JP2002222741A - Method of manufacturing polarizable electrode for electric double layer capacitor and electric double layer capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which a polarizable electrode for electric double layer capacitor which is excellent in current collecting efficiency and electrostatic capacity can be manufactured by reducing the ESR characteristic of the electrode by improving the dispersibility of active carbon powder, and to provide an electric double layer capacitor using the electrode. SOLUTION: The method of manufacturing the polarizable electrode 3 is composed of a step of kneading the active carbon powder with a conductivity imparting agent having a smaller particle diameter than the carbon powder has by adding a small quantity of water-soluble binder solution containing a dissolved or scattered resin, a step of obtaining paste by further kneading the kneaded product to a prescribed viscosity by adding a dispersing solvent little by little, and a step of removing the dispersing solvent by applying the paste to charge collecting metal foil 1. Since the compressive force and shear force of the polarizable electrode 3 can be improved by improving the dispersibility of the active carbon powder and conductivity imparting agent, the ESR characteristic of the electrode 3 can be lowered and the electrostatic capacity of the electrode 3 can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polarizable electrode for an electric double layer capacitor used for an electric double layer capacitor, and an electric double layer capacitor using the polarizable electrode.

[0002]

2. Description of the Related Art Electric double layer capacitors are used as backup power sources for microcomputers, memory devices, timers and the like.

The structure of this type of electric double layer capacitor is as follows.
As shown in FIG. 3, external lead wires 34 and 35 are attached to an aluminum foil 31 having a thickness of 20 to 50 μm, and the surface of the aluminum foil 31 is made of a mixed powder obtained by mixing activated carbon powder with a desired binder and conductive agent. A conductive layer (not shown) is formed by applying a paste, and an activated carbon layer containing activated carbon as a main component is formed thereon. A polarizable electrode having an activated carbon layer formed on this aluminum foil 31 3
2 is wound so as to face each other with a separator 33 interposed therebetween, thereby forming a capacitor element 36. The capacitor element 36 is immersed in an electrolytic solution and the polarizable electrode 32 and the separator 33 are immersed in the electrolytic solution ( (Not shown), and inserted into an aluminum case 38, and the opening of the aluminum case 38 is sealed using a packing 37.

The method of manufacturing the polarizable electrode 32 is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-67610, in which activated carbon powder, carbon black, and a small amount of binder are kneaded in a dry system to form a binder and activated carbon powder. It is described that the binding force becomes strong, so that even if the polarizable electrode is formed into a roll, defects due to compressive force and shear force are unlikely to occur.

[0005]

However, in the above-mentioned conventional method for manufacturing the polarizable electrode 32, the dispersed state of the activated carbon powder, the binder and the conductive agent is problematic, and the activated carbon powder is simply mixed with the binder and the conductive agent. However, there is a problem that the resistance of the polarizable electrode alone (hereinafter, referred to as ESR) increases.

In the technique described in the above-mentioned Japanese Patent Application Laid-Open No. 4-67610, activated carbon powder, carbon black,
If a small amount of binder is kneaded dry, the formability can be improved by improving the compressive force and shear force, but the electrostatic capacity and ESR characteristics of the polarizable electrode cannot be improved depending on the kneading conditions. However, there is a problem that it is difficult to optimize the kneading conditions.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. An object of the present invention is to improve the dispersibility of activated carbon powder, reduce the ESR characteristics of a polarizable electrode, and provide an electric double layer capacitor excellent in current collection efficiency and capacitance. It is an object of the present invention to provide a method for manufacturing a polar electrode and an electric double layer capacitor using the polarizable electrode.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention provides an activated carbon powder, a conductivity-imparting agent having a particle size smaller than the activated carbon powder, and a resin. Or a step of kneading a small amount of a dispersed water-soluble binder solution, a step of gradually adding a dispersion solvent to the kneaded product and kneading to a predetermined viscosity to form a paste, and applying the paste to a current collector metal foil And removing the dispersing solvent by performing the method described above. Since the dispersibility of the activated carbon powder and the conductivity-imparting agent can be increased to improve the compressive force and the shear force, the ESR characteristics and the capacitance can be improved. This has the effect that a polarizable electrode having excellent characteristics can be obtained.

