JP2016081586A - Porous layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous layer capable of suppressing an increase in concentration of hydrofluoric acid in a nonaqueous electrolyte secondary battery.SOLUTION: There is provided a porous layer including an inorganic filler component having a calcium element content of 10 ppm by mass or more and 500 ppm by mass or less.SELECTED DRAWING: None

Description

  The present invention relates to a porous layer.

Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are widely used as batteries used in personal computers, mobile phones, portable information terminals, and the like. The non-aqueous electrolyte secondary battery may generate abnormal heat due to an internal short circuit or an external short circuit. In order to ensure safety during abnormal heat generation, a separator having a shutdown function is used. A polyolefin porous film is used as a separator having a shutdown function. Furthermore, a separator having a porous layer containing an inorganic filler and a binder resin has been proposed as a separator that ensures safety even in the case of severe abnormal heat generation.
Patent Document 1 describes a laminated porous film in which a porous layer containing cellulose ether and alumina fine particles is laminated on a polyolefin porous film.

JP 2004-227972 A

  In a non-aqueous electrolyte secondary battery equipped with a conventional separator, hydrofluoric acid may be produced as a by-product in the battery, and the member in the battery is corroded by the by-produced hydrofluoric acid, resulting in deterioration of battery characteristics. There was a thing.

The present invention includes the following inventions.
[1] A porous layer containing an inorganic filler component having a calcium element content of 10 ppm to 500 ppm by mass.
[2] The porous layer according to [1], wherein a ratio of the inorganic filler component exceeds 50% by volume with respect to a total of 100% by volume of solids contained in the porous layer.
[3] The porous layer according to [1] or [2], further including a binder resin, wherein the content of the inorganic filler component with respect to 100 parts by mass of the binder resin is 100 to 10,000 parts by mass.
[4] The porous layer according to any one of [1] to [3], wherein the content of the inorganic filler component with respect to 100 parts by mass of the binder resin is 500 to 10,000 parts by mass.
[5] The porous layer according to any one of [1] to [4], wherein the inorganic filler component contains a metal oxide.
[6] A laminated porous film comprising the porous layer according to any one of [1] to [5] on at least one surface of the substrate porous film.
[7] A separator provided with the porous layer according to any one of [1] to [5].
[8] A non-aqueous electrolyte secondary battery including the separator according to [7].

  The porous layer of the present invention can suppress an increase in the concentration of hydrofluoric acid in a non-aqueous electrolyte secondary battery including such a porous layer.

In a non-aqueous electrolyte secondary battery, it was brought into the non-aqueous electrolyte secondary battery by an electrolyte containing fluorine, such as lithium hexafluorophosphate, and battery components such as electrodes, separators, and electrolytes. It is known that hydrofluoric acid is produced by reaction with water.
When producing a non-aqueous electrolyte secondary battery, in order to reduce the amount of water brought in from such components, and to prevent mixing of water during production, the battery components are dried and the battery is produced in a dry environment. Actions to be taken are being taken.
However, it is virtually impossible to make the moisture brought into the non-aqueous electrolyte secondary battery zero, and there is a considerable amount of fluorination in the non-aqueous electrolyte secondary battery due to the reaction between water and the electrolyte containing fluorine. Hydrogen acid is produced.
According to the porous layer of the present invention, it is possible to suppress an increase in the concentration of hydrofluoric acid thus produced in the battery.

<Porous layer>
The porous layer of the present invention (hereinafter sometimes referred to as B layer) may be used alone as a separator, or may be laminated with other layers and used as a separator. Among these, a laminated porous film in which a B layer is laminated on at least one surface of a substrate porous film (hereinafter also referred to as A layer) is suitably used as a separator.

