JP2019216033A - Separator for nonaqueous secondary battery and the nonaqueous secondary battery - Google Patents

Abstract

To provide a separator for a nonaqueous secondary battery, capable of configuring the nonaqueous secondary battery which reduce an HF concentration and a gas generation amount, a battery characteristic, specifically, has an excellent cycle characteristic while having an excellent heat resistance.SOLUTION: A separator for a nonaqueous secondary battery, comprises: a porous base material; a binder resin provided on one surface or both surfaces of the porous base material; and a heat resistance porous layer containing a first inorganic particle made of an apatite, and a mean particle diameter (D50) of the first inorganic particle is 0.01 μm or more and 3.0 μm or less.SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous secondary battery separator and a non-aqueous secondary battery.

  Non-aqueous secondary batteries represented by lithium ion secondary batteries are widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, camcorders, and the like. Also, non-aqueous secondary batteries typified by lithium ion secondary batteries are characterized by their high energy density, and are being studied for use as batteries for power storage and for electric vehicles. With the spread of such non-aqueous secondary batteries, there is an increasing demand for enhancing the safety of the batteries.

  The separator, which is one of the members constituting the non-aqueous secondary battery, is required to have heat resistance that does not easily break even when the temperature inside the battery becomes high, in order to ensure the safety of the battery. As a separator having improved heat resistance, a separator provided with a porous layer containing inorganic particles on a porous substrate is known (for example, see Patent Documents 1 to 7).

JP 2011-044419 A JP-A-2015-115321 WO 2014/14836 pamphlet WO 2016/056289 pamphlet WO 2016/056288 pamphlet WO 2016/031492 pamphlet WO 2017/146237 pamphlet

As the non-aqueous electrolyte for a secondary battery, a non-aqueous electrolyte obtained by dissolving a fluorine-containing electrolyte such as LiPF _{6 in} a solvent such as cyclic carbonate, chain carbonate, or ether can obtain a high-voltage and high-capacity battery. However, LiPF ₆ is hydrolyzed even with a small amount of water to produce hydrogen fluoride (HF). Further, it is known that, in a conventional separator having a porous layer containing an inorganic filler, in a battery impregnated with an electrolytic solution, water derived from the filler acts on the electrolyte to generate HF. The HF concentration inside the secondary battery is further increased. Such a non-aqueous secondary battery having an increased HF concentration causes deterioration and is not always satisfactory in battery characteristics such as cycle characteristics, electric capacity, and storage stability. Further, in the case of a conventional separator provided with a porous layer containing an inorganic filler, when exposed to a high temperature for a long time, the electrolyte may be decomposed.
In view of the above-mentioned problems, a non-aqueous secondary battery capable of forming a non-aqueous secondary battery having excellent heat resistance, reduced HF concentration and gas generation amount in the battery, and excellent in battery characteristics, particularly excellent cycle characteristics. It is an object to provide a battery separator.

  Specific means for solving the above problems include the following aspects.

[1] A porous substrate, comprising: a heat-resistant porous layer provided on one or both surfaces of the porous substrate and containing first inorganic particles made of a binder resin and apatite; A separator for a non-aqueous secondary battery, wherein the average primary particle size (D50) of one inorganic particle is 0.01 μm or more and 3.0 μm or less.
[2] The non-aqueous secondary battery separator according to [1], wherein the first inorganic particles have an average primary particle size (D50) of 0.01 μm or more and 1.0 μm or less.
[3] The non-aqueous secondary battery separator according to [1] or [2], wherein the binder resin includes a polyvinylidene fluoride-based resin.
[4] The non-aqueous secondary battery separator according to [3], wherein the polyvinylidene fluoride resin has a weight average molecular weight of 500,000 to 3,000,000.
[5] The above, wherein the binder resin contains at least one selected from the group consisting of wholly aromatic polyamide, polyamideimide, poly-N-vinylacetamide, polyacrylamide, copolymerized polyether polyamide, polyimide and polyetherimide. The separator for a non-aqueous secondary battery according to [1] or [2].
[6] The non-aqueous secondary battery according to any one of [1] to [5], wherein a volume ratio of the first inorganic particles in the heat-resistant porous layer is 10% by volume to 90% by volume. Secondary battery separator.
[7] The above-mentioned [1] to [5], wherein the heat-resistant porous layer contains, in addition to the first inorganic particles, second inorganic particles different from the first inorganic particles. The separator for a non-aqueous secondary battery according to any one of the above.
[8] The non-aqueous system according to [7], wherein the content of the first inorganic particles is 5 to 95% by volume based on the total mass of the first inorganic particles and the second inorganic particles. Secondary battery separator.
[9] The above-mentioned [7] or [8], wherein the second inorganic particles include at least one selected from the group consisting of metal oxides, metal hydroxides, metal nitrides, metal salts, and clays. For non-aqueous secondary batteries.
[10] The non-aqueous secondary material according to [9], wherein the second inorganic particles include at least one selected from the group consisting of alumina, boehmite, zinc oxide, magnesium oxide, magnesium hydroxide, and barium sulfate. Battery separator.
[11] Any of the above [7] to [10], wherein a total volume ratio of the first inorganic particles and the second inorganic particles in the heat-resistant porous layer is 10% by volume to 90% by volume. 2. The separator for a non-aqueous secondary battery according to claim 1.
[12] A non-aqueous secondary battery separator according to any one of [1] to [11], provided between the positive electrode, the negative electrode, and the positive electrode and the negative electrode. Non-aqueous secondary battery that obtains electromotive force by doping and undoping.

  According to the present disclosure, a separator for a non-aqueous secondary battery capable of forming a non-aqueous secondary battery having excellent heat resistance, reduced HF concentration and gas generation amount in the battery, and excellent in battery characteristics, particularly excellent cycle characteristics. Is provided.

  Hereinafter, embodiments of the present disclosure will be described. These descriptions and examples illustrate the embodiments, and do not limit the scope of the embodiments.

  In the present disclosure, a numerical range indicated by using “to” indicates a range including numerical values described before and after “to” as a minimum value and a maximum value, respectively.

  In the present disclosure, the term “step” is included in the term as well as an independent step, even if it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

  In the present disclosure, when referring to the amount of each component in the composition, when a plurality of types of substances corresponding to each component are present in the composition, unless otherwise specified, the plurality of types of the components present in the composition are not specified. Means the total amount of the substance.

  In the present disclosure, the “MD direction” means a long direction in a porous substrate and a separator manufactured in a long shape, and the “TD direction” means a direction orthogonal to the “MD direction”. . In the present disclosure, the “MD direction” is also referred to as a “machine direction”, and the “TD direction” is also referred to as a “width direction”.

  In the present disclosure, when the stacking relationship of each layer constituting the separator is expressed by “above” and “below”, a layer closer to the base material is referred to as “below”, and a layer farther from the base material is referred to as “lower”. Above. "

  In the present disclosure, the notation “(meth) acryl” means “acryl” or “methacryl”.

  In the present disclosure, a “monomer unit” of a resin is a constituent unit of the resin, and means a constituent unit obtained by polymerizing a monomer.

  In the present disclosure, the heat-resistant resin refers to a resin having a melting point of 200 ° C. or higher, or a resin having no melting point and a decomposition temperature of 200 ° C. or higher. That is, the heat-resistant resin in the present disclosure is a resin that does not melt and decompose in a temperature range of less than 200 ° C.

