JP2000294462A - Electrode-forming agent for activated carbon electrode and activated carbon electrode obtained therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably soften activated carbon electrode layers and enhance their adhesion to collectors by composing a solvent with a mixture of a good solvent and a plasticizer of vinylidene fluoride polymer compounds. SOLUTION: An electrode-forming agent is composed of activated carbon, vinylidene fluoride polymer compounds and a solvent. Inherent viscosity of the vinylidene fluoride polymer compounds which serve as a binder is arranged at about 0.5-20.0 dl/g. The solvent is composed of a mixture of a good solvent and a plasticizer of vinylidene fluoride polymer compounds. The plasticizer has a average molecular weight of about 500 or more, and is composed of at least one kind of aliphatic polyesters. The electrode-forming agent 1a is coated on collectors 1b, and the solvent is selectively removed by vaporization to obtain polarizable electrodes 1. Then, a separator 2 is sandwiched between the two polarizable electrodes 1, which are sealed between a stainless-steel cap 3 and a stainless-steel can 4 containing the electrolyte solution 5 with a packing 6 to form an electric double-layer capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode mixture for forming an activated carbon electrode having excellent handleability, an activated carbon electrode obtained by using the mixture, and an electric electrode having the electrode with improved reliability. The present invention relates to a multilayer capacitor.

[0002]

2. Description of the Related Art With the recent development of electronic or electric equipment, there is a strong demand for development of various power supplies in addition to commercial power supplies with large wiring. In particular, the electric double layer capacitor has a large capacity and a long life, is capable of rapid filling, is easy to charge and discharge, has excellent cycle characteristics compared to the secondary battery, and has the most reliable Ni among the secondary batteries. Since it has the feature of being inexpensive as compared with -Cd batteries, functional applications are expected in many fields as new energy devices. Further, the application of the electric double-layer capacitor to a small electric power such as a backup power supply of an electronic device and a large electric power field such as an auxiliary power supply of an electric vehicle or a hybrid car is being studied. Along with this, there is a demand for higher performance such as a larger capacity of the polarizable electrode.

[0003] An electric double layer capacitor is a capacitor that utilizes capacitance accumulated in an electric double layer generated at an interface between a polarizable electrode and an electrolyte. The electric double layer capacitor is roughly classified into an organic solvent type and an aqueous solution type depending on the electrolytic solution to be used. The organic solvent type is advantageous as a high capacity capacitor because the withstand voltage is high and the capacity can be increased. The polarizable electrode is required to have a large specific surface area and bulk density, be electrochemically inert, and have a low electric resistance. The polarizable electrode structure for an electric double layer capacitor is composed of a powdered activated carbon material, a conductive material for providing electric conductivity, a binder as a binder, and a metal current collector. As a method of manufacturing the electrode structure, a method of adding a solvent to a mixture of a powdered activated carbon material, a conductive material, and a binder to form a mixed slurry, coating or dipping the current collector on a collector, and then drying the mixed slurry (for example,
JP-A-10-64765), powdered activated carbon material,
A solvent is added to a mixture of a conductive material and a binder that is insoluble in a solvent, and the mixture is kneaded, molded, dried, and then pressed and heat-treated and dried. (For example, see Japanese Unexamined Patent Publication No. 9-2
75041), and considering the cost of the manufacturing process, the former manufacturing method is particularly preferable.

Polyvinylidene fluoride has attracted attention as a binder in terms of electrochemical stability and the like.
No. 5761 discloses a fluorine-containing polymer such as polyvinylidene fluoride and N-methyl 2-pyrrolidone, toluene,
A slurry comprising an organic solvent such as ethyl acetate, dimethyl phthalate, etc., activated carbon powder, and a conductivity imparting agent is coated on the current collector, and then dried to remove the organic solvent to form a polarizable electrode. There is disclosed a method for manufacturing an electric double layer capacitor having the steps of: A similar technique is also disclosed in JP-A-8-213289.

