JP2003229335A - Electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive electric double-layer capacitor that uses a large amount of familiar grain residues as raw materials in accordance with the consideration of an ecomaterial, uses a porous carbon material as a polarization electrode material, and has a large capacity and small internal resistance. <P>SOLUTION: In the electric double-layer capacitor utilizing an electric double layer that is generated in the interface between a polarization electrode and an aqueous-solution-based electrolyte and an organic-solvent-based electrolyte, a polarization electrode 2 is formed of a carbon layer where a first carbon material originated in grain residues and a second carbon material that covers the surface of the first carbon material or is made of a thermosetting resin compounded with the surface of the first carbon material are burned. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric double layer capacitor, and more particularly to a polarizable electrode material and an electric double layer capacitor using the same.

[0002]

2. Description of the Related Art An electric double layer capacitor is a large-capacity capacitor composed of a pair of polarizable electrodes and an electrolytic solution and utilizing electric charges of the electric double layer generated at the interface between the polarizable electrode and the electrolytic solution. Therefore, the electrostatic capacitance of the electric double layer capacitor is largely controlled by the specific surface area of the polarizable electrode on which the electric double layer is formed, the resistance of the electrode, and the like.

In particular, in order to increase the electrostatic capacity per unit volume of the electrode, it is considered necessary to have a structure of a porous body satisfying durability and mechanical strength and having a large specific surface area.

Therefore, in order to satisfy the requirements for the polarizable electrode, activated carbon particles made of coconut shell or carbon fiber made of phenol resin as a starting material are used.

There are two types of electrolytes used in electric double layer capacitors: aqueous electrolytes such as aqueous sulfuric acid solutions and organic solution electrolytes obtained by adding an electrolyte to an organic solvent such as propylene carbonate. Further, one using an aqueous solution type electrolytic solution is called an aqueous solution type electric double layer capacitor, and one using an organic solution type electrolytic solution is called an organic liquid type electric double layer capacitor.

The structure of the aqueous electric double layer capacitor is
The polarizable electrodes are opposed to each other with the separator interposed therebetween, and the outside of the polarizable electrodes is made of a metal or other layer having a low electric resistance or resistance, called a collector, and an insulating rubber. As the polarizable electrode, a slurry-like one in which activated carbon is mixed with a concentrated sulfuric acid aqueous solution or a pellet-like one is used.

On the other hand, the electrode structure of the organic solution type electric double layer capacitor is mainly in the form of a sheet. The polarizable electrode sheet is obtained by dispersing activated carbon powder, a conductive material and a binder in methanol, water or the like to form a slurry, applying the slurry to a positive and negative electrode current collector foil made of an aluminum etching foil, and then drying. The main structure is a spiral wound type in which the electrode sheet is spirally wound through a separator, which is impregnated with a mixed liquid of propylene carbonate and tetraethylammonium perchlorate and which is housed in a rubber cap and an aluminum case. Positive and negative electrode tab terminals are respectively caulked to the exposed surface of the electrode sheet on which the polarizable electrode is not applied, and lead terminals are formed on the current collector foil. Further, as a polarizable electrode, a carbide obtained by carbonizing a curable spherical phenol resin and a heat-reactive phenol resin are filled in a mold, pressurized, heat-cured, heat-treated in an inert atmosphere, and then activated. The solid polarizable electrodes used are also used.

[0008]

In the electric double layer capacitor, the polarizable electrode is not only excellent in cost but also has a large surface area and electric resistance in order to increase the capacitance. It is required to be small, have high mechanical strength, excellent corrosion resistance, and excellent withstand voltage. Since the electric double layer capacitor utilizes the property of accumulating electric charges like a plate capacitor, it is necessary to increase the surface area of the polarizable electrode in order to increase the capacitance. Therefore, coconut palm activated carbon powder, activated carbon fiber, and the like, which are processed to have a large specific surface area, are often used. For example, in a wound type capacitor, activated carbon powder or the like is kneaded into a sheet by kneading PTFE (polytetrafluoroethylene) or PVDF (polyvinylidene fluoride) as a binder, and in the case of a coin type, the above-mentioned activated carbon or activated carbon is used. Fiber cloth is used. The capacitance accumulated in the electric double layer is generally represented by the following mathematical formula 1.

[0009]

[Equation 1]

From the equation (1), it can be understood that an electric double layer capacitor having a small capacity and a large capacity can be obtained by using an electrode having a high conductivity and a large specific surface area. Further, in order to obtain a large-sized and large-capacity electric double layer capacitor, a large area is required and a large amount of polarizable electrode material is required.
However, even if activated carbon having a large specific surface area of 3000 m ² / g is used, its bulk density is reduced to 0.3 g / cm ³ , so the capacity per volume is reduced, and the element is downsized and activated carbon is used. Is a problem in terms of manufacturing cost.

