Separator for nonaqueous secondary battery, and nonaqueous secondary battery

Abstract

This separator for a nonaqueous secondary battery is provided with: a porous base material; and an adhesive porous layer that is disposed on one or both surfaces of the porous base material and that contains polyvinyl chloride-based resin and inorganic particles.

Description

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

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

[0002] Organofluorine compounds have been used in a wide range of manufacturing and industrial applications due to their useful properties such as heat resistance, chemical resistance, and surface activity. In recent years, reports have been published about the ecotoxicity and human toxicity of organofluorine compounds, and restrictions on the production and use of organofluorine compounds have been tightened worldwide.

[0003] Separators containing polyvinylidene fluoride resins are known as battery separators. However, as the production and use of organic fluorine compounds are increasingly restricted, there is an urgent need to develop separators with low or no polyvinylidene fluoride resin content.

[0004] Patent Document 1 discloses a separator for a lithium ion secondary battery, which comprises a polyolefin resin (A), a resin (B), and a thermoplastic resin (C), in which the resin (B) is present on the surface of a microporous film formed of at least the polyolefin resin (A), and is selected from the group consisting of polyvinyl chloride, polycarbonate, polyamide, polybutylene terephthalate, and polyethylene terephthalate, and is copolymerized with at least a part of the polyolefin resin (A).

[0005] Japanese Patent Application Laid-Open No. 2018-200788

[0006] To prevent internal short circuits in a battery, separators are required to have adhesive properties to electrodes. While separators containing a polyvinylidene fluoride resin in the surface layer have excellent adhesive properties to electrodes, separators that have excellent adhesive properties to electrodes even if the content of the polyvinylidene fluoride resin in the surface layer is low or even if the surface layer does not contain a polyvinylidene fluoride resin are desired. Furthermore, to prevent internal short circuits in a battery, separators are required to have thermal dimensional stability so that they do not easily shrink even when the temperature inside the battery becomes high.

[0007] The present disclosure has been made under the above circumstances, and an object of the present disclosure is to provide a separator for a non-aqueous secondary battery that has excellent adhesion to electrodes and thermal dimensional stability.

[0008] The present disclosure also has the following aspect. A separator having a surface layer on one or both sides of a porous substrate tends to hinder ion migration at the interface between the porous substrate and the surface layer. The resistance to ion migration exhibited by the interface between the porous substrate and the surface layer increases with repeated charging and discharging of the secondary battery, resulting in deterioration of the cycle characteristics of the secondary battery. In general, the greater the difference in air permeability between a separator and the porous substrate, the greater the resistance to ion migration at the interface between the porous substrate and the surface layer. Therefore, it is desirable for the separator to have a small difference in air permeability from the porous substrate.

[0009] One aspect of the present disclosure has been made in light of the above-mentioned circumstances, and an object of one aspect of the present disclosure is to provide a separator for a nonaqueous secondary battery that has excellent adhesion to an electrode and a relatively small difference in air permeability from a porous substrate.

[0010] The present disclosure also has the following aspect: A separator having a surface layer on one or both sides of a porous substrate tends to hinder ion migration at the interface between the porous substrate and the surface layer. The resistance to ion migration exhibited by the interface between the porous substrate and the surface layer increases with repeated charge and discharge of the secondary battery, resulting in a deterioration in the cycle characteristics of the secondary battery.

[0011] One aspect of the present disclosure has been made in light of the above-mentioned circumstances, and an object of one aspect of the present disclosure is to provide a separator for a non-aqueous secondary battery that has excellent adhesion to electrodes and improves the cycle characteristics of the battery.

[0012] Specific means for solving the above problems include the following aspects. <1> A separator for a non-aqueous secondary battery comprising a porous substrate and an adhesive porous layer containing a polyvinyl chloride resin and inorganic particles, the adhesive porous layer being disposed on one or both sides of the porous substrate. <2> The separator for a non-aqueous secondary battery according to <1>, wherein a volume ratio of the polyvinyl chloride resin to the inorganic particles contained in the adhesive porous layer is 90:10 to 20:80. <3> The separator for a non-aqueous secondary battery according to <1> or <2>, wherein the inorganic particles contained in the adhesive porous layer have an average primary particle size of 0.01 μm to 2 μm. <4> The separator for a non-aqueous secondary battery according to any one of <1> to <3>, wherein the inorganic particles include first inorganic particles having an average primary particle size of 0.5 μm to 1.0 μm and second inorganic particles having an average primary particle size smaller than that of the first inorganic particles. <5> The separator for a nonaqueous secondary battery according to <4>, wherein the proportion of the first inorganic particles to the total amount of the first inorganic particles and the second inorganic particles contained in the adhesive porous layer is 30% by volume to 70% by volume. <6> The separator for a nonaqueous secondary battery according to <4> or <5>, wherein the average primary particle size of the second inorganic particles is 0.01 μm or more and less than 0.5 μm. <7> The separator for a nonaqueous secondary battery according to any one of <1> to <6>, wherein, when the air permeability of the porous substrate is P1 and the air permeability of the nonaqueous secondary battery separator is P2, the value of (P2 - P1) / P1 is 0.85 or less. <8> The separator for a nonaqueous secondary battery according to <7>, wherein the air permeability of the porous substrate is 40 sec / 100 mL to 200 sec / 100 mL. <9> The separator for a non-aqueous secondary battery according to any one of <1> to <8>, wherein the inorganic particles comprise at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles. <10> The separator for a non-aqueous secondary battery according to any one of <1> to <9>, wherein the polyvinyl chloride resin contained in the adhesive porous layer has an average degree of polymerization of 550 to 1200. <11> The separator for a non-aqueous secondary battery according to any one of <1> to <9>, wherein the adhesive porous layer has a mass per unit area of ​​0.6 g / m per one side of the separator for a non-aqueous secondary battery. ２ ~2.0 g / m ２<12> The separator for a nonaqueous secondary battery according to any one of <1> to <11>, wherein the air permeability of the separator for a nonaqueous secondary battery is 100 sec / 100 mL to 500 sec / 100 mL. <13> The separator for a nonaqueous secondary battery according to any one of <1> to <12>, wherein the porous substrate comprises a polyolefin microporous membrane. <14> The separator for a nonaqueous secondary battery according to any one of <1> to <13>, wherein the porous substrate comprises: a polyolefin microporous membrane; and a heat-resistant layer, disposed on one or both sides of the polyolefin microporous membrane, containing at least one of inorganic particles and a heat-resistant resin. <15> The separator for a nonaqueous secondary battery according to any one of <1> to <14>, wherein the adhesive porous layer is substantially free of a fluorine-containing resin. <16> 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 <15>, which is disposed between the positive electrode and the negative electrode; wherein the non-aqueous secondary battery generates an electromotive force by doping and dedoping lithium ions.

[0013] According to the present disclosure, a separator for a non-aqueous secondary battery is provided that has excellent adhesion to electrodes and thermal dimensional stability.

[0014] According to one aspect of the present disclosure, there is provided a separator for a non-aqueous secondary battery that has excellent adhesion to an electrode and a relatively small difference in air permeability from a porous substrate.

[0015] According to one aspect of the present disclosure, there is provided a separator for a non-aqueous secondary battery that has excellent adhesion to an electrode and improves the cycle characteristics of the battery.

[0016]

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

[0017] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in an example.

[0018] In the present disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" means that it may be only A, only B, or a combination of A and B.

[0019] In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0020] In the present disclosure, when referring to the amount of each component in a composition, if the composition contains multiple substances corresponding to each component, the total amount of the multiple substances present in the composition is referred to unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be included. If the composition contains multiple types of particles corresponding to each component, the particle size of each component refers to the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0021] In this disclosure, MD (Machine Direction) refers to the longitudinal direction of a separator manufactured in a long shape, and TD (Transverse Direction) refers to the direction perpendicular to the MD in the plane direction of the separator. In this disclosure, TD is also referred to as the "width direction."

[0022] In the present disclosure, when the stacking relationship of each layer constituting a separator is expressed as "upper" and "lower," the layer closer to the porous substrate is referred to as "lower," and the layer farther from the porous substrate is referred to as "upper."

[0023] In the present disclosure, the volume of the porous layer excluding pores is referred to as the "solid content volume."

[0024] In the present disclosure, performing a heat press treatment after the separator is permeated with an electrolyte solution is referred to as "wet heat press," and performing a heat press treatment without permeating the separator with an electrolyte solution is referred to as "dry heat press."

[0025] In the present disclosure, the term "monomer unit" of a polymer or resin means a structural unit of the polymer or resin, which is formed by polymerization of a monomer. In the present disclosure, the term "(meth)acrylic" means either "acrylic" or "methacrylic".

[0026] <Separator for Non-Aqueous Secondary Battery> The separator for a non-aqueous secondary battery according to the present disclosure (also simply referred to as a "separator" in the present disclosure) includes a porous substrate and an adhesive porous layer containing a polyvinyl chloride resin and inorganic particles, which is disposed on one or both sides of the porous substrate.

