Separator for nonaqueous secondary battery, and nonaqueous secondary battery

Abstract

Provided is a separator for a nonaqueous secondary battery comprising: a polyolefin microporous membrane; a surface layer (FA) that is disposed on one surface of the polyolefin microporous membrane and contains a polyvinylidene fluoride resin and / or an acrylic resin; and a surface layer (C) that is disposed on the other surface of the polyolefin microporous membrane and contains a polyvinyl chloride resin.

Description

Separator for non-aqueous secondary batteries and non-aqueous secondary batteries

[0001] This disclosure relates to a separator for non-aqueous secondary batteries and a non-aqueous secondary battery.

[0002] The adhesion of the separator for non-aqueous secondary batteries to the electrodes is important from the following viewpoints: (1) To prevent the separator from peeling off the electrodes due to the expansion and contraction of the electrode active material layer during charging and discharging. (2) To increase the rigidity of the battery cell by adhering the separator to the electrodes, thereby preventing deformation of the battery cell due to the expansion and contraction of the electrode active material layer during charging and discharging. (3) To prevent the formation of an electrolyte layer between the electrodes and the separator, thereby increasing the energy density of the battery.

[0003] Separators are known that have a surface layer with excellent adhesion to electrodes. For example, Patent Document 1 discloses a separator for non-aqueous secondary batteries comprising a porous substrate, a heat-resistant layer containing barium sulfate particles and a binder resin, and a surface layer made of polyvinylidene fluoride resin particles and acrylic resin particles.

[0004] Japanese Patent Publication No. 2021-192385

[0005] Generally, the positive electrode active material layer is a composite layer in which an active material such as a lithium-containing transition metal oxide is bound with a binder resin made of polyvinylidene fluoride-based resin. A separator surface layer containing polyvinylidene fluoride-based resin or acrylic resin adheres easily to this composite layer. On the other hand, generally, the negative electrode active material layer is a composite layer in which an active material such as graphite is bound with a binder resin made of styrene-butadiene copolymer. Adhering a separator surface layer containing polyvinylidene fluoride-based resin or acrylic resin to this composite layer requires a relatively high-temperature, high-pressure bonding treatment. When a high-temperature, high-pressure bonding treatment is applied to adhere the separator surface layer to the electrode, the pores of the separator become clogged, impairing ion mobility and reducing the charge-discharge characteristics of the battery.

[0006] There are also the following problems with the high-temperature and high-pressure adhesion treatment of the separator to the electrode. If a high-temperature and high-pressure adhesion treatment is performed on a large-area battery such as an in-vehicle battery, the equipment required for the treatment becomes large-scale. In addition, the form of the exterior material for which the high-temperature and high-pressure adhesion treatment can be performed is limited. If the exterior material is a flat aluminum laminate film pack, it is easy to apply high temperature and high pressure, so the electrode and the separator can be housed in the exterior material and the adhesion treatment can be performed. On the other hand, it is difficult to effectively apply high temperature and high pressure to a metal can without damaging the metal can.

[0007] The present disclosure has been made in view of the above situation. An object of the present disclosure is to provide a separator for a non-aqueous secondary battery that exhibits excellent adhesiveness to both the positive electrode and the negative electrode by a relatively low-temperature and low-pressure adhesion treatment.

[0008] The following embodiments are included as specific means for solving the above problems: <1> A separator for a non-aqueous secondary battery, comprising: a polyolefin microporous membrane; a surface layer (FA) disposed on one surface of the polyolefin microporous membrane and containing a polyvinylidene fluoride resin and / or an acrylic resin; and a surface layer (C) disposed on the other surface of the polyolefin microporous membrane and containing a polyvinyl chloride resin. <2> The separator for a non-aqueous secondary battery according to <1>, further comprising an inorganic particle layer containing inorganic particles between the polyolefin microporous membrane and the surface layer (FA) and / or between the polyolefin microporous membrane and the surface layer (C), wherein the inorganic particles account for 90% by mass or more. <3> The separator for a non-aqueous secondary battery according to <2>, wherein the average primary particle size of the inorganic particles contained in the inorganic particle layer is 10 nm to 500 nm. <4> The separator for a non-aqueous secondary battery according to <2> or <3>, wherein the inorganic particles include at least one selected from the group consisting of γ-alumina particles, boehmite particles, and barium sulfate particles. <5> The separator for a non-aqueous secondary battery according to any one of <1> to <4>, further comprising a heat-resistant resin layer containing a heat-resistant resin, wherein the heat-resistant resin accounts for more than 10% by mass, between the polyolefin microporous membrane and the surface layer (FA) and / or between the polyolefin microporous membrane and the surface layer (C). <6> The separator for a non-aqueous secondary battery according to <5>, wherein the heat-resistant resin includes at least one selected from the group consisting of aromatic polyamide, polyimide, and polyamideimide. <7> The separator for a non-aqueous secondary battery according to <5> or <6>, wherein the heat-resistant resin layer further contains inorganic particles. <8> A separator for a non-aqueous secondary battery according to any one of <1> to <7>, wherein the average degree of polymerization of the polyvinyl chloride resin contained in the surface layer (C) is 500 to 1400. <9> A separator for a non-aqueous secondary battery according to any one of <1> to <8>, wherein the weight-average molecular weight of the polyvinylidene fluoride resin contained in the surface layer (FA) is 600,000 to 2,000,000. <10> A separator for a non-aqueous secondary battery according to any one of <1> to <9>, wherein the polyvinylidene fluoride resin includes a polyvinylidene fluoride resin having hexafluoropropylene units.<11> The separator for a non-aqueous secondary battery according to any one of <1> to <10>, wherein the acrylic resin is acrylic resin particles. <12> The surface layer (FA) is a surface layer (F) containing a polyvinylidene fluoride resin, and the surface layer (F) and / or the surface layer (C) further contains inorganic particles. The separator for a non-aqueous secondary battery according to any one of <1> to <11>. <13> The surface layer (FA) is a surface layer (A) containing an acrylic resin, and there is further provided a heat-resistant resin layer containing a heat-resistant resin and occupying more than 10% by mass between the polyolefin microporous membrane and the surface layer (A). The surface layer (A) is a layer formed by adhering acrylic resin particles to the heat-resistant resin layer. The separator for a non-aqueous secondary battery according to any one of <1> to <12>. <14> A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery according to any one of <1> to <13> disposed between the positive electrode and the negative electrode, and obtaining an electromotive force by doping and de-doping of lithium ions.

[0009] According to the present disclosure, a separator for a non-aqueous secondary battery is provided that exhibits excellent adhesion to both the positive electrode and the negative electrode by a relatively low-temperature and low-pressure adhesion treatment.

[0010] It is a schematic cross-sectional view of an example of the separator of the present disclosure. It is a schematic cross-sectional view of another example of the separator of the present disclosure. It is a schematic cross-sectional view of another example of the separator of the present disclosure. It is a schematic cross-sectional view of another example of the separator of the present disclosure. It is a schematic cross-sectional view of another example of the separator of the present disclosure. It is a schematic cross-sectional view of another example of the separator of the present disclosure. It is a graph showing the wet adhesion of the separator. It is a graph showing the cycle characteristics of the battery. It is a graph showing the wet adhesion of the separator.

[0011] Hereinafter, embodiments of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the embodiments.

[0012] In this disclosure, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples.

[0013] In this disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" may be A alone, B alone, or a combination of A and B.

[0014] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0015] When referring to the amount of each component in a composition in this disclosure, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition. In this disclosure, each component may contain multiple types of particles. If there are multiple types of particles corresponding to each component in the composition, the particle size of each component refers to the value for a mixture of those multiple particles present in the composition, unless otherwise specified.

[0016] In this disclosure, MD (Machine Direction) means the longitudinal direction in a separator manufactured in a long shape, and TD (Transverse Direction) means the direction perpendicular to MD in the planar direction of the separator. In this disclosure, TD is also referred to as the "width direction".

[0017] In this disclosure, when the stacking relationship of each layer constituting the separator is expressed as "upper layer" and "lower layer," the layer closer to the polyolefin microporous membrane is called the "lower layer," and the layer further away from the polyolefin microporous membrane is called the "upper layer."

[0018] In this disclosure, the volume of the porous layer excluding the voids is referred to as the "solids volume."

[0019] In this disclosure, the process of impregnating a separator with an electrolyte solution and then performing a heat press treatment is referred to as "wet heat press," and the process of performing a heat press treatment without impregnating the separator with an electrolyte solution is referred to as "dry heat press."

[0020] In this disclosure, "monomer unit" of a polymer or resin means a constituent unit of a polymer or resin, which is formed by the polymerization of monomers. In this disclosure, the notation "(meth)acrylic" means that either "acrylic" or "methacrylic" is acceptable.

[0021] <Separator for Non-Aqueous Secondary Battery> The separator for non-aqueous secondary battery of the present disclosure (also simply referred to as "separator" in this disclosure) comprises a polyolefin microporous membrane, a surface layer (FA) disposed on one side of the polyolefin microporous membrane containing a polyvinylidene fluoride resin and / or an acrylic resin, and a surface layer (C) disposed on the other side of the polyolefin microporous membrane containing a polyvinyl chloride resin.

[0022] The separator of this disclosure has one outermost layer which is a surface layer (FA) and the other outermost layer which is a surface layer (C).

[0023] The separator of this disclosure has a surface layer (FA) containing a polyvinylidene fluoride resin that exhibits excellent adhesion to the positive electrode, and a surface layer (C) containing a polyvinyl chloride resin that exhibits excellent adhesion to the negative electrode. The separator of this disclosure exhibits excellent adhesion to both the positive and negative electrodes by bonding treatment at relatively low temperature and low pressure.

[0024] The surface layer (FA) contains at least one of a polyvinylidene fluoride resin and an acrylic resin. In this disclosure, a surface layer containing at least a polyvinylidene fluoride resin is referred to as surface layer (F), and a surface layer containing at least an acrylic resin is referred to as surface layer (A).

[0025] The details of the polyolefin microporous membrane and each layer of the separator of this disclosure are described below.

[0026] [Polyolefin Microporous Membrane] A polyolefin microporous membrane refers to a microporous membrane containing polyolefin. A microporous membrane is a membrane that has a large number of micropores inside, with the micropores interconnected, allowing gas or liquid to pass from one side to the other.

[0027] The separator of this disclosure has a shutdown function by comprising a polyolefin microporous membrane. The shutdown function refers to a function that prevents thermal runaway of the battery by blocking ion movement when the battery temperature rises, as the constituent material of the porous structure melts and the pores of the porous structure become blocked.

[0028] Examples of polyolefin microporous membranes include those used in conventional battery separators, and it is preferable to select one from among these that has sufficient mechanical properties and ion permeability.

[0029] From the viewpoint of exhibiting a shutdown function, a polyethylene-containing microporous membrane (hereinafter referred to as "polyethylene microporous membrane") is preferred among the polyolefin microporous membranes. The polyethylene content is preferably 95% by mass or more relative to the mass of the polyethylene microporous membrane.

[0030] From the viewpoint of possessing heat resistance that prevents the film from easily breaking when exposed to high temperatures, polyolefin microporous membranes containing polypropylene are preferred.

[0031] From the viewpoint of possessing both a shutdown function and heat resistance that prevents easy rupture when exposed to high temperatures, polyolefin microporous membranes containing polyethylene and polypropylene are preferred. Examples of polyolefin microporous membranes containing polyethylene and polypropylene include microporous membranes in which polyethylene and polypropylene are mixed in a single layer. In such microporous membranes, from the viewpoint of achieving both a shutdown function and heat resistance, it is preferable to include 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. From the viewpoint of achieving both a shutdown function and heat resistance, polyolefin microporous membranes having a laminated structure of two or more layers, in which at least one layer contains polyethylene and at least one layer contains polypropylene, are also preferred.

[0032] The polyolefin used in the polyolefin microporous membrane is preferably one with a weight-average molecular weight (Mw) of 100,000 to 5,000,000. A polyolefin with an Mw of 100,000 or more provides sufficient mechanical properties to the microporous membrane. A polyolefin with an Mw of 5,000,000 or less exhibits good shutdown characteristics and facilitates the molding of the microporous membrane.

[0033] Methods for producing polyolefin microporous membranes include: a method in which molten polyolefin resin is extruded from a T-die to form a sheet, which is then crystallized, stretched, and subsequently heat-treated to form a microporous membrane; and a method in which molten polyolefin resin together with a plasticizer such as liquid paraffin is extruded from a T-die, which is then cooled to form a sheet, stretched, the plasticizer is extracted, and then heat-treated to form a microporous membrane.