Further, activated carbon generally has a considerably low electric conductivity, and the internal resistance of the electrode becomes large only with activated carbon so that a large current cannot be taken out. Therefore, when the electrode is formed by using activated carbon powder, the polarizable electrode is used. Carbon black such as acetylene black or furnace black that enhances electrical conductivity is mixed therein as a conductive material. However, if the mixing ratio of the conductive material is increased for the purpose of lowering the internal resistance, the mixing ratio of the activated carbon decreases, and the capacity of the electric double layer capacitor decreases. When expensive fibrous activated carbon is used, although there is no need for a conductive material, the conductivity of the fibers themselves is not great and the fibers are kept in electrical contact with each other, so sufficient conductivity is maintained. It is hard to say that it has, and it is essential to form a conductive layer such as forming a sprayed layer of aluminum on the contact surface with the case metal. Therefore, there is a demand for an inexpensive porous carbon material having a large bulk density, a low specific resistance and an excellent mechanical strength.

[0012] Palm trees are agricultural resources but not domestic resources that are a large consumer of electric double layer capacitors. Phenolic resin is also a domestic resource because it uses petroleum resources as a raw material.

Therefore, in recent years, it has been awaited to realize an electric double layer capacitor which is cost-effective by using a porous carbon material which is abundant in Japan and is an environment-friendly material.

Therefore, the technical problem of the present invention is to solve the above-mentioned problems of the prior art, and in accordance with the idea of eco-material,
An object of the present invention is to provide a large-capacity, low-internal-resistance, inexpensive electric double-layer capacitor that uses a large amount of grain residue that is familiar to us as a raw material and uses a porous carbon material as a polarizable electrode material.

[0015]

According to the present invention, there is provided an electric double layer capacitor utilizing an electric double layer produced at an interface between a polarizable electrode and an aqueous solution type electrolytic solution and an organic solvent type electrolytic solution. Is formed of a carbon layer obtained by firing a first carbon material derived from grain residue and a second carbon material which is a thermosetting resin that covers the surface of the first carbon material or is combined with the first carbon material. An electric double layer capacitor is obtained.

Further, according to the present invention, in the electric double layer capacitor, an electric double layer capacitor is obtained, wherein the first carbon material is a carbon material derived from rice bran residue.

Further, according to the present invention, in the electric double layer capacitor, the carbon material derived from the rice bran, which is defatted from rice bran, and the thermosetting resin as the second carbon material are mixed and molded, An electric double layer capacitor is obtained, in which a dry molded body obtained by carbonizing and firing the molded body in an inert atmosphere is used as the polarizable electrode.

Further, according to the present invention, in any one of the electric double layer capacitors, an electric double layer capacitor characterized in that the second carbon material is a phenol resin can be obtained.

Further, according to the present invention, a porous carbon material obtained by firing a mixture of a first carbon material derived from rice bran residue and a second carbon material made of a thermosetting resin, a conductive material and an adhesive material. In an electric double layer capacitor using a polarizable electrode in which the above-mentioned compound is mixed, the compounding ratio of the porous carbon material and the conductive material in the polarizable electrode is set to 60% by weight or more and 30% by weight or less, respectively. An electric double layer capacitor is obtained.

Further, according to the present invention, the mixture of the first carbon material derived from the rice bran residue and the second carbon material composed of the thermosetting resin is fired to form a porous carbon material containing an adhesive. In an electric double layer capacitor using a polar electrode,
An electric double layer capacitor is obtained in which the mixing ratio of the porous carbon material in the polarizable electrode is 60% by weight or more.

Further, according to the present invention, in any one of the above electric double layer capacitors, the electric double layer capacitor is obtained in which the average particle diameter of the porous carbon material is 40 μm or less.

Furthermore, according to the present invention, in any one of the electric double layer capacitors described above, an electric double layer capacitor characterized in that the thermosetting resin is a phenol resin can be obtained.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION First, the present invention will be described in detail.

In the present invention, a porous carbon material obtained by squeezing a large amount of cheap grain residue in Japan and adding a thermosetting resin to it, firing, crushing and classifying in an inert atmosphere is used as a polarizable electrode. An inexpensive electric double layer capacitor having a large capacity and a low internal resistance is provided.

