JP2002015954A - Electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long service life electric double-layer capacitor which can suppress heating terminals of a collector and cells, even when charging/ discharging is made with a large current. SOLUTION: The capacitor 1 comprises cells 5, each composed of a laminate of two polarizable electrodes 2 containing active carbon, a separator 3 interposed between the electrodes 2, 2, and collectors 4, 4 laminated on the opposite surfaces of the electrodes 2 to the surfaces at the separator 3, a sealing member 7 for sealing the cell 5, and sheet-like terminals 4a a part of them projecting out from the sealing member 7. The main surface of the terminal 4a is formed with a rough surface and/or rugged notches are formed into the side ends of the terminals 4a.

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 suitable as a high-voltage power supply.

[0002]

2. Description of the Related Art An electric double layer capacitor is a capacitor using an electric double layer formed by polarization of ions at an interface between an electrode and an electrolyte, and has both functions of a capacitor and a battery. In addition to being able to charge a large amount of electrostatic capacity and capable of rapid charging and discharging as compared with the above, it has attracted attention as an auxiliary power supply for a large-capacity motor, such as a small memory backup power supply or a driving source of a car.

[0003] As a general example of such an electric double layer capacitor, a separator made of an insulating porous material is interposed between two polarizable electrodes containing activated carbon and an electrolytic solution, and the polarizable electrode is formed. In a sealing member made of an insulator such as a plastic or a thermoplastic resin, a plurality of cells each made of a stacked body in which a current collector made of a metal foil or the like is arranged on each surface opposite to the surface on the separator side are stacked. There is known a multilayer electric double-layer capacitor having a configuration housed and sealed.

On the other hand, the electric double-layer capacitor having the above structure has attracted attention as a power supply for supplying energy to components that require a very large amount of energy instantaneously, for example, at the time of start-up. It is known that a large current can be rapidly charged and discharged.

[0005]

However, the conventional electric double layer capacitor described above has a structure sealed in a sealing member, so that it can be rapidly charged and discharged with a large current of several A to several hundred A. In this case, Joule heat generated in the current collectors and terminals is accumulated in the cell stack, and the electrolytic solution is decomposed, the capacitance is reduced, and the reliability of the electric double layer capacitor is reduced. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to efficiently discharge heat even when charging and discharging a large capacity, thereby suppressing heat generation inside the electric double layer capacitor. An object of the present invention is to provide a multilayer electric double-layer capacitor that can be improved in reliability and has a small size and high productivity and a long life.

[0007]

The present inventors have studied the above problems and found that the surface and side edges of the terminal connected to the current collector are formed in an uneven shape to increase the surface area of the terminal. As a result, it has been found that the heat generated in the electric double layer capacitor can be efficiently radiated to the outside with a simple structure, resulting in a small, highly productive and highly reliable electric double layer capacitor.

That is, the electric double layer capacitor of the present invention comprises two polarizable electrodes containing activated carbon, a separator interposed between the polarizable electrodes, and a surface of the polarizable electrode on the separator side. A sealing member for sealing a cell made of a laminate with a current collector laminated on each of the opposite surfaces,
A sheet-like terminal provided integrally with a part of a peripheral portion of the current collector and projecting outside the sealing member; and a main terminal of the sheet-like terminal. A flat surface is formed by an uneven surface, and / or an uneven cutout is formed at a side end of the sheet-like terminal.

Here, it is preferable that a plurality of the cells are stacked, and a plurality of terminals are connected to the periphery of the current collector every other outside the sealing member.

[0010]

FIG. 1 is a schematic sectional view showing an example of an electric double layer capacitor according to the present invention. According to FIG. 1, an electric double layer capacitor 1 has a rectangular sheet-like separator 3 disposed and interposed between a sheet-like polarizable electrode 2 and a rectangular sheet-like plane forming a positive electrode and a negative electrode. Yes,
On the other surface of the polarizable electrodes 2 and 2 opposite to the surface on which the separators are provided, current collectors 4 and 4 each having a rectangular sheet-like plane forming a positive electrode and a negative electrode are laminated and bonded, respectively. The laminate of 2, 2, the separator 3, and the current collectors 4, 4 constitutes one unit cell 5.

Here, as the activated carbonaceous structure constituting the polarizable electrode 2, an activated carbon having a high specific surface area and containing a binder for binding the activated carbon can be suitably used. It may be carbonized to improve capacity, reduce internal resistance, and improve heat dissipation. Also, in order to maintain the high capacitance of the electric double layer capacitor 1 and obtain the necessary strength as a structure, it is desirable that the activated carbon has a specific surface area of 1,000 to 3,000 m ² / g.

