Separator for non-aqueous secondary battery and non-aqueous secondary battery

Abstract

To provide a separator for a non-aqueous secondary battery which is excellent in thermal dimensional stability and adhesion to an electrode, and improves battery cycle characteristics and impact resistance.SOLUTION: A separator for a non-aqueous secondary battery includes a porous base material, a heat-resistant layer which is arranged on one side or both sides of the porous base material, and contains inorganic particles and a binder resin, and an adhesive layer which is arranged on one side or both sides of the laminate of the porous base material and the heat-resistant layer, and contains a polyvinylidene fluoride-based resin, wherein the mass ratio of the inorganic particles in the heat-resistant layer is 95 mass% or more, the average primary particle diameter of the inorganic particles contained in the heat-resistant layer is 0.01 μm to 0.30 μm, and the adhesive layer has a porous structure such that fibrils containing the polyvinylidene fluoride-based resin are connected to each other in three-dimensional meshes.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a separator for a nonaqueous secondary battery and a nonaqueous secondary battery. [Background technology]

[0002] Patent Document 1 discloses a separator for a non-aqueous secondary battery, which includes a porous substrate, a heat-resistant porous layer provided on one or both sides of the porous substrate and containing a binder resin and inorganic particles having an average primary particle size of 0.01 μm or more and less than 0.45 μm, and an adhesive layer provided on one or both sides of a laminate of the porous substrate and the heat-resistant porous layer, in which adhesive resin particles are adhered to the laminate. Patent Document 2 discloses a separator for a non-aqueous secondary battery, comprising a porous substrate and an adhesive layer on one or both sides of the porous substrate, the adhesive layer containing at least one selected from the group consisting of (i) adhesive resin particles containing a phenyl group-containing acrylic resin and a polyvinylidene fluoride resin, and (ii) a mixture of adhesive resin particles containing a phenyl group-containing acrylic resin and adhesive resin particles containing a polyvinylidene fluoride resin. Patent Document 3 discloses a ceramic-polymer composite-coated lithium ion separator including a polyolefin porous separator, a ceramic coating layer applied to one or both sides of the separator, and a polymer coating layer applied to the ceramic surface or the separator surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 246497 [Patent Document 2] JP 2023-040938 A [Patent Document 3] Special Publication No. 2019-523518 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a separator for a nonaqueous secondary battery that has excellent thermal dimensional stability and adhesion to electrodes, and also improves the cycle characteristics and impact resistance of the battery. [Means for solving the problem]

[0005] Specific means for solving the above problems include the following aspects. <1> A porous substrate; A heat-resistant layer containing inorganic particles and a binder resin arranged on one or both sides of the porous substrate; An adhesive layer containing a polyvinylidene fluoride resin arranged on one or both sides of a laminate of the porous substrate and the heat-resistant layer, The mass ratio of the inorganic particles in the heat-resistant layer is 95 mass% or more, The inorganic particles contained in the heat-resistant layer have an average primary particle size of 0.01 μm to 0.30 μm; the adhesive layer has a porous structure in which fibrils containing the polyvinylidene fluoride resin are connected in a three-dimensional network shape; Separator for non-aqueous secondary batteries. <2> The heat-resistant layers are disposed on both sides of the porous substrate. <1> The non-aqueous secondary battery separator according to claim 1 . <3> The inorganic particles include at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles. <1> or <2> The non-aqueous secondary battery separator according to claim 1 . <4> The inorganic particles include barium sulfate particles. <1> or <2> The non-aqueous secondary battery separator according to claim 1 . <5> The polyvinylidene fluoride resin includes the following polyvinylidene fluoride resin A and polyvinylidene fluoride resin B, <1> ~ <4> 1. A non-aqueous secondary battery separator according to any one of the above items 1 to 5. Polyvinylidene fluoride resin A: a polyvinylidene fluoride resin containing vinylidene fluoride and hexafluoropropylene as polymerization components, in which the proportion of hexafluoropropylene in the total of vinylidene fluoride and hexafluoropropylene is more than 1.5 mol % and not more than 5 mol %; Polyvinylidene fluoride resin B: A polyvinylidene fluoride resin containing vinylidene fluoride and hexafluoropropylene as polymerization components, in which the proportion of hexafluoropropylene in the total of vinylidene fluoride and hexafluoropropylene is more than 5 mol % and not more than 15 mol %. <6> The polyvinylidene fluoride resin includes the following polyvinylidene fluoride resin C: <1> ~ <5> 1. A non-aqueous secondary battery separator according to any one of the above items 1 to 5. Polyvinylidene fluoride resin C: A polyvinylidene fluoride resin containing vinylidene fluoride, hexafluoropropylene, and a monomer represented by the formula (1) described below as polymerization components. <7> The binder resin of the heat-resistant layer contains at least one selected from the group consisting of butadiene-based polymers and acrylic-based resins. <1> ~ <6> 10. The separator for a non-aqueous secondary battery according to claim 9, <8> The thickness of each of the heat-resistant layers is 0.1 μm to 2 μm. <1> ~ <7> 10. The separator for a non-aqueous secondary battery according to claim 9, <9> The thickness of the porous substrate is 1 μm to 7 μm. <1> ~ <8> 10. The separator for a non-aqueous secondary battery according to claim 9, <10> The mass per unit area of ​​the adhesive layer is 0.5 g / m on both sides in total. 2 ~3g / m 2 That is, <1> ~ <9> 10. The separator for a non-aqueous secondary battery according to claim 9, <11> a difference between the Gurley value of the laminate and the Gurley value of the nonaqueous secondary battery separator is 30 seconds / 100 mL or less; <1> ~ <10> 10. The separator for a non-aqueous secondary battery according to claim 9, <12> A positive electrode, a negative electrode, and a conductive material disposed between the positive electrode and the negative electrode. <1> ~ <11> and a non-aqueous secondary battery separator according to any one of the above items, Electromotive force is obtained by doping and dedoping lithium ions. Non-aqueous secondary battery. Effect of the Invention

[0006] According to the present disclosure, there is provided a non-aqueous secondary battery separator that has excellent thermal dimensional stability and adhesion to electrodes, and improves the cycle characteristics and impact resistance of the battery. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Diagram 2] FIG. 2 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Diagram 3] FIG. 2 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Figure 4] FIG. 2 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Diagram 5] FIG. 2 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Figure 6] 1 is a SEM image of an example embodiment of an adhesive layer provided on a separator of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present disclosure will be described. These descriptions and examples are merely illustrative of the embodiments, and are not intended to limit the scope of the embodiments.

[0009] In the present disclosure, a numerical range indicated using "~" indicates a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

[0010] In the present disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" means that it may be only A, it may be only B, or it may be a combination of A and B.

[0011] In the present disclosure, the term "step" includes not only an independent step, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0012] In the present disclosure, when referring to the amount of each component in a composition, in cases where multiple substances corresponding to each component are present in the composition, unless otherwise specified, it means the total amount of those multiple substances present in the composition. In the present disclosure, the particles corresponding to each component may include multiple types. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0013] In the present disclosure, MD (Machine Direction) means the longitudinal direction of a separator produced in a long shape, and TD (Transverse Direction) means the direction perpendicular to MD in the plane direction of the separator. In the present disclosure, TD is also referred to as "width direction."

[0014] In the present disclosure, when the stacking relationship of each layer constituting a separator is expressed as "upper" and "lower", the layer closer to the porous substrate is referred to as "lower" and the layer farther from the porous substrate is referred to as "upper".

[0015] In the present disclosure, the volume of the porous layer excluding the pores is referred to as the "solids volume."

[0016] In the present disclosure, performing a heat press treatment after impregnating a separator with an electrolyte is referred to as "wet heat press", and performing a heat press treatment without impregnating a separator with an electrolyte is referred to as "dry heat press".

[0017] In the present disclosure, the term "monomer unit" of a polymer or resin means a structural unit of a polymer or resin, which is formed by polymerization of a monomer. In the present disclosure, the term "(meth)acrylic" means either "acrylic" or "methacrylic".

[0018] <Separator for non-aqueous secondary batteries> The separator for a nonaqueous secondary battery according to the present disclosure (also simply referred to as "separator" in the present disclosure) comprises a porous substrate, a heat-resistant layer containing inorganic particles and a binder resin and disposed on one or both sides of the porous substrate, and an adhesive layer containing a polyvinylidene fluoride resin and disposed on one or both sides of a laminate of the porous substrate and the heat-resistant layer.

[0019] In the separator of the present disclosure, the mass ratio of inorganic particles in the heat-resistant layer is 95 mass% or more, the inorganic particles contained in the heat-resistant layer have an average primary particle size of 0.01 μm to 0.30 μm, and the adhesive layer has a porous structure in which fibrils containing polyvinylidene fluoride resin are connected in a three-dimensional network pattern.

[0020] By virtue of having the above-described configuration, the separator of the present disclosure has excellent thermal dimensional stability and adhesion to electrodes, and also improves the cycle characteristics and impact resistance of the battery.

[0021] The mass proportion of the inorganic particles in the heat-resistant layer is 95 mass % or more, preferably 96 mass % or more, and more preferably 97 mass % or more, from the viewpoints of thermal dimensional stability of the separator and improving impact resistance of the battery. The mass ratio of the inorganic particles in the heat-resistant layer is preferably 99 mass% or less, more preferably 98 mass% or less, from the viewpoint of the formability of the heat-resistant layer. In other words, the mass ratio of the binder resin in the heat-resistant layer is preferably 1 mass% or more, more preferably 2 mass% or more, from the viewpoint of the formability of the heat-resistant layer.

[0022] The average primary particle size of the inorganic particles contained in the heat-resistant layer is 0.01 μm or more, preferably 0.05 μm or more, and more preferably 0.08 μm or more, from the viewpoint of ion permeability of the heat-resistant layer. The average primary particle size of the inorganic particles contained in the heat-resistant layer is 0.30 μm or less, preferably 0.20 μm or less, and more preferably 0.15 μm or less, from the viewpoint of making the heat-resistant layer thin and from the viewpoint of formability of the heat-resistant layer containing a large amount of inorganic particles.

[0023] The heat-resistant layer contains inorganic particles at 95% by mass or more for the purpose of improving the thermal dimensional stability of the separator and the impact resistance of the battery. In order to form a heat-resistant layer containing a large amount of inorganic particles and to form it as thin as possible, the inorganic particles have an average primary particle size of 0.30 μm or less.

