Porous multilayer film

Abstract

An object of the present invention is to provide a thin multilayer porous film having high heat resistance, high ion permeability, and high light permeability, and a nonaqueous electrolyte battery separator and a nonaqueous electrolyte battery each including the multilayer porous film.SOLUTION: In the multilayer porous film, a porous layer containing inorganic particles is laminated on at least one surface of a polyolefin base material layer, the thickness of the polyolefin base material layer is 8 μm or less, and the puncture strength of the polyolefin base material layer in terms of weight is 85gf / (g / m2) or more. The inorganic particles have an average particle size D50 of 0.05 μm or more and less than 0.30 μm, the inorganic particles have a D90 of 0.10 μm or more and 0.40 μm or less, the porous layer has a total thickness of 0.1 μm or more and 3.0 μm or less, and a ratio of a light transmittance of the multilayer porous membrane at a wavelength of 550 nm to a light transmittance of the polyolefin substrate layer at a wavelength of 550 nm is 0.4 or more and less than 1.0.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 separator interposed between a positive electrode plate and a negative electrode plate 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 or substrate layer containing a polyolefin resin are used.

[0003] In recent years, there has been a demand for thinner separators to increase the capacity of non-aqueous electrolyte batteries, and there has also been a demand for thinner and stronger polyolefin substrate layers. Furthermore, multilayer porous membranes, in which a heat-resistant layer made of inorganic particles and a binder is formed on a polyolefin substrate layer to improve heat resistance, are known as separators for non-aqueous electrolyte batteries (Patent Documents 5 to 7). Furthermore, the optical transparency of substrate layers, multilayer porous membranes, or separators has been investigated to detect foreign matter on the surface of the polyolefin substrate layer or foreign matter introduced during the coating process of the substrate layer (Patent Documents 1 to 4).

[0004] Patent Document 1 discloses that, from the viewpoint of being able to stack one electrode while checking the position of the other electrode when stacking a separator and multiple electrodes, and from the viewpoint of maintaining electrolyte permeability by forming a fine concave-convex pattern on at least one surface of the base layer, the fine concave-convex pattern has a high light transmittance region in which the light transmittance in the wavelength range of 625 to 645 nm is more than 10% and not more than 90%, and a low light transmittance region in which the light transmittance is lower than that of the high light transmittance region but is not less than 10% and less than 60%, and that the area ratio of the high light transmittance region to the low light transmittance region is not less than 0.01% and not more than 20%.

[0005] Patent Document 2 describes a method for making a fabric with a basis weight of 3.0 g / m from the viewpoint of easily detecting defects such as pinholes and scratches.2 The following discloses a polyolefin microporous membrane having a thickness of 4 μm or less, a light transmittance at a wavelength of 660 nm of 40% or less, and containing polyethylene as the main component. Patent Document 2 also suggests that coating defects can be suppressed when the polyolefin microporous membrane is used as a substrate, but the subject of the basic evaluation is only the polyolefin microporous membrane as a substrate, and there is no specific description of inorganic particles in the coating solution or the coating thickness.

[0006] Patent Document 3 discloses a separator having a porous layer containing inorganic particles and a heat-resistant resin on at least one side of a porous substrate, and in order to ensure low heat shrinkage, dimensional stability at high temperatures, and heat-resistant membrane rupture resistance, the presence or absence of a melting point of the heat-resistant resin, the areal heat shrinkage at 140°C, and the variation in light transmittance at a wavelength of 800 nm measured at 5 m intervals in the longitudinal direction of the porous substrate. Patent Document 3 lists aramid resin as a specific example of the heat-resistant resin, but does not mention the basis weight equivalent puncture strength of the porous substrate, the particle size distribution of the inorganic particles, particularly the distribution on the relatively large particle size side, for example, D 90 There is no specific description about this.

[0007] Patent Document 4 discloses a separator having a porous polymer substrate and an organic-inorganic composite porous layer containing inorganic particles and a binder polymer disposed on at least one surface of the porous polymer substrate, in order to ensure the generally required qualities of a separator, such as thermal rupture resistance, shutdown characteristics, safety during overcharge, and prevention or mitigation of internal short circuits and thermal runaway. Patent Document 4 discusses the BET specific surface area of ​​the inorganic particles, the relationship between the thickness of the organic-inorganic composite porous layer and the porous polymer substrate, the arithmetic mean roughness of the surface of the organic-inorganic composite porous layer, and the ratio of the light transmittance after leaving the separator at 25°C for 1 hour to the light transmittance after leaving it at 190°C for 1 hour, but does not specify the wavelength related to the light transmittance, and the total thickness of the organic-inorganic composite porous layer is only a relatively thick layer of 5 μm or more. Patent Document 4 also discusses the basis weight equivalent puncture strength of the porous polymer substrate, the particle size distribution of the inorganic particles, particularly the distribution on the relatively large particle size side, e.g., D 90 There is no specific description about this.

[0008] Patent Document 5 discloses a method for obtaining a multilayer porous membrane by coating a microporous membrane substrate with a latex containing non-conductive particles having a predetermined average particle size and a water-soluble polymer containing 70.0 to 99.0 wt. % of (meth)acrylamide-derived structural units (commonly abbreviated as "PAAM"), from the viewpoints of preventing filler detachment from the multilayer porous membrane or porous layer in an electrolyte, vibration resistance, heat shrinkage resistance, and high-power and high-temperature cycle characteristics of the battery. Patent Document 5 also discloses that the latex contains a water-insoluble polymer containing ethylenically unsaturated carboxylic acid monomer units in a proportion of 1.5 to 5.0 wt. % and having an electrolyte swelling ratio of more than 1.0 to 3.0. However, Patent Document 5 does not disclose the basis weight-equivalent pin puncture strength of the microporous membrane or details of the particle size and particle size distribution of the non-conductive particles.

[0009] Patent Document 6 specifies the total thickness of the porous layer disposed on the base layer, the area ratio of each hole or the number of holes in the porous layer, the proportion occupied by inorganic particles, the aspect ratio of the inorganic particles, etc., from the viewpoint of safety in a nail penetration test of a nonaqueous electrolyte battery having a multilayer porous membrane as a separator.

[0010] Patent Document 7 discloses that, from the viewpoint of safety of a non-aqueous electrolyte battery having an electrode with a relatively high nickel (Ni) content, the porous layer disposed on the polyolefin substrate layer contains an inorganic filler, a water-insoluble binder, a water-soluble binder, and a polyacrylic acid-based dispersant, and also studies the thermal shrinkage rate of a multilayer porous film having a polyolefin substrate layer and a porous layer in propylene carbonate at a temperature of 140°C or less. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2020-68094 [Patent Document 2] International Publication No. 2018 / 164057 [Patent Document 3] International Publication No. 2018 / 155288 [Patent Document 4] Special Publication No. 2023-529141 [Patent Document 5] International Publication No. 2017 / 195563 [Patent Document 6] International Publication No. 2021 / 006357 [Patent Document 7] International Publication No. 2022 / 186257 Summary of the Invention [Problem to be solved by the invention]

[0012] In connection with the thinning of separators, the separator substrate layer has become thinner and stronger, but if the heat-resistant layer placed on the substrate layer is also made thinner, heat resistance may be reduced. On the other hand, if the thickness or density of the heat-resistant layer is increased to maintain heat resistance, the ion permeability of the separator equipped with the heat-resistant layer may be reduced.

