JP2003282366A - Electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor having high safety and high capacity. <P>SOLUTION: An electric double-layer capacitor uses a separator containing a copolymer P, which comprises a polymer containing an acid radical containing monomer and a thermoplastic polymer. When the copolymer P is a block copolymer, which is composed of a polymer block B1 composed of the acid radical containing monomer and a thermoplastic polymer block B2, a high-performance electric double-layer capacitor is attained. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safe and high capacity electric double layer capacitor.

[0002]

2. Description of the Related Art An electric double layer capacitor utilizing an electric double layer generated at the interface between a polarizable electrode and an electrolytic solution is used as a backup power source for personal computers, a power source for hybrid vehicles, and a power source for starting a starter motor.

The electric double layer capacitor has a structure in which an electrolytic solution is filled between polarizable electrodes facing each other through a separator in a cell. As the electrolytic solution, an aqueous electrolytic solution such as a sulfuric acid aqueous solution or a non-aqueous electrolytic solution is used, but an electric double layer capacitor using the non-aqueous electrolytic solution has a high capacity and is widely used. The non-aqueous electrolyte may evaporate in a high temperature atmosphere, the internal pressure may rise, the shape of the capacitor may be deformed, the characteristics may deteriorate, and a fire may occur. In addition, the electrolytic solution may leak, which may cause a failure of a device equipped with the electric double layer capacitor.

[0004]

An object of the present invention is to provide an electric double layer capacitor capable of preventing vaporization and leakage of a non-aqueous electrolyte solution.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a copolymer P composed of a polymer containing an acid group-containing monomer and a thermoplastic polymer is used.
The present inventors have found an electric double layer capacitor using a separator containing. According to the present invention, the separator containing the copolymer P swells with the non-aqueous electrolytic solution to form a gel electrolyte, so that vaporization and leakage of the non-aqueous electrolytic solution can be prevented. In addition, the acid group present in the copolymer P expresses affinity for the electrolytic solution, and the capacity of the electric double layer capacitor can be improved.

When the copolymer P is a block copolymer composed of a polymer block B1 composed of an acid group-containing monomer and a thermoplastic polymer block B2, a copolymer in which acid groups are present randomly. As compared with the polymer P, a larger number of acid groups go out, so that the affinity for the electrolytic solution becomes higher. Copolymer
As the acid group of P, a sulfonic acid group and / or a carboxylic acid group can be used predominantly.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The copolymer P comprising the polymer containing the acid group-containing monomer and the thermoplastic polymer relating to the electric double layer capacitor of the present invention exhibits affinity for the electrolytic solution due to the effect of the acid group. As the thermoplastic polymer, an isoprene-based polymer,
Examples thereof include a styrene-based polymer, a butadiene-based polymer, a polyorganosiloxane-based polymer, a polyvinylidene fluoride-based polymer, a polyolefin-based polymer and a copolymer of these polymers. The polymer containing an acid group-containing monomer is obtained by adding an acid group-containing monomer to the thermoplastic polymer by a graft polymerization method, or by adding an acid group by a sulfonation treatment, a plasma treatment, a corona treatment, or the like. It can be obtained by The acid group is preferably a sulfonic acid group and / or a carboxylic acid group.

The acid group content of the copolymer P relating to the electric double layer capacitor of the present invention is preferably 0.5 to 20 mmol / g, more preferably 2 to 10 mmol / g. When the acid group content of the copolymer P is less than 0.5 mmol / g, the affinity for the electrolytic solution becomes low and a high capacity electric double layer capacitor cannot be obtained. When the acid group content of the copolymer P exceeds 20 mmol / g,
The mechanical strength of the copolymer P is insufficient.

The copolymer P relating to the electric double layer capacitor of the present invention may be a copolymer in which acid groups are randomly present, but a polymer block comprising an acid group-containing monomer. A block copolymer composed of B1 and a thermoplastic polymer block B2 is more likely to have an acid group going outward. When the acid group of the copolymer P goes outward, the affinity for the electrolytic solution is improved.

The separator containing the copolymer P including the polymer containing the acid group-containing monomer and the thermoplastic polymer, which is related to the electric double layer capacitor of the present invention, is formed of only the copolymer P. Film. This film is swollen by an electrolytic solution and exhibits ionic conductivity, but may be a porous film that does not cause short circuit of electrodes. The film formed of the copolymer P can be manufactured by a uniaxial stretching method, a biaxial stretching method, a casting method, or the like.

The surface of a porous thin film such as a nonwoven fabric or a porous film may be coated with the copolymer P, or the pores of the porous thin film may be filled with the copolymer P. In order to coat a part of the surface of the porous thin film with the copolymer P or to fill the pores, a method of impregnating the solution or dispersion containing the copolymer P with the porous thin film and then drying Generally used. A surfactant, alcohol, or the like as a wetting agent or a defoaming agent may be added to the treatment liquid.

In the electric double layer capacitor of the present invention,
Surface treatment such as corona discharge treatment, glow discharge treatment, plasma discharge treatment, and ultraviolet irradiation treatment for the porous thin film before being dipped in the treatment liquid containing the copolymer P and for the porous thin film dried after being dipped You may do it.

