JP2002141045A - Non-aqueous electrolyte battery separator and non- aqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte battery separator that has small degradation of air permeability of the separator at each part inside the battery even if it is stored for a long period at 20 deg.C-80 deg.C that is assumed in summer or in the automobile, and thereby can make longer the battery life, and a non- aqueous electrolyte battery using this separator. SOLUTION: The non-aqueous electrolyte separator is made of a porous film that contains a cross-linked substance made by cross-linking a polyolefine system polymer and a polymer having double bond and that has a rate of rise of 10% or less before and after storage of the Gurley value measured in accordance with the JIS P8117 when it is stored for 20 days at 60 deg.C under the pressure of 500 kPa (gauge pressure) by fixing the surrounding with a frame.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separator for a non-aqueous electrolyte battery using a porous film containing a crosslinked product obtained by cross-linking a polyolefin polymer and a polymer having a double bond, and a non-aqueous solution. The present invention relates to an electrolyte battery.

[0002]

2. Description of the Related Art Non-aqueous electrolyte batteries using a light metal such as lithium as an electrode have a high energy density and low self-discharge. I have. As an electrode of such a nonaqueous electrolyte battery, a spiral wound body having a wide effective electrode area secured by laminating and winding a strip-shaped positive electrode, a negative electrode, and a separator is used. The separator interposed between the electrodes basically prevents both electrodes from being short-circuited, and allows the battery to react by allowing ions to permeate due to its porous structure. If an abnormal current is generated due to an incorrect connection or the like, a resin having a so-called shutdown function (SD function) that stops the battery reaction by thermally deforming the resin and closing the micropores as the battery internal temperature rises is safe. It is adopted from the viewpoint of improving the performance.

As a separator having such an SD function, for example, a microporous film made of polyethylene, a microporous film having a multilayer structure of polyethylene and polypropylene, and the like are known. In addition, a porous film further containing a rubber or the like in addition to the polyolefin polymer has been proposed (for example, Japanese Patent Publication No. 1-18091, Japanese Patent Application Laid-Open No. 6-1630).
No. 23).

[0004]

However, a non-aqueous electrolyte battery using the above-mentioned conventional separator is not always in the initial state when it is stored in a high-temperature state such as in a long-term charge / discharge cycle or in a summer or in an automobile. Could not be maintained for a long time. For example, when a battery is stored at 20 ° C. to 80 ° C., which is assumed in a summer or in an automobile, the separator gradually deforms due to the internal tension and pressure of the battery roll, and the air permeability decreases (Gurley value). Rises)
However, it has been found that this causes a decrease in battery life and the like.

In order to improve the heat resistance, Japanese Patent Application Laid-Open
JP-A-308866 discloses a method for obtaining a microporous porous film having high strength and excellent high-temperature characteristics by laminating a single film made of low-melting polyethylene and high-melting polypropylene. The weak low-melting-point polyethylene portion inside is liable to be deformed, and when kept in a high temperature state, the deterioration proceeds, and the battery life is likely to be shortened.

Accordingly, an object of the present invention is to reduce the air permeability of the separator in each part of the battery even when the battery is stored at 20 ° C. to 80 ° C. for a long period of time, which is assumed in a summer or in an automobile. The present invention provides a separator for a non-aqueous electrolyte battery that can be made longer, and a non-aqueous electrolyte battery using the same.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies on various physical properties, materials, etc. of a porous film constituting a separator, and found that a double bond is formed with a polyolefin polymer. The present inventors have found that a porous film containing a crosslinked product obtained by crosslinking a polymer having the polymer has less decrease in air permeability and membrane strength when stored at a high temperature for a long period of time, and completed the present invention.

That is, the separator for a non-aqueous electrolyte battery of the present invention comprises a porous film containing a crosslinked product obtained by crosslinking a polyolefin polymer and a polymer having a double bond. When fixed and stored at 60 ° C for 20 days under a pressure of 500 kPa (gauge pressure), JIS
The increase rate before and after storage of the Gurley value measured according to P8117 is 10% or less. Note that the parameter values in the present invention are all values measured by the measuring method of the embodiment.

In the above, the periphery is fixed at 130 ° C.
When stored for 3 days, the rate of decrease in the piercing strength measured using a pressure needle having a tip diameter of 0.5 mm before and after storage is 1
It is preferably 0% or less.

