Separator for nonaqueous secondary battery and nonaqueous secondary battery

Abstract

To provide a separator for a nonaqueous secondary battery which adheres to an electrode by a wet heat pressing.SOLUTION: A separator for a nonaqueous secondary battery includes: a porous substrate; and an adhesive porous layer containing an acrylic resin (1) disposed on one surface or both surfaces of the porous substrate. The acrylic resin (1) contains (meth)acrylic acid, a (meth)acrylamide monomer, and at least one of methyl (meth)acrylate and butyl (meth)acrylate as a polymerization component. A total proportion of the (meth)acrylic acid and the (meth)acrylamide monomer in all the polymerization components is 20 mol % or more, and a molar ratio of the (meth)acrylic acid to the (meth)acrylamide monomer is 40:60 to 60:40.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] 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 binder composition for lithium ion secondary batteries, which comprises: (A) component: a particulate copolymer containing, as monomer units, a monomer containing at least one aldehyde group or ketone group, a (meth)acrylic acid ester monomer, a carboxylic acid group-containing monomer, and a crosslinkable monomer; (B) component: a hydrazine-based crosslinking agent; and / or (C) component: a semicarbazide compound derived from hydrazine and at least one isocyanate compound selected from the group consisting of aliphatic isocyanates and alicyclic isocyanates.

[0005] Patent Document 2 discloses an aqueous resin composition for a binder of a heat-resistant layer of a lithium-ion secondary battery separator, which contains a radical polymer (A) whose essential raw materials are an acrylic monomer (a1) having an alkyl group with 4 to 18 carbon atoms, at least one monomer (a2) selected from diacetone(meth)acrylamide and N-methylol(meth)acrylamide, an unsaturated monomer (a3) ​​having a carboxyl group, and acrylonitrile (a4), and an aqueous medium (B).

[0006] Patent Document 3 describes a polymer composite containing non-conductive particles and (meth)acrylamide monomer units at a ratio of 40 mass % or more and having a weight average molecular weight of 3.0 × 10 5 A non-aqueous composition for a secondary battery functional layer is disclosed, which comprises a water-soluble polymer having a water content of less than 100% and a particulate polymer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-157895 [Patent Document 2] International Publication No. 2021 / 251092 [Patent Document 3] International Publication No. 2017 / 026095 Summary of the Invention [Problem to be solved by the invention]

[0008] To prevent internal short circuits in batteries, separators are required to have adhesive properties to electrodes. While separators containing polyvinylidene fluoride resins in their surface layers have excellent adhesive properties to electrodes, there is a demand for separators that have adhesive properties to electrodes even if the content of polyvinylidene fluoride resin in the surface layer is low or even if the surface layer does not contain polyvinylidene fluoride resin.

[0009] In the battery manufacturing process, in order to increase productivity and battery performance, a process is performed in which the separator is impregnated with an electrolyte solution and then the separator and electrodes are heat-pressed together (this process is called "wet heat pressing"). During this process, if the resin on the separator surface is excessively swollen by the electrolyte solution, the separator will not adhere well to the electrode, or even if it does adhere to the electrode, the separator will easily peel off.

[0010] It is against this background that the present disclosure has been made. An object of the present disclosure is to provide a separator for a non-aqueous secondary battery that is bonded to an electrode by wet heat pressing. [Means for solving the problem]

[0011] Specific means for solving the above problems include the following aspects. <1> A porous substrate; An adhesive porous layer containing an acrylic resin (1) arranged on one or both sides of the porous substrate, The acrylic resin (1) contains (meth)acrylic acid, a (meth)acrylamide-based monomer, and at least one of methyl (meth)acrylate and butyl (meth)acrylate as polymerization components, the total proportion of the (meth)acrylic acid and the (meth)acrylamide-based monomer in all polymerization components is 20 mol% or more, and the molar ratio of the (meth)acrylic acid to the (meth)acrylamide-based monomer is 40:60 to 60:40. Separator for non-aqueous secondary batteries. <2> The acrylic resin (1) has a total ratio of methyl (meth)acrylate and butyl (meth)acrylate of 10 mol % to 80 mol % of all polymerization components. <1> The non-aqueous secondary battery separator according to claim 1. <3> the adhesive porous layer further contains inorganic particles; <1> or <2> The non-aqueous secondary battery separator according to claim 1. <4> The nonaqueous secondary battery separator has an air permeability of 100 seconds / 100 mL to 1000 seconds / 100 mL. <1> ~ <3> 1. The separator for a non-aqueous secondary battery according to any one of the above. <5> The porous substrate comprises a polyolefin microporous membrane; <1> ~ <4> 1. The separator for a non-aqueous secondary battery according to any one of the above. <6> The porous substrate is a polyolefin microporous membrane; 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; <1> ~ <4> 1. The separator for a non-aqueous secondary battery according to any one of the above. <7> the adhesive porous layer is substantially free of a fluorine-containing resin; <1> ~ <6> 1. The separator for a non-aqueous secondary battery according to any one of the above. <8> a positive electrode, a negative electrode, and a conductive material disposed between the positive electrode and the negative electrode; <1> ~ <7> and the non-aqueous secondary battery separator according to any one of the above items, Electromotive force is generated by doping and dedoping of lithium ions. Non-aqueous secondary battery. [Effects of the Invention]

[0012] According to the present disclosure, a separator for a non-aqueous secondary battery is provided that is bonded to an electrode by wet heat pressing. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an SEM image of the surface of the separator of Example 1. [Figure 2] 1 is an SEM image of the surface of the separator of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0014]

[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.

