JP3101058B2 - Battery separator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator used in a battery for preventing a short circuit between positive and negative electrodes.

[0002]

2. Description of the Related Art Separators that are incorporated in batteries such as silver oxide batteries and mercury batteries and that prevent short circuit between positive and negative electrodes have a small thickness, excellent ionic conductivity, and a positive electrode active material such as silver ions. It is required to have a function of suppressing the permeation of a substance.

A graft membrane is known as such a separator. For example, U.S. Pat. No. 3,427,206 describes a battery separator in which a polyolefin film is graft-copolymerized with an ethylenically unsaturated carboxylic acid such as acrylic acid or methacrylic acid. Describes a battery separator in which acrylic acid or methacrylic acid is graft-copolymerized on a non-stretched polymer film.

[0004]

In order to incorporate a separator into a battery, first, the separator is punched into a predetermined size and shape, and then the separator is loaded into a battery case. Swells when it comes into contact with an electrolytic solution such as a KOH aqueous solution or an NaOH aqueous solution in the case. Although the degree of swelling varies somewhat depending on the type of grafted monomer, grafting ratio, etc., swelling of about 10% often occurs. When the separator swells, it becomes wrinkled, causing an increase in the internal resistance of the battery or causing a local battery reaction to shorten the battery life.

According to the latter graft film using an unstretched film, the degree of swelling upon contact with an electrolytic solution can be reduced, but there is technical difficulty in producing the unstretched film.

Accordingly, it is an object of the present invention to provide a separator having a small degree of swelling upon contact with an electrolytic solution by a simple method.

[0007]

Means for Solving the Problems To achieve such an object, the present inventors have made intensive studies and found that the degree of swelling in an electrolytic solution can be reduced by adding a specific amount of water to a graft membrane. The present invention has been completed.

That is, the battery separator according to the present invention is characterized in that a vinyl monomer capable of imparting conductivity to a plastic substrate is graft-copolymerized and contains 5 to 30% by weight of water. Is what you do.

The plastic base material used in the present invention includes polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, Thermoplastics such as acrylonitrile, polycarbonate, polystyrene, polyamide, polyvinyl alcohol, polydimethylsiloxane, and ethylene-propylene terpolymer can be used without particular limitation. The shape of the plastic substrate may be a film, a porous film, a woven fabric, a nonwoven fabric, or the like. The thickness of the substrate is not limited, but is usually about 10 to 200 μm.

A vinyl monomer capable of imparting conductivity is graft-copolymerized on the plastic substrate. As the vinyl monomer, a carboxyl group, an amino group, a quaternized amino group, a sulfone group, a phosphone group, a phosphine, which can directly form a salt by being graft-copolymerized on a plastic substrate and then reacted with an acid or a base. Group, a compound having a functional group such as a phenolic hydroxyl group in the molecule or an anhydride thereof, and a functional group capable of forming a salt by reacting with an acid or a base such as styrene in the molecule. However, those which can introduce a functional group capable of forming a salt by means such as sulfonation after graft copolymerization can also be used.

Specific examples of such vinyl monomers include those having a carboxyl group, such as acrylic acid and α.
-Ethylacrylic acid, β-ethylacrylic acid, α-pentylacrylic acid, β-nonylacrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and the like, and examples of the anhydride include maleic anhydride and the like. Can be

Examples of the vinyl monomer having an amino group include N-vinylphenylamine, allylamine, diallylamine, triallylamine, vinylpyridine, methylvinylpyridine, ethylvinylpidazine, vinylpyrrolidone, vinylcarbazole, vinylimidazole,
Aminostyrene, alkylaminostyrene, dialkylaminostyrene, trialkylaminostyrene, dimethylaminoethyl methacrylate, diethylamino methacrylate, dicyclohexylaminoethyl methacrylate, di-n-propylaminoethyl methacrylate, t
-Butylaminoethyl methacrylate, diethylaminoethyl acrylate, and the like are used, and as the monomer having a quaternary amino group, hydrochloride, sulfate, nitrate, phosphate, and the like of the vinyl monomer having the amino group are used.

