JPH10172870A - Electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the resistivity of a polar electrode, charge-discharge electric capacitance and charging-discharging rate by using a carbon material contg. dispersed fine particles of a metal or metal compd. as an electrode material. SOLUTION: A polar electrode material has a structure of dispersed fine particles of a metal or metal compd. in a carbon material which may be any one of active carbon, active carbon fiber or carbon black in the macrostructure. The metal or metal compd. is at least one metal selected from elements attaching to groups IIa, IIIb, IVb, Vb, VIb, VIIb, VIII, Ib, IIb, and IIIa in the periodic table, or metal compd. such as oxide or carbide thereof. The metal or metal compd. content to carbon material is 0.1-40wt.% as a metal, N- adsorption BET specific surface area of the polar electrode material is about 500-3000m<2> /g, and mean pore diameter is about 10-40Å.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance electric double-layer capacitor utilizing the electric double-layer principle and a material for a polarizable electrode thereof.

[0002]

2. Description of the Related Art Conventionally, electric double layer capacitors have been used as backup power supplies for semiconductor memories, backup power supplies for electronic devices such as microcomputers and IC memories, batteries for solar clocks, and power supplies for driving motors. Is also being studied as a power source for electric vehicles and as an auxiliary storage unit for energy conversion and storage systems.

Conventionally, the following two types of polarizable electrodes have been used for electric double layer capacitors. That is, first, a powdered activated carbon obtained by activating sawdust, coconut shell, pitch, or the like is pressed or rolled with an appropriate binder to form a polarizable electrode. Second, phenol-based, rayon-based, acrylic-based, and pitch-based fibers are infusibilized and activated by carbonization to form activated carbon or activated carbon fibers.
It is a polarizable electrode such as a fibrous, paper-like or sintered body.

The electric capacity of an electric double layer capacitor using a polarizable electrode formed of a carbon material such as activated carbon, activated carbon fiber or carbon black basically depends on the surface characteristics of the carbon material and the nitrogen adsorption BET specific surface area. It is said. Increasing the specific surface area of the carbon material is considered to be an effective method for increasing the electric capacity per unit weight, but there is a limit in increasing the specific surface area. Also, the pore diameter becomes smaller as the specific surface area is increased, especially when an organic solvent-based electrolyte is used, because electrolyte ions having a diameter larger than the pore diameter cannot enter the pores,
Eventually, a part of the area is not used. On the other hand, the relationship between the surface characteristics and the electric capacity of the carbon material has not been clarified yet, and it is extremely difficult to control the surface characteristics.

[0005] Another important characteristic of electric double layer capacitors is the internal resistance. Generally, since a carbon material has a large specific resistance and a large ion diffusion impedance in a pore, there is a problem that the internal resistance of a capacitor using a carbon material as a polarizable electrode is inferior to a capacitor using another metal. Examination examples for reducing the internal resistance of a carbon-based electric double layer capacitor are described in JP-A-3-104206 and JP-A-2-277206.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a conventional electric double layer capacitor using a carbon material such as activated carbon or activated carbon fiber as a material for a polarizable electrode. It is an object of the present invention to provide a novel polarizable electrode having improved electric capacity, higher electric capacity, lower internal resistance, and high-speed charge / discharge characteristics.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above-mentioned object, and as a result, as a material for a polarizable electrode of an electric double layer capacitor, a metal such as activated carbon or activated carbon fiber has been used. By using a compound in which compound fine particles are dispersed, the charge / discharge electric capacity, internal resistance, charge / discharge speed, and electric efficiency are all superior to a conventional capacitor that uses a simple carbon material as a polarizable electrode material. It has been found that an electric double layer capacitor can be obtained. Such electric double-layer capacitors in which fine particles of a metal or a metal compound are dispersed have been rapidly developed in recent years as well as conventional power supplies for backing up semiconductor memories and power supplies for electronic devices such as microcomputers and IC memories. It can also exert its advantages as an auxiliary unit for electric vehicles, natural gas vehicles and electric energy storage systems.