<Non-aqueous secondary battery separator>
A non-aqueous secondary battery separator of the present disclosure (also referred to as a “separator” in the present disclosure) includes a porous substrate, and a heat-resistant porous layer provided on one or both surfaces of the porous substrate. .

  In the separator according to the present disclosure, the heat-resistant porous layer includes a binder resin and first inorganic particles made of apatite, and the first inorganic particles have an average primary particle size (D50) of 0.01 μm or more. 0 μm or less.

In the separator of the present disclosure, the apatite includes natural apatite and / or hydroxyapatite. Natural apatite is a basic calcium phosphate represented by a composition formula Ca ₅ (PO ₄ ) ₃ (F, Cl, OH), and hydroxyapatite (Hydoroxyapatite) is a basic calcium phosphate represented by a composition formula Ca ₅ (PO ₄ ) ₃ (OH). Has interchangeability. Specifically, calcium ion sites are exchanged for cations, phosphate groups and hydroxide ion sites are exchanged for anions, and especially hydroxide ion sites are easily exchanged for fluorine ions. Since such apatite has excellent HF adsorption ability, HF in the battery can be removed. Therefore, battery characteristics, particularly cycle characteristics, can be improved. Apatite is also less likely to decompose the electrolyte or the electrolyte than magnesium hydroxide or alumina as in the prior art, and is therefore less likely to generate gas. Therefore, by using the apatite particles as the inorganic filler of the heat-resistant porous layer, a separator is obtained in which gas generation hardly occurs and battery swelling and deformation hardly occur.

  In the separator of the present disclosure, the average primary particle size (D50) of the first inorganic particles made of apatite is 3.0 μm or less from the viewpoint of increasing the heat resistance of the heat-resistant porous layer. When the average primary particle size of the first inorganic particles is 3.0 μm or less, the heat resistance of the heat-resistant porous layer increases. The reason for this is that, due to the small particle size of the first inorganic particles, the packing density of the particles is increased, and the number of contact points between the first particles and the binder resin is increased. It is considered that shrinkage of the heat resistant porous layer is suppressed. It is also considered that the connection of a large number of particles having a small particle diameter makes it difficult for the heat-resistant porous layer to break when exposed to a high temperature.

  From the above viewpoint, the average primary particle size of the apatite particles is more preferably 1.0 μm or less, further preferably 0.6 μm or less, and particularly preferably 0.3 μm or less.

  In the separator of the present disclosure, the average primary particle size (D50) of the first inorganic particles contained in the heat-resistant porous layer is 0.01 μm or more. When the average primary particle size (D50) of the first inorganic particles is 0.01 μm or more, aggregation of the particles can be suppressed, and a highly uniform heat-resistant porous layer can be formed. In addition, from the viewpoint of heat resistance, the smaller the particle size of the first inorganic particles, the more preferable. However, the specific surface area of the inorganic particles is increased, and the problem that HF and gas are easily generated in the battery is likely to occur. However, in the present disclosure, since the apatite particles having an average primary particle size (D50) of 0.01 μm or more are used as the first inorganic particles, such a problem hardly occurs, and excellent heat resistance can be achieved at the same time. it can. From such a viewpoint, the average primary particle size (D50) of the first inorganic particles is more preferably equal to or greater than 0.05 μm, and still more preferably equal to or greater than 0.10 μm.

  Hereinafter, the details of the porous substrate and the heat-resistant porous layer included in the separator of the present disclosure will be described.

[Porous substrate]
In the present disclosure, the porous substrate means a substrate having pores or voids therein. Examples of such a substrate include a microporous membrane; a porous sheet made of a fibrous material, such as a nonwoven fabric or paper; and a composite porous sheet obtained by laminating one or more other porous layers on the microporous membrane or porous sheet. Quality sheet; and the like. In the present disclosure, a microporous film is preferable from the viewpoint of reducing the thickness and strength of the separator. A microporous membrane is a membrane that has a large number of micropores inside and has a structure in which these micropores are connected, so that gas or liquid can pass from one surface to the other. I do.

  As the material of the porous substrate, a material having electric insulation is preferable, and either an organic material or an inorganic material may be used.

  The porous substrate desirably contains a thermoplastic resin in order to provide a shutdown function to the porous substrate. The shutdown function refers to a function of dissolving the constituent materials and closing the pores of the porous base material to block the movement of ions and prevent thermal runaway of the battery when the battery temperature rises. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ° C. is preferable. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and among them, polyolefins are preferable.

  As the porous substrate, a microporous membrane containing polyolefin (referred to as “polyolefin microporous membrane” in the present disclosure) is preferable. As the polyolefin microporous membrane, for example, a polyolefin microporous membrane applied to a conventional battery separator can be mentioned, and it is preferable to select a membrane having sufficient mechanical properties and ion permeability from these.

  The microporous polyolefin membrane is preferably a microporous membrane containing polyethylene from the viewpoint of exhibiting a shutdown function, and the content of polyethylene is preferably 30% by mass or more based on the total mass of the microporous polyolefin membrane.

  The microporous polyolefin membrane may be a microporous membrane containing polypropylene from the viewpoint of having heat resistance that does not easily break when exposed to high temperatures.

  The polyolefin microporous membrane may be a polyolefin microporous membrane containing polyethylene and polypropylene, from the viewpoint of providing a shutdown function and heat resistance that does not easily break when exposed to high temperatures. Examples of such a polyolefin microporous membrane include a microporous membrane in which polyethylene and polypropylene are mixed in one layer. The microporous membrane preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene from the viewpoint of achieving both a shutdown function and heat resistance. Further, from the viewpoint of achieving both a shutdown function and heat resistance, a microporous polyolefin membrane having a laminated structure of two or more layers, at least one layer containing polyethylene, and at least one layer containing polypropylene is also preferable.

  As the polyolefin contained in the polyolefin microporous membrane, a polyolefin having a weight average molecular weight (Mw) of 100,000 to 5,000,000 is preferable. When the Mw of the polyolefin is 100,000 or more, sufficient mechanical properties can be imparted to the microporous membrane. On the other hand, when the Mw of the polyolefin is 5,000,000 or less, the shutdown characteristics of the microporous film are good, and the microporous film is easily formed.

  As a method for producing a microporous polyolefin membrane, a method in which a molten polyolefin resin is extruded from a T-die to form a sheet, which is crystallized, stretched, and then heat-treated to form a microporous membrane: liquid paraffin, etc. A method in which a polyolefin resin melted together with a plasticizer is extruded from a T-die, cooled, formed into a sheet, stretched, and then a plasticizer is extracted and heat-treated to form a microporous film.

  Examples of the fibrous porous sheet include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and heat resistant materials such as wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. And porous sheets made of fibrous material such as cellulose resin and the like, such as nonwoven fabric and paper.

  Examples of the composite porous sheet include a sheet in which a functional layer is laminated on a porous sheet made of a microporous membrane or a fibrous material. Such a composite porous sheet is preferable from the viewpoint that a further function can be added by the functional layer. Examples of the functional layer include a porous layer made of a heat-resistant resin and a porous layer made of a heat-resistant resin and an inorganic filler from the viewpoint of imparting heat resistance. Examples of the heat-resistant resin include one or more heat-resistant resins selected from wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Examples of the inorganic filler include metal oxides such as alumina; and metal hydroxides such as magnesium hydroxide. As a method of compounding, a method of applying a functional layer to a microporous film or a porous sheet, a method of bonding the functional layer with the microporous film or the porous sheet with an adhesive, A method of thermocompression bonding with a functional layer may be used.

