Separator for power storage device and power storage device including same

Abstract

The present invention provides a separator for power storage devices, the separator comprising a base material 10 which is a polyolefin microporous membrane that contains a polyolefin as a main component, and a cover layer 20 which is arranged on at least one surface of the base material 10. With respect to this separator for power storage devices, the cover layer 20 contains an inorganic filler 1 and a thermoplastic polymer; the thermoplastic polymer forms particulate polymers 2 that protrude from an inorganic filler portion L1; and the coefficient of static friction of the cover layer 20 is 0.40 to 0.60.

Description

[Technical Field]

[0001] The present disclosure relates to a separator for an electricity storage device and an electricity storage device including the same. [Background technology]

[0002] Development of energy storage devices, typified by lithium-ion secondary batteries, is currently underway. Energy storage devices generally include a positive electrode, a negative electrode, and a microporous membrane separator between them. The separator functions to prevent direct contact between the positive and negative electrodes and to allow ions to pass through the electrolyte solution held within the micropores. Separators are required to have safety features, such as the ability to quickly stop the battery reaction in the event of abnormal heating (fuse characteristics) and the ability to maintain their shape even at high temperatures and prevent dangerous situations in which the positive and negative electrodes would directly react with each other (short-circuit resistance).

[0003] Non-aqueous secondary batteries such as lithium ion secondary batteries are available in various shapes, such as cylindrical, prismatic, and pouch shapes, depending on their applications. The manufacturing method for batteries varies depending on the shape of the battery. For example, a manufacturing method for a prismatic battery includes a step of pressing a laminate of electrodes and a separator, or a wound laminate of electrodes and a separator, and inserting the laminate into a rectangular outer can.

[0004] In particular, in recent years, with the aim of increasing the capacity of electricity storage devices, the volume of electricity storage devices has been reduced by hot pressing a laminate of electrodes and a separator or by hot pressing a wound body obtained by winding a laminate of electrodes and a separator. In this case, in order to fix the electrodes and separator after hot pressing and maintain the volume at the time of pressing, a technique is known in which a coating layer containing a thermoplastic polymer that exhibits adhesive properties under specified conditions is disposed on a substrate to improve adhesion between the entire separator and the electrodes.

[0005] Patent Document 1 describes a separator with a porous coating layer containing organic polymer particles, which aims to enhance safety by increasing the bonding strength between the separator and electrodes without the need for a humidification phase separation process for an organic binder polymer or a secondary coating process for an adhesive layer. In this separator, the organic polymer particles protrude from the surface of the porous coating layer to a height of 0.1 μm to 3 μm.

[0006] Patent Document 2 describes a separator with a functional layer containing inorganic particles and a particulate polymer, with the aim of providing a separator with excellent adhesion, heat resistance, and improved electrolyte injection properties. In this functional layer, when viewed from above, the inorganic particles account for more than 90% of the surface area per unit area of ​​the functional layer, and the volume average particle diameter of the particulate polymer is within a specific range and is larger than the thickness of the inorganic particle layer.

[0007] Patent Document 3 describes a separator having a functional layer containing inorganic particles and a particulate polymer, with the aim of providing a functional layer for electrochemical devices that has excellent process adhesion and can enable the electrochemical device to exhibit excellent cycle characteristics. The functional layer has particle-shedding portions, and when the surface of the functional layer for electrochemical devices is viewed from above, the ratio of the area of ​​the particle-shedding portions to the total area of ​​the particulate polymer and the particle-shedding portions is 0.1% to 40.0%, and the volume-average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing the inorganic particles.

[0008] Patent Document 4 focuses on the lamination properties, insulation properties, curling, adhesion to electrodes, and use of polyvinylidene fluoride (PVDF) of separators for non-aqueous secondary batteries, as well as the cycle characteristics of non-aqueous secondary batteries. For laminates in which a resin-containing porous layer is laminated on at least one side of a porous film containing polyolefin as a main component, the document describes the relationship between the critical surface tension of the outermost surface of the porous layer and the critical surface tension of the interface side of the porous film, or the relationship between the increase in dielectric strength per unit area of ​​the porous layer and the increase in polyolefin content per unit area of ​​the porous film. Patent Document 4 also describes that when this porous layer is formed as a functional layer, it can have a specific coefficient of dynamic friction. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2016-0118979 [Patent Document 2] International Publication No. 2020 / 175079 [Patent Document 3] International Publication No. 2021 / 085144 [Patent Document 4] International Publication No. 2016 / 031466 Summary of the Invention [Problem to be solved by the invention]

[0010] However, these conventional separators have the following problems. For example, in Patent Document 1, the adhesive polymer has poor dispersibility in a coating state, which causes the adhesive polymer to aggregate in areas on the separator, resulting in uneven adhesion to the electrodes, reducing the overall adhesive strength, and causing problems such as deterioration of heat resistance (heat shrinkage resistance). In Patent Documents 2 and 3, the binding strength of the coating layer is insufficient, leaving room for improvement in suppressing powder shedding during the manufacturing process and, ultimately, in adhesive strength to the electrodes. Note that while the technology described in Patent Document 4 relates to the productivity of nonaqueous secondary batteries equipped with electrodes, there is still room for improvement in the productivity of separators for nonaqueous secondary batteries.

[0011] Furthermore, with improvements in electrode materials and high-density modularization of multiple nonaqueous secondary batteries (single cells) (increasing the volumetric energy density of the module), there has been a continuing demand for improvements in the output characteristics (rate characteristics) and / or cycle characteristics of batteries including separators.

[0012] In view of the above circumstances, an object of the present invention is to provide a separator for an electricity storage device that can improve productivity, and an electricity storage device including the separator. [Means for solving the problem]

[0013] Examples of embodiments of the present disclosure are listed below. [1] a substrate that is a polyolefin microporous membrane containing polyolefin as a main component; a coating layer disposed on at least one surface of the substrate, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; the particulate polymer includes particulate polymer protruding from the surface of the inorganic filler portion, The static friction coefficient of the coating layer is 0.40 or more and 0.60 or less. Separators for power storage devices. [2] Item 2. The separator for an electricity storage device according to item 1, wherein a portion of the surface of the protruding particulate polymer is missing. [3] 3. The separator for an electricity storage device according to item 1 or 2, wherein, upon observation of the surface of the coating layer, the proportion of the area of ​​the particulate polymer detached parts to the total area of ​​the particulate polymer is 10% or less. [4] the coating layer is formed in a gradient shape so as to become thicker toward the protruding particulate polymer, 4. The separator for an electricity storage device according to any one of items 1 to 3, wherein the average value of the slope ratio L2 / L1 of the coating layer is 1.2 or more, where L1 is the thickness of the inorganic filler portion and L2 is the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler formed in the sloped shape. [5] the coating layer is formed in a gradient shape so as to become thicker toward the protruding particulate polymer, 5. The separator for an electricity storage device according to any one of items 1 to 4, wherein an average value of a coverage rate (L2-L1) / (L3-L1) of the protruding particulate polymer is 0.4 or more, where L1 is a thickness of the inorganic filler portion, L2 is a maximum distance from the boundary line between the substrate and the coating layer to an outer surface of the inorganic filler formed in the inclined shape, and L3 is a maximum distance from the boundary line between the substrate and the coating layer to an outline of the protruding particulate polymer. [6] 6. The separator for an electricity storage device according to any one of items 1 to 5, wherein 20% or more of the protruding particulate polymer is in contact with the surface of the substrate. [7] 7. The separator for an electricity storage device according to any one of items 1 to 6, wherein the coating layer has a 180° peel strength from the substrate of 200 gf / cm or more. [8] In observing the surface of the coating layer, Voronoi division is performed using the protruding particulate polymer as a kernel point, and the area (s i 8. The separator for an electricity storage device according to any one of items 1 to 7, wherein the coefficient of variation (cv) of the above-mentioned (cv) is 0.10 or more and 0.60 or less. [9] 9. The separator for an electricity storage device according to any one of items 1 to 8, wherein the number of the protruding particulate polymers is 50% or more of the total number of particulate polymers contained in the coating layer.

[10] 10. The separator for an electricity storage device according to any one of items 1 to 9, wherein the particle size distribution of the particulate polymer is 1.1 or less.

[11] 11. The separator for an electricity storage device according to any one of items 1 to 10, wherein the particulate polymer is a primary particle.

[12] Item 12. The separator for an electricity storage device according to item 11, wherein the primary particles have an average particle size of 1 μm or more and 10 μm or less.

[13] 13. The separator for an electricity storage device according to any one of items 1 to 12, which has a TD heat shrinkage rate of 5% or less at 130° C. for 1 hour.

[14] 14. The separator for an electricity storage device according to any one of items 1 to 13, which has a TD heat shrinkage rate of 5% or less at 150° C. for 1 hour.

[15] 15. The separator for an electricity storage device according to any one of items 1 to 14, wherein the amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the inorganic filler contained in the coating layer.

[16] 16. The separator for an electricity storage device according to any one of items 1 to 15, wherein the protruding particulate polymer protrudes by at least 0.1 times the thickness of the inorganic filler portion.

[17] 17. The separator for an electricity storage device according to any one of items 1 to 16, wherein the protruding particulate polymer comprises at least one selected from the group consisting of a copolymer containing (meth)acrylate as a monomer, a styrene-butadiene copolymer, and a copolymer containing a fluorine atom.

[18] 18. The separator for an electricity storage device according to any one of items 1 to 17, wherein the protruding particulate polymer comprises a copolymer containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers.

[19] 19. The separator for an electricity storage device according to any one of items 1 to 18, wherein the protruding particulate polymer comprises a copolymer containing a polyfunctional (meth)acrylate as a monomer.

[20] 20. The separator for a power storage device according to any one of items 1 to 19, wherein the separator for a power storage device has a methylene chloride soluble content of 0.05% by mass to 0.80% by mass relative to the total mass of the separator for a power storage device. [twenty one] 21. The separator for an electricity storage device according to any one of items 1 to 20, wherein the total amount of metal cations contained in the coating layer is 0.1 ppm or more and 100 ppm or less based on the total mass of the coating layer. [twenty two] 22. An electricity storage device comprising the separator for an electricity storage device according to any one of items 1 to 21. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to prevent misalignment of a separator for an electricity storage device, to prevent misalignment of a wound body of a separator for an electricity storage device and an electrode, and / or, for example, in the manufacture of a separator for an electricity storage device or an electricity storage device, to improve the grip between a membrane such as a separator for an electricity storage device and a roll, allowing the membrane to be transported with low tension during slitting, and to reduce or eliminate curl in the longitudinal direction (MD) of the separator, thereby improving the productivity of separators for electricity storage devices. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram of the surface of a coating layer in the present embodiment. [Figure 2] FIG. 2 is a schematic diagram of a cross section taken along the line AA in FIG. [Figure 3] FIG. 2 is a schematic diagram showing an example of an observation of the surface of a coating layer in the present embodiment. [Figure 4] This is an example of the results of identifying the protruding particulate polymer in FIG. 3. [Figure 5] This is an example of the Voronoi division result for Figure 4. [Figure 6] FIG. 5 shows an example of the results of extracting Voronoi polygons corresponding to closed regions. [Figure 7] This is an example of how to set up 10 sections that cover 95 fields of view. [Figure 8] FIG. 2 is a schematic diagram illustrating that a part of the surface of the particulate polymer protruding from the inorganic filler portion is missing in the coating layer according to the present embodiment. [Figure 9] FIG. 10 is a schematic diagram showing an inspection jig for evaluating step misalignment and a wound body set thereon. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an exemplary embodiment of the present disclosure (hereinafter abbreviated as "the present embodiment") will be described, but the present disclosure is not limited to the present embodiment.

[0017] As used herein, longitudinal direction (MD) means the machine direction of the continuous microporous membrane molding, and transverse direction (TD) means the direction crossing the MD of the microporous membrane at an angle of 90°.

[0018] 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 constitutes the largest mass of 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. The scale, shape, length, etc. of each part shown in the drawings may be exaggerated for clarity.

[0019] <Separator for power storage device> The separator for an electricity storage device of this embodiment includes a substrate that is a microporous polyolefin film containing a polyolefin as a main component, and a coating layer disposed on at least one surface of the substrate. The coating layer includes an inorganic filler and a particulate polymer of a thermoplastic polymer.

[0020] <Amount of Particulate Polymer> The amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less, preferably 3 parts by mass or more and 30 parts by mass or less, more preferably 5 parts by mass or more and 20 parts by mass or less, and even more preferably 5 parts by mass or more and 15 parts by mass or less, relative to 100 parts by mass of the inorganic filler. By using the particulate polymer in an amount of 1 part by mass or more and 50 parts by mass or less, it is possible to increase the adhesive strength with the electrode while maintaining ion permeability. From the viewpoint of improving heat shrinkage resistance, an amount of 10 parts by mass or less is preferred.

[0021] <Protrusion amount of particulate polymer> The particulate polymer may include particulate polymer protruding by 0.1 times or more the thickness of the inorganic filler portion of the coating layer.

[0022] As used herein, "thickness of the inorganic filler portion" refers to the distance (L1) between the surface of the polyolefin microporous membrane and the outermost surface of the layer of inorganic filler stacked thereon (layer of inorganic filler), and is measured from an SEM image of the cross section of the coating layer. The "inorganic filler portion" refers to a portion that does not contain particulate polymer and is 1.5D or more away from the center of each protruding particulate polymer in the horizontal direction (toward the surface of the coating layer), where D is the diameter of each protruding particulate polymer. Measurement conditions are explained in the Examples section.

[0023] When the protrusion of the particulate polymer is 0.1 times or more the thickness of the inorganic filler portion, the adhesive strength with the electrode can be increased. Furthermore, when the protrusion of the particulate polymer is 0.1 times or more the thickness of the inorganic filler portion, a gap is formed between the separator and the electrode. This gap can mitigate the effects of expansion and contraction of the electrode due to charging and discharging of the electricity storage device, suppress distortion of the wound body, and improve cycle characteristics. From this viewpoint, the protrusion of the particulate polymer is preferably 0.2 times or more, or 0.3 times or more. From the viewpoint of suppressing detachment of the particulate polymer from the separator, the protrusion of the particulate polymer is preferably 5 times or less, more preferably 4 times or less, 3 times or less, 2 times or less, 1 time or less, or 0.4 times or less.

[0024] In this specification, "protruding" means that the particulate polymer protrudes toward the surface side of the coating layer beyond the "thickness of the inorganic filler portion." In the protruding portion of the particulate polymer (hereinafter referred to as "protruding portion"), a portion of the protruding portion may be covered with an inorganic filler. From the viewpoint of preventing the particulate polymer from slipping off the coating layer and obtaining a higher adhesive strength, it is preferable that a portion of the periphery of the protruding portion is covered with an inorganic filler. Furthermore, from the viewpoint of ensuring a contact area between the particulate polymer and the electrode and obtaining a higher adhesive strength, it is preferable that the center of the protruding portion is exposed on the surface of the coating layer.

[0025] In this specification, "a state in which the particulate polymer protrudes by 0.1 times or more the thickness of the inorganic filler portion" means that, when the thickness of the inorganic filler portion measured from an SEM image of the cross section of the coating layer is L1 and the maximum distance from the boundary line between the substrate and coating layer to the outline of the protruding particulate polymer is L3, the average value of the ratio (L3-L1) / L1 is 0.1 or more. In this specification, "the maximum distance from the boundary line between the substrate and coating layer to the outline of the protruding particulate polymer" means the distance to the point on the outline of the protruding particulate polymer that is farthest from the boundary line between the substrate and coating layer.

[0026] In this specification, "a state in which the particulate polymer protrudes from the coating layer by 0.1 times or more the thickness of the inorganic filler portion of the coating layer" means, in other words, that the maximum distance (L3) from the substrate-coating layer boundary to the outline of the protruding particulate polymer measured from an SEM image of the coating layer cross section is 1.1 times or more the thickness (L1) of the inorganic filler portion of the coating layer.

[0027] The number of protruding particulate polymers is preferably 50% or more of the total number of particulate polymers contained in the coating layer. This allows the advantageous effects of the protruding particulate polymers to be obtained. The ratio of the number of protruding particulate polymers to the total number of particulate polymers contained in the coating layer (number of protruding particulate polymers / total number of particulate polymers) is also expressed as the protrusion ratio, and is considered to be one index of the degree of protrusion of the particulate polymers in the coating layer. The protrusion ratio is more preferably 60% or more, 70% or more, or 80% or more, with a theoretical upper limit of 100%.

[0028] <Gradient shape of coating layer, contact ratio between particulate polymer and substrate, 180° peel strength> The separator for an electricity storage device of this embodiment preferably has one or more of the following characteristics (1) to (3). (1) The coating layer is formed in a gradient such that it becomes thicker toward the protruding polymer particles; (2) 20% or more of the protruding particulate polymer is in contact with the surface of the substrate; (3) The 180° peel strength of the coating layer from the substrate (hereinafter simply referred to as "180° peel strength") is 200 gf / cm or more;

[0029] Feature(1): In the separator for an electric storage device, the coating layer is preferably formed in a gradient so that it becomes thicker toward the protruding particulate polymer. This prevents the particulate polymer from sliding off the coating layer and increases the adhesive strength with the electrode. In this specification, "graded" means that when the thickness of the inorganic filler portion of the coating layer is L1 and the maximum distance from the substrate-coating layer boundary to the outer surface of the inorganic filler in the gradient-formed coating layer is L2, the average value of the gradient ratio L2 / L1 of the coating layer is 1.1 (e.g., 1.10) or more.

[0030] For an example of the relationship between L1 and L2, see the schematic diagram in Figure 2. The gradient is preferably such that the thickness of the coating layer changes continuously so that it gradually becomes thicker toward the protruding particulate polymer, and preferably does not include discontinuous changes due to missing coating layers. The absence of missing coating layers tends to improve heat resistance and / or cycle characteristics. The gradient may be gentler as it moves away from the protruding particulate polymer and steeper as it approaches the protruding portion of the protruding particulate polymer. Also, when the inorganic filler covers a part of the protruding portion, the slope on the protruding portion may become gentler again toward the center of the protruding portion. The average value of the slope ratio L2 / L1 of the coating layer is preferably 1.2 (e.g., 1.20) or more, 1.3 (e.g., 1.30) or more, 1.4 (e.g., 1.40) or more, 1.5 (e.g., 1.50) or more, or 1.7 (e.g., 1.70) or more.

