KR101606157B1 - Base material for lithium ion secondary battery, and separator for lithium ion secondary battery - Google Patents

Abstract

Characterized in that it comprises polyester nonwoven fabrics made of polyester staple fibers having an average fiber diameter of not more than 5.0 mu m and a fiber length of not more than 2 mm as an essential component and has high safety at the time of overcharging, And a separator for a lithium ion secondary battery using the substrate.

Description

TECHNICAL FIELD [0001] The present invention relates to a base for a lithium ion secondary battery and a separator for a lithium ion secondary battery. BACKGROUND OF THE INVENTION [0002]

TECHNICAL FIELD The present invention relates to a base material for a lithium ion secondary battery that can be suitably used for a lithium ion secondary battery such as a lithium ion secondary battery and a lithium ion polymer secondary battery, and a separator for a lithium ion secondary battery using the base material.

BACKGROUND ART [0002] With the recent spread of portable electronic devices and their high performance, secondary batteries having high energy density are demanded. As this type of battery, a lithium ion secondary battery using an organic electrolytic solution (nonaqueous electrolytic solution) has attracted attention. This lithium ion secondary battery has a high energy density in that an average voltage of about 3.7 V, which is about three times that of a conventional secondary battery, is obtained. Since an aqueous electrolyte such as an alkaline secondary battery can not be used, A nonaqueous electrolyte solution having resistance to oxidation and reduction is used. Since the non-aqueous electrolyte is flammable, there is a risk of ignition or the like, and attention is paid to safety in its use. There are several possible cases of exposure to such hazards as ignition, especially overcharging is dangerous.

In order to prevent overcharging, a non-aqueous secondary battery in the current situation is subjected to constant voltage / constant current charging, and a battery is equipped with a precise IC (protection circuit). The cost of this protection circuit is high, which is a cause of high cost of the non-aqueous secondary battery.

When overcharging is prevented in the protection circuit, it is assumed that the protection circuit does not work well, and it is difficult to say that it is intrinsically safe. The present non-aqueous secondary battery has been studied to have a safety fuse for a safety valve and PTC device and a thermal fuse for a separator in order to break the protection circuit when the battery is overcharged and to safely destroy the battery when the battery is overcharged. However, even if the above-mentioned means is equipped, the safety at the time of overcharging is surely guaranteed depending on the overcharged condition, and actually, the ignition of the non-aqueous secondary battery is still occurring.

As a separator, a film-like porous film made of a polyolefin such as polyethylene and the like is often used. When the temperature inside the battery reaches about 130 캜, the separator is melted to prevent micropores, , And a thermal fuse function (shutdown function) that cuts off the current. In some circumstances, when the temperature further rises, the polyolefin itself is melted and short-circuited, suggesting a possibility of thermal runaway. Therefore, a heat-resistant separator which does not melt and shrink even at a temperature near 200 ° C is being developed.

As the heat-resistant separator, there are nonwoven fabrics composed of polyester fibers and nonwoven fabrics in which aramid fibers as heat-resistant fibers are blended with polyester fibers, which is not practical because of the large hole diameter and internal short-circuiting (see, for example, Patent Document 1 ~ 3). On the other hand, an example in which a nonwoven fabric composed of polyester fibers is laminated on a film-like porous film made of polyolefin to form a composite, an example in which heat resistance is imparted by incorporation of filler particles in a nonwoven fabric or woven fabric, (See, for example, Patent Documents 4 to 6). However, the nonwoven fabric used as the base material has a large hole and low surface smoothness, so that unevenness of the surface when composite is formed by surface coating is large, and composite cargo such as filler particles and resin is easily removed Or the like.

Japanese Patent Application Laid-Open No. 2003-123728 (no overseas family) Japanese Laid-Open Patent Publication No. 2007-317675 (International Publication No. 2001/67536 pamphlet, US Patent Application Publication No. 2003/0003363) Japanese Patent Application Laid-Open No. 2006-19191 (no overseas family) Japanese Unexamined Patent Application Publication No. 2005-293891 (no overseas family) Japanese Published Patent Application No. 2005-536857 (International Publication No. 2004/021476 pamphlet, US Patent Application Publication No. 2006/0024569) Japanese Laid-Open Patent Publication No. 2007-157723 (International Publication No. 2006/062153 pamphlet, US Patent Application Publication No. 2007/0264577)

A problem to be solved by the present invention is to provide a base material for a lithium ion secondary battery which has high safety at the time of overcharging and which is suitable for combination, and a separator for a lithium ion secondary battery using the base material.

