JP3270175B2 - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To obtain an electric double-layer capacitor which is excellent in vibration and shock resistance and prevented from decreasing in electrostatic capacity and increasing in ESR even if it is left to stand in an environment of high temperature. CONSTITUTION:Auxiliary electrolytic solution such as gel of dilute sulfuric acid 5 or quartz wool or water-absobing polymer charged with liquid dilute sulfuric acid is filled into a gap between the inner face of a cylindrical gasket and the outer face of a laminate composed of polarizable electrode 1A/separator 3/polarizable electrode 1B. Auxiliary electrolytic solution is used not only for replenishing a decrease in electrolytic solution caused by evaporation or leakage in an electric double-layer capacitor but also for serving as a shock absorber to a mechanical shock applied to the capacitor from outside. Therefore, an electric double-layer capacitor of this design is enhanced in high-temperature resistance and shock resistance.

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 a polarizable electrode such as activated carbon impregnated with a liquid electrolyte (electrolyte).

[0002]

2. Description of the Related Art An electric double layer capacitor is formed at an interface between an activated carbon and an electrolyte by impregnating the electrolyte into a porous solid which is electrochemically stable and conductive to an electrolyte such as activated carbon. A large capacitance of the order of Farad (F) can be easily realized by using the electric double layer.
This large capacity, that is, a large capacity reaching 10 to 50 F / cm ³ , means that the thickness of the electric double layer corresponding to the dielectric layer of a normal capacitor is as small as the diameter of the molecule, and that the activated carbon is porous. The effective surface area is extremely large. This large capacity allows this type of capacitor to be used as a battery replacement, such as a backup power source for IC memories and microprocessors.
Unlike batteries that use electrochemical phenomena, the polarizable electrode and electrolyte formed by the activated carbon do not undergo a chemical change during charge / discharge, so the life in use involving repeated charge / discharge, that is, charge / discharge Repeat life is much longer than batteries.

However, although the electric double layer capacitor has a large capacitance, its equivalent series resistance (ESR: Eq
universal Series Resistanc
Since e) is high, its use is limited, for example, it is not suitable for a high-frequency component removal in a signal processing circuit or a smoothing circuit for rectifier output. Therefore, it is desired to develop new applications that make use of the easiness of realizing a large capacity and the long life of repeated charge and discharge.

A large capacity and low resistance (E
The technology for realizing the SR) is disclosed in Japanese Patent Application Laid-Open Nos. 4-288361 and 63-226019 by the same assignee of the present invention. In the polarizable electrode materials described in these publications, as a means for keeping the activated carbon and the electrolytic solution in contact, a mixture of activated carbon powder or fiber and a phenol resin is heated in an inert gas atmosphere, and carbonized phenol resin is used. A porous solid material obtained by binding activated carbon powders (or fibers) is used. The solid material is impregnated with an electrolytic solution to form a polarizable electrode of an electric double layer capacitor. This polarizable electrode has a higher density and a lower resistivity than the conventional polarizable electrode, that is, a polarizable electrode composed of a paste-like mixture of activated carbon and an electrolytic solution, so that the capacity per unit volume of the electric double layer capacitor is large. Can be further increased, and the ESR can be further reduced. In particular, Japanese Patent Application Laid-Open No. 4-2
The polarizable electrode according to the invention disclosed in Japanese Patent No. 88361 has a large effect of increasing the capacity and reducing the resistance (ESR), and is mechanically strong. By combining an electric double-layer capacitor in which dilute sulfuric acid is impregnated in the polarizable electrode in parallel with a lead-acid battery for automobiles, the repetitive charge / discharge life of the lead-acid battery can be extended at least about 6 to 7 times that of the conventional battery. Is shown in the above publication. This application example shows that the electric double layer capacitor is effective for miniaturizing and extending the life of the electric energy supply source in an electromechanical energy conversion mechanism such as an actuator or a motor.

In general, the above electric double layer capacitor is
Basically, a pair of polarizable electrodes, each impregnated with an electrolytic solution, are stacked and housed in the inner space of a gasket made of a thin cylindrical insulating material with a plate-shaped separator made of an insulating material inserted between them. It has a strategic configuration. A flat current collector made of a conductive material is provided on each of both end surfaces of the cylindrical gasket so as to constitute a lid plate and a bottom plate of the gasket. These current collectors form a terminal plate for the outside of the pair of polarizable electrodes, and also form a sealing member for the electrolyte together with the gasket.

