JP2000252175A - Electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electric double-layer capacitor, in which electrical resistances between components thereof are small and for which a device for applying pressure to the components is not necessary. SOLUTION: In an electric double-layer capacitor, having polarizable electrodes 3, a separator 4, and collectors 1 laminated one upon another, at least one of a powdered material, a mesh material, and a porous body composed of a material manifesting fluidity when heated is made present between each electrode 3 and collector 1 and on the surfaces of the separator 4, and heated under pressure and thereafter cooled. Thereafter, these components are adhered to one another.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double-layer capacitor, and more particularly to an electric double-layer capacitor used for power storage, in which a current collector and a polarizable electrode are laminated.

[0002]

2. Description of the Related Art Electric double layer capacitors include those using an aqueous electrolyte as an electrolyte and those using a non-aqueous electrolyte. In the case of using an aqueous electrolyte, the withstand voltage of the capacitor is limited by the decomposition voltage of water, whereas in the case of using a non-aqueous electrolyte, a capacitor with a high withstand voltage can be obtained. The stored energy per hit can be increased. As the non-aqueous electrolyte, a solution obtained by dissolving an onium ion-based electrolyte represented by tetraethylammonium tetrafluoroborate in a polar solvent that does not release hydrogen ions such as propylene carbonate is generally used.

[0003] If water having a low decomposition voltage is mixed in the non-aqueous electrolyte, the electrolysis of water occurs before the decomposition of the non-aqueous electrolyte starts, and the characteristics of the non-aqueous electrolyte cannot be exhibited. Contamination must be avoided as much as possible. for that reason,
The components must be sufficiently dewatered and the assembly operation must be performed in an extremely dry atmosphere and sealed to prevent the ingress of moisture from the air into the manufactured capacitor. An electric double layer capacitor is formed by coating a polarizable electrode on a current collector made of aluminum or the like, or by laminating a plate-like body, laminating via a separator, or winding the laminated body to produce a capacitor element, and forming a vacuum. After dehydrating by heating below, a non-aqueous electrolytic solution is injected, put in a capacitor container, and terminals are connected, followed by sealing.

As the polarizable electrode, a powdery activated carbon, and a sheet-like material obtained by kneading carbon black and a binder as a conductive auxiliary material are generally used. As the binder, a so-called easily fiberized, chemically stable polymer compound represented by polytetrafluoroethylene is used, and the structure entangled with these fine fibers makes it possible to use the activated carbon or carbon. The polarizable electrode is formed in a sheet shape due to the self-aggregation property of the black fine powder. Since the sheet-shaped polarizable electrode must be electrically coupled to an external electrode or a load of the capacitor, a foil-shaped metal called a current collector is used. This metal needs to have excellent electrical conductivity and corrosion resistance to the electrolytic solution in the cell, and aluminum is generally used.

[0005] The surface of the aluminum foil of the current collector is easily oxidized to form a passive layer. Although the passivation layer is useful for corrosion resistance, it becomes a problem when used as a current collector because the passivation layer acts electrically as a nonconductor. Therefore, as aluminum foil,
Not only a material having a low electric resistance, a high corrosion resistance and a high purity is selected, but also a substrate chemically treated to remove and roughen an oxide layer on the surface is used. By this treatment, the surface of the aluminum foil is roughened with a very thin natural oxide film. Is brought into close contact with the sheet-shaped polarizable electrode, and both are mechanically pressed using an attachment plate or the like. The mechanical compression may be performed from the outside of the package after assembling into the cell, and the required pressing pressure is usually 1.5 to 2 kg /.
cm ² .

Due to this pressing force, a concentrated stress is applied to the surface of the roughened aluminum foil at a local portion of the roughened surface, and a very thin natural oxide film at that portion is mechanically destroyed. As a result, it is considered that the aluminum substrate and the polarizable electrode are brought into electrical contact. This can be easily confirmed by observing the change in the electric resistance while changing the applied pressing pressure. However, usually 1.5-2k
In order to apply the required mechanical pressing force of about g / cm ^2, supporting plates are required on both sides of the electric double layer capacitor, but they must be sufficiently strong and not easily changed according to the size of the cell. Therefore, the larger the cell, the larger the size and weight must be.

For example, in a rectangular cell, the surface on the electrode side is 5
When the size is about 10 cm × 10 cm, the pressing pressure is 100 kgf
Becomes In the case of a larger cell, the attachment plate becomes heavier than the cell itself. This means that the stored energy density per unit weight of the cell is greatly impaired. Also, if the electric double layer capacitor is placed in an overvoltage or high temperature state under some conditions, the electrolytic solution is decomposed inside and gas is generated, and this gas is separated from the current collector even in the stage of minute bubbles. This will degrade the electrical contact between the polar electrodes.

