Separator for non-aqueous electrolyte secondary battery, member for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Abstract

To provide a separator which can provide a non-aqueous electrolyte secondary battery with excellent cycle characteristics.SOLUTION: The separator for a non-aqueous electrolyte secondary according to the present disclosure includes a first layer including a resin for which α×Ra is 10 or less, in which α represents an exponent of the Mark-Houwink-Sakurada equation as determined from the intrinsic viscosity and the weight-average molecular weight, and Ra denotes the Hansen solubility parameter distance from diethyl carbonate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a separator for a nonaqueous electrolyte secondary battery, a member for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery. [Background technology]

[0002] 2. Description of the Related Art Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, have a high energy density and are therefore widely used as batteries for personal computers, mobile phones, personal digital assistants, vehicle-mounted devices, and the like.

[0003] As a component of such non-aqueous electrolyte secondary batteries, separators with excellent heat resistance have been developed. For example, as disclosed in Patent Document 1, a laminate separator in which a porous layer containing a heat-resistant resin is laminated on a substrate is known. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-030686 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned conventional techniques have room for further improvement in terms of the cycle characteristics of the battery. An object of one aspect of the present invention is to provide a separator that enables a non-aqueous electrolyte secondary battery with excellent cycle characteristics to be obtained. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors conducted extensive research and found that by using a resin in which the product α×Ra, which is the index α of the Mark-Houwink-Sakurada equation calculated from the intrinsic viscosity and the weight average molecular weight, and the distance Ra of the Hansen solubility parameter, falls within a specific range, it is possible to realize a separator that enables a nonaqueous electrolyte secondary battery with excellent cycle characteristics to be obtained.

[0007] The separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention has an index α calculated by the Mark-Houwink-Sakurada equation represented by the following formula (I) and a distance Ra (unit: MPa) between the index α and diethyl carbonate as the Hansen solubility parameter: 1 / 2 ) and a resin in which the product α×Ra is 10 or less. [η] = KM α (I) (In the formula, [η] is the intrinsic viscosity of the resin (unit: dL / g), M is the weight average molecular weight of the resin, and K is a constant.) Effect of the Invention

[0008] According to one aspect of the present invention, a separator that enables a nonaqueous electrolyte secondary battery with excellent cycle characteristics to be obtained can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present invention will be described below, but the present invention is not limited thereto. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less."

[0010] [1. Separator for non-aqueous electrolyte secondary batteries] The separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention has an index α calculated by the Mark-Houwink-Sakurada equation represented by the following formula (I) and a distance Ra (unit: MPa) between the index α and diethyl carbonate in the Hansen solubility parameter: 1 / 2 ) and a resin in which the product α×Ra is 10 or less. [η] = KM α (I) (In the formula, [η] is the intrinsic viscosity of the resin (unit: dL / g), M is the weight average molecular weight of the resin, and K is a constant.) Hereinafter, the separator for non-aqueous electrolyte secondary batteries will also be referred to simply as "separator." Diethyl carbonate will also be referred to as "DEC," Hansen solubility parameter as "HSP," and Hansen solubility parameter distance as "HSP distance."

[0011] The separator can provide a non-aqueous electrolyte secondary battery with excellent cycle characteristics, and the mechanism behind this is speculative, but is thought to be as follows.

[0012] When the resin molecular chains are twisted, the index α becomes smaller. This is because the molecular chains of the polymeric resin take on a random coil shape in solution, making it difficult for the solvent to flow inside the polymer coil. In addition, when the resin molecular chains are twisted, the density of the resin decreases. This is because the volume of the resin increases. When the density of the resin in the layer containing the resin decreases, the gaps between the fibers become larger accordingly, and the pores of the layer become larger. This improves the electrolyte retention of the separator.

[0013] Furthermore, in the resin, a small HSP distance Ra between the resin and DEC indicates a high affinity between the resin and the electrolyte, and therefore a separator having a first layer containing the resin has a high affinity between the electrolyte and the separator.

[0014] The fact that α×Ra is 10 or less indicates that both the index α and the HSP distance Ra are small. This indicates that the pore size in the first layer is large, so that the electrolyte retention is high, and the electrolyte affinity of the resin constituting the first layer is also high. As a result, the separator having the first layer containing the resin with α×Ra of 10 or less can provide a nonaqueous electrolyte secondary battery with improved cycle characteristics.

[0015] The intrinsic viscosity [η] of the resin in formula (I) can be determined by measuring a solution with a resin concentration of 0.5 g / dL in 98% concentrated sulfuric acid at 30°C. The weight average molecular weight M of the resin can be determined by standard GPC (gel permeation chromatography) techniques. If the intercept of the linear approximation of ln[η] on the y-axis and lnM on the x-axis is α, it is expressed as a constant K = exp(α). The exponent α can be determined as the slope of the linear approximation of ln[η] on the y-axis and lnM on the x-axis by measuring the intrinsic viscosity [η] and the weight average molecular weight M for multiple types of resins that are composed of the same structural unit but have different weight average molecular weights.

