JP2662885B2 - Manufacturing method of electric double layer capacitor - Google Patents

Abstract

PURPOSE:To provide a long life electric double layer capacitor with its leakage current reduced for a long period of time by forming a polarizable electrode using activated carbon and/or conductive carbon coated with resin. CONSTITUTION:A 200cc toluene of 1% by weight concentration of acrylic resin is added to 100 pts by weight coconut shell activated carbon powder including 20% by weight acetylene black, and is mixed and stirred. Thereafter, the solvent is evaporated and dried, and the surface of the activated carbon and carbon powder is coated with resin. Then, tetra fluorine ethylene resin dispersion (40% of solids, and solvent water) is added to the activated carbon and the carbon powder both having been coated with resin, blended with a three rolls to prepare a 0.5mm thick sheet, on one surface of which an aluminum layer is formed by deposition to prepare a polarizable electrode material that is cut into a 10mm diameter and 0.5mm thickness. Then, the resulting material is dipped in a gamma-butyro lacton electrolytic solution of 1mol tetraethyl ammonium perchlorate in which solution a polarizable electrode material is then impregnated and coating resin is dissolved to prepare polarizable electrodes 2, 2'.

Description

Description: TECHNICAL FIELD The present invention relates to an electric double layer capacitor, and more particularly, to an improved electric double layer capacitor.

[Conventional technology]

Electric double-layer capacitors have capacitances several thousand times per unit volume compared to conventional capacitors, so they can have both functions of a capacitor and a battery. As a backup power supply.

As shown in FIG. 1, for example, an electric double-layer capacitor is a non-electronically conductive and ion-permeable porous separator (for example, a porous separator made of polypropylene or a porous separator made of non-woven fabric using polypropylene fibers) 1. Are provided with a pair of polarizable electrodes 2, 2 '. These polarizable electrodes 2, 2 'are formed by kneading, for example, activated carbon, conductive carbon, and a binder (for example, a dispersion of tetrafluoroethylene resin) together with a solvent to form a sheet, and then evaporating the solvent and drying the sheet. A conductive current-collecting electrode 3, which is punched to a predetermined size, and further comprises an electron-conductive and ion-impermeable
It is made by impregnating the electrolyte solution after providing 3 '. Next, the structure including the porous separator and the polarizable electrode is housed in a container in which a metal case 4 and a metal cap 5 are crimped via an insulating gasket 6 to form an electric double layer capacitor.

[Problems to be solved by the invention]

However, the electric double layer capacitor made by the above-mentioned conventional manufacturing method, when subjected to a high-temperature load test (70 ° C., applying a 2.8 V voltage and holding for 1000 hours), the leakage current value becomes large, and a long-term life test is performed. There was a problem with the stability of.

An object of the present invention is to provide an electric double-layer capacitor having a small leakage current value over a long period of time and a long life.

[Means for solving the problem]

In order to solve the above problems, the present invention provides a non-electronically conductive and ion-permeable porous separator, and a polarizable electrode provided on at least one side of the porous separator. In a method for manufacturing an electric double layer capacitor having a current collecting electrode, wherein the polarizable electrode contains activated carbon, conductive carbon, an electrolytic solution, and a binder, the polarizable electrode is dissolved in the electrolytic solution on the surface of the activated carbon and / or the conductive carbon. Forming a polarizable electrode using a step of coating a resin having a property or swelling property and using the activated carbon and / or the conductive carbon coated with the resin together with the binder made of a resin having no solubility in the electrolytic solution. An object of the present invention is to provide a method for manufacturing an electric double layer capacitor, which comprises a step. At this time, it is also possible to knead the activated carbon and conductive carbon coated with the resin, the binder, and the solvent to form a sheet-like molded body, and then impregnate the electrolyte. Heating can also be used for the impregnation of the electrolytic solution.

 Next, the present invention will be described in detail.

In order to manufacture the polarizable electrode of the electric double layer capacitor in the present invention, first, there is a step of coating activated carbon and / or conductive carbon with a resin having a solubility or swelling property in an electrolytic solution.