Means for Solving the Problems As a result of intensive studies to solve the above problems,

(1) A base material for a lithium ion secondary battery comprising a nonwoven fabric of polyester-based short fibers, which comprises polyester-based extreme ultrafine fibers having an average fiber diameter of 5.0 m or less and a fiber length of 2 mm or less as essential components A base material for a lithium ion secondary battery,

(2) a substrate for a lithium ion secondary battery according to the above (1), wherein the polyester-based extreme fiber has an aspect ratio (fiber length / fiber diameter) of 20 to 800,

(3) A base material for a lithium ion secondary battery as described in (1) or (2) above, wherein the content of the polyester-based extreme fiber relative to the nonwoven fabric is 1 to 30 mass%

(4) A process for impregnating or coating a slurry containing inorganic or organic filler particles with the base material for a lithium ion secondary battery according to any one of (1) to (3) A process for impregnating or coating a slurry for a lithium ion secondary cell, a process for impregnating or coating a slurry for forming a porous film, a process for integrally forming a laminate of a porous film, and a process for impregnating or coating a solid electrolyte or a gel electrolyte. I got it.

A base material (1) for a lithium ion secondary battery according to the present invention comprises a polyester-based short fiber non-woven fabric and has a polyester-based extreme fiber having an average fiber diameter of 5.0 m or less and a fiber length of 2 mm or less as an essential component And is superior in compactness and uniformity as compared with a base material for a conventional lithium ion secondary battery. As a result, surface unevenness at the time of composite formation is small due to surface coating, and detachment of the composite material does not occur well, and good quality can be realized. In addition, since it is made of polyester staple fibers, it has high heat resistance and high safety at the time of overcharging.

(2) for a lithium ion secondary battery having an aspect ratio (fiber length / fiber diameter) of 20 to 800 and a nonwoven fabric containing 1 to 30 mass% of a polyester based extreme fiber, (3) is more excellent in denseness and uniformity as a base material.

The separator for a lithium ion secondary battery of the present invention can be provided by using the base materials (1), (2) and (3) for a lithium ion secondary battery of the present invention.

Hereinafter, the base for a lithium ion secondary battery of the present invention will be described in detail. The base material for a lithium ion secondary battery of the present invention is a polyester-based short-staple nonwoven fabric comprising a polyester-based extreme fiber having an average fiber diameter of 5.0 m or less and a fiber length of 2 mm or less as an essential component. The average fiber diameter refers to an arithmetic mean value of ten fiber diameters measured by taking an enlarged photograph of a magnification of 3000 times under a microscope.

In the base material for a lithium ion secondary battery of the present invention, when the average fiber diameter of the polyester-based extreme ultraviolet fibers exceeds 5.0 m, the number of fibers in the thickness direction is decreased, and the required compactness can not be secured. If the fiber length exceeds 2 mm, the number of fibers to be overlapped increases, and the number of fibers in the whole fiber becomes small, so that necessary uniformity can not be ensured. More preferable average fiber diameter of the polyester based extreme fiber is 0.5 to 5.0 mu m, and more preferable is the fiber length is 0.05 to 2 mm.

In order to balance the compactness and the uniformity, the aspect ratio (fiber length / fiber diameter) of the polyester extreme fiber is more preferably 20 to 800, and still more preferably 80 to 700.

In the base for a lithium secondary battery of the present invention, the preferable content of the polyester-based extreme fiber is 1 to 30% by mass, and more preferably 5 to 20% by mass. If it is less than 1% by mass, the denseness and uniformity may not be improved. If it exceeds 30% by mass, the required strength may not be exhibited as a base material.

The average fiber diameter of the short fibers other than the polyester-based extreme fibers contained in the substrate for a lithium ion secondary battery of the present invention is preferably 0.1 to 10.0 탆. If it is more than 10.0 占 퐉, the number of fibers in the thickness direction becomes small, so that necessary compactness may not be secured. When the thickness is less than 0.1 占 퐉, it is difficult to stably produce fibers. More preferably, the average fiber diameter is 0.5 to 5.0 mu m.

The weight per unit area of the substrate for a lithium ion secondary battery of the present invention is preferably 6.0 to 30.0 g / m 2. If it is more than 30.0 g / m < 2 >, the majority of the separator is occupied only by the substrate, and the effect due to the complexation can not be obtained well. If it is less than 6.0 g / m < 2 >, uniformity is not obtained well and large unevenness It tends to be easier to do. And more preferably 8.0 to 20.0 g / m 2. In addition, the weight per unit area means the basis weight based on the method prescribed in JIS P 8124 (Paper and Paperboard-Balance Measurement Method).

