JP2006032371A - Electric double layer capacitor and its fabrication process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and high capacity electric double layer capacitor inexpensively by a convenient process. <P>SOLUTION: A porous conductive film 1 is employed as a current collector and since it is used as a filter for low pressure suction filtering 6 polarizable electrode solution 5 where carbon nanotubes 2 and micropowder active carbon 3 are dispersed uniformly using an ultrasonic wave and a substance containing the carbon nanotubes 2 is laminated on the porous conductive film 1, contact area between the current collector and the carbon nanotubes can be increased. In the vicinity of a thin hole 4, a contact surface only between the current collector and the carbon nanotubes 2 is constituted and contact resistance between the current collector and the polarizable electrode is reduced. Furthermore, a good contact surface having no void on the interface is formed by suction force. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor using carbon nanotubes and a method for manufacturing the same.

  Conventionally, in an electric double layer capacitor, a polarizable electrode layer composed of a carbon material such as activated carbon and an electrolytic solution is formed on both sides of a separator such as a polypropylene nonwoven fabric having ion permeability and non-electron conductivity, and both sides thereof are formed. A current collector made of aluminum or the like having non-ion permeability and electron conductivity is provided, and a frame-shaped gasket made of insulating rubber or the like is installed between each periphery of the separator and the current collector. ing.

  A plate-like positive electrode and negative electrode in which an activated carbon-based electrode layer is formed on a current collector are alternately laminated via separators, and this laminate is placed in a case, and an electrolytic solution is injected into the case to enter the electrode layer. A multilayer electric double layer capacitor that has been infiltrated has been proposed (for example, see Patent Document 1).

  In addition, an electric double layer capacitor in which a carbon nanotube having a higher electrical conductivity and lower internal resistance than activated carbon particles is stacked on a current collector has also been proposed (see, for example, Patent Document 2, Patent Document 3 or Patent Document 4). ).

  In addition, for the purpose of sufficiently reducing the internal resistance of the polarizable electrode, an electric double layer capacitor using a mixture of activated carbon particles and carbon nanotubes as a polarizable electrode has also been proposed (see, for example, Patent Document 5). .

Furthermore, with regard to the joining of the current collector and the polarizable electrode, a conductive film such as a polyethylene film is used as the current collector, and the carbon nanotubes synthesized by the thermal decomposition method (CVD method) are used as the polarizable electrode. An electric double layer capacitor that vertically transfers carbon nanotubes onto a conductive film by heating and cooling the film has also been proposed (see, for example, Patent Document 6).
JP-A-4-154106 JP 10-32482 A JP 2000-1224079 A JP 2003-234254 A JP 2003-257797 A JP 2004-30926 A

  However, in the conventional electric double layer capacitor, when activated carbon is used as the polarizable electrode, activated carbon generally has a large electric resistance value, so the internal resistance of the polarizable electrode is increased, and a large current cannot be taken out, Since activated carbon is particulate, there is a limit to the surface area per unit electrode volume. In addition, when carbon nanotubes are used as polarizable electrodes, there is a problem in that the process of joining the current collector and the carbon nanotubes is complicated and the equipment becomes large, resulting in an increase in manufacturing cost, and the adhesion with the current collector is not sufficient. However, there was a problem that the internal resistance that was initially planned could not be reduced and sufficient effects could not be exhibited.

  Therefore, an object of the present invention is to provide a small-sized and large-capacity electric double layer capacitor at a low cost by a simple method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has realized a small and large-capacity electric double layer capacitor having a large surface area per unit electrode volume. In addition, a method for producing a composite film of a current collector and a polarizable electrode has been developed by a simple method, and an electric double layer capacitor having excellent performance can be provided at low cost.

  That is, the present invention has the following features.

  [1] A pair of composite films obtained by laminating a material containing carbon nanotubes synthesized by an arc discharge method serving as a polarizable electrode on a porous conductive film serving as a current collector is laminated with a material containing carbon nanotubes. An electric double layer capacitor characterized in that the sides face each other so as not to contact each other.

  [2] The electric double layer capacitor according to [1], wherein a composite material of carbon nanotubes and finely powdered activated carbon is used as the substance containing the carbon nanotubes.

  [3] In manufacturing the electric double layer capacitor according to [1] or [2], a substance containing the carbon nanotubes is dispersed in a solution, and a porous conductive film is used as a filter to perform vacuum suction filtration. A method for producing an electric double layer capacitor comprising laminating a substance containing carbon nanotubes on a conductive conductive film.

  [4] When manufacturing the electric double layer capacitor according to [1] or [2], a substance containing the carbon nanotubes previously formed into a film shape or a tape shape is overlaid on the porous conductive film, A method for producing an electric double-layer capacitor comprising: infiltrating a solution from the substrate, discharging the solution under reduced pressure from the opposite side, discharging the solution, and laminating a substance containing carbon nanotubes on the porous conductive film.

