JP2002134091A - Non-aqueous electrolyte battery separator and non-aqueous electrolyte battery - Google Patents

Abstract

(57) [Summary] [Problem] 20 ° C to 8 assumed in summer or in a car
Even when stored for a long time in a charged state at 0 ° C., a non-aqueous electrolyte battery separator that has a small decrease in discharge capacity after storage and can prolong the battery life, and a non-aqueous electrolyte battery using the same. provide. SOLUTION: The storage elastic modulus G ₂₀ (Pa) at 20 ° C.
A non-aqueous electrolyte battery separator comprising a porous film having a structure retention index Y (−) of 2.0 or more calculated from the following formula and a storage elastic modulus G ₈₀ (Pa) at 80 ° C .: ^{_{Y = (G 80/10 8}} ) × (G 80 / G 20)

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for a non-aqueous electrolyte battery using a porous film having an excellent structure maintaining function against temperature changes, and a non-aqueous electrolyte battery using the same.

[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, a separator made of a microporous polyethylene film is known. Above all, a separator made of ultra-high molecular weight polyethylene serving as a skeleton of a porous structure and polyethylene having a relatively low molecular weight imparting an SD function has a large strength and an elastic modulus, and is a separator that suitably exhibits the SD function. Attention has been paid.

[0004]

However, a non-aqueous electrolyte battery using the above-mentioned conventional separator does not always have an initial state when stored in a high-temperature state such as in a long-term charge / discharge cycle or in a summer or in an automobile. It could not be maintained for a long time. Specifically, when storing the battery in a charged state at 20 ° C. to 80 ° C. which is assumed in a summer or in a car,
Due to the deformation of the separator due to the internal tension and pressure of the battery roll, the discharge capacity after storage decreases,
As a result, problems such as a reduction in battery life occur. For this reason, prolonging the life of the non-aqueous electrolyte battery is a major issue not only for the use of small portable devices and power storage devices, but also for the reduction of the environmental load due to long-term use.

In view of the above problems, for example, from the viewpoint of heat resistance, Japanese Patent Application Laid-Open No. Sho 63-308866 discloses a high strength and excellent strength by laminating a single film made of low melting point polyethylene and high melting point polypropylene. Although a method for obtaining a microporous porous membrane having high-temperature characteristics has been disclosed, the weak low-melting-point polyethylene portion in the laminate is likely to be deformed, and if kept at a high temperature, the deterioration proceeds and the battery life is shortened. Easy to fall.

Accordingly, an object of the present invention is to reduce the discharge capacity after storage and prolong the battery life even when stored for a long time in a charged state at 20 ° C. to 80 ° C., which is assumed in summer or in an automobile. It is an object of the present invention to provide a separator for a non-aqueous electrolyte battery which can be used, 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 and materials of a porous film constituting a separator.
And a non-aqueous electrolyte battery using a porous film having a structure retention index Y calculated from the storage elastic modulus at 80 ° C. of 2.0 or more are excellent in charge / discharge cycle life and high-temperature storage property. The invention has been completed.

That is, the separation for a non-aqueous electrolyte battery of the present invention.
Is the storage modulus G at 20 ° C. ₂₀(Pa) and 80 ° C
Elastic modulus G₈₀(Pa), calculated by the following formula
Having a structure retention index Y (-) of 2.0 or more
It is characterized by being made of a film.

Y = (G _80/10 ⁸ ) × (G ₈₀ / G ₂₀ ) Here, the storage elastic modulus is a value obtained by the measuring method described in Examples.

In the above, it is preferable to contain a crosslinked product obtained by crosslinking the ultrahigh molecular weight polyethylene and the polymer having a double bond.

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.

According to the separator for a non-aqueous electrolyte battery of the present invention, the storage elastic modulus at a high temperature (80 ° C.)
The ratio of the storage elastic modulus before and after the temperature rise is preferably balanced, and the structure maintenance index Y becomes equal to or more than a certain value. The decrease in the discharge capacity after storage is small, and the battery life can be extended. Details of the reason are unknown,
In the conventional separator, the structure retention index Y is less than 2.0, and the _G80 is low or the change before and after the temperature rise is large, so that the porous structure changes when the battery temperature rises, It is presumed that the separator of the present invention has such a small structural change that the porous structure tends to change during storage, and thus the battery performance is unlikely to deteriorate even when stored at a high temperature for a long time in a charged state.