[0024] The adhesive layer contains a polyvinylidene fluoride resin and has a porous structure in which fibrils containing the polyvinylidene fluoride resin are connected in a three-dimensional network. This structure gives the adhesive layer excellent ion permeability and excellent adhesion to the electrode. This structure also makes it possible to make the adhesive layer thinner while maintaining mechanical strength, thereby improving the cycle characteristics of the battery.

[0025] The layer structure of the separator of the present disclosure will be described with reference to the drawings. Figures 1 to 5 are schematic cross-sectional views of embodiments of the separator of the present disclosure. Figures 1 to 5 are schematic cross-sectional views mainly for explaining the stacking order of layers, and the structure of each layer is omitted or simplified. In Figures 1 to 5, layers having similar functions are denoted by the same reference numerals and will be described.

[0026] The separator 10A shown in Fig. 1 is a separator in which heat-resistant layers 30 are arranged on both sides of a porous substrate 20, and adhesive layers 50 are arranged on both sides of a laminate 40 of the porous substrate 20 and two heat-resistant layers 30. One heat-resistant layer 30 and the other heat-resistant layer 30 may be the same or different in terms of components and / or composition. One adhesive layer 50 and the other adhesive layer 50 may be the same or different in terms of components and / or composition.

[0027] 2 is a separator in which heat-resistant layers 30 are disposed on both sides of a porous substrate 20, and an adhesive layer 50 is disposed on one side of a laminate 40 of the porous substrate 20 and two heat-resistant layers 30. One heat-resistant layer 30 and the other heat-resistant layer 30 may be the same or different in components and / or composition.

[0028] 3 is a separator in which a heat-resistant layer 30 is disposed on one side of a porous substrate 20, and adhesive layers 50 are disposed on both sides of a laminate 40 of the porous substrate 20 and one heat-resistant layer 30. One adhesive layer 50 and the other adhesive layer 50 may be the same or different in terms of components and / or composition.

[0029] 4 is a separator in which a heat-resistant layer 30 is disposed on one side of a porous substrate 20, and an adhesive layer 50 is disposed on one side of a laminate 40 of the porous substrate 20 and one heat-resistant layer 30. In the separator 10D, the adhesive layer 50 is disposed on the surface of the heat-resistant layer 30.

[0030] 5 is a separator in which a heat-resistant layer 30 is disposed on one side of a porous substrate 20, and an adhesive layer 50 is disposed on one side of a laminate 40 of the porous substrate 20 and one heat-resistant layer 30. In the separator 10E, the adhesive layer 50 is disposed on the surface of the porous substrate 20.

[0031] The heat-resistant layer 30 is a layer containing inorganic particles and a binder resin, and is a layer disposed on the surface of the porous substrate 20. The heat-resistant layer 30 may be present on only one side of the porous substrate 20, or may be present on both sides of the porous substrate 20. When the heat-resistant layer 30 is present on both sides of the porous substrate 20, the thermal dimensional stability of the separator is superior, and the safety of the battery can be improved. In addition, the separator is less likely to curl, and the handling during battery production is excellent. When the heat-resistant layer 30 is present on only one side of the porous substrate 20, the ion permeability of the separator is superior. In addition, the thickness of the entire separator can be suppressed, and a battery with a higher energy density can be produced.

[0032] The adhesive layer 50 is a layer containing a polyvinylidene fluoride resin, and is a layer disposed on the surface of the porous substrate 20 or the heat-resistant layer 30, and exists as the outermost layer of the separator. The adhesive layer 50 may be present on only one side of the laminate 40, or on both sides of the laminate 40. When the adhesive layer 50 is present on only one side of the laminate 40, it is preferable that the adhesive layer 50 is disposed on the surface of the heat-resistant layer 30. The adhesive layer 50 may be disposed on one side or both sides of the laminate 40 according to the composition or surface properties of the positive or negative electrode of the battery. When the adhesive layer 50 is present on only one side of the laminate 40, the thickness of the entire separator can be reduced, and a battery with a higher energy density can be manufactured.

[0033] The porous substrate, heat-resistant layer, and adhesive layer of the separator of the present disclosure will be described in detail below.

[0034] [Porous base material] In the present disclosure, the porous substrate means a substrate having pores or gaps therein. Examples of such substrates include microporous membranes; porous sheets such as nonwoven fabrics and paper made of fibrous materials; composite porous sheets obtained by laminating one or more other porous layers on these microporous membranes or porous sheets; and the like. In the present disclosure, a microporous membrane is preferred from the viewpoint of thinning and strength of the separator. The microporous membrane means a membrane having a large number of micropores therein, a structure in which the micropores are connected, and which allows gas or liquid to pass from one surface to the other surface.

[0035] The material of the porous substrate is preferably an electrically insulating material.

[0036] The porous substrate preferably contains a thermoplastic resin in order to provide the porous substrate with a shutdown function. The shutdown function refers to a function in which, when the battery temperature rises, the constituent material dissolves and blocks the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. The thermoplastic resin is preferably a thermoplastic resin having a melting point of less than 200°C. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and the like, and among these, polyolefins are preferred.

[0037] The porous substrate is preferably a microporous membrane containing polyolefin (referred to as a "polyolefin microporous membrane" in the present disclosure). Examples of the polyolefin microporous membrane include polyolefin microporous membranes used in conventional battery separators, and it is preferable to select one having sufficient mechanical properties and ion permeability from these.

[0038] From the viewpoint of exhibiting a shutdown function, the polyolefin microporous membrane is preferably a microporous membrane containing polyethylene, and the polyethylene content is preferably 95% by mass or more based on the total mass of the polyolefin microporous membrane.

[0039] The polyolefin microporous film is preferably a microporous film containing polypropylene, from the viewpoint of heat resistance such that the film does not easily break when exposed to high temperatures.

[0040] From the viewpoint of having a shutdown function and heat resistance that does not easily break when exposed to high temperatures, the polyolefin microporous film is preferably a polyolefin microporous film containing polyethylene and polypropylene. An example of a polyolefin microporous film containing polyethylene and polypropylene is a microporous film in which polyethylene and polypropylene are mixed in one layer. From the viewpoint of achieving both the shutdown function and heat resistance, the microporous film preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. Also, from the viewpoint of achieving both the shutdown function and heat resistance, a polyolefin microporous film having a laminated structure of two or more layers, at least one layer containing polyethylene and at least one layer containing polypropylene, is also preferred.

[0041] The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight (Mw) of 100,000 to 5,000,000. When the Mw of the polyolefin is 100,000 or more, the microporous membrane can be imparted with sufficient mechanical properties. On the other hand, when the Mw of the polyolefin is 5,000,000 or less, the microporous membrane has good shutdown properties and is easy to mold.

[0042] Examples of methods for producing a polyolefin microporous membrane include a method in which a molten polyolefin resin is extruded through a T-die to form a sheet, which is crystallized, stretched, and then heat-treated to form a microporous membrane; a method in which a molten polyolefin resin together with a plasticizer such as liquid paraffin is extruded through a T-die, cooled to form a sheet, stretched, the plasticizer is extracted, and then heat-treated to form a microporous membrane; and the like.

[0043] Examples of the porous sheet made of a fibrous material include porous sheets such as nonwoven fabrics and papers made of fibrous materials such as polyesters 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; and cellulose.

[0044] In the present disclosure, a heat-resistant resin refers to a resin having a melting point of 200° C. or higher, or a resin having no melting point and a decomposition temperature of 200° C. or higher. In other words, a heat-resistant resin in the present disclosure refers to a resin that does not melt or decompose in a temperature range below 200° C.

[0045] The composite porous sheet may be a sheet in which a functional layer is laminated on a porous sheet made of a microporous membrane or a fibrous material. Such a composite porous sheet is preferable from the viewpoint of enabling further addition of functions by the functional layer. For example, from the viewpoint of imparting heat resistance, the functional layer may be a porous layer made of a heat-resistant resin. The heat-resistant resin may be one or more heat-resistant resins selected from wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Examples of the composite method include a method of coating a functional layer on a microporous membrane or a porous sheet, a method of bonding a microporous membrane or a porous sheet to a functional layer with an adhesive, and a method of thermocompression bonding a microporous membrane or a porous sheet to a functional layer.

[0046] The surface of the porous substrate may be subjected to various surface treatments in order to improve wettability with a coating liquid for forming a heat-resistant layer or an adhesive layer, as long as the properties of the porous substrate are not impaired. Examples of the surface treatments include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0047] -Characteristics of porous substrate- From the viewpoint of mechanical strength, the thickness of the porous substrate is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. From the viewpoint of increasing the energy density of the battery, the thickness of the porous substrate is preferably 7 μm or less, and more preferably 6 μm or less.

[0048] The thickness of the porous substrate is measured using a contact thickness meter at 20 points within a 10 cm square area and the average is calculated.

[0049] From the viewpoint of suppressing short-circuiting of the battery, the Gurley value of the porous substrate is preferably 30 seconds / 100 mL or more, more preferably 50 seconds / 100 mL or more, and even more preferably 70 seconds / 100 mL or more. The Gurley value of the porous substrate is preferably 200 seconds / 100 mL or less, more preferably 180 seconds / 100 mL or less, and even more preferably 160 seconds / 100 mL or less, from the viewpoint of ion permeability and from the viewpoint of preventing the porous structure from being blocked at the boundary between the porous substrate and the heat-resistant layer or the adhesive layer when exposed to high temperatures. The Gurley value of the porous substrate is determined by measurement using a Gurley densometer in accordance with JIS P8117:2009.

[0050] The porosity of the porous substrate is preferably 30% to 60% from the viewpoint of ion permeability. The porosity ε (%) of the porous substrate is calculated by the following formula. ε={1-Ws / (ds·t)}×100 Here, Ws is the basis weight of the porous substrate (g / m 2 ), ds is the true density of the porous substrate (g / cm 3 ), t is the thickness (μm) of the porous substrate. Basis weight is the mass per unit area.

[0051] [Heat-resistant layer] The heat-resistant layer contains at least inorganic particles and a binder resin.

[0052] -Inorganic particles- Examples of inorganic particles include metal oxide particles, metal hydroxide particles, metal sulfate particles, metal carbonate particles, metal nitride particles, and clay mineral particles.

