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

Abstract

To provide a non-aqueous secondary battery separator that can easily remove moisture by drying and has excellent short-circuit resistance.SOLUTION: A nonaqueous secondary battery separator includes a polyolefin microporous membrane, a heat-resistant porous layer disposed on one or both sides of the polyolefin microporous membrane and containing a heat-resistant resin having at least one of an amide bond and an imide bond in its molecule and inorganic particles, and an adhesive layer disposed on one or both sides of a laminate of the polyolefin microporous membrane and the heat-resistant porous layer and containing adhesive resin particles, and the polyolefin microporous membrane has a Gurley value of 99 seconds / 100 mL or less, the nonaqueous secondary battery separator has a Gurley value of 160 seconds / 100 mL or less, and the difference between the Gurley value of the nonaqueous secondary battery separator and the Gurley value of the polyolefin microporous membrane is 20 seconds / 100 mL to 60 seconds / 100 mL.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a separator for a non-aqueous secondary battery and a non-aqueous 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 containing an aromatic resin and inorganic particles, and an adhesive layer in which adhesive resin particles adhere to the heat-resistant porous layer.

[0003] Patent Document 2 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 at least one of a heat-resistant resin having at least one of an amide bond and an imide bond in the molecule and inorganic particles, 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 adhere to the laminate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-164113 [Patent Document 2] International Publication No. 2019 / 130994 Summary of the Invention [Problem to be solved by the invention]

[0005] A nonaqueous secondary battery separator is known that has a heat-resistant porous layer and an adhesive layer on a polyolefin microporous membrane. In this separator, when the heat-resistant porous layer is formed on the polyolefin microporous membrane, the heat-resistant resin that is the material for the heat-resistant porous layer may penetrate into the pores of the polyolefin microporous membrane and remain there. Because polyolefins are hydrophobic resins, polyolefin microporous membranes are inherently hydrophobic. However, when the heat-resistant resin is a resin having a hydrophilic group (e.g., polyamide, polyimide, or polyamideimide), the presence of the heat-resistant resin makes the pores of the polyolefin microporous membrane more susceptible to water. Therefore, moisture penetrates into the pores of the polyolefin microporous membrane during the water washing process after coating and solidifying the material for the heat-resistant porous layer. Furthermore, when an aqueous dispersion containing adhesive resin particles is used to form the adhesive layer, moisture penetrates into the pores of the heat-resistant porous layer and the polyolefin microporous membrane. This separator requires a large amount of moisture to be removed by drying during the drying process during production, and is also prone to absorbing moisture from the environment even after production.

[0006] If a separator for a non-aqueous secondary battery contains moisture, it can deteriorate the cycle characteristics of the battery and cause internal short circuits. To prevent the separator from bringing moisture into the non-aqueous secondary battery, a step of drying the separator is sometimes included in the battery manufacturing process.

[0007] It is desirable that the non-aqueous secondary battery separator be one from which moisture can be easily removed in the drying process during separator production and the drying process during battery production. One way to make it easier to remove moisture by drying is to make the separator's porous structure coarser or thinner, but this raises concerns about the safety of the battery, which is the responsibility of the separator.

[0008] It is against this background that the present disclosure has been made. An object of the present disclosure is to provide a separator for a nonaqueous secondary battery that can easily remove moisture by drying and has excellent short-circuit resistance. [Means for solving the problem]

[0009] Specific means for solving the above problems include the following aspects. <1> a polyolefin microporous membrane; a heat-resistant porous layer disposed on one or both sides of the polyolefin microporous membrane, the heat-resistant porous layer containing a heat-resistant resin having at least one of an amide bond and an imide bond in its molecule and inorganic particles; an adhesive layer containing adhesive resin particles, which is disposed on one or both sides of the laminate of the polyolefin microporous membrane and the heat-resistant porous layer; A separator for a non-aqueous secondary battery comprising: the polyolefin microporous membrane has a Gurley value of 99 seconds / 100 mL or less; The nonaqueous secondary battery separator has a Gurley value of 160 seconds / 100 mL or less, the difference between the Gurley value of the nonaqueous secondary battery separator and the Gurley value of the polyolefin microporous membrane is 20 seconds / 100 mL to 60 seconds / 100 mL; Separator for non-aqueous secondary batteries. <2> a coverage rate of the adhesive resin particles on the surface of the nonaqueous secondary battery separator is 20% to 60% on each side on which the adhesive layer is disposed; <1> The non-aqueous secondary battery separator according to claim 1. <3> The thickness of the non-aqueous secondary battery separator is 5 μm to 17 μm. <1> or <2> The non-aqueous secondary battery separator according to claim 1. <4> The polyolefin microporous membrane has a thickness of 4 μm to 9 μm. <1> ~ <3> 1. The separator for a non-aqueous secondary battery according to any one of the above. <5> the heat-resistant porous layer is disposed on only one side of the polyolefin microporous membrane; The heat-resistant porous layer has a thickness of 0.5 μm to 4 μm. <1> ~ <4> 1. The separator for a non-aqueous secondary battery according to any one of the above. <6> the heat-resistant porous layers are disposed on both sides of the polyolefin microporous membrane; The heat-resistant porous layer has a total thickness of 1 μm to 8 μm on both sides. <1> ~ <4> 1. The separator for a non-aqueous secondary battery according to any one of the above. <7> The pores of the polyolefin microporous membrane contain a heat-resistant resin having at least one of an amide bond and an imide bond in its molecule. <1> ~ <6> 1. The separator for a non-aqueous secondary battery according to any one of the above. <8> The heat-resistant resin contains at least one selected from the group consisting of wholly aromatic polyamide, polyimide, and polyamideimide. <1> ~ <7> 1. The separator for a non-aqueous secondary battery according to any one of the above. <9> The inorganic particles include at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles. <1> ~ <8> 1. The separator for a non-aqueous secondary battery according to any one of the above. <10> the adhesive resin particles include at least one selected from the group consisting of acrylic resin particles, polyvinylidene fluoride resin particles, and styrene-butadiene rubber particles; <1> ~ <9> 1. The separator for a non-aqueous secondary battery according to any one of the above. <11> a positive electrode, a negative electrode, and a conductive material disposed between the positive electrode and the negative electrode; <1> ~ <10> and the non-aqueous secondary battery separator according to any one of the above items, Electromotive force is generated by doping and dedoping of lithium ions. Non-aqueous secondary battery. [Effects of the Invention]

[0010] According to the present disclosure, a separator for a nonaqueous secondary battery is provided that can easily remove moisture by drying and has excellent short-circuit resistance. [Brief explanation of the drawings]

[0011] [Figure 1]FIG. 1 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Figure 3] FIG. 1 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Figure 4] FIG. 1 is a schematic cross-sectional view of an example of a separator according to the present disclosure. [Figure 5] FIG. 1 is a schematic cross-sectional view of an example of a separator according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0023] The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

[0013] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, 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. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0014] 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, only B, or a combination of A and B.

[0015] 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.

[0016] In the present disclosure, when referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0017] In this disclosure, MD (Machine Direction) refers to the longitudinal direction of a separator manufactured in a long shape, and TD (Transverse Direction) refers to the direction perpendicular to MD in the plane direction of the separator. In this disclosure, TD is also referred to as the "width direction."

[0018] 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 polyolefin microporous membrane is referred to as "lower," and the layer farther from the polyolefin microporous membrane is referred to as "upper."

[0019] In the present disclosure, the volume of the porous layer excluding pores is referred to as the "solid content volume."

[0020] In the present disclosure, performing a heat press treatment after the separator is permeated with an electrolyte solution is referred to as "wet heat press," and performing a heat press treatment without permeating the separator with an electrolyte solution is referred to as "dry heat press."