  Content of the calcium element contained in the inorganic filler component which B layer contains is 10 mass ppm or more and 500 mass ppm or less, Preferably, it is 300 mass ppm or less. When the content of the calcium element is 10 mass ppm or more, an increase in the concentration of hydrofluoric acid in the nonaqueous electrolyte secondary battery can be sufficiently suppressed. On the other hand, when it exceeds 500 mass ppm, there exists a possibility that decomposition | disassembly and gelatinization of electrolyte solution may be accelerated | stimulated.

  The content of calcium element contained in the inorganic filler component can be measured by performing ICP emission analysis after pressure sulfuric acid decomposition according to JIS R 9301.

The measurement of the calcium element content of the inorganic filler component is preferably performed after washing the inorganic filler. Examples of the cleaning method include a method of immersing an inorganic filler in diethyl carbonate (DEC), a method of immersing in N-methyl-2-pyrrolidone (NMP), a method of immersing in ion exchange water, and the like. These methods may be repeated or combined.
Moreover, these methods may be performed on the inorganic filler in a powder state, or may be performed on the inorganic filler after being formed into a porous layer or a laminated porous film.

The inorganic filler component includes one or more inorganic fillers. Inorganic fillers include talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, magnesium oxide, titanium oxide, alumina, mica, zeolite , Glass, calcium carbonate, calcium sulfate, calcium oxide and the like.
The inorganic filler is preferably a metal oxide from the viewpoint of heat resistance and chemical stability.

  Content of the calcium element of an inorganic filler component can be adjusted by combining the said inorganic filler. That is, by mixing an inorganic filler having a high calcium element content and an inorganic filler having a low calcium element content in an appropriate ratio, the calcium element content of the inorganic filler component is 10 mass ppm or more and 500 mass ppm. Adjust to the following.

  The ratio of the inorganic filler component contained in the B layer exceeds 50% by volume, preferably 70% by volume or more, and 90% by volume or more, with respect to the total 100% by volume of the solid content contained in the B layer. It is more preferable. In this specification, solid content means a substance which is solid at 25 ° C. and atmospheric pressure.

  The B layer preferably contains a binder resin. The binder resin is a resin having the ability to bind inorganic fillers. Further, by selecting the type and content of the binder resin contained in the B layer, the B layer can function as an adhesive layer or a heat-resistant layer. In the laminated porous film in which the B layer is laminated on the A layer, the B layer gives the laminated porous film functions such as adhesion to the electrode and maintaining the heated shape above the melting point of the A layer. can do. Hereinafter, specific examples of the B layer include an adhesive layer and a heat-resistant layer, but the B layer is not limited thereto.

  When the B layer is an adhesive layer, the non-aqueous electrolyte secondary battery obtained by laminating the positive electrode and the negative electrode via a separator having the B layer is provided between the separator and the positive electrode and between the separator and the negative electrode. The gaps can be satisfactorily bonded to the respective B layers.

  When the B layer is a heat-resistant layer, the separator provided with the B layer is excellent in shape stability at a high temperature and excellent in heat shape maintaining characteristics at a temperature equal to or higher than the melting point of the A layer.

  When layer B is an adhesive layer, the binder resin has excellent adhesion to the positive electrode and the negative electrode, is insoluble in the battery electrolyte, and is electrically stable within the battery usage range. A resin is preferred. Examples of such resins include polyvinylidene fluoride resins. Examples of the polyvinylidene fluoride resin include a homopolymer of vinylidene fluoride (that is, polyvinylidene fluoride), a copolymer of vinylidene fluoride and another copolymerizable monomer, and a mixture thereof.

