JP5140896B2 - Porous film and battery separator using the same - Google Patents

Porous film and battery separator using the same Download PDF

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Publication number
JP5140896B2
JP5140896B2 JP2001178251A JP2001178251A JP5140896B2 JP 5140896 B2 JP5140896 B2 JP 5140896B2 JP 2001178251 A JP2001178251 A JP 2001178251A JP 2001178251 A JP2001178251 A JP 2001178251A JP 5140896 B2 JP5140896 B2 JP 5140896B2
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Prior art keywords
porous film
molecular weight
fine particles
sheet
polyolefin
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JP2002069221A (en
Inventor
大次郎 星田
勉 高橋
武 山田
泰雄 篠原
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住友化学株式会社
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2/00Constructional details or processes of manufacture of the non-active parts
    • H01M2/14Separators; Membranes; Diaphragms; Spacing elements
    • H01M2/16Separators; Membranes; Diaphragms; Spacing elements characterised by the material
    • H01M2/164Separators; Membranes; Diaphragms; Spacing elements characterised by the material comprising non-fibrous material
    • H01M2/166Mixtures of inorganic and organic non-fibrous material
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous film, a battery separator using the same, and a battery.
[0002]
[Prior art]
Polyolefin porous films are used in various applications such as sanitary materials, medical materials, and battery separators.
[0003]
As a polyolefin porous film, a porous film obtained by stretching a sheet in which fine particles are blended with polyolefin is known. For example, a porous film obtained by stretching a sheet obtained by kneading and forming a polyolefin resin, fine particles and triglyceride (Japanese Patent Laid-Open No. 62-10141) is disclosed, for example, as a lithium ion secondary battery. When used for applications that require puncture strength, such as battery separators, there is a problem that the puncture strength is not sufficient.
Examples of polyolefin porous films with excellent piercing strength include, for example, kneading a high-molecular polyethylene resin and a large amount of plasticizer with the same weight or more as the resin, then forming it into a sheet, and removing the plasticizer contained in the sheet A porous film obtained by stretching the film after it has been disclosed is disclosed (Japanese Patent Laid-Open No. 9-157423).
However, in the production of the porous film, a step of immersing the sheet in an organic solvent and extracting a large amount of the plasticizer is indispensable, so that there is a problem that the steps are many and complicated.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a porous film that has excellent puncture strength and can be easily manufactured, a battery separator and a battery using the same.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors kneaded high molecular weight polyolefin, low molecular weight thermoplastic resin and fine particles, formed into a sheet, and then stretched the sheet to produce The present inventors have found that the porous film to be manufactured has excellent puncture strength and can be easily manufactured, and has reached the present invention.
[0006]
That is, the present invention relates to the following [1] to [4].
[1] The weight average molecular weight is 5 × 10 Five The above high molecular weight polyolefin and a weight average molecular weight of 2 × 10 Four A porous film obtained by kneading the following thermoplastic resin and fine particles, forming the sheet, and then stretching the sheet.
[2] A laminated porous film having a laminated structure of the porous film of [1] above and a porous film made of a heat-resistant resin.
[3] A battery separator comprising the porous film of [1] or the laminated porous film of [2].
[4] A battery including the battery separator according to [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. Five Or more, preferably 1 × 10 6 ~ 15 × 10 6 Of the range. Weight average molecular weight 5 × 10 Five If it is less than the range, it is difficult to obtain a high-strength porous film. On the other hand, the upper limit is not particularly limited, but 15 × 10 6 If it exceeds 1, it is difficult to form into 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. Among these, high molecular weight polyethylene mainly composed of ethylene is preferable.
[0008]
The thermoplastic resin used in the present invention has a weight average molecular weight of 2 × 10. Four The following resins are preferably used that are compatible with the high molecular weight polyolefin.
The compatible resin means that the high molecular weight polyolefin and the resin are mixed at a ratio of 7: 3 to 3: 7, for example, at 200 ° C. and 90 r.m. using a lab plast mill (Toyo Seiki) or the like. p. m. When a resin composition obtained by melting and mixing a resin composition for 10 minutes at a DSC measurement or a resin composition obtained by melting and mixing both at the above ratio is formed into a film by press molding and stretching. It is a resin from which a homogeneous film can be obtained.
