JP2002075801A - Electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor which is superior in capacity density and has less deterioration due to repetitive charging and discharging. SOLUTION: This electric double-layer capacitor is provided with polarizable electrodes which are arranged opposite to each other with a separator in between, and the internal resistance of one polarizable electrode is 0.5 to 1.5 times as large as that of the other polarizable electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor having a large capacitance.

[0002]

2. Description of the Related Art An electric double layer capacitor is provided with a pair of polarizable electrodes via a porous separator and utilizes the capacitance of an electric double layer formed on the surface of the polarizable electrode in an electrolyte solution. There is a feature that a capacitor having an extremely large capacitance as compared with a general capacitor is obtained, and wide use is expected from a backup use of an electronic device to a power storage use.

A polarizable electrode used for an electric double layer capacitor is stable in an electrolyte solution, has a large specific surface area,
Activated carbon, which is advantageous for forming an electric double layer having a large capacitance, is generally used. The polarizable electrode is one using a sintered body in the form of an electrode, granular or fibrous activated carbon, and a slurry formed by kneading a conductive material and a binder into a sheet-like electrode, and a current collector. An application type electrode in which a slurry is applied on a conductor such as an aluminum foil by various application methods is used.

In an electric double layer capacitor used for storing a large amount of electric energy, such as electric power storage and a power source for a vehicle, the operating voltage is required to be higher than that using an aqueous electrolytic solution. It is considered that those using a possible non-aqueous solvent-based electrolyte are excellent in terms of energy density. There are various characteristics required for electric double layer capacitors, such as the capacitance per unit volume related to the energy density per volume, the internal resistance that affects the response speed, and the service life such as the number of times of charging and discharging. It is important to improve any of these characteristics, but the repetition life of the charge / discharge cycle is extremely important especially in applications where a large amount of electric energy is repeatedly charged and discharged.

There are various factors that cause deterioration of characteristics, and there are items that can be dealt with by controlling quality during manufacturing or controlling during charging and discharging. Some of them were difficult to deal with. For example, the phenomenon that the electric double layer capacitor is degraded by the applied voltage can be dealt with to some extent by selecting the electrolytic solution to be used.
There has been a demand to increase the operating voltage of the electric double layer capacitor as much as possible to increase the electric capacity available for charging and discharging, which has been difficult. A study of the deterioration of the electric double layer capacitor using the organic electrolyte revealed that the electrode on the negative electrode side deteriorated earlier than the electrode on the positive electrode side in particular.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to prevent an electric double layer capacitor from deteriorating in an electric double layer capacitor, and particularly to an electric double layer capacitor using a non-aqueous electrolyte. It is an object to prevent deterioration.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric double-layer capacitor in which polarizable electrodes are arranged to face each other with a separator interposed therebetween, so that the internal resistance of one polarizable electrode is equal to the internal resistance of the other polarizable electrode. The problem can be solved by an electric double layer capacitor in the range of 0.5 to 1.5 times the resistance. Further, the electric double capacitor has an internal resistance of the polarizable electrode which is adjusted by adjusting at least one of a pore size distribution of the conductive porous substance and a density of the polarizable electrode.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The main cause of the present invention is that the deterioration of an electric double layer capacitor using a non-aqueous electrolyte is mainly caused by deterioration of a negative electrode side faster than a positive electrode side electrode. It has been found that the voltage applied to the negative electrode is higher than that of the positive electrode. Although the reason is not clear, the electrolytic solution obtained by dissolving a tetraalkylammonium borofluoride in propylene carbonate or a sulfolane-based solvent, which is used as a non-aqueous solvent in an electric double layer capacitor, is not used in the electrolytic solution. It is considered that there exist ions solvated with borofluoride and ions solvated with tetraalkylammonium. As a result, when a voltage is applied, one electrode mainly contains ions solvated with borofluoride, and the other electrode contains ions solvated with tetraalkylammonium.

Polarizable electrode It is considered that the positive electrode and the negative electrode behave differently in the pore diameter and the packing density in the porous carbon constituting the polarizable electrode because the size of each ion is different. The voltage of the negative electrode, which is a polarizable electrode mainly containing ions solvated with tetraalkylammonium, is higher than the voltage applied to the positive electrode, and the negative electrode to which the applied voltage is large deteriorates early. Since deterioration of one electrode means deterioration of the electric double layer capacitor itself, the electric double layer capacitor deteriorates early.

Accordingly, the present invention makes the voltages applied to the polarizable electrodes equal to each other by making the internal resistances of the respective polarizable electrodes substantially equal, thereby preventing one of the polarizable electrodes from being deteriorated early. Is what you do. It is preferable that the internal resistances of the positive electrode and the negative electrode are equal, but the object of the present invention can be achieved if one value is 1.5 times the other value.

