JPS62222618A - Electric double-layer capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric double layer capacitor, and more specifically, by using activated carbon fibers as polarizable electrodes, the processability and utilization efficiency of the polarizable electrodes are improved, and The present invention provides an electric double layer capacitor with a large charging capacity per unit volume.

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. 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 mass-producing electric double layer capacitors. In other words, the current collector and activated carbon electrode layer formed when the polarizable electrode is spirally wound! II fi, variations in capacity due to falling off, etc., decrease in utilization efficiency of the activated carbon electrode layer, and increase in internal resistance during use, resulting in changes in capacity and variations in charging time, etc., which are important problems in terms of commercial 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.

There are four types of raw material fibers for activated carbon fibers: 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 electrolytes.

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, once 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 and the carbonization yield decreases, resulting in electrical resistance, Flexibility is evil.

In order to use it as a polarizable electrode of an electric double layer capacitor, the carbonization yield is 1, although it varies depending on the type of raw material fiber.
About 0 to 80% is preferable, and if the carbonization yield is less than 10%, the specific surface area becomes large, but the raw material fiber loses its flexibility and may wind into a spiral, or conversely, if the carbonization yield is 80%.
The above-mentioned materials are excellent in electrical resistance, flexibility, carbon fiber strength, etc., but are not preferable because the specific surface area becomes small and the electric capacity per unit volume becomes small.

Here, the carbonization yield of fiber is referred to as the carbonization yield, and in the case of phenol fiber, the carbonization yield of carbon fiber is 50 to 58%, and the carbonization yield of activated carbon fiber is 1
It will be about 8 to 55%.

Table 1 shows the characteristics of different types of carbon fibers. As is clear from this table, acrylic and pitch-based materials are generally slightly more flexible and have a slightly smaller specific surface area. In addition, although rayon-based fibers have a large specific surface area, the fibers are brittle, and although felt-like carbon fibers are popular,
It is difficult to make paper, it is impossible to make it into paper form, and there are problems with chemical resistance and 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 it can be used to fabricate woven fabrics. It is particularly excellent as a polarizable electrode for electric double layer capacitors because it can be activated carbonized as it is and is strong and flexible. In addition, paper making using phenolic carbon fiber as a raw material has a number of advantages, especially paper making 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, a current collector is made of powdered coconut husk charcoal and etched with aluminum punching metal (t=0.1m+n), and activated carbon electrode layers with a thickness of 200μ are formed on both sides of this current collector. was processed by rolling and cut into a shape with electrode dimensions (20 ci x 2.5 co + x 0.5 mm) to obtain an electrode. 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 m + nφ 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,
Activated carbon fiber raw materials consisting of pitch-based felt-like activated carbon fibers, phenolic-based felt-like activated carbon fibers, phenolic-based cross-like activated carbon fibers, and phenol-based paper-like activated carbon fibers were used as polarizable electrode shapes (20 cm x
A PTFE separator is inserted between the electrodes of each activated carbon fiber, and the activated carbon fiber is wound into a spiral shape using a winder. At this time, a step of about In11 m 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 housingd in the same manner as the conventional product described above, and the electrolyte was
Propylene carbonate was used as a solvent and IM/e's tetraethylammonium barchlorate was used as an electrolyte.

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 a polarizable electrode and a collector electrode layer is formed thereon, the capacitance 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 drawings]

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

Claims (3)

[Claims] (1) An electric double layer capacitor comprising a polarizable electrode made of activated carbon fibers, a separator interposed between the polarizable electrodes, an electrolyte, and a conductive collector electrode formed on the activated carbon fibers. . (2) The electric double layer capacitor according to claim 1, wherein the conductive collector electrode is formed by spraying metal. (3) The electric double layer capacitor according to claim 1 or 2, wherein the conductive collector electrode is made of aluminum.