Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer or spacer insulating structure
Reexamination Certificate
1997-09-05
2002-04-30
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer or spacer insulating structure
C429S145000, C429S249000, C429S250000, C429S247000
Reexamination Certificate
active
06379836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a separator paper for isolating an anode active material and a cathode active material in several alkaline-batteries, such as the alkaline-manganese battery, the silver oxide battery, and the air-zinc battery, in each of which the alkali electrolyte is used, and more specifically relates to the separator paper which has high denseness capable of preventing an internal shortage caused by zinc oxide dendrite due to not adding mercury, and which simultaneously has a higher heavy discharging performance due to increased liquid impregnate properties of the electrolyte.
2. Description of the Prior Art
A characteristic property required of the separator for isolating the anode active material and the cathode active material in alkaline-batteries, is to prevent internal shortage caused by touching of the anode active material with the cathode active material, in order to have a desirable durability, due to the fact that it does not cause shrinkage or deformation with use of a depolarization agent such as potassium hydroxide and manganese dioxide, and to hold sufficient quantity of the electrolyte required of produce electromotive without blocking the ionic conduction.
The separator paper of the prior art uses a paper of mixed paper making consisting of synthetic fiber and cellulose fiber, more specifically, it is mixed with vinylon fiber of alkali proof synthetic fiber as the main material, viscose rayon fiber of acid proof cellulose fiber, linter pulp including more than 98% &agr;-cellulose, mercerized wood pulp, polynosic rayon fiber, and polyvinyl alcohol fiber added as a binder.
The present applicant has disclosed a separator paper in the Japanese Patent Laid-Open Publication No.2-119049, in which by mixing alkali proof cellulose fibers applicable for beating, such as mercerized wood pulp, mercerized esparto pulp, mercerized Manila hemp pulp, polynosic rayon, and synthetic fiber to produce the separator paper which includes alkali proof cellulose fiber falling within 10 to 50 weight %, and has a beating degree with said alkali proof cellulose fiber falling within a 500 to 0 ml range of the CSF (Canadian Standard Freeness) value. A separator paper for the alkaline-battery is also disclosed in the Japanese Patent Laid-Open Publication No.62-154559, in which part or all of the fibers which form the separator paper is the synthetic fiber having the fineness of less than 0.8 denier (d) instead of the fiber of a larger fineness of 1 to 3 denier (d) used in the prior art.
Furthermore, another separator paper is disclosed in the Japanese Patent Laid-Open Publication No.5-74439. The separator paper disclosed in it is made by beating polynosic rayon fiber into CSF 300 to 700 ml and interweaving with vinylonfiber of less than 0.4 denier (d) in fineness.
These separator papers made by interweaving the cellulose fibers and synthetic fibers, have sufficient durability against electrolyte and desulphation agents, but have hole diameters which are insufficiently large in regards to protecting internal shortages of the cell, caused by contacting between both electrodes of the active materials. It is therefore required to take measures such as, to laminate the paper in layers in order to make the hole diameter substantially small, or to overlap the paper with some separator material such as cellophane film which has microscopic holes.
Measures have been taken in the alkaline-battery using zinc as a cathode active material, in which the surfaces of zinc particles are amalgamated with mercury to convert it into an active material, in order to prevent self discharging of the cathode and to promote an electromotive force reaction. Recently, in regards to preventing the ecological disruption caused by mercury contamination, the required amount of mercury consumption is being gradually decreased. That is, no mercury can be used with the battery, this has been a prerequisite since 1992.
If no mercury is added, corrosion of zinc as the cathode active material is apt to occur. This results in the deposition of an electrically-conductive crystal zinc oxide compound called “dendrite”, which makes electrical contacts between both electrodes of the active materials to cause an internal shortage, and significantly reduces the battery capacity. To prevent such internal shortage caused by the deposition of zinc oxide dendrite, a fine separator paper is required which has a smaller sized hole diameter than that of conventional paper. More specifically, it requires such separator paper to have more than 2 sec/100 ml airtightness, in order to prevent the internal shortage caused by the deposition of zinc oxide.
On the other hand, alkaline-batteries, more specifically alkaline manganese batteries have gained a wide variety of uses for portable electrical power supply, as well as with its progress toward non-mercury type development of cathode, and its increasing application; It is also required to improve battery performance, such as more extended discharging time in the form of continuous or intermittent discharging, and above all, heavy discharging performance.
As portable electronic devices, such as notebook type personal computers, liquid crystal display TV sets, and cellular phones, come into wide use, the demand for the alkaline manganese battery as the power source of these electric devices, (in which heavy discharging is required) is rapidly increased, and so, improvement of the heavy discharging performance is strongly requested. Such conventional electric devices require a large consumption of electricity, so it is common to use a secondary battery such as nickel-cadmium battery for these electronic devices. The application of the alkaline manganese battery takes notice, while electronic devices requiring heavy discharge from alkaline manganese batteries are also increasing, since it is easily available and simple to handle, along with saving power in electronic devices becoming more common. The heavy discharge mentioned above may be defined as a concept event wherein a high current discharge occurs with the load resistance being less than 3&OHgr;.
Under the heavy discharge, however, a higher electric discharge current occurs compared with under a light load of more than 10 &OHgr; resistance, as for the alkaline manganese battery which is an inside-out type structure, wherein battery reaction hardly occurs at the inner region of the active material, as the electric discharge current increases, the utilizing ratio of the active material becomes exponentially reduced, which results in reducing battery capacity thereof. For example, it is known that the utilizing ratio of the active material with a 2 &OHgr; resistance load, which produces heavy discharge, is simply decreased to less than 20%. For this reason, it is said to be a significant improvement for 1 or 2 minutes of extended discharge time, if it is realized with less than 3 &OHgr; of resistance load, and such is of course a desirable improvement and is strongly demanded. To increase the battery capacity under such heavy discharge, increment of active material or decrement of electrical resistance value is not effective. Instead, it is desirable to increase the amount of liquid impregnate properties for the electrolyte in the separator or the active material, so as to encourage the diffusion of ions due to rapid battery reaction. That is, more of the electrolyte should be given to the separator paper, in order to encourage the diffusion of zinc ions of cathode and not to lower the conductivity. More specifically, a separator paper having more than 550% of liquid impregnate ratio is desirable, in regards to the increase of the heavy discharge capacity.
It is, however, difficult to satisfy simultaneously both of the aforementioned requests of airtightness and the liquid impregnate ratio. That is, although part of the electrolyte retained in the separator within the battery may have been moved toward the anode active material and toward the cathode side (during its disch
Kubo Yoshiyo
Mizobuchi Akio
Yamanoue Motoi
Brouillette Gabrielle
Martin Angela J.
Nippon Kodoshi Corporation
Shlesinger & Arkwright & Garvey LLP
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