Separator for electricity storage device

Abstract

It is an object of the present invention to provide a multilayer porous film capable of realizing a thin heat-resistant layer having high heat resistance and low resistance, and a nonaqueous electrolyte battery separator and a nonaqueous electrolyte battery each including the multilayer porous film.SOLUTION: A multilayer porous film comprising a polyolefin microporous film and a porous layer laminated on the microporous film and containing inorganic particles and a water-soluble polymer binder, wherein the multilayer porous film has an air permeability of 300sec / 100cm3 or less, the porous layer has a thickness of 0.01 μm or more and less than 5.00 μm per at least one surface of the microporous film, the inorganic particles have an average particle size D50 of 0.01 μm or more and less than 0.50 μ m, and the water-soluble polymer binder contains more than 30.0% by mass and 99.0% by mass or less of a (meth) acrylamide-derived monomer unit. And a cyano group-containing monomer unit in an amount of 1.0 mass% or more and less than 70.0 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a multilayer porous membrane, and more particularly to a multilayer porous membrane that is suitably used as a separator disposed between a positive electrode and a negative electrode in a non-aqueous electrolyte battery. [Background technology]

[0002] In conventional non-aqueous electrolyte batteries, a power generating element consisting of a positive electrode plate, a negative electrode plate, and a separator interposed therebetween is impregnated with an electrolyte. Generally, separators are required to have ion permeability and safety features such as a shutdown function, so separators equipped with a microporous membrane containing a polyolefin resin are used.

[0003] Furthermore, multilayer porous membranes, in which a heat-resistant layer made of inorganic particles and a binder is formed on a polyolefin microporous membrane for the purpose of improving heat resistance, are known as separators for nonaqueous electrolyte batteries. As the heat-resistant layer, porous layers containing inorganic fillers and polymers containing structural units derived from (meth)acrylamide (commonly abbreviated as "PAAM") have been investigated (Patent Documents 1 to 5).

[0004] Patent Document 1 discloses that a multilayer porous membrane is obtained by coating a microporous membrane substrate with a latex containing a filler having a predetermined average particle size and 70 to 99% by weight of PAAM, from the viewpoints of preventing filler detachment from the multilayer porous membrane or porous layer, heat shrinkage resistance, and high battery output and high-temperature cycle characteristics. However, Patent Document 1 does not disclose the air permeability of the multilayer porous membrane, the air permeability of the porous layer containing the filler and PAAM, the pin puncture strength in terms of basis weight of the microporous membrane, or the weight-average molecular weight of the PAAM.

[0005] Patent Document 2 discloses that a coating layer is formed on a substrate using a slurry containing PAAM having a weight-average molecular weight of 300,000 to 6,000,000, from the viewpoints of high peel strength between the substrate and the coating layer, battery charge / discharge characteristics, and slurry storage stability. However, Patent Document 2 does not specifically disclose the air permeability and heat shrinkage rate of the multilayer porous membrane comprising the substrate and the coating layer, the air permeability of the coating layer, the pin puncture strength converted into basis weight of the substrate, the average particle size of the slurry, etc.

[0006] Patent Document 3 discloses that a porous layer is provided on a substrate using PAAM containing monomer units derived from more than 80% by weight but less than 95% by weight of acrylamide, more than 0% by weight but not more than 15% by weight of acrylonitrile, and more than 0% by weight but not more than 15% by weight of acrylic acid, in order to ensure high peel strength between the substrate and the porous layer and high heat resistance of the porous layer. However, Patent Document 3 does not specifically disclose the air permeability of the multilayer porous membrane including the substrate and the porous layer, the air permeability of the porous layer, the pin puncture strength converted into basis weight of the substrate, or additives or physical properties of the slurry containing inorganic particles and PAAM.

[0007] Patent Document 4 discloses a multilayer porous membrane containing 20 to 80% by weight of PAAM and hydrazide from the viewpoints of filler binding property, adhesion, battery rate characteristics, output characteristics, etc. However, Patent Document 4 does not consider the air permeability of the multilayer porous membrane including a microporous membrane and a porous layer, the air permeability of the porous layer, the pin puncture strength converted into basis weight of the microporous membrane, the physical properties of the inorganic particles used in the porous layer, or the shape and physical properties of the polymer.

[0008] Patent Document 5 discloses that when a slurry containing non-conductive particles having a predetermined average particle size and PAAM is applied to a porous polyolefin resin substrate, the slurry contains 1 ppm by mass to 47 ppm by mass of divalent or higher metal ions to improve coatability and adhesion of the non-conductive particles. However, Patent Document 5 does not specifically disclose the air permeability of the porous layer containing non-conductive particles and PAAM, the air permeability and heat shrinkage rate of the multilayer porous membrane comprising the porous polyolefin resin substrate and the porous layer, or the pin puncture strength converted into basis weight of the porous polyolefin resin substrate. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2017 / 195563 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-067681 [Patent Document 3] Special Publication No. 2023-551961 [Patent Document 4] International Publication No. 2023 / 053990 [Patent Document 5] International Publication No. 2023 / 182119 Summary of the Invention [Problem to be solved by the invention]

[0010] In recent years, in order to improve battery capacity, separators for non-aqueous electrolyte batteries that do not contribute to charge / discharge reactions have been required to be thinner, and the heat-resistant layer laminated or coated on the separator substrate has also been required to be thinner. Thinner heat-resistant layers can be achieved by using inorganic particles with relatively small particle sizes, but the increased surface area of ​​the inorganic particles requires more efficient binding by a binder than conventional methods. In other words, if the particle size of the inorganic particles is reduced and the binder amount is increased to ensure adhesion between the inorganic particles and ensure heat resistance, the air permeability and resistance of the non-aqueous electrolyte battery separator increase, resulting in a problem of reduced output and cycle characteristics of the non-aqueous electrolyte battery. Therefore, conventional multilayer porous membranes such as those described in Patent Documents 1 to 5 have not been able to realize separators for non-aqueous electrolyte batteries having a heat-resistant layer that is thin, highly heat-resistant, and low-resistance.

[0011] In view of the above circumstances, an object of the present invention is to provide a multilayer porous membrane that can realize a heat-resistant layer that is thin, highly heat-resistant, and low-resistance, and a separator for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery that include the same. [Means for solving the problem]

[0012] The above problems are solved by the following technical means. (1) A multilayer porous membrane having a microporous membrane containing a polyolefin resin as a main component and a porous layer containing inorganic particles and a water-soluble polymer binder laminated on at least one surface of the microporous membrane, The air permeability of the multilayer porous membrane is 300 sec / 100 cm 3 is as follows: the porous layer has a thickness of 0.01 μm or more and less than 5.00 μm per side of the microporous membrane; The average particle size D of the inorganic particles 50 is 0.01 μm or more and less than 0.50 μm, The water-soluble polymer binder contains more than 30.0 mass% and not more than 99.0 mass% of monomer units derived from (meth)acrylamide, and contains 1.0 mass% or more and less than 70.0 mass% of cyano group-containing monomer units. Multilayer porous membrane. (2) The microporous membrane has a puncture strength converted into basis weight of 0.49 N / (g / m 2 2. The multilayer porous membrane according to item 1, wherein (3) The air permeability of the porous layer is 100 sec / 100 cm 3 3. The multilayer porous membrane according to item 1 or 2, wherein: (4) The multilayer porous membrane according to any one of items 1 to 3, wherein the water-soluble polymer binder is non-particulate and has a weight-average molecular weight of 300,000 or more. (5) The multilayer porous membrane according to any one of items 1 to 4, wherein the water-soluble polymer binder contains less than 20.0% by mass of (meth)acrylic acid monomer units. (6) The multilayer porous membrane according to any one of items 1 to 5, wherein the multilayer porous membrane contains a water-insoluble polymer binder. (7) The multilayer porous membrane according to any one of items 1 to 6, wherein the multilayer porous membrane has a heat shrinkage rate at 150°C of 10% or less in both MD and TD. (8) The multilayer porous membrane according to any one of items 1 to 7, which is a separator for a non-aqueous electrolyte battery. (9) A non-aqueous electrolyte battery comprising a positive electrode, the multilayer porous membrane according to any one of items 1 to 8, a negative electrode, and a non-aqueous electrolyte. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a multilayer porous membrane having a thin heat-resistant layer that has both high heat resistance and low resistance, and it is also possible to realize a separator for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery using the same. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a detailed description will be given of an embodiment of the present invention (hereinafter abbreviated as "the present embodiment") for the purpose of illustrating it, but the present invention is not limited to the following embodiment. In this specification, the upper and lower limits of each numerical range can be arbitrarily combined. Furthermore, when a certain component contains a specific component as a main component, it means that the content of the specific component is 50 mass% or more based on the mass of the component. Unless otherwise specified, the physical properties or numerical values ​​described in this specification are measured or calculated by the methods described in the examples.

[0015] In this specification, MD refers to the machine direction of the continuous molding of the microporous polyolefin membrane, and TD refers to the direction crossing the MD of the microporous polyolefin membrane at an angle of 90°.

[0016] As used herein, the term "(meth)acrylic" refers to either acrylic or methacrylic, the term "(meth)acrylate" refers to either acrylate or methacrylate, and the term "(meth)acrylonitrile" refers to either acrylonitrile or methacrylonitrile.

[0017] <Multilayer porous membrane> The multilayer porous membrane according to this embodiment comprises a porous membrane containing a polyolefin resin as a main component (hereinafter sometimes abbreviated as "PO microporous membrane") and a porous layer containing inorganic particles and a water-soluble polymer binder laminated on at least one surface of the PO microporous membrane.

[0018] The multilayer porous membrane according to this embodiment has an air permeability of 300 sec / 100 cm 3 the thickness of the porous layer on at least one side of the microporous membrane is 0.01 μm or more and less than 5.00 μm, and the average particle size D of the inorganic particles in the porous layer is 50 is 0.01 μm or more and less than 0.50 μm, and the water-soluble polymer binder contains more than 30.0 mass % and not more than 99.0 mass % of monomer units derived from (meth)acrylamide, and contains 1.0 mass % or more and less than 70.0 mass % of cyano group-containing monomer units.

[0019] As mentioned above, the average particle size D is 0.01 μm or more and less than 0.50 μm. 50 By employing inorganic particles with a relatively small particle size, such as the above, and using a water-soluble polymer binder, such as water-soluble polyacrylamide, having a specific ratio of monomer units derived from (meth)acrylamide and cyano group-containing monomer units such as an acrylonitrile skeleton as the binder, it is possible to achieve high heat resistance in the porous layer disposed in the microporous membrane without increasing the total amount of binder, and thereby to realize a multilayer porous membrane having a heat-resistant layer that is thin, highly heat-resistant, and low-resistance.

[0020] Generally, the porous layer comprising inorganic particles and water-soluble polymer binder has a structure in which the inorganic particles are bonded together and the surface is coated with the water-soluble polymer binder.Although the multilayer porous film according to this embodiment is not intended to be bound by theory, the water-soluble polymer binder is used as the water-soluble polymer binder with high heat resistance, such as polyacrylamide, and the polyacrylamide contains a predetermined amount of cyano group-containing monomer units such as acrylonitrile skeleton, thereby improving the binding ability of the water-soluble polymer binder to the inorganic particle surface, and thus improving the heat resistance of the porous layer.In addition, in this embodiment, the polyacrylamide contains a predetermined amount of cyano group-containing monomer units such as acrylonitrile skeleton, thereby improving the dispersibility of the water-soluble polymer binder, and can achieve high heat resistance while suppressing the total amount of binder in the porous layer.

[0021] The multilayer porous membrane according to the present embodiment can be used as a separator for a non-aqueous electrolyte battery (hereinafter, may be abbreviated as separator), and has a thin, highly heat-resistant and low-resistance porous layer, so that it can ensure electrical insulation even under harsh environments such as high temperatures (hereinafter, referred to as "high-temperature insulation resistance"), and can also improve the energy density, capacity, output and cycle characteristics of the non-aqueous electrolyte battery.

[0022] The multilayer porous membrane may have a porous layer on one or both sides of the microporous PO membrane, for example, a two-layer structure including a first porous layer containing inorganic particles and a microporous PO membrane, or a three-layer structure including, in order, a first porous layer, a microporous PO membrane, and a second porous layer containing inorganic particles.

[0023] The multilayer structure is not limited to a two-layer structure of first porous layer-PO microporous membrane or a three-layer structure of first porous layer-PO microporous membrane-second porous layer, and may include, as desired, one or more additional layers between the first porous layer and the PO microporous membrane, between the second porous layer and the PO microporous membrane, or on at least one surface or outer surface of the multilayer porous membrane. Examples of additional layers include an additional PO microporous membrane, an additional porous layer containing inorganic particles and a binder polymer, a resin layer containing 50% or more by mass of a resin other than polyolefin (PO), and a thermoplastic polymer-containing layer containing a binder component having adhesive properties such as a thermoplastic polymer.

[0024] In the multilayer porous membrane according to this embodiment, the thickness of the microporous PO membrane is 8 μm or less, and the puncture strength of the microporous PO membrane converted into basis weight is 85 gf / (g / m 2 ) or more, and the average particle size D of the inorganic particles contained in the porous layer 50 is 0.05 μm or more and less than 0.30 μm, and the particle size D of the inorganic particles contained in the porous layer 90 is 0.10 μm or more and 0.45 μm or less, the total thickness of the porous layers is 0.1 μm or more and 3.0 μm or less, and the ratio of the light transmittance at a wavelength of 550 nm of the multilayer porous film to the light transmittance at a wavelength of 550 nm of the PO microporous film is 0.4 or more and less than 1.0.

[0025] The multilayer porous film according to this embodiment can achieve high light transmittance, high heat resistance, low resistance, and thin film due to the unique combination of the above-mentioned configurations. The relationship between the above-mentioned configurations and high light transmittance, high heat resistance, low resistance, or thin film is thought to be as follows, without wishing to be bound by theory.

[0026] Regarding light transmittance, the voids in the porous layer and the inorganic particles have different refractive indices, which causes scattering of light due to refraction in the multilayer porous film, resulting in reduced transparency. On the other hand, the smaller the size of the inorganic particles, the smaller the difference in refractive index between the voids and the inorganic particles, which is thought to suppress light scattering and increase transparency. Furthermore, the smaller the proportion of particles with relatively large particle sizes, the less likely light scattering by large particle sizes occurs, which is thought to further increase transparency. The multilayer porous film according to this embodiment has appropriate light transmittance, which tends to make it easier to identify foreign matter or unmelted material inside or on the surface of the substrate after the porous layer is placed on the PO microporous film.

[0027] The heat resistance is thought to be affected by the filler such as inorganic particles in the porous layer and the resin binder that may be contained in the porous layer.

[0028] The effect of the filler on heat resistance is thought to be that the smaller particle size of the inorganic particles increases the number of contact points between the fillers, thereby dispersing the shrinkage stress of the PO microporous membrane and improving the heat shrinkage resistance of the multilayer porous membrane. Furthermore, when the multilayer porous membrane is used as a separator for a nonaqueous electrolyte battery, if the battery temperature rises above the resin melting point due to thermal runaway or the like, the base layer tends to flow into the voids in the electrode layer, which can cause the separator for the nonaqueous electrolyte battery to become too thin and make it difficult to maintain insulation. In contrast, in this embodiment, the smaller the inorganic particles in the porous layer arranged on the surface of the base layer, the narrower the pore size of the porous layer, thereby suppressing resin flow. For example, it is thought that this blocks molten resin from the base layer, thereby improving the heat resistance of the battery.

[0029] Regarding the influence of the resin binder on heat resistance, it is preferable to use a water-soluble polymer binder that coats the surfaces of the inorganic particles contained in the porous layer and has stable binding properties even at high temperatures, because the shape of the porous layer is maintained even in a high-temperature environment, thereby improving heat resistance.

[0030] The components of the multilayer porous membrane according to this embodiment will be described below.