[0013] Furthermore, if the thickness of the heat-resistant layer increases, the light transmittance of the separator having the heat-resistant layer decreases, which may make it difficult to check for foreign matter on the surface of the separator substrate or foreign matter that gets mixed in during the coating process for the substrate.

[0014] Therefore, conventional separators have had the problem that it is difficult to realize a thin-film separator with high heat resistance, ion permeability, and light permeability.

[0015] In view of the above circumstances, an object of the present invention is to provide a thin multilayer porous membrane having high heat resistance, ion permeability, and light permeability, as well as a separator for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery including the same. [Means for solving the problem]

[0016] The above problems are solved by the following technical means. (1) A multilayer porous membrane in which a porous layer containing inorganic particles is laminated on at least one surface of a polyolefin substrate layer, The thickness of the polyolefin substrate layer is 8 μm or less, The polyolefin substrate layer has a puncture strength converted into basis weight of 85 gf / (g / m 2 ) or more, The average particle size D of the inorganic particles 50 is 0.05 μm or more and less than 0.30 μm, The particle size D of the inorganic particles 90 is 0.10 μm or more and 0.45 μm or less, The total thickness of the porous layer is 0.1 μm or more and 3.0 μm or less, 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 polyolefin base layer is 0.4 or more and less than 1.0; Multilayer porous membrane. (2) Particle size D of the inorganic particles 10 Item 2. The multilayer porous membrane according to item 1, wherein the average particle size is 0.01 μm or more and 0.20 μm or less. (3) The air permeability of the porous layer is 50 sec / 100 cm 3 and the air permeability of the multilayer porous membrane is 200 sec / 100 cm or less. 3 3. The multilayer porous membrane according to item 1 or 2, wherein: (4) The multilayer porous film according to any one of items 1 to 3, wherein the multilayer porous film has a light transmittance at a wavelength of 550 nm of 4.0% or more and less than 10.0%. (5) The multilayer porous membrane according to any one of items 1 to 4, wherein the porous layer contains a water-soluble polymer in a volume ratio of 1% to 10%. (6) The multilayer porous membrane according to any one of items 1 to 5, wherein the inorganic particles have an aspect ratio of 1 or more and 3 or less. (7) 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 the MD and TD directions. (8) The multilayer porous membrane according to any one of items 1 to 7, wherein the ratio of the coating thickness of the porous layer to the pin puncture strength of the polyolefin substrate layer is less than 0.004 μm / gf. (9) The particle diameter of the inorganic particles is expressed by the following formulas (1) and (2): Formula (1):D 90 / D 50 ≦2.0 Formula (2):D 50 / D 10 ≦2.0 9. The multilayer porous membrane according to any one of items 1 to 8, which satisfies the above. (10) The multilayer porous membrane according to any one of items 1 to 9, which is a separator for a non-aqueous electrolyte battery. (11) A non-aqueous electrolyte battery comprising a positive electrode, the multilayer porous membrane according to any one of items 1 to 10, a negative electrode, and a non-aqueous electrolyte. [Effects of the Invention]

[0017] According to the present invention, a thin multilayer porous membrane having high heat resistance, ion permeability, and light permeability can be provided, and by using the membrane, it is possible to improve the heat resistance, ion permeability, and light permeability of a separator for a nonaqueous electrolyte battery and to reduce the thickness of the separator, and thus it is also possible to provide a nonaqueous electrolyte battery. DETAILED DESCRIPTION OF THE INVENTION

[0018] 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.

[0019] 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°.

[0020] 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.

[0021] <Multilayer porous membrane> The multilayer porous membrane according to this embodiment comprises a polyolefin substrate layer (hereinafter sometimes abbreviated as "PO substrate layer") containing polyolefin resin as a main component, and a porous layer containing inorganic particles laminated on at least one side of the polyolefin substrate layer.

[0022] In the multilayer porous membrane according to this embodiment, the thickness of the PO substrate layer is 8 μm or less, and the PO substrate layer has a puncture strength converted into basis weight of 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 base layer is 0.4 or more and less than 1.0.

[0023] 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.

[0024] Regarding light transmittance, the voids in the porous layer and the inorganic particles have different refractive indices, so light refraction causes scattering 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 substrate layer.

[0025] 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.

[0026] The influence 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 substrate layer 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 temperature due to thermal runaway or the like, the substrate 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, it has been found that the smaller the inorganic particles in the porous layer arranged on the surface of the substrate layer, the narrower the pore size of the porous layer, thereby suppressing resin flow, and, for example, blocking molten resin from the substrate layer, thereby improving the heat resistance of the battery.

[0027] 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 this allows the shape of the porous layer to be maintained even in a high-temperature environment and improves heat resistance.

[0028] Furthermore, from the viewpoint of maintaining or improving heat resistance and ion permeability, it is preferable that the ratio of the coating thickness (μm) of the porous layer to the puncture strength (gf) of the PO substrate layer (coating thickness of porous layer / puncture strength of substrate layer) is less than 0.004.

[0029] The reduction in thickness of the multilayer porous membrane can be achieved by specifying the thickness of the PO substrate layer and the layer thickness of the porous layer as described above. In this embodiment, the thickness (TB) of the PO substrate layer is set to 8 μm or less, and the total thickness of the porous layer is set to 0.1 μm or more and 3.0 μm or less, which contributes to the reduction in thickness of the multilayer porous membrane and allows the membrane to have low resistance and maintain ion permeability even when used as a separator.

[0030] The improvement in ion permeability and low resistance of the multilayer porous membrane are thought to be due to the influence of fillers such as inorganic particles in the porous layer and the influence of a resin binder that may be contained in the porous layer.

[0031] The influence of the filler on improving ion permeability and low resistance can be thought of as maintaining or improving ion permeability and ensuring the coating density of the porous layer by specifying the particle size distribution of the inorganic particles as described above or by suitably specifying the range of the aspect ratio.

[0032] Regarding the effect of the resin binder on improving ion permeability and reducing resistance, the use of a water-soluble polymer binder that coats the surfaces of the inorganic particles is preferable because it does not fill the voids in the porous layer, and binding properties can be imparted by adding a small amount of resin binder, and ion permeation is not inhibited.

[0033] Furthermore, by optimizing the particle size distribution of fillers such as inorganic particles as described above, the coating density of the porous layer can be reduced, and / or the resistance of the multilayer porous film can be reduced by adjusting the amount of resin binder used.

[0034] From the above viewpoint, the multilayer porous membrane according to this embodiment tends to improve ion permeability and facilitate realization of low resistance. This tendency is remarkable, for example, in resistance measurement performed in a low-temperature environment such as a temperature of around 0°C.

[0035] Furthermore, in this embodiment, from the viewpoint of achieving high strength in addition to high light transmittance, high heat resistance, low resistance, and thin film, the basis weight (g / m 2 ) (hereinafter referred to as the basis weight converted puncture strength) is 85gf / (g / m 2 ) or more, i.e., 0.833N / (g / m 2 ) or more was found. 2 ) or more achieves high strength, which in turn contributes to preventing breakage during battery production and maintaining the impact resistance of the battery.