[0021] In the present disclosure, the term "(meth)acrylic" means either "acrylic" or "methacrylic."

[0022] In the present disclosure, the term "monomer unit" of a polymer or resin refers to a structural unit of the polymer or resin, which is formed by polymerization of a monomer.

[0023] <Separator for non-aqueous secondary batteries> The separator for a nonaqueous secondary battery of the present disclosure (also simply referred to as "separator" in the present disclosure) comprises a polyolefin microporous membrane, a heat-resistant porous layer disposed on one or both sides of the polyolefin microporous membrane and containing a heat-resistant resin having at least one of an amide bond and an imide bond in its molecule and inorganic particles, and an adhesive layer disposed on one or both sides of a laminate of the polyolefin microporous membrane and the heat-resistant porous layer and containing adhesive resin particles.

[0024] In the present disclosure, a heat-resistant resin having at least one of an amide bond and an imide bond in the molecule is referred to as a "heat-resistant resin (AI)."

[0025] The layer structure of the separator of the present disclosure will be described with reference to the drawings. 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.

[0026] 1 is a separator in which heat-resistant porous layers 30 are disposed on both sides of a polyolefin microporous membrane 20, and adhesive layers 50 are disposed on both sides of a laminate 40 of the polyolefin microporous membrane 20 and two heat-resistant porous layers 30. One heat-resistant porous layer 30 and the other heat-resistant porous layer 30 may be the same or different in terms of ingredients and / or composition. One adhesive layer 50 and the other adhesive layer 50 may be the same or different in terms of ingredients and / or composition.

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

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

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

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

[0031] The heat-resistant porous layer 30 is a layer containing a heat-resistant resin (AI) and inorganic particles, and is disposed on one side of the polyolefin microporous membrane 20. The heat-resistant porous layer 30 may be disposed on only one side of the polyolefin microporous membrane 20, or on both sides of the polyolefin microporous membrane 20. When the heat-resistant porous layer 30 is disposed on both sides of the polyolefin microporous membrane 20, the heat resistance of the separator is superior, and the safety of the battery can be improved. In addition, the separator is less likely to curl, and handling during battery production is excellent. When the heat-resistant porous layer 30 is disposed on only one side of the polyolefin microporous membrane 20, the ion permeability of the separator is superior. In addition, the overall thickness of the separator can be reduced, allowing the production of a battery with higher energy density.

[0032] The adhesive layer 50 is a layer disposed on the surface of the polyolefin microporous membrane 20 or the heat-resistant porous layer 30, and exists as the outermost layer of the separator. The adhesive layer 50 may be disposed on only one surface of the laminate 40, or on both surfaces of the laminate 40. When the adhesive layer 50 is disposed on only one surface of the laminate 40, it is preferable that the adhesive layer 50 be disposed on the surface of the heat-resistant porous layer 30. The adhesive layer 50 may be disposed on one or both surfaces of the laminate 40 depending on the composition or surface properties of the positive or negative electrode of the battery. When the adhesive layer 50 is disposed on only one surface of the laminate 40, the overall thickness of the separator can be reduced, and a battery with higher energy density can be manufactured.

[0033] The adhesive layer 50 is a layer containing adhesive resin particles 52. The adhesive layer 50 may be a layer in which the adhesive resin particles 52 adhere to the laminate 40 by their own properties, or may be a layer in which the adhesive resin particles 52 are bound to the laminate 40 by another resin.

[0034] From the viewpoint of excellent adhesion to the electrode, the adhesive layer 50 preferably has a structure in which the adhesive resin particles 52 are arranged adjacent to each other on the surface of the laminate 40. From the viewpoint of permeability of the electrolyte solution into the separator, the adhesive layer 50 preferably has a structure in which the adhesive resin particles 52 are scattered on the surface of the laminate 40. From the viewpoint of increasing the energy density of the battery, the adhesive layer 50 preferably has a structure in which the adhesive resin particles 52 are arranged in a single layer in the thickness direction. The adhesive layer 50 may also have a structure in which multiple layers of the adhesive resin particles 52 are stacked in the thickness direction.

[0035] In a separator adhered to an electrode, the adhesive resin particles 52 contained in the adhesive layer 50 may melt partially or completely when heat is applied to adhere the separator to the electrode, causing adjacent adhesive resin particles 52 to bond together, and some or all of the particles may not retain their particle shape.

[0036] In the separator of the present disclosure, the polyolefin microporous membrane has a Gurley value of 99 seconds / 100 mL or less, the separator has a Gurley value of 160 seconds / 100 mL or less, and the difference between the Gurley values ​​of the separator and the polyolefin microporous membrane is 20 seconds / 100 mL to 60 seconds / 100 mL. By virtue of the above-described configuration, the separator of the present disclosure is easy to remove moisture by drying and has excellent short-circuit resistance.

[0037] If the Gurley value of the polyolefin microporous membrane is 100 seconds / 100 mL or more, moisture may not be sufficiently removed by drying. From the viewpoint of easy moisture removal by drying, the Gurley value of the polyolefin microporous membrane is 99 seconds / 100 mL or less, preferably 95 seconds / 100 mL or less, and more preferably 90 seconds / 100 mL or less. The Gurley value of the polyolefin microporous membrane is preferably in the above range, also from the viewpoint of ion permeability of the separator. From the viewpoint of short circuit resistance of the separator, the Gurley value of the polyolefin microporous membrane 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.

[0038] If the Gurley value of the separator exceeds 160 seconds / 100 mL, it may not be possible to sufficiently remove moisture by drying. From the viewpoint of facilitating removal of moisture by drying, the Gurley value of the separator is 160 seconds / 100 mL or less, preferably 150 seconds / 100 mL or less, and more preferably 140 seconds / 100 mL or less. From the viewpoint of ion permeability, the Gurley value of the separator is preferably in the above range. From the viewpoint of short circuit resistance, the Gurley value of the separator is preferably 100 seconds / 100 mL or more, more preferably 110 seconds / 100 mL or more, and even more preferably 120 seconds / 100 mL or more.

[0039] It is presumed that the difference between the Gurley value of the separator and the Gurley value of the polyolefin microporous membrane occurs because the separator of the present disclosure has a heat-resistant porous layer disposed on one or both sides of the polyolefin microporous membrane and the heat-resistant resin (AI), which is the material of the heat-resistant porous layer, penetrates and remains in the pores of the polyolefin microporous membrane. If the difference between the Gurley value of the separator and the Gurley value of the polyolefin microporous membrane is more than 60 seconds / 100 mL, the heat-resistant porous layer may be too thick or the amount of heat-resistant resin (AI) present in the pores of the polyolefin microporous membrane may be too large, and therefore moisture may not be sufficiently removed by drying. From the viewpoint of easy moisture removal by drying, the difference between the Gurley value of the separator and the Gurley value of the polyolefin microporous membrane is 60 seconds / 100 mL or less, preferably 50 seconds / 100 mL or less, and more preferably 40 seconds / 100 mL or less. From the viewpoint of the cycle characteristics of the battery, the difference between the Gurley value of the separator and the Gurley value of the polyolefin microporous membrane is preferably in the above range. If the difference between the Gurley value of the separator and the Gurley value of the polyolefin microporous membrane is less than 20 seconds / 100 mL, the heat-resistant porous layer may be too thin, causing an internal short circuit in the battery. From the viewpoint of short-circuit resistance, the difference between the Gurley value of the separator and the Gurley value of the polyolefin microporous membrane is 20 seconds / 100 mL or more, preferably 25 seconds / 100 mL or more, and more preferably 30 seconds / 100 mL or more.

