JP2018133244A - Separator for nonaqueous secondary battery and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous secondary battery which suppresses deformation of the battery due to swelling caused by generated gas when a battery is produced and is excellent in heat resistance even with a separator having a porous layer containing a heat resistant filler such as aluminum hydroxide.SOLUTION: The separator for a nonaqueous secondary battery includes: a porous substrate; and a heat resistant porous layer provided on one side or both sides of the porous substrate. The heat resistant porous layer includes: (1) a binder resin; (2) particles of zinc oxide; and (3) one or more heat resistant fillers selected from a group consisting of a metal hydroxide and a metal oxide other than zinc oxide. The content of the zinc oxide particles with respect to the total amount of the zinc oxide particles and the heat resistant filler is 2 mass% or more and less than 100 mass%.SELECTED DRAWING: None

Description

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

  Non-aqueous secondary batteries typified by lithium ion secondary batteries are widely used for mobile power and storage purposes because of their high energy density, flexible and lightweight structure, and longer life than other batteries. . In recent years, non-aqueous secondary batteries have been required to have higher energy density, and accordingly, ensuring safety has been regarded as important.

  Separators play an important role in ensuring safety in non-aqueous secondary batteries such as lithium ion secondary batteries. Specifically, it is desirable that the separator has a heat resistance of the membrane itself and a shutdown function in which the pores of the membrane are blocked and the current is cut off when the temperature of the battery rises. As a technology related to heat resistance, a separator in which a porous layer containing a filler such as aluminum hydroxide and a heat resistant resin such as a meta-type wholly aromatic polyamide is formed on a polyethylene microporous film (for example, patent document) 1-2), a separator in which a porous layer containing magnesium hydroxide and a polyvinylidene fluoride resin is formed on a polyolefin microporous membrane (see, for example, Patent Document 3), or a polyolefin microporous membrane A separator (for example, see Patent Documents 4 to 5) in which a particle-containing resin layer made of inorganic particles and a resin is formed on is proposed.

International Publication No. 2008/062727 International Publication No. 2008/156033 International Publication No. 2014/021293 International Publication No. 2015/068325 International Publication No. 2015/097953

  In a separator having a porous layer containing a heat-resistant filler such as aluminum hydroxide, moisture present in a trace amount in the battery impregnated with the electrolyte tends to act on the electrolyte and impair the stability of the electrolyte. In some cases, gas is generated by inducing decomposition. When such a phenomenon occurs, there is a problem that the battery itself swells and the battery is deformed.

  The present invention has been made in view of the above, and even in a separator having a porous layer containing a heat-resistant filler such as aluminum hydroxide, gas generation is suppressed when a battery is produced, and the heat resistance is improved. An object is to provide an excellent separator for a non-aqueous secondary battery.

The present invention adopts the following configuration in order to solve the above problems.
1. A porous substrate;
A non-aqueous secondary battery separator comprising a heat-resistant porous layer provided on one side or both sides of the porous substrate,
The heat-resistant porous layer comprises (1) a binder resin, (2) zinc oxide particles, (3) a metal hydroxide, and one or more selected from the group consisting of metal oxides other than zinc oxide. Including a heat-resistant filler, and
The content of the zinc oxide particles relative to the total amount of the zinc oxide particles and the heat-resistant filler is 2% by mass or more and less than 100% by mass,
Separator for non-aqueous secondary battery.
2. 2. The separator for a non-aqueous secondary battery according to 1 above, wherein the heat-resistant filler is one or more heat-resistant fillers selected from the group consisting of magnesium hydroxide, aluminum hydroxide, aluminum oxide, boehmite, and magnesium oxide.
3. 3. The separator for a non-aqueous secondary battery according to 1 or 2 above, wherein the zinc oxide particles have an average particle diameter of 0.1 μm or more and 1 μm or less.
4). The binder resin is a copolymer including a vinylidene fluoride monomer unit and a hexafluoropropylene monomer unit, and the hexafluoropropylene monomer unit includes the vinylidene fluoride monomer unit and the The non-aqueous system according to any one of claims 1 to 3, which is a polyvinylidene fluoride resin that is 1.0 mol% or more and 7.0 mol% or less with respect to the total amount of hexafluoropropylene monomer units. Secondary battery separator.
5. The separator for a non-aqueous secondary battery according to 4 above, wherein the polyvinylidene fluoride resin has a weight average molecular weight of 600,000 to 3,000,000.
6). 6. The non-aqueous two-phase composition according to claim 1, wherein the total content of the zinc oxide particles and the heat-resistant filler in the heat-resistant porous layer is 40% by volume or more and 85% by volume or less. Secondary battery separator.
7). A positive electrode, a negative electrode, and the separator for a nonaqueous secondary battery according to any one of the above 1 to 6 disposed between the positive electrode and the negative electrode, and is generated by doping and dedoping of lithium. Non-aqueous secondary battery that obtains electric power.

  According to the present invention, even in a separator having a porous layer containing a heat-resistant filler such as aluminum hydroxide, gas generation is suppressed when a battery is produced, and a non-aqueous secondary battery excellent in heat resistance A separator is provided.

Schematic diagram explaining the hexagonal shape

Embodiments of the present invention will be described below. It should be noted that the description of the embodiment and the examples illustrate the present invention and do not limit the scope of the present invention.
In the present specification, numerical ranges indicated using “to” indicate ranges including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

<Separator for non-aqueous secondary battery>
The separator for a non-aqueous secondary battery according to the present disclosure includes at least a porous substrate and a heat-resistant porous layer provided on one side or both sides of the porous substrate. The heat-resistant porous layer provided on the porous substrate comprises (1) a binder resin, (2) zinc oxide particles, and (3) a metal hydroxide and a metal oxide other than zinc oxide. One or more heat-resistant fillers selected, and the content of the zinc oxide particles and the zinc oxide particles relative to the total amount of the heat-resistant filler is in the range of 2% by mass to less than 100% by mass.
The separator for nonaqueous secondary batteries of this indication may have further other layers.

  Non-aqueous secondary batteries have conventionally contained fillers for the purpose of increasing the heat resistance and strength of the battery, and are selected from the group consisting of metal oxides and metal oxides other than zinc oxide. The one or more heat-resistant fillers that act on the electrolyte in the layer impregnated with the electrolytic solution may impair the stability of the solution, and may cause decomposition of the electrolytic solution and the electrolyte to generate gas. is there.

In view of the above situation, in the separator for a non-aqueous secondary battery of the present disclosure, the heat-resistant porous layer in contact with the electrode is formed with a composition containing a specific filler in a specific ratio in addition to the binder resin. Specifically, the heat-resistant porous layer in the present disclosure uses, as a filler, one or more heat-resistant fillers selected from the group consisting of metal hydroxides and metal oxides excluding zinc oxide, together with zinc oxide particles. The zinc oxide particles are formed so that the content ratio of the zinc oxide particles satisfies a specific range. Thereby, generation | occurrence | production of the gas accompanying decomposition | disassembly of the electrolyte solution and electrolyte induced by metal oxides other than a metal hydroxide and zinc oxide is suppressed, and the swelling (deformation of a battery) by generated gas is suppressed. Moreover, since the separator for non-aqueous secondary batteries of this indication contains the particle | grains of a zinc oxide and a heat resistant filler, it is excellent in heat resistance.
Hereinafter, the separator for a non-aqueous secondary battery of the present disclosure will be described in detail.

[Porous substrate]
The non-aqueous secondary battery separator of the present disclosure includes a porous substrate. The porous substrate means a substrate having pores or voids inside.
As a porous substrate, a porous sheet such as a nonwoven fabric and paper made of a microporous film and a fibrous material, and a composite in which one or more other porous layers are laminated on a microporous film or a porous sheet Examples thereof include a porous sheet. Here, the microporous membrane is a membrane that has a large number of micropores inside and that allows the passage of gas or liquid from one surface to the other by virtue of the structure in which the micropores are connected to each other. Refers to that.

The material for the porous substrate is preferably an electrically insulating material, and may be either an organic material and / or an inorganic material.
The porous substrate preferably contains a thermoplastic resin from the viewpoint of imparting a shutdown function to the porous substrate. The shutdown function refers to a function of preventing thermal runaway of the battery by blocking the movement of ions by dissolving the material and closing the pores of the porous base material when the battery temperature increases. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ° C. is preferable, and polyolefin is particularly preferable.