[0027] The separator of the present disclosure has an adhesive porous layer containing a polyvinyl chloride resin and inorganic particles on one or both sides of a porous substrate. Examples of embodiments of the separator of the present disclosure include the following embodiments (1) to (3).

[0028] Form (1): A separator having adhesive porous layers containing a polyvinyl chloride resin and inorganic particles on both sides of a porous substrate as outermost layers of the separator, wherein the adhesive porous layer on one side of the separator and the adhesive porous layer on the other side of the separator may be the same or different in components and / or composition.

[0029] Form (2): A separator having an adhesive porous layer containing a polyvinyl chloride resin and inorganic particles as the outermost layer of the separator on one side of a porous substrate, and another layer on the other side of the porous substrate.

[0030] Form (3): A separator having an adhesive porous layer containing a polyvinyl chloride resin and inorganic particles as the outermost layer of the separator on one side of the porous substrate, and no layer on the other side of the porous substrate (i.e., the surface of the porous substrate is exposed).

[0031] The separator of the present disclosure has excellent adhesion to electrodes due to the adhesive porous layer containing a polyvinyl chloride resin. The separator of the present disclosure has excellent thermal dimensional stability, being resistant to thermal shrinkage even at high temperatures, due to the adhesive porous layer containing inorganic particles. The separator of the present disclosure has excellent electrolyte permeability and ion permeability through the adhesive porous layer due to the adhesive porous layer containing inorganic particles.

[0032] In one embodiment of the separator of the present disclosure, the adhesive porous layer contains first inorganic particles with an average primary particle size of 0.5 μm to 1.0 μm and second inorganic particles with an average primary particle size smaller than that of the first inorganic particles. The relatively large particle size of the first inorganic particles forms a favorable porous structure in the adhesive porous layer, resulting in a relatively small difference in air permeability between the separator and the porous substrate. The smaller the difference in air permeability between the separator and the porous substrate, the lower the ion migration resistance at the interface between the porous substrate and the surface layer tends to be, thereby improving the cycle characteristics of the battery. Meanwhile, the relatively small particle size of the second inorganic particles increases the surface area (specific surface area) of the inorganic particles per unit volume, increasing the number of contact points between the inorganic particles and the resin and resulting in a robust porous structure of the adhesive porous layer. This makes the separator less susceptible to interfacial failure between the adhesive porous layer and the porous substrate and cohesive failure of the adhesive porous layer, resulting in the separator being less susceptible to peeling from the electrode.

[0033] When the resin contained in the adhesive porous layer swells in the electrolyte, not only the micropores in the adhesive porous layer but also the areas filled with the resin can become sites for ion migration. This phenomenon is more likely the more easily the resin swells in the electrolyte. However, polyvinyl chloride resins are less likely to swell in the electrolytes used in non-aqueous secondary batteries than polyvinylidene fluoride resins. Therefore, separators having an adhesive porous layer containing polyvinyl chloride resins tend to have lower ion permeability than separators having an adhesive porous layer containing polyvinylidene fluoride resins. In contrast, one embodiment of a separator has excellent ion permeability because the adhesive porous layer contains first inorganic particles and second inorganic particles, resulting in a favorable porous structure. A separator with excellent ion permeability improves the cycle characteristics of a battery.

[0034] In another example of an embodiment of the separator of the present disclosure, when the air permeability of the porous substrate is P1 (seconds / 100 mL) and the air permeability of the separator for a nonaqueous secondary battery is P2 (seconds / 100 mL), the value of (P2-P1) / P1 is 0.85 or less. This means that the difference in air permeability between the separator and the porous substrate is relatively small. A separator with a larger difference in air permeability from the porous substrate tends to have a higher ion migration resistance at the interface between the porous substrate and the surface layer. The ion migration resistance at the interface between the porous substrate and the surface layer increases with repeated charge / discharge of the secondary battery, resulting in a deterioration in the cycle characteristics of the secondary battery. Therefore, from the perspective of improving the cycle characteristics of the secondary battery, it is desirable for the separator to have a small difference in air permeability from the porous substrate.

[0035] From the viewpoint of improving the cycle characteristics of the battery, the separator has a (P2-P1) / P1 value of 0.85 or less, preferably 0.8 or less, and more preferably 0.7 or less. The smaller the (P2-P1) / P1 value, the better from the viewpoint of improving the cycle characteristics of the battery. However, if the (P2-P1) / P1 value is too small, it reflects that the porous structure of the adhesive porous layer is coarse and / or the adhesive porous layer is too thin. If the porous structure of the adhesive porous layer is coarse or the adhesive porous layer is too thin, the adhesion of the separator to the electrode decreases. From the viewpoint of excellent adhesion of the separator to the electrode, the (P2-P1) / P1 value is preferably 0.2 or more, more preferably 0.25 or more, and even more preferably 0.3 or more.

[0036] An example of a method for adjusting the value of (P2-P1) / P1 to 0.85 or less is to promote phase separation of the coating layer when forming the adhesive porous layer by a wet coating method, such as adding a phase separation agent to the solvent used to prepare the coating liquid or increasing the temperature of the coagulation liquid.

[0037] In the separator of the present disclosure, the volume ratio of polyvinyl chloride resin to inorganic particles contained in the adhesive porous layer is preferably polyvinyl chloride resin:inorganic particles=90:10 to 20:80, more preferably 88:12 to 45:55, and even more preferably 85:15 to 55:45. When the volume ratio of polyvinyl chloride resin to inorganic particles is within the above range, a good balance can be achieved between the adhesiveness of the separator to the electrodes and the thermal dimensional stability of the separator.

[0038] In one embodiment, the volume ratio of the polyvinyl chloride resin to the inorganic particles contained in the adhesive porous layer is preferably 80:20 to 20:80, more preferably 70:30 to 30:70, and even more preferably 60:40 to 40:60. When the volume ratio of the polyvinyl chloride resin to the inorganic particles is within the above range, a good balance can be achieved between the adhesiveness of the separator to the electrodes and the permeability of the electrolyte solution and the ion permeability of the adhesive porous layer.

[0039] The porous substrate and adhesive porous layer of the separator of the present disclosure will be described in detail below.

[0040] [Porous substrate] In the present disclosure, the porous substrate refers to a substrate having pores or voids therein. Examples of such substrates include a microporous membrane; a porous sheet made of a fibrous material, such as a nonwoven fabric or paper; and a composite porous sheet obtained by laminating one or more other porous layers on the microporous membrane or porous sheet.

[0041] The material of the porous substrate is preferably an electrically insulating material.

[0042] From the viewpoint of thinning and strength of the separator, the porous substrate is preferably a microporous membrane. A microporous membrane refers to a membrane having a large number of micropores therein, with the micropores interconnected, allowing gas or liquid to pass through from one surface to the other.

[0043] From the viewpoint of thermal dimensional stability, the porous substrate is preferably a composite porous substrate in which one or more porous heat-resistant layers are laminated on a microporous membrane. The porous heat-resistant layer is preferably a heat-resistant layer containing at least one of inorganic particles and a heat-resistant resin. In the present disclosure, the heat-resistant resin refers to a resin having a melting point of 200°C or higher, or a resin having no melting point and a decomposition temperature of 200°C or higher. In other words, the heat-resistant resin in the present disclosure refers to a resin that does not melt or decompose in a temperature range below 200°C.

[0044] The porous substrate preferably contains a thermoplastic resin to impart a shutdown function to the porous substrate. The shutdown function refers to a function in which, when the battery temperature rises, the constituent materials dissolve and block the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. The thermoplastic resin preferably has a melting point of less than 200°C. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and polyolefins are particularly preferred.

[0045] As the porous substrate, from the viewpoint of imparting a shutdown function to the porous substrate, a porous substrate containing a microporous membrane containing polyolefin (referred to as "polyolefin microporous membrane" in the present disclosure) is preferred. Porous substrates containing a polyolefin microporous membrane include porous substrates consisting only of a polyolefin microporous membrane (i.e., a polyolefin microporous membrane) and composite porous substrates in which a porous heat-resistant layer is disposed on one or both sides of a polyolefin microporous membrane. Here, the porous heat-resistant layer is preferably a heat-resistant layer containing at least one of inorganic particles and a heat-resistant resin.

[0046] Examples of the polyolefin microporous membrane include polyolefin microporous membranes that are used in conventional battery separators, and it is preferable to select one from these that has sufficient mechanical properties and ion permeability.

[0047] From the viewpoint of exhibiting a shutdown function, the polyolefin microporous membrane is preferably a microporous membrane containing polyethylene, and the polyethylene content is preferably 95% by mass or more based on the total mass of the polyolefin microporous membrane.

[0048] The polyolefin microporous film is preferably a microporous film containing polypropylene, from the viewpoint of heat resistance that prevents the film from easily breaking when exposed to high temperatures.

[0049] From the viewpoint of providing a shutdown function and heat resistance that does not easily rupture when exposed to high temperatures, the polyolefin microporous membrane is preferably a polyolefin microporous membrane containing polyethylene and polypropylene. Examples of the polyolefin microporous membrane containing polyethylene and polypropylene include a microporous membrane in which polyethylene and polypropylene are mixed in one layer. From the viewpoint of achieving both the shutdown function and heat resistance, the microporous membrane preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. Also from the viewpoint of achieving both the shutdown function and heat resistance, a polyolefin microporous membrane having a laminate structure of two or more layers, at least one layer containing polyethylene and at least one layer containing polypropylene, is preferred.

