JP2012076384A - Laminated porous film and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated porous film which can quickly shut down a battery when abnormal heat generation occurs in the battery, can maintain the shut down state over a wide temperature range, and has piercing strength used as a separator.SOLUTION: The laminated porous film includes a porous layer (A) formed of a polyethylene-based resin and a porous layer (B) formed of a heat-resistant resin and an inorganic filler where, when the resin component included in the porous layer (A) is 100 wt.%, the porous layer (A) includes 5 to 70 wt.% of ultra-high molecular weight polyethylene of which the weight-average molecular weight is 1,000,000 or larger and 5 to 40 wt.% of linear chain low-density polyethylene of which the weight-average molecular weight is 50,000 to 800,000.

Description

The present invention relates to a laminated porous film and a battery.

Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are widely used as batteries for personal computers, mobile phones, portable information terminals, electric vehicles, and the like because of their high energy density. Lithium secondary batteries use flammable organic solvents, so there is a possibility of explosion if an internal short circuit or external short circuit occurs due to damage such as damage to the battery or the equipment that uses the battery. Therefore, the demand for safety is increasing with the recent increase in energy density.

In the non-aqueous electrolyte secondary battery, a separator is disposed between the positive electrode and the negative electrode so as not to contact each other. Since a high puncture strength and a shutdown function are required for the separator, a porous film made of ultrahigh molecular weight polyethylene is widely used (see, for example, Patent Document 1).

JP-A-6-325747

However, when a porous film formed only from ultra-high molecular weight polyethylene as described in Patent Document 1 is used as a separator, the temperature at which shutdown is started is high, and the separator breaks at a high temperature. There was a problem that.

The object of the present invention is to quickly shut down when abnormal heat is generated inside the battery, maintain the shutdown state over a wide range of temperatures, and has a piercing strength that can be used as a separator. It is to provide a laminated porous film and a battery comprising such a laminated porous film.

That is, the present invention relates to the following [1] to [3].
[1] A laminated porous film including a porous layer (A) formed from a polyethylene-based resin and a porous layer (B) formed from a heat-resistant resin and an inorganic filler,
When the porous layer (A) is 100% by weight of the resin component contained in the porous layer (A), 5 to 70% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more, A laminated porous film comprising 5 to 40% by weight of a linear low density polyethylene having a weight average molecular weight of 5 to 800,000.
[2] The porous layer (A) contains 1 to 30% by weight of a polyolefin wax having a weight average molecular weight of 500 to 3000 when the resin component contained in the porous layer (A) is 100% by weight. [1] A laminated porous film.
[3] A battery comprising the laminated porous film of [1] or [2].

  According to the present invention, when abnormal heat generation occurs inside the battery, the battery can be quickly shut down, and the shut-down state can be maintained over a wide range of temperatures, and has a piercing strength that can be used as a separator. A laminated porous film and a battery including such a laminated porous film can be provided.

  The present invention is a laminated porous film comprising a porous layer (A) formed from a polyethylene-based resin, and a porous layer (B) formed from a heat-resistant resin and an inorganic filler, the porous layer When (A) is 100% by weight of the resin component contained in the porous layer (A), the weight average molecular weight is 5 to 70% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more. It is a laminated porous film containing 5 to 40% by weight of a linear low density polyethylene that is 5 to 800,000.

First, the porous layer (A) formed from a polyethylene resin will be described.

The porous layer (A) has an ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more, preferably 5 to 70% by weight, preferably 100% by weight of the resin component contained in the porous layer (A). Contains 10 to 50% by weight. When the amount of the ultrahigh molecular weight polyethylene contained in the porous layer (A) is 5% by weight or more, the laminated porous film containing such a porous layer (A) has excellent puncture strength.
Examples of the ultrahigh molecular weight polyethylene in the present invention include ethylene homopolymers and copolymers obtained by copolymerizing ethylene with α-olefins such as propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. Can be mentioned.

The porous layer (A) is composed of 5 to 40% by weight of linear low density polyethylene having a weight average molecular weight of 5 to 800,000 when the resin component contained in the porous layer (A) is 100% by weight. More preferably, it contains 10 to 40%. When the amount of the linear low density polyethylene contained in the porous layer (A) is 5% by weight or more, the laminated porous film including such a porous layer (A) can be shut down at a low temperature. .
The linear low density polyethylene in the present invention is a copolymer obtained by copolymerizing ethylene and an α-olefin such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene. A polymer is mentioned.
The density of the linear low density polyethylene is usually 0.910 to 0.930.