The thermoplastic resin has a weight average molecular weight of 2 × 10 Four Or less, preferably 1 × 10 Four The following thermoplastic resins, more preferably a weight average molecular weight of 2 × 10 Four The following polyolefins. Examples of the polyolefin include polyethylene and polypropylene. Among them, the weight average molecular weight is 2 × 10. Four The following polyethylene is more preferable because it has excellent compatibility with the high molecular weight polyolefin, and has the same branching as the high molecular weight polyolefin used. Specifically, the density difference between the two is ± 0.02 g / cm. Three , Preferably ± 0.01 g / cm Three Those within the range are more preferred because they are more excellent in compatibility. Weight average molecular weight 2 × 10 Four If it exceeds 1, the compatibility with the high molecular weight polyolefin tends to decrease.
[0009]
The amount of the high molecular weight polyolefin and the thermoplastic resin is such that the high molecular weight polyolefin is 30 to 90% by weight and the thermoplastic resin is 70 to 10% by weight with respect to the sum of these weights. Preferably, the high molecular weight polyolefin is 60 to 80% by weight, and the thermoplastic resin is 40 to 20% by weight. If the amount of the high-molecular-weight polyolefin is too large, the porous film will not be homogeneous or will tend to be difficult to form into a sheet, and if it is too small, the strength will tend to be difficult to develop.
In addition, the range in which the compatibility does not decrease, usually the weight average molecular weight is 2 × 10 Four For 100 parts by weight of the following thermoplastic resin, not a high molecular weight polyolefin but a weight average molecular weight of 2 × 10 Four The thermoplastic resin which is not the following thermoplastic resins may be contained in 70 parts by weight or less. Such thermoplastic resins usually have a weight average molecular weight of 2 × 10. Four Over 5 × 10 Five For example, linear low molecular weight polyethylene and the like can be mentioned.
[0010]
The weight average molecular weight of the high molecular weight polyolefin, thermoplastic resin or other resin used in the present invention is a weight average molecular weight in terms of polystyrene determined by GPC measurement. For example, GPC measurement is performed at 140 ° C. using o-dichlorobenzene as a solvent.
[0011]
The average particle size 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. Moreover, it is preferable that an average particle diameter is 0.02 micrometer or more. If the average particle size is too small, it may be difficult to fill the resin and there may be insufficient opening due to stretching. The average particle diameter refers to a primary particle diameter calculated from a particle size distribution obtained by a laser scattering method of fine particles dispersed in air.
[0012]
As the fine particles used in the present invention, inorganic or organic fine particles generally called fillers are used.
Specific 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, oxidation Calcium, magnesium oxide, titanium oxide, alumina, mica, zeolite, glass powder, zinc oxide and the like are used. Of these, calcium carbonate and barium sulfate, which are easy to obtain those having a small particle size and have little moisture, are preferred. When the moisture is low, there is little adverse effect on battery performance when used as a non-aqueous battery separator.
As the organic fine particles, known resin particles are used. As the resin, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate or the like alone or in combination of two or more kinds of polymers. Polycondensation resins such as melamine and urea are preferred.
[0013]
The fine particles used in the present invention may be removed by washing with water after stretching the sheet.
The fine particles used in the present invention are preferably water-soluble fine particles because they can be removed by washing with a neutral, acidic or alkaline aqueous solution depending on the kind of the fine particles when it is necessary to remove them. The water-soluble fine particles are not particularly limited as long as they can be dissolved in neutral, acidic, and alkaline aqueous solutions among the above organic and inorganic fine particles. For example, talc, clay, kaolin, diatomaceous earth, calcium carbonate, carbonate Examples include magnesium, barium carbonate, magnesium sulfate, calcium oxide, magnesium hydroxide, calcium hydroxide, zinc oxide, and silica, with calcium carbonate being preferred.
[0014]
Further, the fine particles used in the present invention were subjected to a surface treatment in order to improve dispersibility with the high molecular weight polyolefin and the thermoplastic resin, promote interfacial peeling from the resin, or prevent absorption of moisture from the outside. Those are preferred. Examples of the surface treatment agent include higher fatty acids such as stearic acid and lauric acid, or metal salts thereof.