When a crosslinked product obtained by crosslinking an ultrahigh molecular weight polyethylene and a polymer having a double bond is contained, the ultrahigh molecular weight polyethylene develops a high elastic modulus by stretching orientation in forming a porous film. Since it is easy to crosslink with the polymer, it is advantageous for maintaining the elastic modulus at high temperature.

On the other hand, according to the nonaqueous electrolyte battery of the present invention,
Since the separator for a non-aqueous electrolyte battery according to any one of the above is used, it is assumed to be 20 ° C. to 8
Even when stored for a long time in a charged state at 0 ° C., the decrease in the discharge capacity after storage is small, and the battery life is extended.

[0015]

Embodiments of the present invention will be described below.

The separator for a non-aqueous electrolyte battery according to the present invention comprises:
From the storage modulus G ₂₀ at 20 ° C. (Pa) and the storage modulus G ₈₀ at 80 ° C. (Pa), maintaining the structure index Y calculated by the following equation - a porous film is 2.0 or more () However, the structure maintenance index Y (-) is preferably 3.0 or more, more preferably 4.0 or more.

Y = (G _80/10 ⁸ ) × (G ₈₀ / G ₂₀ ) In particular, since the effect of the storage elastic modulus G ₈₀ is large, the storage elastic modulus G ₈₀ is preferably 5.0 × 10 ⁸ or more, and 6 0.0 × 10 ⁸
The above is more preferable.

The material of the separator is not particularly limited, and polyolefin resins such as polyethylene, polypropylene and polybutylene, nylon, cellulose acetate, polyacrylonitrile and the like can be used, but polyethylene and polypropylene are preferred.

Further, as the polyethylene, high-density polyethylene, low-density polyethylene and the like are preferable, and high-density polyethylene and ultrahigh-molecular-weight polyethylene are particularly porous.
It is preferable from the viewpoint of film strength. In particular, ultrahigh molecular weight polyethylene is preferable, those having a weight average molecular weight of 500,000 or more are preferable, and those having a weight average molecular weight of 1,000,000 or more are more 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.

Further, after obtaining a porous film containing a polymer having a double bond in a molecular chain such as polybutadiene or polynorbornene (including an unvulcanized product of a crosslinkable rubber), a cross-linking treatment is carried out in a subsequent step. You may. As a result, it is possible to obtain a porous film containing a crosslinked product obtained by crosslinking an ultrahigh molecular weight polyethylene or the like with a polymer having a double bond. At that time, it is preferable that a polymer having a double bond is blended in the porous film in an amount of 3 to 40% by weight, particularly 5 to 35% by weight.

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 60% by weight or less, particularly preferably 50% by weight or less.

The thickness of the separator for a non-aqueous electrolyte battery of the present invention is preferably 5 to 50 μm. Porosity is 20-80%
Is preferable, and the average pore size is preferably 0.01 to 0.5 μm. JIS as a comprehensive property by these
The air permeability conforming to P8117 is 100 to 1000 sec.
c / 100 ml is preferred.

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. At this time, a porous film that satisfies Y ≧ 2 can be suitably obtained by adjusting the stretching ratio in the stretching step or performing high-magnification biaxial stretching. In particular, a rolling step of pressing between the surfaces of two belts is effective in performing high-magnification biaxial stretching to increase the elastic modulus. Examples of the dry film forming method include a method of stretching a film having an amorphous portion while heating the film at a predetermined temperature to make the film porous.

Further, the porous film containing the polymer having a double bond is subjected to crosslinking treatment of the double bond site with heat, ultraviolet rays, electron beams, etc., so that the heat resistance is increased and the film is stored at a high temperature. Improving the elastic modulus is also effective.

Next, the non-aqueous 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 electrolytic solution, for example, an electrolytic solution 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.

[0029]

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 by a scanning electron microscope with a 1/10000 thickness gauge.

(Air permeability) Measured according to JIS P8117.

