阅读说明：本技术 非水系二次电池用隔膜及非水系二次电池 (Separator for nonaqueous secondary battery and nonaqueous secondary battery ) 是由 本多劝 西川聪 于 2020-06-03 设计创作，主要内容包括：本发明的一个实施方式提供非水系二次电池用隔膜,其具备：多孔质基材；耐热性多孔质层,其被设置于上述多孔质基材的一面或两面,并含有粘结剂树脂、及平均一次粒径为0.01μm以上且小于0.45μm的无机粒子；和粘接层,其被设置于上述多孔质基材与上述耐热性多孔质层的层叠体的一面或两面,且是粘接性树脂粒子附着于上述层叠体上而成的。(One embodiment of the present invention provides a separator for a nonaqueous secondary battery, including: a porous substrate; a heat-resistant porous layer provided on one or both surfaces of the porous base material, the heat-resistant porous layer containing a binder resin and inorganic particles having an average primary particle diameter of 0.01 μm or more and less than 0.45 μm; and an adhesive layer provided on one or both surfaces of a laminate of the porous base material and the heat-resistant porous layer, the adhesive layer being formed by adhesive resin particles adhering to the laminate.)

1. A separator for a nonaqueous secondary battery, comprising:

a porous substrate;

a heat-resistant porous layer which is provided on one or both surfaces of the porous base material and contains a binder resin and inorganic particles having an average primary particle diameter of 0.01 μm or more and less than 0.45 μm; and

and an adhesive layer provided on one or both surfaces of a laminate of the porous base material and the heat-resistant porous layer, the adhesive layer being formed by adhesive resin particles adhering to the laminate.

2. The separator for a nonaqueous secondary battery according to claim 1, wherein the heat shrinkage rates in the MD direction and the TD direction when the separator for a nonaqueous secondary battery is subjected to a heat treatment at 150 ℃ for 1 hour are 10% or less.

3. The separator for a nonaqueous secondary battery according to claim 1 or 2, wherein the heat shrinkage rates in the MD direction and the TD direction when the separator for a nonaqueous secondary battery is subjected to a heat treatment at 130 ℃ for 1 hour are 6% or less.

4. The separator for a nonaqueous secondary battery according to any one of claims 1 to 3, wherein the heat-resistant porous layer has a porosity of 30% to 70%.

5. The separator for a nonaqueous secondary battery according to any one of claims 1 to 4, wherein the mass ratio of the inorganic particles in the heat-resistant porous layer is 50 to 90% by mass relative to the total mass of the heat-resistant porous layer.

6. The separator for a nonaqueous secondary battery according to any one of claims 1 to 5, wherein the inorganic particles contain at least one selected from the group consisting of magnesium-based particles and barium-based particles.

7. The nonaqueous secondary battery separator according to any one of claims 1 to 6, wherein the binder resin contains at least one selected from the group consisting of wholly aromatic polyamide, polyamideimide, and polyimide.

8. The separator for a nonaqueous secondary battery according to any one of claims 1 to 7, wherein the adhesive resin particles comprise a mixture of first adhesive resin particles comprising a polyvinylidene fluoride resin and second adhesive resin particles comprising an acrylic resin.

9. The separator for a nonaqueous secondary battery according to any one of claims 1 to 8, wherein the heat-resistant porous layer has a mass per unit area of 2.0g/m in total on both sides²～10.0g/m²。

10. The separator for a nonaqueous secondary battery according to any one of claims 1 to 9, wherein the heat-resistant porous layer has a thickness of 0.5 μm to 4.0 μm per one surface.

11. The separator for a nonaqueous secondary battery according to any one of claims 1 to 10, wherein a difference between a Gurley value of the separator for a nonaqueous secondary battery and a Gurley value of the porous base material is 20 sec/100 mL to 300 sec/100 mL.

12. A nonaqueous secondary battery comprising a positive electrode, a negative electrode, and the separator for a nonaqueous secondary battery according to any one of claims 1 to 11, which is disposed between the positive electrode and the negative electrode, wherein the nonaqueous secondary battery obtains electromotive force by doping/dedoping lithium.

Technical Field

The present invention relates to a separator for a nonaqueous secondary battery and a nonaqueous secondary battery.

Background

Nonaqueous secondary batteries typified by lithium ion secondary batteries have been widely used as power sources for portable electronic devices such as notebook personal computers, cellular phones, digital cameras, and camcorders. In addition, nonaqueous secondary batteries typified by lithium ion secondary batteries have been studied for use as batteries for power storage and electric vehicles due to their high energy density.

As nonaqueous secondary batteries have become popular, it is increasingly required to ensure safety and stable battery characteristics. Specific measures for ensuring safety and stable battery characteristics include improving the heat resistance of the separator and improving the adhesion between the electrode and the separator.

As a separator having improved heat resistance, a separator including a heat-resistant porous layer containing at least one of inorganic particles and a heat-resistant resin is known. As a separator having improved adhesion to an electrode, a separator including an adhesive layer containing a resin having adhesion to an electrode is known. For example, the separators disclosed in patent documents 1 to 7 include both a heat-resistant porous layer and an adhesive layer.

Patent document 1: japanese patent No. 5971662

Patent document 2: japanese patent No. 5976015

Patent document 3: japanese patent No. 5946257

Patent document 4: japanese patent No. 6112115

Patent document 5: international publication No. 2013/151144

Patent document 6: japanese patent laid-open publication No. 2013-20769

Patent document 7: japanese patent No. 6513893

Disclosure of Invention

Problems to be solved by the invention

However, in the separator including both the heat-resistant porous layer and the adhesive layer as in the conventional art, since the number of layers is large, the film thickness as a whole of the separator tends to be large. From the viewpoint of improving the energy density of the battery, it is desired to further reduce the thickness of the separator. On the other hand, in order to make the separator thin, it is considered to form the heat-resistant porous layer thin. However, when the heat-resistant porous layer is formed to be thin, the heat resistance of the separator tends to be lowered. As described above, in the separator including both the heat-resistant porous layer and the adhesive layer, the thinning of the separator and the heat resistance are in a trade-off relationship, and how to realize both of them at the same time is a technical problem.

Embodiments of the present disclosure have been made in view of the above-described situation.

An object of an embodiment of the present disclosure is to provide a separator for a nonaqueous secondary battery, which can realize both thinning and heat resistance, in a separator for a nonaqueous secondary battery including a heat-resistant porous layer and an adhesive layer, and to achieve the object.

Means for solving the problems

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

[1] A separator for a nonaqueous secondary battery, comprising:

a porous substrate;

a heat-resistant porous layer provided on one or both surfaces of the porous base material, the heat-resistant porous layer containing a binder resin and inorganic particles having an average primary particle diameter of 0.01 μm or more and less than 0.45 μm; and

and an adhesive layer provided on one or both surfaces of a laminate of the porous base material and the heat-resistant porous layer, the adhesive layer being formed by adhesive resin particles adhering to the laminate.

[2] The separator for a nonaqueous secondary battery according to [1], wherein the heat shrinkage rates in the MD direction and the TD direction when the separator for a nonaqueous secondary battery is subjected to a heat treatment at 150 ℃ for 1 hour are 10% or less.

[3] The separator for a nonaqueous secondary battery according to the above [1] or [2], wherein the heat shrinkage rates in the MD direction and the TD direction when the separator for a nonaqueous secondary battery is subjected to a heat treatment at 130 ℃ for 1 hour are 6% or less.

[4] The separator for a nonaqueous secondary battery according to any one of the above [1] to [3], wherein the heat-resistant porous layer has a porosity of 30% to 70%.

[5] The separator for a nonaqueous secondary battery according to any one of the above [1] to [4], wherein a mass ratio of the inorganic particles in the heat-resistant porous layer is 50% by mass to 90% by mass with respect to a total mass of the heat-resistant porous layer.

[6] The separator for a nonaqueous secondary battery according to any one of the above [1] to [5], wherein the inorganic particles include at least one selected from the group consisting of magnesium-based particles and barium-based particles.

[7] The nonaqueous secondary battery separator according to any one of the above [1] to [6], wherein the binder resin contains at least one selected from the group consisting of wholly aromatic polyamide, polyamideimide, and polyimide.

[8] The separator for a nonaqueous secondary battery according to any one of the above [1] to [7], wherein the adhesive resin particles comprise a mixture of first adhesive resin particles comprising a polyvinylidene fluoride resin and second adhesive resin particles comprising an acrylic resin.

[9]As described above [1]-above [8]The separator for a nonaqueous secondary battery according to any one of the above items, wherein the heat-resistant porous layer has a mass per unit area of 2.0g/m in total on both sides²～10.0g/m²。

[10] The separator for a nonaqueous secondary battery according to any one of the above [1] to [9], wherein the heat-resistant porous layer has a thickness of 0.5 μm to 4.0 μm per one surface.

[11] The separator for a nonaqueous secondary battery according to any one of the above [1] to [10], wherein a difference between a Gurley value of the separator for a nonaqueous secondary battery and a Gurley value of the porous base material is 20 seconds/100 mL to 300 seconds/100 mL.

[12] A nonaqueous secondary battery comprising a positive electrode, a negative electrode, and the separator for a nonaqueous secondary battery according to any one of [1] to [11] disposed between the positive electrode and the negative electrode, wherein the nonaqueous secondary battery obtains an electromotive force by doping and dedoping of lithium.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, a separator for a nonaqueous secondary battery having a heat-resistant porous layer and an adhesive layer can be provided, which can realize both a reduction in thickness and heat resistance.

Drawings

Fig. 1A is a schematic cross-sectional view showing one embodiment of a separator for a nonaqueous secondary battery according to the present disclosure.

Fig. 1B is a schematic cross-sectional view showing another embodiment of the separator for a nonaqueous secondary battery according to the present disclosure.

Fig. 1C is a schematic cross-sectional view showing another embodiment of the separator for a nonaqueous secondary battery according to the present disclosure.

Fig. 1D is a schematic cross-sectional view showing another embodiment of the separator for a nonaqueous secondary battery according to the present disclosure.

Detailed Description

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

In the present disclosure, the numerical range shown by "to" indicates a range including numerical values before and after "to" as a minimum value and a maximum value, respectively. In the numerical ranges recited in the present disclosure in stages, the upper limit value or the lower limit value recited in a certain numerical range may be replaced with the upper limit value or the lower limit value recited in another numerical range recited in stages. In the numerical ranges described in the present disclosure, the upper limit or the lower limit described in a certain numerical range may be replaced with the values shown in the examples.

In the present disclosure, the term "step" includes not only an independent step but also a step that is not clearly distinguished from other steps, and is included in the term as long as the desired purpose of the step is achieved.

In the present disclosure, references to the amounts of each ingredient in the composition, and the presence of a plurality of substances belonging to each ingredient in the composition, refer to the total amount of the plurality of substances present in the composition, unless otherwise specified.

In the present disclosure, the "MD direction" refers to a longitudinal direction (i.e., a conveying direction) of a porous base material and a separator manufactured in a long shape, and is also referred to as a "machine direction". The "TD direction" is a direction perpendicular to the "MD direction" and is also referred to as a "transverse direction".

In the present disclosure, a combination of 2 or more preferred embodiments is a more preferred embodiment.

In the present disclosure, in terms of the amount of each component in the composition or layer, when a plurality of substances belonging to each component are present in the composition, the total amount of the plurality of substances present in the composition is referred to unless otherwise specified.

In the present disclosure, "mass%" and "weight%" mean the same, and "parts by mass" and "parts by weight" mean the same.

