JP2001297744A - Separator for battery and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a battery obtained through polymer including hydrophilic group and a battery with improved performance by restraining a polymer containing a hydrophilic group from isolating in an electrolyte solution. SOLUTION: With the separator for the battery with a part of the surface of an unwoven fabric made of at least a kind of polyolefin system fabric coated with hydrophilic group containing ultra-branched polymer, the hydrophilic group containing ultra-branched polymer should be either grafted in a fabric or make itself formed in a bridging structure, so that it does not get isolated in a electrolyte solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a battery separator and a battery, and more particularly to a battery separator and a battery for an alkaline secondary battery such as a nickel-cadmium battery, a nickel-zinc battery, and a nickel-hydrogen battery.

[0002]

2. Description of the Related Art At present, alkaline secondary batteries such as nickel-cadmium batteries, nickel-zinc batteries and nickel-hydrogen batteries have become widespread as driving power sources for not only small consumer devices but also large devices. Alkaline secondary batteries have characteristics such as high output, high energy density, long life, and high capacity, and are expected to be used in a wide range of industrial fields.

[0003] An alkaline secondary battery is composed of at least a positive electrode, a negative electrode, a battery separator, and an electrolytic solution.
Battery separators used in alkaline secondary batteries have good affinity for electrolyte (alkaline aqueous solution), excellent liquid absorption and liquid retention properties, and can withstand prolonged charge / discharge cycles. Alkaline resistance and oxidation resistance, low internal resistance, sufficient air permeability that does not hinder the permeation of gas and ions generated inside the battery, compatible with battery miniaturization There is a demand for performance such as being a thin film so as to be uniform, having a uniform thickness, and having excellent mechanical strength.

[0004] A nonwoven fabric is generally used as a battery separator satisfying the above characteristics. As the fibers constituting the nonwoven fabric, polyester fibers, polyvinyl chloride fibers, polyvinyl alcohol fibers, polyacrylonitrile fibers, polyamide fibers, polyolefin fibers, and the like are used. As a conventional alkaline secondary battery, in a nickel-cadmium battery which has been generally used, a nonwoven fabric made of a polyamide-based fiber having an excellent affinity for an electrolytic solution is often used.

[0005] In an alkaline secondary battery, when a charged battery is stored at a high temperature, a self-discharge phenomenon in which the capacity is reduced has become a problem. One possible cause is considered to be a reduction reaction of the positive electrode by a decomposition product of the battery separator. In particular, polyamide-based fibers that have been used in nickel-cadmium battery separators have the disadvantage that they are hydrolyzed by the electrolytic solution, so that decomposition products are apt to occur, and the self-discharge phenomenon is promoted. This phenomenon is more problematic in a nickel-hydrogen battery using a hydrogen storage alloy as the negative electrode than in a nickel-cadmium battery.

[0006] For this reason, in nickel-hydrogen batteries, nonwoven fabrics containing polyolefin fibers having excellent alkali resistance and oxidation resistance as main components have come to be used predominantly. However, since polyolefin fibers have low affinity for the electrolyte, sulfonation, graft polymerization of hydrophilic monomers, corona discharge, surfactant immersion,
It is necessary to perform a hydrophilic treatment represented by a hydrophilic group-containing polymer coating treatment.

[0007] Among the above-mentioned hydrophilization treatments, the sulfonation treatment and the graft polymerization treatment involve, in polyolefin fibers, a functional group having an ability to trap impurities such as sulfonic acid groups and carboxylic acid groups and an ion exchange ability to develop an affinity for an electrolytic solution. Since it can be introduced via a chemical bond, there is an advantage that free matter is hardly generated from the separator and the battery is hardly deteriorated. However, since the sulfonation treatment uses concentrated sulfuric acid, there is a disadvantage that the fibers are deteriorated and the mechanical strength of the separator is reduced. In addition, the graft polymerization treatment is a treatment in which a monomer and / or an oligomer having a carboxylic acid group is mainly bonded to a fiber constituting the nonwoven fabric. However, since the monomer having a carboxylic acid group has strong irritation, There is a problem that the working environment in the hydrophilic treatment is deteriorated.