[0016] α×Ra is preferably 9 or less, more preferably 8 or less, even more preferably 7 or less, particularly preferably 6 or less, and most preferably 5 or less. The lower limit of α×Ra is not particularly limited, but may be, for example, 3 or more.

[0017] The exponent α is preferably equal to or less than 0.8, and more preferably equal to or less than 0.7. The lower limit of the exponent α is not particularly limited, but may be, for example, equal to or more than 0.3.

[0018] Hansen solubility parameter (δ) is defined as three-dimensional parameters (δD, δP, δH) and is expressed by the following formula (II). Details of HSP are described in "PROPERTIES OF POLYMERS" (author: DWVAN KREVELEN, publisher: ELSEVIER SCIENTIFIC PUBLISHING COMPANY, 5th edition, published in 1989). δ 2 =(δD) 2 +(δP) 2 +(δH) 2 (II) δD: London dispersion force term δP: Molecular polarization term (dipole force term) δH: Hydrogen bond term δD, δP, and δH can be calculated using HSPiP (Hansen Solubility Parameters in Practice), a program developed by the group of Dr. Hansen, who proposed HSP. In this specification, Ver. 5.4.07 was used.

[0019] The HSP distance Ra indicates the distance between the HSPs of two substances. The HSP distance Ra is an index that indicates the affinity between two substances, and the smaller the value, the higher the affinity between the two substances.

[0020] The HSPs of two substances A and B are δ A and δ B of, δ A =(δD A , δP A , δH A ) δ B =(δD B , δP B , δH B ) Assuming this, the HSP distance Ra can be calculated by the following formula (III). Ra = [4 × (δD A -δD B ) 2 +(δP A -δP B ) 2 +(δH A -δH B ) 2 ] 1 / 2 (III) The HSP of DEC is ΔD=15.1, ΔP=6.3, and ΔH=3.5. The HSP distance Ra with DEC is preferably 13 or less, and more preferably 12 or less. The lower limit of the HSP distance Ra with DEC is not particularly limited, but may be, for example, 10 or more.

[0021] Hereinafter, a resin having an α×Ra of 10 or less will be referred to as resin (A). The first layer may contain only one type of resin (A), or may contain two or more types.

[0022] The structure constituting the repeating unit of the resin (A) is not particularly limited, but preferably contains an aromatic 6-membered ring. The number of aromatic 6-membered rings contained in one repeating unit is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, particularly preferably 4 or more, and most preferably 5 or more.

[0023] Examples of the structures constituting the repeating unit of the resin (A) include a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a tetracene ring, a triphenylene ring, a pyrene ring, a chrysene ring, a pentacene ring, and a fluorene ring. The repeating unit may contain only one of these structures, or may contain two or more of these structures. These structures may be substituted with an alkyl group having 1 to 5 carbon atoms, a halogen atom, a halogenated alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a carboxyl group, a nitro group, a cyano group, a cyanate group, or the like. In the repeating unit, these structures may be bonded by a single bond, an amide bond, an ester bond, an ether bond, or the like.

[0024] From the viewpoint of reducing the index α, it is preferable that the resin (A) contains two or more benzene rings in the repeating unit. Also, from the viewpoint of reducing the HSP distance Ra with DEC, it is preferable that the resin (A) contains three or more benzene rings in the repeating unit.

[0025] The repeating unit preferably contains a fluorene ring, and more preferably contains a 9,9-bis(phenyl)fluorene skeleton. In this specification, the structure represented by the following formula (1) is referred to as a 9,9-bis(phenyl)fluorene skeleton. Here, each R independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a halogen atom.

[0026] [ka]

[0027] For example, poly(paraphenylene terephthalamide) has an α×Ra of more than 10, as described in the Examples.

[0028] Examples of the resin (A) include aromatic polyamide, aromatic polyimide, aromatic polyamideimide, aromatic polyether ketone, aromatic polyether ether ketone, aromatic polyarylate, aromatic polysulfone, aromatic polyether sulfone, aromatic polyether imide, aromatic polycarbonate, etc., and from the viewpoint of heat resistance, the resin (A) is preferably an aromatic polyamide. Also, from the viewpoint of compatibility between ion permeability and heat resistance, the resin (A) is preferably an aromatic polyamide having a repeating unit containing a fluorene ring, more preferably an aromatic polyamide having a repeating unit containing a 9,9-bis(phenyl)fluorene skeleton, and even more preferably an aromatic polyamide having a repeating unit in which a 9,9-bis(phenyl)fluorene skeleton and a benzene ring are bonded by an amide bond.