The present invention relates to a carbon material (for example, activated carbon,
Metal or metal compound (IIa, IIIb, IVb, V in the periodic table of elements) in activated carbon fiber or carbon black
b, VIb, VIIb, VIII, Ib, IIb and I
The present invention relates to a material for a polarizable electrode of an electric double layer capacitor having a structure in which fine particles of one or more metals selected from Group IIa elements or oxides or carbides thereof are dispersed.

The present invention relates to a polarizable electrode comprising a material for an electrode, a porous separator, and an electric double layer capacitor comprising an electrolytic solution as a constituent material.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Material for Polarizable Electrode The macro form of the carbon material used for the material for the polarizable electrode may be any one of activated carbon, activated carbon fiber and carbon black. Examples of the metal or metal compound include Be, Mg, Ca, Sr, and Ba in Group IIa of the periodic table.
Group IIIb Sc, Y; Group IV Ti, Zr, Hf; V
V, Nb, Ta of group b; Cr, Mo, W; V of group VIb
Group IIb Mn, Tc, Re; Group VIII Fe, C
o, Ni, Ru, Rh, Pd, Os, Ir, Pt; Ib
Group Cu, Ag, Au; Group IIb Zn, Cd, Hg;
One or more metals (zero valence) selected from group IIIa B, Al, Ga, In, Tl and the like, or metal compounds such as oxides and carbides of the metals can be used.

In a preferred embodiment, the content of the metal or metal compound relative to the carbon material is 0.1% as the metal.
And the nitrogen-adsorbed BET specific surface area of the polarizable electrode material is 5 to 40 wt%, preferably 0.5 to 10 wt%.
About 00-3000 m ² / g, usually 700-1600
m ² / g, and the average pore diameter is about 10 to 40 Å.

Production of Polarizable Electrode Material The polarizable electrode of the electric double layer capacitor can be produced, for example, by the following two methods.

The first method is to use an organic material such as a pitch-based, phenol-based, rayon-based, acrylic-based, synthetic naphthalene-pitch-based organic material which is a precursor of fine particles of a metal or a metal compound. A metal compound such as a metal complex or an inorganic metal compound is dispersed in advance by an appropriate method, and further subjected to a normal carbon fiber production process such as spinning, infusibilization, carbonization, and activation, or a carbon material production process such as activated carbon. This is a method for obtaining a carbon material containing fine particles of a metal or a metal compound.

For example, isotropic coal tar pitch is dissolved in a solution obtained by dissolving silver acetate in a mixed solvent of quinoline and acetic acid, mixed uniformly, and then the solvent is removed by distillation under reduced pressure. By infusing at -400 ° C and heat-treating in steam at 700-900 ° C, an isotropic activated carbon fiber in which fine particles of metallic silver and silver oxide are dispersed can be produced.

In the second method, an organic material such as a pitch-based, phenol-based, rayon-based, acrylic-based, or synthetic naphthalene pitch-based material, which is a precursor of a carbon material such as activated carbon, activated carbon fiber, and carbon black, is mixed with a metal powder. By mixing and pressurizing the powder particles to form a composite while miniaturizing the powder particles, a precursor of a carbon material in which metal fine particles are dispersed can be obtained. The precursor of the carbon material in which the obtained metal fine particles are dispersed is further spun, infusibilized, carbonized, passed through a normal carbon fiber or activated carbon manufacturing process such as activation, and finally a metal or metal compound. This is a method for obtaining a carbon material containing fine particles.

For example, a coal tar pitch containing fine silver particles is obtained by mechanical alloying from an isotropic coal tar pitch and silver powder, and this is further spun.
Infusible at 250-400 ° C in air, 700-400 in steam
By performing the heat treatment at 900 ° C., an isotropic activated carbon fiber in which silver metal and silver oxide are dispersed can be produced.
In the mechanical alloying process, a fixed amount of a sample is charged into a metal container containing a vibrating ball, and a high-energy ball mill is vibrated at a low temperature in a vacuum or in an inert gas atmosphere such as an argon gas, thereby obtaining a sample. particles are processed to expose the fresh surface, the newly formed surfaces are forge welding, so as to coalesce, this is repeated, collision and compression
Fineness and homogenization are further promoted by the impact force.