Recently, a method of coating the surface of a fiber constituting a nonwoven fabric with a hydrophilic group-containing polymer has been disclosed as a method having a favorable working environment. However, as the content of the hydrophilic group-containing polymer increases, the viscosity of the solution or dispersion of the polymer increases, and there is a problem that the coating treatment becomes difficult.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery separator obtained by coating a hydrophilic group-containing polymer with high workability, and wherein the hydrophilic group-containing polymer is contained in an electrolytic solution. An object of the present invention is to provide a battery with improved performance by suppressing separation.

[0010]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found the following invention.

That is, (1) in a battery separator in which a part of the fiber surface of a nonwoven fabric made of at least one kind of polyolefin fiber is coated with a hydrophilic group-containing hyperbranched polymer, the polymer is chemically bonded to the fiber. A battery separator characterized in that it is electrically bonded.

(2) In a battery separator comprising a nonwoven fabric made of at least one kind of polyolefin-based fiber, in which a part of the fiber surface is coated with a hydrophilic group-containing hyperbranched polymer, the polymer forms a crosslinked structure. A battery separator, comprising:

(3) A nonwoven fabric made of at least one polyolefin fiber is immersed in a treatment solution containing a hydrophilic group-containing hyperbranched polymer, and then dried to remove a part of the fibers constituting the nonwoven fabric. Battery separator coated with coalescence.

(4) The battery separator according to the above (3), wherein the nonwoven fabric is subjected to a hydrophilic treatment before being immersed in a treatment liquid containing a hydrophilic group-containing hyperbranched polymer.

(5) The battery separator as described in (3) or (4) above, wherein the non-woven fabric immersed in the treatment liquid containing the hydrophilic group-containing hyperbranched polymer is irradiated with actinic rays.

(6) Any one of the above (3) to (5), wherein the nonwoven fabric immersed in a treatment liquid containing a hydrophilic group-containing hyperbranched polymer and then dried is subjected to a hydrophilic treatment. The battery separator as described in the above.

(7) The above (1), wherein the hydrophilic group-containing hyperbranched polymer contains a reactive double bond group.
The battery separator according to any one of (1) to (6).

(8) The battery separator according to any one of (1) to (7), wherein the hydrophilic group-containing hyperbranched polymer is a dendrimer.

(9) When the hydrophilic group is a hydroxyl group, an ether group,
At least one selected from a sulfonic acid group and a carboxylic acid group
The battery separator according to any one of the above (1) to (8), which is a seed.

(10) A battery using the battery separator according to any one of (1) to (9).

Since the battery separator of the present invention is a non-woven fabric made of polyolefin fibers, it has an alkali resistance and an oxidation resistance to an electrolytic solution. Also, since a part of the fiber surface constituting the nonwoven fabric is coated with the hydrophilic group-containing hyperbranched polymer, it has a good affinity for an alkaline electrolyte.

In the case of a battery separator in which a part of the fiber surface constituting the nonwoven fabric is coated with a hydrophilic group-containing hyperbranched polymer, if the amount of the hydrophilic group in the hydrophilic group-containing hyperbranched polymer is large, the said The viscosity of the polymer solution or dispersion increases,
The application method is limited. In addition, there are cases where the coating cannot be applied uniformly to the fiber surface. Since the hydrophilic group-containing polymer according to the battery separator of the present invention is a hyperbranched polymer,
Since the viscosity in a solution state is lower than that of a linear polymer having the same molecular weight, such a problem relating to coating can be solved.

As in the battery separator (1) or (2) of the present invention, a part of the fiber surface is chemically bonded to the hydrophilic group-containing hyperbranched polymer, When the molecule forms a crosslinked structure, the polymer is not released into the electrolytic solution even if the content of the hydrophilic group of the polymer is increased.

In the battery separator (1) or (2) of the present invention, a nonwoven fabric comprising at least one kind of polyolefin fiber is immersed in a treatment liquid containing a hyperbranched polymer having a hydrophilic group, and then dried. Can be obtained by At this time, as in the battery separator (4) of the present invention, if the nonwoven fabric is subjected to a hydrophilic treatment before being immersed in the treatment liquid containing the hydrophilic group-containing hyperbranched polymer, the nonwoven fabric becomes a treatment liquid. Since it is easily wetted, it is not necessary to add a surfactant or the like which deteriorates the characteristics of the battery to the treatment liquid.