It is preferable that the porous layer (A) further contains a polyolefin wax having a weight average molecular weight of 500 to 3,000. The weight average molecular weight of the polyolefin wax is preferably 500-2500.
The amount of the polyolefin wax contained in the porous layer (A) is 1 to 30% by weight, preferably 3 to 20% by weight, when the resin component contained in the porous layer (A) is 100% by weight. It is.
Polyolefin waxes include ethylene polymers, polyethylene polymers such as ethylene-α-olefin copolymers, polypropylene polymers such as propylene homopolymers, propylene-α-olefin copolymers, 4-methylpentene- 1 polymer, poly (butene-1), ethylene-vinyl acetate copolymer and the like. It is preferable to select a polyolefin wax having excellent compatibility with ultrahigh molecular weight polyethylene. Specifically, it is preferable to use a polyethylene wax such as an ethylene homopolymer or an ethylene-α-olefin copolymer.

  The weight average molecular weights of ultra high molecular weight polyethylene, linear low density polyethylene, and polyolefin wax can be generally determined by GPC measurement.

The production method of the porous layer (A) is as follows: (1) Ultra high molecular weight polyethylene, linear low density polyethylene, optionally polyolefin wax, and filler are kneaded to obtain a resin composition. (2) Method of removing the filler after the method of (1), (3) Ultra high molecular weight polyethylene, linear low density polyethylene, optionally polyolefin Wax and filler are kneaded to obtain a resin composition, a sheet is prepared using the resin composition, the filler is removed from the sheet, and then stretched. (4) Ultrahigh molecular weight polyethylene and linear chain The low-density polyethylene is kneaded with a solvent component such as liquid paraffin to obtain a resin composition, a sheet is prepared using the resin composition, the sheet is stretched, and then dissolved from the stretched film. (5) Sheet molding of ultra high molecular weight polyethylene and linear low density polyethylene, and annealing treatment at 100 to 140 ° C., followed by 0 to 40 ° C. And then stretching at 70 to 130 ° C.
In particular, a method using the fillers (1) to (3) is preferable.

  As the filler, inorganic or organic fine particles generally called a filler can be used. Inorganic fine particles include calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, oxidation Fine particles such as magnesium, titanium oxide, alumina, mica, zeolite, glass powder, and zinc oxide are used. As the organic fine particles, known resin fine particles are used. As the resin, a polymer obtained by polymerizing monomers such as styrene, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, methyl acrylate alone or in combination of two or more kinds. Examples thereof include fine particles of a polycondensation resin such as coalescence, melamine, and urea.

  When manufacturing a porous layer (A) using the resin composition containing a filler, it is preferable to remove a filler before extending | stretching the sheet | seat which consists of this resin composition, or extending | stretching. Therefore, it is preferable to use a filler that can be easily removed with an aqueous solution such as neutral, acidic, or alkaline. For example, among the above-mentioned fine particles, talc, clay, kaolin, diatomaceous earth, calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, calcium oxide, calcium oxide, magnesium hydroxide, calcium hydroxide, zinc oxide and silica can be mentioned. Among these, calcium carbonate is preferable.

The average particle size of the filler is preferably 0.01 to 3 μm, more preferably 0.02 to 1 μm, and most preferably 0.05 to 0.5 μm. If a filler having an average particle size of 3 μm or less is used, a laminated porous film having a better piercing strength can be obtained. If a filler having a mean particle diameter of 0.01 μm or more is used, the filler is easily dispersed uniformly. An open porous layer (A) can be obtained.

It is preferable to use a filler that has been surface-treated. When a surface-treated filler is used, the filler is easily dispersed in a resin such as ultra high molecular weight polyethylene or linear low density polyethylene, and the interface between the resin and filler such as ultra high molecular weight PE or linear low density polyethylene. Can be expected to be easily peeled off and prevent moisture absorption from the outside. Examples of the surface treatment agent include higher fatty acids such as stearic acid and lauric acid, and metal salts thereof.