In the present disclosure, when the stacking relationship of the layers constituting the separator is represented by "upper" and "lower", a layer closer to the substrate is referred to as "lower", and a layer farther from the substrate is referred to as "upper".

In the present disclosure, when the embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. The sizes of the components in the drawings are conceptual only, and the relative relationship between the sizes of the components is not limited to this.

In the present disclosure, the expression "(meth) acryl-" refers to "acryl-" or "methacryl-".

The weight average molecular weight (Mw) in the present disclosure is a value measured by Gel Permeation Chromatography (GPC).

Specifically, Mw was measured by dissolving a sample of the microporous polyethylene membrane in o-dichlorobenzene under heating and measuring the solution by GPC (Alliance GPC 2000 type manufactured by Waters, column: GMH6-HT and GMH6-HTL) at a column temperature of 135 ℃ and a flow rate of 1.0 mL/min. Molecular weight monodisperse polystyrene (available from Tosoh corporation) can be used for the molecular weight calibration.

The heat-resistant resin in the present disclosure means a resin having a melting point of 180 ℃ or higher, or a resin having no melting point and having a decomposition temperature of 180 ℃ or higher. That is, the heat-resistant resin in the present disclosure means a resin that does not melt or decompose in a temperature region lower than 180 ℃.

< separator for nonaqueous Secondary Battery >

The separator for a nonaqueous secondary battery (hereinafter, also referred to as "separator") according to the present disclosure includes: a porous substrate; a heat-resistant porous layer provided on one or both surfaces of the porous base material, the heat-resistant porous layer containing a binder resin and inorganic particles having an average primary particle diameter of 0.01 μm or more and less than 0.45 μm; and an adhesive layer provided on one or both surfaces of a laminate of the porous base material and the heat-resistant porous layer, the adhesive layer being formed by adhesive resin particles adhering to the laminate.

Examples of the layer structure of the separator of the present disclosure will be described with reference to the drawings.

Fig. 1A-1D are each a schematic cross-sectional view of an embodiment of a diaphragm of the present disclosure. Fig. 1A to 1D are schematic cross-sectional views mainly for explaining a lamination sequence of layers, and the structures of the layers are abstracted or simplified. In fig. 1A to 1D, layers having the same functions are described with the same reference numerals.

The separator 10A shown in fig. 1A is a separator in which the heat-resistant porous layers 30 are disposed on both surfaces of the porous substrate 20, and the adhesive layers 50 are disposed on both surfaces of the laminate 40 of the porous substrate 20 and 2 heat-resistant porous layers 30.

The separator 10B shown in fig. 1B is a separator in which the heat-resistant porous layers 30 are disposed on both surfaces of the porous substrate 20, and the adhesive layer 50 is disposed on one surface of the laminate 40 of the porous substrate 20 and 2 heat-resistant porous layers 30.

The separator 10C shown in fig. 1C is a separator in which the heat-resistant porous layer 30 is disposed on one surface of the porous substrate 20, and the adhesive layers 50 are disposed on both surfaces of the laminate 40 of the porous substrate 20 and one heat-resistant porous layer 30.

The separator 10D shown in fig. 1D is a separator in which the heat-resistant porous layer 30 is disposed on one surface of the porous substrate 20, and the adhesive layer 50 is disposed on one surface of the laminate 40 of the porous substrate 20 and one heat-resistant porous layer 30. In the separator 10D, the adhesive layer 50 is disposed on the surface of the heat-resistant porous layer 30.

In addition, although not shown, the separator of the present disclosure may be a separator in which a heat-resistant porous layer is disposed on one surface of a porous substrate and an adhesive layer is disposed on the other surface of the porous substrate.

Heat resistant porous layer

The heat-resistant porous layer in the present disclosure is a layer disposed on a porous substrate (preferably, on the surface of the porous substrate). The heat-resistant porous layer may be present on only one side of the porous substrate, or may be present on both sides of the porous substrate. When the heat-resistant porous layer is present on both surfaces of the porous substrate, the separator has more excellent heat resistance, and the safety of the battery can be further improved. In addition, the separator is less likely to curl, and the workability in battery production is excellent. When the heat-resistant porous layer is present 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 with higher energy density can be manufactured.

Examples of the form of the heat-resistant porous layer include the following forms (a) and (b).

Form (a):

the heat-resistant porous layer contains a binder resin and inorganic particles, and the inorganic particles are bonded to each other with the binder resin interposed therebetween.

Form (b):

the heat-resistant porous layer is provided with: an inner layer formed on the porous base material and containing a binder resin and inorganic particles; and a porous film formed so as to cover the outer surface of the inner layer, the porous film containing a binder resin. The inner layer has a porous structure in which inorganic particles are bonded to each other via a binder resin and have a larger diameter than the porous film. The heat-resistant porous layer as a whole exhibits a so-called skin-core structure.

Adhesive layer-

The adhesive layer in the present disclosure is a layer disposed on the surface of the porous substrate or the heat-resistant porous layer, and is present as the outermost layer of the separator. The adhesive layer may be present on only one side of the laminate or may be present on both sides of the laminate. When the adhesive layer is present on only one surface of the laminate, the adhesive layer is preferably disposed on the surface of the heat-resistant porous layer. The adhesive layer may be disposed on one surface or both surfaces of the laminate depending on the composition or surface properties of the positive electrode or negative electrode of the battery. When the adhesive layer is present on only one side of the laminate, the thickness of the entire separator can be suppressed, and a battery with higher energy density can be manufactured.

The adhesive layer in the present disclosure is a layer in which adhesive resin particles are attached to the surface of the laminate.

For example, in the separators 10A to 10D, the adhesive layer 50 has a structure in which a plurality of adhesive resin particles 52 are arranged adjacent to each other on the surface of the laminate 40 to form a layer, and has a single-layer structure in which the adhesive resin particles 52 do not overlap in the thickness direction. However, the adhesive layer in the present disclosure is not limited to the above structure, and may have a structure in which a large number of adhesive resin particles are scattered on the surface of the laminate, or may have a multilayer structure of 2 or more layers in which a plurality of adhesive resin particles are stacked in the thickness direction. The adhesive layer in the present disclosure preferably has a structure in which a plurality of adhesive resin particles are arranged adjacent to each other on the surface of the laminate from the viewpoint of more excellent adhesion to the electrode, and preferably has a single-layer structure in which the adhesive resin particles do not overlap in the thickness direction from the viewpoint of improving the energy density of the battery.

The porous base material, the heat-resistant porous layer, and the adhesive layer of the separator of the present disclosure will be described in detail below.

[ porous base Material ]

The porous substrate in the present disclosure refers to a substrate having pores or voids therein.

Examples of such a base material include: a microporous membrane; porous sheets made of fibrous materials such as nonwoven fabrics and paper; and so on. In the present disclosure, a microporous membrane is preferable from the viewpoint of making the separator thin and improving the strength. The microporous membrane is a membrane comprising: in the structure in which a large number of fine holes are formed in the inside and the fine holes are connected, a gas or a liquid can pass through from one surface to the other surface.

The material of the porous substrate is preferably a material having electrical insulation properties, and may be an organic material or an inorganic material.

In order to impart the shutdown function to the porous base material, the porous base material preferably contains a thermoplastic resin. The shutdown function means the following functions: when the temperature of the battery rises, the constituent material melts to block the pores of the porous base material, thereby blocking the movement of ions and preventing thermal runaway of the battery. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ℃ is preferable. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene, and among them, polyolefins are preferred.

As the porous substrate, a microporous film containing polyolefin (referred to as "polyolefin microporous film") is preferred. The polyolefin microporous membrane is, for example, a polyolefin microporous membrane suitable for a conventional battery separator, and is preferably selected from those having sufficient mechanical properties and ion permeability.

The polyolefin microporous membrane is preferably a polyethylene microporous membrane containing polyethylene from the viewpoint of exhibiting a shutdown function. The content of polyethylene in the polyolefin microporous membrane is preferably 95% by mass or more based on the mass of the entire polyolefin microporous membrane.

The polyolefin microporous membrane is preferably a microporous membrane containing polypropylene, from the viewpoint of having heat resistance such that membrane breakage does not easily occur when exposed to high temperatures.

The polyolefin microporous membrane is preferably a polyolefin microporous membrane containing polyethylene and polypropylene, from the viewpoint of having a shutdown function and heat resistance such that the membrane is less likely to be broken 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 mass% or more of polyethylene and 5 mass% or less of polypropylene in view of achieving both shutdown function and heat resistance. From the viewpoint of achieving both the shutdown function and the heat resistance, a polyolefin microporous membrane having a laminated structure of 2 or more layers, at least 1 layer containing polyethylene and at least 1 layer containing polypropylene, is also preferable.

The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight (Mw) of 10 to 500 ten thousand. When the Mw of the polyolefin is 10 ten thousand or more, good mechanical properties can be imparted to the microporous membrane. On the other hand, when the Mw of the polyolefin is 500 ten thousand or less, the shutdown properties of the microporous membrane are good and the microporous membrane is easily molded.

Examples of the method for producing the polyolefin microporous membrane include the following methods: a method in which a sheet is formed by extruding a molten polyolefin resin from a T-die, and is subjected to crystallization treatment, stretching, and heat treatment to form a microporous film; a method in which a polyolefin resin melted together with a plasticizer such as liquid paraffin is extruded from a T-die, cooled to form a sheet, stretched, then the plasticizer is extracted, and heat-treated to form a microporous film; and so on.

Examples of the porous sheet made of a fibrous material include porous sheets made of a fibrous material such as a nonwoven fabric and paper, and the porous sheets are made of a polyester such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat-resistant resins such as wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide; cellulose; and so on.

For the purpose of improving wettability with a coating liquid for forming a heat-resistant porous layer or a resin particle dispersion for forming an adhesive layer, various surface treatments may be applied to the surface of the porous substrate within a range that does not impair the properties of the porous substrate. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

Characteristics of the porous substrate

The thickness of the porous substrate is preferably 12.0 μm or less, and more preferably 10.0 μm or less, from the viewpoint of improving the energy density of the battery. From the viewpoint of the production yield of the separator and the production yield of the battery, the thickness of the porous base material is preferably 3.0 μm or more, and more preferably 5.0 μm or more.

From the viewpoint of suppressing a short circuit of a battery or obtaining good ion permeability, the Gurley value (JIS P8117: 2009) of the porous substrate is preferably 50 sec/100 mL to 400 sec/100 mL, and more preferably 50 sec/100 mL to 200 sec/100 mL.

The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining an appropriate membrane resistance and shutdown function.

The porosity of the porous substrate was determined by the following calculation method. That is, the constituent materials are a, b, c, …, n, and the masses of the constituent materials are Wa, Wb, Wc, …, Wn (g/cm)²) The true densities of the constituent materials are da, db, dc, …, dn (g/cm)³) 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

The puncture strength of the porous base material is preferably 200g or more from the viewpoint of the production yield of the separator and the production yield of the battery.

The puncture strength of the porous substrate is: maximum puncture load (G) measured by conducting a puncture test using a Kato Tech KES-G5 hand-held compression tester under conditions of a needle tip radius of curvature of 0.5mm and a puncture speed of 2 mm/sec.

[ Heat-resistant porous layer ]

The heat-resistant porous layer in the present disclosure is provided on one or both surfaces of a porous substrate, and contains a binder resin and inorganic particles having an average primary particle diameter of 0.01 μm or more and less than 0.45 μm. The heat-resistant porous layer is a film having a large number of fine pores and allowing a gas or a liquid to pass through from one surface to the other surface.