Like the battery separator (5) of the present invention, the non-woven fabric immersed in a treatment solution containing a hydrophilic group-containing hyperbranched polymer is irradiated with actinic rays to thereby produce the battery separator (1) of the present invention. Or (2) can be obtained. Further, when the hydrophilic group-containing hyperbranched polymer contains a reactive double bond group, as in the battery separator (7) of the present invention, the battery separator (1) of the present invention or (2) can be obtained.

As in the battery separator (6) of the present invention, the battery separator is immersed in a treatment liquid containing a hydrophilic group-containing hyperbranched polymer,
Next, the dried nonwoven fabric can be subjected to a hydrophilic treatment to increase the affinity for the electrolytic solution.

In the battery separator of the present invention, the hydrophilic group contained in the hydrophilic group-containing hyperbranched polymer includes a hydroxyl group,
Examples thereof include an ether group, a sulfonic acid group, and a carboxylic acid group. In particular, the carboxylic acid group and the sulfonic acid group can trap impurities inside the battery and suppress the self-discharge phenomenon of the battery. In addition, when the hydrophilic group-containing polymer is a hyperbranched polymer and has an ether bond in the molecule, the matrix of the hyperbranched polymer can capture impurities, and has a higher self-discharge suppressing ability. Can be expressed.

In the battery separator of the present invention, when the hyperbranched polymer is a dendrimer, there is an advantage that the molecular weight and the branched terminal group can be quantitatively controlled, and the desired self-discharge suppressing ability and the electrolyte can be obtained. Can be obtained.

In the battery separator of the present invention, the hydrophilic group-containing hyperbranched polymer that partially covers the fiber surface plays a role as a binder, so that the mechanical strength of the battery separator can be increased. Further, since the acid group-containing polymer according to the battery separator of the present invention has low irritancy, it does not adversely affect the human body even during the manufacturing operation.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The hydrophilic group-containing hyperbranched polymer according to the battery separator of the present invention has a structure radially branched from a branch point of a compound serving as a nucleus, for example, a starburst polymer,
Hyperbranched polymers, star polymers, dendrimers and the like can be mentioned. For example, Newk
ome, G .; R. , Et al. , "Dendriti
c Molecules: Concepts, Synt
hesis, Perspectives "; VCH V
erlagsgesellshaft mbH (W
einheim, Germany, 1996), Ha
wker, C.W. J. , Et al. J .; Chem. S
oc. Chem. Commun. , 1990, 10
10, Tomalia, D .; A. , Et al. A
ngew. Chem. Int. Ed. Engl. , 29
Vol., 138 (1990); Hawker, C .;
J. , Et al; Am. Chem. Soc. , 1
12, 7638 (1990), Frechet,
J. M. J. Science, 263, 1710 (1994); A. Tomalia; Nikkei Science,
July, p. 38 (1995), Masaaki Kakimoto; Chemistry, 50
Volume, 608 (1995), Masato Suzuki; Overseas Polymer Research, 65 (1997), Toko Imae, Yoko; Chemistry, 54
Vol. 72, (1999); Fisher, M .; , Et
Al. Angew. Chem. Int. Ed. ,
38, 884 (1999), Smith, D .;
K. , Et al. Chem. Eur. J. , 4,1
It is described in documents such as page 353 (1998). Among them, the dendrimer can be more preferably used because the molecular weight and the branched terminal group can be easily controlled.

The hydrophilic group-containing hyperbranched polymer according to the battery separator of the present invention can be obtained by (1) a synthesis method of increasing the number of generations from a base nucleus by a stepwise synthesis reaction, and (2) a polyfunctional monomer. It can be synthesized by polycondensation or polyaddition, (3) chain polymerization of monomers having both polymerization initiation ability, and (4) multi-branch polymerization. Among them, in the method (1), the compounds serving as branch components necessary for constituting each generation are gradually reacted, so that the molecular weight can be controlled. (1) is D
The average method (a method of constructing a molecule outward from a base nucleus) and the Convergent method (a method of synthesizing structural units at the terminal of a molecule, sequentially linking these to a high molecular weight, and finally bonding the molecule to the base nucleus) ), And either method may be used. Among them, the dendrimer synthesized in (1) can be more preferably used because the molecular weight and the branched terminal group can be easily controlled. FIG. 1 is a conceptual diagram of each generation of dendrimer.