(Storage Elastic Modulus) A sample in which a porous film was prepared in a strip shape (length 40 mm × width 10 mm, thickness 2
0-30 μm), prepared by Seiko Electronics Co., Ltd.
The measurement was performed using a DM5600 viscoelastic spectrometer under the conditions of a measurement width of 20 mm, an amplitude of 0.2 μm (displacement: tensile direction), a frequency of 10 Hz, and a temperature rising rate of 5 ° C./min. From the obtained viscoelasticity graph, the storage elastic modulus of 20 ° C., 8
The value at 0 ° C. was read to give the respective storage modulus.

(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. %).

PREPARATION EXAMPLE 1 Ring-opening polymer of norbornene
Powder (NOSOLEX NB, weight average molecular weight 2,000,000 or more)
Above) 5% by weight, ultra high molecular weight polymer with a weight average molecular weight of 3,000,000
20 parts by weight of a polymer composition comprising 95% by weight of ethylene
And 80 parts by weight of liquid paraffin are uniformly mixed into a slurry
And dissolve at 160 ° C for about 60 minutes using a small kneader
Kneaded. Thereafter, these kneaded materials were cooled to 0 ° C.
It was sandwiched between rolls or a metal plate and rapidly cooled into a sheet. This
These quenched sheet resins are heated at 117 ° C to a sheet thickness.
Is heat-pressed until the thickness becomes 0.4 to 0.6 mm.
Simultaneous biaxial stretching at a temperature of 7 ° C. to 3.8 × 3.8 times vertically and horizontally
Then, the solvent was removed using heptane. afterwards,
Heat the obtained porous film in air at 85 ° C for 6 hours.
Treated, then heat treated at 125 ° C for 2 hours, according to the present invention
To obtain a porous film. This porous film is I
From the measurement of R and the gel fraction, the crosslinked structure was confirmed, and the thickness was 2
6 μm, air permeability 300, storage elastic modulus at 20 ° C. 3.1 × 10
⁹ Pa, 80 ° C. storage elastic modulus 1.25 × 10 ⁹ Pa
Was.

[Preparation Example 2] A polymer composition comprising 10% by weight of a powder of a ring-opening polymer of norbornene (NOSOLEX NB, weight average molecular weight of 2,000,000 or more) and 90% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2,000,000 20 parts by weight of the product and 80 parts by weight of liquid paraffin were uniformly mixed in a slurry state, and were melted and kneaded at a temperature of 160 ° C. for about 60 minutes using a small kneader. Thereafter, these kneaded materials were sandwiched between rolls or metal plates cooled to 0 ° C. and rapidly cooled in a sheet shape. These quenched sheet resins are heat-pressed at a temperature of 115 ° C. until the sheet thickness becomes 0.4 to 0.6 mm, and are simultaneously biaxially stretched at a temperature of 115 ° C. to 3.8 × 3.8 times in length and width. The solvent was removed using heptane. Thereafter, the obtained porous film was heat-treated in air at 85 ° C. for 6 hours, and then heat-treated at 130 ° C. for 2 hours to obtain a porous film according to the present invention. This porous film was confirmed to have a crosslinked structure by measurement of IR and gel fraction, and had a thickness of 25 μm, an air permeability of 480, and a storage elastic modulus at 20 ° C. of 3.6 × 1.
It was 0 ⁹ Pa, 80 ℃ storage modulus 1.0 × 10 ⁹ Pa.

[Preparation Example 3] 20% by weight of a powder of a ring-opened polymer of norbornene (NOSOREX NB, weight average molecular weight of 2,000,000 or more), 20% by weight of polyethylene having a weight average molecular weight of 300,000, and more than 3,000,000 weight average molecular weight 20 parts by weight of a polymer composition composed of 60% by weight of high molecular weight polyethylene and 80 parts by weight of liquid paraffin were uniformly mixed in a slurry form, and were melted and kneaded at a temperature of 160 ° C. for about 60 minutes using a small kneader. Thereafter, these kneaded materials were sandwiched between rolls or metal plates cooled to 0 ° C. and rapidly cooled in a sheet shape. These quenched sheet resins were heat-pressed at 115 ° C. until the sheet thickness became 0.4 to 0.6 mm.
The film was simultaneously biaxially stretched 3.5 × 3.5 times at a temperature of 5 ° C. and desolvated using heptane. afterwards,
The obtained porous film was heat-treated in air at 85 ° C. for 6 hours and then at 110 ° C. for 2 hours to obtain a porous film according to the present invention. This porous film was confirmed to have a crosslinked structure by measurement of IR and gel fraction, and had a thickness of 24 μm.
m, air permeability 330, storage elastic modulus at 20 ° C. 2 × 10 ⁹ Pa,
The storage elastic modulus at 80 ° C. was 1.1 × 10 ⁹ Pa.