  The amount of filler contained in the resin composition is 100 parts by volume when the total volume of ultrahigh molecular weight polyethylene, linear low density polyethylene and polyolefin wax contained in the resin composition is 100 parts by volume. On the other hand, it is preferably 15 to 150 parts by volume, more preferably 25 to 100 parts by volume. If it is 15 parts by volume or more, it can be sufficiently opened by stretching to obtain a good porous layer (A), and if it is 150 parts by volume or less, the proportion of the resin contained in the layer is high. In addition, a porous layer (A) having excellent strength can be obtained.

  Further, the resin composition used for forming the porous layer (A) is made of additives (antistatic agents, plasticizers, lubricants, antioxidants) that are generally used as long as they do not impair the purpose of the present invention. , Nucleating agents, etc.).

  In order to produce a resin composition, it is preferable to use a kneading device having a high shearing force as a kneading device for kneading ultrahigh molecular weight polyethylene, linear low density polyethylene or the like. , Banbury mixer, single screw extruder, twin screw extruder and the like.

In the case of using a resin composition containing a polyolefin wax, it is preferable to produce the resin composition by the following method.
That is, after kneading ultra high molecular weight polyethylene and polyolefin wax in a weight ratio of ultra high molecular weight polyethylene / polyolefin wax = 30/70 to 90/10, more preferably 40/60 to 80/20, molecular weight 5 This is a method of adding ~ 800,000 linear low density polyethylene and kneading.
The kneading method in this case includes a method of kneading pellets of ultrahigh molecular weight PE and polyolefin wax and linear low density polyethylene, a device for kneading ultrahigh molecular weight polyethylene and polyolefin wax, Examples include a method of continuous kneading by connecting a device for kneading by adding chain low density polyethylene, a method of side-feeding linear low density polyethylene to a device for kneading ultrahigh molecular weight polyethylene and polyolefin wax, and the like. .

  The method for forming a sheet using the resin composition is not particularly limited, and examples thereof include inflation processing, calendar processing, T-die extrusion processing, and Skyf method. The resin kneaded material may be continuously fed from the kneading apparatus into the sheet molding machine or the resin composition after kneading may be once pelletized and the pellets may be fed into the sheet molding machine.

  The method of stretching the sheet obtained by molding the resin composition to form a porous film is not particularly limited, but can be produced by stretching using a known device such as a tenter, roll, or autograph. . The stretching may be uniaxial or biaxial, and the stretching may be performed in one step or in multiple steps. The draw ratio is preferably 2 to 12 times, and more preferably 4 to 10 times. The stretching temperature is usually from a softening point to a melting point of the ultra high molecular weight polyethylene and preferably from 80 ° C to 120 ° C. By stretching at such a temperature, the film hardly breaks during stretching and the ultrahigh molecular weight polyethylene is difficult to melt, so that the holes generated by the interface peeling between the resin and the filler are difficult to close. Moreover, in order to stabilize the form of a hole after extending | stretching, you may perform a heat setting process as needed.

  After removing at least a part of the filler from the sheet obtained by molding the resin composition, the porous layer (A) may be produced by stretching. Or after extending | stretching the sheet | seat obtained by shape | molding a resin composition, you may remove at least one part filler and manufacture a porous layer (A). Examples of the method for removing the filler include a method of immersing the sheet or the stretched film in a liquid capable of dissolving the filler.

Next, the porous layer (B) (hereinafter sometimes referred to as a heat-resistant layer) formed from a heat-resistant resin and an inorganic filler will be described.

  Examples of the heat-resistant resin forming the heat-resistant layer include water-soluble polymers such as polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, and polymethacrylic acid, and aromatic polyaramid (hereinafter referred to as “aramid”). And nitrogen-containing aromatic polymers such as aromatic polyimide (hereinafter sometimes referred to as “polyimide”) and aromatic polyamideimide.

As the water-soluble polymer, polyvinyl alcohol, cellulose ether, and sodium alginate are preferable, and cellulose ether is more preferable. Specific examples of the cellulose ether include carboxymethyl cellulose (hereinafter sometimes referred to as CMC), hydroxyethyl cellulose, carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose, and the like, and CMC with small deterioration is most preferable.

  As the nitrogen-containing aromatic polymer, an aramid is preferable because it is easy to form a porous heat-resistant layer having a uniform film thickness and excellent air permeability. Among the aramids, a para-oriented aromatic polyamide (hereinafter referred to as “para-aramid”) is preferable. Most preferred).