[0015] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0016] 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.

[0017] 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.

[0018] In the present disclosure, when referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0019] In this disclosure, MD (Machine Direction) refers to the longitudinal direction of a separator manufactured in a long shape, and TD (Transverse Direction) refers to the direction perpendicular to MD in the plane direction of the separator. In this disclosure, TD is also referred to as the "width direction."

[0020] 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."

[0021] In the present disclosure, the volume of the porous layer excluding pores is referred to as the "solid content volume."

[0022] 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."

[0023] In the present disclosure, the term "(meth)acrylic" means either "acrylic" or "methacrylic."

[0024] In the present disclosure, the term "monomer unit" of a polymer or resin refers to a structural unit of the polymer or resin, which is formed by polymerization of a monomer.

[0025] <Separator for non-aqueous secondary batteries> The separator for a nonaqueous secondary battery of the present disclosure (also simply referred to as "separator" in the present disclosure) comprises a porous substrate and an adhesive porous layer containing an acrylic resin (1) disposed on one or both sides of the porous substrate.

[0026] The acrylic resin (1) is an acrylic resin containing (meth)acrylic acid, a (meth)acrylamide monomer, and at least one of methyl (meth)acrylate and butyl (meth)acrylate as polymerization components, in which the total proportion of the (meth)acrylic acid and the (meth)acrylamide monomer in all polymerization components is 20 mol % or more, and the molar ratio of the (meth)acrylic acid to the (meth)acrylamide monomer is 40:60 to 60:40.

[0027] The separator of the present disclosure adheres to the electrode by wet heat pressing because the adhesive porous layer contains the acrylic resin (1). The mechanism is presumed to be as follows.

[0028] Wet heat pressing is a process in which the separator is permeated with an electrolyte solution and then heat-pressed. During this process, if the resin on the separator surface is excessively swollen by the electrolyte solution, the separator will not adhere well to the electrode, or even if it does adhere to the electrode, the separator will easily peel off. It is believed that when the electrolyte solution penetrates into the acrylic resin (1), hydrogen bonds are formed between the carboxyl groups of the (meth)acrylic acid units and the amide bonds of the (meth)acrylamide monomer units. The formation of these hydrogen bonds between the molecules of the acrylic resin (1) prevents the acrylic resin (1) from swelling excessively with the electrolyte solution. As a result, it is believed that the adhesive porous layer containing the acrylic resin (1) adheres to the electrode by wet heat pressing and is unlikely to peel off from the electrode.

[0029] The following structural formula shows an example of the hydrogen bond formed between the carboxy group of the (meth)acrylic acid unit and the amide bond of the (meth)acrylamide-based monomer unit: This example shows the hydrogen bond formed between the carboxy group of the methacrylic acid unit and the amide bond of the N-methylmethacrylamide unit.

[0030] [ka]

[0031] In the acrylic resin (1), from the viewpoint of ensuring the number of hydrogen bonds formed between the carboxy groups of the (meth)acrylic acid units and the amide bonds of the (meth)acrylamide-based monomer units, the total proportion of (meth)acrylic acid and (meth)acrylamide-based monomers in all polymerization components is 20 mol % or more, preferably 25 mol % or more, more preferably 30 mol % or more, and even more preferably 35 mol % or more. The total proportion of (meth)acrylic acid and (meth)acrylamide monomers in all polymerization components of the acrylic resin (1) may be, for example, 90 mol% or less, 70 mol% or less, 50 mol% or less, 45 mol% or less, or 40 mol% or less.

[0032] In the acrylic resin (1), from the viewpoint of efficiently forming hydrogen bonds between the carboxy groups of the (meth)acrylic acid units and the amide bonds of the (meth)acrylamide-based monomer units, the molar ratio of the polymerization components, (meth)acrylic acid and (meth)acrylamide-based monomer, is 40:60 to 60:40, preferably 45:55 to 60:40, and more preferably 50:50 to 60:40.

[0033] The acrylic resin (1) contains at least one of methyl (meth)acrylate and butyl (meth)acrylate as a polymerization component from the viewpoints of solubility in an organic solvent constituting a coating liquid for forming an adhesive porous layer, control of the glass transition temperature, etc. From the above viewpoints, the acrylic resin (1) preferably contains both methyl (meth)acrylate and butyl (meth)acrylate as polymerization components. From the above viewpoints, the total proportion of methyl (meth)acrylate and butyl (meth)acrylate in all polymer components of the acrylic resin (1) is preferably 10 mol % to 80 mol %, more preferably 30 mol % to 70 mol %, and even more preferably 50 mol % to 65 mol %.

[0034] The structural units of the acrylic resin (1) can be analyzed by nuclear magnetic resonance (NMR). The acrylic resin (1) extracted from the adhesive porous layer or the acrylic resin (1) used to form the adhesive porous layer is used as a sample for analysis.

[0035] The separator of the present disclosure has an adhesive porous layer containing an acrylic resin (1) 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).

[0036] Form (1): A separator having adhesive porous layers containing acrylic resin (1) on both sides of a porous substrate as the outermost layers of the separator. The adhesive porous layer on one side of the separator and the adhesive porous layer on the other side may be the same or different in components and / or composition.

[0037] Form (2): A separator having an adhesive porous layer containing the acrylic resin (1) as the outermost layer of the separator on one side of the porous substrate, and another layer on the other side of the porous substrate.

[0038] Form (3): A separator having an adhesive porous layer containing an acrylic resin (1) on one side of a porous substrate as the outermost layer of the separator, and no layer on the other side of the porous substrate (i.e., the surface of the porous substrate is exposed).