Examples of the structure of the dendrimer relating to the battery separator of the present invention include those described in Newkome, G .;
R. , Et al. , “Dendritic Mole
cules: Concepts, Synthesis,
Perspectives "; VCH Verlags
Gesellshaft mbH (Weinhei
m, Germany, 1996), and B
uhleier, E .; , Et al. Synthes;
is, p. 155 (1978), de Braband
er-van den Berg, E .; M. M. , Et
al. Angew. Chem. Int. Ed. En
gl. 32, p. 1308 (1993), the polypropylene imine structure, Hawker, C .;
J. , Et al. J .; Am. Chem. Soc. ,
112, p. 7638 (1990); Hawker, C .; J. ,
et al. J .; Am. Chem. Soc. , 113
Vol., P.4583 (1991), the aromatic polyester structure, Malmstorm, E. et al. , Et
al. Macromolecules, 28, 16
Poly [2,2-) reported on page 98 (1995).
Bis (hydroxymethyl) propionic acid] structure, Uch
ida, H .; , Et al. J .; Am. Chem. S
oc. , 112, 7077 (1990), Mor
Ikawa, A .; , Et al. ; Polymer
J. , 24, p. 573 (1992), by Roovers, J. et al. , Et
al. Polym. Preprints, Volume 33, 1
82, (1992), Moore, J. et al. S. , Et al. ; Mac
romolecules, 24, 5893 (199
1 year), Kawaguchi, T .; , Et al. ;
J. Am. Chem. Soc. Vol. 117, p. 2159 (1995), a polyphenylene acetylene structure, Newkome, G .; R. , Et al. ,
J. Org. Chem. , 50, 2003 (198
5 years), the polyether amide structure, T
omalia, D .; A. , Et al, Angew. C
hem. Int. Ed. Engl. 29, p. 138 (1990), the polyamidoamine structure described in Jayaraman, M .; , Et al; A
m. Chem. Soc. 120, 12996 (1
998), Sunder, A .; , Et al. ; Ma
cromolecules, 32, 4240 (19
(1999).

Of these, the alkaline secondary battery preferably has a polypropylene imine structure, a polybenzyl ether structure, a polyphenylene acetylene structure, a polyether amide structure, a polyamidoamine structure, or an aliphatic polyether structure. In particular, in nickel-hydrogen secondary batteries, there are no bonds susceptible to hydrolysis, such as ester bonds and amide bonds, and there is no nitrogen-containing polybenzyl ether structure or aliphatic polyether structure that promotes the self-discharge phenomenon. Is most preferred. The polyether bond can capture a polyvalent metal ion as an impurity and suppress the self-discharge phenomenon of the battery.

The molecular weight of the hydrophilic group-containing hyperbranched polymer relating to the battery separator of the present invention is 300 to 10,000.
0, more preferably 700 to 40,000. In addition, by making the branched terminal group a hydroxyl group, a sulfonic acid group, or a carboxylic acid group, the affinity for the electrolyte of the battery separator and the ability to suppress self-discharge can be improved.

In the battery separator of the present invention, in order to coat a part of the fiber surface of the nonwoven fabric with the hyperbranched polymer having a hydrophilic group, the treatment liquid containing the polymer is subjected to dip coating, rod coating, knife coating. , Reverse roll coating, screen coating,
Generally, a method of applying to a nonwoven fabric by a coating method such as gravure roll coating, screen printing coating, or spray coating, followed by drying. The treatment liquid may be either a dispersion liquid or a homogeneous solution.

Examples of the medium that can be used for the treatment liquid containing the hydrophilic group-containing hyperbranched polymer relating to the battery separator of the present invention include water, toluene, xylene, cyclohexane, methylcyclohexane, petroleum distillate, methanol , Ethanol, n-propanol, isopropanol, butanol, tetrahydrofuran, dioxane,
Dioxolan, methyl cellosolve, ethyl cellosolve,
Cellosolve acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl acetate, ethyl acetate, butyl acetate, methylene chloride, tricrene and the like can be mentioned. Further, in order to improve workability, a surfactant or the like may be added as a wetting agent or a defoaming agent.