The invention according to claim 2 is characterized in that the activated carbon powder comprises:
A step of kneading a conductivity-imparting agent having a particle size smaller than that of the activated carbon powder and a small amount of a water-soluble binder solution in which the resin is dissolved or dispersed, and further adding a dispersion solvent little by little to the kneaded product to a predetermined viscosity. It is a manufacturing method consisting of a step of kneading into a paste and a step of shaping the paste to remove a dispersing solvent, increasing the dispersibility of the activated carbon powder and the conductivity-imparting agent to increase the compressive force and the shearing force. Since it can be improved, it has an effect that a molded article of a polarizable electrode having excellent ESR characteristics and capacitance can be obtained.

A third aspect of the present invention is the method according to the first or second aspect, wherein the average particle size of the conductivity-imparting agent is 1/10 or less of the average particle size of the activated carbon powder. Thus, the dispersibility of the activated carbon powder and the conductivity-imparting agent can be increased to improve the density of the polarizable electrode.

According to a fourth aspect of the present invention, in the first or second aspect, the activated carbon powder is made of petroleum coke-based activated carbon, and its surface functional group content is 0.1 to 1.0 meq.
/ G of the production method, the use of petroleum coke-based activated carbon makes it easier to regulate the amount of surface functional groups, and reduces the DC leakage current of the electric double layer capacitor obtained from the regulated polarizable electrode. This has the effect of lowering the temperature and suppressing self-discharge.

When the surface functional group content of the petroleum coke-based activated carbon is less than 0.1 meq / g, the wettability with the dispersing solvent is deteriorated, and the dispersibility cannot be increased.
If it exceeds 1.0 meq / g, the DC leakage current increases,
It is not preferable because self-discharge cannot be suppressed.

[0013] The invention according to claim 5 is to knead an activated carbon powder, a conductivity imparting agent having a particle size smaller than the activated carbon powder, and a small amount of a water-soluble binder solution in which a resin is dissolved or dispersed. A paste obtained by adding a dispersion solution little by little and kneading to a predetermined viscosity is applied to a current collecting metal foil, and a dispersing solvent is removed. This is an electric double layer capacitor in which an electrolyte impregnated is sealed in an aluminum case, and can have excellent ESR characteristics and capacitance.

According to a sixth aspect of the present invention, an activated carbon powder, a conductivity-imparting agent having a particle size smaller than the activated carbon powder, and a small amount of a water-soluble binder solution obtained by dissolving or dispersing a resin are kneaded and dispersed in the kneaded product. An electric double layer capacitor in which a polarizable electrode formed by forming a paste kneaded to a predetermined viscosity by adding a solvent little by little and removing the dispersing solvent, together with an electrolytic solution through a separator in a lower bottom portion and an upper lid portion, is formed. Yes, it can be excellent in ESR characteristics and capacitance.

[0015]

(Embodiment 1) FIG. 1 (a),
2B is a schematic partial cutaway perspective view of the wound electric double layer capacitor according to the first embodiment of the present invention, and an enlarged sectional view of a main part of a polarizable electrode. FIG. In the figure, reference numeral 3 denotes a pair of polarizable electrodes having an activated carbon layer 2 formed on the surface of a current collecting metal foil 1. Reference numerals 5 and 6 denote external lead wires attached to the current collecting metal foil 1, and the pair of polarizable electrodes 3.
Is wound so as to face each other with the separator 4 interposed therebetween to obtain the capacitor element 7.

After the capacitor element 7 is impregnated with an electrolytic solution (not shown), a cylindrical aluminum case 9 having a bottom is formed.
The opening of the aluminum case 9 is sealed with a sealing material 8 provided with a hole through which the external lead wires 5 and 6 pass.

As the current collecting metal foil 1 used for the polarizable electrode 3, a valve metal such as tantalum, aluminum, or titanium can be used. Further, an alloy which contains these elements and produces a valve action, for example, an aluminum-based alloy containing titanium can also be used. Most preferred is aluminum, especially high purity aluminum.

The current collecting metal foil 1 is formed into a sheet having a desired thickness. The thickness of the sheet is in the range of 10 μm to 100 μm.
箔 60 μm foil is good.