Although the carbon component added as the binder is present between the activated carbon particles, when the carbonization treatment is performed, the ratio of the carbon component to the activated carbonaceous structure is 5 to 5.
The content is preferably 50% by weight, whereby the sinterability and bonding between the activated carbon particles can be enhanced.

Further, the polarizable electrode 2 is preferably a disk, a rectangular (in FIG. 1, rectangular) plate-like body, or the like. J in terms of reliability of mechanical strength that can withstand
Three-point bending strength at room temperature according to ISR1601 is 3
It is preferably at least 0 kPa, particularly preferably at least 60 kPa. Further, the thickness of the polarizable electrode 2 is preferably 1.5 mm or less, particularly preferably 0.6 mm or less from the viewpoint of reducing the internal resistance.

The separator 3 is made of pulp, polyethylene, polypropylene, polyvinylidene fluoride (P
An organic film such as VdF) or a glass fiber nonwoven fabric and ceramics can be used, and are formed to insulate the polarizable electrodes 2 from each other. It is formed of a porous body through which ions can pass. The separator 3
Is preferably 0.02 to 0.15 mm in order to prevent a short circuit or the like and reduce the internal resistance.

Further, the polarizable electrode 2 and the separator 3
An aqueous solution of sulfuric acid or nitric acid, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (γ-
BL), N, N-dimethylformamide, sulfolane,
An electrolyte such as a non-aqueous electrolyte obtained by combining a non-aqueous solvent such as 3-methylsulfolane and an electrolyte such as a quaternary ammonium salt such as tetraethylammonium tetrafluoroborate or a quaternary sulfonium salt or a quaternary phosphonium salt is impregnated. In the present invention, it is desirable to use a non-aqueous electrolyte having a high decomposition voltage. The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.5 to 2 mol / l in order to stably obtain a high capacitance.

The current collector 4 is made of conductive metal foil such as aluminum, titanium, tantalum, platinum, or gold, or stainless steel, and exchanges electric charges between the polarizable electrodes 2 and 2. In particular, it is desirable to use a metal foil mainly composed of aluminum from the viewpoint of heat dissipation and corrosion resistance to a non-aqueous electrolyte having a high decomposition voltage. The current collector 4
The thickness is preferably thin in order to reduce the internal resistance, but in consideration of breakage due to handling during assembly, etc.
About 02 to 0.10 mm is desirable.

According to the present invention, a sheet-like terminal 4 a is formed integrally with the current collector 4 at a part (corner in FIG. 1) of the peripheral portion (one side) of the current collector 4. However, according to the present invention, a major feature is that the main plane of the terminal 4a is formed by an uneven surface and / or an uneven cutout is formed at a side end of the sheet-like terminal 4a. Yes,
As a result, even when a large current is discharged from the electric double layer capacitor 1, the heat generated at the terminal 4a can be efficiently radiated, the temperature rise inside the electric double layer capacitor 1 is suppressed, and the deterioration of the electrolytic solution and the polarization electrode As a result of being able to prevent partial destruction, the life of the electric double layer capacitor 1 can be extended and the reliability can be improved.

Here, as shown in the side view and the plan view of the current collector 4 and the terminal 4a in FIG.
A terminal 4a having a surface roughness (Ra) of 0.5 μm or more, particularly 0.5 to 2 μm, (b) a terminal 4a having a main surface formed in a zigzag shape, (c) a terminal 4a One type or two or more types having a flat surface formed in a wavy shape, and (d) having a concave or convex cutout at the side end of the terminal 4a can be suitably used. In order to increase the specific surface area of the terminal 4a and improve heat dissipation while preventing an increase in the resistance of the terminal 4a, it is desirable that the height of the projections of the irregularities is 1 to 3 mm. The pitch between the tops is 1-5m
m is desirable.

According to (b) to (d) of the above structure, when the terminal 4a is connected to another member or when the terminals 4a converge as described later, the current collector 4 and the terminal 4a
There is also an effect that the concentration of stress generated at the interface with the terminal 4 can be reduced to prevent the short circuit of the terminal 4a.

According to FIG. 1, the terminals 4a of the plurality of current collectors 4 are provided on the same side of the laminate, and the terminals 4a of the adjacent current collectors 4 are provided at different positions on the same side. Have been. That is, a plurality of cells 5 are stacked so that the terminals 4a of the current collector 4 alternately form the positive terminal and the negative terminal, and the cells 5 are stacked in a cell stack 6 Is formed. Then, two sets of terminals provided at the same site are contacted or joined to each other to form a positive terminal and a negative terminal, respectively. In addition, the positive electrode terminal and the negative electrode terminal are disposed at positions where they do not contact to prevent a short circuit.