[0036] From the viewpoint of realizing high light transmittance, high heat resistance, low resistance, and thin film of the multilayer porous film, the particle size or particle size distribution of the inorganic particles contained in the porous layer, for example, the average particle size D 50 , particle size D 90 , and particle size D 10 , D 90 / D 50 , D 50 / D 10 It is preferable to specify 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 substrate layer (the ratio of light transmittance 多孔層 / PO基材層@550nm ) is specified to be greater than or equal to 0.4 and less than 1.0.

[0037] 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 a PO substrate. Generally, a white LED is used as a light source in inspecting separators for non-aqueous electrolyte batteries, and the wavelength of 550 nm is near the central wavelength of the wavelength range of the white LED.

[0038] 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 since it is thin, has high heat resistance and low resistance, it can improve the battery characteristics of a non-aqueous electrolyte battery, such as energy density, capacity, output, and cycle characteristics.

[0039] The multilayer porous membrane according to this embodiment can be provided, but is not limited to, by, for example, reducing the particle size of fillers such as inorganic particles in a coating material for constituting the porous layer, adjusting the particle size distribution or aspect ratio, adjusting the volume fraction of a resin binder, or optimizing the amount of water-soluble polymer binder added in the manufacturing process of a PO substrate layer, a multilayer porous membrane, or a separator, or in the process of arranging a porous layer on a PO substrate layer, and thus a thin coating film that can achieve both light transparency and heat resistance can also be realized.

[0040] The multilayer porous membrane according to this embodiment is preferably one in which a porous layer is formed by applying a slurry containing inorganic particles to the surface of a polyolefin substrate layer, from the viewpoint of efficiently preventing relaxation of residual stress caused by the stretching step in the separator molding process. The structure of the multilayer porous membrane may have a porous layer on one or both sides of the PO substrate layer, and examples thereof include a two-layer structure including a first porous layer containing inorganic particles and a PO substrate layer, or a three-layer structure including, in order, a first porous layer, a PO substrate layer, and a second porous layer containing inorganic particles.

[0041] The multilayer structure is not limited to a two-layer structure of a first porous layer-PO substrate layer or a three-layer structure of a first porous layer-PO substrate layer-second porous layer, and one or more additional layers may be formed, as desired, between the first porous layer and the PO substrate layer, between the second porous layer and the PO substrate layer, or on at least one surface or the outer surface of the multilayer porous membrane. Examples of the additional layer include an additional PO substrate layer, an additional porous layer containing inorganic particles and a binder polymer, a resin layer containing 50% by mass or more of a resin other than polyolefin (PO), and a thermoplastic polymer-containing layer containing a binder component having an adhesive function such as a thermoplastic polymer.

[0042] The components of the multilayer porous membrane according to this embodiment will be described below.

[0043] <Porous layer> The porous layer is a layer laminated on at least one surface of the PO substrate layer and contains inorganic particles. The porous layer may optionally contain a water-soluble polymer such as a water-soluble polymer binder, a binder other than the water-soluble polymer binder, a dispersant, etc. The porous layer is preferably formed by applying a slurry containing inorganic particles to the surface of the polyolefin substrate layer. The formation method can be selected from coaters, inkjet printing, electrospinning, etc., as long as the object of the present invention is achieved.

[0044] The thickness (T) of the porous layer per at least one side of the PO substrate layer is preferably within the range of 0.1 μm≦T≦3.0 μm, since a thin layer can be achieved with high heat resistance and low resistance, thereby improving the characteristics of the nonaqueous electrolyte battery. From the same viewpoint, the thickness (T) of the porous layer per at least one side of the PO substrate layer is more preferably 2.0 μm or less, even more preferably 1.50 μm or less, and particularly preferably 1.00 μm or less, with the lower limit being preferably 0.10 μm or more, and more preferably 0.50 μm or more.

[0045] The thickness T of the porous layer described above may include cases where the porous layer is formed on at least one side of the PO substrate layer and cases where the porous layer is formed on both sides of the PO substrate layer. When the porous layer is formed on both sides of the PO microporous membrane, the total thickness of the porous layer preferably falls within the above-mentioned range. In any case, the total thickness (TT) of the porous layer is within the range of 0.1 μm≦TT≦3.0 μm from the viewpoints of achieving a thin layer, high heat resistance, and low resistance, and also improving the characteristics of the nonaqueous electrolyte battery. The lower limit of the total thickness (TT) of the porous layer is preferably greater than 0.1 μm, more preferably 0.2 μm or more, and even more preferably 0.5 μm or more, from the viewpoints of maintaining or improving heat resistance. The upper limit of the total thickness (TT) of the porous layer is preferably 3.0 μm or less from the viewpoints of maintaining light transmittance, maintaining ion permeability, improving battery capacity, and suppressing water content.

[0046] (Inorganic particles) Average particle size of inorganic particles D 50 0.05μm≦D 50 The smaller the average particle diameter D of the inorganic particles is within the range of <0.30 μm, the easier it is to achieve high light transmittance, high heat resistance, low resistance, thin film properties, and high strength of the multilayer porous film. 50 The lower limit of the average particle size D of the inorganic particles is preferably more than 0.05 μm, more preferably 0.06 μm or more, and even more preferably 0.07 μm or more, from the viewpoints of maintaining or improving ion permeability and suppressing an increase in viscosity of a slurry containing the inorganic particles. 50 The upper limit of the thickness is preferably 0.29 μm or less, more preferably less than 0.20 μm, from the viewpoint of maintaining light transmittance and heat resistance.

[0047] Inorganic particle diameter D 90 0.10μm≦D 90 The smaller the particle size D is within the range of ≦0.45 μm, the easier it is to achieve high light transmittance, high heat resistance, low resistance, thin film properties, and high strength of the multilayer porous film. 90From the viewpoint of maintaining or improving ion permeability, the lower limit of the particle diameter D of the inorganic particles is preferably more than 0.10 μm, more preferably 0.11 μm or more, and even more preferably 0.12 μm or more. 90 From the viewpoint of maintaining light transmittance and heat resistance, the upper limit of is preferably less than 0.45 μm, more preferably 0.44 μm or less, even more preferably less than 0.35 μm, and particularly preferably 0.25 μm or less.

[0048] Inorganic particle diameter D 10 From the viewpoint of high light transmittance, high heat resistance, and low resistance, the particle diameter D of the inorganic particles is preferably 0.01 μm or more and 0.20 μm or less. 10 The lower limit of the particle diameter D of the inorganic particles is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.04 μm or more, from the viewpoints of maintaining or improving ion permeability and suppressing an increase in viscosity of a slurry containing the inorganic particles. 10 The upper limit of 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, from the viewpoint of maintaining light transmittance and heat resistance.

[0049] The particle size, average particle size and particle size distribution of the inorganic particles in the porous layer must satisfy the following relationship from the viewpoint of high light transmittance: D 50 <0.20 μm; and D 90 <0.35 μm It is preferable that the following is satisfied.

[0050] The particle size, average particle size and particle size distribution of the inorganic particles in the porous layer are determined based on the following formulas (1) and (2) from the viewpoint of achieving both high light transmittance and high heat resistance: 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.

[0051] Inorganic particle D 90 / D50 From the viewpoint of maintaining 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.

[0052] Inorganic particle D 50 / D 10 From the viewpoint of maintaining 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 10 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.

[0053] 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, during the process of disposing the porous layer on the PO substrate layer or during the process of manufacturing the separator.

[0054] 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.

[0055] The material of the inorganic particles used in the porous layer is not particularly limited, but may be an inorganic filler for the porous layer, and is preferably one that has high heat resistance and electrical insulation properties and is electrochemically stable within the range of use of the nonaqueous electrolyte battery.

