JP2001135295A - Separator for batteries - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for batteries superior in mechanical strength against flaws or the like by properly blending inorganic fine particles which contain a specified metal oxides as major components. SOLUTION: This separator for batteries is composed of single or multi- layered porous film that is made porous through drawing method and is featured with the porous film containing 100 to 5,000 ppm for inorganic fine particles, having a mean particle size 0.1 to 10 μm having at least single kind of metal oxide selected among groups of silicon oxides, aluminum oxides and magnesium oxides as the major components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a battery separator useful as a constituent material of a lithium battery.

[0002]

2. Description of the Related Art Hitherto, polyolefin-based porous films have been used as separators for batteries and diaphragms for electrolytic capacitors. In particular, with the advancement of technology in recent years, high precision and high performance separators have been required for lithium batteries and the like.

Taking a battery as an example, a non-aqueous electrolyte battery such as a lithium battery having a high energy density, a high electromotive force and little self-discharge, particularly a lithium secondary battery has been developed and put into practical use in recent years. Examples of the negative electrode of a lithium battery include metallic lithium, an alloy of lithium and another metal, a carbon material capable of adsorbing or intercalating lithium ions such as carbon and graphite, and a conductive material doped with lithium ions. Polymer materials and the like are known, and as the positive electrode, for example, (CF _x ) _n
Fluorinated graphite, MnO ₂ , V ₂ O ₅ , CuO, A
Metal oxides such as g ₂ CrO ₄ , TiO ₂ , LiCoO ₂ and LiMn ₂ O ₄ , sulfides and chlorides are known.

As a non-aqueous electrolytic solution, an organic solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, tetrahydrofuran or the like is used. ₆ , LiBF ₄ , LiCl
O ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN
A solution in which an electrolyte such as (SO ₂ C ₂ F ₅ ) ₂ is dissolved is used.

[0005] The role of the separator, which is a constituent material of such a lithium battery, is to prevent short-circuiting of the positive and negative electrodes and not to hinder the battery reaction, and to prevent heat generation and ignition of the battery due to thermal obstruction due to abnormal heat. For the purpose of improving the mechanical strength which is closely related to the safety of the battery, in particular, the following various porous films have been proposed.

[0006] A porous film using a raw material resin having a high molecular weight (JP-A-2-94356, JP-A-3-105)
No. 851). A porous film using a thermoplastic resin or a non-woven fabric as a support (Japanese Patent Application Laid-Open No. 3-245457,
JP-A-1-258358 and the like).

[0007] One of the properties of the separator that reflects the safety of the battery is that the surface is damaged by minute projections. The surface of the electrode plate of a lithium battery often has irregularities of about several μm. For this reason, when a porous film is incorporated into a lithium battery as a battery separator, there is a concern that the film may be damaged by irregularities on the surface of the electrode plate. Since the damage of the separator causes a short circuit of the battery, it is important to improve not only the strength of the separator itself but also the surface damage due to minute projections.

On the other hand, for the purpose of improving the strength, a method of blending an inorganic filler into a porous film made of a polyolefin resin or a method of providing a surface protective layer containing inorganic fine particles is known. In the method of blending an inorganic filler (Japanese Patent Application Laid-Open No. 62-167332), the purpose is not only to improve the strength of the inorganic filler but also to impart uniformity of stretched porosity. Is resin amount 10
Suitable as a battery separator because the reliability of the shutdown function to prevent heat generation and ignition of the battery due to thermal clogging (resin part) is abnormal at an abnormal time (50 to 500 parts by weight with respect to 0 part by weight). Absent. In the method of providing a surface protective layer containing inorganic fine particles (Japanese Patent Application Laid-Open No. H11-80395), the step of disposing a surface protective layer containing inorganic fine particles on the surface of a porous film becomes complicated in the manufacturing process. ,
Since the air permeability is increased by applying the surface protective layer, a low air permeability cannot be obtained, and there is still room for improvement.