In the electric double layer capacitor of the present invention,
By irradiating the porous thin film dipped in the treatment liquid containing the copolymer P with actinic rays, the copolymer is chemically bonded to the surface of the porous thin film, or the copolymer is crosslinked. , Mechanical strength can be expressed. The actinic rays mentioned here include ultraviolet rays, radiation (α rays, γ rays, electron beams, X rays, neutron rays) and the like. Of these, ultraviolet rays and electron beams are most preferably used from the viewpoints of handling and deterioration of the porous thin film and the copolymer P.

The porous thin film that can be used in the electric double layer capacitor of the present invention contains a plurality of fibers having different materials, fiber diameters and fiber lengths, so that the porosity, mechanical strength, heat resistance, etc. A non-woven fabric capable of controlling the above properties can be predominantly used.

Nonwoven fabrics that can be used in the electric double layer capacitor of the present invention include cellulosic fibers, polyolefin fibers, polyester fibers, polyvinyl chloride fibers, polyvinyl alcohol fibers, polyacrylonitrile fibers, and polyamide fibers. , Fluororesin fiber,
It is composed of glass fiber, wholly aromatic polyamide fiber, wholly aromatic polyester fiber, recycled fiber, semi-synthetic fiber, natural fiber and the like. The fibers constituting the non-woven fabric may be fibrillated.

The thickness of the separator relating to the electric double layer capacitor of the present invention is not particularly limited, but it is preferably thin from the viewpoint that the electric double layer capacitor can be miniaturized.
It is 200 μm, and more preferably 10 to 100 μm.

In the electric double layer capacitor of the present invention,
As a medium of the electrolytic solution, an aprotic polar solvent having a high dielectric constant, a low viscosity one, or an organic solvent which is electrochemically stable and dissolves an electrolyte salt is used.
For example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, carbonates such as ethylmethyl carbonate, lactones such as γ-butyrolactone, amide solvent such as dimethylformamide, dimethylacetamide, sulfolane, acetonitrile, dimethyl sulfoxide, tetrahydrofuran, Examples thereof include dimethoxyethane. These electrolytic solutions are present in 0 to 99% in the electrolytic solution relating to the electric double layer capacitor of the present invention.

Examples of the electrolyte salt that can be used in the electric double layer capacitor of the present invention include cations selected from metal cations, ammonium ions, amidinium ions, guanidinium ions and the like, and chlorine ions and bromine ions. , Iodine ion, perchlorate ion, thiocyanate ion, tetrafluoroborate ion, nitrate ion, A
sF6-, PF6-, stearyl sulfonate ion, octyl sulfonate ion, dodecylbenzene sulfonate ion, naphthalene sulfonate ion, dodecyl naphthalene sulfonate ion, 7,7,8,8-tetracyano-p-quinodimethane ion, X1SO3-, [(X1S
O2) (X2SO2) N]-, [(X1SO2) (X2
SO2) (X3SO2) C]-and [(X1SO2)
Examples of the compound include an anion selected from (X2SO2) YC]-and the like. However, X1, X2, X3 and Y are electron withdrawing groups. Furthermore, preferably X
1, X2 and X3 are each independently a perfluoroalkyl group or a perfluoroaryl group having 1 to 6 carbon atoms, and Y is a nitro group, a nitroso group, a carbonyl group, a carboxyl group or a cyano group. X1, X2 and X3 may be the same or different. These electrolytes are present in the electrolytic solution that can be used in the electric double layer capacitor of the present invention in an amount of 0.1 to 60%, preferably 1.0 to 40%.

In the electric double layer capacitor of the present invention, a carbonaceous electrode containing a carbon material as a main component is used for both the positive electrode and the negative electrode. Activated carbon, carbon black, polyacene or the like can be used as the carbon material. If necessary, a conductive material may be added to the carbonaceous electrode in order to enhance the conductivity, and an organic binder resin is added to form a sheet on the metal current collector to be integrated with the current collector. Electrodes may be formed. As the organic binder resin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide resin, polyamideimide resin or the like can be used. Further, as the metal current collector, a foil such as aluminum or stainless steel, a net, or the like can be used.

[0020]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 Production of Electrically Insulating Porous Thin Film 70% by mass of bleached softwood kraft pulp with a refiner up to 280 ml of Canadian standard freeness (CSF), fineness 0.1 dtex, fiber length 3 mm, melting point 25
20% by mass of polyester fibers at 5 ° C. and 10% by mass of microfibrillated cellulose were dispersed in water using a pulper, and then diluted with water to a predetermined concentration to prepare a slurry. From this slurry by a wet method using a cylinder paper machine,
A wet non-woven fabric having a basis weight of 18 g / m ² and a thickness of 75 μm was obtained.
The wet-processed non-woven fabric is calendered to have a basis weight of 18 g /
A porous thin film a having m ² , thickness of 50 μm and porosity of 74% was obtained.