[0015]
The blending ratio of the fine particles with respect to 100 parts by volume of the high molecular weight polyolefin and the thermoplastic resin is preferably 15 to 50 parts by volume, more preferably 25 to 35 parts by volume, although it depends on the type of fine particles and the state of the surface treatment. It is. When the blending ratio is too small, the film resistance may increase because the opening after stretching may be insufficient. On the other hand, if the amount is too large, the continuity of the resin is interrupted, and the stretch breakage is likely to occur, and the strength of the film may be reduced.
[0016]
In addition, the resin used for the porous film of the present invention, if necessary, is generally used as an additive (antistatic agent, plasticizer, lubricant, antioxidant, nucleating agent as long as the object of the present invention is not impaired) Etc.) may be added.
[0017]
The value of the membrane resistance defined by the following formula (1) of the porous film of the present invention depends on the material of the porous film, but when the film is used alone as a battery separator, it is 5 seconds · μm. 2 / 100 cc or less is preferable.
[0018]
Film resistance (sec / μm) 2 / 100cc) = td 2 (1)
[T in formula (1) represents air permeability [Gurley value] (seconds / 100 cc),
d represents the hole diameter [bubble point method] (μm). ]
[0019]
It shows that ion permeability is so favorable that membrane resistance is small. When a separator having good ion permeability is used, a battery having excellent load characteristics, which is an important property in a secondary battery such as a lithium ion battery, is obtained. A battery having excellent load characteristics is a battery having a large electric capacity that can be taken out when a large current is passed.
In addition, the porous film of this invention may be further laminated | stacked with the porous layer which consists of polyolefin, a polyurethane, etc. as needed.
[0020]
The porous film of the present invention has a weight average molecular weight of 5 × 10. Five The above high molecular weight polyolefin and a weight average molecular weight of 2 × 10 Four The following thermoplastic resin, fine particles, and if necessary, a high molecular weight polyolefin has a weight average molecular weight of 2 × 10 Four It is manufactured by kneading the following thermoplastic resin which is not also a thermoplastic resin, forming it into a sheet shape, and then stretching the sheet. In addition, the porous film obtained by extending | stretching a sheet | seat and removing a microparticles | fine-particles, for example by water washing is also contained in the polycrystalline film of this invention.
Specific examples of the method for producing the porous film of the present invention include, for example, a composition comprising a high molecular weight polyolefin and a thermoplastic resin, fine particles, and if necessary, stretching aids such as fatty acid esters and other additives. Are mixed using a Henschel mixer, a super mixer, a tumbler type mixer, or the like, and then kneaded using a single screw or twin screw type extruder to be pelletized.
Next, the pellet is melted and formed into a sheet using a known molding machine such as an extrusion molding machine equipped with a T die 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 being pelletized.
The sheet is made porous by a known method such as a roll method or a tenter method, usually by stretching at least uniaxially at a temperature of room temperature or higher and lower than the softening point of the resin to cause interfacial peeling between the resin and the fine particles. A film is manufactured. Stretching may be performed in one stage or may be divided into multiple stages. Moreover, after extending | stretching, in order to stabilize the form of a hole, you may perform a heat setting process as needed.
[0021]
Next, the laminated porous film of the present invention will be described.
The laminated porous film of the present invention has a laminated structure of the porous film of the present invention and a porous film made of a heat resistant resin. In addition to the characteristics of the porous film of the present invention, the laminated porous film has little shrinkage when heated.
In the laminated porous film of the present invention, a porous layer made of polyolefin, polyurethane or the like may be further laminated as required.
The porous film made of the heat resistant resin may contain an inorganic fine powder. Content of inorganic fine powder is 1-1500 weight part with respect to 100 weight part of heat resistant resins, Preferably it is 5-100 weight part. The particle size of the inorganic fine powder is preferably smaller than the film thickness of the heat-resistant porous film, the average particle size of the primary particles is preferably 1.0 μm or less, more preferably 0.5 μm or less, and More preferably, it is 1 μm or less. The type of inorganic fine powder is not particularly limited, but alumina, silica, titanium dioxide, zirconium oxide, or calcium carbonate is preferable. These inorganic fine powders may be used alone or in combination of two or more. Further, the porosity of the heat-resistant porous film can be controlled by the content of the inorganic fine powder to improve the ion permeability.