  Para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4,4′-biphenylene). , 1,5-naphthalene, 2,6-naphthalene, and the like, which are substantially composed of repeating units bonded in the opposite direction (orientation positions extending coaxially or in parallel). Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly ( (Paraphenylene 2,6-naphthalene dicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, etc. Para-aramid having a similar structure is exemplified.

When providing the heat-resistant layer, a coating solution obtained by dissolving a heat-resistant resin in a solvent is usually used. When the heat resistant resin is a water-soluble polymer, water can be used as the solvent, and an alcohol such as methanol, ethanol, propanol, isopropyl alcohol or the like may be added to such an extent that the solubility is not impaired. When the heat-resistant resin is para-aramid, a polar amide solvent or a polar urea solvent can be used as the solvent. Specifically, N, N-dimethylformamide, N, N-dimethylacetamide, N- Examples thereof include methyl-2-pyrrolidone and tetramethylurea.

  When para-aramid is used as the heat-resistant resin, it is preferable to add an alkali metal or alkaline earth metal chloride during the para-aramid polymerization for the purpose of improving the solubility of para-aramid in a solvent. Specific examples include, but are not limited to lithium chloride or calcium chloride. The amount of the chloride added to the polymerization system is preferably 0.5 to 6.0 mol, more preferably 1.0 to 4.0 mol, per 1.0 mol of the amide group produced by condensation polymerization. If the chloride is 0.5 mol or more, the resulting para-aramid is sufficiently soluble, and if it is 6.0 mol or less, the chloride does not remain dissolved in the solvent. In general, the alkali metal or alkaline earth metal chloride is often 2% by weight or more and the solubility of para-aramid is often sufficient. At 10% by weight or less, the alkali metal or alkaline earth metal chloride is polar. In many cases, it is completely dissolved without being dissolved in a polar organic solvent such as an amide solvent or a polar urea solvent.

  In the present invention, the coating liquid used for forming the heat-resistant layer particularly preferably contains ceramic powder as an inorganic filler. By forming a heat-resistant layer using a coating solution in which ceramic powder is added to a solution having an arbitrary heat-resistant resin concentration, it is possible to form a heat-resistant layer having a uniform film thickness and a fine porosity. . The air permeability can be controlled by the amount of ceramic powder added. In the ceramic powder of the present invention, the average particle diameter of the primary particles is preferably 1.0 μm or less, more preferably 0.5 μm or less, from the viewpoint of the strength of the porous film and the smoothness of the heat-resistant layer surface. More preferably, it is 0.1 μm or less.

The content of the ceramic powder is preferably 1% by weight to 99% by weight in the heat resistant layer, and more preferably 5% by weight to 95% by weight. When it is 1% by weight or more, the ion permeability is excellent, and when it is 99% by weight or less, the film strength is excellent. The shape of the ceramic powder to be used is not particularly limited, and can be spherical or random.

  Examples of the ceramic powder in the present invention include ceramic powders made of electrically insulating metal oxides, metal nitrides, metal carbides, and the like. For example, powders of alumina, silica, titanium dioxide, zirconium oxide and the like are preferably used. The ceramic powders may be used alone, or two or more kinds thereof may be mixed, and the same or different ceramic powders having different particle sizes may be arbitrarily mixed and used.

As a method of laminating the heat-resistant layer on the porous layer (A), a method of separately manufacturing the heat-resistant layer and then laminating with the porous layer (A), ceramic powder and heat-resistant on at least one side of the porous layer (A) Examples include a method of forming a heat-resistant layer by applying a coating solution containing a functional resin, and the latter method is preferable from the viewpoint of productivity. Specifically, the latter method includes a method including the following steps.
(A) A slurry-like coating liquid in which 1 to 8000 parts by weight of ceramic powder is dispersed in 100 parts by weight of a heat-resistant resin in a polar organic solvent solution containing 100 parts by weight of a heat-resistant resin is prepared. (B) The coating liquid Is applied to at least one surface of the porous layer (A) to form a coating film.
(C) The heat-resistant resin is deposited from the coating film by drying and removing the solvent, or immersed in a solvent that does not dissolve the heat-resistant resin, and then dried.
The coating liquid is preferably applied continuously by a coating apparatus described in JP-A-2001-316006 and a method described in JP-A-2001-23602.

