Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
2001-01-03
2002-05-21
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S504000, C361S526000, C029S025030
Reexamination Certificate
active
06392867
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a safe electric double layer capacitor for power supplies for starting cell motors or as back-up power supplies for hybrid vehicle power supplies or personal computers, etc.
BACKGROUND ART
Electric double layer capacitors, wherein a non-woven fabric of polyethylene or polypropylene or a microporous film is interposed as a separator between two polarized electrodes where an electrode surface is formed on a collector surface using a binder of activated carbon or carbon particles and a polyvinylidene fluoride based polymer or polarized electrodes where aluminum is plasma-deposited on an activated carbon fiber cloth so as to form a conductive layer, and the separator being impregnated with a nonaqueous electrolytic solution, have high output and superior cycle characteristics and thus advances are being made in technology thereof.
When electric double layer capacitors employing nonaqueous electrolytic solution are subjected to high-temperatures, the nonaqueous electrolytes vaporize and the internal pressure of the nonaqueous electrolytes increases so that the shape of the capacitor changes, thereby causing not only changes in the characteristics of the capacitor dramatically but also causing risks of explosions and fire, pausing difficulties with regards to safety management.
A further problem with electric double layer capacitors is that carbon particles produced by such effect of coming apart and the like may move to the opposing electrode when carbon electrodes using activated carbon or carbon particles are employed. Particles produced by the coming apart may then move to the anode side by electromigration and such and thereby causing the leakage current to increase or short-circuits to occur more easily. The migration of particles between electrodes means self-discharge and the ability to prevent migration of particles is substantially related to the fundamental performance of the capacitor.
On the other hand, the degree of difficulty of ionic migration within the electrolytic solution is manifested in the form of liquid resistance, and an increase in this value shows a tendency of difficulty in smooth charging and discharging of the capacitor. It has therefore been necessary to increase the number of holes per unit surface area of the separator in order to reduced the resistance. This can also be achieved by making the separator thin because the fluid resistance can also be lowered by narrowing the distance between the electrodes. Generally, an extremely strongly polarized organic solvent is employed as the electrolyte for an electric double layer capacitor so that a great deal of salt may be dissolved in the solvent, and thus it is necessary that the separator does not react with this solvent or become dissolved by the solvent and also that the electrolyte including the separator must be resistant to mechanical stresses.
Various types of separators have been proposed for such separators. Examples may be found in such as high-density separators referred to as capacitor papers, low-density capacitor paper referred to as electrolytic paper, micro-porous items substance of polyethelene or polypropelene film, and non-woven fabric using polyethelene or polypropelene fibers. However, in the case of capacitor papers there is high inhibition against the conductivity of the electrolyte thereby making it impossible to obtain the desired electrostatic capacitance and internal resistance, and on the other hand in the case of electrolytic papers, the average pore diameter is greater than the size of the carbon particles and carbon particles therefore pass through the papers whereby the papers could not be made into the desired low leakage current capacitors.
Technology for an electric double layer capacitor with the capacitor having increased fluid retention of the nonaqueous electrolytic solution and with good handling characteristics of the nonaqueous electrolyte layer is disclosed in Japanese Patent Laid-open Publication No. Hei 6-36972.
One of the noticeable features of this capacitor is the use as separators of sustances each having 1 to 20% by weight of acrylic resin particles of a particle diameter of 10 to 100 &mgr;m. In the case of electric double layer capacitors employing this separator there are recognized improvement in the permeability of nonaqueous electrolytic solution into the separator structure, fluid retention characteristics and the capacitor assembly process, but there still remains difficulty with the capacitors that vaporization of the nonaqueous electrolytic solution can not yet be prevented.
Technology for an electric double layer capacitor employing, as a microporous separator which prevent the passage of carbon particles, bacterial cellulose obtained from an acetic acid bacteria stationary culture is disclosed in Japanese Patent Laid-open Publication No. Hei 9-129509. A major feature of this capacitor is the use of cellulose with a microfilament mesh structure as the separator. However, in case of capacitors employing this separator it is possible to prevent the passage of carbon particles, but there is still difficulty that the evaporation of the aqueous electrolytic solution can not be prevented.
Developments in electric double layer capacitors without these kinds of problems are in progress and there has been used technologies for solidifying nonaqueous electrolytic solution in particular for forming the nonaqueous electrolytic solution into a gel using as gelling agents polymers of polyacrylonitrile or acrylonitrile and (meta) acrylate. The polymer gel electrolyte obtained by heating and dissolving the acrylonitrile based polymer into the nonaqueous electrolytic solution and followed by cooling the same exhibits good ionic conduction, fluid retention and prevention of the passage of carbon particles, but the gel electrolyte shows high tackiness and thereby pausing difficulty in handling, whereby the assembly of electric double layer capacitors using this gel electrolyte faces therefore many difficulties and the manufacture of high-performance electric double layer capacitors becomes extremely difficult.
DISCLOSURE OF THE INVENTION
The inventors carried out investigations with the object of manufacturing in an efficient manner a high-performance electric double layer capacitor by improving the handling characteristics of each part in an assembly step, wherein the nonaqueous electrolytic solution does not evaporate, the prevention of the passage of carbon particles is good, and the capasitor is safe, and wherein the characteristics of impregnation and liquid retention for nonaqueous electrolytic solution are good. The inventors then found from the results that this object can be achieved by using as a carrier of the nonaqueous electrolytic solution a fibrous sheet-like substance comprising mainly a fiber-like substance or pulp-like substance of organic polymer soluble in the nonaqueous electrolytic solution and having gel-forming properties, and thereby completing the present invention. The gist of the invention is directed to an electric double layer capacitor with a polymer gel electrolyte layer interposed between polarizable electrodes, and is characterized in that an electrolyte is used wherein a fibrous sheet, comprising mainly a fiber-like or pulp-like material of an organic polymer which is soluble in or swellable by a nonaquerous electrolytic solution to form a gell, with a nonaquerous electrolytic solution and thereafter a part of the fibrous sheet is dissolved or swollen to give a gel.
BEST MODE FOR CARRYING OUT THE INVENTION
The fiber-like or pulp-like material to be used in the practice of the present invention has a shape similar in appearance to a fiber of about 1 to 100 &mgr;m in apparent diameter and a length of approximately 5 mm or less may be preferably used. A fibrous sheet-like material formed from a fiber-like or pulp-like material having the apparent diameter which is too small in apparent diameter is not preferable because it shows insufficient strength or insufficient handling characte
Chiba Tomoyoshi
Hamada Mitsuo
Hosako Yoshihiko
Yamada Teruyuki
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Reichard Dean A.
Thomas Eric W.
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