[0031] The coating layer may be formed in a gradient such that it becomes thicker toward the protruding particulate polymer, so that the inorganic filler covers a part of the protruding portion so as to follow the contour of the particulate polymer. Preferably, the inorganic filler covers a part of the periphery of the protruding portion so as to follow the contour of the particulate polymer. In addition, it is preferable that the vicinity of the center of the protruding portion is exposed on the surface of the coating layer. When the maximum distance from the boundary line between the substrate and the coating layer to the outline of the protruding particulate polymer (the distance to the point on the outline of the protruding particulate polymer that is farthest from the boundary line between the substrate and the coating layer) is L3, the average value of the coverage ratio of the protruding portion (L2-L1) / (L3-L1) is preferably 0.4 (e.g., 0.40) or more.

[0032] For an example of the relationship between L1, L2, and L3, see the schematic diagram in Figure 2. When the average value of the gradient ratio L2 / L1 is 1.1 or more, or the average value of the coverage ratio (L2-L1) / (L3-L1) is 0.4 or more, the particulate polymer is prevented from slipping off the coating layer and the adhesive strength with the electrode is increased. The upper limit of the average value of the gradient ratio L2 / L1 may be 5.0 or less, 4.0 or less, 3.0 or less, 2.8 or less, 2.5 or less, 2.3 or less, 2.0 or less, or 1.8 or less, from the viewpoint of ensuring the adhesive area between the particulate polymer and the electrode and increasing the adhesive strength with the electrode. Furthermore, the upper limit of the coverage ratio (L2-L1) / (L3-L1) is preferably less than 1.0 (e.g., 1.00), 0.9 (e.g., 0.90) or less, 0.8 (e.g., 0.80) or less, or 0.7 (e.g., 0.70) or less. A coverage ratio of 1.0 or more means that the inorganic filler on the protruding portion of the particulate polymer reaches the top of the outline of the protruding particulate polymer (the point farthest from the boundary line between the substrate and the coating layer). A coverage ratio of less than 1.0 ensures a sufficient contact area between the particulate polymer and the electrode, thereby increasing the adhesive strength with the electrode. A coverage ratio of 0.8 or less increases the contact area between the particulate polymer and the electrode, thereby increasing the adhesive strength with the electrode.

[0033] Feature (2): In the separator for an electricity storage device, the contact rate between the protruding particulate polymer and the surface of the substrate is preferably 20% or more, more preferably 50% or more, and even more preferably 70% or more. The "contact rate" is calculated from an image of the cross section of the coating layer of the separator for an electricity storage device observed with an SEM. As the amount of protruding particulate polymer in contact with the substrate increases, the binding strength between the substrate and the particulate polymer further increases, improving the 180° peel strength and the adhesive strength with the electrode. The upper limit of the contact rate between the protruding particulate polymer and the surface of the substrate may be 100% or less.

[0034] Feature(3): The separator for an electricity storage device preferably has a 180° peel strength of 200 gf / cm or more, more preferably 230 gf / cm or more, and even more preferably 250 gf / cm or more. 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. A 180° peel strength of 200 gf / cm or more increases the adhesive strength with the electrode and suppresses thermal shrinkage. The upper limit of the 180° peel strength may be 500 gf / cm or less.

[0035] The separator for an electricity storage device of this embodiment may have any combination of the above characteristics (1) to (3), i.e., combinations of (1) and (2), (1) and (3), (2) and (3), or (1), (2) and (3). Among these, from the viewpoint of higher adhesive strength and smaller thermal shrinkage, the combination of (1), (2) and (3) is preferred, i.e., the coating layer is formed in a gradient such that it becomes thicker toward the protruding particulate polymer, the contact rate between the protruding particulate polymer and the substrate surface is 20% or more, and the 180° peel strength is 200 gf / cm or more.

[0036] Here, the separator for an electricity storage device of this embodiment has the following features (4) and / or (5) in addition to the above features (1) to (3) or any combination of the above features (1) to (3).

[0037] Feature(4): In the case of separators for power storage devices, the surface of the coating layer is observed, and Voronoi division is performed using protruding particulate polymers as kernel points. The area of ​​the resulting Voronoi polygon (s i The coefficient of variation (cv) of the distribution of the protruding particulate polymer is 0.10 or more and 0.60 or less. In a coating layer having a coefficient of variation (cv) within this range, the distribution of the protruding particulate polymer is highly uniform. The coefficient of variation (cv) is preferably 0.20 or more, 0.25 or more, or 0.30 or more, and is preferably 0.55 or less, 0.50 or less, or 0.45 or less.

[0038] In a separator having the above characteristic (4), the distribution of the protruding particulate polymer is highly uniform, and therefore the distribution of the regions between the protruding particulate polymers is also highly uniform. Therefore, by using a separator having the above characteristic (4), the uniformity of the in-plane distribution of lithium ion migration through the regions between the electrodes can be improved, and as a result, the rate characteristics and / or cycle characteristics can be improved.

[0039] Furthermore, in a separator having the above characteristic (4), the distribution of the protruding particulate polymer is highly uniform, and therefore the distribution of the contact area between the protruding particulate polymer and the electrode is also highly uniform before and after the hot pressing process. Therefore, by using a separator having the above characteristic (4), the uniformity of the in-plane distribution of the stress of the protruding particulate polymer applied to the electrode can be improved, and ultimately, the adhesion to the electrode can be improved.

[0040] Furthermore, in a separator having the above characteristic (4), the distribution of the protruding particulate polymer is highly uniform, and therefore the distribution of the proportion of the inorganic filler having heat resistance is also highly uniform. Therefore, by using a separator having the above characteristic (4), the uniformity of the in-plane distribution of the heat resistance provided by the inorganic filler can be improved, and ultimately, heat shrinkage resistance can be improved.

[0041] Here, it has been conventionally believed that there may be a trade-off between "adhesion to the electrode" and "heat shrinkage resistance," and that there may be a trade-off between "adhesion to the electrode" and "rate characteristics" and / or "cycle characteristics." Specifically, it has been believed that, because particulate polymers do not have sufficient heat resistance, increasing the content of particulate polymers to improve "adhesion to the electrode" makes it difficult to improve "heat shrinkage resistance." Furthermore, because the presence of particulate polymers creates resistance for ions, it has been believed that increasing the content of particulate polymers makes it difficult to improve "rate characteristics" and / or "cycle characteristics." In response to these issues, according to the present embodiment, by adjusting the coefficient of variation (cv) within a predetermined range, it is possible to simultaneously achieve improved adhesion to the electrode, improved heat shrinkage resistance, and improved rate characteristics and / or cycle characteristics of the electricity storage device, as described above.

[0042] The coefficient of variation (cv) can be adjusted within the above range by, for example, changing the particle size and content of the thermoplastic polymer in the coating solution to be applied to the substrate, the viscosity and application amount of the coating solution, and the coating method and conditions. For example, the viscosity of the coating solution to be applied to the substrate can be adjusted to a predetermined range; the particle size of the thermoplastic polymer in the coating solution can be reduced; turbulent stirring can be performed when the coating solution is supplied to the substrate in the coating process; ultrasonic treatment can be performed on the coating solution applied to the substrate; etc.

[0043] "Voronoi tessellation" refers to dividing a plurality of points (kernel points) arranged at any position in a certain metric space into regions based on which of the kernel points other points in the same space are closer to. A diagram containing the regions obtained in this way is called a Voronoi diagram. In a Voronoi diagram, the boundaries of the multiple regions become part of the bisectors of each kernel point, and each region forms a polygon (Voronoi polygon). Here, in this specification, the kernel points are "protruding particulate polymers," and more specifically, the center points of the protruding portions of the protruding particulate polymers when observed on the surface.

[0044] In the observation field of the coating layer, each protruding particulate polymer is regarded as a circle having an average diameter (l). A perpendicular bisector is drawn between each of the adjacent protruding particulate polymers, and the polygon enclosed by the perpendicular bisector for each polymer is called a "Voronoi polygon." Regions that are not enclosed when Voronoi tessellated in the observation field are not considered. Examples of unenclosed regions include regions obtained by Voronoi tessellation of a polymer when the polymer is present at the boundary of the observation field and the entire protruding portion of the polymer is not observed.

[0045] The area of ​​the Voronoi polygon (s i ) can be measured using image analysis if necessary, and the area of ​​the Voronoi polygon (s i ) by the total number of Voronoi polygons (n) to be handled, and calculate the area (s i The average value (m) of the Voronoi polygons is then calculated. i ) and the total number (n) and average value (m) of Voronoi polygons to be handled, the area (s i The standard deviation (sd) of the Voronoi polygon area (s i The coefficient of variation (cv) of Coefficient of variation (CV) = standard deviation (SD) / mean value (M) It is calculated as follows.

[0046] The coefficient of variation (cv) is considered to represent the in-plane distribution or aggregation state of the protruding particulate polymer. If the coefficient of variation (cv) is 0.10 or more, it can be evaluated that the protruding particulate polymer is randomly dispersed and arranged on the surface of the coating layer. If the coefficient of variation (cv) is 0.60 or less, it can be evaluated that the protruding particulate polymer is not excessively aggregated.

[0047] The observation means for the coating layer is preferably selected appropriately depending on the size or distribution state of the thermoplastic polymer. Furthermore, as for the microscope, an electron microscope, an atomic force microscope, an optical microscope, a differential interference microscope, etc. can be used. Among these, when dealing with the distribution state of dispersed particles as in this embodiment, it is preferable to use an electron microscope or an atomic force microscope. As the observation means for the coating layer, the methods shown in the Examples section are particularly adopted.

[0048] The observation field should ensure an average observation field of the coating layer. The projected area of ​​the observation field should be appropriately adjusted so that the average distribution state of the protruding particulate polymer can be grasped. For example, the number of protruding particulate polymers to be treated is preferably about 80 to 200 per field. This observation field can be obtained by observing the coating layer using a preset observation means and magnification. For example, Figure 3 is a schematic diagram of an example of observation of the surface of the coating layer using a scanning electron microscope as the observation means at a magnification of 1000x. The dispersion state of such thermoplastic polymer particles can be analyzed by Voronoi tessellation.

[0049] In observations using a scanning electron microscope, a magnification appropriate for analysis by Voronoi tessellation is set according to the particle diameter of the thermoplastic polymer particles. Specifically, the magnification is set so that the number of thermoplastic polymer particles observed in one field of view is preferably 40 to 300, more preferably 60 to 240, and even more preferably 80 to 200. This allows for appropriate analysis by Voronoi tessellation. For example, if the content of thermoplastic polymer particles with a particle diameter of about 2.0 μm is about 10 parts by mass relative to 100 parts by mass of inorganic filler in the coating layer, a magnification of 5000 times is appropriate. If the content of thermoplastic polymer particles with a particle diameter of about 3.5 μm is about 10 parts by mass relative to 100 parts by mass of inorganic filler in the coating layer, a magnification of about 1000 times is appropriate for analysis by Voronoi tessellation.

[0050] The protruding particulate polymers contained in the observation field obtained by the above observation method are identified. For example, the protruding particulate polymers are identified from the observation field by the naked eye or by using image processing software. Figure 4 shows an example of the results of identifying the protruding particulate polymers contained in the observation field of Figure 3 using image processing software.

[0051] The protruding particulate polymers identified by surface observation of the coating layer can be subjected to Voronoi division as defined above. Specifically, a coating liquid containing a thermoplastic polymer is applied to a substrate, and the surface of the coating film is photographed to obtain an image. The protruding portions of the protruding particulate polymers identified in the obtained image are regarded as circles with an average diameter (l), and Voronoi division is performed to draw Voronoi polygons. For example, the Voronoi polygons may be drawn manually or using image processing software. The area (si) of the drawn Voronoi polygons is then calculated.

[0052] For example, Figure 5 shows an example of the results of obtaining Voronoi polygons by Voronoi division using the protruding particulate polymers identified in Figure 4 as kernel points. Among the Voronoi polygons shown in Figure 5, Voronoi polygons corresponding to closed regions were automatically extracted using image processing software, and the results are shown in Figure 6.

[0053] The total number of protruding particulate polymers in the observation field and the area of ​​the Voronoi polygon (s i ) is obtained. Then, the coefficient of variation (cv) can be calculated in accordance with the above. The distribution of the protruding particulate polymer may vary depending on the field of observation. Therefore, it is preferable to use the average value of the values ​​calculated for a plurality of fields of observation as the coefficient of variation (cv). The number of fields of observation is preferably 3 or more.

[0054] It is particularly preferable to use the average value of the values ​​calculated for 10 fields of view determined as follows. i) Each measurement field: Image captured by a scanning electron microscope ii) How to set the field of view: a) Set the starting field of view, b) A total of 10 fields of view, consisting of the starting field and nine fields of view consisting of regions adjacent to the starting field in one axial direction at 5 mm intervals, are set as measurement fields.

[0055] Each of the measurement visual fields is preferably an image taken at a magnification set so that the number of protruding particulate polymers observed in one visual field is 80 or more and 200 or less.

[0056] A preferred method for setting the 10 fields of view in this embodiment will be described below with reference to FIG. i) As described above, the captured image can be an image captured by a scanning electron microscope with a magnification of 1000x. In the image of Figure 7, first, a starting field of view (I) is set. Since one field of view is composed of an image captured by a scanning electron microscope with a magnification of 1000x, the scale of one field of view is approximately 100 µm x 100 µm, and a field of view suitable for Voronoi tessellation evaluation based on protruding particulate polymers is formed. Next, nine fields of view (II to X) are set adjacent to the starting field of view (I) in a uniaxial direction at 5 mm intervals. Each of these fields of view (II to X) is composed of an image captured at the same magnification as the starting field of view (I).

[0057] The surface observation of the coating layer is preferably carried out on a region that is not involved in ion conduction. For example, the coating layer of a separator immediately after production and that has not yet been incorporated into an energy storage device can be observed. When the energy storage device is in use or has been used, a preferred aspect of this embodiment is to observe the so-called "edge" portion of the separator (a region near the outer edge of the separator that is not involved in ion conduction). As can be seen from the above evaluation method, when 10 fields of view are observed, a separator piece approximately 45 mm long is measured, and therefore the dispersion state of the thermoplastic polymer on the surface can be accurately evaluated.

[0058] The fact that Voronoi tessellation is possible as described above is presumed to indicate that the particulate polymers are present as single-layer particles in the coating layer without substantial overlapping. For example, when the particulate polymers overlap each other in multiple layers in the coating layer, the concept of the area occupied by a single particle does not hold, and Voronoi tessellation cannot be performed. In the separator of the present embodiment, it is preferable that the particulate polymers in the coating layer are arranged so as not to substantially overlap each other, and that the above requirements are adjusted to fall within the above-mentioned ranges.

[0059] The coating layer on the substrate preferably has a pattern in which the particulate polymers are dispersed throughout the entire surface of the substrate. The particulate polymers may form clusters in some areas, but it is preferable that the particulate polymers are dispersed as a whole to the extent that the coefficient of variation (cv) is satisfied. It is preferable that the particulate polymers are dispersed as a whole to the extent that the coefficient of variation (cv) is satisfied.

[0060] Feature(5): In the electricity storage device separator, the coating layer has a static friction coefficient of 0.40 or more and 0.60 or less. When the coating layer has a static friction coefficient within this range, it is possible to prevent misalignment of the electricity storage device separator and / or the winding of the electricity storage device separator and the electrode, thereby improving the productivity of the electricity storage device separator.

[0061] Furthermore, in the electricity storage device separator having the feature (5), when the static friction coefficient of the coating layer is within the range of 0.40 or more and 0.60 or less, for example, in the production of the electricity storage device separator or the electricity storage device, the gripping ability between the film of the electricity storage device separator or the like and the roll is improved, the film can be transported with low tension during slitting, and MD curl of the separator can be reduced or eliminated, thereby improving productivity.

[0062] From the viewpoint of further improving the productivity of separators for electricity storage devices, the static friction coefficient of the coating layer is preferably 0.41 or more and 0.59 or less, more preferably 0.41 or more and 0.57 or less, and even more preferably 0.41 or more and 0.55 or less.

[0063] In a separator for an electric storage device having feature (5), the particulate polymer protruding from the surface of the inorganic filler portion contained in the coating layer is preferably composed of a thermoplastic polymer, and the protruding particulate polymer preferably has a portion of its surface missing. If the protruding particulate polymer has a portion of its surface missing, a sufficient exposed area of ​​the thermoplastic polymer can be secured to prevent winding slippage during winding of the separator or during production of an electric storage device, thereby improving gripping performance with the roll and with the electrode.

[0064] In this specification, the term "a portion of the surface of the protruding particulate polymer is missing" means that the exposed surface of at least one of the protruding polymer particles is not spherical or that a portion of the exposed surface has a discontinuous surface. The partial loss of the surface of the particulate polymer protruding from the surface of the inorganic filler portion contained in the coating layer increases the contact area between the wound body and the protruding particulate polymer when the separator for an electric storage device is wound into a wound body, thereby preventing misalignment of the separator during winding and improving productivity. Figure 8 is a schematic diagram illustrating the partial loss of the surface of the particulate polymer protruding from the inorganic filler portion in the coating layer of the separator for an electric storage device having feature (5). For example, when the cross-sectional shape of the protruding particulate polymer can be observed as a trapezoid, parallelogram, or polygon, the protruding particulate polymer may be considered to be missing. Among these, from the viewpoint of further improving the productivity of separators for electricity storage devices, it is more preferable to use a sphere made of particulate polymer, the surface of which is partly scraped into a flat surface as shown in Figure 8(a), a sphere having a flat region on part of the surface as shown in Figure 8(b), or a sphere made of particulate polymer, the surface of which is partly chipped.

[0065] From the same viewpoint as above, the defect rate of the spherical surface of the protruding particulate polymer is preferably within a range of 0.74 to 0.93, and in surface observation of the coating layer, the ratio of the area of ​​the particulate polymer fallen parts to the total area of ​​the particulate polymer is preferably 10% or less, more preferably less than 0.1%, for example, 0%. Methods for calculating the defect rate, methods for observing the surface of the coating layer, and methods for calculating the ratio of the area of ​​the particulate polymer fallen parts to the total area of ​​the particulate polymer will be described in detail in the Examples.

[0066] Examples of means for adjusting the static friction coefficient of the coating layer within the above range and / or chipping off part of the surface of the protruding particulate polymer include controlling the conditions of the coating and drying step in which a coating liquid is applied to a substrate in the manufacturing process of a separator for an electricity storage device, such as the particle size and content of the thermoplastic polymer in the coating liquid to be applied to the substrate, the viscosity and application amount of the coating liquid, as well as the coating method and application conditions, or the conditions after the coating and drying step, such as the pressure applied to the coated surface, the speed of the conveying roll with which the coated surface comes into contact, the shape of the inorganic filler in the coating layer, and the peel strength of the coating layer.