The surface of the current collecting metal foil 1 may be roughened by etching or the like. For example, an etching method is a method of chemically and / or electrically etching in an acidic solution.

By roughening the surface of the current collecting metal foil 1, the contact area with the activated carbon layer increases, and the ESR characteristics can be further reduced.

Next, the activated carbon layer 2 comprises activated carbon powder,
A step of kneading a conductivity-imparting agent having a particle size smaller than that of the activated carbon powder and a small amount of a water-soluble binder solution in which a resin is dissolved or dispersed, and further adding a dispersion solvent little by little to the kneaded product to a predetermined viscosity. It is obtained by manufacturing from a step of kneading into a paste and a step of applying the paste to a current collector metal foil to remove a dispersion solvent.

[0022] This makes it possible to enhance the dispersibility of the activated carbon powder and the conductivity-imparting agent to improve the compressive force and the shear force, thereby obtaining a polarizable electrode having excellent ESR characteristics and electrostatic capacity. .

By setting the average particle size of the above-mentioned conductivity-imparting agent to 1/10 or less of the average particle size of the activated carbon powder, the dispersibility of the activated carbon powder and the conductivity-imparting agent is increased, and the density of the polarizable electrode 3 is improved. Can be done.

When the activated carbon powder is made of petroleum coke-based activated carbon and its surface functional group content is in the range of 0.1 to 1.0 meq / g, the direct current of the electric double layer capacitor obtained from the polarizable electrode 3 is reduced. Leakage current can be reduced and self-discharge can be suppressed.

Hereinafter, a specific example of the first embodiment will be described.

(Example 1) 30 μm thick as current collecting metal foil
m high-purity aluminum foil (Al: 99.99% or more)
Was used and electrolytic etching was performed in a hydrochloric acid-based etching solution to roughen the surface of the aluminum foil.

Next, an activated carbon layer was formed on the surface of the aluminum foil. The formation of this activated carbon layer is based on an average particle size of 5
μm petroleum coke-based activated carbon powder (surface functional group content: 0.
5meq / g) and an average particle diameter of 0.05 as a conductivity-imparting agent.
After mixing a water-soluble binder solution (CMC concentration: 50%) in which μm of carbon black and carboxymethyl cellulose (hereinafter abbreviated as CMC) are dissolved in a weight ratio of 10: 2: 1 and sufficiently kneaded with a kneader, A dispersion solvent of methanol and water is added little by little and further kneaded to prepare a paste having a predetermined viscosity. Thereafter, the paste is applied to the surface of an aluminum foil and dried in an atmosphere at 100 ° C. for 1 hour. Formed.

Next, the aluminum foil on which the activated carbon layer was formed was cut into a size of 30 mm × 400 mm to obtain 2 mm.
One set of polarizable electrodes was obtained.

Next, an external lead wire is attached to the aluminum foil of the polarizable electrode, and the two polarizable electrodes are arranged so as to face each other via a separator having a thickness of 50 μm.
This was wound to obtain a capacitor element.

Next, the capacitor element was impregnated with an electrolytic solution. The electrolytic solution used was one obtained by dissolving 4-ethylammonium boron tetrafluoride in propylene carbonate.

Thereafter, this capacitor element was inserted into a bottomed cylindrical aluminum case and sealed with a sealing material to obtain a wound electric double layer capacitor.

Example 2 In Example 1, the amount of surface functional groups of the petroleum coke-based activated carbon powder was set to 0.1 meq /
A wound-type electric double layer capacitor was obtained in the same manner as in Example 1 except that g was used.

Example 3 In Example 1, the surface functional group content of the petroleum coke-based activated carbon powder was set to 1.0 meq /
A wound-type electric double layer capacitor was obtained in the same manner as in Example 1 except that g was used.

Example 4 In Example 1, the amount of surface functional groups in the petroleum coke-based activated carbon powder was set to 0.05 meq.
/ G was obtained in the same manner as in Example 1 except that the capacitor of the present invention was used.

Example 5 In Example 1, the amount of surface functional groups of the petroleum coke-based activated carbon powder was set to 1.5 meq /
A wound-type electric double layer capacitor was obtained in the same manner as in Example 1 except that g was used.