[0029] The first layer may contain, in addition to the resin (A), a resin other than the resin (A). This other resin is hereinafter also referred to as resin (B). That is, the resin (B) is a resin having an α×Ra of more than 10. The separator may contain only one type of resin (B), or may contain two or more types.

[0030] In 100% by weight of the resin contained in the first layer, the proportion of the resin (A) is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. In 100% by weight of the resin contained in the first layer, the proportion of the resin (A) may be 100% by weight or less.

[0031] Examples of the resin (B) include polyolefin resins, (meth)acrylate resins, fluorine-containing resins, polyamide resins, polyimide resins, polyester resins, rubbers, resins having a melting point or glass transition temperature of 180° C. or higher, water-soluble polymers, polycarbonate, polyacetal, etc. Among these resins, polyamide resins, polyimide resins, polyester resins, and resins having a melting point or glass transition temperature of 180° C. or higher are more preferred from the viewpoint of heat resistance.

[0032] As the polyamide resin, aramid resins such as aromatic polyamides and fully aromatic polyamides are preferred. As the aramid resin, for example, para-aramid and meta-aramid are exemplified, with para-aramid being preferred. As the para-aramid, there are para-oriented or para-oriented para-aramids having a structure similar thereto, such as poly(paraphenylene terephthalamide), poly(parabenzamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly(2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, poly(4,4'-diphenylsulfonyl terephthalamide), and paraphenylene terephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer. Of these, poly(paraphenylene terephthalamide) is more preferred.

[0033] Examples of polyester resins include aromatic polyesters such as polyarylates and liquid crystal polyesters.

[0034] Examples of rubbers include styrene-butadiene copolymers and hydrogenated products thereof, methacrylate copolymers, acrylonitrile-acrylate copolymers, styrene-acrylate copolymers, ethylene propylene rubber, and polyvinyl acetate.

[0035] Examples of fluorine-containing resins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, and the like, as well as fluorine-containing rubbers having a glass transition temperature of 23° C. or lower among the above-mentioned fluorine-containing resins.

[0036] Examples of resins having a melting point or glass transition temperature of 180° C. or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide, and polyetheretherketone.

[0037] Examples of the water-soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, and polymethacrylic acid.

[0038] The separator may be composed of only the first layer, or may be laminated with a layer different from the first layer as described later. The first layer may be disposed between the polyolefin porous film and at least one of the positive electrode and the negative electrode as a member constituting the nonaqueous electrolyte secondary battery. The first layer may be disposed on the active material layer of at least one of the positive electrode and the negative electrode. The first layer may be disposed between the polyolefin porous film and at least one of the positive electrode and the negative electrode so as to be in contact with them. The first layer disposed between the polyolefin porous film and at least one of the positive electrode and the negative electrode may be one layer or two or more layers. The first layer is preferably an insulating layer containing a resin. The resin used for the first layer is preferably insoluble in the electrolyte of the nonaqueous electrolyte secondary battery and is preferably electrochemically stable within the range of use of the battery.

[0039] From the viewpoint of ensuring adhesion to the electrode and high energy density, the thickness of each first layer is preferably in the range of 0.5 μm to 10 μm, and more preferably in the range of 1 μm to 5 μm. When the thickness of each first layer is 0.5 μm or more, internal short circuit due to damage to the nonaqueous electrolyte secondary battery can be sufficiently suppressed, and the amount of electrolyte held in the first layer becomes sufficient. When the thickness of each first layer is 10 μm or less, the permeation resistance of metal ions in the nonaqueous electrolyte secondary battery can be suppressed, so that the deterioration of rate characteristics and cycle characteristics can be suppressed. In addition, the increase in the distance between the positive electrode and the negative electrode can be suppressed, so that the deterioration of the internal volume efficiency of the nonaqueous electrolyte secondary battery can be suppressed.

[0040] The basis weight of the first layer, i.e., the weight per unit area, can be appropriately determined in consideration of the strength, film thickness, weight and handling properties of the first layer. The basis weight of the first layer per layer is 0.5 to 20 g / m 2 It is preferable that the thickness is 0.5 to 10 g / m 2By setting the basis weight of the first layer within these numerical ranges, the weight energy density and volume energy density of the nonaqueous electrolyte secondary battery can be increased.

[0041] The first layer may be a porous layer. The porosity of the first layer may be 0 to 90% by volume, but is preferably 20 to 90% by volume, and more preferably 30 to 80% by volume, so that sufficient ion permeability can be obtained. The pore size of the pores in the first layer is preferably 1.0 μm or less, and more preferably 0.5 μm or less. By setting the pore size to these sizes, the nonaqueous electrolyte secondary battery can obtain sufficient ion permeability.

