JP2006222256A - Electric-double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric-double-layer capacitor wherein the air-tightness of the periphery of its each electrode terminal excels over a long term, in the electric-double-layer capacitor wherein a laminate comprising electrode sheets and separators impregnated with an electrolyte is sealed in a flat container, while the end of its each aluminum electrode terminal is exposed to the external. <P>SOLUTION: In the electric-double-layer capacitor excelling in a long-term reliability, the surface of its each aluminum electrode terminal which faces at least the stuck portion of its container to its electrode terminal is coated with an oxide film by an anodic oxidation processing (alumite processing), etc. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is a square electric double layer capacitor that accumulates electricity in an electric double layer that is an interface between a polarizable electrode such as activated carbon and an electrolytic solution, and has an excellent electric secrecy around the electrode terminal It relates to a capacitor.

  In recent years, an electric double layer capacitor that accumulates electricity in an electric double layer that is an interface between a polarizable electrode such as activated carbon and an electrolytic solution has been put into practical use as a power storage medium. As a general configuration of an electric double layer capacitor, an electric sheet having a configuration in which a current collector such as a metal foil and a polarizable electrode such as activated carbon and separators are alternately laminated and impregnated with an electrolytic solution. A multilayer capacitor cell is formed, and the electric double layer capacitor cell is sealed in a container to form an electric double layer capacitor.

  In addition, an electric double layer capacitor is manufactured by forming a laminated body of an electrode sheet and a separator in a sandwich shape in a square electric double layer capacitor and in a roll shape in a cylindrical electric double layer capacitor. (Positive electrode body and negative electrode body) Lead portions are connected to the respective terminals, and the laminated body is accommodated in a container. Then, an electrolytic solution is injected from the opening of the container to impregnate the laminated body with the electrolytic solution. Many methods of sealing the container with the tip of the electrode terminal exposed to the outside have been practiced.

  In such an electric double layer capacitor, an organic electrolytic solution capable of obtaining a high withstand voltage is generally used as the electrolyte, but there is a disadvantage that the withstand voltage is lowered and deteriorated easily due to a small amount of moisture absorption. As a result, the laminate is sufficiently dried before injecting the electrolyte, and the subsequent operation is performed in an inert gas atmosphere until the container is sealed. In addition, as a constituent material of the container, a metal foil whose surface is coated with an adhesive synthetic resin is usually used. When the container is sealed, for example, a heated heat seal bar is used to open the container opening ( The bonding portion is pressed and heat-sealed with an aluminum electrode terminal sandwiched therebetween.

As described above, the electric double layer capacitor needs to keep the inside of the container airtight for a long period from the manufacturing process to the expiration of the use period, and conventionally, means for improving the airtightness of the container has been developed. I came. As a technique for improving the airtightness of the periphery of the electrode terminal, for example, a technique described in the following patent document has been developed.
JP-A-11-195561 JP 2000-77270 A JP 2001-102037 A JP 2002-237436 A

However, depending on the type of electrolyte, when it comes into contact with an aluminum electrode terminal, it gradually corrodes the aluminum electrode terminal, and passes through the gap between the corroded electrode terminal member and the container and oozes out of the container. In addition to impairing the aesthetics of the electrode terminal periphery, there is a risk of reducing the airtightness of the electrode terminal periphery.
Therefore, the problem to be solved by the present invention is to provide an electric double layer capacitor having an electrode terminal excellent in corrosion resistance against an electrolytic solution and excellent in airtightness in the periphery of the electrode terminal for a long period of time.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention applied an oxide film coating on the surface of the aluminum electrode terminal facing at least the bonded portion of the container by anodizing (alumite treatment) or the like, The inventors have found that the corrosion resistance of the electrode terminal to the electrolyte is improved, and that the airtightness around the electrode terminal can be maintained at a high level for a long time.
That is, the present invention is an electric double layer capacitor in which a laminate of an electrode sheet and a separator impregnated with an electrolyte is sealed in a flat container with the tip of an aluminum electrode terminal exposed to the outside, The electric double layer capacitor is characterized in that at least the surface of the aluminum electrode terminal facing the bonded portion of the container is covered with an oxide film.