Further, in the improvement of a porous membrane for a separator using a resin modifying additive such as inorganic fine particles, the additive is not decomposed or denatured by an electrochemical reaction other than the battery reaction during use of the battery. As described in the specification of Japanese Patent Application No. 11-6045 filed earlier by the present inventors,
Preferably, the oxidation potential of the inorganic fine particles is +4.5 V or more with respect to lithium. An object of the present invention is to provide a porous film that is excellent in reliability and safety during use of a battery and does not inhibit a battery reaction, that is, a battery separator, as a lithium battery separator.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that by appropriately blending inorganic fine particles containing a specific metal oxide as a main component, excellent reliability and safety and excellent battery reaction can be obtained. It has been found that a porous film that does not hinder the formation of a porous film can be obtained. That is, the present invention is a battery separator comprising a single-layer or laminated porous film porous by a stretching method, wherein the porous film is at least one kind selected from the group consisting of silicon oxide, aluminum oxide, and magnesium oxide. Average particle size 0.1 mainly composed of metal oxide
The present invention relates to a battery separator containing 100 to 5000 ppm of inorganic fine particles of 10 to 10 μm.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The material used for the battery separator of the present invention is not particularly limited, and polyolefin resins such as polypropylene and polyethylene can be used. Further, the porous film of the present invention may have any structure of a single-layer porous film and a laminated porous film. When the porous film is a laminated porous film, at least one layer of the laminated porous film contains inorganic fine particles. Should be included.

The polypropylene used in the present invention preferably has a number average molecular weight of 50,000 or more, more preferably 70,000 or more, and a ratio of the number average molecular weight to the weight average molecular weight of 8 or less, because of its high mechanical strength. The crystallization temperature of the polypropylene is preferably 110 ° C. or higher, more preferably 112 ° C. or higher.

The polyethylene used in the present invention includes:
Any of high-density polyethylene, medium-density polyethylene, linear low-density polyethylene and the like may be used, but high-density polyethylene is preferred. Polyethylene having a number average molecular weight of 10,000 or more, more preferably 20,000 or more, is preferred because of its high mechanical strength.

In the present invention, the number average molecular weights of polypropylene and polyethylene were determined in terms of standard polystyrene using a 150C gel permeation chromatograph manufactured by WATERS. Two Shodex HT-806M columns were used, and the measurement was performed at 135 ° C. in orthodichlorobenzene adjusted to 0.3 wt / vol%. The melting point of polypropylene was measured using DSC-7 manufactured by PerkinElmer. The sample was held at 230 ° C for 10 minutes to completely remove the heat history, and then completely melted. After cooling to room temperature at 10 ° C / min, the maximum value of the melting curve was measured at a heating rate of 10 ° C / min. And

The inorganic fine particles contained in the battery separator of the present invention are composed mainly of at least one metal oxide selected from the group consisting of silicon oxide, aluminum oxide and magnesium oxide, and are a constituent material of a lithium secondary battery. It is desirable not to swell and dissolve in the non-aqueous electrolyte. When the inorganic fine particles contain organic substances that swell and dissolve in the non-aqueous electrolyte,
It is not suitable because the battery reaction may be hindered when the battery is used. The average particle diameter of the inorganic fine particles is 0.1 to 10 μm.
m, more preferably 0.5 to 3 μm. If the average particle size of the inorganic fine particles is smaller than this range, the effect of improving mechanical strength such as scratch resistance of the battery separator cannot be expected,
On the other hand, if it is larger than this range, the appearance of the battery separator is poor due to poor dispersion of the inorganic fine particles.

The true specific gravity of the inorganic fine particles used in the present invention is preferably 1.5 or more, particularly preferably 2 or more. If the true specific gravity of the inorganic fine particles is too small, the effect of improving the mechanical strength such as the flaw of the battery separator is small, which is not appropriate.
Also, the oxidation potential of the inorganic fine particles is +
It is preferably 4.5 V or more, particularly +5 V or more, because it is electrochemically stable.

The measurement of the oxidation potential shown in the present invention was carried out using a non-aqueous electrolyte prepared by dissolving LiPF ₆ in dimethyl carbonate to have a concentration of 1 M / L. The inorganic fine particles were suspended in this non-aqueous electrolyte so as to have a concentration of 0.05 M / L. Using a metallic lithium foil as a reference electrode and a platinum electrode as a working electrode, the potential was swept from ± 0 V to +4.5 V at a rate of 10 mV / sec, and the voltage at which a current of 0.1 mA was detected was taken as the oxidation potential. .

In the present invention, the method of blending the inorganic fine particles with polypropylene or polyethylene is not particularly limited, but it can be blended by kneading using a usual kneader. For example, pellets can be obtained by melt-kneading using a single-screw extruder, a twin-screw extruder, a mixing roll, or the like. Further, it may be blended by dry blending using a Henschel mixer, a tumbler or the like. The mixing ratio of the inorganic fine particles to the battery separator is 100 to
5000 ppm, more preferably 300 to 4000 p
pm. If the amount of the inorganic fine particles is smaller than this range, the effect of improving mechanical strength such as scratch resistance of the battery separator cannot be expected. If the amount is larger than this range, it is difficult to make the separator porous by the stretching method, and the air permeability is low. This is not suitable because a battery separator having a low battery density cannot be obtained.

