Separator for energy storage devices and energy storage devices including the same

Abstract

To provide a separator for power storage device capable of improving productivity of power storage device such as cell production property, and a power storage device including the same.SOLUTION: A separator for power storage device includes: a base material 10, which is a polyolefin microporous membrane containing polyolefin as a major component; and a coating layer 20 disposed on at least one surface of the base material 10. The coating layer 20 includes an inorganic filler 1 and a thermoplastic polymer particulate polymer. The particulate polymer includes a particulate polymer 2 protruding from a surface of a part of the inorganic filler 1. The static friction coefficient of the coating layer 20 is from 0.10 to less than 0.40.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a separator for energy storage devices and an energy storage device including the same. [Background technology]

[0002] The development of energy storage devices, typified by lithium-ion secondary batteries, is actively underway. Generally, energy storage devices include a positive electrode, a negative electrode, and a microporous membrane separator between them. The separator has the function of preventing direct contact between the positive and negative electrodes and allowing ions to pass through the electrolyte held in the micropores. The separator is required to have safety properties such as the ability to quickly stop the battery reaction in the event of abnormal overheating (fuse properties) and the ability to maintain its shape even at high temperatures to prevent the dangerous situation of the positive and negative electrodes directly reacting (short-circuit resistance properties).

[0003] Non-aqueous secondary batteries, such as lithium-ion batteries, are marketed in a variety of shapes, including cylindrical, prismatic, and pouch types, depending on their application. The manufacturing method of the battery differs depending on its shape. For example, the manufacturing method of a prismatic battery involves pressing a laminate of electrodes and a separator, or a wound laminate of electrodes and a separator, and inserting it into a rectangular outer casing.

[0004] In recent years, in order to increase the capacity of energy storage devices, efforts have been made to reduce the volume of energy storage devices by heat-pressing a laminate of electrodes and separators, or by heat-pressing a wound laminate of electrodes and separators. In this process, a technique is known in which a coating layer containing a thermoplastic polymer that exhibits adhesive function under predetermined conditions is placed on the substrate to fix the electrodes and separators after heat-pressing and maintain the volume at the time of pressing, thereby improving the adhesion between the entire separator and the electrodes.

[0005] Patent Document 1 describes a separator having a porous coating layer containing organic polymer particles, with the aim of increasing the bonding strength between the separator and the electrode and enhancing safety without performing a humidification phase separation step of the organic binder polymer and a secondary coating step of the 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 comprising a functional layer containing inorganic particles and particulate polymer, with the aim of providing a separator that has excellent adhesion and heat resistance and improves electrolyte injection properties. In this functional layer, when viewed from above, the area occupied by inorganic particles per unit area of ​​the functional layer surface exceeds 90%, the volume-average particle diameter of the particulate polymer is within a specific range, and the volume-average particle diameter of the particulate polymer is greater than the thickness of the inorganic particle layer.

[0007] Patent Document 3 describes a separator comprising a functional layer containing inorganic particles and particulate polymer, with the aim of providing a functional layer for electrochemical elements that exhibits excellent process adhesion and excellent cycle characteristics for electrochemical elements. This functional layer has a particle shedding area, and when the surface of the functional layer for electrochemical elements is viewed in plan view, the ratio of the area of ​​the particle shedding area to the total area of ​​the particulate polymer and the particle shedding area is 0.1% or more and 40.0% or less, and the volume average particle diameter of the particulate polymer is greater than the thickness of the inorganic particle layer containing inorganic particles. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Korean Published Patent Publication No. 10-2016-0118979 [Patent Document 2] International Publication No. 2020 / 175079 [Patent Document 3] International Publication No. 2021 / 085144 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, these conventional separators had the following problems. For example, in Patent Document 1, the poor dispersibility of the adhesive polymer in its paint state caused areas where the adhesive polymer aggregated on the separator, resulting in uneven adhesion to the electrode and a decrease in overall adhesion strength, as well as a deterioration in heat resistance (heat shrinkage resistance). In Patent Documents 2 and 3, the bonding strength of the coating layer was insufficient, and there was still room for improvement in suppressing powder shedding during the manufacturing process and, consequently, in the adhesion strength to the electrode.

[0010] Furthermore, with improvements in electrode materials and the high-density modularization of multiple non-aqueous secondary batteries (single cells) (increasing the volumetric energy density of the module), there was still a need to improve the output characteristics (rate characteristics) and / or cycle characteristics of batteries, including the separator.