[0053] Examples of metal oxides constituting the metal oxide particles include silica, alumina, boehmite (alumina monohydrate), titania, zirconia, magnesium oxide, and barium oxide, with alumina being preferred. Examples of metal hydroxides constituting the metal hydroxide particles include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide, with magnesium hydroxide being preferred. Examples of metal sulfates constituting the metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred. Examples of metal carbonates constituting the metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides constituting the metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0054] The inorganic particles may be surface-modified with a silane coupling agent or the like.

[0055] The inorganic particles may be used alone or in combination of two or more kinds.

[0056] From the viewpoints of stability in the electrolyte and electrochemical stability, the inorganic particles are preferably at least one type selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles.

[0057] As the inorganic particles, metal sulfate particles are preferred, and barium sulfate particles are more preferred, from the viewpoint of being less likely to decompose the electrolytic solution or electrolyte and therefore less likely to cause gas generation inside the battery.

[0058] The particle shape of the inorganic particles is not limited, and may be any of spherical, elliptical, plate-like, needle-like, and amorphous. From the viewpoint of suppressing short circuits in the battery, the inorganic particles contained in the heat-resistant layer are preferably plate-like particles or non-aggregated primary particles.

[0059] The average primary particle size of the inorganic particles contained in the heat-resistant layer is from 0.01 μm to 0.30 μm, preferably from 0.05 μm to 0.20 μm, and more preferably from 0.08 μm to 0.15 μm.

[0060] The average primary particle size of inorganic particles is obtained by measuring the long diameter of 100 inorganic particles randomly selected in observation with a scanning electron microscope (SEM) and averaging the long diameters of the 100 particles. The sample used for SEM observation is inorganic particles that are materials forming the heat-resistant layer, or inorganic particles removed from the heat-resistant layer. There is no limitation on the method for removing inorganic particles from the heat-resistant layer. The method includes, for example, a method in which the heat-resistant layer peeled off from the separator is immersed in an organic solvent that dissolves the binder resin, and the inorganic particles are removed by dissolving the binder resin with the organic solvent; a method in which the heat-resistant layer peeled off from the separator is heated to about 800°C to eliminate the binder resin and remove the inorganic particles; and the like.

[0061] Density of inorganic particles (g / cm 3 From the viewpoint of making the inorganic particle content of the heat-resistant layer 95% by mass or more and from the viewpoint of the stability over time and coatability of the coating solution for forming the heat-resistant layer, the average particle diameter is preferably 1.5 to 11.0, more preferably 2.0 to 5.5, and even more preferably 3.5 to 5.0.

[0062] The mass proportion of the inorganic particles in the heat-resistant layer is 95 mass % or more, preferably 96 mass % to 99 mass %, and more preferably 97 mass % to 98 mass %.

[0063] When the inorganic particles are barium sulfate particles, the mass proportion of the barium sulfate particles in the heat-resistant layer is preferably 95 mass % or more, more preferably 96 mass % to 99 mass %, and further preferably 97 mass % to 98 mass %.

[0064] When heat-resistant layers are present on both sides of the porous substrate, the type and / or content of inorganic particles contained in one heat-resistant layer may be the same as or different from the type and / or content of inorganic particles contained in the other heat-resistant layer.

[0065] -Organic particles- The heat-resistant layer may contain organic particles. Examples of the organic particles include particles made of crosslinked polymers such as crosslinked poly(meth)acrylic acid, crosslinked poly(meth)acrylic acid ester, crosslinked polysilicone, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensate; particles made of heat-resistant polymers such as polysulfone, polyacrylonitrile, aramid, and polyacetal; and the like. The resin constituting the organic particles may be a mixture, modified product, derivative, copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) or crosslinked product of the above-exemplified materials.

[0066] The organic particles may be used alone or in combination of two or more kinds.

[0067] -Binding resin- The binder resin contained in the heat-resistant layer has the function of binding the inorganic particles contained in the heat-resistant layer together, as well as the function of adhering the heat-resistant layer to the porous substrate, the function of adhering the heat-resistant layer to the electrode, the function of improving the heat resistance of the heat-resistant layer, etc. The binder resin contained in the heat-resistant layer may have a particle shape in the heat-resistant layer, or may not have a specific shape, and may have any form as long as it can bind the inorganic particles together.

[0068] From the viewpoint of binding a large amount of inorganic particles, the binder resin contained in the heat-resistant layer preferably contains at least one selected from the group consisting of butadiene-based polymers and acrylic-based resins.

[0069] Examples of butadiene-based polymers include homopolymers of butadiene and copolymers of butadiene and styrene-based monomers (i.e., styrene-butadiene copolymers). These resins may be used alone or in combination of two or more.

[0070] Examples of styrene-based monomers constituting the styrene-butadiene copolymer include styrene, α-methylstyrene; alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene; halogen-substituted styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene; and fluorine-substituted styrenes such as 4-fluorostyrene and 2,5-difluorostyrene. As the styrene-based monomer, styrene and α-methylstyrene are preferred, and styrene is more preferred. The styrene-based monomer may be used alone or in combination of two or more kinds.

[0071] The styrene-butadiene copolymer may be copolymerized with a small amount of an acrylic monomer. The acrylic monomer is preferably an alkyl (meth)acrylate. The alkyl group at the ester moiety of the alkyl (meth)acrylate is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. Specific examples of the acrylic monomer include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. The acrylic monomer may be used alone or in combination of two or more kinds.

[0072] Examples of the acrylic resin include homopolymers or copolymers of acrylic monomers, and copolymers of acrylic monomers and styrene monomers. These resins may be used alone or in combination of two or more.

[0073] Examples of the acrylic monomer of the acrylic resin include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. As the acrylic monomer, (meth)acrylic acid alkyl ester is preferred. The alkyl group of the ester moiety of the (meth)acrylic acid alkyl ester is preferably an alkyl group having 1 to 10 carbon atoms, and more preferably an alkyl group having 1 to 8 carbon atoms. The acrylic monomer may be used alone or in combination of two or more kinds.

[0074] Examples of styrene monomers for acrylic resins include styrene, α-methylstyrene, alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene, halogen-substituted styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene, and fluorine-substituted styrenes such as 4-fluorostyrene and 2,5-difluorostyrene. As styrene monomers, styrene and α-methylstyrene are preferred, and styrene is more preferred. The styrene monomers may be used alone or in combination of two or more.

[0075] The heat-resistant layer may contain other resins other than butadiene-based polymers and acrylic resins. Examples of other resins include fully aromatic polyamides (also known as aramids), polyamideimides, poly-N-vinylacetamides, polyacrylamides, copolymerized polyether polyamides, polyimides and polyetherimides, fluorine-based resins, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), polysulfones, polyketones, polyether ketones, polyether sulfones, and mixtures thereof. These resins may be used alone or in combination of two or more.

[0076] The mass ratio of other resins to the total resin of the heat-resistant layer is preferably 10 mass % or less, more preferably 5 mass % or less, even more preferably 1 mass % or less, and particularly preferably substantially none is contained. The total mass proportion of the butadiene-based polymer and acrylic resin in the entire resin of the heat-resistant layer is preferably 90 mass % or more, more preferably 95 mass % or more, further preferably 99 mass % or more, and particularly preferably 100 mass %.

[0077] The mass proportion of the binder resin in the heat-resistant layer is preferably 1 mass % or more, and more preferably 2 mass % or more, from the viewpoint of formability of the heat-resistant layer. From the viewpoint of increasing the content of inorganic particles in the heat-resistant layer, the mass proportion of the binder resin in the heat-resistant layer is preferably 5 mass % or less, more preferably 4 mass % or less, and further preferably 3 mass %.

[0078] When heat-resistant layers are present on both sides of the porous substrate, the type and / or content of the binder resin contained in one heat-resistant layer may be the same as or different from the type and / or content of the binder resin contained in the other heat-resistant layer.

[0079] -Other ingredients- The heat-resistant layer may contain additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming agent, and a pH adjuster. The dispersant is added to the coating liquid for forming the heat-resistant layer for the purpose of improving dispersibility, coatability, or storage stability. The wetting agent, antifoaming agent, and pH adjuster are added to the coating liquid for forming the heat-resistant layer for the purpose of improving compatibility with the porous substrate, suppressing air entrapment in the coating liquid, or adjusting the pH, for example.

[0080] -Characteristics of heat-resistant layer- From the viewpoint of the heat resistance of the battery, the thickness of each heat-resistant layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 0.8 μm or more. The thickness of each heat-resistant layer is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 1.2 μm or less, from the viewpoints of ion permeability and energy density of the battery.

[0081] When the heat-resistant layer is present on both sides of the porous substrate, the thickness of the heat-resistant layer, calculated as the total thickness of both sides, is preferably 0.2 μm or more, more preferably 1.0 μm or more, and even more preferably 1.5 μm or more, and is preferably 4 μm or less, more preferably 3 μm or less, and even more preferably 2.5 μm or less.

[0082] The thickness of the heat-resistant layer is the thickness of the flat membrane after removing the adhesive layer from the separator minus the thickness of the porous substrate. The thickness of the flat membrane after peeling the adhesive layer from the separator is measured at 20 points within a 10 cm square using a contact thickness meter and the average is calculated.

[0083] The porosity of the heat-resistant layer is preferably 20% to 70% from the viewpoint of ion permeability. The porosity ε (%) of the heat-resistant layer is calculated by the following formula.

[0084]

number

[0085] [Adhesive layer] The adhesive layer is a layer disposed on the surface of the heat-resistant layer or the porous substrate, and exists as the outermost layer of the separator. The adhesive layer has a large number of gaps or fine pores, and allows gas or liquid to pass from one surface to the other.

[0086] -Polyvinylidene fluoride resin- The adhesive layer contains a polyvinylidene fluoride resin. Examples of polyvinylidene fluoride resins include homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride and halogen-containing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene; copolymers of vinylidene fluoride and other monomers other than halogen-containing monomers; copolymers of vinylidene fluoride, halogen-containing monomers, and other monomers other than halogen-containing monomers; and mixtures thereof. The polyvinylidene fluoride resins may be used alone or in combination of two or more.

