JPH0577281B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing an electric double layer capacitor. Conventionally, as polarizable electrodes for this type of electric double layer capacitor, thin metal plates such as aluminum, nets, or punched metals have been used as they are, or the surfaces of these current collector metals have been roughened by etching or other means. Polarizable electrodes were manufactured by using the resulting metal current collector as a metal current collector, and by mold-pressing a polarizable electrode material made of activated carbon onto both surfaces of the metal current collector, or by rolling a rubber-like material to support it. . However, in polarizable electrodes manufactured using such current collectors, the contact between the metal current collector and the activated carbon electrode is not strong, and in particular, the polarizable electrodes made thin by rolling rollers are wound into a spiral structure. In this case, the activated carbon electrode layer on the outside of the current collector and the activated carbon electrode layer on the inside of the current collector have opposite stresses, so the contact between the current collector and the activated carbon electrode becomes weaker, and as a result, there is no electricity. There were drawbacks such as a gradual increase in the internal resistance of the double layer capacitor and a gradual decrease in the utilization efficiency of the activated carbon electrode layer. Furthermore, in the case of the conventional structure described above, these problems become even more serious when electric double layer capacitors are mass-produced in large quantities. That is, when the polarizable electrode is spirally wound, the current collector and the activated carbon electrode layer may peel off or fall off, resulting in variations in capacity, a decrease in the utilization efficiency of the activated carbon electrode layer, and an increase in internal resistance during use. Changes in capacity and variations in charging time may occur.
This has become an important issue in terms of product value. In order to solve these drawbacks, the present invention is characterized in that activated carbon fibers are used for the polarizable electrodes, and the current collecting electrodes are formed thereon by thermal spraying. First, to explain in detail the carbon fiber used in the present invention, activated carbon fiber that meets the purpose of the present invention has a large specific surface area, low electrical resistance, and has the flexibility and drawing strength necessary for processing into flaky spiral shapes. It must have chemical resistance to withstand prolonged contact with the electrolyte. There are four types of carbon fibers suitable for these purposes: phenol type (cured novolac fiber), rayon type, acrylic type, and pitch type.
In addition, there are two methods: one method uses these raw material fibers to make carbon fibers, one method carbonizes these raw material fibers to make carbon fibers, and then activates them to make activated carbon fibers. The method of activating and producing activated carbon fibers is shown in the figure. As can be understood from this figure, there are two methods for obtaining activated carbon fibers: a method in which raw material fibers are directly carbonized and activated, and a method in which carbon fibers are once made into carbon fibers and then activated. Generally, once carbon fiber is formed, it is heated to 700 to 800℃ in a mixed gas atmosphere consisting of water vapor and nitrogen.
Activation is performed at a temperature of Additionally, in general, the specific surface area of carbon fibers, electrical resistance, and flexibility are inversely proportional to each other. Yield decreases, and electrical resistance and flexibility deteriorate. In order to use it as a polarizable electrode of an electric double layer capacitor, the carbonization yield is preferably about 10 to 80%, although it varies depending on the type of raw material fiber. If the carbonization yield is less than 10%, the specific surface area of the carbonized fibers will be large, but the fibers will not have flexibility and are not practical. Furthermore, when the carbonization yield is greater than 80%, the electrical resistance, flexibility, and strength of the carbonized fibers are excellent;
This is not preferable because the specific surface area becomes small and the electric capacity per unit volume becomes small. Here, carbonization yield of fiber is expressed as weight of carbon fiber/weight of raw fiber x 100 (%) or weight of activated carbon fiber/weight of raw fiber x 100 (%). In the case of phenol fibers, the carbonization yield of carbon fibers is 50-58%, and the carbonization yield of activated carbon fibers is about 18-55%. Table 1 shows the characteristics of different types of carbon fibers. As is clear from this table, acrylic and pitch type materials are generally somewhat flexible and have a slightly small surface area. In addition, although rayon-based fibers have a large surface area, they are brittle, and although felt-like carbon fibers are popular, they are difficult to make into paper, and they have poor chemical resistance and water resistance. I have a problem with sexuality. On the other hand, phenolic carbon fibers are made from cured novolac fibers, and since the cured novolac fibers are infusible and have low heat shrinkage, there is no need to make the raw material fibers infusible beforehand, and the phenolic carbon fibers can be woven into fabrics. The nonwoven fabric can be activated carbonized as it is, and is strong and flexible, so it can be used as a polarizable electrode for electric double layer capacitors.

