JP2002069221A - Porous film and battery separator using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film which is excellent in puncturing strength and can be produced in a simple and easy way, and to provide a battery separator and a battery using it. SOLUTION: The porous film is produced by kneading a high-molecular weight polyolefin having a weight-average molecular weight of 5×105 or higher, a thermoplastic resin having a weight-average molecular weight of 2×104 or lower, and fine particles, forming a sheet from the kneaded material, and stretching the sheet. The battery separator contains the porous film. The battery contains the separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous film, a battery separator using the same, and a battery.

[0002]

2. Description of the Related Art Porous polyolefin films are used in a variety of applications such as sanitary materials, medical materials, and battery separators.

As a polyolefin porous film, a porous film obtained by stretching a sheet in which fine particles are mixed with polyolefin is known. For example, a porous film obtained by stretching a sheet obtained by kneading and molding a polyolefin resin, fine particles and triglyceride is disclosed (Japanese Patent Application Laid-Open No. 62-10141).
However, when used in applications requiring puncture strength, such as a battery separator for a lithium ion secondary battery, there is a problem that the puncture strength is not sufficient. As a polyolefin porous film having excellent piercing strength, for example, a high-molecular polyethylene resin and a large amount of plasticizer of the same weight or more as the resin are kneaded, then molded into a sheet, and the plasticizer contained in the sheet is removed. After that, a porous film obtained by stretching the film is disclosed (JP-A-9-157423). However, in the production of this porous film, a step of immersing the sheet in an organic solvent to extract a large amount of a plasticizer is essential, and therefore, there is a problem that the steps are complicated and complicated.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a porous film having excellent piercing strength and which can be easily manufactured, a battery separator and a battery using the porous film.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, kneaded a high-molecular-weight polyolefin, a low-molecular-weight thermoplastic resin, and fine particles, and formed a sheet. Later, they found that a porous film produced by stretching the sheet had excellent piercing strength and could be easily produced, and reached the present invention.

That is, the present invention provides the following [1] to
This is related to [4]. [1] A high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, a thermoplastic resin having a weight average molecular weight of 2 × 10 ⁴ or less, and fine particles are kneaded, formed into a sheet, and then stretched. A porous film made by: [2] A laminated porous film having a laminated structure of the porous film of the above [1] and a porous film made of a heat-resistant resin. [3] A battery separator including the porous film of [1] or the laminated porous film of [2]. [4] A battery including the battery separator of [3].

[0007]

DETAILED DESCRIPTION OF THE INVENTION The high molecular weight polyolefin used in the present invention has a weight average molecular weight of 5 × 10 ⁵ or more, preferably 1 × 10 ⁶ to 15 × 10 ⁶ . If the weight average molecular weight is less than 5 × 10 ^5, it is difficult to obtain a high-strength porous film. On the other hand, the upper limit is not particularly limited, but if it exceeds 15 × 10 ⁶ , it is difficult to form a sheet. Examples of the high molecular weight polyolefin include a high molecular weight homopolymer or copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. Of these, high molecular weight polyethylene mainly composed of ethylene is preferred.

The thermoplastic resin used in the present invention has a weight average molecular weight of 2 × 10 ⁴ or less, and a resin compatible with the high molecular weight polyolefin is preferably used. A compatible resin is a mixture of a high molecular weight polyolefin and the resin in a kneading machine, for example, Labo Plastomill (Toyo Seiki), at a ratio of 7: 3 to 3: 7, for example, at 90 ° C. and 90 ° C.
r. p. m. Of resin composition melt-mixed for 10 minutes at
A resin from which a resin having a melting point peak in SC measurement or a resin composition obtained by melt-mixing both in the above ratio at the above ratio is press-formed and stretched to obtain a visually uniform film when formed into a film. It is. The thermoplastic resin has a weight average molecular weight of 2 × 10 ⁴ or less, preferably 1 × 10 ^4.
The following thermoplastic resins, more preferably polyolefins having a weight average molecular weight of 2 × 10 ⁴ or less. Examples of the polyolefin include polyethylene and polypropylene, and among them, the weight average molecular weight is 2 × 1
0 ⁴ The following polyethylene, since the excellent compatibility with high molecular weight polyolefin, more preferably, has a high molecular weight polyolefin equal branch to be used, the density difference between them in particular is ± 0.02 g / cm ³ , preferably ±
Those having a range of 0.01 g / cm ³ are more preferable because they have more excellent compatibility. 2 × weight average molecular weight
If it exceeds 10 ⁴ , the compatibility with the high molecular weight polyolefin tends to decrease.