[0087] As the polyvinylidene fluoride resin, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer) is preferable from the viewpoint of adhesion to the electrode. In the present disclosure, the VDF-HFP copolymer includes both a copolymer obtained by polymerizing only VDF and HFP, and a copolymer obtained by polymerizing VDF, HFP, and other monomers. By increasing or decreasing the content of HFP, the crystallinity, heat resistance, and resistance to dissolution in an electrolyte of the VDF-HFP copolymer can be controlled within an appropriate range.

[0088] The polyvinylidene fluoride resin preferably contains a polyvinylidene fluoride resin A and a polyvinylidene fluoride resin B. In the present disclosure, polyvinylidene fluoride resin A means a polyvinylidene fluoride resin containing VDF and HFP as polymerization components, in which the proportion of HFP in the total of VDF and HFP is more than 1.5 mol % and 5 mol % or less. In the present disclosure, polyvinylidene fluoride resin B means a polyvinylidene fluoride resin containing VDF and HFP as polymerization components, in which the proportion of HFP in the total of VDF and HFP is more than 5 mol % and 15 mol % or less.

[0089] The polyvinylidene fluoride resin A may contain other monomers as polymerization components other than VDF and HFP. Examples of the other monomers include halogen-containing monomers such as tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene, and monomers represented by the formula (1) described below. When polyvinylidene fluoride resin A contains a monomer represented by formula (1) as a polymerization component, polyvinylidene fluoride resin A is also polyvinylidene fluoride resin C.

[0090] VDF and HFP are preferably the main monomers of the halogen-containing monomers constituting the polyvinylidene fluoride resin A. The total of VDF and HFP constituting the polyvinylidene fluoride resin A is preferably 80 mol % or more, more preferably 90 mol % or more, and even more preferably 100 mol %, based on the total of the halogen-containing monomers.

[0091] The proportion of HFP in the total of VDF and HFP in the polyvinylidene fluoride resin A is preferably more than 1.5 mol% and not more than 5 mol%, more preferably more than 1.5 mol% and not more than 4 mol%. When the proportion of HFP in the polyvinylidene fluoride resin A is within this range, a fine porous structure is likely to develop in the adhesive layer, and since excessive swelling of the VDF-HFP copolymer in the electrolyte can be suppressed, pore blockage is unlikely to occur, and therefore the cycle characteristics of the battery are excellent.

[0092] The polyvinylidene fluoride resin B may contain other monomers as polymerization components other than VDF and HFP. Examples of the other monomers include halogen-containing monomers such as tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene, and monomers represented by the formula (1) described below. When polyvinylidene fluoride resin B contains a monomer represented by formula (1) as a polymerization component, polyvinylidene fluoride resin B is also polyvinylidene fluoride resin C.

[0093] VDF and HFP are preferably the main monomers of the halogen-containing monomers constituting the polyvinylidene fluoride resin B. The total of VDF and HFP constituting the polyvinylidene fluoride resin A is preferably 80 mol % or more, more preferably 90 mol % or more, and even more preferably 100 mol %, based on the total of the halogen-containing monomers.

[0094] The proportion of HFP in the total of VDF and HFP in the polyvinylidene fluoride resin B is more than 5 mol% and 15 mol% or less, and preferably more than 5 mol% and 10 mol% or less. When the proportion of HFP in the polyvinylidene fluoride resin B is within this range, the porosity and average pore size of the adhesive layer do not become too large, and high mobility of the polymer chain when heated and ease of swelling in the electrolyte are ensured, so that the adhesive layer and the electrode are excellent in adhesion by both dry heat press and wet heat press.

[0095] Each of the polyvinylidene fluoride resins A and B preferably has a weight average molecular weight (Mw) of 400,000 to 2,000,000. When the Mw of each of the polyvinylidene fluoride resins A and B is 400,000 or more, the adhesive layer can have mechanical properties that can withstand adhesion treatment with the electrode, and the adhesive layer has better adhesion to the electrode. From this viewpoint, the Mw of each of the polyvinylidene fluoride resins A and B is more preferably 500,000 or more, even more preferably 600,000 or more, and even more preferably 700,000 or more. When the Mw of each of the polyvinylidene fluoride resins A and B is 2 million or less, the resin is easily softened by heat pressing, so that the adhesive layer is easily adhered to the electrode, and the viscosity of the coating liquid for coating and molding the adhesive layer is not too high, so that the moldability and crystal formation are good, and the adhesive layer is well made porous. From this viewpoint, the Mw of each of the polyvinylidene fluoride resins A and B is more preferably 1.5 million or less, and even more preferably 1.2 million or less.

[0096] Both polyvinylidene fluoride resin A and polyvinylidene fluoride resin B preferably have an Mw of 600,000 or more. When the Mw of both resins is 600,000 or more, the adhesive layer has excellent thermal dimensional stability, and as a result, deformation during storage of the battery at high temperatures is suppressed. From this viewpoint, the Mw of both resins is more preferably 700,000 or more, and even more preferably 800,000 or more.

[0097] From the viewpoint of excellent adhesion to the electrode, the weighted average of Mw of polyvinylidene fluoride resin A contained in the adhesive layer and Mw of polyvinylidene fluoride resin B contained in the adhesive layer (average of Mw of both resins weighted by the content ratio (mass basis)) is preferably 600,000 or more and 2,000,000 or less. The lower limit of the weighted average is more preferably 700,000 or more, even more preferably 800,000 or more, and even more preferably 900,000 or more, and the upper limit of the weighted average is more preferably 1,500,000 or less, even more preferably 1,200,000 or less, and even more preferably 1,100,000 or less.

[0098] The content ratio of polyvinylidene fluoride resin A to polyvinylidene fluoride resin B in the adhesive layer (polyvinylidene fluoride resin A:polyvinylidene fluoride resin B) is preferably 15:85 to 85:15 on a mass basis. That is, the proportion of polyvinylidene fluoride resin A in the total amount of polyvinylidene fluoride resin A and polyvinylidene fluoride resin B is preferably 15 mass% to 85 mass% (the proportion of polyvinylidene fluoride resin B is 15 mass% to 85 mass%). When polyvinylidene fluoride resin A is 15% by mass or more of the total amount of polyvinylidene fluoride resin A and polyvinylidene fluoride resin B, a fine porous structure is easily developed in the adhesive layer, and excessive swelling of the VDF-HFP copolymer in the electrolyte is suppressed, so that pore blockage is unlikely to occur. On the other hand, when polyvinylidene fluoride resin B is 15% by mass or more of the total amount of polyvinylidene fluoride resin A and polyvinylidene fluoride resin B, high mobility of the polymer chain when heated and ease of swelling in the electrolyte are ensured. Therefore, when the content ratio of polyvinylidene fluoride resin A to polyvinylidene fluoride resin B is in the range of 15:85 to 85:15, the balance between the behavior of the VDF-HFP copolymer as a polymer and the surface morphology of the adhesive layer is good, and the adhesion between the adhesive layer and the electrode is excellent by both dry heat press and wet heat press, resulting in excellent battery cycle characteristics and dimensional stability. From the above viewpoints, the proportion of polyvinylidene fluoride resin A is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more. From the above viewpoints, the proportion of polyvinylidene fluoride resin B is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more. The content ratio of polyvinylidene fluoride resin A to polyvinylidene fluoride resin B in the adhesive layer (polyvinylidene fluoride resin A:polyvinylidene fluoride resin B) is more preferably 20:80 to 80:20, even more preferably 25:75 to 75:25, even more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40, on a mass basis.

[0099] When the adhesive layer contains polyvinylidene fluoride resins A and B, the total proportion of polyvinylidene fluoride resins A and B in the entire polyvinylidene fluoride resins contained in the adhesive layer is preferably 20% by mass to 80% by mass, more preferably 30% by mass to 70% by mass, and even more preferably 40% by mass to 60% by mass.

[0100] The polyvinylidene fluoride resin preferably contains polyvinylidene fluoride resin C from the viewpoint of superior adhesion to the electrode by wet heat press. In the present disclosure, polyvinylidene fluoride resin C refers to a polyvinylidene fluoride resin containing vinylidene fluoride, hexafluoropropylene, and a monomer represented by the following formula (1) as polymerization components. Polyvinylidene fluoride resin C may be polyvinylidene fluoride resin A or polyvinylidene fluoride resin B, or may not be polyvinylidene fluoride resin A or polyvinylidene fluoride resin B.

[0101] [ka]

[0102] In formula (1), R 1 , R 2 and R 3 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, a carboxy group, or a derivative of a carboxy group; X represents a single bond, an alkylene group having 1 to 5 carbon atoms, or an alkylene group having 1 to 5 carbon atoms and having a substituent; Y represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted with at least one hydroxy group, an alkyl group having 1 to 5 carbon atoms substituted with at least one carboxy group, or -ROC(=O)-(CH2) n -C(=O)-OH (R represents an alkylene group having 1 to 5 carbon atoms, and n represents an integer of 0 or more).

[0103] In formula (1), R 1 , R 2 and R 3 The halogen atom represented by may be any one of a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and is preferably a fluorine atom.

[0104] In formula (1), R 1 , R 2 and R 3Examples of the alkyl group having 1 to 5 carbon atoms represented by R include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl groups; and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl groups. 1 , R 2 and R 3 As the alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 4 carbon atoms is preferable, and an alkyl group having 1 to 3 carbon atoms is more preferable.

[0105] In formula (1), R 1 , R 2 and R 3 Examples of the derivative of the carboxy group represented by the formula: 4 (R 4 represents an alkyl group. 4 Examples of R include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl groups; and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl groups. 4 As the alkyl group, an alkyl group having 1 to 5 carbon atoms is preferable, an alkyl group having 1 to 4 carbon atoms is more preferable, and an alkyl group having 1 to 3 carbon atoms is further preferable.

[0106] In formula (1), examples of the alkylene group having 1 to 5 carbon atoms represented by X include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and n-pentylene, and branched alkylene groups such as isopropylene, isobutylene, sec-butylene, tert-butylene, isopentylene, neopentylene, and tert-pentylene. The alkylene group having 1 to 5 carbon atoms represented by X is preferably an alkylene group having 1 to 4 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms.

