JPH1196989A - Separator for battery and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide battery separator with excellent affinity with electrolyte and a battery using the battery separator. SOLUTION: This separator is made by applying hydrophilic treatment to nonwoven fabric of at least one kind of polyorefinic fiber by using silicone surfactant with alkoxy group. Since the silicone surfactant contains polyalkyleneoxide group and acid group, it has further excellent affinity with electrolyte, and in addition, since the polyorefinic fiber is a divided type compound fiber and the nonwoven fabric is made by wet manufacturing and/or stream interlacing, battery performance is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates 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, which have excellent compatibility with an electrolytic solution and high performance. The present invention relates to a battery separator exhibiting a liquid absorbing property and a liquid retaining property, and a battery using the battery separator.

[0002]

2. Description of the Related Art At present, alkaline secondary batteries such as nickel-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries, etc., have become widespread as driving power supplies for large-sized appliances such as small consumer appliances and automobiles. Alkaline secondary batteries are
It has characteristics such as high output, high energy density, long life, and high capacity, and is used in a wide range of industrial fields.

An alkaline secondary battery is composed of at least a positive electrode, a negative electrode, a battery separator, and an electrolyte. Battery separators used in alkaline secondary batteries include:
It has good affinity with electrolyte solution (alkaline aqueous solution), excellent liquid absorption rate and liquid retention property, and has alkali resistance and oxidation resistance that can withstand repeated charge and discharge for a long time. It has a low internal resistance, has sufficient permeability not to hinder the transmission of gas and ions generated inside the battery, and has a uniform thickness and mechanical thickness Performance such as excellent strength is required.

As a battery separator satisfying the above characteristics, a nonwoven fabric is generally used. As 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, a nickel-cadmium battery generally used in many cases uses a nonwoven fabric made of a polyamide fiber having an excellent affinity for an electrolytic solution.

[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, since polyamide fibers are hydrolyzed by an electrolytic solution, they have a disadvantage that decomposition products are easily generated and a self-discharge phenomenon is promoted. This self-discharge phenomenon is more problematic in nickel-hydrogen batteries using a hydrogen storage alloy as the negative electrode.

[0006] For this reason, nonwoven fabrics containing polyolefin-based fibers having excellent alkali resistance and oxidation resistance as main components have come to be used predominantly. However, since the polyolefin fiber has a low affinity for the electrolytic solution, it is necessary to perform a hydrophilic treatment such as a sulfonation treatment, a grafting treatment of a hydrophilic monomer, a corona discharge treatment, and a surfactant immersion treatment.

[0007] Among the above-mentioned hydrophilic treatments, the sulfonation treatment and the grafting treatment can introduce ion exchange groups such as sulfonic acid groups and carboxylic acid groups into the polyolefin-based fiber. Has the advantage that it is not released from the polyolefin fiber. Further, it is considered that the ion exchange group can capture impurities such as nitrogen compounds and polyvalent metal ions contained in the battery and improve battery characteristics. However, the sulfonation treatment and the grafting treatment have disadvantages such as a high treatment cost and a decrease in the mechanical strength of the battery separator due to fiber deterioration.

The hydrophilization treatment by corona discharge treatment has a problem that the hydrophilicity decreases with time. Further, in the surfactant immersion treatment, there is a problem that the surfactant is released from the nonwoven fabric in the battery, which may promote the self-discharge phenomenon of the battery.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery separator excellent in affinity with an electrolytic solution and a battery using the battery separator. In particular,
Provided are a battery separator for an alkaline secondary battery such as a nickel-cadmium battery, a nickel-zinc battery, and a nickel-hydrogen battery, and a battery using the battery separator.

[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.

(1) A battery separator, wherein a nonwoven fabric made of at least one kind of polyolefin-based fiber is subjected to a hydrophilic treatment with a silicone surfactant containing an alkoxy group.

(2) The battery separator according to the above (1), wherein the alkoxy group forms a crosslinked structure by heat treatment, and the silicone surfactant is fixed to the nonwoven fabric.

(3) The above (1), wherein the silicone surfactant contains a polyalkylene oxide group.
Or the battery separator according to (2).