The type of the binder resin of the heat-resistant porous layer is not particularly limited as long as the binder resin can bind the inorganic particles. The binder resin of the heat-resistant porous layer is preferably a heat-resistant resin from the viewpoint of improving the heat resistance of the separator. The binder resin of the heat-resistant porous layer is preferably a resin that is stable to an electrolytic solution and also electrochemically stable. The binder resin may be used alone or in combination of two or more.

Examples of the binder resin of the heat-resistant porous layer include polyvinylidene fluoride resin, wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, polyketone, polyetherimide, poly-N-vinylacetamide, polyacrylamide, copolyetherpolyamide, fluorine-based rubber, acrylic resin, styrene-butadiene copolymer, cellulose, polyvinyl alcohol, and the like.

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

The binder resin of the heat-resistant porous layer is preferably a heat-resistant resin containing at least one selected from the group consisting of wholly aromatic polyamides, polyamideimides, and polyimides, from the viewpoint of excellent heat resistance. Among them, from the viewpoint of durability, wholly aromatic polyamides are preferable. The wholly aromatic polyamide may be of a meta-type or a para-type. Among the wholly aromatic polyamides, the meta-type wholly aromatic polyamide is preferable from the viewpoint of easy formation of a porous layer and excellent oxidation reduction resistance in the electrode reaction. A small amount of aliphatic monomer may be copolymerized in the wholly aromatic polyamide.

The wholly aromatic polyamide used as the binder resin of the heat-resistant porous layer is specifically preferably polyisophthaloyl metaphenylene diamine or polyparaphenylene terephthalamide, and more preferably polyisophthaloyl metaphenylene diamine.

The binder resin of the heat-resistant porous layer is preferably a polyvinylidene fluoride resin (PVDF resin) from the viewpoint of adhesion between the heat-resistant porous layer and the adhesive layer. Examples of the PVDF resin include: homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride with other monomers (polyvinylidene fluoride copolymers); mixtures of polyvinylidene fluoride and polyvinylidene fluoride copolymers. Examples of the monomer copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, trichloroethylene, vinyl fluoride, trifluoropropropyl ether, ethylene, (meth) acrylic acid, methyl (meth) acrylate, vinyl acetate, vinyl chloride, acrylonitrile, and the like. These monomers may be used alone or in combination of two or more. The weight average molecular weight (Mw) of the PVDF-based resin is preferably 60 to 300 ten thousand. The acid value of the PVDF resin is preferably 3mgKOH/g to 20 mgKOH/g. The acid value of the PVDF resin can be controlled by introducing a carboxyl group into the PVDF resin, for example. The introduction and the amount of the carboxyl group into the PVDF resin can be controlled by: as the polymerization component of the PVDF-based resin, a monomer having a carboxyl group (for example, (meth) acrylic acid, (meth) acrylate, maleic acid, maleic anhydride, maleate, and fluorine substitution products thereof) is used, and the polymerization ratio thereof is adjusted.

The inorganic particles in the present disclosure are not particularly limited, and examples thereof include: particles of metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide; particles of metal oxides such as silica, alumina, zirconia, magnesia, and barium titanate; particles of carbonates such as calcium carbonate and magnesium carbonate; particles of sulfates such as barium sulfate and calcium sulfate; and so on. The inorganic particles are preferably particles containing at least one selected from the group consisting of magnesium-based particles and barium-based particles from the viewpoint of stability to an electrolytic solution and electrochemical stability.

Here, the magnesium-based particles refer to inorganic particles containing a magnesium compound, and specific examples thereof include magnesium hydroxide, magnesium oxide, and the like.

The barium-based particles are inorganic particles containing a barium compound, and specific examples thereof include barium sulfate and barium titanate.

The inorganic particles may be surface-modified with a silane coupling agent or the like.

The particle shape of the inorganic particles is not limited, and may be spherical, elliptical, plate-like, needle-like, or irregular. The inorganic particles contained in the heat-resistant porous layer are preferably plate-like particles or unagglomerated primary particles from the viewpoint of suppressing a short circuit of the battery.

The inorganic particles may be used alone or in combination of two or more.

It is important that the average primary particle diameter of the inorganic particles contained in the heat-resistant porous layer is 0.01 μm or more and less than 0.45 μm. When the average primary particle size of the inorganic particles is 0.01 μm or more, aggregation of the particles is suppressed, and a heat-resistant porous layer having high uniformity can be formed. From such a viewpoint, the average primary particle diameter of the inorganic particles is more preferably 0.05 μm or more, and still more preferably 0.10 μm or more. When the average primary particle size of the inorganic particles is less than 0.45 μm, the heat resistance can be improved even in a structure in which the heat-resistant porous layer is made thin. The mechanism is considered as follows. That is, since the particle diameter of the inorganic particles is small, the surface area (specific surface area) of the inorganic particles per unit volume becomes large. Therefore, the number of contact points between the inorganic particles and the binder resin increases. This suppresses shrinkage of the heat-resistant porous layer when exposed to high temperatures. Further, it is presumed that since a large number of inorganic particles having a small particle diameter are connected to each other, the heat-resistant porous layer is less likely to be broken when exposed to high temperature. From such a viewpoint, the average primary particle diameter of the inorganic particles is more preferably 0.40 μm or less, still more preferably 0.30 μm or less, and particularly preferably 0.20 μm or less.

The average primary particle diameter of the inorganic particles is determined by: in observation by a Scanning Electron Microscope (SEM), 100 inorganic particles were randomly selected, the long diameters thereof were measured, and the long diameters of 100 particles were averaged. The sample to be observed by SEM is an inorganic particle as a material of the heat-resistant porous layer or an inorganic particle taken out from the separator. The method for removing the inorganic particles from the separator is not limited, and examples thereof include: heating the diaphragm to about 800 ℃ to eliminate the binder resin and taking out the inorganic particles; a method in which the separator is immersed in an organic solvent, the binder resin is dissolved in the organic solvent, and the inorganic particles are taken out; and so on.

In the present disclosure, the mass ratio of the inorganic particles in the heat-resistant porous layer is preferably 50 to 90 mass% with respect to the total mass of the heat-resistant porous layer. When the mass ratio of the inorganic particles in the heat-resistant porous layer is 50 mass% or more, the heat resistance of the separator can be suitably improved, and from such a viewpoint, it is more preferably 55 mass% or more, and still more preferably 60 mass% or more. The mass ratio of the inorganic particles in the heat-resistant porous layer is preferably 90 mass% or less, more preferably 85 mass% or less, and even more preferably 80 mass% or less, from the viewpoint that the heat-resistant porous material is not easily peeled from the porous substrate.

The heat-resistant porous layer may contain additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming agent, and a pH adjuster. The dispersant may be added to the coating liquid for forming the heat-resistant porous layer for the purpose of improving dispersibility, coatability, or storage stability. The wetting agent, the defoaming agent, and the pH adjuster may be added to the coating liquid for forming the heat-resistant porous layer for the purpose of, for example, improving affinity with the porous base material, suppressing entrainment of air bubbles into the coating liquid, or adjusting pH.

Characteristics of the heat-resistant porous layer-

In the separator of the present disclosure, the thickness of the heat-resistant porous layer is preferably 0.5 μm or more per surface, more preferably 0.8 μm or more per surface, from the viewpoint of heat resistance and handling properties of the separator, and is preferably 4.0 μm or less per surface, more preferably 3.5 μm or less per surface, from the viewpoint of handling properties of the separator and energy density of the battery. The thickness of the heat-resistant porous layer is preferably 1.0 μm or more, more preferably 1.6 μm or more, preferably 8.0 μm or less, and more preferably 7.0 μm or less, in terms of the total of both surfaces, regardless of whether the heat-resistant porous layer is present only on one surface or on both surfaces of the porous substrate.

In the separator of the present disclosure, the mass per unit area of the heat-resistant porous layer is preferably 2.0g/m in total on both sides²～10.0g/m². From the viewpoint of heat resistance and handling properties of the separator, the mass of the heat-resistant porous layer is preferably 2.0g/m in total of both surfaces²Above, more preferably 3.0g/m²From the viewpoint of handling of the separator and energy density of the battery, the above is preferably 9.0g/m²Hereinafter, more preferably 8.0g/m²The following.

In the separator of the present disclosure, the porosity of the heat-resistant porous layer is preferably 30% to 70%. The porosity of the heat-resistant porous layer is preferably 30% or more, and more preferably 40% or more, from the viewpoint of ion permeability of the separator. In the case where small inorganic particles having an average primary particle diameter of 0.01 μm or more and less than 0.45 μm are used as the inorganic particles, the porosity of the heat-resistant porous layer is preferably 70% or less, more preferably 65% or less, and even more preferably 60% or less, from the viewpoint of making the heat-resistant porous layer have a denser structure and improving the heat resistance. The porosity ∈ (%) of the heat-resistant porous layer was determined by the following equation.

ε＝{1-(Wa/da+Wb/db+Wc/dc+…+Wn/dn)/t}×100

Here, the constituent materials of the heat-resistant porous layer are a, b, c, …, and n, and the mass of each constituent material is Wa, Wb, Wc, …, Wn (g/cm)²) The true densities of the constituent materials are da, db, dc, …, dn (g/cm)³) The thickness of the heat-resistant porous layer is t (cm).

In the separator of the present disclosure, the peel strength between the porous base material and the heat-resistant porous layer is preferably 5N/m or more, more preferably 10N/m or more, even more preferably 15N/m or more, and even more preferably 20N/m or more, from the viewpoint of the adhesive strength between the separator and the electrode. From the viewpoint of ion permeability, the peel strength is preferably 75N/m or less, more preferably 60N/m or less, and still more preferably 50N/m or less. In the case where the separator of the present disclosure has the heat-resistant porous layers on both surfaces of the porous substrate, the peel strength between the porous substrate and the heat-resistant porous layer is preferably in the above range on both surfaces of the porous substrate.

[ adhesive layer ]

The adhesive layer in the separator of the present disclosure is provided on one or both surfaces of a laminate of a porous base material and a heat-resistant porous layer, and has a structure in which adhesive resin particles are adhered. In the adhesive layer, a gas or a liquid can pass through gaps between the adhesive resin particles from one surface to the other surface. The structure to which the adhesive resin particles are adhered includes not only a form in which the resin retains the particle shape in the manufactured separator, but also the following forms: in the separator manufactured using the resin particles as the material of the adhesive layer, a part of the resin particles is melted by heat treatment or drying treatment without retaining the particle shape.

Since the adhesive layer has a structure in which the adhesive resin particles adhere to the heat-resistant porous layer or the porous base material, the interface between the heat-resistant porous layer or the porous base material and the adhesive layer is not easily broken. In addition, since the adhesive layer has a structure in which the adhesive resin particles adhere to each other and are connected, the adhesive layer has excellent toughness and is less likely to be broken by aggregation.

The adhesive resin particles are particulate resins having adhesion to the electrodes of the battery. The type of the adhesive resin particles can be selected according to the composition of the positive electrode or the negative electrode. The adhesive resin particles are preferably resin particles that are stable to an electrolytic solution and also electrochemically stable.

Examples of the adhesive resin particles include particles containing a polyvinylidene fluoride resin, a fluorine-containing rubber, an acrylic resin, a styrene-butadiene copolymer, a homopolymer or copolymer of a vinyl nitrile compound (such as acrylonitrile or methacrylonitrile), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyether (such as polyoxyethylene or polyoxypropylene), or a mixture of 2 or more of these. Among them, particles containing a polyvinylidene fluoride resin and/or an acrylic resin are preferable from the viewpoint of excellent oxidation resistance.

