JP2001143973A - High density electrode made mainly of spherical activated carbon and electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high density electrode with high electrostatic capacity per volume and low resistance as an electrode in an electric double layer capacitor. SOLUTION: A high density electrode contains spherical activated carbon of 50 to 95 wt.% with average grain size of 1 to 10 μm and minute hole volume of 1.5 cm3/g or below, conductivity applying material of 30 wt.% or below, and polymer combining material of 0.5 to 20 wt.%. Then, an electric double layer capacitor with apparent density of 0.6 g/cm3 or above is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density electrode of an electric double layer capacitor mainly composed of spherical activated carbon and an electric double layer capacitor provided with this electrode.

The electric double layer capacitor of the present invention has a high energy density per volume and can be suitably used for a wide range of applications such as a power supply for various portable devices, a standby power supply for home electric appliances, an optical communication UPS, and a power supply for electric vehicles.

[0003]

2. Description of the Related Art As an electric double layer capacitor, an element in which a separator is interposed between a pair of electrodes mainly composed of activated carbon formed on a current collector is insulated from a metal case and a metal lid together with an electrolytic solution. A coin type sealed in a metal case by a gasket, or a winding element formed by winding a pair of sheet-like electrodes via a separator is housed in a metal case together with an electrolytic solution, and the electrolytic solution does not evaporate from an opening of the case. There is known a wound type that is sealed.

Further, as an application for large current and large capacity, a multilayer electric double layer capacitor in which an element formed by laminating a large number of sheet-like electrodes via a separator is incorporated has been proposed (Japanese Patent Application Laid-Open No. HEI 4 (1999) -1994). -154106, JP-A-3-
No. 203311 and JP-A-4-286108). In this method, a sheet-shaped electrode formed into a rectangular shape is used as a positive electrode and a negative electrode, a plurality of layers are alternately stacked via a separator to form a laminated element, and a positive electrode lead member and a negative electrode lead member are connected to the ends of the positive electrode and the negative electrode by caulking. Housed in the case in a state,
The element is impregnated with an electrolytic solution and sealed with a lid.

Conventionally, a high-dielectric solvent such as water or propylene carbonate has been used for an electrolytic solution of an electric double layer capacitor in order to dissolve the electrolyte at a high concentration.
Also, as the electrodes, those mainly composed of activated carbon having a large specific surface area are used because the electric double layer capacitor formed on the surface thereof contributes to the capacitance (capacitance) of the electric double layer capacitor. ing.

The important performance requirements for an electric double layer capacitor are generally: a) high capacitance, b) high energy density, c) high durability in repeated charge and discharge cycles, d. ) Low internal resistance.

In particular, in the case of an electric double layer capacitor used as a power supply for a passenger car such as a power supply for an electric car, etc., as easily understood, a passenger's riding space and a luggage mounting space as large as possible in the vehicle are required. In order to ensure this, first, it is the most strongly required condition that a large capacitance can be obtained in a small volume without occupying as much space in the vehicle as possible as the power supply itself. Furthermore, it is strongly required that the power supply that keeps driving the motor has low internal resistance and high long-term reliability.

In order to increase the capacitance per unit volume of the electric double layer capacitor, basically, it is sufficient to fill the predetermined volume of activated carbon having a large capacitance per unit weight to the maximum. .

As described above, in order to maximize the capacitance per unit volume, conventionally, activated carbon is processed into an electrode using various methods as described below. That is,

A) Activated carbon powder is kneaded with a solvent of an electrolytic solution such as sulfuric acid to form a slurry, and is formed by pressing under pressure (US Pat. No. 3,288,641).

B) A carbon paste made of a viscous substance obtained by adding a polytetrafluoroethylene (hereinafter referred to as PTFE) as a binder to a mixture of the activated carbon powder and the electrolytic solution, if necessary, is coated on the current collector. Things (Tokugyo Sho 5
No. 3-7025, JP-B-55-41015).

C) A kneaded product comprising activated carbon, a binder such as PTFE, and a liquid lubricant is preformed, and then stretched or rolled to form a sheet (Japanese Patent Application Laid-Open No. 63-107).
011 and JP-A-2-235320).

D) Activated carbon powder and PTFE are mixed to form a paste, coated and dried on a current collector, heated to a temperature equal to or higher than the melting point of PTFE, and press-molded (JP-A-9-36).
005).

E) An activated carbon powder and a powdery or granular phenolic resin are carbonized, and the activated carbon powder is combined with a phenolic resin carbide to obtain a solid electrode (Japanese Patent No. 2778425).

According to studies by the present inventors, it is difficult to obtain an electrode having a sufficiently high capacitance per unit volume by these known methods of processing activated carbon powder or particles into an electrode. . One of the reasons is presumed to be that the filling rate of the activated carbon powder when the activated carbon powder is formed into a sheet-like electrode is low.

Usually, activated carbon is a carbon source derived from plants such as sawdust and coconut shell; a carbon source derived from coal and petroleum-based materials such as coke and pitch; or a synthetic polymer such as phenolic resin, furfuryl alcohol resin, and vinyl chloride resin. A carbonaceous material obtained by carbonizing and activating a carbon material is mechanically pulverized by a pulverizer into fine powder. The pulverized activated carbon obtained by such mechanical pulverization has a so-called crushed shape having uniformly irregular corners and sharp edges.