(4) The battery separator according to the above (1), (2) or (3), wherein the silicone surfactant contains an acid group.

(5) The battery separator according to the above (4), wherein the acid group is a carboxylic acid group and / or a sulfonic acid group.

(6) The battery separator according to any one of the above (1) to (5), wherein the at least one polyolefin fiber is a splittable conjugate fiber.

(7) The battery separator as described in any one of (1) to (6) above, wherein the nonwoven fabric contains fibers having a hydroxyl group.

(8) The battery separator according to any one of (1) to (7), wherein the nonwoven fabric is a wet-laid nonwoven fabric.

(9) The battery separator according to any one of (1) to (8) above, wherein the nonwoven fabric is a hydroentangled nonwoven fabric.

(10) The above-mentioned (1) to (9), wherein the nonwoven fabric contains microfibrillated cellulose.
The battery separator according to any one of the above.

(11) A battery containing the battery separator according to any one of the above (1) to (10).

The battery separator of the present invention is a nonwoven fabric made of at least one kind of polyolefin fiber, and has been subjected to a hydrophilic treatment with a silicone surfactant containing an alkoxy group. In this silicone surfactant, the alkoxy groups are cross-linked to each other and become insoluble in the electrolytic solution, do not release from the nonwoven fabric in the battery, and do not contribute to the self-discharge phenomenon.

Further, as in the battery separator (2) of the present invention, by performing the heat treatment, the crosslinking of the akoxy group progresses in a shorter time, and more alkoxy groups form a crosslinking structure. Thus, the fixation to the nonwoven fabric is further strengthened. Note that, unlike the grafting treatment and the sulfonation treatment, the fibers constituting the nonwoven fabric are not deteriorated by the heat treatment, so that there is no problem that the mechanical strength of the battery separator is reduced.

In the battery separator (3) of the present invention, when the silicone surfactant contains a polyalkylene oxide group, the nonwoven fabric can have hydrophilicity more easily.

Also in the battery separator (4) of the present invention, the nonwoven fabric can be made hydrophilic by the silicone surfactant containing an acid group.

The battery separator (5) of the present invention, in which the acid group of the silicone surfactant is a carboxylic acid group and / or a sulfonic acid group, not only contributes to the development of hydrophilicity but also to the self-discharge phenomenon. An impurity serving as a promoter can be captured to improve battery characteristics.

In the battery separator (6) of the present invention, since at least one kind of the polyolefin fiber is a fine splittable conjugate fiber, a battery separator having a good electrolyte retention property can be obtained.

In the battery separator (7) of the present invention, the nonwoven fabric contains fibers having hydroxyl groups. Since the hydroxyl groups can crosslink with the alkoxy groups of the silicone surfactant, the silicone surfactant is used. It can be easily and firmly fixed to the nonwoven fabric.

In the battery separator (8) of the present invention, the nonwoven fabric is a wet-laid nonwoven fabric. The wet-laid nonwoven fabric has a better formation than the dry-laid nonwoven fabric, can be formed into a thin film, and can advantageously cope with miniaturization of the battery.

In the battery separator (9) of the present invention, since the non-woven fabric is a hydro-entangled non-woven fabric, the fibers are strongly entangled three-dimensionally and have very high mechanical strength.

In the battery separator (10) of the present invention,
Although the nonwoven fabric contains microfibrillated cellulose as a binder, the microfibrillated cellulose is entangled with the polyolefin-based fiber, so that the mechanical strength of the nonwoven fabric can be increased.

The battery (11) of the present invention has the above-mentioned battery separators (1) to (1) having excellent affinity for an electrolytic solution.
0), excellent battery characteristics such as high capacity, suppression of self-discharge phenomenon, and long life can be exhibited.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The silicone surfactant relating to the battery separator of the present invention has an alkoxy group. Examples of the alkoxy group include a methoxy group, an ethoxy group, and a butoxy group. The alkoxy group self-condenses to form a crosslinked structure, forms a film on the fibers constituting the nonwoven fabric, and becomes insoluble in the electrolytic solution. Therefore, when incorporated in a battery, the silicone surfactant does not release from the battery separator to the electrolyte solution, the electrode, and the like, so that the self-discharge characteristics are not affected.