The resin having solubility or swelling property in the electrolytic solution differs depending on the electrolytic solution. Electrolytes include non-aqueous and aqueous systems.
Examples of the former include, for example, propylene carbonate, γ
Esters such as butyrolactone, nitriles such as acetonitrile, halides such as chloroform, ketones such as acetone, amides such as dimethylformamide,
In solvents such as amines such as pyridine, ethers such as tetrahydrofuran, alcohols such as butanol, nitro compounds such as nitromethane, and sulfur compounds such as dimethyl sulfoxide, ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , ^{_{AlCl 4 -, CF 3 SO 3}} -
And a solution in which one or more of lithium salts and other metal salts, alkylammonium salts, and alkylphosphonium salts are dissolved.

Examples of the resin having solubility or swelling property in the non-aqueous electrolyte solution include, for example, an acrylic resin comprising a polymer of an acrylic monomer such as polymethyl (meth) acrylate, polyethyl (meth) acrylate, poly (meth) acrylate, and polyacrylonitrile. Alternatively, these monomers and other monomers such as resins such as styrene-acrylonitrile copolymers, polyvinyl homopolymer resins such as polyvinyl acetate and polyvinyl chloride, polyvinyl chloride vinyl acetate copolymers, and vinylidene chloride copolymers Resin, acetal resin, polyamide resin such as nylon, polyurethane resin,
Examples thereof include polycarbonate resins, polyalkylene oxide resins such as polyethylene oxide, copolymer resins of vinylidene fluoride and ethylene trifluoride, cellulose derivatives such as ethyl cellulose and cellulose acetate, and rubbers such as butyl rubber and natural rubber.

As the aqueous electrolyte, for example, an aqueous solution of an acid such as sulfuric acid, nitric acid, or hydrochloric acid, or an aqueous solution in which an electrolyte such as sodium chloride is dissolved in water or a mixed solution of water and an organic solvent that dissolves in water is used. Although a sulfuric acid aqueous solution is generally used.

Examples of the resin having solubility or swelling property in the aqueous electrolyte include polyvinyl acetate, a copolymer of vinyl chloride and vinyl acetate, a polyamide resin such as nylon, a polyalkylene oxide resin such as polyethylene oxide, ethyl cellulose, and the like. Examples thereof include cellulose derivatives such as cellulose acetate, polyvinylpyrrolidone, polyglutamic acid, modified polyethylene oxide having high absorbency, polyacrylic acid grafted starch, and acrylic monomer and vinyl acetate copolymer.

When a mixed solution of water and an organic solvent is used as the solvent for the aqueous electrolyte solution, alcohol or the like can be used as the organic solvent soluble in water.

Examples of the activated carbon used in the present invention include, for example, those obtained by carbonizing a resin such as a resol-type phenol resin or a novolak-type phenol resin and then activating the resin to produce a spherical or other shape. Spherical particles are preferred in that the packing density can be increased and the capacitance can be increased. Various degrees of polycondensation of the resole type phenol resin can be used, but not limited thereto, a modified phenol resin modified with another resin and other thermosetting resins can also be used.

In addition to the above, activated carbon made from natural materials such as conventionally used coconut shell activated carbon, phenol,
Activated carbon made of artificial polymer materials such as rayon and polyacrylonitrile can be used alone or in combination, and the shape thereof may be an amorphous one such as fiber (fiber) or cloth.

Examples of the conductive carbon used in the present invention include acetylene black by a furnace method, carbon black by another furnace method or an impact method, and carbon black by a channel method.

As the coating amount of the resin on the activated carbon and the conductive carbon, the total amount of the activated carbon and the conductive carbon
The range is preferably 0.1 to 20% by weight, more preferably 1 to 1% by weight.
3% by weight. If the amount is less than 0.1% by weight, the effect of reducing the leakage current in the high temperature load test of the completed electric double layer capacitor is small. The resistance of the electrode itself increases, which lowers the charging efficiency.

As a method of coating the activated carbon and the conductive carbon with the resin, a solution of the resin, that is, a resin having solubility or swelling property in a non-aqueous electrolyte is dissolved in a non-aqueous solvent such as toluene, and an aqueous electrolyte. A resin having solubility or swelling property in water or an organic solvent having water and solubility, for example, a solution prepared by dissolving in a mixture of lower alcohol and water was prepared, and activated carbon and / or conductive carbon were mixed and stirred therein. Thereafter, the solvent is removed by volatilization. In the case where both the activated carbon and the conductive carbon are coated with the above resin, either the activated carbon or the conductive carbon may be used first, or after mixing and stirring at the same time, the solvent may be removed by volatilization and dried. Alternatively, each of the conductive carbons may be mixed and stirred with the above resin solution, then mixed, and then dried similarly.