The internal resistance of the polarizable electrode can be adjusted by various means, and may be realized by using materials having different characteristics for the positive electrode and the negative electrode. Use the same material for both electrodes,
A polarizable electrode having a different internal resistance may be manufactured in the process of manufacturing the polarizable electrode. In other words, there are various factors that affect the internal resistance of the polarizable electrode. However, since there are various factors that affect the mobility of ions moving inside the polarizable electrode, they are formed inside the polarizable electrode and electrolyzed. It can be changed by adjusting the size of the pores into which the liquid enters.

More specifically, the internal resistance is changed by adjusting the density of the polarizable electrode by changing the degree of compression of the polarizable electrode composed of the porous material and the binder using porous materials having the same characteristics. Can be done. That is, the density of the negative electrode, which is affected by the mobility of the cation having a relatively large size, is reduced, and the voids in the polarizable electrode are increased,
In addition, by increasing the density of the positive electrode, which is affected by the mobility of the anion whose relative size is small, and reducing the voids in the polarizable electrode, the internal resistance of the negative electrode and the internal resistance of the positive electrode can be made equal. It becomes possible. Further, since the miniaturization of the air gap affects not only the internal resistance but also the capacitance, it is possible to increase the apparent capacitance while maintaining the internal resistance by compression.

[0013] The polarizable electrode of the electric double layer capacitor of the present invention is formed by activating activated carbon particles with a conductive substance such as carbon black.
When pressure-molding a polarizable electrode from a kneaded material kneaded with a binder or the like, it may be manufactured by molding by changing the molding pressure, or a kneaded material such as a doctor blade may be formed on a current collector such as aluminum. After applying by
It may be manufactured by pressurizing and compressing.

As the activated carbon particles, activated carbon obtained by activating a coconut shell, phenol resin, or charcoal of petroleum pitch to increase the surface area with water vapor, hydroxide, or the like is reduced to a particle diameter of 2 μm to 30 μm, preferably about 10 μm. It is preferable to use ordered particles. When a polarizable electrode is manufactured by pressure molding, polytetrafluoroethylene or the like can be used as a binder. In the case of pressure molding after coating on the current collector, at least one kind of elastomer selected from polytetrafluoroethylene, butyl rubber, ethylene propylene diene rubber, butadiene rubber, and nitrile rubber can be used. Of these, butyl rubber is preferred. The binder is preferably used in an amount of 3 to 20 parts by weight based on 100 parts by weight of the activated carbon particles. If the amount is less than 3 parts by weight, it is difficult to achieve sufficient binding, and if the amount is more than 20 parts by weight, adverse effects are exerted on resistance and capacity.

When a kneaded material is applied to produce a polarizable electrode, a metal oxide such as zinc oxide, magnesium oxide, aluminum oxide, silicon oxide, vanadium oxide, etc., which is stable in the operating potential range of an electric double layer capacitor. Substance particles may be added, whereby it is possible to prevent a decrease in electrical characteristics due to the activated carbon particles being completely covered by the binder. The metal oxide particles used for such a purpose are 1 to 8 parts by weight based on 100 parts by weight of the binder.
It is preferably set to 1 part by weight, more preferably 1 to 5 parts by weight, further preferably 1 to 3 parts by weight. Further, the metal oxide particles preferably have an average particle diameter of 0.1 μm to 5 μm, more preferably 0.5 μm to 1 μm, as measured by a light scattering method.

The conductive particles include carbon black, acetylene black and graphite.
The average particle size is preferably from 0.05 μm to 1.0 μm, more preferably from 0.1 μm to 0.5 μm. Further, a crosslinking agent for crosslinking the elastomer may be added to the binder. By adding a cross-linking agent, an electric double layer capacitor with a small change over time can be obtained. Examples of the crosslinking agent include sulfur, peroxides such as dicumyl peroxide, tetraalkylthiuram disulfide, rubber crosslinking agents such as carbamine zinc derivatives,
A crosslinking aid may be added to these. The crosslinking agent is a binder 1
Preferably 0.5 to 8 parts by weight, more preferably 1 to 5 parts by weight, and even more preferably 1 to 3 parts by weight, per 100 parts by weight. When an elastomer is used, it is preferable to use an organic solvent that is a substance that dissolves the elastomer and does not adversely affect the materials used.Toluene, xylene, tetrahydrofuran, cyclohexane,
It is preferable to use normal hexane or the like. The kneading can be performed by a kneader, a mixer or the like.

As the current collector, a thin or net-like base made of aluminum, stainless steel, nickel, titanium, a conductive elastomer or the like can be used. Further, on the surface of these substrates, fine irregularities may be formed by etching or the like to increase the adhesion with the coating layer,
What applied the colloidal carbon etc. to the surface may be used. Further, in the electric double layer capacitor of the present invention, a propylene carbonate solution of tetraethylammonium tetrafluoroborate, trimethylammonium tetrafluoroborate or the like can be used as the electrolyte.