Referring to FIG. 2 schematically showing an electric double layer capacitor described in the above-mentioned Japanese Patent Application Laid-Open No. 4-288361, this capacitor has a pair of flat polarizable electrodes 1A /
1B and a plate-shaped separator 3 made of a porous insulating material inserted between these electrodes. Polarizing electrode 1A / 1
B is obtained by forming a mixture of activated carbon powder and a phenolic resin into a plate and then heat-treating the mixture at a high temperature of about 1000 ° C., wherein sulfuric acid having a concentration of about 30 wt% is soaked as an electrolyte. It is embedded. Polarizing electrode 1
The activated carbon portion of A / 1B selectively adsorbs positive ions (H ⁺ ) and negative ions (SO ₄ ^2- ) at the interface with the electrolytic solution to form an electric double layer. The separator 3 holds the polarizable electrodes 1A / 1B in a state where they are separated from each other, and allows ions of the electrolyte in the electrolytic solution to pass therethrough. With the configuration shown in FIG. 2, this electric double layer capacitor is equivalent to a structure in which two flat electrodes are opposed to each other in a layer of an electrolytic solution.

The laminate of the polarizable electrodes 1A / 1B and the separator 3 is accommodated in a cylindrical gasket 4 made of insulating rubber, and a flat current collector 2A / 2B made of conductive rubber is provided on an end surface of the gasket 4. Provided. The current collector 2A tightly adheres to the polarizable electrode 1A and the upper surface of the gasket 4,
B adheres to the polarizable electrode 1B and the lower surface of the gasket 4. Thus, these current collectors 2A / 2B form a terminal plate for connecting the polarizable electrodes 1A / 1B to the outside, and together with the gasket 4, form an airtight container for the electrolyte.

As described above, although a new application has been found due to an increase in capacity and a reduction in ESR, there still remains a great problem in securing reliability. That is, when the polarizable electrode is exposed to a high temperature environment for a long period of time, it loses the solvent of the electrolytic solution to decrease the capacitance of the capacitor and increase the ESR. In applications where a power supply for driving a starter motor for an automobile is configured by combining with a storage battery, the capacitor is installed in an environment such as an engine room where it is subject to high temperature vibrations and shocks. It is.

[0008] In order to secure the vibration resistance and shock resistance of the capacitor, a mechanical pressure is externally applied to the pair of current collectors when the capacitor is housed in the gasket. The prior art paste-based mixture-based polarizable electrode is more suitable for the pressing step than the solid material-based polarizable electrode described in the above-mentioned publication. In the former case, it is difficult to realize sufficient vibration resistance even after the pressurizing step. That is, in the former electric double layer capacitor, the polarizable electrodes 1A / 1B are formed in advance by press or the like into the shapes shown in the figure, and the separators 3 are interposed and overlapped, and then, are housed in the gasket 4. Since it is manufactured, an appropriate amount of a gap 9 is provided between the cylindrical inner surface of the gasket 4 and the outer surfaces of the laminated body of the polarizable electrodes 1A / 1B and the separator 3 in consideration of the dimensional accuracy of tools and the like in the assembly process. Must be provided. The gap 9 allows the polarizable electrodes 1A / 1B to move in a direction parallel to the surface of the current collector 2A / 2B when vibration or shock is applied to the capacitor. Even after being housed in a gasket in the shape of a separator, it tends to shift in a plane parallel to the plane of the separator. Therefore, when a lateral impact is applied to the capacitor, the polarizable electrodes 1A / 1B and the current collector 2
The adhesion state between A / 2B and A / 2B is impaired, and ESR increases. In a high-temperature environment, the electrolytic solution infiltrated into the polarizable electrodes 1A / 1B evaporates and leaks out from a close contact portion between the gasket 4 and the current collectors 2A / 2B. And increase in ESR.

Therefore, an object of the present invention is to provide vibration resistance,
An object of the present invention is to provide an electric double layer capacitor which has excellent impact resistance and does not cause a decrease in capacitance and an increase in ESR even when exposed to a high-temperature environment for a long period of time.