It is preferable that the polyolefin polymer is polyethylene having a weight average molecular weight of 500,000 or more.

On the other hand, a non-aqueous electrolyte battery according to the present invention is characterized by using any one of the separators for a non-aqueous electrolyte battery described above.

[Effects] According to the separator for a non-aqueous electrolyte battery of the present invention, a cross-linked product is contained to reduce the rate of increase in the Gurley value before and after storage under high-temperature and high-pressure storage. The results show that relatively high temperatures (about 60
C) for a long period of time, there is little decrease in the air permeability of the separator in each part of the battery, which can prolong the battery life. Although the details of the reason are unknown, in a polyolefin polymer having no crosslinked structure,
It is difficult to prevent the creep phenomenon even at a temperature equal to or lower than the melting point (about 60 ° C.), and it is difficult to maintain the porous structure. On the other hand, the porous film containing a crosslinked product can substantially eliminate the creep phenomenon, It is considered that the porous structure is easily maintained inside.

When the rate of decrease in the piercing strength before and after storage is 10% or less, even if the temperature rises due to erroneous connection or overcharge, the safety of the battery is maintained by maintaining the membrane strength to prevent a short circuit. Can be enhanced.

When the polyolefin polymer is polyethylene having a weight-average molecular weight of 500,000 or more, such a high-molecular-weight polyethylene tends to exhibit mechanical properties as a separator by stretching orientation when forming a porous structure. In addition, since a cross-linking reaction with a polymer having a double bond easily occurs, a decrease in air permeability when stored at a high temperature for a long time can be further reduced.

On the other hand, according to the nonaqueous electrolyte battery of the present invention,
In order to use the separator for a non-aqueous electrolyte battery according to any of the above, even when stored at a relatively high temperature for a long period of time, a decrease in the air permeability of the separator in each part in the battery is small, and thus the battery life can be prolonged. it can.

[0016]

Embodiments of the present invention will be described below.

The separator for a non-aqueous electrolyte battery according to the present invention comprises:
When the peripheral part is fixed to a frame and stored at 60 ° C. for 20 days under a pressure of 500 kPa (gauge pressure), the rate of increase in the Gurley value measured according to JIS P8117 before and after storage is 10%.
Consisting of the following porous film, the rate of increase is particularly 5%
The following is preferred.

When the porous film is fixed around the periphery of the porous film and stored at 130 ° C. for 3 days, the tip diameter is 0.5 mm.
It is preferable that the rate of decrease in the piercing strength measured using a pressure needle before and after storage is 10% or less.

Further, the porous film was heated at 135 ° C. for 60 minutes with the periphery thereof fixed to the frame to obtain a transparent film with microporous clogged.
When storing at 50 ° C. for 50 hours, it is preferable that a decrease rate of the piercing strength measured using a pressure needle having a tip diameter of 0.5 mm before and after storage is 10% or less.

The porous film in the present invention contains a crosslinked product obtained by crosslinking a polyolefin polymer and a polymer having a double bond. The crosslinked product can be obtained, for example, by heat-crosslinking a resin composition containing a polyolefin-based polymer and a polymer having a double bond in the presence of oxygen, ozone, an oxygen compound, or the like.
For this reason, the porous film in the present invention may simultaneously contain a partially remaining polyolefin-based polymer or a polymer having a double bond.

Examples of the polyolefin-based polymer include polyethylene, polypropylene, and polybutylene, but polyethylene and polypropylene are preferred. Examples of polyethylene include ultra high molecular weight polyethylene, high density polyethylene, low density polyethylene, etc.
Polyethylene having a weight average molecular weight of 500,000 or more, particularly polyethylene having a weight average molecular weight of 1,000,000 or more is preferable. Further, as the polypropylene, isotactic polypropylene, syndiotactic polypropylene and the like are preferable, and among them, isotactic polypropylene having high crystallinity is preferable because a porous structure is easily formed.

Examples of the polymer having a double bond include polybutadiene, polynorbornene, polyisoprene, and uncured products of other crosslinkable rubbers, and polynorbornene is particularly preferable. These polymers preferably have a weight average molecular weight of 500,000 or more.