When the B layer is a heat-resistant layer, the binder resin is preferably a resin that has excellent heat resistance, is insoluble in the battery electrolyte, and is electrochemically stable within the battery usage range. Examples of such resins include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polytetrafluoroethylene and polyvinylidene fluoride resins; fluorine-containing rubbers such as ethylene-tetrafluoroethylene copolymers; styrene-butadiene copolymers and the like Rubbers such as hydrides, methacrylate copolymers, acrylonitrile-acrylate copolymers, styrene-acrylate copolymers, polyvinyl acetate, ethylene-vinyl acetate-versaic acid vinyl polymers; polyphenylene ethers, Polysulfone, polyethersulfone, polyphenylene sulfide, aramid, polyetherimide, polyamideimide, polyetheramide, polyester and other resins having a melting point and glass transition temperature of 180 ° C. or higher; polyvinyl alcohol Le, polyethylene glycol, cellulose ethers, sodium alginate, polyacrylic acid, polyacrylamide, water-soluble polymers such as polymethacrylic acid, and the like.
Among the above polymers, water-soluble polymers are preferable in terms of process and environmental load. Among the water-soluble polymers, at least one selected from the group consisting of cellulose ether, polyvinyl alcohol and sodium alginate is preferable, and cellulose ether is particularly preferable.
Specific examples of the cellulose ether include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose, and the like. CMC and HEC excellent in chemical stability are preferable. In particular, CMC is preferable.

  The ratio of the binder resin contained in the B layer is more than 50% by volume, preferably 70% by volume or more, and 90% by volume or more, with respect to the total 100% by volume of the polymer contained in the B layer. Is more preferable, and it is further more preferable that it is 95 volume% or more.

  In addition to the binder resin, the B layer may contain other components as long as the function of the B layer is not impaired. Examples of other components include fine particles, a dispersant, a plasticizer, a pH adjuster, and a polymer.

  The content of the inorganic filler component with respect to 100 parts by mass of the binder resin is preferably 100 to 10000 parts by mass, more preferably 500 to 10000 parts by mass, and still more preferably 1000 to 5000 parts by mass. By containing 100 parts by mass or more of the inorganic filler component with respect to 100 parts by mass of the binder resin, the concentration increase of hydrofluoric acid in the non-aqueous electrolyte secondary battery can be further suppressed, and the inorganic filler component is 500 parts by mass. By including the above, the production of hydrofluoric acid can be further suppressed. If the content of the inorganic filler component with respect to 100 parts by mass of the binder resin is 10000 parts by mass or less, powder falling off of the inorganic filler from the B layer hardly occurs.

  The porosity of B layer is 30-90 volume% normally, Preferably it is 40-85 volume%. The pore diameter of the voids in the B layer is preferably 3 μm or less, more preferably 1 μm or less, as the diameter of the sphere when the hole is approximated to a sphere. When the average pore size is 3 μm or less, when a non-aqueous electrolyte secondary battery is manufactured, even if the carbon powder, which is the main component of the positive electrode or the negative electrode, or a small piece thereof falls off, it is difficult to short-circuit.

Although the thickness of B layer is based also on the function, it is 0.1 micrometer or more and 15 micrometers or less normally, Preferably it is 1 micrometer or more and 10 micrometers or less. When the thickness of the B layer is 10 μm or less, when a non-aqueous electrolyte secondary battery including the B layer is manufactured, good load characteristics are easily expressed, and when the thickness is 0.1 μm or more, the function of the B layer is expressed. Easy to do.
In the case of a separator having a plurality of B layers, for example, when the B layer is formed on both surfaces of the A layer, the thickness of the B layer is the total thickness of all the plurality of B layers.

<Substrate porous film>
The A layer has a structure having pores connected to the inside thereof, and gas and liquid can pass from one surface to the other surface.

  Examples of the substrate porous film include a polyolefin porous film and a nonwoven fabric made of polyethylene terephthalate or cellulose. Among these, a polyolefin porous film that can be melted to become nonporous (shutdown function) when the battery is abnormally heated is preferable.

  The ratio of the polyolefin to the solid content contained in the layer A is usually more than 50% by volume, preferably 70% by volume or more, more preferably 90% by volume or more, and more preferably 95% by volume or more. preferable.

The polyolefin contained in the A layer may contain a high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ to 15 × 10 ⁶ in that the strength of the entire laminated porous film including the A layer and the A layer is increased. preferable.