  The surface of the porous substrate is subjected to various surface treatments within a range that does not impair the properties of the porous substrate for the purpose of improving wettability with a coating solution for forming a heat-resistant porous layer. May be. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[Properties of porous substrate]
The thickness of the porous substrate has good mechanical properties, and from the viewpoint of increasing the energy density of the battery, is preferably 25 μm or less, more preferably 15 μm or less, from the viewpoint of the production yield of the separator and the production yield of the battery. , Preferably 4 μm or more, more preferably 6 μm or more.

  The Gurley value (JIS P8117: 2009) of the porous substrate is preferably 50 seconds / 100 mL to 400 seconds / 100 mL from the viewpoint of ion permeability or suppression of short circuit of the battery.

The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining an appropriate film resistance and a shutdown function. The porosity of the porous substrate is determined according to the following calculation method. That is, the constituent materials are a, b, c, ..., n, the mass of each constituent material is Wa, Wb, Wc, ..., Wn (g / cm ² ), and the true density of each constituent material is da, , db, dc,..., dn (g / cm ³ ), and when the film thickness is t (cm), the porosity ε (%) can be obtained from the following equation.
ε = {1- (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100

  The average pore diameter of the porous substrate is preferably from 15 nm to 100 nm from the viewpoint of ion permeability or suppression of short circuit of the battery. The average pore size of the porous substrate is measured using a palm porometer according to ASTM E1294-89.

  The piercing strength of the porous substrate is preferably 200 gf (2.0 N) or more from the viewpoint of the production yield of the separator and the production yield of the battery. The piercing strength of the porous substrate is the maximum piercing load measured by performing a piercing test using a KAT-G5 KES-G5 handy compression tester under the conditions of a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec. (Gf).

[Heat-resistant porous layer]
In the separator of the present disclosure, the heat-resistant porous layer contains at least a binder resin and first inorganic particles made of apatite. The heat-resistant porous layer is a layer having a large number of micropores and allowing gas or liquid to pass from one surface to the other surface.

  In the separator of the present disclosure, the heat-resistant porous layer may be on only one surface of the porous substrate, or may be on both surfaces of the porous substrate. When the heat-resistant porous layer is on both sides of the porous substrate, the heat resistance of the separator is more excellent, and the safety of the battery can be further improved. In addition, the separator is less likely to curl, and is excellent in handleability during battery production. When the heat-resistant porous layer is on only one side of the porous substrate, the separator has more excellent ion permeability. Further, the thickness of the entire separator can be suppressed, and a battery having a higher energy density can be manufactured.

  The kind of the binder resin of the heat resistant porous layer is not particularly limited as long as it can bind the inorganic particles. The binder resin for the heat-resistant porous layer is preferably a heat-resistant resin (a resin having a melting point of 200 ° C. or higher, or a resin having no melting point and a decomposition temperature of 200 ° C. or higher). The binder resin for the heat-resistant porous layer is preferably a resin that is stable to the electrolytic solution and electrochemically stable. As the binder resin, one type may be used alone, or two or more types may be used in combination.

  The binder resin of the heat-resistant porous layer preferably has adhesiveness to the electrode of the battery, and the type of the binder resin may be selected according to the composition of the positive electrode or the negative electrode. When the heat resistant porous layer is on both sides of the porous substrate, the binder resin of one heat resistant porous layer and the binder resin of the other heat resistant porous layer may be the same or different.

  As the binder resin for the heat-resistant porous layer, a polymer having a polar functional group or an atomic group (for example, a hydroxyl group, a carboxy group, an amino group, an amide group, or a carbonyl group) is preferable.

  As the binder resin for the heat-resistant porous layer, specifically, polyvinylidene fluoride resin, wholly aromatic polyamide, polyamideimide, polyimide, polyether sulfone, polysulfone, polyether ketone, polyketone, polyetherimide, poly- Examples include N-vinylacetamide, polyacrylamide, copolymerized polyether polyamide, fluorine-based rubber, acrylic resin, styrene-butadiene copolymer, cellulose, and polyvinyl alcohol.

  The binder resin for the heat-resistant porous layer may be a particulate resin, and examples thereof include resin particles such as polyvinylidene fluoride resin, fluorine rubber, and styrene-butadiene copolymer. The binder resin of the heat-resistant porous layer may be a water-soluble resin such as cellulose or polyvinyl alcohol. When using a particulate resin or a water-soluble resin as a binder resin for the heat-resistant porous layer, a coating liquid is prepared by dispersing or dissolving the binder resin in water, and a dry coating method is performed using the coating liquid. A heat-resistant porous layer can be formed on a porous substrate.

  As the binder resin of the heat-resistant porous layer, from the viewpoint of excellent heat resistance, a wholly aromatic polyamide, polyamideimide, poly-N-vinylacetamide, polyacrylamide, copolymerized polyether polyamide, polyimide, or polyetherimide is preferable. . These resins are preferably heat-resistant resins (resins having a melting point of 200 ° C. or higher, or resins having no melting point and a decomposition temperature of 200 ° C. or higher).

  Among heat-resistant resins, a wholly aromatic polyamide is preferable from the viewpoint of durability. The wholly aromatic polyamide may be meta type or para type. Among the wholly aromatic polyamides, meta-type wholly aromatic polyamides are preferred from the viewpoint of easy formation of the porous layer and excellent oxidation-reduction resistance in the electrode reaction. A small amount of an aliphatic monomer may be copolymerized in the wholly aromatic polyamide.

  As the wholly aromatic polyamide used as the binder resin of the heat-resistant porous layer, specifically, polymetaphenylene isophthalamide, polyparaphenylene terephthalamide or copolyparaphenylene • 3.4′oxydiphenylene · terephthalamide is preferable. And polymetaphenylene isophthalamide are more preferred.

  As the binder resin of the heat resistant porous layer, polyvinylidene fluoride resin (PVDF resin) is preferable from the viewpoint of adhesiveness to the electrode.

  PVDF-based resin is suitable as a binder resin for the heat-resistant porous layer from the viewpoint of adhesiveness to the electrode. When the heat-resistant porous layer contains a PVDF-based resin, the adhesion between the heat-resistant porous layer and the electrode is improved, and as a result, the strength (cell strength) of the battery is improved.

  Examples of PVDF-based resins include homopolymers of vinylidene fluoride (ie, polyvinylidene fluoride); copolymers of vinylidene fluoride and other monomers (polyvinylidene fluoride copolymer); polyvinylidene fluoride and polyvinylidene fluoride A mixture of copolymers. Examples of monomers copolymerizable with vinylidene fluoride include, for example, tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, trichloroethylene, vinyl fluoride, perfluoroalkyl vinyl ether, (meth) acrylic acid, and the like. Carboxyl group-containing monomer, methyl (meth) acrylate, (meth) acrylate, vinyl acetate, vinyl chloride, acrylonitrile and the like. These monomers may be used alone or in a combination of two or more.

  As the PVDF-based resin contained in the heat-resistant porous layer, from the viewpoint of the adhesion to the electrode, a PVDF-based resin containing a vinylidene fluoride monomer unit (VDF unit) and a hexafluoropropylene monomer unit (HFP unit) is used. A polymer (VDF-HFP copolymer) is more preferred. When the VDF-HFP copolymer is used as the binder resin for the heat-resistant porous layer, the crystallinity and heat resistance of the binder resin can be easily controlled within an appropriate range, and the heat resistance during the hot pressing process for bonding the separator to the electrode is improved. Flow of the porous layer can be suppressed.