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

[0040] [Porous base material] In the present disclosure, a porous substrate refers to a substrate having internal pores or voids. Examples of such substrates include microporous membranes, porous sheets made of fibrous materials such as nonwoven fabrics and paper, and composite porous sheets in which one or more other porous layers are laminated on the microporous membranes or porous sheets.

[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, a heat-resistant resin refers to a resin with a melting point of 200°C or higher, or a resin without a melting point but with a decomposition temperature of 200°C or higher. In other words, a heat-resistant resin in the present disclosure refers to a resin that does not melt or decompose in a temperature range below 200°C.

[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 thermoplastic resins include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and polyolefins are particularly preferred.

[0045] As the porous substrate, a porous substrate containing a microporous membrane containing polyolefin (referred to as a "polyolefin microporous membrane" in the present disclosure) is preferred from the viewpoint of imparting a shutdown function to the porous substrate. Examples of porous substrates containing a polyolefin microporous membrane include a porous substrate consisting of only a polyolefin microporous membrane (i.e., a polyolefin microporous membrane) and a composite porous substrate 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 prevents the film from easily rupturing when exposed to high temperatures, the polyolefin microporous film is preferably a polyolefin microporous film containing polyethylene and polypropylene. Examples of polyolefin microporous films containing polyethylene and polypropylene include microporous films in which polyethylene and polypropylene are mixed in one layer. From the viewpoint of achieving both the shutdown function and heat resistance, the microporous film preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. Also from the viewpoint of achieving both the shutdown function and heat resistance, a polyolefin microporous film having a 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 the 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, the heat-resistant layer being 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 type thickness meter and the average is calculated.

[0060] From the viewpoint of suppressing internal short circuits in the battery, 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. 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 50 sec / 100 mL to 180 sec / 100 mL, more preferably 70 sec / 100 mL to 160 sec / 100 mL or less, and even more preferably 90 sec / 100 mL to 140 sec / 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] 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 Here, Ws is the basis weight of the porous substrate (g / m 2 ), ds is the true density of the porous substrate (g / cm 3 ), t is the thickness (μm) of the porous substrate. Basis weight is the mass per unit area.

[0063] [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 numerous gaps or micropores, allowing gas or liquid to pass through from one surface to the other.

[0064] In the separator of the present disclosure, the adhesive porous layer preferably has a network structure containing an acrylic resin (1). The network structure of the adhesive porous layer means a structure in which the resin is continuously connected in a network shape and has a large number of pores. The network structure of the adhesive porous layer may be a planar network structure in the surface direction of the separator, or a three-dimensional network structure in the surface direction and thickness direction of the separator. The three-dimensional mesh structure of the adhesive porous layer may be flattened by the heat press used to bond the separator to the electrode, and part or all of the separator may have a planar mesh structure when bonded to the electrode.

[0065] The network structure of the adhesive porous layer can be confirmed by observing the surface of the separator with a scanning electron microscope (SEM).

[0066] Examples of the form of the mesh structure of the adhesive porous layer include a porous structure in which fibrils containing acrylic resin (1) are connected in a two-dimensional or three-dimensional mesh structure; a mesh-like microporous structure containing acrylic resin (1); and the like.

[0067] When the adhesive porous layer contains inorganic particles, examples of the form of the adhesive porous layer include a structure in which inorganic particles are bound or trapped in a porous structure in which fibrils containing acrylic resin (1) are connected in a two-dimensional or three-dimensional network pattern; a structure in which inorganic particles are bound or trapped in a network-like microporous structure containing acrylic resin (1); and a layered structure in which acrylic resin (1) connects a large number of inorganic particles together, forming voids between the inorganic particles.

[0068] -Acrylic resin (1)- The acrylic resin (1) contains at least (meth)acrylic acid, a (meth)acrylamide monomer, and at least one of methyl (meth)acrylate and butyl (meth)acrylate as polymerization components. The acrylic resin (1) may contain other monomers as polymerization components.

[0069] The (meth)acrylamide monomer is preferably a (meth)acrylamide monomer represented by the following formula (1).

[0070] [ka]

[0071] In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 and R 3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. The alkyl group may be linear, branched, or cyclic. R 2 and R 3 are each independently preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a hydrogen atom or a methyl group.

[0072] The (meth)acrylamide monomer is preferably at least one selected from the group consisting of acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N,N-dimethylacrylamide, and N,N-dimethylmethacrylamide.

[0073] The total proportion of (meth)acrylic acid and (meth)acrylamide monomers in all polymerization components of the acrylic resin (1) is 20 mol% or more, preferably 20 mol% to 90 mol%, more preferably 20 mol% to 70 mol%, even more preferably 20 mol% to 50 mol%, still more preferably 25 mol% to 45 mol%, still more preferably 30 mol% to 40 mol%, and particularly preferably 35 mol% to 40 mol%. The proportion of (meth)acrylic acid in all polymer components of the acrylic resin (1) is preferably 10 mol % to 50 mol %, more preferably 15 mol % to 40 mol %, still more preferably 20 mol % to 30 mol %, and particularly preferably 20 mol % to 25 mol %. The proportion of the (meth)acrylamide monomer in all polymer components of the acrylic resin (1) is preferably 10 mol % to 40 mol %, more preferably 10 mol % to 30 mol %, even more preferably 10 mol % to 25 mol %, and particularly preferably 15 mol % to 20 mol %.