The present inventors formed such mechanically crushed activated carbon into an electrode by the above-mentioned respective forming methods, and observed the cross section in detail with a microscope. It was clearly recognized that the activated carbon particles having a shape caused bridging with each other, and that many excessive voids were formed in the electrode. It is presumed that a conventional electrode formed by processing activated carbon has such an excess space, which prevents high-density filling of activated carbon powder, and makes it impossible to sufficiently increase the capacitance per unit volume.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an electrode in which activated carbon powder is densely packed per unit volume.
Another object of the present invention is to provide an electric double layer capacitor which uses this high-density electrode and has a high capacitance per unit volume, a low internal resistance, and excellent long-term reliability.

The inventors of the present invention have conducted intensive studies from such a viewpoint. As a result, the use of activated carbon having a specific particle size, which is spherical or nearly spherical and has substantially no corners or sharpness, enables the unit volume of activated carbon to be reduced. Was found to be able to obtain a high-density electrode filled with high density. The present invention has been made based on such findings.

[0020]

According to the present invention, 50 to 95% by mass of spherical activated carbon having an average particle size of 1 to 10 μm and a pore volume of 1.5 cm ³ / g or less, Mass% or less, and 0.5 to 20 mass% of a polymer binder, and a bulk density of 0.6 g / cm ³ or more. ,
It is called the electrode of the present invention. ), Are provided.

Further, according to the present invention, an electric double layer capacitor (hereinafter referred to as an electric double layer capacitor of the present invention) comprising such a high-density electrode is provided.
Is provided.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, a spherical activated carbon having an average particle diameter of 1 to 10 μm and a pore volume of 1.5 cm ³ / g or less (hereinafter, referred to as a spherical activated carbon in the present invention) is used.

As an example in which a conventional spherical activated carbon is used as an electrode material of an electric double layer capacitor, a mesophase small sphere (mesophase pitch small) is prepared by heating a bituminous substance such as petroleum heavy oil such as coal tar or coal tar pitch. It has been proposed to use spherical activated carbon, which is produced as a sphere), carbonized and activated after separation and purification, as an electrode material (Japanese Patent Laid-Open No. 2-2).
No. 5227). However, in the case of mesophase spheres, it is difficult to sufficiently increase the particle size before carbonization,
Since the sphere after the carbonization treatment has a nanometer level much smaller than the particle diameter specified in the present invention, which leads to an increase in internal resistance when an electrode is formed, it is not possible to achieve the object of the present invention. Can not.

It should be noted that, as a reminder, the spherical activated carbon derived from the mesophase pitch microspheres is the one in which the shape of the spherical pitch inevitably formed in the synthesis process happens to become activated carbon, Although its density can be increased, its main purpose is to obtain 2,000 to 5,000 m ² / g, preferably 3, which cannot be obtained with ordinary activated carbon.
It is intended to utilize a high specific surface area of 000 to 4,500 m ² / g, and has a different basic technical idea from the spherical activated carbon in the present invention.

The spherical activated carbon in the present invention is composed of spherical particles having extremely high sphericity, as shown in a scanning electron micrograph in FIG. In the present invention,
Circularity is defined using the projected cross-sectional area of the particles when the particles are observed with a microscope. The circularity in the present invention is defined as a value obtained by dividing the circumference of a circle equal to the projected cross-sectional area of a particle on a microscope image by the projected contour length of the particle. The spherical activated carbon of the present invention has an average circularity of 0.8 to 1.0, preferably 0.9 to 1.0, and more preferably 0.95 to 1.0.

Actually, spherical activated carbon may be partially broken in a manufacturing process as described later, and may have corners, sharpness, and dents on the surface. As long as the average circularity of particles having a particle size of 1 μm or more on a microscope image falls within the range specified above, there is substantially no problem in obtaining a high-density electrode. Treated as spherical activated carbon as defined in the invention. It is also possible to use the activated carbon crushed in the same manner as a mixture with the spherical activated carbon in the present invention. In this case, it suffices that the circularity of the mixture specified below satisfies the numerical values specified above.

In the present invention, the particle size of a particle is calculated by analyzing the projected cross-sectional area of the particle on a microscope image, and is defined as a value corresponding to the diameter of a circle having the same area as the area of the particle. You. In the present invention, particles having a particle size of less than 1 μm according to this definition are not used for calculating the average circularity. For the degree of circularity, at least 100 or more, preferably 200 or more particles are measured on a microscope image in terms of measurement accuracy, and the average is determined.

The spherical activated carbon according to the present invention has an average particle size in the range of 1 to 10 μm. When the average particle size is smaller than 1 μm, the density of the electrode can be further increased, but the voids in the electrode become too small, so that the impregnation of the electrolyte into the electrode becomes insufficient and the internal resistance of the electrode increases. . On the other hand, if the average particle size exceeds 10 μm, it is not preferable because the density of the electrodes cannot be increased and the capacitance per unit volume of the capacitor decreases.

In the present invention, the average particle size is determined by adding 0.1 g of activated carbon powder to 50 cm ³ of ethanol,
After irradiating an ultrasonic wave of KHz and power of 45 W for 10 minutes or more to sufficiently disperse the powder, it is calculated by a laser scattering method using ethanol and a dispersion medium (using a Microtrac type 2 granulometer manufactured by Leeds and Northrup). It is shown by the calculated cumulative volume 50% particle size (D50).

The granular activated carbon of the present invention has a pore volume of 1.5 cm ³ / g or less. When the pore volume exceeds this value, the bulk density of the activated carbon itself becomes small, so the number of activated carbon particles present per unit volume of the electrode is sufficiently large, because the weight of activated carbon per unit volume is small, As a result, the capacitance per unit volume decreases, which is not preferable. Although the lower limit of the pore volume is not particularly specified, it is practically 0.3 cm ³ /
g or more.