However, in the activated carbon electrode obtained by the above method, the activated carbon electrode layer obtained by coating is easily peeled off from the current collector, and the flexibility is poor, so that the handling property of the entire activated carbon electrode is poor. However, there is a drawback that it lacks reliability. Japanese Patent Application Laid-Open No. H10-64517 discloses the use of a vinylidene fluoride rubber for the purpose of improving the above disadvantages. However, vinylidene fluoride rubber has a drawback that the electric double layer capacitor obtained by detachment of the electrode layer during use of the capacitor tends to be swelled easily by the organic solvent-based electrolyte and has low reliability.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an activated carbon electrode which has an activated carbon electrode layer which has good adhesion to a current collector and has improved flexibility and which has excellent handleability. The main object is to provide a highly reliable electric double layer capacitor by using a mixture, an activated carbon electrode (polarizable electrode) obtained therefrom, and the activated carbon electrode.

[0007]

According to the study of the present inventors, in order to achieve the above object, an electrode mixture used for forming an activated carbon electrode layer by coating on a current collector is provided. It has been found that it is extremely effective to include a plasticizer for the vinylidene fluoride polymer in addition to the good solvent for the ordinary vinylidene fluoride polymer.

That is, according to the present invention, there is provided an electrode mixture comprising activated carbon, a vinylidene fluoride polymer having an inherent viscosity of 0.5 to 20.0 dl / g, and a solvent,
An electrode mixture, wherein the solvent comprises a mixture of a good solvent of a vinylidene fluoride polymer and a plasticizer, and the electrode mixture is coated on a current collector to form an electrode mixture layer. A polarizable electrode having an activated carbon electrode layer obtained by selectively removing a solvent from the electrode mixture is provided. Preferably, the activated carbon electrode layer extracts a plasticizer by contacting the electrode mixture layer with a poor solvent of a vinylidene fluoride polymer after volatilizing and removing at least a part of the solvent from the electrode mixture layer as necessary. And by further evaporating the poor solvent.
By extracting and removing the plasticizer with the poor solvent in this way, the vinylidene fluoride-based polymer as the binder in the activated carbon electrode layer becomes porous, which significantly remarkably softens the above-mentioned activated carbon electrode layer and makes it a current collector. It is understood that this contributes to the improvement of the adhesion.

Further, according to the present invention, there is provided an electric double layer capacitor in which an electrolyte is held between a pair of polarizable electrodes, at least one of which is the above-mentioned polarizable electrode.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The vinylidene fluoride polymer constituting the electrode mixture of the present invention and functioning as a binder in the obtained activated carbon electrode layer is a homopolymer of vinylidene fluoride or vinylidene fluoride 50. A copolymer of not less than 50% by weight and not more than 50% by weight of a copolymerizable monomer is appropriately selected and used.

The monomer copolymerizable with the vinylidene fluoride monomer includes, for example, hydrocarbon monomers such as ethylene and propylene, vinyl fluoride, ethylene trifluoride, ethylene trifluoride chloride, Fluorinated monomers such as fluorinated ethylene, hexafluoropropylene, and fluoroalkyl vinyl ethers; carboxyl group-containing monomers such as monomethyl maleate and monomethyl citrate; or allyl glycidyl ether and glycidyl crotonate; Examples include, but are not necessarily limited to, epoxy group-containing vinyl monomers. Among them, vinylidene fluoride copolymers containing propylene hexafluoride and ethylene trifluoride chloride are preferably used.

The vinylidene fluoride polymer as a binder has an inherent viscosity of 0.5 to 20.0 dl /
g, especially 0.5 dl / g to 5.0 dl / g, from the viewpoint of electrode adhesion, mechanical strength and the like. Here, the inherent viscosity is used as a measure of the molecular weight of the polymer.
It refers to the logarithmic viscosity at 30 ° C. of a solution dissolved in N-dimethylformamide.

As described above, the solvent constituting the electrode mixture of the present invention together with the vinylidene fluoride polymer is a mixture of a good solvent for the vinylidene fluoride polymer and a plasticizer. These need not be mixed prior to the formation of the electrode mixture, but may be mixed in the electrode mixture before the coating step for forming the electrode.

Here, a good solvent for the vinylidene fluoride polymer is defined as a binder solution having a concentration of 1% by weight or more, preferably 5% by weight or more of the vinylidene fluoride polymer at room temperature (25 ° C.). An organic solvent having a dissolving ability that can be formed, and a preferable example thereof is N-methyl-2-
Examples include pyrrolidone, dimethylformamide, N, N-dimethylacetamide, N, N-dimethylsulfoxide, hexamethylphosphoramide, acetone, 1,4-dioxane, tetrahydrofuran, methyl acetate, tetramethylurea, and triethyl phosphate. These good solvents can be used alone or in combination of two or more.