[0074] The molar ratio of (meth)acrylic acid to (meth)acrylamide monomer, which are polymerization components of the acrylic resin (1), is 40:60 to 60:40, preferably 45:55 to 60:40, and more preferably 50:50 to 60:40.

[0075] The total proportion of methyl (meth)acrylate and butyl (meth)acrylate in all polymer components of the acrylic resin (1) is preferably 10 mol % to 80 mol %, more preferably 30 mol % to 70 mol %, and even more preferably 50 mol % to 65 mol %. The proportion of methyl (meth)acrylate in all polymer components of the acrylic resin (1) is preferably 10 mol % to 65 mol %, more preferably 25 mol % to 60 mol %, and even more preferably 40 mol % to 55 mol %. The proportion of butyl (meth)acrylate in all polymer components of the acrylic resin (1) is preferably 5 mol % to 25 mol %, more preferably 10 mol % to 20 mol %, and even more preferably 10 mol % to 15 mol %.

[0076] The butyl (meth)acrylate is at least one selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate, and t-butyl methacrylate, and is preferably at least one of n-butyl acrylate and n-butyl methacrylate.

[0077] Examples of such monomers include lower alkyl (meth)acrylate esters (having an alkyl group with 8 or less carbon atoms) other than methyl (meth)acrylate and butyl (meth)acrylate. Examples of the lower alkyl (meth)acrylate esters include ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, n-heptyl (meth)acrylate, isoheptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0078] Examples of such monomers include styrene-based monomers. Examples of styrene-based monomers include styrene, α-methylstyrene, and alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene. Preferred styrene-based monomers are styrene and α-methylstyrene, with styrene being more preferred.

[0079] Examples of such monomers include vinyl nitrile compounds, such as acrylonitrile and methacrylonitrile.

[0080] The total proportion of (meth)acrylic acid, (meth)acrylamide monomers, methyl (meth)acrylate, and butyl (meth)acrylate in all polymer components of the acrylic resin (1) is preferably 30 mol% to 100 mol%, more preferably 60 mol% to 100 mol%, and even more preferably 90 mol% to 100 mol%.

[0081] An example of the acrylic resin (1) includes an acrylic resin (1) containing, as polymerization components, (meth)acrylic acid, a (meth)acrylamide monomer represented by formula (1), methyl (meth)acrylate, and butyl (meth)acrylate. The total proportion of the monomers in the total polymerization components of the acrylic resin (1) is preferably 90 mol % to 100 mol %. The proportion of each monomer in the total polymerization components of the acrylic resin (1) is preferably 20 mol % to 25 mol % for (meth)acrylic acid, preferably 15 mol % to 20 mol % for the (meth)acrylamide monomer represented by formula (1), preferably 40 mol % to 55 mol % for methyl (meth)acrylate, and preferably 10 mol % to 15 mol % for butyl (meth)acrylate.

[0082] An example of the acrylic resin (1) is an acrylic resin (1) containing, as polymerization components, (meth)acrylic acid, at least one of N-methyl(meth)acrylamide and N,N-dimethyl(meth)acrylamide, methyl (meth)acrylate, and n-butyl (meth)acrylate. The total proportion of the above monomers in all polymerization components of the acrylic resin (1) is preferably 90 mol % to 100 mol %. The proportion of each monomer in the total polymerization components of the acrylic resin (1) is preferably 20 mol % to 25 mol % for (meth)acrylic acid, preferably 15 mol % to 20 mol % for the total of N-methyl(meth)acrylamide and N,N-dimethyl(meth)acrylamide, preferably 40 mol % to 55 mol % for methyl (meth)acrylate, and preferably 10 mol % to 15 mol % for n-butyl (meth)acrylate.

[0083] The weight average molecular weight of the acrylic resin (1) is preferably from 50,000 to 500,000, and more preferably from 80,000 to 400,000. The weight-average molecular weight of the acrylic resin (1) is a polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC). The acrylic resin (1) extracted from the adhesive porous layer or the acrylic resin (1) used to form the adhesive porous layer is used as a sample for measurement.

[0084] -Other resins- The adhesive porous layer may contain a resin other than the acrylic resin (1). Examples of the other resin include acrylic resins other than the acrylic resin (1), 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.

[0085] 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 the acrylic resin (1) 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 %.

[0086] The adhesive porous layer preferably does not substantially contain a fluorine-containing resin. Examples of fluorine-containing resins include polyvinylidene fluoride resins and fluorine-containing rubbers. 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 monomers other than halogen-containing monomers; copolymers of vinylidene fluoride, halogen-containing monomers, and monomers other than halogen-containing monomers; and mixtures thereof.

[0087] The adhesive porous layer being substantially free of fluorine-containing resin means that the mass ratio of 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 does not contain a fluorine-containing resin.

[0088] -particle- The adhesive porous layer may further contain particles, which may include inorganic particles and / or organic particles.

[0089] An example of an embodiment of the adhesive porous layer is one that does not substantially contain particles. The adhesive porous layer being substantially free of particles means that the volume ratio of particles to the acrylic resin (1) and particles contained in the adhesive porous layer is less than 5 volume %. In this embodiment, the volume ratio of particles to the acrylic resin (1) and particles contained in the adhesive porous layer is 0 volume % or more and less than 5 volume %.

[0090] -Inorganic particles- The adhesive porous layer may contain inorganic particles. From the viewpoint of thermal dimensional stability, i.e., resistance to thermal shrinkage even at high temperatures, the separator preferably includes an adhesive porous layer containing inorganic particles.

[0091] Examples of inorganic particles include metal oxide particles, metal hydroxide particles, metal sulfate particles, metal carbonate particles, metal nitride particles, and clay mineral particles.