  Examples of the polyolefin include high molecular weight homopolymers or copolymers obtained by polymerizing olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. Among these, high molecular weight polyethylene mainly having ethylene and having a weight average molecular weight of 1,000,000 or more is preferable.

  The A layer may contain other components as long as the function of the A layer is not impaired. Examples of other components include fine particles, a dispersant, a plasticizer, a pH adjuster, and a polymer.

  The thickness of the A layer varies depending on the thickness of the B layer, but is preferably 4 μm or more and 40 μm or less, and more preferably 7 μm or more and 30 μm or less.

  The porosity of the A layer is preferably 20 to 80% by volume, more preferably 30 to 70% by volume. It is excellent in ion permeability as it is the said range, and when the laminated porous film is used as a separator for a nonaqueous electrolyte secondary battery, excellent characteristics are exhibited.

  The pore diameter of the void in the A layer is preferably 3 μm or less as the diameter of the sphere when the hole is approximated to a sphere in that it has excellent ion permeability and can prevent particles from entering from the positive electrode or the negative electrode. The following is more preferable.

As the basis weight of the layer A, the strength, film thickness, handling property and weight of the laminated porous film, and further, the weight energy density and volume energy density of the battery when the laminated porous film is used as a battery separator are increased. in that it can ^usually from ^{4g / m 2 ~15g / m 2} , preferably ^{5g / m 2 ~12g / m 2} .

  As a method for producing the A layer, for example, a method of adding a plasticizer to a thermoplastic resin to form a film, and then removing the plasticizer with an appropriate solvent (see JP-A-7-29563), and a thermoplastic resin Examples thereof include a method of removing fine particles after adding fine particles to form a film (see JP 2002-69221 A).

<Method of laminating layer B on at least one side of layer A>
As a method of laminating the B layer on at least one surface of the A layer, a method of separately preparing and bonding the A layer and the B layer, a coating liquid containing the component of the B layer and the medium (hereinafter referred to as B liquid) And a method of removing the medium by applying it on the A layer, and a method of preparing the B liquid and applying it on the A layer to remove the medium is preferable.

  The medium is a solvent or a dispersion medium, and any medium that can uniformly or stably dissolve or disperse the components of the B layer may be used. Examples of the medium include water, alcohols such as methanol, ethanol and isopropanol, acetone, toluene, xylene, hexane, N-methylpyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide and the like. The medium may be used alone or in combination as long as it is compatible.

  The application method for applying the B liquid to the A layer is not particularly limited as long as it can uniformly wet coat, and a conventionally known method can be adopted. Examples of the coating method include a capillary coating method, a spin coating method, a slit die coating method, a spray coating method, a roll coating method, a screen printing method, a flexographic printing method, a bar coater method, a gravure coater method, and a die coater method. .

  The thickness of the B layer can be controlled by adjusting the coating amount of the B liquid, the concentration of the binder resin in the B liquid, and the like. Usually, the application of the B liquid to the A layer and the removal of the medium from the B liquid applied to the A layer are continuously performed while conveying the A layer. By doing in this way, even if A layer is long, it is possible to laminate A layer and B layer continuously.

  The method for obtaining the liquid B is not particularly limited as long as it is a method capable of obtaining a homogeneous liquid B. Preferably, methods such as a mechanical stirring method, an ultrasonic dispersion method, a high pressure dispersion method, and a media dispersion method are used. Among these, the high-pressure dispersion method is preferable because it is easy to disperse the inorganic filler more uniformly. As long as there is no particular problem such as the occurrence of precipitates, the mixing order at that time may be mixed by adding the binder resin and the inorganic filler to the medium at one time, or may be added to the medium in any order. They may be mixed, or may be mixed after each is dissolved or dispersed in a medium.