[0034] - Characteristics of Polyolefin Microporous Films - From the viewpoint of mechanical strength, the thickness of the polyolefin microporous film 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 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 area using a contact-type length measuring instrument and averaging the results.

[0035] The porosity of the polyolefin microporous membrane is preferably 30% to 60% from the viewpoint of excellent electrolyte permeability and ion permeability. The porosity ε (%) of the polyolefin microporous membrane is calculated by the following formula: ε = {1 - Ws / (ds・t)} × 100 where Ws is the mass per unit area (i.e., basis weight) (g / m²) of the polyolefin microporous membrane. ２ ), ds is the true density (g / cm³) of the polyolefin microporous membrane. ３ ), t is the thickness of the polyolefin microporous membrane (μm).

[0036] From the viewpoint of suppressing internal short circuits in the battery, the air permeability of the polyolefin microporous membrane is preferably 80 seconds / 100 mL or more, more preferably 90 seconds / 100 mL or more, and even more preferably 100 seconds / 100 mL or more. From the viewpoint of excellent electrolyte permeability and ion permeability, the air permeability of the polyolefin microporous membrane 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. The air permeability of the polyolefin microporous membrane is the value measured using a Gurley densometer in accordance with JIS P8117:2009 "Paper and cardboard - Test methods for air permeability and air permeability resistance (intermediate region) - Gurley method".

[0037] [Surface layer (F)] The surface layer (F) contains at least a polyvinylidene fluoride resin. The surface layer (F) may contain other components besides the polyvinylidene fluoride resin. The surface layer (F) may contain inorganic particles.

[0038] The surface layer (F) has a porous structure. Examples of the porous structure of the surface layer (F) include the following forms.

[0039] - A structure in which fibrils containing polyvinylidene fluoride resin are linked together in a two-dimensional or three-dimensional network. - A structure in which fibrils containing polyvinylidene fluoride resin are linked together in a two-dimensional or three-dimensional network, and inorganic particles are bound to or trapped in the fibrils. - A network microporous membrane containing polyvinylidene fluoride resin. - A structure in which inorganic particles are bound to or trapped in a network microporous membrane containing polyvinylidene fluoride resin. - A layered structure in which polyvinylidene fluoride resin links many inorganic particles together, with voids between the inorganic particles. - A layered structure in which polyvinylidene fluoride resin particles are arranged adjacent to each other in a two-dimensional or three-dimensional manner, with voids between the particles. - A layered structure in which polyvinylidene fluoride resin particles and inorganic particles are arranged adjacent to each other in a two-dimensional or three-dimensional manner, with voids between the particles. - A layered structure in which polyvinylidene fluoride-based resin particles are scattered on a polyolefin microporous membrane or other layer.

[0040] As an example of an embodiment of the surface layer (F), a layer in which polyvinylidene fluoride resin particles are attached to a polyolefin microporous membrane or other layer is provided. From the viewpoint of ion permeability of the surface layer (F), the average primary particle size of the polyvinylidene fluoride resin particles is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. From the viewpoint of thinning the surface layer (F) and suppressing delamination between the surface layer (F) and the polyolefin microporous membrane or other layer, and maintaining adhesion of the separator to the electrode, the average primary particle size of the polyvinylidene fluoride resin particles is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less.

[0041] The average primary particle size of polyvinylidene fluoride resin particles is determined by measuring the major axis of 100 randomly selected polyvinylidene fluoride resin particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is either polyvinylidene fluoride resin particles that form the surface layer (F), or polyvinylidene fluoride resin particles extracted from the surface layer (F).

[0042] When the surface layer (F) contains polyvinylidene fluoride resin particles, in a separator that is bonded to an electrode, some or all of the polyvinylidene fluoride resin particles contained in the surface layer (F) may melt due to the heat applied to bond the separator to the electrode, causing adjacent polyvinylidene fluoride resin particles to connect, and some or all of them may not maintain their particle shape.

[0043] -Polyvinylidene fluoride resins- Examples of polyvinylidene fluoride resins include: homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride and halogen-containing monomers; copolymers of vinylidene fluoride and monomers other than halogen-containing monomers; copolymers of vinylidene fluoride, halogen-containing monomers, and monomers other than halogen-containing monomers; and mixtures thereof. Examples of halogen-containing monomers include hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene. Copolymers include alternating copolymers, random copolymers, block copolymers, and graft copolymers.

[0044] Polyvinylidene fluoride resins may be used individually or in mixtures of two or more types.

[0045] The total weight-average molecular weight (Mw) of the polyvinylidene fluoride resin contained in the surface layer (F) is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more, from the viewpoint of preventing blockage of the pores in the surface layer (F) when heat is applied to the separator during battery manufacturing. The total Mw of the polyvinylidene fluoride resin contained in the surface layer (F) is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,200,000 or less, from the viewpoint of allowing the polyvinylidene fluoride resin to soften appropriately when heat is applied to the separator during battery manufacturing, and ensuring good adhesion between the surface layer (F) and the electrodes.

[0046] The total Mw of the polyvinylidene fluoride resin contained in the surface layer (F) is the molecular weight in polystyrene equivalent, measured by gel permeation chromatography (GPC). The polyvinylidene fluoride resin extracted from the surface layer (F) or the polyvinylidene fluoride resin used to form the surface layer (F) is used as the sample.

[0047] As a polyvinylidene fluoride-based resin, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer) is preferred from the viewpoint of adhesion to electrodes. In this disclosure, the VDF-HFP copolymer includes both copolymers obtained by polymerizing only VDF and HFP, and copolymers obtained by polymerizing VDF, HFP, and other monomers. By increasing or decreasing the HFP content, the crystallinity, heat resistance, and degree of swelling in the electrolyte of the VDF-HFP copolymer can be controlled to an appropriate range.

[0048] The polyvinylidene fluoride resin preferably contains the following polyvinylidene fluoride resin (1) and polyvinylidene fluoride resin (2).

[0049] - Polyvinylidene fluoride resin (1): 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 greater than 1.5 mol% and 5 mol% or less. - Polyvinylidene fluoride resin (2): 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 greater than 5 mol% and 15 mol% or less.

[0050] Polyvinylidene fluoride resins (1) and (2) may each contain monomers other than VDF and HFP as polymerization components. Examples of other monomers include halogen-containing monomers such as tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene.

[0051] The polyvinylidene fluoride resins (1) and (2) each preferably have a total of 80 mol% or more of VDF and HFP in relation to the total of halogen-containing monomers, more preferably 90 mol% or more, and even more preferably 100 mol%.

[0052] The polyvinylidene fluoride resin (1) facilitates the development of a fine porous structure in the surface layer (F), and also suppresses excessive swelling of the polyvinylidene fluoride resin in relation to the electrolyte, thus preventing pore blockage. The polyvinylidene fluoride resin (2) prevents the porosity and average pore diameter of the surface layer (F) from becoming too large, and ensures high mobility of the polymer chains when heated and easy swelling in relation to the electrolyte, resulting in good adhesion between the surface layer (F) and the electrode.

[0053] The polyvinylidene fluoride resins (1) and (2) each preferably have a weight-average molecular weight (Mw) of 600,000 to 2,000,000. When the Mw of the polyvinylidene fluoride resins (1) and (2) is 600,000 or more, the surface layer (F) can be made to have mechanical properties that can withstand bonding treatment with the electrode, resulting in superior adhesion to the electrode. From this viewpoint, the Mw of the polyvinylidene fluoride resins (1) and (2) is more preferably 700,000 or more, and even more preferably 800,000 or more. When the Mw of the polyvinylidene fluoride resins (1) and (2) each is 2,000,000 or less, the resin softens easily by hot pressing, making it easier for the surface layer (F) to adhere to the electrode. Furthermore, the viscosity of the coating liquid used for coating and molding the surface layer (F) does not become too high, resulting in good moldability and crystal formation, and good porosity of the surface layer (F). From this perspective, the Mw of polyvinylidene fluoride resins (1) and (2) is more preferably 1.5 million or less, and even more preferably 1.2 million or less.

[0054] The weighted average of the Mw of polyvinylidene fluoride resin (1) and polyvinylidene fluoride resin (2) contained in the surface layer (F) (the average weighted by the content ratio (mass basis) of the Mw of both resins) is preferably 600,000 to 2,000,000 from the viewpoint of the ion permeability of the surface layer (F) and adhesion to the electrode. The lower limit of the weighted average is more preferably 700,000 or more, and even more preferably 800,000 or more, and the upper limit of the weighted average is more preferably 1,500,000 or less, and even more preferably 1,200,000 or less.

[0055] Preferably, the proportion of polyvinylidene fluoride resin (1) in the total amount of polyvinylidene fluoride resin (1) and polyvinylidene fluoride resin (2) contained in the surface layer (F) is 15% to 85% by mass (the proportion of polyvinylidene fluoride resin (2) is 15% to 85% by mass). When polyvinylidene fluoride resin (1) accounts for 15% by mass or more of the total amount of polyvinylidene fluoride resin (1) and polyvinylidene fluoride resin (2), a fine porous structure is easily developed in the surface layer (F), and excessive swelling of the polyvinylidene fluoride resin in relation to the electrolyte is suppressed, making pore blockage less likely. On the other hand, if the polyvinylidene fluoride resin (2) is 15% by mass or more of the total amount of polyvinylidene fluoride resin (1) and polyvinylidene fluoride resin (2), then high mobility of the polymer chains when heated and ease of swelling in the electrolyte are ensured. From the above viewpoint, the proportion of polyvinylidene fluoride resin (1) to the total amount of polyvinylidene fluoride resin (1) and polyvinylidene fluoride resin (2) is preferably 15% by mass to 85% by mass, preferably 30% by mass to 85% by mass, and more preferably 45% by mass to 85% by mass.

[0056] In a form in which the surface layer (F) contains polyvinylidene fluoride resins (1) and (2), the total proportion of polyvinylidene fluoride resins (1) and (2) to the total resin contained in the surface layer (F) is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0057] -Other Resins- The surface layer (F) may contain resins other than polyvinylidene fluoride resins. Examples of other resins include acrylic resins, butadiene-acrylonitrile resins, fluororubber, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethylcellulose, hydroxyalkylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyethers (polyethylene oxide, polypropylene oxide, etc.). These resins may be used individually or in mixtures of two or more.

[0058] The mass percentage of other resins in the total resin of the surface layer (F) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. The mass percentage of polyvinylidene fluoride resin in the total resin of the surface layer (F) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0059] - Inorganic particles - The surface layer (F) may contain inorganic particles. From the viewpoint of increasing the rigidity of the separator, it is preferable that the surface layer (F) contains inorganic particles.

[0060] Examples of inorganic particles include metal oxide particles, metal hydroxide particles, metal sulfate particles, metal carbonate particles, metal nitride particles, and clay mineral particles.

[0061] Examples of metal oxides constituting 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 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 metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred. Examples of metal carbonates constituting metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides constituting metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0062] The inorganic particles may be inorganic particles whose surface has been modified with a silane coupling agent or the like.

[0063] Inorganic particles may be used individually or in combination of two or more types.

[0064] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0065] There are no limitations on the particle shape of the inorganic particles; they may be spherical, elliptical, plate-shaped, needle-shaped, or irregularly shaped. From the viewpoint of suppressing internal short circuits in the battery, the inorganic particles contained in the surface layer (F) are preferably plate-shaped particles or non-aggregated primary particles.

[0066] The average primary particle size of the inorganic particles contained in the surface layer (F) is preferably 0.01 μm to 1 μm, more preferably 0.1 μm to 1 μm, and even more preferably 0.5 μm to 1 μm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the polyolefin microporous membrane or other layers.

[0067] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the surface layer (F), or inorganic particles extracted from the surface layer (F). There are no restrictions on the method for extracting inorganic particles from the surface layer (F). For example, the method involves immersing the surface layer (F) peeled from the separator in an organic solvent that dissolves polyvinylidene fluoride resin to dissolve the polyvinylidene fluoride resin and extract the inorganic particles; or heating the surface layer (F) peeled from the separator to about 800°C to remove the polyvinylidene fluoride resin and extract the inorganic particles; and so on.

[0068] In a form in which the surface layer (F) contains inorganic particles, the mass ratio of inorganic particles to the surface layer (F) is preferably 40% to 90% by mass, more preferably 50% to 80% by mass, and even more preferably 60% to 70% by mass, from the viewpoint of increasing the rigidity of the separator and the adhesion of the surface layer (F) to the electrode.

[0069] In a form in which the surface layer (F) does not contain inorganic particles, the mass percentage of polyvinylidene fluoride resin in the surface layer (F) is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0070] In one example of the embodiments of the separator of this disclosure, the mass ratio of inorganic particles in the surface layer (F) may be 0% to 10% by mass, 0% to 5% by mass, or 0% by mass.