[0092] Examples of metal oxides that constitute the metal oxide particles include silica (silicon dioxide), alumina (aluminum oxide), boehmite (alumina monohydrate), titania (titanium oxide), zirconia (zirconium oxide), magnesium oxide, and barium oxide, with alumina being preferred. Examples of metal hydroxides constituting the metal hydroxide particles include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide, with magnesium hydroxide being preferred. Examples of metal sulfates constituting the metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred. Examples of metal carbonates constituting the metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides that constitute the metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0093] The inorganic particles may be surface-modified with a silane coupling agent or the like.

[0094] The inorganic particles may be used alone or in combination of two or more kinds.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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 0.05 μm to 1 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 viewpoint, the average primary particle size of the inorganic particles is more preferably 0.05 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 μm or less, and even more preferably 0.5 μm or less.

[0099] The average primary particle size of inorganic particles is determined by measuring the long diameters of 100 randomly selected inorganic particles during observation with a scanning electron microscope (SEM) and averaging the long diameters of the 100 particles. The sample used for SEM observation is inorganic particles that are the material 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 approximately 800°C to remove the binder resin and remove the inorganic particles.

[0100] When the adhesive porous layer contains inorganic particles, the volume ratio of the inorganic particles to the acrylic resin (1) and inorganic particles contained in the adhesive porous layer is preferably 5 to 50% by volume, more preferably 10 to 40% by volume, and even more preferably 15 to 30% by volume, 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.

[0101] 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.

[0102] An example of an embodiment of the adhesive porous layer is one that is substantially free of inorganic particles. The adhesive porous layer being substantially free of inorganic particles means that the volume ratio of inorganic particles to the acrylic resin (1) and inorganic particles contained in the adhesive porous layer is less than 5 volume %. In this embodiment, the volume ratio of inorganic particles to the acrylic resin (1) and inorganic particles contained in the adhesive porous layer is 0 volume % or more and less than 5 volume %.

[0103] -Organic particles- The adhesive porous layer may contain organic particles, such as particles made of crosslinked polymers such as crosslinked poly(meth)acrylic acid, crosslinked poly(meth)acrylic acid ester, crosslinked polysilicone, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensate; and particles made of heat-resistant polymers such as polysulfone, polyacrylonitrile, aramid, and polyacetal. The resin constituting the organic particles may be a mixture, modified product, derivative, copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) or crosslinked product of the above-exemplified materials.

[0104] The organic particles may be used alone or in combination of two or more kinds.

[0105] An example of an embodiment of the adhesive porous layer is one that is substantially free of organic particles. The adhesive porous layer being substantially free of organic particles means that the volume ratio of organic particles to the acrylic resin (1) and organic particles contained in the adhesive porous layer is less than 5% by volume. In this embodiment, the volume ratio of organic particles to the acrylic resin (1) and organic particles contained in the adhesive porous layer is 0% by volume or more and less than 5% by volume.

[0106] -Other ingredients- The adhesive porous layer may contain additives such as dispersants such as surfactants, wetting agents, antifoaming agents, and pH adjusters. Dispersants are added, for example, to the 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 the 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.

[0107] -Characteristics of the adhesive porous layer- When the adhesive porous layer does not substantially contain inorganic particles, the mass per unit area of ​​the adhesive porous layer is 0.3 g / m per one side of the separator from the viewpoint of achieving a good balance between adhesion to the electrode and electrolyte permeability and ion permeability. 2 ~2g / m 2 It is preferable that the density is 0.4 g / m 2 ~1.5g / m 2 More preferably, 0.5 g / m 2 ~1g / m 2 is more preferred.

[0108] When adhesive porous layers that do not substantially contain inorganic particles are present on both sides of the separator, the mass per unit area of ​​the adhesive porous layers on both sides is 0.6 g / m 2 ~4g / m 2 is preferred, and 0.8 g / m 2 ~3g / m 2 is more preferable, and 1 g / m 2 ~2g / m 2 is more preferred.

[0109] When the adhesive porous layer contains inorganic particles, the mass per unit area of ​​the adhesive porous layer is set to 0.5 g / m per one side of the separator from the viewpoint of achieving a good balance between adhesion to the electrode and permeability of the electrolyte and ion permeability. 2 ~3g / m 2 It is preferable that the density is 0.8 g / m 2 ~2.5g / m 2 is more preferable, and 1 g / m 2 ~2g / m 2 is more preferred.

[0110] When adhesive porous layers containing inorganic particles are present on both sides of the separator, the mass per unit area of ​​the adhesive porous layers on both sides must be 1 g / m 2 ~6g / m 2 is preferred, and 1.5 g / m 2 ~5g / m 2 More preferably, 2 g / m 2 ~4g / m 2 is more preferred.

[0111] 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.

[0112] [Separator characteristics] From the viewpoint of mechanical strength, the thickness of the separator is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 9 μm or more. From the viewpoint of the energy density of the battery, the thickness of the separator is preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less. The thickness of the separator is measured at 20 points within a 10 cm square using a contact thickness meter and the average is calculated.

[0113] From the viewpoint of suppressing internal short circuits in the battery, the air permeability of the separator is preferably 100 seconds / 100 mL or more, more preferably 110 seconds / 100 mL or more, and even more preferably 120 seconds / 100 mL or more. From the viewpoint of ion permeability, the air permeability of the separator is preferably 1000 seconds / 100 mL or less, more preferably 700 seconds / 100 mL or less, and even more preferably 500 seconds / 100 mL or less. The air permeability of the separator is measured using a digital Oken air permeability tester in accordance with JIS P8117:2009.

