JPH1180395A - Porous film and separator for nonaqueous electrolyte cell or battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous electrolyte cell or battery, hardly causing internal short-circuiting due to the penetration or the like of electroconductive particles and having a high surface hardness and to obtain a porous film suitable for composing the separator. SOLUTION: This porous film having a surface protecting layer is obtained by using a polyolefin porous film such as polyethylene or polypropylene as a substrate, coating at least one surface of the substrate with a mixture containing inorganic fine particles such as aluminum oxide or silicon dioxide and a resin to be a binder and then ultrasonically treating the resultant coated substrate in ethanol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a porous membrane and a separator for a non-aqueous electrolyte battery.

[0002]

2. Description of the Related Art Various types of batteries have been put to practical use, and porous films, non-porous films, nonwoven fabrics, papers, and the like have been proposed as battery separators suitable for each type. These battery separators are required to have properties such as affinity (wetting property) with the electrolyte and liquid retention, low electric resistance and high air permeability, high mechanical strength, and chemical stability. Among these properties, affinity with electrolyte and liquid retention,
Electric resistance and air permeability are related to the discharge characteristics of the battery and are required to facilitate the movement of ions in the battery reaction. Mechanical strength is a characteristic required to reduce the occurrence of an internal short circuit due to breakage of a separator or the like in a battery assembly process or the like. In addition, since the battery separator is exposed to the oxidizing / reducing atmosphere inside the battery, it is necessary to use a chemically stable material that is unlikely to cause decomposition, reaction, and the like. Is often used.

In particular, in recent years, attention has been paid to a small, lightweight, high energy density lithium battery in order to cope with a cordless electronic device. In this lithium battery, since there is a possibility that the battery temperature may rise excessively due to an external short circuit or overuse, etc., a safety valve, a PTC element (Positi
ve Temperature Coeficient; interrupts current when excessive current flows), and various safety devices such as current control circuit are provided. The separator used therefor also has a function of stopping the battery reaction by making it nonporous at an appropriate temperature and increasing its electrical resistance to prevent an excessive increase in temperature (this is called a "shutdown (SD) function"). ) Is required.

As a separator suitable for such a lithium battery, a porous film of a polyolefin represented by polypropylene (hereinafter, referred to as "PP") or polyethylene (hereinafter, referred to as "PE") is frequently used. Among them, a mixture containing two or more kinds of resins having different melting points such as PP and PE, a multilayer film or a porous film having a concentration gradient is excellent in characteristics such as SD characteristics, and environmental and cost aspects. High practicality (Japanese Patent Laid-Open No. 4-181)
651, JP-A-4-206257, JP-A-6-55629, JP-A-7-216118, and the like.

[0005]

However, since the surface layer of these battery separators is made of a soft material such as polyolefin, the conductive particle powder peeled off from the electrode during winding or storage of the battery is not used. , There is a problem that an internal short circuit may occur.

In JP-A-1-304933, the surface vacancy diameter is 0.05 to 3 μm and the porosity is 30 to 90%.
There is a description of a polyolefin microporous film having a coating layer mainly composed of 0.1 to 6 g of a siloxane polymer per 10 g of polyolefin constituting the microporous film. By adopting such a configuration, it is expected that a higher mechanical strength can be obtained as compared with a porous film of polyolefin alone. However, it is difficult to obtain a sufficient mechanical strength, and the internal short circuit failure rate cannot be reduced. Further, a high temperature or a long time is required for curing the polysiloxane. When a high temperature is used, the pores are closed due to the contraction of the microporous film, and when the curing is performed for a long time, the cost increases.

The present invention relates to a separator for a non-aqueous electrolyte battery having excellent mechanical strength, particularly excellent surface hardness, and a small internal short circuit failure rate during battery production / storage, and a porous material suitable for constituting such a separator. It is intended to provide a membrane.

[0008]

Means for Solving the Problems In order to achieve the above object, a first embodiment of the porous membrane of the present invention is a porous membrane having a gas-permeable surface protective layer containing inorganic fine particles on at least one surface thereof. Is formed. By adopting such a configuration, a porous membrane having high mechanical strength (surface hardness) and hardly causing breakage or penetration of fine particles or the like can be obtained. When used as a separator for a non-aqueous electrolyte battery, It is possible to provide a nonaqueous electrolyte battery having a small internal short circuit failure rate due to penetration of conductive fine particles during production / storage. Here, “having air permeability” means J
Gurley seconds measured by the method described in IS K8117 is 10,000 seconds / 100 cc or less. Further, in the porous film, the surface hardness of the surface on which the surface protective layer is formed is preferably 4H or more in pencil hardness, whereby the internal short-circuit failure rate of the nonaqueous electrolyte battery is more reliably reduced. can do.