[0042] The first layer may contain a filler. The filler may be an inorganic filler or an organic filler. As the filler, a filler made of an inorganic oxide such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, or boehmite is preferred, a filler made of calcium oxide, magnesium oxide, or alumina is more preferred, and a filler made of alumina is even more preferred. A nonaqueous electrolyte secondary battery having a first layer containing a filler with high thermal conductivity has excellent heat dissipation properties within the battery, and therefore its safety is further improved. In the first layer, the content of the filler is preferably 70% by weight or less, more preferably 60% by weight or less, based on the total weight of the first layer, i.e., the total weight of the resin and the filler. The content of the filler is preferably 10% by weight or more, more preferably 20% by weight or more, based on the total weight of the first layer.

[0043] [2. Laminated separator for non-aqueous electrolyte secondary batteries] The separator may further include a second layer containing a polyolefin resin, and the first layer may be laminated on the second layer. That is, the separator may be a separator formed by laminating a first layer containing a resin (A) and a second layer containing a polyolefin resin. In this specification, such a separator is also called a laminate separator. The explanation of [1. Separator for non-aqueous electrolyte secondary battery] can be used as the explanation of the first layer. The above-mentioned second layer may be a substrate. The first layer may be laminated on one side or both sides of the second layer.

[0044] The second layer contains a polyolefin resin, and is generally a porous film mainly composed of a polyolefin resin. That is, the second layer may be a polyolefin porous film. In addition, "mainly composed of a polyolefin resin" means that the proportion of the polyolefin resin in the porous film is 50% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more of the total material constituting the porous film.

[0045] The polyolefin resin has a weight average molecular weight of 5×10 5 ~15×10 6 It is more preferable that the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more, since this improves the strength of the resulting laminate separator.

[0046] The polyolefin resin is not particularly limited, but examples thereof include thermoplastic resins such as homopolymers or copolymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. Examples of the homopolymers include polyethylene, polypropylene, and polybutene. Examples of the copolymers include ethylene-propylene copolymers.

[0047] Among these, polyethylene is more preferred because it can prevent excessive current from flowing through the laminated separator at a lower temperature. This prevention of excessive current from flowing is also called shutdown. Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene having a weight-average molecular weight of 1 million or more. Among these, ultra-high molecular weight polyethylene having a weight-average molecular weight of 1 million or more is more preferred.

[0048] The thickness of the porous film is preferably 4 to 40 μm, and more preferably 5 to 20 μm. If the thickness of the porous film is 4 μm or more, internal short circuit of the battery can be sufficiently prevented. On the other hand, if the thickness of the porous film is 40 μm or less, the nonaqueous electrolyte secondary battery can be prevented from becoming large.

[0049] The weight per unit area of ​​the porous film, i.e., the weight per unit area, can be appropriately determined in consideration of the strength, film thickness, weight, and handleability. However, in order to increase the weight energy density and volume energy density of the nonaqueous electrolyte secondary battery, the weight per unit area is preferably 4 to 20 g / m. 2 is preferably 4 to 12 g / m 2 More preferably, the thickness is 5 to 10 g / m 2 It is even more preferable that:

[0050] The porous film has many interconnected pores inside, allowing gas and liquid to pass from one side to the other. The air permeability of the porous film is preferably 30 to 500 sec / 100 mL, more preferably 50 to 300 sec / 100 mL, in Gurley value. When the porous film has the above air permeability, sufficient ion permeability can be obtained.

[0051] The porosity of the porous film is preferably 20 to 80% by volume, more preferably 30 to 75% by volume, so as to increase the amount of electrolyte retained and to obtain a function of reliably preventing the flow of excessive current at a lower temperature. The pore size of the pores in the porous film is preferably 0.3 μm or less, more preferably 0.14 μm or less, so as to obtain sufficient ion permeability and to prevent particles from entering the positive and negative electrodes.

[0052] The laminate separator preferably has an air permeability of 30 to 1000 sec / 100 mL, more preferably 50 to 800 sec / 100 mL, in Gurley value, and when the laminate separator has the above air permeability, sufficient ion permeability can be obtained in a nonaqueous electrolyte secondary battery.

[0053] The thickness of the laminated separator is preferably 5.5 μm to 45 μm, and more preferably 6 μm to 25 μm.

[0054] The laminated separator may include a third layer different from the first and second layers, if necessary, within the scope of the present invention. Examples of the third layer include known porous layers such as a heat-resistant layer, an adhesive layer, and a protective layer.

[0055] The third layer may be provided on one or both sides of the laminated separator. When the laminated separator includes the first layer on both sides of the second layer, the third layer may be provided on the first layer on both sides, or on the first layer on one side. When the laminated separator includes the first layer on only one side of the second layer, the third layer may be provided on the first layer, or on the side of the second layer where the first layer is not provided. The third layer may be provided on the outermost layer of the laminated separator.