  Since the electric double layer capacitor of the present invention has a structure in which at least the surface of the aluminum electrode terminal facing the bonded portion of the container is covered with an oxide film by anodizing or the like, the electrode terminal surface of this part is corroded by the electrolytic solution. The airtightness around the electrode terminal can be maintained over a long period of time. As a result, it is possible to maintain the performance of the electric double layer capacitor at a high level over a long period of time.

The present invention is applied to a rectangular electric double layer capacitor provided with an electrode terminal (hereinafter referred to as an aluminum electrode terminal) made of pure aluminum, an aluminum alloy, or a material mainly composed of aluminum.
Hereinafter, although the electric double layer capacitor of this invention is demonstrated in detail based on FIGS. 1-4, this invention is not limited by these.
1 and 2 are configuration diagrams showing an example of the electric double layer capacitor of the present invention. FIG. 3 is a cross-sectional view illustrating an example of a cross section along line aa ′ in FIGS. 1 and 2. FIG. 4 is a cross-sectional view showing an example of a cross section of an aluminum electrode terminal of the electric double layer capacitor of the present invention.

  As shown in FIGS. 1 and 2, the electric double layer capacitor of the present invention includes an electrode sheet impregnated with an electrolytic solution and a separator laminate 1 in a flat container 2 and a tip of an aluminum electrode terminal 3 externally. An electric double layer capacitor that is sealed in an exposed state, and at least a surface 5 of the aluminum electrode terminal 3 facing the bonding portion 4 of the container is covered with an oxide film 6 (shaded portion). It is a multilayer capacitor. That is, as shown in FIG. 3, the electric double layer capacitor in which the side surface of the aluminum electrode terminal 3 is covered with the oxide film 6 in the horizontal cross section in the bonding portion 4 of the flat container 2.

  In the present invention, the aluminum oxide film may be provided only on the surface 5 facing the bonding portion 4 of the container as shown in FIG. 1, but as shown in FIG. You may provide in the peripheral part with the surface 5 which faces. When the oxide film is provided on the peripheral portion, it is usually provided with a width of 1 cm or less. Of the surfaces of the aluminum electrode terminals, the side to be accommodated in the container has a surface to be welded with the lead portion of the laminate in a later step. Except for this, it is also possible to cover all with an oxide film. Further, the surface of the tip portion on the side exposed to the outside of the container is usually not covered with an oxide film.

In the present invention, the formation of the oxide film on the surface of the aluminum electrode terminal is usually carried out by covering the portion where the oxide film is not formed with a mask and then anodizing (alumite treatment). The method of anodizing treatment is not particularly limited. For example, sulfuric acid, oxalic acid, chromic acid or the like is used as a treating solution (electrolytic solution). oxidation of the aluminum is performed in 1 to 20A / dm ² about conditions. At the time of anodizing, pretreatment such as alkali treatment on the surface of the aluminum electrode terminal or post-treatment such as steam treatment is performed as necessary. Thus, the thickness of the oxide film formed on the surface of the electrode terminal is usually about 1 to 100 μm.

  In the electric double layer capacitor of the present invention, the cross-sectional shape of the aluminum electrode terminal may be a flat rectangle, but at least the cross-sectional shape of the portion facing the bonding portion 4 of the container is as shown in FIG. It is preferable that the shape is formed thinly toward the side end, for example, a flat hexagon, octagon, parallelogram, trapezoid, ellipse, or a similar shape. By making the cross section of the electrode terminal into such a shape, there is no step when the electrode terminal 3 and the bonding portion 4 of the container are bonded, and a gap is hardly generated. As a result, the airtightness around the electrode terminal can be further improved. The cross-sectional shape of the portion that does not face the bonding portion 4 of the container is the same as the portion that faces the bonding portion of the container, or is a flat rectangle.

