JPH05335005A - Separator - Google Patents

Abstract

PURPOSE:To provide a lithium ion battery which is free from violent spout of the electrolyte decomposition gas out of a battery vessel accompanied with particulates of the active material even in case it is, in charged state, placed on a hot plate or the like which is heated to 250 deg.C approximately. CONSTITUTION:A separator concerned consists of aramid fiber as polymeride of all-aromatic polyamide and shaped in a paper-like sheet having air permeability, wherein the structure is such that synthetic pulp as polymeride of all- aromatic polyamide is dispersed in non-woven or woven fabric of aramid fibers or in voids therein. Otherwise, the separator may be a draughty film with a number of pores opened which consists of aramid resin as polymeride of all- aromatic polyamide.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a separator.
In particular, the present invention relates to a separator used in a battery in which ions of light metals such as lithium and sodium are used as carriers of an ionic current between a positive electrode and a negative electrode.

[0002]

2. Description of the Related Art Conventionally, in non-aqueous electrolyte batteries,
When it is forcibly heated from the outside of the battery, even if the safety valve is activated, it not only ejects the electrolytic solution from the battery container, but also decomposes the electrolytic solution with fine particles of the active material and the melted material of the separator. May spurt out, which may damage the equipment itself using the battery and cause physical or human damage to the surrounding area.

At present, a non-aqueous electrolyte battery is disclosed in JP-A-54.
The separators disclosed in JP-A-52157 and JP-A-59-207230 are used. In a battery using such a separator, the positive electrode and the negative electrode are short-circuited, and when the temperature of the battery rises, the fine holes opened in the separator are blocked, and as a result, the ionic current inside the battery is blocked, and It is possible to prevent the battery temperature from rising and prevent the battery from exploding. Further, for the purpose of obtaining the same effect, JP-A-61-223260.
JP-A-63-308866, JP-A-1-
There has been proposed a battery of non-aqueous electrolyte solution using a separator mainly composed of two or more kinds of resins having different melting points as disclosed in Japanese Patent No. 258358.

For example, a non-aqueous electrolyte battery using a lithium composite oxide as a positive electrode active material disclosed in JP-A-55-136131, or JP-A-62-908.
No. 63, JP-A No. 63-299056, a non-aqueous electrolyte battery, that is, a non-aqueous battery using a lithium composite oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material. In the battery of the electrolytic solution, even if the battery having the structure of the present invention is not used, if the separator having the above-described characteristics is used, the electrolytic solution is discharged from the battery container even if the temperature of the battery rises due to a short circuit inside or outside the battery. It means that there is no abnormal situation such as a gush.

However, when the lithium ion battery of the non-aqueous electrolyte solution using the separator and the electrode as described above is charged, it is put in an oven or placed on a hot plate to make the battery. In the case where is forcibly heated from the outside, not only the electrolytic solution is ejected from the battery container, but also the decomposition gas of the electrolytic solution is rapidly ejected along with the fine particles of the active material, the melt of the separator, etc. Sometimes.

[0006]

SUMMARY OF THE INVENTION According to the present invention, even when the battery is forcibly heated from the outside, the decomposition gas of the electrolytic solution is discharged from the battery container along with the fine particles of the active material, the melt of the separator and the like. It is an object of the present invention to provide a safer battery that does not burst suddenly.

[0007]

The present invention is a separator made of a wholly aromatic polyamide polymer. The separator used in the present invention is a non-woven fabric made of aramid fibers which is a polymer of wholly aromatic polyamide, a woven fabric, or a polymer of wholly aromatic polyamide in the interstices of aramid fibers which is a polymer of wholly aromatic polyamide. It is a breathable paper-like sheet having a structure in which synthetic pulp is dispersed, or a breathable film made of aramid resin, which is a polymer of wholly aromatic polyamide, having many fine holes.