[0067] More specifically, means for controlling the conditions of the coating and drying processes include, for example, adjusting the viscosity of the coating liquid to be applied to the substrate within a predetermined range; reducing the particle size of the thermoplastic polymer in the coating liquid; performing turbulent agitation when supplying the coating liquid to the substrate during the coating process; and subjecting the coating liquid applied to the substrate to ultrasonic treatment.

[0068] More specifically, means for controlling the conditions after the coating and drying process include, for example, controlling the tension applied in the direction perpendicular to the surface where the coated surface contacts the transport roll to a predetermined value or higher; making the speed of the transport roll where the coated surface contacts slower than the separator transport speed; forming the inorganic filler in an inclined shape so that the protruding particulate polymer does not slide off from the surrounding inorganic filler part; and increasing the peel strength of the coating layer.

[0069] <Methylene chloride solubles> The separator for an electric storage device according to this embodiment preferably has a methylene chloride soluble content of 0.05% by mass or more and 0.80% by mass or less, more preferably 0.10% by mass or more and 0.60% by mass or less, and even more preferably 0.15% by mass or more and 0.50% by mass or less, based on the total mass of the separator for an electric storage device. The "methylene chloride soluble content" refers to components extracted into methylene chloride when the separator is immersed in methylene chloride. The methylene chloride soluble content mainly consists of plasticizers mixed during the production of the substrate. By including a methylene chloride soluble content of 0.10% by mass or more, the bonding strength between the substrate and the coating layer is further enhanced, making it easier to adjust the 180° peel strength to 200 gf / cm or more. By including a methylene chloride soluble content of 0.60% by mass or less, the internal resistance of the battery can be reduced. Methods for adjusting the methylene chloride soluble content to 0.05% by mass or more and 0.80% by mass or less include adjusting the extraction time, type of extraction solvent, temperature of the extraction solvent, number of extractions, etc. in the plasticizer extraction process during base material production if the process is batchwise, or adjusting the extraction time, type of extraction solvent, temperature of the extraction solvent, amount of extraction solvent supplied, etc. if the process is continuous.

[0070] <Metal cations> In the separator for an electricity storage device of this embodiment, the total amount of metal cations contained in the coating layer is preferably 0.1 ppm or more and 100 ppm or less, more preferably 0.1 ppm or more and 70 ppm or less, and even more preferably 0.1 ppm or more and 50 ppm or less, based on the total mass of the coating layer. When the total amount of metal cations is adjusted to a low amount, the inorganic filler and the particulate polymer are easily dispersed and applied uniformly in the formation of the coating layer. As the metal cation, sodium ions (Na + ), calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ ) and the like. One method for adjusting the total amount of metal cations to 0.1 ppm or more and 100 ppm or less is to wash the filler, which is the raw material for the coating layer, with water before use. The number of washings may be one or more, but the more washings are performed, the lower the total amount of metal cations contained in the filler.

[0071] <Heat shrinkage rate> The separator for an electricity storage device of this embodiment preferably has a TD heat shrinkage rate at 130°C for 1 hour of 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1%. The TD heat shrinkage of the separator for an electricity storage device of this embodiment at 150°C for 1 hour is preferably 5% or less, more preferably 0% to 3% or less, and even more preferably 0% to 1% or less. When the TD heat shrinkage is 5% or less, the occurrence of a short circuit can be more effectively suppressed in areas other than those to which external force is applied when heat is generated due to a short circuit during a crash test. This more reliably prevents an increase in temperature throughout the battery and the associated smoke and fire that may result. The heat shrinkage of the separator for a power storage device of this embodiment can be adjusted by appropriately combining the above-mentioned stretching operation of the substrate with heat treatment. While suppressing the heat shrinkage in TD, the heat shrinkage in MD is also preferably 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1%.

[0072] <Air permeability of separator> The separator for an electricity storage device preferably has an air permeability of 10 seconds / 100 cm 3 More than 10000 seconds / 100cm 3 Less than 40 seconds / 100cm, preferably less than 40 seconds / 100cm 3 More than 500 seconds / 100cm 3 Less than 50 seconds / 100cm, more preferably 3 More than 250 seconds / 100cm 3 Below 60 seconds / 100cm, particularly preferably 3 More than 200 seconds / 100cm 3 This results in high ion permeability. The air permeability is the air resistance measured in accordance with JIS P-8117.

[0073] <Base material> The substrate is a polyolefin microporous membrane containing polyolefin as a main component, and preferably has the following features (1), (2), or a combination thereof: (1) The membrane thickness is 1 μm to 30 μm, and the air permeability is 500 sec / 100 cm 3 (2) The polyolefin microporous membrane has a crystal long period of 37.0 nm or more as measured by small-angle X-ray scattering (SAXS).

[0074] Aspect (1): Without being bound by theory, it is believed that the polyolefin microporous membrane can be stretched at a rate of 500 sec / 100 cm within a thickness range of 1 μm to 30 μm. 3 By having an air permeability below 100°C and a post-compression porosity of 30% or more, it is believed that, for example, in the production of a nonaqueous secondary battery using a polyolefin microporous membrane as a separator, the electrical resistance of the polyolefin microporous membrane can be reduced or an increase in electrical resistance can be suppressed after the pressing step, thereby achieving high output and high cycle characteristics of the nonaqueous secondary battery. The suppression of resistance increase by the polyolefin microporous membrane is remarkable when an electrode that easily expands and contracts in the cell of the nonaqueous secondary battery is used, and is more remarkable when a high-capacity electrode used in an on-board battery or the like or a silicon (Si)-containing negative electrode is used.

[0075] The porosity after compression is thought to be related to the structure of the main component of the polyolefin microporous membrane, which reduces resistance and / or suppresses resistance increase in nonaqueous secondary batteries. From the viewpoints explained above, the porosity of the polyolefin microporous membrane after compression is preferably 31% or more, more preferably 32% or more, and even more preferably 33% or more. The upper limit of the porosity of the polyolefin microporous membrane after compression can be determined depending on the porosity before compression, and may be, for example, preferably 60% or less, more preferably 50% or less.

[0076] The post-compression porosity of the polyolefin microporous membrane can be adjusted within the above-described numerical ranges, for example, in the production process of the polyolefin microporous membrane by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretch ratio in the biaxial stretching process, the preheating coefficient in the biaxial stretching process, the stretch coefficient in the biaxial stretching process, the MD / TD stretching temperature in the biaxial stretching process, the heat setting temperature, etc. Alternatively, the post-compression porosity of the polyolefin microporous membrane can be adjusted within the above-described numerical ranges by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretch ratio in the biaxial stretching process, the preheating coefficient in the biaxial stretching process, the stretch coefficient in the biaxial stretching process, the ratio of the preheating coefficient to the stretch coefficient, etc.

[0077] Comparing the porosity of a polyolefin microporous membrane before and after a compression test is preferable from the viewpoint of identifying the structure of the main component of the membrane that can reduce resistance and / or suppress resistance increase in a nonaqueous secondary battery and achieve high output and high cycle characteristics. A preferred numerical range for the porosity of a polyolefin microporous membrane before or without a compression test (hereinafter simply referred to as "porosity") will be described later.

[0078] Aspect (2): Without being bound by theory, it has been found that a polyolefin microporous membrane with a long crystal period of 37.0 nm or more surprisingly improves the structural uniformity and compression resistance of the polyolefin microporous membrane, thereby improving the reaction uniformity within a nonaqueous secondary battery. This is believed to enable the nonaqueous secondary battery to achieve high power output and high cycle performance, even after a pressing process during fabrication of the nonaqueous secondary battery using the polyolefin microporous membrane as a separator. The improved structural uniformity and compression resistance of the polyolefin microporous membrane are particularly pronounced when electrodes that easily expand and contract within the cell of a nonaqueous secondary battery are used, and are even more pronounced when high-capacity electrodes or silicon (Si)-containing negative electrodes used in automotive batteries, etc., are used.

[0079] Without being bound by theory, it is believed that the crystalline long period obtained by SAXS measurement is related to the polyethylene structure, which improves the structural uniformity and compression resistance of the membrane and the reaction uniformity in a nonaqueous secondary battery. It is also believed that the crystalline long period of the polyolefin microporous membrane correlates with the porosity of the membrane after compression. From the viewpoints explained above, the crystalline long period of the polyolefin microporous membrane is preferably 37.0 nm to 60.0 nm, 38.0 nm to 55.0 nm, 40.0 nm to 50.0 nm, or 42.0 nm to 50.0 nm.

[0080] The crystal long period of the polyolefin microporous membrane can be adjusted to within the above-described numerical ranges by, for example, controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretch ratio in the biaxial stretching step, the preheating coefficient in the biaxial stretching step, the stretch coefficient in the biaxial stretching step, the MD / TD stretching temperature in the biaxial stretching step, the heat setting temperature, etc. in the production process of the polyolefin microporous membrane.

[0081] The separator for an electricity storage device of this embodiment has a substrate that is a polyolefin microporous membrane containing polyolefin as a main component. "Containing as a main component" means that the mass of the target component (polyolefin) constitutes the largest mass in the entire substrate. The polyolefin content in the polyolefin microporous membrane is, for example, more than 50 parts by mass, preferably 75 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, particularly preferably 98 parts by mass or more, and may even be 100 parts by mass, based on the total mass of the substrate.

[0082] Polyolefins have excellent coatability when a coating liquid is applied onto the film, which is advantageous for making the separator thinner, thereby increasing the ratio of active material in the electricity storage device and increasing the capacity per volume. The polyolefin microporous film can be one that has been used as a substrate for conventional separators, and is preferably a porous film with fine pores that is non-electronically conductive, ionic conductive, highly resistant to organic solvents, and has a high pore size.

[0083] The polyolefin may be a polyolefin that can be used in conventional extrusion, injection, inflation, blow molding, etc. Examples of polyolefins include homopolymers containing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc. as monomers, as well as copolymers and multi-stage polymers of two or more of these monomers. These homopolymers, copolymers, and multi-stage polymers may be used alone or in combination of two or more.

[0084] Examples of polyolefins include polyethylene, polypropylene, and polybutene, among others, from the viewpoints of reducing or suppressing an increase in the electrical resistance of the membrane, and the compression resistance and structural uniformity of the membrane. More specific examples include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and ethylene-propylene rubber.

[0085] These may be used singly or in combination of two or more. Among these, the polyolefin is preferably at least one selected from the group consisting of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene, from the viewpoint of shutdown characteristics in which pores are closed by thermal melting. In particular, high-density polyethylene is preferred because of its low melting point and high strength, and high-density polyethylene having a density of 0.93 g / cm as measured in accordance with JIS K 7112 is preferred. 3 Polyethylenes having a molecular weight of 100 or more are more preferred. Examples of polymerization catalysts used in the production of these polyethylenes include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. It is preferred that the main component of the polyolefin is polyethylene, and the content of polyethylene relative to the total mass of the polyolefins in the substrate is preferably 50 parts by mass or more.

[0086] To improve the heat resistance of the substrate, the polyolefin microporous membrane preferably contains polypropylene and a polyolefin other than polypropylene. Examples of the polyolefin resin other than polypropylene include homopolymers containing ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc. as monomers, copolymers of two or more of these monomers, and multi-stage polymers.

[0087] The amount of polypropylene relative to the total mass of polyolefin in the substrate (polypropylene / polyolefin) may be 0% and is not particularly limited, but from the viewpoint of achieving both heat resistance and good shutdown function, it is preferably 1 part by mass to 35 parts by mass, more preferably 3 parts by mass to 20 parts by mass, and even more preferably 4 parts by mass to 10 parts by mass. From the same viewpoint, the content ratio of olefin resin other than polypropylene, such as polyethylene, relative to the total mass of polyolefin in the polyolefin microporous membrane (olefin resin other than polypropylene / polyolefin) is preferably 65 parts by mass to 99 parts by mass, more preferably 80 parts by mass to 97 parts by mass, and even more preferably 90 parts by mass to 96 parts by mass.

[0088] From the viewpoints of crystallinity, high strength, compression resistance, etc. when formed into a polyolefin microporous membrane for a nonaqueous secondary battery, the polyolefin microporous membrane is preferably a porous membrane formed from a polyethylene composition in which polyethylene accounts for 50 to 100% by mass of the resin components constituting the microporous membrane. The proportion of polyethylene in the resin components constituting the porous membrane is more preferably 60 to 100% by mass, even more preferably 70 to 100% by mass, and still more preferably 90 to 100% by mass.

[0089] The viscosity average molecular weight of the polyolefin is preferably 30,000 to 6,000,000, more preferably 80,000 to 3,000,000, and even more preferably 150,000 to 2,000,000. A viscosity average molecular weight of 30,000 or more is preferred because the entanglement of polymers tends to result in higher strength. On the other hand, a viscosity average molecular weight of 6,000,000 or less is preferred from the viewpoint of facilitating uniform melt-kneading and improving moldability in the extrusion and stretching steps. Furthermore, a viscosity average molecular weight of less than 1,000,000 is preferred because the pores tend to be easily blocked when the temperature rises, resulting in a better shutdown function.

[0090] When the polyolefin microporous membrane contains polyethylene as the main component, the lower limit of the viscosity average molecular weight (Mv) of at least one polyethylene is preferably 600,000 or more, more preferably 700,000 or more, from the viewpoints of membrane orientation and rigidity, and the upper limit of the Mv of the polyethylene may be, for example, 2,000,000 or less. From the same viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin constituting the polyolefin microporous membrane is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and may be 100% by mass. From the viewpoints of reduced fluidity of the membrane when melted and short-circuit resistance in a nail penetration test, the proportion of polyethylene with an Mv of 600,000 or more in the polyolefin resin constituting the polyolefin microporous membrane is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, still more preferably 70% by mass or more, and may be 100% by mass.

[0091] The viscosity average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at a measurement temperature of 135° C. using decalin as a solvent according to ASTM-D4020, using the following formula: Polyethylene: [η] = 6.77 × 10 -4 Mv 0.67 (Chiang's formula) Polypropylene: [η] = 1.10 × 10 -4 Mv 0.80

[0092] For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the viscosity average molecular weight of which is less than 1 million, may be used.

[0093] The substrate may contain other resins in addition to polyolefin, such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene.

[0094] The substrate may contain any additives. Such additives are not particularly limited and include, for example, plasticizers, polymers other than polyolefins; inorganic particles; phenolic, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. The total content of these additives 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, per 100 parts by mass of the polyolefin resin in the polyolefin microporous membrane.

[0095] The substrate preferably contains a plasticizer. When the substrate contains a plasticizer, the adhesive strength between the substrate and the coating layer is improved, making it easier to control the 180° peel strength to 200 gf / cm or more. The amount of plasticizer is preferably 0.1 to 1.6 parts by mass, more preferably 0.2 to 1.2 parts by mass, and even more preferably 0.3 to 1.0 parts by mass, based on the total mass of the substrate. By using a plasticizer amount within the above range, the adhesive strength between the substrate and the coating layer can be improved while reducing the internal resistance of the battery. Examples of plasticizers include hydrocarbons such as liquid paraffin, esters such as dioctyl phthalate and dibutyl phthalate, and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred.

[0096] The porosity of the substrate is preferably 30% or more and 65% or less, more preferably 35% or more and 60% or less. It is even more preferably 35% or more and 50% or less, and may be 40% or more and 50% or less. This allows the coating layer to be appropriately impregnated into the micropores of the substrate, making it easier to control the 180° peel strength to 200 gf / cm or more. The porosity is determined by the volume (cm) of the substrate sample. 3 ), mass (g), membrane density (g / cm 3 ) to the following formula: Porosity = (volume - mass / film density) / volume x 100 Here, for example, in the case of a polyolefin microporous membrane made of polyethylene, the membrane density is 0.95 g / cm 3 The porosity can be adjusted by changing the stretch ratio of the polyolefin microporous membrane, for example.

[0097] The air permeability of the substrate is preferably 10 seconds / 100 cm 3 More than 450 seconds / 100cm 3 Less than 40 seconds / 100cm, preferably less than 40 seconds / 100cm 3 More than 300 seconds / 100cm 3 Less than 50 seconds / 100cm, more preferably 3 More than 250 seconds / 100cm 3 Below 60 seconds / 100cm, particularly preferably 3 More than 200 seconds / 100cm 3 Also, 60 seconds / 100cm 3 More than 150 seconds / 100cm 3 or less. This allows the coating layer to adequately penetrate the micropores of the substrate, making it easier to control the 180° peel strength to 200 gf / cm or more. The air permeability is the air resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretch ratio of the substrate, etc.

[0098] The average pore size of the substrate is preferably 0.15 μm or less, more preferably 0.10 μm or less, and preferably 0.01 μm or more. An average pore size of 0.15 μm or less is suitable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing a decrease in capacity. From the viewpoint of improving density, it is preferably 0.08 μm or less. The average pore size can be adjusted by changing the stretching ratio when manufacturing the substrate, for example.

[0099] The pin puncture strength of the substrate is preferably 200 gf or more, more preferably 300 gf or more, even more preferably 400 gf or more, and preferably 2,000 gf or less, more preferably 1,000 gf or less. A pin puncture strength of 200 gf or more is preferable from the viewpoint of preventing film rupture due to fallen active material, etc., when the separator is wound together with the electrodes, and from the viewpoint of preventing the risk of short circuit due to expansion and contraction of the electrodes during charge and discharge. On the other hand, a pin puncture strength of 2,000 gf or less is preferable from the viewpoint of reducing width contraction due to orientation relaxation during heating. The pin puncture strength is measured according to the method described in the Examples. The pin puncture strength can be adjusted by adjusting the stretch ratio and / or stretching temperature of the substrate.

[0100] The type, molecular weight, and composition of the polyolefin resin constituting the polyolefin microporous membrane can be adjusted, for example, by controlling the type, molecular weight, and blending ratio of polymer raw materials such as polyolefin in the production process of the polyolefin microporous membrane. Also, a multilayer polyolefin resin microporous membrane having a structure in which two or more layers of the same or different polyolefin resin microporous membranes are laminated can be prepared as described above.

[0101] A microporous polyolefin membrane has a porous structure in which a large number of very small pores gather to form dense interconnected pores, and therefore has excellent ion permeability and high strength when containing an electrolyte solution.

[0102] The thickness of the substrate (hereinafter referred to as substrate film thickness) is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 6 μm or more, particularly preferably 7 μm or more, and preferably 100 μm or less, more preferably 60 μm or less, even more preferably 50 μm or less, particularly preferably 16 μm or less. A substrate film thickness of 2 μm or more is preferred from the viewpoint of improving mechanical strength. On the other hand, a substrate film thickness of 100 μm or less is preferred because it reduces the volume occupied by the separator in the electricity storage device, which tends to be advantageous in terms of increasing the capacity of the electricity storage device.