The plasticizer has a poor ability to dissolve a vinylidene fluoride-based polymer by itself, but has an action of plasticizing it. The weight average molecular weight (in the present specification, “molecular weight” means polystyrene equivalent molecular weight by GPC (gel permeation chromatography)) is preferably 500 or more and 10,000 or less, more preferably 800 or more and 3000 or less. When the weight average molecular weight is 500 or less, the amount of bleed from the vinylidene fluoride-based polymer as the binder increases, and thus the resin is easily peeled off during drying after coating the electrode mixture. On the other hand, if the weight average molecular weight is 10,000 or more, the viscosity of the electrode mixture becomes high, so that workability is remarkably reduced, which is not preferable. Specific examples include, for example, adipic acid-based polyesters such as adipic acid-propylene glycol system and adipic acid-1,3-butylene glycol system, and sebacic acid such as sebacic acid-propylene glycol system and sebacic acid-3-butylene glycol system. Aliphatic polyester plasticizers comprising an aliphatic dibasic acid and glycol, such as polyesters, azelaic acid-propylene glycols, and azelaic acid-based polyesters such as azelaic acid-1,3-butylene glycol, and the like. . Of the above, adipic acid-based polyester is particularly preferred because of appropriate compatibility with the vinylidene fluoride-based polymer. The amount of the plasticizer can be appropriately selected. Usually, the solvent is used within a range that does not lower the solubility of the vinylidene fluoride polymer as a whole. Preferably, it is 3 to 50% by weight, more preferably 10 to 40% by weight in the solvent. If the content is less than 3% by weight, the effect of adding the plasticizer is so small that the electrode may peel off. If the content is 50% by weight or more, the solubility of the vinylidene fluoride-based polymer as a whole solvent decreases, and the electrode mixture for coating is gelled, which is not preferable.

The solvent comprising the combination of the plasticizer and the good solvent generally has a solid content concentration of a combination of a vinylidene fluoride polymer, activated carbon, and other solid components added as necessary. Generally, it is preferably used in an amount capable of forming a solution or slurry of about 0.5 to 50% by weight, more preferably about 15 to 35% by weight.

[0017] Activated carbon the specific surface area constituting the electrode mixture of the present invention together with the vinylidene fluoride polymer and a solvent is 500~3000m ² / g, especially 800～2500M ²
/ G can be suitably used, and specific examples include:
Examples of the activated carbon include coconut-based activated carbon, phenol-based activated carbon, petroleum / coal coke-based activated carbon, petroleum / coal pitch-based activated carbon, polyvinylidene chloride-based activated carbon, polyacene-based activated carbon, phenolic resin-based activated carbon, and polyacrylonitrile-based activated carbon.

The electrode mixture of the present invention comprises at least the above-mentioned vinylidene fluoride polymer, a solvent and activated carbon. Usually, a conductive material is further added to impart electrical conductivity. Specific examples of the conductive material include carbon black, natural graphite, artificial graphite, metal oxides such as titanium oxide and ruthenium oxide, and metal fibers. Can be used. Among them, Ketjen black, acetylene black or furnace black, which is a kind of carbon black, is preferably used. The amount of the conductive material to be added can be selected according to the required degree of conductivity.
Generally, the total amount of the activated carbon and the conductive material is 5 to 99 parts by weight, especially 9 to 5 parts by weight per 1 part by weight of the vinylidene fluoride polymer.
It is preferable to use it in such a ratio that it becomes 0 parts by weight.

The electrode mixture of the present invention can be obtained as a slurry by mixing the above-mentioned components of the electrode mixture in an arbitrary order and heating if necessary.
The prepared mixture slurry has good coatability on the current collector.

The polarizable electrode of the present invention can be obtained by applying the above-described electrode mixture of the present invention on a current collector and selectively removing the solvent by, for example, volatilization. Specific examples of the current collector used include aluminum,
Examples include metal foils such as stainless steel, titanium, and tantalum.

The coating method may be a known method, and among them, the doctor blade method is preferably used. The current collector to which the mixture has been applied is dried at 50 to 200 ° C. and, if necessary, subjected to a pressing step to provide a polarizable electrode structure for an electric double layer capacitor.