[0114] The porosity of the separator is preferably 30% to 60% from the viewpoint of ion permeability. The porosity ε (%) of the separator is calculated by the following formula.

[0115]

number

[0116] [Separator manufacturing method] 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 this disclosure, a wet coating method is a method in which a coating layer is solidified in a coagulation liquid, and a dry coating method is a method in which a coating layer is solidified by drying. An embodiment of the wet coating method is described below. In the following description, the "adhesive porous layer" will be simply referred to as the "porous layer."

[0117] 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.

[0118] The coating liquid for forming the porous layer is prepared by dissolving the acrylic resin (1) in a solvent. If necessary, other components (e.g., inorganic particles) besides the acrylic resin (1) may be dissolved or dispersed in the coating liquid.

[0119] The solvent used to prepare the coating liquid includes a solvent that dissolves the acrylic resin (1) (hereinafter also referred to as a "good solvent"), such as polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0120] 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, butanediol, and ethylene glycol.

[0121] 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, the mixed solvent preferably contains 60% by mass or more of the good solvent and 5% by mass to 40% by mass of the phase separation agent.

[0122] 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. When the porous layer contains inorganic particles, 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] The coagulation liquid generally contains the good solvent and phase separation agent used in preparing the coating liquid, as well as water. From the viewpoint of productivity, it is preferable 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.

[0127] 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. Furthermore, water is 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.

[0128] 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.

[0129] 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.

[0130] <Non-aqueous secondary battery> The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery that generates electromotive force by doping and dedoping of lithium ions, and includes a positive electrode, a negative electrode, and the separator of the present disclosure. "Doping" refers to the phenomenon of lithium ions entering the active material of the electrode.

[0131] 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.

[0132] The nonaqueous secondary battery of the present disclosure includes the separator of the present disclosure, which makes it difficult for the electrodes and the separator to separate, and therefore the nonaqueous secondary battery of the present disclosure is less likely to develop an internal short circuit.

[0133] 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.

[0134] An example of the positive electrode is a structure in which an active material layer containing a positive electrode active material and a binder resin is disposed on a current collector. The active material layer may further contain a conductive additive. Examples of the positive electrode active material include lithium-containing transition metal oxides, specifically, LiCoO2, LiNiO2, and LiMn 1 / 2 Ni 1 / 2 O2, LiCo 1 / 3 Mn 1 / 3 Ni 1 / 3 O2, LiMn2O4, LiFePO4, LiCo 1 / 2 Ni 1 / 2 O2, LiAl 1 / 4 Ni 3 / 4 Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, and graphite powder. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil, each having a thickness of 5 μm to 20 μm.

[0135] An example of an embodiment of the negative electrode is a structure in which an active material layer containing a negative electrode active material and a binder resin is disposed on a current collector. The active material layer may further contain a conductive additive. Examples of negative electrode active materials include materials capable of electrochemically absorbing lithium ions, such as carbon materials; alloys of lithium with silicon, tin, aluminum, etc.; and Wood's alloy. Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers. Examples of the current collector include copper foil, nickel foil, stainless steel foil, and the like, each having a thickness of 5 μm to 20 μm. Alternatively, a metallic lithium foil may be used as the negative electrode instead of the above-described negative electrode.

[0136] The electrolyte solution is preferably a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of lithium salts include LiPF6, LiBF4, and LiClO4. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted derivatives thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone. These may be used alone or in combination. The electrolyte solution is preferably a solution in which a cyclic carbonate and a chain carbonate are mixed in a mass ratio (cyclic carbonate:chain carbonate) of 20:80 to 40:60, and a lithium salt is dissolved in the range of 0.5 mol / L to 1.5 mol / L.

[0137] 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.

[0138] The nonaqueous secondary battery of the present disclosure is preferably produced by first 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 either of the following production methods (1) and (2).

[0139] Manufacturing method (1): The laminate is dry heat pressed to temporarily bond the electrodes and separator, and then placed in an exterior packaging (for example, an aluminum laminate film pack; the same applies below), and an electrolyte is poured into it. Next, the laminate is wet heat pressed from above the exterior packaging to bond the electrodes and separator and seal the exterior packaging.

[0140] Manufacturing method (2): The laminate is placed in an exterior packaging material and an electrolyte solution is poured into it. The laminate is then wet heat pressed onto the exterior packaging material to bond the electrodes and separator together and seal the exterior packaging material.

[0141] 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 the range of 1 minute to 12 hours.

[0142] In production method (1), 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 the range of 0.5 minutes to 1 hour.

[0143] When manufacturing a laminate in which a separator is disposed between a positive electrode and a negative electrode, the method of disposing the separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of a positive electrode, a separator, and a negative electrode in this order (so-called stack method), or a method of stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them in the length direction. [Example]

[0144] 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.

[0145] In the following description, syntheses, treatments, manufacturing, etc. were carried out at room temperature (25°C ± 3°C) unless otherwise specified.

[0146] <Measurement and evaluation methods> The measurement and evaluation methods used in the examples and comparative examples are as follows.

[0147] [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 averaged. 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.

[0148] [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).

[0149] [Analysis of acrylic resin (1)] The acrylic resin (1) used to form the adhesive porous layer was used as a sample, and the structural units of the resin were analyzed by NMR. The weight average molecular weight of the acrylic resin (1) used for forming the adhesive porous layer was measured by GPC using polystyrene as a standard sample.