[0022]
As a heat-resistant resin for forming a porous film made of a heat-resistant resin, 18.6 kg / cm in accordance with JIS K 7207 2 At least one heat-resistant resin selected from resins having a deflection temperature under load of 100 ° C. or higher in the measurement under load is preferable. Furthermore, in order to be safer even under high temperatures 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 load deflection temperature of 200 ° C. or higher.
[0023]
Examples of the resin having a deflection temperature under load of 100 ° C. or higher include polyimide, polyamideimide, aramid, polycarbonate, polyacetal, polysulfone, polyphenylsulfide, polyetheretherketone, aromatic polyester, polyethersulfone, and polyetherimide. It is done. Examples of the resin having a deflection temperature under load of 200 ° C. or higher include polyimide, polyamideimide, aramid, polyethersulfone, and polyetherimide. Furthermore, the heat resistant resin is particularly preferably selected from the group consisting of polyimide, polyamideimide and aramid.
[0024]
Moreover, as a heat resistant resin in this invention, it is preferable that a limiting oxygen index is 20 or more. The critical oxygen index is the minimum oxygen concentration at which a specimen placed in a glass tube can continue to burn. 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.
[0025]
As a method for producing the laminated porous film of the present invention, for example, a method of laminating the porous film of the present invention and a porous film made of a heat-resistant resin by an adhesive, heat fusion, etc .; Examples of the substrate include a method in which a solution made of a heat-resistant resin is applied in a solution state to form a solution layer, and then a solvent is removed from the solution to form the laminated porous film of the present invention.
[0026]
As the latter method, for example, the laminated porous film of the present invention can be produced by a method including the following steps (a) to (e).
(A) A solution composed of a heat resistant resin and an organic solvent is prepared. When the inorganic fine powder is contained, a slurry solution is prepared by dispersing 1 to 1500 parts by weight of the inorganic fine powder with respect to 100 parts by weight of the heat resistant resin.
(B) A coating film is formed by applying the solution or slurry solution to a porous film.
(C) The heat-resistant resin is deposited in the coating film.
(D) The organic solvent is removed from the coating film.
(E) The coating film is dried.
[0027]
Here, a polar organic solvent is usually used as the organic solvent. Examples of the polar organic solvent include N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, and tetramethylurea.
[0028]
As a method for precipitating the heat-resistant resin on the porous film, a method of leaving the porous film in an atmosphere controlled at a constant humidity and precipitating the heat-resistant resin, and then immersing the porous film in a coagulation liquid Can be given. The coagulation liquid may be an aqueous solution or an alcoholic solution, and is not particularly limited. However, an aqueous solution or an alcoholic solution containing a polar organic solvent solvent is used industrially because the solvent recovery process is simple. The aqueous solution of a polar organic solvent is more preferable. Alternatively, the porous film can be immersed in the coagulating liquid without being allowed to stand in an atmosphere controlled at a constant humidity and precipitating the heat resistant resin.
In addition, in the case of a heat-resistant resin that does not re-dissolve once deposited from a solution (for example, aramid), a part or all of the solvent is evaporated and the heat-resistant resin is precipitated at the same time, that is, the precipitation step and the next solvent removal The steps can be performed simultaneously.
[0029]
As a method for removing the polar organic solvent, a part or all of it may be evaporated, or it may be extracted and removed with a solvent that can dissolve the polar organic solvent, such as water, an aqueous solution, or an alcohol solution. When removing using water, it is preferable to use ion-exchange water. It is also industrially preferable to wash with an aqueous solution containing a certain concentration of polar organic solvent and then further with water.
[0030]
After removing the polar organic solvent, drying is performed. In the drying step, the solvent for washing is evaporated and removed by heating. It is preferable that the drying temperature at this time is below the heat deformation temperature of a porous film.
[0031]
Furthermore, the case where para-oriented aromatic polyamide (hereinafter, sometimes referred to as para-aramid) is specifically used as the heat-resistant resin is exemplified.
