JP2009111107A - Electrode sheet and electrochemical capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remarkably suppress a rise of inner resistance by repetition of charging/discharging in an electrode sheet where a polarizing electrode is formed on a surface of a collector such as metal foil through a conductive bonding layer and in an electrochemical capacitor using the sheet. <P>SOLUTION: In the electrode sheet, a layer comprising active carbon and carbon black is formed on the surface of metal foil through the conductive bonding layer comprising silicate of alkali metal and/or silicate of alkaline earth metal. In the electrochemical capacitor, the electrode sheet is used. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode sheet and an electrochemical capacitor using the electrode sheet. More specifically, the electrode sheet forms a polarizable electrode on the surface of a current collector such as a metal foil via a conductive adhesive layer, And an electrochemical capacitor using the same.

  In recent years, electrochemical capacitors such as 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 have begun to be put into practical use as a storage medium. As a general structure of an electrochemical capacitor, an electrode sheet made of a current collector such as a metal foil and a polarizable electrode such as activated carbon and a separator are alternately laminated to form a laminate, and further impregnated with an electrolyte. The laminated body is sealed in a container to form an electrochemical capacitor cell.

  In addition, an electrochemical capacitor cell is manufactured by forming a laminate of an electrode sheet and a separator in a sandwich shape for a square electrochemical capacitor and in a roll shape for a cylindrical electrochemical capacitor. Lead body and negative electrode body) are connected to the respective terminals, and the laminate is stored in a container, and then an electrolyte is injected from the opening of the container to impregnate the laminate with the electrolyte, and the tip of the electrode terminal is Many methods have been implemented to seal the container while it is exposed to the outside.

  In such an electrochemical capacitor, the electrode sheet is generally manufactured by forming a polarizable electrode containing activated carbon on the surface of a current collector such as a metal foil via a conductive adhesive layer. Conventionally, conductive materials such as carbon black, activated carbon, and binders such as polytetrafluoroethylene and cellulose are often used as components of polarizable electrodes. In addition, as a constituent component of the conductive adhesive layer, in order to increase the adhesive strength with the current collector, it usually has better adhesion to a metal foil such as a binder than a component with good conductivity such as carbon black. Many ingredients are used.

In an electrochemical capacitor, the components of the polarizable electrode and the conductive adhesive layer, the bonding method, and the like are factors that greatly influence the quality of important performance such as internal resistance. Therefore, many binder components for polarizable electrodes and conductive adhesive layers as described in Patent Documents 1 to 4, for example, have been developed with the aim of excellent uniformity and adhesive strength.
JP-A-9-270370 Japanese Patent Application Laid-Open No. 11-162794 JP 11-329904 A JP 2002-222741 A

However, no increase in internal resistance due to repeated charge / discharge could be significantly improved by using any binder.
Therefore, the problem to be solved by the present invention is to charge and discharge an electrode sheet in which a polarizable electrode is formed on a surface of a current collector such as a metal foil via a conductive adhesive layer, and an electrochemical capacitor using the electrode sheet. It is to provide a device capable of greatly suppressing the increase in internal resistance due to repetition of the above.

  As a result of intensive investigations to solve these problems, the present inventors have used an alkali metal silicate and / or an alkaline earth metal silicate as a binder component of the conductive adhesive layer. The inventors have found that an increase in internal resistance of an electrochemical capacitor due to repeated discharge can be significantly suppressed as compared with the conventional one, and have reached the electrode sheet of the present invention and an electrochemical capacitor using the same.

That is, in the present invention, a layer containing activated carbon and carbon black is formed on the surface of a metal foil via a conductive adhesive layer containing an alkali metal silicate and / or an alkaline earth metal silicate. This is an electrode sheet.
The present invention also provides an electrochemical capacitor comprising a laminate in which the electrode sheet and the separator are laminated, and an electrolyte solution sealed in a container.

  Since the conductive adhesive layer in the present invention contains an alkali metal silicate and / or an alkaline earth metal silicate as a binder component, the polarizable electrode and the current collector are not reduced without lowering the conductivity. Adhesive strength can be improved. As a result, the increase in the internal resistance of the electrochemical capacitor due to repeated charging and discharging is significantly smaller than that of the conventional one, and the lifetime of the electrochemical capacitor can be greatly extended.