As in the battery separator (2) of the present invention, if a heat treatment is performed after a silicone surfactant is adhered, crosslinking of alkoxy groups proceeds rapidly and in large quantities.
Immobilization to a nonwoven fabric is further promoted. Heat treatment is 80
It is preferable to carry out at -150 ° C. When a heat-fusible fiber such as a polyethylene fiber is used as the fiber constituting the nonwoven fabric, the temperature is preferably from 80 to 130 ° C., which is a temperature range at which the heat-fusible fiber does not melt.

The silicone surfactant relating to the battery separator of the present invention preferably contains a polyalkylene oxy group in order to develop a good affinity for an electrolyte in a nonwoven fabric made of polyolefin fibers. The acid group also has an advantageous effect on the affinity for the electrolyte. Further, as the acid group, a carboxylic acid group and / or a sulfonic acid group are more preferable. The carboxylic acid group and / or sulfonic acid group functions as an ion exchange group, and by trapping impurities in the battery, suppresses the self-discharge phenomenon of the battery and contributes to a longer life.

In the battery separator of the present invention, a nonwoven fabric made of at least one kind of polyolefin fiber is used. As the polyolefin-based fiber, a fiber made of a polyolefin alone or a fiber made of a copolymer of an olefin and another monomer can be used. Further, a blended fiber of a polyolefin-based fiber and another fiber may be used. (Poly) olefins include (poly)
Examples thereof include ethylene, (poly) propylene, (poly) butene, ethylene-propylene copolymer, ethylene-butene-propylene copolymer, and (poly) methylpentene. Examples of the monomer copolymerizable with the olefin include vinyl butyrate, vinyl acetate, vinyl alcohol (sometimes saponified after polymerization of vinyl acetate), and vinyl chloride.

The cross-sectional shape of the fiber which can be used for the non-woven fabric of 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,
A leaf shape or the like can be used. Further, fibers having voids can also be used. In order to obtain a sufficient liquid retaining property as a battery separator, it is preferable to use fine splittable conjugate fibers.

The fiber which can be used for the non-woven fabric of the battery separator of the present invention preferably has a fiber diameter of 1 to 30 μm. If the fiber diameter is smaller than 1 μm, the nonwoven fabric becomes too dense, the porosity is reduced, and the liquid retention is reduced. On the other hand, when the thickness is larger than 30 μm, the porosity is increased, but the specific surface area is reduced, and the effect of the hydrophilic treatment with the silicone surfactant is hardly exhibited. Further, the fiber length is preferably 1 to 50 mm. If the fiber length is greater than 50 mm, fiber entanglement occurs when producing a nonwoven fabric,
The formation and uniformity of the battery separator deteriorate.

The nonwoven fabric relating to the battery separator of the present invention can be produced by any of a dry papermaking method and a wet papermaking method. In order to meet the demand for thinner and more uniform batteries required for battery separators in order to reduce the size and weight of batteries,
Wet papermaking is preferred. In the wet papermaking method, papermaking is performed by uniformly dispersing a polyolefin fiber and a binder in water.
Further, a dispersant, an antifoaming agent and the like may be appropriately added at the time of papermaking.

The nonwoven fabric relating to the battery separator of the present invention is preferably a hydroentangled nonwoven fabric having excellent mechanical strength. The hydroentangled nonwoven fabric is obtained by placing the nonwoven fabric in a single layer or multiple layers on a support, spraying a water stream from above the web, and three-dimensionally intermingling the fibers constituting the nonwoven fabric. This hydroentanglement treatment may be performed on only one side of the nonwoven fabric or on both sides.

The battery separator of the present invention may contain a binder in order to maintain the strength of the nonwoven fabric during papermaking. As a binder, it has excellent alkali resistance,
It is preferable to use bacterial cellulose which is in a fiber form and can be entangled with polyolefin-based fibers.