[0040] The Gurley values ​​of the polyolefin microporous membrane and separator are values ​​measured using a Gurley densometer in accordance with JIS P8117:2009 "Paper and paperboard - Test method for air permeability and air resistance (intermediate range) - Gurley method."

[0041] The Gurley value of the microporous polyolefin membrane can be controlled by adjusting the stretching ratio during membrane formation. The Gurley value of the separator can be controlled by the Gurley value of the polyolefin microporous membrane and the thickness and porosity of the heat-resistant porous layer. The porosity of the heat-resistant porous layer can be controlled by the primary particle size and content of the inorganic particles contained in the heat-resistant porous layer, the viscosity of the coating liquid for forming the heat-resistant porous layer, the resin concentration, and solidification conditions, etc.

[0042] The polyolefin microporous film, heat-resistant porous layer, and adhesive layer contained in the separator of the present disclosure will be described in detail below.

[0043] [Polyolefin microporous membrane] In the present disclosure, a microporous polyolefin membrane refers to a microporous membrane containing a polyolefin, which has a structure in which numerous micropores are interconnected inside and allows gas or liquid to pass from one side to the other.

[0044] The polyolefin microporous film may be a microporous film made of only polyolefin, or a microporous film made of polyolefin and a material other than polyolefin (for example, a resin such as an acrylic resin, a styrene resin, or a butadiene rubber). The polyolefin microporous membrane preferably contains polyolefin in an amount of 95% by mass or more, more preferably 99% by mass or more, of the total mass.

[0045] Examples of the polyolefin microporous membrane include polyolefin microporous membranes that are conventionally used in battery separators, and it is preferable to select one from these that has sufficient mechanical properties and ion permeability.

[0046] From the viewpoint of exhibiting a shutdown function (a function in which, when the battery temperature rises, the constituent materials dissolve and block the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery), the polyolefin microporous membrane is preferably a microporous membrane containing polyethylene, and the polyethylene preferably accounts for 95 mass% or more of the total mass of the polyolefin microporous membrane. In the present disclosure, a microporous membrane in which polyethylene is the resin that accounts for the largest mass proportion of all the resins that make up the microporous membrane is referred to as a polyethylene microporous membrane.

[0047] The polyolefin microporous film is preferably a microporous film containing polypropylene, from the viewpoint of heat resistance that prevents film rupture when exposed to high temperatures.

[0048] The polyolefin microporous membrane is preferably a polyolefin microporous membrane containing polyethylene and polypropylene, from the viewpoint of providing a shutdown function and heat resistance such that the membrane does not easily rupture when exposed to high temperatures. An example of a polyolefin microporous membrane containing polyethylene and polypropylene is a microporous membrane in which polyethylene and polypropylene are mixed in one layer. From the viewpoint of achieving both a shutdown function and heat resistance, the microporous membrane preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. Another example of a polyolefin microporous membrane containing polyethylene and polypropylene is a polyolefin microporous membrane having a laminate structure of two or more layers, at least one of which contains polyethylene and at least one of which contains polypropylene.

[0049] The polyolefin contained in the polyolefin microporous membrane preferably has 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. When the Mw of the polyolefin is 5,000,000 or less, the microporous membrane has good shutdown properties and is easy to mold.

[0050] The weight-average molecular weight of the polyolefin constituting the microporous polyolefin membrane is determined by dissolving the microporous polyolefin membrane in o-dichlorobenzene under heating and measuring it by gel permeation chromatography (GPC). Polystyrene or the like is used for molecular weight calibration.

[0051] Examples of methods for producing a polyolefin microporous membrane include a method in which molten polyolefin is extruded through a T-die to form a sheet, which is crystallized, stretched, and then heat-treated to form a microporous membrane; and a method in which molten polyolefin 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 the sheet is heat-treated to form a microporous membrane.

[0052] The surface of the polyolefin microporous membrane may be subjected to various surface treatments, such as corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment, to improve wettability with a coating liquid for forming a heat-resistant porous layer or an adhesive layer, provided that the properties of the polyolefin microporous membrane are not impaired.

[0053] -Characteristics of polyolefin microporous membranes- From the viewpoint of mechanical strength, the thickness of the polyolefin microporous film is preferably 3 μm or more, more preferably 4 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 polyolefin microporous film is preferably 10 μm or less, more preferably 9 μm or less, and even more preferably 8 μm or less. The thickness of the polyolefin microporous film is determined by measuring 20 points within a 10 cm square using a contact type measuring device and averaging the measurements.

[0054] From the viewpoint of ion permeability, the porosity of the polyolefin microporous membrane is preferably 30% to 60%. The porosity ε (%) of the polyolefin microporous membrane is calculated by the following formula. ε={1-W / (d t)}×100 where W is the mass per unit area of ​​the polyolefin microporous membrane (g / m 2 ), and d is the true density of the polyolefin microporous membrane (g / cm 3 ) and t is the thickness (μm) of the microporous polyolefin membrane.

[0055] An example of the form of the polyolefin microporous membrane is one having a heat-resistant resin (AI) in the pores. The heat-resistant resin (AI) is a heat-resistant resin (AI) that has entered the pores of the polyolefin microporous membrane when the heat-resistant porous layer is formed. The details and preferred form of the heat-resistant resin (AI) present in the pores of the polyolefin microporous membrane are the same as those of the heat-resistant resin (AI) contained in the heat-resistant porous layer (described below).

[0056] Examples of the form of a polyolefin microporous membrane having a heat-resistant resin (AI) in its pores include a polyolefin microporous membrane having a heat-resistant resin (AI) in the pores in the region close to the surface of the microporous membrane; and a polyolefin microporous membrane having a heat-resistant resin (AI) in the pores throughout the entire microporous membrane. Examples of the form of the heat-resistant resin (AI) in the pores include a form in which the heat-resistant resin (AI) covers part or all of the wall surfaces of the pores, a form in which fibrous heat-resistant resin (AI) is contained in the pores, and a combination thereof. When the heat-resistant resin (AI) in the pores has any of these forms, it is preferable from the viewpoint of facilitating permeation of the electrolyte solution into the polyolefin microporous membrane.

[0057] The presence of heat-resistant resins (AIs) in the pores of microporous polyolefin membranes can be confirmed by elemental imaging, which combines a transmission electron microscope with energy dispersive X-ray spectroscopy. AIs are easily stained by ruthenium tetroxide (RuO4), so they can be detected by Ru imaging.

[0058] In the present disclosure, the Gurley value of a polyolefin microporous membrane is a value measured without a heat-resistant resin (AI) in the pores, that is, measured using only the polyolefin microporous membrane. In the present disclosure, the porosity of a polyolefin microporous membrane is a value calculated without a heat-resistant resin (AI) in the pores, that is, for the polyolefin microporous membrane alone.

[0059] [Heat-resistant porous layer] The porous layer means a layer having a large number of fine pores through which gas or liquid can pass from one surface to the other. The heat-resistant porous layer is a porous layer that has heat resistance by containing a heat-resistant material (for example, a heat-resistant resin and / or inorganic particles).

[0060] In the present disclosure, a heat-resistant resin refers to a resin with a melting point of 200°C or higher, or a resin without a melting point but with 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.

[0061] In the present disclosure, the heat-resistant porous layer is a porous layer containing a heat-resistant resin (AI) and inorganic particles. The heat-resistant porous layer may be a porous layer made only of a heat-resistant resin (AI) and inorganic particles, or a porous layer made of a heat-resistant resin (AI) and inorganic particles in addition to other materials.

