JP2008270349A - Electrode for electric double-layer capacitor and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for electric double-layer capacitor ensuring excellent performance as the electric double-layer capacitor and having excellent mechanical strength. <P>SOLUTION: The electrode for electric double-layer capacitor containing activated charcoal, conductive particle, combined resin, and a predetermined amount of metal reinforcing material with the activated charcoal partially combined with the metal reinforcing material. The electrode for electric double-layer capacitor can be manufactured by kneading a mixture containing the activated charcoal, conductive particle, combined resin and metal reinforcing material with a kneader while a shearing stress is applied thereto, breaking the kneaded material into pieces and molding them into a sheet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizable electrode used for an electric double layer capacitor and a method for manufacturing the same.

  The electric double layer capacitor uses a large capacitance of the electric double layer formed on the surface of the polarizable electrode in the electrolytic solution. Since the electric double layer capacitor does not use chemical reaction, it is capable of rapid charging / discharging with high output and high reliability compared to a secondary battery with chemical reaction, and it does not use harmful substances. There is. For this reason, application to a wide range of applications such as backup of electronic devices, power storage of home appliances and office machines, power sources for automobiles, output leveling of wind power and solar power generation has begun.

  The polarizable electrodes constituting these electric double layer capacitors are usually made by adding conductive particles such as carbon black (hereinafter sometimes abbreviated as CB) to activated carbon powder having a large specific surface area. A material obtained by kneading together with a binder resin such as fluoroethylene (hereinafter sometimes abbreviated as PTFE), forming into a sheet by rolling or compression molding, and bonding to a metal foil such as aluminum is used.

  PTFE, which is a binding resin, is fiberized by kneading, rolling, and compression molding, and entangles and binds activated carbon and CB. Thereby, the electrode which maintained the sheet | seat shape can be obtained. However, when the electrode area is increased, mechanical strength is insufficient only by bonding with fiberized PTFE, and cracks are generated at the time of rolling and compression molding, and breakage is likely to occur at the time of handling. It is thought that the strength can be improved by increasing the amount of PTFE added. However, if PTFE as an insulator increases, the internal resistance of the electric double layer capacitor increases and the amount of activated carbon relatively decreases. The electrostatic capacity is reduced.

  For this reason, it is proposed to use a fluoropolymer resin that can be melt-molded in addition to PTFE (see, for example, Patent Document 1). The amount of the fluorine-containing polymer resin that can be melt-molded to be used in combination is relatively small to 1 to 50% by mass with respect to PTFE, thereby suppressing the deterioration of the electric double layer capacitor performance. However, there is no change in the insulator component, and there is a problem that the internal resistance increases or the capacitance decreases more or less.

  In order not to increase the internal resistance, a method of using a phenol resin as a binder and carbonizing it has been proposed (see, for example, Patent Document 2). In this method, the activated carbon particles are tightly bonded by bonding the binders covering the surface of the activated carbon particles to each other, and the activated carbon particles and the binder are bonded firmly by carbonizing the binder, and the conductivity is also maintained. Be drunk. However, in this method, a carbonization treatment step of heating at 800 ° C. in an inert gas atmosphere is essential, and the number of electrode manufacturing steps is increased. In addition, an electrode manufactured through the carbonization treatment step is generally brittle. There is also a high possibility that it will not be advantageous in reducing cracks.

  In addition, in order to prevent corrosion of the aluminum current collector, aluminum powder is also added to the electrode coating paste (see, for example, Patent Document 3). However, the electrode obtained by this method can prevent the corrosion of the aluminum current collector, but cannot improve the mechanical strength.

JP-A-11-307402 JP-A-6-97004 JP-A-10-106900

Thus, in the conventional method, it is necessary to increase the number of steps, and the electrode for the electric double layer capacitor whose mechanical strength is improved while maintaining the performance as the electric double layer capacitor such as capacitance and internal resistance. There was a problem that it was difficult to manufacture.
Accordingly, the present invention has been made to solve the above-described problems, and has an excellent performance as an electric double layer capacitor and an electric double layer capacitor electrode having excellent mechanical strength, and such an electric It aims at providing the method of manufacturing the electrode for double layer capacitors efficiently.