[0056] 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 being more preferred. The inorganic particles may be used alone or in combination.

[0057] 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.

[0058] The aspect ratio of the inorganic particles is preferably 1 or more and 3 or less from the viewpoint of high heat resistance and low resistance of the multilayer porous membrane. 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 viewpoint of suppressing the moisture content 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).

[0059] The lower limit of the BET specific surface area of ​​inorganic particles is 7.00 m 2 / g or more, and 9.00m 2 / g or more is more preferable, and 10.00m 2 / g or more is more preferable, and 20.0m 2 It is particularly preferable that the BET specific surface area of ​​the inorganic particles is 7.00 m / g or more. 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. The upper limit of the BET specific surface area of ​​the inorganic particles is 200 m from the viewpoint of suppressing the water content. 2 / g or less, and 100m 2 / g or less is more preferable, and 70m 2 / g or less is more preferable, 2 It is particularly preferable that the saturation coefficient is 1 / g or less.

[0060] The mass ratio of inorganic particles in the porous layer (W i ) is preferably 90% or more, more preferably 92% or more, and even more preferably 94% or more. i When the W content is 90% or more, the proportion of other components, such as resin binders, is relatively low, which suppresses an increase in the air permeability of the porous layer relative to the PO substrate layer and battery resistance, thereby improving battery characteristics. i The upper limit is not particularly limited, but may be, for example, less than 100% or 99% or less.

[0061] The volume fraction of inorganic particles in the porous layer (V i ) is preferably 80% or more, more preferably 83% or more, even more preferably 85% or more, and particularly preferably 87% or more, based on 100% by volume of the volume of the porous layer excluding voids. i When the ratio is 80% or more, the ratio of inorganic particles to other components, such as resin binders, increases, which can suppress an increase in the air permeability of the PO substrate layer due to the porous layer and reduce the electrical resistance of the multilayer porous membrane. iThe upper limit of is not limited, but may be, for example, 95% or less, 93% or less, 92% or less, or 91% or less.

[0062] (resin binder) From the viewpoint of maintaining heat resistance and ion permeability, the porous layer preferably contains a water-soluble polymer as a resin binder, more preferably a water-soluble polymer binder, and may optionally contain a binder other than the water-soluble polymer binder, a dispersant, and the like.

[0063] From the viewpoints of high light transmittance, high heat resistance, and low resistance, the volume fraction of the water-soluble polymer 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 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.

[0064] 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.

[0065] 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 non-particulate.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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, even more preferably the content of (meth)acrylic acid monomer units is 10.0 mass% or less, even more preferably in the range of 0.0 mass% to 5.0 mass%, and particularly preferably more than 0.0 mass% to 2.0 mass% or less.

[0073] The (meth)acrylic acid monomer units can be introduced by (co)polymerization using, for example, monomers such as acrylic acid and methacrylic acid.

[0074] 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% to 20.0% by mass, and more preferably more than 0.0% by mass and less than 20.0% by mass.

[0075] 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.

[0076] From the viewpoint of the effects of the present invention, the (meth)acrylic acid ester monomer preferably does not contain a hydroxyl group.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] From the viewpoints of high light transmittance, high heat resistance, and low resistance, the volume fraction Va of 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 voids is 100% by volume. From the viewpoint of maintaining heat resistance, the lower limit of the volume fraction of the water-soluble polymer binder in the porous layer is preferably 0.5% by volume or more, more preferably 1.0% by volume or more, and even more preferably 2.0% by volume or more. From the viewpoint of maintaining ion permeability, the upper limit of the volume fraction of the water-soluble polymer binder 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.

[0081] - 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 particulate. Furthermore, the glass transition temperature (Tg) of the water-insoluble polymer binder is preferably 30°C or lower from the viewpoint of binding inorganic particles and improving heat resistance.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] The average particle size (D 50 ) is preferably adjusted in accordance with the reduction in particle size of the inorganic particles, and its upper limit is preferably 0.15 μm or less, more preferably 0.10 μm or less, even more preferably 0.08 μm or less, and particularly preferably 0.06 μm or less. Its lower limit is not particularly limited and may be, for example, 0.01 μm or more.

[0087] Inorganic particle D 50 D of water-insoluble polymer binders 50 From the viewpoint of high peel strength, the ratio is preferably 1.0 or less, more preferably 0.6 or less, and particularly preferably 0.4 or less. The lower limit is preferably 0.2 or more.

[0088] From the viewpoints of thermal shrinkage suppression ability and permeability, the volume fraction Vb of the water-insoluble polymer binder in the porous layer is preferably 1% by volume or more, and the upper limit is preferably 20% by volume or less, more preferably 15% by volume or less, and even more preferably 10% by volume or less, where the volume of the porous layer excluding voids is taken as 100% by volume.

[0089] From the viewpoint of realizing high heat resistance of the porous layer by controlling the binding points of the inorganic particles while suppressing the binder amount, it is preferable that the volume fraction Vb of the water-insoluble polymer binder is higher than the volume fraction Va of the water-soluble polymer binder (i.e., the ratio Vb / Va > 1.0), and the lower limit of the ratio Vb / Va is more preferably 2.0 or more, even more preferably 4.0 or more, and particularly preferably 5.0 or more. The upper limit of the ratio Vb / Va is preferably 15.0 or less, more preferably 10 or less, and even more preferably 7 or less.

[0090] 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:

[0091] 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.

[0092] (dispersant) The porous layer may optionally contain a dispersant in addition to the inorganic particles and resin binder. In this embodiment, the water-soluble polymer may contain a dispersant. Examples of dispersants include polycarboxylates such as polyacrylates, sulfonates, and polyoxyethers. Examples of polyacrylates include sodium polyacrylate. The content of the dispersant is preferably 0.5% by volume or more, more preferably 1.0% by volume or more, and even more preferably 1.5% by volume or more, based on 100% by volume of the volume of the porous layer excluding the voids. Furthermore, the content of the dispersant is preferably 10.0% by volume or less, more preferably 5.0% by volume or less, and even more preferably 2.0% by volume or less, based on 100% by volume of the volume of the porous layer excluding the voids.

[0093] (Physical properties of porous layers) The air permeability of the porous layer is 50sec / 100cm 3 Preferably, it is less than 40 sec / 100 cm 3 Less than 30 sec / 100 cm, more preferably 3 Below 20 sec / 100 cm, especially preferred 3The lower limit is preferably 0 sec / 100 cm 3 More than 1 sec / 100 cm 3 More preferably, 5 sec / 100 cm 3 The air permeability of the porous layer is 50 sec / 100 cm 3 By keeping the thickness below 100 nm, ion permeability is maintained, electrical resistance is reduced, and the characteristics of the non-aqueous electrolyte battery tend to be improved.

[0094] The layer density in the porous layer has a lower limit of 1.0 g / (m 2 ·μm) or more, and more preferably 1.3 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 1.0 g / (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.

[0095] The 180° peel strength of the porous layer from the multilayer porous membrane or PO substrate layer is preferably 280 to 330 gf / cm, more preferably 300 to 320 gf / cm. 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.

[0096] The 90° peel strength of the porous layer from the multilayer porous membrane or PO substrate layer is preferably 10 to 30 gf / cm, more preferably 15 to 25 gf / cm, from the viewpoints of adhesion to the electrode and suppression of thermal shrinkage. 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 an angle of 90° with the substrate.

