JPH11213980A - Separator for battery and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator capable of remarkably increasing winding speed, and which is thin and compact. SOLUTION: An acrylic adhesive in which graphite is dispersed is applied to both surfaces of a polyethylene film, a polypropylene film, or its composite film to constitute a separator for a battery. The thickness of the adhesive layer is 5-15 μm, the adhering strength to the electrode film is 10 g/2 cm or more, the adhesive layer is porous, the gas transmission rate of the film prescribed in JIS P8117 is 800 sec/100 cc or less, the molecular weight of the acrylic adhesive is 1,000,000 or more, and gel ratio after curing is 90% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator.

[0002]

2. Description of the Related Art In recent years, demand for secondary batteries, including notebook type personal computers, has been increasing. Along with this, there is a growing demand for an improvement in the energy density of the battery, and there is a demand for a lighter and thinner battery case. In addition, diversification of the shape is progressing, and improvement in moldability is expected. A conventional battery is in a state where a separator for separating the battery is sandwiched between a positive electrode and a negative electrode, wound and filled with an electrolyte. However, since the separator and each electrode are not fixed, some gaps are present, which hinders the improvement of the energy density per volume. Further, since both the electrode and the separator are wound simultaneously at the time of winding, the positional accuracy of the film is strictly required, and the winding speed cannot be increased, and it is difficult to improve the productivity.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thinner and more compact separator which can greatly increase the winding speed and replace the conventional adhesive separator.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a battery separator comprising an acrylic adhesive in which graphite or graphite is dispersed on both sides of a polyethylene film, a polypropylene film, or a composite film thereof. The thickness of the adhesive layer is 5 to 15 μm, the adhesive strength with the electrode film is 10 g / 2 cm or more, the adhesive layer is formed porous, and the air permeability of the film according to JIS P8117 is 800 per 100 cc. Second or less, the molecular weight of the acrylic pressure-sensitive adhesive is 1,000,000 or more, and the gel fraction after curing is 90% or more. A more preferred embodiment is a battery separator in which the amount of graphite or graphite added is 700 to 1800 parts by weight based on 100 parts by weight of a binder, and the average particle size of graphite or graphite is 0.1 to 5.0 μm. Also, a thin card battery using these battery separators.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The pressure-sensitive adhesive used in the present invention has a thickness of 5 to 15 μm and an adhesive strength to an electrode film of 1 to 1.
0 g / 2 cm or more. The thickness is preferably 8 to 10 μm
m is good. If it is less than 5 μm, the adhesive strength will be less than 10 g / 2 cm, and a displacement will occur after bonding. On the other hand, when the thickness exceeds 15 μm, the thickness becomes too large, and the distance between the electrode and the separator becomes wider than that of a normal battery.
The amount of graphite or graphite to be added is preferably 700 to 1800 parts by weight, more preferably 800 to 1200 parts by weight, based on 100 parts by weight of the binder. If the amount is less than 700 parts by weight, the pressure-sensitive adhesive layer is not porous. If the amount exceeds 1800 parts by weight, the viscosity is too high at the time of coating, and it is difficult to apply a uniform thickness. The average particle size of these additives is preferably 0.1 to 5.0 μm. When the thickness is less than 0.1 μm, the viscosity increases during the formation of the coating, and it is difficult to form the coating. On the other hand, 5.0μ
If it exceeds m, agglomeration is remarkable and a problem occurs in the stability of the paint.

Further, the air permeability of the porous separator with an adhesive is 800 seconds or less per 100 cc according to JIS P8117, and preferably 500 seconds or less.
If the time exceeds 800 seconds, the ion transfer resistance of Li ions and the like in the electrolytic solution increases, which is not suitable for practical use. The molecular weight of the acrylic pressure-sensitive adhesive used in the present invention is 1,000,000 or more, and the gel fraction after curing is 90% or more. When the molecular weight is less than 1,000,000, the pressure-sensitive adhesive layer is deteriorated by the electrolytic solution. On the other hand, if the gel fraction is less than 90%, the electrolytic solution resistance is similarly poor, which is not suitable for practical use.

[0007]

EXAMPLES The effects of the present invention will be described in detail below with reference to examples, but these are merely examples and the present invention is not limited thereto. The case is made of PP / PE /
A varnish obtained by adding fine particle size graphite in an acrylic adhesive is coated on both sides of a porous multilayer film consisting of three layers of PP, and heat treatment is performed at 40 ° C. for 48 hours. Obtained. The air permeability of the obtained separator was measured according to JIS P8117, and then the separator and the electrode film were bonded together.
In C / EC = 1/1), the mixture was treated at 60 ° C. for 48 hours, the adhesive strength was measured, and the gel fraction of the used adhesive was measured.
Tables 1 and 2 show battery case configurations and measurement results of Examples and Comparative Examples.
3 is shown. Note PP: Polypropylene PE: Polyethylene DEC: Diethylene carbonate EC: Ethylene carbonate

[0008]

[Table 1]

[0009]

[Table 2]

[0010]

[Table 3]

[0011]

According to the present invention, a porous pressure-sensitive adhesive layer having electrolyte resistance to a separator and highly filled with graphite or graphite with a fine particle diameter is formed on both surfaces, and the separator and the electrode are separated from each other. Improving the energy density per volume by providing cell adhesion and reducing the cell volume by eliminating adhesion and eliminating the positioning process when winding the electrode and separator, and producing the winding process during cell assembly A battery with greatly improved performance can be obtained. Such a battery can respond to recent demands for improvement in energy density and productivity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a layer configuration of a separator with an adhesive used in the present invention.

[Explanation of symbols]

 1: adhesive layer 2: PP / PE / PP porous film 3: adhesive layer

Claims (4)

[Claims] 1. A battery separator comprising an acrylic adhesive in which graphite or graphite is dispersed on both sides of a polyethylene film, a polypropylene film, or a composite film thereof, wherein the adhesive layer has a thickness of 5 to 15 μm. And the adhesive strength with the electrode film is 10
g / 2 cm or more, the pressure-sensitive adhesive layer is formed porous, and the air permeability of the film according to JIS P8117 is 1
800 cc or less per 00 cc, the molecular weight of the acrylic pressure-sensitive adhesive is 1,000,000 or more, and the gel fraction after curing is 9
0% or more of a battery separator. 2. The battery separator according to claim 1, wherein the amount of graphite or graphite added is 700 to 1800 parts by weight based on 100 parts by weight of the binder. 3. The battery separator according to claim 1, wherein the graphite or graphite has an average particle size of 0.1 to 5.0 μm. 4. A thin card battery using the battery separator according to claim 1, 2 or 3.