[0050] The polyolefin contained in the polyolefin microporous membrane preferably has a weight-average molecular weight (Mw) of 100,000 to 5,000,000. When the Mw of the polyolefin is 100,000 or more, the microporous membrane can be imparted with sufficient mechanical properties. On the other hand, when the Mw of the polyolefin is 5,000,000 or less, the microporous membrane has good shutdown properties and is easy to mold.

[0051] Examples of methods for producing a polyolefin microporous membrane include a method in which a molten polyolefin resin is extruded through a T-die to form a sheet, which is crystallized, stretched, and then heat-treated to form a microporous membrane; and a method in which a molten polyolefin resin together with a plasticizer such as liquid paraffin is extruded through a T-die, cooled to form a sheet, stretched, the plasticizer is extracted, and then heat-treated to form a microporous membrane.

[0052] Examples of porous sheets made of fibrous materials include porous sheets such as nonwoven fabrics and paper. Examples of fibrous materials include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, heat-resistant resins such as wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide, and cellulose.

[0053] An example of a composite porous sheet is a sheet in which a functional layer is laminated on a microporous membrane or a porous sheet made of a fibrous material. Such a composite porous sheet is preferable from the viewpoint that the functional layer can add further functions. For example, an example of the functional layer is a porous heat-resistant layer from the viewpoint of imparting heat resistance to the composite porous sheet. Methods for combining a microporous membrane or a porous sheet with a functional layer include a method of coating the functional layer on the surface of the microporous membrane or porous sheet, a method of bonding the microporous membrane or porous sheet and the functional layer with an adhesive, and a method of thermocompression bonding the microporous membrane or porous sheet and the functional layer.

[0054] An example of an embodiment of a composite porous sheet is a composite porous substrate comprising a polyolefin microporous membrane and a heat-resistant layer containing at least one of inorganic particles and a heat-resistant resin, disposed on one or both sides of the polyolefin microporous membrane. The heat-resistant layer is a porous layer. Examples of inorganic particles include metal oxide particles (silica, alumina, boehmite, titania, zirconia, magnesium oxide, barium oxide, etc.), metal hydroxide particles (magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide, etc.), metal sulfate particles (barium sulfate, calcium sulfate, etc.), metal carbonate particles (calcium carbonate, magnesium carbonate, barium carbonate, etc.), metal nitride particles (boron nitride, aluminum nitride, etc.), and clay mineral particles (calcium silicate, talc, etc.). The inorganic particles may be surface-modified with a silane coupling agent or the like. Examples of heat-resistant resins include wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide.

[0055] When the composite porous substrate contains inorganic particles in the heat-resistant layer, the heat-resistant layer preferably also contains a binder resin that binds the inorganic particles. The binder resin may be a heat-resistant resin or a non-heat-resistant resin. Examples of non-heat-resistant resins include butadiene-based polymers (e.g., butadiene homopolymers, styrene-butadiene copolymers), and acrylic resins (e.g., homopolymers or copolymers of acrylic monomers, copolymers of acrylic monomers and styrene monomers).

[0056] A method for disposing a heat-resistant layer containing at least one of inorganic particles and a heat-resistant resin on one or both sides of a polyolefin microporous membrane includes coating one or both sides of the polyolefin microporous membrane with a coating liquid containing at least one of inorganic particles and a heat-resistant resin.

[0057] In this disclosure, the term "porous substrate" includes "composite porous substrate."

[0058] The surface of the porous substrate may be subjected to various surface treatments to improve wettability with the coating liquid for forming the adhesive porous layer, as long as the properties of the porous substrate are not impaired. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0059] -Characteristics of porous substrate- From the viewpoint of mechanical strength, the thickness of the porous substrate is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. From the viewpoint of increasing the energy density of the battery, the thickness of the porous substrate is preferably 10 μm or less, more preferably 9 μm or less, and even more preferably 8 μm or less. The thickness of the porous substrate is measured at 20 points within a 10 cm square using a contact thickness meter and the average is determined.

[0060] The air permeability of the porous substrate is preferably 50 seconds / 100 mL or more, more preferably 70 seconds / 100 mL or more, and even more preferably 90 seconds / 100 mL or more from the viewpoint of suppressing internal short circuits in the battery. The air permeability of the porous substrate is preferably 220 seconds / 100 mL or less, more preferably 200 seconds / 100 mL or less, and even more preferably 180 seconds / 100 mL or less from the viewpoint of excellent electrolyte permeability and ion permeability. The air permeability of the porous substrate is measured using a digital Oken air permeability tester in accordance with JIS P8117:2009.

[0061] When the porous substrate is a porous substrate consisting solely of a polyolefin microporous membrane (i.e., a polyolefin microporous membrane), the air permeability is preferably 40 seconds / 100 mL to 200 seconds / 100 mL, preferably 50 seconds / 100 mL to 200 seconds / 100 mL, more preferably 50 seconds / 100 mL to 180 seconds / 100 mL, more preferably 60 seconds / 100 mL to 180 seconds / 100 mL, more preferably 70 seconds / 100 mL to 160 seconds / 100 mL or less, and even more preferably 90 seconds / 100 mL to 140 seconds / 100 mL. When the porous substrate is a composite porous substrate in which a porous heat-resistant layer is disposed on one or both sides of a polyolefin microporous membrane, the air permeability is preferably 90 sec / 100 mL to 220 sec / 100 mL, more preferably 100 sec / 100 mL to 210 sec / 100 mL or less, and even more preferably 110 sec / 100 mL to 200 sec / 100 mL.

[0062] When the porous substrate is a porous substrate consisting solely of a polyolefin microporous membrane (i.e., a polyolefin microporous membrane), from the viewpoint of controlling the values ​​of (P2-P1) and (P2-P1) / P1 within preferred ranges, the air permeability is preferably 40 sec / 100 mL to 200 sec / 100 mL, more preferably 45 sec / 100 mL to 185 sec / 100 mL, and even more preferably 50 sec / 100 mL to 170 sec / 100 mL.

[0063] The porosity of the porous substrate is preferably 30% to 60% from the viewpoint of excellent electrolyte permeability and ion permeability. The porosity ε (%) of the porous substrate is calculated by the following formula: ε = {1 - Ws / (ds·t)} × 100, where Ws is the basis weight (g / m ２ ), ds is the true density of the porous substrate (g / cm ３ ), t is the thickness (μm) of the porous substrate. Basis weight is the mass per unit area.

[0064] [Adhesive Porous Layer] The adhesive porous layer is a layer disposed on the surface of the porous substrate and is the outermost layer of the separator. The adhesive porous layer has a large number of gaps or micropores, allowing gas or liquid to pass through from one surface to the other.

[0065] In the separator of the present disclosure, the adhesive porous layer contains a polyvinyl chloride resin and inorganic particles. Examples of the adhesive porous layer include a structure in which inorganic particles are bound or trapped in a porous structure in which fibrils containing a polyvinyl chloride resin are connected in a two-dimensional or three-dimensional network, a structure in which inorganic particles are bound or trapped in a network-like microporous structure containing a polyvinyl chloride resin, and a layered structure in which a large number of inorganic particles are connected to each other by a polyvinyl chloride resin, forming voids between the inorganic particles.

[0066] Polyvinyl chloride resins include homopolymers of vinyl chloride (also known as chloroethylene) (i.e., polyvinyl chloride) and copolymers of vinyl chloride with other monomers. In this disclosure, polyvinyl chloride resin refers to a resin in which the proportion of vinyl chloride is the largest among the monomers constituting the resin.

[0067] The monomer other than vinyl chloride constituting the polyvinyl chloride resin is preferably a monomer not containing a fluorine atom. Examples of the monomer other than vinyl chloride 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, and acrylonitrile.

[0068] From the viewpoint of the adhesiveness of the adhesive porous layer to the electrode, the polyvinyl chloride resin preferably contains vinyl chloride in an amount of 50% to 100%, more preferably 70% to 100%, and even more preferably 90% to 100% of the total monomers constituting the polyvinyl chloride resin.

[0069] The adhesive porous layer may contain one type of polyvinyl chloride resin or two or more types of polyvinyl chloride resins.

[0070] The polyvinyl chloride resin contained in the adhesive porous layer 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 adhesive porous layer has excellent mechanical strength and is less likely to peel off from the electrode. From this perspective, 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 adhesive porous layer, and the adhesive porous layer has excellent electrolyte permeability and ion permeability. Furthermore, when the average degree of polymerization of the polyvinyl chloride resin is 1400 or lower, high polymer chain mobility upon heating and ease of swelling in the electrolyte are ensured, making the adhesive porous layer easily adhered to the electrode by both dry heat pressing and wet heat pressing. Furthermore, when the average degree of polymerization of the polyvinyl chloride resin is 1400 or less, the viscosity of the coating liquid used to form the adhesive porous layer is relatively low, and the coating liquid has excellent coatability. From these viewpoints, the average degree of polymerization of the polyvinyl chloride resin is more preferably 1200 or less, and even more preferably 1000 or less.