In the present invention, the number of inorganic fine particles contained in a single-layer or laminated porous film made porous by the stretching method varies depending on the stretching ratio and the like, but is usually 50 to 5,000 particles / mm ² per film area, especially 100-30
It is preferable to adjust the number to 00 pieces / mm ² . If the dispersion state of the inorganic fine particles is excessively out of this range, the effect of improving the mechanical strength such as the scratch resistance of the battery separator cannot be expected.

The layer structure of the battery separator of the present invention includes a single-layer porous film of polyethylene or polypropylene containing inorganic fine particles, a laminated porous film in which polyethylene containing no inorganic fine particles is interposed between polypropylene containing inorganic fine particles, and an inorganic porous film. Laminated porous film sandwiching polyethylene containing inorganic fine particles with polypropylene containing no fine particles, laminated porous film composed of polyethylene containing inorganic fine particles and polyethylene containing no inorganic fine particles, polyethylene containing inorganic fine particles and polypropylene containing inorganic fine particles In the case of a laminated porous film, it is sufficient that at least one layer contains inorganic fine particles.

As a specific method for producing the battery separator of the present invention, for example, in the case of producing a laminated porous film in which polyethylene containing inorganic fine particles is sandwiched by polypropylene containing inorganic fine particles, inorganic fine particles are appropriately mixed. A method for obtaining a laminated porous film by melt-co-extruding polypropylene and polyethylene and then obtaining a laminated porous film by stretching and porosifying the polypropylene and polyethylene films, which are appropriately blended with inorganic fine particles, to obtain a laminated porous film. There are ways to get it. Further, in the stretching and porosification step, when the length of the film in the width direction is greatly reduced and the performance of the porous film such as the air permeability, the porosity, and the maximum pore diameter is impaired, the present inventors have A method of stretching while fixing both ends in the width direction of the film with a chuck, a pinch roll or the like as described in Japanese Patent Application Laid-Open No. H11-297297 filed during the uniaxial stretching after stretching the film uniaxially vertically. It can be improved by a method such as a method of restoring the reduced film length in the width direction by transverse stretching. Either method can produce the battery separator of the present invention.

The melt extrusion method is performed by a melt extrusion molding method using a T-die, an inflation method, or the like. For example, when a film is melt-formed with a T-die, the film is generally formed at a temperature 20 to 60 ° C. higher than the melting temperature of the resin at a draft ratio of 5 to 500, preferably 50 to 300, and the take-up speed is particularly limited. Not usually but 10
Molded at ~ 50 m / min. The melt extruded film is heat treated to increase its crystallinity and its orientation. The heat treatment temperature is 1 for polyethylene film.
It is 100-130 degreeC, Preferably it is 110-125 degreeC, about 110-160 degreeC, Preferably it is 120-150 degreeC about a polypropylene film. If the heat treatment temperature is low, the film is not sufficiently porous, and if it is too high, the film is melted, which is not suitable. The heat treatment time is not particularly limited,
This is performed in a range of seconds to 180 seconds.

The heat-treated polyethylene film has a birefringence of 25 × 10 ^{−3 to} 48 × 10 ⁻³ , preferably ³ × 10 ⁻³ .
The elastic recovery at 50% elongation at 0 × 10 ^{−3 to} 45 × 10 ⁻³ is in the range of 40 to 80%, preferably 50 to 75%. The heat-treated polypropylene film has a birefringence of 10 × 10 ^{−3 to} 25 × 10 ^−3.
-3 , preferably 12 × 10 ^-3 to 23 × 10 ^-3 and 100
% Elongation at 70% to 94%, preferably 7%
Preferably it is in the range of 5 to 93%. If the birefringence and elastic recovery are out of these ranges, the degree of porosity becomes insufficient, which affects the pore size and pore size distribution, porosity, delamination strength, mechanical strength, etc. of the porous film after stretching. The above range is appropriate because the quality tends to vary.