The pore volume of the activated carbon according to the present invention, together with the specific surface area, is determined as follows.
The value was measured using Autosorb-1 (Tachrome) (or a device having an equivalent function).

That is, the relative pressure of the adsorption isotherm obtained by adsorbing nitrogen gas at the liquid nitrogen temperature to a spherical activated carbon sample previously dried at 200 ° C. for 12 hours or more in vacuum is 0.0
The specific surface area is calculated by analyzing the range of 01 to 0.05 by the BET multipoint method, and the pore volume is calculated from the nitrogen gas adsorption amount at a relative pressure of 0.995 of the adsorption isotherm. I do.

The spherical activated carbon in the present invention is BE
The specific surface area determined by the T method is preferably 100 to 2.5
00m^Two / G, more preferably 1,000 to 2,30
0m ^Two / G, more preferably 1,500 to 2,20
0m^Two / G. Specific surface area smaller than this range
The capacitance per unit weight of activated carbon becomes smaller,
If it is larger than this range, the bulk density will decrease, and
Insufficient activated carbon weight per unit volume
Insufficient capacitance per product.

The electrode of the present invention contains the above-mentioned spherical activated carbon in an amount of 50 to 95%, preferably 80 to 95%, based on the total mass of the electrode. If the content is less than 50%, the capacitance of the capacitor is insufficient, and if it exceeds 95%, the content of the polymer binder or the conductivity-imparting material is relatively insufficient,
This leads to insufficient strength of the electrode and an increase in electric resistance, which is not preferable.

In the electrode of the present invention, the polymer binder is contained in an amount of 0.5 to 20%, preferably 1 to 15% based on the total mass of the electrode. If the amount of the binder is less than 0.5%, the strength of the electrode becomes insufficient, and if it exceeds 20%, the electric resistance and the capacitance are increased, which is not preferable.

When the spherical activated carbon or the conductivity-imparting material is formed into the shape of an electrode, the polymer binder binds and fixes these particles, and the activated carbon particles or the conductivity-imparting material particles fall off from the electrode. Added to prevent The polymer binder is not particularly limited and known ones may be used. For example, PTFE, polyvinylidene fluoride, fluoroolefin / vinyl ether copolymer crosslinked polymer,
Carboxymethylcellulose, polyvinylpyrrolidone,
Polyvinyl alcohol or polyacrylic acid is used, most preferably PTFE.

PTFE changes into a complex fiber shape in the electrode sheet processing step described later, and has the effect of maintaining the shape of the particles by confining the activated carbon particles and the conductivity-imparting material particles between the fibers. Play. Therefore, PT
FE rarely causes a decrease in the specific surface area contributing to the development of the capacitance by closing the pores of the activated carbon, and the FE changes its form into a fibrous form. Effectively acts on the binding of the activated carbon, the content of activated carbon in the electrode can be sufficiently increased.

When the crushed activated carbon having many sharp edges (edges) is bonded with fibrous PTFE, the PTFE fibers are cut at the edges of the crushed carbon during the electrode processing step, and the electrode is cut. The strength is reduced and the activated carbon particles are likely to fall off. In contrast, when the spherical activated carbon according to the present invention is used, such inconveniences are much reduced.
Also in this regard, binding spherical activated carbon with PTFE is
preferable.

When a crosslinked polymer is used, amines, polyamines, polyisocyanates, bisphenols, or peroxides are preferred as the crosslinking material.

Basically, if the electrical resistance of the activated carbon is sufficiently low, the conductivity-imparting material does not necessarily need to be contained in the electrode, and the electrode can be composed of spherical activated carbon and a polymer binder. When the specific surface area of the activated carbon increases, the electric resistance of the electrode increases. Therefore, it is preferable to include 30% of the total mass of the electrode as an upper limit according to the value of the specific surface area of the activated carbon. More preferably, the content of the conductivity-imparting material is 20% or less, further preferably 1 to 15%.

Since the conductivity-imparting material basically does not substantially contribute to the development of the capacitance, it is not preferable that the conductivity-imparting material be contained in the electrode in excess of the above-mentioned content.

When the spherical active carbon, the polymer binder, and the conductivity-imparting material are contained, the electrode contains 50 to 95% by mass of the spherical activated carbon and 30% or less of the conductivity-imparting material in a mass ratio. And 0.5 to 20% of a polymer binder.

The conductivity-imparting material is not particularly limited, and known materials may be used, for example, powders of carbon black, natural graphite, artificial graphite, titanium oxide, ruthenium oxide and the like. Among them, it is preferable to use Ketjen black or acetylene black, which is a kind of carbon black, because the effect of improving conductivity with a small amount is large.

The electrode of the present invention is mainly composed of spherical activated carbon,
It contains a polymer binder and, if desired, a conductivity-imparting material, and has a bulk density of 0.6 g / cm ³ or more, preferably 0.65 g / cm ³ or more, more preferably 0.70 g, as an electrode body. / Cm ³ or higher density electrode. The upper limit of the bulk density of the electrode is not particularly specified, but is actually 1.0 g / cm ³ or less.

If the bulk density is lower than the lower limit, the capacitance per unit volume when the electric double layer capacitor is formed does not become a sufficiently large value. Here, the bulk density means
The electrode is formed into a sheet of a predetermined shape, and 200 ° C. in vacuum
After drying for 10 hours in dry nitrogen and measuring the weight and outer diameter of the sheet electrode in dry nitrogen.