[0071] -Other Components- The surface layer (F) may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the surface layer (F) to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the surface layer (F) to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0072] - Characteristics of the surface layer (F) - From the viewpoint of adhesion to the electrodes, the thickness of the surface layer (F) is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more. From the viewpoint of the energy density of the battery, the thickness of the surface layer (F) is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less.

[0073] The thickness of the surface layer (F) is obtained by subtracting the thickness of the flat film (with the surface layer (F) removed) from the thickness of the separator. The thicknesses of the separator and the flat film are determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument and averaging the results.

[0074] The mass per unit area (i.e., basis weight) of the surface layer (F) is 0.8 g / m² from the viewpoint of adhesion to the electrode. ２ Preferably, it is 1.0 g / m ２ The above is more preferable, specifically 1.2 g / m ２ The above is even more preferable. The mass per unit area (i.e., basis weight) of the surface layer (F) is 2.5 g / m² from the viewpoint of the energy density of the battery.２ Preferably, it is 2.0 g / m ２ The following is more preferable: 1.8 g / m ２ The following is even more preferable.

[0075] The mass per unit area (i.e., basis weight) of the surface layer (F) is calculated by subtracting the mass of the flat film with the surface layer (F) removed from the mass of a separator cut to 20 cm x 20 cm, and then dividing the difference in mass by the area.

[0076] [Surface layer (A)] The surface layer (A) contains at least an acrylic resin. The surface layer (A) may also contain other components besides the acrylic resin. The surface layer (A) may also contain inorganic particles.

[0077] The surface layer (A) has a porous structure. Examples of the porous structure of the surface layer (A) include the following forms.

[0078] - A structure in which fibrils containing acrylic resin are linked together in a two-dimensional or three-dimensional network. - A structure in which fibrils containing acrylic resin are linked together in a two-dimensional or three-dimensional network, and inorganic particles are bound to or trapped in the fibrils. - A network microporous membrane containing acrylic resin. - A structure in which inorganic particles are bound to or trapped in a network microporous membrane containing acrylic resin. - A layered structure in which acrylic resin links many inorganic particles together, with voids between the inorganic particles. - A layered structure in which acrylic resin particles are arranged adjacent to each other in a two-dimensional or three-dimensional manner, with voids between the particles. - A layered structure in which acrylic resin particles and inorganic particles are arranged adjacent to each other in a two-dimensional or three-dimensional manner, with voids between the particles. - A layered structure in which acrylic resin particles are scattered on a polyolefin microporous membrane or other layer.

[0079] As an example of an embodiment of the surface layer (A), a layer in which acrylic resin particles are attached to a polyolefin microporous film or other layer is included. From the viewpoint of ion permeability of the surface layer (A), the average primary particle size of the acrylic resin particles is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. From the viewpoint of thinning the surface layer (A) and suppressing delamination between the surface layer (A) and the polyolefin microporous film or other layer, and maintaining adhesion of the separator to the electrode, the average primary particle size of the acrylic resin particles is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less.

[0080] The average primary particle size of acrylic resin particles is determined by measuring the major axis of 100 randomly selected acrylic resin particles during scanning electron microscopy (SEM) observation and averaging the major axes of these 100 particles. The sample used for SEM observation is either acrylic resin particles that form the surface layer (A), or acrylic resin particles extracted from the surface layer (A).

[0081] When the surface layer (A) contains acrylic resin particles, in a separator that is bonded to an electrode, some or all of the acrylic resin particles contained in the surface layer (A) may melt due to the heat applied to bond the separator to the electrode, causing adjacent acrylic resin particles to connect and resulting in some or all of them not maintaining their particle shape.

[0082] - Acrylic Resins - Examples of acrylic resins include homopolymers or copolymers of acrylic monomers; copolymers of acrylic monomers and styrene monomers. Copolymers include alternating copolymers, random copolymers, block copolymers, and graft copolymers. Acrylic resins may be used individually or in mixtures of two or more types.

[0083] 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. Alkyl (meth)acrylate esters are preferred as the acrylic monomers. The alkyl group in the ester portion of the alkyl (meth)acrylate ester is preferably a C1-C10 alkyl group, and more preferably a C1-C8 alkyl group. The acrylic monomers may be used individually or in combination of two or more.

[0084] 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. Styrene and α-methylstyrene are preferred as styrene monomers, with styrene being more preferred. Styrene monomers may be used individually or in combination of two or more.

[0085] -Other Resins- The surface layer (A) may contain resins other than acrylic resins. Examples of other resins include polyvinylidene fluoride resins, butadiene-acrylonitrile resins, fluororubber, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethylcellulose, hydroxyalkylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyethers (polyethylene oxide, polypropylene oxide, etc.). These resins may be used individually or in mixtures of two or more.

[0086] The mass percentage of other resins in the total resin of the surface layer (A) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. The mass percentage of acrylic resin in the total resin of the surface layer (A) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0087] - Inorganic particles - The surface layer (A) may contain inorganic particles. From the viewpoint of increasing the rigidity of the separator, it is preferable that the surface layer (A) contains inorganic particles.

[0088] Examples of inorganic particles include metal oxide particles, metal hydroxide particles, metal sulfate particles, metal carbonate particles, metal nitride particles, and clay mineral particles.

[0089] Examples of metal oxides constituting 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 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 metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred. Examples of metal carbonates constituting metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides constituting metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0090] The inorganic particles may be inorganic particles whose surface has been modified with a silane coupling agent or the like.

[0091] Inorganic particles may be used individually or in combination of two or more types.

[0092] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0093] There are no limitations on the particle shape of the inorganic particles; they may be spherical, elliptical, plate-shaped, needle-shaped, or irregularly shaped. From the viewpoint of suppressing internal short circuits in the battery, the inorganic particles contained in the surface layer (A) are preferably plate-shaped particles or non-aggregated primary particles.

[0094] The average primary particle size of the inorganic particles contained in the surface layer (A) is preferably 0.01 μm to 1 μm, more preferably 0.1 μm to 1 μm, and even more preferably 0.5 μm to 1 μm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the polyolefin microporous membrane or other layers.

[0095] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the surface layer (A), or inorganic particles extracted from the surface layer (A). There are no restrictions on the method of extracting inorganic particles from the surface layer (A). For example, this method involves immersing the surface layer (A) peeled from the separator in an organic solvent that dissolves acrylic resin to dissolve the acrylic resin and extract the inorganic particles; or heating the surface layer (A) peeled from the separator to about 800°C to remove the acrylic resin and extract the inorganic particles; and so on.

[0096] In a form in which the surface layer (A) contains inorganic particles, the mass ratio of inorganic particles to the surface layer (A) is preferably 40% to 90% by mass, more preferably 50% to 80% by mass, and even more preferably 60% to 70% by mass, from the viewpoint of increasing the rigidity of the separator and the adhesion of the surface layer (A) to the electrode.

[0097] In a form in which the surface layer (A) does not contain inorganic particles, the mass percentage of acrylic resin in the surface layer (A) is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0098] In one example of the separator embodiment of the present disclosure, the mass ratio of inorganic particles in the surface layer (A) may be 0% to 10% by mass, 0% to 5% by mass, or 0% by mass.

[0099] - Other Components - The surface layer (A) may contain additives such as a dispersant, a wetting agent, an antifoaming agent, and a pH adjuster. The dispersant is added to the coating liquid for forming the surface layer (A) for the purpose of improving dispersibility, coating property, or storage stability. The wetting agent, the antifoaming agent, and the pH adjuster are added to the coating liquid for forming the surface layer (A) for the purpose of improving the compatibility with the polyolefin microporous membrane or other layers, suppressing air entrainment into the coating liquid, or adjusting the pH.

[0100] - Characteristics of the Surface Layer (A) - From the viewpoint of adhesion to the electrode, the thickness of the surface layer (A) is preferably 0.5 μm or more, more preferably 0.8 μm or more, and still more preferably 1 μm or more. From the viewpoint of the energy density of the battery, the thickness of the surface layer (A) is preferably 3 μm or less, more preferably 2.5 μm or less, and still more preferably 2 μm or less.

[0101] The thickness of the surface layer (A) is a value obtained by subtracting the thickness of the flat membrane from which the surface layer (A) has been removed from the thickness of the separator. The thicknesses of the separator and the flat membrane are determined by measuring 20 points within a 10 cm square using a contact type length measuring instrument and averaging them.

[0102] The mass per unit area (i.e., basis weight) of the surface layer (A) is preferably 0.1 g / m ２ or more, more preferably 0.2 g / m ２ or more, and still more preferably 0.3 g / m ２ or more, from the viewpoint of adhesion to the electrode. The mass per unit area (i.e., basis weight) of the surface layer (A) is preferably 0.8 g / m ２ or less, more preferably 0.5 g / m ２ or less, and still more preferably 0.3 g / m ２ or less, from the viewpoint of the energy density of the battery.

[0103] The mass per unit area (i.e., basis weight) of the surface layer (A) is obtained by subtracting the mass of the flat membrane from which the surface layer (A) has been removed from the mass of the separator cut out into a 20 cm × 20 cm square and dividing the difference in mass by the area.

[0104] [Surface layer (C)] The surface layer (C) contains at least a polyvinyl chloride resin. The surface layer (C) may contain other components besides the polyvinyl chloride resin. The surface layer (C) may contain inorganic particles.

[0105] The surface layer (C) has a porous structure. Examples of the porous structure of the surface layer (C) include the following forms.

[0106] - A structure in which fibrils containing polyvinyl chloride resin are linked together in a two-dimensional or three-dimensional network. - A structure in which fibrils containing polyvinyl chloride resin are linked together in a two-dimensional or three-dimensional network, and inorganic particles are bound to or trapped in the fibrils. - A network microporous membrane containing polyvinyl chloride resin. - A structure in which inorganic particles are bound to or trapped in a network microporous membrane containing polyvinyl chloride resin. - A layered structure in which polyvinyl chloride resin links many inorganic particles together, with voids between the inorganic particles. - A layered structure in which polyvinyl chloride resin particles are arranged adjacent to each other in a two-dimensional or three-dimensional manner, with voids between the particles. - A layered structure in which polyvinyl chloride resin particles and inorganic particles are arranged adjacent to each other in a two-dimensional or three-dimensional manner, with voids between the particles. - A layered structure in which polyvinyl chloride resin particles are scattered on a polyolefin microporous membrane or other layer.

[0107] As an example of an embodiment of the surface layer (C), a layer in which polyvinyl chloride resin particles are attached to a polyolefin microporous membrane or other layer is provided. From the viewpoint of ion permeability of the surface layer (C), the average primary particle size of the polyvinyl chloride resin particles is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. From the viewpoint of thinning the surface layer (C) and suppressing delamination between the surface layer (C) and the polyolefin microporous membrane or other layer, and maintaining adhesion of the separator to the electrode, the average primary particle size of the polyvinyl chloride resin particles is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less.

[0108] The average primary particle size of polyvinyl chloride resin particles is determined by measuring the major axis of 100 randomly selected polyvinyl chloride resin particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is polyvinyl chloride resin particles that form the surface layer (C), or polyvinyl chloride resin particles extracted from the surface layer (C).

[0109] When the surface layer (C) contains polyvinyl chloride resin particles, in a separator that is bonded to an electrode, some or all of the polyvinyl chloride resin particles contained in the surface layer (C) may melt due to the heat applied to bond the separator to the electrode, causing adjacent polyvinyl chloride resin particles to connect, and some or all of them may not maintain their particle shape.

[0110] -Polyvinyl Chloride Resins- Polyvinyl chloride resins include homopolymers of vinyl chloride (also known as chloroethylene) (i.e., polyvinyl chloride) and copolymers of vinyl chloride with other monomers. Copolymers include alternating copolymers, random copolymers, block copolymers, and graft copolymers. In this disclosure, polyvinyl chloride resin means a resin in which vinyl chloride has the highest number proportion among the monomers constituting the resin.

[0111] Examples of monomers other than vinyl chloride that constitute polyvinyl chloride resins include vinyl acetate, alkenes (e.g., ethene, propene, butene, pentene, hexene, etc.), dienes (e.g., butadiene, isoprene, etc.), styrene, α-methylstyrene, alkyl-substituted styrenes (e.g., 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), vinylidene chloride, acrylonitrile, (meth)acrylic acid, (meth)acrylic acid esters, urethane monomers, etc.

[0112] From the viewpoint of adhesion of the surface layer (C) to the electrode, the polyvinyl chloride resin preferably has a polyvinyl chloride content of 50% to 100% of the total monomers constituting the polyvinyl chloride resin, more preferably 70% to 100%, and even more preferably 90% to 100%.