[0062] Examples of the form of the heat-resistant porous layer include a structure in which inorganic particles are bound or trapped in a porous structure in which fibrils containing a heat-resistant resin (AI) are connected in a two-dimensional or three-dimensional network; a structure in which inorganic particles are bound or trapped in a network-like microporous structure containing a heat-resistant resin (AI); and a layered structure in which a heat-resistant resin (AI) connects a large number of inorganic particles together, forming voids between the inorganic particles.

[0063] -Heat-resistant resin (AI)- The heat-resistant resin (AI) may be a homopolymer or a copolymer. Examples of heat-resistant resins (AI) include polyamide, polyimide, polyamideimide, polyacrylamide, polyacrylimide, polyetherpolyamide, polyetherpolyimide, and poly-N-vinylacetamide. These resins may be used alone or in combination of two or more.

[0064] As the heat-resistant resin (AI), polyamide, polyimide and polyamideimide are preferred from the viewpoints of heat resistance, stability to the electrolyte and electrochemical stability. From the viewpoint of durability, a fully aromatic polyamide is preferred as the polyamide. A fully aromatic polyamide refers to a polyamide whose main chain is composed only of benzene rings and amide bonds. However, a small amount of an aliphatic monomer may be copolymerized in a fully aromatic polyamide. A fully aromatic polyamide is also called an aramid.

[0065] The wholly aromatic polyamide may be meta-type or para-type. Among wholly aromatic polyamides, meta-type wholly aromatic polyamides are preferred from the viewpoints of ease of forming a porous layer and excellent oxidation-reduction resistance in electrode reactions. Specific wholly aromatic polyamides are preferably polymetaphenylene isophthalamide or polyparaphenylene terephthalamide, and more preferably polymetaphenylene isophthalamide.

[0066] Meta-type wholly aromatic polyamides are polymers with higher flexibility than para-type wholly aromatic polyamides, and therefore, when a heat-resistant porous layer is formed, they penetrate into the pores of the polyolefin microporous membrane and tend to adhere to the pore wall surfaces or form a fibrous structure. When meta-type aromatic polyamides are adhered to the pore wall surfaces of the polyolefin microporous membrane or when fibrous meta-type aromatic polyamides are contained in the pores, the electrolyte solution tends to penetrate the polyolefin microporous membrane.

[0067] The weight average molecular weight of the heat-resistant resin (AI) contained in the heat-resistant porous layer is 1×10 3 ~1×10 7 Preferably, it is 5 x 10 3 ~5×10 6 is more preferable, and 1×10 4 ~1×10 6 is more preferred.

[0068] The weight average molecular weight of the heat-resistant resin (AI) is a molecular weight measured by GPC in terms of polystyrene. The measurement is performed using the heat-resistant resin (AI) extracted from the heat-resistant porous layer or the heat-resistant resin (AI) used to form the heat-resistant porous layer as a sample.

[0069] The mass proportion of the heat-resistant resin (AI) in the total resin of the heat-resistant porous layer is preferably 90 mass % or more, more preferably 95 mass % or more, even more preferably 99 mass % or more, and particularly preferably 100 mass %.

[0070] The mass proportion of the heat-resistant resin (AI) in the heat-resistant porous layer is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and even more preferably 15% by mass to 30% by mass, from the viewpoint of forming a good porous structure and suppressing interlayer delamination with the polyolefin microporous film.

[0071] When heat-resistant porous layers are present on both sides of the polyolefin microporous membrane, the type and / or content of the heat-resistant resin (AI) contained in one heat-resistant porous layer may be the same as or different from the type and / or content of the heat-resistant resin (AI) contained in the other heat-resistant porous layer.

[0072] -Other resins- The heat-resistant porous layer may contain resins other than the heat-resistant resin (AI). Examples of other resins include acrylic resins, polyvinylidene fluoride resins, styrene-butadiene copolymers, butadiene-acrylonitrile resins, cellulose, polyvinylpyrrolidone, polyether, polysulfone, polyethersulfone, polyketone, and polyetherketone. These resins may be used alone or in combination of two or more.

[0073] The mass proportion of other resins in the total resin of the heat-resistant porous layer is preferably 10 mass % or less, more preferably 5 mass % or less, and even more preferably 1 mass % or less.

[0074] -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.

[0075] Examples of metal oxides that constitute the metal oxide particles include silica (silicon dioxide), alumina (aluminum oxide), boehmite (alumina monohydrate), titania (titanium oxide), zirconia (zirconium oxide), 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 that constitute the metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides that make up the metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0076] The inorganic particles may be surface-modified with a silane coupling agent or the like.

[0077] The inorganic particles may be used alone or in combination of two or more kinds.

[0078] From the viewpoints of stability in the electrolyte and electrochemical stability, the inorganic particles are preferably at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles, and more preferably at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles.

[0079] 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 internal short circuits in the battery, the inorganic particles contained in the heat-resistant porous layer are preferably plate-like particles or non-aggregated primary particles.

[0080] The average primary particle size of the inorganic particles contained in the heat-resistant porous layer is preferably 0.01 μm to 2 μm, more preferably 0.02 μm to 1 μm, and even more preferably 0.03 μm to 0.5 μm, from the viewpoint of forming a good porous structure and suppressing interlayer delamination with the polyolefin microporous film.

[0081] The average primary particle size of inorganic particles is determined by measuring the long diameters of 100 randomly selected inorganic particles during 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 the material for forming the heat-resistant porous layer, or inorganic particles removed from the heat-resistant porous layer. There are no limitations on the method for removing inorganic particles from the heat-resistant porous layer. Examples of such methods include immersing the heat-resistant porous layer peeled off from the separator in an organic solvent that dissolves the heat-resistant resin to remove the inorganic particles; or heating the heat-resistant porous layer peeled off from the separator to approximately 800°C to remove the heat-resistant resin and remove the inorganic particles.

[0082] The mass proportion of the inorganic particles in the heat-resistant porous layer is preferably 50% by mass to 95% by mass, more preferably 60% by mass to 90% by mass, and even more preferably 70% by mass to 85% by mass, from the viewpoints of forming a good porous structure and suppressing interlayer delamination with the polyolefin microporous film.

[0083] When heat-resistant porous layers are present on both sides of the polyolefin microporous membrane, the type and / or content of inorganic particles contained in one heat-resistant porous layer may be the same as or different from the type and / or content of inorganic particles contained in the other heat-resistant porous layer.

[0084] -Organic particles- The heat-resistant porous layer may contain organic particles, such as particles made of crosslinked polymers such as crosslinked poly(meth)acrylic acid, crosslinked poly(meth)acrylic acid ester, crosslinked polysilicone, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensate; and particles made of heat-resistant polymers such as polysulfone, polyacrylonitrile, aramid, and polyacetal. 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.

[0085] The organic particles may be used alone or in combination of two or more kinds.

[0086] -Other ingredients- The heat-resistant porous layer may contain additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming agent, and a pH adjuster. The dispersant is added, for example, to the coating solution for forming the heat-resistant porous 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 coating solution for forming the heat-resistant porous layer for the purpose of improving compatibility with the polyolefin microporous membrane, suppressing air entrapment in the coating solution, or adjusting the pH.

[0087] -Characteristics of heat-resistant porous layer- When the heat-resistant porous layer is present on only one side of the polyolefin microporous membrane, the thickness of the heat-resistant porous layer is preferably 4 μm or less, more preferably 3.5 μm or less, and even more preferably 3 μm or less, from the viewpoint of facilitating moisture removal by drying. When the heat-resistant porous layer is present on only one side of the polyolefin microporous membrane, the thickness of the heat-resistant porous layer is preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 1.5 μm or more, from the viewpoint of short-circuit resistance of the separator.