[0011] In view of the above circumstances, the present invention aims to provide a separator for energy storage devices that can improve the productivity of energy storage devices, such as cell productivity, and an energy storage device including the same. [Means for solving the problem]

[0012] Examples of embodiments of this disclosure are listed below. [1] A substrate which is a polyolefin microporous film containing polyolefin as the main component, A coating layer disposed on at least one surface of the substrate, A separator for energy storage devices, including, The coating layer comprises 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, and The static friction coefficient of the coating layer is 0.10 or more and less than 0.40. Separator for energy storage devices. [2] A separator for an energy storage device as described in item 1, wherein the volume-average particle diameter (MV) / number-average particle diameter (MN), which is shown as the particle size distribution of the aforementioned protruding particulate polymer, is greater than 1.50. [3] The coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer. A separator for an energy storage device according to item 1 or 2, wherein when the thickness of the inorganic filler portion is L1, and the maximum distance from the substrate-coating layer boundary to the outer surface of the inclined inorganic filler is L2, the average value of the inclination ratio L2 / L1 of the coating layer is 1.2 or more. [4] The coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer. A separator for an energy storage device according to any one of items 1 to 3, wherein when the thickness of the inorganic filler portion is L1, the maximum distance from the substrate-coating layer boundary to the outer surface of the inclined inorganic filler is L2, and the maximum distance from the substrate-coating layer boundary to the contour of the protruding particulate polymer is L3, the average value of the coverage rate of the protruding particulate polymer (L2-L1) / (L3-L1) is 0.4 or more. [5] A separator for an energy storage device according to any one of items 1 to 4, wherein 20% or more of the protruding particulate polymer is in contact with the surface of the substrate. [6] A separator for an energy storage device according to any one of items 1 to 5, wherein the 180° peel strength of the coating layer from the substrate is 200 gf / cm or more. [7] In the surface observation of the coating layer, the protruding particulate polymer is used as the parent point for Voronoi tessellation, and the area of ​​the resulting Voronoi polygon (s i A separator for energy storage devices described in any one of items 1 to 6, wherein the coefficient of variation (cv) of the ) is 0.10 or more and 0.60 or less. [8] A separator for an energy storage device according to any one of items 1 to 7, 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] A separator for an energy storage device according to any one of items 1 to 8, wherein the particulate polymer is a primary particle.

[10] A separator for an energy storage device as described in item 9, wherein the average particle size of the primary particles is 1 μm or more and 10 μm or less.

[11] A separator for energy storage devices as described in any one of items 1 to 10, wherein the thermal shrinkage rate of the TD at 130°C for 1 hour is 5% or less.

[12] A separator for energy storage devices as described in any one of items 1 to 11, wherein the thermal shrinkage rate of the TD at 150°C for 1 hour is 5% or less.

[13] A separator for an energy storage device according to any one of items 1 to 12, wherein the amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of the inorganic filler contained in the coating layer.

[14] The aforementioned protruding particulate polymer protrudes from the surface of the inorganic filler portion by a thickness of 0.1 times or more of the inorganic filler portion, as described in any one of items 1 to 13, for a separator for an energy storage device.

[15] A separator for an energy storage device according to any one of items 1 to 14, wherein the protruding particulate polymer comprises at least one selected from the group consisting of copolymers containing (meth)acrylate as a monomer, styrene-butadiene copolymers, and copolymers containing fluorine atoms.

[16] A separator for an energy storage device according to any one of items 1 to 15, wherein the protruding particulate polymer comprises a copolymer containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers.

[17] A separator for an energy storage device according to any one of items 1 to 16, wherein the protruding particulate polymer comprises a copolymer containing a polyfunctional (meth)acrylate as a monomer.

[18] A separator for an energy storage device according to any one of items 1 to 17, wherein the amount of methylene chloride soluble in the separator for the energy storage device is 0.05 parts by mass or more and 0.80 parts by mass or less, relative to the total mass of the separator for the energy storage device.

[19] (Dependent term: total amount of metal cations) A separator for energy storage devices according to any one of items 1 to 18, 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.