[0107] In formula (1), the substituent in the alkylene group having 1 to 5 carbon atoms represented by X includes, for example, a halogen atom, which may be any of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Examples of the alkylene group having 1 to 5 carbon atoms substituted in X include linear alkylene groups such as a methylene group, an ethylene group, an n-propylene group, an n-butylene group, and an n-pentylene group; and branched alkylene groups such as an isopropylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, an isopentylene group, a neopentylene group, and a tert-pentylene group. The alkylene group having 1 to 5 carbon atoms substituted in X is preferably an alkylene group having 1 to 4 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms.

[0108] In formula (1), examples of the alkyl group having 1 to 5 carbon atoms represented by Y include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl groups, and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl groups. The alkyl group having 1 to 5 carbon atoms represented by Y is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms.

[0109] In the formula (1), in the alkyl group having 1 to 5 carbon atoms substituted with at least one hydroxy group represented by Y, examples of the substituted alkyl group having 1 to 5 carbon atoms include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl; and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl. The substituted alkyl group having 1 to 5 carbon atoms in Y is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. The number of hydroxy groups substituted is preferably one or two, more preferably one.

[0110] In the formula (1), examples of the alkyl group having 1 to 5 carbon atoms and substituted with at least one hydroxy group represented by Y include a 2-hydroxyethyl group, a 2-hydroxypropyl group, and a 4-hydroxybutyl group.

[0111] In the formula (1), in the alkyl group having 1 to 5 carbon atoms substituted with at least one carboxy group represented by Y, examples of the substituted alkyl group having 1 to 5 carbon atoms include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl groups; and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl groups. The substituted alkyl group having 1 to 5 carbon atoms in Y is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. The number of substituted carboxy groups is preferably one or two, more preferably one.

[0112] In the formula (1), examples of the alkyl group having 1 to 5 carbon atoms and substituted with at least one carboxy group represented by Y include a 2-carboxyethyl group, a 2-carboxypropyl group, and a 4-carboxybutyl group.

[0113] In formula (1), Y represents -ROC(=O)-(CH2) n In the -C(=O)-OH, R represents an alkylene group having 1 to 5 carbon atoms, and n represents an integer of 0 or more. Examples of R include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and n-pentylene, and branched alkylene groups such as isopropylene, isobutylene, sec-butylene, tert-butylene, isopentylene, neopentylene, and tert-pentylene. R is preferably an alkylene group having 1 to 4 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms. As n, an integer of 0 to 5 is preferable, an integer of 1 to 4 is more preferable, and 2 or 3 is even more preferable. Specific examples of such groups include -(CH2)2-OC(=O)-(CH2)2-C(=O)-OH.

[0114] The monomer represented by formula (1) is, for example, R 1 , R 2 and R 3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, X is a single bond, and Y is an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 3 carbon atoms substituted with at least one hydroxy group.

[0115] Examples of the monomer represented by formula (1) include acrylic monomers, unsaturated dibasic acids, and monoesters of unsaturated dibasic acids.

[0116] Examples of acrylic monomers include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-carboxyethyl (meth)acrylate, 2-carboxypropyl (meth)acrylate, 4-carboxybutyl (meth)acrylate, butenoic acid, pentenoic acid, hexenoic acid, and (meth)acryloyloxyethyl succinic acid. The term "(meth)acrylic" means that it can mean either "acrylic" or "methacrylic".

[0117] Examples of the unsaturated dibasic acid include unsaturated dicarboxylic acids, more specifically, maleic acid, maleic anhydride, citraconic acid, itaconic acid, and the like.

[0118] Examples of monoesters of unsaturated dibasic acids include monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, monoethyl citraconic acid, monomethyl itaconic acid, and monoethyl itaconic acid. Of these, monomethyl maleate and monomethyl citraconic acid are preferred.

[0119] In the polyvinylidene fluoride resin C, the proportion of the monomer represented by formula (1) in all polymerization components is preferably 0.1 mol % or more, more preferably 0.2 mol % or more, and even more preferably 0.5 mol % or more, from the viewpoint of adhesion to electrodes. In the polyvinylidene fluoride resin C, the proportion of the monomer represented by formula (1) in all polymerization components is preferably 5.0 mol % or less, more preferably 4.0 mol % or less, and even more preferably 3.0 mol % or less, from the viewpoint of low influence on the active material contained in the electrode.

[0120] By increasing or decreasing the proportion of hexafluoropropylene (HFP) in the total polymerization components, the crystallinity, adhesion to electrodes, and resistance to dissolution in an electrolyte of the polyvinylidene fluoride resin C can be controlled within appropriate ranges. In the polyvinylidene fluoride resin C, the proportion of HFP in all polymerization components is preferably from 0.5 mol % to 5.0 mol %, more preferably from 0.8 mol % to 4.0 mol %, and even more preferably from 1.0 mol % to 3.0 mol %.

[0121] The polyvinylidene fluoride resin C may contain other monomers as polymerization components other than vinylidene fluoride (VDF), hexafluoropropylene (HFP), and the monomer represented by formula (1). Examples of the other monomers include halogen-containing monomers such as tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene.

[0122] The polyvinylidene fluoride resin C is preferably a terpolymer consisting of VDF, HFP, and a monomer represented by formula (1). As the terpolymer, a VDF-HFP-acrylic acid terpolymer is preferable.

[0123] The weight average molecular weight (Mw) of the polyvinylidene fluoride resin C is preferably from 300,000 to 3,000,000, more preferably from 500,000 to 2,500,000, further preferably from 650,000 to 2,300,000, and even more preferably from 850,000 to 2,000,000.

[0124] When the adhesive layer contains polyvinylidene fluoride resin C, the proportion of polyvinylidene fluoride resin C in the entire polyvinylidene fluoride resin contained in the adhesive layer is preferably 20% by mass to 80% by mass, more preferably 30% by mass to 70% by mass, and even more preferably 40% by mass to 60% by mass, from the viewpoint of keeping the acid value of the entire polyvinylidene fluoride resin in an appropriate range.

[0125] The weight average molecular weight (Mw) of the entire polyvinylidene fluoride resin contained in the adhesive layer is preferably 300,000 or more, more preferably 500,000 or more, even more preferably 650,000 or more, and even more preferably 850,000 or more, from the viewpoint of preventing blockage of pores in the adhesive layer when heat is applied to the adhesive layer during battery production. The Mw of the entire polyvinylidene fluoride resin contained in the adhesive layer is preferably 3 million or less, more preferably 2.5 million or less, even more preferably 2.3 million or less, and even more preferably 2 million or less, from the viewpoint of appropriately softening the polyvinylidene fluoride resin when heat is applied to the adhesive layer during battery production, and of providing good adhesion between the adhesive layer and the electrode.

[0126] The Mw of the entire polyvinylidene fluoride resin contained in the adhesive layer is a polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC). The polyvinylidene fluoride resin extracted from the adhesive layer or the polyvinylidene fluoride resin used to form the adhesive layer is used as a sample.

[0127] The content of the polyvinylidene fluoride resin in the adhesive layer is preferably 85% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and further preferably 95% by mass to 100% by mass, based on the total mass of the adhesive layer.

[0128] -Other resins- The adhesive layer may contain other resins besides polyvinylidene fluoride resin. Examples of other resins include acrylic resins, butadiene-acrylonitrile resins, fluorine-based rubbers, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), or mixtures of two or more of these. These resins may be used alone or in combination of two or more.

[0129] The mass ratio of other resins to the total resin in the adhesive layer is preferably 10 mass % or less, more preferably 5 mass % or less, even more preferably 1 mass % or less, and particularly preferably substantially none is contained. The mass proportion of the polyvinylidene fluoride resin in the total resin of the adhesive layer is preferably 90 mass % or more, more preferably 95 mass % or more, further preferably 99 mass % or more, and particularly preferably 100 mass %.

[0130] -Other ingredients- The adhesive layer may contain additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming agent, and a pH adjuster. The dispersant is added, for example, to the resin particle dispersion liquid for forming the adhesive layer for the purpose of improving dispersibility, coatability, or storage stability. The wetting agent, antifoaming agent, and pH adjuster are added, for example, to the resin particle dispersion liquid for forming the adhesive layer for the purpose of improving compatibility with the heat-resistant layer or the porous substrate, for the purpose of suppressing air entrapment in the resin particle dispersion liquid, or for the purpose of pH adjustment.

[0131] -Characteristics of the adhesive layer- The adhesive layer has a porous structure in which fibrils containing polyvinylidene fluoride resin are connected in a three-dimensional network shape. This porous structure can be confirmed by scanning electron microscope (SEM).

[0132] The mass per unit area of ​​the adhesive layer (total for both sides) is set to 0.5 g / m from the viewpoint of adhesion to the electrode. 2 More than 0.8 g / m is preferable. 2 More preferably, 1 g / m 2 The above is more preferable. The mass per unit area of ​​the adhesive layer (total of both sides) is set at 3 g / m2 in order to ensure that the adhesive layer is thin and the battery has excellent cycle characteristics. 2 Less than 2.5 g / m is preferred. 2 Less than 2 g / m is more preferable. 2 The following is even more preferred:

[0133] To determine the mass per unit area of ​​the adhesive layer, cut the separator into a 20 cm x 20 cm piece, measure the mass of the layer that corresponds to the adhesive layer, and divide the mass by the area to determine the total for both sides.

[0134] [Separator characteristics] From the viewpoint of mechanical strength, the thickness of the separator is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 9 μm or more. From the viewpoint of the energy density of the battery, the thickness of the separator is preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less.

[0135] The thickness of the separator is measured at 20 points within a 10 cm square using a contact thickness meter and the average is calculated.

[0136] From the viewpoint of suppressing short-circuiting of the battery, the Gurley value of the separator is preferably 60 seconds / 100 mL or more, more preferably 70 seconds / 100 mL or more, and even more preferably 80 seconds / 100 mL or more. From the viewpoint of ion permeability, the Gurley value of the separator is preferably 260 sec / 100 mL or less, more preferably 250 sec / 100 mL or less, and even more preferably 240 sec / 100 mL or less.

[0137] The difference between the Gurley value of the laminate (a laminate consisting of a porous substrate and a heat-resistant layer arranged on one or both sides of the porous substrate) and the Gurley value of the separator is preferably 30 seconds / 100 mL or less, more preferably 25 seconds / 100 mL or less, and even more preferably 20 seconds / 100 mL or less.