[0071] The volume ratio of the polyvinyl chloride resin to the solid content volume of the adhesive porous layer is preferably 20% by volume to 90% by volume, more preferably 45% by volume to 88% by volume, and even more preferably 55% by volume to 85% by volume, from the viewpoint of achieving a good balance between the adhesiveness of the separator to the electrodes and the thermal dimensional stability of the separator.

[0072] In one embodiment, the volume ratio of the polyvinyl chloride resin to the solid volume of the adhesive porous layer is preferably 20% by volume to 80% by volume, more preferably 30% by volume to 70% by volume, and even more preferably 40% by volume to 60% by volume, from the viewpoint of achieving a good balance between the adhesiveness of the separator to the electrodes and the permeability of the electrolyte solution and the ion permeability of the adhesive porous layer.

[0073] When adhesive porous layers are present on both sides of the porous substrate, the type and / or content of the polyvinyl chloride resin contained in one adhesive porous layer may be the same as or different from the type and / or content of the polyvinyl chloride resin contained in the other adhesive porous layer.

[0074] -Other Resins- The adhesive porous layer may contain other resins in addition to polyvinyl chloride resins. Examples of other resins include acrylic resins, butadiene-acrylonitrile resins, homopolymers or copolymers of vinyl nitrile compounds (such as acrylonitrile and methacrylonitrile), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethers (such as polyethylene oxide and polypropylene oxide), and mixtures of two or more of these. These resins may be used alone or in combination.

[0075] The mass proportion of other resins in the total resin of the adhesive porous layer is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 1 mass% or less. The mass proportion of polyvinyl chloride resin in the total resin of the adhesive porous layer is preferably 90 mass% or more, more preferably 95 mass% or more, even more preferably 99 mass% or more, and particularly preferably 100 mass%.

[0076] Preferably, the adhesive porous layer does not substantially contain fluorine-containing resin.Examples of fluorine-containing resins include polyvinylidene fluoride resins and fluorine-containing rubber.Examples of polyvinylidene fluoride resins include homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride and halogen-containing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene; copolymers of vinylidene fluoride and other monomers other than halogen-containing monomers; copolymers of vinylidene fluoride, halogen-containing monomers, and other monomers other than halogen-containing monomers; and mixtures thereof.

[0077] The adhesive porous layer being substantially free of a fluorine-containing resin means that the mass proportion of the fluorine-containing resin in the adhesive porous layer is 1 mass% or less. The mass proportion of the fluorine-containing resin in the adhesive porous layer is preferably as small as possible, and is preferably 0.5 mass% or less, more preferably 0.1 mass% or less, and particularly preferably 0 mass%. In other words, it is particularly preferable that the adhesive porous layer is free of a fluorine-containing resin.

[0078] - 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.

[0079] Examples of metal oxides constituting the metal oxide particles include silica (silicon dioxide), alumina (aluminum oxide), boehmite (alumina monohydrate), titania (titanium oxide), zirconia (zirconium oxide), magnesium oxide, barium oxide, etc., with alumina being preferred. Examples of metal hydroxides constituting the metal hydroxide particles include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide, etc., with magnesium hydroxide being preferred. Examples of metal sulfates constituting the metal sulfate particles include barium sulfate, calcium sulfate, etc., with barium sulfate being preferred. Examples of metal carbonates constituting the metal carbonate particles include calcium carbonate, magnesium carbonate, barium carbonate, etc.. Examples of metal nitrides constituting the metal nitride particles include boron nitride, aluminum nitride, etc.. Examples of clay mineral particles include calcium silicate, talc, etc.

[0080] The inorganic particles may be surface-modified with a silane coupling agent or the like.

[0081] The inorganic particles may be used alone or in combination of two or more kinds.

[0082] From the viewpoints of stability in the electrolyte and electrochemical stability, the inorganic particles are preferably at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles, and more preferably at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles.

[0083] As the inorganic particles, metal sulfate particles are preferred, and barium sulfate particles are more preferred, from the viewpoint that they are less likely to decompose the electrolytic solution or electrolyte and therefore are less likely to cause gas generation inside the battery.

[0084] The particle shape of the inorganic particles is not limited, and may be any of spherical, elliptical, plate-like, needle-like, and amorphous. From the viewpoint of suppressing internal short circuits in the battery, the inorganic particles contained in the adhesive porous layer are preferably plate-like particles or non-aggregated primary particles.

[0085] The average primary particle size of the inorganic particles contained in the adhesive porous layer is preferably 0.01 μm to 2 μm, more preferably 0.03 μm to 1.5 μm, more preferably 0.05 μm to 1 μm, more preferably 0.08 μm to 0.8 μm, and even more preferably 0.1 μm to 0.5 μm. When the average primary particle size of the inorganic particles is 0.01 μm or more, a porous structure is easily formed in the adhesive porous layer, and the adhesive porous layer has excellent electrolyte permeability and ion permeability. From this perspective, the average primary particle size of the inorganic particles is more preferably 0.03 μm or more, more preferably 0.05 μm or more, more preferably 0.08 μm or more, and even more preferably 0.1 μm or more. When the average primary particle size of the inorganic particles is 2 μm or less, the adhesive porous layer easily adheres to the electrode and is less likely to peel off from the electrode. From this viewpoint, the average primary particle size of the inorganic particles is more preferably 1.5 μm or less, more preferably 1 μm or less, still more preferably 0.8 μm or less, and even more preferably 0.5 μm or less.

[0086] The average primary particle size of inorganic particles is determined by measuring the long diameters of 100 randomly selected inorganic particles in scanning electron microscope (SEM) observation and averaging the long diameters of the 100 particles. The sample used for SEM observation is inorganic particles that are the material for forming the adhesive porous layer, or inorganic particles removed from the adhesive porous layer. There are no limitations on the method for removing inorganic particles from the adhesive porous layer. Examples of such methods include immersing the adhesive porous layer peeled off from the separator in an organic solvent that dissolves the binder resin to remove the inorganic particles; or heating the adhesive porous layer peeled off from the separator to about 800°C to remove the binder resin and remove the inorganic particles.

[0087] In one embodiment of the separator, the adhesive porous layer contains first inorganic particles having an average primary particle size of 0.5 μm to 1.0 μm and second inorganic particles having an average primary particle size smaller than that of the first inorganic particles. From the viewpoint of forming a good porous structure in the adhesive porous layer, the average primary particle size of the first inorganic particles is 0.5 μm to 1.0 μm, preferably 0.6 μm to 0.9 μm. From the viewpoint of suppressing aggregation between inorganic particles and enhancing the robustness of the porous structure of the adhesive porous layer, the average primary particle size of the second inorganic particles is preferably 0.01 μm or more and less than 0.5 μm, more preferably 0.05 μm to 0.45 μm, and even more preferably 0.1 μm to 0.4 μm.

[0088] In separators in which the adhesive porous layer contains first inorganic particles and second inorganic particles, the average primary particle size of the inorganic particles contained in the adhesive porous layer is preferably 0.01 μm to 2 μm, more preferably 0.03 μm to 1.5 μm, more preferably 0.05 μm to 1 μm, more preferably 0.08 μm to 0.8 μm, and even more preferably 0.1 μm to 0.5 μm. The average primary particle size here refers to the average primary particle size of the entire first inorganic particles and the second inorganic particles combined. When the average primary particle size of the inorganic particles is 0.01 μm or more, a porous structure is easily formed in the adhesive porous layer, and the adhesive porous layer has excellent electrolyte permeability and ion permeability. From this perspective, the average primary particle size of the inorganic particles is preferably 0.03 μm or more, more preferably 0.05 μm or more, more preferably 0.08 μm or more, and even more preferably 0.1 μm or more. When the average primary particle size of the inorganic particles is 2 μm or less, the adhesive porous layer is easily adhered to the electrode and is not easily peeled off from the electrode. From this viewpoint, the average primary particle size of the inorganic particles is more preferably 1.5 μm or less, more preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.5 μm or less.

[0089] The presence of the first inorganic particles and the second inorganic particles in the adhesive porous layer of the separator can be confirmed by the following method. Samples of inorganic particles removed from the adhesive porous layer are subjected to SEM observation and measurement of their major diameters as described above, and a histogram of the major diameters is created. The histogram shows at least one peak in the particle size range of 0.5 μm to 1.0 μm, and at least one peak in the particle size range of 0.01 μm to less than 0.5 μm.

[0090] The volume ratio of the inorganic particles to the solid content volume of the adhesive porous layer is preferably 10 vol% to 80 vol%, more preferably 12 vol% to 55 vol%, and even more preferably 15 vol% to 45 vol%, from the viewpoint of achieving a good balance between the adhesiveness of the separator to the electrode and the thermal dimensional stability of the separator.

[0091] In one embodiment, the volume ratio of the inorganic particles to the solid volume of the adhesive porous layer is preferably 20% by volume to 80% by volume, more preferably 30% by volume to 70% by volume, and even more preferably 40% by volume to 60% by volume, from the viewpoint of achieving a good balance between the adhesiveness of the separator to the electrode and the permeability of the electrolyte solution and the ion permeability of the adhesive porous layer.