Therefore, as a result of intensive research and development to solve the above-described conventional problems, the present inventors have found that activated carbon, conductive particles, binding resin, and a place to solve such problems. It is effective to knead a mixture containing a certain amount of metal reinforcing material while applying shear stress with a kneader or the like, and to make an electrode for an electric double layer capacitor in which activated carbons are partially bonded with a metal reinforcing material. As a result, the present invention has been completed.
That is, the present invention includes activated carbon, conductive particles, a binding resin, and 2% to 20% by mass of a metal reinforcing material, and the activated carbon is partially bonded with the metal reinforcing material. This is an electrode for a double layer capacitor.
The present invention also includes a step of kneading a mixture containing activated carbon, conductive particles, a binding resin and 2% by mass to 20% by mass of a metal reinforcing material while applying a shear stress of 1 MPa or more, and this kneaded product. And a step of forming the pulverized product into a sheet shape.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the performance as an electrical double layer capacitor, the electrode for electrical double layer capacitors which has the outstanding mechanical strength, and its manufacturing method can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a schematic partial cross-sectional view of a polarizable electrode for an electric double layer capacitor according to Embodiment 1 of the present invention. In FIG. 1, the polarizable electrode according to the present embodiment contains activated carbon 1, conductive particles 2, a binding resin 3, and a metal reinforcing material 4. Here, the metal reinforcing material 4 is deformed by shear stress and partially bonds the activated carbons 1, and the binding resin 3 is fiberized by stress such as shear, compression, rolling, etc. The conductive particles 2 and the metal reinforcing material 4 are entangled with each other.
Thus, in the polarizable electrode according to the present embodiment, the metal reinforcing material 4 is locally deformed by applying a large shear stress, and mechanically coupled to the activated carbon 1, so that the mechanical strength is high. Has features. Moreover, since the metal reinforcing material 4 is a metal such as aluminum, conductivity between the activated carbons 1 is also maintained.

The metal reinforcing material 4 used in the present embodiment may be a metal that is not easily altered by the electrolytic solution of the electric double layer capacitor and is relatively soft (preferably having a tensile elastic modulus of 10 GPa to 100 GPa). Specifically, aluminum, gold, silver, zu, lead, magnesium and the like can be mentioned. Among these, it is desirable to use aluminum as the metal reinforcing material 4 from the viewpoint of improving the corrosion resistance and reducing the cost. The form of the metal may be any of powder, flake and fiber. In the case of using powdered metal, more inert and relatively soft gold or silver can also be used. In addition, flaky or fibrous aluminum has a greater effect of improving mechanical strength than powdered aluminum.
The average particle diameter of the powdered metal is usually 5 μm to 200 μm, preferably 10 to 100 μm.
The metal reinforcing material 4 needs to be contained in an amount of 2% by mass to 20% by mass with respect to the polarizable electrode. If the metal reinforcing material 4 is less than 2% by mass, improvement of the mechanical strength of the polarizable electrode cannot be expected. On the other hand, if it exceeds 20% by mass, the capacitance is lowered and the mechanical strength is also lowered. The content of the metal reinforcing material 4 is preferably 2% by mass to 10% by mass with respect to the polarizable electrode.

The activated carbon 1 used in the present embodiment may be activated carbon particles used in known polarizable electrodes and the like, and specifically, phenol-based activated carbon, rayon-based activated carbon, acrylic-based activated carbon, Bitch-based activated carbon, palm Shell activated carbon, cellulose activated carbon and the like can be mentioned. These activated carbons may be used individually by 1 type, and may be used in combination of 2 or more type.
The specific surface area of the activated carbon 1 is usually 500m ² / g~3000m ² / g, preferably 1000m ² / g~2000m ² / g. Moreover, the average particle diameter of the activated carbon 1 is usually 1 μm to 100 μm, preferably 5 to 50 μm.
The activated carbon 1 is preferably contained in an amount of 50% by mass to 90% by mass with respect to the polarizable electrode.

The conductive particles 2 used in the present embodiment may be conductive particles used in known polarizable electrodes and the like. Specifically, carbon black (for example, acetylene black, ketjen black, etc.), Examples include graphite, mesophase carbon, and carbon nanotube. These electroconductive particles may be used individually by 1 type, and may be used in combination of 2 or more type.
The average primary particle diameter of the conductive particles 2 is usually 10 nm to 100 nm, preferably 20 nm to 50 nm.
The conductive particles 2 are preferably contained in an amount of 5% by mass to 20% by mass with respect to the polarizable electrode.

The binding resin 3 used in the present embodiment is not particularly limited as long as it is fiberized by stress such as shearing, compression, and rolling. Specifically, polytetrafluoroethylene (PTFE), modified PTFE, ethylene- Examples thereof include resins made of fluorine-containing polymers such as tetrafluoroethylene copolymer, chlorotriethylfluoroethyl-ethylene copolymer, vinylidene fluoride copolymer, and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. Among these, it is desirable to use polytetrafluoroethylene or modified PTFE as the binding resin 3 from the viewpoint of easy fibrillation.
The binding resin 3 is preferably contained in an amount of 2% by mass to 10% by mass with respect to the polarizable electrode.