Further, in the porous membrane of the present invention, the thermal conductivity is preferably 0.5 kW / m · K or more,
In the porous membrane having such a configuration, the non-aqueous electrolyte battery with high safety can be provided when used as a separator because the non-aqueous electrolyte battery rapidly progresses in nonporous formation when the temperature rises excessively.

[0010] Further, a second embodiment of the porous membrane of the present invention comprises:
It is characterized in that a gas-permeable surface protective layer containing at least one resin selected from melamine resin, urethane resin, alkyd resin and acrylic resin is formed on at least one surface of a film serving as a substrate. With such a configuration, the surface hardness of the porous film can be improved as in the first embodiment. In addition, "has breathability"
Has the same meaning as described above.

Further, according to the non-aqueous electrolyte separator and the battery non-aqueous electrolyte battery of the present invention using the porous membrane as described above, the internal short-circuit failure rate during battery production / storage is small, and safety is improved. And a nonaqueous electrolyte battery having a high

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The porous film of the present invention can be obtained by providing a surface protective layer on one or both sides of a substrate film.
This is a porous film having excellent mechanical strength.

The membrane serving as the substrate may have a porous structure. However, when the porous membrane of the present invention is used as a separator for a non-aqueous electrolyte battery, it has low electric resistance and excellent SD function. It is preferable to use a film having the same.
The excellent SD function refers to, for example, having characteristics such as a rapid increase in electric resistance when the SD function is developed, and an appropriate SD starting temperature and heat resistant temperature. From such a viewpoint, a substrate suitable in the present invention will be described below.

As the material of the substrate, polyolefin, polyamide, polyester, fluororesin and the like can be suitably used. Among them, a polyolefin such as PP or PE is preferable, and a mixture or a multilayer containing PP and PE is particularly preferable because the SD initiation temperature and the heat-resistant temperature of the film are suitable. Further, an antioxidant, a coloring agent, a flame retardant, a filler, and the like may be added to these resins.

The substrate may have a porous structure as described above, and may be a single layer or a multilayer such as a microporous membrane, a mesh, a nonwoven fabric, a woven fabric or a foam. The pore size of the pores is suitably about 0.1 to 200 μm, and a microporous membrane of 0.1 to 1.0 μm is particularly preferred because the pores are quickly closed. The air permeability is suitably not more than 10,000 seconds / 100 cc in Gurley seconds, preferably not more than 2000 seconds / 100 cc, and more preferably not more than 1000 seconds / 100 cc. The thickness of the substrate is suitably 400 μm or less, preferably 1 μm or less.
The thickness is set to 00 μm or less, more preferably 30 μm or less.

The material of the surface protective layer provided on the substrate is as follows:
What is necessary is just to be able to form a thin film having a higher surface hardness than the substrate. Hereinafter, as such a material, an embodiment in which a material containing inorganic fine particles is used will be described as a “first embodiment”, and an embodiment in which a material containing the above-described organic resin is used will be described as a “second embodiment”.

If the thickness of the surface protective layer is too small, it is difficult to secure sufficient strength. If the thickness is too large, the battery characteristics may be adversely affected when used as a separator. Therefore, in both of the first and second embodiments, the thickness of the surface protective layer is suitably 0.5 to 100 μm, preferably 1 to 30 μm, more preferably 1 to 1 μm.
0 μm. The air permeability of the surface protective layer is 10,000 seconds / 100 cc or less in Gurley seconds, preferably 200 seconds.
0 sec / 100 cc or less.

The inorganic fine particles used in the first embodiment are not particularly limited, but those which are hard, light, and poor in conductivity are preferred. Examples include various metal oxides, metal carbides, metal nitrides, metal hydroxides, metal salts, and more specifically, aluminum oxide, silicon dioxide, titanium oxide, zinc oxide, tin oxide,
Examples include zirconium oxide, magnesium oxide, iron oxide, copper oxide, aluminum hydroxide, silicon carbide, and boron nitride.