[0056] For example, the laminated separator further includes an adhesive layer in addition to the first layer and the second layer. In this specification, the adhesive layer means a porous layer having adhesive properties. The adhesive layer may be provided on the surface of the laminated separator that contacts the electrode. Examples of components that contribute to adhesive properties contained in the adhesive layer include acrylic resin, PVDF, etc.

[0057] 3. Manufacturing method of separator for non-aqueous electrolyte secondary battery The first layer can be formed using a coating liquid obtained by dissolving or dispersing a resin in a solvent. The solvent can also be said to be a dispersion medium for dispersing the resin. Examples of the resin include the above-mentioned resin (A) and resin (B). Examples of methods for forming the coating liquid include mechanical stirring, ultrasonic dispersion, high-pressure dispersion, and media dispersion.

[0058] Methods for forming the first layer include, for example, a method in which a coating liquid is directly applied to the surface of a substrate, followed by removal of the solvent; a method in which a coating liquid is applied to a suitable support, followed by removal of the solvent to form a porous layer, followed by pressure bonding the porous layer to the substrate, and then peeling off the substrate; a method in which a coating liquid is applied to a suitable support, followed by pressure bonding the substrate to the coated surface, followed by peeling off the substrate, followed by removal of the solvent; and a method in which a substrate is immersed in a coating liquid to perform dip coating, followed by removal of the solvent.

[0059] The solvent is preferably a solvent that does not adversely affect the substrate, dissolves the resin uniformly and stably, and disperses the filler uniformly and stably. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, N,N-dimethylformamide, acetone, and water.

[0060] The coating liquid may contain a filler. The coating liquid may appropriately contain a dispersant, a plasticizer, a surfactant, a pH adjuster, and the like as components other than the resin and the filler.

[0061] The substrate may be the polyolefin porous film described above, or other films, positive electrodes, negative electrodes, etc. A conventionally known method may be used as a method for applying the coating liquid to the substrate, and specific examples of the method include a gravure coater method, a dip coater method, a bar coater method, and a die coater method.

[0062] When the coating liquid contains an aramid resin, the aramid resin can be precipitated by providing moisture to the coating surface. This may form a first layer. Specific methods for providing moisture to the coating surface include, but are not limited to, a method of exposing the coating surface to a humid atmosphere, a method of spraying water with a spray or the like, and a method of spraying water vapor with a nozzle or the like.

[0063] The method for preparing the resin (A) is not particularly limited, but may be a condensation polymerization method of an aromatic diamine and an aromatic dicarboxylic acid halide. The aromatic diamine and aromatic dicarboxylic acid halide may be selected so that one repeating unit of the obtained resin (A) contains five or more aromatic six-membered rings. From the viewpoint of heat resistance, the aromatic dicarboxylic acid halide is preferably a para-oriented aromatic dicarboxylic acid halide. An example of the aromatic diamine is 9,9-bis(4-aminophenyl)fluorene. An example of the aromatic dicarboxylic acid halide is terephthalic acid dichloride. These may be substituted.

[0064] An example of a method for producing a laminated separator is the above-mentioned method for producing the first layer, in which the above-mentioned porous film is used as the substrate to which the coating liquid is applied.

[0065] The method for producing the porous film is not particularly limited. For example, a polyolefin resin, a pore-forming agent such as an inorganic filler or a plasticizer, and optionally an antioxidant are kneaded and then extruded to produce a sheet-shaped polyolefin resin composition. Then, the pore-forming agent is removed from the sheet-shaped polyolefin resin composition using a suitable solvent. Then, the polyolefin resin composition from which the pore-forming agent has been removed is stretched to produce a polyolefin porous film.

[0066] The inorganic filler is not particularly limited, and examples thereof include inorganic fillers, specifically calcium carbonate, etc. The plasticizer is not particularly limited, and examples thereof include low molecular weight hydrocarbons such as liquid paraffin.

[0067] [4. Components for non-aqueous electrolyte secondary batteries, non-aqueous electrolyte secondary batteries] The nonaqueous electrolyte secondary battery member according to one embodiment of the present invention comprises a positive electrode, the above-mentioned separator, and a negative electrode arranged in this order. The nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes the above-mentioned separator. The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be a thin plate (paper) type, a disk type, a cylindrical type, a prismatic type such as a rectangular parallelepiped, or the like.

[0068] For example, a nonaqueous electrolyte secondary battery member can be formed by arranging a positive electrode, the above-mentioned separator, and a negative electrode in this order. Here, the first layer can be present between the second layer and at least one of the positive electrode and the negative electrode. Next, the nonaqueous electrolyte secondary battery member is placed in a container that will become the housing of the nonaqueous electrolyte secondary battery. After filling the container with the nonaqueous electrolyte, the container is sealed while reducing the pressure. This allows the nonaqueous electrolyte secondary battery to be manufactured.