Example 6 A wound electric double layer capacitor was obtained in the same manner as in Example 1 except that a titanium foil having a thickness of 20 μm was used as the current collecting metal foil.

Example 7 A wound electric double layer capacitor was obtained in the same manner as in Example 1 except that a 15 μm thick titanium foil was used as the current collecting metal foil.

(Comparative Example 1) In Example 1, the formation of the activated carbon layer was carried out by using a petroleum coke-based activated carbon powder (surface functional group content: 0.4 meq / g) having an average particle diameter of 5 μm and a conductivity-imparting agent. Carbon black having a particle size of 0.05 μm,
Water-soluble binder solution in which CMC is dissolved (CMC concentration:
50%) in a weight ratio of 10: 2: 2, and kneaded with a kneader to produce a paste having a predetermined viscosity.
This paste is applied to the surface of aluminum foil and
Example 1 except that it was formed by drying for 1 hour in the air at 0 ° C.
In the same manner as in the above, a wound electric double layer capacitor was obtained.

The wound type electric double layer capacitors of Examples 1 to 7 and Comparative Example 1 were charged at a constant voltage of 2.5 V for 1 hour, and then discharged at a constant current of 100 mA (C ) And ESR characteristics were measured. Furthermore, the wound type electric double layer capacitor is 2.8 in a 75 ° C. constant temperature bath.
After holding for 3000 hours in a state charged with V constant voltage,
Discharge at a constant current of 100 mA, and similarly, capacitance (C)
And ESR characteristics were measured. The results are shown in (Table 1).

[0040]

[Table 1]

ΔC and ΔESR in Table 1 are the capacitance (C) and the ESR characteristic after 3000 hours under the above conditions with respect to the initial capacitance (C) and the value of the ESR characteristic. Are shown respectively.

The number of tests is 50 each, and the capacitance and ESR characteristics are shown by their average values.

As is clear from Table 1, Examples 1 to
The wound type electric double layer capacitors of Example 3 and Examples 6 and 7 have higher dispersibility of the activated carbon powder of the activated carbon layer and the conductivity-imparting agent than the wound type electric double layer capacitor of Comparative Example 1. Therefore, it can be understood that the initial ESR characteristics are low and the changes in ΔC and ΔESR after 3000 hours are small.

In Examples 4 and 5, the petroleum coke-based activated carbon powder had a surface functional group content of 0.05 meq / g and 1.
A wound type electric double layer capacitor using 5 meq / g has a large change in ΔC and ΔESR after 3000 hours. Therefore, the amount of surface functional groups of the petroleum coke-based activated carbon powder is 0.1 to 1.0 meq. / G is preferred.

In the wound type electric double layer capacitors of Examples 1 to 7, no liquid leakage occurred, and in Comparative Example 1, four liquid leakages occurred.

(Embodiment 2) FIG. 2 is a partially cutaway perspective view showing a configuration of a button-type electric double layer capacitor according to Embodiment 2 of the present invention. In the figure, 11a, 1
1b is a pair of polarizable electrodes, and the pair of polarizable electrodes 11
a and 11b are arranged so as to face each other with the separator 12 interposed therebetween. The polarizable electrodes 11a and 11b and the separator 12 are impregnated with an electrolytic solution (not shown).

The pair of polarizable electrodes 11a and 11b are joined by a lower bottom part 15 and an upper lid part 16 so that their peripheral parts are hermetically sealed via an insulating ring packing 14. At this time, the carbon conductive layers 13a and 13b are interposed between the polarizable electrode 11a and the upper lid portion 16 and between the polarizable electrode 11b and the lower bottom portion 15.

In the above configuration, the polarizable electrodes 11a, 1
1b is a step of adding and kneading a small amount of an activated carbon powder and a water-soluble binder solution in which a conductive agent and a resin having a particle size smaller than that of the activated carbon powder are dissolved or dispersed, and further adding a dispersion solvent little by little to a predetermined viscosity. And a process of shaping the paste to remove the dispersion solvent.

Thus, the dispersibility of the activated carbon powder and the conductivity-imparting agent can be increased to improve the compressive force and the shear force, so that a polarizable electrode having excellent ESR characteristics and capacitance can be obtained. .