The high-molecular-weight polyolefin and the high-molecular-weight polyolefin
The amount of thermoplastic resin is based on the sum of these weights.
30 to 90% by weight of the high molecular weight polyolefin,
Preferably the plastic resin is in an amount of 70 to 10% by weight
60-80% by weight of the high molecular weight polyolefin,
More preferably, the amount of the thermoplastic resin is 40 to 20% by weight.
preferable. Too much high molecular weight polyolefin will cause porosity
Quality film is not uniform or formed into a sheet
Tends to be difficult, and too little may cause strength to develop.
There is a tendency. In addition, the range where compatibility does not decrease
Usually, the weight average molecular weight is 2 × 10^FourThe following thermoplastic resin 1
Not a high molecular weight polyolefin for 00 parts by weight
Weight average molecular weight is 2 × 10^FourEven the following thermoplastic resins
70 parts by weight or less of a thermoplastic resin.
Such a thermoplastic resin usually has a weight average molecular weight of 2 ×
10 ^FourExceeds 5 × 10^FiveLess than, for example, linear
Low molecular weight polyethylene etc. are mentioned.

The weight average molecular weight of the high molecular weight polyolefin, thermoplastic resin and other resins used in the present invention is GP
It is a weight average molecular weight in terms of polystyrene obtained by C measurement. The GPC measurement is performed, for example, at 140 ° C. using o-dichlorobenzene as a solvent.

The average particle diameter of the fine particles used in the present invention is usually 3 μm or less, preferably 1 μm or less, more preferably 0.5 μm or less. If the average particle size is too large, the strength tends to decrease. The average particle size is 0.02μ.
m or more. If the average particle size is too small, it may be difficult to fill the resin and the opening may be insufficient due to stretching. The average particle size refers to a primary particle size calculated from a particle size distribution of fine particles dispersed in the air obtained by a laser scattering method.

As the fine particles used in the present invention, inorganic or organic fine particles generally called a filler are used. Specifically, as inorganic fine particles, 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, magnesium oxide, titanium oxide, alumina, mica, Zeolite, glass powder, zinc oxide and the like are used. Among these, calcium carbonate and barium sulfate, which are easy to obtain fine particles and have low moisture content, are preferred. When the water content is low, when used as a non-aqueous battery separator,
There is little adverse effect on battery performance. As organic fine particles,
Known resin particles are used, as the resin, styrene, vinyl ketone, acrylonitrile, methyl methacrylate,
Either one or two or more polymers such as ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate, and polycondensation resins such as melamine and urea are preferable.

The fine particles used in the present invention may be removed by washing with water after stretching the sheet. As the fine particles used in the present invention, water-soluble fine particles are preferable because they can be removed by washing with a neutral, acidic, or alkaline aqueous solution depending on the type of the fine particles when necessary.
The water-soluble fine particles are not particularly limited as long as they can be dissolved in the above-mentioned organic and inorganic fine particles in a neutral, acidic, or alkaline aqueous solution.For example, talc, clay, kaolin, diatomaceous earth, calcium carbonate, carbonate magnesium,
Examples include barium carbonate, magnesium sulfate, calcium oxide, magnesium hydroxide, calcium hydroxide, zinc oxide and silica, with calcium carbonate being preferred.

The fine particles used in the present invention may be subjected to a surface treatment in order to improve the dispersibility with the high-molecular-weight polyolefin and the thermoplastic resin, to promote interfacial separation with the resin, or to prevent the absorption of moisture from the outside. What has been applied is preferred. Examples of the surface treatment agent include higher fatty acids such as stearic acid and lauric acid and metal salts thereof.

The mixing ratio of the fine particles to the total of 100 parts by volume of the high molecular weight polyolefin and the thermoplastic resin depends on the type of the fine particles and the state of the surface treatment, but is preferably 15 to 50 parts by volume, more preferably 25 to 50 parts by volume. 35 parts by volume. If the compounding ratio is too small, the opening after stretching may be insufficient, which may increase the film resistance. If too much, the continuity of the resin is cut off,
In addition to the occurrence of stretch breakage, the strength of the film may be reduced.

The resin used in the porous film of the present invention may contain, if necessary, additives generally used within the range not impairing the object of the present invention (antistatic agent, plasticizer, lubricant, antioxidant, etc.). Nucleating agent).

The value of the membrane resistance of the porous film of the present invention defined by the following formula (1) depends on the material of the porous film. However, when the film is used alone as a battery separator, it is 5%. sec · μm ² / 100cc or less.

[0018] The film resistance (sec ^{· μm 2 / 100cc) = td} 2 (1) [ Eq. (1) medium-t is the air permeability [Gurley Value (sec / 100c
c), and d is the pore diameter [bubble point method] (μ
m). ]

The smaller the membrane resistance, the better the ion permeability. The use of a separator having good ion permeability results in a battery having excellent load characteristics, which is an important property in a secondary battery such as a lithium ion battery. A battery having excellent load characteristics is a battery having a large electric capacity that can be taken out when a large current flows. In addition, the porous film of this invention may be further laminated | stacked with the porous layer which consists of polyolefin, polyurethane, etc. as needed.