Examples of the polyvinylidene fluoride resin include: homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride with other monomers (polyvinylidene fluoride copolymers); mixtures of polyvinylidene fluoride and polyvinylidene fluoride copolymers. Examples of the monomer copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, trichloroethylene, vinyl fluoride, trifluoropropropyl ether, ethylene, (meth) acrylic acid, methyl (meth) acrylate, vinyl acetate, vinyl chloride, acrylonitrile, and the like. These monomers may be used alone or in combination of two or more.

The polyvinylidene fluoride copolymer contained in the adhesive resin particles is preferably a copolymer having 50 mol% or more of a structural unit derived from vinylidene fluoride, from the viewpoint of obtaining mechanical strength capable of withstanding pressurization and heating at the time of battery production.

The polyvinylidene fluoride copolymer contained in the adhesive resin particles is preferably a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, or a copolymer of vinylidene fluoride and trifluoroethylene, and more preferably a copolymer of vinylidene fluoride and hexafluoropropylene. The copolymer of vinylidene fluoride and hexafluoropropylene preferably contains 0.1 to 10 mol% (preferably 0.5 to 5 mol%) of a structural unit derived from hexafluoropropylene.

The weight average molecular weight of the adhesive resin (preferably polyvinylidene fluoride or a polyvinylidene fluoride copolymer) contained in the adhesive resin particles is preferably 1000 to 500 ten thousand, more preferably 1 to 300 ten thousand, and even more preferably 5 to 200 ten thousand.

Examples of the acrylic resin contained in the adhesive resin particles include poly (meth) acrylic acid, poly (meth) acrylate, crosslinked poly (meth) acrylic acid, crosslinked poly (meth) acrylate, and modified acrylic resins may be used. These may be used alone or in combination of two or more. The acrylic resin may be used in the form of a mixture of polyvinylidene fluoride and an acrylic resin or a mixture of a polyvinylidene fluoride copolymer and an acrylic resin.

The adhesive resin particles are preferably polyvinylidene fluoride particles, polyvinylidene fluoride copolymer particles, particles of a mixture of polyvinylidene fluoride and a polyvinylidene fluoride copolymer, particles of a mixture of polyvinylidene fluoride and an acrylic resin, or particles of a mixture of a polyvinylidene fluoride copolymer and an acrylic resin. Here, as the polyvinylidene fluoride copolymer, a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, or a copolymer of vinylidene fluoride and trifluoroethylene is preferable.

The mixture of polyvinylidene fluoride and acrylic resin or the mixture of polyvinylidene fluoride copolymer and acrylic resin constituting the adhesive resin particles preferably contains 20 mass% or more of polyvinylidene fluoride or polyvinylidene fluoride copolymer from the viewpoint of oxidation resistance.

As the adhesive resin particles, 2 or more kinds of adhesive resin particles may be used in combination.

From the viewpoint of well-balanced adjustment of the ion permeability of the adhesive layer, the adhesion between the adhesive layer and the electrode, the peel strength between the adhesive layer and the heat-resistant porous layer, and the handling properties of the adhesive layer, it is preferable to use a mixture of first adhesive resin particles containing a polyvinylidene fluoride resin and second adhesive resin particles containing an acrylic resin. The first adhesive resin particles (hereinafter, also referred to as "resin particles F") are particles containing more than 50 mass% of a polyvinylidene fluoride resin with respect to the total solid content. The second adhesive resin particles (hereinafter, also referred to as "resin particles a") are particles containing more than 50 mass% of an acrylic resin with respect to the total solid content.

Examples of the polyvinylidene fluoride resin contained in the resin particles F include polyvinylidene fluoride, a polyvinylidene fluoride copolymer, and a mixture of polyvinylidene fluoride and a polyvinylidene fluoride copolymer, and preferred embodiments of these polymers are as described above. The resin particles F may contain a resin other than the polyvinylidene fluoride resin.

The amount of the polyvinylidene fluoride resin contained in the resin particles F is more than 50% by mass, preferably 70% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass, based on the total solid content of the resin particles F.

Examples of the acrylic resin contained in the resin particles a include poly (meth) acrylic acid, poly (meth) acrylate, crosslinked poly (meth) acrylic acid, crosslinked poly (meth) acrylate, and the like, and may be a modified acrylic resin. These may be used alone or in combination of two or more. The resin particles a may contain other resins than acrylic resins.

The amount of the acrylic resin contained in the resin particles a is more than 50% by mass, preferably 70% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass, based on the total solid content of the resin particles a.

When the adhesive layer contains a mixture of the resin particles F and the resin particles a, the mass ratio of the resin particles F and the resin particles a contained in the adhesive layer may be adjusted according to the characteristics required for the adhesive layer. The mass ratio of the resin particles F to the resin particles a contained in the adhesive layer (resin particles F: resin particles a) is preferably 50: 50-90: 10. the mass ratio of the resin particles F to the resin particles a is more preferably 60: 40-80: 20.

the mixture of the resin particles F and the resin particles a is preferably a dispersion liquid in which the resin particles F and the resin particles a are dispersed in a dispersion medium as a coating liquid used for producing the adhesive layer. The dispersion medium of the dispersion liquid is not particularly limited as long as it is a dispersion medium in which the polyvinylidene fluoride resin, the acrylic resin, and the heat-resistant porous layer are not dissolved, and water is preferred from the viewpoint of safety of handling. That is, the dispersion liquid is preferably an aqueous dispersion liquid in which the resin particles F and the resin particles a are dispersed in water. When used for producing an adhesive layer, the mass ratio of the resin particles F to the resin particles a contained in the aqueous dispersion is preferably resin particles F: resin particle a ═ 50: 50-90: 10. more preferably, the resin particle F: resin particle a 60: 40-80: 20.

typical commercially available products of the aqueous dispersion liquid in which the resin particles F and the resin particles A are dispersed in water include, for example, Aquatec FMA-12, Aquatec ARC, Aquatec CRX, and the like, manufactured by Arkema corporation; TRD202A manufactured by JSR corporation.

The aqueous dispersion in which the resin particles F and the resin particles a are dispersed in water may be prepared by dispersing the resin particles F and the resin particles a in water, or may be prepared by mixing an aqueous dispersion in which the resin particles F are dispersed in water with an aqueous dispersion in which the resin particles a are dispersed in water.

As the aqueous dispersion in which the resin particles F are dispersed in water, a known aqueous dispersion including a commercially available product can be used, or a known resin particle F including a commercially available product can be dispersed in water and used. As typical commercially available products of the aqueous dispersion liquid in which the resin particles F are dispersed in water, there are mentioned LBG2200LX, LATEX32, KYNAR WATERBORNE RC series (RC-10246, RC-10278, RC-10280, etc.) manufactured by Arkema; XPH838 series, XPH882 series, XPH883 series, XPH884 series, XPH859 series, XPH918 series manufactured by Solvay specialty polymers company; an aqueous PVDF dispersion manufactured by Kureha.

As the aqueous dispersion in which the resin particles a are dispersed in water, a known aqueous dispersion including a commercially available product may be used, or a known resin particle a including a commercially available product may be dispersed in water and used. Typical commercially available products of the aqueous dispersion liquid in which the resin particles a are dispersed in water include, for example: BM-120S manufactured by Zeon corporation of Japan; acrylic particle aqueous dispersion manufactured by DIC; and so on.

The volume average particle diameter of the adhesive resin particles is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.05 μm or more from the viewpoint of forming a good porous structure, and is preferably 1.0 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less from the viewpoint of suppressing the thickness of the adhesive layer.

The adhesive layer may contain components other than the adhesive resin particles within a range not to hinder the effects of the present disclosure. In the adhesive layer, the adhesive resin particles preferably account for 90 mass% or more of the total layer, and more preferably the adhesive resin particles account for 95 mass% or more of the total layer. Further preferably, the adhesive layer substantially contains only the adhesive resin particles.

The adhesive layer in the separator of the present disclosure may contain additives such as a dispersant such as a surfactant, a wetting agent, a defoaming agent, a pH adjuster, and the like.

In the case of using the resin particle dispersion liquid for forming the adhesive layer, a dispersant may be added to the resin particle dispersion liquid for the purpose of improving dispersibility, coatability or storage stability.

In the case of using the resin particle dispersion liquid for forming the adhesive layer, the wetting agent, the defoaming agent, and the pH adjusting agent may be added to the resin particle dispersion liquid for the purpose of, for example, improving the affinity with the heat-resistant porous layer, suppressing the entrainment of air bubbles into the resin particle dispersion liquid, or adjusting the pH.

Examples of the surfactant contained in the adhesive layer include non-reactive anionic surfactants (for example, alkyl sulfates, polyoxyethylene alkyl ether sulfate ester salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkylsulfosuccinate salts, alkyldiphenyl ether disulfonate salts, naphthalene sulfonic acid formaldehyde condensates, polyoxyethylene polycyclic phenyl ether sulfate ester salts, polyoxyethylene styrenated phenyl ether sulfate ester salts, fatty acid salts, alkyl phosphate salts, polyoxyethylene alkylphenyl ether sulfate ester salts, and the like); non-reactive nonionic surfactants (e.g., polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distyrenated phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, fatty acid glycerides, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, alkylalkanolamides, polyoxyethylene alkylphenyl ethers, etc.); a so-called reactive surfactant obtained by introducing an ethylenically unsaturated double bond into the chemical structure of a surfactant having a hydrophilic group and a hydrophilic oil group.

Examples of the anionic surfactant as the reactive surfactant include ethylenically unsaturated monomers having a group selected from a sulfonic acid group, a sulfonate group, a sulfate group, and salts thereof, and preferably compounds having a sulfonic acid group or a group (i.e., an ammonium sulfonate group or an alkali metal sulfonate group) as an ammonium salt or an alkali metal salt thereof. Specific examples thereof include alkylallyl sulfosuccinate, polyoxyethylene alkylphenyl ether sulfate, α - [ 1- [ (allyloxy) methyl ] -2- (nonylphenoxy) ethyl ] - ω -polyoxyethylene sulfate, ammonium α -sulfonato- ω -1- (allyloxymethyl) alkyloxypolyoxyethylene, styrene sulfonate, α - [ 2- [ (allyloxy) -1- (alkyloxymethyl) ethyl ] - ω -polyoxyethylene sulfate, and polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether sulfate.

Examples of the nonionic surfactant as the reactive surfactant include α - [ 1- [ (allyloxy) methyl ] -2- (nonylphenoxy) ethyl ] - ω -hydroxypolyoxyethylene, polyoxyethylene alkylphenyl ether, [ 2- [ (allyloxy) -1- (alkyloxymethyl) ethyl ] - ω -hydroxypolyoxyethylene, and polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether.

The surfactant is used singly or in combination of two or more.

In one embodiment of the separator of the present disclosure, the adhesive layer further comprises a surfactant. The surfactant contained in the adhesive layer is preferably at least one selected from the group consisting of a non-reactive anionic surfactant, a non-reactive nonionic surfactant, a reactive anionic surfactant and a reactive nonionic surfactant. Specific examples of the non-reactive anionic surfactant, the non-reactive nonionic surfactant, the reactive anionic surfactant and the reactive nonionic surfactant include the surfactants described above as being contained in the resin particle dispersion for forming the adhesive layer. When the adhesive layer further contains a surfactant, the mass ratio of the surfactant to the total mass of the adhesive layer is preferably 0.1 to 10 mass%, and more preferably 1 to 8 mass%.