Hereinafter, a specific example of the second embodiment will be described.

Example 8 First, a polarizable electrode was made of petroleum coke-based activated carbon powder having an average particle size of 5 μm (surface functional group content:
0.4 meq / g) and an average particle size of 0.
A water-soluble binder solution (PTFE concentration: 60%) in which 05 μm of carbon black and polytetrafluoroethylene (hereinafter abbreviated as PTFE) was dispersed was mixed at a weight ratio of 10: 2: 1 and kneaded sufficiently with a kneader. Thereafter, a dispersion solvent of water is added little by little, and the mixture is further kneaded to produce a paste having a predetermined viscosity. Thereafter, the paste is molded by a molding machine and dried in the air at 100 ° C. for 1 hour to mold. I got a body.

The molded body was cut into a disk having a size of 100 mm to obtain a pair of polarizable electrodes.

Next, the two polarizable electrodes and a 50 μm thick electrode were used.
An electrolytic solution obtained by dissolving 4-ethylammonium boron tetrafluoride in propylene carbonate was impregnated in a disk-shaped separator having a diameter of 110 mm.

Next, the pair of polarizable electrodes face each other with a separator interposed therebetween, and then the polarizable electrodes are arranged so as to be in contact with the lower bottom and upper lid of the stainless steel container via a conductive layer. Then, the periphery was sealed with an insulating ring packing to obtain a button-type electric double layer capacitor.

Example 9 A button-type electric double layer capacitor was obtained in the same manner as in Example 8 except that carbon black having an average particle size of 0.01 μm was used as the conductivity-imparting agent. .

Example 10 A button-type electric double layer capacitor was obtained in the same manner as in Example 8 except that carbon black having an average particle size of 0.001 μm was used as the conductivity-imparting agent. .

Example 11 A button-type electric double layer capacitor was obtained in the same manner as in Example 8 except that carbon black having an average particle diameter of 0.1 μm was used as the conductivity-imparting agent. .

Comparative Example 2 In Example 8, the activated carbon layer was formed by a petroleum coke-based activated carbon powder having an average particle size of 5 μm (surface functional group content: 0.5 meq / g) and an average particle size as a conductivity-imparting agent. 0.05μm diameter carbon black, P
A water-soluble binder solution (PTFE concentration: 60%) in which TFE is dispersed is mixed at a weight ratio of 10: 2: 2 and kneaded with a kneader to produce a paste having a predetermined viscosity, and then the paste is formed. Then, a button-type electric double layer capacitor was obtained in the same manner as in Example 8 except that a molded product was obtained by drying in air at 100 ° C. for 1 hour.

The button-type electric double-layer capacitors of Examples 8 to 11 and Comparative Example 2 were tested at a constant voltage of 2.5 V for 1
After the battery was charged for 100 hours and then discharged at a constant current of 100 mA, the capacitance (C) and the ESR characteristics were measured. Further, the button-type electric double layer capacitor was charged at a constant voltage of 2.8 V in a constant temperature bath at 75 ° C., held for 3000 hours, discharged at a constant current of 100 mA, and similarly discharged with a capacitance (C ) And ESR characteristics were measured. The results are shown in (Table 2).

[0060]

[Table 2]

ΔC and ΔESR in Table 2 are the capacitance (C) and ESR characteristics after 3000 hours under the above conditions with respect to the initial capacitance (C) and ESR characteristics. Are shown respectively.

The number of test pieces is 50 each, and the capacitance and ESR characteristics are shown by their average values.

As is clear from (Table 2), Examples 8 to
The button-type electric double-layer capacitor of No. 10 is also compared with the button-type electric double-layer capacitor of Comparative Example 2,
Initial ESR characteristics are low, and ΔC after 3000 hours,
It is understood that the change in ΔESR is small. This is also because the same effect as the wound electric double layer capacitor of the first embodiment can be obtained.

The button-type electric double layer capacitor of Example 11 had an average particle diameter of 0.1 μm as a conductivity-imparting agent.
When the average particle size of the conductivity-imparting agent exceeds 1/10 of the average particle size of the activated carbon powder, the dispersibility of the activated carbon powder and the conductivity-imparting agent becomes poor, and the initial characteristics and 3000 ΔC and ΔESR after time also become worse.