[0138] The Gurley value of the separator is measured using a Gurley densometer in accordance with JIS P8117:2009. The Gurley value of the laminate is the Gurley value of the flat membrane obtained by removing the adhesive layer from the separator. The Gurley value of the flat membrane is measured using a Gurley densometer in accordance with JIS P8117:2009.

[0139] From the viewpoint of ion permeability, the porosity of the separator is preferably 30% to 60%. The porosity of the laminate is preferably 30% to 60% from the viewpoint of ion permeability. The porosity ε (%) of the separator (or laminate) is calculated by the following formula.

[0140]

number

[0141] [Separator manufacturing method] The separator of the present disclosure is manufactured, for example, by the following manufacturing method A or manufacturing method B. In manufacturing methods A and B, a heat-resistant layer is formed on a porous substrate by a dry coating method, and an adhesive layer is formed on a laminate by a wet coating method. In the present disclosure, the dry coating method is a method in which a coating layer is dried to solidify the coating layer. In the present disclosure, the wet coating method is a method in which a coating layer is solidified in a coagulation liquid.

[0142] Manufacturing method A (discontinuous manufacturing method): A heat-resistant layer is formed on a porous substrate unwound from a roll by a dry coating method to obtain a laminate of the porous substrate and the heat-resistant layer, and the laminate is temporarily wound up on another roll. Next, an adhesive layer is formed on the laminate unwound from the roll by a wet coating method to obtain a separator, and the completed separator is wound up on another roll.

[0143] Manufacturing method B (continuous manufacturing method): A heat-resistant layer is formed by a dry coating method on a porous substrate unwound from a roll to obtain a laminate of the porous substrate and the heat-resistant layer, and then an adhesive layer is formed by a wet coating method on the laminate to obtain a separator, and the completed separator is wound up on another roll.

[0144] The following describes in detail the steps included in the production method B. The production method B includes the following steps (1) to (7), which are carried out in sequence.

[0145] Step (1): Preparation of coating liquid for forming heat-resistant layer The coating liquid for forming the heat-resistant layer is prepared by dispersing the binder resin and inorganic particles of the heat-resistant layer in a dispersion medium. If necessary, other components than the binder resin and inorganic particles are dissolved or dispersed in the coating liquid.

[0146] The dispersion medium used to prepare the coating liquid is preferably water. The solid content of the coating liquid may be set within a range that provides an appropriate viscosity from the viewpoint of coating suitability, and is preferably about 10% by mass to 60% by mass.

[0147] Step (2): Preparation of coating liquid for forming adhesive layer The adhesive layer-forming coating liquid is prepared by dissolving a polyvinylidene fluoride resin in a solvent. If necessary, other components than the polyvinylidene fluoride resin may be dissolved or dispersed in the coating liquid.

[0148] The solvent used in preparing the coating liquid includes a solvent that dissolves polyvinylidene fluoride resin (hereinafter, also referred to as a "good solvent"). Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide.

[0149] From the viewpoint of forming an adhesive layer having a good porous structure, the solvent used in preparing the coating liquid preferably contains a phase separation agent that induces phase separation. Therefore, the solvent used in preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with the good solvent in an amount within a range that ensures a suitable viscosity for coating. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0150] From the viewpoint of forming a good porous structure, the solvent used for preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent, containing 60% by mass or more of the good solvent and 5% by mass to 40% by mass of the phase separation agent.

[0151] From the viewpoint of forming a good porous structure, the resin concentration in the coating liquid is preferably 1% by mass to 20% by mass.

[0152] Step (3): Coating of heat-resistant layer-forming coating liquid The coating liquid for forming a heat-resistant layer is applied to at least one surface of the porous substrate, and a coating layer is formed on the porous substrate. The method of applying the coating liquid to the porous substrate includes knife coating, Mayer bar coating, die coating, reverse roll coating, roll coating, gravure coating, screen printing, inkjet, spraying, etc. When forming a heat-resistant layer on both sides of the porous substrate, it is preferable from the viewpoint of productivity to apply the coating liquid to both sides of the porous substrate at the same time.

[0153] Step (4): Solidification of the coating layer The porous substrate on which the coating layer that will become the heat-resistant layer is formed is heated, and the dispersion medium (e.g., water) of the coating liquid is dried to form the heat-resistant layer. Drying is performed, for example, by transporting the porous substrate on which the coating layer is formed into a high-temperature environment, or by blowing air onto the porous substrate on which the coating layer is formed. The drying temperature is preferably 40°C to 100°C. This results in a laminate consisting of the porous substrate and the heat-resistant layer.

[0154] Step (5): Coating of adhesive layer-forming coating liquid A coating liquid for forming an adhesive layer is applied to at least one surface of the laminate. Methods for applying the coating liquid include knife coating, gravure coating, Mayer bar coating, die coating, reverse roll coating, roll coating, screen printing, inkjet printing, spraying, etc. When forming adhesive layers on both surfaces of the laminate, it is preferable from the viewpoint of productivity to apply the coating liquid to both surfaces of the laminate at the same time.

[0155] Step (6): Solidification of the coating layer The laminate with the coating layer formed thereon is immersed in a coagulation liquid to induce phase separation in the coating layer while solidifying the polyvinylidene fluoride resin into a fibril-like state, thereby forming an adhesive layer containing the polyvinylidene fluoride resin, thereby obtaining a separator having a porous substrate, a heat-resistant layer, and an adhesive layer.

[0156] The solidification liquid generally contains the good solvent and phase separation agent used in preparing the coating liquid, and water. It is preferable from the viewpoint of productivity that the mixing ratio of the good solvent and the phase separation agent is the same as the mixing ratio of the mixed solvent used in preparing the coating liquid. The content of water in the solidification liquid is preferably 40% by mass to 90% by mass from the viewpoints of forming a porous structure and productivity. The temperature of the solidification liquid is, for example, 20°C to 50°C.

[0157] Step (7): Washing and drying the coating layer The separator is pulled out of the coagulating liquid and washed with water. By washing with water, the coagulating liquid is removed from the separator. Furthermore, by drying, water is removed from the separator. The washing with water is performed, for example, by conveying the separator in a water washing bath. The drying is performed, for example, by conveying the separator in a high-temperature environment, by blowing air on the separator, by bringing the separator into contact with a heat roll, or the like. The drying temperature is preferably 40°C to 80°C.

[0158] Production method A can be carried out by carrying out steps (1) to (4), temporarily winding the laminate onto a roll, and then unwinding the laminate from the roll to carry out steps (5) to (7).

[0159] <Non-aqueous secondary battery> The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery that obtains electromotive force by doping and dedoping lithium ions, and includes a positive electrode, a negative electrode, and the separator of the present disclosure. Doping means occlusion, support, adsorption, or insertion, and refers to the phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.

[0160] The nonaqueous secondary battery of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is enclosed in an exterior material together with an electrolyte solution. The nonaqueous secondary battery of the present disclosure is suitable for nonaqueous electrolyte secondary batteries, particularly lithium ion secondary batteries.

[0161] The nonaqueous secondary battery of the present disclosure has excellent impact resistance and cycle characteristics by including the separator of the present disclosure.

[0162] Hereinafter, examples of the positive electrode, negative electrode, electrolyte, and exterior material included in the nonaqueous secondary battery of the present disclosure will be described.

[0163] An example of the positive electrode is a structure in which an active material layer containing a positive electrode active material and a binder resin is disposed on a current collector. The active material layer may further contain a conductive additive. Examples of the positive electrode active material include lithium-containing transition metal oxides, specifically LiCoO2, LiNiO2, LiMn 1 / 2 Ni 1 / 2 O2, LiCo 1 / 3 Mn 1 / 3 Ni 1 / 3 O2, LiMn2O4, LiFePO4, LiCo 1 / 2 Ni 1 / 2 O2, LiAl 1 / 4 Ni 3 / 4 Examples of the binder resin include polyvinylidene fluoride resin, styrene-butadiene copolymer, etc. Examples of the conductive assistant include carbon materials such as acetylene black, ketjen black, graphite powder, etc. Examples of the current collector include aluminum foil, titanium foil, stainless steel foil, etc., having a thickness of 5 μm to 20 μm.

[0164] An example of the negative electrode is a structure in which an active material layer containing a negative electrode active material and a binder resin is disposed on a current collector. The active material layer may further contain a conductive assistant. The negative electrode active material may be a material capable of electrochemically absorbing lithium ions, specifically, for example, a carbon material; an alloy of lithium with silicon, tin, aluminum, or the like; Wood's alloy; and the like. The binder resin may be, for example, a polyvinylidene fluoride resin, a styrene-butadiene copolymer, and the like. The conductive assistant may be, for example, a carbon material such as acetylene black, ketjen black, graphite powder, or ultrafine carbon fiber. The current collector may be, for example, a copper foil, a nickel foil, a stainless steel foil, or the like having a thickness of 5 μm to 20 μm. In addition, instead of the above-mentioned negative electrode, a metallic lithium foil may be used as the negative electrode.

[0165] The electrolyte is preferably a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF6, LiBF4, and LiClO4. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted derivatives thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone; which may be used alone or in combination. The electrolyte is preferably a solution in which a cyclic carbonate and a chain carbonate are mixed in a mass ratio (cyclic carbonate:chain carbonate) of 20:80 to 40:60, and a lithium salt is dissolved in the range of 0.5 mol / L to 1.5 mol / L.

[0166] Examples of the exterior material include an aluminum laminate film pack, a metal can, etc. The shape of the battery may be rectangular, cylindrical, coin-shaped, etc., and the separator of the present disclosure is suitable for any shape.

[0167] The nonaqueous secondary battery of the present disclosure can be produced by producing a laminate in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode, and then using this laminate, for example, by Production Method 1 or Production Method 2 described below.

[0168] Manufacturing method 1: The laminate is dry heat pressed to temporarily bond the electrodes and separator, then housed in an exterior material (e.g., an aluminum laminate film pack; the same applies below) and an electrolyte is injected into it. Next, the laminate is wet heat pressed from above the exterior material to bond the electrodes and separator and seal the exterior material.

[0169] Manufacturing method 2: The laminate is placed in an exterior material and an electrolyte is poured in. The laminate is then wet heat pressed onto the exterior material to bond the electrodes and the separator and seal the exterior material.

