Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
2000-02-04
2001-12-04
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S503000, C423S44500R
Reexamination Certificate
active
06327136
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an electrode-forming composition for providing an activated carbon electrode with excellent processability or handling characteristic, an activated carbon electrode obtained from the electrode-forming composition, and an electric double layer capacitor equipped with the activated carbon electrode so as to exhibit an improved reliability.
Accompanying the development of electronic and electric devices and apparatus in recent years, there is a strong demand for various types of power supplies or electricity sources in addition to well-developed commercially power supply requiring large-scale cable or wiring. In this respect, an electric double layer capacitor is calling a particular expectation as a new type of energy device for functional applications in many fields in view of advantageous characteristics, such as a large capacity, a long life, quick chargeability, easiness of charging and discharging and better cycle characteristic than secondary batteries. Further, the application of electric double layer capacitor is extended from small-capacity use, such as back-up power supply for electronic devices, up to large-capacity use such as auxiliary energy sources for electromotive vehicles and hybrid cars under consideration. Accompanying therewith, higher performances, such as a higher capacity, are required of polarizable electrodes constituting electric double layer capacitors.
An electric double layer capacitor is a capacitor device utilizing a capacitance of charge stored in an electric double layer capacitor formed at a boundary between a polarizable electrode and an electrolyte. The electric double layer capacitors are roughly divided in terms of electrolytic solutions used therein, i.e., organic solvent-type and aqueous solution-type. An organic solvent-type electric double layer capacitor has a high withstand voltage and can have an increased capacitance, so that it is advantageous as a large-capacity capacitor. The polarizable electrode is required to have large specific surface area and bulk density, be electrochemically inert and have a low resistivity. A polarizable electrode structure for an electric double layer capacitor generally comprises a powdery activated carbon material, an electroconductivity imparting material, a binder material and an electroconductive metal substrate. As processes for producing such electrode structures, there are known a process wherein a solvent is added to a mixture of a powdery activated carbon material, an electroconductivity-imparting material and a binder to form a mixture slurry, which is then applied on an electroconductive substrate by coating or dipping, followed by drying, to form an electrode structure (e.g., as disclosed in Japanese Laid-Open Patent Application (JP-A) 10-64765), and a process wherein a solvent is added to a mixture of a powdery activated carbon material, an electroconductivity-imparting material and a binder insoluble in the solvent, the resultant mixture is kneaded and formed into a sheet, and the sheet, after being dried, is bonded onto an electroconductive substrate via an electroconductive substrate, followed by pressing and heat-treatment for drying, to form an electrode structure (e.g., as disclosed in JP-A 9-275041). The former process is preferable in view of the production cost.
As the binder, polyvinylidene fluoride has been noted for its electrochemical stability, etc. For example, JP-A 8-55761 has disclosed a process for producing an electric double layer capacitor including a step of forming a polarizable electrode wherein a slurry comprising a fluorine-containing polymer, such as polyvinylidene fluoride, an organic solvent, such as N-methyl-2-pyrrolidone, toluene, ethyl acetate or dimethyl phthalate, activated carbon powder, and an optionally added electroconductivity-imparting agent, is applied onto an electroconductive substrate and dried for removal of the organic solvent to form a polarizable electrode. A similar technique is also disclosed in JP-A 8-213289.
However, the polarizable electrode (activated carbon electrode) obtained through the above-mentioned processes has involved a defect that the activated carbon electrode layer formed by the coating is liable to be peeled from the electroconductive substrate and has an insufficient flexibility, so that the resultant entire activated carbon electrode suffers from poor processability and insufficient reliability. In order to solve the above-mentioned defect, JP-A 10-64517 discloses to use a vinylidene fluoride-based rubber. However, such a vinylidene fluoride-based rubber is liable to be swollen with an organic solvent-type electrolytic solution, thus being liable to cause a separation of the electrode layer during use of the capacitor and resulting in an electric double layer capacitor having a low reliability.
SUMMARY OF THE INVENTION
In view of he above-mentioned circumstances of the prior art, a principal object of the present invention is to provide an electrode-forming composition capable of providing an activated carbon electrode layer well adhered to an electroconductive substrate and having an improved flexibility.
Another object of the present invention is to provide an activated carbon electrode having such an activated carbon electrode layer and showing excellent processability.
A further object of the present invention is to provide an electric double layer capacitor including such an activated carbon electrode and exhibiting an improved reliability.
As a result of our study for accomplishing the above-mentioned objects, it has been found very effective to incorporate a plasticizer for a vinylidene fluoride polymer in addition to a good solvent for a vinylidene fluoride polymer ordinarily used within an electrode-forming composition to be applied onto an electroconductive substrate to form an activated carbon electrode layer.
Thus, according to the present invention, there is provided an electrode-forming composition, comprising: activated carbon, a vinylidene fluoride polymer having an inherent viscosity of 0.5-20.0 dl/g, and a solvent, wherein the solvent comprises a mixture of a good solvent and a plasticizer for the vinylidene fluoride polymer.
The present invention further provides an activated carbon electrode (polarizable electrode) formed by applying the above-mentioned electrode-forming composition onto an electroconductive substrate to form a composite layer and selectively removing the solvent from the composite layer to form an activated carbon electrode layer. Preferably, the activated carbon electrode layer is formed by optionally removing at least a portion the solvent by evaporation from the composite layer, then extracting the plasticizer by contacting the composite layer with a poor solvent for a vinylidene fluoride polymer and then evaporating the poor solvent from the composite layer. If the plasticizer is removed by extraction with a poor solvent in this manner, it is assumed that the vinylidene fluoride polymer as the binder in the resultant activated carbon electrode layer is made porous, and this contributes to a remarkably improved flexibility and an improved adhesion with the electroconductive substrate of the activated carbon electrode layer.
The present invention further provides an electric double layer capacitor comprising a pair of polarizable electrodes, and an electrolytic solution disposed between the polarizable electrodes, wherein at least one of the polarizable electrodes comprises an activated carbon electrode structure as mentioned above.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawing.
REFERENCES:
patent: 5682288 (1997-10-01), Wani
patent: 5776637 (1998-07-01), Kashio et al.
patent: 5838531 (1998-11-01), Saito et al.
patent: 6031712 (2000-02-01), Kurihara et al.
patent: 6064561 (2000-05-01), Harada et al.
Meguro Kazuhiro
Sato Hiroshi
Tada Yasuhiro
Kureha Kagaku Kogyo Kabushiki Kaisha
Reichard Dean A.
Thomas Eric
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Electrode-forming composition, activated carbon electrode... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrode-forming composition, activated carbon electrode..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrode-forming composition, activated carbon electrode... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2594620