As the porous substrate, a microporous membrane containing polyolefin (referred to as “polyolefin microporous membrane” in the present specification) is preferable.
As the polyolefin microporous membrane, one having sufficient mechanical properties and ion permeability may be selected from among polyolefin microporous membranes applied to conventional non-aqueous secondary battery separators.
The polyolefin microporous membrane preferably contains polyethylene (that is, a polyethylene microporous membrane) from the viewpoint of exhibiting a shutdown function, and the polyethylene content is preferably 95% by mass or more.

  The polyolefin microporous membrane is preferably a polyolefin microporous membrane containing polyethylene and polypropylene from the viewpoint of imparting heat resistance to such an extent that it will 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. Such a 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, the polyolefin microporous membrane has a laminated structure of two or more layers, at least one layer contains polyethylene and at least one layer contains polypropylene. Is also preferable.

  The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight of 100,000 to 5,000,000. When the weight average molecular weight is 100,000 or more, good mechanical properties can be secured. On the other hand, when the weight average molecular weight is 5 million or less, the shutdown characteristics are good and the film can be easily formed.

  The polyolefin microporous membrane can be produced, for example, by the following method. That is, a melted polyolefin resin is extruded from a T-die to form a sheet, which is crystallized and then stretched, and further heat treated to form a microporous film, or melted together with a plasticizer such as liquid paraffin. In this method, a polyolefin resin is extruded from a T-die into a sheet shape, the extruded resin is cooled and stretched, and then a plasticizer is extracted and heat-treated to form a microporous film.

Examples of porous sheets made of fibrous materials include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat resistant resins such as aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide; Nonwoven fabric, paper, etc. made of the fibrous material of
The heat resistant resin means a polymer having a melting point of 200 ° C. or higher, or a polymer having no melting point and a decomposition temperature of 200 ° C. or higher.

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

[Characteristics of porous substrate]
The average pore size of the porous substrate of the present disclosure is preferably in the range of 20 nm to 100 nm. When the average pore diameter of the porous substrate is 20 nm or more, ions easily move and good battery performance is easily obtained. From such a viewpoint, the average pore diameter of the porous substrate is more preferably 30 nm or more, and further preferably 40 nm or more. On the other hand, when the average pore size of the porous substrate is 100 nm or less, the peel strength between the porous substrate and the porous layer is improved, and a good shutdown function can be exhibited. From such a viewpoint, the average pore diameter of the porous substrate is more preferably 90 nm or less, and further preferably 80 nm or less.
In addition, the average hole diameter of a porous base material is a value measured using a palm porometer, For example, based on ASTM E1294-89, a palm porometer (CFP-1500-A made from PMI) is used. Can be measured.

The thickness of the porous substrate is preferably in the range of 3 μm to 25 μm from the viewpoint of obtaining good mechanical properties and internal resistance. In particular, the thickness of the porous substrate is more preferably in the range of 5 μm to 20 μm.
The Gurley value (JIS P8117: 2009) of the porous substrate is preferably in the range of 50 seconds / 100 cc to 400 seconds / 100 cc from the viewpoint of preventing short circuit of the battery and obtaining sufficient ion permeability.
The porosity of the porous substrate is preferably in the range of 20% or more and 60% or less from the viewpoint of obtaining appropriate film resistance and a shutdown function.
The puncture strength of the porous substrate is preferably 200 g or more from the viewpoint of improving the production yield.

  The porous substrate is preferably subjected to various surface treatments. By performing the surface treatment, wettability with a coating solution for forming a heat-resistant porous layer described later can be improved. Specific examples of the surface treatment include corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, and the like, and the treatment can be performed within a range that does not impair the properties of the porous substrate.

[Heat-resistant porous layer]
The separator for nonaqueous secondary batteries of this indication is equipped with the heat resistant porous layer on the porous substrate. The heat-resistant porous layer is disposed on one or both sides of the porous substrate, and (1) a binder resin, (2) zinc oxide particles, and (3) a metal hydroxide and a metal oxide other than zinc oxide. A porous layer containing one or more heat-resistant fillers selected from the group consisting of:
The heat-resistant porous layer has a large number of micropores inside and has a structure in which the micropores are connected to each other so that gas or liquid can pass from one surface to the other surface.

The heat-resistant porous layer is composed of a binder resin, zinc oxide particles, and a component other than one or more heat-resistant fillers selected from the group consisting of metal hydroxides and metal oxides other than zinc oxide (for example, other fillers). May be included.
The heat-resistant porous layer of the present disclosure may be disposed only on one side of the porous substrate, or may be disposed on both sides. When the heat-resistant porous layer is only on one side of the porous substrate, the thickness of the entire separator can be suppressed, which can contribute to an improvement in battery capacity and is good because the number of laminated layers is small. Easy ion permeability can be obtained. On the other hand, when the heat resistant porous layer is on both surfaces of the porous substrate, the heat resistance of the separator is more excellent, and the safety of the battery can be improved. Moreover, when it exists in both surfaces, it is hard to generate | occur | produce a curl in a separator.

(Binder resin)
The heat resistant porous layer contains at least one binder resin.
The binder resin contained in the heat-resistant porous layer of the present disclosure is not particularly limited as long as it can bind particles of zinc oxide and particles containing a heat-resistant filler. The binder resin is preferably a polymer having a polar functional group or atomic group (polar group such as hydroxyl group, carboxyl group, amino group, amide group, carbonyl group), for example, wholly aromatic polyamide, fluorine resin, polyimide , Polyamideimide, polysulfone, polyketone, polyethersulfone, polyetherketone, polyetherimide, cellulose and the like. Binder resins may be used alone or in combination of two or more.

As the binder resin, a fluororesin and a wholly aromatic polyamide are preferable from the viewpoint of being insoluble in the electrolytic solution and having excellent heat resistance.
Examples of the fluororesin include polyvinylidene fluoride resins such as polyvinylidene fluoride and polyvinylidene fluoride copolymers.

  As the wholly aromatic polyamide, polymetaphenylene isophthalamide, which is a meta-type wholly aromatic polyamide, is preferable in that it easily forms a porous layer and is excellent in redox resistance. In addition, for example, a small amount of an aliphatic component can be copolymerized with the wholly aromatic polyamide.

  A particulate resin may be used as the binder resin of the present disclosure. Examples of the particulate resin include particles containing a resin such as polyvinylidene fluoride resin, fluorine rubber, and styrene-butadiene rubber. The particulate resin can be dispersed in a dispersion medium such as water and used for preparing a coating liquid.

A water-soluble resin may be used as the binder resin of the present disclosure. Examples of the water-soluble resin include cellulose resins and polyvinyl alcohol. The water-soluble resin can be dissolved in water, for example, and used for preparing a coating solution.
The particulate resin and the water-soluble resin are suitable when the coagulation step is performed by a dry manufacturing method.

-Polyvinylidene fluoride resin-
The binder resin of the present disclosure is preferably a polyvinylidene fluoride-based resin because it is more excellent in adhesiveness with the electrode. By containing a polyvinylidene fluoride resin, the strength of the battery (cell strength) increases with the improvement in adhesion to the electrode. For example, the strength required for a soft pack battery is secured, and the quality It also has excellent stability.

  Polyvinylidene fluoride resins include homopolymers of vinylidene fluoride (polyvinylidene fluoride), copolymers of vinylidene fluoride and other copolymerizable monomers (polyvinylidene fluoride copolymer), and mixtures thereof. Can be mentioned.

  Examples of the monomer copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene (HFP), trifluoroethylene, trichloroethylene, vinyl fluoride, and the like, and one kind or two or more kinds can be used. .

  Among the polyvinylidene fluoride resins, a copolymer obtained by copolymerizing at least vinylidene fluoride and hexafluoropropylene is preferable from the viewpoint of adhesiveness to the electrode. A copolymer obtained by copolymerizing vinylidene fluoride and hexafluoropropylene and containing a VDF unit derived from vinylidene fluoride (VDF) and a HFP unit derived from hexafluoropropylene (HFP) (VDF-HFP copolymer) is a resin Since the crystallinity and heat resistance can be controlled within an appropriate range, it is possible to suppress the heat resistant porous layer from flowing during the hot press treatment when the separator is bonded to the electrode.