  Removal of the medium from the B liquid applied on the A layer is preferable because drying is simple. Examples of the drying method include natural drying, air drying, heat drying, reduced pressure drying, and the like, and heat drying is preferable. Although depending on the medium to be used, the drying temperature is preferably 30 to 80 ° C, more preferably 50 to 80 ° C. If it is 30 degreeC or more, sufficient drying speed will be obtained, and if it is 80 degrees C or less, the lamination | stacking porous film with a favorable external appearance will be obtained.

  The thickness of the entire laminated porous film (A layer + B layer) is usually 5 to 50 μm, preferably 8 to 40 μm, and particularly preferably 9 to 30 μm. When the thickness of the entire laminated porous film is 5 μm or less, when a nonaqueous electrolyte secondary battery is produced using the laminated porous film as a separator, an initial failure due to an internal short circuit is likely to occur, and the thickness is 50 μm or more. And the capacity of the battery tends to be small.

  The laminated porous film may contain a porous film other than the A layer and the B layer, for example, a heat resistant film, an adhesive film, a protective film and the like as long as the object of the present invention is not impaired.

  The laminated porous film can be suitably used as a separator for a battery, particularly a non-aqueous electrolyte secondary battery such as a lithium secondary battery.

  When a non-aqueous electrolyte secondary battery is manufactured using a non-aqueous electrolyte secondary battery separator, the separator has high load characteristics, the separator exhibits an excellent shutdown function, and an excellent non-aqueous electrolyte secondary battery Become.

<Nonaqueous electrolyte secondary battery>
A nonaqueous electrolyte secondary battery usually includes a separator, electrodes (a positive electrode and a negative electrode), and a nonaqueous electrolyte. Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery that is a battery in which oxidation and reduction of lithium are performed at both the positive electrode and the negative electrode to store and release electric energy.

<Electrode>
In the electrode, an electrode active material and, if necessary, a conductive material are usually applied to at least one surface of a current collector via a binder.
Examples of the electrode active material include active materials capable of inserting and extracting lithium ions. The electrode active material includes a positive electrode active material and a negative electrode active material. An electrode including a positive electrode active material as an electrode active material is a positive electrode, and an electrode including a negative electrode active material is a negative electrode.

Examples of the positive electrode active material include a metal composite oxide containing at least one metal selected from the group consisting of lithium, iron, cobalt, nickel, and manganese. Preferably, Li _x MO ₂ (where M is One or more transition metals, preferably represents at least one of Co, Mn or Ni, and 1.10>x> 0.05) or Li _x M ₂ O ₄ (wherein M is one or more) Of transition metals, preferably Mn, with 1.10>x> 0.05.
), Specifically, LiCoO ₂ , LiNiO ₂ , Li _x Ni _y Co _(1-y) O ₂ (where 1.10>x> 0.05, 1>y> 0), and a positive electrode active material represented by LiMn ₂ O ₄ .

Examples of the negative electrode active material include various silicon oxides (SiO _{2 and the} like), carbonaceous materials, metal composite oxides, etc., preferably amorphous carbon, graphite, natural graphite, MCMB, pitch-based carbon fiber, polyacene, and the like. A _x M _y O _Z (wherein A is Li, M is at least one selected from Co, Ni, Al, Sn and Mn, O represents an oxygen atom, x, y and z are The numbers are in the range of 1.10 ≧ x ≧ 0.05, 4.00 ≧ y ≧ 0.85, and 5.00 ≧ z ≧ 1.5.).

As the conductive material, conductive carbon such as graphite, carbon black, acetylene black, ketjen black, activated carbon, etc .; graphite-based conductive material such as natural graphite, thermally expanded graphite, scale-like graphite, expanded graphite; vapor grown carbon fiber, etc. Carbon fiber; metal fine particles or metal fiber such as aluminum, nickel, copper, silver, gold, platinum; conductive metal oxide such as ruthenium oxide or titanium oxide; and high conductivity such as polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene Molecule and the like.
Carbon black, acetylene black and ketjen black are preferred in that the conductivity is effectively improved with a small amount.