The polarizable electrode of the present invention is used to make the performance of the obtained electric double layer capacitor more preferable.
It is preferable that the electrode mixture layer from which a part of the solvent has been volatilized and removed has been subjected to a plasticizer extraction and removal treatment with a poor solvent for the vinylidene fluoride-based polymer, if necessary. This is because the performance of the electric double layer capacitor may be reduced depending on the type of the plasticizer. This extraction is performed by removing the good solvent (and the poor solvent) remaining in the activated carbon electrode layer of the polarizable electrode.
Also, there is an effect of reducing the entire amount of the solvent containing. The organic solvent used for the extraction is a poor solvent for the vinylidene fluoride polymer (the solubility is preferably 0.5% by weight or less, more preferably 0.1% by weight or less.
1% by weight or less), and those having compatibility with the plasticizer are preferably used. Those having a boiling point of 100 ° C. or less are more preferable in order to facilitate removal by volatilization. For example, alcohols such as methyl alcohol and isopropyl alcohol, chlorinated hydrocarbons include methylene chloride,
Solvents such as 1,1,1-trichloroethane can be exemplified, and among them, methylene chloride, which is nonflammable and easy to dry, is particularly preferable. When a good solvent of the vinylidene fluoride polymer is used as the extraction solvent, the vinylidene fluoride polymer as a binder flows out of the activated carbon electrode layer during the extraction,
It is not preferable because the function as a binder is lost.

The extraction of the plasticizer is carried out by using an organic solvent which is a poor solvent for the vinylidene fluoride polymer as an extraction solvent.
Although the electrode structure after drying is immersed and left alone in the solvent in an extraction vessel at 00 ° C., preferably 10 to 50 ° C., the extraction effect can be obtained. The extraction effect can be enhanced by adding vibrations such as sound waves. The electrode structure after extraction is 40 to 17 for drying.
Heat treated at 0 ° C. to serve as an activated carbon electrode.

The electric double layer capacitor of the present invention includes:
One having the structure shown in FIG. 1 can be exemplified. That is, FIG. 1 is a cross-sectional view of an example of a single-cell electric double layer capacitor. In this electric double layer capacitor, a separator 2 is sandwiched between two polarizable electrodes 1 and 1 having an activated carbon electrode layer 1a and a current collector 1b, respectively, and a stainless steel cap 3 and a stainless steel It is sealed with a can 4 through a packing 6. As a result, the electrolyte 5 is impregnated in the separator 2 and is disposed between the pair of polarizations 1 and 1. The separator 2 is appropriately formed of a porous or fibrous material, and examples thereof include a nonwoven fabric made of glass fiber, paper, and a porous film made of synthetic resin. Propylene carbonate is generally used as a solvent for the electrolytic solution, and quaternary phosphonium salts and quaternary ammonium salts are generally used as the electrolyte. For example, (C ₂ H ₅ ) ₄ NB
An organic electrolyte such as a propylene carbonate solution of F ₄ can be used. The concentration of the electrolyte in the electrolyte is 5
95% by weight, or 0.1 to 4.0 mol / l, preferably 0.5 to 2.0 mol / l.

[0025]

EXAMPLES The present invention will be described more specifically based on examples and comparative examples.

(Example 1) 90 parts by weight of petroleum pitch-based activated carbon powder (specific surface area: 1200 m ² / g) and carbon black (“DENKA BLACK” manufactured by Denki Kagaku Kogyo KK)
2 parts by weight of polyvinylidene fluoride (“KF # 1700” manufactured by Kureha Chemical Industry Co., Ltd., inherent viscosity 1.7 d)
1 / g) in N-methyl-2-pyrrolidone (10%), 80 parts by weight, a further 114 parts by weight of N-methyl-2-pyrrolidone and an adipic acid-based polyester plasticizer ("ADEKA" manufactured by Asahi Denka Kogyo KK) 47 parts by weight of Sizer PN150 ”and a weight average molecular weight of 2320 were added and mixed at 30 ° C. to obtain an electrode mixture slurry.