On the other hand, if the particle size of the inorganic fine particles is too small, it is difficult to obtain a sufficient reinforcing effect. If the particle size is too large, the total thickness of the porous membrane becomes large, which is unsuitable for use as a separator. is there. Therefore, the average particle diameter of the inorganic fine particles is suitably 20 μm or less, and preferably 0.1 μm or less.
μm to 20 μm. In the case of columnar or fibrous particles, the average particle diameter is preferably 0.1 to 10 μm, and the average particle length is preferably 1 to 100 μm.

As an example of a method for forming a surface protective layer containing inorganic fine particles, there is a method in which inorganic fine particles are dispersed in a solvent, and the solvent is evaporated after casting, dipping or spray coating on a substrate. The solvent is preferably volatile and does not dissolve the substrate and the inorganic fine particles. Examples thereof include ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, aromatics such as toluene, xylene and styrene, and various alcohols such as methanol and ethanol. Or water can be used. Further, an additive such as a surfactant may be added to the solvent, and the ratio of the additive is preferably 5% by weight or less.

Further, a method in which inorganic fine particles are sprayed on a substrate without using a solvent, a method in which a porous ceramic is produced by a conventional method, and this is adhered to the substrate, or a method in which the porous ceramic is simply laminated, can also be adopted.

In order to improve the adhesion of the surface protective layer to the substrate, the brittleness, the ease of cracking, and the like, it is preferable to use the inorganic fine particles in a mixture with a resin serving as a binder. The binder is not particularly limited as long as it is conventionally used. For example, various polyesters, various polyolefins, various rubbers, various acrylic resins, and the like can be used alone or in combination. The mixing weight ratio of the inorganic fine particles to the binder is set to 500 parts or less, preferably 100 parts or less, and more preferably 50 parts or less with respect to 100 parts of the inorganic fine particles. This is because if the ratio of the binder exceeds 500 parts, it is difficult to obtain a sufficient reinforcing effect. The binder may be cured by heating or irradiation with ultraviolet rays.

As a method for forming the surface protective layer when a binder is used, a coating method such as casting, dipping or spray coating can be adopted.
At this time, the above-mentioned solvent can be used if necessary. The solvent is 10 parts per 100 parts of the inorganic fine particles.
It is appropriate to use it in a weight ratio of 000 parts or less.

When the surface protective layer using a binder is formed by the above-described coating method, it is possible to secure the above-mentioned air permeability by adjusting the concentration or the amount of the coating solution used. it can. However, when the coating solution concentration or the coating amount is reduced to improve the air permeability, the concentration of the inorganic fine particles in the surface protective layer is reduced.
There is a limit in improving the strength of the film.

As a method of avoiding the above problem, there is a method of forming a surface protective layer by screen printing so as to have openings such as a mesh. The size of the opening is not particularly limited, but when used as a battery separator, it is appropriate to set the size to 0.1 μm to 1 mm in consideration of the size of conductive particles that cause an internal short circuit. And preferably 5 μm to 20 μm. Further, the openings preferably occupy about 40 to 80% of the total area on the surface of the surface protective layer.

After the surface protective layer is formed by the above-described coating method or the like, the surface protective layer is subjected to ultrasonic treatment in a poor solvent for the resin constituting the surface protective layer, so that the surface protective layer conforms to the pore structure of the substrate. The above-mentioned problem can be avoided by this method. As such a poor solvent, a lower alcohol such as methanol or water can be used.

Further, the above-mentioned problem can be avoided by preparing a surface protective layer having a pore structure in advance and bonding it to a base. For example, a method of producing a porous surface protective layer by extraction, stretching, or addition of a foaming agent, and then laminating or overlapping the substrate, or forming the surface protective layer on a release paper by mesh screen printing, etc. A method of transferring to the surface can be used.

According to a preferred example of the first embodiment,
The object of the present invention is not only to improve the mechanical strength, but also to improve the thermal conductivity. When importance is attached to the improvement of the thermal conductivity, as the inorganic fine particles to be used, aluminum oxide, beryllium oxide, magnesium oxide, mica and the like are preferable. When a binder is used, the amount is preferably 100 parts or less, more preferably 50 parts or less based on 100 parts of the inorganic fine particles.