  0-50 mass parts is preferable with respect to 100 mass parts of electrode active materials, and, as for content of an electrically conductive material, 0-30 mass parts is more preferable.

  Current collector materials include metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloys or stainless steel; carbon materials or activated carbon fibers, nickel, aluminum, zinc, copper, tin, lead or these And an electrically conductive film in which a conductive material is dispersed in a resin such as rubber or styrene-ethylene-butylene-styrene copolymer (SEBS).

Examples of the shape of the current collector include a foil, a flat plate, a mesh, a net, a lath, a punching or an emboss, or a combination thereof (for example, a mesh flat).
Concavities and convexities may be formed on the surface of the current collector by etching.

As the binder, a fluorine-based polymer such as polyvinylidene fluoride;
Polybutadiene, polyisoprene, isoprene-isobutylene copolymer, natural rubber, styrene-1,3-butadiene copolymer, styrene-isoprene copolymer, 1,3-butadiene-isoprene-acrylonitrile copolymer, styrene-1, 3-butadiene-isoprene copolymer, 1,3-butadiene-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate copolymer, styrene-acrylonitrile-1,3-butadiene-itaconic acid copolymer Polymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer, styrene-1,3-butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, acrylonitrile-1,3-butadiene -Methacrylic acid Diene series such as methyl methacrylate copolymer, styrene-1,3-butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer polymer;
Ethylene-propylene copolymer, ethylene-propylene-diene copolymer, polystyrene, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene ionomer, polyvinyl alcohol, vinyl acetate polymer, ethylene-vinyl alcohol copolymer, Olefin polymers such as chlorinated polyethylene, polyacrylonitrile, polyacrylic acid, polymethacrylic acid, chlorosulfonated polyethylene;
Styrene-ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-isoprene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-acrylic acid n A styrenic polymer such as a butyl-itaconic acid-methyl methacrylate-acrylonitrile copolymer;
Acrylate polymers such as polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, 2-ethylhexyl acrylate-methyl acrylate-acrylic acid-methoxypolyethylene glycol monomethacrylate;
Polyamide-based or polyimide-based polymers such as polyamide 6, polyamide 66, polyamide 11, polyamide 12, aromatic polyamide, polyimide;
Ester polymers such as polyethylene terephthalate and polybutylene terephthalate;
Cellulosic polymers such as carboxymethylcellulose, carboxyethylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, carboxyethylmethylcellulose (including salts such as ammonium salts and alkali metal salts thereof);
Styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-isoprene block copolymer, styrene-ethylene-propylene-styrene block Block copolymers such as copolymers;
And ethylene-vinyl chloride copolymer; ethylene-vinyl acetate copolymer; and other methyl methacrylate polymers.

<Non-aqueous electrolyte>
Examples of the nonaqueous electrolytic solution include an electrolytic solution in which an electrolyte such as a lithium salt containing a fluorine atom is dissolved in an organic solvent. Examples of the lithium salt containing a fluorine atom include LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiC (SO ₂ CF ₃ ) ₃ . These lithium salts may be used alone or in combination of two or more.

Examples of the organic solvent used in the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di (methoxy Carbonates such as carbonyloxy) ethane;
Ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran and 2-methyltetrahydrofuran;
Esters such as methyl formate, methyl acetate and γ-butyrolactone;
Nitriles such as acetonitrile and butyronitrile; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide;
Carbamates such as 3-methyl-2-oxazolidone;
Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone; and those obtained by introducing a fluorine substituent into the above organic solvent, and usually a mixture of two or more of these are used. .

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
<Pretreatment of inorganic filler component>
The operation of filtering the inorganic filler component after stirring in diethyl carbonate (DEC) is repeated three times to wash the inorganic filler component, and then dried at 120 ° C. The operation of filtering the obtained inorganic filler component after stirring in N-methyl-2-pyrrolidone (NMP) is repeated three times to further wash the inorganic filler component, and then drying at 120 ° C. The inorganic filler component is further washed by repeating the operation of stirring the obtained inorganic filler component in ion-exchanged water and then filtering three times, and drying at 120 ° C.