[0069] <Positive electrode> The positive electrode is not particularly limited as long as it is generally used as a positive electrode of a non-aqueous electrolyte secondary battery. For example, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder is formed on a positive electrode current collector can be used as the positive electrode. The active material layer may further contain a conductive agent.

[0070] The positive electrode active material may be, for example, a material capable of doping / de-doping metal ions such as lithium ions or sodium ions, etc. Specific examples of such materials include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni.

[0071] Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and organic polymer compound sintered bodies. The conductive agent may be used alone or in combination of two or more kinds.

[0072] Examples of the binder include fluorine-based resins such as polyvinylidene fluoride (PVDF), acrylic resins, and styrene-butadiene rubber. The binder also functions as a thickener.

[0073] Examples of the positive electrode current collector include conductors such as Al, Ni, stainless steel, etc. Among them, Al is more preferable because it is easy to process into a thin film and is inexpensive.

[0074] Examples of methods for producing a positive electrode sheet include a method of pressurizing and molding a positive electrode active material, a conductive agent, and a binder on a positive electrode current collector; a method of forming a paste of a positive electrode active material, a conductive agent, and a binder using an appropriate organic solvent, applying the paste to a positive electrode current collector, drying the paste, and then applying pressure to adhere the paste to the positive electrode current collector.

[0075] <Negative electrode> The negative electrode is not particularly limited as long as it is generally used as a negative electrode of a non-aqueous electrolyte secondary battery. For example, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder is formed on a negative electrode current collector can be used as the negative electrode. The active material layer may further contain a conductive agent.

[0076] The negative electrode active material may be, for example, a material capable of doping / undoping metal ions such as lithium ions or sodium ions. Such materials may be, for example, carbonaceous materials. Examples of carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black, and pyrolytic carbons.

[0077] The negative electrode current collector may be made of, for example, Cu, Ni, stainless steel, etc. Cu is more preferred because it is difficult to form an alloy with lithium and is easy to process into a thin film.

[0078] Examples of the method for producing the negative electrode sheet include a method of pressurizing and molding the negative electrode active material on the negative electrode current collector, a method of forming the negative electrode active material into a paste using an appropriate organic solvent, applying the paste to the negative electrode current collector, drying, and then pressing to fix the paste to the negative electrode current collector, etc. The paste preferably contains the conductive agent and the binder described above.

[0079] <Nonaqueous electrolyte> The non-aqueous electrolyte is not particularly limited as long as it is a non-aqueous electrolyte generally used in non-aqueous electrolyte secondary batteries. For example, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent can be used as the non-aqueous electrolyte. For example, the lithium salt can be LiClO4, LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, Li2B 10 Cl 10 , lithium salts of lower aliphatic carboxylates, LiAlCl4, etc. The lithium salts may be used alone or in combination of two or more.

[0080] Examples of the organic solvent include carbonates, ethers, esters, nitriles, amides, carbamates, sulfur-containing compounds, and fluorine-containing organic solvents obtained by introducing a fluorine group into these organic solvents. The organic solvents may be used alone or in combination of two or more kinds.

[0081] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0082] An embodiment of the present invention may include the following features. <1> The index α calculated by the Mark-Houwink-Sakurada equation represented by the following formula (I) and the distance Ra (unit: MPa) between the Hansen solubility parameters of diethyl carbonate and 1 / 2 ) and a resin in which the product α×Ra is 10 or less. [η] = KM α (I) (In the formula, [η] is the intrinsic viscosity of the resin (unit: dl / g), M is the weight average molecular weight of the resin, and K is a constant.) <2> The resin is an aromatic polyamide. <1> 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1 . <3> the first layer comprises a filler; <1> or <2> 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1 . <4> Further comprising a second layer containing a polyolefin resin, the first layer being laminated on the second layer. <1> ~ <3> 10. The separator for a non-aqueous electrolyte secondary battery according to claim 9, <5> Further comprising an adhesive layer separate from the first layer and the second layer; <4> 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1 . <6> A positive electrode and <1> ~ <5> 13. A non-aqueous electrolyte secondary battery member comprising: the separator for a non-aqueous electrolyte secondary battery according to any one of 1 to 2 above; and a negative electrode, disposed in this order. <7> <1> ~ <5> 13. A non-aqueous electrolyte secondary battery comprising the separator for a non-aqueous electrolyte secondary battery according to claim 12. EXAMPLES

[0083] An embodiment of the present invention will be described below. In this specification, the conveying direction in the production of the laminated separator is also referred to as the MD direction, and the direction parallel to the surface of the laminated separator and perpendicular to the MD direction is also referred to as the TD direction.