The polyester based (short) staple fibers may be heat-sealed (polar) staple fibers (binder staple fibers) or non-heat-sealed (polar) staple fibers. When used as thermally welded (polar) staple fibers, there are core-sheath type, eccentric type, side-by-side type, sea type, orange type, multi-bimetallic type conjugated fiber or single component type. It is particularly preferred to be of the single component type.

In the present invention, polyester eggs, such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, . These may be used alone or in combination of two or more. Among them, when used in a substrate for a lithium ion secondary battery, a polyethylene terephthalate-based material having excellent heat resistance is preferable.

The composite of the base material for a lithium ion secondary battery of the present invention is not particularly limited. The base material for a lithium ion secondary battery of the present invention may be formed by impregnating or coating a slurry containing inorganic or organic filler particles, Impregnating or coating the porous film, laminating and integrating the porous film, and impregnating or coating a solid electrolyte or a gel electrolyte. By performing these treatments, the separator for a lithium ion secondary battery of the present invention can be obtained.

In the base material for a lithium ion secondary battery of the present invention, a nonwoven fabric may be produced by forming a fibrous web and bonding, fusing, or entangling the fibers in the fibrous web. The obtained nonwoven fabric may be used as it is, or may be used as a laminate composed of a plurality of sheets. Examples of the method for producing the fibrous web include a dry method such as a card method and an airlay method, a wet method such as a papermaking method, a spun bond method, and a melt blow method. Of these, the web obtained by the wet method is homogeneous and dense and can be preferably used as a base material for a lithium ion secondary battery. The wet method is a method in which a fiber web is obtained by dispersing fibers in water to obtain a homogeneous paper slurry, and using a paper machine having at least one of a wire of a grinding wheel, a grinding wheel, an inclined grinding wheel, and the like.

As a method for producing a nonwoven fabric from a fibrous web, a water flow lag method, a needle punch method, a binder bonding method, or the like can be used. Particularly, in the case of using the above-described wet method with an emphasis on uniformity, it is preferable to bond the heat-sealed (short) staple fibers by a binder bonding method. By the binder bonding method, a uniform nonwoven fabric is formed from a uniform web. It is preferable to apply pressure to the wet nonwoven fabric thus produced by calendering or the like to adjust the thickness or make the thickness uniform. However, it is preferable to pressurize at a temperature at which the heat welding (polar) staple fibers do not become a film (a temperature lower than the melting point of the thermally welded (polar) staple fibers by 20 deg.

In the base material for a lithium ion secondary battery of the present invention, when a nonwoven fabric is produced by a wet process, the fiber length of the fibers other than the polyester based extreme fiber is preferably more than 2 mm and not more than 7 mm, more preferably 3 to 5 mm desirable. In the case where the fiber length exceeds 7 mm, there is a problem that dispersion of the fibers is difficult in the wet process due to the balance with the average fiber diameter, resulting in poor quality of the fabric, and the formation of a good fiber web becomes impossible . On the other hand, since the fibers other than the polyester-based extreme fibers are entangled with the polyester-based extreme fibers to improve the strength of the base, when the fiber length in the fibers other than the polyester-based extreme fibers is 2 mm or less, The strength required for the substrate may not be developed.

Here, the strength required for the base material is a strength that can withstand a short circuit when the battery is wound after being finished with a separator, and the strength of piercing can be an index. The penetration strength is preferably 30 g or more. More preferably 50 g or more.

Example

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Also, the percentages and percentages in the examples are all by mass unless otherwise noted.

Example 1

40 parts of an oriented crystallized polyethylene terephthalate (PET) staple fiber having a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, a staple fiber having a fineness of 0.1 dtex (average fiber diameter: 3.0 탆), a fiber length of 1 mm, 10 parts of oriented PET-based extruded fibers with a ratio of 329, 50 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together, And the slurry was uniformly prepared for agitation (1% concentration) under agitation with an agitator. The slurry for this purpose was raised by a wet process using a crushing machine and adhered with a cylinder dryer at a temperature of 120 ° C to bond the PET staple fibers for the binder and to develop a nonwoven fabric strength to obtain a nonwoven fabric having a basis weight of 10.2 g / . Next, calendering was carried out at a roll temperature of 180 DEG C to prepare a nonwoven fabric having a basis weight of 10.2 g / m < 2 > and a thickness of 17 mu m to obtain a substrate for a lithium ion secondary battery.