The microfibrillated cellulose relating to the battery separator of the present invention is a fine fiber obtained by highly fibrillating cellulose fibers having high crystallinity. As a method for producing the microfibrillated cellulose according to the present invention, a method using mechanical shearing force, for example, a beater, a conical refiner, a single disc refiner,
A method using various beating machines such as a double disc refiner, a method of passing a small diameter orifice under high pressure, and a method in which an impeller is rotated by a drive shaft with a bell described in JP-A-63-256787 to impact the fiber material. A method using a pulverizer such as a sand mill described in JP-A-4-194097;
A pulverizing method using a ring-shaped pulverizing medium described in 84975, a pulverizing method using a media stirring type pulverizer described in JP-A-6-212587, and the like can be mentioned.

Examples of the raw material of the microfibrillated cellulose relating to the battery separator of the present invention include hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), and softwood bleached sulphite pulp (NBS).
Wood pulp such as chemical pulp such as P), mechanical pulp such as groundwood pulp (GP), and thermomechanical pulp (TMP); And regenerated cellulose fibers and the like can be used.

As the microfibrillated cellulose relating to the battery separator of the present invention, bacterial cellulose can be more preferably used. Bacterial cellulose refers to cellulose fibers produced by microorganisms, including cellulose and heteropolysaccharides having cellulose as a main chain, and β-1,3, β-1,2.
It contains sugar glucans. The components other than cellulose in the case of the heteropolysaccharide are mannose, fructose,
Hexoses such as galactose, xylose, arabinose, rhamnose, and glucuronic acid, pentoses, and organic acids. In addition, these polysaccharides exist as one kind or a mixture of two or more kinds.

Microorganisms that produce bacterial cellulose that can be used in the battery separator of the present invention are not particularly limited, but may be Acetobacter aceti subsp. Xylinum (Acetobacter acet).
i subsp xylium) ATCC 1082
1 or Acetobacter pasteurian (Acet
obeter pasteurium), Acetobacter lance
ens), Sarsina Ventriculi
ventriculi), Bacterium xyloides, Pseudomonas bacteria, Agrobacterium bacteria, etc., which produce bacterial cellulose can be used.

The method for producing bacterial cellulose that can be used for the battery separator of the present invention includes the following.
General bacterial culture methods can be used. That is, a stationary culture method, a stirring culture method, an aeration culture method, a shaking culture method, or a combination thereof can be used.
Specifically, JP-A-59-120159 and JP-A-61-1
No. 52296, No. 61-212295, No. 62-26
No. 5990, No. 62-175190, No. 63-202
No. 394, No. 62-36467, No. 63-7494
0, JP-A-3-174091, JP-A-5-51885,
6-113873, 6-206904, 6-
No. 233691, No. 7-39386, No. 7-7976
No. 9, No. 7-107986, No. 7-118301,
No. 7-118303, No. 9-25302, Tokuyo Sho 6
Methods described in JP-A-2-500630 and JP-A-2-500116 can be used.

The battery (11) of the present invention uses the battery separator described above.

[0048]

The present invention will be described below in detail with reference to examples.

Example 1 Dry-type papermaking nonwoven fabric (core weight: 50 g / m ² ) consisting of a core-sheath fiber having a fineness of 1.5 denier and a fiber length of 20 mm, comprising polypropylene as a core component subjected to hydrophilic treatment and polyethylene as a sheath component.
Is heat calendered (150 ° C., 20 kg / cm ² )
After thermocompression bonding of the fibers, the fibers were immersed in the liquid shown in Table 1, and then dried at 100 ° C. for 2 minutes to obtain a battery separator A.

[0050]

[Table 1]

Example 2 Dry-type nonwoven fabric (basis weight: 50 g / m ² ) consisting of a core-sheath fiber having a fineness of 1.5 denier and a fiber length of 20 mm comprising polypropylene as a core component subjected to hydrophilic treatment and polyethylene as a sheath component.
Is heat calendered (150 ° C., 20 kg / cm ² )
After thermocompression bonding of the fiber, the fiber was immersed in the liquid shown in Table 2, and then dried at 100 ° C. for 2 minutes to obtain a battery separator B.