The electrode sheet of the present invention is distributed on the surface of a current collector (or electrode) such as a metal foil via a conductive adhesive layer in a power storage medium such as an electric double layer capacitor, a lithium ion secondary battery, or a hybrid battery. It is applied to an electrode sheet that forms a polar electrode.
In addition, the electrochemical capacitor of the present invention can be applied to both a rectangular electrochemical capacitor and a cylindrical electrochemical capacitor using the electrode sheet configured as described above.

The basic structure of the electrode sheet of the present invention is that a conductive adhesive layer containing an alkali metal silicate and / or an alkaline earth metal silicate on the surface of a current collector made of a metal foil such as an aluminum foil Further, a polarizable electrode composed of a layer containing activated carbon and carbon black is formed on the outer surface thereof.
In addition, as shown in FIG. 1, the basic form of the electrode sheet of the present invention is that the conductive adhesive layer and the polarizable electrode are on both surfaces (shaded portions) of the metal foil 2 excluding the portion that becomes the lead portion 1. Is formed. Note that the conductive adhesive layer and the polarizable electrode can be formed and used only on one side of the metal foil 2.

  Examples of the alkali metal silicate used in the electrode sheet of the present invention include lithium silicate, sodium silicate, potassium silicate and the like, and examples of the alkaline earth metal silicate include calcium silicate. it can. Two or more of these can be used. The conductive adhesive layer in the present invention requires a conductive component such as graphite and carbon black in addition to these silicates. In addition, although activated carbon, thermosetting resin, etc. may be contained, the content rate with respect to the whole electroconductive contact bonding layer of a silicate is 1-80 wt% normally, Preferably it is 2-50 wt%.

  In the present invention, the method for forming the conductive adhesive layer on the surface of the metal foil is not particularly limited. For example, the constituent components of the conductive adhesive layer as described above may be water, an aqueous solvent, or an organic solvent. A conductive adhesive layer can be formed on the surface of the metal foil by preparing a coating solution by dissolving or dispersing in a solvent, coating the solution on the surface of the metal foil, and drying. The thickness of the conductive adhesive layer is usually 2 to 40%, preferably 5 to 25% of the thickness of the metal foil. When the thickness of the conductive adhesive layer is less than 2% of the thickness of the metal foil, the adhesive strength with the metal foil becomes weak, and when it exceeds 40%, the effect of suppressing the increase in the internal resistance of the electrochemical capacitor is small. Become.

  In the present invention, the method for forming the polarizable electrode on the surface of the conductive adhesive layer is not particularly limited. For example, the constituent components of the polarizable electrode containing activated carbon and carbon black as main components are used. A polarizable electrode can be formed on the surface of the conductive adhesive layer by dissolving or dispersing in an organic solvent to produce a coating liquid, coating the liquid on the surface of the conductive adhesive layer, and drying. However, in the present invention, activated carbon (content ratio: about 70 to 90 wt%), carbon black (content ratio: about 3 to 20 wt%), and polyvinylidene fluoride (content ratio: 5 to 5) are included as components of the polarizable electrode. It is preferable that it contains about 15 wt% in that the increase of the internal resistance of the electrochemical capacitor can be further suppressed.

  The electrochemical capacitor of the present invention uses the above electrode sheet. In the present invention, when laminating the electrode sheet and the separator, as shown in FIG. 2, the lead portion 4 of the positive electrode body and the lead portion 5 of the negative electrode body can be connected to the positive electrode terminal 6 and the negative electrode terminal 7, respectively. Are laminated. Thereafter, as shown in FIG. 3, the laminate 8 is housed in a flat container 9 made of a metal foil covered with a plastic film having an opening on at least one side, but the electrode terminal is on the opening side. Stored. When manufacturing an electrochemical capacitor, the laminated body and the container are usually dried before the electrolyte is injected.

In the present invention, an operation of injecting the electrolyte into the container and impregnating the electrochemical capacitor cell with the electrolyte and then depressurizing the inside of the container to remove the gas adsorbed on the polarizable electrode is performed. . By doing in this way, a laminated body can be efficiently impregnated with electrolyte 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.
Thereafter, the container is sealed by pressing, for example, two heated heat seal bars with a flat container made of plastic or metal foil interposed therebetween, and the electrochemical capacitor of the present invention is obtained. In the present invention, the process from injection of the electrolytic solution to sealing of the container is performed under reduced pressure or in an inert gas atmosphere.

