JPH0620875A - 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 solution).

[0002]

2. Description of the Related Art An electric double layer capacitor is formed at an interface between activated carbon and an electrolytic solution by immersing the electrolytic solution in a porous solid which is electrochemically stable and conductive to the electrolytic solution such as activated carbon. By using the electric double layer described above, a large capacitance of farad (F) order can be easily realized.
This large capacity, that is, a large capacity of 10 to 50 F / cm ³ , is 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 the activated carbon is porous. That is because the effective surface area is extremely large. This large capacity makes it possible to use this type of capacitor as a substitute for a battery such as a backup power supply for an IC memory or a microprocessor.
Unlike batteries that utilize electrochemical phenomena, the polarizable electrodes and electrolyte formed by the above activated carbon do not undergo chemical changes during charge and discharge, so the life during repeated charge and discharge, that is, charge and discharge It has a much longer cycle life than batteries.

However, although the electric double layer capacitor has a large electrostatic capacity, its equivalent series resistance (ESR: Eq)
univalent Series Resistancy
Since e) is also high, its application is limited, such as being unsuitable for removing high frequency components in a signal processing circuit or a smoothing circuit for rectifier output. Therefore, it is desired to cultivate new applications by taking advantage of easiness of realization of large capacity and long life of repeated charge / discharge.

Large capacity and low resistance (E
Techniques for realizing the SR) are disclosed in Japanese Patent Application Laid-Open No. 4-288361 and Japanese Patent Application Laid-Open No. 63-226019 by the same assignee as the 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 with each other, a mixture of activated carbon powder or fibers and a phenol resin is heated in an inert gas atmosphere and carbonized with a phenol resin. A porous solid material obtained by binding activated carbon powders (or fibers) together is used. An electrolytic solution is impregnated into this solid material to form a polarizable electrode of an electric double layer capacitor. Since this polarizable electrode has a higher density and a lower resistivity than the polarizable electrode in the prior art, that is, a polarizable electrode composed of a paste-like mixture of activated carbon and an electrolytic solution, it has a capacity per unit volume of an electric double layer capacitor. Can be further increased, and the ESR can be further reduced. Particularly, the above-mentioned JP-A-4-2
The polarizable electrode according to the invention disclosed in Japanese Patent No. 88361 has a large effect of large capacity and low resistance (ESR), and is mechanically strong. By combining an electric double layer capacitor in which dilute sulfuric acid is impregnated into this polarizable electrode in parallel with a lead acid battery for automobiles, it is possible to extend the charge / discharge cycle life of the lead acid battery to at least 6 to 7 times longer than the conventional one. Is shown in the above publication. This application example shows that the electric double layer capacitor is effective for downsizing and prolonging the life of the electric energy supply source in the electromechanical energy conversion mechanism such as an actuator or a motor.

Generally, the above-mentioned electric double layer capacitor is
A pair of polarizable electrodes, each of which is impregnated with an electrolytic solution, is 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. Equipped with a dynamic configuration. Flat plate current collectors made of a conductive material are provided on both end faces of the tubular gasket so as to form a lid plate and a bottom plate of the gasket, respectively. These current collectors form a terminal plate for the outside of the pair of polarizable electrodes, and at the same time form a sealing member for the electrolytic solution together with the gasket.

Referring to FIG. 2 which schematically shows the electric double layer capacitor disclosed in the above-mentioned Japanese Patent Laid-Open No. 4-288361, this capacitor has a pair of flat plate-shaped polarizable electrodes 1A /
1B and a plate-shaped separator 3 made of a porous insulating material and interposed between these electrodes. Polarizing electrode 1A / 1
B is obtained by molding a mixture of activated carbon powder and phenolic resin into a plate and then heat-treating it at a high temperature of about 1000 ° C., in which sulfuric acid having a concentration of about 30 wt% is impregnated as an electrolytic solution. It's included. 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 of being separated from each other and allows the 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 plate-shaped electrodes are opposed to each other in the electrolyte layer.

The laminated body of the polarizable electrodes 1A / 1B and the separator 3 is housed in a tubular gasket 4 made of insulating rubber, and a flat rubber collector 2A / 2B made of conductive rubber is provided on the end surface of the gasket 4. It is provided. The current collector 2A firmly adheres to the polarizable electrode 1A and the upper surface of the gasket 4, and
B adheres to the polarizable electrode 1B and the lower surface of the gasket 4. As a result, these 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 electrolytic solution.