The hyperbranched polymer containing a hydrophilic group according to the battery separator of the present invention may form a crosslinked structure at the stage of synthesis to reduce the solubility in an electrolytic solution. Also,
After immersing the non-woven fabric in the processing solution,
Irradiation with actinic light such as γ-rays, electron beams, X-rays, and neutron rays) to form a crosslinked structure, or a chemical bond between a part of the fiber and a hyperbranched polymer containing a hydrophilic group. May be formed. Of these, ultraviolet rays are the most suitable because they hardly degrade the fibers of the nonwoven fabric. When irradiating with ultraviolet light, as a sensitizer, for example, has an acetophenone structure such as benzoin butyl ether, benzoin ethyl ether, benzyl dimethyl ketal, diethoxy acetophenone, acyloxyme ester, chlorinated acetophenone, hydroxyacetophenone, and acylphosphine oxide. It is possible to use a sensitizer, a sensitizer having a thioxanson structure such as 2-ethylanthraquinone, benzophenone, Michler's ketone, dibenzosuberone, isobutylthioxanson, or benzyl, a peroxide such as benzoyl peroxide, or a metal ion. it can.

In the battery separator of the present invention, the non-woven fabric before immersion in the treatment liquid containing the hydrophilic group-containing hyperbranched polymer or the non-woven fabric dried after immersion includes the following hydrophilic treatment. For example, corona discharge treatment, glow discharge treatment, plasma discharge treatment, ultraviolet irradiation treatment, and the like can be given.

The polyolefin fiber of the battery separator of the present invention is a fiber composed of a polyolefin alone or a fiber composed of a copolymer of an olefin and another monomer. Further, a blended fiber of a polyolefin fiber and another fiber may be used. Examples of the (poly) olefin include (poly) ethylene, (poly) propylene, (poly) methylpentene, (poly) butene, (poly) ethylene-propylene, and (poly) ethylene-butene-propylene. . Other monomers copolymerizable with the olefin include vinyl acetate, vinyl butyrate, and vinyl alcohol (polymerization of vinyl acetate followed by saponification).

The cross-sectional shape of the fiber which can be used for the non-woven fabric according to the battery separator of the present invention is not particularly limited, and may be circular, elliptical, triangular, star-shaped, T-shaped, U-shaped, Y-shaped, or the like.
A leaf shape or the like can be used. Further, fibers having voids can also be used.

The fibers which can be used for the nonwoven fabric of the battery separator of the present invention preferably have a fiber diameter of 1 to 30 μm. In addition, it is preferable to use at least one kind of fine fiber having a fiber diameter of 1 to 10 μm. If the fiber diameter is smaller than 1 μm, the nonwoven fabric becomes too dense, and the air permeability decreases. Conversely, when the thickness is larger than 30 μm, the porosity increases, but the specific surface area decreases, and the liquid retention property decreases. Further, the fiber length is preferably 1 to 50 mm. Fiber length is 50mm
If it exceeds, fibers are entangled in the production of the nonwoven fabric, and the uniformity of the battery separator is lost. The fine fibers may be fibers obtained by splitting splittable conjugate fibers. In particular, among the splittable conjugate fibers, split fibers made of a polyolefin and an ethylene-vinyl alcohol copolymer are preferable.

In the nonwoven fabric according to the battery separator of the present invention, the splittable conjugate fiber can be split by a mechanical shearing force of a beater, a pulper, a refiner or the like, or split by a hydroentanglement treatment.

The nonwoven fabric relating to the battery separator of the present invention can be produced by either a dry method or a wet method.
In order to cope with thinning, it is preferable to use a nonwoven fabric manufactured by a wet method.