This electrode mixture is applied to one side of an aluminum foil having a thickness of about 20 μm by a doctor blade method, and dried by heating (130 ° C., 30 minutes) to obtain a sheet having a coated electrode layer having a thickness of 250 μm. An electrode material was obtained. This sheet includes
No significant curl was observed. This sheet electrode was immersed in methylene chloride at 25 ° C. for 30 minutes to perform an extraction treatment, and further dried by heating at 130 ° C. for 10 minutes. The extracted and dried sheet-shaped electrode is partially used for a flexibility test,
In addition, after punching out 10 pieces into a 17 mm diameter circle and pressing (102 MPa, 1 minute), it was punched out into a 15 mm diameter circle to obtain 10 polarizable electrodes. During the punching operation and the pressing operation, no peeling of the electrode was observed. As shown in FIG. 1, these two electrodes were used as a polarizable electrode 1 and a glass fiber nonwoven fabric separator 2 was coated with a coated electrode 1.
It was housed in a container consisting of a stainless steel cap 3 and a stainless steel can 4 so as to be sandwiched by the a side and to be in contact with the Al foil current collector 1b side. Next, a predetermined electrolytic solution 5 ((C ₂ H ₅ ) ₄ NBF ₄ in propylene carbonate solution: 1 mol / l) is put into a stainless steel container, and sufficiently impregnated into the coating electrode layer 1 a and the separator 2. The ends of the cap 3 and the can 4 were caulked and integrated via the packing 6 made from the resin.

The electric double layer capacitor thus manufactured
The current density was 1.6 mA / cm. ^TwoUp to 2.5V
And maintain the charged state for 3 hours.
Discharge to V and calculate the amount of energy.
The energy capacity was evaluated. The capacity depends on the activated carbon in the electrode.
Calculated as energy capacity per unit weight (mWh / g)
Issued. The electrodes after the above test were taken out and visually observed,
No shape change was observed.

As a curl test of the sheet-like electrode,
The sheet electrode before extraction dried after coating is cut out to a length of 200 mm (width: aluminum foil 200 mm, coating part 110
mm), stand on a flat aluminum plate with the coated side down,
The distance from the aluminum plate to the surface of the coated portion at the most raised portion was measured. The result of the measurement was 2 mm, and almost no curl was observed.

Further, as a flexibility test, the sheet-like electrode after extraction and drying was cut into a length of 300 mm (width:
Aluminum foil 200mm, coating part 110mm), 30mmφ
The sheet-like electrode was held on the metal roll so that the aluminum foil was on the roll side, and the coated portion of 20 cm was slid back and forth four times to evaluate the degree of peeling. As a result, the flexibility of the coated portion was good, and no peeling of the electrode layer was observed.

The results are shown in Table 1 below together with those of the following Examples and Comparative Examples.

Example 2 90 parts by weight of petroleum pitch-based activated carbon powder (specific surface area: 1200 m ² / g) and carbon black (“DENKA BLACK” manufactured by Denki Kagaku Kogyo KK)
To 2 parts by weight, 160 parts by weight of a solution obtained by dissolving 5% of polyvinylidene fluoride (manufactured by Kureha Chemical Industry Co., Ltd., inherent viscosity: 8.8 dl / g) in N-methyl-2-pyrrolidone, and further N-methyl-2- 34 parts by weight of pyrrolidone and an adipic acid-based polyester plasticizer ("Adekaizer PN150" manufactured by Asahi Denka Kogyo KK, weight average molecular weight 232)
0) 47 parts by weight were added and mixed at 30 ° C. to obtain an electrode mixture slurry.

This electrode mixture was applied on one side of the same aluminum foil as used in Example 1 by a doctor blade method,
By heating and drying (130 ° C., 30 minutes), a sheet-like electrode material having a 250 μm-thick coated electrode layer was obtained. This sheet did not show any noticeable curl. This sheet electrode was immersed in methylene chloride at 25 ° C. for 30 minutes to perform an extraction treatment, and further dried by heating at 130 ° C. for 10 minutes. After extracting and drying, a part of the sheet-shaped electrode was used for a flexibility test. In addition, 10 sheets were punched out into a circle having a diameter of 17 mm, pressed (102 MPa, 1 minute), and then punched out into a circle having a diameter of 15 mm. Was obtained. During the punching operation and the pressing operation, no peeling of the electrode was observed. Using the obtained polarizable electrode, an electric double layer capacitor manufactured in the same manner as in Example 1 was evaluated in the same manner as in Example 1. The electrode after the test was taken out and observed visually, but no change in shape was observed.

When a curl test was conducted in the same manner as in Example 1, the height of the lower coating surface rising from the aluminum plate was 1 mm at the maximum, and almost no curl was observed. When the same flexibility test as in Example 1 was performed, the flexibility of the coated portion was good and the electrode layer did not peel at all.