Example 2

49 parts of oriented PET-oriented short fibers having a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, 48 parts of oriented crystallization of a fineness of 0.1 dtex (average fiber diameter: 3.0 탆), a fiber length of 1 mm and an aspect ratio of 329 , PET staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together, and 50 parts of PET-based staple fibers for binder were mixed together. A uniform slurry for agitation (1% concentration) was prepared with stirring. The slurry of this type was drawn up using a wet process by a grinder paper machine and the PET type staple fibers for binder were adhered by a cylinder drier at 120 ° C. to develop the nonwoven fabric strength and a nonwoven fabric having a basis weight of 10.6 g / . Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 10.6 g / m2 and a thickness of 18 占 퐉 to prepare a substrate for a lithium ion secondary battery.

Example 3

49.3 parts of PET-based short fibers obtained by orientation crystallization with a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, and orientation crystallization with a fineness of 0.1 dtex (average fiber diameter: 3.0 탆), a fiber length of 1 mm and an aspect ratio of 329 , PET staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together, and 50 parts of PET-based staple fibers for binder were mixed together. A uniform slurry for agitation (1% concentration) was prepared with stirring. The slurry for this purpose was raised by a wet method using a crusher, and the PET staple fibers for binder were adhered by a cylinder drier at 120 ° C. to develop the nonwoven fabric strength, and a nonwoven fabric having a basis weight of 10.5 g / . Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 10.5 g / m2 and a thickness of 18 占 퐉 to prepare a substrate for a lithium ion secondary battery.

Example 4

20 parts of orientation-crystallized PET-based short fibers having a fineness of 0.06 dtex (average fiber diameter: 2.4 占 퐉) and a fiber length of 3 mm, 20 parts of oriented crystallization of a fineness of 0.1 dtex (average fiber diameter: 3.0 占 퐉), a fiber length of 1 mm and an aspect ratio of 329 , 30 parts of PET-based extreme fibers, 50 parts of PET-based staple fibers for a binder having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together and grasped in pulp water, A uniform slurry for agitation (1% concentration) was prepared with stirring. The slurry for this purpose was raised by a wet process using a crushing machine and adhered to the PET staple fibers for binder by a cylinder drier at 120 ° C. to develop the nonwoven fabric strength to obtain a nonwoven fabric having a basis weight of 9.8 g / . Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 9.8 g / m2 and a thickness of 17 占 퐉 to prepare a substrate for a lithium ion secondary battery.

Example 5

17 parts of PET-based short fibers having an orientation degree of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, 17 parts of oriented crystallization of a fineness of 0.1 dtex (average fiber diameter: 3.0 탆), a fiber length of 1 mm and an aspect ratio of 329 , 33 parts of PET-based extreme fibers, 50 parts of PET-based staple fibers for binders having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together and grasped in pulp water, A uniform slurry for agitation (1% concentration) was prepared with stirring. The slurry of the present invention was raised by a wet method using a papermaking machine and the PET staple fibers for binders were bonded by a cylinder dryer at 120 ° C to develop the nonwoven fabric strength and a nonwoven fabric having a basis weight of 9.6 g / . Next, calendering was carried out at a roll temperature of 180 DEG C to prepare a nonwoven fabric having a basis weight of 9.6 g / m < 2 > and a thickness of 17 mu m to obtain a substrate for a lithium ion secondary battery.

Example 6

40 parts of oriented PET-based short fibers having a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, 40 parts of oriented crystallization of a fineness of 0.1 dtex (average fiber diameter: 3.0 탆), a fiber length of 2 mm and an aspect ratio of 658 , 10 parts of PET-based extreme fibers, 50 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together and grasped in the pulp water, A uniform slurry for agitation (1% concentration) was prepared with stirring. The slurry for this purpose was raised by a wet method using a papermaking machine and the PET staple fibers for binder were adhered by a cylinder drier at 120 ° C. to develop the nonwoven fabric strength and a nonwoven fabric having a basis weight of 10.0 g / . Next, calendering was carried out at a roll temperature of 180 DEG C to prepare a nonwoven fabric having a basis weight of 10.0 g / m < 2 > and a thickness of 17 mu m to obtain a substrate for a lithium ion secondary battery.