Polarizable Electrode The polarizable electrode of the electric double layer capacitor can be manufactured by pressing or rolling the electrode material of the present invention together with a suitable binder. As the binder, polytetrafluoroethylene or the like can be used.

Electric Double Layer Capacitor An electric double layer capacitor can be produced by combining a polarizable electrode produced using the electrode material of the present invention with a porous separator and an electrolytic solution. As the electrolyte and the porous separator, those generally used in electric double layer capacitors can be used.

[0019]

EXAMPLES Examples of the present invention and comparative examples are shown below to further clarify the features of the present invention.

[Preparation of Polarizable Electrode Material] Example 1 Coal tar pitch having a softening point of 280 ° C. (100 parts by weight)
Was prepared by dissolving silver acetate (1.55 parts by weight) in a mixed solvent of quinoline and acetic acid (weight ratio: 1: 1) (301.55).
Parts by weight) and stirred at room temperature for 3 hours. Thereafter, quinoline and acetic acid were removed by distillation under reduced pressure to obtain a coal tar pitch in which silver acetate was dispersed. Coal tar pitch in which the obtained silver acetate is dispersed, is spun at a temperature equal to or higher than the softening point,
Infusibilize while blowing air at 300 ° C for 3 hours.
Steam treatment was performed at 0 ° C. for 6 hours to obtain isotropic activated carbon fibers in which fine particles of silver and silver oxide were dispersed.

The metal content and specific surface area (m ² / g) of the obtained isotropic activated carbon fibers in which fine particles of silver and silver oxide are dispersed.
Table 1 shows the analysis results of the average pore size (angstrom). A nitrogen adsorption experiment was performed using ASAP-2000 manufactured by Shimadzu Corporation to determine the specific surface area and pore distribution.
The specific surface area was determined by the BET equation.

Example 2 Coal tar pitch having a softening point of 280 ° C. (100 parts by weight)
Was dissolved in a solution (304.46 parts by weight) of manganese acetate tetrahydrate (4.46 parts by weight) dissolved in a mixed solvent of quinoline and acetic acid, and the mixture was stirred at room temperature for 3 hours. Thereafter, quinoline and acetic acid were removed by distillation under reduced pressure to obtain a coal tar pitch in which manganese acetate was dispersed. The obtained coal tar pitch in which manganese acetate was dispersed was subjected to spinning, infusibilization and steam treatment in the same manner as in Example 1 to obtain an isotropic activated carbon fiber in which fine particles of manganese and manganese oxide were dispersed.
Metal content and specific surface area (m ² / g) of the obtained isotropic activated carbon fiber in which fine particles of manganese and manganese oxide are dispersed.
Table 1 shows the analysis results of the average pore size (angstrom).

Example 3 Coal tar pitch having a softening point of 280 ° C. (100 parts by weight)
And a certain amount (1.1 parts by weight) of iron powder (particle diameter 10 to 20 m)
After mixing (sh), a so-called mechanical alloying treatment was performed in an argon gas atmosphere at a liquid nitrogen temperature for 12 hours by a vibration ball mill. The obtained coal tar pitch containing iron fine particles was subjected to spinning, infusibilization, and steam treatment in the same manner as in Example 1 to obtain an isotropic activated carbon fiber in which fine particles of iron, iron oxide, and iron carbide were dispersed. . Table 1 shows the results of analysis of the metal content, specific surface area (m ² / g), and average pore size (angstrom) of the obtained isotropic activated carbon fiber in which the fine particles of iron, iron oxide, and iron carbide are dispersed.