The spherical activated carbon in the present invention is obtained by activating spherical graphitizable carbon or non-graphitizable carbon, and these are used alone or in combination.

Graphitizing carbon (sof)
t carbon) is carbon that is graphitized by the graphitization process. Examples of the graphitizable carbon material that forms such graphitizable carbon by heating include general thermoplastic resins, for example, vinyl chloride resin, polyacrylonitrile, butyral resin, polyacetal resin, polyethylene resin, polycarbonate resin, and polypropylene resin. Nyl acetate and the like can be used. Further, pitch-based materials such as petroleum-based pitch and coal-based pitch, and cokes obtained by heat-treating these pitches can be mentioned, and spherical easily graphitized carbon can be obtained by carbonizing the spherical resin and the like. .

Also, non-graphitizing carb
On, hard carbon) is carbon that does not readily reach graphite due to graphitization. Examples of the non-graphitizable carbon material that forms such non-graphitizable carbon by heating include general thermosetting resins such as phenol resin, melamine resin, urea resin, furan resin, epoxy resin, alkyd resin, and unsaturated polyester resin. And a diallyl phthalate resin, a furfural resin, a silicone resin, a xylene resin, a urethane resin, and the like. By carbonizing the spherical resin, a spherical non-graphitizable carbon can be obtained.

The carbonization is performed by nitrogen, argon, helium,
In a non-oxidizing atmosphere of an inert gas such as xenon or neon and a mixed gas thereof in a temperature range of 300 to 2,000 ° C, preferably about 500 to 1,300 ° C,
It is performed by heating and carbonizing a spherical graphitizable carbon material or a non-graphitizable carbon material for 10 minutes to 30 hours.

The apparatus for performing carbonization is not particularly limited, but includes a fixed bed heating furnace, a fluidized bed heating furnace, a moving bed heating furnace,
Any of an internal heating type or an external heating type rotary kiln, an electric furnace, and the like are preferably employed.

In the present invention, those obtained by activating spherical non-graphitizable carbon are particularly preferable. This is because the non-graphitizable carbon can be easily activated by either gas activation or chemical activation, and an activated carbon having a high specific surface area can be obtained. This is because activated activated carbon has a high particle strength, and spherical particles are less likely to be damaged in the activated carbon production process and the electrode formation process.

In the present invention, the carbonization ratio (carbonization yield) during carbonization is high, the raw material cost is low, and the spherical resin can be easily formed. Among them, a spherical phenol resin, which is obtained by activating hard-graphitizable carbon obtained by carbonizing the phenol resin, is most preferable.

As the spherical phenol resin, a commercially available product having a desired particle size can be easily obtained.
Various methods have been proposed for producing spherical phenolic resins (for example, see JP-A-4-15932).
0, JP-A-10-236807, JP-A-11-13
No. 14, JP-A-11-116217 and JP-A-11-1
No. 16648) and the like.

For example, phenols and aldehydes are suspended in water, an organic solvent, or a mixed solvent of water and an organic solvent using an alkali metal catalyst or a combined catalyst of an alkali metal catalyst and an amine catalyst. By heating and curing with stirring in the presence of a stabilizer, spherical phenol is obtained. Particles obtained by this method are preferable because they are close to true spheres and the particle size distribution is relatively sharp.

As the suspension stabilizer, polyvinyl alcohol, hydroxymethylcellulose, hydroxyethylcellulose, soluble starch, gum arabic, methylcellulose, methylcellulose and the like are used, and the suspension stabilizer covers the phenol resin to form micelles. It is considered that spherical particles are formed.

The control of the particle size can be performed by changing the synthesis conditions such as the stirring conditions and the concentration of the suspension stabilizer. For example, increasing the stirring speed or increasing the concentration of the suspension stabilizer decreases the particle size, and decreasing the stirring speed or decreasing the concentration of the suspension stabilizer increases the particle size.
The particle size can be changed in the range of ~ 2,000 μm,
A spherical phenol resin having a particle diameter corresponding to the average particle diameter of 1 to 10 μm specified in the present invention can be easily obtained.

A spherical activated carbon is obtained by activating a spherical carbide obtained by carbonizing such a spherical phenol resin or the like.

Activation is a step of growing and developing the fine pore structure of the solid carbide produced in the carbonization step. The activation is not particularly limited. Basically, the activation can be carried out by either gas activation or chemical activation. However, in order to sufficiently exhibit the characteristics of the activated carbon of the present invention, chemical activation, particularly alkali metal activation, is required. Alkali activation in which a compound and carbon are mixed and heated and fired is preferred.

As the alkali metal compound, alkali carbonates such as potassium carbonate and sodium carbonate can be used, but alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, lithium hydroxide, rubidium hydroxide and cesium hydroxide can be used. It is preferred to use at least one of the above, and potassium hydroxide is most preferred.

[0060] Such an alkali metal compound is added and mixed in a mass ratio of 0.2 to 5.0 times the mass of the carbide, and the melting point of the alkali metal hydroxide or higher, preferably 300 to
In a temperature range of 1,000 ° C., more preferably 400 to 900 ° C., heating is performed in a non-oxidizing atmosphere for 30 minutes to 5 hours. At this temperature, the alkali metal compound chemically strongly erodes the carbide, releases carbon monoxide and carbon dioxide, and forms a complexly developed porous structure in the carbide.

It is preferable to provide a washing step in which the carbonized material after the alkali activation is washed with water to wash the alkali components, neutralized with hydrochloric acid or the like, and washed again with water to wash hydrochloric acid. The carbonized material subjected to the washing step is sufficiently dried, and becomes the spherical activated carbon in the present invention.