Example 7

40 parts of PET-based short fibers having an orientation degree of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, 40 parts of oriented crystallization of 0.1 dtex (average fiber diameter: 3.0 탆), a fiber length of 0.6 mm and an aspect ratio of 197 , 10 parts of PET-based extreme fibers, 50 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together and grasped in the pulp water, A uniform slurry for agitation (1% concentration) was prepared with stirring. The slurry for this purpose was raised by a wet process using a crushing machine and adhered to the PET staple fibers for binder by a cylinder drier at 120 ° C. to develop a nonwoven fabric strength and a nonwoven fabric having a basis weight of 9.9 g / . Next, calendering was carried out at a roll temperature of 180 DEG C to prepare a nonwoven fabric having a basis weight of 9.9 g / m < 2 > and a thickness of 17 mu m to obtain a substrate for a lithium ion secondary battery.

Example 8

40 parts of oriented PET-oriented short fibers with a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, and PET layers with oriented crystallization with a fineness of 0.1 dtex (average fiber diameter: 3.0 탆) , 10 parts of fibers, 20 parts of PET-based extreme fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆), a fiber length of 1 mm and an aspect ratio of 232, a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) And 30 parts of 3 mm PET short staple fibers for binder were mixed together and understood in the water of pulper, and a homogeneous slurry for agitation (1% concentration) was prepared with stirring by an agitator. The slurry for this purpose was raised by a wet process using a papermaking machine, and PET-based staple fibers for binders and PET-based staple fibers for binders were adhered by a cylinder dryer at 120 ° C to develop the nonwoven fabric strength to give a basis weight of 10.1 g / , And a width of 50 cm. Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 10.1 g / m2 and a thickness of 17 占 퐉 to obtain a base material for a lithium ion secondary battery.

Example 9

10 parts of PET-based extruded fibers with orientation degree of 0.06 dtex (average fiber diameter: 2.4 탆), fiber length: 1 mm and aspect ratio: 424, 10 parts of oriented crystallization with a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) 10 parts of PET-based short fibers obtained by orientation-crystallizing fibers having a fineness of 0.1 dtex (average fiber diameter: 3.0 탆) and a fiber length of 3 mm, 30 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) Twenty parts of a PET-based extruded fiber for a binder having a length of 1 mm and an aspect ratio of 232, 30 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together, Under the water, a homogeneous slurry for agitation (1% concentration) was prepared with stirring by an agitator. The slurry for the extrusion was raised by a wet process using a papermaking machine, and PET-based extreme fibers for binders and PET-based staple fibers for binders were bonded by means of a cylinder dryer at 120 ° C to develop the nonwoven fabric strength to give a basis weight of 10.3 g / , And a width of 50 cm. Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 10.3 g / m2 and a thickness of 18 占 퐉 to prepare a substrate for a lithium ion secondary battery.

Example 10

10 parts of PET-based extruded fibers with orientation degree of 0.06 dtex (average fiber diameter: 2.4 탆), fiber length: 1 mm and aspect ratio: 424, 10 parts of oriented crystallization with a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) 10 parts of PET-based short fibers obtained by orientation-crystallizing fibers having a fineness of 0.1 dtex (average fiber diameter: 3.0 탆) and a fiber length of 3 mm, 30 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) 20 parts of PET-based extruded fibers having a length of 0.1 mm and an aspect ratio of 23, 30 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together, Under the water, a homogeneous slurry for agitation (1% concentration) was prepared with stirring by an agitator. The slurry for anchorage was raised by a wet process using a crushing machine and adhered to PET binder staple fibers for binders and a PET staple fiber for binders by a cylinder dryer at 120 ° C to develop the nonwoven fabric strength to have a basis weight of 9.8 g / , And a width of 50 cm. Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 9.8 g / m2 and a thickness of 17 占 퐉 to prepare a substrate for a lithium ion secondary battery.

Example 11

10 parts of PET-based extruded fibers with orientation degree of 0.06 dtex (average fiber diameter: 2.4 탆), fiber length: 1 mm and aspect ratio: 424, 10 parts of oriented crystallization with a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) 10 parts of PET-based short fibers obtained by orientation-crystallizing fibers having a fineness of 0.1 dtex (average fiber diameter: 3.0 탆) and a fiber length of 3 mm, 30 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) 20 parts of PET-based extreme fibers for a binder having a length of 0.05 mm and an aspect ratio of 11, 30 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together, Under the water, a homogeneous slurry for agitation (1% concentration) was prepared with stirring by an agitator. The slurry for anchorage was raised by a wet method using a papermaking machine, and PET-based staple fibers for binders and PET-based staple fibers for binders were adhered by a cylinder dryer at 120 ° C to develop the nonwoven fabric strength and a basis weight of 9.3 g / , And a width of 50 cm. Next, calendering was carried out at a roll temperature of 180 DEG C to prepare a nonwoven fabric having a basis weight of 9.3 g / m < 2 > and a thickness of 16 mu m to obtain a substrate for a lithium ion secondary battery.