[0044]

The present invention will be described below in detail with reference to examples. Example 1 Production of Nonwoven Fabric Split conjugate fiber 80 having a fineness of 3 denier composed of polypropylene and an ethylene-vinyl alcohol copolymer, 0.2 denier (3.9 μm) after fiber division, and a fiber length of 10 mm
1.5 parts denier, fiber length 1 consisting of parts by weight, polypropylene as a core component and polyethylene as a sheath component
A nonionic surfactant 1% by weight solution impregnated with 0 mm core-sheath fiber 19 parts by weight, and a bacterial cellulose 1 part by weight (dry weight) were impregnated with a nonionic surfactant 1% by weight solution. The mixture was put into water and stirred with a high-speed mixer for 3 minutes to disintegrate the fibers, followed by gentle stirring in a chest equipped with a reciprocating rotary stirrer (Agitator, manufactured by Shimazaki Seisakusho). As bacterial cellulose, purified bacterial cellulose obtained by the method described in Examples of JP-A-9-25302 was used. Then, a 0.1% by weight aqueous solution of polyacrylamide (viscosity agent) was immediately added as appropriate, and the mixture was stirred gently to prepare a uniform slurry. Using this slurry, a round mesh paper machine was used to
cm, a nonwoven fabric having a basis weight of 50 g / m ² was produced.

Water entanglement treatment The above web was conveyed onto a porous support made of a 100-mesh stainless wire, and was subjected to columnar water flow using five nozzle heads having the conditions shown in Table 1 and tap water.
Both sides were entangled. By the hydroentanglement treatment, 9
5% of splittable conjugate fibers were split into fine fibers. The speed of the entanglement treatment was 20 m / min, and after the entanglement, the mixture was dried at 110 ° C. with a suction drum dryer to obtain a wet-type hydroentangled nonwoven fabric I.

[0046]

[Table 1] {Head number 1 2 3 4 5}ノ ズ ル Nozzle diameter (μm) 120 100 100 100 80 Nozzle interval (mm) 1.2 0.6 0.6 0.6 0.8 Number of rows 2 1 1 1 2 Pressure (kg / cm ² ) 125 125 125 125 10 ──────────────────────────── ────────

Synthesis of Synthetic Compound A of Hyperbranched Polymer Containing Hydrophilic Group 6.7 parts by weight of 1,1,1-tris (hydroxyl) propane in 30% potassium methoxide methanol solution 3.1
After adding 2 parts by weight and melting by heating, methanol was distilled off under reduced pressure. At a bath temperature of 95 to 100 ° C, 11.1 parts by weight of glycidol was slowly added while heating and stirring. After the exothermic reaction occurred, 22.2 parts by weight of glycidol was slowly added dropwise again. 44.4 parts by weight, then 88.
8 parts by weight, 177.6 parts by weight and glycidol were slowly added. Next, 68 parts by weight of glycidyl allyl ether was added, and after the completion of dropping, the mixture was further reacted at the same temperature for 20 minutes (dropping time: about 2.5 hours). After cooling, the reaction mixture was dissolved in 4 L of methanol, and the generated potassium carbonate was removed by filtration through a carbon dioxide gas. The methanol solution was poured into a sufficient amount of acetone, precipitated, the solvent was removed by decantation, and the mixture was dried at 80 ° C. Thus, a hydrophilic group-containing hyperbranched polymer A having a vinyl group at a branched terminal was obtained.

After the corona discharge treatment (total energy per side: 18 kW · min / m ² ) was applied to both surfaces of the non-woven fabric I treated with a hydrophilic group-containing hyperbranched polymer, and impregnated with the preparation shown in Table 2 A 110-watt low-pressure mercury lamp was placed on both sides of the nonwoven fabric at a distance of 3 cm under deoxygenation, irradiated with ultraviolet rays for 90 seconds, and dried. Subsequently, pressure treatment was performed with a 135 ° C. heat roll to obtain a battery separator a. The battery separator a had a basis weight of 53 g / m ² , an acid group-containing composition adhesion amount of 2.5 g / m ² , and a thickness of 170 μm.

[0049]

[Table 2]

Comparative Example 1 The non-woven fabric I having a hydrophilic group-containing polymer fixed thereon was impregnated with the preparation solution shown in Table 3, then pressure-treated with a hot roll at 135 ° C., dried, and the acid group-containing composition was dried. This was fixed to obtain a battery separator a. The battery separator a had a basis weight of 52 g / m ² , an acid group-containing composition adhesion amount of 2.4 g / m ² , and a thickness of 170 μm.