[0103] <Coating layer> The separator for an electricity storage device of this embodiment includes a coating layer disposed on at least one surface of the substrate. That is, the coating layer may be disposed on only one surface of the substrate, or on both surfaces. "Disposed on the surface" means that the coating layer may be disposed on the entire surface of the substrate, or on a portion of the surface. The coating layer is intended to be directly bonded to the electrode. It is preferable that the coating layer is disposed so that the substrate and the electrode are bonded via the coating layer, so that the coating layer is directly bonded to the electrode. The coating layer is preferably a coating layer formed by applying a coating liquid containing an inorganic filler and a particulate polymer to the substrate.

[0104] The coating layer includes an inorganic filler and a particulate polymer of a thermoplastic polymer. The coating layer may further include a resin binder, a water-soluble polymer, and other additives. The coating layer may have at least two Tg's: a Tg based on the particulate polymer made of a thermoplastic polymer, and a Tg based on the thermoplastic polymer that is a binding binder.

[0105] (inorganic filler) The inorganic filler preferably has a melting point or thermal decomposition temperature of 200°C or higher, high electrical insulation, and electrochemical stability within the range of use of an electricity storage device such as a lithium-ion secondary battery. Examples of such inorganic fillers include inorganic oxides (oxide ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (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, 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. These may be used alone or in combination. Among these, the inorganic filler is preferably at least one selected from the group consisting of alumina, barium sulfate, and aluminum oxide hydroxide (boehmite).

[0106] The lower limit of the average particle size of the inorganic filler is preferably 50 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, or 400 nm or more, and the upper limit is preferably 2000 nm or less, 1100 nm or less, 800 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, or 300 nm or less. An average particle size of the inorganic filler of 50 nm or more is preferable from the viewpoint of maintaining voids for ion permeation through the coating layer and improving rate characteristics. An average particle size of the inorganic filler of 2000 nm or less is preferable from the viewpoint of increasing the proportion of inorganic filler in the coating layer and improving heat shrinkage resistance. The average particle size of the inorganic filler is preferably, for example, 180 nm or more and 300 nm or less. This is because, particularly when the coating layer is thin, a uniform coating layer thickness is formed and heat shrinkage resistance is improved. The average particle size of the inorganic filler is also preferably, for example, 150 nm or more and 500 nm or less, or 200 nm or more and 450 nm or less. This is because a high degree of both rate characteristics and heat shrinkage resistance can be achieved. The "average particle size" of the inorganic filler was measured using the method described in the Examples. Methods for adjusting the particle size and its distribution of the inorganic filler include, for example, a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizing device such as a ball mill, a bead mill, or a jet mill. The particle size distribution of the inorganic filler can be such that a graph of particle size versus frequency has one peak. However, it may also be such that there are two peaks or a trapezoidal chart with no peak. The coefficient of variation of the particle size distribution of the inorganic filler is preferably 0.55 or less, more preferably 0.50 or less, and even more preferably 0.45 or less. A coefficient of variation of the particle size distribution of 0.55 or less is preferable from the viewpoints of suppressing deformation at temperatures exceeding the melting point of the substrate and improving the gradient rate of the coating layer and increasing the adhesive strength with the electrode.

[0107] Examples of the shape of the inorganic filler include plate-like, scale-like, needle-like, columnar, spherical, polyhedral, and block-like. A combination of inorganic fillers having these shapes may be used. A block-like shape is preferred from the viewpoint of improving the gradient of the coating layer and increasing the adhesive strength with the electrode.

[0108] The aspect ratio of the inorganic filler is preferably 1.0 or more and 2.5 or less, more preferably 1.1 or more and 2.0 or less. An aspect ratio of 2.5 or less is preferable from the viewpoints of suppressing the amount of moisture adsorption by the separator and suppressing capacity deterioration during repeated cycles, suppressing deformation at temperatures exceeding the melting point of the substrate, and improving the gradient of the coating layer and increasing adhesion to the electrode. The reason why the gradient increases when the aspect ratio of the inorganic filler is 1.0 or more and 2.5 or less is thought to be because the orientation of the particles in the coating layer is small, making it easier to form a laminated structure.

[0109] The particle size distribution of the inorganic filler, calculated by dividing the standard deviation SD of the volume average particle size of the inorganic filler by the D50, is preferably 0.55 or less, more preferably 0.50 or less, and even more preferably 0.45 or less. A particle size distribution of 0.55 or less is preferable from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the substrate and from the viewpoint of improving the gradient of the coating layer and enhancing adhesion to the electrode. The reason why the gradient increases when the particle size distribution of the inorganic filler is 0.55 or less is thought to be because the particle uniformity is increased and the contact rate between particles is improved, making it easier to form a laminated structure.

[0110] The amount of the inorganic filler is, for example, 20 to less than 100 parts by mass, 30 to 80 parts by mass, 35 to 70 parts by mass, or even 40 to 60 parts by mass relative to the total mass of the coating layer.

[0111] (particulate polymer) The particulate polymer is a particle of a thermoplastic polymer. From the viewpoint of improving the adhesion between the separator and the electrode, the particulate polymer preferably contains a thermoplastic polymer having a glass transition temperature or melting point of 20°C or higher and 200°C or lower. The glass transition temperature refers to the midpoint glass transition temperature as defined in JIS K7121 and is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the glass transition temperature can be determined as the temperature at the point where a line extending the low-temperature side baseline of the DSC curve toward the high-temperature side intersects with a line equidistant in the vertical direction from the line extending the high-temperature side baseline of the DSC curve toward the low-temperature side, and a curve representing a step change in the glass transition. More specifically, the glass transition temperature may be determined according to the method described in the Examples. Furthermore, "glass transition" refers to a change in heat flow that occurs on the endothermic side in DSC due to a change in the state of the polymer test piece. This change in heat flow is observed as a step-like change in the DSC curve. The "step-like change" refers to the portion of the DSC curve where the curve moves away from the previous low-temperature baseline and transitions to a new high-temperature baseline. Note that a combination of a step-like change and a peak is also considered a step-like change. Furthermore, in the stepwise change portion, when the upper side is the heat generating side, it can also be expressed as the point where an upwardly convex curve changes to a downwardly convex curve. The "peak" refers to the portion of the DSC curve where the curve leaves the low-temperature baseline and returns to the same baseline. The "baseline" refers to the temperature range of the DSC curve where no transition or reaction occurs in the test specimen.

[0112] The glass transition temperature (Tg) of the particulate polymer is preferably 10° C. or higher and 110° C. or lower, more preferably 45° C. or higher, even more preferably 80° C. or higher, and even more preferably 90° C. or higher, and from the viewpoint of improving adhesive strength after injection of an electrolyte solution and enhancing blocking resistance, it is particularly preferably higher than 90° C. In order to maintain shape stability up to higher temperatures, it can be 92° C. or higher. It is preferable that the Tg of the particulate polymer is 10°C or higher from the viewpoint of preventing adjacent separators from sticking together (blocking) via the coating layer during storage and transportation of the separator for the electricity storage device and during the manufacturing process of the electricity storage device. On the other hand, a Tg of 110°C or less is preferable from the viewpoint of obtaining good adhesive strength with the electrode. The Tg of a particulate polymer can be appropriately adjusted, for example, by changing the type of monomer used in producing the particulate polymer, or, if the particulate polymer is a copolymer, by changing the blending ratio of each monomer. That is, for each monomer used in producing the particulate polymer, the glass transition temperature can be roughly estimated from the generally-disclosed Tg of its homopolymer (for example, as described in "Polymer Handbook" (A Wiley-Interscience Publication)) and the blending ratio of the monomers. For example, a copolymer obtained by copolymerizing a high ratio of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid to give a homopolymer with a Tg of approximately 100°C will have a high Tg, while a copolymer obtained by copolymerizing a high ratio of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate to give a homopolymer with a Tg of approximately -50°C will have a low Tg. The Tg of the copolymer can also be roughly calculated by the FOX formula shown below. 1 / Tg=W1 / Tg1+W2 / Tg2++W i / Tg i +···W n / Tg n where Tg(K) is the Tg of the copolymer, and Tg i (K) is the Tg of the homopolymer of monomer i, and W i is the mass fraction of each monomer. i is an integer of 1 to n, and n is the number of types of monomers constituting the copolymer. However, as the glass transition temperature Tg of the particulate polymer in this embodiment, a value measured by the method using DSC is adopted.

[0113] From the viewpoints of adhesion between the separator and the electrode and preventing the particulate polymer from falling off from the coating layer, the average particle size of the particulate polymer is preferably 0.5 to 5 times, more preferably 1 to 2 times, even more preferably 1.1 to less than 1.5 times, and particularly preferably 1.2 to 1.4 times the thickness of the coating layer. In the present disclosure, the "average particle size" of the particulate polymer refers to the volume average particle size (D50) measured by the measurement method described in the Examples. The "primary particles" of particulate polymers refer to independent particles that are bound together by covalent bonds, while the aggregates formed by two or more primary particles are called "secondary particles."

[0114] The particle size distribution MV / MN of the particulate polymer, calculated by dividing the volume-average particle size MV of the particulate polymer by the number-average particle size MN, is preferably 1.1 or less, more preferably 1.10 or less, and even more preferably less than 1.05. It is preferable that the particle size distribution of the particulate polymer be within the above range in order to ensure uniformity in the thickness of the coating layer, improve cycle characteristics, and increase adhesion to the electrode; to reduce the amount of particulate polymer on the smaller particle size side of the distribution embedded in the coating layer, thereby increasing adhesion to the electrode and improving heat resistance; and to reduce the total thickness of the separator. The lower limit of the particle size distribution MV / MN of the particulate polymer is not particularly limited, but may be, for example, 1.01 or more, or 1.01.

[0115] The particulate polymer contained in the coating layer is preferably in the form of primary particles. The average particle size of the primary particles of the particulate polymer is preferably 1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less, and even more preferably 2 μm or more and 5 μm or less. The particulate polymer being in the form of primary particles means that the particulate polymer is uniformly dispersed in the coating layer, which improves the 180° peel strength, increases the adhesive strength with the electrode, suppresses thermal shrinkage, and ensures the uniformity of the thickness of the coating layer. When the average particle size of the primary particles is 1 μm or more and 10 μm or less, the particulate polymer is likely to form a structure in which it protrudes from the surface of the coating layer, which increases the adhesive strength with the electrode and suppresses thermal shrinkage.

[0116] Examples of the thermoplastic polymer include (meth)acrylic polymers, conjugated diene polymers, polyvinyl alcohol resins, and fluorine-containing resins.

[0117] From the viewpoints of high adhesion to electrodes and low thermal shrinkage, the thermoplastic polymer more preferably contains a (meth)acrylic polymer. The term "(meth)acrylic polymer" refers to a polymer or copolymer containing a (meth)acrylic compound as a monomer. The (meth)acrylic compound can be represented by the following general formula: CH2=CR Y1 -COO-R Y2 In the formula, R Y1 represents a hydrogen atom or a methyl group, and R Y2 represents a hydrogen atom or a monovalent hydrocarbon group. Y2 When is a monovalent hydrocarbon group, it may have a substituent or a heteroatom. Examples of monovalent hydrocarbon groups include linear or branched chain alkyl groups, cycloalkyl groups, and aryl groups. Examples of substituents include hydroxyl groups and phenyl groups, and examples of heteroatoms include halogen atoms and oxygen atoms. The (meth)acrylic compounds may be used alone or in combination of two or more. Examples of (meth)acrylic compounds include (meth)acrylic acid, linear alkyl (meth)acrylates, cycloalkyl (meth)acrylates, (meth)acrylates having a hydroxyl group, and (meth)acrylic acid aryl esters.

[0118] More specifically, examples of the chain alkyl (meth)acrylate include (meth)acrylates having a chain alkyl group having 1 to 3 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group; an n-butyl group, an isobutyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group; and a chain alkyl group having 4 or more carbon atoms, such as a lauryl group. Examples of the (meth)acrylic acid aryl ester include phenyl (meth)acrylate.

[0119] Specific examples of the (meth)acrylate include (meth)acrylates having a chain alkyl group such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate; and (meth)acrylates having an aromatic ring such as phenyl (meth)acrylate and benzyl (meth)acrylate.

[0120] Conjugated diene polymers are polymers containing conjugated diene compounds as monomer units and are preferred because they are compatible with electrodes. Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, and substituted and side-chain conjugated hexadienes. These may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. Conjugated diene polymers may contain (meth)acrylic compounds or other monomers as monomer units, as described below. Examples of such monomers include styrene-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene copolymers and their hydrogenated products, and acrylonitrile-butadiene-styrene copolymers and their hydrogenated products.

[0121] Examples of polyvinyl alcohol resins include polyvinyl alcohol and polyvinyl acetate.

[0122] Fluorine-containing resins are preferred from the viewpoint of voltage resistance, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, and copolymers containing fluorine atoms, such as vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer. The fluorine-containing resin is preferably a copolymer containing fluorine atoms.

[0123] Among the thermoplastic polymers listed above, the particulate polymer preferably contains at least one selected from the group consisting of copolymers containing (meth)acrylate as a monomer, styrene-butadiene copolymers, and copolymers containing fluorine atoms. The copolymers containing (meth)acrylate as a monomer more preferably contain copolymers containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers. By including these specific thermoplastic polymers in the particulate polymer, it is possible to provide a separator for an electricity storage device that has higher adhesive strength with electrodes and a smaller thermal shrinkage rate.

[0124] The particulate polymer preferably contains a crosslinkable monomer. The crosslinkable monomer is not particularly limited, but examples thereof include a monomer having two or more radically polymerizable double bonds, a monomer having a functional group that gives a self-crosslinking structure during or after polymerization, etc. These may be used alone or in combination of two or more.

[0125] Examples of monomers having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylates, with polyfunctional (meth)acrylates being preferred. The polyfunctional (meth)acrylate may be at least one selected from the group consisting of bifunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional (meth)acrylates. Specific examples include polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. Among these, at least one of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferred from the same viewpoint as above.

[0126] (resin binder) The coating layer preferably contains a resin binder for binding the inorganic fillers together and the inorganic filler and the substrate. The type of resin for the resin binder is not particularly limited, but any resin that is insoluble in the electrolyte of an electricity storage device such as a lithium ion secondary battery and is electrochemically stable within the range of use of the electricity storage device such as a lithium ion secondary battery can be used.

[0127] Specific examples of resins for the resin binder include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene-styrene copolymers and their hydrogenated products, methacrylate-acrylate copolymers, styrene-butadiene copolymers and their hydrogenated products ... Examples of suitable resins include rubbers such as ethylene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and resins with a melting point of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester, or resins with no melting point but a decomposition temperature of 200°C or higher. These may be used alone or in combination of two or more.

[0128] The resin binder may include, for example, a resin latex binder. Examples of the resin latex binder include a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable therewith. Examples of the aliphatic conjugated diene monomer include butadiene and isoprene, examples of the unsaturated carboxylic acid monomer include (meth)acrylic acid, and examples of the other monomer include styrene. While there are no particular limitations on the polymerization method for such copolymers, emulsion polymerization is preferred. There are no particular limitations on the emulsion polymerization method, and known methods can be used. There are no particular limitations on the method for adding the monomers and other components, and any of a batch addition method, a divided addition method, and a continuous addition method can be used. The polymerization method can be one-stage polymerization, two-stage polymerization, or multi-stage polymerization with three or more stages.

[0129] Specific examples of the resin binder include the following (1) to (7). (1) Polyolefins, such as polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof; (2) Conjugated diene polymers, such as styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof; (3) Acrylic polymers, such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers; (4) Polyvinyl alcohol-based resins, such as polyvinyl alcohol and polyvinyl acetate; (5) Fluorine-containing resins, such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, and ethylene-tetrafluoroethylene copolymers; (6) Cellulose derivatives, such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and (7) 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, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0130] When the resin binder is a resin latex binder, its volume average particle diameter (D50) may be, for example, 50 nm to 500 nm, 60 nm to 460 nm, or 80 nm to 250 nm. The volume average particle diameter of the resin binder can be controlled by adjusting, for example, the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, etc.

[0131] From the viewpoint of improving the 180° peel strength, the glass transition temperature of the resin binder is preferably 25° C. or lower, more preferably 10° C. or lower, and even more preferably −15° C. or lower. From the viewpoint of transparency, the glass transition temperature of the resin binder is preferably −60° C. or higher.

[0132] The volume average particle diameter (D50) of the resin binder is preferably at least 1 time, more preferably at least 2 times, and even more preferably at least 2.5 times the average pore size of the polyolefin microporous membrane from the viewpoint of improving 180° peel strength. Selecting the volume average particle diameter (D50) of the resin binder in this manner enables the resin binder to be retained on the surface of the polyolefin microporous membrane, improving 180° peel strength. From the viewpoint of improving rate performance, the volume average particle diameter (D50) of the resin binder is preferably no more than 10 times the average pore size of the polyolefin microporous membrane. The content of the resin binder in the coating layer may be, for example, more than 0 part by mass and no more than 50 parts by mass, 1 part by mass to 20 parts by mass, 2 parts by mass to 10 parts by mass, or 3 parts by mass to 5 parts by mass, relative to the total amount of the coating layer, from the viewpoint of maintaining low permeability and suppressing blocking.

[0133] The Tg of the resin binder is preferably less than 40° C. from the viewpoint of wettability to the substrate, adhesion between the substrate and the particulate polymer, adhesion between the coating layer and the particulate polymer, adhesion between the substrate and the coating layer, and adhesion to the electrode. The Tg of the resin binder is more preferably −100° C. or higher, even more preferably −50° C. or higher, and particularly preferably −40° C. or higher from the viewpoint of ion permeability, and is more preferably less than 20° C., even more preferably less than 15° C., and particularly preferably less than 0° C. from the viewpoint of adhesion between the substrate and the particulate polymer.

[0134] (Water-soluble polymer) The coating layer may further contain a water-soluble polymer in addition to the inorganic filler and the particulate polymer of a thermoplastic polymer. The water-soluble polymer may be incompatible with the thermoplastic polymer that constitutes the particulate polymer. In general, the water-soluble polymer functions as a dispersant in a coating liquid for forming a coating layer containing the inorganic filler and the particulate polymer of a thermoplastic polymer, and functions as a dispersant and / or a water-retaining agent when the coating liquid is a water-based paint.

