JP2000331892A - Electric double-layer capacitor and manufacture of electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the handling property of components in assembling steps to efficiently manufacture by providing a polymer gel type anhydrous electrolyte layer between polarizable electrodes and using an activated carbon fiber sheet as a base for these electrodes. SOLUTION: An electric double-layer capacitor is made by setting a fibrous sheet held between polarizable electrodes in a container, pouring an anhydrous electrolyte soln. in the container at a low pressure to impregnate this soln. in the sheet and then dissolving and gelling it. The polarizable electrode pref. uses an activated carbon fiber sheet and more pref. uses an acrylic activated carbon fiber sheet. The specific surface area of the acrylic activated carbon fiber is 500 m2/g or more as measured by the BET method.

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 excellent in safety as a power source for starting a cell motor, a power source for a hybrid vehicle, and a backup power source for a personal computer and the like, and a method of manufacturing an electrode used for the capacitor. is there.

[0002]

2. Description of the Related Art A polarized electrode in which activated carbon or carbon powder is used as a polyvinylidene fluoride-based polymer as a binder and an electrode surface is formed on a current collector surface, or two polarized films in which aluminum is plasma-deposited on an activated carbon fiber cloth to form a conductive layer. An electric double-layer capacitor in which a non-woven fabric such as polyethylene or polypropylene or a microporous film is interposed between electrodes as a separator, and this separator is impregnated with a non-aqueous electrolyte, has high output and excellent cycle characteristics. Is being promoted.

When an electric double layer capacitor using this non-aqueous electrolyte is exposed to a high-temperature atmosphere, the non-aqueous electrolyte is vaporized, its internal pressure is increased, and the shape of the capacitor is deformed.
Not only does the characteristic change significantly, but there is a risk of causing an explosion or fire, and there is a problem in safety management.

[0004] Another problem of the electric double layer capacitor is that in the case of a carbon electrode using activated carbon or carbon powder,
There is a phenomenon that carbon fine particles generated from peeling off from the carbon electrode move to the opposite electrode. The fine particles generated by the peeling of the carbon electrode move to the other electrode side electrophoretically, thereby increasing the leak current and causing a short circuit. Therefore, the movement of the fine particles between the electrodes means self-discharge, and the ability of the fine carbon particles to prevent the movement between the polarizations is greatly related to the basic performance of the capacitor.

On the other hand, the mobility of ion migration in the electrolyte appears in the form of liquid resistance, and an increase in this value tends to make it difficult to smoothly charge and discharge the capacitor. Therefore, in order to reduce the liquid resistance, it is necessary to increase the number of holes per unit area of the separator. Furthermore, the liquid resistance can be reduced by reducing the distance between the electrodes, and this can be achieved by reducing the thickness of the separator. In general, the electrolyte of an electric double layer capacitor uses a very strong polar organic solvent to dissolve a large amount of salt.
It is necessary not to react with this or to dissolve the separator, and it is also required that the electrolyte containing the separator is resistant to mechanical stress.

Various separators have been proposed as such. For example, there are high-density condenser paper called condenser paper, low-density condenser paper called electrolytic paper, polyethylene and polypropylene films having microporosity, and non-woven fabric using polyethylene fiber or polypropylene fiber. However, with condenser paper,
Conductive inhibition is large against the electrolyte, the desired capacitance and internal resistance cannot be obtained, and the average fine pore diameter of electrolytic paper is larger than the carbon fine particles. The leakage current could not be obtained.

Japanese Unexamined Patent Publication (Kokai) No. 6-36972 discloses a technique of an electric double layer capacitor in which the liquid retaining property of the nonaqueous electrolyte of the separator is enhanced and the nonaqueous electrolyte layer is easy to handle. Acrylic resin particles having a particle size of 10 to 100 μm
It has a great feature in that a carrier loaded with ２０20 wt% is used. However, an electric double layer capacitor using this separator has been found to improve the permeability of the non-aqueous electrolyte into the separator structure, improve the liquid retention, and improve the capacitor assembling process. There is a disadvantage that the volatilization of the non-aqueous electrolyte cannot be prevented.