[0084] [Method of evaluating air permeability] The air permeability of the laminated separator was measured based on JIS P 8117 using a digital timer type Gurley densometer (manufactured by Yasuda Seiki Seisakusho Co., Ltd.).

[0085] [Evaluation method of cycle test] The cycle test was performed according to the following procedure. 1. In a coin battery container, from top to bottom, a spring, a spacer (thickness: 0.5 mm), lithium metal (diameter: 15 mm, thickness: 0.5 mm, manufactured by Honjo Metals), two laminated separators (diameter 19 mm, both arranged so that the first layer is in contact with the lithium metal), lithium metal (diameter: 15 mm, thickness: 0.5 mm, manufactured by Honjo Metals), and a spacer (thickness: 0.5 mm) were stacked and stored. 2. 180μL of non-aqueous electrolyte was poured into the container, and after vacuum impregnation, 85μL of non-aqueous electrolyte was poured into the container and the container was crimped and sealed. The composition of the non-aqueous electrolyte was a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate = 3:5:2 (volume ratio), in which LiPF6 was dissolved to a concentration of 1mol / L. 3. A constant current was applied to repeatedly dissolve and deposit lithium metal. The test conditions were: current density: 1.0 mA / cm 2 , Current application time: 1 hour, Capacity: 1.0mAh / cm 2 , temperature: 25°C. 4. The cycle test was terminated when the voltage reached the cutoff value (±1.0 V) or a short circuit occurred (the voltage became 0 V). The number of cycles from the start to the end of the cycle test was measured.

[0086] [Synthesis Example 1: Synthesis of Resin 1] Resin 1 was synthesized according to the following procedure. 1. A 500 mL separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was thoroughly dried. 2. 270.08 g of N-methylpyrrolidone was placed in a flask. 3. Then, 20.11 g of 9,9-bis(4-aminophenyl)fluorene (FDA) was added and allowed to completely dissolve. 4. While maintaining the temperature of the solution at 20±2°C, a total of 11.71 g of terephthalic acid dichloride was added in three portions. 5. The obtained solution was aged for 1 hour while keeping the temperature at 25±2°C to obtain a solution 1 containing resin 1. Resin 1 is an aramid resin containing a structural unit derived from FDA in the repeating unit, and is therefore also called FDA-Ar. Resin 1 has a repeating unit represented by the following formula (3).

[0087] Three types of resin 1 were obtained with the molar ratios of FDA to terephthalic acid dichloride being 1.001, 1.025, and 1.050. The intrinsic viscosities [η] of these resins 1 were 1.5, 0.7, and 0.5, the weight average molecular weights M were 190,000, 63,000, and 46,000, and the K was 2.2×10 -4 Therefore, α was about 0.7. The Ra of Resin 1 was about 12.5.

[0088] [ka]

[0089] [Synthesis Example 2: Synthesis of Resin 2] Resin 2 was synthesized according to the following procedure. 1. A 500 mL separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was thoroughly dried. 2. 204.02 g of N-methylpyrrolidone was placed in a flask. 3. Then, 15.10 g of 9,9-bis(4-amino-3-methylphenyl)fluorene (MeFDA) was added and allowed to completely dissolve. 4. While maintaining the temperature of the solution at 20±2°C, a total of 8.089 g of terephthalic acid dichloride was added in three portions. 5. The obtained solution was aged for 1 hour while keeping the temperature at 20±2°C to obtain a solution 2 containing resin 2. Resin 2 is an aramid resin containing a structural unit derived from MeFDA in the repeating unit, and is therefore also called MeFDA-Ar. Resin 2 has a repeating unit represented by the following formula (4).

[0090] Three types of resin 2 were obtained with the molar ratios of MeFDA to terephthalic acid dichloride being 1.001, 1.025, and 1.050. The intrinsic viscosities [η] of these resins 2 were 0.7, 0.6, and 0.5, the weight average molecular weights M were 63,000, 44,000, and 29,000, and the K was 1.2×10 -2 Therefore, α was about 0.4. The Ra of Resin 2 was about 11.9.

[0091] [ka]

[0092] [Synthesis Example 3: Synthesis of Resin 3] Resin 3 was synthesized according to the following procedure. 1. A 500 mL separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was thoroughly dried. 2. 199.89 g of N-methylpyrrolidone was placed in a flask. 3. Then, 15.51 g of 9,9-bis(4-amino-3-fluorophenyl)fluorene (FFDA) was added and allowed to completely dissolve. 4. While maintaining the temperature of the solution at 20±2°C, a total of 8.08 g of terephthalic acid dichloride was added in three portions. 5. The obtained solution was aged for 1 hour while keeping the temperature at 25±2°C to obtain a solution 3 containing resin 3. Resin 3 is also called FFDA-Ar because it is an aramid resin containing a structural unit derived from FFDA in the repeating unit. Resin 3 has a repeating unit represented by the following formula (5).

