JP2716334B2 - Electric double layer capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor using solid activated carbon as a polarizable electrode.

[0002]

2. Description of the Related Art As shown in FIGS. 4 and 5, a polarizable electrode 16 of an electric double layer capacitor is a flat or disk-shaped solid activated carbon. A carbon composite material or the like is used. When the electrolytic solution is an aqueous solution, carbon, conductive rubber, conductive plastic, or the like is used for the current collector 7, and when the electrolytic solution is a non-aqueous solution, a metal foil or the like is used, and is electrically connected to the solid activated carbon. . The gasket 8 is made of plastic or rubber, and is bonded to the current collector 7 with an adhesive. The separator 9 is a porous film or a glass fiber papermaking body, and electrically insulates between the pair of polarizable electrodes 16.

Since the withstand voltage of the electric double layer capacitor is the electrolysis voltage of the electrolytic solution, the required withstand voltage is realized by electrically connecting the basic cells 10 in series. FIG. 4 shows an electric double-layer capacitor using an aqueous electrolytic solution. Six basic cells 10 with a withstand voltage of 0.9 V are connected in series, and the withstand voltage is 5.5 V. The above-described electrolyte injection into the electric double layer capacitor is performed by injecting the electrolyte through an injection hole 15 formed in a side surface of the gas socket 8.
After the injection of the electrolyte, the injection hole 15 is melted to seal the electrolyte.

The above-mentioned polarizable electrode 16 has several μm.
There are countless holes of m, and the electrolyte enters inside through these holes. However, it is very difficult to completely inject the electrolyte into these pores. Conventionally, Japanese Unexamined Patent Publication No.
In the coin-shaped electric double-layer capacitor shown in FIG. 5 in which activated carbon was solidified with a binder and used as a polarizable electrode, as shown in FIG. However, this method has a disadvantage that the impregnating property of the entire polarizable electrode 17 does not increase only near the surface where the scratch 18 exists.

[0005]

With this conventional polarizable electrode, it is impossible to completely impregnate the inside with the electrolyte. Further, even when the surface is scratched, improvement of the entire impregnation property cannot be expected only near the surface. As a result, gases such as nitrogen and oxygen remain inside the polarizable electrode. Since this residual gas comes out of the polarizable electrode due to a temperature change or charge / discharge, there is a problem that the internal pressure in the basic cell increases, causing leakage of the electrolytic solution, damage to the basic cell, and the like. .

It is an object of the present invention to provide a highly reliable electric double layer capacitor which does not cause electrolyte leakage or breakage due to an increase in internal pressure in a basic cell.

[0007]

According to the present invention, there is provided an electric double layer capacitor obtained by using a solid activated carbon as a polarizable electrode and injecting an electrolytic solution into the polarizable electrode. Either a through hole having a diameter is formed so that a decrease in capacitance is 10% or less, or one of a highly oriented graphite powder and a graphite whisker is added to the solid activated carbon in a weight ratio of 1% to 10%. Less than that added.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a first embodiment of the present invention, and FIG. 2 is a plan view of the polarizable electrode of FIG. First
The structure of this embodiment is the same as the structure of the conventional electric double layer capacitor shown in FIG. The polarizable electrode 1 of the first embodiment has nine through holes 4 as shown in FIG.

The method of manufacturing the polarizable electrode 1 is as follows. First, powdered activated carbon and a powdery phenol resin are mixed at a weight ratio of 60/40. The mixture was dry mixed using a ball mill and then granulated. This mixed powder was injection-molded in a mold having nine core pins (diameter 2 mm). The molded product has a size of 70 × 50 × 4 mm and the portion of the core pin becomes the through hole 4. This molded article was heat-treated at 900 ° C. in a non-oxidizing atmosphere. The heat treatment time is 2 hours, and the heating rate is 50 ° C./h. Since the contraction rate of the polarizable electrode is isotropically contracted at 5%, the diameter of the through hole becomes 1.9 mm, and the polarizable electrode 1 having nine through holes 4 is obtained.