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

[Example 1]
(Production of electrode sheet)
A mixer was charged with 2.3 kg of potassium silicate, 1 kg of graphite, 0.2 kg of carbon black, and 6.5 kg of 1% ammonia water containing 2% of an anionic surfactant, and then stirred to conduct conductive adhesion. A coating solution for the layer was prepared. This coating solution was applied with a width of 105 mm to the center of one side of an aluminum foil having a width of 150 mm and a thickness of 30 μm using a single-side coating apparatus. The unwinding speed and winding speed of the aluminum foil were 4 m / min. Moreover, 120-150 degreeC dry air was introduce | transduced from the hot air introduction port of the coating apparatus, and it was made to dry. The other side was coated in the same manner. As a result, conductive adhesive layers each having a thickness of about 4 μm were formed on both surfaces of the aluminum foil.

  Next, after putting activated carbon, carbon black, and polyvinylidene fluoride into the mixer, an organic solvent containing N, N-dimethylformamide (DMF) is injected in several portions, mixed, and coated for a polarizable electrode. A working solution was prepared. This coating liquid was applied to one side of the conductive adhesive layer of the aluminum foil using a single-side coating apparatus. The unwinding speed and winding speed of the aluminum foil were 4 m / min. Moreover, 40-150 degreeC dry air was introduce | transduced from the hot air introduction port of the coating apparatus, and it was made to dry. The other side was coated in the same manner. Furthermore, it cut | disconnected in the shape as shown in FIG. 1, and obtained the electrode sheet in which the polarizable electrode about 60-70 micrometers thick was formed in the surface of the electroconductive contact bonding layer.

(Production of electric double layer capacitor)
A total of 30 electrode sheets manufactured as described above and a paper separator (thickness: 50 μm) are stacked so that the lead portions can be alternately connected to the positive and negative electrode terminals, and the lead portions are removed. A square laminate (thickness 10 mm) having a side of 100 mm was manufactured. Next, after the lead part of the positive electrode body and the lead part of the negative electrode body were bonded to the electrode terminals by welding, they were dried under reduced pressure at 160 ° C. for 24 hours using a vacuum dryer.
In addition, a square flat container having a side of 150 mm and having an aluminum foil whose surface was covered with a plastic film as a base material was dried under reduced pressure at 105 ° C. for 15 hours using a vacuum dryer. This flat container has an opening on one side.

  After the laminate and the flat container were cooled to room temperature in a nitrogen atmosphere, the laminate was inserted into the container as shown in FIG. Next, 90 ml of an electrolytic solution in which an ammonium salt or the like was dispersed in a propylene carbonate solvent was injected from the opening of a flat container. After completing the injection of the electrolytic solution, the laminate was decompressed by a vacuum pump for 30 minutes, and the laminate was decompressed. During this period, the electrode terminal was energized to perform electrolytic purification. Thereafter, the opening of the container was heat sealed at 150 ° C., and the flat container was sealed to obtain an electric double layer capacitor.

(Investigation of the performance of electric double layer capacitors)
After 10 electric double layer capacitors manufactured as described above were charged and discharged at 0 to 2.5 V at room temperature (25 ° C.) (1 hour after starting charging and discharging to 0 V over 30 minutes) 10 times. As a result of measuring the internal resistance, all were 0.9 to 1.1 mΩ, and it was confirmed that the performance was excellent.
Next, this electric double layer capacitor was charged at 2.5 V in an environment of 60 ° C., and this state was maintained for 2000 hours (accelerated deterioration test). Thereafter, charging and discharging at 0 V to 2.5 V (1 hour after starting charging, discharging to 0 V over 30 minutes) at room temperature (25 ° C.) was repeated 10 times, and then the internal resistance was measured. As a result, all were 1.0-1.3 mΩ, and it was confirmed that the increase in internal resistance was small.

[Example 2]
(Production of electric double layer capacitor)
In the production of the electrode sheet of Example 1, a coating solution for the conductive adhesive layer was prepared in the same manner as in Example 1 except that sodium silicate was used instead of potassium silicate. In the same manner as in Example 1, an electrode sheet was produced.
Next, an electric double layer capacitor was manufactured in the same manner as in Example 1 except that this electrode sheet was used.