[0088] When the heat-resistant porous layer is present on both sides of the polyolefin microporous membrane, the total thickness of the heat-resistant porous layer on both sides is preferably 8 μm or less, more preferably 7 μm or less, and even more preferably 6 μm or less, from the viewpoint of facilitating moisture removal by drying. When the heat-resistant porous layer is present on both sides of the polyolefin microporous membrane, the thickness of the heat-resistant porous layer on both sides in total is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more, from the viewpoint of short-circuit resistance of the separator.

[0089] The thickness of the heat-resistant porous layer is the thickness of the flat membrane obtained by removing the adhesive layer from the separator, minus the thickness of the polyolefin microporous membrane. The thickness of the flat membrane obtained by removing the adhesive layer from the separator is measured at 20 points within a 10 cm square using a contact-type measuring device and the average of the measurements is obtained.

[0090] When the heat-resistant porous layer is present on only one side of the polyolefin microporous membrane, the mass per unit area of ​​the heat-resistant porous layer (i.e., basis weight) is 1 g / m 2 ~4.5g / m 2 It is preferable that the density is 1.5 g / m 2 ~4g / m 2 More preferably, 2 g / m 2 ~3.5g / m 2 is more preferred.

[0091] When the heat-resistant porous layer is present on both sides of the polyolefin microporous film, the mass per unit area (i.e., basis weight) of the heat-resistant porous layer is 2 g / m in total on both sides. 2 ~9g / m 2 It is preferable that the density is 3 g / m 2 ~8g / m 2 More preferably, 4 g / m 2 ~7g / m 2 is more preferred.

[0092] The mass per unit area of ​​the heat-resistant porous layer (i.e., basis weight) is the value obtained by subtracting the basis weight of the polyolefin microporous membrane from the basis weight of the flat membrane obtained by removing the adhesive layer from the separator. The basis weight of the flat membrane obtained by removing the adhesive layer from the separator is calculated by cutting the separator into a 20 cm x 20 cm piece, removing the adhesive layer, measuring the mass, and dividing the mass by the area.

[0093] The porosity of the heat-resistant porous layer is preferably 20% to 70% from the viewpoint of ion permeability. The porosity ε (%) of the heat-resistant porous layer is calculated by the following formula.

[0094]

number

[0095] Here, for constituent material 1, constituent material 2, constituent material 3, ..., constituent material n of the heat-resistant porous layer, the mass per unit area of ​​each constituent material is W1, W 2、 W3, …, W n (g / cm 2 ) and the true densities of the constituent materials are d1, d2, d3, ..., d n (g / cm 3 ) and the thickness of the heat-resistant porous layer is t (cm).

[0096] [Adhesive layer] The adhesive layer is a layer disposed on the surface of the heat-resistant porous layer or the polyolefin microporous membrane, and exists as the outermost layer of the separator. The adhesive layer has numerous gaps or micropores, allowing gas or liquid to pass from one surface to the other.

[0097] The adhesive layer may be a layer consisting of adhesive resin particles alone, or may be a layer consisting of adhesive resin particles and materials other than adhesive resin particles, such as non-particulate resins, dispersants, wetting agents, antifoaming agents, and pH adjusters.

[0098] From the viewpoint of adhesion to the electrode, the mass ratio of the adhesive resin particles in the adhesive layer is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 99 mass% or more. The mass ratio of the adhesive resin particles in the adhesive layer may be 100 mass%.

[0099] -Adhesive resin particles- Examples of adhesive resin particles include acrylic resin particles, polyvinylidene fluoride resin particles, styrene-butadiene rubber particles, fluorine-containing rubber particles, butadiene-acrylonitrile resin particles, and cellulose particles. Among these, at least one selected from the group consisting of acrylic resin particles, polyvinylidene fluoride resin particles, and styrene-butadiene rubber particles is preferred from the viewpoint of excellent adhesion to electrodes.

[0100] Examples of the acrylic resin constituting the acrylic resin particles 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.

[0101] Examples of acrylic monomers for acrylic resins 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. Preferred acrylic monomers are (meth)acrylic acid alkyl esters. The alkyl group at the ester moiety of the (meth)acrylic acid alkyl esters is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. One type of acrylic monomer may be used alone, or two or more types may be used in combination.

[0102] Examples of styrene-based monomers for acrylic resins include styrene and 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. One type of styrene-based monomer may be used alone, or two or more types may be used in combination.

[0103] Examples of polyvinylidene fluoride resins constituting polyvinylidene fluoride resin particles include homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride with other monomers (polyvinylidene fluoride copolymers); and mixtures of polyvinylidene fluoride and polyvinylidene fluoride copolymers. Examples of monomers copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, trichloroethylene, vinyl fluoride, trifluoroperfluoropropyl ether, ethylene, (meth)acrylic acid, methyl (meth)acrylate, (meth)acrylic acid esters, vinyl acetate, vinyl chloride, and acrylonitrile. These monomers may be used alone or in combination of two or more.

[0104] The polyvinylidene fluoride copolymer is preferably a copolymer containing 50 mol % or more of vinylidene fluoride units, from the viewpoint of imparting to the adhesive resin particles mechanical strength that can withstand pressure and heat during battery production. The polyvinylidene fluoride copolymer is preferably a copolymer of vinylidene fluoride and hexafluoropropylene, and the copolymer preferably contains 0.1 mol % to 10 mol % (preferably 0.5 mol % to 5 mol %) of hexafluoropropylene units.

[0105] The styrene-butadiene rubber constituting the styrene-butadiene rubber particles may be an emulsion polymer or a solution polymer, or may be a random copolymer or a block copolymer. The styrene content of the styrene-butadiene rubber is preferably 20% by mass to 50% by mass.

[0106] The average primary particle size of the adhesive resin particles is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more, from the viewpoint of ion permeability of the adhesive layer. The average primary particle size of the adhesive resin particles is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less, from the viewpoint of thinning the adhesive layer, suppressing interlayer delamination between the adhesive layer and the heat-resistant porous layer or the polyolefin microporous membrane, and maintaining adhesion of the separator to the electrode.

[0107] The average primary particle size of the adhesive resin particles is determined by measuring the long diameters of 100 adhesive resin particles randomly selected during observation with a scanning electron microscope (SEM) and averaging the long diameters of the 100 particles. The sample used for SEM observation is adhesive resin particles that are the material forming the adhesive layer, or adhesive resin particles removed from the adhesive layer.

[0108] The coverage of the separator surface by the adhesive resin particles is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more on each side on which the adhesive layer is disposed, from the viewpoint of excellent adhesion to the electrode and excellent cycle characteristics of the battery. The coverage of the separator surface by the adhesive resin particles is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less on each side on which the adhesive layer is disposed, from the viewpoint of facilitating the removal of moisture from the separator by drying and of providing the battery with excellent cycle characteristics.

[0109] The coverage rate of the separator surface by adhesive resin particles is the percentage of the area covered by adhesive resin particles when the separator is viewed in plan view. This coverage rate is determined by imaging the separator surface from the direction perpendicular to the surface using a scanning electron microscope (SEM), randomly selecting 10 square areas, determining the coverage rate for each area, and then calculating the average value for the 10 areas.

[0110] The coverage of the separator surface with the adhesive resin particles can be controlled by the resin particle concentration and coating amount of the adhesive resin particle dispersion liquid for forming the adhesive layer.

[0111] When adhesive layers are present on both sides of the separator, the type and / or coverage of adhesive resin particles contained in one adhesive layer may be the same as or different from the type and / or coverage of adhesive resin particles contained in the other adhesive layer.