In the present invention, the birefringence is a value measured using a polarizing microscope and a Berek compensator under crossed Nicols. The elastic recovery rate is based on the following equations (1) and (2). Equation (1) is for a polyethylene film, and equation (2) is for a polypropylene film. In addition, polyethylene film is 25 ° C, 65%
At a relative humidity, the sample was set to a tensile tester with a sample width of 15 mm and a length of 2 inches, stretched to 50% at a speed of 2 inches / min, held in a stretched state for 1 minute, and then relaxed at the same speed. , Polypropylene film is 2
Sample width 10 mm, length 5 at 5 ° C., 65% relative humidity
It was set in a tensile tester at 0 mm, stretched to 100% at a speed of 50 mm / min, and immediately relaxed at the same speed.

Equation (1) Elastic recovery rate (%) = [(length at 50% elongation−length at 50% elongation when load becomes 0) / (length at elongation−length before elongation) Sa)] x 100

Equation (2) Elastic recovery rate (%) = [(length at 100% elongation−100)
% Length when load becomes 0 after elongation) / Length before elongation] ×
100

In the case of producing a laminated porous film having a three-layer structure in which polypropylene containing inorganic fine particles is sandwiched by polypropylene containing inorganic fine particles, the heat-treated polypropylene film and polyethylene film are laminated by thermocompression bonding. Lamination is performed by unwinding three films from three sets of raw roll stands, nipping and heating between heated rolls, and laminating. At this time, it is necessary to perform thermocompression bonding so that the birefringence and elastic recovery of each film do not substantially decrease.

The temperature of the heated roll, that is, the thermocompression bonding temperature is 110 to 130 ° C., preferably 115 to 125 ° C.
° C. If the temperature is too low, the adhesiveness between the films is weak and peeling occurs in the subsequent stretching step, and if it is too high, the birefringence and elastic recovery of the film decrease due to the melting of polyethylene, making it difficult to make the film porous. The above range is appropriate. The nip pressure for thermocompression bonding is 1 to 3 kg / cm ² , and the unwinding speed is 0.5 to 8 m / min. The peel strength between the thermocompression-bonded films is 3 to 60 g / 15.
A range of mm is preferred.

The heat-treated and laminated film is made porous by stretching. Stretching is performed in the order of low-temperature stretching and then high-temperature stretching, and is usually performed at a peripheral speed difference of a stretching roll. The temperature for the low temperature stretching is -20 to 50C, particularly preferably 20 to 35C. If the stretching temperature is low, the film is likely to break during the operation, while if it is too high, the porosity becomes insufficient, which is not suitable. Low-temperature stretching ratio is 5-200
%, Preferably in the range of 10 to 100%. If the stretching ratio is too low, only a material having a low porosity can be obtained, and if it is too high, a material having a predetermined porosity and pore size cannot be obtained, so the above range is appropriate. In the present invention, the low-temperature stretching ratio (E ₁ ) complies with the following equation (3). In the formula (3), L ₁ means the film size after low-temperature stretching, and L ₀ means the film size before low-temperature stretching.

Equation (3) E ₁ = [(L ₁ −L ₀ ) / L ₀ ] × 100

The low temperature stretched film is then hot stretched. High temperature stretching is 70-1 in a heated air circulation oven.
The reaction is carried out at a temperature of 30 ° C, particularly preferably 100 to 125 ° C. If the stretching temperature is out of the above range, the porosity becomes insufficient, which is not appropriate. The high-temperature stretching is preferably performed at a temperature 40 to 100 ° C. higher than the low-temperature stretching temperature. The high temperature stretching ratio is in the range of 100 to 400%.
If the stretching ratio is too low, the porosity becomes insufficient, and if it is too high, the desired air permeability, porosity and pore size cannot be obtained, so the above range is appropriate. In the present invention, the high-temperature stretching ratio (E ₂ ) complies with the following equation (4). In the formula (4), L ₂ means a film size after high-temperature stretching, and L ₁ means a film size after low-temperature stretching.

Equation (4) E ₂ = [(L ₂ −L ₁ ) / L ₁ ] × 100

In the present invention, after the low-temperature stretching and the high-temperature stretching, the porous film is heat-set. The heat setting is such that the film length after stretching is 10 to 50 in order to prevent the film from shrinking in the stretching direction due to residual stress applied during stretching.
%, Or a method in which heating is performed such that the dimension in the stretching direction is not changed.
By this heat fixing, it is possible to obtain a battery separator satisfying the intended problem with good dimensional stability.