(Investigation of the performance of electric double layer capacitors)
Ten electric double layer capacitors manufactured as described above were repeatedly charged and discharged at 0 V to 2.5 V at room temperature (25 ° C.) 10 times, and the internal resistance was measured. It was confirmed that the performance was excellent.
Next, this electric double layer capacitor was charged at 2.5 V in an environment of 60 ° C., and this state was maintained for 2000 hours. Then, 0V-2.5V charging / discharging was repeated 10 times at room temperature (25 degreeC), Then, internal resistance was measured. As a result, all were 1.1 to 1.3 mΩ, and it was confirmed that the increase in internal resistance was small.

[Example 3]
(Production of electric double layer capacitor)
In the production of the electrode sheet of Example 1, a coating liquid for the conductive adhesive layer was prepared in the same manner as in Example 1 except that calcium silicate was used instead of potassium silicate. In the same manner as in Example 1, an electrode sheet was produced.
Next, an electric double layer capacitor was manufactured in the same manner as in Example 1 except that this electrode sheet was used.

(Investigation of the performance of electric double layer capacitors)
Ten electric double layer capacitors manufactured as described above were repeatedly charged and discharged at 0 V to 2.5 V at room temperature (25 ° C.) 10 times, and the internal resistance was measured. It was confirmed that the performance was excellent.
Next, this electric double layer capacitor was charged at 2.5 V in an environment of 60 ° C., and this state was maintained for 2000 hours. Then, 0V-2.5V charging / discharging was repeated 10 times at room temperature (25 degreeC), Then, internal resistance was measured. As a result, all were 1.1 to 1.4 mΩ, and it was confirmed that the increase in internal resistance was small.

[Comparative Example 1]
(Production of electric double layer capacitor)
In the production of the electrode sheet of Example 1, a coating liquid for the conductive adhesive layer was prepared in the same manner as in Example 1 except that a cellulose binder was used instead of potassium silicate. An electrode sheet was prepared in the same manner as in Example 1.
Next, an electric double layer capacitor was manufactured in the same manner as in Example 1 except that this electrode sheet was used.

(Investigation of the performance of electric double layer capacitors)
Ten electric double layer capacitors manufactured as described above were repeatedly charged and discharged at 0 V to 2.5 V at room temperature (25 ° C.) 10 times, and the internal resistance was measured. It was confirmed that the performance was excellent.
Next, this electric double layer capacitor was charged at 2.5 V in an environment of 60 ° C., and this state was maintained for 2000 hours. Then, 0V-2.5V charging / discharging was repeated 10 times at room temperature (25 degreeC), Then, internal resistance was measured. As a result, all were 1.7-2.0 mΩ, and it was confirmed that the increase in internal resistance was large.

  As described above, it was confirmed that the electrochemical capacitor of the example of the present invention can significantly suppress the increase in internal resistance due to repeated charging and discharging as compared with the electrochemical capacitor of the comparative example.

The top view which shows an example of the application part of a coating liquid in the electrode sheet of this invention The perspective view which shows an example of the laminated body in this invention Configuration diagram showing an example of an electric double layer capacitor of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lead part 2 Metal foil 3 Electrode sheet 4 Lead part of positive electrode body 5 Lead part of negative electrode body 6 Positive electrode terminal 7 Negative electrode terminal 8 Laminated body 9 Container

Claims (6)

  A layer containing activated carbon and carbon black is formed on the surface of the metal foil via a conductive adhesive layer containing alkali metal silicate and / or alkaline earth metal silicate. Electrode sheet.   The electrode sheet according to claim 1, wherein the conductive adhesive layer contains graphite and carbon black in addition to alkali metal silicate and / or alkaline earth metal silicate.   The electrode sheet according to claim 1, wherein the alkali metal silicate is lithium silicate, sodium silicate, or potassium silicate.   The electrode sheet according to claim 1, wherein the alkaline earth metal silicate is calcium silicate.   The electrode sheet according to claim 1, wherein the thickness of the conductive adhesive layer is 2 to 40% of the thickness of the metal foil.   An electrochemical capacitor comprising a laminate in which the electrode sheet according to any one of claims 1 to 5 and a separator are laminated, and an electrolyte solution sealed in a container.

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