In the present invention, what can be used as an oil obtained by pressing the grain residue is excellent in degreasing after the oil or wax is pressed from the rice bran. An appropriate amount of an organic substance such as phenol resin is mixed with this, dried, and carbonized and baked at a temperature of 300 to 1100 ° C. in an inert atmosphere such as nitrogen gas to obtain a powder having high hardness. This powder has a structure in which the surface of a porous carbon material derived from grain residues is covered with a highly graphitized carbon material derived from a thermosetting resin. Therefore, it is a carbon material having a large specific surface area and excellent electrical conductivity. This powder is mechanically crushed, and a classification process having a specific particle size distribution is performed by using a wind fly or a sieve. It is possible to add carbon black or an aqueous solution of sulfuric acid to this porous carbon powder and use it as a paste as it is, or to process it into a sheet-like polarizable electrode for use.

For use as a sheet-like polarizable electrode, the porous carbon powder is mixed and stirred with carbon black such as furnace black, an adhesive material such as carboxymethyl cellulose, and ethanol to prepare a slurry. This slurry is applied to a conductive base material such as an aluminum foil, dried and used as a sheet-like polarizable electrode sheet.

In addition, a phenol resin or the like is added to the porous carbon powder, shaped into a predetermined shape, and fired at 300 to 1100 ° C. in an inert atmosphere to be used as a solid polarizable electrode. This greatly improves the bulk density.

Further, when it is desired to increase the capacitance,
As a method for increasing the pores and increasing the surface area, the porous carbon material after firing is subjected to steam activation treatment (steam: saturated steam by bubbling with nitrogen gas, 1,000 ° C. or less, 0.5 to
3 hours) and can be used in the same manner as the above method.

Further, the present invention will be described in detail as follows.
The porous carbon raw material used in the present invention is one obtained by squeezing oil from grain dregs. For example, it is preferable to use defatted bran after squeezing oil or wax from rice bran. There are roughly two methods for producing the porous carbon material.

As the manufacturing method for using the powder of the porous carbon material, there are the following methods (a) and (b).

(A) Degreased bran and an organic substance such as phenol resin are mixed, pressure-molded, dried, and carbonized and baked at a temperature of 300 to 1100 ° C. in an inert atmosphere such as nitrogen gas to have a predetermined shape, Dry grinding to obtain particle size distribution,
How to classify.

(B) Degreased bran and an organic substance such as phenol resin are mixed and carbonized and baked at a temperature of 300 to 1100 ° C. in an inert atmosphere such as nitrogen gas without pressure molding.
A method of performing dry pulverization and classification to obtain a predetermined shape and particle size distribution.

As the production for use as a solid fired sheet, (c) the porous carbon powder and phenol resin are mixed and pressure-molded into a required shape, and the mixture is placed in an inert atmosphere such as nitrogen gas. There is a method of carbonizing and firing at a temperature of 300 to 1100 ° C.

By using these methods, it is possible to obtain a powder which is porous, has a high hardness, and has good conductivity. The obtained powder characteristics are shown in Table 1 below.

[0035]

[Table 1]

A conductive material or an adhesive is added to these porous carbon powders to be used as a polarizable electrode as exemplified below, or as a solid electrode.

The electrolyte used in the present invention
Is also commonly used for electric double layer capacitors
A polar organic solvent with an electrochemically stable electrolyte
What was dissolved in and the sulfuric acid aqueous solution are used suitably. The above
As the electrolyte, (C_TwoH₅) _FourN⁺Or (C_FourH₉)_Four
N⁺, (C_TwoH₅)_FourP⁺Such as quaternary onium cation
And BF_Four ⁻And PF₆ ⁻, ClO_Four ⁻Anions such as
A salt consisting of is preferably used.

As the organic solvent, carbonates such as propylene carbonate, butylene carbonate and diethyl carbonate, lactones such as g-butyrolactone, sulfolane and acetonitrile can be preferably used. These may be used alone or in combination of two or more.

The porous, ion-permeable, electrically insulating separator may be, but is not limited to, a polyethylene non-woven fabric having a porosity of 18%.

Next, specific examples and comparative examples of the present invention will be described. However, the following examples are merely examples, and the present invention is not limited thereto.

Example 1 FIG. 1 is a diagram showing the structure of a wound electric double layer capacitor using an organic solution type electrolytic solution used for electrode evaluation.

First, degreased bran particles impregnated with a phenol resin were dried at 110 ° C., and carbonized at 900 ° C. in a nitrogen gas atmosphere. The firing time was 100 hours. This powder was crushed and classified to obtain a porous carbon powder having an average particle size of 30 μm.