In the case of using para-aramid, 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, the para-oriented aromatic dicarboxylic acid is 1.00 mol of the para-oriented aromatic diamine. By adding 0.94 to 0.99 mol of acid dihalide and performing condensation polymerization at a temperature of −20 ° C. to 50 ° C., the para-aramid concentration is 1 to 10% and the intrinsic viscosity is usually 1.0 to 2.8 dl / The solution which consists of para-aramid which is g, and an organic solvent is created. By using this solution, a laminated porous film in which a para-aramid porous film is laminated on a porous film by the above-described production method can be produced. In the case of para-aramid, in order to remove the solvent and the chloride, it can be washed with the same solvent as the coagulation liquid such as water and methanol. However, the polymer is precipitated at the same time when a part or all of the solvent is evaporated. Thereafter, the chloride may be removed by a method such as washing with water.
[0032]
The battery separator according to the present invention includes the porous film or the laminated porous film. The membrane resistance of the porous film or laminated porous film used for the battery separator is preferably 5 or less from the viewpoint of ion permeability.
In addition, since there is little shrinkage | contraction when heat | fever is applied, what contains the said laminated porous film from a viewpoint of the improvement of safety | security is preferable.
[0033]
When the battery separator of the present invention includes 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. If the porosity is less than 30% by volume, the amount of electrolyte retained may be reduced, and if it exceeds 80%, the strength may be insufficient and the shutdown function may be reduced. Moreover, 5-50 micrometers is preferable, as for the thickness of a porous film, 10-50 micrometers is more preferable, More preferably, it is 10-30 micrometers. If the thickness is too thin, the shutdown function may be insufficient, or the battery may be short-circuited during winding, and if it is too thick, high electrical capacity may not be achieved. The pore diameter of the porous film is preferably 0.1 μm or less, and more preferably 0.08 μm or less. By reducing the pore diameter, a porous film having a small membrane resistance value is obtained even with the same air permeability.
[0034]
When the battery separator of the present invention includes the laminated porous film of the present invention, among the laminated porous films, preferred porosity and pore diameter of the porous film are the same as those of the porous film. However, the film thickness is preferably 5 to 50 μm, more preferably 10 to 50 μm, and still more preferably 10 to 30 μm as the whole laminated porous film. Among the laminated porous films, the porosity of the porous film made of a heat resistant resin is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. If the porosity is too small, the amount of electrolyte retained tends to be small, and if it is too large, the strength of the porous film made of a heat-resistant resin tends to be insufficient. The film thickness of the heat resistant porous film is preferably 0.5 μm to 10 μm, more preferably 1 μm to 5 μm. If the film thickness is too thin, the heat-resistant porous film tends not to be able to suppress shrinkage during heating, and if the film thickness is too thick, the load characteristics tend to deteriorate when the battery is used.
[0035]
The battery of the present invention includes the battery separator of the present invention.
In the following, components other than the battery separator will be described by taking, as an example, the case where the battery of the present invention is a non-aqueous electrolyte secondary battery such as a lithium battery, but is not limited thereto.
[0036]
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. As the lithium salt, LiClO Four , LiPF 6 , LiAsF 6 , LiSbF 6 , LiBF Four , LiCF Three SO Three , LiN (SO 2 CF Three ) 2 , LiC (SO 2 CF Three ) Three , Li 2 B Ten Cl Ten , Lower aliphatic carboxylic acid lithium salt, LiAlCl Four Among them, one kind or a mixture of two or more kinds can be mentioned. LiPF containing fluorine as lithium salt 6 , LiAsF 6 , LiSbF 6 , LiBF Four , LiCF Three SO Three , LiN (CF Three SO 2 ) 2 , And LiC (CF Three SO 2 ) Three It is preferable to use at least one selected from the group consisting of:
[0037]
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.
[0038]
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. The mixed solvent of cyclic carbonate and non-cyclic 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 the negative electrode active material. In addition, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable.
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 the material 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, in view of high average discharge potential, a lithium-based layered lithium composite oxide based on an α-NaFeO2 type structure such as lithium nickelate and lithium cobaltate and a lithium based on a spinel type structure such as lithium manganese spinel are preferable. A composite oxide is mentioned.
[0039]
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.
[0040]
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.
[0041]
Examples of the carbonaceous material as the conductive agent 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.
[0042]
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. As a carbonaceous material, a carbonaceous material mainly composed of graphite materials such as natural graphite and artificial graphite, because it has a high potential flatness and a low average discharge potential, so that a large energy density can be obtained when combined with a positive electrode. Is preferred.
[0043]
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.
[0044]
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.
[0045]
【Example】
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.