The electric double layer capacitor of the present invention is mainly composed of a step of laminating an electrode sheet and a separator, a step of storing the laminate in a flat container having an opening (bonding portion), a step of injecting an electrolyte into the container, The laminated body is manufactured through a process of reducing the pressure and a process of sealing the container.
When laminating an electrode sheet (a positive electrode body and a negative electrode body) and a separator, the positive electrode body and the negative electrode body, or the lead portion of the positive electrode body and the lead portion of the negative electrode body are respectively the above-described aluminum electrode terminals (positive electrode terminal and negative electrode terminal). It is laminated so that it can be connected to. The laminate is dried or dried under reduced pressure in order to remove moisture and the like to a very low concentration. Further, a flat container having an opening on at least one side for housing the laminate is also dried or dried under reduced pressure.

Next, the positive electrode body and the negative electrode body of the laminate or the lead portions thereof are bonded to the aluminum electrode terminals by welding or caulking, and the aluminum electrode terminals are on the opening (bonding portion) side of the container. In a flat container.
Thereafter, an electrolytic solution is injected into the container from the opening. Subsequently, the container is connected to the decompression device, and the laminate is decompressed. By this decompression treatment, the gas adsorbed on the polarizable electrode such as activated carbon is removed, and the laminate can be efficiently impregnated with the electrolytic solution.

In addition, if necessary, between the injection of the electrolyte and the sealing of the container, the electrode terminal is energized and subjected to electrolytic purification in order to electrolyze and remove moisture and functional groups contained in the polarizable electrode. You can also.
After the depressurization treatment of the laminate, the container is sealed. The container can be sealed by, for example, pressing two heated heat seal bars while sandwiching the container. In the present invention, the process from injection of the electrolytic solution to sealing of the container is performed in a dry inert gas atmosphere.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these.

(Production of electric double layer capacitor)
Of the surfaces of aluminum electrode terminals (positive terminal and negative terminal) having a length of 60 mm, a width of 30 mm, and a thickness of 1.0 mm, the surface (including the thickness surface) facing the bonded portion of the container and the periphery thereof are 2 mm. An oxide film was formed with a width of. The oxide film was formed by covering the portion where the oxide film was not formed with a mask, and then anodizing using sulfuric acid as the treatment liquid under the conditions of an applied voltage of 20 V and an applied current of 2 A / dm ² . Moreover, the heat-pressed water vapor was made to contact as post-processing. The thickness of the oxide film was about 40 μm.

  Next, a positive electrode body, a negative electrode body, and a paper separator obtained by bonding an aluminum foil to a polarizable electrode made of a mixture of activated carbon, carbon black, PTFE, and the like. A total of 30 sheets were laminated so that each could be connected to an electrode terminal, and a square laminate (thickness 15 mm) having a side of 100 mm was produced. After the lead part of the positive electrode body and the lead part of the negative electrode body of the laminated body are bonded to the aluminum electrode terminals (positive electrode terminal and negative electrode terminal) by welding, they are depressurized at 160 ° C. for 12 hours using a vacuum dryer. Dried.

  Also, a square flat container with a side of 150 mm, which is made of aluminum foil (thickness 0.07 mm) whose surface is coated with a polyethylene film (thickness 0.03 mm), is heated at 80 ° C. using a vacuum dryer. And dried under reduced pressure for 15 hours. The flat container has an opening on one side. After the laminate and the flat container to which the aluminum electrode terminals are bonded by welding are cooled to room temperature in a nitrogen atmosphere, the flat electrode is placed on the flat container so that the aluminum electrode terminals are on the opening (bonding part) side of the container. Inserted.

