JPH0380335B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing polarizable electrodes used in electric double layer capacitors and the like. Conventional technology Polarizable electrodes for electric double layer capacitors using activated carbon are made by adding conductive materials such as graphite and carbon black, and binders such as polytetrafluoroethylene to activated carbon powder to form a paste, and then forming the paste into a punched metal. It is well known that the material is pressure-bonded to a current collector material such as . In addition, as another type, one has been proposed in which a current collector is provided on one side of the activated carbon fiber cloth using a sprayed metal layer, etc.
Publication No. 99714). Problems to be Solved by the Invention In the former electrode, the activated carbon surface is covered with a binder, resulting in a loss of area for forming an electric double layer. The latter electrode does not have the above-mentioned disadvantages, makes it possible to obtain a small capacitor with a large capacity, and is also extremely easy to manufacture if starting from activated carbon fiber cloth. However, in order to obtain activated carbon fiber cloth, it is necessary to carbonize and activate the fiber cloth. A lead time of 4 to 6 months is required to obtain the desired fabric from the spinning state, and this long lead time poses manufacturing problems in order to quickly respond to user requests. It is also difficult to keep inventory of fabrics with different product numbers and weaving methods. When configuring a large capacitor,
Activated carbon fiber cloth, which does not require a binder, is characterized by good volumetric efficiency. However, although activated carbon fiber cloth obtained from phenolic novolac resin fibers can be activated to have a specific surface area of up to 2500 m ² /g, the porosity increases when the specific surface area exceeds 2300 m ² /g. The mechanical strength of the product decreases, making it impossible to mass-produce it or achieving dimensional accuracy. Therefore, it is difficult to increase the carbonization activation degree of the activated carbon fiber cloth too much in order to improve the characteristics of the capacitor. In view of the above, an object of the present invention is to provide a method for obtaining a large-capacity polarizable electrode in an electric double layer capacitor at low cost. Means to Solve the Problems In order to achieve the above objective, we have two steps: carbonizing and activating long filament-shaped synthetic fibers to obtain activated carbon fibers, and cutting the activated carbon fibers to produce activated carbon fiber pulp. , a step of mixing activated carbon fiber pulp with a fibrous material and forming it into a sheet, a step of forming a large number of small holes in the paper product, and a step of forming a metal spray layer on one side. A method for manufacturing a polarizable electrode for an electric double layer capacitor having the present invention. Effects According to the present invention, since there is no step of processing raw material fibers into cloth, the number of work steps and period can be significantly shortened, and the specific surface area of activated carbon fibers can be increased, and the density of activated carbon fibers in electrodes can be increased. By this, a polarizable electrode for an electric double layer capacitor can be obtained. EXAMPLE The figure shows an example of a manufacturing process for a polarizable electrode of an electric double layer capacitor according to the present invention. First, raw fibers, such as long filaments of phenolic synthetic fibers, are converged into roving or tow-like fibers, and this convergent yarn is carbonized.
Activate. The obtained activated carbon fibers are cut into appropriate lengths to obtain activated carbon fiber pulp. If the activated carbon fibers are cut in air, the fibers become too fine, so it is preferable to cut the activated carbon fibers using water as a medium using a Jyusa, Refineer, JJordan pulverizer, or the like. On the other hand, the desired electrode has flexibility, impact resistance,
A fibrous material for imparting mechanical strength is prepared and mixed with the activated carbon fiber pulp. This mixing is performed using water as a dispersion medium. In this step, the activated carbon fiber pulp and fibrous material swell in water and the convergent fibers are loosened, so that the pulp becomes more uniform. In this step, dispersion aids and binding aids required in subsequent steps are added as necessary. Next, the above-mentioned mixture is made into a paper according to paper-making technology, rolled with a calendar roll, and dried. A metal such as aluminum is thermally sprayed onto one side of the sheet thus obtained (hereinafter referred to as activated carbon paper) to form a current collector layer, and the sheet is cut into a desired shape to form a polarizable electrode. Note that it is preferable to perform needle punching on the activated carbon sheet before forming the current collector layer. This needle punching process is for forming a large number of small holes by piercing a paper sheet with a large number of regularly arranged needles. When metal is thermally sprayed onto the activated carbon paper with many small holes formed in this way, some of the sprayed metal bites into the small holes. This makes it possible to suppress deterioration of electrode characteristics due to swelling of the polarizable electrode during high temperature storage. Furthermore, if necessary, the activated carbon paper may be subjected to moisture-proofing treatment. The activated carbon fiber pulp and fibrous material for obtaining activated carbon paper will be explained in more detail below. The synthetic fibers used as raw materials for obtaining the activated carbon fiber pulp include phenolic, acrylic, rayon, and pitti fibers, with phenolic fibers having an excellent carbon density being particularly suitable. The fiber diameter is 5~