Example 12

20 parts of PET-based extreme fibers having orientation degree of 0.06 dtex (average fiber diameter: 2.4 탆), fiber length: 0.6 mm and aspect ratio of 254, 20 parts of oriented crystallization with a fineness of 0.1 dtex (average fiber diameter: 3.0 탆) , PET staple fibers for binders having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together and were understood in the water of a pulper, A uniform slurry for agitation (1% concentration) was prepared with stirring. The slurry for this purpose was raised by a wet process using a paper machine and adhered to the PET staple fibers for binder by a cylinder drier at 120 ° C to develop the nonwoven fabric strength and a nonwoven fabric having a basis weight of 10.1 g / . Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 10.1 g / m2 and a thickness of 17 占 퐉 to obtain a base material for a lithium ion secondary battery.

Example 13

20 parts of PET-based extruded fibers obtained by orientation-crystallizing a fiber having a fineness of 0.06 dtex (average fiber diameter: 2.4 탆), a fiber length of 2 mm and an aspect ratio of 849, 20 parts of oriented crystallization with a fineness of 0.1 dtex (average fiber diameter: 3.0 탆) , PET staple fibers for binders having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together and were understood in the water of a pulper, A uniform slurry for agitation (1% concentration) was prepared with stirring. This slurry for anchorage was raised by a wet method using a crushing machine and adhered to the PET staple fibers for binder by a cylinder drier at 120 ° C to develop the nonwoven fabric strength to obtain a nonwoven fabric having a basis weight of 10.4 g / . Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 10.4 g / m2 and a thickness of 17 占 퐉 to obtain a substrate for a lithium ion secondary battery.

Example 14

20 parts of PET-based extruded fibers with orientation degree of 0.06 dtex (average fiber diameter: 2.4 탆), fiber length: 1 mm and aspect ratio: 424, 10 parts of PET-based short fibers obtained by orientation crystallization with a fineness of 0.3 dtex (average fiber diameter: 5.3 탆) and a fiber length of 3 mm, 20 parts of PET-based short fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) 50 parts of PET-based staple fibers for a binder having a length of 3 mm were mixed together and understood in the water of a pulper to prepare a homogeneous slurry for agitation (1% concentration) with stirring by an agitator. The slurry for this purpose was raised by a wet process using a crushing machine and adhered to the PET staple fibers for binder by a cylinder drier at 120 ° C. to develop a nonwoven fabric strength and a nonwoven fabric having a basis weight of 9.9 g / . Next, calendering was carried out at a roll temperature of 180 DEG C to prepare a nonwoven fabric having a basis weight of 9.9 g / m < 2 > and a thickness of 17 mu m to obtain a substrate for a lithium ion secondary battery.

Example 15

10 parts of PET-based extreme fibers having orientation degree of 0.004 dtex (average fiber diameter 0.70 占 퐉), fiber length 0.5 mm and aspect ratio 714, orientation crystallization with a fineness of 0.06 dtex (average fiber diameter 2.4 占 퐉) and a fiber length of 3 mm 20 parts PET short staple fibers, 20 parts PET short staple fibers having orientation degree of 0.1 dtex (average fiber diameter 3.0 탆) and fiber length 3 mm, 0.2 dtex (average fiber diameter: 4.3 탆) 50 parts of 3 mm PET short staple fibers for binder were mixed together and understood in the water of pulper, and a homogeneous slurry for agitation (1% concentration) was prepared with stirring by an agitator. The slurry for anchorage was raised by a wet process using a crushing machine and adhered with a cylinder dryer at a temperature of 120 ° C to bond the PET staple fibers for a binder and to develop a nonwoven fabric strength to obtain a nonwoven fabric having a basis weight of 9.7 g / . Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 9.7 g / m2 and a thickness of 16 占 퐉 to prepare a substrate for a lithium ion secondary battery.