[20] An energy storage device including a separator for energy storage devices as described in any one of items 1 through 19. [Effects of the Invention]

[0013] According to this disclosure, for example, in the manufacture of cylindrical energy storage devices, it is possible to prevent pin detachment defects from the wound body obtained by winding the separator for energy storage devices around the pins, and / or to make it easier to insert the wound body into the device casing such as a cylindrical can, thereby improving the productivity of energy storage devices, such as cell productivity. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of the surface of the coating layer in this embodiment. [Figure 2] This is a schematic diagram of the AA section in Figure 1. [Figure 3] This is a schematic diagram showing an example of the surface of the coating layer observed in this embodiment. [Figure 4] Figure 3 shows an example of the results obtained by identifying the protruding particulate polymer. [Figure 5] Figure 4 shows an example of the results obtained from a Voronoi partition. [Figure 6]This is an example of the results obtained by extracting Voronoi polygons corresponding to closed regions in Figure 5. [Figure 7] This is an example of how to set up 10 sections that encompass 95 fields of view. [Modes for carrying out the invention]

[0015] The following describes exemplary embodiments of this disclosure (hereinafter abbreviated as "these embodiments"), but this disclosure is not limited to these embodiments.

[0016] In this specification, the longitudinal direction (MD) refers to the machine direction of continuous microporous membrane molding, and the width direction (TD) refers to the direction that intersects the MD of the microporous membrane at a 90° angle.

[0017] In this specification, the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, the presence of a specific component as the main component of a certain component means that the content of that specific component constitutes the largest mass within the mass of that component. Unless otherwise specified, the physical properties or numerical values ​​described herein are measured or calculated by the methods described in the examples. The scale, shape, and length of each part shown in the drawings may be exaggerated for clarity.

[0018] 《Separator for energy storage devices》 The separator for the energy storage device of this embodiment includes a substrate which is a polyolefin microporous film mainly composed of polyolefin, 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.

[0019] <Amount of particulate polymer> The amount of particulate polymer is 1 to 50 parts by mass, preferably 3 to 30 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of inorganic filler. By having an amount of particulate polymer of 1 to 50 parts by mass, it is possible to increase the adhesion to the electrode while maintaining ion permeability. From the viewpoint of improving heat shrinkage resistance, 10 parts by mass or less is preferred.

[0020] <Amount of particulate polymer protrusion> The particulate polymer may include particulate polymers that protrude at a thickness of 0.1 times or more the thickness of the inorganic filler portion of the coating layer.

[0021] In this specification, "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 fillers stacked on top of it (the layer of inorganic fillers), and is measured from an SEM image of the cross-section of the coating layer. The "inorganic filler portion" refers to the portion that does not contain particulate polymers, which is located at least 1.5D horizontally (in the direction of the surface of the coating layer) from the center of each protruding particulate polymer, where D is the diameter of each protruding particulate polymer. The measurement conditions are described in the Examples section.

[0022] By having particulate polymer protrusions of 0.1 times or more the thickness of the inorganic filler portion, the adhesion to the electrode can be increased. Furthermore, by having particulate polymer protrusions of 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 the expansion and contraction of the electrode due to charging and discharging of the energy storage device, suppressing distortion of the wound body and improving cycle characteristics. From this viewpoint, the particulate polymer protrusion is preferably 0.2 times or more, or 0.3 times or more. From the viewpoint of suppressing the shedding of the particulate polymer from the separator, the particulate polymer protrusion 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.

[0023] In this specification, "protrusion" means that the particulate polymer protrudes toward the surface of the coating layer beyond the "thickness of the inorganic filler portion." In the protruding portion of the particulate polymer (hereinafter referred to as the "protruding portion"), a part of the protruding portion may be covered with the inorganic filler. From the viewpoint of preventing the particulate polymer from sliding off the coating layer and obtaining higher adhesive strength, it is preferable that a part of the periphery of the protruding portion is covered with the inorganic filler. Furthermore, from the viewpoint of ensuring a contact area between the particulate polymer and the electrode and obtaining higher adhesive strength, it is preferable that the central part of the protruding portion is exposed on the surface of the coating layer.

[0024] In this specification, "a state in which particulate polymer protrudes by 0.1 times or more the thickness of the inorganic filler portion" means that, if L1 is the thickness of the inorganic filler portion measured from the SEM image of the cross-section of the coating layer, and L3 is the maximum distance from the substrate-coating layer boundary to the contour of the protruding particulate polymer, then the average value of the ratio (L3-L1) / L1 is 0.1 or more. In this specification, "the maximum distance from the substrate-coating layer boundary to the contour of the protruding particulate polymer" means the distance from the point on the contour of the protruding particulate polymer that is furthest from the substrate-coating layer boundary.