The polymer having a double bond is preferably contained in the porous film in an amount of 1 to 40% by weight, particularly preferably 5 to 35% by weight. If the content is less than 1% by weight, crosslinking does not proceed sufficiently, and the rate of increase in the Gurley value after high-temperature and high-pressure storage tends to increase. On the other hand, if the content exceeds 40% by weight, the mechanical properties of the obtained porous film tend to decrease.

For the purpose of lowering the shutdown temperature of the separator and increasing the safety, among the above resin components,
Those having a relatively low melting point may be used in combination, and thermoplastic elastomers and graft copolymers may be used in combination. As the thermoplastic elastomer, polystyrene, polyolefin, polydiene, vinyl chloride,
Examples include thermoplastic elastomers such as polyesters. Examples of the graft copolymer include a graft copolymer having a polyolefin in the main chain and a vinyl-based polymer having an incompatible group in the side chain as a side chain, and include polyacryls, polymethacryls, polystyrene, polyacrylonitrile, and polyoxyethylene. Alkylenes are preferred. In addition,
Here, the incompatible group means a group incompatible with the polyolefin, and includes, for example, a group derived from a vinyl polymer. The content of these SD components in the porous film is preferably 1 to 40% by weight, particularly preferably 5 to 25% by weight.

The thickness of the non-aqueous electrolyte battery separator of the present invention is preferably 5 to 100 μm. Porosity 20-80
% Is preferable, and the average pore size is 0.01 to 0.5 μm
Is preferred. JIS as a comprehensive property by these
Air permeability (Gurley value) conforming to P8117 is 100 to
1000 sec / 100 ml is preferable.

Next, a method for producing a porous film according to the present invention will be described. For the production of the porous film, a known method such as a dry film forming method and a wet film forming method can be used. For example, the resin composition is mixed with a solvent, kneaded, extruded into a sheet while being heated and dissolved, cooled and gelled (solidified), and then stretched in a uniaxial direction or more by rolling or stretching under heating. Can be produced by extracting. It is preferable to use an antioxidant so that the oxidation reaction does not proceed during kneading and heat dissolution.

The crosslinking between the polyolefin polymer and the polymer having a double bond is preferably carried out after extraction and removal.
By subjecting the porous film to a cross-linking treatment with heat, ultraviolet rays, an electron beam or the like, a cross-linked product obtained by cross-linking the two in a stretched and oriented state can be obtained.

The initial adjustment of the Gurley value in the present invention is as follows.
The gelation can be performed by changing the cooling rate, the heat treatment conditions, the stretching conditions, and the like. In addition, the rate of increase in Gurley value before and after storage and the rate of decrease in piercing strength before and after storage are adjusted by the content of the polymer having a double bond, the type of polyolefin polymer, stretching conditions, crosslinking conditions, and the like. Can be.

Next, the nonaqueous electrolyte battery of the present invention will be described. The non-aqueous electrolyte battery uses the separator of the present invention as described above, and its structure is, for example, a strip-shaped negative electrode,
The wound electrode body obtained by laminating and winding the positive electrode and the separator is accommodated in a battery can, an electrolytic solution is injected into the battery can, and necessary members such as insulating plates above and below the battery are appropriately arranged according to a commercially available battery. It is configured.

As the electrolyte, for example, an electrolyte obtained by dissolving a lithium salt in an organic solvent is used. Examples of the organic solvent include, but are not particularly limited to, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, esters such as methyl propionate, butyl acetate, acetonitrile, and the like. Nitriles, 1,2-dimethoxyethane,
1,2-dimethoxymethane, dimethoxypropane, 1,
Ethers such as 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-1,3-dioxolane, and further alone such as sulfolane;
Alternatively, two or more kinds of mixed solvents can be used.

As the negative electrode, one obtained by integrating an alkali metal or a compound containing an alkali metal with a current collecting material such as a stainless steel net is used. Examples of the alkali metal at this time include lithium, sodium, potassium and the like, and examples of the compound containing the alkali metal include alloys of the alkali metal and aluminum, lead, indium, potassium, cadmium, tin, magnesium, etc. Examples include a compound of a metal and a carbon material, and a compound of a low-potential alkali metal and a metal oxide or sulfide. When a carbon material is used for the negative electrode, any carbon material can be used as long as it can dope and undope lithium ions. For example, graphite, pyrolytic carbons, cokes, glassy carbons, and firing of organic polymer compounds Body, mesocarbon microbeads, carbon fiber, activated carbon and the like can be used.