  The electric double layer capacitor according to the present invention has a structure including a composite film in which a substance containing carbon nanotubes as a polarizable electrode is laminated on a porous conductive film as a current collector. It is an electric double layer capacitor. In addition, since a composite film of a current collector and a polarizable electrode can be produced by a simple method, an electric double layer capacitor having excellent performance can be provided at low cost.

  Embodiments of an electric double layer capacitor and a method for manufacturing the same according to the present invention will be described below with reference to the drawings.

  Carbon nanotubes (CNT) are nano-sized long fine carbon fibers made by rounding graphene in which carbon atoms are regularly arranged in a hexagonal shape, and single-walled carbon nanotubes (SWCNT) are graphene tubes The diameter is 1 to several nm.

  Further, multi-walled carbon nanotubes (MWCNTs) in which graphene tubes are concentrically overlapped with each other have a diameter of several nanometers to several tens of nanometers.

  Carbon nanotubes are mainly synthesized by arc discharge method and pyrolysis method (CVD method). Generally, carbon nanotubes synthesized by arc discharge method have better crystallinity than carbon nanotubes synthesized by CVD method. And is characterized by excellent strength and electrical conductivity. Further, when the area specific capacity, which is one evaluation of the performance of the capacitor as a polarizable electrode, was investigated, as shown in Table 1, the area specific capacity of the carbon nanotubes by the arc discharge method is nearly twice as high as that of the CVD method. The value is shown.

  In order to exhibit the characteristics as a capacitor, it is necessary that the above-mentioned specific area capacity is high and the specific surface area is large, but the specific surface area can be increased by activation treatment etc. Specific capacity is a property unique to the material and is difficult to change easily. The reason why the area specific capacity of carbon nanotubes by the arc discharge method is high is considered to be due to its high crystallinity.

  In addition, said measurement was performed by the tripolar cell, using the propylene carbonate solution (concentration = 0.5 mol / L) of tetraethylammonium tetrafluoroborate for electrolyte solution. The current density is 40 mA / g, and the measurement potential region is 2 to 4 V vs. Li / Li +.

  From these results, it is possible to realize a small-sized and large-capacity electric double layer capacitor by using a carbon nanotube by an arc discharge method for the polarizable electrode of the electric double layer capacitor. Furthermore, the capacity | capacitance per unit volume can be further raised by filling fine powder activated carbon in the clearance gap between carbon nanotubes as a polarizable electrode.

However, in order to realize a small and large-capacity electric double layer capacitor, there are the following two problems.
(1) The internal resistance of the polarizable electrode and the contact resistance between the current collector and the polarizable electrode are reduced.
(2) Achieve a reduction in the thickness of the current collector and polarizable electrode.

  In response to the above problem (1), the internal resistance of the polarizable electrode is reduced by using a material containing carbon nanotubes synthesized by arc discharge method with good crystallinity and high electrical conductivity as the polarizable electrode. Although it is possible, further ingenuity is required to reduce the contact resistance with the current collector. In order to reduce the contact resistance with the current collector, it is necessary to increase the contact area between the current collector and the carbon nanotube. However, if amorphous carbon or fine powdered activated carbon contained as an impurity is interposed between the two, , Which increases the contact resistance.

  Therefore, as shown in FIGS. 1 and 2, a porous conductive film 1 is used as a current collector, and this is used as a filter, and carbon nanotubes 2 and finely powdered activated carbon 3 are uniformly dispersed using ultrasonic waves or the like. By subjecting the polarizable electrode solution 5 to suction filtration 6 under reduced pressure, a substance containing the carbon nanotubes 2 is laminated on the porous conductive film 1, so that the contact area between the current collector and the carbon nanotubes can be increased. In other words, by using the porous conductive film 1 as a filter, impurity amorphous carbon and finely powdered activated carbon are discharged from the pores 4 at the beginning of filtration, but the carbon nanotubes 2 are several μm or more in length. Therefore, it does not permeate the pores 4 and is laminated on the porous conductive film 1. After the carbon nanotubes 2 block the pores 4 to some extent, the solution permeates, but the amorphous carbon and fine powder activated carbon 3 cannot be permeated and are laminated. Therefore, in the vicinity of the pore 4, a contact surface of only the current collector and the carbon nanotube 2 is formed, and the contact resistance between the current collector and the polarizable electrode is reduced. In addition, a good contact surface having no void at the interface can be formed by the suction force. The solution may be anything as long as the polarizable electrode material is uniformly dispersed, and water or alcohol can be used. After lamination of the polarizable electrode, the solution is removed by drying using a heater 7 or the like.