[0135] The content of the water-soluble polymer in the coating layer is preferably 0.04 to 5 parts by mass, more preferably 0.04 to 1.5 parts by mass, and even more preferably 0.1 to 1 part by mass, per 100 parts by mass of the inorganic filler. By having the content of the water-soluble polymer in the coating layer be 0.04 parts by mass or more, the binding strength between the inorganic components is improved, and thermal shrinkage can be further suppressed. Furthermore, settling of the components during preparation of the coating layer slurry can be suppressed, enabling stable dispersion. By having the content of the water-soluble polymer in the coating layer be 5 parts by mass or less, streaks and unevenness during coating layer formation can be suppressed.

[0136] The water-soluble polymer also contributes to the binding between inorganic fillers in the coating layer. From the viewpoint of suppressing thermal shrinkage of the separator, the water-soluble polymer preferably exhibits a weight loss rate of less than 10% at 150°C when the weight at 50°C is taken as 100% in thermogravimetry.

[0137] The water-soluble polymer may be a polymer derived from a natural product, a synthetic product, a semi-synthetic product, or the like. However, from the viewpoint of forming inorganic and organic components into paints, particularly water-based paints, the water-soluble polymer is preferably an anionic, cationic, amphoteric, or nonionic polymer, and more preferably an anionic, cationic, or amphoteric polymer.

[0138] Examples of anionic polymers include modified starches such as carboxymethyl starch and starch phosphate; anionic cellulose derivatives such as carboxymethyl cellulose; ammonium salts or alkali metal salts of polyacrylic acid; gum arabic; carrageenan; sodium chondroitin sulfate; sulfonic acid compounds such as sodium polystyrene sulfonate, sodium polyisobutylene sulfonate, and naphthalene sulfonic acid condensate salts; and polyethyleneimine xanthate salts. Among these, from the viewpoint of achieving an appropriate balance between rigidity, rate characteristics, and cycle characteristics of an electricity storage device, anionic polymers containing a metal salt as a counter cation are preferred; anionic cellulose derivatives and ammonium salts or alkali metal salts of polyacrylic acid are also preferred; and from the viewpoint of achieving a balance between heat resistance and rate characteristics, alkali metal salts of polyacrylic acid are more preferred, with sodium polyacrylate being even more preferred.

[0139] The ammonium salt or alkali metal salt of polyacrylic acid is a compound having -COO groups derived from multiple carboxylic acid groups. - It refers to a polymer in which at least one of the moieties forms a salt with an ammonium ion or an alkali metal ion. Examples of alkali metal ions include sodium ions (Na + ), potassium ions (K + ) etc.

[0140] The ammonium salt or alkali metal salt of polyacrylic acid may be at least one of the following (I) to (III): (I) Monomers having one ammonium salt or alkali metal salt of a carboxylic acid (C i ) or a homopolymer of multiple monomers (C i ) copolymers with other monomers; (II) Monomers having a plurality of ammonium salts or alkali metal salts of carboxylic acids (C ii ) homopolymer or monomer (C ii ) and other monomers; and (III) Ammonium salts or alkali metal salts of polymers or copolymers obtained by polymerizing or copolymerizing monomers having one or more carboxylic acids.

[0141] Monomers having one ammonium salt or alkali metal salt of a carboxylic acid (C i ) include, for example, sodium (meth)acrylate and ammonium (meth)acrylate.

[0142] Monomers having a plurality of ammonium salts or alkali metal salts of carboxylic acids (C ii Examples of the (meth)acryloyloxy)undecane-1,1-dicarboxylic acid include ammonium salts and sodium salts of 11-(methacryloyloxy)undecane-1,1-dicarboxylic acid; ammonium salts, monosodium salts, and disodium salts of ethylenically unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and citraconic acid; and alicyclic polycarboxylic acids having a (meth)acryloyl group.

[0143] Monomer (C i ) or monomer (C ii Examples of monomers copolymerizable with the copolymer include (meth)acrylamide; ethylenically unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and citraconic acid; and ethylenically unsaturated dicarboxylic acid anhydrides such as maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0144] Examples of the ammonium salts or alkali metal salts of polymers or copolymers obtained by polymerizing or copolymerizing a monomer having one or more carboxylic acids include sodium polyacrylate and ammonium polyacrylate.

[0145] The structures of the ammonium salts or alkali metal salts of polyacrylic acid described in (I) to (III) above may overlap with each other. The ammonium salts or alkali metal salts of polyacrylic acid described in (I) to (III) above preferably have a low content of polyvalent cations when dissolved in water. Examples of polyvalent cations include magnesium ions, calcium ions, and iron ions. Reducing the content of these ions stabilizes the dispersibility of the particulate polymer in the mixed slurry with the particulate polymer.

[0146] Examples of cationic polymers include cationic starch, chitosan, gelatin, homopolymers or copolymers of dimethylaminoethyl (meth)acrylate quaternary salts, homopolymers or copolymers of dimethylallylammonium chloride, polyamidines and their copolymers, polyvinylimidazoline, dicyandiamide condensates, epichlorohydrin-dimethylamine condensates, and polyethyleneimine.

[0147] Examples of amphoteric polymers include dimethylaminoethyl (meth)acrylate quaternary salt-acrylic acid copolymers, Hofmann degradation products of polyacrylamide, and the like.

[0148] Examples of nonionic polymers include starch and its derivatives; cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, and their ammonium salts or alkali metal salts; gums such as guar gum and modified versions thereof; and synthetic polymers and modified versions thereof, such as polyvinyl alcohol, polyacrylamide, polyethylene glycol, polymethyl vinyl ether, polyisopropyl acrylamide, and copolymers of vinyl alcohol and other monomers.

[0149] The water-soluble polymer may or may not have an amide bond-containing cyclic structure. The water-soluble polymer having an amide bond-containing cyclic structure refers to a homopolymer or copolymer having a group having an amide bond-containing cyclic structure and a backbone derived from a polymerizable double bond. The water-soluble polymer having an amide bond-containing cyclic structure may have one or more amide bond-containing cyclic structures.

[0150] Examples of the group having an amide bond-containing cyclic structure include the group of the following formula (2): [ka] Specific examples of the water-soluble polymer having an amide bond-containing cyclic structure include homopolymers of monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond, such as poly(N-vinylcaprolactam), which is a homopolymer of N-vinylcaprolactam, and polyvinylpyrrolidone (PVP), which is a homopolymer of vinylpyrrolidone; copolymers of two or more monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.); and copolymers of one or more monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.) with one or more other monomers having a polymerizable double bond (monomers other than the monomer having a group having an amide bond-containing cyclic structure and a polymerizable double bond).

[0151] Examples of monomers copolymerizable with the monomer having a group with an amide bond-containing cyclic structure and a polymerizable double bond include vinyl acyclic amides; (meth)acrylic acid and esters thereof; (meth)acrylamide and derivatives thereof; styrene and derivatives thereof; vinyl esters such as vinyl acetate; α-olefins; basic unsaturated compounds such as vinylimidazole and vinylpyridine and derivatives thereof; carboxyl group-containing unsaturated compounds and acid anhydrides thereof; vinyl sulfonic acid and derivatives thereof; vinyl ethylene carbonate and derivatives thereof; and vinyl ethers.

[0152] (additives) The coating layer may consist of only an inorganic filler, a particulate polymer of a thermoplastic polymer, and an arbitrary water-soluble polymer, or may further contain additives other than these. Examples of additives include low-molecular-weight dispersants other than water-soluble polymers; thickeners; antifoaming agents; and pH adjusters such as ammonium hydroxide. Specific examples of low-molecular-weight dispersants include monomers (C ) having multiple ammonium salts or alkali metal salts of carboxylic acids. ii ), and non-polymerizable compounds having a plurality of ammonium salts or alkali metal salts of carboxylic acids (for example, sodium alginate and sodium hyaluronate).

[0153] Specific examples of the antifoaming agent include those represented by the following formula (A): [ka] {where, R 5 ~R 8 are each independently an alkyl group having 1 to 10 carbon atoms, and n and m are each independently an integer of 0 or greater, provided that n+m=0 or greater and 40 or less. It is preferable to use a surfactant (acetylene-based surfactant) containing an ethoxylated acetylene glycol represented by the formula:

[0154] Specific examples of the alkyl group having 1 to 10 carbon atoms may be linear, branched, or cyclic, and include, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group.

[0155] Specific examples of the acetylene glycol represented by formula (A) include 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 5,8-dimethyl-6-dodecyne-5,8-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 4,7-dimethyl-5-decyne-4,7-diol, 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, an ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (ethylene oxide addition mole number: 1.3), and 2,4,7,9-tetramethyl-5-decyne-4,7-diol. Examples of the antifoaming agent include an ethoxylated product (number of moles of ethylene oxide added: 4), an ethoxylated product of 3,6-dimethyl-4-octyne-3,6-diol (number of moles of ethylene oxide added: 4), an ethoxylated product of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (number of moles of ethylene oxide added: 6), an ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 10), an ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 30), and an ethoxylated product of 3,6-dimethyl-4-octyne-3,6-diol (number of moles of ethylene oxide added: 20). One type of antifoaming agent may be used alone, or two or more types may be used in combination.

[0156] The acetylene-based surfactant can be obtained as a commercially available product, and examples of such commercially available products include Olfine SPC (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 80 parts by mass, pale yellow liquid), Olfine AF-103 (manufactured by Nissin Chemical Industry Co., Ltd., pale brown liquid), Olfine AF-104 (manufactured by Nissin Chemical Industry Co., Ltd., pale brown liquid), Olfine SK-14 (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfine AK-02 (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfine AF-201F (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfine D-10PG (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50 parts by mass, pale yellow liquid), and Olfine E- Examples of such active ingredients include 1004 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow liquid), Olfine E-1010 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow liquid), Olfine E-1020 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow liquid), Olfine E-1030W (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 75 parts by mass, pale yellow liquid), Surfynol 420 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow viscous material), Surfynol 440 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow viscous material), and Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50 parts by mass, pale yellow viscous material).

[0157] As the surfactant additive, polyether surfactants and / or silicone surfactants can be used in place of or in addition to acetylene surfactants. Representative examples of polyether surfactants include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene dodecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, and polyoxyethylene-polyoxypropylene block copolymers. Among these, polyethylene glycol is particularly preferred. These surfactants may be used alone or in combination.

[0158] Polyether surfactants are also available as commercially available products, and examples of such commercially available products include E-D052, E-D054, and E-F010 (manufactured by San Nopco Ltd.).

[0159] The silicone surfactant may be linear, branched, or cyclic, as long as it contains at least a silicone chain, and may contain either a hydrophobic group or a hydrophilic group. Specific examples of the hydrophobic group include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl; cyclic alkyl groups such as cyclohexyl; and aromatic hydrocarbon groups such as phenyl. Specific examples of the hydrophilic group include amino, thiol, hydroxyl, alkoxy, carboxylic acid, sulfonic acid, phosphoric acid, nitric acid, and their organic or inorganic salts, ester, aldehyde, glycerol, and heterocyclic groups. Representative examples of silicone surfactants include dimethyl silicone, methylphenyl silicone, chlorophenyl silicone, alkyl-modified silicone, fluorine-modified silicone, amino-modified silicone, alcohol-modified silicone, phenol-modified silicone, carboxy-modified silicone, epoxy-modified silicone, fatty acid ester-modified silicone, and polyether-modified silicone.

[0160] Silicone surfactants can be obtained as commercially available products, and examples of such commercially available products include BYK-300, BYK-301, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-320, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 (all trade names, manufactured by BYK-Chemie Japan Co., Ltd.), KM-80, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, and KF-640. , KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.), SH-28PA, SH8400, SH-190, SF-8428 (all trade names, manufactured by Dow Corning Toray Co., Ltd.), Polyflow KL-245, Polyflow KL-270, Polyflow KL-100 (all trade names, manufactured by Kyoeisha Chemical Co., Ltd.), Silface SAG002, Silface SAG005, and Silface SAG0085 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.).

[0161] (amount of coating layer) The amount of the coating layer relative to the substrate, i.e., the amount of the coating layer per unit area of ​​one surface of the substrate, is preferably 0.5 g / m by weight. 2 More preferably, 1.0 g / m 2 The volume is preferably 0.15 cm or more. 3 / m 2 More than 0.30cm, preferably 3 / m 2 The upper limit of the amount of the coating layer is preferably 10.0 g / m 2 Less than 7.0 g / m 2 The volume is preferably 3.50 cm or less. 3 / m 2 Less than or equal to 2.50 cm, preferably 3 / m 2The amount of the coating layer is preferably equal to or greater than the above lower limit in terms of improving the adhesive strength between the coating layer and the electrode and suppressing thermal shrinkage, and the amount of the coating layer is preferably equal to or less than the above upper limit in terms of suppressing a decrease in ion permeability.

[0162] (Coating layer thickness) The thickness of one of the coating layers disposed on at least one of the substrates (thickness of the inorganic filler portion) is preferably 0.3 μm to 5.0 μm, more preferably 0.5 μm to 2.5 μm, and even more preferably 0.7 μm to 1.3 μm. When the coating layer has a thickness of 0.3 μm or more, thermal shrinkage can be further suppressed and the adhesive force between the electrode and the substrate can be more easily made uniform, resulting in improved characteristics of the electricity storage device. A thickness of 1.3 μm or less is preferable in that a decrease in ion permeability can be suppressed and a thin-film separator for an electricity storage device can be obtained. In other words, by reducing the thickness of the separator, an electricity storage device with a large capacity per volume can be manufactured. On the other hand, from the viewpoint of further suppressing thermal shrinkage and preventing the particulate polymer from slipping off the coating layer, the thickness of the coating layer is preferably 1.6 μm or more, or 2.1 μm or more. The thickness can be adjusted, for example, by changing the type or concentration of the particulate polymer in the coating liquid to be applied to the substrate, the amount of the coating liquid to be applied, the coating method, the coating conditions, etc. However, the method for adjusting the thickness of the coating layer is not limited thereto.

[0163] Fig. 1 is a schematic diagram of the surface of the coating layer of the separator for an electricity storage device of this embodiment. As shown in Fig. 1, inorganic filler (1) and particulate polymer (2) of a thermoplastic polymer protruding from the inorganic filler are present on the surface of the coating layer (10). In Fig. 1, the particulate polymer is present in the form of primary particles without agglomerating with other particulate polymers.

[0164] Fig. 2 is a cross-sectional view taken along the line AA of the separator for a power storage device shown in Fig. 1. As shown schematically in Fig. 2, the coating layer (20) is formed in a sloping shape, so that it continuously becomes thicker from an inorganic filler portion 1.5D or more away from the volume center of each particulate polymer in the horizontal direction (the surface direction of the coating layer) toward the protruding particulate polymer (2). The slope of the sloping coating layer becomes gentler the farther away from the protruding particulate polymer and becomes steeper the closer to the protruding particulate polymer. The inorganic filler (1) covers a part of the periphery of the protruding portion so as to ride along the contour of the particulate polymer, and the center of the protruding portion is exposed on the surface of the coating layer.

[0165] <<Method for manufacturing separator for electricity storage device>> <Method for manufacturing substrate> The method for producing substrate can adopt known production method, for example, can adopt either wet porosity method or dry porosity method.Example of wet porosity method includes, for example, when substrate is polyolefin microporous film, melt-knead polyolefin resin composition and plasticizer, form into sheet, optionally stretch, then extract plasticizer to make porous; melt-knead polyolefin resin composition that mainly comprises polyolefin resin, extrude at high draw ratio, then heat treatment and stretch to peel polyolefin crystal interface to make porous; melt-knead polyolefin resin composition and inorganic filler, form into sheet, then stretch to peel polyolefin and inorganic filler interface to make porous; and dissolve polyolefin resin composition, then immerse in poor solvent for polyolefin, solidify polyolefin and simultaneously remove solvent to make porous.

[0166] Methods for producing the substrate include, for example, the chemical bonding method, in which a web is immersed in a binder and dried to bond the fibers together; the thermal bonding method, in which heat-melting fibers are mixed into the web and the fibers are partially melted to bond the fibers together; the needle punch method, in which a web is repeatedly pierced with barbed needles to mechanically entangle the fibers; and the hydroentanglement method, in which a high-pressure water stream is sprayed from a nozzle onto the web through a net (screen) to entangle the fibers together.

[0167] As an example of a method for producing a polyolefin microporous membrane, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded and formed into a sheet, and then the plasticizer is extracted will be described below. The polyolefin resin composition and the plasticizer are melt-kneaded. Examples of melt-kneading methods include adding the polyolefin resin and, if necessary, other additives to a resin kneading device such as an extruder, kneader, Labo Plastomill, kneading roll, or Banbury mixer, and then adding and kneading the plasticizer at a desired ratio while heating and melting the resin components. In this case, it is preferable to pre-knead the polyolefin resin, other additives, and plasticizer at a predetermined ratio using a Henschel mixer or the like before adding them to the resin kneading device. More preferably, only a portion of the plasticizer is added during pre-kneading, and the remaining plasticizer is kneaded while being side-fed into the resin kneading device.

[0168] As the plasticizer, a non-volatile solvent capable of forming a homogeneous solution at a temperature equal to or higher than the melting point of the polyolefin can be used. Examples of plasticizers include 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. Of these, liquid paraffin is preferred.

[0169] The ratio of the polyolefin resin composition to the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and molded into a sheet. For example, the mass fraction of the plasticizer in a composition consisting of the polyolefin resin composition and the plasticizer is preferably 30 parts by mass or more and 80 parts by mass or less, more preferably 40 parts by mass or more and 70 parts by mass or less. By setting the mass fraction of the plasticizer in this range, it is preferable to achieve both melt tension during melt molding and the ability to form a uniform and fine pore structure.

[0170] The melt-kneaded product obtained by heating, melting, and kneading as described above is molded into a sheet. Examples of methods for producing a sheet-shaped molded product include extruding the melt-kneaded product into a sheet through a T-die or the like, contacting it with a thermal conductor, and solidifying it by cooling to a temperature sufficiently lower than the crystallization temperature of the resin component. Thermal conductors used for cooling and solidifying include metal, water, air, and plasticizer itself, but metal rolls are preferred due to their high thermal conductivity. In this case, sandwiching the melt-kneaded product between the metal rolls when contacting them further increases the thermal conductivity efficiency, orients the sheet, increasing film strength and improving the surface smoothness of the sheet, making it more preferable. The die lip spacing when extruding into a sheet from a T-die is preferably 400 μm or more and 3000 μm or less, more preferably 500 μm or more and 2500 μm or less.