[0031] <Porous layer> The porous layer is laminated on at least one side of the microporous membrane containing a polyolefin resin as a main component, and is a layer containing inorganic particles and a water-soluble polymer binder. The porous layer may optionally contain a binder other than the water-soluble polymer binder, a dispersant, etc.

[0032] When the thickness (T) of the porous layer on at least one side of the PO microporous membrane is within the range of 0.01 μm≦T<5.00 μm, the membrane achieves a thin layer with high heat resistance and low resistance, ensures high-temperature insulation resistance, and ultimately improves the energy density, capacity, output, and cycle characteristics of nonaqueous electrolyte batteries. From the viewpoint of improving high-temperature insulation resistance and battery characteristics, the thickness (T) of the porous layer on at least one side of the PO microporous membrane is preferably 4.00 μm or less, more preferably 3.00 μm or less, even more preferably 2.00 μm or less, particularly preferably 1.50 μm or less, and most preferably 1.00 μm or less, with the lower limit being preferably 0.10 μm or more, more preferably 0.50 μm or more. When the multilayer porous membrane is used as a separator for a non-aqueous electrolyte battery, the porous layer is preferably thin from the viewpoint of improving the volumetric energy density of the electricity storage device, as long as the multilayer porous membrane can maintain a high balance of properties as a separator for a non-aqueous electrolyte battery.

[0033] The thickness T of the porous layer described above may be in the case where the porous layer is formed on at least one side of the PO microporous membrane, or in the case where the porous layer is formed on both sides of the PO microporous membrane. When the porous layer is formed on both sides of the PO microporous membrane, the total thickness of the porous layer is preferably within the above-mentioned range.

[0034] (Inorganic particles) Average particle size D of inorganic particles in the porous layer 50 0.01μm≦D 50The smaller the particle size is within the range of <0.50 μm, the more compatible it is with a water-soluble polymer binder containing a monomer unit derived from (meth)acrylamide and a cyano group-containing monomer unit, and the higher the heat resistance of the porous layer can be realized. This makes it possible to realize a multilayer porous membrane having a thin, highly heat-resistant, and low-resistance heat-resistant layer.

[0035] Average particle size of inorganic particles D 50 From the viewpoint of compatibility with the water-soluble polymer binder and from the viewpoint of achieving a thin porous layer and high heat resistance and low resistance at the same time, D is preferably 0.05 μm or more, more preferably 0.06 μm or more, even more preferably 0.07 μm or more, and particularly preferably 0.10 μm or more. 50 From the same viewpoint and from the viewpoint of maintaining high light transmittance and improving the accuracy of detecting foreign matter in the multilayer porous membrane, the thickness is preferably 0.45 μm or less, more preferably 0.40 μm or less, even more preferably 0.30 μm or less, and particularly preferably 0.20 μm or less.

[0036] Inorganic particle diameter D 90 From the viewpoint of compatibility with the water-soluble polymer binder and from the viewpoint of achieving a thin porous layer and high heat resistance and low resistance at the same time, D is preferably 0.10 μm or more, more preferably 0.11 μm or more, even more preferably 0.12 μm or more, and particularly preferably 0.20 μm or more. 90 From the same viewpoint and from the viewpoint of maintaining high light transmittance and improving the accuracy of detecting foreign matter in the multilayer porous membrane, the thickness is preferably less than 0.70 μm, more preferably less than 0.50 μm, even more preferably less than 0.45 μm, particularly preferably less than 0.35 μm, and most preferably 0.25 μm or less.

[0037] Inorganic particle diameter D 10 From the viewpoint of compatibility with the water-soluble polymer binder and from the viewpoint of achieving a thin porous layer and high heat resistance and low resistance at the same time, D is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.04 μm or more. 10From the same viewpoint and from the viewpoint of maintaining high light transmittance and improving the accuracy of detecting foreign matter in the multilayer porous membrane, the thickness is preferably 0.20 μm or less, more preferably 0.15 μm or less, and even more preferably 0.10 μm or less.

[0038] The particle size, average particle size and particle size distribution of the inorganic particles in the porous layer should satisfy the following relationship in terms of maintaining high light transmittance: D 50 <0.20 μm; and D 90 <0.35 μm It is preferable that the following is satisfied.

[0039] Furthermore, the average particle size D of the inorganic particles 50 and D 90 and D 10 From the viewpoint of thinning the porous layer, achieving high heat resistance and low resistance, and maintaining high permeability, the following formulas (1) and (2) are satisfied: Formula (1):D 90 / D 50 ≦2.0 Formula (2):D 50 / D 10 ≦2.0 It is preferable that the relationship expressed by the following formula be satisfied.

[0040] Inorganic particle D 90 / D 50 From the viewpoint of maintaining high light transmittance and heat resistance, the upper limit of D is preferably 2.0 or less, more preferably 1.9 or less, and even more preferably 1.8 or less. 90 / D 50 From the viewpoint of maintaining ion permeability, the lower limit of is preferably 1.2 or more, more preferably 1.3 or more, and even more preferably 1.4 or more.

[0041] Inorganic particle D 50 / D 10 From the viewpoint of maintaining high light transmittance, the upper limit of D is preferably 2.0 or less, more preferably 1.9 or less, even more preferably 1.8 or less, and particularly preferably 1.7 or less. 50 / D 10From the viewpoint of maintaining ion permeability, the lower limit of is preferably 1.2 or more, more preferably 1.3 or more, and even more preferably 1.4 or more.

[0042] The particle size, average particle size, or particle size distribution of the inorganic particles described above can be achieved, for example, by selecting the type of inorganic particle raw material, dispersing, stirring, or controlling the particle size of the inorganic particles in the inorganic particle-containing slurry, in the process of disposing a porous layer on a microporous membrane or substrate, or in the process of manufacturing a separator.

[0043] Specifically, examples of methods for adjusting the particle size distribution of inorganic particles include grinding inorganic particles using a ball mill, bead mill, jet mill, etc. to obtain the desired particle size distribution, and blending inorganic particles having multiple particle size distributions.

[0044] The material of the inorganic particles used in the porous layer is not particularly limited, but it is preferable that the material has high heat resistance and electrical insulation properties, and is electrochemically stable within the range of use of the non-aqueous electrolyte battery.

[0045] Examples of inorganic particle materials include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum oxide hydroxide, or boehmite, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. Among these, at least one selected from the group consisting of alumina, boehmite, and barium sulfate is preferred from the viewpoint of stability in nonaqueous electrolyte batteries, with boehmite or barium sulfate being more preferred. The inorganic particles may be used alone or in combination.

[0046] Examples of the shape of the inorganic particles include plate-like, scale-like, polyhedral, needle-like, columnar, granular, spherical, spindle-like, and block-like shapes, and a combination of multiple types of inorganic particles having the above shapes may be used. A combination of multiple types of inorganic particles having the above shapes may also be used.

[0047] The aspect ratio of the inorganic particles is preferably 1.0 or more and 3.0 or less, from the viewpoints of the total porosity of the porous layer and the bonding points between the inorganic particles via the water-soluble polymer binder. The lower limit of the aspect ratio of the inorganic particles is preferably 1.0 or more, more preferably 1.1 or more, from the viewpoint of maintaining ion permeability. The upper limit of the aspect ratio of the inorganic particles is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less, from the viewpoints of suppressing the moisture content of the porous layer and maintaining heat resistance. The aspect ratio of the inorganic particles can be determined by image analysis of images taken with a scanning electron microscope (SEM).

[0048] The BET specific surface area of ​​the inorganic particles is 7.00m 2 / g or more 200m 2 / g or less, and 2 / g or more 100m 2 / g or less is more preferable, and 8.00m 2 / g over 50.0m 2 / g or less is more preferable, and 10.0m 2 / g or more 30.0m 2 It is particularly preferable that the BET specific surface area of ​​the inorganic particles is 7.00 m / g or less. 2 / g or more, the pore size of the porous layer becomes small, the current density of the nonaqueous electrolyte battery becomes uniform, and the cycle performance tends to improve, and the number of contact points between inorganic particles in the porous layer increases, and the heat resistance tends to improve. Furthermore, when the BET specific surface area of ​​the inorganic particles is within the above range, it is easy to realize an average particle size suitable for this embodiment. Furthermore, from the viewpoint of suppressing the moisture content of the porous layer, it is preferable that the BET specific surface area of ​​the inorganic particles is within the above range.

[0049] The mass ratio of inorganic particles in the porous layer (Wi ) is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more. i When W is 80% or more, the proportion of other components, such as resin binders, is relatively small, suppressing an increase in the air permeability of the porous layer relative to the microporous PO membrane and / or battery resistance, thereby improving battery performance. i The upper limit is not particularly limited, but may be, for example, less than 100% or 99% or less.

[0050] The volume fraction of inorganic particles in the porous layer excluding the pore volume (V i ) is preferably 65% ​​or more, more preferably 70% or more, even more preferably 75% or more, particularly preferably 80% or more, and most preferably 85% or more, with the volume of the porous layer excluding voids being 100% by volume. i When the ratio of inorganic particles to other components, such as resin binders, is 65% or more, the ratio increases, suppressing an increase in the air permeability of the microporous PO membrane due to the porous layer and reducing the electrical resistance of the multilayer porous membrane. i The upper limit of is not limited, but may be, for example, 95% or less, 93% or less, 92% or less, or 91% or less.

[0051] (resin binder) The porous layer contains a water-soluble polymer binder as the resin binder, and may contain a binder other than the water-soluble polymer binder, if desired.

[0052] The porous layer according to this embodiment preferably contains a water-insoluble polymer binder in addition to a water-soluble polymer binder. In this case, the porous layer preferably has a structure in which the water-soluble polymer binder coats at least a portion of the surfaces of the inorganic particles, and the water-insoluble polymer binder is dispersed throughout the porous layer to bond the inorganic particles or inorganic particles coated with the water-soluble polymer binder to each other. This structure reduces the amount of moisture contained in the porous layer, improving the heat resistance of the porous layer and the peel strength between the porous layer and the microporous PO membrane.

[0053] Water-soluble polymer binder The water-soluble polymer binder according to this embodiment is used as a resin binder and is water-soluble. The water-soluble polymer binder according to this embodiment is preferably a polymer that, when 1.0 g of the polymer is dissolved in 100 g of water at 25° C., has an insoluble content of less than 1.0 mass %. The water-soluble polymer binder according to this embodiment is preferably non-particulate.

[0054] When the water-soluble polymer binder contains more than 30.0 mass % to 99.0 mass % of monomer units derived from (meth)acrylamide and 1.0 mass % to less than 70.0 mass % of cyano group-containing monomer units, it is compatible with the relatively small particle size inorganic particles described above, and can control the binding points of the inorganic particles while suppressing the amount of binder, thereby achieving high heat resistance of the porous layer.

[0055] If desired, the water-soluble polymer binder may contain repeat units other than the (meth)acrylamide-derived monomer units and the cyano group-containing monomer units.

[0056] From the viewpoint of compatibility with inorganic particles and control of binding points of inorganic particles, the lower limit of the content of monomer units derived from (meth)acrylamide in the water-soluble polymer binder is preferably 40.0 mass% or more, more preferably 50.0 mass% or more, even more preferably 60.0 mass% or more, still more preferably 70.0 mass% or more, and particularly preferably 80.0 mass% or more, and the upper limit is preferably 97.0 mass% or less, more preferably 95.0 mass% or less, even more preferably 85.0 mass% or less, and particularly preferably 90.0 mass% or less.

[0057] The (meth)acrylamide-derived monomer units can be introduced by (co)polymerization using, for example, (meth)acrylamide, dialkyl(meth)acrylamide, or derivatives thereof as a monomer.

[0058] From the viewpoint of compatibility with inorganic particles and control of the binding points of inorganic particles, the lower limit of the content of cyano group-containing monomer units in the water-soluble polymer binder is preferably 3.0 mass% or more, more preferably 5.0 mass% or more, even more preferably 10.0 mass% or more, still more preferably 15.0 mass% or more, and particularly preferably 20.0 mass% or more, and the upper limit is preferably 60.0 mass% or less, more preferably 50.0 mass% or less, even more preferably 40.0 mass% or less, and particularly preferably 30.0 mass% or less.

[0059] The cyano group-containing monomer unit can be introduced by (co)polymerization using a monomer having a cyano group and a polymerizable group, for example, a monomer having a (meth)acrylonitrile skeleton, a cyanoacrylate skeleton, or the like.

[0060] From the viewpoint of high heat resistance, the water-soluble polymer binder preferably contains (meth)acrylic acid monomer units, and from the viewpoint of optimizing heat resistance, it is more preferable that the water-soluble polymer binder contains less than 20.0 mass% of (meth)acrylic acid monomer units, and the content of (meth)acrylic acid monomer units is even more preferably 10.0 mass% or less, still more preferably in the range of 0.0 mass% or more and 5.0 mass% or less, and particularly preferably more than 0.0 mass% and 2.0 mass% or less.

[0061] The (meth)acrylic acid monomer units can be introduced by (co)polymerization using, for example, monomers such as acrylic acid and methacrylic acid.

[0062] If desired, the water-soluble polymer binder may contain a monomer unit derived from a (meth)acrylic acid ester. The content of the monomer unit derived from a (meth)acrylic acid ester in the water-soluble polymer binder is preferably in the range of 0.0 mass % or more and 20.0 mass % or less, and more preferably more than 0.0 mass % and less than 20.0 mass %.

[0063] The monomer units derived from a (meth)acrylic acid ester can be introduced by (co)polymerization using a monomer such as a (meth)acrylic acid alkyl ester, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, or 2-ethylhexyl methacrylate.

[0064] From the viewpoint of the effects of the present invention, the (meth)acrylic acid ester monomer preferably does not contain a hydroxyl group.

[0065] Specific examples of the water-soluble polymer binder include (meth)acrylamide-(meth)acrylonitrile copolymer, (meth)acrylamide-(meth)acrylonitrile-(meth)acrylic acid copolymer, (meth)acrylamide-(meth)acrylonitrile-(meth)acrylic acid ester copolymer, (meth)acrylamide-(meth)acrylonitrile-(meth)acrylic acid-(meth)acrylic acid ester copolymer, and the like.

[0066] From the viewpoint of improving the heat resistance and peel strength of the porous layer, the weight average molecular weight (Mw) of the water-soluble polymer binder is preferably 300,000 or more as its lower limit, more preferably more than 300,000, even more preferably 350,000 or more, even more preferably 400,000 or more, still more preferably 500,000 or more, particularly preferably 600,000 or more, particularly preferably 700,000 or more, significantly preferably 800,000 or more, far more preferably 900,000 or more, and most preferably 1,000,000 or more, and the upper limit is preferably 4,000,000 or less, more preferably 3,000,000 or less, and even more preferably 2,000,000 or less.

[0067] The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the water-soluble polymer binder (hereinafter referred to as dispersity or Mw / Mn) is preferably 30 or less, more preferably 20 or less, even more preferably 10 or less, even more preferably 5 or less, and particularly preferably 3 or less, from the viewpoint of improving the high heat resistance and high peel strength of the porous layer. The lower limit of Mw / Mn is not limited and may be, for example, 1 or more.

[0068] From the viewpoint of ensuring high heat resistance of the porous layer while suppressing the binder amount, the mass proportion Wa of the water-soluble polymer binder in the porous layer is, based on the mass of the porous layer, preferably 4.0 mass% or less as its upper limit, more preferably 3.0 mass% or less, even more preferably 2.0 mass% or less, and particularly preferably 1.0 mass% or less; and preferably 0.1 mass% or more as its lower limit, more preferably 0.5 mass% or more.

[0069] - Non-water-soluble polymer binder The porous layer preferably contains a water-insoluble polymer binder from the viewpoints of achieving both high peel strength and low moisture content, and from the viewpoint of heat resistance. The water-insoluble polymer binder is preferably a particulate polymer that disperses in water. The glass transition temperature (Tg) of the water-insoluble polymer binder is preferably 30°C or lower, more preferably 10°C or lower, from the viewpoint of binding inorganic particles and improving heat resistance.