【table】

[Table] is particularly excellent. In addition, paper making using phenolic carbon fiber as a raw material has a number of advantages.In particular, paper is made using phenolic carbon fiber as a raw material and special Kynol (trade name of phenolic fiber manufactured by Nippon Kynor Co., Ltd.) as a binder. It was recognized that the resulting product has extremely excellent features in many aspects such as flexibility, electrical resistance, chemical resistance, winding strength, processing accuracy, electric capacity, and cost. Next, as a conventional example, aluminum punching metal (t = 0.1 mm) is made using powdered coconut charcoal as raw material.
A current collector is prepared by etching the current collector, and activated carbon electrode layers with a thickness of 200μ are processed by rolling on both sides of this current collector, and the electrode dimensions (20 cm x 2.5 cm
The electrode was obtained by cutting it into a shape of 0.5 mm). An aluminum lead is attached to this by a known method, a polypropylene separator is inserted between the two electrodes, and the material is wound into a spiral shape using a winder. Then, this was placed in an aluminum case with a diameter of 16 mmφ and a length of 33 mm, and a conventional product was obtained by grooving the case, attaching a lid, injecting electrolyte (vacuum impregnation), and caulking. Next, examples of the present invention will be described: rayon-based felt-like activated carbon fiber, acrylic-based felt-like activated carbon fiber, pitch-based felt-like activated carbon fiber, phenolic-based felt-like activated carbon fiber, phenolic-based cross-like activated carbon fiber, and phenolic paper Each activated carbon fiber raw material consisting of activated carbon fibers is used to form a polarizable electrode (20 cm x 2.5 cm x 0.5 cm).
mm) and cut each activated carbon fiber between the electrodes.
Insert a PTFE separator and wind it up into a spiral using a winder. At this time, only the opposite end face is 1
Roll it up with a step of about mm. To take out the electrode, an aluminum conducting wire is used, and a collector electrode and a lead terminal of the electrode are simultaneously formed from both end faces by a plasma spraying method using aluminum powder. The electrode made of activated carbon fiber thus obtained was assembled and housed in the same manner as the conventional product described above. The electrolytic solution used was one in which propylene carbonate was used as a solvent and 1M/tetraethylammonium perchlorate was used as an electrolyte. Table 2 shows a comparison of the characteristics of the electric double layer capacitor produced by the manufacturing method of the embodiment of the present invention and the electric double layer capacitor of the conventional example. As can be seen from this table, when activated carbon fibers are used as polarizable electrodes, the capacity per unit volume and internal resistance can be significantly improved. As described above, according to the manufacturing method of the present invention, the winding processability is easy, the capacitance per unit volume and internal resistance are significantly reduced, and the activated carbon fibers and the current collecting electrode are connected by thermal spraying. It also has high mechanical strength and will not peel off. Therefore, it is possible to stabilize quality, improve yield, and reduce cost, and its industrial value is extremely great.

[Brief explanation of drawings]

The figure is an explanatory diagram of a method for manufacturing carbon fiber used in the electric double layer capacitor of the present invention.

【table】

【table】

Claims (1)

[Claims] 1. Polarizable electrodes mainly composed of activated carbon fibers are wound up with their ends staggered from each other through a separator, and conductive collector electrodes are formed on the ends by thermal spraying. A manufacturing method for a characteristic electric double layer capacitor. 2. A method for manufacturing an electric double layer capacitor according to claim 1, characterized in that a phenol fiber activated to carbonize is used as the activated carbon fiber material.