In Examples and Reference Examples, the physical properties and the like of porous films were measured by the following methods.
(1) Air permeability: A method defined in JISP8117.
(2) Average pore diameter: Conforms to ASTM F316-86.
(3) Film thickness: compliant with JISK7130.
(4) Puncture strength: The maximum stress (gf) when the pin was punctured at 200 mm / min at the place where the porous film was fixed with a 12 mmφ washer was defined as the puncture strength. In addition, the shape of this pin used the pin diameter of 1 mmΦ and the 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 allowed to stand at an arbitrary temperature (t) for 10 minutes. The shrinkage rate was calculated by the following equation.
Shrinkage rate (%) = (L twenty five -L t ) / L twenty five } × 100
(L twenty five Is the length of the separator in the TD direction 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 measurement method. For a solution obtained by dissolving 0.5 g of para-aramid polymer in 100 ml of 96-98% sulfuric acid and 96-98% sulfuric acid, the flow time was measured at 30 ° C. with a capillary viscometer, and the ratio of the obtained flow times was Thus, the intrinsic viscosity was determined.
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 represents the para-aramid concentration (dl / g) in the para-aramid sulfate solution.
[0046]
Example 1
<Manufacture of porous film>
Kneading was performed using a lab plast mill (Toyo Seiki Seisakusho). Ultra high molecular weight polyethylene powder 70 parts by weight (Hi-Zex Million 340M, manufactured by Mitsui Chemicals, Ltd., weight average molecular weight 3 million, density 0.93), polyethylene wax powder (High Wax 110P, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 1000, density 0.92) 30 Part by weight and 0.05 part by weight of an antioxidant (Irg1010, manufactured by Sumitomo Chemical Co., Ltd.) were mixed as they were in powder form, and then kneaded at 200 ° C. for 10 minutes with a lab plast mill to obtain a uniform kneaded product. The rotation speed of the blade at this time was 60 rpm. Next, 70 parts by volume of this kneaded product was put into a lab plast mill, and after melting, 30 parts by volume of calcium carbonate (Starpigot A15, manufactured by Shiraishi Calcium Co., Ltd., average particle size 0.15 μm) was added. The resulting kneaded product 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. × 5 cm) and uniaxially stretched by an autograph (AGS-G, Shimadzu Corp.) to make a porous film, which was stretched at 100 ° C. and a stretching speed of 50 mm / min. The obtained porous film was immersed in a hydrochloric acid / ethanol solution (hydrochloric acid: ethanol = 1: 1) to dissolve calcium carbonate, and after dissolution, the porous film was washed with ethanol and decreased at 60 ° C. Dried. The properties of the obtained porous film are shown in Table 1, it shows a shrinkage in Table 2.
A 1: 1 kneaded product of the ultrahigh molecular weight polyethylene and the polyethylene wax powder produced in the same manner 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. And when the obtained sheet | seat was cut | disconnected to appropriate size and uniaxial stretching was performed at 100 degreeC with the autograph, the homogeneous film was obtained and it was confirmed that both are compatible.
[0047]
Example 2
<Synthesis of para-aramid solution>
Poly (paraphenylene terephthalamide) (hereinafter abbreviated as PPTA) was synthesized using a 5 liter (l) separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port. The flask was sufficiently dried, charged with 4200 g of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), 272.65 g of calcium chloride dried at 200 ° C. for 2 hours 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 132.91 g of paraphenylenediamine (hereinafter abbreviated as PPD) was added and completely dissolved. While maintaining this solution at 20 ± 2 ° C., 243.32 g of terephthalic acid dichloride (hereinafter abbreviated as TPC) was added in 10 divided portions every about 5 minutes. Thereafter, the solution was aged for 1 hour while maintaining at 20 ± 2 ° C., and stirred for 30 minutes under reduced pressure in order to remove bubbles. The obtained polymerization liquid showed optical anisotropy. A part was sampled, reprecipitated with water and taken out as a polymer, and the intrinsic viscosity of the obtained PPTA was measured and found to be 1.97 dl / g.
Next, 100 g of this polymerization solution was weighed into a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a liquid addition port, and the NMP solution was gradually added. Finally, a PPTA solution having a PPTA concentration of 2.0% by weight was prepared, and this was designated as solution A.