  The VDF-HFP copolymer contained in the heat-resistant porous layer may be a copolymer comprising only VDF units and HFP units, or a copolymer containing other monomer units other than VDF units and HFP units. May be. Other monomers include, for example, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, trichloroethylene, vinyl fluoride and the like.

  The content of the VDF unit in the VDF-HFP copolymer is preferably at least 91 mol% from the viewpoint of controlling the crystallinity and heat resistance of the VDF-HFP copolymer within an appropriate range.

  The content of the HFP unit in the VDF-HFP copolymer is preferably at least 0.2 mol%, more preferably at least 0.5 mol%, from the viewpoint of swelling moderately when the electrolyte is impregnated. Is more preferable, and from the viewpoint of being difficult to dissolve in the electrolytic solution, it is preferably at most 7 mol%, more preferably at most 6 mol%.

  The PVDF resin contained in the heat resistant porous layer preferably has a weight average molecular weight (Mw) of 500,000 to 3,000,000. When the Mw of the PVDF-based resin is 500,000 or more, a heat-resistant porous layer having mechanical properties that can withstand hot pressing when the separator is bonded to the electrode is easily obtained. The adhesiveness between them is improved. In this respect, the Mw of the PVDF-based resin is more preferably equal to or greater than 550,000, and still more preferably equal to or greater than 1,000,000. On the other hand, when the Mw of the PVDF-based resin is 3,000,000 or less, the viscosity at the time of molding the heat-resistant porous layer does not become too high, the moldability and crystal formation are improved, and the heat-resistant porous layer is easily made porous. . From this viewpoint, the Mw of the PVDF-based resin is more preferably 2.5 million or less, and still more preferably 2.3 million or less.

  The PVDF-based resin contained in the heat-resistant porous layer preferably has an acid value of 2 mgKOH / g to 30 mgKOH / g. The acid value of the PVDF-based resin can be controlled, for example, by introducing a carboxy group into the PVDF-based resin. The introduction of the carboxy group into the PVDF resin and the amount of the carboxy group to be introduced depend on the monomer having a carboxy group as a polymerization component of the PVDF resin (for example, (meth) acrylic acid, (meth) acrylic acid ester, maleic acid, maleic anhydride, , Maleic acid ester, and their fluorine-substituted products) and adjusting the polymerization ratio thereof.

  In the separator of the present disclosure, the heat-resistant porous layer may include another resin other than the binder resin. The other resin is used for the purpose of improving the adhesiveness of the heat-resistant porous layer to the electrode and adjusting the ion permeability or the membrane resistance of the heat-resistant porous layer. Other resins include, for example, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl butyral, polyvinyl pyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc. ).

  In the separator of the present disclosure, the total content of other resins other than the binder resin contained in the heat-resistant porous layer is preferably 5% by mass or less based on the total amount of the resin contained in the heat-resistant porous layer. It is more preferably at most 1% by mass, more preferably at most 1% by mass.

  The separator of the present disclosure contains first inorganic particles made of apatite in the heat-resistant porous layer. The average primary particle diameter of the first inorganic particles contained in the heat-resistant porous layer is 0.01 μm or more and 3.0 μm or less. The lower limit is more preferably 0.05 μm or more, further preferably 0.10 μm or more, and the upper limit is more preferably 2 μm or less, further preferably 1 μm or less.

  The shape of the first inorganic particles is not limited, and may be spherical, elliptical, plate-like, needle-like, or amorphous. The first inorganic particles are preferably non-aggregated primary particles from the viewpoint of increasing the packing density of the particles and increasing the heat resistance.

  From the viewpoint of heat resistance, the volume ratio of the first inorganic particles in the heat-resistant porous layer is preferably 10% by volume or more, more preferably 30% by volume or more, and further preferably 50% by volume or more. The volume ratio of the first inorganic particles in the heat-resistant porous layer is preferably 90% by volume or less, more preferably 85% by volume or less, and is preferably 80% by volume, from the viewpoint that the heat-resistant porous layer is hardly peeled off from the porous substrate. % Is more preferable.

In the separator according to the present disclosure, the heat-resistant porous layer may include, in addition to the first inorganic particles, second inorganic particles different from the first inorganic particles.
In general, non-aqueous secondary battery separators have conventionally contained inorganic particles for the purpose of enhancing the heat resistance and strength of the battery, but inorganic particles such as metal hydroxides and metal oxides are particularly electrolytes. In some cases, impairing the stability of the solution and inducing the decomposition of the electrolyte solution and the electrolyte to generate gas. However, in the separator of the present disclosure, since the heat-resistant porous layer contains apatite particles having a specific particle size as the first inorganic particles, the heat-resistant porous layer is caused by the second inorganic particles such as a metal hydroxide and a metal oxide. The generation of gas accompanying the decomposition of the electrolytic solution and the electrolyte induced by the gas is suppressed, and the swelling (deformation of the battery) due to the generated gas is suppressed.

  The second inorganic particles are added to the heat-resistant porous layer to impart a desired function, for example, selected from the group consisting of metal oxides, metal hydroxides, metal nitrides, metal salts and clays. It is preferable to include at least one of them. Examples of the metal oxide include silica, alumina, titania, zirconia, and magnesium oxide. Examples of the metal hydroxide include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide. Examples of the metal nitride include boron nitride and silicon nitride. Examples of the metal salt include carbonates such as calcium carbonate and magnesium carbonate; sulfates such as calcium sulfate and barium sulfate. Examples of the clay include clay minerals such as calcium silicate and talc. As the second inorganic particles, particles of a metal hydroxide, particles of a metal oxide or a metal salt are preferable from the viewpoints of stability to an electrolytic solution and electrochemical stability. In particular, the second inorganic particles are selected from the group consisting of alumina, boehmite, zinc oxide, magnesium oxide, magnesium hydroxide, and barium sulfate from the viewpoint that the effect of preventing HF / gas generation by the first inorganic particles is suitably obtained. It is preferable to include at least one of them. Other inorganic particles may be surface-modified with a silane coupling agent or the like.

  The shape of the second inorganic particles is not limited, and may be spherical, elliptical, plate-like, needle-like, or irregular. The second inorganic particles are preferably non-aggregated primary particles. As the second inorganic particles, one type may be used alone, or two or more types may be used in combination.

  The average primary particle size (D50) of the second inorganic particles is preferably 0.01 μm to 5 μm. The lower limit is more preferably 0.1 μm or more, and the upper limit is more preferably 1 μm or less.

  In the heat-resistant porous layer, the content of the first inorganic particles is preferably 5 to 95% by volume based on the total mass of the first inorganic particles and the second inorganic particles. When the content of the first inorganic particles is 5% by volume or more, a remarkable effect of suppressing the generation of gas accompanying the decomposition of the electrolyte and the electrolyte induced by the heat-resistant filler can be obtained. From such a viewpoint, the content of the first inorganic particles is more preferably 20% by volume or more, further preferably 30% by volume or more. On the other hand, when the content of the first inorganic particles is 90% by volume or less, it is preferable because a shape effect due to the second inorganic particles can be imparted. From such a viewpoint, the content of the first inorganic particles is more preferably equal to or less than 90% by volume, and still more preferably equal to or less than 85% by volume.