[0113] The polyvinyl chloride resin contained in the surface layer (C) may be one type or two or more types.

[0114] The polyvinyl chloride resin contained in the surface layer (C) preferably has an average degree of polymerization of 500 to 1400, more preferably 550 to 1200, and even more preferably 600 to 1000. When the average degree of polymerization of the polyvinyl chloride resin is 500 or higher, the surface layer (C) has excellent mechanical strength and is less likely to peel off from the electrode. From this viewpoint, the average degree of polymerization of the polyvinyl chloride resin is more preferably 550 or higher, and even more preferably 600 or higher. When the average degree of polymerization of the polyvinyl chloride resin is 1400 or lower, a porous structure is easily formed in the surface layer (C), and the permeability of the electrolyte and ion permeability in the surface layer (C) are excellent. Furthermore, when the average degree of polymerization of the polyvinyl chloride resin is 1400 or lower, high mobility of the polymer chains when heated and ease of swelling in the electrolyte are ensured, so the surface layer (C) adheres easily to the electrode by either dry heat pressing or wet heat pressing. Furthermore, if the average degree of polymerization of the polyvinyl chloride resin is 1400 or less, the viscosity of the coating liquid used to form the surface layer (C) is relatively low, and the coating liquid exhibits excellent applicability. From these viewpoints, it is more preferable that the average degree of polymerization of the polyvinyl chloride resin be 1200 or less, and even more preferable that it be 1000 or less.

[0115] -Other Resins- The surface layer (C) may contain resins other than polyvinyl chloride resins. Examples of other resins include acrylic resins, butadiene-acrylonitrile resins, fluororubber, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethylcellulose, hydroxyalkylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyethers (polyethylene oxide, polypropylene oxide, etc.). These resins may be used individually or in mixtures of two or more.

[0116] The mass percentage of other resins in the total resin of the surface layer (C) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. The mass percentage of polyvinyl chloride resin in the total resin of the surface layer (C) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0117] - Inorganic particles - The surface layer (C) may contain inorganic particles. From the viewpoint of increasing the rigidity of the separator, it is preferable that the surface layer (C) contains inorganic particles.

[0118] In a separator having a surface layer (F), the embodiments of the inorganic particles contained in the surface layer (C) are preferably the same as the embodiments of the inorganic particles contained in the surface layer (F). The description of the inorganic particles relating to the surface layer (F) is applied to the surface layer (C) by replacing "surface layer (F)" with "surface layer (C)".

[0119] In a separator having a surface layer (A), the embodiments of the inorganic particles contained in the surface layer (C) are preferably the same as the embodiments of the inorganic particles contained in the surface layer (A). The description of the inorganic particles relating to the surface layer (A) is applied to the surface layer (C) by replacing "surface layer (A)" with "surface layer (C)".

[0120] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0121] The average primary particle size of the inorganic particles contained in the surface layer (C) is preferably 0.01 μm to 1 μm, more preferably 0.1 μm to 1 μm, and even more preferably 0.5 μm to 1 μm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the polyolefin microporous membrane or other layers.

[0122] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the surface layer (C), or inorganic particles extracted from the surface layer (C). There are no restrictions on the method for extracting inorganic particles from the surface layer (C). For example, this method involves immersing the surface layer (C) peeled from the separator in an organic solvent that dissolves polyvinyl chloride resin to dissolve the polyvinyl chloride resin and extract the inorganic particles; or heating the surface layer (C) peeled from the separator to about 800°C to remove the polyvinyl chloride resin and extract the inorganic particles; and so on.

[0123] In a form in which the surface layer (C) contains inorganic particles, the mass ratio of inorganic particles to the surface layer (C) is preferably 40% to 90% by mass, more preferably 50% to 80% by mass, and even more preferably 60% to 70% by mass, from the viewpoint of increasing the rigidity of the separator and the adhesion of the surface layer (C) to the electrode.

[0124] In a form in which the surface layer (C) does not contain inorganic particles, the mass ratio of polyvinyl chloride resin to the surface layer (C) is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0125] In one example of the separator embodiment of the present disclosure, the mass percentage of inorganic particles in the surface layer (C) may be 0% to 10% by mass, 0% to 5% by mass, or 0% by mass.

[0126] -Other Components- The surface layer (C) may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the surface layer (C) to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the surface layer (C) to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0127] - Characteristics of the surface layer (C) - From the viewpoint of adhesion to the electrodes, the thickness of the surface layer (C) is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more. From the viewpoint of the energy density of the battery, the thickness of the surface layer (C) is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less.

[0128] The thickness of the surface layer (C) is the thickness of the separator minus the thickness of the flat film after removing the surface layer (C). The thickness of the separator and the flat film are determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument and averaging the results.

[0129] The mass per unit area (i.e., basis weight) of the surface layer (C) is 0.8 g / m² from the viewpoint of adhesion to the electrode. ２ Preferably, it is 1.0 g / m ２ The above is more preferable, specifically 1.2 g / m ２ The above is even more preferable. The mass per unit area (i.e., basis weight) of the surface layer (C) is 2.5 g / m² from the viewpoint of the energy density of the battery. ２ Preferably, it is 2.0 g / m ２ The following is more preferable: 1.8 g / m ２ The following is even more preferable.

[0130] The mass per unit area (i.e., basis weight) of the surface layer (C) is calculated by subtracting the mass of the flat film from which the surface layer (C) has been removed from the mass of a separator cut to 20 cm x 20 cm, and then dividing the difference in mass by the area.

[0131] [Inorganic Particle Layer] The separator of this disclosure may include an inorganic particle layer containing inorganic particles between the polyolefin microporous membrane and the surface layer (FA), and / or between the polyolefin microporous membrane and the surface layer (C).

[0132] A separator having a surface layer (F) may include an inorganic particle layer containing inorganic particles between the polyolefin microporous membrane and the surface layer (F), and / or between the polyolefin microporous membrane and the surface layer (C).

[0133] A separator having a surface layer (A) may include an inorganic particle layer containing inorganic particles between the polyolefin microporous membrane and the surface layer (A), and / or between the polyolefin microporous membrane and the surface layer (C).

[0134] In the separator of this disclosure, the inorganic particle layer is a porous layer in which the mass ratio of inorganic particles to the total mass of the layer is 90% by mass or more. In this disclosure, a porous layer is a layer having a large number of micropores inside, with a structure in which the micropores are connected, and through which a gas or liquid can pass from one surface to the other.

[0135] Examples of embodiments of a separator comprising an inorganic particle layer include the following embodiments (1) to (3).

[0136] Embodiment (1): A separator having an inorganic particle layer between a polyolefin microporous membrane and a surface layer (FA), and having an inorganic particle layer between a polyolefin microporous membrane and a surface layer (C). In this separator, one inorganic particle layer and the other inorganic particle layer may be the same or different in terms of components and / or composition.

[0137] Morphology (2): A separator having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (FA), and not having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (C).

[0138] Morphology (3): A separator having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (C), and not having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (FA).

[0139] The inorganic particle layer contains at least inorganic particles and optionally a binder resin.

[0140] From the viewpoint of improving the impact resistance of the battery, the mass ratio of inorganic particles in the inorganic particle layer is 90% by mass or more, preferably 92% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. The mass ratio of inorganic particles in the inorganic particle layer may be 100% by mass.

[0141] The inorganic particle layer may contain a binder resin to form the layer and maintain its structure. The mass percentage of inorganic particles in the inorganic particle layer is, for example, 10% by mass or more, 8% by mass or more, or 5% by mass or more.

[0142] - 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.

[0143] Examples of metal oxides constituting 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 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 metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred. Examples of metal carbonates constituting metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides constituting metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0144] The inorganic particles may be inorganic particles whose surface has been modified with a silane coupling agent or the like.

[0145] Inorganic particles may be used individually or in combination of two or more types.

[0146] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0147] From the viewpoint of being able to obtain relatively small particle sizes inexpensively as inorganic particles, at least one selected from the group consisting of γ-alumina particles, boehmite particles, and barium sulfate particles is more preferable.

[0148] There are no limitations on the particle shape of the inorganic particles; they may be spherical, elliptical, plate-shaped, needle-shaped, or irregularly shaped. From the viewpoint of suppressing internal short circuits in the battery, the inorganic particles contained in the inorganic particle layer are preferably plate-shaped particles or non-aggregated primary particles.

[0149] The average primary particle size of the inorganic particles contained in the inorganic particle layer is preferably 10 nm to 500 nm, more preferably 10 nm to 300 nm, even more preferably 20 nm to 200 nm, and still more preferably 30 nm to 100 nm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the inorganic particles and the polyolefin microporous membrane or other layers.

[0150] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the inorganic particle layer, or inorganic particles extracted from the inorganic particle layer. There are no restrictions on the method for extracting inorganic particles from the inorganic particle layer. For example, this method involves immersing the inorganic particle layer peeled from the separator in an organic solvent that dissolves the binder resin, thereby dissolving the binder resin and extracting the inorganic particles; or heating the inorganic particle layer peeled from the separator to about 800°C to remove the binder resin and extract the inorganic particles; and so on.

[0151] -Binding Resin- The binding resin has the function of binding inorganic particles contained in the inorganic particle layer together, as well as adhering the inorganic particle layer to a polyolefin microporous membrane or other layers. The binding resin contained in the inorganic particle layer may have a particle shape, or it may not have a specific shape, and any form is acceptable as long as it can bind the inorganic particles together.

[0152] The binder resin may be a heat-resistant resin or a non-heat-resistant resin. Examples of heat-resistant resins include aromatic polyamides, polyimides, polyamide-imides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Examples of non-heat-resistant resins include butadiene polymers (e.g., butadiene homopolymers, styrene-butadiene copolymers) and acrylic resins (e.g., acrylic monomer homopolymers or copolymers, copolymers of acrylic monomers and styrene monomers). These resins may be used individually or in mixtures of two or more.

[0153] -Other Components- The inorganic particle layer may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the inorganic particle layer to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the inorganic particle layer to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0154] - Characteristics of the inorganic particle layer - In a configuration in which the inorganic particle layer is present on only one side of the polyolefin microporous membrane, the thickness of the inorganic particle layer is preferably 0.5 μm to 3 μm, more preferably 0.8 μm to 2.5 μm, and even more preferably 1 μm to 2 μm, from the viewpoint of the battery's impact resistance and the permeability of the electrolyte.

[0155] In a configuration where the inorganic particle layer is present on both sides of the polyolefin microporous membrane, the total thickness of the inorganic particle layer on both sides is preferably 0.5 μm to 5 μm, more preferably 0.8 μm to 4 μm, and even more preferably 1 μm to 3 μm, from the viewpoint of the battery's impact resistance and the permeability of the electrolyte.

[0156] The thickness of the inorganic particle layer is obtained by subtracting the thickness of the flat film after removing the inorganic particle layer from the thickness of the flat film obtained by removing the upper layer from the separator to expose the inorganic particle layer. The thickness of the flat film is determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument and averaging the results.

[0157] [Heat-resistant resin layer] The separator of this disclosure may include a heat-resistant resin layer containing a heat-resistant resin between the polyolefin microporous membrane and the surface layer (FA), and / or between the polyolefin microporous membrane and the surface layer (C).

[0158] A separator having a surface layer (F) may include a heat-resistant resin layer containing a heat-resistant resin between the polyolefin microporous membrane and the surface layer (F), and / or between the polyolefin microporous membrane and the surface layer (C).

[0159] A separator having a surface layer (A) may include a heat-resistant resin layer containing a heat-resistant resin between the polyolefin microporous membrane and the surface layer (A), and / or between the polyolefin microporous membrane and the surface layer (C).

[0160] In the separator of this disclosure, the heat-resistant resin layer is a porous layer in which the mass ratio of the heat-resistant resin to the total mass of the layer is greater than 10% by mass. In this disclosure, a porous layer is a layer having a large number of micropores inside, with a structure in which the micropores are connected, and through which gas or liquid can pass from one surface to the other.

[0161] In this disclosure, a heat-resistant resin refers to a resin with a melting point of 200°C or higher, or a resin that does not have a melting point but has a thermal decomposition temperature of 200°C or higher. In other words, a heat-resistant resin in this disclosure is a resin that does not melt or decompose in the temperature range below 200°C.

[0162] Examples of embodiments of a separator equipped with a heat-resistant resin layer include the following embodiments (11) to (13).

[0163] Embodiment (11): A separator having a heat-resistant resin layer between a polyolefin microporous membrane and a surface layer (FA), and having a heat-resistant resin layer between a polyolefin microporous membrane and a surface layer (C). In this separator, one heat-resistant resin layer and the other heat-resistant resin layer may be the same or different in terms of components and / or composition.

[0164] Morphology (12): A separator having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (FA), and not having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (C).