[0070] The water-insoluble polymer binder is not particularly limited, but examples thereof include particulate acrylic polymers, etc. The acrylic polymer is a polymer containing a (meth)acrylic compound as a monomer unit, and is preferable from the viewpoint of electrical resistance, and is more preferably a latex of an acrylic polymer.

[0071] As long as the acrylic polymer is water-insoluble and particulate, (meth)acrylic acid may be used as the (meth)acrylic compound.In addition, the (meth)acrylic acid ester used in the acrylic polymer may include, for example, (meth)acrylic acid alkyl esters, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate; epoxy group-containing (meth)acrylic acid esters, such as glycidyl acrylate, glycidyl methacrylate; and these may be used alone or in combination of two or more.

[0072] The acrylic polymer may also be obtained by copolymerizing other monomers copolymerizable with the (meth)acrylic compound. Examples of the copolymerizable other monomers include unsaturated carboxylic acid alkyl esters, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated monomers containing a hydroxyalkyl group, unsaturated carboxylic acid amide monomers, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, and the like. These may be used alone or in combination of two or more. Among the above, unsaturated carboxylic acid alkyl ester monomers are particularly preferred. Examples of unsaturated carboxylic acid alkyl ester monomers include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and the like. These may be used alone or in combination of two or more.

[0073] Specific examples of the acrylic polymer include methacrylic acid ester-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, and acrylonitrile-acrylic acid ester copolymers.

[0074] The average particle size (D 50) is preferably adjusted in accordance with the size reduction of the inorganic particles, but from the viewpoint of efficiently achieving binding at the interface between the inorganic particles or between the inorganic particles and the microporous PO membrane, the upper limit is preferably 0.20 μm or less, more preferably 0.15 μm or less, even more preferably 0.10 μm or less, and particularly preferably 0.05 μm or less, and the lower limit is not particularly limited and may be, for example, 0.01 μm or more.

[0075] From the viewpoint of thermal shrinkage suppression ability and permeability, the mass proportion Wb of the water-insoluble polymer binder contained in the porous layer has a lower limit of preferably 0 mass% or more, more preferably more than 0 mass%, and an upper limit of preferably 5.0 mass% or less, more preferably 4.0 mass% or less, even more preferably 3.0 mass% or less, and particularly preferably 2.0 mass% or less.

[0076] From the viewpoint of achieving both high heat resistance and low resistance in the porous layer by controlling the binding points of the inorganic particles while suppressing the amount of binder, it is preferable that the mass fraction Wb of the water-insoluble polymer binder is higher than the mass fraction Wa of the water-soluble polymer binder (i.e., the ratio Wb / Wa > 1.0), and the lower limit of the ratio Wb / Wa is more preferably 4.0 or more, even more preferably 4.5 or more, and the upper limit of the ratio Wb / Wa is more preferably 8.0 or less, even more preferably 7.0 or less.

[0077] Other polymers Optionally, the porous layer may also contain polymers other than the polymeric binders described above, such as the following resins: Polyolefins: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof; Conjugated diene polymers: for example, styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof; Polyvinyl alcohol-based resins: for example, polyvinyl alcohol, polyvinyl acetate; Fluorine-containing resins: for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer; Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; Resins having a melting point and / or glass transition temperature of 180°C or higher, or polymers having no melting point but a decomposition temperature of 200°C or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester, poly(meth)acrylamide; It may include the following:

[0078] When the multilayer porous membrane is used as a separator for a non-aqueous electrolyte battery, the porous layer may contain, as another polymer, a thermoplastic polymer to improve adhesion between the separator and the electrode. Such a thermoplastic polymer may have a glass transition temperature or melting point of 20°C or higher and 200°C or lower, and an average particle size of 0.5 to 5 times the thickness of the porous layer.

[0079] From the viewpoints of high light transmittance, high heat resistance, and low resistance, the volume fraction of the water-soluble polymer including the water-soluble polymer binder in the porous layer is preferably 1% by volume or more and 10% by volume or less, where the volume of the porous layer excluding the voids is 100% by volume. From the viewpoint of maintaining heat resistance, the lower limit of the volume fraction of the water-soluble polymer in the porous layer is preferably 1.0% by volume or more, more preferably 2.0% by volume or more, and even more preferably 2.5% by volume or more. From the viewpoint of maintaining ion permeability, the upper limit of the volume fraction of the water-soluble polymer in the porous layer is preferably 10.0% by volume or less, more preferably 9.5% by volume or less, and even more preferably 9.0% by volume or less.

[0080] (dispersant) The porous layer may optionally contain a dispersant in addition to the inorganic particles and resin binder. Examples of dispersants include polycarboxylates such as polyacrylates, sulfonates, and polyoxyethers. Examples of polyacrylates include sodium polyacrylate. The dispersant content is preferably 0.0% by mass or more, more preferably greater than 0.0% by mass, even more preferably 0.2% by mass or more, and particularly preferably 0.4% by mass or more, based on the solid content of the porous layer. Furthermore, the dispersant content is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.8% by mass or less, based on the solid content of the porous layer.

[0081] (Physical properties of porous layers) The air permeability of the porous layer is 100sec / 100cm 3 It is preferable that the speed is less than 50 sec / 100 cm, and more preferably 50 sec / 100 cm 3 Less than 40 sec / 100 cm, more preferably 3 More preferably, 30 sec / 100 cm or less 3 Below 20 sec / 100 cm, especially preferred 3 The lower limit is preferably 1 sec / 100 cm or less. 3 More than 5 seconds / 100 cm is preferable. 3 The air permeability of the porous layer is 100 sec / 100 cm 3 When the thickness of the porous layer is not more than 100 cm, the electrical resistance is reduced, which in turn tends to improve the capacity and cycle characteristics of the non-aqueous electrolyte battery. From the same viewpoint, the air permeability per thickness of the porous layer is preferably 30 (sec / 100 cm 3 ) / μm or less, more preferably 25 (sec / 100cm 3 ) / μm or less, more preferably 20 (sec / 100cm 3 ) / μm or less, particularly preferably 15 (sec / 100cm 3 ) / μm or less, and the lower limit is preferably 1 (sec / 100 cm 3 ) / μm or more, more preferably 3 (sec / 100cm3 ) / μm or more.

[0082] The layer density in the porous layer has a lower limit of 0.5 g / (m 2 ·μm) or more, and more preferably 1.0 g / (m 2 ·μm) or more, more preferably 1.5g / (m 2 ·μm) or more, with the upper limit being 5.0g / (m 2 ·μm) or less, and more preferably 4.0 g / (m 2 ·μm) or less, more preferably 3.0 g / (m 2 ·μm) or less. The layer density in the porous layer is 0.5g / (m 2 ·μm) or more is preferable from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the microporous PO membrane, and 2 A thickness of 0.1 μm or less is preferable from the viewpoint of maintaining the ion permeability of the porous layer and suppressing capacity degradation during repeated cycles.

[0083] The 180° peel strength of the porous layer from the multilayer porous membrane or microporous PO membrane is preferably 200 N / m or more, more preferably 250 N / m or more, even more preferably 300 N / m or more, even more preferably 350 N / m or more, and particularly preferably 400 N / m or more. The upper limit of the 180° peel strength is preferably 500 N / m or less. The "180° peel strength" refers to the strength when the coating layer is peeled off so that the surface of the coating layer facing the substrate forms an angle of 180° with the substrate. When the 180° peel strength is within the above range, the adhesive strength with the electrode is increased and thermal shrinkage is suppressed.

[0084] The 90° peel strength of the porous layer from the multilayer porous membrane or microporous PO membrane is preferably 10 N / m or more, more preferably 15 N / m or more, and even more preferably 20 N / m or more, from the viewpoints of adhesion to the electrode and suppression of thermal shrinkage. The upper limit of the 90° peel strength is preferably 30 N / m or less. The "90° peel strength" refers to the strength when the coating layer is peeled off so that the surface of the coating layer facing the substrate forms a 90° angle with the substrate.

[0085] The upper limit of the average pore size of the porous layer is preferably 0.30 μm or less, more preferably 0.20 μm or less, even more preferably 0.15 μm or less, and particularly preferably 0.10 μm or less, and the lower limit is preferably 0.01 μm or more.

[0086] The value of the average pore size of the porous layer / gas-liquid pore size of the microporous PO membrane is preferably 6.0 or less, more preferably 5.0 or less, even more preferably 3.0 or less, and even more preferably 2.5 or less.

[0087] The amount of water per unit volume of the porous layer can be measured by the method described in the Examples, and is preferably 5.0 mg / (μm m 2 ) or less, more preferably 4.0 mg / (μm m 2 ) or less, more preferably 3.0 mg / (μm m 2 ) or less, and even more preferably 2.5 mg / (μm m 2 ) is as follows.

[0088] <Polyolefin microporous membrane> Porous membranes containing polyolefin as a primary component (microporous PO membranes) contain polyolefin and are preferably composed of polyolefin. The polyolefin may be in the form of a microporous polyolefin, such as a polyolefin membrane, a polyolefin fiber woven fabric, or a polyolefin fiber nonwoven fabric. Examples of polyolefins include homopolymers, copolymers, and multistage polymers obtained using monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. These polymers may be used alone or in combination of two or more. From the viewpoint of the melt viscosity, shutdown, and meltdown properties of microporous PO membranes usable as separators, the polyolefin is preferably at least one selected from the group consisting of polyethylene, polypropylene, and copolymers thereof, more preferably polypropylene, and even more preferably an ethylene-propylene copolymer or a mixture of polyethylene and polypropylene.

[0089] Specific examples of polyethylene include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), high-molecular-weight polyethylene (HMWPE), and ultra-high-molecular-weight polyethylene (UHMWPE).

[0090] In this specification, high molecular weight polyethylene (HMWPE) refers to polyethylene with a viscosity average molecular weight (Mv) of 100,000 or more. Generally, the Mv of ultra-high molecular weight polyethylene (UHMWPE) is 1,000,000 or more, and therefore, by definition, high molecular weight polyethylene (HMWPE) in this specification includes UHMWPE.

[0091] In this specification, high density polyethylene means polyethylene with a density of 0.942 to 0.970 g / cm 3 In the present invention, the density of polyethylene refers to a value measured in accordance with D) density gradient tube method described in JIS K7112 (1999).

[0092] Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene.

[0093] Specific examples of the copolymer of ethylene and propylene include an ethylene-propylene random copolymer and an ethylene-propylene rubber.

[0094] When the polyolefin (PO) contained in the PO microporous membrane contains polyethylene (PE), the PE content is from 50% to 100% by mass, based on the total mass of the resin components constituting the PO microporous membrane, and from the viewpoint of fuse properties or meltdown properties, is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 93% by mass or more.

[0095] When the PO contained in the PO microporous membrane contains polypropylene (PP), the PP content is more than 0 mass% and less than 50 mass% based on the total mass of the resin components constituting the PO microporous membrane, and from the viewpoints of melt viscosity and fuse properties, is preferably 30 mass% or less, more preferably 20 mass% or less, even more preferably 10 mass% or less, and particularly preferably 7 mass% or less.

[0096] In addition to the polyolefins listed above, the microporous PO membrane may further contain resins such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polyvinylidene fluoride, nylon, and polytetrafluoroethylene.

[0097] With respect to the melt index (MI) of the PO microporous membrane at 190°C, from the viewpoint of suppressing high viscosity of the PO resin composition during membrane formation and thereby suppressing the occurrence of defective products, the lower limit is preferably 0.01 g / 10 min or more, and more preferably 0.05 g / 10 min or more, and the upper limit is preferably 0.70 g / 10 min or less, more preferably 0.60 g / 10 min or less, even more preferably 0.40 g / 10 min or less, particularly preferably 0.30 g / 10 min or less, and most preferably 0.20 g / 10 min or less.

[0098] PO microporous membrane basis weight (g / m 2 ) (hereinafter referred to as the basis weight converted puncture strength) is 50gf / (g / m 2 ) or more, i.e., 0.49N / (g / m 2 ) or more is preferable. 2 A PO microporous membrane having a puncture strength in terms of basis weight of 0.60 N / (g / m) or more tends to be resistant to rupture and has improved heat resistance. From the viewpoint of resistant to rupture, the PO microporous membrane preferably has a puncture strength in terms of basis weight of 0.60 N / (g / m) or more. 2 ) or more, more preferably 0.70 N / (g / m 2 ) or more, and even more preferably 0.80 N / (g / m 2) or more, particularly preferably 0.90 N / (g / m 2 ) or more, most preferably 1.00 N / (g / m 2 From the viewpoint of improving the safety of the non-aqueous electrolyte battery while maintaining the strength of the microporous PO membrane, the puncture strength in terms of basis weight is preferably 3.00 N / (g / m 2 ) or less, more preferably 2.00 N / (g / m 2 ) is as follows.

[0099] The pin puncture strength of the PO microporous membrane not converted into basis weight (hereinafter simply referred to as pin puncture strength) is preferably at least 100 gf, i.e., at least 0.98 N, more preferably at least 1.47 N, and even more preferably at least 1.96 N, from the viewpoints of preventing breakage and improving heat resistance, and is preferably at most 9.80 N, more preferably at most 5.88 N, and even more preferably at most 4.90 N, from the viewpoint of improving the safety of nonaqueous electrolyte batteries while maintaining membrane strength.

[0100] The pin puncture strength or the pin puncture strength converted to basis weight can be increased by increasing the orientation of molecular chains due to the shear force or stretching applied to the molded product during extrusion. However, as the strength increases, the thermal stability deteriorates due to an increase in residual stress, so the strength is controlled according to the purpose.

[0101] The thickness (TB) of the PO microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, even more preferably 3.0 μm or more, still more preferably 4.0 μm or more, and particularly preferably 4.5 μm or more to ensure voltage resistance, and is preferably 30.0 μm or less, more preferably 20.0 μm or less, even more preferably 16.0 μm or less, still more preferably 12.0 μm or less, still more preferably 9.0 μm or less, and particularly preferably 7.0 μm or less to ensure the capacity of a nonaqueous electrolyte battery. The thickness TB of the PO microporous membrane can be adjusted, for example, by controlling the die lip gap, the stretch ratio in the stretching step, etc.

[0102] The porosity of the microporous PO membrane is preferably 20% or more, more preferably 30% or more, even more preferably 35% or more, and particularly preferably 40% or more from the viewpoint of permeability, and is preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, and particularly preferably 50% or less from the viewpoint of membrane strength. The porosity of the microporous PO membrane can be adjusted, for example, by controlling the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, the relaxation rate during heat setting, etc., or by combining these.

[0103] The air permeability of the microporous PO membrane is preferably 10 sec / 100 cm from the viewpoint of preventing excessive current from flowing between multiple electrodes through the microporous PO membrane. 3 More than 30sec / 100cm, preferably 30sec / 100cm 3 More preferably, 50 sec / 100 cm 3 More than 70 sec / 100 cm is particularly preferable. 3 From the viewpoint of permeability, it is preferably 300 sec / 100 cm 3 Less than 250sec / 100cm, preferably 3 More preferably, 200 sec / 100 cm 3 Less than 150 sec / 100 cm, more preferably 3 Below 100 sec / 100 cm, particularly preferably 3 The following is the result.

[0104] The viscosity-average molecular weight (Mv) of the PO microporous membrane has a lower limit of preferably 400,000 or more, more preferably 450,000 or more, and even more preferably 500,000 or more, and an upper limit of preferably 1,300,000 or less, more preferably 1,200,000 or less, and even more preferably 1,150,000 or less. When the PO microporous membrane has an Mv of 400,000 or more, the melt tension during melt-forming is increased, improving formability, and polymer entanglement tends to result in high membrane strength. When the Mv is 1,300,000 or less, the raw materials are easily melt-kneaded uniformly, which tends to improve sheet formability, particularly thickness stability. Furthermore, when the multilayer porous membrane is used as a separator for a nonaqueous electrolyte battery, the pores tend to be easily blocked at elevated temperatures and maintain this state up to high temperatures, tending to provide good fuse function.