[0097] The upper limit of the average pore size of the porous layer 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 0.08 μm or less, and the lower limit is preferably 0.01 μm or more.

[0098] <Polyolefin base layer> The PO substrate layer may be in any form as long as it contains a polyolefin as a main component and functions as a porous layer or a separator substrate, and may be formed, for example, as a microporous membrane containing a polyolefin as a main component (hereinafter sometimes abbreviated as a "PO microporous membrane") or as a monolayer containing a polyolefin as a main component. From the viewpoints of productivity and the process for disposing the porous layer, the PO substrate layer is preferably a PO microporous membrane.

[0099] The microporous polyolefin membrane contains a polyolefin, and is preferably composed of a 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 a microporous polyolefin membrane usable as a separator, 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.

[0100] 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).

[0101] 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.

[0102] 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).

[0103] Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene.

[0104] Specific examples of the copolymer of ethylene and propylene include an ethylene-propylene random copolymer and an ethylene-propylene rubber.

[0105] When the polyolefin (PO) contained in the PO base layer contains polyethylene (PE), the PE content is 50% by mass or more and 100% by mass or less, based on the total mass of the resin components constituting the PO base layer, and from the viewpoint of fuse characteristics or meltdown characteristics, it 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.

[0106] When the PO contained in the PO base layer 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 base layer, and from the viewpoint of melt viscosity and fuse characteristics, it 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.

[0107] In addition to the polyolefins listed above, the PO substrate layer may further contain resins such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polyvinylidene fluoride, nylon, and polytetrafluoroethylene.

[0108] From the viewpoint of suppressing high viscosity of the PO resin composition during film formation and suppressing the occurrence of defective products, the melt index (MI) of the PO base layer at 190°C has a lower limit of preferably 0.01 g / 10 min or more, and more preferably 0.05 g / 10 min or more, and an upper limit of 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.

[0109] The puncture strength of the PO substrate layer in terms of basis weight is set to 0.833 N / (g / m) from the viewpoints of preventing breakage during the manufacture of non-aqueous electrolyte batteries and maintaining the impact resistance of non-aqueous electrolyte batteries. 2 ), and more preferably 0.84 N / (g / m 2 ) or more, more preferably 0.90 N / (g / m 2 ) or more, particularly preferably 1.00 N / (g / m 2 ) or more. From the viewpoint of improving the safety of non-aqueous electrolyte batteries while maintaining the strength of the PO microporous membrane, the puncture strength converted into basis weight is 1.96 N / (g / m 2 ) or less.

[0110] The puncture strength not converted into basis weight of the PO substrate layer (hereinafter simply referred to as puncture strength) is preferably 100 gf or more, i.e., 0.98 N or more, more preferably 1.47 N or more, and even more preferably 1.96 N or more, from the viewpoint of suppressing breakage and improving heat resistance, and is preferably 4.90 N or less, more preferably 3.92 N or less, from the viewpoint of improving the safety of non-aqueous electrolyte batteries while maintaining membrane strength.

[0111] 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.

[0112] The thickness (TB) of the PO substrate layer is preferably less than 8 μm, more preferably 7 μm or less, and even more preferably 6 μm or less from the viewpoint of maintaining ion permeability, and is particularly preferably 5 μm or less from the viewpoint of achieving both ion permeability and the capacity of the nonaqueous electrolyte battery. The lower limit of TB is preferably 2 μm or more, more preferably 3 μm or more, from the viewpoint of maintaining heat resistance. The thickness TB of the PO substrate layer can be adjusted, for example, by controlling the die lip gap, the draw ratio in the drawing step, etc.

[0113] The porosity of the PO base layer is preferably 20% or more, more preferably 30% or more, and even more preferably 32% 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 the base layer. The porosity of the PO base layer 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.

[0114] The air permeability of the PO substrate layer is preferably 10 sec / 100 cm from the viewpoint of preventing excessive current from flowing between the multiple electrodes through the PO substrate layer. 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 Below 150 sec / 100 cm, particularly preferably 3 is.

[0115] The viscosity-average molecular weight (Mv) of the PO substrate layer is preferably 400,000 or more, more preferably 450,000 or more, and even more preferably 500,000 or more, and is preferably 1,300,000 or less, more preferably 1,200,000 or less, and even more preferably 1,150,000 or less. When the Mv of the PO substrate layer is 400,000 or more, the melt tension during melt molding is increased, improving moldability, and polymer entanglement tends to result in high film strength. When the Mv of the PO substrate layer is 1,300,000 or less, the raw materials are easily melt-mixed uniformly, which tends to improve sheet moldability, particularly thickness stability. Furthermore, when used as a separator for a nonaqueous electrolyte battery, pores tend to be easily blocked at elevated temperatures, resulting in good fuse function.

[0116] The PO substrate layer preferably has low electronic conductivity, high ionic conductivity, high resistance to organic solvents, and fine pore size. The PO substrate layer can be used alone as a separator for a lithium ion secondary battery, and is particularly suitable for use as a separator for a nonaqueous electrolyte lithium ion secondary battery.

[0117] <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.

[0118] (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 acid esters, methacrylic acid 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 a hydroxyl group, sulfonic acid group, carboxyl group, amide group, or cyano group can also be used as monomers used in synthesizing the thermoplastic polymer.

[0119] 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.

[0120] (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.

[0121] 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.

[0122] 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").

[0123] 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.

[0124] (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.

[0125] 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).

[0126] 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.

[0127] (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.

[0128] 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.

[0129] 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, the monomer composition of which is typically 30 to 90 mass% vinylidene fluoride, 50 to 9 mass% tetrafluoroethylene, and 20 to 1 mass% hexafluoropropylene. These fluororesin particles may be used alone or in combination of two or more.

[0130] 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.

[0131] The monomer having a hydroxy group is not particularly limited, but examples thereof include vinyl monomers such as penteneol.

[0132] 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.

[0133] The monomer having an amino group is not particularly limited, but examples thereof include 2-aminoethyl methacrylate.

[0134] 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.

[0135] The monomer having an amide group is not particularly limited, but examples thereof include acrylamide (AM), methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide.

[0136] The monomer having a cyano group is not particularly limited, but examples thereof include acrylonitrile (AN), methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate.

[0137] 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.

[0138] (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.

[0139] 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.

[0140] Specifically, it is determined by the intersection of a line extending from the low-temperature baseline to the high-temperature side of the DSC curve with 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] The "peak" refers to the portion of a DSC curve from when the curve leaves the baseline until when it returns to the baseline.

[0145] "Baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs in the test specimen.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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 give 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 give a polymer with a Tg of about -50°C, will have a low Tg.

[0151] 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.}

[0152] (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.

[0153] 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.

[0154] 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.

[0155] (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.

[0156] 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.

[0157] Average particle size D of granular thermoplastic polymer P From 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.

[0158] (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 2More 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 0.08 g / m 2 A range exceeding this is preferred.

[0159] (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.

[0160] The term "dot-like" means 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.

[0161] 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 substrate layer or electrode, improving the strength of the multilayer porous membrane, or suppressing an increase in air permeability to the PO substrate layer, 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, particularly preferably 500 μm or less, and most preferably 300 μm.