[0051]

[Table 3]

The following characteristics were evaluated for the battery separator and the battery separator a. As a comparative example, a battery separator z, a grafted polyolefin-based fiber-containing nonwoven fabric x used as a separator in a commercially available nickel-hydrogen battery (basis weight 50 g / m ² ,
Thickness 220 μm) and non-woven fabric y containing sulfonated polyolefin fiber (basis weight 58 g / m ² , thickness 280)
μm) was evaluated in the same manner, and the results are summarized in Table 4.

(I) Liquid absorption rate: A 2.5 × 18 cm test piece was sampled from each battery separator, preliminarily dried at 40 ± 5 ° C. to reduce the water content to the official moisture content or less, and then the test piece was removed. The specimen was left in a standard temperature and humidity test room, and then weighed at intervals of one hour or more. The mass difference before and after the measurement was within 0.1% of the subsequent mass (moisture equilibrium state). . Next, the test pieces were hung down on a water tank containing a potassium hydroxide solution having a specific gravity of 1.3 at 20 ± 2 ° C., with the lower ends thereof aligned with a horizontal bar having a predetermined height, and the horizontal bars were lowered to lower each test piece. The lower end of the sample was not immersed in the liquid by 5 mm, and the height (m) of the potassium hydroxide solution increased by capillary action after 5 minutes.
m) was measured.

(Ii) Electrolyte retention rate: A test piece having a size of 10 × 10 cm was sampled from each battery separator, and the weight when water equilibrium was established was defined as W (g). Next, the test piece was spread and immersed in the potassium hydroxide solution, allowed to stand for one hour or more, taken out of the solution, suspended at one corner of the test piece, and measured for weight W ₁ after 10 minutes. The electrolyte retention rate (%) was calculated from the following equation (1).

[0055]

## EQU1 ## Electrolyte retention rate (%) = [(W ₁ −W) / W] × 100

(Iii) Tensile strength: When wound around an electrode plate, the tensile strength (N) in the longitudinal (papermaking flow) direction is a measure of the strength required for winding while pulling in the flow direction.
/ M) was measured. The tensile strength is JIS-P-8113
With each battery separator, width 2cm, length 20cm
And a Tensilon measuring machine (Orientec; H
Using TM-100), the load at break was measured 10 times, and the average value was shown. (Iv) Air permeability: Frazier air permeability (cm ³ / cm ² / sec) was measured as an evaluation of the ease with which oxygen generated from the positive electrode side passes through the battery separator to the negative electrode side.
As for the Frazier air permeability, the air amount passing through the test piece was measured five times using a Frazier-type air permeability tester according to JIS-L-1096, and the average value was shown.

(V) Battery self-discharge characteristics: Foamed nickel electrode as positive electrode, hydrogen storage alloy as negative electrode, potassium hydroxide solution with specific gravity of 1.3 as electrolyte, and separators for batteries of Examples and Comparative Examples as separators A nickel-hydrogen battery was manufactured using each of the separators. One of these batteries
After the battery was charged at a constant current of 120% at C, the battery was discharged at a constant current of 1 C until the battery voltage reached 1.0 V, and the initial discharge capacity V ₁ was measured. Next, when charging at 120% constant current at 1 C, 6
After being left in a thermostat at 0 ° C. for 3 days, the battery was discharged at a constant current of 1 C, the discharge capacity V ₂ was measured, and the capacity storage rate (%) was obtained from the following equation (2).

[0058]

[Equation 2] Capacity storage rate (%) = (V ₂ / V ₁ ) × 100

(Vii) Electrolyte absorption rate after alkali treatment: A 2.5 × 18 cm test piece was collected from each battery separator and immersed in a potassium hydroxide solution having a specific gravity of 1.3 at 70 ° C. for 3 days. Then, it was washed with ion-exchanged water until neutral. After that, pre-drying was performed at 40 ± 5 ° C. to make the moisture content equal to or less than the official moisture content, and the test piece was left in a test room in a standard temperature / humidity state. The mass difference between before and after is within 0.1% of the mass after (moisture equilibrium state). Next, the test piece was
A horizontal bar of a predetermined height is fixed on a water tank containing a potassium hydroxide solution having a specific gravity of 1.3 ° C., and the lower end thereof is fixed to a horizontal bar, and the horizontal bar is lowered. The height (mm) at which the potassium hydroxide solution rose by capillary action after 30 minutes was measured,
It was used as an index of alkali resistance.