<Application of para-aramid solution>
As the porous film, the polyethylene porous film of Example 1 was used. Using a bar coater manufactured by Tester Sangyo Co., Ltd. (clearance: 200 μm), a film of liquid A, which is a heat-resistant resin solution, was applied to a porous film placed on glass, and in this state, a constant temperature and humidity of 30 ° C. and 65% When kept in the tank for about 3 minutes, PPTA precipitated and a cloudy film was obtained. The film was immersed in a 30% NMP / water solution for 5 minutes. After soaking, the deposited film was peeled from the glass plate. After thoroughly washing with ion-exchanged water, the wet membrane was taken out of the water and free water was wiped off. This membrane was sandwiched between nylon cloths and further sandwiched between aramid felts. With the membrane sandwiched between nylon cloth and aramid felt, place an aluminum plate, cover it with nylon film, seal the nylon film and aluminum plate with gum, and attach a conduit for decompression. . The whole was put into a heat oven and the membrane was dried while reducing the pressure at 60 ° C. to obtain a laminated porous film. The physical properties of the film are shown in Table 1, and the shrinkage rate is shown in Table 2.
[0048]
Comparative Example 1
Laboplastmill was heated to 200 ° C., linear low density polyethylene (LLDPE) (FS240A, weight average molecular weight 110,000, manufactured by Sumitomo Chemical Co., Ltd.) 82 parts by weight, low density polyethylene (LDPE) (F208-1, 18 parts by weight of a weight average molecular weight of 80,000 (manufactured by Sumitomo Chemical Co., Ltd.) was added, and after these polyethylenes (abbreviated as PEs) were melted, hydrotalcite (DHT-4A, average particle diameter of 0.4 μm) with respect to 70 parts by volume of PEs. (Manufactured by Kyowa Chemical Industry Co., Ltd.) 30 parts by volume, and then 0.1 parts by weight of antioxidant (the total amount of PEs is 100 parts by weight) was added 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. And the obtained sheet | seat was cut | disconnected to appropriate size, and it uniaxially stretched by the autograph and was made to open, and it was set as the microporous film. The stretching was performed at 30 ° C. and a stretching speed of 50 mm / min. The physical properties of the obtained porous film are shown in Table 1.
[0049]
Comparative Example 2
Laboplast mill is heated to 200 ° C., and polypropylene (FS2011D, weight average molecular weight 410,000, Sumitomo Chemical Co., Ltd.) 70 parts by volume is added. After melting polypropylene, hydrotalcite (DHT-4A, average particle size 0.4 μm) (Manufactured by Kyowa Chemical Industry Co., Ltd.) 30 parts by volume and then 0.05 parts by weight of antioxidant (based on 70 parts by weight of polypropylene) were added and kneaded for 5 minutes at 100 rpm. The sheet was processed into a sheet having a thickness of 60 to 70 μm by a press and solidified by a cooling press, and the obtained sheet was cut into an appropriate size, and uniaxially stretched by an autograph to open a hole 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.
[0050]
Comparative Example 3
49 parts by weight of ultra high molecular weight polyethylene powder (Hi-Zex Million 340M, manufactured by Mitsui Chemicals, Ltd., weight average molecular weight 3 million), 34 parts by weight of metallocene LLDPE (SP4060, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 70,000), metallocene LDPE ( G808, manufactured by Sumitomo Chemical Co., Ltd., weight average molecular weight 55,000) 17 parts by weight, antioxidant (Irg1010, manufactured by Sumitomo Chemical Co., Ltd.) 0.05 parts by weight was kneaded at 200 ° C. for 10 minutes in a lab plast mill. I took it out as a thing. The resin composition was 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 was cut into an appropriate size and 100 ° C. by an autograph. As a result of uniaxial stretching, it was visually observed that the obtained sheet was not compatible with powdered ultrahigh molecular weight polyethylene, and the kneaded product was not compatible. confirmed. Next, 70 parts by volume of this kneaded product was put into a lab plast mill, and after melting, 30 parts by volume of calcium carbonate (Starpigot A15, manufactured by Shiraishi Calcium Co., Ltd., average particle size 0.15 μm) was added. The resulting 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, and the obtained sheet was cut into an appropriate size. The film was uniaxially stretched by an autograph to open a porous film, which was stretched at 100 ° C. and at a stretching speed of 50 mm / min, and then the resulting porous film was treated with a hydrochloric acid / ethanol solution (hydrochloric acid: ethanol). = 1: 1) to dissolve calcium carbonate, and after dissolution, the porous film was washed with ethanol and dried under reduced pressure at 60 ° C. The physical properties of the obtained porous film were shown. It was shown in 1.