Japanese Unexamined Patent Publication (Kokai) No. 9-129509 discloses a technique of an electric double layer capacitor using bacterial cellulose obtained by standing culture of acetic acid bacteria as a microporous separator for preventing penetration of carbon fine particles. . This capacitor has a great feature in that cellulose having a fine fiber network structure is used as a separator. However, a capacitor using this separator can prevent penetration of carbon fine particles,
Again, there is the disadvantage that the volatilization of the non-aqueous electrolyte cannot be prevented.

The development of an electric double layer capacitor free of such difficulties is also underway. In particular, a technique for solidifying a non-aqueous electrolyte, and particularly for gelling a non-aqueous electrolyte, polyacrylonitrile is used as a gelling agent. And acrylonitrile and (meth) acrylate copolymer are used. After heating and dissolving these acrylonitrile-based polymers in a non-aqueous electrolyte, the polymer gel electrolyte that has been cooled and gelled exhibits good ionic conductivity, liquid-trapping properties, and the ability to prevent penetration of carbon fine particles, but has high adhesion, There are difficulties in handling, and it is extremely difficult to assemble an electric double layer capacitor using this gel electrolyte, and it is extremely difficult to industrially produce a high-performance electric double layer capacitor.

On the other hand, there have been the following two types of base materials for polarizable electrodes conventionally used. That is, the first is
Powdered activated carbon obtained by activating sawdust, coconut shell, pitch and the like is press-formed or rolled together with a suitable binder to form a polarizable electrode. Second, phenolic, rayon-based, acrylic-based, pitch-based fibers and the like are subjected to flame resistance and carbonization activation treatment to form activated carbon or activated carbon fibers, which are felt, fibrous, paper, or sintered. And the like.

For example, as disclosed in Japanese Patent Application Laid-Open No. 3-85711, an active carbon fiber as an electrode material contains zinc or a compound thereof as disclosed in Japanese Patent Application Laid-Open No. 3-85711. Thus, a polarizable electrode having a large capacity and a small self-discharge can be obtained. However, the method is a polymerization, spinning, flameproofing, activation each step,
Alternatively, zinc or a compound thereof needs to be added in any step, which complicates the step and is not industrially preferable.

[0012]

SUMMARY OF THE INVENTION Generally, the capacity per unit weight of activated carbon used in an electric double layer capacitor is proportional to the specific surface area of activated carbon. In order to increase the capacitance per unit weight of activated carbon, it is necessary to use activated carbon having a high specific surface area.

The present inventors have proposed an electric double layer capacitor,
As a result of studying the purpose of improving the handling of each part in the assembly process and making it efficiently, a polymer gel type non-aqueous electrolyte layer was provided between the polarized electrodes, and an activated carbon fiber sheet was used as the polarized electrode It has been found that the object can be achieved by using as a base material, and the present invention has been completed. The gist of the invention is an electric double layer capacitor including a polymer gel type nonaqueous electrolyte layer between polarized electrodes, and using an activated carbon fiber sheet as a base material as the polarized electrodes. Further, the activated carbon fiber sheet is obtained by subjecting a fiber made of an acrylonitrile copolymer to a flame-resistant treatment in an oxidizing gas atmosphere, and then cutting the obtained flame-resistant fiber to have a length of 1 mm or more and less than 5 mm. It is characterized by being manufactured by blending with a binder to form an oxidized fiber sheet, followed by a steam activation treatment.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The polymer gel type non-aqueous electrolyte layer used in carrying out the present invention includes a fibrous material of an organic polymer soluble in a non-aqueous electrolyte and capable of forming a gel,
It is preferable to use a fibrous sheet mainly composed of pulp-like material as a carrier for the non-aqueous electrolyte. The fibrous material and the pulp-like material used in forming the polymer gel electrolyte layer of the present invention are fibrous materials having a fiber diameter of about 1 to 100 μm, and those having a fiber length of about 5 mm or less are preferably used.