Example 4 Coal tar pitch having a softening point of 280 ° C. (100 parts by weight)
Was prepared by dissolving silver acetate (1.55 parts by weight) in a mixed solvent of quinoline and acetic acid (weight ratio: 1: 1) (301.55).
Parts by weight) and stirred at room temperature for 3 hours. Thereafter, quinoline and acetic acid were removed by distillation under reduced pressure to obtain a coal tar pitch in which silver acetate was dispersed. The obtained coal acetate pitch in which silver acetate is dispersed is pulverized into a powder having an average particle size of 60 mesh, subjected to infusibilization while blowing air at 300 ° C. for 3 hours, and then subjected to steam treatment at 800 ° C. for 6 hours.
Activated carbon in which silver and silver oxide fine particles were dispersed was obtained. Table 1 shows the results of analysis of the metal content, specific surface area (m ² / g), and average pore diameter (angstrom) of the obtained isotropic activated carbon fibers in which the fine particles of silver and silver oxide are dispersed.

Comparative Example 1 A coal tar pitch having a softening point of 280 ° C. was spun as it was at a temperature equal to or higher than the softening point, subjected to an infusibilization treatment while blowing air at 300 ° C. for 3 hours, and then subjected to a steam treatment at 800 ° C. for 6 hours. As a result, an isotropic activated carbon fiber was obtained. Table 1 shows the analysis results of the specific surface area (m ² / g) and the average pore diameter (angstrom) of the obtained isotropic activated carbon fiber.

Comparative Example 2 A coal tar pitch having a softening point of 280 ° C. was treated with an average particle diameter of 60.
The powder was pulverized into a mesh powder, subjected to infusibility treatment while blowing air at 300 ° C. for 3 hours, and then subjected to steam treatment at 800 ° C. for 6 hours to obtain activated carbon. Specific surface area (m ² / g) and average pore size (angstrom) of the obtained activated carbon
Table 1 shows the analysis results.

[0027]

[Table 1]

[Measurement of Resistivity] The resistivity of a polarizable electrode using the carbon material (electrode material) prepared in Examples and Comparative Examples was measured by the following procedure. Table 2 shows the results.

(1) Production of Electrode To each sample (electrode material) prepared in each of the examples and comparative examples, 5 wt% of polytetrafluoroethylene (PTFE) powder was added and mixed well in a mortar. These mixed powders were molded using a tablet molding machine at a molding pressure of 7500 kg / cm.
Under the conditions of ² , a test piece having a thickness of about 0.3 to 0.5 mm was formed. Molded test piece (13 mmφ × 0.3-0.
5 mm) was processed into a strip shape (approximately 1 mm width × 12 mm length). The processed test piece was fixed on the test piece support, and a gold wire (0.08 mmφ) was attached to the terminal with a silver paste. The terminals were connected according to a straight-line four-terminal method. At this time, the distance between the voltage measurement terminals was precisely measured to the order of 10 μm. The gold wires with the terminals were connected to the four terminals of the test piece support with silver paste.

(2) Measurement of Electric Resistance The electric resistance was measured using a digital multimeter 3478A manufactured by HEWLETT PACKARD. A linear four-terminal method not affected by contact resistance was used for measuring the electrical resistivity. The calculation of the electrical resistivity was in accordance with the following equation.

Ρ = R · (W · T / L) where ρ is the electrical resistivity (Ωcm), R is the resistance (Ω), W is the specimen width (cm), and T is the specimen thickness (cm). And L represent the distance (cm) between the voltage measurement terminals.

[0032]

[Table 2]

[Evaluation of Capacitor Characteristics] The characteristics of capacitors (charge / discharge characteristics, electric capacity, etc.) of polarizable electrodes using the carbon materials (electrode materials) prepared in Examples and Comparative Examples were evaluated by the following methods. did. Table 3 shows the results. FIG. 1 shows the discharge curves of the electrode materials prepared in Examples 1 to 3 and Comparative Example 1 in a charge / discharge cycle test under a low voltage.