  From the viewpoint of heat resistance, the total volume ratio of the first inorganic particles and the second inorganic particles in the heat-resistant porous layer is preferably 10% by volume or more, more preferably 20% by volume or more, and 30% by volume or more. Is more preferred. The total volume ratio of the first inorganic particles and the second inorganic particles is preferably 90% by volume or less, more preferably 85% by volume or less, from the viewpoint that the heat-resistant porous layer is difficult to peel off from the porous substrate. More preferably, it is not more than% by volume.

  In the separator of the present disclosure, the heat-resistant porous layer may further contain an organic filler. Examples of the organic filler include cross-linked poly (meth) acrylic acid, cross-linked poly (meth) acrylate, cross-linked polysilicone, cross-linked polystyrene, cross-linked polydivinylbenzene, cross-linked styrene-divinylbenzene copolymer, melamine resin, phenol Particles composed of a crosslinked polymer such as resin and benzoguanamine-formaldehyde condensate; particles composed of a heat-resistant polymer such as polysulfone, polyacrylonitrile, aramid, polyacetal, and the like. One of these organic fillers may be used alone, or two or more thereof may be used in combination.

  In the separator of the present disclosure, the heat-resistant porous layer may include additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming agent, and a pH adjuster. The dispersant is added to a coating solution for forming a heat-resistant porous layer for the purpose of improving dispersibility, coating property, or storage stability. Wetting agents, defoamers, and pH adjusters are used in coating liquids for forming heat-resistant porous layers, for example, for the purpose of improving compatibility with a porous base material, air entrapment in the coating liquid. It is added for the purpose of suppressing or adjusting the pH.

[Characteristics of heat-resistant porous layer]
The thickness of the heat-resistant porous layer is preferably 0.5 μm or more on one side, more preferably 1 μm or more on one side, from the viewpoint of heat resistance or handling properties of the separator, and more preferably 1 μm or more on one side, from the viewpoint of separator handling properties or battery energy density. It is preferably 5 μm or less, more preferably 4 μm or less on one side. The thickness of the heat-resistant porous layer is preferably 1 μm or more, more preferably 2 μm or more, and more preferably 10 μm, even when the heat-resistant porous layer is on only one side or both sides of the porous substrate. Or less, more preferably 8 μm or less.

The mass of the heat-resistant porous layer per unit area is preferably 1.0 g / m ² or more, more preferably 2.0 g / m ² or more, as a total of both surfaces, from the viewpoint of heat resistance or handleability of the separator. from the viewpoint of handleability or the battery energy density is preferably 10.0 g / ^{m 2} or less as the sum of two-sided, 8.0 g / ^{m 2} or less is more preferable.

  When the heat-resistant porous layer is on both surfaces of the porous substrate, the difference between the one surface and the other surface related to the mass of the heat-resistant porous layer is, from the viewpoint of suppressing the curl of the separator, relative to the total of both surfaces. Is preferably not more than 20% by mass.

  The porosity of the heat-resistant porous layer is preferably 30% or more from the viewpoint of ion permeability of the separator, and is preferably 80% or less from the viewpoint of thermal dimensional stability of the separator. The method for determining the porosity of the heat-resistant porous layer is the same as the method for determining the porosity of the porous substrate.

  The average pore size of the heat-resistant porous layer is preferably from 10 nm to 200 nm. When the average pore diameter is 10 nm or more, when the heat-resistant porous layer is impregnated with the electrolytic solution, the pores are unlikely to be blocked even if the resin contained in the heat-resistant porous layer swells. When the average pore size is 200 nm or less, the uniformity of ion transfer is high, and the cycle characteristics and load characteristics of the battery are excellent.

The average pore size (nm) of the heat-resistant porous layer is calculated by the following equation, assuming that all pores are cylindrical.
d = 4V / S
The average pore diameter in the formula, d is the heat-resistant porous layer (diameter), V is the pore volume of the heat resistant porous layer 1 m ² per, S is indicative of the air hole surface area of 1 m ² per heat resistant porous layer.
Pore volume V of the heat-resistant porous layer 1 m ² per is calculated from porosity of the heat resistant porous layer.
Pore surface area S of the heat-resistant porous layer 1 m ² per is determined by the following methods.
First, a specific surface area of the porous substrate (m 2 ^{/ g)} and specific surface area of the separator (m 2 ^{/ g),} by applying the BET equation to the nitrogen gas adsorption method, it is calculated from the nitrogen gas adsorption. The specific surface area (m ² / g) is multiplied by each basis weight (g / m ² ) to calculate the pore surface area per 1 m ² . Then, by subtracting the pore surface area of the porous substrate 1 m ² per the pore surface area per separator 1 m ^2, to calculate the pore surface area S of the heat-resistant porous layer 1 m ² per.

  The peel strength between the porous substrate and the heat-resistant porous layer is preferably 0.1 N / 10 mm or more, more preferably 0.2 N / 10 mm or more, and 0.3 N or more, from the viewpoint of the adhesive strength of the separator to the electrode. / 10 mm or more is more preferable. From the above viewpoint, the peel strength between the porous substrate and the heat-resistant porous layer is preferably as high as possible, but the peel strength is usually 2 N / 10 mm or less. When the separator of the present disclosure has a heat-resistant porous layer on both surfaces of the porous substrate, the peel strength between the porous substrate and the heat-resistant porous layer is within the above range on both surfaces of the porous substrate. Preferably, there is.

[Characteristics of separator]
The thickness of the separator of the present disclosure is preferably 6 μm or more, more preferably 7 μm or more, from the viewpoint of mechanical strength of the separator, and is preferably 25 μm or less, more preferably 20 μm or less, from the viewpoint of battery energy density.

  The piercing strength of the separator of the present disclosure is preferably 160 gf (1.6 N) to 1000 gf (9.8 N), and is preferably 200 gf (2.0 N) to 600 gf (5N) from the viewpoint of mechanical strength of the separator or short-circuit resistance of the battery. .9N) is more preferred. The method for measuring the piercing strength of the separator is the same as the method for measuring the piercing strength of the porous substrate.

  The porosity of the separator according to the present disclosure is preferably 30% to 60% from the viewpoint of the handleability, ion permeability, and mechanical strength of the separator.

  The Gurley value (JIS P8117: 2009) of the separator of the present disclosure is preferably 50 seconds / 100 mL to 800 seconds / 100 mL, and more preferably 100 seconds / 100 mL to 450 seconds / 100 mL from the viewpoint of the balance between mechanical strength and ion permeability. More preferred.

  In the separator of the present disclosure, from the viewpoint of ion permeability, the value obtained by subtracting the Gurley value of the porous base material from the Gurley value of the separator is preferably 300 seconds / 100 mL or less, more preferably 150 seconds / 100 mL or less, and 100 seconds. / 100 mL or less is more preferable. Although the lower limit of the value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the separator is not particularly limited, it is usually 10 seconds / 100 mL or more in the separator of the present disclosure.

The film resistance of the separator of the present disclosure, in view of the load characteristics of the ^{battery, 1Ω · cm 2 ~10Ω · cm} 2 is preferred. Here, the membrane resistance of the separator is a resistance value in a state where the separator is impregnated with the electrolytic solution, and 1 mol / L LiBF ₄ -propylene carbonate: ethylene carbonate (mass ratio 1: 1) is used as the electrolytic solution. It is a value measured by the alternating current method at 20 ° C.

  The curvature of the separator of the present disclosure is preferably from 1.2 to 2.8 from the viewpoint of ion permeability.

