JPH0219615B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a small-sized, large-capacity wet type electric double layer capacitor. Structure of conventional example and its problems Figure 1 shows one example of a conventional wet electric double layer capacitor.
A configuration example is shown. Polarizable electrode body 1 (schematically shown)
In this method, powdered activated carbon is used, which is kneaded into a slurry using an electrolytic solution such as sulfuric acid, and then formed under pressure using a press. Such polarizable electrode bodies 1 are placed facing each other with a separator 2 in between, placed in a rubber bag 3, and the top and bottom are sealed with conductive rubber 4 to form a current collector. Further, a polymer substance is used as a binder in the polarizable electrode body 1. The capacitor having the configuration shown in FIG. 1 has the following drawbacks. Unless a large amount of binder is used (more than activated carbon), the strength of the electrode is very weak, and it is particularly difficult to form large electrodes. Since the polarizable electrode body is weak and brittle, it is extremely difficult to form a current collector thereon. Since it is difficult to increase the specific surface area of granular activated carbon to 1500 m ² /g or more, there is a limit to the electric double layer formation area. Granular activated carbon is very easily dispersed as dust, causing pollution during the manufacturing process. Furthermore, FIG. 2 shows another conventional configuration example. Activated carbon fiber cloth is used as the polarizable electrode body 6, and a metal layer such as aluminum, titanium, stainless steel, or a conductive resin layer is formed as the current collector 7.
A separator 8 is interposed between these, and after injecting an electrolytic solution, the positive and negative electrodes are insulated from each other by a gasket 9, and a coin-shaped case 10 and a sealing plate 11 are used to seal the casing. In the case of a metal current collector, plasma spraying or arc spraying is used, and in the case of a current collector made of conductive resin, carbon is mainly used as conductive particles by screen printing or spraying. Alternatively, it is formed using either the dip method. A capacitor having such a structure is obtained by, for example, activated carbon fiber cloth by carbonizing and activating a phenolic synthetic resin fiber cloth.
It has a very high specific surface area (~2500 m ² /g), high energy density, and sufficiently strong strength, so it is easy to form a current collector by plasma spraying or the like. However, activated carbon fiber cloth has a porosity of over 90% when not pressurized (even when pressurized)
(occupying more than 60% of the space), the loss of space is very large. Furthermore, since there are many spaces as described above, there is little contact between individual fibers, resulting in a high contact resistance. If activation is continued to further increase the specific surface area, the strength of the fiber cloth itself will decrease significantly, making it unfit for actual use. Normally, fiber fabrics obtained by carbonization activation of phenolic raw materials have a strength that can be thermally sprayed at approximately 2100 m ² /g, and at present it is not possible to use anything higher than that. How to use it is requested. OBJECTS OF THE INVENTION An object of the present invention is to obtain a small-sized, large-capacity electric double layer capacitor with improved electric double layer energy density per unit volume. Structure of the Invention The present invention uses a disk-like or sheet-like material formed by mixing pulverized activated carbon fibers with a fluororesin and then forming the mixture under pressure as a polarizable electrode body, and has a current collector layer on at least one side. By having
It has improved energy density per unit volume while maintaining strength. Description of Examples Before describing specific examples, a method for producing pulverized activated carbon fibers used in the polarizable electrode of the present invention will be described. Figure 3 shows a flowchart of the manufacturing process. First, synthetic fibers such as phenol and acrylonitrile, or rayon and pitch fibers are processed into long filaments and choppy filaments. Furthermore, these are formed into convergent filaments in the form of rovings or tows, and activated carbonized by catalyst activation or steam activation. At this time, in the case of finol-based materials, the specific surface area can be increased to 2,500 to 3,000 m ² /g. Further, the activated carbon fibers are cut and pulverized, and a binder such as a fluororesin is added and mixed in an amount of about 3 to 30 wt%, and then pressed. If an aqueous fluororesin is used at this time, a considerable amount of water oozes out. A current collector made of an aluminum or nickel layer is formed in a thickness of 100 to 300 μm on at least one side of the polarizable electrode body thus formed by plasma spraying or arc spraying. The current collector may be made of conductive paint. Next, dry. When fluororesin is used as a binder, the drying temperature can be raised to about 250 to 360°C, making it possible to produce electrodes with sufficient strength. 250~360
Since it can be dried at a temperature of .degree. C., when an organic electrolyte is used as the electrolyte, the water contained therein is relatively easily dispersed, resulting in a capacitor with good pressure resistance. Example 1 Roving phenolic fiber (diameter 20 μm)
was carbonized and activated to obtain tow-like activated carbon fibers. The specific surface area of this activated carbon fiber was 2700 m ² /g as measured by the BET method. This material was added to water and finely ground with a mixer. The fiber length was 1 mm or less. The pulverized activated carbon fibers were mixed with 8 wt % of fluororesin and placed in a press mold with a diameter of 14 mm ψ and pressed at 3 tons/cm ² . This electrode was dried at 300℃ for 12 hours, and an aluminum layer was coated on one side by plasma spraying as shown in Figure 4.
A current collector 7 was formed with a thickness of 300 μm. A pair of polarizable electrodes (1 mm thick) 13 were placed facing each other with a polypropylene separator 8 interposed therebetween, and a 1 mol propylene carbonate solution of tetraethylammonium perchlorate was injected to form a coin-shaped capacitor as shown in FIG. 4. Other parts similar to those in the conventional example shown in FIG. 2 are designated by the same reference numerals, and description thereof will be omitted.
Table 1 shows the characteristics of this capacitor. From the same table, it can be seen that this capacitor is small and has a large capacity.

