JP2001110392A - Battery separator and manufacturing method thereof - Google Patents

Abstract

(57) [Problem] To provide a battery separator having high strength, strong stiffness, and high hydrophilicity, and an efficient production method thereof. SOLUTION: A battery separator made of a nonwoven fabric using a splittable conjugate fiber containing an ethylene vinyl alcohol copolymer having at least one component having an ethylene content of 20 to 70 mol% and a melt index of 0.5 to 8 g / 10 min. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to secondary batteries such as lead batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, and aluminum-air batteries. The present invention relates to a suitable battery separator and a manufacturing method thereof.

[0002]

2. Description of the Related Art In general, batteries such as secondary batteries use a separator for separating an anode active material and a cathode active material. This separator can prevent an internal short circuit between the anode material and the cathode material and has a low internal resistance H. It has a high electrolyte absorbing property to generate a sufficient electromotive reaction. The occupancy of the battery is small and the amount of anode active material and cathode active material can be increased (the battery life can be extended). It does not cause shrinkage or deterioration of the electrolyte such as potassium hydroxide or sulfuric acid. Various performances such as having excellent durability are required. In particular, in a secondary battery separator, durability during an oxidation-reduction reaction accompanying charge / discharge is highly required.

[0003] As a battery separator having the above performance, a separator using an olefin fiber having excellent chemical resistance has been studied. For example, a separator having a melt-blown non-woven fabric layer made of an olefin-based fiber (Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 282794, Japanese Patent Application Laid-Open No. 7-280627) and the like have been proposed. However, since the olefin fiber has high hydrophobicity, it is necessary to perform a hydrophilization treatment such as a sulfonation treatment, a plasma discharge treatment, and a corona discharge treatment in order to improve the electrolyte retention of the separator.
Therefore, there is a problem that the process becomes complicated and the cost is increased for commercialization. In order to solve the above problems, use of an ethylene-vinyl alcohol copolymer-containing fiber has been studied. Ethylene vinyl alcohol copolymer has higher hydrophilicity than polypropylene-based polymer, polyethylene-based polymer and the like, so that excellent effects can be obtained in terms of liquid retention and wettability.

[0004] For example, Japanese Patent Application Laid-Open No. 3-257755 proposes a method using a splittable conjugate fiber comprising a polyolefin polymer and a specific ethylene-vinyl alcohol copolymer. According to this method, it is not necessary to perform a hydrophilization treatment such as a sulfonation treatment, and since a polyolefin polymer having excellent heat-resistant alkali resistance is used in combination, an excellent effect can be obtained in terms of durability. Furthermore, it is also possible to split the splittable fiber by a water entanglement treatment or the like to obtain a separator having more excellent separating properties.

[0005]

However, the method described in the above publication has a problem in terms of efficiency because the spinnability of the splittable conjugate fiber is low, and also has a problem in that the mechanical performance is low. It was difficult to obtain a high separator. When the stiffness of the separator is low, it is difficult to install the separator in a battery, and the separator is damaged by an impact or the like, and an internal short circuit is likely to occur. Furthermore, since the staple is likely to occur during the spinning of the conjugate fiber, the conjugate fiber cannot be sufficiently split even if it is attempted to be split by a hydroentanglement treatment or the like. Therefore, it has been difficult to highly enhance the separator property of the separator. An object of the present invention is to provide a battery separator which has higher stiffness and is capable of highly improving the separating property and the like, and an efficient production method thereof.

[0006]