Further, vinyl monomers having a sulfone group include styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate, 3-chloro-4-vinylbenzene sulfonic acid, and 2-cyclylamide-2-. Methylpropylsulfonic acid, 2-acryloyloxybenzenesulfonic acid, 2-acryloyloxynaphthalene-2-sulfonic acid, 2-methacryloyloxynaphthalene-2-sulfonic acid and the like are used.

Next, vinyl monomers having a phosphon group include allylphosphonic acid, acid phosphoxyethyl methacrylate, 3-chloro-2-acid phosphoxypropyl methacrylate, 1-methylvinylphosphonic acid, 1-phenylvinylphosphonic acid, 2-phenylvinylphosphonic acid, 2-methyl-2-phenylvinylphosphonic acid, 2- (3-chlorophenyl) vinylphosphonic acid,
2-diphenylvinylphosphonic acid and the like.

The vinyl monomers having a phosphine group include allylphosphinic acid, and those having a phenolic hydroxyl group include O-oxystyrene and O-vinylanisole.

In the present invention, when acrylic acid and / or methacrylic acid is used as a vinyl monomer to be graft-copolymerized on a plastic substrate, the monomer is selected from hydroxyalkyl acrylate or hydroxyalkyl methacrylate together with this monomer. At least one monomer can be graft copolymerized. As such an alkyl ester, those having an alkyl group having 1 to 4 carbon atoms are preferred, and hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxy methacrylate are preferred. Specific examples thereof include oxymethyl, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

[0017] The battery separator obtained by graft-copolymerizing the above-mentioned hydroxyalkyl ester together with acrylic acid and / or methacrylic acid on a plastic substrate has improved oxidation resistance. In such an embodiment, the composition ratio after the graft copolymerization is preferably such that the amount of the hydroxyalkyl ester unit is 100 parts by weight or less based on 100 parts by weight of the acrylic acid or methacrylic acid unit. It turns out that.

A method for obtaining a battery separator by graft copolymerizing a vinyl monomer onto a plastic substrate is described in US Pat. No. 3,427,206 or JP-A-54-140136. Contacting the substrate with the vinyl monomer,
Simultaneous irradiation method of irradiating this with radiation such as electron beam and graft copolymerization, or irradiating the plastic substrate with radiation in the presence of oxygen to generate peroxide and hydroperoxide on the substrate, Since the pre-irradiation method in which the base material is brought into contact with a vinyl monomer to carry out graft copolymerization is already known, these methods can also be employed to obtain the battery separator of the present invention. The graft ratio of the battery separator according to the present invention is appropriately set depending on the type of the monomer to be graft-copolymerized, but is usually about 20 to 80%.

The battery separator according to the present invention is obtained by graft copolymerizing a vinyl monomer onto a plastic substrate as described above, and then contacting with water to reduce the moisture content to 5 to 3%.
0 wt%, preferably 10 to 20 wt%. Prior to contact with water,
A salt can also be formed by contacting with a liquid having the same composition as an electrolytic solution such as an aqueous KOH solution or an aqueous NaOH solution.
If the water content is too low, the degree of swelling when contacting the electrolytic solution in the battery cannot be reduced, and if it is too high, the concentration of the electrolytic solution will change when loaded into the battery. .

Since the battery separator according to the present invention needs to contain the above-mentioned predetermined amount of water until it is loaded into the battery, it is preferable to store the battery separator sealed with a moisture-impermeable material such as a plastic film. preferable. Further, this separator can be used as a simple substance consisting of itself, but can also be used by being laminated with cellophane, a porous plastic film, a woven fabric, a nonwoven fabric, or the like.

[0021]

The present invention will be described in more detail with reference to the following examples.