[0025] In this specification, "a state in which 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 line measured from the SEM image of the cross-section of the coating layer to the contour of the protruding particulate polymer is 1.1 times or more the thickness (L1) of the inorganic filler portion of the coating layer.

[0026] 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 for favorable acquisition of the effects of the protruding particulate polymers. 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 positioned as one of the indicators of the degree of protrusion of particulate polymers in the coating layer. The protrusion ratio is more preferably 60% or more, 70% or more, or 80% or more, and theoretically the upper limit is 100%.

[0027] <Inclined morphology of the coating layer, contact ratio between particulate polymer and substrate, 180° peel strength> The separator for the energy storage device of this embodiment preferably has one or more of the following features (1) to (3). (1) The coating layer is formed in a sloping manner, becoming thicker towards the protruding particulate polymer; (2) More than 20% 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 also simply referred to as "180° peel strength") is 200 gf / cm or more;

[0028] Feature (1): In separators for energy storage devices, it is preferable that the coating layer is formed in a sloping manner so that it becomes thicker towards the protruding particulate polymer. This prevents the particulate polymer from sliding off the coating layer and increases the adhesion to the electrodes. In this specification, "sloping manner" means that when L1 is the thickness of the inorganic filler portion of the coating layer and L2 is the maximum distance from the substrate-coating layer boundary to the outer surface of the inorganic filler of the coating layer formed in a sloping manner, the average value of the slope ratio L2 / L1 of the coating layer is 1.1 (for example, 1.10) or more.

[0029] For an example of the relationship between L1 and L2, please refer to the schematic diagram in Figure 2. Preferably, the thickness of the coating layer changes continuously so that the coating layer gradually becomes thicker toward the protruding particulate polymer, and preferably does not include discontinuous changes where the coating layer is missing. The absence of gaps in the coating layer tends to improve heat resistance and / or cycle characteristics. The slope may be gentler the further it is from the protruding particulate polymer and steeper the closer it is to the protruding portion of the particulate polymer. Also, if 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 coating layer slope ratio L2 / L1 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.

[0030] The coating layer may be formed in a sloping manner so that it becomes thicker towards the protruding particulate polymer, thereby allowing the inorganic filler to cover a portion of the protruding portion by resting on the contour of the particulate polymer. Preferably, the inorganic filler covers a portion of the periphery of the protruding portion by resting on the contour of the particulate polymer. Furthermore, it is preferable that the area near the center of the protruding portion is exposed on the surface of the coating layer. If L3 is the maximum distance from the substrate-coating layer boundary to the contour of the protruding particulate polymer (the distance from the substrate-coating layer boundary to the point on the contour of the protruding particulate polymer that is furthest from the substrate-coating layer boundary), then the average value of the coverage rate of the protruding portion (L2-L1) / (L3-L1) is preferably 0.4 (for example, 0.40) or more.

[0031] For an example of the relationship between L1, L2, and L3, please refer to the schematic diagram in Figure 2. A mean value of 1.1 or higher for the gradient ratio L2 / L1, or a mean value of 0.4 or higher for the coverage ratio (L2-L1) / (L3-L1), prevents the particulate polymer from sliding off the coating layer and increases adhesion to the electrode. The upper limit of the mean 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 securing the adhesion area between the particulate polymer and the electrode and increasing adhesion to 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 higher means that the inorganic filler resting on the protruding portions of the particulate polymer reaches the top of the contour of the protruding particulate polymer (the point furthest from the substrate-coating layer boundary). A coverage ratio of less than 1.0 ensures a contact area between the particulate polymer and the electrode, increasing the adhesion to the electrode. A coverage ratio of 0.8 or lower further increases the contact area between the particulate polymer and the electrode, resulting in even greater adhesion to the electrode.

[0032] Feature (2): The separator for energy storage devices has a contact rate between the protruding particulate polymer and the substrate surface that 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 obtained by observing the cross-section of the coating layer of the separator for energy storage devices using a scanning electron microscope (SEM). Increasing the amount of particulate polymer that protrudes and is in contact with the substrate further increases the bonding strength between the substrate and the particulate polymer, improving the 180° peel strength and increasing the adhesion strength to the electrodes. The upper limit of the contact rate between the protruding particulate polymer and the substrate surface may be less than 100% or 100%.