In the method of manufacturing an electric double layer capacitor, the polarizable electrode is manufactured by directly applying the current on the current collector using a coating apparatus such as a doctor blade without separately manufacturing the polarizable electrode. Methods are also known. In this method, a constituent material such as activated carbon powder is used to convert polyvinylidene fluoride (PVD).
F) was stirred with an adhesive material in which N-methylpyrrolidone (NMP) was dissolved to form a slurry, and the slurry was applied to the collector electrode. This is a method for obtaining a polar electrode. The electric double layer capacitor manufactured by this method has a problem that the capacitance of a certain amount of activated carbon is reduced to about half, probably because the pores of the activated carbon are filled in the adhesive material. This is not a preferable method for the large-capacity electric double layer capacitor.

[0009]

SUMMARY OF THE INVENTION In an electric double layer capacitor in which a current collector is laminated with a polarizable electrode in which an activated carbon material is bonded with a fibrous binder, the conductive connection between the current collector and the polarizable electrode is enhanced. It is another object of the present invention to provide an electric double layer capacitor in which a cell can be easily assembled.

[0010]

SUMMARY OF THE INVENTION The present invention provides a polarizable electrode,
In an electric double-layer capacitor in which a separator and a current collector are laminated, a substance that exhibits fluidity by heating is present between a polarizable electrode and a current collector, and the electric element is heated under pressure, and then cooled and bonded. It is a multilayer capacitor. The electric double layer capacitor according to the above, wherein a substance which exhibits fluidity by heating is also present on the separator surface. Further, the electric double layer capacitor described above, wherein the substance that exhibits fluidity by heating is at least one of a powder, a net, and a porous body selected from polyethylene and polypropylene.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method in which a current collector and a polarizable electrode are heated and fluidized by applying a substance exhibiting fluidity by heating in the form of a dot or a line, and then pressurizing the material. After cooling to ambient temperature, the pressure is removed and the current collector and the polarizable electrode are bonded.

According to the present invention, even when an insulating material such as a synthetic resin is used as a material for bonding the current collector and the polarizable electrode, the adhesive material causes a gap between the current collector and the polarizable electrode. Since the adhesive strength of the two is increased, the conductive connection between the two can be enhanced as compared with the case where no adhesive substance is used.

The electric double layer capacitor of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an assembling process of the electric double layer capacitor of the present invention. As shown in FIG. 1A, a dispersion of adhesive substance particles 2 flowing by heating is applied to a current collector 1 made of an aluminum plate whose surface has been roughened. The dispersion can be applied by a coating method such as brush coating or a printing method such as screen printing or stencil printing. As the adhesive substance particles, thermoplastic resin particles such as polyethylene resin particles and polypropylene resin particles can be used. Rubber-based materials and the like can also be used as long as they are electrochemically stable under an applied voltage.

Next, as shown in FIG. 1 (B), two current collectors 1 coated with the dispersion of the adhesive substance particles are made of activated carbon or the like on the surface coated with the dispersion of the adhesive substance particles. A pressing jig is applied from both sides of the current collector 1 in a state where the polarizable electrodes 3 are stacked, and a separator 4 is further stacked between the polarizable electrodes so that the respective constituent materials do not shift. Pressurized by 5.

The coating amount of the dispersion of the adhesive substance particles is preferably an amount that covers 0.1% to 10% of the area of the current collector in a molten state, and 0.5% to 2%. Is more preferable. If it exceeds 10%, the conductive contact area decreases and the electric resistance increases, which is not preferable. On the other hand, if it is 0.5% or less, sufficient adhesive strength cannot be obtained.

The current collector 1 coated with the adhesive substance particles
The polarizable electrode 3 made of activated carbon or the like is laminated on the surface to which the dispersion of the adhesive substance particles is applied, and the separator 4 is further laminated between the polarizable electrodes. The pressure is applied from both sides of the current collector 1 by the pressing jig 5 in a state in which the above-mentioned condition does not occur. The pressure to be applied is 0.
It is preferably set to ^{1kg / cm 2 ~5kg / cm 2} , and more preferably set to ^{0.5kg / cm 2 ~2kg / cm 2} .

Next, heating is performed in a heating device in a pressurized state. The heating temperature varies depending on the type of the adhesive substance particles to be used and the constituent materials such as the separator. However, when polyethylene resin particles are used, the heating temperature is from 120 ° C to 200 ° C.
, And the heating time is preferably 0.5 to 1 hour. The heating atmosphere may be an air atmosphere, but is preferably performed in an inert atmosphere such as a nitrogen atmosphere so that oxidation of aluminum does not proceed.