[0018]

The present invention will be described below with reference to examples. Example 1 and Comparative Example 1 82 mg of activated carbon having an average pore diameter of 1.6 nm measured by the BET method, 9 mg of carbon black, and 9 g of polytetrafluoroethylene powder were mixed together and compacted into a disk shape having a diameter of 20 mm. At that time, the molding pressure was adjusted to obtain one having a density of 0.55 g / ml. The pressure was reduced to 1.33 Pa (10 ^-2 Torr) in a vacuum desiccator, and the pressure was reduced to 110 ° C.
For 4 hours to obtain a polarizable electrode A. The molding pressure was changed in the same manner as for the polarizable electrode A to change the density to 0.74.
g / ml of the polarizable electrode B was obtained. Each electrode was combined as shown in Table 1 and laminated via a glass fiber separator, and as shown in FIG. 1, the negative electrode 1 and the positive electrode 2 were placed via a separator 3 as shown in the electric double layer capacitor of the embodiment. And an electrode made of the same material as the negative electrode is disposed as a reference electrode 4 above the positive electrode 1 and the negative electrode 2,
After being placed in a container 5 made of a flexible film in which an aluminum film and a synthetic resin film are laminated, the inside is decompressed, and then filled with a 1.0 M tetraethylammonium tetrafluorate propylene carbonate solution, and then sealed. After manufacturing the electric double layer capacitors 1 to 4 and charging them to 2.5 V with a constant current of 5 mA,
After holding for 15 minutes, a charge / discharge test of discharging at a constant current of 5 mA was performed for 3 cycles, and the internal resistance of the positive electrode and the negative electrode was determined from the current at the start of the discharge and the voltage of the positive electrode and the negative electrode measured with respect to the reference electrode. Indicated.

The charge / discharge energy was calculated from the charge / discharge test, and the capacitance C was obtained from the following equation. The results are shown in Table 1. E = 0.5 CV ² Also, Table 1 shows the capacity decrease rate (%) of the capacity decrease at the 5000th cycle with respect to the capacity obtained in the first charge / discharge cycle.

Example 2 and Comparative Example 2 A butyl rubber (Nihon Butyl II
R065) and 1,000 parts by weight of toluene were added, and the mixture was heated to 80 ° C. to dissolve the butyl rubber. Then, activated carbon (M25 manufactured by Osaka Gas Chemicals, particle size: 10 μm) 10
0 parts by weight and 20 parts by weight of carbon black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size: 0.53 μm) were added, and the mixture was stirred for 24 hours to completely disperse. The obtained kneaded material was applied on a 30-μm-thick aluminum foil, dried, calendered to produce a polarizable electrode having a thickness of 150 μm, and the density was adjusted to 0.55 g / ml of polarizable electrode C and a density of 0.74 g / m
Thus, 1 polarizable electrode D was obtained. These electrodes were combined as shown in Table 1 to produce electric double layer capacitors 5 to 8, and subjected to a charge / discharge test in the same manner as in Example 1 to determine the internal resistance of the negative electrode, the internal resistance of the positive electrode, the capacitance, and the capacitance. The deterioration rate was measured.

[0021]

[Table 1] Electrode type Internal resistance (Ω) Unit electrostatic capacity Internal resistance Capacity degradation negative electrode Positive electrode Negative electrode Positive capacity (F / ml) (ΩF) Rate (%) Capacitor 1 AB 0.454 0.473 21.8 20.2 6.2 Capacitor 2 A A 0.788 0.525 16.0 21.0 9.8 Carrier 3 BB 1.114 0.478 21.8 34.7 12.6 Carrier 4 BA 1.453 0.363 19.0 34.5 13.9 Carrier 5 C D 0.577 0.601 17.7 20.8 6.8 Carrier 6 C C 1.004 0.669 12.8 21.4 10.3 Carrier 7 D 13.5 5.0 8 DC 1.857 0.464 15.0 34.8 14.1

[0022]

According to the electric double layer capacitor of the present invention, the internal resistances of the positive electrode and the negative electrode are made equal to each other, so that the voltages applied to the positive electrode and the negative electrode can be made substantially equal. An electric double layer capacitor can be obtained in which the density is improved, one of the electrodes is not deteriorated at an early stage, the electric characteristics are excellent, and the rate of deterioration due to repeated charging and discharging is small.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electric double layer capacitor according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Reference electrode,
5… Container

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Nakamura 1-1, Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture 1 Inside Power System Co., Ltd. (72) Inventor Didio Okamura 2-19 Minamiota, Minami-ku, Yokohama-shi, Kanagawa -6

Claims (2)

[Claims] In an electric double-layer capacitor in which polarizable electrodes are arranged to face each other with a separator interposed therebetween, the internal resistance of one polarizable electrode is equal to 0.1% of the internal resistance of the other polarizable electrode.
An electric double layer capacitor characterized by being in the range of 5 to 1.5 times. 2. The method according to claim 1, wherein the internal resistance of the polarizable electrode is adjusted by adjusting at least one of the pore size distribution of the conductive porous substance and the density of the polarizable electrode. Electric double capacitor.