A fibrous sheet made of a fibrous material or pulp having an extremely small fiber diameter is not preferable because its strength is insufficient and its handling property is insufficient. On the other hand, a fibrous sheet made from a fiber having an excessively large fiber diameter is inferior in impregnation and solubility of the non-aqueous electrolyte, and inferior in the formability of a polymer gel electrolyte layer having good performance. Further, there is a disadvantage that it is difficult to make a fibrous sheet made of a fiber having a long fiber length or a pulp-like material having a uniform thickness.

The fibers or pulp-like materials used in the present invention may be those having a large number of fibrils. These fibers or pulp-like materials may be prepared by melting a polymer soluble in a non-aqueous electrolyte with a melt-spinning method, a wet-spinning method, or a flash method. It can be produced by a spinning method or a spray coagulation spinning method of a polymer organic solvent solution.

As the fiber form, a pulp-like material, a monofilament-like material, a side-by-side type composite fiber, a true conjugate composite fiber, a sea-island type composite fiber, or a split fiber of a composite fiber can be used. As a composite fiber,
A composite fiber of non-aqueous electrolyte soluble polymers or a composite fiber of a non-aqueous electrolyte soluble polymer and a non-aqueous electrolyte non-soluble polymer can be used.

The non-aqueous electrolyte soluble or swellable polymer used in carrying out the present invention includes polyacrylonitrile, polymethacrylonitrile, acrylonitrile / vinyl acetate copolymer, acrylonitrile / vinyl chloride copolymer, acrylonitrile / methacrylonitrile copolymer, Polymethyl methacrylate, vinylidene fluoride /
Examples include hexafluoropropylene copolymer, polyethylene oxide, polypropylene oxide, ethylene oxide / propylene oxide block copolymer, polyvinyl acetate, and acetylated cellulose. Among these polymers, a polymer having an acrylonitrile unit polymerization amount of 50% by weight or more, more preferably 60% by weight or more, is preferable in view of its handleability, supportability of a non-aqueous electrolyte, and gel formation.

The fibrous sheet made of fibers or pulp used in carrying out the present invention may be a nonwoven fabric of short fibers, a paper-like sheet made of pulp, or a knitted fabric made of fibers of a polymer insoluble in a non-aqueous electrolyte. A woven structure of a woven fabric in which the above short fibers and pulp-like materials are entangled and engaged can be used.

In forming the fibrous sheet used in the present invention, the fibers or pulp constituting the support may be natural pulp, polyethylene pulp, aromatic polyamide pulp, polypropylene pulp or polyolefin fiber, polyvinylidene fluoride, or the like. System fibers, aromatic polyamide fibers, polyphenylene sulfide fibers, polysulfone fibers, ceramic fibers, glass fibers, and the like can be used.

The fibrous sheet used in carrying out the present invention preferably has a fiber or pulp content of 50% by mass or more made of a non-aqueous electrolyte-soluble or swellable polymer. The fiber or pulp-like material made of the non-aqueous electrolyte-insoluble polymer or natural product contained in the fibrous sheet greatly contributes to the improvement of the strength of the gel electrolyte sheet-like material made from the fibrous sheet-like material. It is a component that does.