Example 16

10 parts of PET-based short fibers obtained by orientation crystallization with a fineness of 0.004 dtex (average fiber diameter 0.70 mu m) and a fiber length of 3 mm, orientation crystallization with a fineness of 0.06 dtex (average fiber diameter: 2.4 mu m), a fiber length of 1 mm, and an aspect ratio of 424 20 parts of PET-based extruded fibers, 20 parts of PET-based short fibers obtained by orientation crystallization with a fineness of 0.1 dtex (average fiber diameter: 3.0 탆) and a fiber length of 3 mm, 0.2 dtex (average fiber diameter: 4.3 탆) 50 parts of 3 mm PET short staple fibers for binder were mixed together and understood in the water of pulper, and a homogeneous slurry for agitation (1% concentration) was prepared with stirring by an agitator. The slurry for this purpose was raised by a wet process using a crushing machine and adhered to the PET staple fibers for binder by a cylinder drier at 120 ° C. to develop the nonwoven fabric strength to obtain a nonwoven fabric having a basis weight of 9.8 g / . Next, calendering was carried out at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 9.8 g / m2 and a thickness of 16 占 퐉 to prepare a substrate for a lithium ion secondary battery.

(Comparative Example 1)

50 parts of oriented PET-oriented short fibers having a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, PET staple fibers for binders having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) 50 parts were mixed together and understood in the water of pulper, and uniform agitation slurry (1% concentration) was prepared with stirring by an agitator. The slurry for this purpose was raised by a wet process using a crushing machine and adhered with a cylinder dryer at a temperature of 120 ° C to bond the PET staple fibers for the binder and to develop a nonwoven fabric strength to obtain a nonwoven fabric having a basis weight of 10.2 g / . Next, calendering was carried out at a roll temperature of 180 DEG C to prepare a nonwoven fabric having a basis weight of 10.2 g / m < 2 > and a thickness of 17 mu m to obtain a substrate for a lithium ion secondary battery.

(Comparative Example 2)

40 parts of orientation-crystallized PET-based short fibers having a fineness of 0.06 dtex (average fiber diameter: 2.4 탆) and a fiber length of 3 mm, PET-based extreme ultrafine fibers having an orientation crystallized with a fineness of 0.3 dtex (average fiber diameter: 5.3 탆) 10 parts of fibers, 50 parts of PET-based staple fibers having a fineness of 0.2 dtex (average fiber diameter: 4.3 탆) and a fiber length of 3 mm were mixed together and understood in the water of pulper, An agitation slurry (1% concentration) was prepared. The slurry for this purpose was raised by a wet method using a crusher, and the PET staple fibers for binder were adhered by a cylinder drier at 120 ° C. to develop the nonwoven fabric strength, and a nonwoven fabric having a basis weight of 10.5 g / . Next, calendering was performed at a roll temperature of 180 占 폚 to prepare a nonwoven fabric having a basis weight of 10.5 g / m2 and a thickness of 19 占 퐉, thereby forming a base for a lithium ion secondary battery.

<Evaluation>

The following evaluations were carried out on the substrate for a lithium ion secondary battery obtained in Examples and Comparative Examples, and the results are shown in Table 1. [

[Heating property of substrate]

(PE) microporous membrane (microporous membrane) having a thickness of 20 mu m which is a conventionally known separator as the base materials of Examples 1 to 16 and Comparative Examples 1 and 2 and Comparative Example 3 was left in a thermostatic chamber at 150 DEG C for 30 minutes , And the shrinkage percentage of each substrate was measured to evaluate the heating characteristics. The shrinkage percentage was measured as follows. The length of each substrate piece was measured after leaving for 30 minutes in a thermostatic chamber at 150 캜 with two glass plates fixed by a clip therebetween by cutting the substrate piece cut into 5 cm 占 5 cm and measuring the length Was defined as the shrinkage percentage.

[Production of separator]

1000 g of flaky boehmite (average particle diameter: 1 占 퐉, aspect ratio: 10), 800 g of water, 200 g of isopropyl alcohol and 375 g of polyvinyl butyral were placed in a vessel and stirred with a stirrer (trade name: ) For 1 hour and dispersed to obtain a homogeneous slurry. The nonwoven fabrics of Examples 1 to 16 and Comparative Examples 1 and 2 were respectively passed through the slurry, and the slurry was applied by pulling up the slurry, then passed between gaps having a predetermined gap, and then dried, A separator having a porous film having a thickness of 3 탆 was obtained.

[Evaluation of Coating Property of Substrate]

The produced separator was subjected to thickness measurement at arbitrary 10 points. When the difference was 1 占 퐉 or less,?, 1 占 퐉, 2 占 퐉 or less and? When it exceeded 2 占 퐉. In addition, the thickness means a value measured by a method specified in JIS B 7502, that is, a value measured by an external micrometer at the time of 5 N load.