Porous carbon powder 8 having an average particle diameter of 30 μm
5 wt% is uniformly dispersed in a mixed solution of water and ethanol, and 5 wt% of furnace black, which is a kind of carbon black, is mixed and stirred. Melt 10% by weight of carboxymethyl cellulose in water. Both liquids are further mixed and stirred to form a slurry.

As shown in FIG. 1, an activated carbon slurry is applied to an aluminum foil, which is to be the pyroelectric body 1 and is roughened by a chemical etching method with a thickness of 30 μm. After drying in air for 10 minutes, drying at 110 ° C for 6 hours, and after drying, heat and pressure treatment is performed to the extent that the collector foil is not deformed and the polarizable electrode layer is an electrode sheet with a thickness of 150 mm (polarizable electrode). It was set to 2.
The current collector 1 of the obtained electrode sheet 2 and the battledore of the lead terminal 5 are connected by needle crimping by a pressing method, and then a 25 mm thick electrically insulating separator 3 is arranged between the pair of electrode bodies to form a spiral shape. A wound element was produced by winding up to a predetermined diameter. After drying the wound element at 120 ° C.,
It is stored in a bottomed cylindrical aluminum case 7 and contains 0.8 ml of tetraethylammonium tetrafluoroborate.
An electrolytic solution prepared by dissolving it in propylene carbonate at a concentration of ol / l was dropped, and sealed with a rubber cap 6 to produce a wound electric double layer capacitor.

The results of the electrical characteristics evaluated in Example 1 are shown in Table 2 below.

Example 2 80% by weight of the porous carbon powder having an average particle diameter of 30 μm of Example 1 is uniformly dispersed in a mixed solution of water and ethanol, and 10% by weight of furnace black is mixed and stirred. Except for this condition, all were created under the same conditions as in Example 1 above.
evaluated.

Example 3 70% by weight of the porous carbon powder having an average particle diameter of 30 μm of Example 1 is uniformly dispersed in a mixed solution of water and ethanol, and 20% by weight of furnace black is mixed and stirred. Except for this condition, all were created under the same conditions as in Example 1 above.
evaluated.

Example 4 60% by weight of the porous carbon powder having an average particle size of 30 μm of Example 1 is uniformly dispersed in a mixed solution of water and ethanol, and 30% by weight of furnace black is mixed and stirred. Except for this condition, all were created under the same conditions as in Example 1 above.
evaluated.

Example 5 50% by weight of the porous carbon powder having an average particle diameter of 30 μm of Example 1 is uniformly dispersed in a mixed solution of water and ethanol, and 40% by weight of furnace black is mixed and stirred. Except for this condition, all were created under the same conditions as in Example 1 above.
evaluated.

Example 6 90% by weight of porous carbon powder having an average particle size of 30 μm of Example 1 is uniformly dispersed in a mixed solution of water and ethanol and stirred. Except for this condition, all were prepared and evaluated under the same conditions as in Example 1 above.

Comparative Example As a comparative example, 80% by weight of phenol-based activated carbon (specific surface area 1,500 m ² / gr) is uniformly dispersed in a mixed solution of water and ethanol, and 10% by weight of furnace black is mixed and stirred. Except for this condition, all were prepared and evaluated under the same conditions as in Example 1 above.

Table 2 below shows the results of the electrical characteristic evaluation performed in Examples 1 to 5 of the present invention and Comparative Example. As shown in Table 2, the porous carbon powder obtained by using the grain residue as a raw material showed good internal resistance as compared with the phenol-based activated carbon. Moreover, as a result of evaluating the influence of the fluctuations of the porous carbon powder, furnace black, and carboxymethyl cellulose on the electrical characteristics, when the porous carbon powder contained 60% by weight or more, the capacitance density was 12 F / cc or more. It showed a large value. Further, as furnace black is added, the internal resistance decreases, but when it exceeds 30% by weight, the capacitance density also extremely decreases. Carboxylmethyl cellulose fills the pores of the porous carbon powder, so care must be taken not to increase it more than necessary.

Similarly, as a result of evaluating the average particle size, when the average particle size exceeds 40 mm, the packing density is decreased and the capacity is decreased.

[0054]

[Table 2]

(Example 8) FIG. 2 is a sectional view showing a cell structure of an electric double layer capacitor using an aqueous electrolyte solution used for electrode evaluation.