40 μm is preferred, and 10 to 20 μm is particularly preferred. When the fiber diameter exceeds 40μm, the specific surface area is 2500~3000
It is not possible to obtain activated carbon fibers with preferable characteristics such as m ² /g and pore volume of about 13 c.c./g. Furthermore, when the fiber diameter is smaller than 10 μm, the fiber is thin and has poor fiber efficiency, is easily broken during the activated carbonization process, and has poor workability. The fiber length as activated carbon fiber pulp is 0.1~
30 mm is suitable, and a range of 0.5 to 5 mm is preferred. The fibrous substances that make up the polarizable electrode along with the activated carbon fiber pulp mentioned above include natural fibers, polyvinyl alcohol-based, acrylonitrile-based, polystyrene-based, fluororesin-based fibers, and rayon pulp for papermaking, as well as fibers made by kneading. It is also possible to use an aqueous dispersion of tetrafluoroethylene resin powder. Furthermore, inorganic fibers such as asbestos and glass fibers can be added to provide electrolyte resistance, and metal fibers, synthetic fibers, and carbon fibers plated with metal can also be added to improve internal resistance. . In the process of mixing activated carbon fiber pulp and fibrous material, surfactants are added to promote the dispersibility and entanglement of fibers, and aluminum hydroxide and other fillers are added to improve adsorption between fibers. It is also good to add polyethylene oxide, polyvinylpyrrolidone, etc. In the papermaking process, a dispersion aid, a binding aid, etc. are added to the activated carbon fiber pulp and the fibrous material, and the mixture is mixed using water as a medium, followed by papermaking using a normal paper machine. The basis weight is preferably 40-200g/ ^m2 , especially 80-200g/m2.
160g/ ^m2 is good. It is also possible to process a paper roll to form irregularities or a large number of small holes in the resulting activated carbon paper. It is preferable that the small holes have a diameter of about 0.3 to 3.0 mm, as in the case of forming holes in activated carbon paper as described above. When the small pores are filled with the sprayed metal forming the current collector, the current collecting ability when used as a polarizable electrode is improved and swelling is suppressed. When activated carbon paper absorbs moisture during storage, it swells, causing poor adhesion to the current collector formed by thermal spraying.
When used as a capacitor, the rate of capacity deterioration during high temperature storage increases. In order to eliminate such inconveniences, it is preferable to subject activated carbon paper to a moisture-resistant treatment. Examples of moisture-resistant treatments include impregnating the material with alumina sol, aqueous dispersion of fluororesin, etc., and drying it under pressure using a calender roll machine. Methods for forming a current collector on activated carbon paper include applying a conductive paint, plasma spraying, arc spraying, etc., and plasma spraying, particularly plasma spraying under reduced pressure, is preferred. Thermal spray metals include aluminum,
Valve metals such as titanium and tantalum, alloys based on these, stainless steel SUS430, SUS444,
Fe-Cr based alloys such as high chromium stainless steel are preferred. The thickness of the sprayed layer is preferably about 100 to 300 μm. The polarizable electrode of the electric double layer capacitor of the present invention can also be applied to a large electric double layer capacitor of about 200 to 2000 F/cell. For this purpose, it is preferable to use a current collector auxiliary material in addition to the sprayed metal layer. The current collector auxiliary material is preferably made of the same material as the current collector, but an etched aluminum foil strip with a purity of 99.99% or higher and a thickness of 50 to 200 μm is particularly suitable. Next, specific examples will be described. Example 1 Various raw material fibers in the form of tow were carbonized and activated at 900°C in a mixed atmosphere of nitrogen gas and water vapor.
The obtained activated carbon fibers and water were mixed at a weight ratio of 5:95 and pulverized using a juicer mixer or a dispersion mill. The obtained activated carbon fiber pulp was mixed with paper pulp, made into a paper using a normal paper machine, rolled with a calendar roll, and dried. The fabric weight of 120 g/m ² obtained in this way was applied to one side of the activated carbon paper with a thickness of approximately 300 μm by plasma spraying to a thickness of approximately 300 μm.
After forming a 100 μm aluminum layer, it was cut into predetermined dimensions. This pair of polarizable electrodes were placed opposite to each other with a separator in between, and an etched aluminum foil having a thickness of 80 μm was further laminated as a current collector auxiliary material on the aluminum layer side, and these were spirally wound. This electrode assembly was inserted into a cylindrical metal case with a bottom, and after injecting an electrolyte, the case was sealed with a gasket passed through the electrode lead to form an electric double layer capacitor. The size of this capacitor is 12 mm in diameter and 23 mm in height, and the size of the positive electrode side of the polarizable electrode is 13 x 60 mm, and the size of the negative electrode side is 13 x
It is 70mm. A mixed paper made of manila hemp and glass fiber was used as the separator, and as an electrolytic solution, 1 mole of tetraethylammonium perchlorate was dissolved in a mixed solvent of γ-butyrolactone and propylene carbonate.