According to the present invention, there are provided (1) an ethylene content of 20 to 70 mol% and a melt index of 0.
Battery separator made of nonwoven fabric using splittable conjugate fiber containing at least one component of ethylene vinyl alcohol copolymer of 5 to 8 g / 10 min, (2) ethylene content of 20 to 70 mol%, melt index of 0.5 to
Battery separator using splittable conjugate fiber composed of 8 g / 10 min of ethylene vinyl alcohol copolymer and polypropylene-based polymer, (3) splittable conjugate fiber is divided and reduced in diameter (1) or ( Battery separator according to 2), (4) ethylene content of 20 to 70
Mol%, melt index 0.5-8g / 10min
A battery separator for forming a nonwoven sheet using splittable conjugate fibers containing at least one component of the ethylene vinyl alcohol copolymer of the present invention, and subjecting the nonwoven fabric to a hydroentanglement treatment to split the splittable conjugate fibers. Manufacturing method.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has been found to be able to obtain a battery separator excellent in various performances by using a splittable conjugate fiber containing at least one specific ethylene-vinyl alcohol copolymer. It is. By using the ethylene-vinyl alcohol copolymer-containing fiber, a battery separator having high hydrophilicity and excellent liquid retention properties can be obtained, but when using any ethylene-vinyl alcohol copolymer, the “stiffness” is high. It is difficult to obtain a separator. In order to obtain a desired separator, it is necessary to use at least an ethylene vinyl alcohol copolymer having a melt index of 0.5 to 8 g / 10 min. By using a copolymer having such a melt index, not only can conjugate fibers hardly cause sticking to be efficiently spun, but the stiffness of the separator increases, so that the permeability in the battery assembly step becomes good, and It is hardly deformed even if it receives an impact due to falling when using batteries,
An excellent effect that generation of an internal short circuit due to deformation can be suppressed is obtained. Furthermore, since the sticking hardly occurs during the spinning of the conjugate fiber, the dividing property is remarkably improved, and the diameter can be easily reduced by performing a hydroentanglement treatment or the like.

[0008] If the melt index of the copolymer is too high, the strength will be reduced, the stiffness of the separator will be weakened, and the fiber will tend to adhere during spinning, so that the splitting property will also be reduced. Conversely, if the melt index is too small, the spinnability of the conjugate fiber becomes insufficient. It is more preferably 1.0 g / 10 min or more from the viewpoint of spinnability, and 7 g / 1 from the viewpoint of mechanical performance and splitting property of the conjugate fiber.
More preferably, it is 0 min or less.

In the present invention, the ethylene content is 2
0-70 mol%, preferably 30-55 mol%, especially 5
It is necessary to use a copolymer of 0 mol% or less. If the ethylene content is low, problems arise in spinnability, durability, etc.
If the ethylene content is too high, the effect of the present invention cannot be obtained because the hydrophobicity becomes too low. The content of the vinyl alcohol unit is 30 to 80 mol%, particularly 45 to 7 mol%.
It is preferably 0 mol%, particularly preferably 50 mol% or more. A component other than the vinyl alcohol component (or vinyl acetate component) and the ethylene component may be contained as long as the effects of the present invention are not impaired, but from the viewpoint of efficiently obtaining the effects of the present invention, 30 mol% or less of copolymer components other than ethylene units and vinyl alcohol units,
It is preferably at most mol%. The method for producing the ethylene-vinyl alcohol-based copolymer used in the present invention is not particularly limited, but can be efficiently produced by saponifying the ethylene-vinyl acetate-based copolymer. From the viewpoint of hydrophilicity, the saponification degree of the vinyl alcohol unit is preferably at least 95 mol%, particularly preferably at least 98 mol%. The average molecular weight of the copolymer is 5 from the viewpoint of spinnability, hot water resistance and the like.
It is preferably set to about 00 to 5000, particularly about 800 to 3500.

The components other than the ethylene-vinyl alcohol copolymer constituting the splittable conjugate fiber are not particularly limited, and for example, melt-spinnable polymers such as polyolefin-based polymers and polyamide-based polymers can be suitably used. By using a composite fiber containing such other components, the durability, swelling resistance, mechanical performance, and the like of the separator can be improved, and the fiber can be further divided into ultrafine fibers. It is preferable to use at least a polyolefin polymer having a vinyl alcohol unit content of less than 30 mol% from the viewpoints of spinnability, splitting property, durability and the like of the conjugate fiber, and it is more preferable to use at least a polypropylene polymer. The polypropylene resin used is not particularly limited, but a resin having a weight average molecular weight of 80,000 to 150,000 is more preferable from the viewpoint of spinnability.

The structure of the composite fiber is not particularly limited, and may be composed of three or more components. However, from the viewpoints of spinnability, splitting properties and the like, a bicomponent composite fiber is preferable. Among them, a conjugate fiber in which at least one component is divided into two or more, particularly four or more regions by another component in the cross section of the conjugate fiber is preferable. From the viewpoint of ease of division, it is preferable that all components constituting the conjugate fiber are divided into two or more regions by other components in the fiber cross section, and the total number of divisions (total number of regions) in the conjugate fiber cross section , The total number of layers) is preferably 8 to 20. Further, from the viewpoint of ease of division and spinnability, each layer is preferably substantially continuous in the fiber length direction.