[0170] In the manufacturing method 1 and the manufacturing method 2, the pressing temperature of the wet heat press is preferably 50° C. to 95° C., and more preferably 60° C. to 90° C. The pressing pressure of the wet heat press is preferably 0.1 MPa to 2 MPa, and more preferably 0.5 MPa to 1.5 MPa. The pressing time of the wet heat press is preferably adjusted according to the pressing temperature and pressing pressure, and is adjusted, for example, in the range of 1 minute to 20 hours.

[0171] When manufacturing a laminate in which a separator is disposed between a positive electrode and a negative electrode, the method of disposing the separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of a positive electrode, a separator, and a negative electrode in this order (a so-called stack method), or a method of stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them up in the length direction. EXAMPLES

[0172] The separator and nonaqueous secondary battery of the present disclosure will be described in more detail below with reference to examples. The materials, amounts, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the separator and nonaqueous secondary battery of the present disclosure should not be interpreted as being limited by the specific examples shown below.

[0173] In the following description, syntheses, treatments, manufactures, etc. were carried out at room temperature (25° C.±3° C.) unless otherwise specified.

[0174] <Measurement and evaluation methods> The measurement and evaluation methods applied in the examples and comparative examples are as follows.

[0175] [Thickness of porous substrate and separator] The thickness of the porous substrate and the separator was measured at 20 points within a 10 cm square using a contact thickness meter (Mitutoyo Corporation, LITEMATIC VL-50S) and the average was calculated. A spherical probe with a sphere radius of 10 mm (Mitutoyo Corporation) was used as the measurement terminal, and the load was adjusted so that 0.19 N was applied during the measurement.

[0176] [Thickness of heat-resistant layer] The thickness of the flat membrane was calculated by subtracting the thickness of the porous substrate from the thickness of the flat membrane after removing the adhesive layer from the separator. The thickness of the flat membrane was measured at 20 points within a 10 cm square area using a contact thickness meter (Mitutoyo Corporation, LITEMATIC VL-50S) and calculated by averaging the measurements. A spherical probe with a sphere radius of 10 mm (Mitutoyo Corporation) was used as the measurement terminal, and the measurement was adjusted so that a load of 0.19 N was applied during measurement.

[0177] [Mass per unit area of ​​adhesive layer] The separator was cut to a size of 20 cm x 20 cm, the mass of the layer corresponding to the adhesive layer was measured, and the mass was divided by the area to calculate the total basis weight (g / m2) of both sides. 2 ) was sought.

[0178] [Gurley value of porous substrate, laminate and separator] The Gurley values ​​(sec / 100 mL) of the porous substrate, the laminate, and the separator were measured using a Gurley densometer (Toyo Seiki Co., Ltd., G-B2C) in accordance with JIS P8117:2009. The Gurley value of the laminate was subtracted from the Gurley value of the separator to obtain the difference in the Gurley values.

[0179] [Average primary particle size of inorganic particles] The inorganic particles used to form the heat-resistant layer were used as samples and observed with a scanning electron microscope (SEM) to determine the average primary particle size. Specifically, the major axis of 100 inorganic particles randomly selected during SEM observation was measured, and the average of the major axes of the 100 particles was taken as the average primary particle size (μm).

[0180] [Heat shrinkage rate] The separator was cut into a rectangle of TD 60 mm × MD 180 mm to prepare a test specimen. Marks were made on the test specimen at points 20 mm and 170 mm from one end on the line dividing TD in half (referred to as points A and B, respectively). In addition, marks were made on the test specimen at points 10 mm and 50 mm from one end on the line dividing MD in half (referred to as points C and D, respectively). A clip was attached to the test specimen (the clip was attached between the end closest to point A and point A), and the specimen was hung in an oven at a temperature of 150°C and heat-treated for 30 minutes without tension. The lengths between AB and CD were measured before and after heat treatment, and the heat shrinkage was calculated using the following formula. The heat shrinkage of the three test specimens was then averaged.

[0181] MD heat shrinkage rate (%) = {(length of AB before heat treatment - length of AB after heat treatment) ÷ length of AB before heat treatment} × 100

[0182] TD heat shrinkage rate (%) = {(CD length before heat treatment - CD length after heat treatment) ÷ CD length before heat treatment} x 100

[0183] [Adhesion to electrodes (1)] 300g of artificial graphite as the negative electrode active material, 7.5g of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as the binder, 3g of carboxymethylcellulose as the thickener, and an appropriate amount of water were mixed by stirring with a twin-arm mixer to prepare a negative electrode slurry. This negative electrode slurry was applied to one side of a 10μm thick copper foil, dried, and pressed to obtain a negative electrode having a negative electrode active material layer.

[0184] The negative electrode obtained above was cut into a rectangle of width 15 mm x length 70 mm, and the separator was cut into a rectangle of TD 18 mm x MD 74 mm. Release paper of width 15 mm x length 70 mm was prepared. A laminate in which the negative electrode, separator, and release paper were stacked in this order was inserted into a pack made of aluminum laminate film, and the pack was heat-pressed in the stacking direction of the laminate using a heat press machine, thereby bonding the negative electrode and the separator. The heat press conditions were a temperature of 90 ° C, a pressure of 9 MPa, and a time of 10 seconds. Thereafter, the laminate was removed from the pack, and the release paper was peeled off to prepare a test piece.

[0185] The uncoated surface of the negative electrode of the test piece was fixed to a metal plate with double-sided tape, and the metal plate was fixed to the lower chuck of a Tensilon (A&D, STB-1225S). At this time, the metal plate was fixed to the Tensilon so that the length direction of the test piece (i.e., the MD of the separator) was the direction of gravity. The separator was peeled off from the negative electrode by about 2 cm from the bottom end, and the end was fixed to the upper chuck, and a 180° peel test was performed. The tensile speed of the 180° peel test was 20 mm / min, and the load (N) from 10 mm to 40 mm after the start of the measurement was collected at 0.4 mm intervals, and the average was calculated. The loads of 10 test pieces were then averaged to obtain the adhesive strength (N / 15 mm) between the electrode and the separator.

[0186] [Adhesion to electrodes (2)] A test secondary battery was prepared as described below. A compression type bending test (three-point bending measurement) was performed on the battery. The measurement was performed by attaching a compression type bending test jig to a Tensilon (A&D Co., Ltd., STB-1225S). The distance between the supports was 4 cm, and the battery was placed on the support so that the short side of the battery was parallel to the long direction of the indenter and the compression position during measurement was the center of the long direction of the electrode in the battery. The measurement was started by setting the displacement to 0 when the indenter was lowered until a load of 0.1 N was applied. The compression speed during measurement was 2 mm / min, and the measurement was performed up to a displacement of 2 mm. The elastic modulus gradient (unit: N / mm) in the load-displacement curve obtained from this result was taken as the adhesive strength.

[0187] [Battery cycle characteristics (capacity retention rate)] Ten test secondary batteries were prepared as described below. In an environment of 20°C, the battery was subjected to three cycles of constant current and constant voltage charging at 0.1C, 4.2V, and 15 hours, and constant current discharging at 0.1C and 2.5V cutoff, and the discharge capacity after the three cycles was taken as the cell capacity. Next, in an environment of 20°C, the battery was subjected to 300 cycles of constant current charging at 3C and 4.2V cutoff, and constant current discharging at 3C and 2.5V cutoff. The charge capacity at the 300th cycle was divided by the cell capacity to calculate the average of the 10 batteries, and the obtained value (%) was taken as the capacity retention rate.

[0188] [Battery impact resistance (compressive fracture strength)] Ten test secondary batteries, which will be described later, were prepared. The test secondary batteries were charged at a constant current and constant voltage in an environment at a temperature of 20°C. Specifically, the test secondary batteries were charged at 0.1C up to 4.2V and held at 4.2V for 3 hours. Next, the test secondary batteries were placed on a horizontal stand with the positive electrode side facing up and fixed with adhesive tape. A spherical terminal with a diameter of 5mm was placed on the center of the test secondary battery and gradually lowered at a speed of 100mm / min to apply a load to the test secondary battery. The load value (unit: N) was obtained at the moment when the voltage of the test secondary battery dropped to 3.5V, and the average of the 10 batteries was calculated.

[0189] <Preparation of separator and battery> [Example 1] -Making the separator- Styrene butadiene rubber (SBR) and barium sulfate particles (average primary particle size 0.10 μm) were added to water and stirred to obtain coating liquid (1). Coating liquid (1) had an SBR concentration of 3.5 mass% and a barium sulfate particle:SBR ratio of 97:3.

[0190] As polyvinylidene fluoride resin A, a binary copolymer (weight average molecular weight 1.13 million) with a polymerization ratio (molar ratio) of VDF:HFP=97.6:2.4 was prepared. As polyvinylidene fluoride resin B, a binary copolymer (weight average molecular weight 860,000) with a polymerization ratio (molar ratio) of VDF:HFP=94.3:5.7 was prepared. Polyvinylidene fluoride resin A and polyvinylidene fluoride resin B were mixed at a mass ratio of A:B=70:30.

[0191] A mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc:TPG=70:30 [mass ratio]) was prepared. A polyvinylidene fluoride resin (the above-mentioned mixture of polyvinylidene fluoride resin A and polyvinylidene fluoride resin B) was dissolved in the mixed solvent to a concentration of 5.0 mass % to obtain a coating solution (2).

[0192] An appropriate amount of coating liquid (1) was placed on a pair of Mayer bars, and a polyethylene microporous membrane (thickness 5.6 μm, Gurley value 120 sec / 100 mL) was passed between the Mayer bars to coat both sides with equal amounts of coating liquid (1) and dried. Next, an appropriate amount of coating liquid (2) was placed on a pair of Mayer bars, and a polyethylene microporous membrane having a coating layer of coating liquid (1) was passed between the Mayer bars to coat both sides with equal amounts of coating liquid (2), and the coating layer was solidified by immersion in a coagulation liquid (DMAc:TPG:water=30:8:62 [mass ratio], liquid temperature 40°C), washed in a water washing tank at a water temperature of 40°C, and dried. In this way, a separator having a heat-resistant layer and an adhesive layer formed on both sides of the polyethylene microporous film was obtained.

