JP3460776B2 - Electric double layer capacitor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention
Seki to <br/> the electric double layer capacitor capable of rapid charging and discharging at a large current. 2. Description of the Related Art An electric double layer capacitor is composed of an element having one or more pairs of polarizable electrodes comprising a current collector and a polarizable electrode layer mainly composed of activated carbon powder having a large specific surface area. A capacitor that is immersed and stores electric charge using an electric double layer formed in the electrolyte that is in contact with the large surface of activated carbon powder.It is characterized by a much larger capacity than other types of capacitors. . In addition, when compared with a secondary battery that involves a chemical reaction when charging and discharging, an electric double layer capacitor that does not involve a chemical reaction has an excellent feature that the capacity and the like are less likely to deteriorate even when repeatedly charged and discharged. However, the electric resistance in the polarizable electrode layer mainly composed of activated carbon powder is quite large, and the connection resistance between the polarizable electrode layer and the current collector is added to increase the internal resistance of the electric double layer capacitor. However, there is a problem that charging and discharging cannot be performed with a large current. As measures to solve this problem, the current collector may be made of etched aluminum foil, the current collector and the polarizable electrode layer may be bonded with a conductive adhesive, or the polarizable electrode layer may be thinned. By increasing the opposing area of the opposing polarizable electrodes by stacking the elements, adding a conductive agent powder having an average particle size smaller than the activated carbon powder into the polarizable electrodes, or selecting an electrolyte having a small electric resistance. Or how to do it. [0004] One example is disclosed in Japanese Patent Application Laid-Open No. 56-67920.
No. 50 as a conductive agent powder added to the polarizable electrode layer.
An electric double layer capacitor using various carbon blacks having an average particle size of 0 μm or less is disclosed. Examples of carbon black include varieties such as channel black, furnace black, thermal black, and acetylene black. An electric double layer capacitor using channel black is disclosed. Although the above-mentioned various conventional measures are also effective in reducing the internal resistance of the electric double layer capacitor, the internal resistance of the electric double layer capacitor which can be realized by variously combining these measures depends on the purpose of use. There is still a demand for an electric double-layer capacitor suitable for power applications that cannot be said to be sufficiently low, has a low internal resistance, and can be charged and discharged with a large current. [0006] An object of the present invention is to solve the above, in addition to the measures for reducing internal resistance of the electric double layer capacitor in the prior art described above, provides an electric double layer capacitor can be further reduced internal resistance Is to do. [0007] To achieve the above object,
Because, the onset Ming, activated carbon powder, a conductive agent powder and a pair of sheet-like polarizable electrode polarizable electrode layer is formed by coating on a current collector metal foil containing a binder like each sheet wound in a state sandwiching the separator between the polarizable electrodes comprising elements, or forming polarizable electrode layer containing activated carbon powder, a conductive material powder and a binder is coated on a current collector of a metal foil An element in which a large number of sheet-like polarizable electrodes are stacked with a separator interposed between each sheet-like polarizable electrode,
Electric double sealed in container with non-aqueous electrolyte
In layer capacitor, and the conductive agent powder fine conductive powders, an average grain size of the average particle diameter of the fine conductive powders wherein
1/3 following 0.01~0.1μm a is fine carbon powder and Tona Rutotomoni, the fine conductive powders mosquitoes
Carbon black, and the binder is polyvinylidene.
And the current collector of the metal foil is
Aluminum foil which has been subjected to a non-aqueous electrolytic solution.
Adds tetraethylammonium to propylene carbonate
That it is characterized by an electrolytic solution obtained by dissolving a tetrafluoroborate. [0008] As described above , not only one kind of fine conductive agent powder but also fine carbon powder conductive agent is mixed in the polarizable electrode layer to pack conductive agent powder particles in a micro region. It has been found that the state can be improved and thereby the electrical resistance in the polarizable electrode layer can be reduced, and the electric double layer capacitor of the present invention has been invented based on this finding. That is,
In order to obtain a packing effect of the conductive agent powder particles in a micro area, the average particle diameter of the fine carbon powder is
The average particle diameter of the fine conductive agent powder is 1/3 or less.