The polyvinylidene fluoride resin is preferably a VDF-HFP copolymer containing 93 mol% or more of VDF units as a structural unit. When the VDF unit is contained in an amount of 93 mol% or more, good mechanical properties and heat resistance can be ensured even under hot press conditions at a low temperature or the like.
The fibril diameter of the polyvinylidene fluoride resin contained in the heat resistant porous layer is preferably in the range of 10 nm to 1000 nm from the viewpoint of cycle characteristics.

  A battery having a separator having a heat-resistant porous layer containing a polyvinylidene fluoride-based resin generally has a process in which electrodes and separators are overlapped and wound or electrodes and separators are stacked alternately. The laminate is manufactured, and the laminate is housed in an exterior material and subjected to a heat press treatment (wet heat press) in a state where an electrolytic solution is injected. According to the wet heat press, the polyvinylidene fluoride resin is hot-pressed in contact with the electrolyte and swollen, which is advantageous in that the adhesion between the electrode and the separator is improved and the charge / discharge characteristics are excellent. is there. On the other hand, during wet heat press, the stability of the liquid is likely to decrease due to the action of the heat-resistant filler as the temperature rises, and the decomposition of the electrolytic solution and the electrolyte is more likely to be induced, but the electrolyte solution contains zinc oxide particles. Further, the generation of gas due to the decomposition of the electrolyte is suppressed, and the phenomenon that the battery swells is suppressed.

  Adhesion by heat press includes adhesion by wet heat press in which the separator is impregnated with the electrolytic solution and then adhesion to the electrode, and adhesion by dry heat press in which the separator is adhered and temporarily fixed before impregnation with the electrolytic solution. Both are easily affected by the content of HFP units and the weight average molecular weight of the VDF-HFP copolymer.

  In order to improve the adhesion by wet heat press, it is important to have an appropriate fluidity, that is, an appropriate weight average molecular weight. Further, in order to give flexibility to the resin and swell the separator without dissolving it with the electrolytic solution, it is important that the ratio of HFP units is in an appropriate range.

  Focusing on the copolymerization component of the VDF-HFP copolymer, from the viewpoint of improving adhesion by wet heat pressing at an appropriate temperature, the hexafluoropropylene (HFP) monomer unit is vinylidene fluoride (VDF) single unit. The total amount of the monomer unit and the hexafluoropropylene (HFP) monomer unit is preferably in the range of 1.0 mol% or more and 7.0 mol% or less.

Specifically, when the copolymerization ratio of the HFP unit in the VDF-HFP copolymer is 1.0 mol% or more, it swells appropriately when the electrolyte is impregnated, and the adhesion by wet heat press is improved. It's easy to do. On the other hand, when the copolymerization ratio of the HFP unit is 7.0 mol% or less, it is difficult to dissolve in the electrolytic solution, and it is preferable to apply to the heat-resistant porous layer.
From the same viewpoint as described above, the content of HFP units in the VDF-HFP copolymer is preferably 2.0 mol% or more and 6.0 mol% or less.

  As a VDF-HFP copolymer, in addition to the copolymer which consists only of a VDF unit and an HFP unit, the other copolymerization component copolymerizable with vinylidene fluoride may be contained. Examples of monomers copolymerizable with vinylidene fluoride other than hexafluoropropylene include tetrafluoroethylene, trifluoroethylene, trichloroethylene, chlorotrifluoroethylene, vinyl fluoride, and the like, and one or more are used. be able to.

  The weight average molecular weight (Mw) of the polyvinylidene fluoride resin is preferably in the range of 600,000 to 3,000,000. When the weight average molecular weight is 600,000 or more, it is easy to obtain a heat-resistant porous layer having mechanical properties that can withstand the heat press treatment during adhesion to the electrode, and adhesion between the electrode and the heat-resistant porous layer. In particular, the adhesiveness by wet heat press is excellent. From the same viewpoint as described above, the weight average molecular weight of the polyvinylidene fluoride resin is more preferably 800,000 or more, and more preferably 1,000,000 or more.

On the other hand, when the weight average molecular weight is 3 million or less, the viscosity at the time of molding does not become too high, the moldability and crystal formation become good, and it becomes easy to be porous. Therefore, from the viewpoint of improving moldability and crystal formability and improving adhesiveness, the weight average molecular weight of the polyvinylidene fluoride resin is preferably 2.5 million or less, and more preferably 2 million or less.
The weight average molecular weight (Mw) of the polyvinylidene fluoride resin is a molecular weight measured by gel permeation chromatography (hereinafter also referred to as GPC) under the following conditions and converted to polystyrene.

<Conditions>
・ GPC: GPC-900 (manufactured by JASCO)
・ Column: TSKgel Super AWM-H x 2 (manufactured by Tosoh Corporation)
-Mobile phase solvent: dimethylformamide (DMF)
Standard sample: monodisperse polystyrene [manufactured by Tosoh Corporation]
-Column temperature: 140 ° C
-Flow rate: 10 ml / min A polyvinylidene fluoride resin can be obtained by emulsion polymerization or suspension polymerization.
The acid value of the polyvinylidene fluoride resin is preferably in the range of 3 mgKOH / g to 20 mgKOH / g.

  The acid value can be controlled, for example, by introducing a carboxyl group into the polyvinylidene fluoride resin. The introduction and introduction amount of the carboxyl group into the polyvinylidene fluoride-based resin is a monomer having a carboxyl group as a polymerization component of the VDF-HFP copolymer that is the polyvinylidene fluoride-based resin (for example, carboxylic acid ester, maleic acid, It can be controlled by adjusting the polymerization ratio using (maleic anhydride).

-Other resins-
The heat-resistant porous layer of the present disclosure may include other resins other than the binder resin. Examples of other resins include fluorine rubber, acrylic resin, styrene-butadiene copolymer, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, Polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc.) and the like can be mentioned.
The total content of other resins in the heat-resistant porous layer is preferably 5% by mass or less, more preferably 3% by mass or less, and more preferably 1% by mass or less with respect to the total amount of the resin contained in the heat-resistant porous layer. Is more preferable, and it is especially preferable that it is below the detection limit.

(Zinc oxide particles)
The heat-resistant porous layer of the present disclosure contains one or more heat-resistant fillers selected from the group consisting of metal oxides and metal oxides other than zinc oxide, and zinc oxide particles. Zinc oxide particles are inorganic particles that are stable to the electrolyte and electrochemically stable. By selectively containing zinc oxide particles as inorganic particles, not only the slipperiness and heat resistance of the separator are improved, but also the effect of suppressing blistering (battery deformation) due to the generated gas caused by the heat-resistant filler component. is there. This is considered because zinc oxide itself takes in hydrogen fluoride generated in the battery and suppresses decomposition of the electrolytic solution by hydrogen fluoride.

  The average particle diameter of the zinc oxide particles of the present disclosure is preferably in the range of 0.1 μm to 1 μm. When the average particle size is 0.1 μm or more, the effect of suppressing gas generation is excellent. Moreover, it is easy to make a heat resistant porous layer into a thin film as an average particle diameter is 1 micrometer or less. Furthermore, since the zinc oxide particle size greatly affects the adhesion at the separator / electrode interface, and the zinc oxide particle size is too small or too large, the adhesion is low, so the average particle size of the zinc oxide particles is The range of 0.2 μm to 0.5 μm is more preferable.

  The average particle diameter is a value measured using a laser diffraction particle size distribution measuring apparatus, and is measured using, for example, a master sizer 2000 manufactured by Sysmex Corporation. Specifically, the central particle diameter (in the volume particle size distribution) of a dispersion obtained by mixing and dispersing zinc oxide particles, water (dispersion medium), and nonionic surfactant (Triton X-100; dispersant). D50) is the average particle size.

  The shape of the zinc oxide of the present disclosure may be any shape, for example, a spherical shape, a scale shape, a plate shape, a hexagonal plate shape, or a needle shape. The shape of the particles is preferably a hexagonal plate shape from the viewpoint of suppressing an increase in the viscosity of the coating liquid. The form of the zinc oxide particles is preferably primary particles that are not aggregated.