By forming the nine through holes 4 having a diameter of 1.9 mm in the polarizable electrode 1 as described above, the reduction of the capacitance is suppressed to 10% or less, and the through holes 4 are positioned at point-symmetric positions. By providing, it is possible to improve the impregnation property by causing isotropic shrinkage during heat treatment.

FIG. 3 is a plan view of a polarizable electrode according to a second embodiment of the present invention. The structure of the second embodiment is the same as the structure of the first embodiment shown in FIG. 1 except for the polarizable electrodes. Second
As shown in FIG. 3, the polarizable electrode 2 of Example 1 contains a graphite powder 5.

The method for manufacturing the polarizable electrode 2 is as follows. First, powdered activated carbon, powdery phenol resin, and graphite powder 5 are mixed at a weight ratio of 55/40/5. As a result of X-ray diffraction, the graphite powder 5 used had an interlayer distance of 3.38 angstroms on the carbon net plane. The mixture was dry mixed using a ball mill and then granulated.
This mixed powder was formed into a size of 70 × 50 × 4 mm by injection molding and heat-treated at 900 ° C. in a non-oxidizing atmosphere. The heat treatment time is 2 hours, and the heating rate is 50 ° C /
h. Weight loss rate is 10% activated carbon, 65% resin,
Since the graphite content is 1% or less, the mixing ratio after the heat treatment is 49.5 / 26/5 by weight, and the polarizable electrode 2 containing 6.2% of the graphite powder 5 is obtained.

Since highly oriented graphite can intercalate various ions including sulfate ions, the impregnation of the electrolyte is facilitated by adding graphite powder or graphite whisker to solid activated carbon utilizing this property. Graphite powder 5
The weight ratio of 1% or more to less than 10% makes the through hole 4 of the polarizable electrode 1 of the first embodiment shown in FIG.
In the same manner as described above, the decrease in capacitance can be suppressed to 10% or less.

The electric double layer capacitors of the first and second embodiments using the polarizable electrodes 1 and 2, respectively, were prototyped.
Since the prototype method is the same with any polarizable electrode,
The first embodiment using the polarizing electrode 1 will be described as an example. First, the polarizable electrode 1 and the current collector 7 are pressed. Conductive rubber was used for the current collector 7. With respect to the current collectors 7 arranged on both sides of the stacked body 11, the polarizable electrode 1 is crimped on only one side, and the rest of the current collectors 7 are crimped on both sides of the current collector 7. This is adhered to an ABS gasket 8 using an epoxy adhesive. At this time, the separator 9 of the glass fiber papermaking body is arranged as shown in FIG. In this way, the stacked body 1 including the six basic cells 10 sharing the current collector 7
Get 1. Next, the terminal body 12 and the insulating sheet 13 are arranged, and the laminated body 11 is pressed by fixing the pressing plate 14 with bolts from both sides. Next, the gas is exhausted from one of the two injection holes 15 by a vacuum pump, and sulfuric acid as an electrolyte is injected from the other. The injection time was 2, 4, 8, 12, 24 hours. After the injection, the injection hole 15 is melted and sealed,
The electric double layer capacitor of the first embodiment using the polarizing electrode 1 was obtained. Similarly, an electric double layer capacitor of the second embodiment was obtained. For comparison, electric double layer capacitors of Conventional Example 1 and Conventional Example 2 using the polarizable electrode 16 and the polarizable electrode 17 were prototyped, respectively.

The method for manufacturing the polarizable electrode 16 of the first conventional example is as follows. First, powdered activated carbon and a powdery phenol resin are mixed at a weight ratio of 60/40. The mixture was dry-mixed using a ball mill, granulated, and injection-molded.
The molded article has a size of 70 × 50 × 4 mm. This molded article was heat-treated at 900 ° C. in a non-oxidizing atmosphere.
The heat treatment time is 2 hours, and the heating rate is 50 ° C./h.

The polarizable electrode 17 of Conventional Example 2 was obtained by scratching the surface of the polarizable electrode 16 with abrasive paper.
Abrasive paper having a particle size of 180 was used for 3 minutes in a wet system. The trial production method of the electric double layer capacitor using the polarizing electrodes 16 and 17 is the same as the trial production method using the polarizable electrode 1.