Example 1 A polyethylene film having a thickness of 25 μm was exposed to air at 20 M
After irradiating the rad with an electron beam, it is immersed in a 40% by weight aqueous solution of methacrylic acid and heated at a temperature of 40 ° C. for 7 hours for graft copolymerization (graft ratio: 45%).

This graft membrane is immersed in a KOH aqueous solution (KOH concentration 40% by weight) to form a potassium salt, and then immersed in water to obtain a separator having a water content of 30% by weight. And sealed.

The water content (%) is determined by weighing the weight (W ₁ ) of the separator in a water-containing state and the weight (W ₂ ) after heating and drying the separator at a temperature of 60 ° C. for 2 hours. This is the value calculated in 1.

[0025]

(Equation 1)

Example 2 The procedure of Example 1 was repeated except that the graft copolymerization time was changed to 6 hours to obtain a graft membrane having a graft ratio of 39%.

The graft membrane was immersed in a KOH aqueous solution (KOH concentration 40% by weight) to form a potassium salt, and then immersed in water to obtain a separator having a water content of 12% by weight. And sealed.

Example 3 Example 1 except that the graft copolymerization time was 5 hours.
In the same manner as described above, a graft membrane having a graft ratio of 35% is obtained.

The graft membrane was immersed in a KOH aqueous solution (KOH concentration: 40% by weight) to form a potassium salt, and then immersed in water to obtain a separator having a water content of 6% by weight. And sealed.

Example 4 The separator obtained in Example 2 and cellophane were overlapped and adhered to obtain a two-layered separator, which was sandwiched between two polyethylene films and sealed.

COMPARATIVE EXAMPLE The graft membrane in Example 1 was replaced with a KOH aqueous solution (KOH concentration 4
0% by weight) to form a potassium salt, washed with water and dried to obtain a separator having a water content of 3% by weight.

The properties of the separators obtained in the above Examples and Comparative Examples were tested as follows, and the results are shown in Table 1. In Table 1, the unit of the water content and the degree of swelling are “%”, the unit of the electric resistance is “Ω · cm ² ”. "X" indicates that no wrinkles were generated by immersion.

A. Electric resistance Measured according to JIS C2313. Note that a KOH aqueous solution (KOH concentration: 40% by weight) was used as an electrolyte. The liquid temperature at the time of measurement was 25 ° C.

B. Swelling degree The separator was cut so that the vertical and horizontal dimensions were each 100 mm, and this was cut into a 25 ° C. KOH aqueous solution (KOH concentration 4).
0% by weight) and taken out, and the area (Smm ² ) was calculated from the dimensions after the removal, and the area (Smm ² ) was obtained by the following equation ( ² ).

[0035]

(Equation 2)

C. Electrolyte immersion test The separator was punched out into a circle having a diameter of 5 cm, the outer periphery thereof was fixed with a jig, and a 25 ° C KOH aqueous solution (KOH concentration 40
% By weight) for 20 hours, and the occurrence of wrinkles was visually observed.

[0037]

[0038]

According to the present invention, a separator having a small degree of swelling even when it comes into contact with an electrolytic solution can be provided by a simple means of allowing the graft membrane to contain water as described above.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Yamaguchi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nippon Denko Corporation Examiner Masayuki Miyake (56) References JP-A-54-22535 (JP, A) JP-A-54-148228 (JP, A) JP-A-58-93157 (JP, A) JP-A-53-78535 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) H01M 2/14-2/18

Claims (2)

(57) [Claims] 1. A plastic substrate, wherein a vinyl monomer capable of imparting conductivity is graft-copolymerized, and
A battery separator containing 30% by weight of water. 2. A plastic substrate, wherein at least one of acrylic acid or methacrylic acid and at least one monomer selected from hydroxyalkyl acrylate or hydroxyalkyl methacrylate are graft-copolymerized, and A battery separator containing 30% by weight of water.