[0162] The distance between dots 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 substrate layer or electrode, improving the strength of the multilayer porous membrane, or suppressing an increase in air permeability to the PO substrate layer, 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.

[0163] 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

[0164] 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.

[0165] The shape or total coverage area ratio of the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration of the coating liquid, the coating amount of the polymer solution, the coating method, and the coating conditions.

[0166] <Characteristics of multilayer porous membrane> The air permeability of the multilayer porous membrane is set at 200 sec / 100 cm from the viewpoint of low resistance. 3 The upper limit of the air permeability of the multilayer porous membrane is more preferably 200 sec / 100 cm from the viewpoint of maintaining ion permeability. 3 Less than 180sec / 100cm, more preferably less than 180sec / 100cm 3 More preferably, 150 sec / 100 cm or less 3 The air permeability of the multilayer porous membrane is preferably 0 sec / 100 cm 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 More than 10 sec / 100 cm 3 That's all.

[0167] The multilayer porous membrane has both the following characteristics in terms of low resistance and maintaining or improving ion permeability: ·Air permeability of porous layer ≦50sec / 100cm 3 Multilayer porous membrane air permeability ≦200sec / 100cm 3 It is preferred that the compound has the following structure:

[0168] The heat shrinkage rate (150°C heat shrinkage rate) of the multilayer porous membrane when left in an atmosphere at 150°C for 1 hour is preferably 10% or less, more preferably 5% or less, even more preferably 2% or less, and particularly preferably 1% or less, in both the MD and TD directions. 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 the MD and TD directions under dry conditions after the multilayer porous membrane is left 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 in an oven for 1 hour.

[0169] The upper limit of the heat shrinkage rate of the multilayer porous membrane at 130°C (130°C heat shrinkage rate) in both the MD and TD directions 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 the MD and TD directions, 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 130°C heat shrinkage rate can be measured and calculated under dry conditions after leaving the multilayer porous membrane in an oven for 1 hour in both the MD and TD directions.

[0170] 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.

[0171] The total thickness of the multilayer porous membrane is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 4 μm or more in order to ensure voltage resistance. The total thickness of the multilayer porous membrane is preferably 11 μm or less because this prevents the capacity of the nonaqueous electrolyte battery in which the multilayer porous membrane is mounted from deteriorating, more preferably 9 μm or less, even more preferably 8 μm or less, and particularly preferably 7 μm or less.

[0172] In the multilayer porous membrane, the ratio of the air permeability of the porous layer to the air permeability of the PO substrate layer (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 PO substrate layer, 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 ensuring the safety of the nonaqueous electrolyte battery by preventing excessive current from flowing between the multiple electrodes via the multilayer porous membrane.

[0173] 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.

[0174] <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 disposing a porous layer on at least one surface of the microporous PO membrane.

[0175] 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.

[0176] 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.

[0177] (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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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 or TD.

[0196] 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.

[0197] From the viewpoint of the effects of the PO base layer according to this embodiment, the thickness of the microporous PO membrane produced as described above is preferably 8 μm or less, and more preferably 7 μm or less.

[0198] (Porous layer arrangement method) The porous layer can be disposed on at least one surface of the microporous polypropylene membrane by any known method, such as disposing, coating, laminating, or extruding. 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.

[0199] 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.

[0200] In the process of disposing the porous layer, the particle size D of the inorganic particles contained in the porous layer described above 50 , D 10 and D 90 , and particle size distribution D 90 / D 50 and D 50 / D 10 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.

[0201] The average particle size (D 50 ) is preferably adjusted in accordance with the reduction in particle size of the inorganic particles, and its upper limit is preferably 0.15 μm or less, more preferably 0.10 μm or less, even more preferably 0.08 μm or less, and particularly preferably 0.06 μm or less. Its lower limit is not particularly limited and may be, for example, 0.01 μm or more.

[0202] When the total of the inorganic particles, resin binder, and dispersant contained in the coating liquid or slurry is taken as 100 volume %, the lower limit of the inorganic particle ratio is preferably 80% or more, more preferably 83% or more, and even more 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 percentage 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 binders, 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. When the porous layer suppresses an increase in the air permeability of the PO microporous membrane, reducing the electrical resistance of the multilayer porous membrane.

[0203] 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 90% or more, more preferably 92% or more, and even more preferably 94% or more, and the upper limit is preferably less than 100%, more preferably 99% or less.

[0204] In forming the 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, the ratio of the volume fraction Vb' of the water-insoluble polymer binder to the volume fraction Va' of the water-soluble polymer binder contained in the slurry or coating liquid (Vb' / Va') preferably exceeds 1.0, and the lower limit of the ratio Vb' / Va' is more preferably 2.0 or more, even more preferably 4.0 or more, and particularly preferably 5.0 or more. The upper limit of the ratio Vb' / Va' is preferably 15.0 or less, more preferably 10 or less, and even more preferably 7 or less.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] 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 can achieve the required layer thickness or coating area, and can be selected from coaters, inkjet printing, electrospinning, etc. within the scope of achieving the objects of the present invention. Examples include gravure coater, small-diameter gravure coater, reverse roll coater, transfer roll coater, kiss coater, dip coater, knife coater, air doctor coater, blade coater, rod coater, squeeze coater, cast coater, die coater, screen printing, spray coating, inkjet printing, electrospinning, etc.

[0210] In one embodiment, the inorganic particle-containing slurry is applied to the PO microporous membrane so that the total coating thickness of the porous layer is preferably 3.0 μm or less, and the lower limit thereof is preferably 0.1 μm or more, from the viewpoints of suppressing an increase in the air permeability of the PO microporous membrane, forming a strong porous layer, thinning the resulting multilayer porous membrane or separator, high heat resistance (i.e., ability to suppress thermal shrinkage), and light transmittance.

[0211] In one embodiment, the inorganic particle-containing slurry is applied to the PO microporous membrane so that the ratio of light transmittance at a wavelength of 550 nm before and after coating is preferably 0.4 or more and less than 1.0, from the viewpoints of thinning, heat resistance (i.e., ability to suppress thermal shrinkage), and light transmittance of the resulting multilayer porous membrane or separator.

[0212] 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.

[0213] 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. Some 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 shrinkage stress in the MD direction.

[0214] (Method for forming a thermoplastic polymer-containing layer) The method for forming a thermoplastic polymer-containing layer on a PO microporous membrane or porous layer serving as a PO base layer is not particularly limited, and examples include a method of applying a coating liquid containing a thermoplastic polymer to the PO microporous membrane or porous layer.

[0215] 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 and 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.

[0216] 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.

[0217] 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.

[0218] 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.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] The drying rate of the coating is 0.03 g / (m 2 ·s) or more, and 0.05g / (m 2 ·s) or more, 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.

[0223] <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 properties of the nonaqueous electrolyte battery, such as energy density, capacity, output, and cycle characteristics. 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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.

[0228] 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.

[0229] 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.

[0230] 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.

[0231] 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]

[0232] 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.

[0233] Testing and Evaluation Methods

[0234] <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 substrate layers was calculated using 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

[0235] <Thickness (μm) of polyolefin substrate layer, multilayer porous membrane, and porous layer> The thicknesses of the polyolefin substrate layer 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. In addition, 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.

[0236] <Melt index (MI) of polyolefin base layer (g / 10 min)> The melt index (MI) of the polyolefin substrate layer (PO substrate layer) 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.