Further, the porosity of the fibrous sheet used in carrying out the present invention is preferably in the range of 20 to 80% by volume to improve the impregnation of the fibrous sheet with the non-aqueous electrolyte and obtain a uniform property. This is preferable because it constitutes a non-aqueous electrolyte polymer gel layer provided with

Specific examples of the non-aqueous electrolytic solution used in carrying out the present invention include those having a high dielectric constant or a low viscosity in an aprotic polar solvent, those having an electrochemical stability and the following electrolytes. An organic solvent that dissolves the salt well or a mixture thereof is appropriately selected. Specific examples thereof include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate, and diethyl carbonate.
Carbonates such as carbonate, ethyl methyl carbonate (EMC), lactones such as γ-butyrolactone (BL), amide solvents such as dimethylformamide (DMF) and dimethylacetamide (DMAC), sulfolane, acetonitrile, dimethyl sulfone Foxide (DMS
O), tetrahydrofuran, dimethoxyethane and the like.

As a specific example of the electrolyte salt, a quaternized alkylammonium salt is preferable as the electrolyte in a non-aqueous solvent, and a specific example is a (R ₄ N) ⁺ (M) ⁻ structure. . Examples of the alkyl group represented by R include methyl, ethyl, and butyl groups, and examples of M as the anion component include a tetrafluoroboron (BF ₄ ) and perchlorate (ClO ₄ ) group.

The electric double layer capacitor of the present invention is housed in a container with a fibrous sheet sandwiched between polarized electrodes,
A non-aqueous electrolyte is injected into this container, preferably under reduced pressure, and after this electrolyte is sufficiently impregnated into a fibrous sheet,
It can be made by gelling after dissolution.

The lamination of the polarizing electrode and the fibrous sheet for forming the non-aqueous electrolyte allows these materials to be handled in a non-adhesive state, so that the capacitor assembling step can reduce the defective rate.

Since the impregnation of the fibrous sheet with the non-aqueous electrolyte can utilize the capillary phenomenon based on the fiber structure, the impregnation of the non-aqueous electrolyte of the fibrous sheet is fast, no non-impregnated portions are generated, and microvoids are not generated. And an electric double layer capacitor having a polymer gel electrolyte layer.

On the other hand, as the polarized electrode material used in carrying out the present invention, any activated carbon having a large specific surface area can be used, but as a form, there is little generation of fine powder and a fibrous material which is excellent in handleability. It is preferable to use a sheet-like material, that is, an activated carbon fiber sheet. More preferably, it is preferable to use an acrylic activated carbon fiber sheet having high mechanical strength and excellent workability. The specific surface area of the acrylic activated carbon fiber used is preferably 500 m ² / g or more.

The activated carbon fiber used in the present invention has a specific surface area of 500 m ² / g or more as measured by the BET method by subjecting an acrylonitrile-based polymer fiber to a flame-resistant treatment in an oxidizing atmosphere and subjecting it to steam activation treatment. You can do it.

The activated carbon fiber sheet used in carrying out the present invention has a length of 1 mm for the oxidized yarn made as described above.
~ 5mm carbon fibrous material, and dispersed in water together with polyethylene pulp, polypropylene pulp, natural pulp, etc. as a binder component, and paper-formed by a wet paper-making method to obtain a flame-resistant fiber sheet-like material. It can be obtained by performing a steam activation treatment. The polarized electrode formed by this method has a high specific surface area of the activated carbon fiber, does not peel off the activated carbon fiber from the polarized electrode, and has good handleability.

[0031]

The present invention will be described in more detail with reference to the following examples.

Reference Example 1 An oxidized fiber sheet was prepared by the following method.

The fiber made of the acrylonitrile copolymer was heated in air at 240 ° C. for 1 hour under tension to make it flame-resistant. After cutting the obtained oxidized fiber to a length of 3 mm,
90 parts by mass of the oxidized fiber and 10 parts by mass of pulp-like polypropylene (manufactured by Mitsui Chemicals, SWP Y600) were mixed, and a sheet was prepared from an aqueous dispersion of this mixture by a wet papermaking method. Sheet weight is 50 g / m ² , sheet thickness 400μ
m, and the sheet had a tensile strength of 2.1 MPa / 15 mm.