[0092] The proportion of the first inorganic particles in the total amount of the first inorganic particles and the second inorganic particles contained in the adhesive porous layer of the separator is preferably 30 vol% to 70 vol%, more preferably 35 vol% to 65 vol%, and even more preferably 40 vol% to 60 vol%, from the viewpoints of forming a good porous structure in the adhesive porous layer and making the porous structure of the adhesive porous layer robust.

[0093] When adhesive porous layers are present on both sides of the porous substrate, the type and / or content of inorganic particles contained in one adhesive porous layer may be the same as or different from the type and / or content of inorganic particles contained in the other adhesive porous layer.

[0094] -Organic Particles- The adhesive porous layer may contain organic particles. Examples of organic particles include particles made of crosslinked polymers such as crosslinked poly(meth)acrylic acid, crosslinked poly(meth)acrylic acid ester, crosslinked polysilicone, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensate; and particles made of heat-resistant polymers such as polysulfone, polyacrylonitrile, aramid, and polyacetal. The resin constituting the organic particles may be a mixture, modified product, derivative, copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer), or crosslinked product of the above-mentioned exemplified materials.

[0095] The organic particles may be used alone or in combination of two or more kinds.

[0096] -Other Components- The adhesive porous layer may contain additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming agent, and a pH adjuster. Dispersants are added, for example, to a coating liquid for forming the adhesive porous layer for the purpose of improving dispersibility, coatability, or storage stability. Wetting agents, antifoaming agents, and pH adjusters are added, for example, to a coating liquid for forming the adhesive porous layer for the purpose of improving compatibility with the porous substrate, preventing air entrapment in the coating liquid, or adjusting the pH.

[0097] - Characteristics of adhesive porous layer - The mass per unit area of ​​the adhesive porous layer was 0.6 g / m per side of the separator. ２ ~3.0g / m ２ It is preferable that the density is 0.6 g / m ２ ~2.5g / m ２ is preferred, and 0.6 g / m ２ ~2.0 g / m ２ More preferably, 0.8 g / m ２ ~1.8g / m ２ More preferably, 1.0 g / m ２ ~1.5g / m ２ It is more preferable that the mass per unit area of ​​the adhesive porous layer is 0.6 g / m per one side of the separator. ２ When the adhesive porous layer has a mass per unit area of ​​0.8 g / m or more per one side of the separator, the adhesive porous layer has excellent adhesion to the electrodes and excellent thermal dimensional stability of the separator. ２ More preferably, 1.0 g / m or more ２ More preferably, the mass per unit area of ​​the adhesive porous layer is 3.0 g / m per one side of the separator. ２ From this viewpoint, the mass per unit area of ​​the adhesive porous layer is 2.5 g / m per one side of the separator. ２ More preferably, 2.0 g / m or less ２ More preferably, 1.8 g / m or less ２ More preferably, 1.5 g / m or less ２ The following is even more preferred:

[0098] When the adhesive porous layer is on both sides of the separator, the mass per unit area of ​​the adhesive porous layer is 1.2 g / m in total for both sides. ２ ~6.0g / m ２ is preferred, and 1.2 g / m ２ ~5.0g / m ２ is preferred, and 1.6 g / m ２ ~4.0g / m ２ More preferably, 1.6 g / m ２ ~3.6g / m ２ More preferably, 2.0 g / m ２ ~3.0g / m ２ is more preferred.

[0099] The mass per unit area of ​​the adhesive porous layer is determined by cutting the separator into a 20 cm x 20 cm piece, peeling off the adhesive porous layer, measuring the mass, and dividing the mass by the area.

[0100] [Separator Properties] From the viewpoint of mechanical strength, the thickness of the separator is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 9 μm or more. From the viewpoint of the energy density of the battery, the thickness of the separator is preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less. The thickness of the separator is determined by measuring 20 points within a 10 cm square using a contact thickness meter and averaging the measurements.

[0101] From the viewpoint of suppressing internal short circuits in the battery, the separator's air permeability is preferably 70 seconds / 100 mL or more, preferably 100 seconds / 100 mL or more, more preferably 120 seconds / 100 mL or more, and even more preferably 150 seconds / 100 mL or more. From the viewpoint of ion permeability, the separator's air permeability is preferably 500 seconds / 100 mL or less, more preferably 400 seconds / 100 mL or less, and even more preferably 300 seconds / 100 mL or less. The separator's air permeability is measured using a digital Oken air permeability tester in accordance with JIS P8117:2009.

[0102] From the viewpoint of ion permeability, the porosity of the separator is preferably 30% to 60%. The porosity ε (%) of the separator is calculated by the following formula:

[0103]

[0104] 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).

[0105] When the air permeability of the porous substrate is P1 (seconds / 100 mL) and the air permeability of the separator is P2 (seconds / 100 mL), from the viewpoint of excellent adhesion to the electrode and improving the cycle characteristics of the battery, the value of (P2-P1) / P1 is preferably 0.2 to 0.85, more preferably 0.25 to 0.8, and even more preferably 0.3 to 0.7.

[0106] When the air permeability of the porous substrate is P1 (seconds / 100 mL) and the air permeability of the separator is P2 (seconds / 100 mL), from the viewpoint of excellent adhesion to the electrode and improving the cycle characteristics of the battery, the value of (P2-P1) is preferably 30 seconds / 100 mL to 65 seconds / 100 mL, more preferably 35 seconds / 100 mL to 62 seconds / 100 mL, and even more preferably 40 seconds / 100 mL to 60 seconds / 100 mL.

[0107] [Method for Manufacturing Separator] The separator of the present disclosure can be manufactured, for example, by forming an adhesive porous layer on a porous substrate by a wet coating method or a dry coating method. In the present disclosure, the wet coating method is a method in which a coating layer is solidified in a coagulation liquid, and the dry coating method is a method in which a coating layer is solidified by drying. An embodiment of the wet coating method will be described below. In the following description, the "adhesive porous layer" will be simply referred to as the "porous layer."

[0108] The wet coating method includes, for example, a step of applying a coating liquid to one or both sides of a porous substrate to form a coating layer, a step of immersing the porous substrate having the coating layer in a coagulation liquid to solidify the coating layer and form a porous layer, and a step of lifting the laminate consisting of the porous substrate and the porous layer out of the coagulation liquid, washing with water, and drying.

[0109] The coating liquid for forming the porous layer is prepared by dissolving or dispersing a polyvinyl chloride resin and inorganic particles in a solvent. If necessary, other components besides the polyvinyl chloride resin and inorganic particles may be dissolved or dispersed in the coating liquid.

[0110] The solvent used in preparing the coating liquid includes a solvent that dissolves polyvinyl chloride resin (hereinafter also referred to as a "good solvent"), such as polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0111] The solvent used to prepare the coating solution may contain a phase separation agent that induces phase separation in order to form a porous layer with a good porous structure. Therefore, the solvent used to prepare the coating solution may be a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with the good solvent in an amount that ensures a viscosity appropriate for coating. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0112] When the solvent used to prepare the coating liquid is a mixed solvent of a good solvent and a phase separation agent, from the viewpoint of forming a good porous structure, a mixed solvent containing 60% by mass or more of the good solvent and 5% by mass to 40% by mass of the phase separation agent is preferred.

[0113] The resin concentration in the coating liquid is preferably 1% by mass to 20% by mass from the viewpoint of forming a good porous structure, and the inorganic particle concentration in the coating liquid is preferably 0.5% by mass to 50% by mass from the viewpoint of forming a good porous structure.

[0114] The coating liquid may contain a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjuster, etc. These additives may remain in the porous layer as long as they are electrochemically stable within the range of use of the nonaqueous secondary battery and do not inhibit the reaction within the battery.

[0115] Examples of means for applying the coating liquid to the porous substrate include a Mayer bar, a die coater, a reverse roll coater, a roll coater, a gravure coater, etc. When forming a porous layer on both sides of the porous substrate, it is preferable from the viewpoint of productivity to apply the coating liquid to both sides of the porous substrate simultaneously.

[0116] The coating layer is solidified by immersing the porous substrate with the coating layer formed thereon in a coagulation liquid to induce phase separation in the coating layer while solidifying the resin, thereby obtaining a laminate consisting of the porous substrate and the porous layer.

[0117] The coagulation liquid generally contains the good solvent and phase separation agent used in preparing the coating liquid, as well as water. It is preferable from a production standpoint that the mixing ratio of the good solvent and the phase separation agent be the same as the mixing ratio of the mixed solvent used in preparing the coating liquid. From the viewpoints of forming a porous structure and productivity, the water content in the coagulation liquid is preferably 40% by mass to 90% by mass. The temperature of the coagulation liquid is, for example, 20°C to 50°C.

[0118] After the coating layer is solidified in the coagulating liquid, the laminate is lifted out of the coagulating liquid and washed with water. The coagulating liquid is removed from the laminate by washing with water. The water is then removed from the laminate by drying. The washing with water is carried out, for example, by transporting the laminate in a water bath. The drying is carried out, for example, by transporting the laminate in a high-temperature environment, by blowing air on the laminate, or by bringing the laminate into contact with a heat roll. The drying temperature is preferably 40°C to 80°C.