The porous film of the present invention comprises a high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, a thermoplastic resin having a weight average molecular weight of 2 × 10 ⁴ or less, fine particles, and, if necessary, a high molecular weight. It is manufactured by kneading a thermoplastic resin which is neither a polyolefin nor a thermoplastic resin having a weight average molecular weight of 2 × 10 ⁴ or less, forms a sheet, and stretches the sheet. In addition, the porous film obtained by stretching the sheet and removing fine particles by, for example, washing with water is also included in the polynomial film of the present invention. As a method for producing the porous film of the present invention, specifically, for example,
After mixing fine particles, a stretching aid such as a fatty acid ester and other additives with a composition comprising a high molecular weight polyolefin and a thermoplastic resin using a Henschel mixer, a super mixer, a tumbler type mixer, etc. Alternatively, the mixture is kneaded using a twin screw extruder to form pellets. Next, the pellets are melted and formed into a sheet using a known molding machine such as an extrusion molding machine equipped with a T-die or the like, or an inflation molding machine equipped with a cylindrical die. In some cases, it can be directly formed into a sheet by a molding machine without pelletizing. The sheet is stretched at least uniaxially at a temperature not lower than the room temperature and lower than the softening point of the resin, by a known method such as a roll method and a tenter method, thereby causing an interface separation between the resin and the fine particles. Manufacture film. Stretching may be performed in one step or may be divided into multiple steps. After the stretching, a heat setting treatment may be performed as needed to stabilize the shape of the holes.

Next, the laminated porous film of the present invention will be described. The laminated porous film of the present invention is characterized by having a laminated structure of the porous film of the present invention and a porous film made of a heat-resistant resin. The laminated porous film has little shrinkage when heated, in addition to the features of the porous film of the present invention. In the laminated porous film of the present invention, a porous layer made of polyolefin, polyurethane or the like may be further laminated as necessary. Further, the porous film made of the heat resistant resin may contain an inorganic fine powder. The content of the inorganic fine powder is 1 to 1500 parts by weight, preferably 5 to 10 parts by weight based on 100 parts by weight of the heat-resistant resin.
0 parts by weight. The particle size of the inorganic fine powder is preferably smaller than the thickness of the heat-resistant porous film, and the average particle size of the primary particles is preferably 1.0 μm or less, more preferably 0.5 μm or less, and preferably 0.1 μm or less. More preferably, it is 1 μm or less. The type of the inorganic fine powder is not particularly limited, but is preferably alumina, silica, titanium dioxide, zirconium oxide, or calcium carbonate. These inorganic fine powders may be used alone or in combination of two or more. In addition, the porosity of the heat-resistant porous film can be controlled by the content of the inorganic fine powder, and the ion permeability can be improved.

Examples of the heat-resistant resin for forming the porous film made of the heat-resistant resin include JIS K7207-compliant 18.
At least one heat-resistant resin selected from resins having a deflection temperature under load of 100 ° C. or higher when measured under a load of 6 kg / cm ² is preferable. In order to be safer even at a high temperature due to severe use, the heat-resistant resin in the present invention is more preferably at least one heat-resistant resin selected from resins having a deflection temperature under load of 200 ° C. or higher.

The resin having a deflection temperature under load of 100 ° C. or higher includes polyimide, polyamideimide, aramid, polycarbonate, polyacetal, polysulfone, polyphenylsulfide, polyetheretherketone,
Aromatic polyester, polyethersulfone, polyetherimide and the like can be mentioned. The deflection temperature under load is 20
Examples of the resin at 0 ° C. or higher include polyimide, polyamideimide, aramid, polyethersulfone, and polyetherimide. Further, it is particularly preferable that the heat-resistant resin is selected from the group consisting of polyimide, polyamideimide and aramid.

Further, the heat-resistant resin in the present invention includes:
The limiting oxygen index is preferably 20 or more. The limiting oxygen index is the minimum oxygen concentration at which a specimen placed in a glass tube can keep burning. This is because the heat-resistant porous layer is preferably flame-retardant in consideration of oxygen generated from the positive electrode material at a high temperature, in addition to heat resistance. Specific examples of such a resin include the above-described heat-resistant resin.

The method for producing the laminated porous film of the present invention includes, for example, a method of laminating the porous film of the present invention and a porous film made of a heat-resistant resin with an adhesive, heat fusion, or the like; Quality film as a substrate,
A method of applying a solution composed of a heat-resistant resin in a solution state to form a solution layer, followed by desolvation treatment to obtain a laminated porous film of the present invention, and the like.

