Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
2000-02-16
2002-07-02
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, C429S251000
Reexamination Certificate
active
06413674
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a highly-airtightened porous paper used principally as an industrial material such as a battery separator, a separator used in an electrolytic capacitor or various types of filters and, more particularly, to novel paper that has minute pores, denseness, and a high degree of airtightness and is made from cellulose which has superior heat and chemical resistance and is a reproducible natural resource.
Further, the present invention relates to a non-aqueous battery. More particularly, this invention is intended to improve various characteristics of the non-aqueous battery, such as heat resistance, ion transmissivity, liquid-holding characteristics, and an internal short circuit, to a greater extent by use of a separator which has minute pores, denseness, and a high degree of airtightness and is made from cellulose which electronically separates the activity of a positively active substance from a negatively active substance.
2. Description of the Background Art
Paper is one of the most familiar articles and is used for packaging foods or beverages or decorating a house, to say nothing of being used as newspapers or book papers. Further, the paper is used as an industrial material in many applications and is one of modern sciences subjects of study. In general, paper is manufactured by dispersing into water cellulose which is prepared by cooking vegetable fibers with chemicals, removing the wet paper web from a papermaking slurry with a screen, and drying this scooped wet paper web.
The cellulose fibers of the paper are bonded together primarily by means of the hydrogen bonding of the cellulose. Specifically, when water evaporates from the wet paper web during the drying process, adjacent cellulose fibers are forcefully attracted together by the strong surface tension of the water. When the distances between the fibers are reduced, Van der Waal's force acts on the fibers to thereby attract the fibers together to a much greater extent. Finally, the fibers are brought into close contact with each other by hydrogen bonding. The degree of hydrogen bonding and the diameter of the fiber determine the extent of the air gap between the fibers, i.e., the degree of airtightness of the paper.
Cellulose which forms paper is a natural macromolecule and is able to resist heat in the vicinity of 230° C. and it has a high resistance to chemicals such as acid, alkaline, or organic solvents. For these reasons, paper is widely used as an inexpensive industrial material, such as a separator used in a battery or an electrolytic capacitor, or as various types of filters.
A porous film is also used as an industrial material in the same applications as the paper. This porous film is as thin as 10 to 40 &mgr;m, and minute pores of about 0.1 &mgr;m in size are uniformly formed on the entire film surface. Accordingly, the film is used as a filter. Further, in spite of the high degree of electrical insulating characteristics of the film itself, the electrical resistance of the film when it is impregnated with an electrolyte is low. For this reason, the porous film is used as an industrial material, e.g. as separators used in various types of batteries.
Thermoplastic resin included in petroleum resin or a cellulose derivative such as cellulose acetate is used as material for the porous film. A porous film is manufactured from thermoplastic resin by heating and fusing thermoplastic resin in the form of a film, and dissolving a previously drawn or mixed inorganic substance into the acid. When a porous film is manufactured from a cellulose derivative, a film is formed by dissolving the cellulose derivative into a solvent such as acetic acid or acetone, and drawing the thus-formed film.
In addition, non-aqueous batteries, such as lithium batteries or lithium ion secondary batteries, are compact and lightweight and have a large energy density by weight. It is for these reasons that in recent years, the non-aqueous battery has sprung into wide use as a power source of portable electronic equipment, such as cellular phones, notebook computers, or self-contained video cameras. The volume of production of the non-aqueous battery significantly increases year by year. The non-aqueous battery uses as an electrolyte a non-aqueous solvent; e.g., an aprotic organic solvent such as propylene carbonate, methyl ethyl carbonate, ethylene carbonate, methyl propionic acid, &ggr;-butyrolactone, or diethoxyethane. A substance, such as LiBF
4
, LiPF
6
, or CH
3
SO
3
Li, is dissolved as an electrolyte into the foregoing solvent. A lithium-contained oxide substance such as LiCoO
2
or LiNiO
2
is used as the positively active substance, and a carbon material such as graphite is used as the negatively active substance.
Elements which determine the performance of the non-aqueous battery include the prevention of an internal short circuit as a result of the positively active substance coming into contact with the negatively active substance for the purpose of reducing the proportion of short-circuit failures; retaining the sufficient and required amount of electrolyte for an electromotive reaction; and ensuring a superior transmissivity of a charge carrier required for the reaction of a battery, i.e., a reduction in the impedance, or particularly equivalent series resistance (hereinafter referred to as ESR), in order to reduce the internal resistance of the battery without impeding the transmission of ions. The proportion of short-circuit failures to ESR's is greatly dependent on the separator.
Short-circuit failures have two types of proportions: the proportion of short-circuit failures which occurred at the time of assembly of the battery and the proportion of short-circuit failures which occurred at the time of the use of the battery in the market. In either case, a short circuit arises in the weak portion of the separator. For example, if a pin hole is formed in the separator, a short circuit occurs in the pin hole. To reduce the proportion of short-circuit failures, there is a demand for a separator which is formed as uniformly as possible and has a high density without a pore such as a pin hole. In other words, there is a demand for a separator having a high degree of airtightness.
Contrary to the improvement of the proportion of short-circuit failures, in order to reduce the ESR, a porous separator, i.e. a separator having a low degree of airtightness is demanded to ensure pores which permit the passage of ions. This is due to ionic conduction, which is effected in the non-aqueous battery, where electric charges move as a result of the transmission of charged ions in the non-aqueous battery. As described above, there are two contradictory demands for the separator, i.e., a separator having a high degree of denseness or a high degree of airtightness in order to reduce the proportion of short-circuit failures, and a porous separator having a low degree of airtightness in order to improve the ESR of the battery.
A polyolefine-based porous film or unwoven fabric is used as a separator which has a high degree of airtightness and pores and is to be used in a non-aqueous battery. More specifically, porous polypropylene or polyethylene film is commercially available. A polyolefine-based unwoven fabric is principally used in coin-type batteries, and a polyolefine-based porous film is principally used in cylindrical batteries.
The polyolefine-based porous film is as thin as 10 to 40 &mgr;m, and minute pores are uniformly formed on the entire film surface, so that an air resistance of thousands of seconds/100 cc to tens of thousands of seconds/100 cc are obtained. In spite of a high degree of electrical insulating characteristics of the film itself, the electrical resistance of the film when it is impregnated with an electrolyte is low. For this reason, the porous film is used as a separator.
If the polyolefine-based porous film is heated to an abnormally high temperature, the film is fused at an internal temperature of about 120 to 170° C., thereby re
Jinzenji Teruyuki
Mizobuchi Taiji
Chaney Carol
Liniak, Berenato, Lonacre & White, LLC
Nippon Kodashi Corporation
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