[0105] The gas-liquid pore size of the PO microporous membrane is preferably 30 nm or more, more preferably 40 nm or more. The gas-liquid pore size of the PO microporous membrane is preferably 70 nm or less, more preferably 60 nm or less, and even more preferably 50 nm or less. The half-dry pore size of the PO microporous membrane is preferably 20 nm or more, more preferably 30 nm or more. The half-dry pore size of the PO microporous membrane is preferably 60 nm or less, more preferably 50 nm or less. When the gas-liquid pore size and / or half-dry pore size of the PO microporous membrane are within the above-mentioned ranges, the ionic conductivity and voltage resistance of the multilayer porous membrane are easily achieved. The pore size of the PO microporous membrane can be adjusted by, for example, controlling the polyolefin composition ratio, the type of polyolefin or plasticizer, the cooling rate of the extruded sheet, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, and the relaxation rate during heat setting, or by combining these.

[0106] The microporous PO membrane preferably has low electronic conductivity, ionic conductivity, high resistance to organic solvents, and fine pores. The microporous PO membrane can be used alone as a separator for a lithium ion secondary battery, and is particularly suitable for use as a laminate-type separator for a lithium ion secondary battery.

[0107] <Thermoplastic polymer-containing layer> At least one surface or the outer surface of the multi-layer porous membrane according to one embodiment may optionally include a thermoplastic polymer-containing layer. The thermoplastic polymer-containing layer contains a thermoplastic polymer. The thermoplastic polymer layer may optionally include a particulate polymer and / or have a dot pattern.

[0108] (thermoplastic polymer) Thermoplastic polymers include, but are not limited to, polyolefin resins such as polyethylene, polypropylene, and α-polyolefin; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene and copolymers thereof; diene polymers containing conjugated dienes such as butadiene and isoprene as monomer units, copolymers containing these, and hydrogenated versions thereof; acrylic polymers containing acrylic esters, methacrylic esters, and the like as monomer units, or copolymers containing these, and hydrogenated versions thereof; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; resins having a melting point and / or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester, and mixtures thereof. Furthermore, monomers having at least one group selected from the group consisting of a hydroxyl group, a sulfonic acid group, a carboxyl group, an amide group, and a cyano group can also be used as the monomer used in synthesizing the thermoplastic polymer.

[0109] Among these thermoplastic polymers, diene-based polymers, acrylic polymers, and fluorine-based polymers are preferred because they have excellent binding properties with the electrode active material, strength, and flexibility.

[0110] (Diene polymer) The diene polymer is not particularly limited, but is a polymer containing a monomer unit obtained by polymerizing a conjugated diene having two conjugated double bonds, such as butadiene or isoprene. Examples of conjugated diene monomers include, but are not particularly limited to, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. These may be polymerized alone or copolymerized.

[0111] The proportion of monomer units obtained by polymerizing a conjugated diene in the diene polymer is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more of the total diene polymer.

[0112] The diene polymer is not particularly limited, but examples thereof include homopolymers of conjugated dienes such as polybutadiene and polyisoprene, and copolymers of conjugated dienes with copolymerizable monomers. The copolymerizable monomer is not particularly limited, but examples thereof include the (meth)acrylate monomers described below and the following monomers (hereinafter also referred to as "other monomers").

[0113] The "other monomers" are not particularly limited, but examples thereof include α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene-based monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, and divinylbenzene; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; methyl vinyl ether, and ethyl vinyl ether. vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; acrylic acid ester and / or methacrylic acid ester compounds such as methyl acrylate and methyl methacrylate; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; and amide monomers such as acrylamide, N-methylolacrylamide, and acrylamido-2-methylpropanesulfonic acid, and the like. These may be used alone or in combination of two or more.

[0114] (acrylic polymer) The acrylic polymer is not particularly limited, but is preferably a polymer containing a monomer unit obtained by polymerizing a (meth)acrylate monomer. When the thermoplastic polymer-containing layer contains an acrylic polymer as the thermoplastic polymer, it preferably contains a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer. When the thermoplastic polymer of the thermoplastic polymer-containing layer contains a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer, the adhesive strength is improved when the multilayer porous membrane or separator has a low basis weight, which is preferable.

[0115] The (meth)acrylate monomer is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, and decyl (meth)acrylate. Examples of the acrylate include alkyl (meth)acrylates such as acrylate, lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, and stearyl (meth)acrylate; hydroxy group-containing (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; amino group-containing (meth)acrylates such as aminoethyl (meth)acrylate; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate (GMA).

[0116] The proportion of monomer units obtained by polymerizing (meth)acrylate monomers is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more of the total acrylic polymer. Examples of the acrylic polymer include homopolymers of (meth)acrylate monomers and copolymers of the same with monomers copolymerizable therewith. Copolymerizable monomers include the "other monomers" listed in the section on diene polymers above, and these may be used alone or in combination of two or more.

[0117] (Fluorine-based polymer) The fluorine-containing polymer is not particularly limited, but examples thereof include a homopolymer of vinylidene fluoride and a copolymer of the homopolymer and a copolymerizable monomer. The fluorine-containing polymer is preferred from the viewpoint of electrochemical stability.

[0118] The proportion of monomer units obtained by polymerizing vinylidene fluoride is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more. The monomer copolymerizable with vinylidene fluoride is not particularly limited, and examples thereof include fluorine-containing ethylenically unsaturated compounds such as vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, and fluoroalkyl esters of acrylic acid or methacrylic acid; fluorine-free ethylenically unsaturated compounds such as cyclohexyl vinyl ether and hydroxyethyl vinyl ether; and fluorine-free diene compounds such as butadiene, isoprene, and chloroprene.

[0119] Among fluoropolymers, vinylidene fluoride homopolymers, vinylidene fluoride / tetrafluoroethylene copolymers, vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, etc. are preferred. A particularly preferred fluoropolymer is vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, and its monomer composition is usually 30% by mass to 90% by mass of vinylidene fluoride, 9% by mass to 50% by mass of tetrafluoroethylene, and 1% by mass to 20% by mass of hexafluoropropylene. These fluororesin particles may be used alone or in combination of two or more.

[0120] Furthermore, as the monomer used in synthesizing the thermoplastic polymer, a monomer having a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, an amide group, or a cyano group can also be used.

[0121] The monomer having a hydroxy group is not particularly limited, but examples thereof include vinyl monomers such as penteneol.

[0122] The monomer having a carboxyl group is not particularly limited, but examples thereof include unsaturated carboxylic acids having an ethylenic double bond such as (meth)acrylic acid and itaconic acid, and vinyl monomers such as pentenoic acid.

[0123] The monomer having an amino group is not particularly limited, but examples thereof include 2-aminoethyl methacrylate.

[0124] The monomer having a sulfonic acid group is not particularly limited, but examples thereof include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, (meth)acrylic acid-2-ethylsulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0125] The monomer having an amide group is not particularly limited, but examples thereof include acrylamide (AM), methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide.

[0126] The monomer having a cyano group is not particularly limited, but examples thereof include acrylonitrile (AN), methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate.

[0127] The thermoplastic polymer may be used alone or in a mixture of two or more types, but preferably contains two or more types of polymers. The thermoplastic polymer may be used together with a solvent, and the solvent may be one that can uniformly and stably disperse the thermoplastic polymer, such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, hexane, etc., with aqueous solvents being preferred. The thermoplastic polymer may also be used in the form of a latex.

[0128] (glass transition temperature of thermoplastic polymer) From the viewpoints of ensuring a sufficient distance between the electrode and the separator in a non-aqueous electrolyte battery while exhibiting adhesion to the substrate, suppressing blocking, and adhesive strength between the separator and the electrode, and shortening the injection time of the electrolyte, the thermoplastic polymer constituting the thermoplastic polymer-containing layer preferably has thermal properties of having at least two glass transition temperatures, at least one of which is in a range of 20°C or less, and at least one of which is in a range of 30°C or higher and 120°C or lower.

[0129] The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). In this specification, the glass transition temperature may also be expressed as Tg.

[0130] Specifically, it is determined by the intersection of a line drawn by extending the low-temperature baseline of the DSC curve toward the high-temperature side and a tangent to the inflection point of the step-like change in the glass transition. For more details, see the methods described in the Examples.

[0131] Here, "glass transition" refers to the heat change that occurs on the endothermic side in DSC due to a change in the state of the polymer specimen. This heat change is observed as a step change or a combination of a step change and a peak in the DSC curve.

[0132] The term "step change" refers to the portion of a DSC curve where the curve leaves the previous baseline and transitions to a new baseline. This term also includes a combination of a peak and a step change.

[0133] The "inflection point" refers to the point at which the gradient of the step-like change in the DSC curve is maximum. It can also be expressed as the point at which the step-like change changes from an upwardly convex curve to a downwardly convex curve.

[0134] The "peak" refers to the portion of a DSC curve from when the curve leaves the baseline until when it returns to the baseline.

[0135] "Baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs in the test specimen.

[0136] In one embodiment, at least one of the glass transition temperatures of the thermoplastic polymers used is in the range of 20°C or lower, thereby providing excellent adhesion to the microporous membrane and suppressing blocking, thereby achieving the effect of excellent adhesion between the separator and the electrode. From the viewpoints of handleability and blocking resistance, the glass transition temperature is preferably -100°C or higher, more preferably -50°C or higher, even more preferably -40°C or higher, or particularly preferably -6°C or higher, and from the viewpoint of adhesion to the microporous membrane, it is preferably 20°C or lower, more preferably 10°C or lower, or particularly preferably 0°C or lower.

[0137] In one embodiment, at least one of the glass transition temperatures of the thermoplastic polymers used is in the range of 30°C to 120°C, thereby providing excellent adhesiveness and handling between the separator and electrode, and further enabling the distance between the electrode surface and the separator substrate surface to be maintained in a nonaqueous electrolyte battery, and shortening the injection time of the electrolyte. From the viewpoints of handleability and blocking resistance, the glass transition temperature is preferably 30°C or higher, more preferably 40°C or higher, even more preferably 70°C or higher, or particularly preferably 95°C or higher, and from the viewpoint of adhesive strength, it is preferably 150°C or lower, more preferably 130°C or lower, or particularly preferably 120°C or lower.

[0138] The thermoplastic polymer having two glass transition temperatures can be achieved, for example, by blending two or more types of thermoplastic polymers, but is not limited to this method.

[0139] In particular, polymer blends can control the glass transition temperature of the entire thermoplastic polymer by combining polymers with high and low glass transition temperatures. Furthermore, multiple functions can be imparted to the entire thermoplastic polymer. For example, blending two or more polymers, particularly those with a glass transition temperature in the range of 30°C or higher and those with a glass transition temperature in the range of 20°C or lower, can achieve both stickiness resistance and wettability to a polyolefin microporous membrane. The blending ratio of the polymer with a glass transition temperature in the range of 30°C or higher to the polymer with a glass transition temperature in the range of 0.1:99.9 to 99.9:0.1, preferably 5:95 to 95:5, even more preferably 50:50 to 95:5, and even more preferably 60:40 to 90:10. Furthermore, viscoelasticity can be controlled by combining a highly viscous polymer with a highly elastic polymer.

[0140] In one embodiment, the glass transition temperature (Tg) of a thermoplastic polymer can be adjusted by, for example, changing the monomer components and the ratio of each monomer used to produce the thermoplastic polymer. That is, the Tg can be roughly estimated from the Tg of the homopolymer generally listed for each monomer used to produce the thermoplastic polymer (for example, as described in "Polymer Handbook" (A Wiley-Interscience Publication)) and the blending ratio of the monomers. For example, a copolymer containing a high proportion of monomers such as styrene, methyl methacrylate, and acrylonitrile, which gives a polymer with a Tg of about 100°C, will have a high Tg. For example, a copolymer containing a high proportion of monomers such as butadiene, which gives a polymer with a Tg of about -80°C, or n-butyl acrylate and 2-ethylhexyl acrylate, which gives a polymer with a Tg of about -50°C, will have a low Tg.

[0141] The Tg of a polymer can be roughly calculated using the FOX formula (the following formula (1)). The glass transition point of the thermoplastic polymer of the present invention is measured by the above-mentioned method using DSC. 1 / Tg=W1 / Tg1+W2 / Tg2++W i / Tg i +···W n / Tg n (1) In formula (1), Tg(K) is the Tg of the copolymer, Tg i (K) is the Tg of the homopolymer of each monomer i, W i indicates the mass fraction of each monomer.}

[0142] (Structure of Thermoplastic Polymer-Containing Layer) In the thermoplastic polymer-containing layer, it is preferred that a thermoplastic resin having a glass transition temperature of 30°C or higher and 120°C or lower is present on the outermost surface side of the multilayer porous membrane, and a thermoplastic resin having a glass transition temperature of 20°C or lower is present on the interface side between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. The term "outermost surface" refers to the surface of the thermoplastic polymer-containing layer that contacts the electrode when the multilayer porous membrane or separator is laminated with an electrode. The term "interface" refers to the surface of the thermoplastic polymer-containing layer that contacts the polyolefin microporous membrane or porous layer.

[0143] In the thermoplastic polymer-containing layer, the presence of a thermoplastic polymer having a glass transition temperature of 30°C or higher and 120°C or lower on the outermost surface side of the multilayer porous membrane tends to provide better adhesion to the microporous membrane, and as a result, better adhesion between the separator and the electrode. Furthermore, the presence of a thermoplastic polymer having a glass transition temperature of 20°C or lower on the interface side between the polyolefin microporous membrane and the thermoplastic polymer-containing layer tends to provide better adhesion and handleability between the separator and the electrode. By having such a thermoplastic polymer-containing layer, the separator tends to have better adhesion and handleability between the separator and the electrode.

[0144] The above-mentioned structure can be achieved by, for example, (a) the thermoplastic polymer comprises a particulate thermoplastic polymer and a binder resin that adheres the particulate thermoplastic polymer to the polyolefin microporous membrane with the particulate thermoplastic polymer exposed on the surface, the particulate thermoplastic polymer having a glass transition temperature in the range of 30°C to 120°C, and a thermoplastic polymer having a glass transition temperature of 20°C or lower present at the interface between the polyolefin microporous membrane and the thermoplastic polymer-containing layer, or (b) the thermoplastic polymer has a laminated structure, the thermoplastic polymer in the part that will become the outermost layer in the separator has a glass transition temperature in the range of 30°C to 120°C, and a thermoplastic polymer having a glass transition temperature of 20°C or lower present at the interface between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. Note that (b) the thermoplastic polymer may have a laminated structure consisting of polymers with different Tg.

[0145] (average particle size of thermoplastic polymer) The structure of the thermoplastic polymer is not particularly limited, but may be, for example, granular. Such a structure tends to improve the adhesiveness between the separator and the electrode and the handleability of the separator. Here, granular refers to a state in which individual thermoplastic polymer particles have contours as measured with a scanning electron microscope (SEM), and may be elongated, spherical, polygonal, or the like.

[0146] The particle size distribution and median diameter of the granular thermoplastic polymer can be measured using a laser particle size distribution analyzer (Microtrac MT3300EX manufactured by Nikkiso Co., Ltd.). If necessary, the particle size distribution of the granular thermoplastic polymer can be adjusted using the particle size distribution of water or the binder polymer as a baseline. The particle size at which the cumulative frequency is 50% is defined as D. 50 and D of the granular thermoplastic polymer 50 D P Let's say.

[0147] Average particle size D of granular thermoplastic polymer PFrom the viewpoints of being able to maintain the distance between the plurality of electrodes via the separator while exhibiting adhesive strength between the separator and the electrodes, and of shortening the time required for injecting an electrolyte into a nonaqueous electrolyte battery including the separator, the thickness is preferably 100 nm or more, more preferably 130 nm or more, even more preferably 320 nm or more, and most preferably 400 nm or more, and / or is preferably 1000 nm or less, more preferably 700 nm or less, even more preferably 590 nm or less, and most preferably 550 nm or less.