[0165] Morphology (13): A separator having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (C), and not having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (FA).

[0166] As an example of an embodiment of a separator having a surface layer (A), there is a form (11) or form (12) in which the surface layer (A) is a layer in which acrylic resin particles are attached to a heat-resistant resin layer. This embodiment is preferred from the viewpoint that the surface layer (A) has excellent ion permeability and that the surface layer (A) is easy to maintain as a layer.

[0167] The heat-resistant resin layer contains at least a heat-resistant resin and may also contain other components.

[0168] The mass ratio of heat-resistant resin to the heat-resistant resin layer is more than 10% by mass, preferably 15% by mass or more, and more preferably 20% by mass or more, from the viewpoint of improving the heat resistance of the separator and suppressing internal short circuits in the battery. The mass ratio of heat-resistant resin to the heat-resistant resin layer may be 100% by mass.

[0169] The heat-resistant resin layer may contain inorganic particles from the viewpoint of increasing the rigidity of the separator or from the viewpoint of easily making the layer porous. In a form in which the heat-resistant resin layer contains inorganic particles, the mass ratio of inorganic particles to the heat-resistant resin layer is preferably 50% by mass or more and less than 90% by mass, more preferably 60% by mass to 85% by mass, and even more preferably 70% by mass to 85% by mass.

[0170] - Heat-resistant resins - Examples of heat-resistant resins include aromatic polyamides, polyimides, polyamide-imides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Heat-resistant resins may be used individually or in mixtures of two or more types.

[0171] As for the heat-resistant resin, at least one selected from the group consisting of aromatic polyamides, polyimides, and polyamide-imides is preferred from the viewpoint of durability and heat resistance.

[0172] As a heat-resistant resin, all-aromatic polyamides (also known as aramids) are more preferred from the viewpoint of durability and heat resistance. All-aromatic polyamides may be meta-type or para-type. Among all-aromatic polyamides, meta-type all-aromatic polyamides are preferred from the viewpoint of easily forming porous layers and having excellent oxidation-reduction resistance in electrode reactions. Specifically, polymetaphenylene isophthalamide or polyparaphenylene terephthalamide are preferred as all-aromatic polyamides, and polymetaphenylene isophthalamide is more preferred.

[0173] In a form in which the heat-resistant resin layer contains a total aromatic polyamide, the mass percentage of the total aromatic polyamide in the total resin of the heat-resistant resin layer is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0174] - Inorganic Particles - The heat-resistant resin layer may contain inorganic particles. From the viewpoint of increasing the rigidity of the separator, it is preferable that the heat-resistant resin layer contains inorganic particles.

[0175] Examples of embodiments of inorganic particles contained in the heat-resistant resin layer are the same as examples of embodiments of inorganic particles contained in the inorganic particle layer. The description of inorganic particles relating to the inorganic particle layer is applied to the heat-resistant resin layer by replacing "inorganic particle layer" with "heat-resistant resin layer".

[0176] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0177] From the viewpoint of being able to obtain relatively small particle sizes inexpensively as inorganic particles, and from the viewpoint of not generating gas inside the battery, metal sulfate particles are preferred, and barium sulfate particles are more preferred.

[0178] The average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.01 μm to 1 μm, more preferably 0.02 μm to 1 μm, and even more preferably 0.03 μm to 1 μm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the polyolefin microporous membrane or other layers.

[0179] In a configuration where the surface layer (F) is a layer in which polyvinylidene fluoride resin particles are attached to a heat-resistant resin layer, or where the surface layer (C) is a layer in which polyvinyl chloride resin particles are attached to a heat-resistant resin layer, the average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.3 μm or less, more preferably 0.1 μm or less, and even more preferably 0.08 μm or less, from the viewpoint of suppressing the peeling of the surface layer (F) or surface layer (C) from the heat-resistant resin layer. The average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more, from the viewpoint of forming a good porous structure without aggregation.

[0180] In a configuration where the surface layer (A) is a layer in which acrylic resin particles are attached to a heat-resistant resin layer, or where the surface layer (C) is a layer in which polyvinyl chloride resin particles are attached to a heat-resistant resin layer, the average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.3 μm or less, more preferably 0.1 μm or less, and even more preferably 0.08 μm or less, from the viewpoint of suppressing the peeling of the surface layer (A) or surface layer (C) from the heat-resistant resin layer. The average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more, from the viewpoint of forming a good porous structure without aggregation.

[0181] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the heat-resistant resin layer, or inorganic particles extracted from the heat-resistant resin layer. There are no restrictions on the method for extracting inorganic particles from the heat-resistant resin layer. For example, this method involves immersing the heat-resistant resin layer peeled from the separator in an organic solvent that dissolves the heat-resistant resin, thereby dissolving the resin and extracting the inorganic particles; or heating the heat-resistant resin layer peeled from the separator to approximately 800°C to remove the heat-resistant resin and extract the inorganic particles; and so on.

[0182] -Other Components- The heat-resistant resin layer may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the heat-resistant resin layer to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the heat-resistant resin layer to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0183] - Characteristics of the heat-resistant resin layer - In a configuration where the heat-resistant resin layer is present on only one side of the polyolefin microporous membrane, the thickness of the heat-resistant resin layer is preferably 0.5 μm to 4 μm, more preferably 1 μm to 3.5 μm, and even more preferably 1.5 μm to 3 μm, from the viewpoint of balancing the heat resistance and energy density of the battery.

[0184] In a configuration where the heat-resistant resin layer is present on both sides of the polyolefin microporous film, the thickness of the heat-resistant resin layer is preferably 1 μm to 5 μm in total on both sides, more preferably 1.5 μm to 4 μm, and even more preferably 2 μm to 3 μm, from the viewpoint of balancing the heat resistance and energy density of the battery.

[0185] The thickness of the heat-resistant resin layer is obtained by subtracting the thickness of the flat film after removing the heat-resistant resin layer from the thickness of the flat film obtained by removing the upper layer from the separator to expose the heat-resistant resin layer. The thickness of the flat film is determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument and averaging the results.

[0186] In a configuration where the heat-resistant resin layer is present on only one side of the polyolefin microporous membrane, the mass per unit area (i.e., basis weight) of the heat-resistant resin layer is 0.8 g / m², from the viewpoint of balancing the heat resistance and energy density of the battery. ２ ~2.5 g / m ２ Preferably, it is 1.0 g / m ２ ~2.0 g / m ２ More preferably, 1.2 g / m ２ ~1.8 g / m ２ That is even more preferable.

[0187] In a configuration where the heat-resistant resin layer is present on both sides of the polyolefin microporous film, the mass per unit area (i.e., basis weight) of the heat-resistant resin layer should be 0.8 g / m² in total for both sides, from the viewpoint of balancing the heat resistance and energy density of the battery. ２ ~4.0 g / m ２ Preferably, it is 1.0 g / m ２ ~3.0 g / m ２ More preferably, 1.2 g / m ２ ~2.0 g / m ２ That is even more preferable.

[0188] The mass per unit area (i.e., basis weight) of the heat-resistant resin layer is calculated by subtracting the mass of the flat film obtained by removing the heat-resistant resin layer from the mass of the flat film obtained by removing the heat-resistant resin layer from a separator cut to 20 cm x 20 cm, and then dividing the difference in mass by the area.

[0189] [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 14 μm or less, and even more preferably 13 μm or less.

[0190] The thickness of the separator is determined by measuring 20 points within a 10 cm square area using a contact-type length measuring device and averaging the results.

[0191] From the viewpoint of ion permeability, the porosity of the separator is preferably 30% to 60%. The porosity ε (%) of the separator is calculated using the following formula.

[0192]

[0193] Here, for the separator's constituent material 1, constituent material 2, constituent material 3, ..., constituent material n, the mass per unit area of ​​each constituent material is W. １ , W ２、 W ３ ..., W ｎ (g / cm ２ ) and the true density of each constituent material is d １ d ２ d ３ , ..., d ｎ (g / cm ３ ) and the thickness of the separator is t (cm).

[0194] From the viewpoint of suppressing internal short circuits in the battery, the permeability of the separator is preferably 80 seconds / 100 mL or more, more preferably 90 seconds / 100 mL or more, and even more preferably 100 seconds / 100 mL or more. From the viewpoint of ion permeability, the permeability of the separator is preferably 260 seconds / 100 mL or less, more preferably 250 seconds / 100 mL or less, and even more preferably 240 seconds / 100 mL or less.

[0195] The air permeability of the separator was measured using a Gurley densometer in accordance with JIS P8117:2009 "Paper and cardboard - Test methods for air permeability and air resistance (intermediate region) - Gurley method".

[0196] In a configuration in which an inorganic particle layer and / or a heat-resistant resin layer are arranged on a separator, the thickness and mass per unit area (i.e., basis weight) of these layers are preferably set using the thermal shrinkage rate of the separator as an indicator. When the separator with the inorganic particle layer and / or heat-resistant resin layer is heat-treated at a temperature of 130°C for 60 minutes, the thermal shrinkage rates of MD and TD are preferably 10% or less, respectively.

[0197] The thermal shrinkage rate of the separator is measured by the following method. Cut the separator into a rectangle with dimensions TD 60 mm x MD 180 mm to make a test specimen. Mark the specimen at points 20 mm and 170 mm from one end on the line that bisects TD (referred to as points A and B, respectively). Furthermore, mark the specimen at points 10 mm and 50 mm from one end on the line that bisects MD (referred to as points C and D, respectively). Attach a clip to the specimen (the clip should be placed between the end closest to point A and point A), suspend it in an oven at 130°C, and heat treat it for 60 minutes under no tension. Measure the lengths between A and B and between C and D before and after the heat treatment, and calculate the thermal shrinkage rate using the following formula.

[0198] Thermal shrinkage rate of MD (%) = {(Length of AB before heat treatment - Length of AB after heat treatment) ÷ Length of AB before heat treatment} × 100 Thermal shrinkage rate of TD (%) = {(Length of CD before heat treatment - Length of CD after heat treatment) ÷ Length of CD before heat treatment} × 100

[0199] [Laminated Structure of Separators] The laminated structure of the separators of this disclosure will be described with reference to the drawings. Figures 1 to 6 are schematic cross-sectional views of embodiments of the separators of this disclosure. Figures 1 to 6 are schematic cross-sectional views mainly for explaining the layering order, and the structure of each layer is abstracted or simplified. In Figures 1 to 6, layers having similar functions are denoted by the same reference numerals and described accordingly.

[0200] Figure 1 is a schematic cross-sectional view of a separator that does not have an inorganic particle layer and a heat-resistant resin layer. The separator shown in Figure 1 is a separator in which a surface layer (FA) 80, a polyolefin microporous film 20, and a surface layer (C) 90 are laminated in this order.

[0201] Figures 2 and 3 are schematic cross-sectional views of a separator having an inorganic particle layer on one side of a polyolefin microporous membrane. The separator shown in Figure 2 is a separator in which a surface layer (FA) 80, an inorganic particle layer 30, a polyolefin microporous membrane 20, and a surface layer (C) 90 are stacked in this order. The separator shown in Figure 3 is a separator in which a surface layer (FA) 80, a polyolefin microporous membrane 20, an inorganic particle layer 30, and a surface layer (C) 90 are stacked in this order.

[0202] Figure 4 is a schematic cross-sectional view of a separator having inorganic particle layers on both sides of a polyolefin microporous membrane. The separator shown in Figure 4 is a separator in which a surface layer (FA) 80, an inorganic particle layer 30, a polyolefin microporous membrane 20, an inorganic particle layer 30, and a surface layer (C) 90 are laminated in this order. In the separator shown in Figure 4, one inorganic particle layer 30 and the other inorganic particle layer 30 may be the same or different in terms of components and / or composition.

[0203] Figure 5 is a schematic cross-sectional view of a separator having a heat-resistant resin layer on one side of a polyolefin microporous membrane. The separator shown in Figure 5 is a separator in which a surface layer (FA) 80, a heat-resistant resin layer 60, a polyolefin microporous membrane 20, and a surface layer (C) 90 are laminated in this order. In the embodiment shown in Figure 5, the heat-resistant resin layer 60 is positioned between the polyolefin microporous membrane 20 and the surface layer (FA) 80, but the heat-resistant resin layer 60 may also be positioned between the polyolefin microporous membrane 20 and the surface layer (C) 90.