The adhesive layer can be formed using a resin particle dispersion for forming the adhesive layer. For example, it can be formed by: a resin particle dispersion containing the adhesive resin particles and, if necessary, components other than the adhesive resin particles is applied to at least one of the porous base material and the heat-resistant porous layer by coating or the like.

From the viewpoint of adhesion to the electrode, the weight of the adhesive layer is preferably 0.2g/m per surface²Above, more preferably 0.25g/m²Above, more preferably 0.3g/m²Above, permeability from ionsFrom the viewpoint of handling of the separator and energy density of the battery, 2.0g/m is preferable per one surface²Hereinafter, more preferably 1.8g/m²The concentration is more preferably 1.6g/m or less²The following.

The coverage of the adhesive resin particles in the adhesive layer (the area ratio of the particles covering the plane) is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more, with respect to the area of the separator in a plan view. The coating rate of the adhesive resin particles in the adhesive layer is determined by: the surface of the separator was photographed from the vertical direction by a scanning electron microscope, 10 square regions were randomly selected, the coverage of each region was determined, and the average value of 10 points was calculated.

Characteristics of the diaphragm

The thickness of the separator of the present disclosure is preferably 8.0 μm or more, more preferably 9.0 μm or more from the viewpoint of mechanical strength of the separator, and is preferably 20.0 μm or less, more preferably 15.0 μm or less from the viewpoint of energy density of the battery.

The separator of the present disclosure preferably has a puncture strength of 150g to 1000g, more preferably 200g to 600g, from the viewpoint of mechanical strength of the separator or short circuit resistance of the battery. The puncture strength of the separator is measured by the same method as the puncture strength of the porous substrate.

The porosity of the separator of the present disclosure is preferably 30% to 60% from the viewpoint of adhesiveness to an electrode, handling properties of the separator, ion permeability, or mechanical strength.

The membrane resistance of the separator of the present disclosure is preferably 0.5ohm cm from the viewpoint of the load characteristics of the battery²～10ohm·cm²More preferably 1ohm cm²～8ohm·cm²。

From the viewpoint of balance between mechanical strength and ion permeability, the Gurley value (JIS P8117: 2009) of the separator of the present disclosure is preferably 50 sec/100 mL to 800 sec/100 mL, more preferably 80 sec/100 mL to 500 sec/100 mL, and further preferably 100 sec/100 mL to 400 sec/100 mL.

In the separator of the present disclosure, the difference between the Gurley value of the separator and the Gurley value of the porous substrate is preferably 20 seconds/100 mL to 300 seconds/100 mL from the viewpoint of ion permeability. The difference between the Gurley value of the separator and the Gurley value of the porous substrate is more preferably 200 seconds/100 mL or less, and still more preferably 150 seconds/100 mL or less.

The separator of the present disclosure preferably has a tensile strength of 500kgf/cm in the MD direction from the viewpoint of mechanical strength or workability (fixation of the adhesive layer) of the separator²Above, more preferably 600kgf/cm²Above, it is more preferably 700kgf/cm²The above. From the above-mentioned viewpoint, the higher the tensile strength in the MD direction is, the more preferable, and the tensile strength is usually 3000kgf/cm²The following.

The tensile strength in the TD direction of the separator of the present disclosure is preferably 500kgf/cm from the viewpoint of mechanical strength or workability (fixation of the adhesive layer) of the separator²Above, more preferably 600kgf/cm²Above, it is more preferably 700kgf/cm²The above. From the above-mentioned viewpoint, the higher the tensile strength in the TD direction is, the more preferable, and the tensile strength is usually 3000kgf/cm²The following.

The amount of water contained in the separator of the present disclosure (on a mass basis) is preferably 1000ppm or less. When the battery is configured with a smaller amount of water, the reaction between the electrolyte and water is suppressed more and the generation of gas in the battery can be suppressed, thereby improving the cycle characteristics of the battery. From this viewpoint, the amount of water contained in the separator is more preferably 800ppm or less, and still more preferably 500ppm or less.

The separator of the present disclosure preferably has a shrinkage ratio in the MD direction of 6% or less, more preferably 5.5% or less, when heat-treated at 130 ℃ for 1 hour.

The separator of the present disclosure preferably has a shrinkage ratio in the TD direction of 6% or less, more preferably 5.5% or less, when heat-treated at 130 ℃ for 1 hour.

The separator of the present disclosure preferably has a shrinkage ratio in the MD direction of 10% or less, more preferably 9.5% or less, when heat-treated at 150 ℃ for 1 hour.

The separator of the present disclosure preferably has a shrinkage ratio in the TD direction of 10% or less, more preferably 9.5% or less, when heat-treated at 150 ℃ for 1 hour.

The thermal shrinkage of the separator of the present disclosure in the MD and TD directions when heat-treated at 150 ℃ for 1 hour is also more preferably 10% or less.

The shrinkage of the separator after heat treatment at 130 ℃ or 150 ℃ for 1 hour was determined by the following measurement method.

The separator was cut into 100mm in the MD direction × 100mm in the TD direction, and reference lines of lengths of 70mm were drawn in the MD direction and the TD direction so as to pass through the center of the sample of the separator, respectively, to prepare test pieces. The test piece was placed between 2 sheets of paper of A4 size, and then, the test piece was left to stand in an oven at 130 ℃ and 150 ℃ for 1 hour. The MD direction and TD direction lengths of the test pieces before and after the heat treatment were measured, the thermal shrinkage was calculated from the following formula, and the above-described operation was further performed 2 times to average the thermal shrinkage of 3 test pieces to obtain the thermal shrinkage of the separator.

Heat shrinkage (%) is { (length in MD before heat treatment-length in MD after heat treatment) ÷ length in MD before heat treatment } × 100

Heat shrinkage (%) is { (length in TD direction before heat treatment-length in TD direction after heat treatment) ÷ length in TD direction before heat treatment } × 100

The shrinkage rate of the separator of the present disclosure upon heat treatment can be controlled by, for example, the content of the 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.

Method for producing a diaphragm

The separator of the present disclosure is manufactured by, for example, the following manufacturing method a or manufacturing method B. In the production method a and the production method B, the method for forming the heat-resistant porous layer may be a wet coating method or a dry coating method.

Production method B can be any of embodiments B-1 to B-7 described below. Modes B-1 to B-4 are modes in which a heat-resistant porous layer is formed by a wet coating method. Modes B-5 to B-7 are modes in which a heat-resistant porous layer is formed by a dry coating method.

In the present disclosure, the wet coating method refers to a method of curing a coating layer in a solidification liquid, and the dry coating method refers to a method of drying a coating layer and curing the coating layer.

(a) Manufacturing method a (discontinuous manufacturing method):

after a heat-resistant porous layer is formed on a porous substrate that has been unwound from a roll to obtain a laminate of the porous substrate and the heat-resistant porous layer, the laminate is temporarily wound around another roll. Next, an adhesive layer was formed on the laminate discharged from the roll to obtain a separator, and the obtained separator was wound around another roll.

(b) Production method B (continuous production method):

a heat-resistant porous layer and an adhesive layer are continuously or simultaneously formed on a porous base material discharged from a roll, and the resulting separator is wound around another roll.

Next, a mode based on the wet coating method will be described.

Mode B-1:

the coating liquid for forming a heat-resistant porous layer is applied to a porous base material, the coated layer is cured by immersing the porous base material in a coagulating liquid, the coating layer is taken out from the coagulating liquid, washed with water and dried, and then, an adhesive resin particle dispersion is applied and dried.

Mode B-2:

the coating liquid for forming a heat-resistant porous layer is applied to a porous base material, the coated layer is cured by immersing the porous base material in a coagulating liquid, the coating layer is lifted from the coagulating liquid and washed with water, and then, an adhesive resin particle dispersion is applied and dried.

Mode B-3:

the coating liquid for forming a heat-resistant porous layer and the adhesive resin particle dispersion are applied to a porous base material at the same time, and the porous base material is immersed in a coagulating liquid to cure the coating layer of the two layers, and then the coating layer is taken out from the coagulating liquid, washed with water, and dried.

Mode B-4:

the coating liquid for forming a heat-resistant porous layer is applied to a porous base material, immersed in a coagulating liquid to cure the coating layer, lifted from the coagulating liquid, and transferred to a water bath containing adhesive resin particles, whereby the coating layer is washed with water, the adhesive resin particles are adhered, lifted from the water bath, and dried.

Next, a mode based on the dry coating method will be described.

Mode B-5:

the coating liquid for forming a heat-resistant porous layer is applied to a porous base material and dried, and then the adhesive resin particle dispersion liquid is applied and dried.

Mode B-6:

the coating liquid for forming a heat-resistant porous layer is applied to the porous base material, and then the adhesive resin particle dispersion liquid is applied and dried.

Mode B-7:

the coating liquid for forming two heat-resistant porous layers and the adhesive resin particle dispersion are simultaneously applied to the porous base material and dried.

Hereinafter, the details of the steps included in the production method will be described by taking the production method B of the embodiment B-1 as an example.

In the production method B of the embodiment B-1, the heat-resistant porous layer is formed on at least one surface of the porous substrate by a wet coating method to obtain a laminate of the porous substrate and the heat-resistant porous layer, and then the adhesive layer is formed on at least one surface of the laminate by a dry coating method. The production method B of the embodiment B-1 comprises the following steps (1) to (7), and the steps (1) to (7) are performed in this order.

Step (1): preparation of coating liquid for Forming Heat-resistant porous layer

The coating liquid for forming a heat-resistant porous layer (hereinafter, referred to as "coating liquid" in the description of the production method) is prepared by dissolving or dispersing a binder resin and inorganic particles in a solvent. If necessary, other resins than the binder resin or other components than the resin are dissolved or dispersed in the coating liquid.

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

The solvent used in the preparation of the coating liquid preferably contains a phase separation agent that induces phase separation from the viewpoint of forming a porous layer having a good porous structure. Therefore, the solvent used for preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase-separating agent. The phase separation agent is preferably mixed with the good solvent in an amount within a range capable of ensuring a viscosity suitable for coating. Examples of the phase separating agent include water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

The solvent used for the preparation of the coating liquid is preferably a mixed solvent of a good solvent and a phase-separating agent, which contains 60 mass% or more of the good solvent and 40 mass% or less of the phase-separating agent, from the viewpoint of forming a good porous structure.

The binder resin concentration in the coating liquid is preferably 1 to 20% by mass from the viewpoint of forming a good porous structure.

Step (2): preparation of adhesive resin particle Dispersion

The adhesive resin particle dispersion is prepared by dispersing adhesive resin particles in water. In order to improve the dispersibility of the adhesive resin particles in water, a surfactant may be added to the adhesive resin particle dispersion. The adhesive resin particle dispersion may be a commercially available product or a commercially available dilution.

The concentration of the adhesive resin particles in the adhesive resin particle dispersion is preferably 1 to 60% by mass from the viewpoint of coating suitability.

Step (3): application of coating liquid

The coating liquid is applied to at least one surface of the porous base material to form a coating layer on the porous base material. Examples of the method of applying the coating liquid to the porous base material include a doctor blade coating method, a meyer bar coating method, a die coating method, a reverse roll coating method, a gravure coating method, a screen printing method, an ink jet method, and a spray method. When the heat-resistant porous layers are formed on both surfaces of the porous substrate, the coating liquid is preferably applied to both surfaces of the porous substrate at the same time from the viewpoint of productivity.

Step (4): curing of coating layers

The porous substrate having the coating layer formed thereon is immersed in a solidifying solution, and the binder resin is cured while phase separation is induced in the coating layer, thereby forming a heat-resistant porous layer. In this way, a laminate composed of the porous substrate and the heat-resistant porous layer was obtained.