The button-type electric double layer capacitors of Examples 8 to 11 had no liquid leakage, and Comparative Example 2 had four liquid leakages.

[0066]

As described above, the present invention comprises a step of adding a small amount of an activated carbon powder and a binder solution obtained by dissolving or dispersing a resin having a particle diameter smaller than that of the activated carbon powder and a resin; From the step of adding the paste little by little and kneading to a predetermined viscosity to form a paste, and the step of applying the paste to a current collecting metal foil to remove the dispersion solvent or the step of forming the paste and removing the dispersion solvent. The manufacturing method can increase the dispersibility of the activated carbon powder and the conductivity-imparting agent to improve the compressive force and the shearing force. Therefore, a polarizable electrode having a low ESR and a high capacity can be used as a current collecting metal foil. Can be formed. An electric double layer capacitor using this polarizable electrode can obtain a high capacity electric double layer capacitor with a small ESR.

[Brief description of the drawings]

FIG. 1 (a) is a schematic partial cutaway perspective view of a wound electric double layer capacitor according to a first embodiment of the present invention. (B) Polarizable electrodes of the electric double layer capacitor according to the first embodiment. Main part enlarged sectional view

FIG. 2 is a partially cutaway perspective view showing a configuration of a button-type electric double layer capacitor according to a second embodiment of the present invention.

FIG. 3 is a schematic partial cutaway perspective view of a conventional wound-type electric double layer capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Current-collecting metal foil 2 Activated carbon layer 3, 11a, 11b Polarized electrode 4, 12 Separator 5, 6 External lead wire 7 Capacitor element 8 Sealing material 9 Aluminum case 13a, 13b Carbon conductive layer 14 Ring packing 15 Lower bottom 16 Top lid

Claims (6)

[Claims] 1. A step of kneading an activated carbon powder, a conductivity-imparting agent having a particle size smaller than the activated carbon powder, and a small amount of a water-soluble binder solution in which a resin is dissolved or dispersed, and further adding a dispersion solvent to the kneaded product. A method for producing a polarizable electrode for an electric double layer capacitor, comprising: a step of adding a little by little and kneading to a predetermined viscosity to form a paste; and a step of applying the paste to a current collecting metal foil to remove a dispersion solvent. 2. A step of kneading an activated carbon powder, a conductivity-imparting agent having a particle size smaller than that of the activated carbon powder, and a small amount of a water-soluble binder solution in which a resin is dissolved or dispersed, and further adding a dispersion solvent to the kneaded product. A method for producing a polarizable electrode for an electric double layer capacitor, comprising a step of adding a little by little and kneading to a predetermined viscosity to form a paste, and a step of forming the paste to remove a dispersion solvent. 3. The method for producing a polarizable electrode for an electric double layer capacitor according to claim 1, wherein the average particle size of the conductivity-imparting agent is 1/10 or less of the average particle size of the activated carbon powder. 4. The polarizable electrode for an electric double layer capacitor according to claim 1, wherein the activated carbon powder is petroleum coke-based activated carbon and the surface functional group content is in the range of 0.1 to 1.0 meq / g. Production method. 5. Kneading activated carbon powder, a conductivity-imparting agent having a particle size smaller than the activated carbon powder, and a small amount of a water-soluble binder solution obtained by dissolving or dispersing a resin, and further adding a dispersion solution little by little to the kneaded product. A paste kneaded to a predetermined viscosity is applied to a current-collecting metal foil, and a dispersing solvent is removed. A polarizable electrode is wound through a separator to form a capacitor element. The capacitor element is impregnated with an electrolyte. An electric double layer capacitor sealed in an aluminum case. 6. Kneading an activated carbon powder, a conductivity-imparting agent having a particle size smaller than the activated carbon powder, and a small amount of a water-soluble binder solution in which a resin is dissolved or dispersed, and adding a dispersion solvent little by little to the kneaded product. An electric double layer capacitor in which a polarizable electrode formed by forming a paste kneaded to a predetermined viscosity and removing a dispersion solvent is sealed in a lower bottom portion and an upper lid portion together with an electrolytic solution via a separator.