As the latter method, for example, the following (a) to
The laminated porous film of the present invention can be produced by the method including the step (e). (A) A solution comprising a heat-resistant resin and an organic solvent is prepared. When the inorganic fine powder is contained, a slurry solution is prepared by dispersing the inorganic fine powder in an amount of 1 to 1500 parts by weight with respect to 100 parts by weight of the heat-resistant resin. (B) applying the solution or slurry solution to a porous film to form a coating film. (C) depositing the heat-resistant resin in the coating film. (D) removing the organic solvent from the coating film; (E) drying the coating film;

Here, a polar organic solvent is usually used as the organic solvent. As the polar organic solvent, for example, N,
N'-dimethylformamide, N, N'-dimethylacetamide, N-methyl-2-pyrrolidone, tetramethylurea and the like can be mentioned.

As a method of depositing the heat-resistant resin on the porous film, the porous film is left in an atmosphere controlled at a constant humidity to precipitate the heat-resistant resin, and then the porous film is placed in a coagulating liquid. The method of immersion is mentioned. As the coagulation liquid, an aqueous solution or an alcohol-based solution may be used, and is not particularly limited. An aqueous solution or an alcohol-based solution containing a polar organic solvent is used, but the solvent recovery step is industrially simplified. And an aqueous solution of a polar organic solvent is more preferable. Alternatively, the porous film can be immersed in a coagulation liquid without leaving a heat-resistant resin by leaving it in an atmosphere controlled at a constant humidity. Furthermore, in the case of a heat-resistant resin that does not redissolve once precipitated from a solution (for example, aramid), a part or all of the solvent is evaporated and the heat-resistant resin is simultaneously precipitated, that is, the precipitation step and the subsequent solvent removal The steps can be performed simultaneously.

As a method for removing the polar organic solvent, a part or the whole may be evaporated, or the solvent may be extracted and removed with a solvent capable of dissolving the polar organic solvent such as water, an aqueous solution, or an alcohol solution. When removing with water, it is preferable to use ion-exchanged water. It is also industrially preferable to further wash with water after washing with an aqueous solution containing a certain concentration of a polar organic solvent.

After removing the polar organic solvent, drying is performed.
In the drying step, the solvent for washing is evaporated and removed by heating. The drying temperature at this time is preferably equal to or lower than the heat deformation temperature of the porous film.

Further, a case where a para-oriented aromatic polyamide (hereinafter sometimes referred to as para-aramid) is used as the heat-resistant resin will be specifically described. When para-aramid is used, for example, in a polar organic solvent in which 2 to 10% by weight of an alkali metal or alkaline earth metal chloride is dissolved, 1.00 mol of para-oriented aromatic diamine and para-oriented aromatic dicarboxylic acid are used. Acid dihalide 0.94 to 0.9
By adding 9 mol and performing condensation polymerization at a temperature of −20 ° C. to 50 ° C., a para-aramid concentration of 1 to 10% and an intrinsic viscosity of usually 1.0 to 2.8 dl / g and an organic solvent are used. A solution consisting of Using this solution, a laminated porous film in which a para-aramid porous film is laminated on a porous film can be produced by the above-mentioned production method. In the case of para-aramid, to remove the solvent and the chloride, it can be washed with the same solvent as a coagulating liquid such as water or methanol, but a part or all of the solvent was evaporated and a polymer was precipitated at the same time. Thereafter, the chloride may be removed by a method such as washing with water.

The battery separator of the present invention is characterized by containing the above-mentioned porous film or laminated porous film. The above-mentioned membrane resistance of the porous film or the laminated porous film used for the battery separator is preferably 5 or less from the viewpoint of ion permeability. In addition, since shrinkage when applying heat is small, from the viewpoint of improving safety,
Those containing the above laminated porous film are preferred.

When the battery separator of the present invention contains the porous film of the present invention, the porosity of the porous film is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. The porosity is 30% by volume
If it is less than 80%, the amount of retained electrolyte may decrease, and
%, The strength becomes insufficient and the shutdown function may be reduced. The thickness of the porous film is preferably 5 to 50 μm, more preferably 10 to 50 μm.
50 μm is preferred, and more preferably 10 to 30 μm
It is. If the thickness is too small, the shutdown function may be insufficient, or the battery may be short-circuited at the time of winding. If the thickness is too large, a high electric capacity may not be achieved. The pore size of the porous film is preferably 0.1 μm or less,
0.08 μm or less is more preferable. As the pore diameter becomes smaller, a porous film having a smaller value of membrane resistance is obtained even with the same air permeability.