Subsequently, 90 ml of an electrolytic solution in which an ammonium salt or the like was dissolved in a propylene carbonate solvent was injected from the opening of the container. After the injection of the electrolytic solution was completed, the container was connected to a vacuum pump, and the pressure was reduced by the vacuum pump for 30 minutes, and the laminate was subjected to a pressure reduction treatment. During this period, the electrode terminal was energized to perform electrolytic purification.
Thereafter, the opening of the container (the bonded part of the container) was heat-sealed at 150 ° C., and the flat container was sealed to obtain an electric double layer capacitor configured as shown in FIG.

(Investigation around the electrode terminals)
Ten such electric double layer capacitors were manufactured, and charging and discharging were repeated for two months in an environment of a temperature of 70 ° C. and a humidity of 60%. About each electric double layer capacitor, the opening part (bonding part of a container) of the container was cut | disconnected and the cross section was observed using the electron microscope. As a result, no corrosion was observed in any of the electric double layer capacitors.

In manufacturing the electric double layer capacitor of Example 1, the aluminum electrode terminal was electrically operated in the same manner as in Example 1 except that a hexagonal cross-sectional shape was used as shown in FIG. A double layer capacitor was fabricated. Each electrode terminal had a length of 60 mm, a width of 30 mm, a thickness of 1.0 mm (center portion), and an end portion angle of 45 degrees.
Ten such electric double layer capacitors were manufactured, and the periphery of the electrode terminal was examined in the same manner as in Example 1. As a result, no corrosion was observed in any of the electric double layer capacitors.

(Comparative Example 1)
In the production of the electric double layer capacitor of Example 1, an electric double layer capacitor was produced in the same manner as in Example 1 except that an aluminum electrode terminal without an oxide film was used.
Ten such electric double layer capacitors were manufactured, and the periphery of the electrode terminal was examined in the same manner as in Example 1. As a result, minute corroded portions were observed for the four electric double layer capacitors.

  As described above, it was found that the electric double layer capacitor of the present invention hardly corrodes the peripheral portion of the aluminum electrode terminal and can maintain the airtightness of the peripheral portion of the electrode terminal for a long time.

Configuration diagram showing an example of an electric double layer capacitor of the present invention The block diagram which shows an example of the electric double layer capacitor other than FIG. 1 of this invention Sectional drawing which shows the example of the a-a 'cross section in FIG.1 and FIG.2. Sectional drawing which shows the example of the cross section of the aluminum electrode terminal of the electric double layer capacitor of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminated body 2 Flat container 3 Aluminum electrode terminal 4 Bonding part 5 Surface which faces the bonding part of aluminum electrode terminal 6 Oxide film

Claims (7)

  An electrode sheet impregnated with an electrolyte solution and a laminate of separators is an electric double layer capacitor sealed in a flat container with the tip of an aluminum electrode terminal exposed to the outside, and at least the aluminum electrode terminal An electric double layer capacitor characterized in that the surface of the container facing the bonded portion is covered with an oxide film.   2. The electric double layer capacitor according to claim 1, wherein the oxide film is formed with a width of 1 cm or less around the surface of the electrode terminal facing the bonded portion of the container, in the periphery thereof.   2. The electric double layer capacitor according to claim 1, wherein the oxide film is formed on all surfaces of the electrode terminal on the side accommodated in the container except for a surface to be welded to the lead portion of the laminate.   The electric double layer capacitor according to claim 1, wherein the oxide film is formed by anodization.   The electric double layer capacitor according to claim 1, wherein the oxide film has a thickness of 1 to 100 μm.   The electrical cross section according to claim 1, wherein the cross-sectional shape of the portion of the aluminum electrode terminal facing the bonded portion of the container is a flat hexagon, octagon, parallelogram, trapezoid, ellipse, or a similar shape. Double layer capacitor. 2. The electric double layer capacitor according to claim 1, wherein the cross-sectional shape of the aluminum electrode terminal is a flat hexagon, octagon, parallelogram, trapezoid, ellipse, or a similar shape throughout.

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