[0148] (Basis weight per side of thermoplastic polymer-containing layer) In the separator according to one embodiment, the basis weight per side of the thermoplastic polymer-containing layer is preferably 0.03 g / m from the viewpoint of adhesive strength. 2 More preferably, 0.04 g / m 2 More preferably, 0.06 g / m 2 On the other hand, 0.3 g / m 2 Preferably, it is 0.15 g / m or less. 2 It is more preferable that the content is 0.10 g / m or less, and particularly preferable that the content is 0.10 g / m or less. 2 The basis weight of the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration of the coating liquid or the amount of the polymer solution applied. From the viewpoint of improving the cycle characteristics of the battery by suppressing deformation of the cell shape due to expansion and contraction of the electrodes within a range that does not impair the effects of this embodiment, the basis weight per side of the thermoplastic polymer-containing layer is set to 0.08 g / m 2 A range exceeding this is preferred.

[0149] (Shape of thermoplastic polymer-containing layer, coverage ratio of substrate surface by thermoplastic polymer-containing layer) The thermoplastic polymer-containing layer may have a pattern in which the thermoplastic polymer is dispersed over the entire surface of the multilayer porous membrane, or may have an island-like configuration. When the thermoplastic polymer is present in a sea-stripe pattern, its arrangement pattern may be, for example, a dotted pattern, a striped pattern, a lattice pattern, a striped pattern, a tortoiseshell pattern, a random pattern, or a combination thereof. Among these, the thermoplastic polymer-containing layer preferably has a dotted pattern.

[0150] The dot-like structure indicates that the polyolefin microporous membrane has portions containing a thermoplastic polymer and portions not containing a thermoplastic polymer, and the portions containing the thermoplastic polymer are present in the form of islands. Note that in the thermoplastic polymer-containing layer, the portions containing the thermoplastic polymer may be independent.

[0151] The diameter of the dots in the thermoplastic polymer-containing layer is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more, from the viewpoints of improving adhesion to the PO microporous membrane or electrode, improving the strength of the multilayer porous membrane, and suppressing an increase in the air permeability of the PO microporous membrane, and on the other hand, is preferably 1,200 μm or less, more preferably 1,100 μm or less, even more preferably 1,000 μm or less, still more preferably 500 μm or less, and even more preferably 300 μm.

[0152] The dot-to-dot distance in the thermoplastic polymer-containing layer is preferably 100 μm or more, more preferably 120 μm or more, and even more preferably 140 μm or more, from the viewpoints of improving adhesion to the PO microporous membrane or electrode, improving the strength of the multilayer porous membrane, and suppressing an increase in the air permeability of the PO microporous membrane, and on the other hand, is preferably 3,500 μm or less, more preferably 3,300 μm or less, and even more preferably 3,000 μm or less.

[0153] The adhesive strength of the thermoplastic polymer-containing layer to the electrode is preferably 0.5 N / m or more and 50 N / m or less as a dry adhesive strength, and 0.5 N / m or more and 50 N / m or less as a wet adhesive strength. It is more preferable that the thermoplastic polymer-containing layer has an adhesive strength within the above numerical range when facing the surface of an electrode material that can generally be used as a negative electrode.

[0154] In one embodiment, the total coverage area ratio of the thermoplastic polymer-containing layer to the substrate surface is preferably 3% or more, or 4% or more, or 5% or more, or 10% or more, or 20% or more, or 30% or more, or 40% or more, and preferably 90% or less, or 80% or less, or 75% or less, or 70% or less, from the viewpoint of maintaining the adhesive strength of the multilayer porous membrane or separator with the electrode while reducing the resistance of the battery. If the coverage area of ​​the thermoplastic polymer-containing layer is small, the distance between the separator and the electrode interface becomes uneven, resulting in uneven current distribution, which makes it easier for the temperature to rise in (heating) safety tests. Furthermore, if the coverage area of ​​the thermoplastic polymer-containing layer is large, the resistance of the battery increases, leading to poor results in rate tests. The total coverage area ratio S of the thermoplastic polymer-containing layer present on the substrate surface is calculated using the following formula: S (%) = total coverage area of ​​thermoplastic polymer-containing layer ÷ surface area of ​​substrate × 100

[0155] The total coverage area ratio (%) of the coating pattern of the thermoplastic polymer-containing layer relative to the substrate surface is measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). After photographing the separator sample at 30x magnification (coaxial epi-illumination), the automatic area measurement mode is selected and the total coverage area ratio of the thermoplastic polymer is measured. The coverage area ratio for each sample is calculated as the arithmetic mean of three measurements.

[0156] The shape or total coverage area of ​​the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration of the coating solution, the coating amount of the polymer solution, the coating method, and the coating conditions.

[0157] <Characteristics of multilayer porous membrane> The air permeability of the multilayer porous membrane was set to 300 sec / 100 cm in consideration of the optimization of the thin, highly heat-resistant, and low-resistance porous layer, as well as the energy density, capacity, output, and cycle characteristics of a non-aqueous electrolyte battery equipped with the multilayer porous membrane as a separator. 3 From the viewpoint of ion permeability and further reducing the resistance to further improve the capacity and cycle characteristics of the battery, it is preferably 200 sec / 100 cm 3 Less than 200sec / 100cm, preferably 3 Less than 150 sec / 100 cm, more preferably 3 Below 100 sec / 100 cm, particularly preferably 3 The air permeability of the multilayer porous membrane is preferably 10 sec / 100 cm or less from the viewpoint of ensuring the safety of the non-aqueous electrolyte battery by preventing excessive current from flowing between the electrodes through the multilayer porous membrane. 3 That's all.

[0158] The heat shrinkage rate of the multilayer porous membrane when left in an atmosphere at 150°C for 1 hour (150°C heat shrinkage rate) is preferably 10% or less, more preferably 5% or less, even more preferably 2% or less, and particularly preferably 1% or less, in both MD and TD. The lower limit is preferably 0% or more. A multilayer porous membrane with a 150°C heat shrinkage rate of 10% or less not only enables the separator to be made thinner and have high heat resistance, thereby contributing to improved productivity, but also contributes to improved energy density and safety when incorporated into a non-aqueous electrolyte battery as a thin-film separator. The 150°C heat shrinkage rate can be measured and calculated in both MD and TD under dry conditions after the multilayer porous membrane is left standing in an oven for 1 hour, or under wet conditions after the multilayer porous membrane is immersed in a non-aqueous solvent such as propylene carbonate or a non-aqueous electrolyte containing it and then left standing in an oven for 1 hour.

[0159] The upper limit of the heat shrinkage rate of the multilayer porous membrane at 130°C (130°C heat shrinkage rate) in both MD and TD is preferably 10% or less, more preferably 5% or less, and the lower limit is preferably 0% or more. When the 130°C heat shrinkage rate is 10% or less in both MD and TD, rupture of the multilayer porous membrane is suppressed when an abnormality occurs in the battery, which is preferable from the viewpoint of suppressing short circuits. The measurement and calculation of the 130°C heat shrinkage rate in both MD and TD can be performed under dry conditions after leaving the multilayer porous membrane in an oven for 1 hour.

[0160] The multilayer porous membrane preferably contains the water-insoluble polymer binder described above from the viewpoint of achieving both high peel strength and low moisture content, and from the viewpoint of heat resistance. The location of the water-insoluble polymer binder in the multilayer porous membrane is not particularly limited, and for example, the water-insoluble polymer binder may be located inside or outside the porous layer.

[0161] The total thickness of the multilayer porous membrane is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more in order to ensure voltage resistance. The total thickness of the multilayer porous membrane is preferably 30.0 μm or less because this makes it difficult for the capacity of a nonaqueous electrolyte battery in which the multilayer porous membrane is mounted to deteriorate, more preferably 25 μm or less, even more preferably 20 μm or less, and particularly preferably 15 μm or less.

[0162] In the multilayer porous membrane of this embodiment, the ratio (T / TB) of the thickness (TB) of the PO microporous membrane to the thickness (T) of the porous layer is preferably 0.05 or more and / or 0.35 or less. A multilayer porous membrane having a thickness ratio (T / TB) within the above range not only enables the use of thinner separators, thereby contributing to improved productivity, but also contributes to improved energy density and safety when incorporated into a nonaqueous electrolyte battery as a thin-film separator. The thickness ratio (T / TB) may be measured and calculated for either one or both sides of the PO microporous membrane. From the viewpoint of the mechanism of action and thickness measurement principle of the present invention, measurement and calculation for both sides of the PO microporous membrane are preferred. Specifically, the total thickness of the porous layers disposed in the multilayer porous membrane is measured and calculated as T.

[0163] In the multilayer porous membrane, the ratio of the air permeability of the porous layer to the air permeability of the polyolefin microporous membrane (air permeability increase rate of the multilayer porous membrane) is preferably 0.01 or more so as not to deteriorate the air permeability of the polyolefin microporous membrane, from the viewpoint of ion permeability and reducing resistance to improve the capacity and cycle characteristics of the nonaqueous electrolyte battery, and is preferably 0.40 or less, more preferably 0.30 or less, and even more preferably 0.20 or less, from the viewpoint of preventing excessive current from flowing between multiple electrodes through the multilayer porous membrane to ensure the safety of the nonaqueous electrolyte battery.

[0164] From the viewpoint of preventing breakage and improving the safety of the non-aqueous electrolyte battery while maintaining the membrane strength, the lower limit of the puncture strength of the multilayer porous membrane is preferably 0.98 N or more, more preferably 1.47 N or more, and even more preferably 1.96 N or more, and the upper limit is preferably 9.81 N or less, more preferably 5.88 N or less, and even more preferably 4.90 N or less.

[0165] The multilayer porous membrane of this embodiment preferably has a ratio of the light transmittance at a wavelength of 550 nm of the multilayer porous membrane to the light transmittance at a wavelength of 550 nm of the PO microporous membrane of 0.4 or more and less than 1.0. Because the multilayer porous membrane of this embodiment has such light transmittance, foreign matter or unmelted material inside or on the surface of the substrate tends to be easily detected after the porous layer is disposed on the PO microporous membrane.

[0166] The light transmittance of the multilayer porous membrane at a wavelength of 550 nm is preferably 4.0% or more from the viewpoint of maintaining light transmittance, and is preferably less than 10.0% from the viewpoint of maintaining the accuracy of detecting coating voids in the PO microporous membrane. Generally, a white LED is used as a light source in the inspection of separators for nonaqueous electrolyte batteries, and the wavelength of 550 nm is near the central wavelength of the wavelength range of the white LED.

[0167] <Method for manufacturing multilayer porous membrane> The multilayer porous membrane according to this embodiment can be produced by a known method, for example, by forming a microporous PO membrane and then arranging a porous layer on at least one surface of the microporous PO membrane.

[0168] If desired, the multilayer porous membrane can be produced by, for example, forming a PO microporous membrane and then disposing a first porous layer on one side of the PO microporous membrane and a second porous layer on the other side of the PO microporous membrane. Alternatively, the PO microporous membrane and the porous layer can be produced by coextrusion, or the first and second porous layers can be extruded onto both sides of the PO microporous membrane, respectively, or the PO microporous membrane and the porous layer can be bonded together after being separately produced.

[0169] Furthermore, the method for producing a multilayer porous membrane may optionally include a step of obtaining a multilayer porous membrane by arranging a porous layer on at least one surface of a microporous PO membrane, and forming a thermoplastic polymer-containing layer on at least one surface of the obtained multilayer porous membrane.

[0170] (Method for producing a polyolefin microporous membrane) The method for producing the polyolefin microporous membrane (PO microporous membrane) is not particularly limited, and any known production method can be used.

[0171] In general, methods for producing microporous polyolefin membranes are broadly divided into wet and dry processes. In the wet process, an extractable material is added to and dispersed in polyolefin, and the resulting mixture is molded and then extracted with a liquid such as a solvent to create pores. Examples of dry processes include (a) a method in which an unstretched product having a crystalline lamellar structure is formed during melt extrusion molding, and the product is then stretched primarily uniaxially to cause lamella cleavage and create pores; and (b) a method in which incompatible particles such as inorganic particles are added to polyolefin and then stretched to peel the interface between the different materials and create pores.

[0172] The microporous PO membrane according to this embodiment can be produced, for example, by the following method: (1) A method in which a polyolefin resin composition and a pore-forming material are melt-kneaded to form a sheet, which is then stretched as necessary, and the pore-forming material is extracted to make the sheet porous; (2) A method in which a polyolefin resin composition is melt-kneaded and extruded at a high draw ratio, and then heat-treated and stretched to separate the polyolefin crystal interface, thereby making the resin porous; (3) A method in which a polyolefin resin composition and an inorganic filler are melt-kneaded and formed into a sheet, and then the interface between the polyolefin and the inorganic filler is peeled off by stretching to make the sheet porous; (4) A method in which a polyolefin resin composition is dissolved and then immersed in a poor solvent for the polyolefin to solidify the polyolefin and simultaneously remove the solvent, thereby making the composition porous; etc.

[0173] As an example of a method for producing a microporous PO membrane, a method in which a polyolefin resin composition and a pore-forming material are melt-kneaded and formed into a sheet, and then the pore-forming material is extracted will be described below.

[0174] First, the polyolefin resin composition and the pore-forming material are melt-kneaded. Examples of the melt-kneading method include a method in which the polyolefin resin and, if necessary, other additives are fed into a resin kneading device such as an extruder, a feeder, a lab plasto mill, a kneading roll, or a Banbury mixer, and the pore-forming material is introduced at an arbitrary ratio while the resin components are heated and melted, and then kneaded.

[0175] Examples of the pore-forming material include plasticizers, inorganic materials, and combinations thereof. The plasticizer is not particularly limited, but examples include non-volatile solvents capable of forming a homogeneous solution at or above the melting point of the polyolefin, such as hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among plasticizers, liquid paraffin is preferred because, when the polyolefin resin is polyethylene and / or polypropylene, it is highly compatible with these resins, and even when the molten mixture is stretched, interfacial peeling between the resin and the plasticizer is unlikely to occur, making it easier to perform uniform stretching. The inorganic material is not particularly limited and includes, for example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These may be used alone or in combination of two or more. Among these inorganic materials, silica, alumina, and titania are preferred from the viewpoint of electrochemical stability, and silica is particularly preferred from the viewpoint of ease of extraction.

[0176] Next, the melt-kneaded material is molded into a sheet. Examples of methods for producing a sheet-shaped molded product include extruding the melt-kneaded material into a sheet through a T-die or the like, contacting it with a thermal conductor, and solidifying it by cooling it to a temperature sufficiently lower than the crystallization temperature of the resin component. Examples of thermal conductors used for cooling and solidifying include metal, water, air, and plasticizers. Among these, metal rolls are preferred because of their high thermal conductivity. Furthermore, sandwiching the extruded material between metal rolls when contacting them is more preferred because it further increases the thermal conductivity efficiency, orients the sheet, increasing film strength, and tends to improve the surface smoothness of the sheet. When extruding the melt-kneaded material from a T-die into a sheet, the die lip spacing is preferably 200 μm or more, more preferably 500 μm or more, and preferably 3,000 μm or less, and more preferably 2,500 μm or less. When the die lip gap is 200 μm or more, the occurrence of scum and other deposits is reduced, and the impact on film quality such as streaks and defects is minimal, reducing the risk of film rupture in the subsequent stretching process.On the other hand, when the die lip gap is 3,000 μm or less, the cooling rate is fast, preventing uneven cooling and maintaining the thickness stability of the sheet.

[0177] The sheet-like molded body may also be rolled. Rolling can be performed, for example, by a pressing method using a double belt press or the like. Rolling can increase the orientation, particularly in the surface layer portion. The rolling area ratio is preferably more than 1 and not more than 3, and more preferably more than 1 and not more than 2. When the rolling ratio exceeds 1, the surface orientation increases, and the membrane strength of the finally obtained porous membrane tends to increase. On the other hand, when the rolling ratio is 3 or less, the difference in orientation between the surface layer portion and the central interior is small, and a porous structure that is uniform in the membrane thickness direction tends to be formed.