When the battery separator of the present invention includes the laminated porous film of the present invention, the porous film preferably has the same porosity and pore size as those of the above porous film. . However, regarding the film thickness, 5 to 50 μm as a whole of the laminated porous film
Is preferably, more preferably, 10 to 50 μm, and further preferably, 10 to 30 μm. Among the laminated porous films, the porosity of the porous film made of a heat-resistant resin is 3
It is preferably from 0 to 80% by volume, more preferably from 40 to 7% by volume.
0% by volume. If the porosity is too small, the holding amount of the electrolytic solution tends to be small. If the porosity is too large, the strength of the porous film made of a heat-resistant resin tends to be insufficient. The thickness of the heat-resistant porous film is preferably from 0.5 μm to 10 μm, more preferably from 1 μm to 5 μm. If the film thickness is too small, the heat-resistant porous film tends to be unable to suppress the shrinkage during heating, and if the film thickness is too large, the load characteristics tend to be poor when the battery is used.

The battery of the present invention is characterized by including the battery separator of the present invention. Hereinafter, components other than the battery separator will be described by taking, as an example, a case where the battery of the present invention is a nonaqueous electrolyte secondary battery such as a lithium battery, but is not limited thereto.

As the non-aqueous electrolyte solution, for example, a non-aqueous electrolyte solution obtained by dissolving a lithium salt in an organic solvent can be used. LiClO ₄ , LiP
F ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF
₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ C
One or a mixture of two or more of F ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , a lithium salt of a lower aliphatic carboxylic acid, LiAlCl _{4, and the} like. As the lithium salt, LiPF ₆ containing fluorine Among these, LiAsF _6, LiSbF
₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ )
It is preferable to use one containing at least one selected from the group consisting of Li ₂ and LiC (CF ₃ SO ₂ ) ₃ .

As the organic solvent used in the non-aqueous electrolyte solution, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate,
Ethyl methyl carbonate, 4-trifluoromethyl-
Carbonates such as 1,3-dioxolan-2-one, 1,2-di (methoxycarbonyloxy) ethane;
1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2
Ethers such as 3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran and 2-methyltetrahydrofuran; methyl formate, methyl acetate, γ-
Esters such as butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfolane, dimethylsulfoxide; A sulfur-containing compound such as 1,3-propane sultone or a compound obtained by introducing a fluorine substituent into the above-mentioned organic solvent can be used. Usually, a mixture of two or more of these compounds is used.

Among these, a mixed solvent containing a carbonate is preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate, or a mixed solvent of a cyclic carbonate and an ether is more preferable. The mixed solvent of cyclic carbonate and acyclic carbonate has a wide operating temperature range, excellent load characteristics, and is hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as a negative electrode active material. And a mixed solvent containing ethylene 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 usually carried on a current collector is used. Specifically, a material containing a material capable of doping and undoping lithium ions, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder can be used as the positive electrode active material. Materials capable of doping / dedoping lithium ions include V, Mn, Fe, Co, Ni
And a lithium composite oxide containing at least one transition metal. Among them, preferably, since the average discharge potential is high, lithium nickel oxide, a layered lithium composite oxide based on α-NaFeO 2 type structure such as lithium cobaltate, and lithium based on spinel type structure such as lithium manganese spinel are preferable. A composite oxide is exemplified.

The lithium composite oxide may contain various additional elements, particularly Ti, V, Cr, Mn, Fe, C
o, the sum of the number of moles of at least one metal selected from the group consisting of Cu, Ag, Mg, Al, Ga, In, and Sn and the number of moles of Ni in lithium nickelate,
It is preferable to use a composite lithium nickelate containing the metal such that the content of the at least one metal is 0.1 to 20 mol%, since the cyclability in high capacity use is improved.

As the thermoplastic resin as the binder,
Polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, ethylene-tetrafluoroethylene copolymer Examples include a polymer, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene.

Examples of the carbonaceous material as the conductive agent include natural graphite, artificial graphite, coke, 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 used in combination may be selected.

As the negative electrode sheet, for example, a material capable of doping / de-doping with lithium ions, lithium metal or lithium alloy can be used. Materials that can be doped / dedoped with lithium ions include natural graphite,
Carbonaceous materials such as artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds, oxides and sulfides that dope and dedope lithium ions at a lower potential than the positive electrode Chalcogen compounds. As a carbonaceous material, a carbonaceous material mainly composed of a graphite material such as natural graphite and artificial graphite, in that a high energy density can be obtained when combined with a positive electrode because the potential flatness is high and the average discharge potential is low. Is preferred.

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 is 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 using a solvent or the like, applying a paste on the current collector, drying and pressing, or the like, is used. 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 square type, and the like.