The battery separator manufactured in this manner varies depending on the manufacturing conditions, but has an air permeability of 30%.
~ 800 sec / 100cc, more preferably 100 ~ 7
00 sec / 100 cc, maximum pore size 0.02 to 3 μm, porosity 30 to 85%. If the air permeability is too high, the lithium ion conductivity is reduced, so that the function as a battery separator is not sufficient. If the air permeability is too low, the mechanical strength decreases, so the above range is appropriate. If the maximum pore diameter and the porosity are not in these ranges, the capacity characteristics of the battery are undesirably deteriorated. Further, the thickness of the battery separator is adjusted to 5 to 100 μm, particularly preferably 20 to 40 μm, from the viewpoint of mechanical strength, performance, miniaturization and the like.

In the present invention, a battery separator having excellent mechanical strength such as scratch resistance was obtained by appropriately mixing inorganic fine particles containing a specific metal oxide as a main component. Here, the term “scratchability” means the degree of damage to the separator due to press-fitting or rubbing of the minute projections. Further, in the battery separator of the present invention, the breakdown voltage related to the insulation strength of the porous film is also improved by adding the inorganic particles. That is, the present invention can provide a battery separator that is excellent in reliability and safety and does not impair battery performance by improving the damageability and breakdown voltage due to the addition of the inorganic fine particles.

[0036]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 A polypropylene having a number average molecular weight of 70000 and a crystallization temperature of 112 ° C. was added to a polypropylene having a true specific gravity of 2.36 containing silicon oxide as a main component.
Inorganic fine particles having an average particle size of 2.1 μm were compounded using a twin-screw kneader so as to be 2000 ppm with respect to the resin.
The oxidation potential of the inorganic fine particles was +4.5 V or more with respect to lithium. The polypropylene containing the inorganic fine particles was melt-extruded into a film using a T-die having a discharge width of 1000 mm and a discharge lip opening of 2 mm. The discharge film is
It was led to a cooling roll of 80 ° C., cooled by blowing cool air of 25 ° C., and then taken off at 50 m / min. The thickness of the obtained polypropylene composition film was 11.4.
μm. This unstretched polypropylene film
After heat-treating at 135 ° C. for 60 seconds with the take-off direction fixed, the system was cooled to room temperature. The birefringence of the heat-treated unstretched polypropylene film is 22.6 × 10 ⁻³ ,
The elastic recovery at 100% elongation was 93%.

The polyethylene has a number average molecular weight of 200
A high-density polyethylene having a density of 00, a density of 0.964 and a melting point of 134 ° C. was melt-extruded using a T-die having a discharge width of 1000 mm and a discharge lip opening of 2 mm. The discharge film is 1
After being led to a cooling roll at 17 ° C. and cooled by blowing cool air at 25 ° C., it was taken off at 20 m / min. The thickness of the obtained polyethylene film was 9.5 μm. This unstretched polyethylene film is heat-treated at 120 ° C. for 60 seconds with the take-off direction fixed,
Cooled to room temperature. The birefringence of the heat-treated unstretched polyethylene film was 35.5 × 10 ⁻³ , and the elastic recovery at 50% elongation was 52%.

The heat-treated polyethylene film and polypropylene film were laminated in a three-layer structure in which polypropylene was disposed on the surface layer and polyethylene was disposed on the inner layer (intermediate layer). The lamination unwinds the polypropylene film and the polyethylene film from the three roll stands at an unwind speed of 6.5 m / min, respectively, and guides them to the heating roll.
Thermocompression bonding was carried out at a temperature of 120 ° C. and a linear pressure of 1.8 kg / cm, and then guided to a 50 ° C. cooling roll at the same speed and wound up. Winding speed is 6.5m / min, unwinding tension is 0.9kg
Met. The thickness of the obtained unstretched laminated film was 31.
It was 6 μm.

The unstretched laminated film was stretched at a low temperature by 25% between nip rolls kept at 30 ° C. At this time, the distance between the rolls was 350 mm, and the roll speed on the supply side was 2 m / mi.
n. The laminated film stretched at low temperature continues to be 12
It is guided into a hot-air circulation oven heated to 3 ° C., stretched at a high temperature to a total stretching amount of 180% between the rolls using a difference in roll peripheral speed, and then rolled to a temperature of 123 ° C.
The film was heat-set for 72 seconds with a relaxation of 0% to obtain a continuous laminated porous film, that is, a battery separator.