[Preparation Example 4] Polymer composition comprising 10% by weight of a powder of a ring-opening polymer of norbornene (NOSOLEX NB, weight average molecular weight of 2,000,000 or more) and 90% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 20 parts by weight of the product and 80 parts by weight of liquid paraffin were uniformly mixed in a slurry state, and were melted and kneaded at a temperature of 160 ° C. for about 60 minutes using a small kneader. Thereafter, these kneaded materials were sandwiched between rolls or metal plates cooled to 0 ° C. and rapidly cooled in a sheet shape. These quenched sheet resins are heat-pressed at a temperature of 115 ° C. until the sheet thickness becomes 0.4 to 0.6 mm, and simultaneously biaxially stretched 4.5 × 4.5 times at a temperature of 115 ° C. The solvent was removed using heptane. Thereafter, the obtained porous film was heat-treated in air at 85 ° C. for 6 hours, and then heat-treated at 130 ° C. for 4 hours to obtain a porous film according to the present invention. This porous film was confirmed to have a crosslinked structure by measurement of IR and gel fraction, and had a thickness of 25 μm, an air permeability of 350, and a storage elastic modulus of 2.1 × 1 at 20 ° C.
It was 0 ⁹ Pa, 80 ℃ storage modulus 6.7 × 10 ⁸ Pa.

[Preparation Example 5] A polymer composition 20 comprising 35% by weight of polyethylene having a weight average molecular weight of 200,000 and 65% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 3,000,000.
Parts by weight and 80 parts by weight of liquid paraffin are uniformly mixed in a slurry state, and the mixture is mixed at a temperature of 160 ° C. using a small kneader to form about 6 parts by weight.
The mixture was dissolved and kneaded for 0 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 has a thickness of 25 μm, an air permeability of 100, and a storage elastic modulus of 2.2 × 1 at 20 ° C.
0 was ⁸ Pa, 80 ° C. storage modulus 6.8 × 10 ⁷ Pa.

[Preparation Example 6] A polymer composition 15 comprising 65% by weight of polyethylene having a weight average molecular weight of 200,000 and 35% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1.5 million.
Parts by weight and 85 parts by weight of liquid paraffin are uniformly mixed in the form of a slurry, and the mixture is mixed at a temperature of 160 ° C. using a small kneader to form a slurry.
The mixture was dissolved and kneaded for 0 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 are heat-pressed at a temperature of 115 ° C. until the sheet thickness becomes 0.4 to 0.6 mm, and are biaxially stretched at a temperature of 115 ° C. 4 × 4 times vertically and horizontally, and heptane is used. To remove the solvent. afterwards,
The obtained porous film was heat-treated in air at 85 ° C. for 1 hour, and then heat-treated at 115 ° C. for 1 hour to obtain a porous film. This porous film has a thickness of 26 μm, an air permeability of 560, a storage elastic modulus of 20 ° C. of 6.5 × 10 ⁸ Pa, 80
° C storage elastic modulus was 3.2 × 10 ⁸ Pa.

[Preparation Example 7] A polymer composition 15 comprising 33% by weight of polyethylene having a weight average molecular weight of 200,000 and 67% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 3,000,000.
Parts by weight and 85 parts by weight of liquid paraffin are uniformly mixed in the form of a slurry, and the mixture is mixed at a temperature of 160 ° C. using a small kneader to form a slurry.
The mixture was dissolved and kneaded for 0 minutes. Thereafter, these kneaded materials were sandwiched between rolls or metal plates cooled to 0 ° C. and rapidly cooled in a sheet shape. These quenched sheet resins are heat-pressed at 115 ° C. until the sheet thickness becomes 0.4 to 0.6 mm, and are simultaneously biaxially stretched 4 × 4 times at 115 ° C. using heptane. To remove the solvent. afterwards,
The obtained porous film was heat-treated in air at 85 ° C. for 1 hour, and then heat-treated at 115 ° C. for 1 hour to obtain a porous film. This porous film had a thickness of 26 μm, an air permeability of 290, a storage elastic modulus at 20 ° C. of 8 × 10 ⁸ Pa, and a storage elastic modulus at 80 ° C. of 3.5 × 10 ⁸ Pa.