[0150] [Solubility of resin in dimethylacetamide] The resin used to form the adhesive porous layer was used as a sample. The resin was added to dimethylacetamide at a concentration of 20% by mass and stirred at room temperature for 5 hours. The test solution after stirring was visually observed, and the solubility of the resin was classified as follows. G: The resin was completely dissolved. NG: Resin remained undissolved.

[0151] [Electrolyte resistance of resin] The resin used to form the adhesive porous layer was used as a sample. The resin and dimethylacetamide were mixed and stirred to prepare a resin solution with a concentration of 20% by mass. The resin solution was applied to a glass plate and dried to prepare a resin film with a thickness of 200 μm. The resin film was immersed in an electrolyte solution (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) at room temperature for 72 hours. After immersion, the resin film was visually observed, and its shape was classified as follows: G: The resin film maintained its shape. NG: The resin film was deformed.

[0152] [Average primary particle size of inorganic particles] The inorganic particles used to form the adhesive porous layer were observed under a scanning electron microscope (SEM) to determine the average primary particle size. The major axis of 100 randomly selected inorganic particles was measured on the SEM image, and the average of the major axes of the 100 particles was taken as the average primary particle size (μm).

[0153] [Mass per unit area of ​​adhesive porous layer] The separator was cut into a 20 cm x 20 cm piece, the adhesive porous layer was peeled off, and the mass was measured. The mass was then divided by the area to calculate the mass per unit area (g / m) of both sides combined. 2 ) was sought.

[0154] [Wet adhesion to electrodes] A positive electrode slurry was prepared by mixing 89.5 parts by weight of lithium cobalt oxide powder (positive electrode active material), 4.5 parts by weight of acetylene black (conductive additive), 6 parts by weight of polyvinylidene fluoride (binder resin), and an appropriate amount of N-methyl-2-pyrrolidone in a twin-arm mixer. The positive electrode slurry was applied to 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. Hereinafter, in the description of this test, "electrode" means "positive electrode."

[0155] The electrode was cut into a rectangle measuring 15 mm wide x 70 mm long. The separator was cut into a rectangle measuring 18 mm long x 74 mm long. Release paper measuring 15 mm wide x 70 mm long was prepared. The separator was placed on the active material layer of the electrode, and then the release paper was placed on top of the separator to produce a laminate.

[0156] The laminate was inserted into an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was poured into the laminate, allowing the electrolyte to soak into the laminate. The pack was then heat-pressed in the stacking direction of the laminate using a heat press (wet heat press) to bond the electrodes and separators. The heat press conditions were a temperature of 85°C, a pressure of 1 MPa, and a time of 5 minutes. After heat pressing, the laminate was removed from the pack, and the release paper was peeled off to obtain a wet adhesive test piece.

[0157] The uncoated side of the test specimen's electrode was fixed to a metal plate with double-sided tape, and the metal plate was fixed to the lower chuck of a Tensilon (A&D Corporation, STB-1225S). The metal plate was fixed to the Tensilon so that the longitudinal direction of the test specimen (i.e., the separator's MD) was aligned with the direction of gravity. The separator was peeled approximately 2 cm from the bottom edge of the electrode, and this edge was fixed to the upper chuck for a 180° peel test. The tensile speed for the 180° peel test was 20 mm / min. Loads (N) were measured from 10 mm to 40 mm after the start of the test at 0.4 mm intervals, and the average was calculated. The loads for 10 test specimens were then averaged to determine the adhesive strength between the electrode and separator (N / 15 mm).

[0158] [Heat shrinkage rate] The separator was cut into a rectangle measuring 60 mm in TD and 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 into two equal parts in TD (referred to as points A and B, respectively). Marks were also made on the test specimen at 10 mm and 50 mm from one end on the line dividing the test specimen into two equal parts 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 a heat treatment for 60 minutes without tension. The lengths between points A and C and between points C and D were measured before and after the heat treatment, and the thermal shrinkage was calculated using the following formula. The thermal shrinkage of the three test specimens was then averaged.

[0159] MD heat shrinkage rate (%) = {(length of AB before heat treatment - length of AB after heat treatment) ÷ length of AB before heat treatment} × 100

[0160] TD heat shrinkage rate (%) = {(CD length before heat treatment - CD length after heat treatment) ÷ CD length before heat treatment} × 100

[0161] <Preparation of separator and battery> [Example 1] -Separator production- The acrylic resin (1) was dissolved in dimethylacetamide (DMAc) to prepare a coating solution (1) having an acrylic resin (1) concentration of 8.0 mass %. The monomer composition of the acrylic resin (1) used in Example 1 is as shown in Table 1.

[0162] An appropriate amount of coating liquid (1) was placed on a Mayer bar, and coating liquid (1) was applied to both sides of a polyethylene microporous membrane (thickness 6 μm, air permeability 100 sec / 100 mL). Coating was performed so that the coating amount was equal on both sides of the polyethylene microporous membrane. The polyethylene microporous membrane on which the coating layer was formed was immersed in a coagulation liquid (DMAc:water=50:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer. The polyethylene microporous membrane 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 membrane.

[0163] -Preparation of positive electrode- A positive electrode slurry was prepared by mixing 89.5 parts by weight of lithium cobalt oxide powder (positive electrode active material), 4.5 parts by weight of acetylene black (conductive additive), 6 parts by weight of polyvinylidene fluoride (binder resin), and an appropriate amount of N-methyl-2-pyrrolidone in a twin-arm mixer. The positive electrode slurry was applied to both sides of a 20 μm-thick aluminum foil, dried, and pressed to obtain a positive electrode with positive electrode active material layers on both sides.