The hexagonal plate-like particle of the present disclosure is a particle having a hexagonal surface in which particles satisfying all of (1) and (2) out of 100 particles in a transmission electron micrograph are 50% or more. It is.
(1) Have a hexagonal surface (2) Lmin / Lmax ≧ 0.7
Lmax: The length of the maximum diagonal line among the three diagonal lines of the hexagonal surface of the hexagonal plate-like particles.
Lmin: means the length of the diagonal line that is the smallest of the three diagonal lines of the hexagonal surface of the hexagonal plate-like particles.

  Lmin / Lmax means the deviation from the diagonal length of the regular hexagon when Lmax is the length of the diagonal of the regular hexagon. The closer the value is to 1, the smaller the deviation from the regular hexagon is. Is big. Lmin / Lmax is 0.7 or more, more preferably 0.9 or more.

In the above definition, the three diagonal lines are B, C, D, E, and F in order from the vertex adjacent to A, where A is one vertex of the hexagon on the hexagonal surface. Mean diagonal line AD connecting A and D, diagonal line BE connecting B and E, and diagonal line CF connecting C and F. Of the diagonal lines AD, BE and CF, the diagonal line having the maximum length is shown. The length of the diagonal line was Lmax, and the length of the diagonal line having the minimum length was Lmin. In order to facilitate understanding of each of these parameters, a schematic diagram is shown in FIG.
The value of each parameter was measured based on a transmission electron micrograph, and Lmax and Lmin were measured with a ruler.

  The hexagonal plate-like particles of the present disclosure preferably have an aspect ratio of 2.5 or more and less than 100, more preferably 2.7 or more, and most preferably 3.0 or more.

  The aspect ratio of the hexagonal plate-like particles in the present disclosure is the constant direction diameter (particles) of the particles in which the hexagonal surface of the hexagonal plate-like particles are facing forward in an image taken with a scanning electron microscope (SEM). The particle diameter (μm) defined by the distance between two parallel lines in a certain direction across the particle; the particle whose hexagonal surface on the image is facing forward was measured in a certain direction) was measured for 100 particles. The average value is L, and the average value obtained by measuring the thickness (μm) (the length of the short side of the rectangle) of 100 particles for the particles whose hexagonal plate-shaped side faces are facing forward (particles that look rectangular). When T is T, a ratio of these values; a value obtained as L / T.

  Inclusion of zinc oxide particles relative to the total content of zinc oxide particles and one or more heat-resistant fillers selected from the group consisting of metal hydroxides and metal oxides other than zinc oxide in the heat-resistant porous layer The amount is in the range of 2% by weight to less than 100% by weight. If the content of zinc oxide particles is less than 2% by mass, the effect of suppressing the generation of gas accompanying decomposition of the electrolyte and electrolyte induced by the heat-resistant filler becomes insufficient. If the content of zinc oxide particles is 2% by mass or more, the effect of suppressing gas generation can be sufficiently obtained, but it is more preferably 10% by mass or more, and further preferably 20% by mass or more. preferable.

In the heat-resistant porous layer of the present disclosure, the total content of one or more heat-resistant fillers selected from the group consisting of zinc oxide particles and metal hydroxides and metal oxides other than zinc oxide is the heat-resistant porous layer. It is preferable that it is 30 volume% or more and 85 volume% or less with respect to solid content of a quality layer.
When the total content of the zinc oxide particles and the heat-resistant filler is 30% by volume or more, the heat resistance is improved. For the same reason as described above, the total content of the zinc oxide particles and the heat-resistant filler is more preferably 35% by volume or more, and further preferably 40% by volume or more.
In addition, when the total content of the zinc oxide particles and the heat-resistant filler is 85% by volume or less, the particles and the filler are excellent in handleability without falling off. For the same reason as described above, the total content of the zinc oxide particles and the heat-resistant filler is more preferably 75% by volume or less, and further preferably 70% by volume or less.

(Heat resistant filler)
Since the heat-resistant porous layer of the present disclosure contains one or more heat-resistant fillers selected from the group consisting of metal oxides and metal oxides other than zinc oxide, a heat-resistant effect is obtained and the heat resistance of the separator is improved. improves. On the other hand, the above heat-resistant filler generally acts on the electrolyte in the layer impregnated with the electrolytic solution and tends to impair the stability of the liquid, and may cause decomposition of the electrolytic solution and the electrolyte to generate gas. is there. In the present disclosure, a predetermined amount of zinc oxide particles is used in combination with the heat-resistant filler. Thereby, generation | occurrence | production of the gas accompanying decomposition | disassembly of electrolyte solution and electrolyte is suppressed, and the swelling (deformation of a battery) by gas is suppressed.

Among the heat-resistant fillers of the present disclosure, examples of metal oxides other than zinc oxide include alumina, titania, magnesia, silica, zirconia, and the like. Examples of metal hydroxides include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide and the like.
Among heat-resistant fillers, 1 selected from the group consisting of magnesium hydroxide, aluminum hydroxide, aluminum oxide, boehmite (alumina monohydrate), and magnesium oxide from the viewpoint that the effect of improving heat resistance and battery strength can be achieved at low cost. More than one type of heat resistant filler is preferred.

The average particle size of the heat-resistant filler of the present disclosure is preferably 0.01 μm to 10 μm. The average particle diameter is more preferably a lower limit of 0.1 μm or more, and more preferably an upper limit of 5 μm or less.
The particle size distribution of the heat-resistant filler of the present disclosure is preferably 0.1 μm <d90−d10 <3 μm.
The average particle size and particle size distribution of the heat resistant filler are values measured in the same manner as the average particle size and particle size distribution of the zinc oxide particles.

(Other fillers)
The heat-resistant porous layer of the present disclosure may contain other fillers in addition to the zinc oxide particles and the heat-resistant filler as long as the effects of the present invention are not impaired. As the other filler, either an inorganic filler made of an inorganic material or an organic filler made of an organic material may be used. By appropriately containing other fillers, it is possible to control the slipperiness and heat resistance of the separator.

When other fillers are used in combination, the content, the average particle diameter, and the particle size distribution are preferably controlled within a range not impairing the effects of the present invention.
Examples of the other inorganic fillers include carbonates such as calcium carbonate and magnesium carbonate, sulfates such as barium sulfate and calcium sulfate, and clay minerals such as calcium silicate and talc.

Examples of organic fillers include cross-linked acrylic resins such as cross-linked polymethyl methacrylate, or cross-linked polystyrene, and cross-linked polymethyl methacrylate is preferred.
In addition, other fillers may be used alone or in combination of two or more. Moreover, you may use the filler surface-modified by the silane coupling agent etc.
The content of the other filler is less than 5% by mass with respect to the total amount of the zinc oxide particles and the heat-resistant filler from the viewpoint of more effectively suppressing the generation of gas accompanying decomposition of the electrolytic solution and the electrolyte. It is preferable.
Moreover, in the heat resistant porous layer, the total content of the zinc oxide particles, the heat resistant filler, and the other filler is 30% from the solid content of the heat resistant porous layer from the viewpoint of improving the heat resistance. The content is preferably at least mass%, more preferably at least 50 mass%.

(Other ingredients)
The heat-resistant porous layer of the present disclosure may contain a dispersant such as a surfactant and other additives as necessary, as long as the effects of the present invention are not impaired. By including the dispersant, the dispersibility, the coatability, and the storage stability can be improved.
In addition, the heat-resistant porous layer includes a wetting agent for improving familiarity with the porous substrate, an antifoaming agent for suppressing air entrainment in the coating liquid, and a pH adjusting agent containing acid or alkali. Various additives such as may be contained. The additive may remain as long as it is electrochemically stable in the range of use of the lithium ion secondary battery and does not inhibit the reaction in the battery.

[Characteristics of heat-resistant porous layer]
In the non-aqueous secondary battery separator of the present disclosure, when the heat-resistant porous layer is formed by coating, the coating amount is 1.0 g / m ² or more as the total of both surfaces of the porous substrate. It is preferably 0 g / m ² or less.

  “Total of both surfaces of porous substrate” refers to the coating amount of one surface when the heat-resistant porous layer is provided on one surface of the porous substrate, and the heat-resistant porous layer is a porous substrate. When it is provided on both sides of the material, it indicates the total coating amount on both sides.