As the positive electrode, for example, metal oxides such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, vanadium pentoxide, and chromium oxide, and metal nitrides such as molybdenum disulfide are used. Used as an active material, a mixture obtained by appropriately adding a conductive additive or a binder such as polytetrafluoroethylene to these positive electrode active materials is formed into a molded body using a current collector material such as a stainless steel net as a core material. Finished products are used.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and the like specifically showing the configuration and effects of the present invention will be described below. In addition, the test method in an Example is as follows.

(Film Thickness) The cross section of the porous film was measured with a 1/10000 thickness gauge and a scanning electron microscope.

(Porosity) From the thickness (t), weight (W), resin density (d), and area (S), the following equation is used: Air efficiency (%) = (1−W / (S × d × t)) ) × 100.

(Air permeability) The initial Gurley value and the Gurley value after storage were measured according to JIS P8117.
The Gurley value after storage was measured using a sample cut to 100 × 100 mm, the periphery of which was fixed with a SUS frame, and put in a bat so that hot air did not directly hit it.
The Gurley value was measured after storing at 60 ° C. for 20 days under a pressure of (gauge pressure).

(Confirmation of cross-linked structure) C in IR spectrum
The disappearance of the absorption peak (960 cm ^-1 ) derived from the = C double bond was confirmed. Further, a sample of 10 mm square was sandwiched between metal meshes and dissolved in hot xylene (255 ° C.), and the ratio of remaining components was measured as a gel fraction, and the gel fraction of the porous film before heat treatment (usually 0%) was measured. %).

Example 1 15.0 parts by weight of ultra-high molecular weight polyethylene having a weight average molecular weight of 2,000,000 and a polynorbornene resin (Nosorex NB, weight average molecular weight of 20)
100,000 or more, manufactured by Nippon Zeon Co., Ltd.) 2.14 parts by weight of a polyolefin composition and 85 parts by weight of liquid paraffin,
Irganox 1010 and BHT as antioxidants
Is 0.5% by weight with respect to the polyethylene, respectively.
3% by weight is further added and uniformly mixed into a slurry,
The mixture was melted and kneaded at a temperature of 160 ° C. using a biaxial kneader.
Thereafter, these kneaded materials were sandwiched between metal plates cooled to 0 ° C., and rapidly cooled into a sheet of 5 mm.

These quenched sheets were heat-pressed at a temperature of 115 ° C. until the sheet thickness became 0.7 mm.
At the temperature of ° C., it is simultaneously stretched 3.5 × 3.5 times vertically and horizontally,
The solvent was removed using heptane. After desolvation,
Heat treatment was performed in air at 85 ° C. × 12 h + 120 ° C. × 2 h to obtain a porous film. This porous film is I
The crosslinked structure was confirmed from the measurement of R and the gel fraction.
4 μm, porosity 40%, initial Gurley value 600 sec /
100cc, Gurley value after storage 620sec / 100c
c.

Example 2 In Example 1, 6.0 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 and high density polyethylene 9.0 having a weight average molecular weight of 200,000 were used.
Parts by weight and polynorbornene resin (NOSOLEX N
B, weight average molecular weight of 2,000,000 or more, ZEON CORPORATION
Example 1 except that a polyolefin composition of 1.22 parts by weight and liquid paraffin of 85 parts by weight were used.
In the same manner as in the above, a porous film was obtained. This porous film was confirmed to have a crosslinked structure by measurement of IR and gel fraction, and had a thickness of 25 μm, a porosity of 39%, and an initial Gurley value of 50.
0sec / 100cc, Gurley value after storage 530sec
/ 100cc.

Example 3 In Example 1, 11.5 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000, 3.5 parts by weight of a thermoplastic elastomer (TPE821, manufactured by Sumitomo Chemical Co., Ltd.) and polynorbornene resin (No. Porous film in the same manner as in Example 1 except that Solex NB, a weight average molecular weight of 2,000,000 or more, and a polyolefin composition consisting of 1.22 parts by weight of Nippon Zeon Co., Ltd. and 85 parts by weight of liquid paraffin are used. I got This porous film was confirmed to have a crosslinked structure by measurement of IR and gel fraction, a film thickness of 24 μm, a porosity of 38%, an initial Gurley value of 520 sec / 100 cc, and a Gurley value of 542 s after storage.
ec / 100 cc.