  The amount of water (based on mass) contained in the separator of the present disclosure is preferably 1000 ppm or less. The smaller the water content of the separator, the more the reaction between the electrolytic solution and water is suppressed when the battery is configured, the more the gas generation in the battery can be suppressed, and the cycle characteristics of the battery are improved. In this respect, the water content of the separator is more preferably equal to or less than 800 ppm, and still more preferably equal to or less than 500 ppm.

  The separator of the present disclosure has an area shrinkage ratio of preferably 35% or less, more preferably 30% or less, and still more preferably 20% or less when heat-treated at 135 ° C. for 0.5 hour.

  In the separator of the present disclosure, the shrinkage in the MD direction when heat-treated at 135 ° C. for 0.5 hour is preferably 25% or less, more preferably 20% or less, still more preferably 15% or less, and still more preferably 10% or less. .

  The separator of the present disclosure has a TD shrinkage ratio of preferably 25% or less, more preferably 20% or less, still more preferably 15% or less, even more preferably 10% or less when heat-treated at 135 ° C. for 0.5 hour. .

  Shrinkage rate when the separator of the present disclosure is heat-treated is controlled by, for example, the content of inorganic particles in the heat-resistant porous layer, the thickness of the heat-resistant porous layer, the porosity of the heat-resistant porous layer, and the like. obtain.

  The separator of the present disclosure may further have another layer other than the porous substrate and the heat-resistant porous layer. Other layers include an adhesive layer provided as an outermost layer mainly for the purpose of bonding to an electrode.

[Separator manufacturing method]
The separator of the present disclosure can be manufactured, for example, by forming a heat-resistant porous layer on a porous substrate by a wet coating method or a dry coating method. In the present disclosure, the wet coating method is a method of solidifying a coating layer in a coagulation liquid, and the dry coating method is a method of drying and solidifying a coating layer. An embodiment of the wet coating method will be described below.

  The wet coating method is a method of coating a coating liquid containing a binder resin and inorganic particles on a porous base material, immersing the coating liquid in a coagulation liquid to solidify the coating layer, withdrawing from the coagulation liquid, washing with water, and drying. It is.

  The coating liquid for forming a heat-resistant porous layer is prepared by dissolving or dispersing a binder resin and inorganic particles in a solvent. In the coating liquid, other components other than the binder resin and the inorganic particles are dissolved or dispersed as necessary.

  The solvent used for preparing the coating liquid includes a solvent that dissolves the binder resin (hereinafter, also referred to as “good solvent”). Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide.

  The solvent used for preparing the coating liquid preferably contains a phase separating agent that induces phase separation from the viewpoint of forming a porous layer having a favorable porous structure. Therefore, the solvent used for preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent. It is preferable that the phase separation agent is mixed with a good solvent in an amount within a range that ensures a viscosity suitable for coating. Examples of the phase separating agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

  From the viewpoint of forming a good porous structure, the solvent used for preparing the coating liquid is a mixed solvent of a good solvent and a phase separating agent, which contains the good solvent in an amount of 60% by mass or more, and contains 40% by mass of the phase separating agent. % Is preferable.

  The resin concentration of the coating liquid is preferably 1% by mass to 20% by mass from the viewpoint of forming a good porous structure. The inorganic particle concentration of the coating liquid is preferably 2% by mass to 50% by mass from the viewpoint of forming a good porous structure.

  Examples of means for applying the coating liquid to the porous substrate include a Meyer bar, a die coater, a reverse roll coater, a roll coater, and a gravure coater. When the heat-resistant porous layer is formed on both surfaces of the porous substrate, it is preferable from the viewpoint of productivity to apply the coating liquid to the porous substrate simultaneously on both surfaces.

  The solidification of the coating layer is performed by immersing the porous substrate on which the coating layer is formed in a coagulation liquid, and solidifying the binder resin while inducing phase separation in the coating layer. Thus, a laminate including the porous substrate and the heat-resistant porous layer is obtained.

  The coagulation liquid generally contains water and a good solvent and a phase separation agent used for preparing the coating liquid. The mixing ratio of the good solvent and the phase separation agent is preferably adjusted to the mixing ratio of the mixed solvent used for preparing the coating liquid in terms of production. The content of water in the coagulation liquid is preferably from 40% by mass to 90% by mass from the viewpoint of formation of a porous structure and productivity. The temperature of the coagulating liquid is, for example, 20 ° C to 50 ° C.

  After the coating layer is solidified in the coagulation liquid, the laminate is pulled out of the coagulation liquid and washed with water. By washing with water, the coagulating liquid is removed from the laminate. Further, water is removed from the laminate by drying. Washing is performed, for example, by transporting the laminate in a water bath. Drying is performed by, for example, transporting the laminate in a high-temperature environment, exposing the laminate to air, bringing the laminate into contact with a heat roll, and the like. The drying temperature is preferably from 40C to 80C.

  The separator of the present disclosure can also be manufactured by a dry coating method. The dry coating method is a method of forming a heat-resistant porous layer on a porous substrate by applying a coating solution to a porous substrate, drying the coating layer and volatilizing and removing the solvent. . However, the dry coating method is more preferable than the wet coating method since the coated layer after drying tends to be denser than the wet coating method, so that a good porous structure can be obtained.

  The separator of the present disclosure can also be manufactured by a method in which a heat-resistant porous layer is formed as an independent sheet, and the heat-resistant porous layer is stacked on a porous base material and composited by thermocompression bonding or an adhesive. As a method for producing the heat-resistant porous layer as an independent sheet, there is a method of forming the heat-resistant porous layer on the release sheet by applying the above-mentioned wet coating method or dry coating method.

<Non-aqueous secondary battery>
The non-aqueous secondary battery of the present disclosure is a non-aqueous secondary battery that obtains an electromotive force by doping / dedoping lithium, and includes a positive electrode, a negative electrode, and a non-aqueous secondary battery separator of the present disclosure. The dope means occlusion, support, adsorption, or insertion, and means a phenomenon in which lithium ions enter an active material of an electrode such as a positive electrode.

  The nonaqueous secondary battery of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is enclosed in an exterior material together with an electrolytic solution. The nonaqueous secondary battery of the present disclosure is suitable for a nonaqueous electrolyte secondary battery, particularly a lithium ion secondary battery.

  The nonaqueous secondary battery of the present disclosure is excellent in safety because the separator of the present disclosure suppresses gas generation inside the battery and has excellent heat resistance. Further, since the separator of the present disclosure reduces the HF concentration inside the battery, the separator is also excellent in battery characteristics such as cycle characteristics.

  Hereinafter, exemplary embodiments of the positive electrode, the negative electrode, the electrolytic solution, and the exterior material included in the nonaqueous secondary battery of the present disclosure will be described.

An example of the embodiment of the positive electrode includes a structure in which an active material layer including a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further include a conductive aid. Examples of the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _{1 / 3} O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _1/2 Ni _1/2 O ₂ , LiAl _1/4 Ni _3/4 O _{2 and the} like. Examples of the binder resin include a polyvinylidene fluoride resin, a styrene-butadiene copolymer, and the like. Examples of the conductive aid include carbon materials such as acetylene black, Ketjen black, and graphite powder. Examples of the current collector include an aluminum foil, a titanium foil, and a stainless steel foil having a thickness of 5 μm to 20 μm.

In the non-aqueous secondary battery of the present disclosure, the heat-resistant porous layer also has excellent oxidation resistance, so that the heat-resistant porous layer is disposed in contact with the positive electrode of the non-aqueous secondary battery, so that the positive electrode active As a substance, LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , which can be operated at a high voltage of 4.2 V or more, is easily applied.