【table】

[Table] Table 1 shows the capacity immediately after manufacture of capacitors constructed using various activated carbon fiber pulps and 65℃ at 65℃.
It shows the ratio of the capacity after storage for a month to the initial capacity (capacity retention rate). Note that No. 15 is a comparative capacitor using a polarizable electrode with an aluminum sprayed layer provided on an activated carbon width of 150 g/m ² made from phenolic fiber cloth. Nos. 1 to 7 show comparisons when phenolic fibers with different diameters were used as raw materials. When the fiber diameter is 3 μm or less, it is easily oxidized during carbonization and activation, and the fiber breaks and becomes powdery. Furthermore, if the diameter is 40 μm or more, the activation efficiency is poor. In view of carbonization yield, specific surface area, and capacitor properties, the fiber diameter is preferably 5 to 40 μm, particularly 10 to 20 μm. Nos. 8 and 9 use pitch fibers, acrylic fibers, and rayon fibers as raw material fibers. All of these have lower carbonization yields than phenol-based fibers, and the resulting activated carbon fibers are brittle and in the form of fine powder, resulting in poor yields when processed into activated carbon paper. Furthermore, the capacitor characteristics are also inferior. Next, Nos. 11 to 14 show comparisons when the mixing ratio of activated carbon fiber pulp, that is, the ratio occupied in the mixture with paper pulp as a fibrous material, is changed.
It can be seen that as the mixing ratio of activated carbon fibers increases, the capacitor capacity also increases. If the proportion of paper pulp is large, the internal resistance will be large, and if the proportion of paper pulp is small, papermaking will be difficult. The polarizable electrode using activated carbon fiber pulp has approximately twice the capacity per unit area compared to No. 15 using activated carbon fiber cloth, but it can be seen that it deteriorates significantly due to high temperature storage. Example 2 Table 2 shows a comparison when the basis weight of activated carbon paper was changed based on No. 3 of Example 1.

[Table] It is observed that the capacity increases in proportion to the basis weight, and deterioration due to high temperature storage also decreases.
However, when the area weight exceeds 200g/m ² , papermaking becomes extremely difficult. Appropriate basis weight is 80 to 160 g/m ² . Example 3 The basis weight of activated carbon paper was kept constant at 120g/ ^m2 ,
Embossed or perforated,
Table 3 shows a comparison between the samples and those further subjected to moisture resistance treatment.

[Table] No. 20 has a hemispherical recess with a diameter of 1 mm on activated carbon paper.
Embossed with a pitch of 1.5mm, also No.
Nos. 21 to 24 are electrodes formed by drilling holes with a diameter of 0.1 to 1 mm so that the distance between the holes is 1 mm, and then thermally spraying aluminum. Embossed No.20 has the highest capacity retention rate after storage.
It is recognized that the improvement is about 10% compared to the conventional one, and the improvement of about 20% for the one with holes. This is because a sprayed aluminum layer is formed in the recesses and holes, which improves current collection and prevents the activated carbon paper from swelling due to the electrolyte during high-temperature storage. Conceivable. Next, Nos. 25 to 30 are coated with alumina sol on activated carbon paper.
Electrodes are constructed by impregnating polytetrafluoroethylene (PTFE) aqueous dispersion or polyethylene oxide aqueous solution, drying at 120℃, and then thermally spraying aluminum without drilling holes. be. The amount of the moisture-resistant treatment agent adhered was equivalent to 3% by weight of the activated carbon paper in terms of solid content. It can be seen that the moisture resistance treatment improves the deterioration of characteristics during high-temperature storage, and in particular, when used in combination with hole processing, the characteristics can be improved to almost the same as Comparative Example No. 15. Example 4 When polytetrafluoroethylene, acrylonitrile, and polyethylene fibers were used instead of paper pulp in No. 3, the capacity immediately after the capacitor was 5.1F, and the capacity retention rate after high-temperature storage was 61 to 62. It was %. The current collector auxiliary material in Example 5 No. is an etched aluminum foil with a thickness of 80 μm.
80μm thick smooth aluminum foil, punched, punched and etched, 60μm thick stainless steel SUS430 smooth foil, punched and lathed. When used, there was almost no difference in capacitor characteristics from No. 3. However, when the current collector auxiliary material was removed, the immediate capacity was 4.6F, and the capacity retention rate after storage was 48%. Effects of the Invention As described above, according to the present invention, a large-capacity polarizable electrode in an electric double layer capacitor can be obtained through a simple process. Further, by performing hole processing prior to forming the current collector, deterioration of characteristics at high temperatures can be significantly improved.

[Brief explanation of drawings]

The figure is a block diagram showing an example of the manufacturing process of a polarizable electrode for an electric double layer capacitor according to the present invention.

Claims (1)

[Claims] 1 A process of carbonizing and activating long filament-shaped synthetic fibers to obtain activated carbon fibers, a process of cutting the activated carbon fibers to make activated carbon fiber pulp, and a process of mixing the activated carbon fiber pulp with a fibrous substance and making paper. A method for producing a polarizable electrode for an electric double layer capacitor, comprising the steps of forming into a sheet, forming a large number of small holes in the paper product, and then forming a metal sprayed layer on one side.