The coagulation liquid generally contains a good solvent and a phase-separating agent used for preparation of the coating liquid, and water. The mixing ratio of the good solvent to the phase-separating agent is preferably in terms of production when the mixing ratio of the mixed solvent used in the preparation of the coating liquid is the same. From the viewpoint of formation of a porous structure and productivity, the content of water in the coagulation liquid is preferably 40% by mass to 90% by mass. The temperature of the solidification solution is, for example, 20 ℃ to 50 ℃.

Step (5): water washing and drying of coating layer

The laminate was pulled up from the solidification solution and washed with water. The solidified liquid was removed from the laminate by washing with water. Further, water was removed from the laminate by drying. The water washing is performed by, for example, transporting the laminate in the water washing bath. The drying is performed, for example, by the following method: transporting the laminate in a high temperature environment; blowing air to the laminated body; the laminate is brought into contact with a heating roller. The drying temperature is preferably 40 ℃ to 80 ℃.

Step (6): coating of adhesive resin particle dispersion

The adhesive resin particle dispersion is applied to at least one surface of the laminate. Examples of the method for applying the adhesive resin particle dispersion include a doctor blade coating method, a gravure coating method, a meyer bar coating method, a die coating method, a reverse roll coating method, a screen printing method, an ink jet method, and a spray method.

Step (7): drying of adhesive resin particle dispersion

The adhesive resin particle dispersion liquid on the laminate is dried to attach the adhesive resin particles to the surface of the laminate. The drying is performed, for example, by conveying the laminate into a high-temperature environment, blowing air to the laminate, or the like. The drying temperature is preferably 40 ℃ to 100 ℃.

The manufacturing method a for manufacturing the first separator or the manufacturing method B of the embodiments B-2 to B-4 may be performed by partially omitting or modifying the above-described steps (1) to (7).

The manufacturing method a for manufacturing the second separator or the manufacturing method B of the embodiments B-2 to B-7 can be performed by omitting or modifying the above-described steps (1) to (7).

< nonaqueous Secondary Battery

The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery that obtains electromotive force by doping and dedoping lithium, and includes a positive electrode, a negative electrode, and the separator for a nonaqueous secondary battery of the present disclosure. Doping refers to absorption, loading, adsorption, or intercalation, and refers to 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 sealed in an outer casing together with an electrolyte 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 has excellent adhesion between the separator and the electrode, and therefore has excellent productivity and cycle characteristics (capacity retention rate).

Hereinafter, examples of the positive electrode, the negative electrode, the electrolyte solution, and the outer material of the nonaqueous secondary battery according to the present disclosure will be described.

An example of the embodiment of the positive electrode is a structure in which an active material layer containing a positive electrode active material and a binder resin is molded on a current collector. The active material layer may further include a conductive aid. As the positive electrode active material, for example, a transition metal oxide containing lithium, specifically, LiCoO can be mentioned₂、LiNiO₂、LiMn_1/2Ni_1/2O₂、LiCo_{1/ 3}Mn_1/3Ni_1/3O₂、LiMn₂O₄、LiFePO₄、LiCo_1/2Ni_1/2O₂、LiAl_1/4Ni_3/4O₂And the like. Examples of the binder resin include a polyvinylidene fluoride resin and a styrene-butadiene copolymer. 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 nonaqueous secondary battery of the present disclosure, when the adhesive layer of the separator of the present disclosure contains a polyvinylidene fluoride resin, since the polyvinylidene fluoride resin has excellent oxidation resistance, LiMn that can be operated at a high voltage of 4.2V or more can be easily applied by disposing the adhesive layer on the positive electrode side of the nonaqueous secondary battery_1/2Ni_{1/ 2}O₂、LiCo_1/3Mn_1/3Ni_1/3O₂And the like as the positive electrode active material.

An example of the embodiment of the negative electrode is a structure in which an active material layer containing a negative electrode active material and a binder resin is molded on a current collector. The active material layer may further include a conductive aid. Examples of the negative electrode active material include materials capable of electrochemically occluding lithium, and specific examples thereof include: a carbon material; alloys of silicon, tin, aluminum, etc. with lithium; a wood alloy; and so on. Examples of the binder resin include a polyvinylidene fluoride resin and a styrene-butadiene copolymer. 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 to 20 μm. In addition, a metal lithium foil may be used as the negative electrode instead of the above negative electrode.

The electrolyte is a solution obtained by dissolving a lithium salt in a nonaqueous solvent. The lithium salt includes, for example, LiPF₆、LiBF₄、LiClO₄And the like. Examples of the nonaqueous solvent include cyclic carbonates such as ethylene carbonate, 1, 2-propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine substitutes thereof; cyclic esters such as γ -butyrolactone and γ -valerolactone; and the like, and these may be used alone or in combination. The electrolyte solution is preferably prepared by mixing a cyclic carbonate and a chain carbonate in a ratio of 20: 80-40: 60 (cyclic carbonate: chain carbonate) and a lithium salt dissolved therein in a range of 0.5 to 1.5 mol/L.

Examples of the outer packaging material include a metal can and an aluminum laminated film package. The shape of the battery is square, cylindrical, button-shaped, etc., and the separator of the present disclosure is suitable for any shape.

Examples of the method for producing a nonaqueous secondary battery according to the present disclosure include: a manufacturing method including a step of impregnating a separator with an electrolyte and performing a hot press treatment (referred to as "wet hot press" in the present disclosure) to bond the separator to an electrode; the method includes a step of performing hot pressing (referred to as "dry hot pressing" in the present disclosure) without impregnating the separator with an electrolyte solution, thereby bonding the separator to the electrode.

The nonaqueous secondary battery of the present disclosure can be produced by, for example, the following production methods 1 to 3 using a roll produced by disposing the separator of the present disclosure between a positive electrode and a negative electrode and winding the roll in the longitudinal direction. The same applies to the case where an element manufactured by a method (so-called stacking method) in which at least 1 layer of each of the positive electrode, the separator, and the negative electrode is sequentially stacked is used instead of the roll.

The manufacturing method 1: the wound body is subjected to dry hot pressing to bond the electrode and the separator, and then, is stored in an outer packaging material (for example, an aluminum laminated film package, the same applies hereinafter), an electrolyte solution is injected into the wound body, and the wound body is further subjected to wet hot pressing from above the outer packaging material to bond the electrode and the separator, and to seal the outer packaging material.

The manufacturing method 2: the wound body is housed in an outer covering material, an electrolyte solution is injected into the wound body, and the wound body is subjected to wet hot pressing from the outer covering material to bond the electrode and the separator and seal the outer covering material.

The manufacturing method 3: the wound body is subjected to dry hot pressing to bond the electrode and the separator, and then is stored in an outer packaging material, and an electrolyte solution is injected into the wound body to seal the outer packaging material.

As the conditions for hot pressing in the above-mentioned production methods 1 to 3, the respective pressing temperatures of dry hot pressing and wet hot pressing are preferably 60 to 120 ℃, more preferably 70 to 100 ℃, and the pressing pressure is taken as per 1cm²The load of the electrode is preferably 0.5kg to 90 kg. The pressing time is preferably adjusted according to the pressing temperature and the pressing pressure, and is adjusted, for example, within a range of 0.1 to 60 minutes.

In the above-described production method 1 or 3, the wound body may be temporarily bonded by applying normal-temperature pressurization (pressurization at normal temperature) to the wound body before dry hot pressing. In the above-described manufacturing method 2, the roll body may be temporarily bonded by applying pressure at normal temperature before the roll body is housed in the outer covering material.

Examples

The separator and the nonaqueous secondary battery according to the present disclosure will be described in more detail below with reference to examples. Materials, amounts used, ratios, processing steps, and the like shown in the following examples may be appropriately changed without departing from the gist of the present disclosure. Therefore, the scope of the separator and the nonaqueous secondary battery of the present disclosure should not be construed in a limiting manner based on the specific examples shown below.

< measuring method, evaluation method >

The measurement methods and evaluation methods applied in examples and comparative examples are as follows.

[ average Primary particle diameter of inorganic particles ]

The inorganic particles before being added to the coating liquid for forming the heat-resistant porous layer were used as a sample, 100 particles were randomly selected in observation by a Scanning Electron Microscope (SEM), the long diameters thereof were measured, and the average value thereof was calculated as the average primary particle diameter (μm) of the inorganic particles. The SEM magnification is 5-30 ten thousand times. When the inorganic particles taken out of the separator are used as a sample, the inorganic particles are taken out by the method for taking out the inorganic particles from the separator, which is described in the item for explaining the average primary particle size of the inorganic particles. The average primary particle diameter of the inorganic particles taken out was measured by the method described above.

[ thickness of porous base Material and separator ]

The thickness (. mu.m) of the porous substrate and the separator was determined by measuring 20 spots with a contact thickness meter (Mitutoyo Co., LITEMATIC VL-50) and averaging the measured values. As the measurement terminal, a cylindrical terminal having a diameter of 5mm was used, and the adjustment was made so as to apply a load of 0.01N during the measurement.

[ thickness of Heat-resistant porous layer ]

The thickness (sum of both surfaces, μm) of the heat-resistant porous layer was determined by subtracting the thickness (μm) of the porous substrate from the thickness (μm) of a laminate comprising the porous substrate and 2 heat-resistant porous layers provided on both surfaces of the porous substrate. The thickness of one surface of the heat-resistant porous layer was determined by dividing the thickness of the heat-resistant porous layer (the sum of both surfaces) by 2.

[ weight per unit area ]

Weight per unit area (per 1 m)²Mass of (2), g/m²) The mass was measured by cutting a sample into 10cm × 30cm, and dividing the mass by the area.

[ coating amounts of respective layers ]

Coating weight (g/m) of each layer²) Is the weight per unit area (g/m) after formation of the layer²) The weight per unit area (g/m) before formation of the layer was subtracted²) And then the result is obtained.

[ Gurley value ]

Gurley values (sec/100 mL) of the porous substrate and the separator were determined in accordance with JIS P8117: 2009, measured by using a Gurley type air permeability measuring instrument (toyo seiki, G-B2C). In the following table, a value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the separator is referred to as a Gurley difference (sec/100 mL).

[ porosity of porous base Material ]

The porosity ∈ (%) of the porous substrate was determined by the following equation.

ε＝{1-Ws/(ds·t)}×100

Ws: weight per unit area (g/m) of porous substrate²) And ds: true Density (g/cm) of porous substrate³) And t: the thickness (cm) of the porous substrate.

[ porosity of Heat-resistant porous layer ]

The porosity ∈ (%) of the heat-resistant porous layer was determined by the following equation.

ε＝{1-(Wa/da+Wb/db+Wc/dc+…+Wn/dn)/t}×100

Here, the constituent materials of the heat-resistant porous layer are a, b, c, …, and n, and the mass of each constituent material is Wa, Wb, Wc, …, Wn (g/cm)²) The true densities of the constituent materials are da, db, dc, …, dn (g/cm)³) The thickness of the heat-resistant porous layer is t (cm).

[ Heat shrinkage ratio ]

The separator was cut into 100mm in the MD direction × 100mm in the TD direction, and reference lines of lengths of 70mm were drawn in the MD direction and the TD direction so as to pass through the center of the sample of the separator, respectively, to prepare test pieces. The test piece was placed between 2 sheets of paper of A4 size, and then, the test piece was left to stand in an oven at 130 ℃ and 150 ℃ for 1 hour. The MD direction and TD direction lengths of the test pieces before and after the heat treatment were measured, the thermal shrinkage was calculated from the following formula, and the above-described operation was further performed 2 times to average the thermal shrinkage of 3 test pieces to obtain the thermal shrinkage of the separator.