[0051]
Comparative Example 4
70 parts by weight of ultra-high molecular weight polyethylene powder (Hi-Zex Million 340M, manufactured by Mitsui Chemicals, 3 million weight average molecular weight), 30 parts by weight of polyethylene wax powder (high wax 110P, manufactured by Mitsui Chemicals, weight average molecular weight 1000), antioxidant (Irg1010, manufactured by Sumitomo Chemical Co., Ltd.) After 0.05 parts by weight were uniformly mixed, the mixture was kneaded at 200 ° C. for 10 minutes with a lab plast mill and taken out as 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. 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.
[0052]
Comparative Example 5
Ultra high molecular weight polyethylene powder 70 parts by volume (Hi-Zex Million 340M, Mitsui Chemicals, weight average molecular weight 3 million, density 0.93), antioxidant (Irg1010, manufactured by Sumitomo Chemical) 0.05 parts by weight uniformly in powder form After mixing, the mixture was kneaded at 200 ° C. for 10 minutes in a lab plast mill. Thereafter, 30 parts by volume of calcium carbonate (Starpigot A15, manufactured by Shiraishi Calcium Co., Ltd., average particle size of 0.15 μm) was added and kneaded for 5 minutes at 200 ° C. The obtained kneaded product was hot pressed at 200 ° C. When processed into a sheet having a thickness of 60 to 70 μm and solidified by a cooling press, a clean thin film sheet could not be obtained even if sufficient preheating was performed.
[0053]
[Table 1]
Physical properties of porous films and laminated porous films
[0054]
[Table 2]
Shrinkage of porous film and composite porous film
[0055]
【Effect of the invention】
The porous film of the present invention can be easily produced, has excellent puncture strength, and can be suitably used as a battery separator, particularly a lithium ion secondary battery separator.

Claims (12)

  1. A high molecular weight polyolefin having a weight average molecular weight of 5 × 10 5 or more and 15 × 10 6 or less, a thermoplastic resin having a weight average molecular weight of 2 × 10 4 or less, and fine particles as a pore-opening agent ( the fine particles are the polyolefin and the thermoplastic A porous film formed by stretching the sheet after being kneaded and molded into a sheet shape.
  2.   2. The porous film according to claim 1, wherein the average particle diameter of the fine particles is 3 μm or less.
  3.   3. The porous film according to claim 1, wherein the high molecular weight polyolefin is in a proportion of 30 to 90% by weight with respect to the sum of the weights of the high molecular weight polyolefin and the thermoplastic resin.
  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 any one of claims 1 to 5, the film resistance defined by the following equation of the porous film (1), characterized in that it is less than 5 seconds · μm 2 / 100cc.
    Film resistance (sec · μm 2 / 100cc) = td 2 (1)
    [In formula (1), t represents air permeability [Gurley value] (second / 100 cc), and d represents pore diameter [bubble point method] (μm). ]
  7. Battery separator which comprises a porous film according to any one of claims 1-6.
  8. A battery comprising the battery separator according to claim 7 .
  9. Weight average molecular weight 5 × 10 Five 15 × 10 or more 6 The following high molecular weight polyolefin and a weight average molecular weight of 2 × 10 Four The following thermoplastic resin and water-soluble fine particles as a pore-opening agent (the fine particles are not the polyolefin and the thermoplastic resin) are kneaded and formed into a sheet, and then the sheet is stretched. A method for producing a porous film, comprising: stretching a porous film sheet, and then washing with water to remove fine particles.
  10. The method for producing a porous film according to claim 9, wherein the average particle diameter of the fine particles is 3 μm or less.
  11. The method for producing a porous film according to claim 9 or 10, wherein the high molecular weight polyolefin is in a proportion of 30 to 90% by weight with respect to the sum of the weights of the high molecular weight polyolefin and the thermoplastic resin.
  12. The method for producing a porous film according to claim 9, wherein the thermoplastic resin is polyethylene.
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