[Table] Figure 5 shows the polarizable electrode surface of this capacitor.
A 100x micrograph is shown. It can be seen that the activated carbon fibers are very densely filled. The activated carbon fiber in this example has a specific surface area of
It is extremely large at 2700 m ² /g, and activated carbon fiber cloth cannot provide sufficient mechanical strength. Also, by the method of this example, the diameter is 100 mm and the thickness is 3.
It was also possible to easily obtain sufficient strength for large polarizable electrodes of mm size. Example 2 A coin-shaped capacitor having the same structure as in Example 1 was prepared using a polarizable electrode binder and an electrolyte having the characteristics shown in Table 2. The electrode is circular with a diameter of ψ14. Further, various characteristics of this example are similarly shown. From the table, it can be seen that the phenolic activated carbon fiber exhibits the best capacitance properties.
Furthermore, an electrode with strong mechanical strength can be obtained with a binder amount of about 5 wt%. This is thought to be due to the entanglement of the fibers. Furthermore, as the amount of binder increases, the mechanical strength increases, but the resistance value also increases and the capacitance value decreases. Therefore, from a practical balance of these, the amount of binder should be approximately 5~
Approximately 30wt% is considered to be good. The current collector is a sprayed layer of aluminum in both cases.

【table】

[Table] Example 3 A polarizable electrode having the same components and dimensions as in Example 1 was used, and as a current collector, a nickel layer of approximately 300 μm was formed by plasma spraying of nickel powder. A capacitor similar to that shown in Fig. 4 was prepared using a 20wt% potassium hydroxide solution as the electrolyte. Table 4 shows the capacitor characteristics of this example. Unlike Examples 1 to 3, since an aqueous electrolyte is used, the capacitor has low impedance and is capable of strong discharge.

[Table] Example 4 Instead of the nickel current collector in Example 3,
A similar capacitor was formed by applying a conductive paint containing carbon as conductive particles and using it as a current collector. Table 4 shows the capacitor characteristics. Since an organic binder was used in the conductive paint, the charge/discharge characteristics were worse than in Example 4.

[Table] Effects of the Invention According to the present invention, it is possible to obtain a small-sized, large-capacity capacitor that has a higher energy density and excellent charge/discharge characteristics than conventional products.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional double layer capacitor.
FIG. 2 is a sectional view of another conventional example, FIG. 3 is a manufacturing process diagram of a polarizable electrode of a capacitor of the present invention, FIG. 4 is a sectional view showing the structure of a capacitor in an embodiment of the present invention, and FIG. The figure is a micrograph showing the shape and structure of fibers on the surface of the polarizable electrode of the present invention. 7... Current collector, 8... Separator, 9... Gasket, 10... Case, 11... Sealing plate, 13
...Polarizable electrode body.

Claims (1)

[Scope of Claims] 1. A disk-shaped or sheet-shaped electrode in which a polarizable electrode body is formed by mixing crushed activated carbon fibers and fluororesin and forming the mixture under pressure, and a current collector layer provided on at least one side of the disk-shaped or sheet-shaped electrode. An electric double layer capacitor comprising: 2. The electric double layer capacitor according to claim 1, wherein the amount of fluororesin is 50% or less of the polarizable electrode body excluding the current collector layer in weight percent. 3. The electric double layer capacitor according to claim 1, wherein the current collector layer is in contact with the outer case. 4. The electric double layer capacitor according to claim 1, wherein the current collector layer is made of aluminum, titanium, tantalum, nickel, or stainless steel formed by plasma spraying or arc spraying. 5. The electric double layer capacitor according to claim 1, wherein the current collector layer formed on the polarizable electrode body is made of a conductive paint containing carbon particles as conductive particles. 6. The method according to claim 1, wherein the pulverized activated carbon fibers used in the polarizable electrode body are obtained by carbonizing and activating phenolic fibers, polyacrylonitrile fibers, or rayon fibers. Electric double layer capacitor. 7. The electric double layer capacitor according to claim 1, characterized in that an organic electrolyte is used as the electrolyte.