REFERENCE EXAMPLE 2 The oxidized fiber sheet prepared in Reference Example 1 was subjected to a steam activation treatment by the method disclosed in JP-A-9-31759. That is, the oxidized sheet was placed in a furnace and activated at 800 ° C. for 5 minutes by supplying steam at a rate of 5 g / min. The specific surface area of the activated carbon fiber sheet subjected to the activation treatment was 1500 m ² / g.
This sheet has a thickness of 220 μm and a tensile strength of 1.7 MPa.
/ 15 mm.

[Reference Example 3] The flame-resistant fiber sheet prepared in Reference Example 1 was tensioned at 1000 ° C. for 3 minutes, and 5 g of water vapor was applied.
/ Minute and supplied to a furnace for activation treatment to obtain an activated carbon fiber sheet. The specific surface area was 1200 (m ² / g), the tensile strength was 1.5 MPa / mm ² , and the thickness of the sheet was 180 μm.

Example 1 A 25 μm-thick polyacrylonitrile fibril having a thickness of 25 μm was placed between two polarizing electrodes obtained by welding a nickel net as a current collector to the activated carbon fiber sheet used in Reference Example 2 to form a polarizing electrode. The sheet was sandwiched and inserted into a button-shaped airtight container so as not to short-circuit between the electrodes. An injection port for the electrolyte is prepared in the closed container in advance, and after degassing the gas from this injection port by a vacuum operation, [(CH ₃ ) ₄
N] ⁺ BF ₄ ⁻ was dissolved in an electrolytic solution consisting of a mixture of ethylene carbonate and propylene carbonate in a weight ratio of 2: 1 by injection, and the opening was closed with a sealant. Next, the container was heated to 100 ° C. and then cooled to room temperature to gel the polyacrylonitrile fibril sheet. When the capacity of this capacitor was set to a charge termination potential of 2 V and a discharge termination potential of 1 V, charge / discharge was performed at a charge / discharge current of 1 mA, and it was 0.35 F / cm ² .

Example 2 An electric double layer capacitor was manufactured in the same manner as in Example 1 except that the activated carbon fiber sheet obtained in Reference Example 3 was used.
It was ²⁰ F / cm ² . Also, the assembly process of the capacitor was extremely easy, and no trouble occurred in the assembly process of the capacitor.

[0038]

According to the present invention, an electric double layer capacitor can be efficiently manufactured by using an acrylic activated carbon fiber sheet as a polarizing electrode material by improving the handleability of each part in the assembly process. It becomes possible and its industrial significance is great.

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Claims (5)

[Claims] 1. An electric double layer capacitor having a polymer gel type non-aqueous electrolyte layer between polarized electrodes, wherein an activated carbon fiber sheet is used as a polarized electrode as a base material. 2. The electric double layer capacitor according to claim 1, wherein an activated carbon fiber sheet mainly composed of acrylic activated carbon fibers is used as the activated carbon fiber sheet. 3. The electric double layer capacitor according to claim 1, wherein the activated carbon fiber has a specific surface area of 500 m ² / g or more measured by an N ₂ adsorption BET method. 4. A fiber comprising an acrylonitrile polymer as a polarizing electrode, which is subjected to a flame-proof treatment in an oxidizing gas atmosphere.
4. An activated carbon fiber sheet obtained by mixing a flame-resistant fiber cut to a fiber length of 1 to 5 mm with a fibrous binder into a flame-resistant fiber sheet, and subjecting the fiber to a steam activation treatment. The electric double layer capacitor according to any one of the above. 5. A flame-resistant fiber obtained by treating an acrylonitrile-based polymer fiber in an oxidizing atmosphere to obtain a fiber having a fiber length of 1 to 5 mm.
The sheet-like material obtained by blending the cut flame-resistant fiber and the binder fiber is subjected to a steam activation treatment, and the flame-resistant fiber N
A method for producing a sheet-like electrode, wherein the specific surface area measured by a _two- adsorption BET method is 500 m ² / g or more.