Heat shrinkage (%) is { (length in MD before heat treatment-length in MD after heat treatment) ÷ length in MD before heat treatment } × 100

Heat shrinkage (%) is { (length in TD direction before heat treatment-length in TD direction after heat treatment) ÷ length in TD direction before heat treatment } × 100

[ peeling Strength between porous base Material and Heat-resistant porous layer ]

The separator was subjected to a T-peel test. Specifically, a tape (product No. 550, width 12mm, 3M corporation, korea) was attached to one surface of the separator (in the case of attachment, the longitudinal direction of the tape was aligned with the MD direction of the separator), and the separator and the tape were cut into 12mm in the TD direction and 70mm in the MD direction. The tape was slightly peeled off together with the adhesive layer and the heat-resistant porous layer immediately below, and the end portion separated into two portions was held by Tensilon (Orientec, RTC-1210A) to perform a T-peel test. The adhesive tape is used as a support for peeling the adhesive layer and the heat-resistant porous layer from the porous base material. The tensile rate in the T-shaped peeling test was set at 20 mm/min, and the load (N) from 10mm to 40mm after the start of measurement was sampled at intervals of 0.4mm, and the average value thereof was calculated and converted into the load per 10mm width (N/10 mm). Further, the load of the three test pieces was averaged, and the average value (N/10mm) was multiplied by 100 to obtain the peel strength (N/m).

[ bonding strength between electrode and separator ]

97g of lithium cobaltate as a positive electrode active material, 1.5g of acetylene black as a conductive assistant, 1.5g of polyvinylidene fluoride as a binder, and an appropriate amount of N-methylpyrrolidone were stirred and mixed by a double arm mixer to prepare a slurry for a positive electrode. The slurry for a positive electrode was applied to one surface of an aluminum foil having a thickness of 20 μm, dried and then pressurized to obtain a positive electrode having a positive electrode active material layer (one surface was applied, and the weight per unit area was 20 mg/cm)²Density of 4.0g/cm³)。

The positive electrode obtained above was cut into a width of 15mm and a length of 70mm, the separator was cut into a width of 18mm in the TD direction and a length of 75mm in the MD direction, and an aluminum foil having a thickness of 20 μm was cut into a width of 15mm and a length of 70 mm. A laminate was produced by stacking the positive electrode, separator, and aluminum foil in this order, and the laminate was contained in an aluminum laminated film package. Next, the inside of the package was made vacuum by using a vacuum sealer, and the laminate and the package were hot-pressed by using a hot press (temperature 85 ℃, load 1MPa, pressing time 30 seconds) to bond the positive electrode and the separator. Then, the package was opened, the laminate was taken out, and the aluminum foil was removed from the laminate to obtain a product as a test piece.

The membrane of the test piece was fixed to the lower cartridge of Tensilon (A & D, STB-1225S). At this time, the separator was fixed with Tensilon so that the longitudinal direction of the test piece (i.e., the MD direction of the separator) became the direction of gravity. The positive electrode was peeled from the separator by about 2cm from the end of the lower part, and the end was fixed to an upper chuck, and a 180 ° peel test was performed. The tensile rate of the 180 ℃ peel test was set at 100 mm/min, and the load (N) of 10mm to 40mm after the start of measurement was taken at intervals of 0.4mm, and the average value thereof was calculated. Further, the load of the three test pieces was averaged to obtain the bonding strength (N/15mm) between the electrode and the separator. In tables 1 and 2, the adhesive strength of the separators of comparative example 1 is defined as a reference value of 100, and the adhesive strength of each separator of examples and comparative examples is shown in percentage.

[ measurement of thermal conductivity ]

As in the above (bonding strength between electrode and separator) for the positive electrode, a positive electrode (coated on both sides and having a weight per unit area of 40 mg/cm) was produced²Density of 4.0g/cm³)。

A slurry for a negative electrode was prepared by stirring and mixing 300g of artificial graphite as a negative electrode active material, 7.5g of a water-soluble dispersion liquid containing 40 mass% of a modified styrene-butadiene copolymer as a binder, 3g of carboxymethyl cellulose as a thickener, and an appropriate amount of water using a double arm mixer. The slurry for a negative electrode was applied to both surfaces of a copper foil having a thickness of 10 μm, dried and then pressed to obtain a negative electrode having a negative electrode active material layer (both-surface application, weight per unit area of 20 mg/cm)²Density of 1.7g/cm³)。

A separator cut into 150mm × 75mm size was stacked on the positive electrode and the negative electrode so as to be a separator/negative electrode/separator/positive electrode/separator, and a test piece was prepared. According to JIS R2616: 2001, the unsteady state hot-wire method measures thermal conductivity (W/m.K) using a thermal conductivity measuring device (QTM-500 manufactured by Kyoto electronic industries, Ltd.) under conditions of a temperature rise range of 30 to 120 ℃ and a temperature rise rate of 5 ℃/min. The thermal conductivity of the test piece was evaluated based on the thermal conductivity according to the following evaluation criteria.

< evaluation criteria >

A: the thermal conductivity is 7.0W/mK or more.

B: the thermal conductivity is 6.5W/mK or more and less than 7.0W/mK.

C: the thermal conductivity is 6.0W/mK or more and less than 6.5W/mK.

D: the thermal conductivity is less than 6.0W/m.K.

[ production yield ]

A positive electrode/negative electrode (double-sided coating) was produced in the same manner as in the production of the positive electrode and negative electrode in the [ measurement of thermal conductivity ].

2 separators (width 108mm) were prepared and overlapped, and one end in the MD direction was wound around a core made of stainless steel. A positive electrode (width: 106.5mm) to which a tab was welded was interposed between 2 separators, and a negative electrode (width: 107mm) to which a tab was welded was disposed on one separator, and the separator was wound to continuously produce 50 wound bodies. The obtained wound body was pressurized at normal temperature (load: 1MPa, pressurizing time: 30 seconds), and then hot-pressed (temperature: 85 ℃, load: 1MPa, pressurizing time: 30 seconds) to obtain a flat battery element.

The thickness of the flat plate-like battery element was measured immediately after hot pressing and after 1 hour from hot pressing, and a case where the change in thickness was 3% or less was judged as passed, and a case where the change in thickness exceeded 3% was judged as failed. The percentage (%) of the number of acceptable battery elements was calculated and evaluated according to the following evaluation criteria.

< evaluation criteria >

A: the proportion of the number of passing products is 100% (the number of failing products is 0).

B: the percentage of the number of passed products is 95% or more and less than 100% (1 or 2 defective products).

C: the qualified number proportion is more than 90% and less than 95% (unqualified 3-5).

[ expansion of Battery ]

And the above [ production yield ]]50 cell elements were fabricated in the same manner. The battery element was contained in an aluminum laminated film package, and the electrolyte was immersed and sealed by a vacuum sealing machine. As the electrolyte, 1mol/L LiPF was used₆-ethylene carbonate: and methyl ethyl carbonate (mass ratio of 3: 7). Then, the aluminum laminated film package containing the battery element and the electrolyte was hot-pressed (temperature 85 ℃, load 1MPa, pressing time 10 seconds) using a hot press to obtain 50 test secondary batteries.

50 test secondary batteries were charged and discharged at 25 ℃ for 100 cycles. The constant current constant voltage charge was made 0.7C and 4.2V, and the constant current discharge was made 0.5C and 2.75V off.

Before and after 100 cycles of charge and discharge, the thickness of the test secondary battery was measured, and a case where the change in thickness was 8% or less was judged as passed, and a case where the change in thickness exceeded 8% was judged as failed. The percentage (%) of the number of acceptable battery elements was calculated and evaluated according to the following evaluation criteria.

< evaluation criteria >

A: the proportion of the number of passing products is 100% (the number of failing products is 0).

B: the percentage of the number of passed products is 95% or more and less than 100% (1 or 2 defective products).

C: the percentage of qualified number is less than 95% (more than 3 unqualified).

[ Collision test ]

50 battery elements were produced in the same manner as in the above-described production yield. 50 test secondary batteries were charged at a constant current of 1C at a temperature of 25 ℃ to 4.2V, and then charged at a constant voltage of 4.2V for a total of 3 hours. A stainless steel rod having a diameter of 15.8mm was placed in the center of the upper surface of a laminate cell (plated cell) according to UL1642 standard set by UL (Underwriters Laboratories Inc.) of the united states, and a 9.1kg weight was dropped onto the stainless steel rod from a height of 61 ± 2.5cm to perform a collision test. Based on the results of the collision test, the case where no gas ejection and ignition occurred and the voltage of the laminate battery decreased within 1 second after the collision was judged as passed, and the case where gas ejection and ignition occurred was judged as failed. The percentage (%) of the number of acceptable battery elements was calculated and evaluated according to the following evaluation criteria.

< evaluation criteria >

A: the proportion of the number of passing products is 100% (the number of failing products is 0).

B: the percentage of the number of passed products is 95% or more and less than 100% (1 or 2 defective products).

C: the percentage of qualified number is less than 95% (more than 3 unqualified).

[ example 1]

Meta-type aramid (polyisophthaloyl metaphenylene diamine, manufactured by teicho corporation, Conex (registered trademark)) and magnesium hydroxide particles (average primary particle diameter of 0.30 μm) were mixed in a mass ratio of 20: 80. and the meta-type aramid was stirred and mixed in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc: TPG: 80: 20[ mass ratio ]) so that the concentration of the meta-type aramid became 5 mass%, to obtain a coating liquid.

Preparation of a film with a thickness of 70: 30 (melting point: 140 ℃ C., volume average particle diameter: 0.2 μm; PVDF particles) and acrylic resin particles (glass transition temperature: 59 ℃ C., volume average particle diameter: 0.5 μm) were dispersed in water at a mass ratio of 7 mass% (solid content concentration).

An appropriate amount of the coating liquid was placed on a pair of mayer rods, and a polyethylene microporous membrane (having a thickness of 6 μm, a porosity of 39%, a Gurley value of 100 sec/100 mL; in table 1, the expression "PE" is the same as below) was passed between the mayer rods, so that the coating liquid was applied equally to both surfaces. The solution was immersed in a coagulating liquid (DMAc: TPG: water: 32: 8: 60[ mass ratio ]]The liquid temperature was 40 ℃ C.), followed by washing in a water bath at a water temperature of 40 ℃ C. and drying to give a coating amount of 3.0g/m²The heat-resistant porous layer of (1). Subsequently, the aqueous dispersion was passed between a pair of bar coaters on which an appropriate amount of the aqueous dispersion was placed, and the aqueous dispersion was applied equally to both surfaces and dried. In this way, a separator in which a heat-resistant porous layer and an adhesive layer were formed on both surfaces of the polyethylene microporous membrane was obtained.

The structure, characteristics and battery evaluation results of the separator of example 1 are shown in table 1 below. The following examples and comparative examples are also summarized in tables 1 and 2.

[ example 2]

Except that the coating amount of the heat-resistant porous layer was changed to 2.3g/m²A separator was produced in the same manner as in example 1.

[ example 3]

A separator was produced in the same manner as in example 1, except that the mass ratio of the inorganic particles in the heat-resistant porous layer was changed to 50 mass%.

[ example 4]

A separator was produced in the same manner as in example 1, except that the mass ratio of the inorganic particles in the heat-resistant porous layer was changed to 90 mass%.

Comparative example 1

The coating amount of the heat-resistant porous layer was changed to 3.1g/m by using magnesium hydroxide particles having an average primary particle diameter of 0.5 μm as the magnesium hydroxide particles²Otherwise, a separator was produced in the same manner as in example 1.