The porous carbon plate has a diameter of 20 mm and a thickness of 0.4.
A polarizable electrode 2 was obtained by impregnating 40 mm sulfuric acid into two processed mm disks. The conductive rubber sheet used as the current collector 1 was processed to have a diameter of 25 mm and a thickness of 0.5 mm. The ion-permeable electrically insulating separator 3 sandwiched between porous carbon plates has a porosity of 18%, a diameter of 22 mm, and a thickness of 0.11.
The thing of mm was used. The insulating rubber as the sealing material 4 was processed to have an outer diameter of 25 mm and an inner diameter of 20 mm. These members were assembled and thermocompression bonded to obtain a cell having a basic structure of an electric double layer capacitor. I made 10 pieces that were also made and stacked
An aluminum plate was joined to the top and bottom ends of the cell to form a lead terminal. When measuring the electrical characteristics, a pressure of 40 Kg / cm 2 was applied from above and below the aluminum plate through the insulating plate.
A good value was obtained without breaking even if a pressure of about twice that which was conventionally evaluated is applied. The results of this electrical property are shown in Table 3 below.

A porous carbon plate was formed by molding a degreased bran impregnated with a phenol resin and drying it at 110 ° C., followed by carbonization and baking at 900 ° C. in a nitrogen gas atmosphere for a baking time of 10 minutes.
The one that took 0 hours was used.

Example 9 The molded body of Example 7 was pulverized and classified to have an average particle size of 30 μm, and 20% by weight of furnace black, which is a kind of carbon black, and 3% by weight of rubber as an adhesive material. Was added and thermocompression-molded to obtain a porous carbon plate. Other than this, the sample was prepared and evaluated under the same conditions as in Example 7 above.

[0059]

[Table 3]

[0060]

[Effects of the Invention] Oil and wax are squeezed from grain residues, which are abundant plant resources in Japan. Especially, defatted bran is used only as an agricultural material for feed and fertilizer, and it is effective to some extent. It has been studied for many years whether it can be used industrially. In the present invention, according to the idea of eco-material, it is a method of industrially utilizing it, and by using the porous carbon material of the present invention, the electrostatic capacity is large, the internal resistance is small, and it is also advantageous in terms of cost. It is possible to obtain a simple electric double layer capacitor.

[Brief description of drawings]

FIG. 1 is a schematic view of a wound electric double layer capacitor used in the present invention.

FIG. 2 is a cell cross-sectional view of the electric double layer capacitor used in the present invention.

[Explanation of symbols]

1 Current collector (aluminum foil) Bipolar electrode (electrode sheet) 3 Electric insulation separator 4 Sealant 5 lead terminals 6 Rubber cap for sealing 7 Aluminum case

Continued front page    (72) Inventor Akio Hasebe             6-7-1, Koriyama, Taihaku-ku, Sendai City, Miyagi Prefecture             Tokin Co., Ltd.

Claims (8)

[Claims] 1. An electric double layer capacitor using an electric double layer generated at an interface between a polarizable electrode and an aqueous electrolyte or an organic solvent electrolyte, wherein the polarizable electrode is a first carbon material derived from grain residue. And an electric double layer capacitor formed by firing a second carbon material that covers the surface of the first carbon material or is composited with the second carbon material. 2. The electric double layer capacitor according to claim 1, wherein the first carbon material is a carbon material derived from rice bran residue. 3. The electric double layer capacitor according to claim 2, wherein the carbon material derived from the rice bran is a mixture of degreased rice bran and a thermosetting resin as the second carbon material, and the molded body is formed. An electric double layer capacitor, characterized in that a dry-molded body obtained by carbonizing and firing in a inert atmosphere is used as the polarizable electrode. 4. The electric double layer capacitor according to any one of claims 1 to 3, wherein the second carbon material is a phenol resin. 5. A polarizable electrode in which a conductive material and an adhesive material are mixed with a porous carbon material obtained by firing a mixture of a first carbon material derived from rice bran residue and a second carbon material made of a thermosetting resin. In the electric double layer capacitor using the electric double layer capacitor, the compounding ratio of the porous carbon material and the conductive material in the polarizable electrode is 60% by weight or more and 30% by weight or less, respectively. 6. Electricity using a polarizable electrode in which an adhesive material is mixed with a porous carbon material obtained by firing a mixture of a first carbon material derived from rice bran residue and a second carbon material composed of a thermosetting resin. An electric double layer capacitor, wherein the compounding ratio of the porous carbon material in the polarizable electrode is 60% by weight or more. 7. The electric double layer capacitor according to claim 5, wherein the porous carbon material has an average particle size of 40 μm.
An electric double layer capacitor having a thickness of m or less. 8. The electric double layer capacitor according to claim 5, wherein the thermosetting resin is a phenol resin.