The molecular structure of the wholly aromatic polyamide polymer that constitutes the separator is not particularly limited to meta type or para type. When aramid fibers are used as the constituent material of the separator, they may be long fibers or short fibers. Furthermore, when adopting a paper-like structure in which synthetic pulp, which is a polymer of wholly aromatic polyamide, is dispersed in the spaces between aramid fibers, which is a polymer of wholly aromatic polyamide, the aramid fiber has a structure such as a nonwoven fabric or a woven fabric. May be configured,
It is not particularly limited. For example, a structure in which short fibers and synthetic pulp are dispersed between fibers such as non-woven fabric and woven fabric,
It may have a structure in which synthetic pulp is dispersed between fibers such as a non-woven fabric or a woven fabric, or a structure such as paper in which synthetic pulp is simply dispersed between short fibers. In this case, from the viewpoint of mechanical strength, it is preferable to use long fibers as the fibers,
For paper-like structures in which synthetic pulp is dispersed between short fibers, longer fiber lengths are preferred.

When a non-woven fabric, a woven fabric, a paper-like sheet or the like is used as the separator, the separator may be partially dotted in the plane or a large number of points in a line, fibers and synthetic pulp are pressed at a high temperature during production. Therefore, the mechanical strength can be further increased. By the way, in order to function as a separator of a battery, it is necessary to have fine air-permeable voids, for example, the weight of wholly aromatic polyamide in the gap of aramid fiber which is a polymer of wholly aromatic polyamide. In the case of adopting a paper-like structure in which synthetic pulp, which is a united body, is dispersed, if the average density seems to exceed 0.7 g / cm3, the air permeability is almost lost, and ions move continuously between the positive and negative electrodes. Cannot be used and cannot withstand use as a separator.

As is generally known, the separator has an air permeability according to JIS-P-8117 (Gurley air permeability method) and is 500 sec / cc per separator.
If it seems to exceed, it cannot be used. Furthermore, the thinner the separator, the more preferable it is, but it is usually about 10 to 200 μm. The battery in which the separator of the present invention is used is not limited to a battery of a water-based electrolytic solution, a battery of a non-aqueous electrolytic solution, or the like, but is generally a battery of a high-density non-aqueous electrolytic solution. Especially effective when applied. Among them, especially JP-A-55-1
Nonaqueous electrolysis using, as a positive electrode, a composite compound composed of lithium and a transition metal and, if necessary, a nontransition metal disclosed in JP-A-3613, JP-A-62-90863 and JP-A-63-299056. The effect of using the separator of the present invention is obtained in a liquid secondary battery, particularly in a battery using a carbonaceous material as the negative electrode active material.

Further, a separator as disclosed in JP-A-54-52157, JP-A-59-207230 and the like is used in combination with a separator made of a wholly aromatic polyamide polymer, and the positive electrode and the negative electrode are It is possible to prevent the battery temperature from rising excessively due to a short circuit outside the battery. However, since it is possible to incorporate a PTC element, a current fuse, a temperature fuse, etc. in the battery, it is not always necessary for the separator to have a function of interrupting the ionic current inside the battery when the temperature of the battery rises. is not.

[0012]

According to the above construction, even if the battery is abnormally heated from the outside while being charged, the decomposition gas of the electrolytic solution is rapidly ejected from the battery container together with the fine particles of the active material. It is possible to provide a battery that is unlikely to occur.

[0013]

EXAMPLES Examples will be shown below to explain the present invention in detail. The positive electrode contains 5% of the active material LiCoO2.
To the compound which added the carbon-based conductive filler of
A 5% DMF solution of polyvinylidene fluoride was added to form a suspension, which was uniformly applied to one side of an aluminum foil. The thickness of the coating film is 116 μm. The two positive electrodes created in this way are overlapped with the metal foil surface,
Used as one piece of positive electrode foil of 232 μm.

For the negative electrode, a carbonaceous material having a true specific gravity of 2.3 as an active material was crushed to an average particle size of about 10 μm, and the same amount of a 5% polyvinylidene fluoride DMF solution was added to form a suspension. Was uniformly applied to one surface of a nickel foil or a copper foil. The thickness of the coating film is 139 μm. The two negative electrodes thus prepared are overlaid with a metal foil and used as one positive electrode foil of 278 μm.