The more preferable ratio of the average particle size of the fine carbon powder to the average particle size of the fine conductive agent powder is 1/5 or less. [0009] The electric double layer capacitor of the present invention, preferably
As had embodiments, activated carbon powder, a conductive agent powder, a binder Contact
A good beauty mixture of solvents, the average particle size 0.01~0.1μm
A slurry prepared by previously dispersing fine carbon powder in a solvent is mixed and kneaded to form a paste of a polarizable electrode material, and the paste is applied to the surface of an etched aluminum foil to form a sheet-like polarizable electrode. a device by winding in a state of sandwiching the separator between each sheet polarizable electrode of the pair of sheet-like polarizable electrode, or across the separator between each sheet polarizable electrode of a number of sheet-shaped polarizable electrodes and elements stacked with, can be prepared by encapsulating the the element in a container together with the non-aqueous electrolyte solution
You . [0010] This production how is, Ru Oh <br/> in real for manufacturing how. That is, the average primary particle size is 0.01 to 0.1.
μm fine carbon powder is usually agglomerated secondary particles, so it is preferable to add a solvent and mix in a mill,
The slurry is pulverized to form a slurry in which fine primary particles are dispersed in a solvent. When manufacturing electric double layer capacitors,
First, a carbon powder composed of fine primary particles is put together with a solvent in, for example, an attrition mill, and wet-milled to prepare a slurry in which the primary particles are dispersed in the solvent. Mixing this slurry with a mixture of polarizable electrode materials,
It is kneaded to make a paste for coating. Normally, the particle size distribution and average particle size of powder particles are often measured by the sedimentation method, but the particle size distribution and average particle size of carbon powder composed of submicron fine particles are determined by particle size analysis like the sedimentation method. It is difficult to measure by the method. For this reason, the average particle size of the fine carbon powder is measured by taking an electron microscope photograph of a fine carbon powder slurry well dispersed in a solvent and taking a sample. DESCRIPTION OF THE PREFERRED EMBODIMENTS There are various types of electric double layer capacitors, such as coin type, wound type, laminated type, etc. In order to be able to charge and discharge with a large current, the electric double layer capacitor of the present invention is It is a wound type or a laminated type. The wound electric double layer capacitor is shown in FIG. 1 described later, and the multilayer electric double layer capacitor has a configuration shown in FIG. Here, the term "laminated element in which a large number of sheet-shaped polarizable electrodes are laminated via a separator" means that six or more sheet-shaped polarizable electrodes, preferably ten or more, are used so that a large-capacity laminated element is obtained. An element in which sheet-shaped polarizable electrodes are laminated. FIG.
, 20 and 21 are current collector terminals, 26 is a negative electrode, 27 is a positive electrode, 30 and 31 are current collector leads, 32 is an aluminum container, 33 is a positive electrode terminal, 34 is a negative electrode terminal, and 35 is an upper lid. Activated carbon includes plant, petroleum, coal, phenolic resin, etc., such as coconut pods. The activation method includes a chemical activation method, such as a molten KOH activation method, and a steam activation method. Can be used. Since the activated carbon powder having a larger specific surface area can increase the capacity of the electric double layer capacitor, it is preferable to use one having a specific surface area of 1500 m ² / g or more. Activated carbon powder having a too large specific surface area has a low packing density and a small capacity per unit volume of the polarizable electrode. Therefore, it is preferable to use a powder of 3000 m ² / g or less. As the conductive agent powder, carbon black,
Examples include graphite powder, conductive organic polymer powder such as polyacetylene, polypyrrole, and polyacene, and metal oxide powder such as ruthenium oxide. Of these, it is preferable to use carbon black because fine powder having a good conductivity improving effect can be obtained at low cost. Since carbon black has a large effect of improving conductivity, it is preferable to use a carbon black of a type having a small average particle size. Fine carbon black conductive agent powder has a considerably large specific surface area and also has the function of forming an electric double layer on the particle surface to store electric charge. Works to increase the capacity of The polarizable electrode layer may be formed in a sheet shape in advance by a roll or the like and then bonded to the current collector with a conductive adhesive. However, in the electric double layer capacitor of the present invention, the polarizable electrode layer is formed on the current collector. Since a polarizable electrode layer having a small thickness and good adhesion can be formed, it is formed by coating a paste on a metal foil current collector. In this method, when a polarizable electrode layer having a desired thickness cannot be formed by a single application, it is necessary to apply the polarizable electrode layers repeatedly. Current collector materials include aluminum, stainless steel,