Comparative example 2

The coating amount of the heat-resistant porous layer was changed to 2.9g/m by using magnesium hydroxide particles having an average primary particle diameter of 0.9 μm as the magnesium hydroxide particles²Otherwise, a separator was produced in the same manner as in example 1.

Comparative example 3

Alumina particles (Sumitomo chemical Co., AKP-3000, volume average particle diameter of 0.45 μm, tetrapod-like particles), carboxymethyl cellulose (Daicel FineChem Ltd., D1200, degree of etherification of 0.8 to 1.0) as a viscosity modifier, acrylic resin (DIC Co., DICNAL LSE-16AD4) as a binder resin, and a nonionic surfactant (SAN NOPCO LIMITED., SN-WET 366) were mixed at a ratio of 94.6: 3.8: 1.4: 0.2 by mass, and water was added thereto and dispersed to prepare a coating liquid having a solid content concentration of 40% by mass.

A PVDF particle dispersion (solid content concentration of 7 mass%) in which polyvinylidene fluoride resin particles (melting point: 140 ℃ C., volume average particle diameter: 0.2 μm) were dispersed in water was prepared.

An appropriate amount of the coating liquid was placed on a pair of meyer rods, a microporous polyethylene membrane (thickness 6 μm, porosity 40%, Gurley 100 sec/100 mL) was passed between the meyer rods, and the coating liquid was applied to both surfaces in equal amounts and dried. Subsequently, the PVDF particle dispersion was passed between a pair of rod coaters on which an appropriate amount of the PVDF particle dispersion was placed, and the same amount of the PVDF particle dispersion was applied to both surfaces of the coated film, followed by drying. In this way, a separator in which a heat-resistant porous layer and an adhesive layer were formed on both surfaces of the polyethylene microporous membrane was obtained.

[ example 5]

Meta-type aramid (polyisophthaloyl metaphenylene diamine, manufactured by teicho corporation, Conex (registered trademark)) and barium sulfate particles (average primary particle diameter of 0.05 μm) were mixed in a mass ratio of 20: 80. and the meta-type aramid was stirred and mixed in dimethylacetamide (DMAc) so that the concentration thereof became 4.5 mass%, thereby obtaining a coating solution.

Prepared in water at a ratio of 70: 30 (melting point: 140 ℃ C., volume average particle diameter: 0.2 μm; PVDF particles) and acrylic resin particles (glass transition temperature: 59 ℃ C., volume average particle diameter: 0.5 μm) were dispersed in an aqueous dispersion (solid content concentration: 7 mass%).

An appropriate amount of the coating liquid was placed on a pair of mayer rods, and a polyethylene microporous membrane (thickness 6 μm, porosity 40%, Gurley value 100 sec/100 mL) was passed between the mayer rods, and the coating liquid was applied to both surfaces in equal amounts. The resulting mixture was immersed in a coagulating liquid (DMAc: water 50: 50[ mass ratio)]The coating layer was cured at a liquid temperature of 40 ℃ and then washed in a water bath at a water temperature of 40 ℃ and dried to give a coating amount of 3.2g/m²The heat-resistant porous layer of (1). Subsequently, the aqueous dispersion was passed between a pair of bar coaters on which an appropriate amount of the aqueous dispersion was placed, and the aqueous dispersion was applied equally to both surfaces and dried. In this way, a separator in which a heat-resistant porous layer and an adhesive layer were formed on both surfaces of the polyethylene microporous membrane was obtained.

[ example 6]

To the flask were added 4200g of N-methylpyrrolidone (NMP), and 272.65g of calcium chloride dried at 200 ℃ for 2 hours was added, and the temperature was raised to 100 ℃. After the calcium chloride was completely dissolved, the liquid temperature was returned to room temperature, and 132.91g of p-phenylenediamine was added and completely dissolved. While the solution was kept at 20. + -. 2 ℃ C, 243.32g of terephthaloyl chloride was added in 10 portions and every 5 minutes. Subsequently, the solution was aged at 20. + -. 2 ℃ for 1 hour, and stirred under reduced pressure for 30 minutes to remove air bubbles. Then, to 100g of the polymerization solution, an NMP solution was gradually added so that the concentration of poly (p-phenylene terephthalamide) (PPTA) was 2 mass%. PPTA and magnesium hydroxide particles (average primary particle diameter of 0.3 μm) were mixed at a mass ratio of 20: stirring and mixing were carried out in the manner of 80 to obtain a coating liquid.

Prepared in water at a ratio of 70: 30 (melting point: 140 ℃ C., volume average particle diameter: 0.2 μm; PVDF particles) and acrylic resin particles (glass transition temperature: 59 ℃ C., volume average particle diameter: 0.5 μm) were dispersed in an aqueous dispersion (solid content concentration: 7 mass%).

An appropriate amount of the coating liquid was placed on a pair of mayer rods, and a polyethylene microporous membrane (thickness: 6 μm, porosity: 40%, Gurley value: 100 sec/100 mL) was passed between the mayer rods to coat the coating liquid on both surfaces in an equal amount. The resulting mixture was immersed in a coagulating liquid (NMP: water: 40: 60[ mass ratio)]Liquid temperature of 40 ℃ C.), the coating layer was cured, followed by washing in a water bath at 40 ℃ C and drying, whereby the coating amount was 3.0g/m²The heat-resistant porous layer of (1). Subsequently, the aqueous dispersion was passed between a pair of bar coaters on which an appropriate amount of the aqueous dispersion was placed, and the aqueous dispersion was applied equally to both surfaces and dried. In this way, a separator in which a heat-resistant porous layer and an adhesive layer were formed on both surfaces of the polyethylene microporous membrane was obtained.

[ example 7]

Barium sulfate particles having an average primary particle diameter of 0.03 μm were used as the inorganic particles, and the coating amount of the heat-resistant porous layer was adjusted to 3.0g/m²A separator was produced in the same manner as in example 5, except that a polyethylene microporous membrane having a thickness of 7 μm, a porosity of 35% and a Gurley value of 160 seconds/100 mL was used as the porous substrate.

[ example 8]

Except that the coating amount of the heat-resistant porous layer was set to 2.4g/m²A separator was produced in the same manner as in example 7.

[ example 9]

Polyamideimide (Solvay corporation, Torlon4000TF) and magnesium hydroxide particles (average primary particle diameter of 0.3 μm) were mixed in a mass ratio of 20: 80. and the polyamide-imide concentration was adjusted to 8 mass% by stirring and mixing in dimethylacetamide (DMAc) to obtain a coating solution.

Prepared in water at a ratio of 70: 30 mass ratio of polyvinylidene fluoride resin particles (melting point 140 ℃ C., volume average particle diameter 0.2 μm) and acrylic resin particles (glass transition temperature 59 ℃ C., volume average particle diameter 0.5 μm) were dispersed in an aqueous dispersion (solid content concentration 7 mass%).

An appropriate amount of the coating liquid was placed on a pair of mayer rods, and a polyethylene microporous membrane (thickness: 6 μm, porosity: 40%, Gurley value: 100 sec/100 mL) was passed between the mayer rods to coat the coating liquid on both surfaces in an equal amount. The coating layer was solidified by immersing the coating layer in a solidifying solution (DMAc: water 40: 60[ mass ratio ], liquid temperature 40 ℃), followed by washing in a water bath at a water temperature of 40 ℃ and drying. Subsequently, the aqueous dispersion was passed between a pair of bar coaters on which an appropriate amount of the aqueous dispersion was placed, and the aqueous dispersion was applied equally to both surfaces and dried. In this way, a separator in which a heat-resistant porous layer and an adhesive layer were formed on both surfaces of the polyethylene microporous membrane was obtained.

[ example 10]

Polyimide (institute of PI technology, Q-VR-X1444) and magnesium hydroxide particles (average primary particle diameter of 0.3 μm) were mixed in a mass ratio of 20: 80. the polyimide was stirred and mixed in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc: TPG: 90: 10[ mass ratio ]) so that the polyimide concentration became 6 mass%, to obtain a coating solution.

Prepared in water at a ratio of 70: 30 (melting point: 140 ℃ C., volume average particle diameter: 0.2 μm; PVDF particles) and acrylic resin particles (glass transition temperature: 59 ℃ C., volume average particle diameter: 0.5 μm) were dispersed in an aqueous dispersion (solid content concentration: 7 mass%).

An appropriate amount of the coating liquid was placed on a pair of mayer rods, and a polyethylene microporous membrane (thickness: 6 μm, porosity: 40%, Gurley value: 100 sec/100 mL) was passed between the mayer rods to coat the coating liquid on both surfaces in an equal amount. The coating layer was solidified by immersing the coating layer in a solidifying solution (DMAc: TPG: water 36: 4: 60[ mass ratio ], liquid temperature 40 ℃), followed by washing in a water bath at 40 ℃ and drying. Subsequently, the aqueous dispersion was passed between a pair of bar coaters on which an appropriate amount of the aqueous dispersion was placed, and the aqueous dispersion was applied equally to both surfaces and dried. In this way, a separator in which a heat-resistant porous layer and an adhesive layer were formed on both surfaces of the polyethylene microporous membrane was obtained.

[ example 11]

Polyvinylidene fluoride resin (VDF-HFP copolymer, VDF: HFP (molar ratio) 97.6: 2.4, weight average molecular weight 113 ten thousand, PVDF) was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc: TPG 90: 10[ mass ratio ]) so that the resin concentration became 4 mass%, and barium sulfate particles (average primary particle diameter 0.05 μm) were stirred and mixed to obtain a coating liquid. In the coating liquid, the mass ratio of the polyvinylidene fluoride resin to the barium sulfate particles was 20: 80.

prepared in water at a ratio of 70: 30 (melting point: 140 ℃ C., volume average particle diameter: 0.2 μm; PVDF particles) and acrylic resin particles (glass transition temperature: 59 ℃ C., volume average particle diameter: 0.5 μm) were dispersed in an aqueous dispersion (solid content concentration: 7 mass%).

An appropriate amount of the coating liquid was placed on a pair of mayer rods, and a polyethylene microporous membrane (thickness: 6 μm, porosity: 40%, Gurley value: 100 sec/100 mL) was passed between the mayer rods to coat the coating liquid on both surfaces in an equal amount. The coating layer was solidified by immersing the coating layer in a solidifying solution (DMAc: TPG: water 36: 4: 60[ mass ratio ], liquid temperature 40 ℃), followed by washing in a water bath at 40 ℃ and drying. Subsequently, the aqueous dispersion was passed between a pair of bar coaters on which an appropriate amount of the aqueous dispersion was placed, and the aqueous dispersion was applied equally to both surfaces and dried. In this manner, a separator in which a heat-resistant porous layer and an adhesive layer were formed on both surfaces of the polyethylene microporous membrane was obtained.

[ example 12]

The amount of the heat-resistant porous layer applied was set to 10.2g/m²A separator was produced in the same manner as in example 5, except that a polyethylene microporous membrane having a thickness of 7 μm, a porosity of 35% and a Gurley value of 160 seconds/100 mL was used as the porous substrate.

[ Table 1]

[ Table 2]

As shown in tables 1 to 2, the separators of the examples were thin films and showed superior heat resistance compared to the comparative examples.

The disclosure of Japanese application laid-open application No. 2019-104514, filed on 6, 4, 2019, is incorporated herein by reference in its entirety.

All documents, patent applications, and technical standards described in the present specification are incorporated by reference into the present specification to the same extent as if each document, patent application, and technical standard was specifically and individually described.