[0119] The separator of the present disclosure can also be manufactured by a dry coating method, which is a method of applying a coating liquid to a porous substrate and drying the coating layer to volatilize and remove the solvent, thereby forming a porous layer on the porous substrate.

[0120] The separator of the present disclosure can also be produced by a method in which the porous layer is produced as an independent sheet, and this porous layer is then superimposed on a porous substrate and combined with thermocompression bonding or an adhesive. Examples of a method for producing the porous layer as an independent sheet include a method in which the porous layer is formed on a release sheet by applying the above-mentioned wet coating method or dry coating method.

[0121] The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery that generates electromotive force by doping and dedoping lithium ions, and includes a positive electrode, a negative electrode, and the separator of the present disclosure. Doping refers to occlusion, support, adsorption, or insertion, and refers to the phenomenon in which lithium ions enter the active material of the electrode.

[0122] The nonaqueous secondary battery of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is enclosed in an exterior material together with an electrolyte solution. The nonaqueous secondary battery of the present disclosure is suitable for nonaqueous electrolyte secondary batteries, particularly lithium ion secondary batteries.

[0123] In the nonaqueous secondary battery of the present disclosure, the separator of the present disclosure has excellent adhesion to the electrodes, so that the electrodes and the separator are less likely to peel off, and internal short circuits are less likely to occur.In the nonaqueous secondary battery of the present disclosure, the separator of the present disclosure has excellent thermal dimensional stability, so that internal short circuits are less likely to occur.

[0124] One embodiment of the nonaqueous secondary battery of the present disclosure has excellent cycle characteristics due to the separator containing first inorganic particles and second inorganic particles in the adhesive porous layer.

[0125] An example of an embodiment of the nonaqueous secondary battery of the present disclosure has excellent cycle characteristics by including a separator in which the value of (P2-P1) / P1, where P1 is the air permeability of the porous substrate and P2 is the air permeability of the separator, is 0.85 or less.

[0126] Hereinafter, examples of the positive electrode, negative electrode, electrolyte, and exterior material included in the nonaqueous secondary battery of the present disclosure will be described.

[0127] An example of the positive electrode is a structure in which an active material layer containing a positive electrode active material and a binder resin is disposed on a current collector. The active material layer may further contain a conductive additive. Examples of the positive electrode active material include lithium-containing transition metal oxides, specifically LiCoO ２ , LiNiO ２ , LiMn １／２ Ni １／２ O ２ , LiCo １／３ Mn １／３ Ni １／３ O ２ , LiMn ２ O ４ , LiFePO ４ , LiCo １／２ Ni １／２ O ２ , LiAl １／４ Ni ３／４ O ２ Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, and graphite powder. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil, each having a thickness of 5 μm to 20 μm.

[0128] An example of an embodiment of the negative electrode includes a structure in which an active material layer containing a negative electrode active material and a binder resin is disposed on a current collector. The active material layer may further include a conductive additive. Examples of negative electrode active materials include materials capable of electrochemically absorbing lithium ions, such as carbon materials; alloys of lithium with silicon, tin, aluminum, etc.; and Wood's alloy. Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers. Examples of current collectors include copper foil, nickel foil, stainless steel foil, and the like, each having a thickness of 5 μm to 20 μm. Alternatively, a metallic lithium foil may be used as the negative electrode instead of the above-described negative electrode.

[0129] The electrolyte is preferably a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ６ , LiBF ４ , LiClO ４ Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted derivatives thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone; which may be used alone or in combination. A suitable electrolyte solution is a solution in which a cyclic carbonate and a chain carbonate are mixed in a mass ratio (cyclic carbonate:chain carbonate) of 20:80 to 40:60, and a lithium salt is dissolved in the range of 0.5 mol / L to 1.5 mol / L.

[0130] Examples of the exterior packaging include aluminum laminate film packs, metal cans, etc. Battery shapes include prismatic, cylindrical, coin-shaped, etc., and the separator of the present disclosure is suitable for any of these shapes.

[0131] The nonaqueous secondary battery of the present disclosure can be produced by producing a laminate in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode, and then using this laminate by, for example, any of the following production methods (1) to (3).

[0132] Manufacturing method (1): The laminate is dry-heat pressed to temporarily bond the electrodes and separator, and then housed in an exterior packaging (e.g., an aluminum laminate film pack; the same applies hereinafter), and an electrolyte solution is poured into it. Next, the laminate is wet-heat pressed from above the exterior packaging to bond the electrodes and separator and seal the exterior packaging.

[0133] Manufacturing method (2): The laminate is placed in an exterior packaging material, and an electrolyte solution is poured into the exterior packaging material. The laminate is then wet-heat pressed onto the exterior packaging material to bond the electrodes and separator together and seal the exterior packaging material.

[0134] Manufacturing method (3): The laminate is dry-heat pressed to bond the electrodes and the separator, and then the laminate is housed in an exterior packaging material, into which an electrolyte solution is injected, and the exterior packaging material is then sealed.

[0135] In the production method (1) or (2), the pressing temperature of the wet heat press is preferably 50°C to 90°C, more preferably 60°C to 80°C. The pressing pressure of the wet heat press is preferably 0.1 MPa to 2 MPa, more preferably 0.5 MPa to 1.5 MPa. The pressing time of the wet heat press is preferably adjusted according to the pressing temperature and pressing pressure, for example, within a range of 1 minute to 12 hours.

[0136] In the production method (1) or (3), the pressing temperature of the dry heat press is preferably 60°C to 90°C, more preferably 70°C to 85°C. The pressing pressure of the dry heat press is preferably 0.5 MPa to 5 MPa, more preferably 0.5 MPa to 3 MPa. The pressing time of the dry heat press is preferably adjusted according to the pressing temperature and pressing pressure, for example, within a range of 0.5 minutes to 1 hour.

[0137] When manufacturing a laminate in which a separator is disposed between a positive electrode and a negative electrode, the method of disposing the separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of a positive electrode, a separator, and a negative electrode in this order (so-called stack method), or a method of stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them in the length direction.

[0138] The separator and nonaqueous secondary battery of the present disclosure will be described in more detail below with reference to examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the separator and nonaqueous secondary battery of the present disclosure should not be construed as being limited by the specific examples shown below.

[0139] In the following description, syntheses, treatments, manufacturing, etc. were carried out at room temperature (25° C.±3° C.) unless otherwise specified.

[0140] <Measurement Methods and Evaluation Methods> The measurement methods and evaluation methods used in the examples and comparative examples are as follows.

[0141] [Thickness of porous substrate and separator] The thickness of the porous substrate and separator was measured at 20 points within a 10 cm square using a contact thickness meter (Mitutoyo Corporation, LITEMATIC VL-50S) and the average was calculated. A spherical probe with a sphere radius of 10 mm (Mitutoyo Corporation) was used as the measurement terminal, and a load of 0.19 N was applied during the measurement.

[0142] [Air Permeability of Porous Substrate and Separator] The air permeability (seconds / 100 mL) of the porous substrate and the separator was measured according to JIS P8117:2009 using a digital Oken air permeability tester (Asahi Seiko Co., Ltd., model EG01).

[0143] [(P2-P1) and (P2-P1) / P1] (P2-P1) and (P2-P1) / P1 were calculated by taking the air permeability of the porous substrate as P1 (seconds / 100 mL) and the air permeability of the separator as P2 (seconds / 100 mL).

[0144] [Average primary particle size of inorganic particles] The inorganic particles used to form the adhesive porous layer were used as samples and observed with a scanning electron microscope (SEM) to determine the average primary particle size. The major axes of 100 randomly selected inorganic particles on the SEM image were measured, and the average value of the major axes of the 100 particles was taken as the average primary particle size (μm). When multiple types of inorganic particles with different particle sizes were used to form the adhesive porous layer, each was used as a sample and observed with the SEM to determine the average primary particle size.

[0145] [Weight per unit area of ​​adhesive porous layer] The separator was cut into a size of 20 cm x 20 cm, the adhesive porous layer was peeled off, and the weight was measured. The weight was divided by the area to obtain the weight per unit area (g / m) of both sides in total. ２ ) was sought.

[0146] [Adhesion to Electrode] 89.5 parts by mass of lithium cobalt oxide powder as a positive electrode active material, 4.5 parts by mass of acetylene black as a conductive additive, 6 parts by mass of polyvinylidene fluoride as a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone were mixed and stirred in a twin-arm mixer to prepare a positive electrode slurry. The positive electrode slurry was applied to one side of a 20 μm thick aluminum foil, dried, and pressed to obtain a positive electrode having a positive electrode active material layer on one side.

[0147] A negative electrode slurry was prepared by mixing 300 parts by mass of artificial graphite as a negative electrode active material, 7.5 parts by mass of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder resin, 3 parts by mass of carboxymethyl cellulose as a thickener, and an appropriate amount of water using a twin-arm mixer. The negative electrode slurry was applied to one side of a 10 μm thick copper foil, dried, and pressed to obtain a negative electrode having a negative electrode active material layer on one side.