Nickel and copper can be used. As the current collector of the aluminum foil, it is preferable to use a current collector having an uneven surface formed by etching to improve the adhesion to the polarizable electrode layer. The thickness of the aluminum foil should be such that the resistance value of the current collector does not increase, so that it does not break when applying paste or winding or laminating the polarizable electrode sheet, and it is easy to connect terminals to the aluminum foil. It is preferably 20 to 150 μm. As the electrolytic solution, a nonaqueous electrolytic solution having a high decomposition voltage is used because the working voltage can be increased and an electric double layer capacitor having a large energy density can be easily obtained. As the non-aqueous electrolyte, it is preferable to use an electrolyte having a wide electric temperature range for the electric double layer capacitor and having high electric conductivity. Specifically, it is preferable to use an electrolytic solution obtained by dissolving tetraethylammonium tetrafluoroborate in propylene carbonate since it is excellent in performance and inexpensive. The concentration of the electrolytic solution is set to 0.6 to 1.0% in propylene carbonate so that good electric conductivity can be obtained.
It is preferable to use one dissolved at 1.4 molar concentration. The separator has fine continuous pores,
Various insulating sheets that are wetted by the electrolyte solution that is not deteriorated by the electrolyte solution can be used. As the separator, it is preferable to use manila paper which is good in performance and inexpensive. The sheet-shaped polarizable electrode may be either a current collector with both surfaces coated with a polarizable electrode layer or a current collector with one surface coated. In a wound-type element, the polarizable electrode layer of the sheet-shaped polarizable electrode to be wound is easily damaged by the introduction of strain. Therefore, it is preferable that the thickness is not too large. Preferably, polar electrodes are used. However, in the case of a stacked type, it is not necessary to bend the sheet-shaped polarizable electrode, and thus it is preferable to use a sheet-shaped polarizable electrode in which a polarizable electrode layer is coated on both surfaces of the current collector. The separators are arranged between all the adjacent sheet-shaped polarizable electrodes so that the adjacent sheet-shaped polarizable electrodes are not short-circuited to each other. The container may be any as long as it is stable with respect to the electrolytic solution and can seal and protect the electrolytic solution with the element. As the metal material of the container, it is preferable to use a stainless steel or aluminum container which is stable to the electrolyte and easily available. Each sheet-shaped polarizable electrode of the element is connected to a terminal wire by caulking or ultrasonic welding at an end thereof, and the terminal wire is passed through an insulating enclosing portion made of rubber or the like and pulled out of the container. It is preferable to use a container having a minimum necessary volume according to the outer shape of the element,
In the case of a wound type element, it is preferable to use a cylindrical container, and in the case of a laminated type element, it is preferable to use a rectangular parallelepiped container. In a preferred electric double layer capacitor of the present invention, the polarizable electrode layer coated on the metal foil contains 3 to 20% by weight of fine carbon powder as a part of the conductive agent, more preferably 8 to 12% by weight. Including. If the amount of the fine carbon powder mixed is small, the effect of reducing the electric resistance of the polarizable electrode layer is small, and even if it exceeds 20% by weight, the effect of reducing the electric resistance of the polarizable electrode layer does not increase any more. The average particle size of the fine carbon powder is preferably 0.01 to 0.1 μm so as to sufficiently secure the effect of reducing the electric resistance of the polarizable electrode layer. It takes a lot of labor to produce a considerable amount of carbon powder having an average particle size smaller than 0.01 μm, and at present, the effect obtained is small in spite of the high cost.