From the viewpoints of liquid absorption properties, liquid retention properties, ease of division, separation properties of the separator, etc., each region (layer) constituting the conjugate fiber is 0.6 dtex or less, particularly 0.3 dtex or less, particularly The size is preferably equal to or less than 0.1 dtex.
The size is preferably equal to or more than 008 dtex, particularly preferably equal to or more than 0.05 dtex. The composite state is not particularly limited, and a composite fiber of a laminar split type, a radial split type, or the like can be suitably used, and can be produced by performing a composite spinning by a conventionally known method. It is preferable to use a laminar split type or a radial split type in view of ease of division and spinning process. Of course, a plurality of types of composite fibers can be used in combination.

From the viewpoints of liquid retention, liquid absorption rate, and ease of splitting, it is preferable to use a conjugate fiber in which an ethylene vinyl alcohol copolymer is present on at least a part of the fiber surface. The amount of the ethylene vinyl alcohol copolymer constituting the fiber is preferably from 10 to 90% by weight, and from the viewpoint of hydrophilicity, it is preferably at least 30% by weight, particularly preferably at least 40% by weight. Further, from the viewpoints of chemical resistance, ease of division, and the like, the content is preferably 80% by weight or less. Of course, as long as the effects of the present invention are not impaired, additives such as an antioxidant and a process aid may be incorporated. The fineness of the conjugate fiber may be appropriately selected, but from the viewpoint of the homogeneity of the nonwoven fabric, the separation property of the nonwoven fabric, the ease of splitting the conjugate fiber, and the like, the conjugate fiber of 0.5 to 10 dtex, particularly 1 to 6 dtex, is more preferable. The compounding amount of the composite fiber is preferably at least 50% by weight / nonwoven fabric, particularly preferably at least 70% by weight / nonwoven fabric, particularly preferably at least 80% by weight. Further, a fiber other than such a conjugate fiber may be blended as a main fiber. From the viewpoints of separation properties, liquid retention properties, and strength, fibers of 0.01 to 3 dtex can be suitably used, and from the viewpoint of chemical resistance and the like, it is preferable to blend polyolefin fibers.

A nonwoven fabric may be formed by using such a main fiber. However, from the viewpoint of enhancing the strength, the “stiffness”, the form stability and the like of the nonwoven fabric, it is preferable to further incorporate a binder, especially a binder fiber. By blending the fibrous binder, the above-mentioned effects can be obtained without increasing the internal resistance more than necessary. The fineness of the binder fiber is preferably about 0.5 to 6 dtex from the viewpoint of nonwoven fabric strength, homogeneity, processability, and the like. Note that the fibrous binder does not need to clearly retain the fiber shape after being formed into a nonwoven fabric, and the above effects can be obtained by manufacturing the nonwoven fabric using the fibrous binder. The binder fiber may be composed of a single component, but is preferably composed of two or more components, since it has an adhesive effect and can maintain sufficient strength. Core-sheath type, side-by-side type,
Composite fibers such as a laminar split type and a radial split type, and sea-island fibers can be suitably used. The cross section of the fiber is not particularly limited, such as a round type, a flat type, a cocoon type, a hollow type, and a T type. chemical resistance,
From the viewpoint of adhesiveness to the splittable conjugate fiber and the like, a polyolefin-based binder fiber is preferable, and among these, a binder fiber using at least a polyethylene-based polymer and / or a polypropylene-based polymer is preferable. In particular, sheath-core type composite fibers having a polyethylene resin as a sheath component and a polypropylene resin as a core component can be more preferably used. The blending amount of the binder fiber is preferably 1 to 30% by weight / nonwoven fabric, particularly preferably 3 to 20% by weight / nonwoven fabric, from the viewpoint of nonwoven fabric strength and internal loss.

The method for producing the nonwoven fabric constituting the battery separator of the present invention is not particularly limited, and may be, for example, a dry method (parallel card method, cross layer method, random webber method, etc.) or a wet papermaking method. In the case of manufacturing a nonwoven fabric by a dry method, the fiber length of the compounded fiber is set to 20.
When producing a nonwoven fabric by a wet papermaking method, the fiber length of the compounded fiber is 0.5 to 30 mm, particularly 1 to 200 mm.
The thickness is preferably 20 mm in terms of dispersibility, homogeneity, manufacturing processability, and the like. When a nonwoven fabric is manufactured by a dry method, it is preferable to use crimped fibers.