[0178] Next, the pore-forming material is removed from the sheet-like formed body to form a porous membrane. For example, a method for removing the pore-forming material includes immersing the sheet-like formed body in an extraction solvent to extract the pore-forming material, followed by thorough drying. The pore-forming material may be extracted by either a batch method or a continuous method. To prevent the porous membrane from shrinking, it is preferable to restrain the edges of the sheet-like formed body during the immersion and drying process. Furthermore, it is preferable that the amount of pore-forming material remaining in the porous membrane is less than 1% by mass relative to the total mass of the porous membrane.

[0179] The extraction solvent used to extract the pore-forming material is preferably a poor solvent for the polyolefin resin and a good solvent for the pore-forming material, with a boiling point lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine-based halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by operations such as distillation. In addition, when an inorganic material is used as the pore-forming material, an aqueous solution of sodium hydroxide, potassium hydroxide, or the like can be used as the extraction solvent.

[0180] It is also preferable to stretch the sheet-like formed body or porous membrane. Stretching may be performed before extracting the pore-forming material from the sheet-like formed body. Stretching may also be performed on the porous membrane from which the pore-forming material has been extracted from the sheet-like formed body. Furthermore, stretching may be performed both before and after extracting the pore-forming material from the sheet-like formed body.

[0181] As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used, but biaxial stretching is preferred from the viewpoint of improving the strength, etc., of the resulting microporous PO membrane. When the sheet-like molded article is stretched biaxially at a high ratio, the molecules are oriented in the planar direction, and the final microporous membrane becomes tear-resistant and has high pin puncture strength.

[0182] Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple stretching. From the viewpoints of improving puncture strength, uniformity of stretching, and shut-down property, simultaneous biaxial stretching is preferred. Furthermore, from the viewpoint of ease of control of plane orientation, sequential biaxial stretching is preferred.

[0183] Here, simultaneous biaxial stretching refers to a stretching method in which MD stretching and TD stretching are carried out simultaneously, and the stretching ratios in each direction may be different. Sequential biaxial stretching refers to a stretching method in which MD and TD stretching are carried out independently, and while stretching is carried out in MD or TD, the other direction is in an unconstrained state or fixed at a fixed length.

[0184] The areal stretching ratio is preferably 20 times or more, more preferably 25 times or more, and preferably 100 times or less, more preferably 70 times or less. The areal stretching ratios in each axial direction are preferably 4 times or more in MD and 4 times or more in TD, more preferably 5 times or more in MD and 5 times or more in TD, and preferably 10 times or less in MD and 10 times or less in TD, and more preferably 8 times or less in MD and 8 times or less in TD. A total areal stretching ratio of 20 times or more tends to impart sufficient strength to the resulting microporous PO membrane, while a total areal stretching ratio of 100 times or less tends to prevent membrane rupture during the stretching step and achieve high productivity.

[0185] To suppress shrinkage of the PO microporous membrane, a heat treatment for heat setting can be performed after the stretching step or after the formation of the PO microporous membrane. The PO microporous membrane may also be subjected to post-treatments such as hydrophilization treatment with a surfactant or crosslinking treatment with ionizing radiation.

[0186] The microporous polypropylene membrane is preferably heat-treated for heat setting to suppress shrinkage. Heat treatment methods include stretching at a predetermined temperature and at a predetermined stretch ratio to adjust physical properties, and / or relaxation at a predetermined temperature and at a predetermined relaxation ratio to reduce stretching stress. The relaxation may be performed after the stretching. These heat treatments can be performed using a tenter or roll stretching machine.

[0187] The stretching operation is preferably performed by stretching the membrane in MD and / or TD by 1.1 times or more, more preferably 1.2 times or more, from the viewpoint of obtaining a microporous PO membrane with even higher strength and higher porosity.

[0188] The relaxation operation is a shrinking operation of the membrane in MD and / or TD. The relaxation rate is the value obtained by dividing the membrane dimension after the relaxation operation by the membrane dimension before the relaxation operation. When both MD and TD are relaxed, the relaxation rate is the value obtained by multiplying the relaxation rate in MD by the relaxation rate in TD. The relaxation rate is preferably 1.0 or less, more preferably 0.97 or less, and even more preferably 0.95 or less. From the viewpoint of membrane quality, the relaxation rate is preferably 0.5 or more. The relaxation operation may be performed in both MD and TD, or may be performed in only one of MD and TD.

[0189] The stretching and relaxation operations after the plasticizer extraction are preferably performed in TD from the viewpoints of process control and hole area control in a 400°C soldering test. The temperature in the stretching and relaxation operations is preferably lower than the melting point (hereinafter also referred to as "Tm") of the polyolefin resin, more preferably in the range of 1°C to 25°C lower than Tm. A temperature in the above range in the stretching and relaxation operations is preferred from the viewpoint of a balance between reduced thermal shrinkage and porosity.

[0190] (Porous layer arrangement method) The porous layer can be disposed on at least one surface of the microporous polypropylene membrane by known methods such as disposing, coating, laminating, extrusion, etc. For example, a porous layer can be formed by applying a coating liquid or slurry containing the inorganic particles described above and, optionally, a resin binder and / or a dispersant to the microporous polypropylene membrane.

[0191] The method for disposing the first porous layer on one side of the PO microporous membrane and the second porous layer on the other side of the PO microporous membrane can be a known disposing method, coating method, laminating method, extrusion method, etc. For example, a method can be used in which a coating liquid or slurry containing the inorganic particles described above and, if desired, the resin binder and / or dispersant described above is applied to both sides of the PO microporous membrane to form porous layers.

[0192] In the process of disposing the porous layer, the average particle size D of the inorganic particles contained in the porous layer described above 50 From the viewpoint of compatibility with the selected inorganic particles and control of binding points, it is preferable to select a water-soluble polymer binder and / or a water-insoluble polymer binder to be used as a resin binder, and if desired, to add a dispersant to provide a coating liquid or slurry. The water-insoluble polymer binder to be selected is preferably in the form of a latex, more preferably in the form of an aqueous latex.

[0193] Average particle size of the water-insoluble polymer in the latex (D 50 ) is preferably adjusted in accordance with the size reduction of the inorganic particles, but from the viewpoint of efficiently achieving binding at the interface between the inorganic particles or between the inorganic particles and the microporous PO membrane, the upper limit is preferably 0.20 μm or less, more preferably 0.15 μm or less, even more preferably 0.10 μm or less, and particularly preferably 0.05 μm or less, and the lower limit is not particularly limited and may be, for example, 0.01 μm or more.

[0194] When the total of the inorganic particles, resin binder, and dispersant contained in the coating liquid or slurry is taken as 100% by volume, the lower limit of the inorganic particle ratio is preferably 65% ​​or more, more preferably 70% or more, even more preferably 75% or more, particularly preferably 80% or more, and most preferably 85% or more, and the upper limit is preferably 95% or less, more preferably 93% or less, even more preferably 92% or less, and particularly preferably 91% or less. When the volume fraction of inorganic particles in the coating liquid or slurry is within the above range, the ratio of inorganic particles to other components contained, such as resin binder, increases, thereby suppressing an increase in the air permeability of the PO microporous membrane due to the porous layer and reducing the electrical resistance of the multilayer porous membrane. The increase in the air permeability of the PO microporous membrane due to the porous layer is suppressed, reducing the electrical resistance of the multilayer porous membrane.

[0195] Furthermore, from the same viewpoint as the volume ratio described above, the mass ratio of the inorganic particles in the coating liquid or slurry, where the total of the inorganic particles, the resin binder, and the dispersant is 100 mass%, the lower limit is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more, and the upper limit is preferably less than 100%, more preferably 99% or less.

[0196] In forming an inorganic particle-containing slurry or coating liquid, from the viewpoints of the interaction between the inorganic particles and the resin binder, increasing the number of contact points between them, and the heat resistance of the multilayer porous membrane or separator, it is preferable that the ratio (Wb' / Wa') of the mass fraction Wb' of the water-insoluble polymer binder to the mass fraction Wa' of the water-soluble polymer binder contained in the slurry or coating liquid exceeds 1.0, more preferably 4.0 or more, and even more preferably 4.5 or more, and the upper limit of the ratio (Wb' / Wa') is more preferably 8.0 or less, and even more preferably 7.0 or less.

[0197] From the viewpoint of improving dispersion stabilization or coatability, various additives such as thickeners, wetting agents, antifoaming agents, and pH adjusters containing acids and alkalis may be added to the coating liquid or slurry. The total amount of these additives added is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, of the active ingredients (the mass of the dissolved additive components when the additives are dissolved in a solvent) per 100 parts by mass of inorganic particles.

[0198] Regarding additives, anionic surfactants include, for example, higher fatty acid salts, alkyl sulfonates, alpha olefin sulfonates, alkanesulfonates, alkyl benzene sulfonates, sulfosuccinate salts, alkyl sulfate salts, alkyl ether sulfate salts, alkyl phosphate salts, alkyl ether phosphate salts, alkyl ether carboxylate salts, alpha sulfo fatty acid methyl ester salts, and methyl taurate salts. Nonionic surfactants include, for example, glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, fatty acid alkanolamides, and alkyl glucosides. Amphoteric surfactants include, for example, alkyl betaines, fatty acid amidopropyl betaines, and alkyl amine oxides. Cationic surfactants include, for example, alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium salts, alkyl dimethyl benzyl ammonium salts, and alkyl pyridinium salts. Other examples include fluorosurfactants and polymer surfactants such as cellulose derivatives, polycarboxylates, and polystyrene sulfonates.

[0199] The medium for the coating liquid or slurry is preferably one that can uniformly and stably disperse or dissolve the inorganic particles or resin binder, and examples thereof include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0200] The method for dispersing or dissolving the inorganic particles and the resin binder in the medium of the coating liquid is not particularly limited as long as it can achieve the dispersion characteristics of the coating liquid or slurry required for the coating step, and examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade or the like.

[0201] Forming a porous layer by applying an inorganic particle-containing coating liquid or slurry to the surface of a polyolefin substrate layer is preferred from the viewpoint of efficiently preventing relaxation of residual stress caused by the stretching step in the separator molding process. The method for applying the coating liquid or slurry to the PO microporous membrane is not particularly limited as long as it is a method that can achieve the required layer thickness or coating area, and examples include gravure coating, small-diameter gravure coating, reverse roll coating, transfer roll coating, kiss coating, dip coating, knife coating, air doctor coating, blade coating, rod coating, squeeze coating, cast coating, die coating, screen printing, and spray coating.

[0202] In one embodiment, from the viewpoints of suppressing an increase in the air permeability of the PO microporous membrane, forming a strong porous layer, reducing the thickness of the resulting multilayer porous membrane or separator, and heat resistance (i.e., the ability to suppress thermal shrinkage), the inorganic particle-containing slurry is applied to a PO microporous membrane so that the coating thickness of the porous layer on at least one side of the PO microporous membrane is preferably less than 5 μm, more preferably 4 μm or less, even more preferably 3 μm or less, still more preferably 2 μm or less, and particularly preferably 1 μm or less, with the lower limit being preferably 0.1 μm or more, more preferably 0.5 μm or more.

[0203] If desired, the PO microporous membrane may be subjected to a surface treatment prior to application of the coating solution. Surface treatment of the PO microporous membrane facilitates application of the coating solution and may improve adhesion between the porous layer and the PO microporous membrane surface after application. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the PO microporous membrane, and examples include corona discharge treatment, plasma discharge treatment, mechanical graining, solvent treatment, acid treatment, and ultraviolet oxidation.

[0204] The method for removing the medium from the coated film after coating is not particularly limited as long as it does not adversely affect the PO microporous membrane, and examples include a method in which the PO microporous membrane is fixed while being dried at a temperature below its melting point, a method in which the membrane is dried under reduced pressure at a low temperature, and extraction drying. Furthermore, a portion of the solvent may be left behind as long as it does not significantly affect the properties of the nonaqueous electrolyte battery. For a multilayer porous membrane comprising a laminate of a PO microporous membrane and a porous layer, it is preferable to appropriately adjust the drying temperature, winding tension, etc., from the viewpoint of controlling the MD shrinkage stress.

[0205] (Method for forming a thermoplastic polymer-containing layer) The method for forming a thermoplastic polymer-containing layer on a microporous PO membrane or porous layer as a substrate is not particularly limited, and examples thereof include a method in which a coating liquid containing a thermoplastic polymer is applied to the microporous PO membrane or porous layer.

[0206] The method for applying a coating solution containing a thermoplastic polymer to a PO microporous membrane or porous layer is not particularly limited as long as it can achieve the required layer thickness or coating area. Examples include gravure coating, small-diameter gravure coating, reverse roll coating, transfer roll coating, kiss coating, dip coating, knife coating, air doctor coating, blade coating, rod coating, squeeze coating, cast coating, die coating, screen printing, spray coating, spray coating, and inkjet coating. Of these, gravure coating and spray coating are preferred because they offer a high degree of freedom in the coating shape of the thermoplastic polymer and allow for easy achievement of a preferred area ratio. For forming a dot pattern in a thermoplastic polymer-containing layer, gravure coating, inkjet coating, and coating methods that allow for easy adjustment of the printing plate are preferred.

[0207] When a thermoplastic polymer is coated onto a PO microporous membrane, if the coating solution penetrates into the interior of the microporous membrane or porous layer, the adhesive resin will fill the surfaces and interiors of the pores, reducing permeability. Therefore, a poor solvent for the thermoplastic polymer is preferred as the medium for the coating solution.

[0208] When a poor solvent for the thermoplastic polymer is used as the medium for the coating solution, the coating solution does not penetrate into the microporous membrane or porous layer, and the adhesive polymer is mainly present on the surface of the microporous membrane, which is preferable from the viewpoint of suppressing a decrease in permeability. Water is a preferred medium. Furthermore, media that can be used in combination with water are not particularly limited, but examples include ethanol and methanol. If desired, an antifoaming agent may be added to the thermoplastic polymer-containing coating solution.

[0209] The thermoplastic polymer-containing coating solution (hereinafter also referred to simply as paint) preferably has a paint viscosity of 30 cP or more, more preferably 50 cP or more, and preferably 100 cP or less, more preferably 80 cP or less, from the viewpoint of adhesiveness of the separator to the electrodes, and from the viewpoint of compatibility with high-temperature storage tests while simultaneously preventing the separator from increasing in temperature and from undergoing cycle deterioration. From the same viewpoint, the pH of the paint is preferably 5 or more, more preferably 5.5 or more, and preferably 7.9 or less, more preferably 7.7 or less.

[0210] Furthermore, prior to coating, it is preferable to surface-treat the microporous membrane as a separator substrate, as this facilitates application of the coating liquid and improves adhesion between the microporous membrane or porous layer and the adhesive polymer. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the microporous membrane, and examples include corona discharge treatment, plasma treatment, mechanical graining, solvent treatment, acid treatment, and ultraviolet oxidation.

[0211] In the case of corona discharge treatment, the corona treatment intensity on the substrate surface is 1 W / (m 2 / min) or more, and 3W / (m 2 / min) or more is more preferable, and 5W / (m 2 / min) or more, and 40 W / (m 2 / min) or less, and 32W / (m 2 / min) or less is more preferable, and 25W / (m 2 / min) or less is more preferable.

[0212] The method for removing the solvent from the coated film after coating is not particularly limited as long as it does not adversely affect the microporous membrane or porous layer, and examples thereof include a method of drying the microporous membrane and / or porous layer at a temperature below their melting point while fixing them, a method of drying under reduced pressure at a low temperature, and a method of immersing the adhesive polymer in a poor solvent for the adhesive polymer to coagulate the adhesive polymer and simultaneously extract the solvent.