Example 1 Lithium cobalt oxide (L
Phosphorus graphite as a conductive aid in iCoO ₂ ) is 9 by weight.
The mixture was added and mixed at 0: 5, and the mixture was mixed with a solution of polyvinylidene fluoride dissolved in N-methylpyrrolidone to form a slurry. This positive electrode mixture slurry was passed through a 70-mesh net to remove large particles, and then uniformly applied to both sides of a positive electrode current collector made of aluminum foil having a thickness of 20 μm, dried, and then, using a roller press. After compression molding, it was 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 film obtained in Preparation Example 1 was used. The positive electrode, the negative electrode and the separator are spirally wound so that both electrodes overlap each other with the separator interposed therebetween. As a spirally wound electrode body, the outside is stopped with a winding tape to form a wound body. The battery was filled in a bottom cylindrical battery case, and the positive and negative electrode leads were welded.

Next, an electrolytic solution prepared by dissolving LiPF6 at a ratio of 1.4 mol / l in a mixed solvent of 2 parts by weight of methyl ethyl carbonate and 1 part by weight of ethylene carbonate was prepared 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.

Example 2 A secondary battery was manufactured in the same manner as in Example 1 except that the porous film formed in Preparation Example 2 was used as a separator.

Example 3 A secondary battery was manufactured in the same manner as in Example 1 except that the porous film formed in Preparation Example 3 was used as a separator.

Example 4 A secondary battery was manufactured in the same manner as in Example 1 except that the porous film formed in Preparation Example 4 was used as a separator.

Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1 except that the porous film formed in Preparation Example 5 was used as a separator.

Comparative Example 2 A secondary battery was manufactured in the same manner as in Example 1 except that the porous film formed in Preparation Example 6 was used as a separator.

Comparative Example 3 A secondary battery was manufactured in the same manner as in Example 1 except that the porous film formed in Preparation Example 7 was used as a separator.

Each of the non-aqueous electrolyte secondary batteries produced above was charged at a constant current of 0.2 C at an upper limit voltage of 4.2 V.
After 5 hours, 2C discharge was performed. The discharge capacity at this time was defined as the initial discharge capacity. Then, the battery was similarly recharged at 0.2 C, and stored in this charged state at 60 ° C. for 20 days. The discharge capacity at the time of performing 2C discharge was defined as the discharge capacity after storage. The ratio of the capacity after storage to the initial discharge capacity at this time was determined as a capacity remaining rate. Table 1 shows the results of Examples and Comparative Examples.

[0052]

[Table 1] As shown in the results of Table 1, in Examples 1 to 4 using a porous film having a structure retention index Y of 2.0 or more, the capacity retention ratio was high, while the structure retention index Y was 2.0. In Comparative Examples 1 to 3, the residual capacity ratio was low. Such a decrease in the remaining capacity ratio leads to a decrease in battery life.

Continued on the front page F term (reference) 5H021 AA06 EE04 HH00 HH06 5H022 AA09 KK01 5H029 AJ12 AK02 AK03 AK05 AL06 AL07 AL08 AL12 AM03 AM04 AM05 AM07 DJ04 HJ00

Claims (3)

[Claims] 1. Storage modulus G ₂₀ (Pa) at 20 ° C.
A non-aqueous electrolyte battery separator comprising a porous film having a structure retention index Y (−) of 2.0 or more calculated from the following formula and a storage elastic modulus G ₈₀ (Pa) at 80 ° C .: ^{_{Y = (G 80/10 8}} ) × (G 80 / G 20) 2. A crosslinked product obtained by crosslinking an ultrahigh molecular weight polyethylene with a polymer having a double bond.
The separator for a non-aqueous electrolyte battery according to the above. 3. A non-aqueous electrolyte battery using the non-aqueous electrolyte battery separator according to claim 1 or 2.