[0171] The sheet-like molded article thus obtained is then preferably stretched. Either uniaxial stretching or biaxial stretching can be suitably used as the stretching treatment. Biaxial stretching is preferred from the viewpoint of the strength of the resulting microporous membrane. When the sheet-like molded article is stretched in the biaxial direction at a high magnification, the molecules are oriented in the plane direction, and the finally obtained porous substrate becomes less likely to tear and has high pin puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improved pin puncture strength, stretching uniformity, and shutdown properties.

[0172] The areal stretching ratio is preferably in the range of 20 to 100 times, more preferably 25 to 50 times. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction and 4 to 10 times in the TD direction, more preferably 5 to 8 times in the MD direction and 5 to 8 times in the TD direction. A stretching ratio within this range is preferred because it can impart more sufficient strength, prevent membrane breakage during the stretching step, and achieve high productivity. The MD direction refers to the machine direction, for example, when continuously molding a polyolefin microporous membrane, and the TD direction refers to the direction crossing the MD direction at an angle of 90°.

[0173] The sheet-like molded article obtained as described above may be further rolled. Rolling can be carried out, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion of the sheet-like molded article. The rolling area ratio is preferably more than 1 and not more than 3, more preferably more than 1 and not more than 2. A rolling ratio within this range is preferred in that it increases the film strength of the finally obtained porous substrate and allows for the formation of a more uniform porous structure in the film thickness direction.

[0174] Next, the plasticizer is removed from the sheet-like molded body to obtain a porous substrate. For example, a method for removing the plasticizer includes immersing the sheet-like molded body in an extraction solvent to extract the plasticizer, followed by thorough drying. The method for extracting the plasticizer may be either a batch method or a continuous method. To prevent shrinkage of the porous substrate, it is preferable to restrain the edges of the sheet-like molded body during the immersion and drying process. The amount of plasticizer removed can be controlled so that it is preferably 0.1 to 1.6 parts by mass, more preferably 0.2 to 1.2 parts by mass, or 0.3 to 1.0 parts by mass, based on the total mass of the resulting substrate. By keeping the amount of plasticizer within the above range, the internal resistance of the battery can be reduced while improving the bonding strength between the substrate and the coating layer.

[0175] As the extraction solvent, it is preferable to use one that is a poor solvent for the polyolefin resin and a good solvent for the plasticizer, and has 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.

[0176] In order to suppress shrinkage of the porous substrate, a heat treatment such as heat setting or heat relaxation may be performed after the stretching step or after the formation of the porous substrate. The porous substrate may also be subjected to post-treatment such as hydrophilization treatment with a surfactant or crosslinking treatment with ionizing radiation or the like.

[0177] An example of a dry porosity method, which is different from the above wet porosity method, will be given below. First, a film is produced by directly stretching and oriented after melt-kneading in an extruder without using a solvent, and then the film is subjected to an annealing step, a cold stretching step, and a hot stretching step in that order to produce a microporous membrane. Examples of dry porosity methods include a method in which a molten resin is stretched and oriented through a T-die from an extruder, and an inflation method, but the method is not particularly limited.

[0178] <Method of Arranging the Coating Layer> A coating layer is formed on at least one surface of the substrate produced as described above. For example, a method for forming the coating layer includes applying a coating liquid containing an inorganic filler and a particulate polymer of a thermoplastic polymer to the substrate, and then removing the medium, which will be described later.

[0179] As the coating liquid, a dispersion in which an inorganic filler and a particulate polymer are dispersed in a solvent or dispersion medium (hereinafter simply referred to as "medium") that does not dissolve the particulate polymer can be used. Preferably, the particulate polymer is synthesized by emulsion polymerization, and the emulsion obtained by the emulsion polymerization can be used as it is as the coating liquid.

[0180] The medium for the coating liquid is preferably one that can uniformly and stably disperse or dissolve the inorganic filler, the particulate polymer, and, if necessary, the water-soluble polymer, and examples thereof include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, methanol, toluene, hot xylene, methylene chloride, and hexane. The medium for the coating liquid is preferably water or a mixed medium consisting of water and a water-soluble organic medium. The water-soluble organic medium is not particularly limited, but examples thereof include ethanol, methanol, etc. Among these, water is more preferred. When the coating liquid is applied to a substrate, if the coating liquid penetrates into the substrate, the particulate polymer containing the polymer will clog the surface and the inside of the pores of the substrate, and the permeability will likely decrease. In this regard, in the case of an aqueous dispersion using water as the medium of the coating liquid, the coating liquid will be less likely to penetrate into the substrate, and the particulate polymer containing the polymer will likely be present mainly on the outer surface of the substrate, which is preferable because it can more effectively suppress the decrease in permeability.

[0181] The volume average particle diameter (D50) of the particulate polymer in the coating liquid may be, for example, 1.0 μm or more and 12 μm or less. From the viewpoint of obtaining a suitable distribution state of the protruding particulate polymer in the coating layer, the volume average particle diameter (D50) is preferably 1.5 μm or more, and also preferably 10 μm or less, 6.0 μm or less, 5.0 μm or less, 3.5 μm or less, 3.0 μm or less, or 2.5 μm or less. When the volume average particle diameter (D50) is equal to or greater than the above-mentioned lower limit, aggregation of the particulate polymer particles can be easily and suitably prevented. Furthermore, when the volume average particle diameter (D50) is equal to or less than the above-mentioned upper limit, the particle diameter difference with the inorganic filler can be kept within a predetermined range, thereby making it easy to suitably control sedimentation of the particulate polymer in the coating liquid. The volume average particle size of the particulate polymer can be controlled by adjusting, for example, the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, and the like for obtaining the particulate polymer.

[0182] The coating liquid may contain any additives, such as dispersants such as surfactants, thickeners, wetting agents, antifoaming agents, and pH adjusters including acids and alkalis.

[0183] Examples of methods for dispersing or dissolving the inorganic filler, the particulate polymer, and, if necessary, the water-soluble polymer in the medium of the coating liquid 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.

[0184] The procedure for preparing the coating solution is preferably to first add the water-soluble polymer to the coating solution in which the inorganic filler is dispersed, and then add the resin binder and the particulate polymer. By preparing the coating solution in this order, the water-soluble polymer adsorbs and protects the metal ions contained in the inorganic filler, and aggregation of the resin binder and the particulate polymer can be prevented.

[0185] From the viewpoint of obtaining a suitable distribution state of the protruding particulate polymer in the coating layer, the viscosity of the coating liquid is preferably 10 mPa·s or more, or 20 mPa·s or more, and is preferably 100 mPa·s or less, 80 mPa·s or less, 60 mPa·s or less, or 40 mPa·s or less. In this embodiment, the thermoplastic polymer contained in the coating liquid is preferably a particle having a large particle size of 1 μm to 10 μm. Therefore, if the viscosity of the coating liquid is 10 mPa·s or more, the thermoplastic polymer can be prevented from settling in the coating liquid. On the other hand, if the viscosity of the coating liquid is 100 mPa·s or less, turbulence in the liquid is likely to occur during stirring, improving the dispersion of the particulate polymer in the coating liquid flow and making it easier to control the coefficient of variation (CV) of the area (si) of the Voronoi polygon within the above range. Furthermore, a coating solution having a viscosity of 10 mPa·s or more and 100 mPa·s or less is preferable from the viewpoints of favorably controlling the settling of the particulate polymer, increasing the gradient of the coating layer, and increasing the contact rate between the particulate polymer and the substrate surface during the process of removing the solvent from the coating film after coating to form a coating layer. Methods for controlling the viscosity of the coating solution include adjusting the aspect ratio of the inorganic filler, the coefficient of variation of the inorganic filler particle size distribution, and the type of thickener. Using these methods, the viscosity of the coating solution can be reduced during the process of immobilizing the coating solution (forming a coating layer by drying) and the meniscus of the coating solution on the particulate polymer can be improved (wettability can be improved), resulting in an improved gradient of the coating layer and increased adhesion to the electrode.

[0186] The substrate may be surface-treated before coating, which is preferable because it makes it easier to apply the coating liquid, improves adhesion between the substrate and the thermoplastic polymer, and makes it easier to control the 180° peel strength to 200 gf / cm or more. Examples of the surface treatment method include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, ultraviolet oxidation, etc. An example of the surface treatment is corona discharge treatment.

[0187] The method for applying the coating liquid onto the substrate is not particularly limited as long as it is a method that can achieve the desired coating pattern, coating film thickness, and coating area. Examples of the coating method include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, inkjet coating method, etc. Among these, gravure coater method or spray coating method is preferred from the viewpoints of high freedom in the coating shape of the particulate polymer and easy achievement of a preferred area ratio.

[0188] The coating method is preferably a gravure coater method or the like, and the shear rate is preferably 40,000 sec -1 Over 120,000sec -1 When the shear rate is within this range, the particulate polymer is well dispersed as primary particles, and it is easier to control the 180° peel strength to 200 gf / cm or more.

[0189] Before or during coating, the coating liquid may be stirred so that the particulate polymer can be coated in a state where it is uniformly dispersed in the coating liquid. A method of turbulent agitation in the coating solution supply tank; A method in which the coating liquid is subjected to ultrasonic treatment (vibration and agitation treatment using ultrasonic waves) just before coating; It is advantageous to carry out these stirring steps in a suitable manner in order to obtain a suitable distribution state of the protruding particulate polymer in the coating layer.

[0190] The method for removing the medium from the coating film after coating is not particularly limited as long as it does not adversely affect the substrate and the coating layer. Examples include a method of drying the substrate at a temperature below its melting point while fixing it, a method of drying it under reduced pressure at a low temperature, and a method of immersing the substrate in a medium that is a poor solvent for the particulate polymer to solidify the particulate polymer into particles and simultaneously extracting the medium.

[0191] From the viewpoint of adjusting the static friction coefficient of the coating layer within the above range and / or chipping off a part of the surface of the protruding particulate polymer, it is preferable to control the conditions after the coating and drying steps as follows: -Controlling the tension applied in the direction perpendicular to the surface where the coated surface contacts the transport roll to a predetermined value or more, for example, 120 N / m or more; - The speed of the conveying roll that the coated surface comes into contact with is made slower than the separator conveying speed; The inorganic filler is formed in a sloping shape so that the protruding polymer particles do not slide off from the surrounding inorganic filler; -Increase the peel strength of the coating layer, for example, to 200 gf / cm or more.

[0192] <Preparation of Separator Wound Body> The obtained separator for an electricity storage device is preferably wound into a wound body. By forming the separator into a wound body, it can be easily unwound at high speed, thereby increasing productivity in the production process of electricity storage devices.

[0193] <Energy storage device> The electricity storage device of this embodiment includes the separator for an electricity storage device of this embodiment. The electricity storage device is not particularly limited, and examples thereof include batteries such as non-aqueous electrolyte secondary batteries, condensers, and capacitors. Among these, to take advantage of the advantages of the separator for an electricity storage device of this embodiment, batteries are preferred, non-aqueous electrolyte secondary batteries are more preferred, and lithium ion secondary batteries are even more preferred. The lithium ion secondary battery includes a positive electrode, a negative electrode, the separator for an electricity storage device of the present embodiment disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. By including the separator for an electricity storage device of the present embodiment, the electricity storage device has excellent characteristics such as electricity storage performance, and in the case of a lithium ion secondary battery, has excellent battery characteristics.

[0194] When the electricity storage device of this embodiment is a lithium ion secondary battery, there are no limitations on the positive electrode, negative electrode, and non-aqueous electrolyte, and known materials can be used for each. A suitable positive electrode may include a positive electrode having a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector. Examples of the positive electrode current collector include aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4. In addition to the positive electrode active material, the positive electrode active material layer may also contain a binder, a conductive material, and the like.

[0195] The negative electrode may preferably have a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector. Examples of the negative electrode current collector include copper foil. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, graphitizable carbon, and composite carbon; silicon, tin, metallic lithium, and various alloy materials.

[0196] 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.

[0197] <Method for manufacturing an electricity storage device> The method for producing an electricity storage device using the separator of this embodiment is not particularly limited, and the following method can be exemplified. First, the separator of this embodiment is manufactured by the above-described method. The size and shape of the separator may be, for example, a vertically elongated shape with a width of 10 mm to 500 mm, preferably 80 mm to 500 mm, and a length of 200 m to 10,000 m, preferably 1,000 m to 6,000 m. Next, the positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are laminated in this order, and wound into a circular or flat spiral to obtain a wound body. The wound body is then placed in a device can (e.g., a battery can) and an electrolyte solution is then injected into it, thereby producing a battery. Alternatively, the electrode and separator may be folded into a wound body, which is then placed in a device container (e.g., an aluminum film) and the electrolyte solution is then injected into it.

[0198] At this time, the wound body can be pressed. Specifically, a method can be exemplified in which a separator, a current collector, and an electrode having an active material layer formed on at least one surface of the current collector are stacked so that the coating layer and the active material layer face each other, and then pressed.

[0199] The pressing temperature is set to T 1.00 It is preferable to carry out the reaction at a temperature of T 1.00 is the temperature at which the minimum DDSC value is obtained between 0°C and 150°C, when the DDSC is the value obtained by differentiating the heat flow difference per unit time measured by DSC (differential scanning calorimetry) with respect to temperature. T 1.00 Pressing at a temperature above this level allows the coating layer to deform sufficiently, resulting in good adhesive strength. For example, a temperature of 35°C or higher is preferred. To prevent clogging of pores or thermal shrinkage in the separator due to heat pressing, the pressing temperature is preferably lower than the melting point of the material contained in the substrate, and more preferably 130°C or lower. The pressing pressure is preferably 20 MPa or less from the viewpoint of preventing clogging of the pores in the separator. The pressing time may be 1 second or less when using a roll press, or several hours when using a surface press, and is preferably 2 hours or less from the viewpoint of productivity. By using the separator for an electricity storage device of this embodiment and going through the above manufacturing process, it is possible to suppress press-back when a wound body made of electrodes and a separator is press-molded, thereby suppressing a decrease in yield in the device assembly process and shortening the production process time.

[0200] Adhesion may be imparted to the wound body without pressing. Specifically, an example of a method is to house the wound body in a device can, inject an electrolyte solution, and impart adhesion between the coating layer of the separator and the opposing electrode by pressure generated in the device can when manufacturing an electricity storage device, or by pressure accompanying expansion and contraction of the electrodes due to charging and discharging of the electricity storage device.

[0201] The electricity storage device, particularly the lithium ion secondary battery, manufactured as described above has excellent battery characteristics (rate characteristics) and durability against long-term continuous operation (cycle characteristics) because it is equipped with the separator of the present embodiment, which has high adhesion to the electrodes and a small thermal shrinkage rate. [Example]

[0202] Hereinafter, embodiments of the present disclosure will be specifically described with reference to examples and comparative examples, but the present disclosure is not limited to these examples and comparative examples.

[0203] <<Measurement and Evaluation Methods>> <Thickness of inorganic filler portion of coating layer, gradient of coating layer, and protrusion amount of particulate polymer> The separator was freeze-fractured, and its cross section was examined using an SEM (Model S-4800, manufactured by Hitachi Corporation). From the obtained field of view, the thickness of the inorganic filler portion of the coating layer, the gradient of the coating layer, and the protrusion amount of the particulate polymer were measured. Specifically, a separator sample was cut into a size of approximately 1.5 mm × 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule and frozen with liquid nitrogen. The sample was then fractured with a hammer. The fractured sample was vapor-deposited with osmium and observed at an accelerating voltage of 1.0 kV and 5000x magnification. As shown schematically in Figure 2, the SEM image of the fractured sample cross section was used to measure the thickness L1 (μm) of the inorganic filler portion of the coating layer, which was the distance from the substrate-coating layer boundary to the outer surface of the coating layer. Furthermore, the maximum distance L2 (μm) from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler in the coating layer formed in a sloping manner, and the maximum distance L3 (μm) to the outline of the protruding particulate polymer were measured, and the slope rate L2 / L1 of the coating layer, the coverage rate of the protruding portion (L2-L1) / (L3-L1), and the protruding amount L3-L1 of the particulate polymer were calculated. The slope rate L2 / L1 of the coating layer, the coverage rate of the protruding portion (L2-L1) / (L3-L1), and the protruding amount L3-L1 of the particulate polymer were measured at 200 points, and the average values ​​were calculated.

[0204] As a method for measuring L1, L2, and / or L3, a method can be used in which each L1 value is determined while polishing the cross section to be observed with an SEM.

[0205] <180° peel strength> A separator cut to 2 mm x 7 mm was attached to a glass plate with double-sided tape on the side opposite the coating layer to be measured, and tape (product name: Mending Tape MP-12, manufactured by 3M) was attached to the coating layer. 5 mm of the tape tip was peeled off, and the tip of the tape was clamped with a chuck using a tensile tester (model AG-IS, SLBL-1kN, manufactured by Shimadzu Corporation) so that the tape was peeled off at an angle of 180° relative to the surface of the separator. The tensile test was performed at a pulling speed of 50 mm / s, a temperature of 25°C, and a relative humidity of 40%, and the tensile strength (gf / cm) was measured.

[0206] Friction test The coated surface of the separator sample was subjected to a friction test with a table material of SKD61 (surface roughness Ra: 0.4 μm) using a Toyo Seiki Seisakusho MH-3 friction tester. The friction tests were conducted twice using the horizontal method with the following conditions: sled mass 200 g, load capacity 20 N, contact area 63 mm x 63 mm (felt material), test speed 100 mm / min, measurement distance 30 mm, temperature 23°C, and humidity 50%. The static friction coefficient was measured, and the average values ​​were calculated and shown in the table below. In the friction test, the separator sample (test specimen) cut to a size of 100 mm x 100 mm was placed so that its back surface was in contact with the felt surface of the sled.

[0207] <Contact ratio between protruding particulate polymer and substrate> The separator was freeze-fractured, and its cross section was observed using an SEM (Model S-4800, manufactured by Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a separator sample was cut into a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was fractured with a hammer. The fractured sample was vapor-deposited with osmium and observed at an accelerating voltage of 1.0 kV and 5000x magnification. Of the particulate polymers protruding from the thickness of the inorganic filler portion in the SEM image, the number of particles in contact with the substrate was counted for 200 particulate polymers with fractured cross sections, and this was determined as the contact ratio between the protruding particulate polymers and the substrate.

[0208] <Proportion of the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer> The separator was freeze-fractured, and the cross section was observed using an SEM (Model S-4800, manufactured by Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a separator sample was cut into a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was fractured with a hammer. The fractured sample was vapor-deposited with osmium and observed at an accelerating voltage of 1.0 kV and 5000x magnification. 200 particulate polymers present on the fractured surface were observed using SEM images, and the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer was counted and recorded as the percentage of the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer.