[0033] Feature (3): The separator for energy storage devices has a 180° peel strength of preferably 200 gf / cm or more, more preferably 230 gf / cm or more, and even more preferably 250 gf / cm or more. "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 a 180° angle with respect to the substrate. A 180° peel strength of 200 gf / cm or more increases the adhesion to the electrodes and suppresses thermal shrinkage. The upper limit of the 180° peel strength may be 500 gf / cm or less.

[0034] The separator for the energy storage device of this embodiment may have any combination of the above features (1) to (3), namely: (1) and (2); (1) and (3); (2) and (3); or (1), (2) and (3). Among these, from the viewpoint of higher adhesive strength and lower thermal shrinkage rate, the combination of (1), (2), and (3) is preferred, namely, 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.

[0035] Herein, the separator for the energy storage device of this embodiment has the following features (4) and / or (5), in addition to the above features (1) to (3), or in any combination of the above features (1) to (3).

[0036] Feature (4): In separators for energy storage devices, surface observation of the coating layer is performed to perform Voronoi tessellation using protruding particulate polymer as parent points, and the area of ​​the resulting Voronoi polygon (s) is determined. i The coefficient of variation (cv) of the coating is 0.10 or more and 0.60 or less. In coating layers where the coefficient of variation (cv) is within this range, the uniformity of the distribution of protruding particulate polymer is high. The coefficient of variation (cv) is preferably 0.20 or more, 0.25 or more, and 0.30 or more, and also preferably 0.55 or less, 0.50 or less, and 0.45 or less.

[0037] A separator having the above characteristic (4) exhibits high uniformity in the distribution of the protruding particulate polymer, and consequently, high uniformity in the distribution of the regions between the protruding particulate polymers. Therefore, by using a separator having the above characteristic (4), it is possible to improve the uniformity of the in-plane distribution of lithium ion transfer through these regions between electrodes, and consequently, to improve the rate characteristics and / or cycle characteristics.

[0038] Furthermore, the separator having the above characteristic (4) exhibits high uniformity in the distribution of the protruding particulate polymer, and consequently, high uniformity in the contact area between the protruding particulate polymer and the electrode, both before and after the hot pressing process. Therefore, by using the separator having the above characteristic (4), it is possible to improve the uniformity of the in-plane stress distribution of the protruding particulate polymer applied to the electrode, and consequently, to improve adhesion to the electrode.

[0039] Furthermore, the separator having the above characteristic (4) exhibits high uniformity in the distribution of protruding particulate polymers, and consequently, high uniformity in the distribution of the inorganic filler having heat-resistant properties. Therefore, by using the separator having the above characteristic (4), it is possible to improve the uniformity of the in-plane distribution of heat-resistant properties due to the inorganic filler, and consequently, to improve heat shrinkage resistance.

[0040] Conventionally, it was believed that there was a trade-off between "adhesion to electrodes" and "heat shrinkage resistance," and also that there was a trade-off between "adhesion to electrodes" and "rate characteristics" and / or "cycle characteristics." Specifically, since particulate polymers do not have sufficient heat resistance, it was thought that increasing the content of particulate polymers to improve "adhesion to electrodes" would make it difficult to improve "heat shrinkage resistance." Furthermore, since the presence of particulate polymers acts as resistance for ions, it was thought that increasing the content of particulate polymers would make it difficult to improve "rate characteristics" and / or "cycle characteristics." In contrast to these points, according to this embodiment, by adjusting the coefficient of variation (cv) to a predetermined range, it is possible to achieve both improved adhesion to electrodes, improved heat shrinkage resistance, and improved rate characteristics and / or cycle characteristics of the energy storage device, as described above.

[0041] Means for adjusting the coefficient of variation (cv) to the above range include, for example, changing the particle size and content of the thermoplastic polymer in the coating solution applied to the substrate, the viscosity and amount of the coating solution applied, and the coating method and coating conditions. For example, this can be done by adjusting the viscosity of the coating solution applied to the substrate to a predetermined range; reducing the particle size of the thermoplastic polymer in the coating solution; performing turbulent stirring when supplying the coating solution to the substrate in the coating process; or applying ultrasonic treatment to the coating solution applied on the substrate.