In the present invention, the polarizable electrode may be one having fluidity in a use state, but may be one that maintains a solid state in a use state as a molded body. In the latter case, the electrode can be easily formed by stacking a collecting electrode. A double-layer capacitor can be manufactured, and it is not necessary to use sealing means for preventing leakage of the electrolyte.

In order to form a polarizable electrode of such a molded body, activated carbon or conductive carbon coated with the above resin is kneaded with a binder and a solvent with a three-roll or the like to form a sheet.
As the binder in this case, a resin having no solubility in the electrolytic solution is used. As the resin, for example, ethylene tetrafluoride (TFH) resin is used, and a dispersion in which this is dispersed in water or the like is used. Thereby, a binder and a solvent can be added.

The sheet-shaped molded body is impregnated with the above-mentioned non-aqueous electrolyte or aqueous electrolyte depending on the type of resin coated with activated carbon or conductive carbon. Simultaneously with or after the impregnation, the resin coated with the activated carbon and the conductive carbon is dissolved or swelled. As this method, room temperature may be used, heating may be performed during the impregnation of the electrolyte solution, heating may be performed after the impregnation of the electrolyte solution, or both may be used in combination. In this way, a polarizable electrode is completed.A pair of the polarizable electrodes is prepared, and the polarizable electrodes are formed on the both sides of the porous separator. Further, current collecting electrodes are provided on the polarizable electrodes on both sides of the porous separator, and are housed in a case. Is completed.

When the polarizable electrode has fluidity, for example, an unvulcanized conductive sheet plate in which a conductive substance is kneaded into rubber (which serves as a current collecting electrode) is used as a bottom plate to form a cylindrical unvulcanized rubber gasket. Activated carbon coated with a resin as described above from the open end to the upper end, a kneaded product of conductive carbon and an electrolytic solution, and the activated carbon and the conductive carbon coating resin were dissolved in the same manner as above. Fill a polarizable electrode consisting of a fluid. Thereafter, the porous separator is applied to the filler side, and a gasket filled with the same polarizable electrode as described above is vulcanized with the filler side applied to the opposite side of the porous separator. The basic cell is completed in this manner. When the basic cell is fixed in a sealed container with a conductive adhesive and connected to lead wires, an electric double layer capacitor is completed.

The porous separator used in the present invention includes, as its material, cellophane, a polymer material such as polypropylene or polyethylene and natural fibers, and as a shape, a microporous film having a large number of minute through holes, a certain thickness. A sponge-like film having a complicated fine pore, a nonwoven fabric or a combination thereof is exemplified. In addition to these, a material that satisfies various properties such as good compatibility with the electrolyte solution, no passage of activated carbon, high ion permeability (or porosity), and sufficient mechanical strength is also used. be able to. From the viewpoint of the capacitor characteristics, those having a relatively small porosity are preferred for those requiring a small leakage current, and those having a relatively large porosity are preferred for those requiring a small series equivalent resistance.

Further, as the conductive current collecting electrode used in the present invention,
Examples thereof include metal foil, conductive rubber, and impregnated flexible graphite that are stable in an aqueous electrolyte solution.

The electric double layer capacitor according to the present invention has not only a structure having polarizable electrodes on both sides of a porous separator and a current collecting electrode on each polarizable electrode, but also a polarizable electrode on one side of the porous separator. And a polarizer and a porous separator each provided with a current collecting electrode.

〔Example〕

Next, an embodiment of the present invention will be described with reference to FIGS.

Example 1 coconut shell activated carbon powder containing 20% by weight of acetylene black
To 100 parts by weight, 200 cc of a toluene solution having a concentration of 1% by weight of an acrylic resin is added and mixed and stirred. Thereafter, the solvent is volatilized and dried, and the surface of the activated carbon and carbon powder is coated with a resin.

Next, activated carbon and carbon treated with this resin are treated with a tetrafluoroethylene (TFE) resin dispersion (solid content: 40%).
%, Solvent water) and kneaded with three rolls to form a sheet having a thickness of 0.5 mm. An aluminum layer was formed on one side of this sheet by vapor deposition, and a polarizable electrode material cut to a diameter of 10 mm and a thickness of 0.5 mm was prepared. Next, this is immersed in 1 mol of tetraethylammonium perchlorate electrolyte solution of γ-butyrolactone to impregnate the electrolyte solution with the polarizable electrode material and to prepare a polarizable electrode in which the above-mentioned coating resin is dissolved. Two polarizable electrodes are formed, opposed to each other via a polypropylene porous separator, and further sealed with a stainless steel case to produce a coin cell as shown in FIG.