[0010]

An electric double layer capacitor according to the present invention comprises: a pair of plate-shaped polarizable electrodes made of a porous conductive solid material impregnated with an electrolyte solution; A plate-like ion-permeable separator member made of an insulating material inserted between the pair of plates, and a pair of plate-like current collectors disposed in conductive contact with both end surfaces of the laminated body of the polarizable electrode and the separator member, respectively. An electric double-layer capacitor including a body member and a cylindrical gasket that accommodates the laminate inside and forms an airtight container for the laminate by coupling with the current collector member. gel auxiliary electrolysis whose and that voids are formed, the effective identical concentrations have a common solvent and solute to the electrolyte solution between the inner side surface and an outer surface of the laminate The solution or impregnated comparable liquid electrolyte solution electrolytic solution holding body and in that filled the entire gap.

[0011]

In the capacitor according to the present invention, since the gel or liquid auxiliary electrolyte is contained in the space, the amount of the electrolyte in the airtight container is larger than that of the conventional capacitor of this type. Therefore, even if the device is placed in a high-temperature environment for a long period of time, the effects of electrolyte loss, that is, a decrease in capacitance and an increase in ESR can be reduced.

Further, the auxiliary electrolyte in the space acts as a buffer against vibrations and shocks applied to the electric double layer capacitor from the outside, so that the vibration resistance and shock resistance can be improved. In addition, since the replenishment of the electrolyte with the auxiliary electrolyte does not depend on the liquid electrolyte, the electrolyte is not scattered due to the rupture of the airtight container or the like.

[0013]

Referring to FIG. 1, the electric double layer capacitor according to the present invention includes a gel electrolyte 5 or a holder for the electrolyte, which is disposed so as to fill the gap 9 (see FIG. 2).
That is, this electric double layer capacitor is provided with the polarizable electrode 1.
In addition to the electrolyte impregnated in A / 1B, an auxiliary electrolyte having substantially the same concentration including the same solute and solvent as the electrolyte is provided. Therefore, the electric double-layer capacitor of the present invention contains a larger amount of electrolyte than the conventional electric double-layer capacitor, and does not cause a decrease in the electrolyte, the accompanying decrease in capacitance or an increase in ESR even in a high-temperature environment. .
Moreover, instead of injecting the liquid electrolyte directly into the gap 9, a gel member or a glass fiber impregnated with the liquid electrolyte is employed to form a buffer member against external vibration and impact. Therefore, the vibration resistance and shock resistance of the capacitor are improved. Hereinafter, the manufacturing process of the electric double layer capacitor according to the embodiment of the present invention will be described in detail.

First, phenol-based powdered activated carbon and powdery phenol-based resin are weighed to obtain a weight ratio of 70:30, and dry-mixed by a high-speed dry mixer. The mixing time is 4 hours. Next, the mixture was hot-pressed at 180 ° C. to form a rectangular flat plate having a length (L) of 70 mm, a width (W) of 50 mm, and a thickness (t) of 4 mm. Heat treatment at 1000 ° C. for 2 hours in the furnace to obtain activated carbon. Approximately 10% isotropic shrinkage occurs during the carbonization heat treatment.
L6.3 mm, W4.5 mm, and t3.6 mm.

Next, the activated carbon plate was used as a polarizable electrode 1A, and a conductive rubber plate having conductivity provided by dispersing carbon in butyl rubber was used as a current collector 2A. cm ² , temperature 80 ° C, time 30
Integrate by hot pressing under the conditions of minutes. Similarly, the polarizable electrode 1B and the current collector 2B are adhered and integrated.

On the other hand, the length (L) is 80 mm and the width (W) is 60
A rectangular plate-shaped insulating butyl rubber having a thickness of 8 mm and a thickness (t) of 8 mm is prepared, and an inner portion thereof is cut off except for a portion having a width of 5 mm on each side to form a frame-shaped gasket 4. One side of the gasket 4 has a through-hole 1 having a circular cross section with a diameter of 3 mm and extending in and out of the gasket in a plane parallel to the plane of the gasket.
0 is provided. In addition, length (L) 70 mm, width (W) 50
A separator 3 made of a rectangular flat plate-shaped porous polyester having a thickness of 0.1 mm and a thickness (t) of 0.1 mm is prepared.

Next, a porous separator 3 is inserted between the above-mentioned integrated body of the polarizable electrode 1A and the current collector 2A and the above-mentioned integrated body of the polarizable electrode 1B and the current collector 2B and housed in the gasket 4. After that, the current collectors 2A / 2B and both end faces of the gasket 4 are bonded by thermocompression bonding to be integrated (for details, see the description of the above publication, page 27, lines 20 to 24).