[0237] <Aspect ratio of inorganic particles in the porous layer> The cross section of the multilayer porous membrane was photographed at a magnification of 10,000 times using a scanning electron microscope (SEM) "HITACHI (trademark) S-4800" (manufactured by Hitachi High-Technologies), and the aspect ratio was determined by image processing of the inorganic particles in the porous layer. Even when inorganic particles were bonded to each other, those for which the length and width of each inorganic particle were clearly recognizable were selected, and the aspect ratio was calculated based on these. Specifically, 10 particles for which the length and width were clearly recognizable were selected, and the average value obtained by dividing the long axis of each inorganic particle by the length of its short axis was used as the aspect ratio. If there were fewer than 10 particles in one field of view with clearly recognizable length and width, 10 particles were selected from images of multiple fields of view.

[0238] <Particle size, average particle size and particle size distribution of inorganic particles> The particle size, average particle size, and particle size distribution 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.

[0239] The inorganic particles were redispersed from the porous layer of the multilayer porous membrane obtained in Examples and Comparative Examples, and subjected to the same laser particle size distribution measurement as above. Specifically, 100 cm of inorganic particles were redispersed in 10 mL of an aqueous solution prepared by adjusting polycarboxylate ammonium ("SN Dispersant 5468" manufactured by SAN NOPCO) as a dispersant to 1 wt% in terms of solid content. 2 After immersing the multilayer porous membrane cut into a size of D for 24 hours, the porous layer was scraped off with a spatula or the like and used as a sample. The sample was subjected to ultrasonic irradiation with an ultrasonic irradiator to redisperse the inorganic particles. If two or more peaks appear due to aggregation of the redispersed particles, the peak with the smallest particle size is selected as the peak with the smallest particle size. 50 , D 10 , D 90 It was confirmed that the particle size, average particle size, and particle size distribution of the inorganic particles redispersed in this manner were approximately the same as the particle size, average particle size, and particle size distribution of the inorganic particle dispersion or slurry coating liquid.

[0240] <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.

[0241] <Air permeability (sec / 100cm 3 ), and the air permeability ratio of the multilayer porous membrane to the polyolefin substrate layer > The air permeability of the multilayer porous membrane and the air permeability of the polyolefin substrate layer, where the air resistance in accordance with JIS P-8117 was used as the air permeability, were measured in accordance with JIS P-8117 using a Gurley air permeability meter "G-B2 (trademark)" manufactured by Toyo Seiki Co., Ltd., by measuring the air resistance of the multilayer porous membrane and the polyolefin substrate layer in an atmosphere of 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 substrate layer from the air permeability of the multilayer porous membrane. Air permeability increase rate = Air permeability of porous layer / Air permeability of polyolefin base layer 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.

[0242] <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, a porous layer portion of the multilayer porous membrane is scraped off from a glass plate using a spatula, 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.

[0243] <Porosity (%)> A 10cm x 10cm square sample was cut from the PO substrate layer 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

[0244] <Piercing strength (N) and area weight conversion piercing strength (N / (g / m 2 ))> Using a Kato Tech handy compression tester "KES-G5 (trademark)," the PO substrate layer 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 PO substrate layer 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.

[0245] <Dry heat shrinkage rate at 150℃ (%)> The multilayer porous membrane was cut into a sample of 100 mm in the MD direction and 100 mm in the TD direction, 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 thermal shrinkage was calculated using the following formula. Measurements were performed in both the MD and TD directions, and the average of both values ​​was expressed as the thermal shrinkage. Heat shrinkage rate (%) = {(100 - length after heating) / 100} x 100

[0246] <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

[0247] In the above measurement of light transmittance, a PO substrate layer and a multilayer porous film are used as samples, and the light transmittance (%) at a wavelength of 550 nm can be obtained for each.

[0248] (Ratio of light transmittance of the multilayer porous film to that of the PO substrate layer at a wavelength of 550 nm) Based on the measurement of the above light transmittance, the light transmittance of the PO base material layer before coating and the multi-layer porous film after coating were measured respectively. For the light transmittance at a wavelength of 550 nm, the ratio of the light transmittance of the multi-layer porous film at a wavelength of 550 nm to the light transmittance of the PO base material at a wavelength of 550 nm was calculated based on the following formula. Ratio of light transmittance = Light transmittance of multi-layer porous film at 550 nm (%) / Light transmittance of PO base material layer at 550 nm (%)

[0249] In addition, the porous layer was removed from the multi-layer porous films obtained in the examples and comparative examples, and the ratio of the light transmittance was calculated in the same manner as above. Specifically, a multi-layer porous film cut into a size of 100 cm 2 was immersed in 10 mL of water for 24 hours, and then the porous layer was scraped off with a spatula or the like, used as a sample, and ultrasonic irradiation was performed with an ultrasonic irradiator to remove the porous layer. The light transmittance of the PO base material layer after removing the porous layer and the light transmittance of the multi-layer porous film before removal were measured respectively. It was confirmed that the ratio of the light transmittance of the multi-layer porous film at a wavelength of 550 nm to the light transmittance of the PO base material layer calculated in this way was generally the same as the ratio of the light transmittance at a wavelength of 550 nm of the multi-layer porous film to the light transmittance of the PO base material at a wavelength of 550 nm.

[0250] <Ratio of coating thickness of porous layer to puncture strength of PO base material layer> According to the above method, the puncture strength of the PO base material layer and the coating thickness of the porous layer on the PO base material layer were measured respectively, and the ratio of the coating thickness of the porous layer to the puncture strength of the PO base material layer was calculated based on the following formula. Ratio of coating thickness of porous layer to puncture strength of PO base material layer (μm / gf) = Coating thickness of porous layer (μm) / Puncture strength of PO base material layer (gf)

[0251] <Measurement of foreign matter detection rate> In a multi-layer porous film having a porous layer formed on a PO base material layer, for foreign matters (for example, unmelted resin, metal powder, carbide, etc.) on the PO base material layer, the inspection range was set to a width of 1000 to 1300 mm and a length of 1000 m, and inspection was performed using an optical foreign matter inspection device, and the detection rate of foreign matters was calculated and evaluated according to the following criteria. (Evaluation criteria) ◎: Foreign object detection rate is 95% to 100%. ○: Foreign matter detection rate is 90% or more but less than 95% △: Foreign matter detection rate is 85% or more but less than 90%. ×: Foreign matter detection rate is less than 85%

[0252] <Resistance measurement of multilayer porous membrane at 0°C> To measure the resistance of the multilayer porous film at a temperature of 0°C, the following coin cell components and an electrolyte prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate / ethyl methyl carbonate (EC / EMC) = 3 / 7 (volume ratio) were used. (Coin cell material) Using a CR2032 case (SUS), a CR2032 gasket (PP), a CR2032 wave washer (SUS), a spacer Φ16 x 1.0 mm (SUS), and a CR2032 cap, multiple multilayer porous membranes punched to Φ19 mm were stacked on top of each other in a coin cell case so that the total thickness was 25 μm to 60 μm, and a gasket was placed on top. 0.10 mL of the above electrolyte solution was dropped onto the center of the multilayer porous membrane. I stacked the spacer, wave washer, and cap and crimped them together using a crimping machine for CR2032.