From the viewpoint of improving the separating property of the separator, it is preferable to use a nonwoven fabric in which the splittable conjugate fiber is divided and reduced in diameter. A method of dividing the conjugate fiber in advance and then forming a nonwoven fabric, for example, in the case of employing a wet papermaking method, a method in which the fiber is defibrated with a beater, a pulper, or the like at the time of slurry preparation and then divided to form a paper may be adopted. However, it is preferable to split the composite fiber after forming the sheet from the viewpoint of manufacturing processability and obtaining a separator excellent in homogeneity and separation property. As the dividing method, it is preferable to adopt a method of dividing by applying a mechanical shearing force from the viewpoint of production efficiency, and it is preferable to divide by a process such as a needle punching process and a water entanglement process. However, when performing the entanglement process by needle punch, it is necessary to pay attention to the fact that if the diameter of the needle used is large, the pore size becomes large when the separator is used for a battery. From the viewpoint of high productivity and efficient splitting of the conjugate fiber, it is preferable to employ the hydroentanglement treatment.

In the water entanglement process, for example, the nozzle diameter is 0.03 mm to 0.3 mm, more preferably 0.09 m
Water pressure of 10 kg / cm ² using a nozzle plate or the like arranged in 1 to 3 rows with a pitch of 0.15 mm to 5 mm, more preferably 0.5 mm to 1.5 mm, and a pitch of 0.15 mm to 5 mm.
A method of treating once or a plurality of times with a water flow of up to 500 kg / cm ² is conceivable. In particular, when a binder fiber is blended, the binder function of the binder fiber is developed after performing the entanglement process, so that the entanglement process and the splitting process can be performed more stably. Also, excellent effects can be obtained from the viewpoint of the splitting property of the composite fiber.

The split state of the splittable conjugate fiber is preferably divided for each region (layer) constituting the conjugate fiber from the standpoint of separation, but it is not necessary that all layers are split. Further, one fiber may have a divided portion and a non-divided portion.
For example, each layer may not be completely divided but may be simply divided into branches. The fiber diameter after the division treatment is preferably about 0.6 dtex or less from the point of separation, particularly about 0.3 dtex or less, particularly preferably about 0.2 dtex or less, because the pressure loss is not increased more than necessary. Is preferably about 0.01 dtex or more, particularly about 0.05 dtex or more. By dividing the splittable conjugate fiber and making it extremely fine, the pore size of the nonwoven fabric can be reduced, and the separating property can be improved.

The average pore size of the separator is preferably 5 to 80 μm, particularly preferably 10 to 50 μm, from the viewpoint of maintaining a high degree of separation without increasing the internal loss more than necessary. The maximum pore size is preferably 150 μm or less, particularly preferably 100 μm or less. In addition, the thickness of the nonwoven fabric is set at about 0.1 in terms of enhancing the handleability, increasing the battery life, and further, in terms of mechanical performance.
It is preferably about 0.05 to 0.25 mm, and the basis weight is 2
The density is preferably about 0 to 80 g / m ² and the density is about 0.1 to 0.6 g / cm ³ .

Further, in the present invention, since a splittable conjugate fiber containing a specific ethylene vinyl alcohol copolymer is used, a separator excellent in stiffness and mechanical performance and having a large liquid absorption amount and a liquid absorption speed can be obtained. can get. More specifically, according to the present invention, the breaking length is 4 km or more, especially 5 km or more nonwoven fabric, furthermore, stiffness 0.44 kgf or more,
In particular, it can be made into a nonwoven fabric of 0.48 kgf or more, more preferably 0.50 kgf or more.
mm ² or more, especially 0.35 g / 2500 mm ² or more, liquid absorption speed 2
A nonwoven fabric having a thickness of not more than 00 sec / 25 mm, particularly 160 sec / 25 mm can be obtained.

The obtained non-woven fabric can be used as it is, or can be processed into a desired shape such as a bag-shaped body or a spiral-shaped body to obtain a battery separator. Of course, a battery separator may be manufactured in combination with a material other than the nonwoven fabric. For example, it can be laminated or spliced with another nonwoven fabric, film, or the like. However, from the viewpoint of efficiently obtaining the effects of the present invention, it is preferable to manufacture the battery separator substantially from only the nonwoven fabric described above. By incorporating the battery separator of the present invention, a battery excellent in various performances can be obtained.