Comparative Example 1 90 parts by weight of petroleum pitch-based activated carbon powder (specific surface area: 1200 m ² / g) and carbon black (“DENKA BLACK” manufactured by Denki Kagaku Kogyo KK)
80 parts by weight of a solution obtained by dissolving 10% of polyvinylidene fluoride ("KF # 1700" manufactured by Kureha Chemical Industry Co., Ltd.) in N-methyl-2-pyrrolidone was added to 2 parts by weight, and 161 parts by weight of N-methyl-2-pyrrolidone was further added. And mixed at 30 ° C. to obtain an electrode mixture slurry.

This electrode mixture was applied on one side of the same aluminum foil as used in Example 1 by a doctor blade method,
By heating and drying (130 ° C., 30 minutes), a sheet-like electrode material having a 250 μm-thick coated electrode was obtained. This sheet was greatly curled toward the coating side. This sheet electrode was immersed in methylene chloride at 25 ° C. for 30 minutes to perform an extraction treatment, and further dried by heating at 130 ° C. for 10 minutes. In the sheet-like electrode after the extraction treatment, the coating electrode layer edge part was partially peeled off. The extracted and dried sheet-shaped electrode was partially used for a flexibility test, and was punched into 10 circular pieces having a diameter of 17 mm and pressed (102 MPa, 1 minute).
The sheet was punched out into a circular shape of 10 mm to obtain 10 polarizable electrodes. During the punching operation and the pressing operation, edge peeling of the coated electrode layers of eight of ten electrodes occurred. An electric double layer capacitor produced in the same manner as in Example 1 except that the two electrodes without peeling were used as the polarizable electrode 1 was evaluated in the same manner as in Example 1. The electrode after the test was taken out and visually observed, but partial peeling was observed at the end of the coated electrode layer.

When a curl test was conducted in the same manner as in Example 1, the height of the lower coating surface rising from the aluminum plate was 25 mm at the maximum, and it was recognized that the curl was remarkable. Further, when the same flexibility test as in Example 1 was performed, the flexibility of the coated portion was poor.
Cracking and peeling occurred in the area of

[0038]

[Table 1]

[0039]

As described above, according to the present invention, an activated carbon electrode comprising a mixture of activated carbon, a vinylidene fluoride polymer, and a solvent containing a plasticizer in addition to a good solvent for the vinylidene fluoride polymer. An electrode mixture for forming is provided. After applying this electrode mixture on the current collector, preferably by performing a plasticizer extraction treatment with a poor solvent of the vinylidene fluoride polymer and a selective removal treatment of the solvent including the volatilization of the solvent, the current collector A polarizable electrode having an activated carbon electrode layer with good adhesion and flexibility and good handleability is obtained, and by using this, an electric double layer capacitor with improved reliability is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a structure of an example of an electric double layer capacitor of the present invention.

[Explanation of symbols]

 1 Polarized electrode (1a: activated carbon electrode layer, 1b: current collector) 2 Separator 3 Cap 4 Can 5 Electrolyte 6 Packing

Claims (6)

[Claims] Activated carbon having an inherent viscosity of 0.5 to 2
An electrode mixture comprising 0.0dl / g of a vinylidene fluoride polymer and a solvent, wherein the solvent comprises a mixture of a good solvent for the vinylidene fluoride polymer and a plasticizer. Agent. 2. The electrode mixture according to claim 1, wherein the weight average molecular weight of the plasticizer is 500 or more. 3. The electrode mixture according to claim 1, wherein the plasticizer comprises at least one aliphatic polyester. 4. An electrode mixture layer is formed by applying the electrode mixture according to claim 1 on a current collector, and a solvent is selectively removed from the electrode mixture layer. An activated carbon electrode structure, comprising: an activated carbon electrode layer. 5. A plasticizer is extracted by volatilizing and removing a part of the solvent from the electrode mixture layer, if necessary, by contacting the electrode mixture layer with a poor solvent of a vinylidene fluoride polymer. The activated carbon electrode structure according to claim 4, comprising an activated carbon electrode layer obtained by selectively removing the solvent from the electrode mixture layer by volatilizing the solvent. 6. An electric double layer capacitor comprising at least one of the activated carbon electrode structures according to claim 4 and 5, wherein an electrolyte is held between a pair of polarizable electrodes.