[0045]

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples. In Examples and Reference Examples, the physical properties of the porous film were measured by the following methods. (1) Air permeability: a method specified in JISP8117. (2) Average pore size: based on ASTM F316-86. (3) Film thickness: based on JIS K7130. (4) Puncture strength: The maximum stress (gf) when a pin was pierced at 200 mm / min at a place where the porous film was fixed with a washer of 12 mmφ was defined as the pierce strength. The shape of the pin used was a pin having a diameter of 1 mmΦ and a tip of 0.5R. (5) Shrinkage ratio of porous film and laminated porous film: The porous film was sandwiched between Teflon (registered trademark) plates and left at an arbitrary temperature (t) for 10 minutes. The shrinkage was determined by the following equation. Shrinkage (%) = (L ₂₅ −L _t ) / L ₂₅ } × 100 (L ₂₅ is the length in the TD direction of the separator at 25 ° C., L _t
Is the length of the separator in the TD direction after standing at t ° C. for 10 minutes.) (5) Intrinsic viscosity of para-aramid: Defined by the following measuring method. For a solution in which 0.5 g of the para-aramid polymer was dissolved in 100 ml of 96-98% sulfuric acid and for a 96-98% sulfuric acid, the flow time was measured at 30 ° C. using a capillary viscometer. Was used to determine the intrinsic viscosity. Intrinsic viscosity = ln (T / T ₀ ) / C [unit: dl / g] where T and T ₀ are the flow times of the para-aramid sulfate solution and sulfuric acid, respectively, and C is the concentration of para-aramid in the para-aramid sulfate solution ( dl / g).

Example 1 <Manufacture of porous film> Kneading was performed using a Labo Plastomill (Toyo Seiki Seisakusho). Ultra high molecular weight polyethylene powder 70 parts by weight (HIZEX Million 340M, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 3,000,000, density 0.93), polyethylene wax powder (Hi Wax 110P, manufactured by Mitsui Chemicals, weight average molecular weight 1000, density 0.92) 30 Parts by weight, antioxidant (Irg1010, manufactured by Sumitomo Chemical Co., Ltd.)
After mixing 0.05 parts by weight of the powder as it was, the mixture was kneaded at 200 ° C. for 10 minutes with a Labo Plastomill to take out a uniform kneaded product. The rotation speed of the blade at this time is 60 rpm
Met. Next, 70 parts by volume of this kneaded material was put into a Labo Plastomill, and after melting, calcium carbonate ((Star Pigot A15, manufactured by Shiraishi Calcium Co., average particle size 0.15
μm) was added and kneaded at 200 ° C. for 5 minutes. The obtained kneaded material was processed into a sheet having a thickness of 60 to 70 μm by a hot press set at 200 ° C., and then solidified by a cooling press. Then, the obtained sheet is cut into an appropriate size (about 8 cm × 5 cm), and an autograph (AGS)
-G, Shimadzu Corp.) and uniaxially stretched to form holes to form a porous film. The stretching was performed at 100 ° C. and the stretching speed was 50 m.
m / min. Next, the obtained porous film was immersed in a hydrochloric acid / ethanol solution (hydrochloric acid: ethanol = 1: 1) to dissolve calcium carbonate. After dissolution, the porous film was washed with ethanol and dried at 60 ° C. under reduced pressure. Table 1 shows the physical properties of the obtained porous film, and Table 2 shows the shrinkage ratio. A 1: 1 kneaded mixture of the ultrahigh molecular weight polyethylene and the polyethylene wax powder produced in the same manner was prepared at 200 ° C.
After processing into a sheet having a thickness of 60 to 70 μm with a hot press set at, the sheet is solidified with a cooling press, and the obtained sheet is cut into an appropriate size.
When the film was uniaxially stretched at, a homogeneous film was obtained, and it was confirmed that both films were compatible.

Example 2 <Synthesis of para-aramid solution> Using a 5-liter (l) separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port, poly (paraphenylene terephthalamide) (hereinafter , Abbreviated as PPTA). The flask was sufficiently dried, and 4200 g of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) was charged.
272.65 g of calcium chloride dried over time was added, and the temperature was raised to 100 ° C. After the calcium chloride was completely dissolved, the temperature was returned to room temperature, and paraphenylenediamine (hereinafter referred to as PP) was added.
132.91 g) and completely dissolved.
While keeping this solution at 20 ± 2 ° C., 243.32 g of terephthalic acid dichloride (hereinafter abbreviated as TPC) was added to 10
Add in portions about every 5 minutes. The solution is then
Aged for 1 hour while maintaining the temperature at ℃ 3
Stirred for 0 minutes. The obtained polymerization liquid showed optical anisotropy. A part was sampled, reprecipitated with water, taken out as a polymer, and the intrinsic viscosity of the obtained PPTA was measured to be 1.97 dl / g. Next, the polymerization solution 10
0 g was weighed into a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a liquid addition port.
The MP solution was added slowly. Finally, a PPTA solution having a PPTA concentration of 2.0% by weight was prepared and used as solution A. <Application of para-aramid solution> As the porous film,
The polyethylene porous film of Example 1 was used.
Bar coater (clearance 2) manufactured by Tester Sangyo Co., Ltd.
(00 μm), a film-form material of liquid A as a heat-resistant resin solution was applied to a porous film placed on glass, and kept in this state at a constant temperature and humidity of 30 ° C. and 65% for about 3 minutes. PPTA was precipitated, and a cloudy film was obtained. The film was immersed in a 30% NMP / water solution for 5 minutes. After immersion,
The deposited film was peeled from the glass plate. After sufficiently washing with flowing ion-exchanged water, a wet film was taken out of the water and free water was wiped off. This film was sandwiched between nylon cloths, and further sandwiched between aramid felts. An aluminum plate was placed with the film sandwiched between nylon cloth and aramid felt, a nylon film was placed on it, the nylon film and the aluminum plate were sealed with gum, and a conduit for decompression was attached. . The whole was put into a hot oven and dried under reduced pressure at 60 ° C. to obtain a laminated porous film. Table 1 shows the physical properties of the film, and Table 2 shows the shrinkage ratio.
It was shown to.