After the gas inside the current collector / polarizable electrode / gasket structure obtained through the above steps is removed by suction from the through-hole 10, 30 wt% from the same through-hole 10 is removed.
And dilute sulfuric acid into the polarizable electrodes 1A / 1B. After this step, excess diluted sulfuric acid in the gap 9 is discharged from the through hole 10.

Next, a colloidal silica solution (silica sol) containing 40 wt% of silica (silicic anhydride) and 96 wt% of
Of a mixed solution having a volume ratio of 50: 7 with concentrated sulfuric acid through hole 10
After that, the through hole 10 is sealed with an adhesive 11. The mixed liquid corresponds to dilute sulfuric acid having a concentration of 20 wt%. At the beginning of mixing, the liquid has a viscosity as low as that of normal 20 wt% diluted sulfuric acid, but gels in about one hour after being injected into the void. . The silica sol has a pH of 2
In the range of 4, the sol is in a metastable state, but when the pH shifts from the above range to the acidic side or the alkaline side, the balance of the surface charge of the silica particles is lost and gelation occurs. In this embodiment, the sulfuric acid in the voids is gelled by utilizing the strong acidity of sulfuric acid used as the electrolytic solution. Since this silica sol shows a gelling phenomenon not only with an inorganic solvent but also with a polar organic solvent, that is, a solvent of an organic electrolyte, not only a capacitor using dilute sulfuric acid as an electrolyte but also an organic electrolyte is used. The same effect as that of the present embodiment can be obtained in the capacitor used. Thus, for example, low ESR
For example, dilute sulfuric acid may be used as the electrolytic solution for a capacitor requiring a high voltage, and an organic electrolytic solution may be used for a capacitor requiring a high withstand voltage. Alumina sol is also known to exhibit the same gelling phenomenon as silica sol. Since silica sol is difficult to use in an alkaline electrolyte due to dissolution of silica in a strongly alkaline region, alumina is stable in both acidity and alkalinity, so a potassium hydroxide solution of about 20 to 30 wt% is used as an electrolyte. And expand the range of choices for electrolytes. Since the silica sol and the alumina sol are uniformly mixed well, not only can they be used alone but also both can be used as a mixture.

The following modifications can be made to the above-described embodiment. Modification 1: Quartz wool 5 (see FIG. 1)
(See (a)), and 30% of silica sol-free was added thereto.
Contains wt% dilute sulfuric acid. Modification 2: Instead of the quartz wool in Modification 1, the voids 9 (see FIG. 2) are filled with the water-absorbing polymer 5. The polymer 5 has a diameter of 100 μm obtained by polymerizing acrylic acid.
A powdery polymer material having a weight of 300 to 1,
It absorbs about 000 times as much water. 3
About 0 to 40% by weight of dilute sulfuric acid is absorbed.

As shown in FIG. 1, six electric double layer capacitors (unit capacitors) obtained through the above-described steps are superposed.
A multilayer electric double layer capacitor (multilayer capacitor) shown in FIG. The number of stacked unit capacitors can be appropriately selected according to the required withstand voltage.

The above-mentioned multilayer capacitor has an electrode terminal plate 7 on the upper end face of a laminate composed of six unit capacitors 6.
A, an insulating plate 12A and a metal pressing plate 8A are provided, and a lower end surface is provided with an electrode terminal plate 7B, an insulating plate 12B and a pressing plate 8B. The stacked body of the unit capacitors is pressed by bolts 13 provided at the four corners of the pressing plates 8A / 8B. This pressing is for reducing the contact resistance between the unit capacitors 6, and the pressing plates 8A / 8B
Sufficient rigidity is provided so that the pressurization can be averaged. The withstand voltage of this multilayer capacitor is the unit capacitor 6
Of about 1.2V, ie, about 7.2V.