  An example of the embodiment of the negative electrode includes a structure in which an active material layer including a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further include a conductive aid. Examples of the negative electrode active material include materials that can electrochemically occlude lithium, and specific examples include carbon materials; alloys of lithium with silicon, tin, aluminum, and the like; wood alloys; and the like. Examples of the binder resin include a polyvinylidene fluoride resin, a styrene-butadiene copolymer, and the like. Examples of the conductive aid include carbon materials such as acetylene black, Ketjen black, and graphite powder. Examples of the current collector include a copper foil, a nickel foil, and a stainless steel foil having a thickness of 5 μm to 20 μm. Further, instead of the above-described negative electrode, a metal lithium foil may be used as the negative electrode.

The electrolyte is a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , and LiClO ₄ . Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted products thereof; cyclic esters such as γ-butyrolactone and γ-valerolactone; and these may be used alone or as a mixture. As an electrolytic solution, cyclic carbonate and chain carbonate are mixed at a mass ratio (cyclic carbonate: chain carbonate) of 20:80 to 40:60, and a lithium salt is in a range of 0.5 mol / L to 1.5 mol / L. Is preferable.

  Examples of the exterior material include a metal can, an aluminum laminate film pack, and the like. Although the shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, the separator of the present disclosure is suitable for any shape.

  Non-aqueous secondary battery of the present disclosure, the separator of the present disclosure is disposed between the positive electrode and the negative electrode, and wound in the longitudinal direction to produce a wound body, put this wound body in the exterior material Further, it can be produced by impregnating with an electrolyte and enclosing the electrolyte. The same applies to a case where an element manufactured by a method of stacking at least one layer of a positive electrode, a separator, and a negative electrode in this order (a so-called stack method) instead of the wound body.

  Hereinafter, the separator and the nonaqueous secondary battery of the present disclosure will be described more specifically with reference to examples. Materials, usage amounts, ratios, processing procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present disclosure. Therefore, the range of the separator and the non-aqueous secondary battery of the present disclosure should not be construed as being limited by the specific examples described below.

<Measurement method, evaluation method>
The measurement methods and evaluation methods applied in the examples and comparative examples are as follows.

[Average primary particle size of inorganic particles]
In observation with a scanning electron microscope (SEM), the major axis of 100 arbitrarily selected particles was measured, the average value was calculated, and the average primary particle diameter (μm) of the inorganic particles was determined.

[Thickness]
The thicknesses of the porous substrate and the separator were measured using a contact-type thickness gauge (LITEMATIC manufactured by Mitutoyo Corporation). The measurement terminal used was a cylindrical one with a diameter of 5 mm, adjusted so that a load of 7 g was applied during the measurement, and measured any 20 points within 10 cm x 10 cm, and calculated the average value did.
The thickness of the heat-resistant porous layer was determined by subtracting the thickness of the porous substrate from the thickness of the separator.

[Porosity]
The porosity of the porous substrate and the separator was determined according to the following calculation method.
The constituent materials are a, b, c, ..., n, the mass of each constituent material is Wa, Wb, Wc, ..., Wn (g / cm2), and the true density of each constituent material is da, db, dc , Dn (g / cm3), and when the film thickness is t (cm), the porosity ε (%) can be obtained by the following equation.
ε = {1- (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100

[Gurle value]
The Gurley value of the porous substrate and the separator was measured with a Gurley type densometer (Toyo Seiki G-B2C) according to JIS P8117: 2009.

[Area shrinkage due to heat treatment]
The separator was cut out to a size of 180 mm in the MD direction × 60 mm in the TD direction to obtain a test piece. The test piece was marked on a line bisecting the TD direction and at positions 20 mm and 170 mm from one end (referred to as points A and B, respectively). Further, marks were made at points 10 mm and 50 mm from one end on a line bisecting the MD direction (points C and D, respectively). Attach a clip to this (the point where the clip is attached is between the end closest to point A and point A), hang it in a temperature-controlled oven, and perform a heat treatment at 120 ° C. for 0.5 hour under no tension. After that, the shrinkage was measured. Thereafter, the test piece after the heat treatment at 120 ° C. was suspended again in an oven whose temperature was adjusted, and heat treated at 135 ° C. for 0.5 hour. In measuring the shrinkage, the length between AB and CD was measured before and after each heat treatment, the area shrinkage was calculated by the following formula, and the area heat shrinkage of 10 test pieces was averaged.
Area shrinkage (%) = {1− (length of AB after heat treatment / length of AB before heat treatment) × (length of CD after heat treatment / length of CD before heat treatment)} × 100

[Spot heating]
The separator was cut out in a size of 50 mm in the MD direction × 50 mm in the TD direction to obtain a test piece. The test piece was placed on a horizontal stand, and the tip of the soldering iron having a tip diameter of 2 mm was heated to a temperature of 260 ° C., and the tip of the soldering iron was brought into point contact with the separator surface for 60 seconds. The area (mm ² ) of holes formed in the separator due to point contact was measured, and the areas of holes of 10 test pieces were averaged. The higher the heat resistance of the separator, the smaller the area of the hole formed in the separator.

[High temperature storage test (gas generation amount)]
The separator was cut out to a predetermined size, placed in a pack made of an aluminum laminated film, an electrolytic solution was injected into the pack to impregnate the separator with the electrolytic solution, and the pack was sealed to obtain a test cell. As the electrolytic solution, a solution obtained by adding 0.1 wt% of ion-exchanged water to 1 mol / L LiPF ₆ -ethylene carbonate: ethyl methyl carbonate (mass ratio 3: 7) was used. The test cell was placed in an environment at a temperature of 85 ° C. for 7 days, and the volume of the test cell before and after the heat treatment was measured. The gas generation amount V (= V2-V1, unit: mL) was obtained by subtracting the volume V1 of the test cell before heat treatment from the volume V2 of the test cell after heat treatment. The V was divided by the area of the separator was calculated gas generation amount per separator 1 m ^2.

[HF concentration]
The electrolyte recovered from the cells after the high-temperature storage test was centrifuged (3000 rpm, 10 minutes) to recover a supernatant, which was diluted with ultrapure water and stirred. This solution was treated with a solid phase extraction cartridge, and quantitative analysis of fluorine ions (F ⁻ ) was performed by ion chromatography (IC).

[Cycle characteristics]
Dissolve 94 g of lithium cobaltate powder as a positive electrode active material, 3 g of acetylene black as a conductive additive, and 3 g of polyvinylidene fluoride as a binder in N-methyl-pyrrolidone so that the concentration of polyvinylidene fluoride becomes 5% by mass. Then, the mixture was stirred with a double-armed mixer to prepare a slurry for the positive electrode. This positive electrode slurry was applied to one surface of an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a positive electrode active material layer.
300 g of artificial graphite as a negative electrode active material, 7.5 g of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder, 3 g of carboxymethyl cellulose as a thickener, and an appropriate amount of water The mixture was stirred and mixed by a type mixer to prepare a negative electrode slurry. This negative electrode slurry was applied to a 10 μm-thick copper foil as a negative electrode current collector, dried and pressed to obtain a negative electrode having a negative electrode active material layer.
The above-described positive electrode and negative electrode (length 70 mm, width 30 mm) were stacked and laminated via the respective separators obtained in the following Examples and Comparative Examples, and a lead tab was welded to obtain a battery element. The battery element was housed in a pack made of an aluminum laminated film, impregnated with an electrolytic solution, and then subjected to a heat press at a pressure of 1 MPa, a temperature of 90 ° C. and a time of 2 minutes to seal the outer package, and perform a secondary test. A battery (thickness: 1.1 mm) was obtained. Here, the electrolytic solution used was 1 mol / L LiPF ₆ -ethylene carbonate: ethyl methyl carbonate (mass ratio 3: 7).
Using the produced test secondary battery, a charge / discharge cycle under the conditions of 45 ° C. and a condition of 4.2 V constant current at 1 C, constant voltage charge for 2 hours, and constant current discharge of 3 V cutoff at 1 C. Is repeated for 500 cycles, and the ratio of the discharge capacity obtained after 500 cycles is determined as a percentage based on the discharge capacity obtained in the first cycle (%; = discharge capacity after 500 cycles / discharge capacity at first cycle x 100). This value was used as an index for evaluating cycle characteristics.