[0060]

[Table 4]

Since the battery separator a of the present invention does not require a washing step such as a grafting treatment and a sulfonation treatment, it can be manufactured under a favorable working environment. Further, the mechanical strength of the battery separator did not decrease as in the sulfonation treatment.

In Example 1, since the prepared solution containing the hyperbranched polymer was used as the hydrophilic group-containing hyperbranched polymer, the viscosity of the prepared solution was low, and the obtained battery separator a was Observation with a microscope revealed that the fibers were almost uniformly coated with the hydrophilic group-containing hyperbranched polymer. In Comparative Example 1, the viscosity of the preparation liquid was high, and the hydrophilic group-containing polymer formed a film on the surface of the nonwoven fabric. Therefore, although the battery separator z uses the same nonwoven fabric as the battery separator a, and the amount of the attached hydrophilic polymer is almost the same, the air permeability is low. Therefore, the nickel-hydrogen battery manufactured using the battery separator z had a very high internal resistance of the battery and did not operate normally.

The battery separator a of the present invention is mainly composed of a polyolefin-based nonwoven fabric having a low affinity for an electrolytic solution, but exhibits a high affinity for an electrolytic solution due to the effect of a hydrophilic group-containing hyperbranched polymer. Was. Also, after alkali treatment,
As in the battery separator z of the comparative example, the hydrophilic group-containing polymer did not fall and showed a high liquid absorption rate. Further, other characteristics were comparable to those of the battery separators x and y of the commercially available batteries. It was confirmed that the self-discharge suppressing effect of the battery using the battery separator a of the present invention was higher than that of a commercially available battery.

[0064]

As described above, the battery separator of the present invention can be obtained with good workability. In addition, it has excellent characteristics in terms of affinity with an electrolytic solution and mechanical strength, and also has excellent resistance to an electrolytic solution. Therefore, the battery of the present invention using the battery separator of the present invention exhibits excellent self-discharge suppressing ability.

[Brief description of the drawings]

Fig. 1 Conceptual diagram of each generation of dendrimer

[Explanation of symbols]

 1 nucleus

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H021 BB09 BB12 BB13 BB15 CC02 CC04 EE04 EE15 EE17 EE34 EE39

Claims (10)

[Claims] 1. A battery separator comprising a nonwoven fabric comprising at least one kind of polyolefin-based fiber, wherein a part of the fiber surface is coated with a hydrophilic group-containing hyperbranched polymer, wherein the polymer is chemically bonded to the fiber. A battery separator characterized in that: 2. A battery separator comprising a nonwoven fabric made of at least one kind of polyolefin-based fiber and a part of the fiber surface coated with a hydrophilic group-containing hyperbranched polymer, wherein the polymer forms a crosslinked structure. A battery separator. 3. A nonwoven fabric comprising at least one kind of polyolefin-based fiber is immersed in a treatment liquid containing a hyperbranched polymer having a hydrophilic group, and then dried to remove a part of the fibers constituting the nonwoven fabric from the copolymer. Battery separator coated with. 4. The battery separator according to claim 3, wherein the nonwoven fabric has been subjected to a hydrophilic treatment before being immersed in a treatment solution containing a hydrophilic group-containing hyperbranched polymer. 5. The battery separator according to claim 3, wherein the non-woven fabric immersed in the treatment liquid containing the hydrophilic group-containing hyperbranched polymer is irradiated with an actinic ray. 6. The battery according to claim 3, wherein the nonwoven fabric is immersed in a treatment liquid containing a hydrophilic group-containing hyperbranched polymer, and then subjected to a hydrophilic treatment. Separator. 7. The battery separator according to claim 1, wherein the hydrophilic group-containing hyperbranched polymer contains a reactive double bond group. 8. The battery separator according to claim 1, wherein the hydrophilic group-containing hyperbranched polymer is a dendrimer. 9. The battery separator according to claim 1, wherein the hydrophilic group is at least one selected from a hydroxyl group, an ether group, a sulfonic acid group, and a carboxylic acid group. 10. A battery using the battery separator according to claim 1.