Normally, the thermal conductivity of an organic material such as polyethylene or polypropylene used for the battery separator is 0.1 to 0.3 kW / m · K alone, but the porosity of the battery separator is 10 to 90 kW / m · K. %, Usually about 40 to 50%, so that the thermal conductivity is usually about 0.001 to 0.1 kW / m · K. But,
According to a preferred example of the first embodiment, 0.5 kW / m
-It is also possible to have a thermal conductivity of K or more. By improving the thermal conductivity, when used as a separator, it is possible to rapidly close pores when an excessive temperature rise occurs, thereby improving the safety of the battery.

In addition to the above-mentioned embodiments, it is also high due to A) bonding of an inorganic fiber non-woven fabric and a porous film, and B) porous film made of a polyolefin or the like to which inorganic fibers or inorganic fine particles are added. A porous film having thermal conductivity can be obtained.

In the second embodiment of the present invention, the resin used as the surface protective layer is a melamine resin, a urethane resin,
Alkyd resin or acrylic resin. These resins may be used alone, but are preferably used in combination in consideration of their properties. As such a mixture,
For example, a mixture of a melamine resin and an alkyd resin or an acrylic resin may be used.

As a method for forming the surface protective layer in the second embodiment, a method in which the surface is coated by casting, dipping, spray coating or the like, and then cured by a method corresponding to the coating film components such as heating, ultraviolet irradiation, or the like can be used. . An additive such as a curing accelerator may be added to the coating liquid in addition to the above-mentioned components for forming a resin coating film. In addition, a solvent may be used if necessary. As such a solvent, a solvent that is volatile and does not dissolve the substrate is used, and examples thereof include hydrocarbons such as toluene, xylene, and hexane, methanol, and isobutyl alcohol. Alcohols, esters such as ethyl acetate and isopropyl acetate, ethers, terpenes and the like can be used.

As in the case of the first embodiment using a binder, methods such as screen printing and ultrasonic treatment in a poor solvent can be used. It is preferable because sufficient air permeability can be ensured without limiting the amount of the polymer. Of course, it is also possible to use a method in which a surface protective layer is independently prepared in advance, made porous by stretching or the like, and then bonded to a substrate.

The above porous membrane has a high surface hardness,
Therefore, when used as a separator, a non-aqueous electrolyte battery that is less likely to be torn or broken due to foreign matter, has a low internal short-circuit failure rate during battery production / storage, and is excellent in safety.

In such a non-aqueous electrolyte battery, a wound electrode body obtained by laminating and winding a strip-shaped negative electrode, a positive electrode and the porous film of the present invention is housed in a battery can together with an electrolytic solution, and other necessary components. It can be obtained by appropriately arranging various members according to a commercially available battery.

As the negative electrode material, a metal material such as lithium metal, a lithium alloy, a carbon material such as carbon or graphite which adsorbs or occludes lithium ions, or a material formed of a conductive polymer doped with lithium ions can be used. As the cathode material, generally (CF _X) fluorinated graphite represented by _{n, CoLiO 2, MnO 2,} V 2 O 5, C
uO, metal oxides such as Ag ₂ CrO ₄ , TiO ₂ , CuS
And the like can be used. Examples of the electrolytic solution include LiPF ₆ , LPF in an organic solvent such as ethylene carbonate, propylene carbonate, acetonitrile, γ-butyrolactone, 1,2-dimethoxyethane, and tetrahydrofuran.
A material obtained by dissolving iCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ or the like with an electrolyte can be used.

[0037]

The present invention will be described below in detail with reference to examples. However, in the following description, “parts” used when expressing the mixing ratio means “parts by weight”. The characteristics of the sample were measured by the following methods.

(Air permeability) According to JIS K-8117,
Gurley type densometer No. manufactured by Yasuda Seiki Seisakusho 32
Using 3-Auto, film area 642 mm ²
The transmission time of c was measured, and this value was obtained by multiplying by 10 times.

(Surface hardness) It was determined by a pencil scratching method specified in JIS K 5400.

(Thermal Conductivity) A film is pressed between two heater plates, and one of the heater plates is heated. After the temperature became constant, the temperature difference ΔT (K) and the heat transfer Q (cal / sec) between the two surfaces of the film were measured, and the measurement results were used as well as the film thickness L (cm) and area A (cm ² ). The thermal conductivity λ was calculated by the following equation. λ (W / m · K) = (Q / A) × (L / ΔT) × 41
8.6

(Shrinkage Ratio) A film was cut to a width of about 10 mm and a length of about 300 mm so that the length direction coincided with the machine direction, and this was kept at 60 ° C. in a state of being placed on a compressed paper without tension. The film was put into a hot air circulating dryer for one hour, the length of the film before and after heating was measured, and the length was determined from the decrease rate.