In the activation step, gas activation can be performed. In this case, the carbonized material is converted to steam,
Under a weakly oxidizing activation gas atmosphere containing any one or more of carbon dioxide (combustion gas), oxygen, hydrogen chloride, chlorine and the like, preferably at 500 to 1,000 ° C, more preferably 700
Heat in a temperature range of ℃ 1,000 ° C. for about 5 minutes to 10 hours. Unorganized parts and the like in the carbide react with these gases in contact with each other and are selectively decomposed and consumed to form a fine porous structure.

The activation step can be performed by combining the above-described alkali activation and gas activation. The apparatus for performing the activation is not particularly limited, and the same apparatus as that used for the carbonization can be used. The fixed-bed heating furnace, the fluidized-bed heating furnace, the moving-bed heating furnace, the internal heating type or the external heating type Any of a rotary kiln, an electric furnace and the like can be suitably used.

The spherical activated carbon in the present invention belongs to the category of fine powder having an average particle size of 1 to 10 μm. For the production, a spherical carbon material having such a particle size from the time of the starting carbon material is used. While maintaining this spherical shape, it is preferable to carbonize and activate to obtain granular activated carbon having the above particle size.In the middle of the process, mechanical pulverization having the problem of occurrence of corners and sharpness described above is not preferable. It is basically desirable not to do it.

However, when handling such fine powders from the beginning of the process, handling of the fine powders such as scattering and powdering of the fine powders in the carbonizing step and the activation step, and difficulties in handling during filtration and washing, etc. In some cases, the accompanying problems cannot be ignored.

In such a case, the fine powder (hereinafter referred to as “primary particles” or “primary particle powder”) is granulated at an appropriate point in time to such a size that there is no problem such as scattering or powdering. A method in which the granulated product is subjected to a carbonization step or an activation step and finally crushed to crush the granulated product into primary particles by a crushing operation can be adopted.

Specifically, the primary particles are granulated at the stage of obtaining a spherical phenol resin or the like, or at the stage of carbonizing it to obtain a spherical carbide.

The granulation may be performed by compression granulation or extrusion granulation by a compression stress granulation mechanism. However, it is preferable that the granulation be relatively weak due to the ease with which it can be finally crushed again into primary particles. Rolling granulation by a granulation mechanism of cohesive force is desirable.

In the case of tumbling granulation, a phenol resin or its primary material made of a carbide thereof is supplied from the upper part of a stirring tank or an inclined rotating drum (rolling drum) granulator or a rotating pan granulator. Supply the particle powder and tumbling and stirring, liquid phenolic resin, liquid pitch, polyvinyl alcohol,
By spraying an aqueous solution of carboxymethylcellulose, gelatin or the like as a binder on the primary particle powder to be tumbled and stirred, the particles are coarsened to about 0.5 to 5 mm.

The granulated coarse particles are subjected to the carbonization step and the activation step according to the primary particles according to the primary particles. The thus-obtained average particle size is 1 to 1.
Coarse particles, which are aggregates of spherical activated carbon of 0 μm, are crushed by a suitable crusher without crushing the shape of the primary particles, and the average particle size of the present invention is 1 to 10 μm.
Of spherical activated carbon.

As the electrolytic solution of the electric double layer capacitor of the present invention, basically, an aqueous electrolytic solution and an organic electrolytic solution can be used. This is preferable because the amount of energy stored per unit increases. In the case of an organic electrolytic solution, the decomposition potential is at least twice as high as that of an aqueous electrolytic solution.
This is because the energy density proportional to 1 / min is more advantageous than the aqueous electrolyte.

More specifically, the electrode material of the electric double layer capacitor of the present invention is constituted by adding the above-mentioned spherical activated carbon particles and a polymer binder, more preferably a conductivity-imparting material. This electrode is made of, for example, powder of carbonaceous material and PTF.
A binder such as E and preferably a conductivity-imparting material are kneaded in the presence of a solvent such as alcohol, preferably roll-rolled or pressed to form an electrode sheet, dried, and then via a conductive adhesive or the like. To be integrated with the current collector. The rolled electrode sheet may be further stretched.

Further, the activated carbon particles are mixed with a binder and, preferably, a conductivity-imparting material together with a solvent to form an activated carbon slurry. The slurry is coated on a current collector, dried, and joined to the current collector to be integrated with the current collector. The electrode may be a rolled electrode, which may be further rolled.

As described above, PTFE changes into a fiber shape in the rolling or pressing process, and confine spherical activated carbon or the like between the fibers.

As the solvent for forming the activated carbon slurry,
Those capable of dissolving the binder are preferable, and N-methylpyrrolidone, dimethylformamide, toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, ethyl acetate, dimethyl phthalate, methanol, ethanol, isopropanol, butanol, water and the like are appropriate. Selected.

The current collector of the electrode may be any conductor that is electrochemically and chemically resistant to corrosion. For example, metals such as stainless steel, aluminum, titanium, tantalum and nickel are used. Among them, stainless steel and aluminum are preferred current collectors in terms of both performance and cost, and aluminum is particularly preferred because of its low electric resistance.

The shape of the current collector may be a foil, a nickel or aluminum foam metal having a three-dimensional structure, or a stainless steel net or wool.

As the electrolytic solution of the electric double layer capacitor of the present invention, a known or well-known aqueous or organic electrolytic solution can be used. The most preferable result is obtained when an organic electrolytic solution is used.