As described above, although new applications have been found by increasing the capacity and reducing ESR, there still remains a big problem in securing reliability. That is, the polarizable electrode loses the solvent of the electrolytic solution when it is placed in a high temperature environment for a long period of time, resulting in a decrease in the capacitance of the capacitor and an increase in the ESR, whereas in the above-mentioned new application, that is, lead. When used as a power source for driving a starter motor of an automobile in combination with a storage battery, the capacitor is installed in an environment such as the engine room where there are many vibrations and shocks at high temperatures, so it is essential to ensure reliability in such an environment. Is.

In order to ensure the vibration resistance and shock resistance of the capacitor, mechanical pressure is applied to the pair of current collectors from the outside when the capacitor is housed in the gasket. The paste-like mixture-based polarizable electrode according to the prior art is more suitable for this pressurizing step than the solid-material-based polarizable electrode described in the above publication. In the former case, it is difficult to realize sufficient vibration resistance even after the pressurizing process. That is, in the former electric double layer capacitor, the polarizable electrodes 1A / 1B are preliminarily molded into a shape as shown by a press or the like, the separator 3 is inserted therebetween, and they are superposed, and then housed in the gasket 4. Since it is manufactured, an appropriate amount of space 9 is provided between the cylindrical inner surface of the gasket 4 and the outer surface of the laminated body of the polarizable electrodes 1A / 1B and the separator 3 in consideration of the dimensional accuracy of a tool in the assembly process. It is necessary to provide. The gap 9 allows the polarizable electrodes 1A / 1B to move in a direction parallel to the surface of the current collectors 2A / 2B when vibration or shock is applied to the capacitor, so that the pair of polarizable electrodes 1A / 1B are cylindrical. Even after being housed in the gasket, it is easy to shift in a plane parallel to the plane of the separator. Therefore, when a lateral impact is applied to this capacitor, these polarizable electrodes 1A / 1B and the current collector 2 are
The contact state with A / 2B is impaired and ESR increases. Further, in a high-temperature environment, the electrolytic solution that has penetrated into the polarizable electrodes 1A / 1B evaporates and leaks from the contact portion between the gasket 4 and the current collectors 2A / 2B. And decrease 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 which 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]

The electric double layer capacitor of the present invention comprises a pair of plate-like polarizable electrodes made of a porous conductive solid material in which an electrolyte solution is impregnated, and these polarizable electrodes. A plate-shaped ion-permeable separator member made of an insulating material that is inserted between the pair of plate-shaped collectors and a pair of plate-shaped current collectors that are arranged in conductive contact with both end faces of the laminate of the polarizable electrode and the separator member. An electric double layer capacitor comprising a body member and a tubular gasket that houses the laminated body inside and forms an airtight container for the laminated body by coupling with the current collector member, wherein the tubular shape of the gasket member A void is formed between the inner surface of the electrolyte and the laminate, and a gel-type auxiliary electrolyte solution having a solvent and a solute common to the electrolyte solution and having substantially the same concentration. The equivalent of the liquid electrolyte solution was impregnated with electrolytic solution holding body and in that filled the gap.

[0011]

Since the capacitor according to the present invention contains the gelled or liquid auxiliary electrolyte in the void, the amount of the electrolyte in the hermetic container is larger than that of the conventional capacitor of this type. Therefore, even if it is placed in a high temperature environment for a long period of time, it is possible to mitigate the influence of loss of the electrolytic solution, that is, the decrease in capacitance and increase in ESR.

Further, since the auxiliary electrolytic solution in the void acts as a cushioning material against vibrations and shocks applied to the electric double layer capacitor from the outside, it is possible to enhance vibration resistance and shock resistance. Since the supplement of the electrolytic solution by the auxiliary electrolytic solution does not depend on the liquid electrolytic solution, the electrolytic solution is not scattered due to rupture of the airtight container.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an electric double layer capacitor according to the present invention comprises a gel electrolyte 5 or a holder for the electrolyte which is arranged so as to fill the void 9 (see FIG. 2).
That is, this electric double layer capacitor has a polarizable electrode 1
In addition to the electrolyte solution that is soaked in A / 1B, an auxiliary electrolyte solution that contains substantially the same solute and solvent as this electrolyte solution and has substantially the same concentration is provided. Therefore, the electric double layer capacitor of the present invention contains a larger amount of electrolytic solution than that of the conventional electric double layer capacitor, and does not cause a decrease in the electrolytic solution even in a high temperature environment, resulting in a decrease in capacitance and an increase in ESR. .
Moreover, instead of directly injecting the liquid electrolytic solution into the voids 9, a gel electrolyte or a glass fiber impregnated with the liquid electrolytic solution is used to form a cushioning member against external vibration and shock. Therefore, the vibration resistance and impact 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, the phenol-based powdered activated carbon and the powdery phenol-based resin are weighed out in a weight ratio of 70:30 and dry-mixed with a high-speed dry mixer. The mixing time is 4 hours. Next, this 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 at 1000 ° C. for 2 hours to obtain activated carbon. During this carbonization heat treatment, isotropic shrinkage of about 10% occurs, so the size of the activated carbon plate after carbonization is
L6.3 mm, W4.5 mm, and t3.6 mm.