[0209] <Methylene chloride solubles> The methylene chloride soluble content in the substrate and separator was measured as follows. A 100 x 100 mm sample of the substrate or separator was neutralized and weighed using a precision balance (W0 (g)). 200 ml of methylene chloride was then added to a sealed container, and the separator was immersed at room temperature for 15 minutes. The separator was then removed, dried at room temperature for 3 hours, neutralized in the same manner as above, and weighed using a precision balance (W1 (g)). The methylene chloride soluble content was calculated using the following formula: Methylene chloride solubles (mass%) = {(W1-W0) / W0} x 100

[0210] <Total amount of metal cations> 0.60 g of separator was placed in a Teflon (registered trademark) pressure decomposition vessel, 10 ml of sulfuric acid was added, and the vessel was sealed and heated in an air bath at 200°C for 15 hours. After cooling, the solution in the vessel was transferred to a 100 ml resin measuring flask and diluted to volume to prepare a sample solution. The sample solution was measured using an inductively coupled plasma atomic emission spectrometry (ICP-OES) (model "ICPE-9000", manufactured by Shimadzu Corporation), and the content of each element was calculated using a calibration curve prepared from the standard solution.

[0211] <Heat shrinkage rate> The separator was cut into samples of 100 mm in the MD and 100 mm in the TD, and left to stand in an oven at 130°C or 150°C for 1 hour. At this time, the sample was sandwiched between two pieces of paper to prevent the 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 formula below. Measurements were taken in the MD and TD, and the TD value was displayed as the thermal shrinkage. Heat shrinkage rate (%) = {(100 - length after heating) / 100} x 100

[0212] <Weight (g / m 2 )〉 The basis weight is the unit area (1m 2 The weight (g) of the polyolefin microporous membrane per unit area (1 m) was measured using an electronic balance (AUW120D) manufactured by Shimadzu Corporation after sampling to 1 m x 1 m. If it was not possible to sample to 1 m x 1 m, the membrane was cut to an appropriate area, the weight was measured, and the unit area (1 m) was used. 2 The weight was converted to weight (g) per unit.

[0213] <Thickness of substrate or separator> A 10 cm × 10 cm square sample was cut from the substrate or separator, and nine points (3 points × 3 points) were selected in a grid pattern to measure the thickness (μm) using a micro thickness meter (Toyo Seiki Seisaku-sho, Type KBM) at room temperature of 23 ± 2° C. The average value of the measurements obtained at the nine points was calculated as the thickness of the substrate or separator.

[0214] <Porosity of substrate> A 10cm x 10cm square sample was cut from the substrate and its volume (cm 3 ) and mass (g). Using these values, the density of the substrate was calculated as 0.95 (g / cm 3 ) and the porosity was calculated using the following formula: Porosity (%) = (1 - mass / volume / 0.95) x 100

[0215] 〈Density (g / cm 3 )〉 The density of the sample was measured by the density gradient tube method (23°C) in accordance with JIS K7112:1999.

[0216] <Air permeability> The air permeability of the substrate and the separator for an electricity storage device was determined as the air permeability resistance measured in accordance with JIS P-8117 using a Gurley air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd. When the coating layer was present on only one side of the substrate, the needle could be pierced from the side where the coating layer was present.

[0217] <Piercing strength> Using a Kato Tech handy compression tester, model KES-G5, the substrate was fixed in a sample holder with an opening diameter of 11.3 mm. Next, a puncture test was performed on the center of the fixed substrate using a needle with a tip radius of curvature of 0.5 mm at a puncture speed of 2 mm / sec in an atmosphere of 25°C, to measure the maximum puncture load, which was taken as the puncture strength (gf). If the coating layer was present on only one side of the substrate, the needle could be punctured from the side where the coating layer was present.

[0218] <Average pore diameter of polyolefin microporous membrane> It is known that the fluid inside a capillary follows Knudsen flow when the mean free path of the fluid is larger than the pore diameter of the capillary, and follows Poiseuille flow when it is smaller. Therefore, it is assumed that the air flow in measuring the air permeability of a thermoplastic polymer-containing layer follows Knudsen flow, and the water flow in measuring the water permeability of a substrate follows Poiseuille flow.

[0219] The average pore size d (μm) of the polyolefin microporous membrane is expressed as the air permeation rate constant R gas (m 3 / (m 2 ·sec·Pa)), water permeation rate constant R liq (m 3 / (m 2 The following equation was used to calculate the thickness of the film from the air pressure (m / sec), the molecular velocity of air (ν), the viscosity of water (η), the standard pressure (Ps) (=101325 Pa), the porosity (ε) (%), and the film thickness (L) (μm). d=2ν×(Rliq / R gas )×(16η / 3Ps)×10 6

[0220] where R gas was calculated from the air permeability (sec) using the following formula: R gas =0.0001 / (air permeability × (6.424 × 10 -4 )×(0.01276×101325))

[0221] Also, R liq is the permeability (cm 3 / (cm 2 sec Pa)) using the following formula: R liq =water permeability / 100

[0222] The water permeability was determined as follows: A thermoplastic polymer-containing layer, which had been immersed in ethanol beforehand, was placed in a stainless steel liquid permeation cell with a diameter of 41 mm. After washing the ethanol out of this layer with water, water was passed through the cell at a differential pressure of about 50,000 Pa. The amount of water permeated (cm) after 120 seconds was measured. 3 ) the amount of water permeable per unit time, unit pressure and unit area was calculated, and this was taken as the permeability.

[0223] Also, ν is the gas constant R (= 8.314), absolute temperature T (K), pi (π), and the average molecular weight of air M (= 2.896 × 10 -2 kg / mol) using the following formula: ν=((8R×T) / (π×M)) 1 / 2

[0224] <Glass transition temperature of thermoplastic polymer> An appropriate amount of an aqueous dispersion containing a thermoplastic polymer (solid content = 38 to 42 parts by mass, pH = 9.0) was placed in an aluminum dish and left to stand at room temperature for 24 hours to obtain a dried film. Approximately 17 mg of the dried film was placed in an aluminum container for measurement, and a DSC curve under a nitrogen atmosphere and a DSC curve were obtained using a DSC measurement device (Shimadzu Corporation, model "DSC6220"). The measurement conditions were as follows: First stage temperature increase program: Start at 30°C, increase temperature at a rate of 10°C per minute. After reaching 150°C Maintain for 5 minutes. Second stage temperature reduction program: Reduce the temperature from 110°C at a rate of 10°C per minute. After reaching -50°C, maintain the temperature for 5 minutes. Third-stage temperature increase program: Increase the temperature from -50°C to 150°C at a rate of 10°C per minute. DSC and DDSC data were collected during this third-stage temperature increase.

[0225] The glass transition temperature of the obtained DSC curve was determined by the method described in JIS-K 7121. Specifically, the glass transition temperature (Tg) was determined as the temperature at the point where a line extending the low-temperature baseline of the DSC curve toward the high-temperature side and a line equidistant in the vertical direction from the line extending the high-temperature baseline of the DSC curve toward the low-temperature side intersect with the curve of the stepwise change in the glass transition.

[0226] <Aspect ratio of inorganic filler in coating layer> The surface of the osmium-deposited separator for a power storage device was observed using a scanning electron microscope (SEM) (model "S-4800," manufactured by Hitachi Corporation) at an accelerating voltage of 1.0 kV and 10,000x magnification to measure the aspect ratio. The inorganic filler in the coating layer was image-processed from the SEM image to determine the aspect ratio. Even when inorganic fillers were bonded to each other, the length and width of each inorganic filler were clearly recognized, and the aspect ratio was calculated based on these. Specifically, 10 particles with clearly recognizable length and width were selected, and the average value of the long axis length of each inorganic filler divided by the short axis length was used as the aspect ratio. When there were fewer than 10 particles with clearly recognizable length and width in one field of view, 10 particles were selected from images of multiple fields of view.

[0227] <Particle size distribution and average particle size of inorganic fillers> The particle size distribution of the inorganic filler was measured using a particle size measuring device (product name "Microtrac UPA150" manufactured by Nikkiso Co., Ltd.) The sample solution to be measured was the pre-coating dispersion liquid, and the measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds. The particle size distribution (Cv value) of the inorganic filler was calculated by dividing the standard deviation SD of the volume average particle size (D50) in the obtained data by the D50 value.

[0228] <Volume average particle diameter (D50) of thermoplastic polymer in aqueous dispersion and volume average particle diameter (D50) of resin binder> The volume average particle diameter (D50) of the thermoplastic polymer in the aqueous dispersion and the volume average particle diameter (D50) of the resin binder were measured using a particle diameter measuring device (product name "Microtrac UPA150" manufactured by Nikkiso Co., Ltd.) The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds, and the particle diameter (D50) value at which the cumulative volume of the obtained data reached 50% was recorded as the volume average particle diameter (D50).

[0229] Observation of the presence or absence of defects on the surface of particulate polymer spheres and calculation of the defect rate The cross section of the osmium-deposited separator for a power storage device was observed at an acceleration voltage of 1.0 kV and a magnification of 10,000 using a scanning electron microscope (SEM) (model "S-4800", manufactured by Hitachi Corporation) for measurement. Specifically, for 200 arbitrary particulate polymers, the maximum width (W) in the horizontal direction relative to the separator surface and the maximum height (H) in the vertical direction relative to the separator surface were measured as shown in Figure 8, and the maximum height (H) was divided by the maximum width (W) to calculate the defect rate, and the average value thereof was used as the defect rate of the particulate polymer.

[0230] <Volume average particle size (D50) and particle size distribution of particulate polymer in coating layer> The cross section of the osmium-deposited separator for a power storage device was measured by observing it with a scanning electron microscope (SEM) (model "S-4800", manufactured by Hitachi Corporation) at an acceleration voltage of 1.0 kV and a magnification of 10,000. Specifically, the area-equivalent circle diameter was measured for 200 random particulate polymers, and the number-average particle diameter MN and volume-average particle diameter MV were calculated from these values, and the particle size distribution of the particulate polymer was calculated as MV / MN.

[0231] <Surface observation of the coating layer and Voronoi division> The surface of the osmium-deposited separator for a power storage device was subjected to elemental mapping using a scanning electron microscope (SEM) (model "SU-8220", manufactured by Hitachi) and energy dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", manufactured by Oxford University Press). Secondary electrons were selected as the SEM detector, and mapping measurements of carbon atoms on the surface of the coating layer on the separator were performed in 10 fields of view at an acceleration and transmission voltage of 3 kV, with 20 mapping accumulations, and at a magnification of 500x or 3000x depending on the particle size of the particulate polymer, as shown in FIG. 7 . The area of ​​the Voronoi polygon (s i ), the total number of Voronoi polygons (n), the mean value (m), the standard deviation (sd), and the coefficient of variation (cv) were obtained as the average values ​​of 10 fields. Specifically, the carbon atom mapping image was subjected to Gaussian Blur processing (Sigma = 5) using image processing software (ImageJ), then binarized using the Threshold function (Auto), and then subjected to Watershed processing. This processed image was subjected to Voronoi division using the cv2.Subdiv2D.getVoronoiFacetList method of the opencv-python library (version 4.5.4.60) in the programming language Python. Furthermore, when Voronoi division was performed in the observation field, unclosed regions were not included in the calculation of the area of ​​the Voronoi polygons.

[0232] <Ratio of particulate polymer falling off> The surface of the osmium-deposited separator for the power storage device was subjected to elemental mapping using a scanning electron microscope (SEM) (model "SU-8220", manufactured by Hitachi) and an energy dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", manufactured by Oxford University Press). Secondary electrons were selected as the SEM detector, and the acceleration transmission was set to 3 kV with 20 mapping accumulations. Carbon atom mapping measurements were performed in 10 fields of view at magnifications ranging from 500x to 3000x depending on the particle size of the particulate polymer. From the carbon atom mapping images, Gaussian spectroscopy was performed using image processing software (ImageJ). After performing blur processing (Sigma = 5), the image was binarized using the threshold function (Auto) and the projected area of ​​the particulate polymer when the coating layer surface was viewed in plan was calculated. The average value of these 10 fields of view was taken as the projected area (Sr) of the particulate polymer when the coating layer surface was viewed in plan. In addition, the SEM images of the same 10 fields of view where the carbon atom mapping measurement was performed were similarly processed using image processing software (ImageJ) to calculate the area of ​​particulate polymer that had slid down when the coating layer surface was viewed in plan. The average value of these 10 fields of view was taken as the area of ​​particulate polymer that had fallen down when the coating layer surface was viewed in plan. From the calculated Sr and Sd values, the particulate polymer falling area ratio Sd / (Sr + Sd) × 100 (%) was calculated.

[0233] <Rate characteristics> a. Preparation of the positive electrode The positive electrode active material was nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co = 1:1:1 (element ratio), density 4.70 g / cm 3 ) as a conductive additive, graphite powder (KS6) (density 2.26 g / cm 3 1.6 parts by mass of acetylene black powder (AB) (density 1.95 g / cm 3 3.8 parts by mass of polyvinylidene fluoride (PVdF) (density 1.75 g / cm 3) as a binder. 3) were mixed in a ratio of 4.2 parts by mass, and the mixture was dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil as a positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression molded using a roll press to prepare a positive electrode. The amount of positive electrode active material applied was 109 g / m 2 It was.

[0234] b. Preparation of negative electrode Graphite powder A (density 2.23 g / cm) was used as the negative electrode active material. 3 87.6 parts by mass of graphite powder B (density 2.27 g / cm 3 A slurry was prepared by dispersing 9.7 parts by mass of carboxymethylcellulose (number average particle diameter 6.5 μm) in purified water, as well as 1.4 parts by mass (solid content equivalent) of ammonium salt of carboxymethylcellulose (aqueous solution with a solid content concentration of 1.83 parts by mass), and 1.7 parts by mass (solid content equivalent) of diene rubber latex (aqueous solution with a solid content concentration of 40 parts by mass). This slurry was applied to one side of a 12 μm thick copper foil as a negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression molded using a roll press to prepare a negative electrode. The amount of negative electrode active material applied was 5.2 g / m 2 It was.

[0235] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0236] d. Battery assembly The separator or substrate was cut into a 24 mm diameter circle, and the positive and negative electrodes were each cut into a 16 mm diameter circle. The negative electrode, separator or substrate, and positive electrode were stacked in this order, with the active material surfaces of the positive and negative electrodes facing each other, and then placed in a lidded stainless steel container. The container and lid were insulated, with the container in contact with the copper foil of the negative electrode, and the lid in contact with the aluminum foil of the positive electrode. A battery was assembled by pouring 0.4 ml of the nonaqueous electrolyte into the container and sealing it.

[0237] e. Evaluation of rate characteristics The simple battery assembled in step d was charged at 25°C at a current of 3 mA (approximately 0.5 C) to a battery voltage of 4.2 V, and then the current was tapered from 3 mA to maintain 4.2 V. This initial charging was carried out for a total of approximately 6 hours. The battery was then discharged at a current of 3 mA to a battery voltage of 3.0 V. Next, the battery was charged at a current of 6 mA (approximately 1.0 C) to a battery voltage of 4.2 V, and then the current was tapered from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. The discharge capacity when the battery was then discharged at a current of 6 mA to a battery voltage of 3.0 V was taken as the 1 C discharge capacity (mAh). Next, the battery was charged at 25°C at a current of 6 mA (approximately 1.0 C) up to a battery voltage of 4.2 V, and then the current was tapered from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. The battery was then discharged at a current of 12 mA (approximately 2.0 C) down to a battery voltage of 3.0 V, and the discharge capacity was taken as the 2C discharge capacity (mAh). The ratio of the 2C discharge capacity to the 1C discharge capacity was then calculated, and this value was used as the rate characteristic. Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) x 100 Evaluation criteria for rate characteristics (%) A (Good): Rate characteristics are over 85% B (Acceptable): Rate characteristics are over 80% and less than 85% C (bad): Rate characteristics are 80% or less

[0238] <Adhesion strength with electrode (before electrolyte injection)> The separator was cut into a rectangular shape of 20 mm wide x 70 mm long, and was layered on a positive electrode cut to a size of 15 mm x 60 mm to form a separator and electrode laminate, and this laminate was pressed under the following conditions. Temperature: 90℃ Press pressure: 1 MPa Press time: 5 seconds The peel strength between the separator and electrode after pressing was measured by a 90° peel test at a peel rate of 50 mm / min using force gauges ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. The average value of the peel strength in the 40 mm length peel test conducted under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Excellent): Peel strength is 5N / m or more B (Excellent): Peel strength is 2N / m or more and less than 5N / m C (Good): Peel strength is 1N / m or more and less than 2N / m D (unacceptable): Peel strength is less than 1N / m

[0239] <Adhesion strength with electrode (after electrolyte injection)> The separator was cut into a rectangular shape measuring 20 mm wide x 70 mm long, and placed on top of a positive electrode cut to 15 mm x 60 mm to form a separator-electrode laminate. This laminate was then inserted into an aluminum laminate film, and 0.4 ml of electrolyte (a mixture of EC / DEC = 1 / 2 containing 1 mol / L LiPF6) was added. After sealing, the battery was left to stand for 12 hours and pressed under the following conditions. Temperature: 90℃ Press pressure: 1 MPa Press time: 1 minute The peel strength between the separator and electrode after pressing was measured by a 90° peel test at a peel rate of 50 mm / min using force gauges ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. The average value of the peel strength in the 40 mm length peel test conducted under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Good): Peel strength is 5N / m or more B (Acceptable): Peel strength is 2N / m or more and less than 5N / m C (poor): Peel strength is 1N / m or more and less than 2N / m D (unacceptable): Peel strength is less than 1N / m

[0240] <Powder shedding> A 12 mm wide x 100 mm long tape (manufactured by 3M) was attached to the coating layer surface of the separator. The force required to peel the tape from the sample at a rate of 50 mm / min was measured using a 90° peel strength tester (manufactured by IMADA, product name IP-5N). Based on the measurement results, the adhesive strength was evaluated according to the following criteria. A (good): 59N / m (6gf / mm) or more B (tolerance): 40N / m or more and less than 59N / m C (poor): Less than 40N / m

[0241] <Cycle characteristics> a. Preparation of the positive electrode The positive electrode active material was nickel, cobalt, and aluminum composite oxide (NCA) (Ni:Co:Al = 90:5:5 (element ratio), density 3.50 g / cm 3 100 parts by mass of acetylene black powder (AB) as a conductive material, 1.25 parts by mass of acetylene black powder (AB) as a conductive material, and 1.0 part by mass of polyvinylidene fluoride (PVdF) as a binder were mixed and dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to both sides of a 15 μm thick aluminum foil that served as a positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to prepare a positive electrode. The amount of positive electrode active material applied at this time was 456 g / m 2 It was.