[0148] 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 18 mm in diameter x 74 mm in length. Release paper measuring 15 mm wide x 70 mm long was prepared. The separator was placed on the active material layer of the electrode (positive or negative electrode), and then release paper was placed on top of the separator to produce a laminate.

[0149] The laminate was inserted into an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF ６ - Ethylene carbonate: ethyl methyl carbonate [mass ratio 3:7]) was injected, and the laminate was impregnated with the electrolyte solution. Next, the pack was heat-pressed in the stacking direction of the laminate using a heat press machine (wet heat press) to bond the electrode (positive electrode or negative electrode) and the separator. After heat pressing, the laminate was removed from the pack, and the release paper was peeled off to obtain a wet adhesive test piece. The heat press conditions were one of the following. Separator (1): temperature 85°C, pressure 1 MPa, time 5 minutes Separator (2): temperature 70°C, pressure 1 MPa, time 5 minutes Separator (3): temperature 70°C, pressure 1 MPa, time 5 minutes

[0150] The laminate was inserted into an aluminum laminate film pack, and the pack was heat-pressed in the stacking direction of the laminate using a heat press (dry heat press) to bond the electrode (positive electrode or negative electrode) to the separator. After heat pressing, the laminate was removed from the pack, and the release paper was peeled off to obtain a dry adhesive test piece. The heat press conditions were one of the following: Separator (1): Temperature 85°C, pressure 1 MPa, time 0.5 minutes Separator (2): Temperature 75°C, pressure 1 MPa, time 0.5 minutes Separator (3): Temperature 75°C, pressure 1 MPa, time 0.5 minutes

[0151] 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 Co., Ltd., STB-1225S). The metal plate was fixed to the Tensilon so that the longitudinal direction of the test specimen (i.e., the MD of the separator) was the direction of gravity. The separator was peeled from the electrode by approximately 2 cm from the lower end, and this end was fixed to the upper chuck, and a 180° peel test was performed. The tensile speed for the 180° peel test was 20 mm / min, and loads (N) were collected from 10 mm to 40 mm after the start of the measurement at 0.4 mm intervals, and the average was calculated. The loads for 10 test specimens were then averaged to determine the adhesive strength (N / 15 mm) between the electrode and the separator.

[0152] [Heat Shrinkage] The separator was cut into a rectangle measuring 60 mm in TD x 180 mm in MD to prepare a test specimen. Marks were made on the test specimen at 20 mm and 170 mm from one end on the line dividing the test specimen in half in TD (referred to as points A and B, respectively). Furthermore, marks were made on the test specimen at 10 mm and 50 mm from one end on the line dividing the test specimen in half in MD (referred to as points C and D, respectively). A clip was attached to the test specimen (the clip was attached between the end closest to point A and point A), and the specimen was hung in an oven at 105°C and subjected to heat treatment for 60 minutes under no tension. The lengths between A and B and between CD were measured before and after heat treatment, and the heat shrinkage was calculated using the following formula. The heat shrinkage of the three test specimens was then averaged.

[0153] MD heat shrinkage rate (%) = {(length AB before heat treatment - length AB after heat treatment) ÷ length AB before heat treatment} × 100

[0154] TD heat shrinkage rate (%) = {(CD length before heat treatment - CD length after heat treatment) ÷ CD length before heat treatment} × 100

[0155] [Cycle Characteristics] Ten non-aqueous secondary batteries, as described below, were prepared. The batteries were subjected to 300 charge / discharge cycles in an environment at a temperature of 25°C. Charging was performed at a constant current and constant voltage of 3C / 4.2V, and discharging was performed at a constant current with a cutoff of 3C / 2.75V. The discharge capacity at the 300th cycle was divided by the initial discharge capacity to calculate the capacity retention rate (%). The average value for the 10 batteries was then calculated, and the average value of the capacity retention rate was classified as follows: P: 30% or more N: less than 30%

[0156] <Preparation of Separator (1) and Battery> [Example 1] -Preparation of Separator- Polyvinyl chloride (average degree of polymerization 690, homopolymer) was dissolved in dimethylacetamide (DMAc), and barium sulfate particles were further dispersed by stirring to prepare a coating solution (1). The coating solution (1) had a polyvinyl chloride concentration of 6.0 mass %, and a polyvinyl chloride:barium sulfate particle volume ratio of 58:42. An appropriate amount of the coating solution (1) was placed on a Mayer bar, and the coating solution (1) was applied to both sides of a polyethylene microporous membrane (thickness 6 μm, air permeability 100 sec / 100 mL). The coating was performed so that the coating amount was equal on both sides of the polyethylene microporous membrane. The polyethylene microporous membrane with the coating layer formed thereon was immersed in a coagulation liquid (DMAc:water = 50:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer. The film was then washed in a water washing tank with water at a temperature of 40° C. and dried. In this way, a separator was obtained in which adhesive porous layers were formed on both sides of the polyethylene microporous film.

[0157] - Preparation of Positive Electrode - 89.5 parts by mass of lithium cobalt oxide powder as the positive electrode active material, 4.5 parts by mass of acetylene black as the conductive additive, 6 parts by mass of polyvinylidene fluoride as the binder resin, and an appropriate amount of N-methyl-2-pyrrolidone were mixed and stirred in a twin-arm mixer to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 20 μm thick aluminum foil, dried, and pressed to obtain a positive electrode having positive electrode active material layers on both sides.

[0158] - Preparation of negative electrode - 300 parts by mass of artificial graphite as a negative electrode active material, 7.5 parts by mass of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder resin, 3 parts by mass of carboxymethyl cellulose as a thickener, and an appropriate amount of water were mixed by stirring using a twin-arm mixer to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides of a 10 μm thick copper foil, dried, and pressed to obtain a negative electrode having a negative electrode active material layer on both sides.

[0159] - Preparation of Battery - The positive electrode and the negative electrode were each cut into a rectangle of 30 mm x 50 mm, and a lead tab was welded to each. The separator was cut into a rectangle of TD 35 mm x MD 55 mm. These were stacked so that the positive electrode and the negative electrode alternated and the separator was sandwiched between the positive electrode and the negative electrode, to prepare a stack consisting of three positive electrodes, three negative electrodes, and five separators. The stack was inserted into an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF ６ A mixture of ethylene carbonate and ethyl methyl carbonate (mass ratio 3:7) was poured into the laminate to allow the electrolyte to penetrate the laminate. The laminate was then heat-pressed (wet heat press) along the stacking direction of the pack using a heat press machine to bond the electrodes and separators. The heat press conditions were a press temperature of 85°C, a press pressure of 1 MPa, and a press time of 5 minutes. A non-aqueous secondary battery was thus obtained.

[0160] [Examples 2 to 12] Separators were produced in the same manner as in Example 1, except that at least one of the average degree of polymerization of polyvinyl chloride, the type of inorganic particles, the average primary particle size and volume ratio, and the coating amount of the adhesive porous layer was changed as shown in Table 1. Non-aqueous secondary batteries were produced using each separator.

[0161] Example 13 A separator was prepared in the same manner as in Example 1, except that the polyethylene microporous membrane was replaced with a composite porous substrate (thickness: 8 μm, air permeability: 140 sec / 100 mL) having porous heat-resistant layers on both sides of the polyethylene microporous membrane. A nonaqueous secondary battery was prepared using this separator. The composite porous substrate had a polyethylene microporous membrane with a thickness of 6 μm and an air permeability of 100 sec / 100 mL, and a heat-resistant layer containing γ-alumina (average primary particle size: 0.01 μm) and styrene-butadiene rubber, with a γ-alumina content of 97% by mass and a thickness of 1 μm per side.

[0162] Comparative Example 1 A separator was prepared in the same manner as in Example 1, except that polyvinyl chloride was replaced with a polyvinylidene fluoride resin (a binary copolymer of vinylidene fluoride and hexafluoropropylene, weight-average molecular weight 1.4 million, hexafluoropropylene 1.5 mol%). A nonaqueous secondary battery was prepared using this separator. However, the heat pressing conditions were changed to a pressing temperature of 85°C, a pressing pressure of 1 MPa, and a pressing time of 0.3 minutes.

[0163] Comparative Example 2 A separator was produced in the same manner as in Example 1, except that no inorganic particles were used to form the adhesive porous layer, and only polyvinyl chloride was used. A nonaqueous secondary battery was produced using this separator.

[0164] In Examples 1 to 12 and Comparative Examples 1 and 2, the adhesive porous layer was applied so that the separator had a thickness of 9 μm or 10 μm, respectively. In Example 13, the adhesive porous layer was applied so that the separator had a thickness of 11 μm.