When the coating amount is 1.0 g / m ² or more, it is preferable in that the heat resistance is further improved. On the other hand, when the coating amount is 10.0 g / m ² or less, the ion permeability is improved, and the load characteristics of the battery are further improved. The coating amount is more preferably 1.5 g / m ² or more and 8.0 g / m ² or less as the total of both surfaces of the porous substrate.

Further, the coating amount on one side of the porous substrate is preferably 0.5 g / m ² or more and 5.0 g / m ² or less, and preferably 0.75 g / m ² or more and 4.0 g / m ² or less. More preferably.

  When the heat-resistant porous layer of the present disclosure is provided on both sides of the porous substrate, the difference between the coating amount on one side and the coating amount on the other side is 20 with respect to the total coating amount on both sides. It is preferable that it is below mass%. When the difference in the coating amount is 20% by mass or less, the separator is difficult to curl, so that the handling property is excellent.

  The thickness of the heat-resistant porous layer of the present disclosure is preferably 0.5 μm or more and 6 μm or less on one side of the porous substrate. When the thickness of the heat resistant porous layer is 0.5 μm or more, it is preferable from the viewpoint of securing sufficient heat resistance. From such a viewpoint, the thickness of the heat-resistant porous layer is more preferably 1 μm or more on one side of the porous substrate. On the other hand, when the thickness of the heat-resistant porous layer is 6 μm or less, the ion permeability becomes better and the load characteristics of the battery are more excellent. From such a viewpoint, the thickness of the heat-resistant porous layer is more preferably 5.5 μm or less, and further preferably 5.0 μm or less, on one side of the porous substrate.

The porosity of the heat-resistant porous layer of the present disclosure is preferably in the range of 30% to 80%. When the porosity is 80% or less, it is easy to secure mechanical properties that can be withstand during hot pressing. On the other hand, if the porosity is 30% or more, the ion permeability becomes better.
The porosity (ε) is a value obtained from the following formula.
ε = {1-Ws / (ds · t)} × 100
In the formula, ε represents porosity (%), Ws represents basis weight (g / m ² ), ds represents true density (g / cm ³ ), and t represents film thickness (μm).

  The average pore diameter of the heat-resistant porous layer of the present disclosure is preferably in the range of 10 nm to 200 nm when a polyvinylidene fluoride resin is used as the binder resin. When the average pore diameter is 200 nm or less, the nonuniformity of the pores is suppressed, the adhesion points are dispersed relatively evenly, and the adhesiveness is further improved. Moreover, when the average pore diameter is 200 nm or less, the uniformity of ion movement is high, and the cycle characteristics and load characteristics are further improved. On the other hand, when the average pore diameter is 10 nm or more, when the heat-resistant porous layer is impregnated with an electrolytic solution, the resin constituting the heat-resistant porous layer swells and blocks the pores, thereby inhibiting the ion permeability. This phenomenon is less likely to occur.

The average pore diameter (diameter, unit: nm) of the heat-resistant porous layer is determined from the pore surface area S of the heat-resistant porous layer made of polyvinylidene fluoride resin calculated from the nitrogen gas adsorption amount and the porosity. Using the calculated pore volume V of the heat-resistant porous layer, it is calculated from the following formula assuming that all the holes are cylindrical.
d = 4 · V / S
Wherein, d represents the average pore size of the heat-resistant porous layer (nm), V represents a pore volume of 1 m ² per heat-resistant porous layer, S is empty 1 m ² per heat-resistant porous layer Represents the pore surface area.
The pore surface area S per 1 m ^{2 of} the heat resistant porous layer is determined by the following method.

By applying the BET equation in a nitrogen gas adsorption method, a specific surface area of the porous substrate (m 2 ^{/ g),} specific surface area of the composite film obtained by laminating a porous substrate and a heat-resistant porous layer (m ² / g) and are measured. The specific surface area is multiplied by the basis weight (g / m ² ), and the pore surface area per 1 m ² is calculated. Next, the pore surface area per 1 m ^{2 of the} porous substrate is subtracted from the pore surface area per 1 m ² of the separator to calculate the pore surface area S per 1 m ² of the heat resistant porous layer.

[Characteristics of separators for non-aqueous secondary batteries]
The porosity of the nonaqueous secondary battery separator of the present disclosure is preferably in the range of 30% to 60% from the viewpoint of improving the mechanical properties of the separator.
The Gurley value according to the Japanese Industrial Standard (JIS P8117: 2009) of the separator for a non-aqueous secondary battery according to the present disclosure is 50 seconds / 100 cc to 800 seconds / 100 cc in terms of excellent balance between mechanical strength and membrane resistance. A range is preferred.

  The separator for a non-aqueous secondary battery according to the present disclosure preferably has a porous structure from the viewpoint of ion permeability. Specifically, a value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the non-aqueous secondary battery separator in a state where the heat resistant porous layer is formed (hereinafter referred to as Gurley value difference) is 300 seconds / 100 cc. Or less, more preferably 150 seconds / 100 cc or less, and even more preferably 100 seconds / 100 cc or less. When the Gurley value difference is 300 seconds / 100 cc or less, the heat-resistant porous layer does not become too dense, the ion permeability is kept good, and excellent battery characteristics are obtained. On the other hand, the Gurley value difference is preferably 0 sec / 100 cc or more, and preferably 10 sec / 100 cc or more in order to increase the adhesive force between the heat-resistant porous layer and the porous substrate.

Membrane resistance of the separator for a nonaqueous secondary battery of the present disclosure, in view of the load characteristics of the battery, 1ohm · cm ² or more 10 ohm · cm ² preferably in the following range. The membrane resistance is a resistance value when the separator is impregnated with an electrolytic solution, and is measured by an alternating current method. Since the value of the membrane resistance varies depending on the type and temperature of the electrolytic solution, the value of the membrane resistance is 20 using a mixed solvent of 1M LiBF ₄ -propylene carbonate / ethylene carbonate (= 1/1; mass ratio) as the electrolytic solution. It is a value measured at ° C.
The curvature of the separator for a non-aqueous secondary battery of the present disclosure is preferably in the range of 1.5 to 2.5 from the viewpoint of ion permeability.

The amount of water contained in the separator for a non-aqueous secondary battery of the present disclosure is preferably 1000 ppm or less. The smaller the moisture content of the non-aqueous secondary battery separator, the more the reaction between the electrolytic solution and water is suppressed when the battery is configured, and the gas generation in the battery can be more effectively suppressed. Thereby, the cycle characteristics of the battery are further improved. From such a viewpoint, the amount of water contained in the non-aqueous secondary battery separator is more preferably 800 ppm or less, and further preferably 500 ppm or less.
The film thickness of the separator for a nonaqueous secondary battery of the present disclosure is preferably 30 μm or less, and more preferably 25 μm or less, from the viewpoint of the energy density and output characteristics of the battery.
The puncture strength of the non-aqueous secondary battery separator of the present disclosure is preferably in the range of 250 g to 1000 g, and more preferably in the range of 300 g to 600 g.

[Method for producing separator for non-aqueous secondary battery]
The separator for a non-aqueous electrolyte battery of the present disclosure is formed by, for example, applying a coating liquid containing a binder resin, zinc oxide particles, and a heat-resistant filler on a porous substrate to form a coating layer. It is manufactured by a method in which the heat-resistant porous layer is integrally formed on the porous substrate by solidifying the resin of the working layer. Specifically, the heat resistant porous layer containing the binder resin can be formed by, for example, the following wet coating method.

  The wet coating method includes (i) a step of dissolving a binder resin in an appropriate solvent and dispersing zinc oxide particles and a heat-resistant filler to prepare a coating solution, (ii) making the coating solution porous A step of coating the substrate, (iii) a step of solidifying the binder resin while inducing phase separation by immersing the porous substrate in an appropriate coagulating liquid, (iv) a water washing step, and (v) This is a film forming method in which a heat-resistant porous layer is formed on a porous substrate by performing a drying process. The details of the wet coating method suitable for the present invention are as follows.

  Solvents for dissolving the binder resin and dispersing the zinc oxide particles and the heat-resistant filler (hereinafter also referred to as “good solvent”) used for preparing the coating liquid include N-methylpyrrolidone, dimethylacetamide, dimethyl Polar amide solvents such as formamide and dimethylformamide are preferably used.