Comparative Example 1 Raboplast mill was heated to 200 ° C., and 82 parts by weight of linear low density polyethylene (LLDPE) (FS240A, weight average molecular weight 110,000, manufactured by Sumitomo Chemical Co., Ltd.) was prepared. ) (F208-1, weight average molecular weight 80,000, manufactured by Sumitomo Chemical Co., Ltd.), and 18 parts by weight of these polyethylenes (abbreviated as PEs) were melted. After 70 parts by volume of PEs were added, hydrotalcite (DHT-4A, 30 parts by volume with an average particle size of 0.4 μm, manufactured by Kyowa Chemical Industry Co., Ltd., and 0.1 part by weight of an antioxidant (the total of the PEs is 1
00 parts by weight. ), And kneaded at 100 rpm for 5 minutes. The obtained kneaded material was processed into a sheet having a thickness of 60 to 70 μm by a hot press set at 200 ° C., and then solidified by a cooling press. Then, the obtained sheet was cut into an appropriate size, uniaxially stretched by an autograph, and opened to form a microporous film. The stretching was performed at 30 ° C. and at a stretching speed of 50 mm.
/ Min. Table 1 shows the physical properties of the obtained porous film.

Comparative Example 2 The temperature of the Labo Plastomill was raised to 200 ° C., 70 parts by volume of polypropylene (FS2011D, weight average molecular weight: 410,000, manufactured by Sumitomo Chemical Co., Ltd.) was added, and after melting the polypropylene, hydrotalcite (DHT-4A, Average particle size 0.4μ
m, manufactured by Kyowa Chemical Industry Co., Ltd.), 30 parts by weight of an antioxidant (based on 70 parts by weight of polypropylene), and kneading at 100 rpm for 5 minutes. The obtained kneaded material was processed into a sheet having a thickness of 60 to 70 μm by a hot press set at 200 ° C., and then solidified by a cooling press. Then, the obtained sheet was cut into an appropriate size, uniaxially stretched by an autograph, and opened to form a microporous film. The stretching was performed at 140 ° C. and a stretching speed of 50 mm / min. Table 1 shows the physical properties of the obtained porous film.

Comparative Example 3 49 parts by weight of ultra high molecular weight polyethylene powder (HIZEX Million 340M, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 30
30,000), 34 parts by weight of metallocene-based LLDPE (SP4060, manufactured by Mitsui Chemicals, Inc., weight-average molecular weight 70,000), 17 parts by weight of metallocene-based LDPE (G808, manufactured by Sumitomo Chemical Co., Ltd., weight-average molecular weight 55,000), antioxidant Agent (Irg101
0, manufactured by Sumitomo Chemical Co., Ltd.) was kneaded with a Labo Plastomill at 200 ° C. for 10 minutes and taken out as a kneaded material. This resin composition is processed into a sheet having a thickness of 60 to 70 μm by a hot press set at 200 ° C., then solidified by a cooling press, and the obtained sheet is cut into an appropriate size. When uniaxial stretching was performed at, it was visually observed that the powdered ultra-high-molecular-weight polyethylene remained in the powder form without being compatible with the obtained sheet, and that the kneaded material was not compatible. confirmed. Next, 70 parts by volume of the kneaded material was put into a Labo Plastomill, and after melting, calcium carbonate ((Star Pigot A15,
30 parts by volume of Shiraishi Calcium Co., Ltd., average particle size 0.15 μm) were charged and kneaded at 200 ° C. for 5 minutes. The obtained kneaded material is a hot press set at 200 ° C. and has a thickness of 60 to 70 μm.
And then solidified by a cooling press.
Then, the obtained sheet was cut into an appropriate size, uniaxially stretched by an autograph, and opened to form a porous film. The stretching was performed at 100 ° C. and a stretching speed of 50 mm / min. Next, the obtained porous film was immersed in a hydrochloric acid / ethanol solution (hydrochloric acid: ethanol = 1: 1) to dissolve calcium carbonate. After dissolution, the porous film was washed with ethanol and dried at 60 ° C. under reduced pressure. Table 1 shows the physical properties of the obtained porous film.