Next, when the pressurizing jig is removed after cooling to room temperature, an electric double layer capacitor in which the current collector and the polarizable electrode are integrated as shown in FIG. 1C can be obtained. Further, in the electric double layer capacitor of the present invention,
The present invention can be used not only for bonding between the current collector and the polarizable electrode but also for bonding between the polarizable electrode and the separator. In the above description, it was described that the dispersion liquid in which the adhesive substance particles were dispersed was applied on the current collector. However, not only on the current collector, but also on the surface of the polarizable electrode in contact with the current collector. Is also good.

In place of the application of the dispersion of the adhesive substance particles, as shown in FIG. 2, a net-like or fibrous member made of an adhesive substance, a perforated plate or the like can be laminated and used in the same manner. FIG. 2A is a diagram illustrating an example in which a net-like member 6 made of an adhesive substance is provided on the current collector 1, and FIG. 2B is a diagram illustrating an example in which a perforated plate 7 is provided. . As a mesh member,
Examples thereof include a net formed from polyethylene or the like, a woven or non-woven fabric formed from a fibrous member, a perforated plate formed by punching a film-like member, and the like. For the net-like member, the net part is 0.1%
-30% is preferred, and 0.5% -1%
0% is more preferable. If more than 10%
It is not preferable because the conductive contact area decreases and the electric resistance increases. On the other hand, if it is 0.5% or less, sufficient adhesive strength cannot be obtained.

When the current collector and the polarizable electrode are adhered to each other by the above-described method, the current collector and the polarizable electrode can be kept in electrical contact with each other without maintaining external pressure, and the cell can be electrically connected. The equivalent series resistance has a value equivalent to that when pressure is applied.

In addition, the external pressurizing mechanism becomes heavier as the cell becomes larger, and greatly impairs the capacitance value per unit weight or volume of the cell. The electric double layer capacitor exerts a great effect when applied to a large electric double layer capacitor. Further, in the above description, the electric double-layer capacitor having a shape in which a flat current collector and a polarizable electrode are laminated has been described. However, a winding type in which a belt-shaped current collector and a polarizable electrode are wound. Also in the electric double layer capacitor, when laminating the strip-shaped current collector and the polarizable electrode, the current collector and the polarizable electrode are bonded and then wound to reduce the number of members at the time of assembly. can do.

[0022]

The present invention will be described below with reference to examples. Example 1 Activated carbon powder formed by using polytetrafluoroethylene as a binder: 110 mm long, 60 mm wide, 0.5 mm thick
A suspension obtained by adding 10 mg of polyethylene powder having a particle size of 1 μm (Suntech PAK manufactured by Asahi Kasei Kogyo Co., Ltd.) to 5 ml of ethanol and applying sufficient stirring to both surfaces of the polarizable electrode was coated with aluminum having a thickness of 0.05 mm. The current collector was laminated and heated at 120 ° C. for 0.5 hour with a pressure of 1 kg / cm ² applied by a holding plate, then cooled with the pressure applied, and the holding plate was removed at room temperature. A measurement cell was prepared. The electric resistance was measured in a state where pressure was applied from the current collectors on both sides of the electric resistance measuring cell, and the change of the electric resistance with respect to the pressure change is shown in FIG.

Comparative Example 1 A dispersion of polyethylene powder was not applied to the surface of the current collector.
FIG. 3 shows a change in electric resistance with respect to a change in pressure in a state where the electrode is directly laminated with the polarizable electrode and pressure is applied from outside the current collector.

[0024]

According to the electric double layer capacitor of the present invention, the electrodes and the current collector are electrically integrated by bonding at innumerable contact points, so that a conventional mechanical pressing mechanism is not required. . As a result, the energy density per unit cell weight was improved. In addition, since the components are integrated, assembly is facilitated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an assembly process of an electric double layer capacitor according to the present invention.

FIG. 2 is a diagram illustrating an example in which another material made of an adhesive substance is used.

FIG. 3 is a diagram illustrating a change in electric resistance with respect to a change in pressure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Current collector, 2 ... Adhesive substance particles, 3 ... Polarizable electrode, 4
... Separator, 5 ... Pressing jig, 6 ... Net-like member, 7 ... Perforated plate

Claims (3)

[Claims] 1. An electric double layer capacitor having a polarizing electrode, a separator and a current collector laminated thereon, wherein a substance which exhibits fluidity by heating is present between the polarizable electrode and the current collector and heated under pressure. An electric double layer capacitor characterized by being cooled and adhered after cooling. 2. The electric double layer capacitor according to claim 1, wherein a substance which exhibits fluidity by heating is also present on the separator surface. 3. A substance which exhibits fluidity by heating,
2. The electric double layer capacitor according to claim 1, wherein the electric double layer capacitor is at least one of a powder selected from polyethylene and polypropylene, a mesh body, and a porous body.