[0022]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. [Melt index g / 10min] Diameter 2.1m
m, a sample was placed in a cylinder having an orifice having a length of 8 mm, and extruded at 190 ° C. under a load of 2160 g.
The weight of the test material spilled in a minute
The melt index was determined in terms of the outflow weight per minute. However, for samples having a melting point of about 190 ° C. or higher, the outflow amount for 10 minutes at a plurality of temperatures equal to or higher than the melting point under a load of 2160 g is calculated. The value was plotted on the vertical axis (logarithm) and the value extrapolated to 190 ° C. was used as the melt index. [Weight average molecular weight] Measured by GPC method.

[Thickness mm Density g / cm ³ ] JIS
P 8118 "Test methods for thickness and density of paper and paperboard"
It measured according to. [Basic weight g / m ² ] Measured according to JIS P 8124 “Measurement of metric basis weight of paper”. [Tear length km] Measured in accordance with JIS P 8113 "Test method for tensile strength of paper and paperboard".

[Liquid absorption g / g] A paper sample of 50 mm × 50 mm was treated with 35% KOH solution at a bath ratio of 1/100 for 24 hours.
The sample was immersed for 30 hours and drained naturally for 30 seconds, the weight of the sample was measured, and the amount of liquid absorbed was calculated by dividing the weight of the retained liquid by the weight of the paper. [Liquid Absorption Speed] The end of the sample was immersed in a 35% KOH solution, and the absorption speed was evaluated based on the time required for the 35% KOH solution to suck up to a height of 25 mm.

[Air permeability cm ³ / cm ² / sec] JIS
L 1096-1996 Measured by a Frazier-type air permeability tester manufactured by Toyo Seiki Seisaku-Sho, Ltd. according to the air permeability measurement method of "General Textile Test Method". [Pore size μm] Measured by colter POROMETER II manufactured by Coulter Electronics Co., Ltd.

[Koshi kgf] A sample of 25 mm × 90 mm was immersed in 35% KOH for 30 minutes, and then wrapped around the center of 20 mm (height) × 7 mmФ in quadruple, and 20 mm (height).
X 9mmФ (inner diameter), set in a tube, and use “Rheometer RT-2010-CW” manufactured by Leotech Co., Ltd.
A method for measuring compressive strength was used.

[Binder Fiber] A 2.2 dtex core-sheath composite fiber ("N-740" manufactured by Kuraray Co., Ltd.) having a sheath component of polyethylene and a core component of polypropylene was used. When the sheet is formed by the dry method, the number of crimps is 12 /
In crimp was applied and cut to a length of 51 mm for use. When a sheet was formed by a wet method, the sheet was cut to a length of 5 mm without crimping and used.

Reference Example 1 Ethylene content of 44 mol%,
Saponification degree 99%, melt index 5.5g / 10m
in ethylene vinyl alcohol copolymer (“E105Y” manufactured by Kuraray Co., Ltd.) 67% by weight, weight average molecular weight 1
The composite spinning was performed at a blending ratio of 33% by weight of polypropylene of No. 05200 to produce a layered splittable conjugate fiber in which both components were alternately laminated (3.6 dtex, total division number 11, ethylene vinyl alcohol copolymer portion). , The average fineness of each layer is about 0.33 dtex).

Reference Example 2 Ethylene content: 32 mol%, degree of saponification: 99%, melt index: 1.3 g /
A layer-split type in which both components are alternately laminated by compound spinning with a mixing ratio of 67% by weight of ethylene vinyl alcohol copolymer (“F101” manufactured by Kuraray Co., Ltd.) for 10 minutes and 33% by weight of polypropylene having a weight average molecular weight of 105,200. A conjugate fiber was produced (1.6 dtex, total division number 11, division number of ethylene vinyl alcohol copolymer portion 6, average fineness of each layer about 0.15 dtex).

