Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
1997-09-23
2001-05-22
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S249000
Reexamination Certificate
active
06235430
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an alkaline storage battery, particularly to an improvement in a separator used therein.
In recent years, alkaline storage batteries such as nickel-cadmium storage batteries and nickel-metal hydride storage batteries are attracting an attention as a power source for driving an electric vehicle since these batteries are expected to have a high output voltage, a high energy density and a long cycle life. Therefore, there increases a demand for further improvement in the performance of such alkaline storage batteries.
As one countermeasure for improving the performance of the alkaline storage batteries, a separator to separate a positive electrode from a negative electrode is investigated. For the separators in the alkaline storage batteries, a non-woven fabric composed of fibers made of an olefin resin such as polypropylene or an amide resin has been used. The separator made of the amide resin demonstrates a high liquid-absorbing property since the amide resin has a high hydrophilic property. However, the amide resin is low in alkali-resistance and heat-resistance. Therefore, the separator of the amide resin can not be stable for a long period at a high temperature which is assumed in a case when the battery is applied in an electric vehicle.
For that reason, investigations are mainly devoted to an improvement in the separator made of the olefin resin which is excellent in mechanical strength, alkali-resistance and heat-resistance. However, the separator made of the olefin resin demonstrates low liquid-absorbing property for an electrolyte since the olefin resin has low hydrophilic property. Therefore, various methods have been proposed for increasing the hydrophilic property and the liquid-absorbing property of the separator, thereby improving life characteristics and discharge characteristics of the battery.
For instance, according to Japanese Laid-Open Patent Publication Sho 62-115657 or Japanese Laid-Open Patent Publication Sho 64-57568, hydrophilic property of a separator made of an olefin resin poor in hydrophilic property is improved by a sulfonation treatment in which the separator is immersed in a concentrated sulfonic acid. However, the sulfonation treatment has a problem of lowering a mechanical strength of the separator because the treatment results in cutting of the carbon-carbon bonds in the resin.
Further, Japanese Laid-Open Patent Publication Hei 7-130392 proposes a method for improving a hydrophilic property of a separator by applying a surfactant which contain s sulfone groups to the separator. Although alkaline storage batteries configured with such separators demonstrate favorable characteristics at room temperature, they cannot have satisfactory life characteristic at high temperature because the surfactant gradually detaches from the surface of the separator.
Incidentally, another means for improving the discharge characteristic of an alkaline storage battery is investigated in making a separator thinner. The decreased thickness of the separator affects decreased electric and physical resistances between a positive electrode and a negative electrode, and also affects an increased proportion of a space occupied by the electrodes which participates in an electrochemical reaction of the battery. However, in a case of making the separator thinner by simply decreasing an amount or pieces of filaments per unit area (that is so called “METSUKE”), the liquid-absorbing property of the separator for an electrolyte is lowered, and the capacity of the battery is also decreased. In addition, since the mechanical strength of the separator is lowered, the separator is made liable to be damaged at the time of assembling the battery. Short-circuiting between the electrodes is also made liable to occur after assembling. In a case of making a diameter of the filament small while maintaining the pieces of the filaments to that of the conventional one, it is possible to reduce the thickness of the separator while maintaining the liquid-absorbing property for the electrolyte and the short-circuit resistance. However, there increases a hazard of lowering the mechanical strength and damaging the separator.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to solve the above-mentioned problems, and to provide an alkaline storage battery which is excellent in reliability and performance at a high temperature. The alkaline storage battery is realized by employing a separator which has sufficient mechanical strength not resulting a damage at assembling or service and stably demonstrates an excellent electrolyte-absorbing property at a high temperature of 40° C. or higher.
An alkaline storage battery of the present invention comprises: an electrode group configured with positive electrodes and negative electrodes piled alternately, and separators interposed therebetween; and a battery case which accommodates the electrode group, wherein the separators are made of non-woven fabrics of an olefin resin comprising first filaments having diameters in the range of 3 to 10 &mgr;m as a main component and second filaments having diameters in the range of 20 to 40 &mgr;m contained at {fraction (1/200)} to {fraction (1/10)} of the whole filaments.
It is preferable that the separators have sulfone groups introduced on their surfaces.
It is also preferable that the olefin resin is polypropylene.
According to the present invention, it is possible to provide a separator which stably demonstrates a high electrode-absorbing property even at a high temperature and has an excellent mechanical strength. By employing the separator, it becomes possible to provide an alkaline storage battery which has an excellent cycle life at a high temperature.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.
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Hoshina Yasuko
Ikoma Munehisa
Ito Noboru
Okamoto Miho
Akin Gump Strauss Hauer & Feld L.L.P.
Chaney Carol
Matsushita Electric - Industrial Co., Ltd.
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