[0213] The drying rate of the coating is 0.03 g / (m 2 ·s) or more, and 0.05g / (m 2 ·s) or more is more preferable, and 0.08g / (m 2 ·s) or more is more preferable, and 4.0 g / (m 2 ·s) or less, and 3.5g / (m 2 ·s) or less, and 3.0g / (m 2 In drying the coating film, it is also preferable to raise the temperature by warming or heating to an extent that does not damage the particle shape of the thermoplastic polymer-containing layer.

[0214] <Separator for non-aqueous electrolyte battery, and non-aqueous electrolyte battery> The multilayer porous membrane according to the present embodiment can be used as a separator for a nonaqueous electrolyte battery, and can improve the energy density, capacity, output, and cycle characteristics of the nonaqueous electrolyte battery while ensuring high-temperature insulation resistance. The nonaqueous electrolyte battery includes a positive electrode, a separator, a negative electrode, and a nonaqueous electrolyte. Specific examples include lithium batteries, lithium secondary batteries, lithium ion secondary batteries, sodium secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, magnesium ion secondary batteries, calcium secondary batteries, calcium ion secondary batteries, aluminum secondary batteries, aluminum ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, electric double layer capacitors, lithium ion capacitors, redox flow batteries, and lithium-sulfur batteries. Among these, from the viewpoint of practicality, lithium batteries, lithium secondary batteries, lithium ion secondary batteries, nickel-metal hydride batteries, and lithium ion capacitors are preferred, and lithium ion secondary batteries are more preferred.

[0215] A nonaqueous electrolyte battery can be produced, for example, by stacking a positive electrode and a negative electrode via a separator made of the multilayer porous membrane described above, and, if necessary, winding or zigzag folding to form a laminated electrode body, a wound electrode body, or a zigzag folded body, which is then loaded into an exterior body, connecting the positive and negative electrodes to the positive and negative electrode terminals of the exterior body via lead bodies or the like, and further injecting a nonaqueous electrolyte solution containing a nonaqueous solvent such as a chain or cyclic carbonate and an electrolyte such as a lithium salt into the exterior body, and then sealing the exterior body.

[0216] The nonaqueous electrolyte battery includes the above-described laminate, a wound laminate, or a zigzag laminate, together with a nonaqueous electrolyte, in an exterior body such as a cylindrical can, a pouch-type case, a laminate case, etc. The nonaqueous electrolyte battery using the multilayer porous membrane according to this embodiment as a separator may not only be excellent in safety, but also in energy density and cycle characteristics.

[0217] When the nonaqueous electrolyte battery is a secondary battery, a positive electrode terminal is welded to an end of a positive electrode laminate consisting of a positive electrode current collector and a positive electrode active material layer, and a negative electrode terminal is welded to an end of a negative electrode laminate consisting of a negative electrode current collector and a negative electrode active material layer, thereby enabling charging and discharging of the secondary battery including the positive electrode laminate with terminals and the negative electrode laminate with terminals.

[0218] Furthermore, the positive electrode laminate with terminals and the negative electrode laminate with terminals are laminated via a separator, and wound or zigzag folded as desired. The resulting laminate, wound body, or zigzag folded body is housed in an outer casing, a nonaqueous electrolyte solution is injected into the outer casing, and the outer casing is sealed, thereby obtaining a secondary battery.

[0219] When a non-aqueous electrolyte secondary battery is produced using the multilayer porous membrane according to this embodiment as a separator, a known positive electrode, negative electrode, and non-aqueous electrolyte may be used.

[0220] The positive electrode material is not particularly limited, but examples thereof include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4.

[0221] The negative electrode material is not particularly limited, but examples thereof include carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and composite carbon; silicon, tin, metallic lithium, and various alloy materials.

[0222] The non-aqueous electrolyte is not particularly limited, but may be an electrolyte solution prepared by dissolving an electrolyte in an organic solvent. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO4, LiBF4, and LiPF6. [Example]

[0223] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples and comparative examples.

[0224] Testing and Evaluation Methods

[0225] <Viscosity average molecular weight (Mv)> The intrinsic viscosity [η] (dl / g) at 135°C in decalin solvent was determined based on ASTM-D4020. The Mv of the polyethylene and polyolefin microporous membranes was calculated by the following formula. [η]=6.77×10 -4 Mv 0.67 The Mv of polypropylene was calculated using the following formula. [η]=1.10×10 -4 Mv 0.80

[0226] <Thickness of polyolefin microporous membrane, multilayer porous membrane, and porous layer (μm)> The thicknesses of the polyolefin microporous membrane and the multilayer porous membrane were measured at room temperature (23±2°C) using a micro thickness gauge "KBM (trademark)" manufactured by Toyo Seiki Co., Ltd., and the coating thickness of the porous layer was calculated from each thickness. From the viewpoint of detection from the multilayer porous membrane, it is also possible to measure the thickness of each layer using a cross-sectional SEM image.

[0227] <Melt index (MI) (g / 10 min) of microporous polyolefin membrane> The melt index (MI) of a polyolefin microporous membrane (PO microporous membrane) was measured according to JIS K7210:1999 (Plastics - Melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics). A load of 21.6 kgf was applied to the membrane at 190°C, and the MI was calculated as the amount of resin (g) that flowed out of an orifice 1 mm in diameter and 10 mm in length in 10 minutes.

[0228] <Particle size, average particle size and particle size distribution of inorganic particles> The particle size distribution and median diameter (μm) of the inorganic particle dispersion or slurry coating liquid were measured using a laser particle size distribution measuring device (Microtrac MT3300EX manufactured by Nikkiso Co., Ltd.). If necessary, the particle size distribution of the inorganic particle dispersion or slurry coating liquid was adjusted using the particle size distribution of water or resin binder as a baseline. The particle size at which the cumulative frequency is 50% was defined as D 50 , the particle size at which the cumulative frequency is 10% is D 10 , the particle size at which the cumulative frequency is 90% is D 90 D 50 is the average particle size.

[0229] <BET specific surface area of ​​inorganic particles (m 2 / g)> The specific surface area of ​​the inorganic particles was measured by the nitrogen adsorption BET method.

[0230] <Air permeability (sec / 100cm 3 ), and the air permeability ratio of the multilayer porous membrane to the polyolefin microporous membrane > The air permeability of the multilayer porous membrane and the polyolefin microporous membrane, where the air resistance in accordance with JIS P-8117 was used as the air permeability, was measured in accordance with JIS P-8117 using a Gurley air permeability meter "G-B2 (trademark)" manufactured by Toyo Seiki Co., Ltd., in an atmosphere at a temperature of 23°C and a humidity of 40%. The air permeability of the porous layer was calculated by subtracting the air permeability of the polyolefin microporous membrane from the air permeability of the multilayer porous membrane. Air permeability increase rate = Air permeability of porous layer / Air permeability of polyolefin microporous membrane The air permeability increase rate was calculated according to the following formula: Furthermore, the air permeability per thickness of the porous layer was also calculated.

[0231] <Content of inorganic particles in the porous layer (mass % and volume %)> The content of inorganic particles in the porous layer can be calculated from the blending ratio of the constituent materials when preparing the coating liquid. Furthermore, from the perspective of detecting from a multilayer porous membrane, it is also possible to measure the weight changes of the organic and inorganic particles using TG-DTA. Specifically, the porous layer portion of the multilayer porous membrane is scraped with a glass plate, and 8 mg to 10 mg of the sample is collected. The sampled porous layer is placed in the apparatus and heated from room temperature to 600°C at a rate of 10°C / min in an air atmosphere, and the weight change is measured and calculated. Note that the mass content and volume content of inorganic particles are interchangeable based on the specific gravity of the inorganic particles.

[0232] <Porosity (%)> A 10cm x 10cm square sample was cut from the microporous membrane and its volume (cm 3 ) and mass (g), and compare them with the film density (g / cm 3 ) the porosity was calculated using the following formula: Porosity (%) = (volume - mass / density) / volume x 100

[0233] <Piercing strength (N) and area weight conversion piercing strength (N / (g / m 2 ))> Using a Kato Tech handy compression tester "KES-G5 (trademark)," a microporous membrane or multilayer porous membrane was fixed with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the center of the fixed microporous membrane or multilayer porous membrane at a temperature of 23°C and a humidity of 40% with a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / sec, to obtain the raw puncture strength (gf) as the maximum puncture load. The obtained puncture strength (N) was converted to basis weight (N / (g / m 2 )) was also calculated.

[0234] <Average pore diameter of porous layer> Acquisition of cross-sectional SEM images of resin-embedded samples The multilayer porous membrane was stained with ruthenium and embedded in room-temperature curing epoxy resin. Smooth cross sections parallel to the TD were prepared using a broad ion beam (BIB). These smooth cross sections were observed using a scanning electron microscope (SEM) and imaged at 7000x magnification to obtain SEM images. From the smooth cross section, multiple SEM images could be obtained from multiple fields of view, or one SEM image could be obtained from a single field of view. The SEM images were obtained so that the entire thickness of the multilayer porous layer was included in the SEM field of view. Regions of the multilayer porous layer, excluding 3% of the thickness of the multilayer porous layer from both the top and bottom, were then cut out and subjected to the image analysis described below. When multiple SEM images were obtained, SEM images were taken at 50 μm intervals along the longitudinal direction of the smooth cross section. Image analysis and pore size analysis The SEM images were then subjected to median filtering with a radius of 2.0 pixels and binarized using the Otsu method under threshold conditions to calculate the area ratio of black and / or white areas. The binarized images were then subjected to pore size analysis using the local thickness method to calculate the pore size distribution, average pore size, maximum pore size, and other parameters. The local thickness method can be performed using the thickness analysis feature of the BoneJ plug-in for the image processing software ImageJ. The spatial size can be defined as the size of the largest circle that fits within a given area. Therefore, even if there are no independent structures or spaces, the spatial size can be defined and the pore size distribution, average pore size, maximum pore size, and other parameters can be calculated. Pore ​​size analysis results SEM images of at least one of the smooth cross sections parallel to the TD prepared by BIB as described above were taken, and pore size analysis was performed using the local thickness method. The average pore size d, pore size distribution D, standard deviation of the pore size distribution D, maximum pore size PS, etc. were calculated. In addition, five SEM images of the smooth cross sections parallel to the TD prepared by BIB as described above were analyzed for pore size using the local thickness method, and the standard deviation of the average pore size d was calculated.

[0235] <Water content per unit volume of porous layer> The multilayer porous membrane was cut into pieces in the range of 0.15-0.20 g and pretreated at 23°C and 40% relative humidity for 12 hours. The weight of each piece was then measured and used as the sample weight (g). The water content (μg) of the pretreated sample was measured using a Karl Fischer apparatus. The heating and vaporization conditions for the measurement were 150°C and 10 minutes. Hydranal Coulomat CG-K (manufactured by SIGMA-ALDRICH) was used as the cathode reagent, and Hydranal Coulomat AK (manufactured by SIGMA-ALDRICH) was used as the anode reagent. The measured water weight (μg), sample weight (g), thickness of the porous layer (μm), and weight of the multilayer porous membrane per unit area (g / m 2)) and the water content per unit volume of the porous layer was calculated using the following formula. Water weight per unit volume (mg / (μm m 2 ))=weight of water / (thickness of porous layer×weight of sample / weight of multilayer porous membrane per unit area) / 1000

[0236] <Dry heat shrinkage rate (%) at 130℃ and 150℃> The multilayer porous membrane was cut into a sample of 100 mm in MD and 100 mm in TD, and left to stand in an oven at 130°C or 150°C for 1 hour. At this time, the sample was sandwiched between 10 sheets of paper to prevent hot air from directly hitting the sample. After removing the sample from the oven and cooling, the length (mm) was measured and the heat shrinkage was calculated using the following formula. Measurements were performed in MD and TD, and the average of both values ​​was expressed as the heat shrinkage. Heat shrinkage rate (%) = {(100 - length after heating) / 100} x 100

[0237] <Measurement of light transmittance (%)> The light transmittance of the sample was measured according to the following sample size, measuring equipment and measuring conditions. Sample size: 5cm x 5cm Measuring equipment: JASCO UV-visible near-infrared spectrophotometer V-630 Measurement conditions: Capture interval 1 nm, scanning speed 400 nm / min, measurement range 390 nm to 850 nm

[0238] In the above measurement of light transmittance, a polyolefin microporous film and a multilayer porous film are used as samples, and the light transmittance (%) at a wavelength of 550 nm can be obtained.

[0239] (Ratio of light transmittance of multilayer porous film to light transmittance of polyolefin microporous film at a wavelength of 550 nm) Based on the above light transmittance measurement, the light transmittance of the polyolefin microporous membrane before coating and the multilayer porous membrane after coating was measured, and the ratio of the light transmittance at a wavelength of 550 nm of the multilayer porous membrane to the light transmittance at a wavelength of 550 nm of the polyolefin microporous membrane was calculated based on the following formula. Light transmittance ratio = Light transmittance (%) of multilayer porous film at 550 nm / Light transmittance (%) of polyolefin microporous film at 550 nm

[0240] The porous layer was removed from the multilayer porous membrane obtained in the Examples and Comparative Examples, and the light transmittance ratio was calculated in the same manner as above. 2 The multilayer porous membrane cut into a size of 100 mm was immersed for 24 hours, and then the porous layer was scraped off with a spatula or the like, used as a sample, and ultrasonicated with an ultrasonic irradiator to remove the porous layer.The light transmittance of the polyolefin microporous membrane from which the porous layer had been removed and the multilayer porous membrane before removal were measured.It was confirmed that the ratio of the light transmittance of the multilayer porous membrane at a wavelength of 550 nm calculated in this way to the light transmittance of the polyolefin microporous membrane was approximately the same as the ratio of the light transmittance at a wavelength of 550 nm described above to the light transmittance of the polyolefin microporous membrane at a wavelength of 550 nm.

[0241] <90° peel strength (N / m)> The surface of the multilayer porous membrane cut into 2 mm x 7 mm was attached to a glass plate with double-sided tape on the side opposite the coating layer to be measured, and tape (product name "Mending Tape MP-12", manufactured by 3M) was attached to the coating layer. 5 mm of the tip of the tape was peeled off, and the tip of the tape was clamped with a chuck in a tensile tester (model "AG-IS, SLBL-1kN, manufactured by Shimadzu Corporation) so that the tape was peeled off at an angle of 90° to the surface direction of the multilayer porous membrane. A tensile test was performed at a pulling speed of 300 mm / s, a temperature of 25°C, and a relative humidity of 40%, and the tensile strength (N / m) was measured.

[0242] <180° peel strength (N / m)> The surface of the multilayer porous membrane cut into 2 mm x 7 mm was attached to a glass plate with double-sided tape on the side opposite the coating layer to be measured, and tape (product name "Mending Tape MP-12", manufactured by 3M) was attached to the coating layer. 5 mm of the tip of the tape was peeled off, and the tip of the tape was clamped with a chuck using a tensile tester (model "AG-IS, SLBL-1kN, manufactured by Shimadzu Corporation) so that the tape was peeled off at an angle of 180° to the surface direction of the multilayer porous membrane. A tensile test was performed at a pulling speed of 50 mm / s, a temperature of 25°C, and a relative humidity of 40%, and the tensile strength (N / m) was measured.

[0243] <Glass transition temperature of thermoplastic polymer (℃)> An appropriate amount of the thermoplastic polymer coating solution (non-volatile content = 30%) was placed on an aluminum dish and dried for 30 minutes in a hot air dryer at 130°C. Approximately 17 mg of the dried film was placed in an aluminum container for measurement, and a DSC curve and a DDSC curve were obtained under a nitrogen atmosphere using a DSC measurement device (Shimadzu Corporation, DSC6220). The measurement conditions were as follows: (First stage heating program) Start at 70°C, increase the temperature at a rate of 15°C per minute, and maintain at 110°C for 5 minutes. (Second stage cooling program) Decrease temperature from 110℃ at a rate of 40℃ per minute. After reaching -50℃, maintain for 5 minutes. (Third stage heating program) The temperature was raised from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were collected during this third temperature rise. The glass transition temperature (Tg) was determined as the intersection of the baseline (a straight line extending the baseline of the obtained DSC curve toward the higher temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to a downward convex curve).