Copolymer impregnation treatment After impregnating the porous thin film a with the aqueous dispersion shown in Table 1, 12
Separator A was obtained by drying with a Yankee dryer at 0 ° C. The separator A had a basis weight of 28 g / m ² , a polymer adhesion amount of 10 g / m ² , and a thickness of 53 μm.

[0023]

[Table 1]

Electric Double Layer Capacitor 80 g of highly active activated carbon having a non-surface area of 2000 m ² / g and an average particle size of 8 μm, 10 g of acetylene black, and 12
100% PVDF (N-methylpyrrolidone solution) 100
g and N-methylpyrrolidone (150 g) were mixed to prepare an activated carbon-containing liquid. This solution was applied onto an aluminum foil to produce a capacitor electrode. After stacking this electrode and separator A and assembling into a rectangular cell, (C ₂ H ₅ ) ₄
NBF ₄ 18.1 parts by weight, propylene carbonate
An electrolytic solution consisting of 81.9 parts by weight was injected to prepare a laminated electric double layer capacitor. The capacitance of the electric double layer capacitor was 18F. A 3 mmφ metal rod was pierced into this electric double layer capacitor, but no liquid leakage occurred.

Example 2 Copolymer Impregnation Treatment After impregnating the porous thin film a with the aqueous dispersion described in Table 2 and draining the water,
Ultraviolet rays were radiated at 85 W / cm using a high pressure mercury lamp, dried with a Yankee dryer at 130 ° C., and then pressure-treated to obtain a separator B. Separator B
Had a basis weight of 30 g / m ² , a copolymer adhesion amount of 12 g / m ² , and a thickness of 53 μm.

[0026]

[Table 2]

Electric Double Layer Capacitor An electric double layer capacitor was manufactured in the same manner as in Example 1 except that Separator B was used as the separator.
The capacitance of the obtained electric double layer capacitor was 21F. A 3 mmφ metal rod was pierced into this electric double layer capacitor, but no liquid leakage occurred.

Example 3 Production of Porous Thin Film Polyester fiber having a fineness of 0.1 dtex, fiber length of 3 mm, melting point of 255 ° C., 30% by mass, fineness of 1.7 dtex, polyester fiber having 10 mm of fiber length, 40% by mass, fiber length of 3 m
m of polyester having a melting point of 255 ° C./modified polyester core-sheath fiber having a melting point of 110 ° C. was dispersed in water together with a dispersion aid using a pulper, and then diluted with water to a predetermined concentration to prepare a slurry. From this slurry, a wet method was used using a cylinder paper machine to obtain a basis weight of 20 g / m ² and a thickness of 60 μm.
m wet non-woven fabric was produced. 1 for this wet non-woven fabric
Thermal calendaring was performed at 80 ° C. The obtained porous thin film b had a basis weight of 20 g / m ² , a thickness of 50 μm and a porosity of 71.
%Met.

Copolymer impregnation treatment After impregnating the porous thin film b with the aqueous dispersion described in Table 3, 12
Separator C was obtained by drying with a Yankee dryer at 0 ° C. The separator C had a basis weight of 38 g / m ² , a polymer adhesion amount of 18 g / m ² , and a thickness of 53 μm.

[0030]

[Table 3]

Electric Double Layer Capacitor An electric double layer capacitor was manufactured in the same manner as in Example 1 except that Separator C was used as the separator.
The capacitance of the obtained electric double layer capacitor was 17F. A 3 mmφ metal rod was pierced into this electric double layer capacitor, but no liquid leakage occurred.

Example 4 The aqueous dispersion shown in Table 1 was cast on a polytetrafluoroethylene sheet, water was removed at 150 ° C., then the mixture was cooled to room temperature and then peeled off to consist of only the copolymer. A separator D was obtained.

Electric Double Layer Capacitor An electric double layer capacitor was manufactured in the same manner as in Example 1 except that Separator D was used as the separator.
The capacitance of the obtained electric double layer capacitor was 22F. A 3 mmφ metal rod was pierced into this electric double layer capacitor, but no liquid leakage occurred.

Example 5 The aqueous dispersion shown in Table 3 was cast on a polytetrafluoroethylene sheet, water was removed at 150 ° C., and the mixture was cooled to room temperature and then peeled off to form a copolymer only. A separator E was obtained.

Electric Double Layer Capacitor An electric double layer capacitor was manufactured in the same manner as in Example 1 except that the separator E was used as the separator.
The capacitance of the obtained electric double layer capacitor was 24F. A 3 mmφ metal rod was pierced into this electric double layer capacitor, but no liquid leakage occurred.

[0036]

As described above, according to the present invention, it is possible to obtain a high-capacity electric double layer capacitor with high safety which can prevent leakage of the non-aqueous electrolyte solution.

Claims (3)

[Claims] 1. An electric double layer capacitor comprising a separator containing a copolymer P comprising a polymer containing an acid group-containing monomer and a thermoplastic polymer. 2. The copolymer P is a block copolymer composed of a polymer block B1 composed of an acid group-containing monomer and a thermoplastic polymer block B2.
The electric double layer capacitor described. 3. The acid group of the copolymer P is a sulfonic acid group and / or a carboxylic acid group.
Or the electric double layer capacitor as described in any one of 2 above.