[0253] Next, the coin cell member was attached to a coin cell connecting jig, and the jig was placed in a constant temperature bath at 0°C. Measurement was carried out under the following conditions using a potentiogalvanostat and a frequency response analyzer manufactured by Toyo Corporation to measure the resistance of the multilayer porous film. Amplitude of modulation potential: 10 mV Frequency range: 10 5 ~10 6 Hz Number of measurement points: 30 / Decade The resistance value per multilayer porous membrane is calculated based on the effective electrode area of ​​Φ16 (= 2 cm 2 ) was calculated using the following formula: Separator resistance (Ω cm 2 ) = Measured value / Number of multilayer porous membranes used for measurement × 2

[0254] Furthermore, the resistance of the multilayer porous film was evaluated based on the rate of increase in resistance relative to the resistance value of the PO substrate layer alone, according to the following criteria. (Evaluation criteria) ◎: Resistance increase rate is less than 20%. ○: Resistance increase rate is 20% or more and less than 35% △: Resistance increase rate is 35% or more but less than 40% ×: Resistance increase rate is 40% or more

[0255] <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.

[0256] The test battery was designed to have a capacity of 1 Ah.

[0257] 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.

[0258] (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 / 3A 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.

[0259] (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.

[0260] (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.

[0261] (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.

[0262] (Evaluation criteria for battery temperature rise test) ◎:Battery surface temperature 170℃ or higher, ○:Battery surface temperature 165℃ or higher, △:Battery surface temperature 160℃ or higher, ×: Battery surface temperature less than 160℃

[0263] Example 1 A polymer composition was prepared using a tumbler blender containing 46.5% by mass of homopolymer polyethylene (PE) with a viscosity average molecular weight (Mv) of 700,000, 46.5% by mass of homopolymer PE with a Mv of 300,000, and 7% by mass of homopolymer polypropylene (PP) with a Mv of 400,000. One part by mass of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant to 99 parts by mass of the polymer composition, and the mixture was dry-blended again using the tumbler blender to obtain a polymer mixture. The resulting polymer mixture was purged with nitrogen and then 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.

[0264] The mixture was melt-kneaded, and the feeder and pump were adjusted so that the ratio of liquid paraffin to the total mixture to be extruded was 68% by mass (resin composition concentration: 32% by mass).

[0265] 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.

[0266] Next, the gel sheet was introduced into a simultaneous biaxial tenter stretching machine, where it was biaxially stretched, and then introduced into a methylene chloride tank and thoroughly immersed in methylene chloride to extract and remove the liquid paraffin. Thereafter, the methylene chloride was dried and removed to obtain a porous body.

[0267] The porous body was then introduced into a TD tenter and heat-set to obtain a polyolefin microporous membrane with a thickness (TB) of 6 μm as a PO substrate layer. The resin composition of the obtained PO substrate layer and the above measurement results are shown in Table 1.

[0268] Next, inorganic particles having the average particle size, particle size distribution, and aspect ratio shown in Table 1, a binder, a dispersant, and water were mixed so that the solid content concentration of the coating liquid was 40%, and the mixture was stirred and dispersed to prepare a coating liquid.

[0269] The surface of the PO substrate layer was subjected to a corona discharge treatment, and then a coating liquid was applied to the treated surface using a gravure coater. The coating liquid on the PO substrate layer was then dried at 60°C to remove water, and a first porous layer containing inorganic particles and having a thickness of 1.5 μm was formed on one side of the PO substrate layer, thereby obtaining 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 1.

[0270] <Examples 2 to 5, 9 to 10 and Comparative Examples 2 to 5> A multilayer porous membrane was formed in the same manner as in Example 1, except that the production conditions and physical properties of the PO substrate layer, 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 Table 1. The various properties of the obtained multilayer porous membrane and the battery including the same as a separator were evaluated by the above-mentioned methods. The evaluation results are shown in Table 1.

[0271] <Examples 6 to 8, 11, 14 to 24 and Comparative Example 1> A multilayer porous membrane was formed in the same manner as in Example 1, except that a polymer composition of 50% by mass of PE of a homopolymer with an Mv of 700,000 and 50% by mass of PE of a homopolymer with an Mv of 300,000 was used, and the physical properties of the PO substrate layer, the type of inorganic particles, the type of components of the porous layer, the coating liquid composition, and the coating conditions were set as shown in Table 1. The various properties of the obtained multilayer porous membrane and the battery including the same as the separator were evaluated by the above-mentioned methods. The evaluation results are shown in Table 1.

[0272] <Examples 12 and 13> A multilayer porous membrane was formed in the same manner as in Example 1, except that 100% by mass of polyethylene (PE), a homopolymer with an Mv of 1 million, was used, and the physical properties of the PO substrate layer, 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 Table 1. The various properties of the obtained multilayer porous membrane and the battery including the same as a separator were evaluated by the above-mentioned methods. The evaluation results are shown in Table 1.

[0273] The basis weight of the PO base layer was adjusted to the values ​​shown in each table by controlling the thickness of the gel sheet to be cast, the porosity and air permeability by controlling the biaxial stretching temperature and heat setting temperature, and the pin puncture strength and the pin puncture strength converted into basis weight by controlling the biaxial stretching temperature and biaxial stretching ratio.

[0274] In Examples 22 and 23, Comparative Examples 3 and 4, a first porous layer and a second porous layer containing inorganic particles were formed on both sides of the PO substrate layer.

[0275] [Table 1-1]

[0276] [Table 1-2]

[0277] [Table 1-3]

[0278] [Table 1-4]

Claims

1. A multilayer porous membrane in which a porous layer containing inorganic particles is laminated on at least one surface of a polyolefin substrate layer, The thickness of the polyolefin substrate layer is 8 μm or less, The polyolefin substrate layer has a puncture strength converted into basis weight of 85 gf / (g / m ２ ) and above, The average particle size D of the inorganic particles ５０ is 0.05 μm or more and less than 0.30 μm, Particle size D of the inorganic particles ９０ is 0.10 μm or more and 0.45 μm or less, The total thickness of the porous layer is 0.1 μm or more and 3.0 μm or less, 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 polyolefin substrate layer is 0.4 or more and less than 1.0; Multilayer porous membrane.

2. Particle size D of the inorganic particles １０ The multilayer porous membrane according to claim 1, wherein the thickness is 0.01 μm or more and 0.20 μm or less.

3. The porous layer has an air permeability of 50 sec / 100 cm ３ and the air permeability of the multilayer porous membrane is 200 sec / 100 cm or less. ３ The multilayer porous membrane according to claim 1 or 2, wherein:

4. The multilayer porous film according to claim 1 or 2, wherein the multilayer porous film has a light transmittance at a wavelength of 550 nm of 4.0% or more and less than 10.0%.

5. 3. The multilayer porous membrane according to claim 1, wherein the porous layer contains a water-soluble polymer in a volume fraction of 1% to 10%.

6. The multilayer porous membrane according to claim 1 or 2, wherein the inorganic particles have an aspect ratio of 1 or more and 3 or less.

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

8. 3. The multilayer porous membrane according to claim 1, wherein the ratio of the coating thickness of the porous layer to the pin puncture strength of the polyolefin substrate layer is less than 0.004 μm / gf.

9. The particle diameter of the inorganic particles is expressed by the following formulas (1) and (2): Equation (1): D ９０ / D ５０ ≤2.0 Equation (2): D ５０ / D １０ ≤2.0 The multilayer porous membrane according to claim 1 or 2, which satisfies the above.

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

11. 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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