Next, this activated carbon plate is used as a polarizable electrode 1A, and a plate-shaped conductive rubber in which carbon is dispersed in butyl rubber to impart conductivity is used as a current collector 2A. cm ² , temperature 80 ° C, time 30
Heat press under the condition of minutes to integrate. Similarly, the polarizable electrode 1B and the current collector 2B are also adhered and integrated.

On the other hand, length (L) 80 mm, width (W) 60
A rectangular flat plate-shaped insulating butyl rubber having a thickness of 8 mm and a thickness (t) of 8 mm is prepared, and the inner portion is cut off leaving a portion having a width of 5 mm on each side to form a frame-shaped gasket 4. On one side of the gasket 4, a through-hole 1 having a circular cross section with a diameter of 3 mm extending inward and outward from the gasket in a plane parallel to the plane of the gasket 1.
0 is set. Also, length (L) 70 mm, width (W) 50
A rectangular flat plate-shaped separator 3 made of porous polyester having a thickness of 0.1 mm and a thickness (t) of 0.1 mm is prepared.

Next, the porous separator 3 is inserted between the integrated body of the polarizable electrode 1A and the current collector 2A and the 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 the both end surfaces of the gasket 4 are bonded by thermocompression bonding to be integrated (for details, see the description of page 20, line 20 to line 24 of the above publication).

After the gas inside the current collector / polarizable electrode / gasket structure obtained through the above steps is removed by suction from the through holes 10, 30 wt% from the same through holes 10 is removed.
Then, dilute sulfuric acid is injected and allowed to soak into the polarizable electrodes 1A / 1B. After this step, excess dilute sulfuric acid in the void 9 is discharged from the through hole 10.

Next, a colloidal silica solution (silica sol) containing 40 wt% silica (silicic anhydride) and 96 wt%
The mixed solution having a volume ratio of 50: 7 with concentrated sulfuric acid of
After being injected into the inside of the gasket 4, the through hole 10 is sealed with the adhesive 11. The mixed solution corresponds to dilute sulfuric acid having a concentration of 20 wt% and has a viscosity as low as that of normal 20 wt% diluted sulfuric acid at the beginning of the mixing, but gels in about 1 hour after being injected into the void. . The silica sol has a pH of 2 to
In the range of 4, the sol is in a metastable state, but when the pH deviates 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 void is gelled by utilizing the strong acidity of sulfuric acid used as the electrolytic solution. This silica sol shows not only an inorganic solvent but also a polar organic solvent, that is, a gelation phenomenon not only in a solvent of an organic electrolytic solution, but not only in a capacitor using diluted sulfuric acid as an electrolytic solution but also in an organic electrolytic solution. Also in the capacitor used, the same effect as this embodiment can be obtained. Thus, for example, low ESR
For example, dilute sulfuric acid may be used as an electrolytic solution for a capacitor requiring a high temperature, and an organic electrolytic solution may be used for a capacitor requiring a high withstand voltage. Alumina sol is also known as a material exhibiting the same gelation phenomenon as silica sol. Since silica sol is difficult to use in alkaline electrolyte due to dissolution of silica in the strongly alkaline region, alumina is stable in both acidity and alkalinity, so 20 to 30 wt% potassium hydroxide solution is used as electrolyte. Allows to be used and widens the range of choice for the electrolyte. Since the silica sol and the alumina sol are mixed uniformly and well, they can be used not only individually but also as a mixture of both.