Examples of the organic solvent include electrochemically stable ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane,
Sulfolane derivative, 3-methylsulfolane, 1,2-dimethoxyethane, acetonitrile, glutaronitrile,
Solvents comprising at least one selected from valeronitrile, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, dimethoxyethane, methylformate, dimethylcarbonate, diethylcarbonate or ethylmethylcarbonate are preferred. These can be used as a mixture.

As the electrolyte of the organic electrolytic solution, R¹ R^Two 
R^Three R^Four N⁺Or R¹ R^Two R^ThreeR^Four P⁺(R¹ , R^Two
 , R^Three , R^Four Are each independently an alkyl having 1 to 6 carbon atoms
Represents a kill group. The quaternary onium cation represented by)
And BF_Four ^-, PF_Four ^-, ClO_Four ^-, CF_Three SO_Three ^-
Or (SO_Two R^Five ) (SO_Two R⁶ ) N^-(R^Five , R⁶ 
Are each independently an alkyl group having 1 to 4 carbon atoms or
Represents a kylene group;^Five And R ⁶ May form a ring
No. A salt consisting of an anion selected from the above) is preferred.

Specifically, for example, (C ₂ H ₅ ) ₄ NB
F ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H
₅ ) ₄ PBF ₄ and (C ₂ H ₅ ) ₃ (CH ₃ ) PBF ₄
And the like are preferred. The concentration of these salts in the electrolyte is from 0.1 to 2.5 mol / l, more preferably from 0.5 to
It is preferably about 2 mol / l.

In the present invention, as the separator inserted between the positive electrode and the negative electrode, for example, a nonwoven fabric of polypropylene fiber, a nonwoven fabric of glass fiber, synthetic cellulose paper, etc. can be suitably used.

The electric double layer capacitor according to the present invention is a coin type in which a separator is interposed between a pair of sheet electrodes and is accommodated in a metal case together with an electrolytic solution, and a pair of positive and negative electrodes are wound through the separator. Any structure such as a round shape and a stacked type in which a large number of sheet electrodes are stacked via a separator can be adopted.

[0084]

[Example 1]

(1) A spherical phenol resin obtained by emulsion-polymerizing phenol and formaldehyde in an aqueous solution containing an alkaline polymerization catalyst and a suspension stabilizer is carbonized at 700 ° C. for 2 hours in nitrogen. A spherical carbide was obtained.

Next, the spherical carbide and potassium hydroxide (hereinafter abbreviated as KOH) were mixed at a mass ratio of 1: 3, and the mixture was placed in a silver crucible.
The temperature was raised to 850 ° C at a heating rate of 250 ° C / h,
Activation was performed by holding at 2 ° C. for 2 hours. The activated product was sufficiently washed with ion-exchanged water, neutralized with 0.1 N hydrochloric acid, and further sufficiently washed with ion-exchanged water. The washed activated product is dried in a vacuum at 250 ° C. for 5 hours, and the average particle size is 5 μm.
m of spherical activated carbon was obtained. The specific surface area of this activated carbon is 2,
000 m ² / g, and the pore volume was 0.9 cm ³ / g. The spherical activated carbon was observed with a scanning electron microscope, and image analysis by a computer was performed on at least 100 particles having a particle diameter of 1 μm or more. As a result, the average circularity of each particle was 0.97.

(2) Next, the obtained activated carbon, furnace black (Ketjen Black EC manufactured by Ketjen Black International) as a conductivity-imparting material, and PTFE as a binder were used at a mass ratio of 8: 1: 1. The resulting mixture was kneaded while adding ethanol, and roll-rolled to obtain an electrode sheet having a thickness of 0.20 mm. At 200 ° C
Vacuum dried for 10 hours. Next, two electrodes having a diameter of 20 mm were punched out of this sheet in dry air, the weight was determined, and the bulk density of the electrodes was calculated from the relationship between the outer dimensions and the weight. The result was 0.68 g / cm ³ . .

Next, these electrodes are used as a positive electrode and a negative electrode,
Each was adhered to an aluminum sheet as a current collector with a graphite-based conductive adhesive.

(3) The positive electrode and the negative electrode adhered to the aluminum sheet were vacuum-dried at 250 ° C. for 4 hours, and then dried at a concentration of 1 mol / 1 (C ₂ H ₅ ) ₃ (C
The electrode was impregnated with a propylene carbonate solution containing H ₃ ) NBF ₄ . Next, the positive electrode and the negative electrode were opposed to each other via a nonwoven fabric separator made of polypropylene, and sandwiched between two glass plates and fixed at a constant pressure to form an element.

Next, the above-mentioned device was treated with (C) at a concentration of 1 mol / 1.
_{2 H 5) 3 (CH 3} ) NBF 4 completely in propylene carbonate solution containing an immersion state to constitute a model type Kiyapashitaseru.

(4) 2.5 V for model-type capacitor cell
, And the capacitance (combined capacitance of the positive and negative electrodes) and the internal resistance were measured. As a result, the capacitance and the internal resistance were 3.0 F and 2.0 Ω, respectively. The results are summarized in Table 1.

The capacitor was repeatedly charged and discharged at a constant current of 1 A between 0 and 2.5 V in a constant temperature bath at 40 ° C. for 3,000 cycles, and the capacitance and internal resistance after 3,000 cycles were measured. It was measured and the long-term reliability was evaluated based on the performance change rate before and after the cycle test. The results are shown in Table 1.