  The laminated porous film including the porous layer (A) of the present invention and a heat-resistant layer is excellent in shutdown property, heat resistance, strength, and ion permeability, and is suitable as a separator for non-aqueous batteries, particularly a lithium secondary battery separator. Can be used for

When the laminated porous film of the present invention is used as a battery separator, the porosity of the porous layer (A) in the laminated porous film is 30 to 80 from the viewpoints of electrolyte retention, film strength, and shutdown performance. % By volume is preferred, more preferably 40-70% by volume, and the porosity of the heat-resistant layer is preferably 30-80% by volume, more preferably 40-70% by volume, from the viewpoint of the amount of retained electrolyte and strength. It is.
The thickness of the laminated porous film is preferably 5 to 50 μm, more preferably 10 to 50 μm, and even more preferably 10 to 30 μm, from the viewpoints of shutdown performance, prevention of battery short-circuiting during winding, and higher battery capacity. In addition, the thickness of the heat resistant layer in the laminated porous film is preferably 0.5 μm to 10 μm, more preferably 1 μm to 5 μm, from the viewpoint of heat resistance.

The battery of the present invention includes the laminated porous film of the present invention as a battery separator. Hereinafter, components other than the battery separator in the case where the battery of the present invention is a nonaqueous electrolyte secondary battery such as a lithium battery will be described in detail.

As the non-aqueous electrolyte solution, for example, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used. Examples of lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , One or a mixture of two or more of lower aliphatic carboxylic acid lithium salts, LiAlCl _{4 and the} like can be mentioned. The lithium salt is selected from the group consisting of LiPF ₆ containing fluorine, LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) ₃ among these. It is preferable to use at least one selected from the above.

Examples of the organic solvent used in the nonaqueous electrolyte solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di ( Carbonates such as methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyl Ethers such as tetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amide; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by introducing a fluorine substituent into the above organic solvent Usually, a mixture of two or more of these is used.

Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable. As a mixed solvent of cyclic carbonate and non-cyclic carbonate, ethylene has a wide operating temperature range, excellent load characteristics, and is difficult to decompose even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. A mixed solvent containing carbonate, dimethyl carbonate and ethyl methyl carbonate is preferred. As the positive electrode sheet, a sheet in which a mixture containing a positive electrode active material, a conductive material, and a binder is supported on a current collector is usually used. Specifically, as the positive electrode active material, a material containing a material that can be doped / undoped with lithium ions, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder can be used. Examples of materials that can be doped / undoped with lithium ions include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among these, a layered lithium composite oxide based on an α-NaFeO ₂ type structure such as lithium nickelate or lithium cobaltate, or a spinel type structure such as lithium manganese spinel is preferable based on a high average discharge potential. Examples include lithium composite oxides.

The lithium composite oxide may contain various additive elements, particularly at least selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Ag, Mg, Al, Ga, In, and Sn. Composite nickel acid containing a metal such that the at least one metal is 0.1 to 20 mol% with respect to the sum of the number of moles of one metal and the number of moles of Ni in lithium nickelate Lithium is preferable because cycle characteristics in use at a high capacity are improved.

As the thermoplastic resin as the binder, polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether Copolymer, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, thermoplastic polyimide, polyethylene, polypropylene and the like.

Examples of the carbonaceous material as the conductive material include natural graphite, artificial graphite, cokes, and carbon black. As the conductive material, each may be used alone, or for example, a composite conductive material system in which artificial graphite and carbon black are mixed and used may be selected.

As the negative electrode sheet, for example, a material capable of doping and dedoping lithium ions, lithium metal, or a lithium alloy can be used. Materials that can be doped / undoped with lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds, and lower potential than the positive electrode. And chalcogen compounds such as oxides and sulfides for doping and dedoping lithium ions. A carbonaceous material mainly composed of a graphite material such as natural graphite or artificial graphite is preferable in that the potential flatness is high and the average discharge potential is low so that a large energy density can be obtained when combined with the positive electrode.

As the negative electrode current collector, Cu, Ni, stainless steel, or the like can be used. In particular, in a lithium secondary battery, Cu is preferable because it is difficult to form an alloy with lithium and it can be easily processed into a thin film. As a method of supporting the mixture containing the negative electrode active material on the negative electrode current collector, a method of pressure molding, or a method of pasting into a paste using a solvent or the like and applying pressure to the current collector by pressing after drying Is mentioned.