  Furthermore, a thin and uniform polarizable electrode layer can also be formed by the vacuum suction filtration method for the above problem (2). That is, the lamination thickness of the polarizable electrode can be controlled by the electrode material concentration of the solution, the suction capability, and the suction time. A polarizable electrode can be continuously laminated using a strip-shaped current collector. In this case, the lamination thickness of the polarizable electrode is controlled by the electrode material concentration and the suction ability of the solution, the length of the suction surface, and the moving speed of the current collector.

  The pore diameter of the porous conductive film is larger than that of amorphous carbon or finely powdered activated carbon, and does not permeate carbon nanotubes. Specifically, a range of 0.1 to 5 μm, preferably 0.4 to 2 μm is suitable. ing. The particle size of the finely powdered activated carbon mixed with the carbon nanotubes is 0.01 to 2 μm, preferably 0.1 to 1 μm. The size of the carbon nanotube is suitably in the range of 1 to 100 nm in diameter, desirably 4 to 20 nm, 1 to 100 μm in length, desirably 5 to 20 μm.

  In addition, a material containing carbon nanotubes previously formed into a film shape or a tape shape is used as a polarizable electrode, and this is overlaid on a porous conductive film as a current collector, and the solution is infiltrated from it onto the opposite side. It is also possible to produce a composite film of a current collector and a polarizable electrode by sucking the solution under reduced pressure and discharging the solution. Also in this case, the amorphous carbon and fine powder activated carbon in the vicinity of the interface are removed, the contact resistance between the current collector and the polarizable electrode is reduced, and a good contact surface without a cavity or the like at the interface can be formed. Furthermore, since the film thickness of the polarizable electrode can be managed in advance, the film thickness can be managed more precisely.

  A coin-type electric double layer capacitor was manufactured using the composite film of the current collector and polarizable electrode thus manufactured. FIG. 3 shows the structure of the manufactured electric double layer capacitor. In FIG. 3, a composite film in which the current collector 8 and the polarizable electrode 9 are integrated has a structure in which they face each other through a separator 10 made of polypropylene nonwoven fabric. In a dry nitrogen atmosphere, an electrolyte solution (a solution of tetraethylammonium tetrafluoroborate in propylene carbonate (concentration = 1 mol / L)) was injected into the container 11 in a glove box and impregnated with the composite membrane. The container 11 was sealed with a stainless steel lid 13. Thus, a coin-type electric double layer capacitor was produced.

A silicon gel porous conductor film having a pore diameter of about 1 to 5 μm is used as a current collector, and fine powder activated carbon having an average particle diameter of about 1 μm is applied to a multi-walled carbon nanotube synthesized by an arc discharge method as a polarizable electrode 1: What was mixed in the weight ratio of 1 was used. Methanol was used as a solution for dispersing the polarizable electrode, and the layers were laminated to a thickness of about 100 μm. When the electric capacity in the unit current collector area of this capacitor was measured, it was about 10000 μF / cm ² , indicating an electric capacity about 10 times that of a general electric double layer capacitor made of activated carbon.

It is a figure which shows the composite film of the collector and polarizable electrode by this invention. It is a figure which shows the method to manufacture the composite film of the electrical power collector and polarizable electrode by this invention. It is a longitudinal cross-sectional view of the electric double layer capacitor by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous conductive film 2 Carbon nanotube 3 Fine powder activated carbon 4 Pore 5 Polarized electrode solution 6 Suction port 7 Heater 8 Current collector 9 Polarized electrode 10 Separator 11 Container 12 Gasket 13 Lid

Claims (4)

  A pair of composite films made by laminating a material containing carbon nanotubes synthesized by an arc discharge method that becomes a polarizable electrode on a porous conductive film that becomes a current collector, and the sides on which the materials containing carbon nanotubes are laminated An electric double layer capacitor characterized by being opposed so as not to contact each other.   2. The electric double layer capacitor according to claim 1, wherein a composite material of carbon nanotubes and finely powdered activated carbon is used as the substance containing the carbon nanotubes.   When manufacturing the electric double layer capacitor according to claim 1 or 2, carbon is deposited on the porous conductive film by dispersing the substance containing the carbon nanotubes in a solution and performing vacuum suction filtration using the porous conductive film as a filter. A method of manufacturing an electric double layer capacitor, comprising laminating a substance containing nanotubes.   In producing the electric double layer capacitor according to claim 1 or 2, a substance containing the carbon nanotubes previously formed in a film shape or a tape shape is overlaid on the porous conductive film, and the solution is infiltrated from above. A method for producing an electric double layer capacitor, comprising sucking a solution under reduced pressure from the opposite side to discharge the solution, and laminating a substance containing carbon nanotubes on the porous conductive film.

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