Depending on the average particle diameter of the conductive agent powder combined with the fine carbon powder, the effect of reducing the obtained electric resistance is small when the fine carbon powder having an average particle diameter larger than 0.1 μm is blended. The average particle size of the fine carbon powder is 0.02 to
0. It is more preferable that the thickness be 0.7 μm. In the preferred electric double layer capacitor of the present invention, carbon black is used as the conductive agent powder. As the conductive agent powder, various kinds of metal oxide powders such as carbon black and ruthenium oxide, graphite powders, and organic conductive material powders such as polyacetylene, polypyrrole, and polyacene can be used. Of these, carbon black has a good conductivity-imparting effect, is relatively easy to obtain, and a well-dispersed powder has a narrow particle size distribution and is easy to use. There are various types of carbon black, such as channel black, furnace black, thermal black, and acetylene black, all of which can be preferably used. As the binder, it is preferable to use a fluororesin-based binder which is stable with respect to the solvent of the non-aqueous electrolyte. When the amount of the binder is large, the electric resistance of the polarizable electrode layer becomes large, so that even a small amount of the binder, a material having a large holding power of the polarizable electrode material is good. preferable. As a binder satisfying this condition, in particular, polyvinylidene fluoride (hereinafter, referred to as
It is preferable to use PVDF. One of the reasons why PVDF is a preferable binder is that PVDF has an easy-to-use solvent called N-methylpyrrolidone (hereinafter abbreviated as NMP). N-methylpyrrolidone does not remain in the product because it is removed by drying before the coated element is incorporated into the container. Fine powders are often produced by precipitation from the gas phase. Fine particles of carbon precipitated from the gas phase such as soot are often aggregated into secondary particles. The powder of the aggregated carbon secondary particles can be converted into a slurry of fine carbon powder composed mostly of primary particles by milling or kneading with a solvent such as NMP, but further reducing the primary particles. It is very difficult. Therefore, the fine carbon powder must be a carbon powder having primary particles of a desired average particle size as a raw material, and the fine carbon powder may be a kind of carbon black. EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the following examples. Example 1 40 parts by weight of petroleum coke-based activated carbon powder (average particle size: 10 μm, specific surface area: 2000 m ² / g) activated by molten KOH, 10 parts by weight of carbon black (average particle size: 2 μm),
PVDF10 parts, to a mixture consisting of NMP40 parts, a slurry containing fine carbon powders dispersed well kneaded by a ceramic roll NMP was added to the channel black (average particle size 0. 0 2 [mu] m) 20 wt% 20 By weight, the mixture was further mixed and kneaded with a ball mill to obtain a paste of a polarizable material (the powder excluding NMP contained 10% by weight of fine carbon powder). This paste is applied by a coater on an etched aluminum foil having a thickness of 50 μm, and 10 g / m ^{2 is applied on} one side of the aluminum foil.
Was formed. The sheet on which the polarizable electrode layer was formed was 13
It was cut into a ribbon having a width of mm to obtain a sheet-shaped polarizable electrode.
After winding a manila paper ribbon having a thickness of 50 μm between a pair of sheet-shaped polarizable electrodes, crimping a terminal wire with a tab to the end of the tape and connecting the same, stopping the outermost periphery with a polypropylene element fixing tape, A wound element having a diameter of 7 mm and a length of 15 mm was obtained. After heating this element to 120 ° C. and drying,
mm, 22 mm in height, housed in a closed aluminum container, a non-aqueous electrolyte solution of 1 mol / L tetraethylammonium tetrafluoroborate dissolved in propylene carbonate is injected into the container, and impregnated in the element.