The results of the performance test outlined below of the multilayer capacitor according to the above embodiment and the two modifications and the six-layer multilayer capacitor comprising the unit capacitor according to the prior art shown in FIG. 2 are as shown in Table 1. (1) After placing the multilayer capacitor to be tested in a 70 ° C. environment for 240 h with a voltage of 5.0 V applied thereto, discharge sufficiently, measure the capacitance, and measure the change in capacitance △ C The ratio ΔC / C (%) to the initial value C was determined.
The capacitance value is measured by applying 5.0 V to the capacitor for 6 hours continuously, discharging at a constant current of 0.1 A, and changing the terminal voltage of the capacitor from 3.0 V to 2.5 V. Was measured. (2) The mechanical frequency is increased from 10 Hz to 2 during a period of 2 hours.
By changing the frequency to 000 Hz, the amount of change in ESRＲthe ratio of the ESR to the initial value ESR △ ESR / ESR (%) was determined. The ESR was measured by measuring the impedance at a test signal frequency of 1 kHz by an AC four-terminal method and calculating the real part thereof.

[0024]

[Table 1]

As shown in Table 1, although the capacitance and ESR of the multilayer capacitor according to the present invention have almost the same initial values as those of the conventional capacitor, after the performance test (1) (high temperature load test), , The rate of change of the capacitance is -4.6% -3.2%, which is about 1/4 to 1/5 of the rate of change (-15.5%) of the comparison object. Is shown. After the performance test (2) (vibration test), the ESR in the comparative example increased by 320%, whereas the change according to the present invention was negligibly small and showed high stability. I have.

In the unit capacitor according to the above embodiment and its modification, the polarizable electrode 1A / separator 3 /
Although the laminate of the polarizing electrodes 1B is formed by pressure welding,
As in Example 17 described in JP-A-4-288361, a structure in which the polarizable electrodes and the separator do not directly contact each other may be used.

[0027]

As described above, in the electric double layer capacitor according to the present invention, the space between the inner surface of the cylindrical gasket and the outer surface of the polarizable electrode / separator laminate is filled with gel-like diluted sulfuric acid or equivalent liquid diluted sulfuric acid. Filling it with an auxiliary electrolyte such as quartz wool or a water-absorbing polymer ensures vibration resistance and impact resistance, and reduces the capacitance and ESR due to long-term operation in a high-temperature environment. Can be prevented.

[Brief description of the drawings]

FIG. 1 (a) is a sectional view of the structure of an electric double layer capacitor according to the present invention. The diagram (b) is the diagram (a)
FIG. 2 is a side view of a multilayer electric double-layer capacitor formed by laminating the above-described double-layer capacitors.

FIG. 2 is a cross-sectional view of a conventional electric double layer capacitor.

[Explanation of symbols]

 1A, 1B Polarized electrodes 2A, 2B Current collector 3 Separator 4 Gasket 5 Gel electrolyte, quartz wool, water-absorbing polymer 6 Unit capacitor 7A, 7B Electrode terminal plate 8A, 8B Pressure plate 9 Void 10 Through hole 11 Adhesive 12A, 12B Insulating plate 13 bolt

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukari Kibi 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation (72) Inventor Atsushi Ochi 5-7-1 Shiba, Minato-ku, Tokyo Japan (56) References JP-A-2-236963 (JP, A) JP-A-62-232113 (JP, A)

Claims (5)

(57) [Claims] 1. A pair of plate-like polarizable electrodes made of a porous conductive solid material impregnated with an electrolyte solution, and a plate-like ion made of an insulating material inserted between these polarizable electrodes. A pair of plate-shaped current collector members, which are disposed in conductive contact with both end surfaces of the laminated body of the polarizable electrode and the separator member,
An electric double-layer capacitor containing the laminate inside and a tubular gasket constituting an airtight container for the laminate by coupling with the current collector member, wherein a tubular inner surface of the gasket member and Outside of the laminate
A gap is formed between the auxiliary electrolyte solution and a gel-like auxiliary electrolyte solution having a common solvent and solute as the electrolyte solution and having the same effective concentration, or an equivalent liquid electrolyte solution. An electric double layer capacitor, wherein the entire space is filled with an electrolyte solution holder. 2. The gelled auxiliary electrolyte obtained by gelling a mixture of a sol solution containing one of silica, alumina and a mixture thereof and an electrolyte solution having a higher concentration than the electrolyte solution. The electric double-layer capacitor according to claim 1, wherein 3. The electric double layer capacitor according to claim 1, wherein the electrolyte solution holder is made of at least one of glass fiber, ceramic and plastic. 4. The electric double layer capacitor according to claim 1, wherein the electrolyte solution holder is a water-absorbing polymer. 5. The electric double layer capacitor according to claim 1, wherein the electrolyte solution is an aqueous solution of sulfuric acid.