Comparative Example 4 Ultra high molecular weight polyethylene powder 70 parts by weight (HIZEX Million 340M, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 30)
100,000), polyethylene wax powder (high wax 11)
0P, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 1000) 30 parts by weight, antioxidant (Irg1010, manufactured by Sumitomo Chemical Co., Ltd.)
After uniformly mixing 0.05 parts by weight, the mixture was kneaded with a Labo Plastomill at 200 ° C. for 10 minutes to take out a uniform kneaded product. The obtained kneaded material was processed into a sheet having a thickness of 60 to 70 μm by a hot press set at 200 ° C., and then solidified by a cooling press. Then, the obtained sheet was cut into an appropriate size and uniaxially stretched by an autograph. The stretching was performed at 100 ° C. and a stretching speed of 50 mm / min.
This film did not become a porous film.

Comparative Example 5 Ultra high molecular weight polyethylene powder 70 parts by volume (HIZEX Million 340M, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 30)
The mixture was uniformly mixed with 0.05 part by weight of an antioxidant (Irg1010, manufactured by Sumitomo Chemical Co., Ltd.) as a powder, and kneaded at 200 ° C. for 10 minutes using a Labo Plastomill. Then, calcium carbonate ((Star Piggot A1
5. Shiraishi calcium company, average particle size 0.15μm)
0 parts by volume were charged and kneaded at 200 ° C. for 5 minutes. The obtained kneaded product was heated to a thickness of 60 to 70 with a hot press set at 200 ° C.
When processed into a sheet having a thickness of μm and solidified by a cooling press, a clean thin film sheet could not be obtained even with sufficient preheating.

[0053]

[Table 1] Physical properties of porous film and laminated porous film

[0054]

[Table 2] Shrinkage of porous film and composite porous film

[0055]

The porous film of the present invention can be easily manufactured, has excellent piercing strength, and can be suitably used as a battery separator, particularly a lithium ion secondary battery separator.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Yamada 2-10-1 Tsukahara, Takatsuki-shi, Osaka Sumika Plastics Tech Co., Ltd. (72) Inventor Yasuo Shinohara 6 Kitahara, Tsukuba-shi, Ibaraki Sumitomo Chemical Co., Ltd. F-term (reference) 4F074 AA17 AA24 AA26 AC17 AC19 AC20 AC21 AC26 AC30 AC32 AC34 AC36 AE06 AG01 CA02 CA04 CA07 CB02 CB03 CB13 CB22 DA03 DA10 DA20 DA31 DA49 4J002 BB03W BB03X BB12X BB16DE0 DG DE046DE076 DJ056 DL006 GF00 GQ00 5H021 BB04 BB05 BB13 CC04 CC08 EE04 EE23 EE31 HH00 HH01 HH03 HH07 HH09 5H029 AJ12 AK03 AL04 AL06 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 DJ04 DJ13 DJ16 EJ12 HJ00 HJH

Claims (10)

[Claims] 1. A high-molecular-weight polyolefin having a weight-average molecular weight of 5 × 10 ⁵ or more, a thermoplastic resin having a weight-average molecular weight of 2 × 10 ⁴ or less, and fine particles are kneaded to form a sheet. A porous film characterized by being stretched. 2. The porous film according to claim 1, wherein the average particle size of the fine particles is 3 μm or less. 3. The high molecular weight polyolefin and the thermoplastic resin are added in an amount of 30 to 9 based on the total weight of the thermoplastic resin.
The porous film according to claim 1 or 2, wherein the proportion is 0% by weight. 4. The porous film according to claim 1, wherein the thermoplastic resin is polyethylene. 5. The porous film according to claim 1, wherein the fine particles are water-soluble fine particles. 6. The porous film according to claim 5, wherein after the sheet is stretched, the sheet is washed with water to remove fine particles. 7. A porous membrane resistance defined by the following formula (1) of the film, porous according to claim 1, characterized in that more than 5 seconds · μm ² / 100cc the film. Film resistance (sec ^{· μm 2 / 100cc) = td} 2 (1) [ Formula (1) Medium t is the air permeability [Gurley Value (sec / 100c
d) represents the pore size [bubble point method] (μm). ] 8. A laminated porous film having a laminated structure of the porous film according to claim 1 and a porous film made of a heat-resistant resin. 9. A battery separator comprising the porous film according to claim 1 or the laminated porous film according to claim 8. 10. A battery comprising the battery separator according to claim 9.