacitor was 96 F / g.

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

Comparative Example 2 An experiment was performed in the same manner as in Example 3 except that a mixture of the activated carbon material 2, a conductive agent and a binder was used for both the positive and negative electrodes of the capacitor. The specific capacitance of the obtained capacitor was 44 F / g.

Table 1 summarizes the above results.

[Table 1]

[0042]

As described above, according to the present invention, a composite of a conductive polymer prepared by an electrolytic polymerization method on activated carbon having an appropriate total amount of acidic groups is used as a polarizable electrode. Therefore, there is an effect that a larger capacity and higher speed charge / discharge can be achieved than the electric double layer capacitor proposed previously.

[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 formed of a composite of a conductive polymer by an electrolytic polymerization method on powdered or fibrous activated carbon. Electric double layer capacitor. 2. The powdered or fibrous activated carbon according to claim 1, wherein the total amount of acidic groups is 0.40 μmol / m 2 based on the total surface area.
An electric double layer capacitor having an average molecular weight of ² or more and 4.0 μmol / m ² or less. 3. The mixing ratio of conductive polymer and activated carbon is 5/9.
The electric double layer capacitor according to any one of claims 1 to 3, wherein the ratio is 5 or more and 90/10 (weight ratio) or less.