[0242] b. Preparation of negative electrode A slurry was prepared by dispersing 86.0 parts by weight of graphite powder and 4.5 parts by weight of silicon oxide (SiO) as the negative electrode active material, and 1 part by weight of sodium carboxymethyl cellulose and 1.0 part by weight of styrene-butadiene rubber (SBR) as binders in purified water. This slurry was applied to both sides of a 7.5 μm-thick copper foil that served as the negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press to produce a negative electrode. The amount of negative electrode active material applied was 266 g / m. 2 It was.

[0243] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate=25:70:5 (weight ratio) to a concentration of 1.4 mol / L.

[0244] d. Battery assembly A positive electrode (63 mm wide), a negative electrode (64 mm wide), and a separator (67 mm wide) were stacked and spirally wound to form a wound body, which was then placed in a cylindrical battery can with an outer diameter of 21 mm and a height of 70 mm, and the nonaqueous electrolyte solution was poured into the can and sealed to assemble the battery.

[0245] e. Evaluation of cycle characteristics The battery assembled in step d was charged at 25°C at a current of 3 mA (approximately 0.5 C) to a battery voltage of 4.2 V, and then charged to a current of 50 mA while maintaining 4.2 V. The battery was then discharged at 0.2 C to a battery voltage of 2.5 V, and the initial capacity was determined. Next, the battery was charged at 0.3 C to a battery voltage of 4.2 V, and then charged to a current of 50 mA while maintaining 4.2 V, and then discharged at 1 C to a battery voltage of 2.5 V. This cycle was repeated, and the cycle characteristics were evaluated using the capacity retention rate after 500 cycles relative to the initial capacity (capacity at the first cycle) according to the following criteria. A (Good): 80% or more capacity retention rate B (Acceptable): Capacity retention rate of 75% or more but less than 80% C (unacceptable): Less than 75% capacity retention

[0246] <<Example of substrate manufacturing>> <Production of polyolefin microporous membrane B1> 45 parts by mass of a homopolymer high-density polyethylene having an Mv of 700,000, 45 parts by mass of a homopolymer high-density polyethylene having an Mv of 300,000, and 10 parts by mass of a mixture of a homopolymer polypropylene having an Mv of 400,000 and a homopolymer polypropylene having an Mv of 150,000 (mass ratio = 4:3) were dry-blended using a tumbler blender. 99 parts by mass of the resulting polyolefin mixture was added with 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant, and the mixture was dry-blended again using the tumbler blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder using a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 × 10 -5 m 2 / s) was injected into the extruder cylinder using a plunger pump. The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in 100 parts by mass of the total mixture extruded was 65 parts by mass, i.e., so that the proportion of the resin composition was 35 parts by mass.

[0247] Next, they were melt-kneaded in a twin-screw extruder while being heated to 230°C, and the resulting molten mixture was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 80°C. The extrudate was brought into contact with the cooling roll, cast, and cooled and solidified to obtain a sheet-like molded product with a thickness of 1.5 mm. This sheet was stretched at a stretching ratio of 7×6.4 at a temperature of 20° C. using a simultaneous biaxial stretching machine, then immersed in methylene chloride to extract and remove the liquid paraffin, dried, and then stretched in the transverse direction by 1.8 times at a temperature of 130° C. using a tenter stretching machine. The stretched sheet was then relaxed by about 10% in the width direction and heat-treated to obtain polyolefin microporous membrane B1 as a substrate. The obtained microporous polyolefin membrane was evaluated according to the above-mentioned methods, and the evaluation results are shown in the table below.

[0248] <Production of polyolefin microporous membrane B2> Polyolefin microporous membrane B2 was produced in the same manner as polyolefin microporous membrane B1, except that the thickness of the sheet-form molded product was changed to 0.5 mm. The results of measurement and evaluation of polyolefin microporous membrane B2 are shown in Table 1.

[0249] [Table 1]

[0250] <<Preparation Example of Water Dispersion of Particulate Polymer>> <Preparation of Water Dispersion A1 of Particulate Polymer> A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., referred to as "KH1025" in the tables; the same applies hereinafter), and 0.5 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, referred to as "SR1025" in the tables; the same applies hereinafter), and the internal temperature of the reaction vessel was raised to 95°C. Subsequently, while maintaining the internal temperature of the vessel at 95°C, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (referred to as "APS(aq)" in the tables; the same applies hereinafter) was added.

[0251] On the other hand, 71.5 parts by mass of methyl methacrylate (MMA), 18.9 parts by mass of n-butyl acrylate (BA), 2 parts by mass of 2-ethylhexyl acrylate (EHA), 0.1 parts by mass of methacrylic acid (MAA), 0.1 parts by mass of acrylic acid (AA), 2 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 5 parts by mass of acrylamide (AM), 0.4 parts by mass of glycidyl methacrylate (GMA), 0.4 parts by mass of trimethylolpropane triacrylate (A-TMPT) (manufactured by Shin-Nakamura Chemical Co., Ltd.), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane (AcSi), 3.0 parts by mass of KH1025, SR1025 A mixture of 3.0 parts by mass of ammonium persulfate, 0.05 parts by mass of sodium p-styrenesulfonate (NaSS), 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes using a homomixer to prepare an emulsion. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. Dropping began 5 minutes after the addition of the ammonium persulfate aqueous solution to the reaction vessel, and the entire amount of emulsion was added dropwise over 150 minutes. During the dropwise addition of the emulsion, the temperature inside the vessel was maintained at 80°C. During this time, the stirring bar placed inside the reaction vessel was constantly stirred using a magnetic stirrer.

[0252] After the dropwise addition of the emulsifying liquid was completed, the internal temperature of the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature to obtain an emulsion. The pH of the resulting emulsion was adjusted to 9.0 using an aqueous ammonium hydroxide solution (25% aqueous solution), yielding an acrylic copolymer latex with a concentration of 40 parts by mass (aqueous dispersion A1). The glass transition temperature (Tg) and volume average particle size (D50) of the thermoplastic polymer contained in the resulting aqueous dispersion A1 were evaluated using the methods described above. The results are shown in the table below.

[0253] <Preparation of Water Dispersions A2 to A5 of Particulate Polymer> Aqueous dispersions A2 to A5 were obtained in the same manner as aqueous dispersion A1, except that the composition of the emulsion was changed as shown in the table below, and the physical properties were evaluated. The results obtained are shown in the table below.

[0254] <Preparation of Water Dispersion A1-1 of Particulate Polymer> A portion of the aqueous dispersion A1 was taken and used as a seed polymer to carry out multi-stage polymerization to synthesize aqueous dispersion A1-1. Specifically, a mixture of 20 parts by mass of aqueous dispersion A1 (solid content equivalent) and 70.4 parts by mass of ion-exchanged water was first added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, and the internal temperature of the reaction vessel was raised to 80°C. Then, while maintaining the internal temperature of the vessel at 80°C, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added. This completes the initial charging process.

[0255] On the other hand, a mixture of 71.5 parts by mass of methyl methacrylate (MMA), 18.9 parts by mass of n-butyl acrylate (BA), 2 parts by mass of 2-ethylhexyl acrylate (EHA), 0.1 parts by mass of methacrylic acid (MAA), 0.1 parts by mass of acrylic acid (AA), 2 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 5 parts by mass of acrylamide (AM), 0.4 parts by mass of glycidyl methacrylate (GMA), 0.4 parts by mass of trimethylolpropane triacrylate (A-TMPT), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane (AcSi), 3 parts by mass of KH1025, 3 parts by mass of SR1025, 0.05 parts by mass of sodium p-styrenesulfonate (NaSS), 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes using a homomixer to prepare an emulsion. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. The addition began 5 minutes after the addition of the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the addition of the emulsion, the temperature inside the vessel was maintained at 80°C. At this time, the stirring bar placed inside the reaction vessel was constantly stirred with a magnetic stirrer.

[0256] After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C while stirring for 90 minutes, and then cooled to room temperature to obtain an emulsion. The pH of the resulting emulsion was adjusted to 9.0 using an aqueous ammonium hydroxide solution (25% aqueous solution), yielding an acrylic copolymer latex with a concentration of 40 parts by mass (aqueous dispersion A1-1). The resulting aqueous dispersion A1-1 was evaluated using the methods described above. The results are shown in Table 2.

[0257] <Preparation of Aqueous Dispersions A2-1, A3-1 to A3-8, A4-1, and A5-1> Copolymer latexes (water dispersions A2-1, A3-1 to A3-8, A4-1, and A5-1) were obtained in the same manner as for water dispersion A1-1, except that the compositions of the seed polymer, monomers, and other raw materials were changed as shown in Table 2. The obtained water dispersions were each evaluated by the above-mentioned methods. The obtained results are shown in Table 2.

[0258] [Table 2-1]

[0259] [Table 2-2]

[0260] <Explanation of Abbreviations> ·emulsifier KH1025: "Aqualon KH1025" registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "ADEKA REASOAP SR1025" registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution NaSS: Sodium p-styrenesulfonate

[0261] Initiator APS(aq): Ammonium persulfate (2% aqueous solution)

[0262] Monomer MAA: methacrylic acid AA: acrylic acid MMA: methyl methacrylate BA: n-butyl acrylate BMA: n-butyl methacrylate EHA: 2-ethylhexyl acrylate CHMA: Cyclohexyl methacrylate St: styrene AN: Acrylonitrile HEMA: 2-hydroxyethyl methacrylate AM: acrylamide GMA: Glycidyl methacrylate A-TMPT: Trimethylolpropane triacrylate AcSi: γ-methacryloxypropyltrimethoxysilane

[0263] <Separator manufacturing example> Example 1 A pre-coating dispersion was prepared by mixing 100 parts by weight of water with 0.3 parts by weight of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) and 100 parts by weight of an inorganic filler, aluminum oxide hydroxide (boehmite, average particle size 450 nm), and processing it through a bead mill. To the pre-coating dispersion, 0.2 parts by weight of a water-soluble polymer component, carboxymethyl cellulose (CMC), was added per 100 parts by weight of the inorganic filler. Then, 4 parts by weight of an acrylic latex suspension (solids concentration 40%, volume average particle size 150 nm, Tg -10°C) as a resin binder, and 10 parts by weight of Water Dispersion A3-5 were mixed and uniformly dispersed to prepare a coating solution (solids content 40 parts by weight) containing a thermoplastic polymer.

[0264] Both surfaces of the polyolefin microporous membrane B1 were treated by corona discharge. Then, a coating solution was applied to one side of the polyolefin microporous membrane B1 using a gravure coater. In the coating solution supply tank, the coating solution was stirred using a Bernoulli flow stirrer BEAG (manufactured by Medec, rotation speed 650 rpm), and the shear rate of the gravure coater was 80,000 sec -1 The coating area ratio of the coating layer to the polyolefin microporous membrane at this time was 100%. The applied coating solution was then dried at 60°C to remove water. In this way, a separator having a coating layer formed on one side of the polyolefin microporous membrane B1 was obtained.

[0265] Examples 2 to 15 and Comparative Examples 1 to 4 Separators of Examples and Comparative Examples were obtained in the same manner as in Example 1, except that the polyolefin microporous membrane, the composition of the coating solution, the coating conditions, etc. were changed as shown in the table below. In Comparative Example 1, an inclined paddle stirrer was used to stir the coating liquid. In the separators of Examples 2 to 15 and Comparative Examples 1 and 2, the particulate polymer was dispersed in the form of primary particles, while in the separator of Comparative Example 4, the particulate polymer was dispersed in the form of secondary particles.

[0266] <Evaluation of curl occurrence, and evaluation of winding and step misalignment> (curl value) The separator was cut into a piece measuring 20 cm in MD x 5 cm in TD and placed on a flat table. After 30 seconds, the MD length (A cm) of the microporous membrane in contact with the table was measured and calculated as the curl value using the following formula. [Curl value] = 20cm - Acm The MD length (A cm) of the separator in contact with the support was measured at all points in the TD direction of the microporous membrane where the separator was in contact with the support. Measurements were performed at a temperature of 23±2°C and a relative humidity of 40%. The evaluation criteria for curl value are as follows:

[0267] (winding misalignment) As an index of winding stability, the winding deviation after slitting was evaluated. The separator was slit into a width of 60 mm using a TH4C (product name) slitter manufactured by Nishimura Manufacturing Co., Ltd. under conditions of a payout tension of 100 N / m, a take-up tension of 100 N / m, and a running speed of 100 m / min, and then 2000 m was wound onto a 3-inch paper tube to obtain a wound body. The degree of winding misalignment of the wound body at this time was evaluated. Note that if a misalignment of less than 0.3 mm occurred after slitting, it was determined that there was no winding misalignment, and if a misalignment of 0.3 mm or more occurred, it was determined that there was winding misalignment. The evaluation was carried out for 10 windings, and the winding misalignment was evaluated based on the number of windings that were judged to have winding misalignment. The evaluation criteria for winding misalignment are as follows:

[0268] (Step misalignment) As an index of impact resistance stability of the separator wound body having a winding length of 2000 m wound around a 3-inch paper tube obtained as described above for "winding misalignment," step misalignment was evaluated as follows. A microporous membrane roll was set on the inspection jig shown in Figure 9 and dropped from a height of 300 mm onto an impact table to apply an impact to the roll. The roll that had been subjected to the impact was placed horizontally, and the distance from the bottom surface of the roll to the top surface of the roll was measured, and the deviation width was calculated using the following formula. The longer this distance, the greater the step deviation. Misalignment width = (distance between the top and bottom surfaces of the winding after step misalignment) - (winding slit width) The evaluation criteria for step misalignment are as follows:

[0269] (Curl evaluation criteria) A: 19cm or more B: Less than 19cm, 15cm or more C: Less than 15cm (Evaluation criteria for winding misalignment) A: Winding misalignment 0 / 10 B: Winding misalignment 1 to 2 turns / 10 turns C: Winding misalignment of 3 or more turns (Evaluation criteria for step misalignment) A: 0mm or more and less than 1mm B: 1mm or more and less than 10mm C: 10mm or more

[0270] The measurement results and evaluation results of the examples and comparative examples are shown in the table below.

[0271] [Table 3-1]

[0272] [Table 3-2]

[0273] [Table 4] [Industrial Applicability]

[0274] The separator for an electricity storage device of the present disclosure can be suitably used in various electricity storage devices, preferably lithium ion secondary batteries. [Explanation of symbols]

[0275] 1. Inorganic filler 2 Particulate polymer 10. Substrate (substrate being a polyolefin microporous membrane) 20 Covering layer H: Maximum height of polymer particles in the direction perpendicular to the separator surface W: Maximum width of the particulate polymer in the horizontal direction to the separator surface

Claims

1. a substrate that is a polyolefin microporous membrane containing polyolefin as a main component; a coating layer disposed on at least one surface of the substrate, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; the particulate polymer includes particulate polymer protruding from the surface of the inorganic filler portion, the static friction coefficient of the coating layer is 0.40 or more and 0.60 or less; a part of the surface of the protruding particulate polymer is defective, and the defect rate of the spherical surface of the protruding particulate polymer is 0.74 to 0.93; Separators for power storage devices.

2. A substrate that is a polyolefin microporous membrane containing polyolefin as a main component; a coating layer disposed on at least one surface of the substrate, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; the particulate polymer includes particulate polymer protruding from the surface of the inorganic filler portion, the static friction coefficient of the coating layer is 0.40 or more and 0.60 or less; the coating layer is formed in a gradient shape so as to become thicker toward the protruding particulate polymer, A separator for an electric storage device, in which the average value of the slope rate L2 / L1 of the coating layer is 1.2 or more, where L1 is the thickness of the inorganic filler portion and L2 is the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler formed in the sloped shape.

3. A substrate that is a polyolefin microporous membrane containing polyolefin as a main component; a coating layer disposed on at least one surface of the substrate, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; the particulate polymer includes particulate polymer protruding from the surface of the inorganic filler portion, the static friction coefficient of the coating layer is 0.40 or more and 0.60 or less; the coating layer is formed in a gradient shape so as to become thicker toward the protruding particulate polymer, A separator for an electricity storage device, in which an average value of a coverage rate (L2-L1) / (L3-L1) of the protruding particulate polymer is 0.4 or more, where L1 is the thickness of the inorganic filler portion, L2 is the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler formed in the inclined shape, and L3 is the maximum distance from the boundary line between the substrate and the coating layer to the outline of the protruding particulate polymer.

4. A substrate that is a polyolefin microporous membrane containing polyolefin as a main component; a coating layer disposed on at least one surface of the substrate, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; the particulate polymer includes particulate polymer protruding from the surface of the inorganic filler portion, the static friction coefficient of the coating layer is 0.40 or more and 0.60 or less; In observing the surface of the coating layer, Voronoi division is performed using the protruding particulate polymer as a base point, and the area (s ｉ The separator for an electricity storage device has a coefficient of variation (cv) of 0.10 or more and 0.60 or less.

5. 5. The separator for an electricity storage device according to claim 1, wherein, upon observation of the surface of the coating layer, the proportion of an area of ​​particulate polymer detached portions to the total area of ​​the particulate polymer is 10% or less.

6. 5. The separator for an electricity storage device according to claim 1, wherein 20% or more of the protruding particulate polymer is in contact with the surface of the substrate.

7. 5. The separator for an electricity storage device according to claim 1, wherein the coating layer has a 180° peel strength from the substrate of 200 gf / cm or more.

8. 5. The separator for an electricity storage device according to claim 1, wherein the number of the protruding particulate polymers is 50% or more of the total number of particulate polymers contained in the coating layer.

9. 5. The separator for an electricity storage device according to claim 1, wherein the particle size distribution of the particulate polymer is 1.1 or less.

10. The separator for an electricity storage device according to any one of claims 1 to 4, wherein the particulate polymer is a primary particle.

11. The separator for an electricity storage device according to claim 10 , wherein the primary particles have an average particle size of 1 μm or more and 10 μm or less.

12. The separator for an electricity storage device according to any one of claims 1 to 4, which has a TD heat shrinkage rate of 5% or less at 130°C for 1 hour.

13. The separator for an electricity storage device according to any one of claims 1 to 4, which has a TD heat shrinkage rate of 5% or less at 150°C for 1 hour.

14. An electricity storage device comprising the separator for an electricity storage device according to any one of claims 1 to 4.

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