[0165] Table 1 shows the configurations of the porous substrate and adhesive porous layer, and Table 2 shows the physical properties and evaluation results of the separator. The mass of the adhesive porous layer shown in Table 1 is the total mass of both sides of the separator. The mass of the adhesive porous layer per separator side in each example and comparative example is half the mass of the adhesive porous layer shown in Table 1. The abbreviations in Table 1 have the following meanings. PVC: polyvinyl chloride VDF-HFP: binary copolymer of vinylidene fluoride and hexafluoropropylene

[0166]

[0167]

[0168] <Preparation of Separator (2) and Battery> [Example 21] -Preparation of Separator- Dimethylacetamide (DMAc) and tripropylene glycol (TPG) were mixed at a mass ratio of 90:10 to prepare a mixed solvent. Polyvinyl chloride (average degree of polymerization 690, homopolymer) was dissolved in the mixed solvent, and two types of barium sulfate particles with different particle sizes were further stirred and dispersed to prepare a coating liquid (1). The coating liquid (1) had a polyvinyl chloride concentration of 6.0 mass%, and a polyvinyl chloride:barium sulfate particle volume ratio of 44:56. An appropriate amount of the coating liquid (1) was placed on a Mayer bar, and the coating liquid (1) was applied to both sides of a polyethylene microporous membrane (thickness 8 μm, air permeability 160 sec / 100 mL). The coating was performed so that the coating amount on the front and back of the polyethylene microporous membrane was equal. The polyethylene microporous membrane with the coating layer formed thereon was immersed in a coagulation liquid (DMAc:TPG:water=45:5:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer. The membrane was then washed in a water washing tank with water at 40°C and dried. A separator with adhesive porous layers formed on both sides of the polyethylene microporous membrane was thus obtained. A nonaqueous secondary battery was fabricated using this separator in the same manner as in Example 1.

[0169] [Examples 22 to 24] Separators were produced in the same manner as in Example 21, except that at least one of the average degree of polymerization of polyvinyl chloride, the type of inorganic particles, the average primary particle size and volume ratio, and the coating amount of the adhesive porous layer was changed as shown in Table 3. Non-aqueous secondary batteries were produced using each separator.

[0170] [Comparative Example 21] A separator was produced in the same manner as in Example 21, except that the thickness and air permeability of the polyethylene microporous membrane, the type and average primary particle size of the inorganic particles, and the coating amount of the adhesive porous layer were changed as shown in Table 3. A nonaqueous secondary battery was produced using this separator. In Comparative Example 21, the coating liquid was prepared using only DMAc as the solvent without using TPG. Barium sulfate particles with an average primary particle size of 0.3 μm were used as the inorganic particles.

[0171] In Examples 21 to 24, the adhesive porous layer was coated so that the separator had a thickness of 10 μm or 11 μm, respectively. In Comparative Example 21, the adhesive porous layer was coated so that the separator had a thickness of 13 μm.

[0172] Table 3 shows the configurations of the porous substrate and adhesive porous layer, and Table 4 shows the physical properties and evaluation results of the separator. The mass of the adhesive porous layer shown in Table 3 is the total mass of both sides of the separator. The mass of the adhesive porous layer per separator side in each example and comparative example is half the mass of the adhesive porous layer shown in Table 3. The abbreviations in Table 3 have the following meanings. PVC: Polyvinyl chloride

[0173]

[0174]

[0175] <Preparation of Separator (3) and Battery> [Example 31] -Preparation of Separator- Dimethylacetamide (DMAc) and tripropylene glycol (TPG) were mixed at a mass ratio of 90:10 to prepare a mixed solvent. Polyvinyl chloride (average degree of polymerization 690, homopolymer) was dissolved in the mixed solvent, and barium sulfate particles were further stirred and dispersed to prepare a coating liquid (1). The coating liquid (1) had a polyvinyl chloride concentration of 6.0 mass%, and a polyvinyl chloride:barium sulfate particle volume ratio of 44:56. An appropriate amount of the coating liquid (1) was placed on a Mayer bar, and the coating liquid (1) was applied to both sides of a polyethylene microporous membrane (thickness 6 μm, air permeability 65 sec / 100 mL). The coating was performed so that the coating amount on the front and back of the polyethylene microporous membrane was equal. The polyethylene microporous membrane with the coating layer formed thereon was immersed in a coagulation liquid (DMAc:TPG:water=45:5:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer. The membrane was then washed in a water washing tank with water at 40°C and dried. A separator with adhesive porous layers formed on both sides of the polyethylene microporous membrane was thus obtained. A nonaqueous secondary battery was fabricated using this separator in the same manner as in Example 1.

[0176] [Examples 32 to 34] Separators were produced in the same manner as in Example 31, except that at least one of the thickness and air permeability of the polyethylene microporous membrane, the type of inorganic particles, the average primary particle size and volume ratio, and the coating amount of the adhesive porous layer was changed as shown in Table 5. Non-aqueous secondary batteries were produced using each separator.

[0177] Example 35 A separator was produced in the same manner as in Example 31, except that the mixed solvent used to prepare the coating liquid was changed to a mixed solvent of DMAc and TPG in a mass ratio of 85:15, and the air permeability of the polyethylene microporous membrane and the coating amount of the adhesive porous layer were changed as shown in Table 5. A nonaqueous secondary battery was produced using this separator.

[0178] Comparative Example 31 A separator was produced in the same manner as in Example 31, except that the coating amount of the adhesive porous layer was changed as shown in Table 5. A nonaqueous secondary battery was produced using this separator.

[0179] In Examples 31 to 35, the adhesive porous layer was coated so that the separator had a thickness of 7 μm, 9 μm, or 11 μm, respectively. In Comparative Example 31, the adhesive porous layer was coated so that the separator had a thickness of 13 μm.

[0180] Table 5 shows the configurations of the porous substrate and adhesive porous layer, and Table 6 shows the physical properties and evaluation results of the separator. The mass of the adhesive porous layer shown in Table 5 is the total mass of both sides of the separator. The mass of the adhesive porous layer per separator side in each example and comparative example is half the mass of the adhesive porous layer shown in Table 5. The abbreviations in Table 5 have the following meanings. PVC: Polyvinyl chloride

[0181]

[0182]

[0183] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0184] The disclosures of Japanese Application No. 2023-221725, filed on December 27, 2023, are incorporated herein by reference in their entirety. The disclosures of Japanese Application No. 2024-122675, filed on July 29, 2024, are incorporated herein by reference in their entirety. The disclosures of Japanese Application No. 2024-122676, filed on July 29, 2024, are incorporated herein by reference in their entirety.

Claims

1. A separator for non-aqueous secondary batteries, comprising a porous substrate and an adhesive porous layer containing a polyvinyl chloride-based resin and inorganic particles, the adhesive porous layer being disposed on one or both sides of the porous substrate.

2. The separator for non-aqueous secondary batteries according to claim 1, wherein the volume ratio of the polyvinyl chloride-based resin to the inorganic particles contained in the adhesive porous layer is 90:10 to 20:

80.

3. The separator for non-aqueous secondary batteries according to claim 1, wherein the average primary particle size of the inorganic particles contained in the adhesive porous layer is 0.01 μm to 2 μm.

4. The separator for non-aqueous secondary batteries according to claim 1, wherein the inorganic particles include first inorganic particles having an average primary particle size of 0.5 μm to 1.0 μm and second inorganic particles having an average primary particle size smaller than that of the first inorganic particles.

5. The separator for non-aqueous secondary batteries according to claim 4, wherein the ratio of the first inorganic particles to the total amount of the first inorganic particles and the second inorganic particles contained in the adhesive porous layer is 30% by volume to 70% by volume.

6. The separator for non-aqueous secondary batteries according to claim 4, wherein the average primary particle size of the second inorganic particles is 0.01 μm or more and less than 0.5 μm.

7. The separator for non-aqueous secondary batteries according to claim 1, wherein when the air permeability of the porous substrate is P1 and the air permeability of the separator for non-aqueous secondary batteries is P2, the value of (P2 - P1) / P1 is 0.85 or less.

8. The separator for non-aqueous secondary batteries according to claim 7, wherein the air permeability of the porous substrate is 40 seconds / 100 mL to 200 seconds / 100 mL.

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

10. The separator for non-aqueous secondary batteries according to claim 1, wherein the average degree of polymerization of the polyvinyl chloride-based resin contained in the adhesive porous layer is 550 to 1200.

11. The mass per unit area of the adhesive porous layer is 0.6 g / m per side of the separator for non-aqueous secondary batteries ２ to 2.0 g / m. ２ The separator for non-aqueous secondary batteries according to claim 1.

12. The separator for non-aqueous secondary batteries according to claim 1, wherein the air permeability of the separator for non-aqueous secondary batteries is 100 seconds / 100 mL to 500 seconds / 100 mL.

13. The separator for non-aqueous secondary batteries according to claim 1, wherein the porous substrate includes a polyolefin microporous membrane.

14. The separator for a non-aqueous secondary battery according to claim 1, wherein the porous substrate includes a polyolefin microporous membrane and a heat-resistant layer containing at least one of inorganic particles and a heat-resistant resin disposed on one or both surfaces of the polyolefin microporous membrane.

15. The separator for a non-aqueous secondary battery according to claim 1, wherein the adhesive porous layer does not substantially contain a fluorine-containing resin.

16. 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 claims 1 to 15 disposed between the positive electrode and the negative electrode, and obtaining an electromotive force by doping and dedoping of lithium ions.

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