[0112] -Other ingredients- The adhesive layer may contain a binder resin that binds the adhesive resin particles to the laminate, and the binder resin is preferably the same type of resin as that contained in the heat-resistant porous layer.

[0113] 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 used to form 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 used to form the adhesive layer for the purpose of improving compatibility with the heat-resistant porous layer or the polyolefin microporous membrane, suppressing air entrapment in the resin particle dispersion, or adjusting the pH.

[0114] [Separator characteristics] From the viewpoint of short-circuit resistance, 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. The thickness of the separator is preferably 17 μm or less, more preferably 15 μm or less, and even more preferably 13 μm or less, from the viewpoint of ease of removing moisture by drying and the energy density of the battery. The thickness of the separator is measured at 20 points within a 10 cm square using a contact type measuring device and then calculated by averaging the measurements.

[0115] The mass per unit area of ​​the separator (i.e., basis weight) is set to 6 g / m from the viewpoint of ease of removing moisture from the separator by drying and from the viewpoint of short-circuit resistance of the separator. 2 ~13g / m 2 Preferably, it is 7 g / m 2 ~12g / m 2 More preferably, 8 g / m 2 ~11g / m2 is more preferred. The mass per unit area of ​​the separator (i.e., basis weight) is determined by cutting the separator into a 20 cm x 20 cm piece, measuring the mass, and dividing the mass by the area.

[0116] [Separator manufacturing method] The separator of the present disclosure can be produced, for example, by the following production method (A) or production method (B). In production methods (A) and (B), a heat-resistant porous layer is formed on a polyolefin microporous membrane by a wet coating method, and an adhesive layer is formed on a laminate by a dry coating method. In the present disclosure, the wet coating method is a method in which a coating layer is solidified in a coagulation liquid. In the present disclosure, the dry coating method is a method in which a coating layer is solidified by drying.

[0117] Manufacturing method (A) (continuous manufacturing method): A heat-resistant porous layer is formed by wet coating on a polyolefin microporous membrane unwound from a roll to obtain a laminate of the polyolefin microporous membrane and the heat-resistant porous layer, and then an adhesive layer is formed on the laminate by dry coating to obtain a separator, and the completed separator is wound up on another roll.

[0118] Production method (B) (discontinuous production method): A heat-resistant porous layer is formed on a polyolefin microporous membrane unwound from a roll by a wet coating method to obtain a laminate of the polyolefin microporous membrane and the heat-resistant porous layer, and the laminate is then temporarily wound up on another roll. Next, an adhesive layer is formed on the laminate unwound from the roll by a dry coating method to obtain a separator, and the completed separator is then wound up on another roll.

[0119] The steps included in the production method (A) are described in detail below. The production method (A) includes the following steps (1) to (7).

[0120] -Step (1): Preparation of coating liquid for forming heat-resistant porous layer- The coating liquid for forming the heat-resistant porous layer is prepared by dissolving and dispersing a heat-resistant resin (AI) and inorganic particles in a solvent. If necessary, other components besides the heat-resistant resin (AI) and inorganic particles may be dissolved or dispersed in the coating liquid.

[0121] The solvent used to prepare the coating liquid includes a solvent that dissolves the heat-resistant resin (AI) (hereinafter also referred to as a "good solvent"). Examples of the good solvent include polar amide solvents. Examples of the polar amide solvent include dimethylacetamide, dimethylformamide, and N-methylpyrrolidone.

[0122] From the viewpoint of forming 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 that ensures a viscosity appropriate for coating. Examples of phase separation agents include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0123] From the viewpoint of forming a good porous structure, the solvent used to prepare 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.

[0124] The resin concentration in the coating liquid is preferably 1% by mass to 20% by mass from the viewpoint of forming a good porous structure, and the inorganic particle concentration in the coating liquid is preferably 0.5% by mass to 50% by mass from the viewpoint of forming a good porous structure.

[0125] -Step (2): Preparation of adhesive resin particle dispersion- The adhesive layer-forming coating liquid is preferably an adhesive resin particle dispersion. The adhesive resin particle dispersion is prepared by dispersing adhesive resin particles in a suitable dispersion medium (e.g., water). A surfactant may be added to the adhesive resin particle dispersion to enhance the dispersibility of the adhesive resin particles in the dispersion medium. The adhesive resin particle dispersion may be a commercially available product or a diluted solution of a commercially available product.

[0126] From the viewpoint of coating suitability, the concentration of adhesive resin particles in the adhesive resin particle dispersion is preferably 1% by mass to 60% by mass.

[0127] -Step (3): Coating of heat-resistant porous layer-forming coating liquid- A coating liquid for forming a heat-resistant porous layer is applied to at least one surface of a polyolefin microporous membrane to form a coating layer on the polyolefin microporous membrane. Examples of coating methods for the coating liquid include knife coating, Mayer bar coating, die coating, reverse roll coating, roll coating, and gravure coating. When forming a heat-resistant porous layer on both surfaces of the polyolefin microporous membrane, it is preferable from the viewpoint of productivity to apply the coating liquid to both surfaces of the polyolefin microporous membrane simultaneously.

[0128] -Step (4): Solidification of the coating layer- The polyolefin microporous membrane having a coating layer that will become the heat-resistant porous layer formed thereon is immersed in a coagulation liquid to induce phase separation in the coating layer while solidifying the heat-resistant resin (AI), thereby obtaining a laminate consisting of the polyolefin microporous membrane and the heat-resistant porous layer.

[0129] The coagulation liquid generally contains the good solvent and phase separation agent used in preparing the coating liquid, as well as water. It is preferable from a productivity perspective that the mixing ratio of the good solvent and the phase separation agent be the same as the mixing ratio of the mixed solvent used in preparing the coating liquid. From the viewpoints of forming a porous structure and productivity, the water content in the coagulation liquid is preferably 40% by mass to 90% by mass. The temperature of the coagulation liquid is, for example, 20°C to 50°C.

[0130] -Step (5): Washing and drying the coating layer- The laminate is pulled out of the coagulating solution and washed with water. By washing with water, the coagulating solution is removed from the laminate. Furthermore, by drying, water is removed from the laminate. The washing with water is carried out, for example, by transporting the laminate in a water bath. The drying is carried out, for example, by transporting the laminate in a high-temperature environment, by blowing air on the laminate, or by bringing the laminate into contact with a heat roll. The drying temperature is preferably 40°C to 80°C.

[0131] -Step (6): Coating of adhesive resin particle dispersion- An adhesive resin particle dispersion is applied to at least one surface of the laminate. Examples of methods for applying the adhesive resin particle dispersion include knife coating, gravure coating, Mayer bar coating, die coating, reverse roll coating, roll coating, screen printing, inkjet printing, and spraying. When adhesive layers are formed on both surfaces of the laminate, it is preferable from the viewpoint of productivity to apply the adhesive resin particle dispersion to both surfaces of the laminate simultaneously.

[0132] -Step (7): Drying of adhesive resin particle dispersion- The adhesive resin particle dispersion on the laminate is dried to adhere the adhesive resin particles to the surface of the laminate. Drying is performed, for example, by transporting the laminate in a high-temperature environment or by blowing air onto the laminate. The drying temperature is preferably 40°C to 100°C.

[0133] The manufacturing method (B) can be carried out by carrying out steps (1) to (5), then temporarily winding the laminate onto a roll, and then unwinding the laminate from the roll to carry out steps (6) and (7).

[0134] <Non-aqueous secondary battery> The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery that generates electromotive force by doping and dedoping of lithium ions, and includes a positive electrode, a negative electrode, and the separator of the present disclosure. "Doping" refers to the phenomenon of lithium ions entering the active material of the electrode.