The positive electrode, the negative electrode, and the separator constitute an electrode body. The electrode body is a cylindrical type having a large hollow portion by winding a separator between the strip-shaped positive electrode and the negative electrode and winding it around a thick shaft. After forming a coil having a spiral structure, the coil is crushed to form a coil having a flat spiral elliptical cross section. This electrode body is 14mm x 41mm x 66mm
The battery is prepared by using a solution obtained by dissolving the electrolyte LiBF4 in a 1: 1 mixed solvent of 1 mol / l propylene carbonate and γ-butyrolactone as an electrolytic solution.

[0016]

Example 1 A separator is, for example, a breathable paper-like sheet having a structure in which synthetic pulp, which is a polymer of wholly aromatic polyamide, is dispersed in the spaces between aramid fibers, which is a polymer of wholly aromatic polyamide. Nomex paper type 411 made by DUPONT (nominal thickness 5mils, basis weight 39
When a battery is manufactured as described above using g / m2 and an average density of 0.28 g / cm3 when dried, about 200
A lithium ion battery having a discharge capacity of 0 mAh can be obtained.

When this battery was charged to an open circuit voltage of 4.2 V, it was placed on a hot plate heated to about 250 ° C. so that the contact area between the battery container and the hot plate was maximized. Although the battery container was slightly swollen and deformed, no gas or the like was ejected, and no change in appearance was observed even after 1 hour. The withstand voltage of the safety valve of the battery is set to about 20 kg / cm 2.

However, DUPONT Nomex paper type 410 (nominal thickness 2 mils, basis weight 40 g / m 2)
2. The average density when dried is 0.72 g / cm3), which is almost impermeable to air, and cannot be used as a separator for batteries because it cannot be charged or discharged at all even when a battery is manufactured as described above. Absent.

[0019]

Comparative Example 1 In order to make the discharge capacity equal to 2000 mAh as in Example 1, a polypropylene non-woven fabric having a basis weight of 30 g / m 2 and a microporous polyethylene film having a film thickness of 35 μm and a porosity of 60% were laminated and used as a separator. Then, the battery is manufactured as described above. This battery is open voltage 4.2V
With the battery fully charged, place it on a hot plate heated to about 250 ° C so that the contact area between the battery container and the hot plate is maximized. After about 10 minutes, the safety valve will electrolyze along with particles of the active material. The decomposition gas of the liquid is ejected and the battery container is deformed.

The withstand voltage of the battery safety valve is about 20 kg /
It is set to cm2.

[0021]

[Comparative Example 2] A lithium ion battery having a discharge capacity of about 3000 mAh can be obtained by manufacturing a battery as described above using a microporous polyethylene film having a film thickness of 35 µm and a porosity of 60% as a separator. With this battery charged to an open-circuit voltage of 4.2 V, put it on a hot plate heated to about 250 ° C so that the contact area between the battery container and the hot plate is maximized. The decomposition gas of the electrolytic solution is ejected along with the fine particles of the substance, and the battery container is deformed.

The withstand voltage of the battery safety valve is about 20 kg /
It is set to cm2.

[0023]

Comparative Example 3 A lithium ion battery having a discharge capacity of about 3000 mAh can be produced by manufacturing a battery as described above using a microporous polypropylene film having a film thickness of 25 μm and a porosity of 65% as a separator. With this battery charged to an open-circuit voltage of 4.2 V, put it on a hot plate heated to about 250 ° C so that the contact area between the battery container and the hot plate is maximized. The decomposition gas of the electrolytic solution is ejected along with the fine particles of the substance, and the battery container is deformed.

The withstand voltage of the safety valve of the battery is about 20 kg /
It is set to cm2.

[0025]

According to the above construction, even when the battery is placed on a hot plate or the like which is heated to about 250 ° C. in a charged state, the electrolytic solution from the battery container is accompanied by fine particles of the active material. It is possible to provide a battery that does not suddenly eject decomposed gas.

Claims (1)

[Claims] 1. A separator comprising a polymer of wholly aromatic polyamide.