[0093] Three types of resin 3 were obtained with the molar ratios of FFDA to terephthalic acid dichloride being 1.001, 1.025, and 1.050. The intrinsic viscosities [η] of these resins 3 were 1.7, 0.8, and 0.5, the weight average molecular weights M were 240,000, 80,000, and 46,000, and the K was 2.1×10 -4 Therefore, α was about 0.7. The Ra of Resin 3 was about 11.6.

[0094] [ka]

[0095] [Synthesis Example 4: Synthesis of Resin 4] Resin 4 was synthesized according to the following procedure. 1. A 3-liter separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was thoroughly dried. 2. 2200g of N-methylpyrrolidone was charged into a flask. 151g of calcium chloride (dried at 200℃ for 2 hours) was added and the temperature was raised to 100℃. 3. After calcium chloride was completely dissolved, the temperature of the solution was returned to room temperature, and then 68.23 g of paraphenylenediamine was added and completely dissolved. 4. While maintaining the temperature of the solution at 20±2°C, a total of 124.61 g of terephthalic acid dichloride was added in three portions. 5. The obtained solution was aged for 1 hour while maintaining the temperature at 20±2°C to obtain a solution 4 containing resin 4. Resin 4 is poly(paraphenylene terephthalamide), i.e., para-aramid. Resin 4 has a repeating unit represented by the following formula (2). The α of resin 4 was determined to be about 1.25 according to Polymer Handbook 4th edition (ed. J. Brandup et.al., published by Wiley-Interscience in 1999). The Ra of resin 4 was about 18.4.

[0096] [ka]

[0097] Example 1 1. Solutions 1 and 4 were mixed so that the weight ratio of resin 1:resin 4 was 50:50. 100 parts by weight of aluminum oxide (average particle size: 0.013 μm) was added to 100 parts by weight of the total amount of resin contained in this mixed solution. The resulting mixture was diluted with NMP and uniformly dispersed using a pressure type disperser to obtain coating solution 1. 2. Polyethylene porous film (thickness: 10.0 μm, weight per unit area: 5.8 g / m 2 ) was coated with Coating Liquid 1. In this manner, Coated Material 1 was obtained. 3. The coated product 1 obtained in step 2 was treated in an oven at 50° C. and humidity of 70% for 2 minutes, thereby forming a porous layer 1 on the polyethylene porous film. 4. The porous layer 1 was washed with water and dried to obtain a laminated separator 1 provided with a porous layer 1. This porous layer corresponds to the first layer.

[0098] Example 2 A laminated separator 2 was obtained by carrying out the same operations as in Example 1, except that, instead of solutions 1 and 4, solutions 2 and 4 were mixed so that the weight ratio of resin 2:resin 4 was 50:50.

[0099] Example 3 A laminated separator 3 was obtained in the same manner as in Example 1, except that, instead of solutions 1 and 4, solutions 3 and 4 were mixed so that the weight ratio of resin 3:resin 4 was 50:50.

[0100] Comparative Example 1 The same operations as in Example 1 were carried out except that Solution 1 containing Resin 1 was not used, to obtain a laminated separator C1.

[0101] [Evaluation results] The compositions and evaluation results of the examples and comparative examples are shown in Table 1.

[0102] [Table 1]

[0103] Examples 1 to 3, which contained a resin having an α×Ra of 10 or less, had a larger number of cycles until short circuiting than Comparative Example 1, which did not contain the resin. Therefore, it was found that the separator according to one embodiment of the present invention can provide a nonaqueous electrolyte secondary battery with excellent cycle characteristics. Moreover, Examples 1 to 3 had a smaller air permeability than Comparative Example 1. [Industrial Applicability]

[0104] One aspect of the present invention can be used in a non-aqueous electrolyte secondary battery.

Claims

1. The index α calculated by the Mark-Houwink-Sakurada equation represented by the following formula (I) and the distance Ra (unit: MPa) between the Hansen solubility parameters of diethyl carbonate １／２ ) and a resin having a product α×Ra of 10 or less. [η]=KM α (I) (In the formula, [η] is the intrinsic viscosity of the resin (unit: dL / g), M is the weight average molecular weight of the resin, and K is a constant.)

2. 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the resin is an aromatic polyamide.

3. 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first layer comprises a filler.

4. Further comprising a second layer including a polyolefin-based resin; 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first layer is laminated on the second layer.

5. 5. The separator for a non-aqueous electrolyte secondary battery according to claim 4, further comprising an adhesive layer in addition to the first layer and the second layer.

6. A member for a non-aqueous electrolyte secondary battery, comprising a positive electrode, the separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, and a negative electrode, arranged in this order.

7. A non-aqueous electrolyte secondary battery comprising the separator for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 5.

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