Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
2001-07-31
2004-05-04
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S249000, C429S253000, C429S254000, C429S006000, C429S006000, C204S296000, C361S512000
Reexamination Certificate
active
06730439
ABSTRACT:
TECHNICAL FIELD
This invention relates to a separator, low in electrical resistance and excellent in resistance to heat and breaking, for batteries or capacitors, comprising a melt-blown non-woven fabric of high-melting resin or laminate having a melt-blown non-woven fabric.
BACKGROUND OF THE INVENTION
Melt-blown non-woven fabrics of polyolefin, in particular polypropylene, have been going into various areas with their favorable characteristics, e.g., various separation membranes and separators, e.g., those for batteries, electrolysis condensers, capacitors and polymer batteries. In particular, these separators are widely used for the lithium batteries (primary and secondary), because they are insoluble in organic solvents and stable to electrolytes and electrode active materials.
Short-circuit of a battery, either inside or outside, is generally accompanied by discharge of large current, and the resultant Joule heat or heat of chemical reaction may cause shrinkage or melting of the separator between the anode and cathode to directly cause short-circuit of these electrodes, possibly aggravating the internal short-circuit, with the result that large quantities of heat and/or gases may be released outside. In order to solve these problems, the separator is preferably provided with a shut-down function, i.e., the function of blocking ions and hence current, or a function of preventing the separator itself from being shrunk or molten.
The conventional separator of non-woven fabric of polyolefin, e.g., polyethylene or polypropylene, tends to suffer short-circuit resulting from melting of the separator, when exposed to high temperature for extended periods, in particular when used in an automobile engine or subjected to soldering, because of low-melting point of polyolefin, around 125 to 140° C. for polyethylene and 160 to 180° C. for polypropylene. The separator for the advanced lithium ion battery or electrical double-layer capacitor is required to have various characteristics, such as high capacity, improved electrical characteristics and productivity, and safety. One of the safety-related functions is the shut-down function, which blocks current, when the electrode is short-circuited to increase temperature inside of the battery, by melting the separator to close its pores before lithium is ignited, in order to prevent hazards, e.g., fire. Another function is melt-down of the separator itself, when temperature further rises after the shut-down, to control combustion or explosion of the battery. These functions are to control temperature run-away when battery is overcharged or tested for heating preservation.
At present, a secondary battery serviceable at high temperature, high in heat resistance and dispensing the shut-down function or replacing it with another safety mechanism is in demand, because of its improved safety-related characteristics, e.g., electrolytic solution of higher resistance to heat, external protective circuit against short-circuit and polymer electrolyte of improved safety. This, in turn, needs a separator of higher resistance to heat and free of short-circuit.
Recently, a battery provided with the conventional separator of polyethylene or polypropylene may be required to work at a temperature higher than its melting point in the vicinity of an automobile engine or for an electrical double-layer capacitor. Moreover, a battery which is assembled using soldering has been developed. Therefore, a separator of higher resistance to heat and lower electrical resistance has been in demand. Another problem to be solved is that a separator of thin polyolefin-based films may be broken or torn, when it is wound or laminated together with the electrode to form a battery.
It is an object of the present invention to provide a heat-resistant separator low in electrical resistance, sufficiently responding to reduced thickness of the films for the battery, excellent in resistance to heat and breaking, not melting even when left at high temperature, and free of short-circuit of the electrode, to solve the problems involved in the conventional techniques. It is another object of the present invention to provide a highly safe, laminated separator having a function of blocking permeability at low temperature.
DISCLOSURE OF THE INVENTION
The inventors of the present invention have found, after having extensively studied to solve the above problems, that use of a non-woven fabric of high-melting resin having specific properties can give a separator of low electrical resistance and excellent in resistance to heat, and that use of the laminate of the non-woven fabric can give a separator resistant to melt down and having a shut-down function, or a separator resistant to heat and breaking even when thickness of the film is reduced, reaching the present invention.
The first invention is a heat-resistant separator composed of a non-woven fabric of high-melting resin, 1 to 20 &mgr;m in average fiber diameter, 5 to 300 g/m
2
in basis weight, 1 to 200 cc/cm/sec in air permeability, and 0.01 to 1.0 mm in thickness.
The second invention is the heat-resistant separator of the first invention having a real part impedance of 20 &OHgr;·cm
2
or less at a frequency of 10 KHz and normal temperature.
The third invention is the heat-resistant separator of the first or second invention having a maximum real part impedance at a frequency of 10 KHz and 100 to 180° C. is 100 times or less of the real part impedance at normal temperature and 200 &OHgr;·cm
2
or less in the absolute value.
The fourth invention is the heat-resistant separator of one of the first to third inventions, wherein the high-melting resin is selected from the group consisting of polyester, polyphenylene sulfide, polymethyl pentene and polyamide.
The fifth invention is the heat-resistant separator of the fourth invention, wherein the polyester is polybutylene terephathalate.
The sixth invention is the heat-resistant separator of one of the first to fifth inventions, wherein the non-woven fabric is melt-blown.
The seventh invention is a laminated heat-resistant separator composed of a laminate having a melt-blown, non-woven fabric layer of high-melting resin, 1 to arm 20 &mgr;m in average fiber diameter, 5 to 300 g/m
2
in basis weight, 1 to 200 cc/cm
2
/sec in air permeability, and 0.01 to 1.0 mm in thickness.
The eighth invention is the laminated heat-resistant separator of the seventh invention, composed of a melt-blown, non-woven fabric layer of high-melting resin and non-woven fabric layer having a shut-down function.
The ninth invention is the laminated heat-resistant separator of the eighth invention, wherein the non-woven fabric layer having a shut-down function is of polyolefin.
The 10
th
invention is a laminated heat-resistant separator of polyphenylene sulfide, comprising two or more laminated layers of melt-blown, non-woven fabric of polyphenylene sulfide, which has a fiber diameter of 2.0 to 8.0 &mgr;m, basis weight of 20 to 60 g/m
2
, air permeability of 10 to 200 cc/cm
2
/sec, thickness of 100 to 300 &mgr;m, and strength of 10N/50 mm or more in the MD direction.
The 11
th
invention is the laminated heat-resistant separator of polyphenylene sulfide of the 10
th
invention, wherein the melt-blown, non-woven fabric of polyphenylene sulfide for the laminated layers has an average fiber diameter of 2.0 to 8.0 &mgr;m, basis weight of 40 to 80 g/m
2
, air permeability of 5 to 20 cc/cm
2
/sec, thickness of 100 to 180 &mgr;m, and strength of 40N/50 mm or more in the MD direction.
The 12
th
invention is the heat-resistant separator of one of the first to 11
th
inventions which is used for a battery or capacitor.
PREFERRED EMBODIMENTS OF THE INVENTION
The present invention provides a heat-resistant separator for batteries or capacitors composed of a non-woven fabric of high-melting resin or a laminate having a layer of the non-woven fabric of high-melting resin. It is described in more detail below.
1. High-Melting resin
The high-melting resin for the present invention has a melting point of 200° C. or higher. Such resins
Kamei Toshikazu
Yamazaki Masaki
Armstrong Kratz Quintos Hanson & Brooks, LLP
Bell Bruce F.
Tonen Tapyrus Co., Ltd.
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