[0204] Figure 6 is a schematic cross-sectional view of a separator having an inorganic particle layer and a heat-resistant resin layer on one side of a polyolefin microporous membrane. The separator shown in Figure 6 is a separator in which a surface layer (FA) 80, a heat-resistant resin layer 60, an inorganic particle layer 30, a polyolefin microporous membrane 20, and a surface layer (C) 90 are laminated in this order. In the embodiment shown in Figure 6, the inorganic particle layer 30 and the heat-resistant resin layer 60 are arranged between the polyolefin microporous membrane 20 and the surface layer (FA) 80, but the inorganic particle layer 30 and the heat-resistant resin layer 60 may also be arranged between the polyolefin microporous membrane 20 and the surface layer (C) 90. In the embodiment shown in Figure 6, the inorganic particle layer 30 and the heat-resistant resin layer 60 are arranged on the same side of the polyolefin microporous membrane 20, but the inorganic particle layer 30 and the heat-resistant resin layer 60 may be arranged on different sides of the polyolefin microporous membrane 20.

[0205] In the examples of configurations shown in Figures 1 to 6, the surface layer (FA) may be either surface layer (F) or surface layer (A).

[0206] The lamination configuration of the separator of this disclosure is not limited to the configurations shown in Figures 1 to 6. Other configurations of the separator of this disclosure include: an example in which an inorganic particle layer and a heat-resistant resin layer are arranged on both sides of a polyolefin microporous membrane; an example in which an inorganic particle layer is arranged on both sides of a polyolefin microporous membrane and a heat-resistant resin layer is arranged on one side of the polyolefin microporous membrane; and an example in which an inorganic particle layer is arranged on one side of a polyolefin microporous membrane and heat-resistant resin layers are arranged on both sides of the polyolefin microporous membrane.

[0207] In a form in which the separator has an inorganic particle layer and a heat-resistant resin layer, there are no restrictions on the stacking order of the inorganic particle layer and the heat-resistant resin layer. From the viewpoint of ease of manufacturing the separator and excellent ion permeability of the separator, it is preferable that the inorganic particle layer is the lower layer and the heat-resistant resin layer is the upper layer.

[0208] [Method for Manufacturing Separators] The separators of this disclosure can be manufactured by forming each layer on a polyolefin microporous membrane using a wet coating method or a dry coating method. In this disclosure, a wet coating method is a method of solidifying the coating layer in a solidifying liquid, and a dry coating method is a method of solidifying the coating layer by drying it.

[0209] Examples of wet coating and dry coating methods are described below. In the following description, layers other than the polyolefin microporous membrane of the separator are collectively referred to as "porous layers."

[0210] -Wet Coating Method- An example of an embodiment of the wet coating method includes the steps of: applying a coating liquid to one or both sides of a substrate to form a coating layer; immersing the substrate having the coating layer in a solidifying solution to solidify the coating layer and form a porous layer; and removing the laminate consisting of the substrate and the porous layer from the solidifying solution and washing and drying it.

[0211] The coating solution is prepared by dissolving or dispersing the porous layer material in a solvent.

[0212] The solvent used in preparing the coating solution includes a solvent that dissolves the resin contained in the porous layer (hereinafter also referred to as the "good solvent"). A good solvent common to polyvinylidene fluoride resins, acrylic resins, polyvinyl chloride resins, and polyamides is a polar amide solvent. Examples of polar amide solvents include dimethylacetamide, dimethylformamide, and N-methylpyrrolidone.

[0213] The solvent used in preparing the coating solution preferably contains a phase-separating agent that induces phase separation, from the viewpoint of forming a good porous structure in the porous layer. Therefore, the solvent used in preparing the coating solution is preferably a mixed solvent of a good solvent and a phase-separating agent. The phase-separating agent is preferably mixed with the good solvent in an amount that ensures a viscosity suitable for coating. Examples of phase-separating agents common to polyvinylidene fluoride resins, acrylic resins, polyvinyl chloride resins, and polyamides include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0214] The solvent used in preparing the coating solution is preferably a mixed solvent of a good solvent and a phase separating agent, from the viewpoint of forming a good porous structure in the porous layer, and is preferably a mixed solvent containing 60% by mass or more of the good solvent and 5% to 40% by mass of the phase separating agent.

[0215] The resin concentration of the coating solution is preferably 1% to 20% by mass, from the viewpoint of forming a good porous structure in the porous layer. If the coating solution contains inorganic particles, the inorganic particle concentration of the coating solution is preferably 0.5% to 50% by mass, from the viewpoint of forming a good porous structure in the porous layer.

[0216] The coating solution may contain dispersants such as surfactants, wetting agents, defoamers, pH adjusters, etc. These additives may remain in the porous layer as long as they are electrochemically stable within the operating range of non-aqueous secondary batteries and do not inhibit reactions within the battery.

[0217] Methods for applying the coating liquid to the substrate include Meyer bar, die coater, reverse roll coater, roll coater, and gravure coater. When forming a porous layer on both sides of the substrate, it is preferable from a productivity standpoint to apply the coating liquid to both sides of the substrate simultaneously.

[0218] The coating layer is solidified by immersing the substrate on which the coating layer is formed in a solidifying solution, thereby inducing phase separation in the coating layer and solidifying the resin. This results in a laminate consisting of the substrate and the porous layer.

[0219] The solidification solution generally contains the good solvent and phase separating agent used in the preparation of the coating solution, along with water. From a production standpoint, it is preferable that the mixing ratio of the good solvent and the phase separating agent match the mixing ratio of the mixed solvent used in the preparation of the coating solution. From the viewpoint of forming a porous structure and productivity, the water content in the solidification solution is preferably 40% to 90% by mass. The temperature of the solidification solution is, for example, 20°C to 50°C.

[0220] After the coating layer is solidified in the solidification solution, the laminate is removed from the solidification solution and washed with water. Washing removes the solidification solution from the laminate. Further drying removes water from the laminate. Washing is performed, for example, by transporting the laminate in a water bath. Drying is performed, for example, by transporting the laminate in a high-temperature environment, blowing air on the laminate, or bringing the laminate into contact with a heat roll. In one embodiment, the drying temperature is set to a temperature that does not melt the resin (for example, a temperature of (glass transition temperature of the resin) or less).

[0221] - Dry Coating Method - An example of an embodiment of the dry coating method includes the steps of: applying a coating liquid to one or both sides of a substrate to form a coating layer; and drying and solidifying the coating layer on the substrate to form a porous layer.

[0222] The coating solution is prepared by dissolving or dispersing the porous layer material in a solvent.

[0223] Water is one example of a solvent used in the preparation of coating solutions. Water is preferred because it is easily removed by drying and has no toxicity to humans or the environment.

[0224] The resin concentration of the coating solution is preferably 1% to 20% by mass, from the viewpoint of coating properties and productivity of the porous layer. If the coating solution contains inorganic particles, the inorganic particle concentration of the coating solution is preferably 0.5% to 50% by mass, from the viewpoint of coating properties and productivity of the porous layer.

[0225] The coating solution may contain dispersants such as surfactants, wetting agents, defoamers, pH adjusters, etc. These additives may remain in the resin particle layer as long as they are electrochemically stable within the operating range of non-aqueous secondary batteries and do not inhibit reactions within the battery.

[0226] Methods for applying the coating liquid to the substrate include Meyer bar, die coater, reverse roll coater, roll coater, and gravure coater. When forming a porous layer on both sides of the substrate, it is preferable from a productivity standpoint to apply the coating liquid to both sides of the substrate simultaneously.

[0227] The coating layer solidifies by drying (i.e., removing the solvent). Drying is performed, for example, by transporting the substrate with the coating layer in a high-temperature environment, by blowing air onto the substrate with the coating layer, or by bringing the substrate with the coating layer into contact with a heat roll. In one embodiment, the drying temperature is set to a temperature that does not melt the resin (for example, a temperature of (glass transition temperature of the resin + 20°C) or lower).

[0228] All porous layers of the separator may be formed by a wet coating method or by a dry coating method. Alternatively, some porous layers of the separator may be formed by a wet coating method and some porous layers by a dry coating method.

[0229] The separator can also be manufactured by preparing the porous layer as an independent sheet and then combining it with a substrate by heat compression or adhesive. One method for preparing the porous layer as an independent sheet is to apply the wet coating method or dry coating method described above to form the porous layer on a release sheet.

[0230] The method for manufacturing the separator may be a discontinuous method or a continuous method.

[0231] • Discontinuous manufacturing method: A lower layer is formed on a substrate unwound from a roll to obtain a laminate of the substrate and the lower layer, and then the laminate is wound onto another roll. Next, an upper layer is formed on the laminate unwound from the roll to obtain a separator, and the resulting separator is wound onto another roll.

[0232] • Continuous manufacturing method: A lower layer is formed on the substrate unwound from a roll to obtain a laminate of the substrate and the lower layer, then an upper layer is formed on the laminate to obtain a separator, and the resulting separator is wound onto another roll.

[0233] <Non-aqueous secondary battery> The non-aqueous secondary battery of this disclosure is a non-aqueous secondary battery that obtains electromotive force by doping and dedoping of lithium ions, and comprises a positive electrode, a negative electrode, and a separator of this disclosure. Doping means absorption, support, adsorption, or insertion, and refers to the phenomenon in which lithium ions enter the active material of the electrode.

[0234] The non-aqueous secondary battery of this disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other via a separator is sealed together with an electrolyte in an outer casing. The non-aqueous secondary battery of this disclosure is suitable for non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries.

[0235] The non-aqueous secondary battery of this disclosure exhibits excellent adhesion to both the positive and negative electrodes through a relatively low-temperature, low-pressure bonding process, which ensures that the pores of the separator remain open during battery manufacturing, resulting in superior charge-discharge characteristics (e.g., cycle characteristics, rate characteristics).

[0236] The following describes examples of the forms of the positive electrode, negative electrode, electrolyte, and outer casing material of the non-aqueous secondary battery of this disclosure.

[0237] An example of a positive electrode embodiment is a configuration in which an active material layer containing a positive electrode active material and a binder resin is arranged on a current collector. The active material layer may further contain a conductive additive. Examples of positive electrode active materials include lithium-containing transition metal oxides. Examples of lithium-containing transition metal oxides include LiCoO ２ LiNiO ２ LiMn １／２ Ni １／２ O ２LiCo １／３ Mn １／３ Ni １／３ O ２ LiMn ２ O ４ LiFePO ４ LiCo １／２ Ni １／２ O ２ LiAl １／４ Ni ３／４ O ２ Examples include polyvinylidene fluoride resins and styrene-butadiene copolymers as binder resins. Examples of conductive additives include acetylene black, Ketjen black, graphite powder, and carbon materials such as ultrafine carbon fibers. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil with a thickness of 5 μm to 20 μm.

[0238] An example of a negative electrode embodiment is a configuration in which an active material layer containing a negative electrode active material and a binder resin is arranged on a current collector. The active material layer may further contain a conductive additive. Examples of negative electrode active materials include materials that can electrochemically absorb lithium ions. Examples of such materials include carbon materials; alloys of silicon, tin, aluminum, etc. with lithium; Wood's alloys; etc. 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 current collectors include copper foil, nickel foil, and stainless steel foil with a thickness of 5 μm to 20 μm. Instead of the above negative electrode, metallic lithium foil may be used as the negative electrode.

[0239] The electrolyte is preferably a solution of lithium salt dissolved in a non-aqueous solvent. For example, LiPF4 is used as the lithium salt. ６ LiBF ４ LiClO ４Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; linear carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and their fluorine-substituted derivatives; and cyclic esters such as γ-butyrolactone and γ-valerolactone. Non-aqueous solvents may be used individually or in mixtures of two or more.

[0240] As the electrolyte, a solution is preferred in which cyclic carbonate and linear carbonate are mixed in a mass ratio (cyclic carbonate:linear carbonate) of 20:80 to 40:60, and a lithium salt is dissolved in it at a concentration of 0.5 mol / L to 1.5 mol / L.

[0241] Examples of exterior materials include aluminum laminate film packs and metal cans. Examples of battery shapes include rectangular, cylindrical, and coin-shaped batteries. The separator of this disclosure is suitable for any of the exterior materials and shapes.

[0242] The non-aqueous secondary battery of this disclosure can be manufactured, for example, by manufacturing a laminate in which the separator of this disclosure is placed between the positive electrode and the negative electrode, and then subjecting this laminate to a wet heat press. Dry heat pressing may be performed in the process of manufacturing the laminate for the purpose of integrating the laminate. Integrating the laminate by dry heat pressing is preferable from the viewpoint of the manufacturing yield and transportability of the separator.

[0243] The non-aqueous secondary battery of this disclosure can be manufactured by first creating a laminate in which the separator of this disclosure is placed between the positive electrode and the negative electrode, and then using this laminate by, for example, the following manufacturing method (1) or manufacturing method (2).

[0244] Manufacturing method (1): After temporarily bonding the electrodes and separators by dry heat pressing the laminate, it is placed in an outer casing and the electrolyte is injected. Next, the laminate is wet heat pressed from above the outer casing to bond the electrodes and separators and seal the outer casing.