A polarizable electrode for an electric double layer capacitor according to the present embodiment comprises a mixture containing activated carbon 1, conductive particles 2, binding resin 3 and 2% by mass to 20% by mass of metal reinforcing material 4 of 1 MPa or more. It can be produced by kneading while applying a shear stress, and then molding the obtained kneaded product into a sheet. By applying a shear stress of 1 MPa or more to a mixture containing activated carbon 1, conductive particles 2, binding resin 3 and metal reinforcing material 4 with a kneader or the like and kneading, a relatively soft metal reinforcing material 4 such as aluminum. The activated carbons 1 are partially bonded with the metal reinforcing material 4. Therefore, the mechanical strength of the polarizable electrode is remarkably improved.
What is necessary is just to set suitably the shearing stress provided to a mixture according to the form of the metal reinforcement material 4 to be used, a kind, etc. in 1 MPa or more, Preferably it is the range of 1 MPa-5 MPa. The shear stress in the present embodiment is a value calculated from the characteristics of the equipment used for kneading. For example, when using a kneader, the shear stress can be obtained from the kneading torque, the area of the minimum gap portion of the roller, and the radius of the roller. it can. The temperature at which the mixture is kneaded is preferably 100 ° C to 150 ° C.

  As a method for forming the pulverized material into a sheet, a known method can be adopted without limitation, and specific examples include compression molding and rolling. When obtaining a sheet-like polarizable electrode of a fixed size, it is preferable to employ compression molding as the molding method. When obtaining a sheet-like polarizable electrode having a constant thickness, the molding method It is preferable to employ rolling. What is necessary is just to set the thickness and magnitude | size of a sheet-like polarizable electrode suitably according to the form of an electric double layer capacitor.

FIG. 2 is a cross-sectional view of an example of an electric double layer capacitor produced using the sheet-like polarizable electrode obtained by the above method. The electric double layer capacitor is formed by impregnating a pair of polarizable electrodes (a positive polarizable electrode 12 and a negative polarizable electrode 13) with an organic electrolyte solution sandwiched between separators 11 in a laminate outer container 14. A positive electrode collector electrode 15 and a negative electrode collector electrode 16 are bonded to the positive electrode polarizable electrode 12 and the negative electrode polarizable electrode 13, respectively, and a tab 17 for taking out an electric current is bonded to the current collector. Yes.
For such an electric double layer capacitor, for example, a pair of polarizable electrodes bonded to a collector electrode using a conductive adhesive is manufactured, and a separator 11 is sandwiched between them, and a tab 17 is bonded to the collector. This can be obtained by sealing the laminate outer container 14 after accommodating it in a laminate outer container 14 and impregnating a polarizable electrode with an organic electrolyte.

  As the separator 11 used in the present embodiment, any separator may be used as long as it is used in a known electric double layer capacitor or the like, and specific examples include cellulose, polyethylene, polypropylene, and polyvinylidene fluoride. It is done.

  The collector electrode used in the present embodiment is not particularly limited as long as it is used in a known electric double layer capacitor or the like, and specifically includes aluminum foil, copper foil, nickel foil, and the like.

The organic electrolytic solution used in the present embodiment may be any one that is used in a known electric double layer capacitor or the like. Specifically, an organic electrolytic solution in which ion dissociable salts are dissolved in an organic solvent. Liquid. Examples of the ion dissociable salts include tetraethylammonium tetrafluoroborate (TEA-BF ₄ ), tetramethylammonium tetrafluoroborate, trimethylethylammonium tetrafluoroborate, dimethyldiethylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, spiro- ( 1,1 ′)-bipyrrolidinium tetrafluoroborate and other tetrafluoroborate salts, tetramethylammonium perchloride, dimethyldiethylammonium perchloride, methyltriethylammonium perchloride, perchloride salts such as tetraethylammonium perchloride, tetramethyl Ammonium hexafluorophosphate, tetraethylammonium hexafluorophosphate Examples of the organic solvent include propylene carbonate, ethylene carbonate, sulfolane, γ-butyrolactone, and acetonitrile. Moreover, you may add these as a main solvent and at least 1 sort (s) of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate as a subsolvent.