The opening of the container was sealed through a terminal wire through a sealing rubber, and ten wound electric double-layer capacitors having an outer diameter of 8 mm and a height of 21 mm having the configuration shown in FIG. 1 were prototyped. In FIG. 1, reference numerals 1 and 2 denote polarizable electrode layers, 3
Is a current collector, 4 is an element, 6 is a separator, 7 is a metal container,
Reference numerals 8 and 9 denote lead wires with tabs, and reference numeral 10 denotes sealing rubber. Example 2 Example 2 was repeated except that the amount of the fine carbon powder slurry mixed with the paste was 30 parts by weight (the paste contained 10% by weight of the fine carbon powder in the solid content excluding NMP) in Example 1. In the same manner as in Example 1, ten wound electric double layer capacitors having the same dimensions were prototyped. Comparative Example 1 Ten wound electric double layer capacitors were prototyped in the same manner as in Example 1 except that the paste of the polarizable electrode material was used without mixing the slurry of fine carbon powder in Example 1. did. The capacity, internal resistance, and LC at 2.5 V of each wound electric double layer capacitor produced as described above were measured. Then, the substrate was kept at 70 ° C. for 1000 hours while a voltage of 2.5 V was applied, and changes in capacitance and internal resistance were examined. These results are summarized in Table 1 in the range of the measurement data. [Table 1] From the above test results, it can be seen that the internal resistance of the electric double layer capacitor according to the present invention was significantly reduced. In addition, as a result of an accelerated durability test at 70 ° C., it was confirmed that deterioration of the capacity and the like was small. According to the present invention, the average particle size of the conductive agent to be added to the paste formed by coating the polarizable electrode layer is 1/3 of the average particle size of the normal conductive agent in addition to the normal conductive agent. By adding the following fine carbon powder conductive agent, the micro-packing property of the powder in the polarizable electrode layer was improved, and the internal resistance of the electric double layer capacitor was significantly reduced. The low internal resistance of electric double-layer capacitors means that they generate less heat during charging and discharging and have a small energy loss during charging and discharging. Electric vehicles that are currently under development and are expected as a means of transportation in the future It is suitable for power applications such as braking energy regeneration, and the industrial use effect of the present invention is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an outline of an example of a wound electric double layer capacitor according to the present invention. FIG. 2 is a perspective view showing an outline of an example of a multilayer electric double layer capacitor according to the present invention. [Explanation of Signs] 1 and 2 polarized electrodes 3 Current collector 4 Element 6 Separator 7 Aluminum container 8, 9 Tabbed lead wire 10 Sealing rubber 20, 21 Current collecting terminal 26 Negative electrode 27 Positive electrode 30, 31 Current collector lead 32 Aluminum container 33 Positive electrode terminal 34 Negative electrode terminal 35 Top cover

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-307250 (JP, A) JP-A-6-204085 (JP, A) JP-A 8-293443 (JP, A) JP-A-63-1988 58814 (JP, A) JP-A-10-4037 (JP, A) JP-A-5-304048 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01G 9/058

Claims (1)

(57) [Claims 1 Activated carbon powder, a conductive agent powder and a pair of sheet-like polarizable electrode layer is formed by coating on a current collector metal foil containing a binder element polarizable electrode is made of the wound in a state sandwiching the separator between each sheet polarizable electrode, or the current collector of the polarizable electrode layer is a metal foil containing activated carbon powder, a conductive material powder and a binder An element in which a large number of sheet-shaped polarizable electrodes formed by coating on are stacked in a state where a separator is sandwiched between each sheet-shaped polarizable electrode,
Electric double sealed in container with non-aqueous electrolyte
In layer capacitor, a conductive agent powder the conductive agent powder is fine, average particle size the
0.01 to 1/3 or less of the average particle diameter of the fine conductive agent powder
Fine carbon powder is 0.1μm and Tona Rutotomo
The fine conductive agent powder is carbon black,
The binder is polyvinylidene fluoride,
The aluminum foil in which the current collector of the metal foil is etched.
Foil, wherein the non-aqueous electrolyte is propylene carbonate.
To tetraethylammonium tetrafluoroborate
An electric double layer capacitor characterized by being an electrolytic solution in which is dissolved .