[0135] 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.

[0136] In the nonaqueous secondary battery of the present disclosure, the separator of the present disclosure has adhesiveness to the electrodes, so that the electrodes and the separator are less likely to peel off from each other, and internal short circuits are less likely to occur. The nonaqueous secondary battery of the present disclosure is less likely to cause internal short circuits and has excellent cycle characteristics because the separator of the present disclosure allows moisture to be easily removed by drying.

[0137] 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.

[0138] 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, and 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 binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, and graphite powder. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil, each having a thickness of 5 μm to 20 μm.

[0139] An example of an embodiment of the negative electrode is a structure in which an active material layer containing a negative electrode active material and a binder resin is disposed on a current collector. The active material layer may further contain a conductive additive. Examples of negative electrode active materials include materials capable of electrochemically absorbing lithium ions, such as carbon materials; alloys of lithium with silicon, tin, aluminum, etc.; and Wood's alloy. Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers. Examples of the current collector include copper foil, nickel foil, stainless steel foil, and the like, each having a thickness of 5 μm to 20 μm. Alternatively, a metallic lithium foil may be used as the negative electrode instead of the above-described negative electrode.

[0140] The electrolyte solution is preferably a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of lithium salts include LiPF6, LiBF4, and LiClO4. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted derivatives thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone. These may be used alone or in combination. The electrolyte solution 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.

[0141] Examples of the exterior packaging include aluminum laminate film packs, metal cans, etc. Battery shapes include prismatic, cylindrical, coin-shaped, etc., and the separator of the present disclosure is suitable for any of these shapes.

[0142] 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 by, for example, any of the following production methods (1) to (3).

[0143] Manufacturing method (1): The laminate is dry heat pressed to temporarily bond the electrodes and separator, and then placed in an exterior packaging (for example, an aluminum laminate film pack; the same applies below), and an electrolyte is poured into it. Next, the laminate is wet heat pressed from above the exterior packaging to bond the electrodes and separator and seal the exterior packaging.

[0144] Manufacturing method (2): The laminate is placed in an exterior packaging material and an electrolyte solution is poured into it. The laminate is then wet heat pressed onto the exterior packaging material to bond the electrodes and separator together and seal the exterior packaging material.

[0145] Manufacturing method (3): The laminate is dry-heat pressed to bond the electrodes and separator, and then housed in an exterior packaging material, into which an electrolyte solution is injected, and then the exterior packaging material is sealed.

[0146] In Production Methods (1) to (3), the pressing temperatures for the wet heat press and dry heat press are each preferably 50°C to 100°C, more preferably 60°C to 90°C. The pressing pressures for the wet heat press and dry heat press are each preferably 0.1 MPa to 2 MPa, more preferably 0.5 MPa to 1.5 MPa. The pressing time is preferably adjusted depending on the pressing temperature and pressing pressure, for example, within the range of 5 seconds to 20 hours.

[0147] 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 (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 in the length direction. [Example]

[0148] The separator and nonaqueous secondary battery of the present disclosure will be described in more detail below with reference to examples. The materials, amounts used, 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 construed as being limited by the specific examples shown below.

[0149] In the following description, synthesis, processing, manufacturing, testing, etc. were carried out at room temperature (25°C ± 3°C) unless otherwise specified.

[0150] <Measurement and evaluation methods> The measurement and evaluation methods used in the examples and comparative examples are as follows.

[0151] [Thickness of polyethylene microporous membrane and separator] The thicknesses (μm) of the polyethylene microporous membrane and separator were measured at 20 points within a 10 cm square using a contact-type measuring instrument LITEMATIC VL-50S (Mitutoyo Corporation) and averaged. A spherical probe with a sphere radius of 10 mm (Mitutoyo Corporation) was used, and the measurement was adjusted so that a load of 0.19 N was applied during measurement.

[0152] [Thickness of heat-resistant porous layer] The thickness (μm) of the polyethylene microporous membrane was calculated by subtracting the thickness (μm) 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 using a contact-type measuring instrument LITEMATIC VL-50S (Mitutoyo Corporation) and the average was calculated. A spherical probe with a sphere radius of 10 mm (Mitutoyo Corporation) was used, and the measurement was adjusted so that a load of 0.19 N was applied during measurement.

[0153] [Basis weight of polyethylene microporous membrane and separator] The polyethylene microporous membrane and the separator were each cut into a 20cm x 20cm piece, and the mass was measured. The mass was divided by the area to determine the basis weight (g / m 2 ) was sought.

[0154] [Weight of heat-resistant porous layer] The basis weight (g / m) of the flat membrane after removing the adhesive layer from the separator 2 ) to calculate the basis weight (g / m 2 The basis weight of the flat membrane was determined by cutting the separator into a piece of 20 cm x 20 cm, removing the adhesive layer, measuring the mass, and dividing the mass by the area.

[0155] [Gurley value of polyethylene microporous membrane and separator] The Gurley values ​​(seconds / 100 mL) of the polyethylene microporous membrane and the separator were measured using a Gurley densometer G-B2C (Toyo Seiki Seisaku-sho, Ltd.) in accordance with JIS P8117:2009. The Gurley value of the polyethylene microporous membrane was subtracted from the Gurley value of the separator to determine the difference in Gurley values.

[0156] [Average primary particle size of inorganic particles] The inorganic particles used to form the heat-resistant porous layer were used as samples and observed by SEM to determine the average primary particle size. The major axes of 100 randomly selected inorganic particles were measured during SEM observation, and the average value of the major axes of the 100 particles was taken as the average primary particle size (μm).

[0157] [Average primary particle size of adhesive resin particles] The dried adhesive resin particle dispersion liquid used to form the adhesive layer was used as a sample and observed with an SEM to determine the average primary particle size. The major axis of 100 adhesive resin particles randomly selected during the SEM observation was measured, and the average value of the major axis of the 100 particles was taken as the average primary particle size (μm).

[0158] [Coverage rate of adhesive resin particles on separator surface] The coverage rate of the separator surface by the adhesive resin particles was determined by taking an image of the separator surface from the direction perpendicular to the surface using an SEM, randomly selecting 10 square areas, determining the coverage rate for each area, and then calculating the average value for the 10 areas.

[0159] [Separator drying suitability] The separator was immersed in a water bath while being transported, and after being removed from the water bath, it was passed through nip rolls to squeeze out the water. Next, while the separator was being transported, air at a temperature of 70°C was blown onto one side, and the other side was brought into contact with a heat roll with a surface temperature of 70°C for 30 seconds. While being transported, one side of 1000 m of the separator (the side not in contact with the heat roll) was visually observed to check for the presence or absence of uneven drying, such as circular or oval spots. After transporting 1000 m of the separator, the surface of the heat roll was visually observed to check for the presence or absence of deposits with a major axis length of 1 cm or more (film-like material that had peeled off from the separator and adhered). The presence or absence of uneven drying and deposits was classified as follows:

[0160] A: There is no uneven drying on the separator surface, and no adhesions on the heat roll surface. B: There is uneven drying on the separator surface, and no adhesion on the heat roll surface. C: There is uneven drying on the separator surface and there is adhesion on the heat roll surface.