The shape of the battery of the present invention is not particularly limited, and may be any of a paper type, a coin type, a cylindrical type, a rectangular shape, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

(1) Puncture strength The maximum stress (gf) when a porous film or a laminated porous film was fixed with a 12 mmφ washer and the pin was punctured at 200 mm / min was measured, and the weight per unit area (g / M ² ) was taken as the puncture strength. (2) Shutdown temperature measurement A 2 x 3 cm square rectangular membrane was impregnated with electrolyte and then sandwiched between two SUS electrodes and fixed with clips. And created a cell. As the electrolytic solution, one obtained by dissolving 1 mol / L LiBF ₄ in a mixed solvent of ethylene carbonate 50 vol%: diethyl carbonate 50 vol% was used. The impedance analyzer terminals were connected to both sides of the assembled cell. The resistance value at 1 kHz was measured. Resistance was measured while increasing the temperature at a rate of 15 ° C./min in an oven. The temperature when the resistance value at 1 kHz reached 1000Ω was taken as the shutdown temperature. Further, after the shutdown, the temperature was further raised, the temperature at which the laminated porous film was torn and the resistance value began to decrease in the measurement was defined as the thermal film breaking temperature.

Example 1
Preparation of porous layer (A ) 12.3 g of ultra high molecular weight polyethylene powder (145 M, manufactured by Mitsui Chemicals) having a weight average molecular weight of about 1,000,000, a melting temperature of 136 ° C., and a density of 0.93 g / cm ^3. An average molecular weight of about 500,000, a melting temperature of 136 ° C., a density of 0.95 g / cm ³ high density polyethylene powder (030S, Mitsui Chemicals) 4.9 g, a weight average molecular weight of about 90,000 and a melting temperature of 117 ° C., 0.92 g 7.4 g / cm ³ linear low density polyethylene (FV403, manufactured by Sumitomo Chemical Co., Ltd.), 39.6 g calcium carbonate (manufactured by Maruo Calcium Co., Ltd.) having an average pore size of 0.1 μm, antioxidant (Irg1010, Ciba Specialty) Chemicals) 0.17% by weight (P168, Ciba Specialty Chemicals) 0.05% by weight were mixed in powder form, and then Laboplast mill (R-60H). Mold) at 200 ° C. and 60 rpm for 3 minutes, and then kneaded at 230 ° C. and 100 rpm for 3 minutes to obtain a resin composition (1). The obtained resin composition (1) was press-molded at 200 ° C. to obtain a sheet having a thickness of about 200 μm. The sheet was immersed in 3N hydrochloric acid overnight to remove calcium carbonate, washed with water and dried to obtain a porous sheet (1). This porous sheet (1) was stretched 4 × 4 times at 120 ° C. using a desktop biaxial stretching machine manufactured by Toyo Seiki Co., Ltd. to obtain a porous layer (1).
Synthesis of para-aramid (poly (paraphenylene terephthalamide)) Production of poly (paraphenylene terephthalamide) using a 3 liter separable flask with stirring blade, thermometer, nitrogen inlet tube and powder addition port went. The flask was sufficiently dried, charged with 2200 g of N-methyl-2-pyrrolidone (NMP), added with 151.07 g of calcium chloride powder vacuum-dried at 200 ° C. for 2 hours, heated to 100 ° C. and completely dissolved. . After returning to room temperature, 68.23 g of paraphenylenediamine was added and completely dissolved. While maintaining this solution at 20 ° C. ± 2 ° C., 124.97 g of terephthalic acid dichloride was added in 10 divided portions every about 5 minutes. Thereafter, the solution was aged for 1 hour while maintaining the temperature at 20 ° C. ± 2 ° C. with stirring. It filtered with the 1500 mesh stainless steel wire mesh. The resulting solution had a para-aramid concentration of 6%.
Preparation of coating solution 100 g of the previously polymerized para-aramid solution was weighed into a flask, 300 g of NMP was added, and the solution was prepared to a para-aramid concentration of 1.5% by weight and stirred for 60 minutes. 6 g of alumina C (manufactured by Nippon Aerosil Co., Ltd., average primary particle size 13 nm), advanced alumina AA-03 (manufactured by Sumitomo Chemical Co., Ltd., average primary particle size 0.4 μm) in a solution having the above-mentioned para-aramid concentration of 1.5% by weight 6 g was mixed and stirred for 240 minutes. The obtained solution was filtered through a 1000 mesh wire mesh, then 0.73 g of calcium oxide was added, and the mixture was neutralized by stirring for 240 minutes, and defoamed under reduced pressure to obtain a coating solution on the slurry.
Preparation of laminated porous film The prepared coating solution was applied to the porous layer (1) with a bar coater so as to have a thickness of 130 µm, and then placed in an oven at 50 ° C and 70% RH for 15 seconds. Aramid was deposited on the quality film. The obtained film was fixed with metal fittings on four sides and dried in an oven at 70 ° C. for 10 minutes, whereby the heat-resistant layer was laminated on the porous layer (1) to obtain a laminated porous film.