(Thickness) The total thickness was measured with a dial gauge of 1/1000 mm. The thickness of each layer of the multilayer film was determined by freeze-fracturing the film and observing the cross section with an optical microscope.

Example 1 Weight average molecular weight (hereinafter referred to as "M
w ”. ) 9.8 × 10 ⁵ PP alone, 50 parts of similar PP and high-density PE 50 with Mw of 2.6 × 10 ⁵
And a mixture of PP layer / PP mixture layer / PP layer / PP layer using a three-layer T-die film forming machine.
A film having a layer structure was formed. At this time, the extrusion temperature was 250 ° C., the draw ratio was 30, and the total thickness of the obtained film was 32 μm (thickness of each layer: PP layer / mixture layer / PP layer = 10/11/11 μm). This film is sandwiched between two 50 μm-thick polyethylene terephthalate films in a clean room at 25 ° C. and a relative humidity of 30%, contacted on a roll surface having a surface temperature of 150 ° C. for about 10 seconds, heat-treated, and wound on an iron core. Was.
This was further placed in a dryer at 125 ° C. and heat-treated for 48 hours. Subsequently, the heat-treated film is heated at 60 ° C.
The film is stretched 78% based on the length of the unstretched film.
The film was stretched at 0 ° C. by 178% based on the length of the unstretched film (total stretching ratio: 256% = 3.56 times). One more
The resulting porous membrane is shrunk by 26% based on the length of the stretched film at 20 ° C. (final stretch ratio: 2.63 times), and used as a substrate. To 100 parts of alumina particles having an average particle diameter of 3 μm (AL15-H manufactured by Showa Denko), 50 parts of PE wax (Sunwax 171P manufactured by Sanyo Chemical Co., Ltd.), 1 part of surfactant, and 1000 parts of xylene were added, and heated and stirred at 100 ° C. Was performed to obtain a mixture. This mixture was cast on a substrate at a temperature of about 80 ° C. Then in methanol
After sonication for 2 minutes, xylene was evaporated with a dryer at 80 ° C. to obtain a porous film A.

(Example 2) 30 parts of polynorbornene rubber (Nosorex manufactured by Zeon Corporation) and 100 parts of xylene 1000 per 100 parts of silica fine particles having an average particle diameter of 1.2 μm
The mixture was heated and stirred at 60 ° C. to prepare a mixture.
The mixture was spray-sprayed on a substrate prepared in the same manner as in Example 1 at a basis weight of 5 g / m ² ,
Drying was performed at 2 ° C. for 2 hours to obtain a porous film B.

Example 3 Average Fiber Diameter 0.3-0.6 μm
m, 100 parts of fibrous potassium titanate particles having an average fiber length of 10 to 20 μm (Tismo D manufactured by Otsuka Chemical Co., Ltd.) and polyester resin (Byron 630 manufactured by Toyobo Co., Ltd.)
100 parts, 250 parts of toluene and 100 parts of methyl isobutyl ketone were added, and the mixture was stirred with a ball mill for 24 hours to obtain a mixture. This mixture was cast at room temperature on a substrate prepared in the same manner as in Example 1. Then, after performing ultrasonic treatment for 2 minutes in methanol, the solvent was evaporated in a dryer at 120 ° C. to obtain a porous film C.

Example 4 90 parts of liquid paraffin was added to a mixture of 2 parts of ultrahigh molecular weight PE having an Mw of 2.5 × 10 ⁶ and 8 parts of 6.8 × 10 ⁵ PE to obtain a solution of a PE composition. 100 parts by weight of this solution was added to 2,6-t-butyl-p
-Cresol ("BHT", manufactured by Sumitomo Chemical Co., Ltd.) 0.1
25 parts and tetrakis [methylene-3- (3,5-di-t
-Butyl-4-hydroxyphenyl) -propionate] methane (“Irganox 1010”, manufactured by Ciba Geigy) as an antioxidant was added and mixed. This mixture was filled in an autoclave equipped with a stirrer to obtain a uniform solution. This solution was extruded from a T-die by an extruder, and a gel upper sheet was formed while being taken up by a cooling roll. The obtained sheet was set on a biaxial stretching machine and biaxially stretched 7 × 7 times at a temperature of 115 ° C. and a stretching speed of 0.5 m / min. The obtained stretched film was washed with methylene chloride to extract and remove the remaining liquid paraffin, and then dried to obtain a substrate as a PE single-layer porous film. A mixture prepared in the same manner as in Example 1 was cast on this substrate at a temperature of about 80 ° C. Then, after performing ultrasonic treatment in methanol for 2 minutes, xylene was evaporated by a dryer at 80 ° C. to obtain a porous film D.