[0161] [Battery short circuit resistance] One hundred nonaqueous secondary batteries, as described below, were prepared. The batteries were charged at a constant current and constant voltage of 1C / 4.2V in a 25°C environment. The charged batteries were placed on a horizontal table with the positive electrode facing up and secured with adhesive tape. A cylindrical terminal with a diameter of 10mm was placed on the center of the battery, and a load of 5kgf was applied. A battery was considered to have a short circuit when its voltage dropped to 3.5V or less. The number of short-circuited batteries out of 100 was classified as follows:

[0162] A:0 pieces B: 1~5 pieces C: 6~9 pieces D: 10 or more

[0163] [Battery cycle characteristics] One hundred non-aqueous secondary batteries, as described below, were prepared. The batteries were subjected to 100 charge / discharge cycles at a temperature of 25°C. Charging was performed at a constant current and constant voltage of 1C / 4.2V, and discharging was performed at a constant current with a cutoff of 1C / 2.75V. The discharge capacity at the 100th cycle was divided by the initial discharge capacity to calculate the capacity retention rate (%). The average value for the 100 batteries was then calculated, and the average capacity retention rate was classified as follows:

[0164] A: Over 90% B: 80% or more but less than 90% C: 70% or more but less than 80% D: Less than 70%

[0165] <Separator and battery manufacturing> [Example 1] -Separator production- Dimethylacetamide (DMAc) and tripropylene glycol (TPG) were mixed in a mass ratio of 95:5 to prepare a mixed solvent. Meta-aramid (polymetaphenylene isophthalamide) and alumina particles (average primary particle size 0.04 μm) were added to the mixed solvent and stirred to prepare coating solution (1). Coating solution (1) had a meta-aramid concentration of 5 mass% and a mass ratio of meta-aramid to alumina particles of 20:80.

[0166] A resin particle dispersion (1) was prepared by dispersing acrylic resin particles (glass transition temperature: 55°C) in water. The resin particle concentration of the resin particle dispersion (1) was 7% by mass, and the average primary particle size of the resin particles was 0.4 µm.

[0167] A polyethylene microporous membrane (thickness 5.9 μm, Gurley coefficient 90 sec / 100 mL) was passed through a pair of Mayer bars carrying an appropriate amount of coating liquid (1), and equal amounts of coating liquid (1) were applied to both sides of the polyethylene microporous membrane. The membrane was then immersed in a coagulation liquid (DMAc:TPG:water=38:2:60 [mass ratio], liquid temperature 25°C) to solidify the coating layer. The membrane was then washed in a water washing tank with water at a temperature of 25°C and dried to obtain a laminate comprising heat-resistant porous layers on both sides of the polyethylene microporous membrane. The laminate was then passed through a pair of bar coaters carrying an appropriate amount of resin particle dispersion liquid (1), and equal amounts of resin particle dispersion liquid (1) were applied to both sides of the laminate, followed by drying. Thus, a separator comprising a heat-resistant porous layer and an adhesive layer on both sides of the polyethylene microporous membrane was obtained. The coverage of the separator surface with acrylic resin particles was 40% on both sides.

[0168] -Preparation of positive electrode- A positive electrode slurry was prepared by mixing 89.5 parts by weight of lithium cobalt oxide powder (positive electrode active material), 4.5 parts by weight of acetylene black (conductive additive), 6 parts by weight of polyvinylidene fluoride (binder resin), and an appropriate amount of N-methyl-2-pyrrolidone in a twin-arm mixer. The positive electrode slurry was applied to both sides of a 20 μm-thick aluminum foil, dried, and pressed to obtain a positive electrode with positive electrode active material layers on both sides.

[0169] - Preparation of negative electrode - A negative electrode slurry was prepared by mixing 300 parts by weight of artificial graphite (negative electrode active material), 7.5 parts by weight of an aqueous dispersion containing 40% by weight of a modified styrene-butadiene copolymer (binder resin), 3 parts by weight of carboxymethyl cellulose (thickener), and an appropriate amount of water in a twin-arm mixer. The negative electrode slurry was applied to both sides of a 10 μm-thick copper foil, dried, and pressed to obtain a negative electrode with a negative electrode active material layer on both sides.

[0170] -Battery manufacturing- The positive and negative electrodes were each cut into a 30 mm × 50 mm rectangle, and a lead tab was welded to each. The separator was cut into a 35 mm × 55 mm rectangle. These were stacked so that the positive and negative electrodes alternated and a separator was sandwiched between them, producing a laminate consisting of three positive electrodes, three negative electrodes, and five separators. The laminate was inserted into an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was poured into the pack to allow the electrolyte to permeate the laminate. The pack and the laminate were then heat-pressed in the stacking direction using a heat press (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 5 minutes. A nonaqueous secondary battery was thus obtained. This nonaqueous secondary battery was subjected to evaluation tests for short-circuit resistance and cycle performance.

[0171] [Examples 2 to 9, Comparative Examples 1 to 3] Each separator was produced in the same manner as in Example 1, except that at least one of the polyethylene microporous membrane, the heat-resistant porous layer, and the adhesive layer was changed as shown in Table 1. The coverage of the separator surface with the acrylic resin particles was controlled by the coating amount of the resin particle dispersion (1). Each separator was used to produce a nonaqueous secondary battery.

[0172] The basis weight of the heat-resistant porous layer shown in Table 1 is the total basis weight of both sides of the separator. When the heat-resistant porous layer is present on both sides of the polyethylene microporous membrane, the basis weight of the heat-resistant porous layer per side is half the basis weight of the heat-resistant porous layer shown in Table 1.

[0173] [Table 1]

[0174] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. a polyolefin microporous membrane; a heat-resistant porous layer disposed on one or both sides of the polyolefin microporous membrane, the heat-resistant porous layer containing a heat-resistant resin having at least one of an amide bond and an imide bond in its molecule and inorganic particles; an adhesive layer containing adhesive resin particles, which is disposed on one or both sides of the laminate of the polyolefin microporous membrane and the heat-resistant porous layer; A separator for a non-aqueous secondary battery comprising: the polyolefin microporous membrane has a Gurley value of 99 seconds / 100 mL or less; the Gurley value of the nonaqueous secondary battery separator is 160 seconds / 100 mL or less; a difference between the Gurley value of the nonaqueous secondary battery separator and the Gurley value of the polyolefin microporous membrane is 20 seconds / 100 mL to 60 seconds / 100 mL; Separator for non-aqueous secondary batteries.

2. 2. The non-aqueous secondary battery separator according to claim 1, wherein a coverage of the adhesive resin particles on the surface of the non-aqueous secondary battery separator is 20% to 60% on each side on which the adhesive layer is disposed.

3. 2. The non-aqueous secondary battery separator according to claim 1, wherein the thickness of the non-aqueous secondary battery separator is 5 μm to 17 μm.

4. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the polyolefin microporous film has a thickness of 4 μm to 9 μm.

5. the heat-resistant porous layer is disposed on only one side of the polyolefin microporous membrane; The heat-resistant porous layer has a thickness of 0.5 μm to 4 μm. The separator for a non-aqueous secondary battery according to claim 1 .

6. the heat-resistant porous layers are disposed on both sides of the polyolefin microporous membrane; The heat-resistant porous layer has a total thickness of 1 μm to 8 μm on both sides. The separator for a non-aqueous secondary battery according to claim 1 .

7. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the pores of the polyolefin microporous membrane contain a heat-resistant resin having at least one of an amide bond and an imide bond in its molecule.

8. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the heat-resistant resin comprises at least one selected from the group consisting of wholly aromatic polyamides, polyimides, and polyamideimides.

9. 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.

10. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the adhesive resin particles include at least one selected from the group consisting of acrylic resin particles, polyvinylidene fluoride resin particles, and styrene-butadiene rubber particles.

11. A non-aqueous secondary battery separator according to any one of claims 1 to 10, wherein the separator is disposed between the positive electrode and the negative electrode; Electromotive force is generated by doping and dedoping of lithium ions. Non-aqueous secondary battery.

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