Metal working – Barrier layer or semiconductor device making – Barrier layer device making
Reexamination Certificate
2000-12-19
2003-04-29
Nguyen, Ha Tran (Department: 2812)
Metal working
Barrier layer or semiconductor device making
Barrier layer device making
C361S512000, C429S247000, C429S248000, C429S249000
Reexamination Certificate
active
06554875
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for manufacturing an electric double-layer capacitor.
BACKGROUND OF THE INVENTION
An electric double-layer capacitor has a relatively high capacity; moreover, it has a long life and a capability of being quickly charged and discharged. Therefore, it has been used not only for conventional applications such as leveling of power sources and absorption of noises but also as a memory backup power source for personal computers as well as a supplement or substitute for secondary batteries. In recent years, it has been expected to be used as a secondary battery for electric automobiles.
This electric double-layer capacitor has such a structure that a pair of electrodes is dipped in an electrolyte solution. When a voltage is applied to this electric double-layer capacitor, ions having an opposite sign to an electrode will be distributed near the electrode to form a layer of the ions while charges having an opposite sign to the ion will be accumulated within the electrode. Then, when a load is placed across the electrodes, the charges within the electrode will be discharged and, at the same time, the ions distributed near the electrode will leave therefrom whereby a neutral state will return.
When a pair of electrodes touch in such an electric double-layer capacitor, the formation of an ion layer near the electrode becomes difficult. Therefore, a separator is usually placed between each electrode pair.
An electric double-layer capacitor with the above-mentioned structure, such as a nonaqueous solution type electric double-layer capacitor where the electrolyte is a nonaqueous solution, can be manufactured as follows:
(1) after materials, i.e. a current collector electrode, an electrode and a separator, are each independently heat dried in a vacuum, those materials are assembled to manufacture an electrode group. Next, the electrode group is inserted into a case followed by impregnation with an electrolyte in a vacuum. Then, the case is sealed to give a nonaqueous solution type electric double-layer capacitor is prepared. According to this method, it would be possible to manufacture an electric double-layer capacitor having a high withstand voltage and an electric double-layer capacitor having a high energy density. However, in this method, there are problems that the manufacture is troublesome since each of the materials is to be heat dried in a vacuum and a big space is needed since plural drying apparatuses are required.
Another method for the manufacture of an electric double-layer capacitor is as follows:
(2) the materials, i.e. the current collector electrode, the electrode and the separator, are assembled together to prepare an electrode group which is subjected to heat drying in a vacuum. Then, the electrode group is inserted into a case, followed by impregnation with an electrolyte in a vacuum. Thereafter, the case is sealed to give a nonaqueous type electric double-layer capacitor. According to this method, heat drying in a vacuum is carried out after fabrication of the electrode group and, therefore, the manufacturing processes can be simplified and the number of drying apparatuses can be reduced whereby a big space is unnecessary. However, because there are varieties in heat resistance among the constituent materials for the electrode group (i.e., among the current collector electrode, the electrode and the separator), heat-drying in a vacuum should be carried out at such a temperature that each material will not be deteriorated. Unfortunately, water cannot be sufficiently removed even by heat drying in a vacuum at such a temperature and, therefore, it is difficult to manufacture an electric double-layer capacitor having a high withstand voltage and an electric double-layer capacitor having a high energy density. On the contrary, when the thermal drying in a vacuum is carried out at such a temperature that water can be well removed, there is a problem that the separator (such as a separator made up of a polypropylene fiber or a cellulose fiber) is significantly deteriorated due to fusion or carbonization, thereby causing a short circuit. As a result, the resulting prior art separator is actually unusable.
SUMMARY OF THE INVENTION
The present invention has been made for solving the above-mentioned problems. An object of the present invention is to provide a process capable of manufacturing an electric double-layer capacitor having a high withstand voltage, an electric double-layer capacitor having a high energy density or an electric double-layer capacitor having a high capacity in an easy manner and without taking up much space.
The present invention relates to a process for the manufacture of an electric double-layer capacitor (hereinafter, referred to as “capacitor”), that is, a process for manufacturing an electric double-layer capacitor, said process including the steps of inserting an electrolyte and an electrode group assembled from a current collector electrode, an electrode and a separator into a case, and sealing the case, which comprises the characteristic steps of:
using, as the separator, a fiber sheet comprising a fiber having fibrils and formed from a resin having a melting or carbonizing temperature of not lower than 300° C. and a fine fiber having a fineness of not more than 0.45 dtex (decitex) and formed from a resin having a softening temperature of not lower than 200° C. and,
after assembling of the electrode group, drying the current collector electrode, the electrode and the separator at the temperature which is lower than the softening temperature of a resin having the lowest softening temperature among the constituent resins for the fibers comprised in the separator but not lower than the boiling point of water.
As a result of an intensive investigation, the present inventors have found that, when an electrode group is assembled from a current collector electrode, an electrode and a specific separator and then dried even for a long period (such as 5 hours or longer) at the temperature higher than the boiling point of water but lower than the softening point of a resin having the lowest softening point among the constituent resins for the fibers contained in the above separator, water can be well removed without deterioration of the specific separator whereby it is possible to manufacture an electric double-layer capacitor having a high withstand voltage, an electric double-layer capacitor having a high energy density or an electric double-layer capacitor having a high capacity in a simple manner without occupying much space.
When no constituents for the above separator are thermally fused, the separator is free from forming a coat, thereby achieving an excellent ionic permeability. As a result, it is possible to manufacture electric double-layer capacitors having higher capacity.
DETAILED DESCRIPTION OF THE INVENTION
The characteristic feature in the capacitor-manufacturing process of the present invention resides in using a specific separator because the specific separator is not deteriorated by heat even when constituent materials are dried (such as heat dried in a vacuum) after the fabrication of an electrode group whereby water can be thoroughly removed with the result that it is possible to manufacture electric double-layer capacitors having a high withstand voltage, electric double-layer capacitors having a high energy density or electric double-layer capacitors having a high capacity in an easy, simple, convenient manner without occupying much space.
The specific separator consists of a fiber sheet containing a fibril-containing fiber formed from a resin having a melting or carbonizing temperature of not lower than 300° C. (hereinafter, referred to as “fibril fiber”) and a fine fiber having a fineness of not more than 0.45 dtex (decitex) and formed from a resin having a softening temperature of not lower than 200° C.
The separators are capable of having a densified structure by entangling the fibrils of the fibril fiber, thereby providing not only an excellent strength but also an
Kimura Fuminori
Kimura Kouji
Kobayashi Takeshi
Shimizu Masahiko
Japan Vilene Co. Ltd.
Nguyen Ha Tran
Oliff & Berridg,e PLC
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