In FIG. 1, the cell stack 6 is sealed and fixed by a sealing member 7 formed on the outer periphery of the cell stack 6 in order to seal and hold the electrolytic solution. The shape of the sealing member 7 is desirably 0.5 to 3 mm in thickness in terms of heat dissipation, shock absorbing properties, and miniaturization of the electric double layer capacitor 1.

The sealing member 7 is made of an insulator having a high thermal conductivity, specifically, silicone rubber, urethane rubber,
Rubber such as butadiene rubber, or alumina, mullite,
It is desirable to be made of at least one kind selected from the group of ceramics such as aluminum nitride, silicon nitride, silicon carbide and the like, and they may be laminated two or more layers. Above all, in the assembling step of accommodating the cell laminate 6 in the sealing member 7 and the electrolyte inlet 9, the polarizable electrode 2 in the cell laminate 6 can be easily assembled without being damaged. , Urethane rubber and butadiene rubber are desirable, and silicon rubber having a thermal conductivity of 1 W / m · K or more is most preferable in terms of high thermal conductivity, high insulation and improvement in mechanical strength. In order to increase the thermal conductivity, it is desirable that the ceramics be made of the above-described ceramics having a thermal conductivity of 3 W / m · K or more.

Further, among the sealing members 7, the cell laminate 6
The sealing members 7 located on the upper and lower surfaces of the cell caulk the cell laminate 6 to enhance the shape retention of the cell laminate 6 and improve the contact state between the polarizable electrode 2, the separator 3 and the current collector 4. In order to reduce the internal resistance of the electric double layer capacitor 1, the electric double layer capacitor 1 may be formed of another member having high rigidity, such as metal such as iron, stainless steel, aluminum, copper, and titanium. Are fixed and sealed to the sealing member 7 by screwing or the like.

An electrolytic solution inlet 9 for injecting and impregnating the electrolytic solution into the polarizable electrode 2 and the separator 3 is formed on the outer peripheral surface of the sealing member 7. After removing moisture adhering to the inside of the laminated body 6, a non-aqueous electrolytic solution is injected and sealed to reduce the amount of moisture in the electric double layer capacitor 1 to prevent the electrolytic solution from deteriorating. The reliability of the multilayer capacitor 1 can be improved.

Further, according to FIG. 1, a plurality of terminals 4a are converged in the sealing member 7 every other one, and the tip of the converging body of the terminal 4a protrudes from the sealing member 7. According to the present invention, in order to enhance heat dissipation, the tip of the terminal 4a is formed so as to protrude to the outside from a through-hole provided in the wall surface of the sealing member 7, particularly 5 mm or more, more preferably 10 mm or more.

Further, according to the present invention, the method of taking out the terminal 4a is not limited to this. For example, as shown in FIG.
a is inserted into each of the plurality of through holes formed in the sealing member 7, and the tip of the terminal 4 a is connected to the conductor layer 11 formed in the wall surface or the outer surface of the sealing member 7 outside the sealing member 7. Connection may be made, whereby the heat radiation of the conductor layer 11 located on the outer surface of the sealing member 7 can be increased, and the heat radiation of the entire electric double layer capacitor 10 can be increased.

It is desirable that the conductor layer 11 be formed with a notch having an uneven shape at the side end, as in the terminal 4a described above, in order to enhance heat dissipation.

[0028]

(Example) 50 parts by weight of polyvinyl butyral (PVB) was mixed with 100 parts by weight of an activated carbon powder sample having a BET value of 2000 m ² / g, and the mixture was stirred by a high-speed mixing stirrer. After the body was subjected to a mesh pass with 40 mesh, a sheet-like formed body was produced by roll forming. After forming a molded body for forming a solid activated carbon electrode by cutting the sheet into a predetermined shape, a heat treatment is performed at 900 ° C. in vacuum to form an activated carbonaceous structure having a size of 50 mm × 50 mm and a thickness of 0.5 mm. Produced.

On the other hand, a 50 mm × 50 mm separator made of pulp and having a thickness of 50 μm, and a 50 mm × 50 mm thickness having a terminal having a width of 10 mm at one end of one side thereof.
And a current collector made of aluminum foil.
A cell laminate was prepared in which nine layers of cells were laminated using the polarizing electrode-separator-polarizable electrode (-collector) as one unit cell. The aluminum current collector used had a shape as shown in Table 1. The cell stack is disposed such that the current collector is located on each of both end faces, and the cell stack is provided with a current collector 10.
And 18 polarizable electrodes and 9 separators. In stacking the cells, the terminals were protruded from the same side surface of the cell stack, and adjacent terminals were alternately arranged at opposite corners.