[0245] Manufacturing method (2): The laminate is placed in an outer material and the electrolyte is injected. Next, the laminate is wet heat pressed from above the outer material to bond the electrodes to the separator and seal the outer material.

[0246] In manufacturing methods (1) and (2), the press temperature, press pressure, and press time of the wet heat press should be set according to the type of exterior material, the size and application of the battery, etc.

[0247] When the outer casing is a metal can, it is generally difficult to implement a wet heat press process. When the outer casing is a metal can, the pressure naturally applied from the metal can is used to bond the electrodes and separator. This pressure is approximately 40 kPa to 200 kPa. After inserting the laminate into the metal can, adding the electrolyte, and sealing it, the electrodes and separator can be bonded by leaving it at 50°C to 80°C for 3 to 20 hours. During the above-mentioned period, the battery may be in any charged state, or it may be charging or discharging. During the above-mentioned period, a part of the outer casing may be opened to release the gas generated inside.

[0248] When manufacturing a laminate with a separator placed between the positive electrode and the negative electrode, the method of placing the separator between the positive electrode and the negative electrode may be a method in which the positive electrode, separator, and negative electrode are stacked in that order in at least one layer each (the so-called stack method), or a method in which the positive electrode, separator, negative electrode, and separator are stacked in that order and wound in the length direction.

[0249] The separator and non-aqueous secondary battery of this disclosure will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing procedures, etc., shown in the following examples can be modified as appropriate without departing from the spirit of this disclosure. Therefore, the scope of the separator and non-aqueous secondary battery of this disclosure should not be interpreted as being limited by the specific examples shown below.

[0250] In the following descriptions, synthesis, processing, and manufacturing were carried out at room temperature (25°C ± 3°C) unless otherwise specified.

[0251] <Measurement Methods and Evaluation Methods> The measurement and evaluation methods applied to the examples and comparative examples are as follows.

[0252] [Average Primary Particle Size of Inorganic Particles] The average primary particle size of inorganic particles was determined by performing SEM observation on inorganic particles used to form the porous layer, measuring the major axis of 100 randomly selected inorganic particles, and averaging the major axes of these 100 particles.

[0253] [Thickness of Polyolefin Microporous Film, Substrate, and Separator] The thickness (μm) of the polyolefin microporous film, substrate, and separator was determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument (Mitutoyo Corporation, LITEMATIC VL-50S) and averaging the results. A spherical measuring probe with a radius of 10 mm (Mitutoyo Corporation) was used, and a load of 0.19 N was applied during measurement.

[0254] [Porosity of Polyolefin Microporous Membrane] The porosity ε (%) of the polyolefin microporous membrane was calculated using the following formula: ε = {1 - Ws / (ds・t)} × 100 where Ws is the basis weight (g / m) of the polyolefin microporous membrane. ２ ), ds is the true density (g / cm³) of the polyolefin microporous membrane. ３ ), t is the thickness of the polyolefin microporous membrane (μm).

[0255] [Air permeability of polyolefin microporous membranes and separators] The air permeability (seconds / 100 mL) of polyolefin microporous membranes and separators was measured in accordance with JIS P8117:2009 using a Gaale densometer (Toyo Seiki Co., Ltd., G-B2C).

[0256] [Porosity of the separator] The porosity ε (%) of the separator was calculated using the following formula.

[0257]

[0258] Here, for the separator's constituent material 1, constituent material 2, constituent material 3, ..., constituent material n, the mass per unit area of ​​each constituent material is W. １ , W ２、 W ３ ..., W ｎ (g / cm ２ ) and the true density of each constituent material is d １ d ２ d ３ , ..., d ｎ (g / cm３ ) and the thickness of the separator is t (cm).

[0259] [Heat Shrinkage Rate of Separator] A rectangle of separator with dimensions TD 60 mm x MD 180 mm was cut out to form a test specimen. Marks were made on the specimen at points 20 mm and 170 mm from one end, along the line that bisects TD (referred to as points A and B, respectively). Furthermore, marks were made at points 10 mm and 50 mm from one end, along the line that bisects MD (referred to as points C and D, respectively). A clip was attached to the specimen (the clip was attached between the end closest to point A and point A), and it was suspended in an oven at 130°C and heat-treated for 60 minutes under no tension. The lengths between A and B and between C and D were measured before and after the heat treatment, and the heat shrinkage rate was calculated using the following formula. The heat shrinkage rates of the three specimens were then averaged.

[0260] Thermal shrinkage rate of MD (%) = {(Length of AB before heat treatment - Length of AB after heat treatment) ÷ Length of AB before heat treatment} × 100 Thermal shrinkage rate of TD (%) = {(Length of CD before heat treatment - Length of CD after heat treatment) ÷ Length of CD before heat treatment} × 100

[0261] [Dry Adhesion to Electrodes] A slurry for the positive electrode was prepared by stirring and mixing 94 parts by mass of lithium cobalt oxide powder, which is the positive electrode active material, 3 parts by mass of acetylene black, which is a conductive additive, 3 parts by mass of polyvinylidene fluoride, which is a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone in a double-arm mixer. The slurry for the positive electrode was applied to one side of a 20 μm thick aluminum foil, dried, and then pressed to obtain a positive electrode having a positive electrode active material layer on one side.

[0262] A slurry for the negative electrode was prepared by mixing 96.2 parts by mass of artificial graphite, which is the negative electrode active material, 7 parts by mass of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer, which is the binder resin, 1 part by mass of carboxymethylcellulose, which is the thickener, and an appropriate amount of water using a double-arm mixer. The slurry for the negative electrode was applied to one side of a 10 μm thick copper foil, dried, and then pressed to obtain a negative electrode having a negative electrode active material layer on one side.

[0263] The electrodes (positive and negative electrodes) were cut into rectangles measuring 15 mm wide x 70 mm long. The separator was cut into a rectangle measuring TD 18 mm x MD 74 mm. A release paper measuring 15 mm wide x 70 mm long was prepared. The separator was placed on top of the active material layer of the electrode (positive or negative electrode), and then the release paper was placed on top of the separator to create a laminate. For the positive electrode, the separator was placed so that the surface layer (FA) was in contact with the positive electrode, and for the negative electrode, the separator was placed so that the surface layer (C) was in contact with the negative electrode. The laminate was placed in an aluminum laminate film pack, and the pack and the laminate were heat-pressed in the direction of the laminate using a heat press (dry heat press) to bond the electrodes (positive or negative electrode) and the separator. The heat press conditions were a temperature of 85°C, a pressure of 2 MPa, and a time of 5 minutes. After heat pressing, the laminate was removed from the pack, the release paper was peeled off, and a dry adhesive test specimen was obtained.

[0264] The uncoated surface of the electrode of the test specimen 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 Corporation, STB-1225S). At this time, the metal plate was fixed to the Tensilon so that the length direction of the test specimen (i.e., the MD of the separator) was in the direction of gravity. The separator was peeled off the electrode by about 2 cm from the lower end, and that end was fixed to the upper chuck, and a 180° peel test was performed. The tensile speed of the 180° peel test was set to 20 mm / min, and the load (N) from 10 mm to 40 mm after the start of measurement was taken at 0.4 mm intervals, and the average was calculated. Furthermore, the load of 10 test specimens was averaged to obtain the adhesive strength (N / 15 mm) between the electrode and the separator.

[0265] [Wet Adhesion to Electrodes] A secondary battery for testing, as described below, was prepared. A compression bending test (three-point bending test) was performed on the battery. The measurement was carried out using a compression bending test fixture attached to a Tensilon (A&D Corporation, STB-1225S). The distance between the support bases was 4 cm, and the battery was placed on the support bases so that the short side of the battery was parallel to the long side of the indenter and the compression position at the time of measurement was at the center of the long side of the electrode inside 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 carried out until the displacement reached 4 mm.

[0266] [Battery Cycle Characteristics] A test secondary battery, as described below, was prepared. At room temperature, the battery was subjected to 300 cycles of constant current charging at 3C and a 4.2V cutoff, and constant current discharging at 3C and a 2.5V cutoff.

[0267] [Battery Impact Resistance (Compression Breaking Strength)] Ten rechargeable batteries, as described below, were prepared for testing. At room temperature, the batteries were charged with a constant current and voltage of 0.1C and 4.2V, and held at 4.2V for 3 hours. Next, the batteries were placed on a horizontal stand with the positive terminal facing upwards and secured with adhesive tape. A spherical terminal with a diameter of 5 mm was placed in the center of the top of the battery and lowered at a speed of 100 mm / min to apply a load to the battery. The load (in N) was determined when the battery voltage dropped to 3.5V, and the average of the 10 batteries was calculated.

[0268] <Manufacturing of a separator and battery having a surface layer (F)> [Example 1] - Manufacturing of a separator - The following two types of PVDF resins were prepared: ・PVDF resin (1): VDF-HFP binary copolymer, VDF:HFP = 97.6:2.4 (molar ratio), weight-average molecular weight 1.13 million ・PVDF resin (2): VDF-HFP binary copolymer, VDF:HFP = 94.3:5.7 (molar ratio), weight-average molecular weight 860,000

[0269] PVDF resin (1) and PVDF resin (2) were dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc:TPG = 80:20 [mass ratio]), and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain coating solution (1). In coating solution (1), the mass ratio of PVDF resin (1) to PVDF resin (2) was (1):(2) = 70:30, the PVDF resin concentration was 4% by mass, and the mass ratio of PVDF resin to magnesium hydroxide particles was PVDF resin:magnesium hydroxide particles = 40:60.

[0270] Polyvinyl chloride (average degree of polymerization 700, homopolymer) was dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]), and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain coating solution (2). Coating solution (2) had a polyvinyl chloride concentration of 6% by mass, and the mass ratio of polyvinyl chloride to magnesium hydroxide particles was polyvinyl chloride:magnesium hydroxide particles = 35:65.

[0271] A polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) was coated with coating liquid (1) on one side and with coating liquid (2) on the other side using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:TPG:water = 34:9:57 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Thus, the separator of Example 1 was obtained.

[0272] - Manufacturing of the positive electrode - 94 parts by mass of lithium cobalt oxide powder, which is the positive electrode active material, 3 parts by mass of acetylene black, which is a conductive additive, 3 parts by mass of polyvinylidene fluoride, which is a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone were stirred and mixed in a double-arm mixer to prepare a slurry for the positive electrode. The slurry for the positive electrode was applied to both sides or one side of a 20 μm thick aluminum foil, dried, and then pressed to obtain a positive electrode having a positive electrode active material layer on both sides or one side.

[0273] - Manufacturing of the negative electrode - 96.2 parts by mass of artificial graphite, which is the negative electrode active material, 7 parts by mass of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer, which is the binder resin, 1 part by mass of carboxymethylcellulose, which is the thickener, and an appropriate amount of water were mixed by stirring in a double-arm mixer to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides or one side of a 10 μm thick copper foil, dried, and then pressed to obtain a negative electrode having a negative electrode active material layer on both sides or one side.

[0274] - Manufacturing of a secondary battery for wet adhesion testing - Double-sided positive electrode and double-sided negative electrode were cut into rectangles of 30 mm x 70 mm. A separator was cut into a rectangle of TD 35 mm x MD 75 mm. These were stacked so that the positive and negative electrodes were alternately arranged and a separator was sandwiched between the positive and negative electrodes to create a laminate consisting of 3 positive electrodes, 3 negative electrodes, and 5 separators. The separators were arranged so that the surface layer (F) was in contact with the positive electrode and the surface layer (C) was in contact with the negative electrode. The laminate was inserted into an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF) was placed inside the pack. ６ Ethylene carbonate:ethyl methyl carbonate (mass ratio 3:7) was injected to impregnate the laminate with the electrolyte. Next, the entire pack was heat-pressed in the stacking direction using a hot press (wet heat press) to bond the electrodes to the separator. The heat-pressing conditions were a press temperature of 70°C, a press pressure of 100 kPa, and a press time of 7 hours. The resulting test secondary battery was used to evaluate the wet adhesion to the electrodes.

[0275] - Manufacturing of secondary batteries for cycle performance testing and shock resistance testing - A single-sided positive electrode was cut into a rectangle of 30 mm x 50 mm. A single-sided negative electrode was cut into a rectangle of 31 mm x 51 mm. A separator was cut into a rectangle of TD 32 mm x MD 52 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 and negative electrodes to create a laminate consisting of one positive electrode, one negative electrode, and one separator. The separator was positioned so that its surface layer (F) was in contact with the positive electrode and its surface layer (C) was in contact with the negative electrode. The laminate was inserted into an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF) was placed inside the pack. ６ An electrolyte solution (ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was injected to impregnate the laminate. Next, the entire pack was heat-pressed in the direction of the laminate using a hot press (wet heat press) to bond the electrodes to the separator. The heat-pressing conditions were a press temperature of 70°C, a press pressure of 100 kPa, and a press time of 7 hours. The resulting test secondary battery was used to evaluate the battery's cycle characteristics and shock resistance.