[0244] <Dot diameter and distance between dots> For the thermoplastic polymer-containing coating solution, the dot diameter of the coating pattern was measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). The sample separator was photographed at 100x magnification (coaxial epi-illumination), and the diameter of each of multiple dots (five points) was measured in measurement mode, and the average value was calculated as the dot diameter. In addition, the distance from the outer edge of a dot to the outer edge of the nearest other dot was measured in measurement mode at five observation points, and the average value was calculated as the dot distance.

[0245] <Adhesion to electrodes> The multilayer porous membrane or separator obtained in each example and comparative example and the negative electrode (manufactured by Enertech, negative electrode material: graphite, conductive additive: acetylene black, L / W: 20 mg / cm on both sides) as an adherend were used. 2 , Cu current collector thickness: 10 μm, negative electrode thickness after pressing: 140 μm) were cut into rectangular shapes with a width of 15 mm and a length of 60 mm, and these were overlaid so that the thermoplastic polymer-containing layer of the multilayer porous membrane or separator and the negative electrode active material faced each other to obtain a laminate, and then the laminate was pressed under the following conditions. Press pressure: 1 MPa Temperature: 90℃ Pressing time: 1 minute The pressed laminate was subjected to a 90° peel test at a peel rate of 50 mm / min using Imada Co., Ltd. force gauges ZP5N and MX2-500N (product names), in which the electrode was fixed and the multilayer porous membrane or separator was gripped and pulled. The peel strength was measured. The average peel strength measured over a 40 mm length under the above conditions was used as the adhesive strength to the electrode. This adhesive strength measurement was performed before and after immersing the laminate in propylene carbonate (PC). The adhesive strength before PC impregnation was expressed as dry adhesive strength, and the adhesive strength after PC impregnation was expressed as wet adhesive strength. When a separator achieving an adhesive strength of preferably 1.0 N / m or more, more preferably 1.8 N / m or more, is used in a nonaqueous electrolyte battery, the adhesive strength between the opposing positive and negative electrodes is excellent. From the viewpoint of ionic resistance, an adhesive strength of 100.0 N / m or less is preferred.

[0246] <Battery temperature rise test> The positive electrode, multilayer porous film, and negative electrode prepared by the following method were stacked in this order, and the long sides of the positive electrode, multilayer film, and negative electrode were wound up to a width of 30 mm, housed in an aluminum laminate film, and three sides were heat-sealed. The positive electrode lead tab and the negative electrode lead tab were each led out from one side of the laminate film. After the heat-sealed sample was dried, the following electrolyte solution was poured into the laminate film, and the remaining side was sealed to prepare a test battery.

[0247] The test battery was designed to have a capacity of 1 Ah.

[0248] The fabricated battery was charged to 4.2 V at a discharge current of 0.5 C in an environment of 25°C. The charged battery was placed in an oven and heated from room temperature to 180°C at a rate of 5°C / min. The test results were evaluated based on the battery surface temperature when the voltage dropped to 2 V or less, according to the following criteria.

[0249] (Preparation of positive electrode) The positive electrode active material is lithium nickel manganese cobalt composite oxide powder (LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 A cathode mixture paste was prepared by mixing 85 parts by weight of a mixed cathode active material (a 70:30 mass ratio of lithium manganese oxide powder (LiMnO2) and lithium manganese composite oxide powder (LiMnO4) mechanically, 6 parts by weight of acetylene black (conductive additive), and 9 parts by weight of PVdF (binder) in N-methyl-2-pyrrolidone (NMP) as a solvent. This cathode mixture paste was uniformly applied to both sides of a 20 μm-thick aluminum foil current collector, dried, and then compression-molded using a roll press to adjust the thickness of the cathode mixture layer to a total thickness of 100 μm. A cathode was fabricated from a rectangular sheet with a short side of 50 mm and a long side of 350 mm, with a 20 mm-long uncoated aluminum foil lead tab attached to the top of the short side.

[0250] (Preparation of negative electrode) A negative electrode mixture paste was prepared by uniformly mixing 91 parts by weight of graphite (negative electrode active material) and 9 parts by weight of PVdF (binder) using NMP as a solvent. This negative electrode mixture paste was uniformly applied to both sides of a 15 μm-thick copper foil current collector, dried, and then compression-molded using a roll press to adjust the thickness of the negative electrode mixture layer to a total thickness of 100 μm. A negative electrode was fabricated from a rectangular sheet with short sides of 52 mm and long sides of 352 mm, with a 20 mm-long lead tab of uncoated copper foil attached to the upper short side.

[0251] (Preparation of Electrolyte) A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1:1 to a concentration of 1.0 mol / L.

[0252] (Preparation of multilayer porous membrane) Samples measuring 54 mm x 360 mm were cut out from the multilayer porous membranes obtained in the Examples and Comparative Examples.

[0253] (Evaluation criteria for battery temperature rise test) A:Battery surface temperature 170℃ or higher, B: Battery surface temperature 165℃ or higher, C: Battery surface temperature 160℃ or higher, D: Battery surface temperature less than 160°C

[0254] <Rate characteristics> (a. Preparation of Positive Electrode) The positive electrode active material was lithium nickel manganese cobalt composite oxide (Li[Ni 1 / 3 Mn 1 / 3 Co 1 / 3 91.2 parts by mass of ]O2), 2.3 parts by mass each of flake graphite and acetylene black as conductive materials, and 4.2 parts by mass of polyvinylidene fluoride (PVdF) as a resin binder were prepared, and these were dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil that would serve as the positive electrode using a die coater, with the positive electrode active material coating amount being 120 g / m.2 After drying at 130°C for 3 minutes, the positive electrode active material was pressed using a roll press so that the bulk density of the positive electrode active material was 2.90 g / cm 3 This positive electrode was compression molded to have an area of ​​2.00 cm. 2 It was punched into a circle.

[0255] (b. Preparation of negative electrode) 96.6 parts by mass of artificial graphite was prepared as the negative electrode active material, and 1.4 parts by mass of ammonium salt of carboxymethyl cellulose and 1.7 parts by mass of styrene-butadiene copolymer latex were prepared as the resin binder. These were dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 16 μm-thick copper foil serving as a negative electrode current collector using a die coater so that the negative electrode active material was 53 g / m 2 After drying at 120°C for 3 minutes, the negative electrode active material was pressed using a roll press so that the bulk density of the negative electrode active material was 1.35 g / cm 3 This was compression molded to form a negative electrode with an area of ​​2.05 cm. 2 It was punched into a circle.

[0256] (c. Preparation of non-aqueous electrolyte) A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl carbonate=1:2 (volume ratio) to a concentration of 1.0 ml / L.

[0257] (d. Battery assembly) The negative electrode, multilayer porous membrane, and positive electrode were stacked in this order from bottom to top, with the active material surfaces of the positive and negative electrodes facing each other. This stack was then placed in a lidded stainless steel metal container, the container body and lid of which were insulated, with the copper foil of the negative electrode and the aluminum foil of the positive electrode in contact with the container body and lid, respectively, to obtain a cell. This cell was then dried under reduced pressure at 70°C for 10 hours. A nonaqueous electrolyte was then poured into the container in an argon box, and the container was sealed to prepare a test battery.

[0258] (e. Evaluation of rate characteristics) The battery assembled in (d. Battery assembly) above was charged at a temperature of 25°C with a current value of 3 mA (approximately 0.5 C) up to a battery voltage of 4.2 V, and then the current value was reduced from 3 mA to maintain 4.2 V. This method was used for the first charge after battery fabrication for a total of approximately 6 hours, and the battery was then discharged at a current value of 3 mA down to a battery voltage of 3.0 V. Next, at 25°C, the battery was charged at a current of 6 mA (approximately 1.0 C) up to a battery voltage of 4.2 V, and then the current was reduced from 6 mA to maintain 4.2 V. This method of charging was continued for a total of approximately 3 hours, and the battery was then discharged at a current of 6 mA down to a battery voltage of 3.0 V, and the discharge capacity at this time was recorded as the 1 C discharge capacity (mAh). Next, at 25°C, the battery was charged at a current of 6 mA (approximately 1.0 C) up to a battery voltage of 4.2 V, and then the current was reduced from 6 mA to maintain 4.2 V, for a total of approximately 3 hours of charging. After that, the battery was discharged at a current of 60 mA (approximately 10 C) down to a battery voltage of 3.0 V, and the discharge capacity at that time was recorded as the 10 C discharge capacity (mAh). The ratio of the 10C discharge capacity to the 1C discharge capacity was calculated, and this value was taken as the rate characteristic. Rate characteristics at 10C (%) = (10C discharge capacity / 1C discharge capacity) x 100 The rate characteristics at 10C were evaluated according to the following criteria. A: Rate characteristics at 10C above 22% B: Rate characteristics at 10C of 20% or more and less than 22% C: Rate characteristics at 10C of 18% or more and less than 20% D: Rate characteristics at 10C below 18%

[0259] <Cycle test> The battery tested for the rate characteristics above was discharged at a discharge current of 1 C to a discharge cut-off voltage of 3 V at a temperature of 25°C, and then charged at a charge current of 1 C to a charge cut-off voltage of 4.2 V. This constituted one cycle, and charge and discharge were repeated. The cycle characteristics were evaluated according to the following criteria, using the capacity retention rate after 300 cycles relative to the initial capacity (capacity at the first cycle). A: Capacity retention rate of 65% or more B: Capacity retention rate of 60% or more but less than 65% C: Capacity retention rate of less than 60%

[0260] <Foreign object detection rate measurement> Multilayer porous membranes having a porous layer formed on a polyolefin microporous membrane were inspected for foreign matter (e.g., unmelted resin, metal powder, carbide, etc.) on the polyolefin microporous membrane using an optical foreign matter inspection device over an inspection range of 1,000 to 1,300 mm wide and 1,000 m long, and the foreign matter detection rate was calculated and evaluated according to the following criteria. (Evaluation criteria) A: Foreign object detection rate is 95% to 100%. B: The detection rate of foreign matter is 90% or more but less than 95%. C: Foreign matter detection rate is 85% or more but less than 90% D: Foreign body detection rate is less than 85%

[0261] Example 1 A polymer blend was prepared using a tumbler blender containing 46.5 wt% homopolymer polyethylene (PE) with a viscosity average molecular weight (Mv) of 700,000, 46.5 wt% homopolymer PE with a Mv of 250,000, and 7 wt% homopolymer polypropylene (PP) with a Mv of 400,000. One part by weight of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant to 99 parts by weight of the polymer blend, and the mixture was dry-blended again using the tumbler blender to obtain a polymer mixture. The resulting polymer mixture was then purged with nitrogen and fed into a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also used. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump.

[0262] The mixture was melt-kneaded, and the feeder and pump were adjusted so that the ratio of liquid paraffin to the total mixture extruded was 68 wt% (resin composition concentration: 32 wt%). The melt-kneading conditions were a set temperature of 200°C, a screw rotation speed of 70 rpm, and a discharge rate of 145 kg / h.

[0263] Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, and cast to obtain a gel sheet having a thickness of 1350 µm.

[0264] The gel sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched. The stretching conditions were an MD magnification of 7.0, a TD magnification of 6.4, and a set temperature of 122°C. The gel sheet was then introduced into a methylene chloride bath and thoroughly immersed in methylene chloride to extract and remove the liquid paraffin. The methylene chloride was then dried and removed to obtain a porous body.

[0265] The porous body was then introduced into a TD tenter and heat-set. The heat-setting temperature was 132°C, the TD maximum magnification was 1.85, and the relaxation rate was 0.784 to obtain a polyolefin microporous membrane (PO microporous membrane D) with a thickness (TB) of 6.0 μm. The resin composition of the obtained polyolefin microporous membrane and the above measurement results are shown in Table 1.

[0266] Next, the particle size (D10 or D90) and average particle size (D 50 ), particle size distribution (D90 / D50 or D50 / D10), and BET specific surface area were used. The inorganic particles were mixed with a water-soluble polymer binder, a water-insoluble polymer binder, additives, etc., as shown in Tables 3 and 4, and then an appropriate amount of water and dispersant was added, followed by stirring and dispersion. If necessary, a bead mill treatment was performed under conditions of a bead diameter of 0.1 mm and a mill rotation speed of 2000 rpm. If necessary, xanthan gum was added as a thickener to the treated mixture to prepare a coating solution.

[0267] After corona discharge treatment was performed on the surface of the polyolefin microporous membrane, a coating solution was applied to the treated surface using a gravure coater.The coating solution on the polyolefin microporous membrane was then dried at 60°C to remove water, and a 1.0 μm thick porous layer containing 95.8 mass% (89.3 volume%) of inorganic particles was formed on one side of the polyolefin microporous membrane to obtain a multilayer porous membrane.The membrane properties of the obtained multilayer porous membrane and the evaluation results of a battery equipped with the multilayer porous membrane as a separator are also shown in Table 4.

[0268] <Examples 2 to 20 and Comparative Examples 1 to 3> A multilayer porous membrane was formed in the same manner as in Example 1, except that the production conditions and physical properties of the polyolefin microporous membrane, the type of inorganic particles, the types of components of the porous layer, the composition of the coating solution, and the coating conditions were set as shown in Tables 1 to 4. The various properties of the obtained multilayer porous membrane and a battery including the same as a separator were evaluated by the above-mentioned methods. The evaluation results are shown in Table 4.

[0269] In Example 3, a thermoplastic polymer-containing adhesive layer was formed in a dot pattern on the surface of the multilayer porous membrane. In Example 14, porous layers containing inorganic particles and a resin binder were formed on both sides of PO microporous membrane B.

[0270] [Table 1]

[0271] [Table 2]

[0272] [Table 3]

[0273] [Table 4-1]

[0274] Table 4-2

[0275] Table 4-3

[0276] Table 4-4

[0277] Table 4-5

[0278] Table 4-6

[0279] Table 4-7

[0280] Table 4-8

Claims

1. A multilayer porous membrane comprising a microporous membrane containing a polyolefin resin as a main component and a porous layer laminated on at least one surface of the microporous membrane, the porous layer containing inorganic particles and a water-soluble polymer binder, The air permeability of the multilayer porous membrane is 300 sec / 100 cm ３ is as follows: the porous layer has a thickness of 0.01 μm or more and less than 5.00 μm per side of the microporous membrane; The average particle size D of the inorganic particles ５０ is 0.01 μm or more and less than 0.50 μm, the water-soluble polymer binder contains more than 30.0 mass% and not more than 99.0 mass% of monomer units derived from (meth)acrylamide, and contains 1.0 mass% or more and less than 70.0 mass% of cyano group-containing monomer units; Multilayer porous membrane.

2. The microporous membrane has a puncture strength converted into basis weight of 0.49 N / (g / m ２ 2. The multilayer porous membrane according to claim 1, wherein the thickness of the porous membrane is 100 μm or more.

3. The porous layer has an air permeability of 100 sec / 100 cm ３ The multilayer porous membrane according to claim 1 or 2, wherein:

4. 3. The multilayer porous membrane according to claim 1, wherein the water-soluble polymer binder is non-particulate and has a weight average molecular weight of 300,000 or more.

5. The multilayer porous membrane according to claim 1 or 2, wherein the water-soluble polymer binder contains less than 20.0% by mass of (meth)acrylic acid monomer units.

6. The multilayer porous membrane according to claim 1 or 2, wherein the multilayer porous membrane contains a water-insoluble polymer binder.

7. The multilayer porous membrane according to claim 1 or 2, wherein the multilayer porous membrane has a heat shrinkage rate at 150°C of 10% or less in both MD and TD.

8. The multilayer porous membrane according to claim 1 or 2, which is a separator for a non-aqueous electrolyte battery.

9. A non-aqueous electrolyte battery comprising a positive electrode, the multilayer porous membrane according to claim 1 or 2, a negative electrode, and a non-aqueous electrolyte.

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