Next, a 1 mm thick silicon rubber is formed on the side surface of the cell laminate other than the terminal protruding surface, and through-holes penetrating in the longitudinal direction are formed at eight corners, and a frame-shaped sealing member is provided. Established. Then, each terminal located at the same corner protruding from the outer peripheral surface of the cell laminate is connected to each other by ultrasonic welding to form a positive electrode terminal and a negative electrode terminal. Protruded.
(Terminal length 3 mm inside gasket).

Further, a pressure plate which is a part of a sealing member made of aluminum of 60 mm × 60 mm × 8 mm and having a through hole at a corner is laminated on both end surfaces of the cell laminate and the gasket. The through-hole penetrating the gasket was aligned, a screw member made of stainless steel was inserted into the through-hole, and the pressure plate and the cell stack were caulked by screwing to a pressure of 0.2 MPa and sealed. .

Then, the gasket is placed in a vacuum atmosphere for 10 minutes.
After drying at 0 ° C., a 1 mol / l non-aqueous electrolyte solution of tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) propylene carbonate (PC) solution was injected from an electrolyte injection port provided at the outer periphery of the gasket. Then, the electrolyte was impregnated into the polarizable electrode and the separator, and then the electrolyte injection port was sealed.

With respect to 100 of the obtained electric double layer capacitors, the number of defective terminals was determined, and the yield rate (%) was calculated. Also, at 70 ° C. and 3.0 V, a current of 5
Charging and discharging were performed at 0 A for 50 hours each, and the temperature of the cell stack was measured with a thermocouple inserted into the inner wall surface of the gasket. Furthermore, the rate of change in capacitance before and after the heavy discharge was continued for 1000 hours was measured. The results are shown in Table 1.

[0034]

[Table 1]

From Table 1, it can be seen that Sample No. having the terminals formed in a flat plate shape and having no irregularities on the side end portions of the terminals. In No. 1, cracks were likely to occur at the interface of the terminal with the current collector, the yield was low, and the temperature of the cell stack increased and the capacitance decreased significantly.

On the other hand, in the case of the sample No. in which the main surface of the sheet-like terminal was formed on the uneven surface according to the present invention. In Nos. 2 to 15, the non-defective rate was as high as 80% or more.
It was suggested that the life was prolonged when the rate of decrease in capacitance after 0 hour was 30% or less.

(Example 2) Sample No. 1 of Example 1 4 were inserted into through holes provided in a frame-shaped gasket made of alumina ceramic having a thickness of 1 mm, and the surface roughness (Ra) of the main plane formed on the outer surface of the gasket was 10%.
An electric double layer capacitor was manufactured and evaluated in the same manner as in Example 1 except that it was connected to a conductor layer having a concave and convex surface having a pitch of 2 mm and a height of 2 mm at the side end portions.
%, Temperature 70 ° C., change rate of capacitance is −10%,
It was found that the heat radiation of the terminals was improved.

[0038]

As described above in detail, in the electric double layer capacitor of the present invention, the main surface of the sheet-like terminal provided integrally with the peripheral portion of the current collector is formed by an uneven surface, and / or By forming an uneven cutout at the side end of the sheet-shaped terminal, it is possible to enhance the heat dissipation of the heat generated in the terminal and prevent the inside of the electric double-layer capacitor from being heated. The decomposition of the electrolytic solution accompanying the rise in the temperature of the capacitor can be suppressed, and the life can be prolonged.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an electric double layer capacitor of the present invention.

FIG. 2 is a plan view and a side view for explaining the shapes of a current collector and terminals of the electric double layer capacitor of the present invention.

FIG. 3 is a schematic sectional view showing an example of another electric double layer capacitor of the present invention.

[Explanation of symbols]

 1, 10 ... Electric double layer capacitor 2 ... Polarizable electrode 3 ... Separator 4 ... Current collector 4a ... Terminal 5 ... Cell 6 ... Cell laminate 7 ... Seal Stop member 9 ・ ・ ・ Electrolyte injection port 11 ・ ・ Conductor layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Kazuo Ikuta 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima Inside the Kyocera Research Institute

Claims (2)

[Claims] 1. A polarizer comprising: two polarizable electrodes containing activated carbon; a separator interposed between the polarizable electrodes; and a surface opposite to the separator-side surface of the polarizable electrode. A sealing member for sealing a cell formed of a laminate with a current collector, and a sheet integrally provided on a part of a peripheral portion of the current collector, a part of which protrudes outside the sealing member An electric double-layer capacitor comprising: a terminal; and a main surface of the sheet-like terminal formed by an uneven surface.
And / or an electric double layer capacitor characterized by forming an uneven cutout at a side end of the sheet-like terminal. 2. The cell according to claim 1, wherein a plurality of the cells are laminated, and a plurality of terminals are connected to the periphery of the current collector every other one outside the sealing member. Or the electric double layer capacitor according to 2.