[0164] - Preparation of negative electrode - A negative electrode slurry was prepared by mixing 300 parts by weight of artificial graphite (negative electrode active material), 7.5 parts by weight of an aqueous dispersion containing 40% by weight of a modified styrene-butadiene copolymer (binder resin), 3 parts by weight of carboxymethyl cellulose (thickener), and an appropriate amount of water in a twin-arm mixer. The negative electrode slurry was applied to both sides of a 10 μm-thick copper foil, dried, and pressed to obtain a negative electrode with a negative electrode active material layer on both sides.

[0165] -Battery manufacturing- The positive and negative electrodes were each cut into a 30 mm x 50 mm rectangle, and a lead tab was welded to each. The separator was cut into a 35 mm x 55 mm rectangle. These were stacked so that the positive and negative electrodes alternated and a separator was sandwiched between them, producing a laminate consisting of three positive electrodes, three negative electrodes, and five separators. The laminate was inserted into an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was poured into the pack to allow the electrolyte to permeate the laminate. The pack and the laminate were then heat-pressed in the stacking direction using a heat press (wet heat press) to bond the electrodes and separators. The heat press conditions were a press temperature of 85°C, a press pressure of 1 MPa, and a press time of 5 minutes. A nonaqueous secondary battery was thus obtained.

[0166] [Example 2] The acrylic resin (1) was dissolved in dimethylacetamide (DMAc), and barium sulfate particles were further stirred and dispersed to prepare a coating solution (2). The coating solution (2) had an acrylic resin (1) concentration of 8.0 mass%, and the acrylic resin (1):barium sulfate particles ratio was 80:20 [volume ratio]. The acrylic resin (1) used in Example 2 was the same as the acrylic resin (1) used in Example 1.

[0167] A separator was produced in the same manner as in Example 1, except that the coating liquid (1) was changed to the coating liquid (2). A non-aqueous secondary battery was produced using this separator.

[0168] [Example 3] A separator was produced in the same manner as in Example 1, except that the acrylic resin (1) was changed to an acrylic resin (1) having the monomer composition shown in Table 1. A nonaqueous secondary battery was produced using this separator.

[0169] [Example 4] A separator was prepared in the same manner as in Example 2, except that the acrylic resin (1) was changed to an acrylic resin (1) having the monomer composition shown in Table 1. A nonaqueous secondary battery was prepared using this separator. The acrylic resin (1) used in Example 4 was the same as the acrylic resin (1) used in Example 3.

[0170] [Comparative Example 1] A separator was produced in the same manner as in Example 2, except that the acrylic resin (1) was changed to a polyvinylidene fluoride resin (a binary copolymer of vinylidene fluoride and hexafluoropropylene, weight average molecular weight 1.4 million, hexafluoropropylene 1.5 mol%).

[0171] Comparative Example 2 A separator was produced in the same manner as in Example 1, except that the acrylic resin (1) was changed to polymethyl methacrylate resin.

[0172] In each of the examples and comparative examples, the adhesive porous layer was applied so that the thickness of the separator became 9 μm. 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.

[0173] The abbreviations in Table 1 have the following meanings. ·Mw: Weight average molecular weight DMAc: Dimethylacetamide VDF-HFP: A copolymer of vinylidene fluoride and hexafluoropropylene PMMA: Polymethyl methacrylate resin ·MAA: methacrylic acid NMMAm: N-methylmethacrylamide DMMAm: N,N-dimethylmethacrylamide MMA: Methyl methacrylate BA: n-butyl acrylate

[0174] [Table 1]

[0175] The surfaces of the separators of Examples 1 and 3 were observed with a scanning electron microscope (SEM). FIG. 1 shows an SEM image (magnification: 20,000) of the surface of the separator of Example 1. FIG. 2 shows an SEM image (magnification: 20,000) of the surface of the separator of Example 3.

[0176] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A porous substrate; An adhesive porous layer containing an acrylic resin (1) arranged on one or both sides of the porous substrate, The acrylic resin (1) contains, as polymerization components, (meth)acrylic acid, a (meth)acrylamide-based monomer, and at least one of methyl (meth)acrylate and butyl (meth)acrylate, wherein the total proportion of the (meth)acrylic acid and the (meth)acrylamide-based monomer in all polymerization components is 20 mol % or more, and the molar ratio of the (meth)acrylic acid to the (meth)acrylamide-based monomer is 40:60 to 60:

40. Separator for non-aqueous secondary batteries.

2. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the acrylic resin (1) has a total ratio of methyl (meth)acrylate and butyl (meth)acrylate of 10 mol % to 80 mol % of all polymerization components.

3. The separator for a non-aqueous secondary battery according to claim 1 , wherein the adhesive porous layer further contains inorganic particles.

4. 2. The non-aqueous secondary battery separator according to claim 1, wherein the non-aqueous secondary battery separator has an air permeability of 100 seconds / 100 mL to 1000 seconds / 100 mL.

5. The separator for a non-aqueous secondary battery according to claim 1 , wherein the porous substrate comprises a polyolefin microporous membrane.

6. The porous substrate is a polyolefin microporous membrane; 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 separator for a non-aqueous secondary battery according to claim 1 .

7. 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the adhesive porous layer is substantially free of a fluorine-containing resin.

8. A non-aqueous secondary battery separator according to any one of claims 1 to 7, wherein the separator is disposed between the positive electrode and the negative electrode; Electromotive force is generated by doping and dedoping of lithium ions. Non-aqueous secondary battery.

Images