[Strength of substrate]

The substrates of Examples 1 to 16 and Comparative Examples 1 and 2 were cut into a rectangular shape of 50 mm width and made constant. The test piece was attached to a 40 mm phi fixed frame fixed with a table type material tester (trade name: STA-1150, Orientech), and a metal needle having a diameter of 1.0 mm (roundness 1.6) Manufactured by Orientech) was passed through the sample surface at a right angle at a constant speed of 50 mm / min. The maximum load g at this time was measured and used as the piercing strength. The sample was subjected to measurement of the piercing strength at five or more points. The smallest among the total measured values was evaluated as?, When it was 50 g or more,?, When it was less than 30 g and less than 50 g, and when it was less than 30 g.

The base material for a lithium ion secondary battery obtained in the Examples is characterized by comprising a PET-based extruded non-woven fabric of PET-based short fibers and having an average fiber diameter of 5 m or less and a fiber length of 2 mm or less as essential components And was superior in denseness and uniformity to conventional lithium ion secondary battery substrates. As a result, a good result was obtained that the unevenness of the surface when composite by surface coating was small. Further, since it is made of PET-based fibers, heat shrinkage is hardly observed at 150 占 폚, and substantially no deformation occurs at the naked eye level. Therefore, the heat resistance is high, and the safety at the time of overcharging is high.

Examples 1, 2, 4, 6 to 10, 12, and 12, wherein the aspect ratio (fiber length / fiber diameter) of the polyester based extreme fibers is 20 to 800 and the content of the polyester based extreme fibers is 1 to 30% 15 and 16 were both excellent in both coatability and strength. Example 11 in which the aspect ratio (fiber length / fiber diameter) of the polyester extreme fiber was less than 20, Example 13 in which the polyester extreme fiber had an aspect ratio (fiber length / fiber diameter) In Example 3 in which the content of the extreme fibers was less than 1% by mass, the unevenness of the surface when composing by surface coating was slightly larger. In Example 5 in which the content of the polyester-based extreme fiber exceeded 30% by mass, the strength was slightly lower.

In Example 14 in which fibers having an average fiber diameter exceeding 5 占 퐉 were contained as fibers other than polyester-based extreme fibers, the unevenness of the surface when compounded by surface coating tended to increase.

On the other hand, in the base material for a lithium ion secondary battery obtained in Comparative Example 1, the PET-based staple fibers used had an average fiber diameter of 2.4 m and a fiber length of 3 mm, an average fiber diameter of 5.0 m or less, Or less. Therefore, the required uniformity of the base material for a lithium ion secondary battery does not satisfy a sufficient requirement. As a result, it was found that surface unevenness occurred when the composite was formed by surface coating.

The base material for a lithium ion secondary battery obtained in Comparative Example 2 has an average fiber diameter of 5.3 占 퐉 and 5.0 占 퐉 in the PET-based extruded fibers having a fiber length of 2 mm or less. As a result, it was found that surface unevenness occurred when the composite was formed by surface coating.

In Comparative Example 3 corresponding to the conventional separator, the heat shrinkage rate is large, and when the battery is used for a battery, shrinkage of the separator occurs when the battery is overcharged with an internal temperature of 150 캜, resulting in a short circuit due to contact between the positive electrode and the negative electrode There is a problem with safety.

Industrial availability

The substrate for a lithium ion secondary battery of the present invention can be preferably used for a lithium ion secondary battery, a lithium ion polymer secondary battery, and the like, and a separator for a lithium ion secondary battery.

Claims (4)

A separator base material for a lithium ion secondary battery comprising a nonwoven fabric of polyester-based short fibers,
Characterized in that polyester based extreme short fibers having an average fiber diameter of 5.0 m or less and a fiber length of 2 mm or less are contained as essential components. The method according to claim 1,
A separator base material for a lithium ion secondary battery having an aspect ratio (fiber length / fiber diameter) of polyester based extreme fibers of 20 to 800. The method according to claim 1,
Wherein the content of the polyester-based extreme fiber relative to the nonwoven fabric is 1 to 30 mass%. A process for impregnating or coating a slurry containing inorganic or organic filler particles, a process for impregnating or coating a slurry containing a resin, a process for impregnating or coating a slurry containing inorganic or organic filler particles, a process for impregnating or coating a slurry containing inorganic or organic filler particles, Wherein the porous film is formed by laminating and integrating a porous film, and a treatment for impregnating or coating a solid electrolyte or a gel electrolyte.