[0052]

[Table 2]

Comparative Example 1 Dry-type nonwoven fabric made of a core-sheath fiber having a fineness of 1.5 denier and a fiber length of 20 mm comprising polypropylene as a core component and polyethylene as a sheath component (basis weight: 50 g / m ² )
Is heat calendered (150 ° C., 20 kg / cm ² )
The fibers were thermocompression-bonded to obtain a battery separator X.

Comparative Example 2 Dry-type nonwoven fabric made of a core-sheath fiber having a fineness of 1.5 denier and a fiber length of 20 mm comprising polypropylene as a core component and polyethylene as a sheath component (basis weight: 50 g / m ² )
Is heat calendered (150 ° C., 20 kg / cm ² )
After thermocompression bonding of the fiber, the fiber was immersed in the liquid shown in Table 3 and then dried at 100 ° C. for 2 minutes to obtain a battery separator Y.

[0055]

[Table 3]

Example 3 Production of Wet Non-Woven Fabric Split fiber 98 having a denier 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
And a hot water-soluble polyvinyl alcohol fiber (VP)
W103; manufactured by Kuraray Co., Ltd.) 2 parts by weight impregnated with a 1% by weight solution of a nonionic surfactant were put into water, stirred for 3 minutes with a high-speed mixer to disintegrate the fibers, and then reciprocally rotated. The mixture was gently stirred in a chest equipped with a machine (Agitator, manufactured by Shimazaki Seisakusho). Next, a 0.1% by weight aqueous solution of polyacrylamide (viscosity agent) was promptly added, followed by gentle stirring to prepare a uniform slurry. Using the slurry, a non-woven fabric having a width of 50 cm and a basis weight of 50 g / m ² was produced using a round-mesh paper machine.

Water entanglement treatment The above nonwoven fabric was conveyed on a porous support made of a 100-mesh stainless steel wire at a speed of 20 m / min, and subjected to a water entanglement treatment with a columnar water flow using a nozzle head shown in Table 4. went. Under the same conditions, the hydroentanglement process was performed also from the back surface. After the hydroentanglement, drying was performed at 130 ° C. using a suction through dryer to obtain a nonwoven fabric a.

[0058]

[Table 4]

The hydrophilized nonwoven fabric a was immersed in the liquid shown in Table 2, and then dried at 100 ° C. for 2 minutes to obtain a battery separator C.

Example 4 Papermaking of Nonwoven Fabric Split dendritic fiber 80 having a denier of 3 denier composed of polypropylene and ethylene-vinyl alcohol copolymer, 0.2 denier (3.9 μm) after fiber splitting, 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. Next, a 0.1% by weight aqueous solution of polyacrylamide (viscosity agent) was promptly added, followed by gentle stirring 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 nonwoven fabric was conveyed on a porous support made of a 100-mesh stainless steel wire at a speed of 20 m / min, and subjected to a water entanglement treatment with a columnar water flow using a nozzle head shown in Table 4. went. Under the same conditions, the hydroentanglement process was performed also from the back surface to obtain a nonwoven fabric b.

The hydrophilic nonwoven fabric b was immersed in the liquid shown in Table 2 and dried at 100 ° C. for 2 minutes to obtain a battery separator D.

Example 5 Hydrophilic treatment The nonwoven fabric b obtained in Example 4 was immersed in the liquid shown in Table 2,
After drying at 60 ° C. for 30 minutes, a battery separator E was obtained.

Comparative Example 3 Production of Nonwoven Fabric Split-type composite fiber 98 having a fineness of 3 denier composed of polypropylene and ethylene-vinyl alcohol copolymer, 0.2 denier (3.9 μm) after fiber division, and a fiber length of 10 mm
And a hot water-soluble polyvinyl alcohol fiber (VP)
W103; manufactured by Kuraray Co., Ltd.) 2 parts by weight impregnated with a 1% by weight solution of a nonionic surfactant were put into water, stirred for 3 minutes with a high-speed mixer to disintegrate the fibers, and then reciprocally rotated. The mixture was gently stirred in a chest equipped with a machine (Agitator, manufactured by Shimazaki Seisakusho). Next, a 0.1% by weight aqueous solution of polyacrylamide (viscosity agent) was promptly added, followed by gentle stirring to prepare a uniform slurry. Using the slurry, a non-woven fabric having a width of 50 cm and a basis weight of 50 g / m ² was produced using a round-mesh paper machine.

