JPH0479127B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electric double layer capacitor, and more specifically, by using activated carbon fiber as a polarizable electrode, the processability and utilization efficiency of the polarizable electrode are improved, and the charging capacity per unit volume is large. The present invention provides 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, polarizable electrodes manufactured using a rolling roller are rolled to form a spiral structure. Since stress is applied to 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, the contact between the current collector and the activated carbon electrode becomes weaker, and therefore the electric double layer There were drawbacks such as a gradual increase in the internal resistance of the 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. In other words, 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 the present invention, in order to solve these drawbacks, a conductive collector electrode is provided directly on the activated carbon fiber serving as the polarizable electrode. The raw material fibers for activated carbon fiber can be categorized as follows:
There are four types: phenol type (cured novolac fiber), rayon type, acrylic type, and pitch type. These raw material fibers must have a large specific surface area when carbonized, have low electrical resistance, withstand flexibility and tensile strength necessary for shaping, and have chemical resistance against long-term contact with electrolyte. The figure below shows a method of forming carbon fibers or activated carbon fibers using these raw material fibers. As can be understood from this figure, there are two methods: one is to carbonize and activate the raw material fiber directly, and the other is to activate it after it has been turned into carbon fiber. Generally, after carbon fibers are formed, activation is performed at a temperature of 700 to 800°C in a mixed gas atmosphere consisting of water vapor and nitrogen. Additionally, since the specific surface area of carbon fibers, electrical resistance, and flexibility are generally inversely proportional to each other, as carbon fibers are activated to activated carbon fibers, the specific surface area increases, the carbonization yield decreases, and the electrical resistance decreases. resistance,
Flexibility deteriorates. 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. Further, if the carbonization yield is higher than 80%, the carbonized fibers have excellent electrical resistance, flexibility, strength, etc., but the specific surface area becomes small and the electric capacity per unit volume becomes small, which is not preferable. Here, the carbonization yield of fiber is

[Table] Carbonization yield is expressed as weight of carbon fiber/weight of raw material fiber x 100 (%) or weight of activated carbon fiber/weight of raw material fiber x 100 (%). The carbonization yield of fibers is 50 to 58%, and the carbonization yield of activated carbon fibers is approximately 18 to 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 smaller specific surface area. In addition, although rayon-based fibers have a large specific surface area, their fibers are brittle, and although felt-like carbon fibers are popular, they are difficult to make into paper, and they have poor chemical resistance. There is a problem with water resistance. 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. Non-woven fabrics can be activated carbonized as they are, and are strong and flexible.

[Table] Therefore, it is particularly excellent as a polarizable electrode for electric double layer capacitors. 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,
Activated carbon fiber raw materials consisting of phenolic felt-like activated carbon fibers, phenolic cross-like activated carbon fibers, and phenolic paper-like activated carbon fibers were used to form polarizable electrodes (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, a step of about 1 mm is provided only on the end face of the opposite electrode, and the electrode is wound. The electrodes are taken out using aluminum conductive wires, and current collectors and lead terminals for both poles are simultaneously formed from both end faces by plasma spraying 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, and the electrolyte was 1M/l of tetraethylammonium perchlorate using propylene carbonate as the solvent. The following was used. Table 2 shows a comparison of the characteristics of the embodiment of the present invention manufactured in this way and the conventional example. As can be seen from this table, according to the present invention in which activated carbon fiber is used as the polarizable electrode and a collector electrode layer is formed thereon,
Capacity per unit volume and internal resistance can be significantly improved. As described above, in the electric double layer capacitor of the present invention, since the conductive electrode layer is formed on the activated carbon fiber, the internal resistance of the element is reduced and the shape of the activated carbon fiber is well maintained.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] 1. A polarizable electrode made of activated carbon fibers, a separator interposed between the polarizable electrodes, and an electrolyte;
An electric double layer capacitor comprising a conductive collector electrode formed in contact with the activated carbon fiber. 2. The electric double layer capacitor according to claim 1, wherein the conductive collector electrode is made of a metal sprayed. 3. The electric double layer capacitor according to claim 1 or 2, wherein the conductive collector electrode is made of aluminum.