Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
1999-04-26
2002-09-10
Kim, John (Department: 1723)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S251000, C429S252000, C429S254000, C429S249000
Reexamination Certificate
active
06447958
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-aqueous electrolyte battery separator comprising a heat-resistant nitrogen-containing aromatic polymer and a ceramic powder, and a lithium secondary battery.
2. Description of the Related Art
A lithium primary battery or lithium secondary battery using a non-aqueous electrolyte is highly useful due to its property that high capacity and high energy density are obtained. As a main structure of these batteries, a separator composed of an electrically insulating porous film is intercalated between positive and negative electrodes, an electrolyte solution containing a lithium salt dissolved is impregnated into pores of the film, and the positive electrode and negative electrode and the separator are laminated, or wound in the form of a roll. It is required for a lithium secondary battery to make various safe measures against problems derived from its high capacity and high energy density, for example, large increase in battery temperature because of short-circuit inside and outside of a battery. For solving such problems, there have been made various ideas for the separator.
Particularly, as a safety precaution to which a separator can contribute, shut down property and short circuit property are under notice. Herein, the term shut down (also referred to as fuse) means that battery temperature increases by troubles such as overcharge, external or internal short, a part of a separator is melted to obstruct pores, and current is cut off, and the temperature in this phenomenon is called shut down temperature. The term short circuit means that temperature further increases from the shut down temperature, the separator is melted and a large hole is formed to cause short again, and the temperature in this phenomenon is called short circuit temperature. Decrease in the shut down temperature and increase in short circuit temperature are required for a non-aqueous electrolyte battery separator.
Conventionally, as a separator of a lithium secondary battery, a thin porous film is used, and for example, Celgard (registered trade mark) manufactured by Hoechst Co. is preferably used as a separator of a lithium secondary battery. However, a non-aqueous electrolyte battery separator having further excellent heat-resistance and higher short circuit temperature has been desired.
Regarding a raw material of such a non-aqueous electrolyte battery separator, use of a whole aromatic polyamide-based polymer having excellent heat-resistance has been investigated. For example, Japanese Patent Application Publication (JP-B) No. 59-36939 describes a method for producing a porous film made of an aromatic polymer, that is aromatic polyamide or aromatic polyimide, JP-B No. 59-14494 describes that a method for producing a porous film made of an aromatic polyamide and that it can be used as a battery separator. Further, Japanese Patent Application Laid-Open (JP-A) No. 5-335005 describes use of Normex (registered trade mark) paper (meta-aramid paper) manufactured by du Pont Co. as a separator of a lithium secondary battery. Likewise, JP-A Nos. 7-78608 and 7-37571 also suggest use of non-woven fabric or paper-like sheet made of meta-aramid as a battery separator. Further, JP-A Nos. 62-37871 and 2-46649 describes use of polyimide as a separator of a non-aqueous electrolyte solution battery. In these publications, a material is employed which exhibits excellent ion permeability and battery property while maintaining heat-resistance.
On the other hand, regarding shut down and short circuit, JP-A No. 3-291848 and JP-B No. 4-1692 suggest, for securing safety of a battery when short is occurred inside or outside of a battery, that a battery separator is allowed to have shut down function which cut off current, by providing an obstruction material which can be heat-melted on a porous film made of a thermoplastic resin and by covering the surface of a micro porous film by heat-melting of this obstruction material. Further, JP-A Nos. 60-52 and 60-136161 suggest that a battery separator is allowed to have shut down function, by adhering a polyethylene-based resin powder onto polypropylene non-woven fabric and by heat-melting the resin to obstruct pores of the non-woven fabric. However, in these suggestions, thermoplastic resins are used, therefore, heat-resistance is not sufficient and short circuit temperature is low, and use is restricted in view of safety.
The present inventors have intensively investigated a separator which does not have problems as described above, and found that a separator containing ceramic powder in a heat-resistant nitrogen-containing aromatic polymer is highly heat-resistant and has high short circuit temperature, and further has excellent ion permeability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a non-aqueous electrolyte battery separator having excellent ion permeability and battery property while maintaining merits of a heat-resistant nitrogen-containing aromatic polymer that heat-resistance is high and short circuit temperature is high.
Another object of the present invention is to provide a non-aqueous electrolyte battery separator which has such safety that shut down occurs in over-heating, has so high short circuit temperature that it is not melted when heated, and further has excellent safety. Further object of the present invention is to provide a lithium secondary battery having high short-circuit temperature and excellent safety by using such as separator.
Namely, the present invention relates to (1) a non-aqueous electrolyte battery separator comprising a heat-resistant nitrogen-containing aromatic polymer and a ceramic powder.
Further, the present invention relates to (2) a non-aqueous electrolyte battery separator comprising a heat-resistant nitrogen-containing aromatic polymer, a ceramic powder, and a substrate made of woven fabric, non-woven fabric, paper or porous film.
Further, the present invention relates to (3) a non-aqueous electrolyte battery separator according to (1) or (2), wherein the non-aqueous electrolyte battery separator contains a thermoplastic polymer which is melted at a temperature of 260° C. or less in an amount of 10% by weight or more based on the whole separator, and said thermoplastic polymer is melted when temperature increases and obstructs pore of said separator.
Moreover, the present invention relates to (4) a non-aqueous electrolyte battery separator comprising a coated film obtained by a method comprising the following steps of:
(a) preparing a slurry solution which may contain a thermoplastic resin which is melted at a temperature of 260° C. or less, by dispersing a ceramic powder in a solution of a polar organic solvent containing a heat-resistant nitrogen-containing aromatic polymer in an amount of 1 to 1500 parts by weight based on 100 parts by weight of said heat-resistant nitrogen-containing aromatic polymer,
(b) producing a coated film by coating said slurry solution,
(c) depositing said heat-resistant nitrogen-containing aromatic polymer on said coated film,
(d) removing the polar organic solvent from said coated film, and
(e) drying said coated film.
Furthermore, the present invention relates to (5) a non-aqueous electrolyte battery separator comprising a coated film obtained by a method comprising the following steps of:
(a) preparing a slurry solution which may contain a thermoplastic resin which is melted at a temperature of 260° C. or less, by dispersing a ceramic powder in a solution of a polar organic solvent containing a heat-resistant nitrogen-containing aromatic polymer in an amount of 1 to 1500 parts by weight based on 100 parts by weight of said heat-resistant nitrogen-containing aromatic polymer,
(b) producing a coated film by coating said slurry solution on a substrate made of woven fabric, non-woven fabric, paper or porous film,
(c) depositing said heat-resistant nitrogen-containing aromatic polymer on said coated film,
(d) removing the polar organic solvent from said coated film, and
(e) drying said c
Nakano Tsuyoshi
Shinohara Yasuo
Tsujimoto Yoshifumi
Kim John
Sorkin David
Sumitomo Chemical Co,. Ltd.
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