The above non-woven fabric was conveyed onto a porous support made of a 100-mesh stainless wire, and the speed was 20 m.
/ Min, and a water entanglement process was performed with a columnar water flow using the nozzle head of Table 1. Under the same conditions, the hydroentanglement process was performed also from the back surface. The nonwoven fabric after the hydroentanglement was dried at 130 ° C. using a suction drum dryer to obtain a battery separator Z.

Evaluation of Battery Separator The following characteristics were evaluated for battery separators A to E and X to Z, and the results are summarized in Table 5.

(I) Electrolyte absorption rate: A test piece of 2.5 × 18 cm was taken from each battery separator and was subjected to 40 ± 5 ° C.
Preliminary drying is performed under the standard moisture content, and the test specimen is left in the test room at the standard temperature and humidity. Then, the test specimen is weighed at intervals of 1 hour or more. (A water 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. With the lower end of 5 mm immersed in the liquid, 30
After a minute, the height (mm) at which the potassium hydroxide solution rose by capillary action 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).

[0069]

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

(Iii) Air permeability: Frazier air permeability (cc / cm ² / sec) was used to evaluate the ease with which oxygen generated from the positive electrode side permeates to the negative electrode side through the battery separator.
c) was measured. Frazier air permeability is JIS-L-1
According to No. 096, the amount of air passing through the test piece was measured five times using a Frazier-type air permeability tester, and the average value was shown.

(Iv) Tensile strength: When wound around an electrode plate, the strength required for winding while pulling in the flow direction and the longitudinal (paper flow direction) tensile strength (kg / 2 cm width).
Tensile strength was measured according to JIS-P-8113. Each battery separator was cut into a width of 2 cm and a length of 20 cm, and the load at the time of breaking was measured 10 times using a Tensilon measuring instrument (Horizon Tech; HTM-100). It measured and showed the average value.

(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, battery separators A to E and X as separators To Z, a nickel-hydrogen battery was produced. 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).

[0073]

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

(Vi) Ion exchange amount: 1 g of a test piece was collected from each battery separator and added to a 1N HCl solution.
After impregnation at 0 ° C. for 1 hour, the pH is adjusted to 6 to 7 with ion exchanged water.
Washed several times until Next, the test piece was dried for 2 hours with a blow dryer at 90 ° C., and cooled to room temperature.
₂ was measured to 0.01 mg. After the test piece after the weight measurement was impregnated with about 110 g of a 0.01 N KOH solution at 70 ° C. for 1 hour, the test piece was taken out, and the solution was cooled to room temperature. Approximately 100 g of the cooled solution was weighed to 0.01 g (S ₁ ), and the pH was measured at 0.02 g by using a pH meter (manufactured by Horiba Ltd.)
Neutralization titration was performed with N HCl solution. The blank solution was titrated in the same manner, and the potassium ion exchange amount was calculated from the following equation (3).

[0075]

(Equation 3)

(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 having a specific gravity of 1.3 ° C. was placed in a water tank containing a potassium hydroxide solution, and the lower end of the horizontal bar was fixed to a predetermined height of the horizontal bar, and the horizontal bar was lowered. After the immersion state, the height (mm) at which the potassium hydroxide solution rose by capillary action was measured 30 minutes later.

[0077]

[Table 5]

The battery separators A to E of the present invention can be obtained without going through steps such as grafting and sulfonation.
The affinity for the electrolyte was improved. There was no deterioration of the fibers constituting the nonwoven fabric, and high mechanical strength was exhibited.

Since the battery separators A and B of the present invention are dry nonwoven fabrics that have been subjected to a hydrophilization treatment with a silicone surfactant containing an alkoxy group, they are compared with the battery separator X of the dry papermaking nonwoven fabric of the comparative example. As a result, the mechanical strength, the liquid absorption rate, the liquid retention, and the capacity storage rate were improved.