Reference Example 3 The same ethylene vinyl alcohol copolymer and polypropylene as in Reference Example 1 were used.
Using the same blending ratio as above, a splittable conjugate fiber in which both components were alternately laminated was manufactured (3.1 dtex, total number of splits 32,
Number of divisions of ethylene vinyl alcohol copolymer part 1
6, average fineness of each layer is about 0.1 dtex). [Reference Example 4] As an ethylene-vinyl alcohol copolymer, the ethylene content was 47 mol%, the degree of saponification was 99%,
An ethylene vinyl alcohol copolymer having a melt index of 14.0 g / 10 min (“G11 manufactured by Kuraray Co., Ltd.
0 ") was used to produce a 3.6 dtex layered splittable conjugate fiber in the same manner as in Reference Example 1 (total split number: 11, ethylene vinyl alcohol copolymer portion split number: 6, average fineness of each layer: approx. 11). 0.33 dtex).

Reference Example 5 The weight average molecular weight is 10520
No. 0 polypropylene was melt spun to produce 1.1 dtex fibers.

Example 1 Splittable conjugate fiber 9 of Reference Example 1
0 parts by weight, 10 parts by weight of the above binder fiber are mixed,
A web having a basis weight of 60 g / m ² was produced using a roller card. Next, nozzle diameter 0.1mm, pitch 0.6m
m, using one row of nozzle plates, water pressure 20kg / c
m ² -80 kg / cm ² -60 kg / cm ² -40 kg /
After performing the water entanglement process once each on the front and back with a water flow of 1 cm ² ,
A hot press treatment was performed at 32 ° C. to obtain a nonwoven fabric having a thickness of 20 μm. The obtained nonwoven fabric has excellent stiffness and mechanical performance,
Further, it had high liquid absorbing properties and had excellent performance as a separator. Moreover, since the splittable conjugate fiber was substantially divided into each region (layer) by the hydroentanglement treatment, it had a high degree of separation characteristics. Table 1 shows the results.

Example 2 A nonwoven fabric was produced in the same manner as in Example 1 except that the splittable conjugate fiber of Reference Example 2 was used. The obtained nonwoven fabric was excellent in stiffness and mechanical performance, had high liquid absorption, and had excellent performance as a separator. Moreover, since the splittable conjugate fiber was substantially divided into each region (layer) by the hydroentanglement treatment, it had a high degree of separation characteristics. Table 1 shows the results. Example 3 90 parts by weight of the splittable conjugate fiber of Reference Example 3 and 10 parts by weight of the above binder fiber were mixed, and a web having a basis weight of 45 g / m ² was produced using a roller card. Next, a water entanglement treatment was performed in the same manner as in Example 1 to a thickness of 15 μm.
m of non-woven fabric was obtained. The obtained nonwoven fabric was excellent in stiffness and mechanical performance, had high liquid absorption, and had excellent performance as a separator. Moreover, since the splittable conjugate fiber was substantially divided into the respective regions (layers) by the hydroentanglement treatment, it had an extremely high separating property. Table 1 shows the results.

Comparative Example 1 A nonwoven fabric was produced in the same manner as in Example 1 except that the splittable conjugate fiber of Reference Example 4 was used. Since the resulting nonwoven fabric was weak, it could not only be efficiently attached to the battery, but also was easily damaged by impact or the like, and an internal short circuit was more likely to occur than in the examples. Table 1 shows the results.

Comparative Example 2 A nonwoven fabric was produced in the same manner as in Example 1, except that the polypropylene fiber of Reference Example 5 was used instead of the splittable conjugate fiber. The obtained nonwoven fabric was inferior in liquid absorption performance and was unsuitable as a battery separator.

[0036]

[Table 1]

Claims (4)

[Claims] 1. A battery separator comprising a nonwoven fabric made of a splittable conjugate fiber containing at least one component of an ethylene vinyl alcohol copolymer having an ethylene content of 20 to 70 mol% and a melt index of 0.5 to 8 g / 10 min. . 2. A battery comprising a nonwoven fabric made of a splittable conjugate fiber comprising an ethylene vinyl alcohol copolymer and a polypropylene polymer having an ethylene content of 20 to 70 mol% and a melt index of 0.5 to 8 g / 10 min. Separator. 3. The battery separator according to claim 1, wherein the splittable conjugate fiber is split to have a reduced diameter. 4. A nonwoven sheet is formed by using a splittable conjugate fiber containing an ethylene vinyl alcohol copolymer having an ethylene content of 20 to 70 mol% and a melt index of 0.5 to 8 g / 10 min as at least one component. And a method for producing a battery separator by dividing the splittable conjugate fiber by subjecting the nonwoven fabric to a hydroentanglement treatment.