Example 2 (1) Spherical activated carbon having an average particle diameter of 3 μm was prepared in the same manner as in Example 1 except that the stirring speed of the mixture during emulsion polymerization of the phenolic resin was twice that of Example 1. Obtained. The specific surface area of this activated carbon is 2,050 m ² / g, and the pore volume is 0.91 cm.
³ / g. The spherical activated carbon was observed with a scanning electron microscope, and image analysis by a computer was performed on at least 100 particles having a particle size of 1 μm or more. The average value of the circularity of each particle was 0.96.

(2) Using the obtained spherical activated carbon, an electrode was formed in exactly the same manner as in Example 1, and the density was measured.
0.7 g / cm ³ .

Using this electrode, a model-type capacitor cell was fabricated in the same manner as in Example 1, and a voltage of 2.5 V was applied to measure the electrostatic capacity (combined capacity of the positive and negative electrodes) and the internal resistance. As a result, the capacitance and the internal resistance respectively become 3.
4F and 2.1Ω. The results are summarized in Table 1.

Further, the capacitor was subjected to a 3,000 cycle charge / discharge test in the same manner as in Example 1 to evaluate long-term reliability. The results are shown in Table 1.

Example 3 (1) A method similar to that of Example 1 was used, except that the concentration of the suspension stabilizer in the mixture during the emulsion polymerization of the phenol resin was changed to 0.8 times that of Example 1. A spherical carbide was obtained.

While stirring the obtained spherical carbide using a small stirring blade type mixer, the water-soluble resole resin diluted to a solid content of 10% was gradually added dropwise as a binder while stirring, and stirring was continued. Was granulated. Further, the granules were heated in a nitrogen atmosphere at 500 ° C. to carbonize the resol resin. This carbide was heated in a small rotary kiln at 850 ° C. for 4 hours in a steam atmosphere to perform an activation treatment. The activated granules are crushed into primary particles using a cutter mill, and the average particle size is 10 μm.
Of granular activated carbon was obtained. The specific surface area of this granular activated carbon is
1,800 m ² / g, pore volume 0.88 cm ³ / g
Met. The spherical activated carbon was observed with a scanning electron microscope, and image analysis was performed by a computer on 100 or more particles having a particle size of 1 μm or more. As a result, the average circularity of each particle was 0.85.

(2) An electrode was formed using the obtained spherical activated carbon in the same manner as in Example 1, and the density was measured.
It was 62 g / cm ³ .

Using this electrode, a model-type capacitor cell was manufactured in the same manner as in Example 1, and a voltage of 2.5 V was applied to measure the electrostatic capacity (combined capacity of the positive and negative electrodes) and the internal resistance. As a result, the capacitance and the internal resistance become 2.
7F and 1.9Ω. The results are summarized in Table 1.

Further, the capacitor was subjected to a 3,000 cycle charge / discharge test in the same manner as in Example 1 to evaluate long-term reliability. The results are shown in Table 1.

[Comparative Example 1] (1) Except that the concentration of the suspension stabilizer in the mixed solution at the time of synthesizing the spherical phenol resin was changed to 0.3 times that of Example 1, spherical particles were prepared in the same manner as in Example 1. A char was obtained.

The obtained spherical carbide was alkali-activated with KOH in the same manner as in Example 1, washed and dried to obtain a spherical activated carbon having an average particle size of 25 μm. The specific surface area of this activated carbon is 1,950 m ² / g, and the pore volume is 0.92 cm.
³ / g. The spherical activated carbon was observed with a scanning electron microscope, and image analysis by a computer was performed on at least 100 particles having a particle size of 1 μm or more. As a result, the average circularity of each particle was 0.98.

(2) An electrode was formed using the obtained spherical activated carbon in the same manner as in Example 1, and the density was measured.
It was 48 g / cm ³ .

Using this electrode, a model-type capacitor cell was fabricated in the same manner as in Example 1, a voltage of 2.5 V was applied, and the electrostatic capacity (combined capacity of the positive and negative electrodes) and the internal resistance were measured. As a result, the capacitance and the internal resistance become 2.
0F and 1.9Ω. The results are summarized in Table 1.

Further, the capacitor was subjected to a 3,000 cycle charge / discharge test in the same manner as in Example 1 to evaluate long-term reliability. The results are shown in Table 1.

Comparative Example 2 (1) 10% by mass of tetramethylenehexamine as a curing agent was added to a novolak-type phenol resin, which is a non-graphitizable carbon material, and mixed well. Next, the temperature of the mixed powder was raised to 200 ° C. at a rate of 200 ° C./h in the air atmosphere, and the mixture was held at 200 ° C. for 2 hours to obtain a cured product. The obtained cured product was carbonized in exactly the same manner as in Example 1 to obtain a massive carbide. This carbide was crushed by a hammer mill to obtain carbon particles having an average particle size of 3 mm. Next, the carbon particles were activated and washed in the same manner as in Example 1, and then pulverized using a ball mill.
Activated carbon having an average particle size of 5 μm was obtained. The specific surface area of this activated carbon is 2,300 m ² / g, and the pore volume is 1.2 cm ³ / g.
g. When this activated carbon was observed with a scanning electron microscope, no spherical particles were contained, and all particles were crushed powder having an irregular sharpness.

The activated carbon was observed with a scanning electron microscope, and image analysis by a computer was performed on at least 100 particles having a particle size of 1 μm or more. The average circularity of each particle was 0.72.

(2) An electrode was formed using the obtained spherical activated carbon in the same manner as in Example 1, and the density was measured.
It was 52 g / cm ³ .