From the viewpoint of forming a good porous structure, it is preferable to mix a phase separation agent that induces phase separation in addition to a good solvent. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol. The phase separation agent is preferably added in a range that can ensure a viscosity suitable for coating.
The solvent is preferably a mixed solvent containing 60% by mass or more of a good solvent and 40% by mass or less of a phase separation agent from the viewpoint of forming a good porous structure.

  The concentration of the resin in the coating liquid is preferably 1% by mass to 20% by mass with respect to the total mass of the coating liquid from the viewpoint of forming a good porous structure. When other components are contained in the heat-resistant porous layer, they may be mixed or dissolved in the coating solution.

  The coagulating liquid is generally composed of a good solvent used for preparing the coating liquid, a phase separation agent, and water. It is preferable in production that the mixing ratio of the good solvent and the phase separation agent is adjusted to the mixing ratio of the mixed solvent used for dissolving the resin. It is appropriate that the concentration of water is 40% by mass to 90% by mass from the viewpoint of formation of a porous structure and productivity.

  A conventional coating method such as a Meyer bar, a die coater, a reverse roll coater, or a gravure coater may be applied to apply the coating liquid to the porous substrate of the present disclosure. When forming a heat resistant porous layer on both surfaces of a porous base material, it is preferable from a viewpoint of productivity to apply a coating liquid to a base material simultaneously on both surfaces.

  The heat-resistant porous layer of the present disclosure can be produced by a dry coating method in addition to the wet coating method described above. The dry coating method is, for example, coating a porous substrate with a coating solution containing a binder resin, zinc oxide particles, a heat-resistant filler, and a solvent, and drying the coating layer to volatilize and remove the solvent. This is a method for obtaining a porous layer. However, since the dry coating method tends to be denser than the wet coating method, the wet coating method is preferred in that a good porous structure can be obtained.

<Non-aqueous secondary battery>
The non-aqueous secondary battery of the present disclosure includes the above-described separator for a non-aqueous secondary battery. Specifically, the non-aqueous secondary battery includes a positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery of the present disclosure that is disposed between the positive electrode and the negative electrode, and is doped with lithium. An electromotive force can be obtained by doping. Thereby, the non-aqueous secondary battery with which the deformation | transformation accompanying the swelling by gas generation was suppressed can be obtained.

In the nonaqueous secondary battery of the present disclosure, a separator is disposed between a positive electrode and a negative electrode, and these battery elements are enclosed in an exterior together with an electrolytic solution. As the non-aqueous secondary battery, a lithium ion secondary battery is suitable.
The dope means occlusion, support, adsorption, or insertion, and means a phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.
The positive electrode may have a structure in which an active material layer containing a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive.

Examples of the positive electrode active material include lithium-containing transition metal oxides, and specifically include 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 polyvinylidene fluoride resin.
Examples of the conductive assistant include carbon materials such as acetylene black, ketjen black, and graphite powder.
Examples of the current collector include aluminum foil, titanium foil, and stainless steel foil having a thickness of 5 μm to 20 μm.

In a non-aqueous secondary battery, when the heat-resistant porous layer of the separator is disposed on the positive electrode side, the heat-resistant porous layer is excellent in oxidation resistance, so LiMn _1/2 that can operate at a high voltage of 4.2 V or higher A positive electrode active material such as Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ is easy to apply and is advantageous.

The negative electrode may have a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive.
Examples of the negative electrode active material include materials that can occlude lithium electrochemically. Examples thereof include carbon materials; alloys of silicon, tin, aluminum, and the like with lithium.

Examples of the binder resin include polyvinylidene fluoride resin and styrene-butadiene rubber.
Examples of the conductive aid include carbon materials such as acetylene black, ketjen black, and graphite powder.

Examples of the current collector include copper foil, nickel foil, and stainless steel foil having a thickness of 5 to 20 μm. Moreover, it may replace with said negative electrode and may use metal lithium foil as a negative electrode.
The electrolytic solution 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 , LiClO _{4, and the} like. Examples of non-aqueous solvents 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; A non-aqueous solvent may be used individually by 1 type, or may be mixed and used.

As an electrolytic solution, cyclic carbonate and chain carbonate are mixed at a mass ratio of 20/80 to 40/60 (= cyclic carbonate / chain carbonate), and lithium salt is in the range of 0.5 mol to 1.5 mol. What was melt | dissolved in is suitable.
Examples of the exterior material include a metal can and a soft pack such as an aluminum laminate film.

In the case of a configuration using a polyvinylidene fluoride resin as a binder resin used in the separator for a non-aqueous secondary battery of the present disclosure, for example, an impact from the outside, expansion and contraction of an electrode accompanying charging / discharging, accompanying charging / discharging Formation of a gap due to poor adhesion between the electrode and the separator due to charging or the like is suppressed, charge / discharge characteristics (cycle characteristics) are improved, and battery strength (so-called cell strength) is further improved. In addition, such a non-aqueous secondary battery separator is favorably bonded to the electrode under an appropriate hot press temperature condition, which contributes to improvement in the quality stability of the soft pack battery.
The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the above-described separator for a non-aqueous secondary battery is suitable for any shape.

  The non-aqueous secondary battery of the present disclosure is, for example, a laminate in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode in the case of using a polyvinylidene fluoride resin as a binder resin of a separator for a non-aqueous secondary battery. After manufacturing this, it can manufacture by the manufacturing method of following 1) -2) using this laminated body, for example.

1) After heat-pressing (dry heat-pressing) the laminate and bonding the electrode and the separator, the laminate is housed in an exterior material (for example, an aluminum laminate film pack; the same applies hereinafter), and an electrolyte is injected therein, and the exterior material The laminate is further hot-pressed (wet heat press) from above, and adhesion between the electrode and the separator and sealing of the exterior material are performed.
2) The laminated body is accommodated in an exterior material, an electrolyte is injected therein, the laminated body is hot-pressed (wet heat press) from above the exterior material, adhesion between the electrode and the separator, sealing of the exterior material, I do.

According to the manufacturing method of 1) above, since the electrode and the separator are bonded prior to housing the laminate in the exterior material, deformation of the laminate that occurs during transportation for housing in the exterior material is suppressed, Excellent battery strength and dimensional stability, and battery characteristics.
In addition, the wet heat press may be performed under such a mild condition that the adhesion between the electrode and the separator, which has been somewhat attenuated by impregnation with the electrolytic solution, is recovered, that is, the temperature of the wet heat press can be set to a relatively low temperature. Therefore, gas generation due to decomposition of the electrolytic solution and electrolyte in the battery during battery manufacture is further suppressed, and the battery strength and dimensional stability and battery characteristics are excellent.
In addition, since the laminate is further hot-pressed in a state where the polyvinylidene fluoride-based resin is swollen in the electrolytic solution, the adhesion between the electrode and the separator becomes stronger, and the battery strength and battery characteristics are excellent.

  According to the production method of 2) above, since the laminate is hot-pressed in a state where the polyvinylidene fluoride resin is swollen in the electrolyte solution, the electrode and the separator are well bonded, and the battery strength and battery characteristics are excellent.

For the non-aqueous secondary battery to which the separator of the present disclosure is applied, for example, any of the manufacturing methods described above can be selected. From the viewpoint of suppressing deformation of the laminated body and further suppressing peeling of the electrode and the separator in response to an increase in the area of the battery, the production method 1) is preferable.
As the wet heat press conditions in the production methods 1) and 2) above, the press pressure is preferably in the range of 0.5 MPa to 2 MPa, and the temperature is preferably in the range of 70 ° C to 110 ° C. Moreover, as for the conditions of dry heat pressing, the press pressure is preferably in the range of 0.5 MPa to 5 MPa, and the temperature is preferably in the range of 20 to 100 ° C.

  In the case of a configuration using a polyvinylidene fluoride resin as a binder resin used in the separator for a non-aqueous secondary battery of the present disclosure, the separator can be adhered by being overlapped with an electrode. Therefore, although pressing is not an essential step in battery production, it is preferable to perform pressing from the viewpoint of strengthening the adhesion between the electrode and the separator. Furthermore, from the viewpoint of further strengthening the adhesion between the electrode and the separator, the press is preferably a press while heating (hot press).