Comparative Example 1 A porous film was obtained in the same manner as in Example 1 except that no polynorbornene resin was added. This porous film showed almost no crosslinked structure from the measurement of IR and gel fraction, and had a film thickness of 23 μm.
Porosity 38%, initial Gurley value 585 sec / 100c
c, Gurley value after storage was 657 sec / 100 cc.

Comparative Example 2 A slurry comprising 15 parts by weight of a polymer composition comprising 9% by weight of polyethylene having a weight average molecular weight of 200,000 and 6% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2,000,000 and 85 parts by weight of liquid paraffin was used. The mixture was uniformly mixed and melt-kneaded at a temperature of 160 ° C. using a small kneader for about 60 minutes. Thereafter, these kneaded materials were sandwiched between rolls or metal plates cooled to 0 ° C. and rapidly cooled in a sheet shape. These cooled sheet-shaped resins were heat-pressed at a temperature of 115 ° C. until the sheet thickness became 0.4 to 0.6 mm, and desolvation treatment was performed using heptane. Then 1
Biaxial stretching was carried out at a temperature of 16 ° C. at the same time, 4 × 4 in length and width. Then, the obtained porous film was heated at 85 ° C. in air.
-Heat treatment was performed for 1 hour and then at 110 ° C for 1 hour to obtain a porous film. This porous film is IR
And a gel fraction, almost no crosslinked structure was observed. The film thickness was 27 μm, the porosity was 37%, and the initial Gurley value was 58.
0sec / 100cc, Gurley value after storage 750sec
/ 100cc.

Comparative Example 3 A porous film was obtained in the same manner as in Example 2 except that no polynorbornene resin was added. This porous film showed almost no crosslinked structure from the measurement of IR and gel fraction, and had a film thickness of 23 μm.
Porosity 38%, initial Gurley value 540 sec / 100c
c, Gurley value after storage was 610 sec / 100 cc.

[Battery Storage Test] Phosphorous graphite as a conductive additive was added to lithium cobalt oxide (LiCoO ₂ ) at a weight ratio of 90: 5 and mixed, and this mixture and polyvinylidene fluoride were dissolved in N-methylpyrrolidone. The resulting solution was mixed to form a slurry. This positive electrode material mixture slurry is
After removing large things by passing through the mesh net,
A positive electrode current collector made of an aluminum foil having a thickness of 20 μm was uniformly coated on both sides and dried, then compression-molded by a roller press machine, cut, and the lead body was welded to produce a belt-shaped positive electrode. .

Next, a carbon material having an average particle size of 10 μm was mixed with a solution of vinylidene fluoride in N-methylpyrrolidone to form a slurry. This negative electrode mixture slurry was passed through a 70-mesh net to remove large ones, and then uniformly coated on both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm, dried, and then roll-pressed. After compression molding and cutting, the lead body was welded to produce a strip-shaped negative electrode.

As the separator, the porous films obtained in Example 2 and Comparative Example 3 were used. The positive electrode, the negative electrode and the separator are wound spirally so that both electrodes overlap each other with the separator interposed therebetween.
In the bottomed cylindrical battery case, and the positive and negative electrode lead bodies were welded.

Next, an electrolytic solution was prepared by dissolving LiPF6 at a ratio of 1.4 mol / liter in a mixed solvent of 2 parts by weight of methyl ethyl carbonate and 1 part by weight of ethylene carbonate as an electrolytic solution. This was poured into a battery case, and after the electrolyte had sufficiently penetrated into the separator and the like, sealing was performed, preliminary charging and aging were performed, and a cylindrical secondary battery was manufactured.

After storing the battery at 60 ° C. for 20 days, the battery was disassembled and the separators of each part of the battery were taken out.
The air permeability of each part was measured. The result is shown in FIG. 1 in comparison with the initial value before winding. Note that a, b, c, and d are obtained by dividing the total length of the separator into four equal parts from the outer peripheral side to the inner peripheral side,
The Gurley value at each central position is shown.