Hereinafter, although an example explains the details of the present invention, the present invention is not limited to these.
<Example 1>
75% by mass of activated carbon having a specific surface area of 1300 m ² / g and an average particle size of 15 μm, 10% by mass of acetylene black having an average primary particle size of 35 nm as conductive particles, and PTFE powder (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) 10% by mass of Teflon (registered trademark) PTFE 6-J) and 5% by mass of aluminum powder (manufactured by Wako Pure Chemical Industries, Ltd.) having an average particle diameter of 40 μm as a metal reinforcing material were dry blended. 50 g of this mixture was kneaded at 100 rpm at 50 rpm for 30 minutes using a small kneader (roller mixer-installed lab plast mill, manufactured by Toyo Seiki Seisakusho Co., Ltd.). The maximum shearing stress estimated from the kneading torque at this time, the area of the minimum gap portion of the roller, and the radius of the roller was 2.4 MPa. The lump of the kneaded product taken out was dried at 150 ° C. for 2 hours, and then finely crushed with a pulverizer.
A predetermined amount of the crushed kneaded material is put into a mold, and compression molded at a pressure of 35 MPa at 150 ° C. for 5 minutes using a hydraulic press to obtain a polarizable electrode sheet having a size of about 100 mm × 100 mm and a thickness of 2 mm. It was. From this sheet, three sample sheets having a size of 10 mm × 50 mm and three sample sheets having a size of 30 mm × 30 mm were cut out.

The tensile strength of a 10 mm × 50 mm sample sheet was measured using a tensile tester. The average value of the three tensile strength measurements was as high as 0.22 MPa.
In addition, a 30 mm × 30 mm sample sheet is placed on a 50 mm × 100 mm gold-plated copper electrode, a 20 mm × 20 mm gold-plated copper electrode is placed thereon, 4 MPa is pressed with a hand press, and the resistance at that time is measured with a milliohm meter. It was measured. The volume resistivity determined from the thickness of the sample and the electrode area was 1.9 Ω · cm.
The electrode for measuring the performance of the electric double layer capacitor is an epoxy-based conductive adhesive (volume resistivity 1 mΩ · cm) in which two sample sheets of 30 mm × 30 mm are each formed on an aluminum foil having a thickness of 50 μm and the conductive filler is carbon. Affixed with Furthermore, after attaching an aluminum tab to the aluminum foil, a cellulosic separator sandwiched between electrodes was placed in an aluminum laminate film outer container and vacuum dried at 200 ° C. for 10 hours. Next, after impregnating the electrode with an organic electrolytic solution in which tetraethylammonium tetrafluoroborate (TEA-BF ₄ ) 1M was dissolved in propylene carbonate, the container was sealed, and the electric double layer capacitor cell having the same configuration as FIG. Was made. The electric double layer capacitor characteristics were calculated by measuring the third cycle after charging and discharging at 2.7 V and 30 mA. It showed excellent characteristics with a capacitance of 48.6F and an internal resistance of 7.9Ω.
The above results are summarized in Table 1.

<Example 2>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that flaky aluminum having a size of about 2 mm × 5 mm and a thickness of 12 μm was used instead of the aluminum powder. The maximum shear stress when the mixture was kneaded was 2.4 MPa, and it was confirmed that the flaky aluminum was finely broken and dispersed by kneading.
The tensile strength of the obtained sheet was as high as 0.25 MPa. The volume resistivity slightly increased to 2.3 Ω · cm. The capacitance was almost unchanged at 48.5F, and the internal resistance slightly increased to 8.2Ω. The results are summarized in Table 1.

<Example 3>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that fibrous aluminum having a length of about 10 mm and a diameter of about 100 μm was used instead of the aluminum powder. The maximum shear stress when the mixture was kneaded was 2.3 MPa, and it was confirmed that the fibrous aluminum was finely broken and dispersed by kneading.
The tensile strength of the obtained sheet was as high as 0.24 MPa. The volume resistivity was 2.0 Ω · cm, the capacitance was 48.5 F, and the internal resistance was 7.9 Ω, almost the same as those obtained in Example 1. The results are summarized in Table 1.

<Example 4>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that the rotation speed when kneading with a small kneader was reduced to 35 rpm and the maximum shearing stress when kneading the mixture was 1.4 MPa.
Although the tensile strength of the obtained sheet was slightly reduced to 0.19 MPa, it was a sufficient value. The volume resistivity was 1.9 Ω · cm, the capacitance was 48.9 F, and the internal resistance was 8.0 Ω, which was almost the same as that obtained in Example 1. The results are summarized in Table 1.