  When manufacturing a laminated body, the system which arrange | positions a separator between a positive electrode and a negative electrode may be a system (what is called a stack system) which laminates | stacks a positive electrode, a separator, and a negative electrode one layer at a time in this order (so-called stack system). Alternatively, the separators may be stacked in this order and rolled in the longitudinal direction. The “longitudinal direction” means the longitudinal direction of the separator manufactured in a long shape, and the direction orthogonal to the longitudinal direction of the separator is the “width direction”.

Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
[Measurement and evaluation]
In the following examples and comparative examples, the following measurements and evaluations were performed. The results of measurement and evaluation are shown in Table 1 below.

(HFP content of polyvinylidene fluoride resin)
The content ratio (HFP content) of hexafluoropropylene monomer units (HFP units) in the polyvinylidene fluoride resin was determined from the NMR spectrum. Specifically, 20 mg of polyvinylidene fluoride resin was dissolved in 0.6 ml of heavy dimethyl sulfoxide at 100 ° C., and the 19F-NMR spectrum was measured at 100 ° C. to obtain.

(Weight average molecular weight of polyvinylidene fluoride resin)
The weight average molecular weight of the polyvinylidene fluoride resin was measured by gel permeation chromatography (GPC) under the following conditions, and calculated in terms of polystyrene.
<Conditions>
・ GPC: GPC-900 (manufactured by JASCO)
Column: TSKgel Super AWM-H (2) (manufactured by Tosoh Corporation)
-Mobile phase solvent: dimethylformamide (DMF)
Standard sample: Monodispersed polystyrene (manufactured by Tosoh Corporation)
-Column temperature: 40 ° C
・ Flow rate: 10ml / min

(Thickening rate of coating solution)
The viscosity of the coating solution containing the binder resin, the zinc oxide particles, and the heat-resistant filler was measured by the following procedure. Using a measurement spindle (SC4-18) with a B-type viscometer (DV-I PRIME manufactured by Brookfield), the viscosity at a spindle rotation speed of 10 rpm was measured. In addition, the liquid temperature of the coating liquid was measured using a thermostat while keeping the temperature at 20 ° C. The viscosity immediately after adjusting the coating solution was set to V0. Moreover, the viscosity of the coating liquid that was mixed in a hermetically sealed container immediately after the coating liquid was adjusted and mixed for 24 hours at 70 rpm with a mix rotor (manufactured by ASONE VMR-5R) under a constant temperature condition of 25 ° C. was defined as Vm. did.
The viscosity increase rate of the coating solution was calculated by the following formula.
Thickening rate of coating liquid = Vm / V0 × 100

(Film thickness)
The thickness of the separator was measured using a contact-type thickness meter (LITEMATIC, manufactured by Mitutoyo Corporation). The measurement terminal was a cylindrical one having a diameter of 5 mm, and was adjusted so that a load of 7 g was applied during the measurement, and the average value of the thickness at 20 points was obtained.

(Heat-resistant)
The area of the hole (mm ² ) generated when the tip of a soldering iron with a tip diameter of 2 mm and a tip temperature of 260 ° C. was applied directly to the separator cut into 5 cm × 5 cm and the tip of the soldering iron was applied for 60 seconds. Was measured to evaluate the heat resistance of the separator.

(Gas generation test)
The separator is cut out to a size of 600 cm ² to make a sample piece. The sample piece is placed in an aluminum laminate film pack, the electrolyte is injected into the pack, the separator is impregnated with the electrolyte, and then sealed. A cell was produced. Here, the electrolytic solution was 1 mol / L LiPF ₆ -ethylene carbonate: ethyl methyl carbonate [mass ratio 3: 7].
The prepared test cell was placed in a temperature environment of 85 ° C. and heat-treated for 20 days. Then, the volume of the test cell before and after the heat treatment is measured, and the gas generation amount V (= V2−V1, unit: ml) is obtained by subtracting the volume V1 of the test cell before the heat treatment from the volume V2 of the test cell after the heat treatment. It was.

(Wet adhesive strength with electrode)
91 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 are dissolved in N-methyl-pyrrolidone so that the concentration of polyvinylidene fluoride is 5% by mass. Then, the mixture was stirred with a double arm mixer to prepare a positive electrode slurry. This positive electrode slurry was applied to one side of an aluminum foil with a thickness of 20 μm, dried and pressed to obtain a positive electrode (single side coating) having a positive electrode active material layer as an electrode for evaluating the wet adhesion between the separator and the electrode. .

The electrode and the aluminum foil (thickness 20 μm) obtained above were cut into a width of 1.5 cm and a length of 7 cm, respectively, and each separator obtained in the following examples and comparative examples was 1.8 cm in width and 7.5 cm in length. Cut into. An electrode-separator-aluminum foil is laminated in order to produce a laminate, and an electrolytic solution (1 mol / L LiBF ₄ -ethylene carbonate: propylene carbonate [mass ratio 1: 1]) is soaked in the laminate to obtain aluminum. Housed in a laminate film pack. Next, the inside of the pack was evacuated using a vacuum sealer, and the laminated body was hot-pressed together with the pack using a hot press to bond the electrode and the separator. The conditions for hot pressing were a pressure of 1 MPa, a temperature of 90 ° C., and a pressing time of 2 minutes. Thereafter, the pack was opened, the laminate was taken out, and the one obtained by removing the aluminum foil from the laminate was used as a measurement sample.

  The uncoated surface of the electrode of the measurement sample was fixed to a metal plate with double-sided tape, and the metal plate was fixed to the lower chuck of Tensilon (manufactured by A & D, STB-1225S). At this time, the metal plate was fixed to Tensilon so that the length direction of the measurement sample was the gravity direction. The separator was peeled from the electrode by about 2 cm from the lower end, and the end was fixed to the upper chuck so that the tensile angle (angle of the separator with respect to the measurement sample) was 180 °. The separator was pulled at a pulling speed of 20 mm / min, and the load when the separator was peeled off from the electrode was measured. Loads from 10 mm to 40 mm at the start of measurement were sampled at intervals of 0.4 mm. The same measurement was performed 3 times, the average was calculated, and it was set as the wet adhesive force (N / 15mm, the adhesive force between the electrode and separator by wet heat press) with an electrode.

(Battery strength)
91 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 are dissolved in N-methyl-pyrrolidone so that the concentration of polyvinylidene fluoride is 5% by mass. Then, the mixture was stirred with a double arm mixer to prepare a positive electrode slurry. This positive electrode slurry was applied to one side 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 negative electrode active material, 7.5 g of water-soluble dispersion containing 40% by mass of modified styrene-butadiene copolymer as binder, 3 g of carboxymethyl cellulose as thickener, and appropriate amount of water The mixture was stirred and mixed with 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 positive electrode and the negative electrode were overlapped and wound through the separators obtained in the following examples and comparative examples, and lead tabs were welded to obtain battery elements. This battery element is housed in an aluminum laminate film pack and impregnated with an electrolytic solution, and then heat press (wet heat press) is performed at a pressure of 1 MPa, a temperature of 90 ° C. for 2 minutes to seal the exterior. Thus, a secondary battery for test (length 65 mm, width 35 mm, thickness 2.5 mm: capacity 700 mAh) was obtained. Here, 1 mol / L LiPF ₆ -ethylene carbonate: diethyl carbonate (mass ratio 3: 7) was used as the electrolytic solution.
The secondary battery for test obtained above was subjected to a three-point bending test in accordance with ISO-178 to obtain battery strength (cell strength).

(Cycle characteristics)
A test secondary battery was produced in the same manner as in the production method for “battery strength”.
Charge / discharge cycle under the conditions of 4.2V constant current at 1C, constant voltage charge for 2 hours, and constant current discharge with 3V cut-off at 1C in a 25 ° C environment using the fabricated test secondary battery The ratio of the discharge capacity obtained after 500 cycles based on the discharge capacity obtained in the first cycle is obtained as a percentage (%; = discharge capacity after 500 cycles / discharge capacity at the first cycle × 100) The obtained value was used as an index for evaluating the cycle characteristics.