Example 2
12.3 g of ultra high molecular weight polyethylene powder having a weight average molecular weight of about 3 million (340M, manufactured by Mitsui Chemicals), polyethylene wax (FNP-0115 having a weight average molecular weight of 1000, a melting temperature of 116 ° C., and a density of 0.95 g / cm ³ (Nippon Seiki Co., Ltd.) 12.3 g, average pore size 0.1 μm calcium carbonate (Maruo Calcium Co., Ltd.) 39.6 g, antioxidant (Irg1010, Ciba Specialty Chemicals Co., Ltd.) 0.17 wt%, (P168) 0.05% by weight (made by Ciba Specialty Chemicals Co., Ltd.) was mixed in the form of powder and then kneaded for 3 minutes at 200 ° C. and 60 rpm in a lab plast mill (R-60H type). Let the obtained kneaded material be a kneaded material (A). 17.6 g of high-density polyethylene powder (030S, manufactured by Mitsui Chemicals, Inc.) having a weight average molecular weight of about 500,000, a melting temperature of 136 ° C., and a density of 0.95 g / cm ³ , and a melting temperature of 117 ° C. 7.0 g of linear low-density polyethylene (FV403, manufactured by Sumitomo Chemical Co., Ltd.) of .92 g / cm ³ , 39.6 g of calcium carbonate (manufactured by Maruo Calcium Co., Ltd.) having an average pore size of 0.1 μm, antioxidant (Irg1010, Ciba) -0.17 g (manufactured by Specialty Chemicals) and 0.05 g (P168, manufactured by Ciba Specialty Chemicals) were mixed in powder form and then kneaded under the same conditions as kneaded product A (kneaded product B). 21.0 g of the kneaded material A and 49.0 g of the kneaded material B were kneaded at 230 ° C. and 100 rpm for 3 minutes using the above-mentioned Labo Plast Mill to obtain a resin composition 2. Resin composition 2 was treated in the same manner as resin composition 1 to obtain a porous film.
Using the obtained porous film 2, the same treatment as in Example 1 was performed to obtain a laminated porous film.

Comparative Example 1
Using 12.3 g of polyethylene powder having a weight average molecular weight of about 500,000 (030S, Mitsui Chemicals), linear low density polyethylene (FV403) having a weight average molecular weight of about 90,000, a melting temperature of 117 ° C., and 0.92 g / cm ^3. Except for not using Sumitomo Chemical Co., Ltd.), the same treatment as in Example 1 was performed to obtain a porous film.

The composition of the resin composition used when forming the porous layer (A) in Examples 1 and 2 is shown in Table 1.
Table 2 summarizes the physical properties of the laminated porous films of Examples 1 and 2 and the porous film of Comparative Example 1.
The puncture strength of a commercially available separator is usually about ^{20 to} 40 gf / (g / m ² ). It can be seen that the porous films of Examples 1 and 2 also have a piercing strength that can be used as a separator.

Claims (3)

A laminated porous film comprising a porous layer (A) formed from a polyethylene-based resin and a porous layer (B) formed from a heat-resistant resin and an inorganic filler,
When the porous layer (A) is 100% by weight of the resin component contained in the porous layer (A), 5 to 70% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more, A laminated porous film comprising 5 to 40% by weight of a linear low density polyethylene having a weight average molecular weight of 5 to 800,000. The porous layer (A) contains 1 to 30% by weight of a polyolefin wax having a weight average molecular weight of 500 to 3000 when the resin component contained in the porous layer (A) is 100% by weight. The laminated porous film described. A battery comprising the laminated porous film according to claim 1.