(Example 5) A porous film E was obtained in the same manner as in Example 2, except that a substrate produced in the same manner as in Example 4 was used.

(Example 6) A porous film F was obtained in the same manner as in Example 3, except that a substrate prepared in the same manner as in Example 4 was used.

Example 7 100 parts of an ultraviolet-curable acrylic urethane oligomer and 3 parts of benzophenone were dissolved in 400 parts of ethyl acetate and stirred at a high speed.
This mixture was cast at room temperature on a substrate prepared in the same manner as in Example 1. After evaporating the ethyl acetate, the film was irradiated with light at a cumulative light amount of 150 mj / cm ² using a high-pressure mercury lamp and cured to obtain a porous film G.

(Example 8) A porous film H was obtained in the same manner as in Example 7, except that a substrate produced in the same manner as in Example 4 was used.

Table 1 shows the results of measuring the characteristics of the porous films A to H obtained in the above examples. Further, as a comparative example, the results of the same measurement performed using the substrates of Examples 1 and 4 on which the surface protective layer was not formed as samples I and J are also described.

[0052]

Table 1 Sample Air permeability Surface hardness Thermal conductivity Shrinkage rate (sec / 100 cc) (Pencil hardness) (kW / mK) (%) A 900 4H 0.9 2.0 B 850 4H 0.8 9C10005H0.72.0D8003H0.91.0E7504H0.71.1F9005H0.61.3G12002H0.122.1H14003H0 .14 1.1 I 800 H 0.08 2.3 J 700 HB 0.1 1.2

Using the porous membranes A to H as separators, 1,000 lithium ion batteries were manufactured for each. The resistance between the electrodes of each battery was measured, and the ratio of those having a resistance of 2 kΩ or less was defined as the internal short-circuit failure rate.

Similarly, ten lithium ion batteries each using the porous membranes A to H as a separator were prepared and specified in the Battery Association of Japan guideline SBA G 1101 “Lithium Secondary Battery Safety Evaluation Standard Guidelines”. A nail penetration test was performed based on the method described above, and the number of batteries that had exploded or ignited was taken as the failure rate due to nail penetration.

Further, as a comparative example, the same measurement was performed using the substrates of Examples 1 and 4 having no surface protective layer as samples I and J, respectively. Table 2 shows the internal short-circuit defect rate and the defect rate due to nail penetration in each sample.

[0056]

[Table 2] Sample Internal short-circuit failure rate Failure rate due to nail penetration (%) (pieces / 10 pieces) A 0.50 B 0.60 C 0.40 D 0.40 E 0.50 F 0 0.30 G 0.70 H 0.50 I 2.34 J 1.11

[0057]

As described above, according to the porous film of the present invention, the surface protective layer containing the inorganic fine particles or the resin as described above is formed on at least one surface of the film serving as the substrate. A porous film having a high surface hardness can be obtained. By using such a porous membrane as a separator in a non-aqueous electrolyte battery, it is possible to reduce the inconvenience that the conductive particles peeled off from the electrode material during production or storage of the battery penetrate the separator, As a result, it is possible to provide a non-aqueous electrolyte battery which is less likely to cause an internal short circuit and has excellent safety.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 10/40 H01M 10/40 Z

Claims (6)

[Claims] 1. A porous film comprising a film serving as a substrate, and a gas-permeable surface protective layer containing inorganic fine particles formed on at least one surface of the film. 2. The porous film according to claim 1, wherein the surface hardness of the surface on which the surface protective layer is formed is 4H or more in pencil hardness. 3. The porous membrane according to claim 1, having a thermal conductivity of 0.5 kW / m · K or more. 4. A gas-permeable surface protective layer containing at least one resin selected from a melamine resin, a urethane resin, an alkyd resin and an acrylic resin is formed on at least one surface of a film serving as a substrate. Porous membrane. 5. A non-aqueous electrolyte battery separator comprising the porous membrane according to claim 1 as a component. 6. A non-aqueous electrolyte battery comprising the separator for a non-aqueous electrolyte battery according to claim 5.