<Elemental analysis of inorganic filler components>
According to JIS R 9301, the concentration of calcium was quantified by ICP emission analysis after pressure sulfuric acid decomposition.

<Production test of hydrofluoric acid>
In a glove box filled with nitrogen gas, 1.0 g of an inorganic filler component was put in a bag in which an aluminum layer and a heat seal layer were laminated, and 2.0 mL of a nonaqueous electrolyte solution was further put therein. As the non-aqueous electrolyte, a mixed solution (3: 5: 2 (volume ratio)) of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate containing LiPF ₆ at a concentration of 1 mol / L was used. The bag was heat sealed to prepare a mixed sample of an inorganic filler and a non-aqueous electrolyte.
The mixed sample was allowed to stand in a ventilated dryer at 85 ° C. for 72 hours, and then cooled to room temperature. In a glove box filled with nitrogen gas, the nonaqueous electrolyte and inorganic filler are separated by centrifugation, and the content of hydrofluoric acid in the separated nonaqueous electrolyte is measured by a nuclear magnetic resonance spectrometer ( NMR) and measured.

<Example 1>
As the inorganic filler component, the inorganic filler component subjected to the above pretreatment was used. The content of calcium element in the inorganic filler component was 110 ppm. By the above method, the amount of hydrofluoric acid generated due to the reaction between the inorganic filler and the nonaqueous electrolytic solution was measured. The results are shown in Table 1.

<Example 2>
As the inorganic filler component, the inorganic filler component subjected to the above pretreatment was used. The content of calcium element in the inorganic filler component was 74 ppm. By the above method, the amount of hydrofluoric acid generated due to the reaction between the inorganic filler and the nonaqueous electrolytic solution was measured. The results are shown in Table 1.

<Example 3>
As the inorganic filler component, the inorganic filler component subjected to the above pretreatment was used. The content of calcium element in the inorganic filler component was 50 ppm. By the above method, the amount of hydrofluoric acid generated due to the reaction between the inorganic filler and the nonaqueous electrolytic solution was measured. The results are shown in Table 1.

<Comparative Example 1>
As the inorganic filler component, an inorganic filler component having a calcium element content of 0.6 ppm was used. By the above method, the amount of hydrofluoric acid generated due to the reaction between the inorganic filler and the nonaqueous electrolytic solution was measured. The results are shown in Table 1.

  It was found that when the inorganic filler component having a calcium element content of 10 ppm to 500 ppm was used, the content of hydrofluoric acid in the non-aqueous electrolyte after the test was low. That is, according to the non-aqueous electrolyte secondary battery including the separator including the porous layer containing such an inorganic filler component, the increase in the concentration of hydrofluoric acid in the non-aqueous electrolyte secondary battery is suppressed. Can do.

Claims (8)

  The porous layer containing the inorganic filler component whose content of calcium element is 10 mass ppm or more and 500 mass ppm or less.   The porous layer according to claim 1, wherein a ratio of the inorganic filler component exceeds 50% by volume with respect to a total of 100% by volume of solids contained in the porous layer.   Furthermore, the porous layer of Claim 1 or 2 which contains binder resin and content of the said inorganic filler component with respect to 100 mass parts of said binder resins is 100-10000 mass parts.   Content of the said inorganic filler component with respect to 100 mass parts of said binder resins is 500-10000 mass parts, The porous layer in any one of Claims 1-3.   The porous layer according to claim 1, wherein the inorganic filler component contains a metal oxide.   A laminated porous film comprising the porous layer according to any one of claims 1 to 5 on at least one side of the substrate porous film.   The separator provided with the porous layer in any one of Claims 1-5.   A nonaqueous electrolyte secondary battery comprising the separator according to claim 7.