[0193] When the surface of the separator was observed by SEM, the adhesive layer had a porous structure in which fibrils were connected in a three-dimensional network. Figure 6 shows a scanning electron microscope (SEM) image of the adhesive layer of the separator of Example 1.

[0194] - Preparation of positive electrode - 89.5 parts by mass of lithium cobalt oxide powder as a positive electrode active material, 4.5 parts by mass of acetylene black as a conductive assistant, 6 parts by mass of polyvinylidene fluoride as a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone were mixed by stirring with a twin-arm mixer to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides or one side of a 20 μm thick aluminum foil, dried, and pressed to obtain a positive electrode having a positive electrode active material layer on both sides or one side.

[0195] - Preparation of negative electrode - A negative electrode slurry was prepared by mixing 300 parts by mass of artificial graphite as a negative electrode active material, 7.5 parts by mass of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder resin, 3 parts by mass of carboxymethylcellulose as a thickener, and an appropriate amount of water with a twin-arm mixer. The negative electrode slurry was applied to both sides or one side of a copper foil with a thickness of 10 μm, dried, and pressed to obtain a negative electrode having a negative electrode active material layer on both sides or one side.

[0196] -Preparation of a battery for evaluating adhesion to electrodes- The double-sided positive electrode and double-sided negative electrode were each cut into a rectangle of 30 mm x 70 mm. The separator was cut into a rectangle measuring TD 35 mm x MD 75 mm. These were stacked so that the positive and negative electrodes were alternated and a separator was sandwiched between the positive and negative electrodes, to produce a laminate consisting of three positive electrodes, three negative electrodes, and five separators. The laminate was inserted into a pack made of aluminum laminate film, and an electrolyte (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was injected into the pack to allow the electrolyte to soak into the laminate. Next, the pack and the laminate were heat-pressed in the stacking direction using a heat press machine (wet heat press) to bond the electrodes and separators. The heat press conditions were a press temperature of 85°C, a press pressure of 1 MPa, and a press time of 2 minutes. The test secondary battery thus obtained was subjected to evaluation of adhesion to the electrodes (2).

[0197] - Preparation of batteries for evaluating cycle characteristics and impact resistance - The single-sided positive electrode and the single-sided negative electrode were each cut into a rectangle of 14 mm x 20 mm. The separator was cut into a rectangle measuring TD 20 mm x MD 26 mm. These were stacked so that the positive electrode active material layer and the negative electrode active material layer faced each other and the separator was sandwiched between the positive electrode and the negative electrode to produce a laminate consisting of one positive electrode, one negative electrode, and one separator. The laminate was inserted into a pack made of an aluminum laminate film, and an electrolyte (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was injected into the pack to allow the electrolyte to soak into the laminate. Next, the pack and the laminate were heat-pressed in the stacking direction using a heat press machine (wet heat press) to bond the electrodes and the separator. The heat press conditions were a press temperature of 80°C, a press pressure of 1 MPa, and a press time of 2 minutes. The test secondary battery thus obtained was subjected to evaluation of the cycle characteristics and impact resistance of the battery.

[0198] [Example 2] A separator was produced in the same manner as in Example 1, except that barium sulfate particles (average primary particle size: 0.10 μm) were replaced with γ-alumina particles (average primary particle size: 0.01 μm). A test secondary battery was produced using this separator.

[0199] [Example 3] A separator was produced in the same manner as in Example 1, except that the barium sulfate particles (average primary particle size: 0.10 μm) were replaced with boehmite particles (average primary particle size: 0.10 μm). A test secondary battery was produced using this separator.

[0200] [Example 4] A separator was prepared in the same manner as in Example 1, except that the barium sulfate particles (average primary particle size 0.10 μm) were replaced with boehmite particles (average primary particle size 0.10 μm), and the coated surface of the heat-resistant layer was replaced with one side of a polyethylene microporous film. A test secondary battery was prepared using this separator.

[0201] [Example 5] A separator was prepared in the same manner as in Example 1, except that the barium sulfate particles (average primary particle size 0.10 μm) were replaced with boehmite particles (average primary particle size 0.10 μm) and the coating amount of the adhesive layer was changed. A test secondary battery was prepared using this separator.

[0202] [Example 6] A separator was prepared in the same manner as in Example 1, except that the barium sulfate particles (average primary particle size 0.10 μm) were replaced with boehmite particles (average primary particle size 0.10 μm) and the coating amount of the adhesive layer was changed. A test secondary battery was prepared using this separator.

[0203] [Example 7] A separator was prepared in the same manner as in Example 1, except that SBR was changed to poly(n-butyl acrylate) and barium sulfate particles (average primary particle size 0.10 μm) were changed to boehmite (average primary particle size 0.10 μm). A test secondary battery was prepared using this separator.

[0204] [Example 8] A separator was produced in the same manner as in Example 1, except that the average primary particle size of the barium sulfate particles was changed from 0.10 μm to 0.30 μm. A test secondary battery was produced using this separator.

[0205] [Example 9] A separator was produced in the same manner as in Example 1, except that the composition of the coating liquid (1) was changed to barium sulfate particles:SBR=95:5 [mass ratio]. A test secondary battery was produced using this separator.

[0206] [Comparative Example 1] A separator was produced in the same manner as in Example 1, except that the composition of the coating liquid (1) was changed to barium sulfate particles:SBR=80:20 [mass ratio]. A test secondary battery was produced using this separator.

[0207] [Comparative Example 2] A separator was prepared in the same manner as in Example 1, except that the barium sulfate particles (average primary particle size 0.10 μm) were replaced with boehmite particles (average primary particle size 2.3 μm), the coated surface of the heat-resistant layer was replaced with one side of a polyethylene microporous film, and the thickness of the heat-resistant layer was changed. A test secondary battery was prepared using this separator.

[0208] [Comparative Example 3] A separator was prepared in the same manner as in Example 1, except that the coating liquid (2) was changed to a PVDF particle dispersion (particle volume average particle size: 0.2 μm, dispersion medium: water, solid content concentration: 7 mass%), and the PVDF particle dispersion was dry-coated on the heat-resistant layer. A test secondary battery was prepared using this separator.

[0209] When the surface of the separator of Comparative Example 3 was observed by SEM, it was found that the adhesive layer had a structure in which resin particles were aligned adjacently in the planar direction.

[0210] The separator of Comparative Example 3 was not evaluated for adhesion to the electrode (1) because it was not adhered to the test negative electrode by heat pressing (dry heat pressing) in the absence of an electrolyte.

[0211] The abbreviations in Table 1 have the following meanings. PE: Polyethylene ·SBR: Styrene butadiene rubber ·PVDF: Polyvinylidene fluoride

[0212] [Table 1]

[0213] All publications, patent applications, and standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0214] 10A, 10B, 10C, 10D, 10E Separator 20 Porous substrate 30 Heat-resistant layer 40 Laminate 50 Adhesive layer

Claims

1. A porous substrate; A heat-resistant layer containing inorganic particles and a binder resin arranged on one or both sides of the porous substrate; An adhesive layer containing a polyvinylidene fluoride resin arranged on one or both sides of a laminate of the porous substrate and the heat-resistant layer, The mass ratio of the inorganic particles in the heat-resistant layer is 95 mass% or more, the inorganic particles contained in the heat-resistant layer have an average primary particle size of 0.01 μm to 0.30 μm; the adhesive layer has a porous structure in which fibrils containing the polyvinylidene fluoride resin are connected in a three-dimensional network shape; Separator for non-aqueous secondary batteries.

2. The separator for a non-aqueous secondary battery according to claim 1 , wherein the heat-resistant layers are disposed on both sides of the porous substrate.

3. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the inorganic particles include at least one kind selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles.

4. The separator for a non-aqueous secondary battery according to claim 1 , wherein the inorganic particles include barium sulfate particles.

5. The separator for a non-aqueous secondary battery according to claim 1 , wherein the polyvinylidene fluoride resin comprises the following polyvinylidene fluoride resin A and polyvinylidene fluoride resin B: Polyvinylidene fluoride resin A: a polyvinylidene fluoride resin containing vinylidene fluoride and hexafluoropropylene as polymerization components, in which the proportion of hexafluoropropylene in the total of vinylidene fluoride and hexafluoropropylene is more than 1.5 mol % and not more than 5 mol %; Polyvinylidene fluoride resin B: A polyvinylidene fluoride resin containing vinylidene fluoride and hexafluoropropylene as polymerization components, in which the proportion of hexafluoropropylene in the total of vinylidene fluoride and hexafluoropropylene is more than 5 mol % and not more than 15 mol %.

6. The separator for a nonaqueous secondary battery according to claim 1 , wherein the polyvinylidene fluoride resin comprises the following polyvinylidene fluoride resin C: Polyvinylidene fluoride resin C: A polyvinylidene fluoride resin containing vinylidene fluoride, hexafluoropropylene, and a monomer represented by the following formula (1) as polymerization components. 【Chemistry 1】 In formula (1), R １ , R ２ and R ３ each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, a carboxy group, or a derivative of a carboxy group; X represents a single bond, an alkylene group having 1 to 5 carbon atoms, or an alkylene group having 1 to 5 carbon atoms and having a substituent; Y represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted with at least one hydroxy group, an alkyl group having 1 to 5 carbon atoms substituted with at least one carboxy group, or -R-O-C(=O)-(CH ２ ) ｎ It represents —C(═O)—OH (R represents an alkylene group having 1 to 5 carbon atoms, and n represents an integer of 0 or more).

7. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the binder resin of the heat-resistant layer comprises at least one selected from the group consisting of butadiene-based polymers and acrylic-based resins.

8. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the heat-resistant layer has a thickness of 0.1 μm to 2 μm per layer.

9. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the porous substrate has a thickness of 1 μm to 7 μm.

10. The mass per unit area of ​​the adhesive layer is 0.5 g / m2 in total on both sides. ２ ~3g / m ２ The separator for a non-aqueous secondary battery according to claim 1 ,

11. 2. The separator for a nonaqueous secondary battery according to claim 1, wherein a difference between a Gurley value of the laminate and a Gurley value of the separator for a nonaqueous secondary battery is 30 seconds / 100 mL or less.

12. A non-aqueous secondary battery separator according to any one of claims 1 to 11, the separator being disposed between the positive electrode and the negative electrode; Electromotive force is obtained by doping and dedoping lithium ions. Non-aqueous secondary battery.

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