[Example 1]
As a polyvinylidene fluoride resin as a binder resin, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer, VDF: HFP (molar ratio)) = 97.6: 2 .4, weight average molecular weight = 1.13 million). This VDF-HFP copolymer was dissolved in a mixed solvent (dimethylacetamide / tripropylene glycol = 80/20 [mass ratio]) so as to have a concentration of 4% by mass, and hexagonal plate-type zinc oxide as a filler. Particles (XZ-300F, manufactured by Sakai Chemical Industry Co., Ltd., average particle size: 0.3 μm), and magnesium hydroxide (Mg (OH) ₂ , Kyowa Chemical Industry Co., Ltd. Kisuma 5P, average primary particle size of 0.8 μm) are added. And the mass ratio of VDF-HFP copolymer, zinc oxide and Mg (OH) ₂ is 40: 6: 54 (= VDF-HFP copolymer: zinc oxide: Mg (OH) ₂ ) A coating solution was prepared. The content of the zinc oxide particles with respect to the total amount of the zinc oxide particles and Mg (OH) ₂ as the heat-resistant filler is 10% by mass.

The prepared coating solution was applied to both sides of a polyethylene microporous membrane (film thickness: 9 μm, porosity: 40%, Gurley value: 152 seconds / 100 cc) as a porous substrate, and a coagulation solution (dimethylacetamide) / Tripropylene glycol / water = 30/8/62 [mass ratio], temperature 40 ° C.) and solidified.
Next, the coated polyethylene microporous membrane was washed with water and further dried to obtain a separator in which a heat-resistant porous layer having a thickness of 5 μm was formed on both sides of the polyethylene microporous membrane.
Moreover, said measurement and evaluation were performed with respect to the obtained separator. The results of measurement and evaluation are shown in Table 1 below.

[Example 2]
In Example 1, except that the content of zinc oxide particles with respect to the total amount of zinc oxide particles and magnesium hydroxide (Mg (OH) ₂ ), which is a heat-resistant filler, was changed from 10% by mass to 20% by mass. In the same manner as in Example 1, a separator having heat-resistant porous layers formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Example 3]
In Example 1, except that the content of zinc oxide particles relative to the total amount of zinc oxide particles and magnesium hydroxide (Mg (OH) ₂ ), which is a heat-resistant filler, was changed from 10% by mass to 80% by mass. In the same manner as in Example 1, a separator having heat-resistant porous layers formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Example 4]
In Example 1, except that the content of zinc oxide particles relative to the total amount of zinc oxide particles and magnesium hydroxide (Mg (OH) ₂ ), which is a heat-resistant filler, was changed from 10% by mass to 90% by mass. In the same manner as in Example 1, a separator having heat-resistant porous layers formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Example 5]
In Example 1, except that magnesium hydroxide (Mg (OH) ₂ ) was replaced with magnesium oxide (MgO, PUREMAG (registered trademark) FNM-G manufactured by Tateho Chemical Industry Co., Ltd., average primary particle size 0.5 μm). In the same manner as in Example 1, a separator having heat-resistant porous layers formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Example 6]
In Example 1, hexagonal plate-type zinc oxide particles (XZ-300F, manufactured by Sakai Chemical Industry Co., Ltd., average particle size: 0.3 μm) were converted into amorphous zinc oxide particles (FINEX30, manufactured by Sakai Chemical Industry Co., Ltd., average particle size). : 0.03 μm) Except that the separator was replaced with 0.03 μm), a separator having a heat-resistant porous layer formed on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example 1, and the obtained separator was measured and evaluated. Went. The results of measurement and evaluation are shown in Table 1 below.

[Example 7]
In Example 1, hexagonal plate-shaped zinc oxide particles (XZ-300F, manufactured by Sakai Chemical Industry Co., Ltd., average particle size: 0.3 μm) were mixed with plate-shaped integrated spherical zinc oxide particles (CANDY ZINC 1000, Sakai Chemical Industry Co., Ltd.). Manufactured, average particle diameter: 1.0 μm), except that the separator having the heat-resistant porous layer formed on both sides of the polyethylene microporous membrane was obtained in the same manner as in Example 1, and the obtained separator Measurements and evaluations were performed. The results of measurement and evaluation are shown in Table 1 below.

[Example 8]
In Example 1, except that the content of zinc oxide particles relative to the total amount of zinc oxide particles and magnesium hydroxide (Mg (OH) ₂ ) as a heat resistant filler was changed from 10% by mass to 2% by mass. In the same manner as in Example 1, a separator having heat-resistant porous layers formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Example 9]
Example 1 except that the polyvinylidene fluoride resin, which is a binder resin, is replaced with Conex (registered trademark; manufactured by Teijin Techno Products), which is a meta-type wholly aromatic polyamide (meta-aramid resin). In the same manner as above, a separator having a heat-resistant porous layer formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Comparative Example 1]
In Example 1, polyethylene microporous material was obtained in the same manner as in Example 1 except that no zinc oxide particles were added and the mass ratio of VDF-HFP copolymer to Mg (OH) ₂ was 40:60. A comparative separator having heat-resistant porous layers formed on both sides of the membrane was obtained. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 1. The results of measurement and evaluation are shown in Table 1 below.

[Comparative Example 2]
In Example 5, except that the zinc oxide particles were not added and the mass ratio of the VDF-HFP copolymer and MgO was 31:69, both sides of the polyethylene microporous membrane were the same as in Example 5. A comparative separator on which a heat-resistant porous layer was formed was obtained. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 1. The results of measurement and evaluation are shown in Table 1 below.

  As shown in Table 1, in the separator of the example in which one or more heat-resistant fillers selected from the group consisting of metal hydroxides and metal oxides other than zinc oxide and zinc oxide particles are used in combination at a predetermined ratio It exhibited good heat resistance, suppressed the generation of gas accompanying decomposition of the electrolytic solution, and suppressed battery shape change (deformation) associated with swelling. Moreover, in the Example containing VDF-HFP copolymer as binder resin, the adhesiveness by wet heat press becomes more favorable compared with Example 9 containing aramid which is another resin, and the strength of the produced battery It was also excellent.

  On the other hand, in the composition containing only the heat-resistant filler and not containing the zinc oxide particles as in Comparative Example 1, although the effect of improving the heat resistance and battery strength by the filler appears, it occurs due to the decomposition of the electrolytic solution. A lot of gas was confirmed.

Claims (7)

A porous substrate;
A non-aqueous secondary battery separator comprising a heat-resistant porous layer provided on one side or both sides of the porous substrate,
The heat-resistant porous layer comprises (1) a binder resin, (2) zinc oxide particles, (3) a metal hydroxide, and one or more selected from the group consisting of metal oxides other than zinc oxide. Including a heat-resistant filler, and
The content of the zinc oxide particles relative to the total content of the zinc oxide particles and the heat-resistant filler is 2% by mass or more and less than 100% by mass,
Separator for non-aqueous secondary battery.   2. The separator for a non-aqueous secondary battery according to claim 1, wherein the heat-resistant filler is one or more heat-resistant fillers selected from the group consisting of magnesium hydroxide, aluminum hydroxide, aluminum oxide, boehmite, and magnesium oxide.   The separator for a non-aqueous secondary battery according to claim 1, wherein the zinc oxide particles have an average particle diameter of 0.1 μm to 1 μm.   The binder resin is a copolymer including a vinylidene fluoride monomer unit and a hexafluoropropylene monomer unit, and the hexafluoropropylene monomer unit includes the vinylidene fluoride monomer unit and the The non-aqueous system according to any one of claims 1 to 3, which is a polyvinylidene fluoride resin that is 1.0 mol% or more and 7.0 mol% or less with respect to the total amount of hexafluoropropylene monomer units. Secondary battery separator.   The separator for a non-aqueous secondary battery according to claim 4, wherein the polyvinylidene fluoride resin has a weight average molecular weight of 600,000 to 3,000,000.   The said heat resistant porous layer WHEREIN: The sum total content of the particle | grains of the said zinc oxide and the said heat resistant filler is 30 volume% or more and 85 volume% or less, The non-according to any one of Claims 1-5. Separator for water-based secondary battery.   A non-aqueous secondary battery separator according to any one of claims 1 to 6, which is disposed between the positive electrode, the negative electrode, and the positive electrode and the negative electrode. A non-aqueous secondary battery that obtains an electromotive force.

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