(1) Assembly of Capacitor (Electrochemical Cell) An electrochemical cell for charge / discharge measurement was assembled using a separable flask sealed with a Viton O-ring made of Pyrex glass. The lid of the separable flask has a total of seven ports, two for the sample electrode, two for the pre-electrolysis Pt electrode, one for the reference electrode, one for the introduction of bubbling gas, and one for the bubbling discharge. Is provided.

The electrolytic solution contained 0.5 mol / L of tetra-n-butylammonium tetrafluoroborate (Bu ₄
A solution of NBF ₄ ) and propylene carbonate (C ₄ H ₆ O ₃ ) solvent was used.

The electrode for evaluation was prepared by washing the carbon material (electrode material) prepared in the examples or comparative examples with propylene carbonate, and drying and molding the same in the same procedure as in the measurement of resistivity. Manufactured. The electrode was further dried under reduced pressure at 100 ° C. for 24 hours immediately before use. After precisely weighing this electrode, an electrolyte solution was prepared (0.5 mol / L-Bu ₄ NB) in a glove bag replaced with argon gas.
F ₄ / PC) and the cell were assembled.

(2) Measurement of Charged Electricity The sealed cell was taken out of the glove bag, the inside of the cell was depressurized by a vacuum pump, and the electrode was degassed until no bubbles were generated. Thereafter, a voltage of 2.5 to 3 V was applied between a pair of Pt electrodes to perform preliminary electrolysis while filling the inside with argon gas and bubbling with a small amount of argon gas. At the stage where impurities in the liquid were completely removed by the preliminary electrolysis, charge / discharge measurement was performed. Charge / discharge measurement is 3.0V
At a constant voltage. From the charge / discharge curve, the amount of charge electricity, the amount of discharge electricity, the efficiency of electricity, etc. per unit weight electrode material were automatically calculated by the software loaded in the personal computer according to the following formula.

Electricity [Ah / g] = Σ (Elapsed time [h]
× measured current [A]) / sample weight [g] Electricity efficiency [%] = (total of electric discharge amount / total of electric charge amount) × 100 The discharge electric capacity and the like are HJ- manufactured by Hokuto Denko Co., Ltd. 101
SM6 charge / discharge device and HJ-SM6 software (V
evaluation 4.00) using the constant voltage method.

[0039]

[Table 3]

A) Increase rate with respect to Comparative Example 1 b) Increase rate with respect to Comparative Example 2

[0041]

According to the present invention, the use of a carbon material in which fine particles of a metal or a metal compound are dispersed as an alternative material for a conventional activated carbon or activated carbon fiber as a material for an electrode makes it possible to provide a unique polarizable electrode. Since the resistance, the charge / discharge electric capacity, and the charge / discharge speed can all be greatly improved, a high-performance electric double layer capacitor can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a typical discharge curve in a charge / discharge cycle test of a sample (electrode) using the carbon material (electrode material) of Examples 1 to 3 and Comparative Example 1.

Claims (5)

[Claims] 1. A material for a polarizable electrode of an electric double layer capacitor having a structure in which fine particles of a metal or a metal compound are dispersed in a carbon material. 2. The metal content of the carbon material is 0.1.
The polarizable electrode material for an electric double layer capacitor according to claim 1, wherein the content is in the range of 1 to 40 wt%. 3. The polarizable electrode material for an electric double layer capacitor according to claim 1, wherein the carbon material is activated carbon, activated carbon fiber or carbon black. 4. The method according to claim 1, wherein the metal or metal compound is represented by IIa, IIIb, IVb, Vb, VIb, VIIb,
The material for a polarizable electrode of an electric double layer capacitor according to any one of claims 1 to 3, wherein the material is one or two or more metals selected from the group VIII, Ib, IIb, and IIIa elements, or an oxide or carbide thereof. . 5. An electric double layer capacitor comprising a polarizable electrode, a porous separator and an electrolytic solution comprising the electrode material according to claim 1.