Using this electrode, a model-type capacitor cell was manufactured in the same manner as in Example 1, and a voltage of 2.5 V was applied to measure the electrostatic capacity (combined capacity of the positive and negative electrodes) and the internal resistance. As a result, the capacitance and the internal resistance become 2.
2F and 2.0Ω. The results are summarized in Table 1.

Further, the capacitor was subjected to a 3,000 cycle charge / discharge test in the same manner as in Example 1 to evaluate long-term reliability. The results are shown in Table 1.

Comparative Example 3 (1) Example 1 was repeated except that the concentration of the suspension stabilizer in the mixture during the synthesis of the spherical phenol resin was changed to 8.0 times that of Example 1.
A spherical carbide was obtained in the same manner as described above.

The obtained spherical carbide was alkali-activated with KOH in the same manner as in Example 1, washed and dried to obtain a spherical activated carbon having an average particle size of 0.5 μm. This activated carbon has a specific surface area of 2,200 m ² / g and a pore volume of 1.13 c.
m ³ / g. The spherical activated carbon was observed with a scanning electron microscope, and image analysis by a computer was performed on at least 100 particles having a particle diameter of 1 μm or more. As a result, the average circularity of each particle was 0.97.

(2) An electrode was formed using the obtained spherical activated carbon in the same manner as in Example 1, and the density was measured.
It was 80 g / cm ³ .

Using this electrode, a model-type capacitor cell was prepared in the same manner as in Example 1, and a voltage of 2.5 V was applied to measure the electrostatic capacity (combined capacity of the positive and negative electrodes) and the internal resistance. As a result, the capacitance and the internal resistance become 2.
5F and 3.6Ω. The results are summarized in Table 1.

Further, the capacitor was subjected to a 3,000 cycle charge / discharge test in the same manner as in Example 1 to evaluate long-term reliability. The results are shown in Table 1.

Comparative Example 4 (1) A spherical activated carbon having an average particle size of 3 μm was obtained under the same conditions as in Example 2 except that the activation temperature was 950 ° C. The specific surface area of the obtained activated carbon was 2,800 m ² / g, and the pore volume was 1.6 cm ³ / g. The spherical activated carbon was observed with a scanning electron microscope, and image analysis by a computer was performed on at least 100 particles having a particle size of 1 μm or more. As a result, the average circularity of each particle was 0.98.

(2) An electrode was formed using the obtained spherical activated carbon in the same manner as in Example 1, and the density was measured.
It was 42 g / cm ³ .

Using this electrode, a coin-type electric double layer capacitor was prepared in the same manner as in Example 1, a voltage of 2.5 V was applied, and the electrostatic capacity (combined capacity of the positive and negative electrodes) and the internal resistance were measured. . As a result, the capacitance and the internal resistance were 1.9 F and 1.7 Ω, respectively. The results are summarized in Table 1.

Further, a charge / discharge test of 3,000 cycles was performed on this capacitor in the same manner as in Example 1, and the long-term reliability was evaluated. The results are shown in Table 1.

[0121]

[Table 1]

[0122]

The electrode of the present invention is a high-density electrode using spherical activated carbon having a specific particle size as an electrode material. An electric double layer capacitor using this high-density electrode has a capacitance per volume. It shows excellent characteristics of high and low internal resistance.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph of a spherical activated carbon.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toru Shimoyama 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa F-term in Asahi Glass Co., Ltd. (reference) 4G046 HA03 HB00 HB02 HB05 HB06 4G075 AA27 AA62 AA63 BA05 BD14 BD16 CA57 CA63

Claims (7)

[Claims] 1. A spherical activated carbon having an average particle diameter of 1 to 10 μm and a pore volume of 1.5 cm ³ / g or less 50 to 95% by mass.
And 30% by mass or less of a conductivity-imparting material, and 0.5 to 20% by mass of a polymer binder, and a bulk density of 0.6 g /
A high-density electrode for an electric double layer capacitor, having a size of at least ³ cm ³ . 2. The high-density electrode according to claim 1, wherein the spherical activated carbon is obtained by activating non-graphitizable carbon. 3. The high-density electrode according to claim 2, wherein the non-graphitizable carbon is obtained by carbonizing a phenol resin. 4. The high-density electrode according to claim 1, wherein the spherical activated carbon has an average circularity of 0.8 to 1.0 in a projected sectional area on a microscope image of particles. 5. An electric double layer capacitor comprising the high-density electrode according to claim 1. 6. The electric double layer capacitor according to claim 5, comprising an organic electrolytic solution in which an electrolyte is dissolved in an organic solvent. 7. The method according to claim 1, wherein the organic solvent in the organic electrolytic solution is ethyl.
Carbonate, propylene carbonate, butylene carbonate
-Carbonate, dimethyl carbonate, ethyl methyl carbonate
Carbonate, diethyl carbonate, acetonitrile,
Lutalonitrile, valeronitrile, sulfolane and sulf
At least one selected from the group consisting of holane derivatives,
As an electrolyte, R¹ R^Two R^Three R^Four N⁺Or R
¹ R^TwoR^Three R^Four P⁺(Where R¹ , R^Two , R^Three , R^Four 
Represents an alkyl group having 1 to 6 carbon atoms each independently.
You. A quaternary onium cation represented by
_Four ^-, PF _Four ^-, ClO_Four ^-, CF_Three SO_Three ^-Or (S
O_Two R^Five ) (SO_Two R⁶ ) N⁺(Where R^Five , R⁶ Is
Each independently represents an alkyl group having 1 to 4 carbon atoms. ) Or
Organic electrolyte in which a salt consisting of an anion selected from
The electric double layer capacitor according to claim 6, further comprising a solution.