The battery separators C to E of the present invention are wet-laid nonwoven fabrics that have been subjected to a hydrophilic treatment with a silicone surfactant containing an alkoxy group. Compared to,
The mechanical strength, liquid absorption rate, liquid retention, and volume storage rate were improved.

In the battery separators A and B of the present invention, the silicone surfactant is insoluble in the electrolytic solution due to crosslinking by the alkoxy group. Therefore, even after the alkali treatment, a high affinity for the electrolytic solution was exhibited. On the other hand, it was confirmed that in the battery separator Y subjected to the hydrophilization treatment using a surfactant having no cross-linking property, the electrolytic solution absorption rate was lost by the alkali treatment.

In the battery separators CE of the present invention, since the splittable conjugate fibers constituting the nonwoven fabric contain an ethylene-vinyl alcohol copolymer, the silicone surfactant binds to the hydroxyl groups of the fibers. , Very tightly bound. Therefore, even when the electrolyte absorption rate (vii) after the alkali treatment was compared with the electrolyte absorption rate (i) before the alkali treatment, there was no significant change. The battery separator A of the present invention in which the fibers constituting the nonwoven fabric do not contain a hydroxyl group,
In B, a slight decrease in the electrolyte solution absorption rate was confirmed by the alkali treatment.

The battery separators CE of the present invention are wet-laid nonwoven fabrics and have been subjected to a hydroentanglement treatment.
In addition, fine splittable composite fibers are used. Therefore, as compared with the battery separators A and B using the dry-type nonwoven fabric, the mechanical strength was strong and the formation was good.

The battery separators D and E of the present invention were produced in the same manner as the battery separator C of the present invention, except that bacterial cellulose was used instead of hot water-soluble polyvinyl alcohol as a binder. . It was confirmed that the battery separators D and E of the present invention exhibited good mechanical strength because bacterial cellulose entangled the polyolefin-based fibers.

The battery separator E of the present invention is manufactured by the same method as the battery separator D except that the heat treatment after the treatment with the silicone surfactant is not performed. In the battery separator E, it was confirmed that, compared to the battery separator D, the cross-linking of the silicone surfactant was insufficient, so that the reduction in the electrolyte absorption rate by the alkali treatment was large.

[0086]

As described above, the battery separator of the present invention can be obtained by an easy and inexpensive method without performing a graft treatment or the like. Further, the battery separator of the present invention has a high hydrophilicity and an ion exchange ability, so that it has a very good affinity for an electrolytic solution. Furthermore, the battery separator of the present invention is a wet-laid nonwoven fabric or a hydroentangled nonwoven fabric, contains splittable conjugate fibers, and further contains bacterial cellulose to provide mechanical strength and liquid retention. It is possible to further enhance such properties. Further, the battery using the battery separator of the present invention has an excellent effect of exhibiting good self-discharge characteristics.

Claims (11)

[Claims] 1. A battery separator, wherein a nonwoven fabric made of at least one kind of polyolefin-based fiber is subjected to a hydrophilic treatment with a silicone surfactant containing an alkoxy group. 2. The battery separator according to claim 1, wherein the alkoxy group forms a crosslinked structure by heat treatment, and the silicone surfactant is fixed to the nonwoven fabric. 3. The battery separator according to claim 1, wherein the silicone surfactant contains a polyalkylene oxide group. 4. The battery separator according to claim 1, wherein the silicone surfactant contains an acid group. 5. The battery separator according to claim 4, wherein the acid group is a carboxylic acid group and / or a sulfonic acid group. 6. The fiber according to claim 1, wherein the at least one polyolefin fiber is a splittable conjugate fiber.
The battery separator according to any one of the above. 7. The battery separator according to claim 1, wherein the nonwoven fabric contains a hydroxyl group-containing fiber. 8. The battery separator according to claim 1, wherein the nonwoven fabric is a wet-laid nonwoven fabric. 9. The battery separator according to claim 1, wherein the nonwoven fabric is a hydroentangled nonwoven fabric. 10. The battery separator according to claim 1, wherein the nonwoven fabric contains microfibrillated cellulose. A battery comprising the battery separator according to any one of claims 1 to 10.