Table 1 shows the thickness, air permeability, maximum pore size, porosity, pencil hardness, micro surface hardness, and breakdown voltage of the obtained battery separator. Further, the battery after the battery separator was rubbed at a load of 400 gf / cm ² and a moving speed of 300 mm / min using a metal surface ground and finished so that the surface roughness index (Ra) became 0.3 μm. FIG. 1 shows a micrograph of the separator for use in the present invention. As is clear from FIG. 1, almost no scratches were found on the separator surface. The above evaluation method was performed as follows. 1) Air permeability Measured according to JIS P8117. A B-type Gurley densometer (manufactured by Toyo Seiki Co., Ltd.) was used as a measuring device. The sample piece is fastened to a circular hole having a diameter of 28.6 mm and an area of 645 mm ² . With the inner cylinder weight of 567 g, the air in the cylinder is allowed to pass from the test hole to the outside of the cylinder. The time required for 100 cc of air to pass was measured and defined as the air permeability (Gurley value). 2) Porosity, maximum pore diameter Measured using a mercury porosimeter manufactured by Yuasa Ionics. After weighing 0.03 to 0.07 g of the sample and evacuating it in a glass cell, mercury is injected and filled. The maximum pore diameter and porosity were determined from the mercury pressure and the amount of mercury injected during the filling. 3) Pencil hardness Measured using a pencil scratch tester manufactured by Toyo Seiki Co., Ltd. A 50 g load is applied to the battery separator five times with a pencil whose core is exposed in a cylindrical shape with a length of about 3 mm, and the battery separator is scratched five times. The hardness symbol at which the pencil was scratched twice or more out of five times was defined as pencil hardness. 4) Micro surface hardness Akashi smile surface material property evaluation system (MZT-4)
The measurement was carried out using. Fix the battery separator,
A load was applied up to 5 gf at a speed of 0.04 gf / sec with a spherical indenter having a diameter of 500 μm, and the pressure was released after holding for 5 seconds. The hardness index was calculated from the indentation depth according to the following equation (5). Formula (5) Indentation index = Load × 2 / Indentation depth / pi 5) Breakdown voltage Measured according to JIS C2110. 50mm × 50
The battery separator cut into mm was sandwiched between electrodes having a diameter of 25 mm by applying a load of 500 g, and an AC voltage was applied at a rate of 0.2 KV / sec. .

Comparative Example 1 A laminated porous film, that is, a battery separator, was obtained in the same manner as in Example 1 except that the inorganic fine particles were not added to the polypropylene. Table 1 shows the thickness, air permeability, maximum pore size, porosity, pencil hardness, micro surface hardness, and breakdown voltage of the obtained battery separator. Further, the battery after the battery separator was rubbed at a load of 400 gf / cm ² and a moving speed of 300 mm / min using a metal surface ground and finished so that the surface roughness index (Ra) became 0.3 μm. FIG. 2 shows a micrograph of the separator for use in the present invention. As is clear from FIG. 2, countless abrasions are seen on the separator surface.

[0043]

[Table 1]

According to the present invention, it is possible to provide a battery separator having excellent mechanical strength such as scratch resistance by appropriately mixing inorganic fine particles containing a specific metal oxide as a main component.

[Brief description of the drawings]

FIG. 1 is a drawing instead of a photograph showing a surface state after a rubbing test on a battery separator obtained in the present invention.

FIG. 2 is a view replacing a photograph showing a surface state after a rubbing test on a battery separator obtained in a comparative example.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ryuichiro Kogure 1010, 1978 Kogushi, Oji, Ube City, Yamaguchi Prefecture Inside Ube Chemical Factory (72) Inventor Kenji Kawabata 10 Ube, 1978 Kogushi, Oji, Ube City, Yamaguchi Prefecture F-term (reference) in Ube Chemical Factory of Kosan Co., Ltd.

Claims (3)

[Claims] 1. A battery separator comprising a single-layer or laminated porous film made porous by a stretching method, wherein said porous film is made of at least one member selected from the group consisting of silicon oxide, aluminum oxide and magnesium oxide. A battery separator comprising 100 to 5000 ppm of inorganic fine particles having a mean particle size of 0.1 to 10 [mu] m containing a metal oxide as a main component. 2. The battery separator according to claim 1, wherein the oxidation potential of the inorganic fine particles contained in the battery separator is +4.5 V or more with respect to lithium. 3. The battery separator according to claim 1, wherein the air permeability is 30 to 800 seconds / 100 cc.
A battery separator having a maximum pore diameter of 0.02 to 3 μm, a porosity of 30 to 85%, and a film thickness of 5 to 100 μm.