The electric double layer capacitors of the first and second embodiments and the electric double layer capacitors of Conventional Examples 1 and 2 produced as described above were subjected to initial characteristics and high-temperature load tests. The test method is as follows. In Test 1, the appearance was checked after applying 5.5 V at 70 ° C. for 240 hours.
In Test 2, an electrolyte solution with an injection time of 24 hours was used. After applying 5.5 V for 1,000 hours at 70 ° C., the appearance, equivalent series resistance (ESR), and capacitance were evaluated. The equivalent series resistance is obtained by measuring an impedance of 1 kHz by an AC four-terminal method and obtaining a real part at that time. The capacitance C is short-circuited at room temperature for 24 hours, charged at 5 V for 12 hours, discharged at a current of 100 mA, and changed from 3 V to 2.5 V.
It is calculated from the time Δt required for the voltage drop ΔV to V. The calculation formula is: C = I × Δt / ΔV = 0.1 × Δt / 0.5

Tables 1 and 2 show the test results, Table 1 shows the electrolyte injection time and the presence or absence of leakage, and Table 2 shows the evaluation results. It can be seen from Table 1 that there is a relationship between the leakage of the electrolyte and the method and time for injecting the electrolyte. Further, it can be seen that the electric double layer capacitor of the present embodiment can shorten the injection time of the electrolytic solution as compared with the conventional example. The liquid leak occurred from the injection hole 15 partially, but mostly from the adhesive surface between the gasket 8 and the gasket 8. According to Table 2, the electric double layer capacitor of this example in which the electrolyte was injected for 24 hours has no problem in appearance and characteristics, improves the impregnation of the electrolyte, and can obtain high reliability.

[0020]

[Table 1] Appearance; ○ no problem, △ liquid seeping, × liquid leak

[0021]

[Table 2] Unit: ESR / mΩ, capacitance / F Appearance: ○ No problem, × liquid leakage

[0022]

As described above, according to the present invention, the electric double layer capacitor is impregnated with the electrolytic solution because one or more through holes are provided in the polarizable electrode or because highly oriented graphite powder or graphite whisker is added. The effect is that the reliability is improved and high reliability is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a plan view of the polarizable electrode of FIG.

FIG. 3 is a plan view of a polarizable electrode according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a configuration of an example of a conventional electric double layer capacitor.

FIG. 5 is a plan view of an example of a polarizable electrode of a conventional electric double layer capacitor.

FIG. 6 is a plan view of another example of the polarizable electrode of the conventional electric double layer capacitor.

[Explanation of symbols]

 1, 2, 3, 16, 17-minute polar electrode 4 Through hole 5 Graphite powder 7 Current collector 8 Gasket 9 Separator 10 Basic cell 11 Stack 12 Terminal plate 13 Insulating sheet 14 Pressing plate 15 Injection hole 18 Scratches

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tabuchi sequentially 7-1, Shiba 5-chome, Minato-ku, Tokyo Inside NEC Corporation (72) Yukari Kibi 5-7-1, Shiba 5-chome, Minato-ku, Tokyo Japan (56) References JP-A-4-288361 (JP, A) JP-A-2-281608 (JP, A) JP-A-3-116708 (JP, A) JP-A-3-201519 ( JP, A) Hikaru 1-133725 (JP, U)

Claims (2)

(57) [Claims] 1. A solid activated carbon used as the polarizable electrodes, before
In the electric double layer capacitor obtained by injecting the electrolytic solution into the polarizable electrode, a through hole having a diameter of at least 1 mm is formed in the solid activated carbon so that the capacitance is reduced by 10%.
An electric double layer capacitor formed as described below and over the entire area of the polarizable electrode. Wherein the solid activated carbon used as the polarizable electrodes, before
In an electric double layer capacitor obtained by injecting an electrolyte into the polarizable electrode, one of a highly oriented graphite powder and a graphite whisker is added to the solid activated carbon in a weight ratio of 1% to 10%. % Electric double layer capacitor.