[0276] [Example 2] - Separator Production - PVDF resin (1) and PVDF resin (2) were dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]) at a mass ratio of 70:30 to obtain a coating solution (3) with a PVDF resin concentration of 5% by mass.

[0277] Polyvinyl chloride (average degree of polymerization 700, homopolymer) was dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]) to obtain a coating solution (4) with a polyvinyl chloride concentration of 7% by mass.

[0278] A substrate (8 μm thick, 48% porosity, 108 seconds / 100 mL) was prepared, having inorganic particle layers (0.5 μm thick on one side, boehmite particles:styrene-butadiene copolymer = 99:1 [mass ratio]) containing boehmite particles (average primary particle size 100 nm) and styrene-butadiene copolymer on both sides of a polyethylene microporous membrane (7 μm thick). Coating liquid (3) was applied to one side of the substrate and coating liquid (4) to the other side using a gravure coater. The coated substrate was immersed in a solidification solution (DMAc:TPG:water = 34:9:57 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Thus, the separator of Example 2 was obtained.

[0279] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1.

[0280] [Comparative Example 1] - Separator Production - The separator of Comparative Example 1 was obtained in the same manner as in Example 1, except that an equal amount of coating liquid (1) was applied to both sides of the polyethylene microporous membrane.

[0281] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1. However, the wet heat press conditions for manufacturing the battery for cycle characteristic testing were changed to a press temperature of 80°C, a press pressure of 1 MPa, and a press time of 2 minutes.

[0282] [Comparative Example 2] - Separator Production - Polyvinyl chloride (average degree of polymerization 700, homopolymer) was dissolved in DMAc, and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain coating solution (5). The coating solution (5) had a polyvinyl chloride concentration of 6% by mass, and the mass ratio of polyvinyl chloride to magnesium hydroxide particles was polyvinyl chloride:magnesium hydroxide particles = 35:65.

[0283] Equal amounts of coating solution (5) were applied to both sides of a polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:water = 50:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Thus, the separator of Comparative Example 2 was obtained.

[0284] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1. However, the wet heat press conditions for manufacturing the battery for cycle characteristic testing were changed to a press temperature of 85°C, a press pressure of 1 MPa, and a press time of 5 minutes.

[0285] Table 1 shows the composition of the substrate, Table 2 shows the composition of the surface layer, and Table 3 shows the physical properties and evaluation results of the separator. The abbreviations in Tables 1 and 2 have the following meanings: PE: polyethylene, VDF-HFP: binary copolymer of vinylidene fluoride and hexafluoropropylene, PVC: polyvinyl chloride

[0286]

[0287]

[0288]

[0289] [Wet Adhesion to Electrodes] Figure 7 shows a graph relating to the wet adhesion between the separator and the electrode (measurement results of a three-point bending test). In Figure 7, (1) is the load displacement curve for Example 1, (2) is the load displacement curve for Example 2, (3) is the load displacement curve for Comparative Example 1, and (4) is the load displacement curve for Comparative Example 2. In Figure 7, (5) is the load displacement curve when the separator and electrode are not adhered.

[0290] As can be seen from Figure 7, in Examples 1 and 2, the gradient corresponding to the elastic modulus from the time deformation is applied to the cell until yield is large, and the yield is also large. On the other hand, in Comparative Example 1, the gradient corresponding to the elastic modulus is small, so it is judged that the electrode and separator are not adhered, and in Comparative Example 2, the load at the time of yield is small, so it is judged that the adhesive force between the electrode and separator is weak. From this, it can be seen that the separators of Examples 1 and 2 showed excellent adhesion to both the positive and negative electrodes through a relatively low-temperature, low-pressure wet bonding treatment.

[0291] [Battery Cycle Characteristics] Figure 8 shows a graph relating to the battery's cycle characteristics. In Figure 8, (1) is the cycle life curve for Example 1, (2) is the cycle life curve for Example 2, (3) is the cycle life curve for Comparative Example 1, and (4) is the cycle life curve for Comparative Example 2.

[0292] As can be seen from Figure 8, Examples 1 and 2 exhibit good cycle characteristics. This indicates that the pores in the separators of Examples 1 and 2 were not blocked by the bonding process during the manufacturing of the test batteries.

[0293] <Manufacturing of a separator and battery having a surface layer (A)> [Example 11] - Manufacturing of a separator - Meta-aramid was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc:TPG = 80:20 [mass ratio]), and barium sulfate particles (average primary particle size 0.05 μm) were dispersed to obtain a coating solution (11). The coating solution (11) had a meta-aramid concentration of 4.5% by mass, and the mass ratio of meta-aramid to barium sulfate particles was meta-aramid:barium sulfate particles = 20:80.

[0294] Polyvinyl chloride (average degree of polymerization 700, homopolymer) was dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]), and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain coating solution (12). The coating solution (12) had a polyvinyl chloride concentration of 6% by mass, and the mass ratio of polyvinyl chloride to magnesium hydroxide particles was polyvinyl chloride:magnesium hydroxide particles = 35:65.

[0295] A resin particle dispersion (11) was prepared in which acrylic resin particles were dispersed in water. The resin particle dispersion (11) had a resin particle concentration of 10% by mass. The acrylic resin particles were copolymer particles of acrylic monomer and styrene monomer, with a polymerization ratio (mass ratio) of acrylic monomer:styrene monomer = 38:62, a glass transition temperature of 52°C, and an average primary particle size of 500 nm.

[0296] A polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) was coated with coating liquid (11) on one side and with coating liquid (12) on the other side using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:TPG:water = 34:9:57 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Then, a resin particle dispersion (11) was applied onto the porous layer formed with coating liquid (11) and dried to solidify the coating layer. Thus, the separator of Example 11 was obtained.

[0297] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1.

[0298] [Comparative Example 11] - Separator Production - Meta-aramid was dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]), and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain a coating solution (13). The coating solution (13) had a meta-aramid concentration of 5% by mass, and the mass ratio of meta-aramid to magnesium hydroxide particles was meta-aramid:magnesium hydroxide particles = 20:80.

[0299] A resin particle dispersion (12) was prepared in which acrylic resin particles and polyvinylidene fluoride resin particles were dispersed in water. The resin particle dispersion (12) had a mass ratio of acrylic resin particles to polyvinylidene fluoride resin particles of 30:70, and a resin particle concentration of 10% by mass. The acrylic resin particles were acrylic resin particles with a glass transition temperature of 59°C and an average primary particle size of 500 nm. The polyvinylidene fluoride resin particles had a melting point of 140°C and an average primary particle size of 250 nm.

[0300] Equal amounts of coating solution (13) were applied to both sides of a polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:TPG:water = 34:9:57 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Then, equal amounts of resin particle dispersion (12) were applied to both sides and dried to solidify the coating layer. Thus, the separator of Comparative Example 11 was obtained.

[0301] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1.

[0302] [Comparative Example 12] - Separator Production - Polyvinyl chloride (average degree of polymerization 700, homopolymer) was dissolved in DMAc, and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain a coating solution (14). The coating solution (14) had a polyvinyl chloride concentration of 6% by mass, and the mass ratio of polyvinyl chloride to magnesium hydroxide particles was polyvinyl chloride:magnesium hydroxide particles = 35:65.

[0303] Equal amounts of coating solution (14) were applied to both sides of a polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:water = 50:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Thus, the separator of Comparative Example 12 was obtained.

[0304] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1.

[0305] Table 4 shows the structure of the polyolefin microporous membrane and heat-resistant resin layer, Table 5 shows the structure of the surface layer, and Table 6 shows the physical properties and evaluation results of the separator. The abbreviations in Tables 4 and 5 have the following meanings: PE: polyethylene, AC: acrylic resin, PVC: polyvinyl chloride, PVDF: polyvinylidene fluoride resin

[0306]

[0307]

[0308]

[0309] [Wet Adhesion to Electrodes] Figure 9 shows a graph relating to the wet adhesion between the separator and the electrode (measurement results of a three-point bending test). In Figure 9, (1) is the load displacement curve for Example 11, (2) is the load displacement curve for Comparative Example 11, and (3) is the load displacement curve for Comparative Example 12. In Figure 9, (4) is the load displacement curve when the separator and electrode are not adhered.

[0310] As can be seen from Figure 9, in Example 11, the gradient corresponding to the elastic modulus from the time deformation is applied to the cell until yield is large, and the yield is also large. On the other hand, in Comparative Example 11, the gradient corresponding to the elastic modulus is small, so it is judged that the electrode and separator are not adhered, and in Comparative Example 12, the load at the time of yield is small, so it is judged that the adhesive force between the electrode and separator is weak. From this, it can be seen that the separator of Example 11 showed excellent adhesion to both the positive and negative electrodes through a relatively low-temperature, low-pressure wet bonding treatment.

[0311] All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

[0312] The disclosure of Japanese application number 2024-231303, filed on 26 December 2024, is incorporated herein by reference in its entirety. The disclosure of Japanese application number 2024-231304, filed on 26 December 2024, is incorporated herein by reference in its entirety.

[0313] 20 Polyolefin microporous membrane 30 Inorganic particle layer 60 Heat-resistant resin layer 80 Surface layer (FA), Surface layer (F), Surface layer (A) 90 Surface layer (C)

Claims

1. A separator for a non-aqueous secondary battery, comprising: a polyolefin microporous membrane; a surface layer (FA) disposed on one side of the polyolefin microporous membrane and containing a polyvinylidene fluoride resin and / or an acrylic resin; and a surface layer (C) disposed on the other side of the polyolefin microporous membrane and containing a polyvinyl chloride resin.

2. The separator for a non-aqueous secondary battery according to claim 1, further comprising an inorganic particle layer containing inorganic particles, wherein the inorganic particles constitute 90% by mass or more, between the polyolefin microporous membrane and the surface layer (FA) and / or between the polyolefin microporous membrane and the surface layer (C).

3. The separator for a non-aqueous secondary battery according to claim 2, wherein the average primary particle size of the inorganic particles contained in the inorganic particle layer is 10 nm to 500 nm.

4. The separator for a non-aqueous secondary battery according to claim 2, wherein the inorganic particles include at least one selected from the group consisting of γ-alumina particles, boehmite particles, and barium sulfate particles.

5. The separator for a non-aqueous secondary battery according to claim 1, further comprising a heat-resistant resin layer containing a heat-resistant resin, wherein the heat-resistant resin accounts for more than 10% by mass, between the polyolefin microporous membrane and the surface layer (FA) and / or between the polyolefin microporous membrane and the surface layer (C).

6. The separator for a non-aqueous secondary battery according to claim 5, wherein the heat-resistant resin comprises at least one selected from the group consisting of aromatic polyamides, polyimides, and polyamideimides.

7. The separator for a non-aqueous secondary battery according to claim 5, wherein the heat-resistant resin layer further contains inorganic particles.

8. The separator for a non-aqueous secondary battery according to claim 1, wherein the average degree of polymerization of the polyvinyl chloride resin contained in the surface layer (C) is 500 to 1400.

9. The separator for a non-aqueous secondary battery according to claim 1, wherein the weight-average molecular weight of the polyvinylidene fluoride resin contained in the surface layer (FA) is 600,000 to 2,000,000.

10. The separator for a non-aqueous secondary battery according to claim 1, wherein the polyvinylidene fluoride resin comprises a polyvinylidene fluoride resin having hexafluoropropylene units.

11. The separator for a non-aqueous secondary battery according to claim 1, wherein the acrylic resin is acrylic resin particles.

12. The separator for a non-aqueous secondary battery according to claim 1, wherein the surface layer (FA) is a surface layer (F) containing a polyvinylidene fluoride resin, and the surface layer (F) and / or the surface layer (C) further contain inorganic particles.

13. The separator for a non-aqueous secondary battery according to claim 1, wherein the surface layer (FA) is a surface layer (A) containing an acrylic resin, and a heat-resistant resin layer containing a heat-resistant resin, wherein the heat-resistant resin accounts for more than 10% by mass, is further provided between the polyolefin microporous membrane and the surface layer (A), and the surface layer (A) is a layer in which acrylic resin particles are attached to the heat-resistant resin layer.

14. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a separator for a non-aqueous secondary battery according to any one of claims 1 to 13 disposed between the positive electrode and the negative electrode, wherein electromotive force is obtained by doping and dedoping lithium ions.

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