<Example 5>
The rotational speed when kneading with a small kneader was reduced to 25 rpm, and the maximum shearing stress when kneading the mixture was 1.1 MPa. The obtained kneaded material was extruded into a molded body having a width of 50 mm and a thickness of 5 mm using a piston-type extruder. This was rolled with a roll mill to obtain a polarizable electrode sheet having a thickness of 2 mm. Other operations are the same as those in the first embodiment.
The tensile strength of the obtained sheet was as high as 0.23 MPa. The volume resistivity was 1.8 Ω · cm, the capacitance was 49.1 F, and the internal resistance was 7.8 Ω, which was almost the same as that obtained in Example 1. The results are summarized in Table 1.

<Example 6>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that the activated carbon content was changed to 78% by mass and the aluminum powder content was changed to 2% by mass. The maximum shear stress when the mixture was kneaded was 1.9 MPa.
Although the tensile strength of the obtained sheet decreased to 0.15 MPa, it was a sufficient value. The volume resistivity slightly increased to 2.0 Ω · cm. The capacitance slightly increased to 49.3F, and the internal resistance slightly increased to 8.2Ω. The results are summarized in Table 1.

<Example 7>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that the activated carbon content was changed to 60% by mass and the aluminum powder content was changed to 20% by mass. The maximum shear stress when the mixture was kneaded was 2.2 MPa.
Although the tensile strength of the obtained sheet decreased to 0.18 MPa, it was a sufficient value. Further, the volume resistivity decreased to 1.2 Ω · cm. The capacitance increased to 40.1F and the internal resistance decreased to 7.1Ω. The results are summarized in Table 1.

<Comparative Example 1>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that the aluminum powder was not added and the content ratio of activated carbon was 80% by mass. The maximum shear stress when the mixture was kneaded was 1.8 MPa.
The tensile strength of the obtained sheet was 0.08 MPa, which was less than half that obtained in Example 1. The results are summarized in Table 1.

<Comparative example 2>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that the rotation speed when kneading with a small kneader was reduced to 10 rpm and the maximum shearing stress when kneading the mixture was 0.5 MPa.
The tensile strength of the obtained sheet was 0.07 MPa, which was less than half of that obtained in Example 1. The results are summarized in Table 1.

<Comparative Example 3>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that the activated carbon content was changed to 79% by mass and the aluminum powder content was changed to 1% by mass. The maximum shear stress when the mixture was kneaded was 1.5 MPa.
The tensile strength of the obtained sheet was 0.10 MPa, almost the same as that obtained in Comparative Example 1. The results are summarized in Table 1.

<Comparative Example 4>
A polarizable electrode sheet was obtained in the same manner as in Example 1 except that the activated carbon content was changed to 50% by mass and the aluminum powder content was changed to 30% by mass. The maximum shear stress when the mixture was kneaded was 1.5 MPa.
The tensile strength of the obtained sheet was as extremely low as 0.05 MPa. The capacitance was also a low value of 32.4F. The results are summarized in Table 1.

3 is a schematic partial cross-sectional view of a polarizable electrode for an electric double layer capacitor according to Embodiment 1. FIG. 1 is a cross-sectional view of an example of an electric double layer capacitor manufactured using a polarizable electrode for an electric double layer capacitor according to Embodiment 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Activated carbon, 2 Conductive particle, 3 Bonding resin, 4 Metal reinforcement, 11 Separator, 12 Positive polarizable electrode, 13 Negative polarizable electrode, 14 Laminate exterior container, 15 Positive collector, 16 Negative collector, 17 Tab.

Claims (8)

  An electrode for an electric double layer capacitor, comprising activated carbon, conductive particles, a binding resin, and 2% by mass to 20% by mass of a metal reinforcing material, wherein the activated carbons are partially bonded with the metal reinforcing material.   The electrode for an electric double layer capacitor according to claim 1, wherein the metal reinforcing material is aluminum.   The electrode for an electric double layer capacitor according to claim 2, wherein the form of the aluminum is powdery.   The electrode for an electric double layer capacitor according to claim 2, wherein the form of the aluminum is flaky.   The electrode for an electric double layer capacitor according to claim 2, wherein the form of the aluminum is fibrous.   A step of kneading a mixture containing activated carbon, conductive particles, a binder resin and 2% to 20% by mass of a metal reinforcing material while applying a shear stress of 1 MPa or more, and pulverizing the kneaded product in a sheet form A method for producing an electrode for an electric double layer capacitor, comprising the step of:   The method for producing an electrode for an electric double layer capacitor according to claim 6, wherein the method of forming the sheet is compression molding.   The method for producing an electrode for an electric double layer capacitor according to claim 6, wherein the method of forming the sheet is rolling.

Images