This coil cell is 70 ℃
After applying a 2.4 V voltage for 1000 hours (high-temperature load test), the leakage current and its capacitance were measured. That is, for the leakage current, by applying a rated voltage of 2.4V Connect the coin cell 11 of the sample as shown in FIG. 2 charges, fixed resistor by measuring the V _R by the voltmeter 12 after 30 minutes The leak current is measured from the resistance value R of 13 by the following equation.

In addition, as shown in FIG.
Is connected to the sample terminals 14 and 15, the switch is connected to the 16 side, and the battery is charged at a constant current of 20 mA. After that, the switch was switched to the 17 side, and a constant current discharge was performed at 5 mA as shown in FIG.
8 to measure the time T _2, which becomes the time T ₁ and 1.0V became 1.5V at. From these measured values, the capacitance is obtained by the following equation.

Here, C: capacitance (Farad) i: current (Amp) T ₁ , T ₂ : time (minute) The results of the above measurement are shown in the table. The capacitance was shown as a rate of change (%) of the value after the high-temperature load test with respect to the value before the test.

Examples 2 to 9 Examples were performed in the same manner as in Example 1 except that the type of activated carbon, the type of coating resin, the resin concentration at the time of resin coating, and the composition of the electrolyte solution were changed to those described in the column of each example in the table. Each of the coin cells 2 to 9 was produced, and the results of measurement of these coin cells in the same manner as in Example 1 are shown in the table.

However, a coin cell was prepared in the same manner as in Example 5 except that acetylene black was not used in Example 1.

Comparative Examples 1 and 2 A coin cell was produced in the same manner as in Example 1 except that the step of coating the activated carbon and carbon with a resin was not used, and the results of measurement in the same manner as in Example 1 are shown in the table.

From the above results, it can be seen that the leak current value of each of the examples after the high temperature load test is significantly smaller than that of the comparative example. This is because the electrolytic solution is fixed to the coating resin on the surface of activated carbon and conductive carbon, so that the charging efficiency is improved,
Although it can be considered that the leakage current value can be reduced,
However, it is not limited to this.

〔The invention's effect〕

According to the present invention, the activated carbon and the conductive carbon are coated with a resin and then dissolved in an electrolytic solution, and a polarizable electrode using a resin having no solubility in the electrolytic solution as a binder is used. The leakage current of the multilayer capacitor can be reduced, the high temperature stability can be improved, and the life can be prolonged.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electric double layer capacitor, FIG. 2 is a leak current measurement circuit diagram, FIG. 3 is a capacitance measurement circuit diagram,
FIG. 4 is an explanatory diagram of the operation. In the figure, 1 is a porous separator, 2 and 2 'are polarizable electrodes,
Reference numerals 3, 3 'denote current collecting electrodes, 4 denotes a metal case, 5 denotes a metal cap, and 6 denotes an insulating material.

Claims (3)

(57) [Claims] 1. A conductive current collecting electrode on both sides of a structure of a non-electron conductive and ion permeable porous separator and a polarizable electrode provided on at least one side of the porous separator, In the method for producing an electric double layer capacitor, wherein the polarizable electrode contains activated carbon, conductive carbon, an electrolytic solution and a binder, a resin having a solubility or swelling property in the electrolytic solution on the surface of the activated carbon and / or the conductive carbon And activated carbon coated with the resin and / or
A method for producing an electric double layer capacitor, comprising a step of using the conductive carbon together with the binder made of a resin having no solubility in the electrolytic solution to produce the polarizable electrode. 2. A step of forming a polarizable electrode, the step of kneading activated carbon and conductive carbon coated with the resin, the binder, and a solvent to form a sheet-shaped molded body;
2. The method for producing an electric double layer capacitor according to claim 1, further comprising a step of impregnating the sheet-like molded body with an electrolytic solution. 3. Activated carbon and / or at the time of or after preparation of a polarizable electrode.
3. The method for producing an electric double layer capacitor according to claim 1, wherein the resin coated with the conductive carbon is dissolved or heated and swelled in an electrolytic solution.