As shown in the results of FIG. 1, in the porous film of the example, even when stored at 60 ° C. for a long time, the air permeability of each part in the battery hardly decreases. On the other hand, in the porous film of the comparative example, when stored at 60 ° C. for a long period of time, the air permeability is greatly reduced, and particularly the air permeability is significantly reduced on the inner peripheral side of the battery.

[Battery Charge / Discharge Cycle Test] For the secondary batteries produced using the porous films obtained in Example 1 and Comparative Example 3 in the same manner as described above, the upper limit voltage was 4.2 V.
To charge at 0.2 C constant current for 5 hours.
2C discharge was performed. The discharge capacity at this time was defined as the initial discharge capacity. When the charge / discharge cycle was repeated 400 times, in the secondary battery of Example 1, the ratio of the initial discharge capacity to the initial cycle in the 200th cycle was 85%, and the discharge capacity was substantially reduced thereafter. Did not. On the other hand, for the secondary battery of Comparative Example 3, 200
In the first cycle, the ratio of the discharge capacity to the initial state was 70%, and thereafter, a decrease in the discharge capacity was observed. That is, when the air permeability is significantly reduced when stored at 60 ° C. for a long time, the cycle life of the battery tends to be short.

[Heat Deterioration Test of Transparent Film]
Using the porous films obtained in Examples 1 to 3 and Comparative Example 1, heating was performed at 135 ° C. for 60 minutes with the periphery fixed with a frame to obtain a transparentized film in which microporosity was closed. Using a transparent film cut into a size of 100 × 100 mm, the periphery was fixed with a SUS frame, put in a bat so that hot air did not directly hit it, and stored at 130 ° C. for 200 hours. Take out the sample every predetermined time, the tip diameter is 0.5mm
The piercing strength was measured using a pressure needle. The result is shown in FIG. 2 as the intensity ratio (%) to the initial value.

Since the porous films of Examples 1 to 3 contain a crosslinked product, even if they are partially melted, the strength can be maintained for a long time in high-temperature storage, and the safety of the battery can be improved. it can. On the other hand, in Comparative Example 1 which does not contain a crosslinked product, even if it is once partially melted, the strength is significantly reduced during high-temperature storage, and there is a concern that the safety of the battery may be reduced.

[Thermal Deterioration Test of Porous Film] Example 1
And the porous film obtained in Comparative Example 1 was 100 × 10
Using the one cut to 0 mm, the periphery was fixed with a SUS frame, placed in a bat so that hot air did not directly hit it, and stored at 130 ° C. for 120 hours. A sample was taken out every predetermined time, and the piercing strength was measured using a pressure needle having a tip diameter of 0.5 mm. The results are shown in FIG. 3 as the intensity ratio (%) to the initial value.

Since the porous film of Example 1 contains a crosslinked product, the strength can be maintained for a long time in high-temperature storage, and the safety of the battery can be improved. On the other hand, in Comparative Example 1, which does not contain a crosslinked product, the strength is significantly reduced during high-temperature storage, and there is a concern that the safety of the battery is reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in Gurley value obtained in a battery storage test.

FIG. 2 is a graph showing a change with time of an intensity ratio obtained in a thermal deterioration test of a transparentized film.

FIG. 3 is a graph showing a change over time of a strength ratio obtained in a thermal degradation test of a porous film.

Claims (4)

[Claims] 1. A porous film containing a cross-linked product obtained by cross-linking a polyolefin polymer and a polymer having a double bond, and the periphery thereof is fixed to a frame to 500 kPa.
A separator for a non-aqueous electrolyte battery, wherein the increase rate of a Gurley value measured according to JIS P8117 before and after storage is 10% or less when stored at 60 ° C. for 20 days under a pressure of (gauge pressure). 2. The method according to claim 1, wherein when storing at 130 ° C. for 3 days with the periphery fixed to a frame, the puncture strength measured by using a pressure needle having a tip diameter of 0.5 mm before and after storage is 10% or less. Item 2. A separator for a non-aqueous electrolyte battery according to Item 1. 3. The polyolefin-based polymer is a polyethylene having a weight average molecular weight of 500,000 or more.
4. The separator for a non-aqueous electrolyte battery according to claim 1. 4. A non-aqueous electrolyte battery comprising the non-aqueous electrolyte battery separator according to claim 1.