<Preparation of separator>
[Example 1]
Polyvinylidene fluoride resin (VDF-HFP copolymer, VDF: HFP (molar ratio) = 97.6: 2.4, weight average molecular weight 1,130,000) was mixed with dimethylacetamide so that the resin concentration became 4% by mass. It is dissolved in a mixed solvent of (DMAc) and tripropylene glycol (TPG) (DMAc: TPG = 90: 10 [mass ratio]), and natural apatite particles (average primary particle size 2.7 μm) are further stirred and mixed. Liquid (P) was obtained.

  An appropriate amount of the coating liquid (P) is applied to a pair of Meyer bars, and a microporous polyethylene membrane (9 μm in thickness, 36% porosity, Gurley value of 168 seconds / 100 mL) is passed between the Meyer bars to form a coating liquid (P). ) Was applied in equal amounts on both sides. This is dipped in a coagulation liquid (DMAc: TPG: water = 30: 8: 62 [mass ratio], liquid temperature 40 ° C.) to solidify the coating layer, and then washed in a water washing tank at a water temperature of 40 ° C., and dried. did. Thus, a separator having a heat-resistant porous layer formed on both sides of the polyethylene microporous membrane was obtained.

[Example 2]
A separator was produced in the same manner as in Example 1, except that the natural apatite particles were changed to other natural apatite particles (average primary particle size: 1.0 μm).

[Example 3]
A separator was produced in the same manner as in Example 1 except that the natural apatite particles were changed to hydroxyapatite particles (average primary particle size: 0.3 μm).
[Example 4]
A separator was produced in the same manner as in Example 1 except that the natural apatite particles were changed to hydroxyapatite particles (average primary particle size: 0.05 μm).
[Example 5]
A separator was produced in the same manner as in Example 1, except that the natural apatite particles were changed to hydroxyapatite particles (average primary particle size: 0.01 μm).
[Example 6]
The meta-type wholly aromatic polyamide is dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc: TPG = 80: 20 [mass ratio]) so that the resin concentration becomes 4% by mass. Further, hydroxyapatite particles (average primary particle diameter: 0.3 μm) were mixed by stirring to obtain a coating liquid (A).
An appropriate amount of the coating liquid (A) was applied to a Meyer bar, and the coating liquid (A) was applied to one surface of a polyethylene microporous membrane (9 μm thick, porosity 36%, Gurley value 168 seconds / 100 mL). This is dipped in a coagulation liquid (DMAc: TPG: water = 30: 8: 62 [mass ratio], liquid temperature 40 ° C.) to solidify the coating layer, and then washed in a water washing tank at a water temperature of 40 ° C., and dried. did. Thus, a separator having a heat-resistant porous layer formed on one side of the polyethylene microporous membrane was obtained.

[Examples 7 and 8]
A separator was produced in the same manner as in Example 3, except that the volume ratio of the hydroxyapatite particles was changed as shown in Table 1.

[Comparative Example 1]
A separator was produced in the same manner as in Example 1 except that the natural apatite particles were changed to other hydroxyapatite particles (average primary particle size: 9.2 μm).

[Comparative Example 2]
A separator was produced in the same manner as in Example 1, except that the natural apatite particles were changed to other hydroxyapatite particles (average primary particle size less than 0.01 μm).

[Comparative Example 3]
A separator was produced in the same manner as in Example 1, except that the natural apatite particles were changed to magnesium hydroxide (average primary particle size: 0.9 μm).

[Examples 9 to 12]
The natural apatite particles were changed to a mixture of hydroxyapatite particles (average primary particle size 0.3 μm) and magnesium hydroxide (average primary particle size 0.5 μm), and as shown in Table 1, the mixture of hydroxyapatite particles and magnesium hydroxide was used. A separator was produced in the same manner as in Example 1 except that the ratio was adjusted.

  Table 1 shows the composition, physical properties, and evaluation results of the separators of Examples 1 to 12 and Comparative Examples 1 to 3.

Claims (12)

A porous substrate,
Provided on one or both surfaces of the porous substrate, a binder resin, and a heat-resistant porous layer containing first inorganic particles made of apatite,
A non-aqueous secondary battery separator, wherein the first inorganic particles have an average primary particle size (D50) of 0.01 μm or more and 3.0 μm or less.   The non-aqueous secondary battery separator according to claim 1, wherein the average primary particle size (D50) of the first inorganic particles is from 0.01 µm to 1.0 µm.   The separator for a non-aqueous secondary battery according to claim 1 or 2, wherein the binder resin includes a polyvinylidene fluoride-based resin.   The non-aqueous secondary battery separator according to claim 3, wherein the weight average molecular weight of the polyvinylidene fluoride resin is 500,000 to 3,000,000.   The binder resin comprises at least one selected from the group consisting of wholly aromatic polyamide, polyamide imide, poly-N-vinylacetamide, polyacrylamide, copolymerized polyether polyamide, polyimide and polyetherimide. The separator for a non-aqueous secondary battery according to claim 2.   The separator for a non-aqueous secondary battery according to any one of claims 1 to 5, wherein a volume ratio of the first inorganic particles in the heat-resistant porous layer is 10% by volume to 90% by volume. .   The heat-resistant porous layer according to any one of claims 1 to 5, wherein, in addition to the first inorganic particles, second inorganic particles different from the first inorganic particles are included. 12. The separator for a non-aqueous secondary battery according to item 9.   The non-aqueous secondary battery separator according to claim 7, wherein the content of the first inorganic particles is 5 to 95% by volume based on the total mass of the first inorganic particles and the second inorganic particles. .   9. The non-aqueous inorganic particle according to claim 7, wherein the second inorganic particles include at least one selected from the group consisting of metal oxides, metal hydroxides, metal nitrides, metal salts, and clays. 10. Secondary battery separator.   The non-aqueous secondary battery separator according to claim 9, wherein the second inorganic particles include at least one selected from the group consisting of alumina, boehmite, zinc oxide, magnesium oxide, magnesium hydroxide, and barium sulfate.   The method according to any one of claims 7 to 10, wherein a total volume ratio of the first inorganic particles and the second inorganic particles in the heat-resistant porous layer is 10% by volume to 90% by volume. The separator for a non-aqueous secondary battery according to the above. A non-aqueous secondary battery separator according to any one of claims 1 to 11, which is disposed between the positive electrode, the negative electrode, and the positive electrode and the negative electrode, and doped and undoped with lithium. Non-aqueous secondary battery that obtains electromotive force.