The following modifications can be made to the above embodiment. Modification 1: The void 9 (see FIG. 2) is replaced with the quartz wool 5 (see FIG. 1).
(See (a)) and filled with 30 parts without addition of silica sol.
Includes wt% dilute sulfuric acid. Modification 2: Instead of the quartz wool in Modification 1, the water absorbing polymer 5 fills the voids 9 (see FIG. 2). The polymer 5 has a diameter of 100 μm obtained by polymerizing acrylic acid.
It is a powdery polymer material of the order of 300 to 1, which is its own weight.
Absorbs about 000 times as much water. 3 in this water-absorbent polymer
Absorb about 0 to 40 wt% of dilute sulfuric acid.

Six electric double layer capacitors (unit capacitors) obtained through the above-mentioned steps are superposed on each other, and FIG.
The multilayer electric double layer capacitor (multilayer capacitor) shown in (b) was used. The number of these laminated unit capacitors can be appropriately selected according to the required withstand voltage.

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

Table 1 shows the results of the performance test of the multilayer capacitor according to the above-described embodiment and the two modifications and the 6-layer multilayer capacitor including the unit capacitor according to the prior art shown in FIG. (1) After a voltage of 5.0 V was applied to the test target multilayer capacitor for 240 h in an environment of a temperature of 70 ° C., the capacitor was sufficiently discharged and then the capacitance was measured, and the amount of change in capacitance ΔC The ratio ΔC / C (%) to the initial value C of was calculated.
The capacitance value is measured by applying 5.0V to the capacitor for 6 hours continuously and then discharging the constant current with a current of 0.1A until the terminal voltage of the capacitor changes from 3.0V to 2.5V. Was measured. (2) Mechanical frequency is changed from 10Hz to 2 during the period of 2 hours.
The value was changed to 000 Hz, and the ratio ΔESR / ESR (%) of the change amount ΔESR of the ESR to the initial value ESR was obtained. The ESR was measured by measuring the impedance at a test signal frequency of 1 kHz by the 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 initial values almost equal to those of the capacitor according to the prior art, after the above performance test (1) (high temperature load test). Then, the rate of change in capacitance is -4.6% to 3.2%, which is about ¼ to ⅕ of the rate of change (-15.5%) in the comparison target, which is a significant improvement. Shows. Further, after the performance test (2) (vibration test), the ESR in the comparison object increased by 320%, while the ESR change according to the present invention was negligible and showed high stability. There is.

In the unit capacitor according to the above-described embodiment and its modification, the polarizable electrode 1A / separator 3 /
The laminated body of the polarizable electrodes 1B is formed by pressure welding.
A structure in which the respective polarizable electrodes and the separator do not directly contact each other as in Example 17 described in JP-A-4-288361 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 tubular gasket and the outer surface of the polarizable electrode / separator laminate is filled with gelled dilute sulfuric acid or equivalent liquid dilute sulfuric acid. Filling with an auxiliary electrolyte such as quartz wool or water-absorbing polymer ensures vibration resistance and impact resistance, and reduces the capacitance and increases the ESR with long-term operation in a high temperature environment. It can be prevented.

[Brief description of drawings]

FIG. 1A is a sectional view of a structure of an electric double layer capacitor according to the present invention. Diagram (b) is diagram (a)
FIG. 3 is a side view of a laminated electric double layer capacitor configured by laminating the double layer capacitors of FIG.

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

[Explanation of symbols]

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

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Atsushi Ochi 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation

Claims (5)

[Claims] 1. A pair of plate-like polarizable electrodes made of a porous conductive solid material which are respectively impregnated with an electrolyte solution, and plate-like ions made of an insulating material inserted between the polarizable electrodes. A transparent separator member, a pair of plate-shaped current collector members arranged in conductive contact with both end surfaces of the laminate of the polarizable electrode and the separator member,
An electric double layer capacitor including a tubular gasket that houses the laminated body inside and constitutes an airtight container for the laminated body by coupling with the current collector member, wherein the tubular inner surface of the gasket member and the A void is formed between the laminated body and a gel-like auxiliary electrolyte solution or equivalent liquid electrolyte solution which has the same solvent and solute as the above-mentioned electrolyte solution and which has the same concentration effectively. An electric double layer capacitor characterized in that the void is filled with an electrolyte solution holder. 2. The gelled auxiliary electrolyte solution is obtained by gelling a mixed solution of a sol solution containing any one of silica, alumina and a mixture thereof and an electrolyte solution having a concentration higher than that of 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 fibrous glass, 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.