[0042] "Voronoi tessellation" refers to the process of dividing a space into regions based on which of several points (generators) located at arbitrary positions within a given metric space are closest to other points in the same space. The resulting diagram containing these regions is called a Voronoi diagram. In a Voronoi diagram, the boundaries of the multiple regions are part of the angle bisectors of each generator, and each region forms a polygon (Voronoi polygon). In this specification, the above-mentioned generators are "protruding particulate polymers," or more precisely, the center points of the protruding portions of the protruding particulate polymers as observed on the surface.

[0043] In the observation field of view of the coating layer, one of the protruding particulate polymers is considered as a single circle with an average diameter (l). Then, perpendicular bisectors are drawn between multiple adjacent protruding particulate polymers, and the polygon enclosed by these perpendicular bisectors for each polymer is called a "Voronoi polygon." When Voronoi tessellation is performed in the observation field, regions that are not closed are not considered. Examples of unclosed regions include regions obtained by Voronoi tessellation of a polymer when a polymer exists at the boundary of the observation field and the entire protruding portion of that polymer is not observed.

[0044] Area of ​​a Voronoi polygon (s i ) can be measured using image analysis if necessary, and the area of ​​the Voronoi polygon (s i The sum of the values ​​of the Voronoi polygons being examined is divided by the total number of Voronoi polygons (n) to obtain the area (s i The average value (m) of the Voronoi polygon is obtained. And the area (s) of the Voronoi polygon is obtained. i From the total number (n) and average value (m) of the Voronoi polygons being handled, the area (s) of the Voronoi polygon can be calculated using a standard method. i The standard deviation (s) of the Voronoi polygon is obtained. i The coefficient of variation (cv) of ) is given by the following formula: Coefficient of variation (cv) = Standard deviation (sd) / Mean (m) It is calculated by [this method].

[0045] The coefficient of variation (cv) mentioned above is thought to represent the in-plane distribution or aggregation state of the protruding particulate polymer. If the coefficient of variation (cv) is 0.10 or higher, it can be evaluated that the protruding particulate polymer is randomly dispersed and located on the surface of the coating layer. If the coefficient of variation (cv) is 0.60 or lower, it can be evaluated that the protruding particulate polymer is not excessively aggregated.

[0046] The means for observing the coating layer is preferably selected appropriately depending on the dimensions or distribution of the thermoplastic polymer. Furthermore, various microscopes such as electron microscopes, atomic force microscopes, optical microscopes, and differential interference microscopes can be used. Among these, when dealing with the distribution of dispersed particles as in this embodiment, an electron microscope or atomic force microscope is preferred. In particular, the methods shown in the Examples section are employed for observing the coating layer.

[0047] The average field of view of the coating layer should be ensured within the observation field. Furthermore, the projected area within the observation field should be appropriately adjusted so that the average distribution state of the protruding particulate polymer can be grasped. For example, it is preferable that the number of protruding particulate polymer particles used as the object of handling is approximately 80 to 200 per field of view. This observation field can be obtained by observing the coating layer using a pre-set observation means and magnification. For example, Figure 3 is a schematic diagram of an example in which the surface of the coating layer is observed using a scanning electron microscope as the observation means and a magnification of 1000x. The dispersion state of such thermoplastic polymer particles can be analyzed by Voronoi cleavage.

[0048] When observing using a scanning electron microscope, the magnification is set appropriately for analysis by Voronoi scaling according to the particle size 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 scaling. For example, if the content of thermoplastic polymer particles with a particle size of about 2.0 μm is about 10 parts by mass per 100 parts by mass of inorganic filler in the coating layer, a magnification of 5000x is appropriate. If the content of thermoplastic polymer particles with a particle size of about 3.5 μm is about 10 parts by mass per 100 parts by mass of inorganic filler in the coating layer, a magnification of about 1000x is appropriate for analysis by Voronoi scaling.

[0049] Identify the protruding particulate polymers contained in the observation field obtained by the above-described observation method. For example, identify the protruding particulate polymers from the observation field visually or using image processing software. FIG. 4 is an example showing the result of identifying the protruding particulate polymers contained in the observation field of FIG. 3 using image processing software.

[0050] For the protruding particulate polymers identified by surface observation of the coating layer, Voronoi division can be performed as defined above. Specifically, after applying a coating solution containing a thermoplastic polymer to a substrate, photograph the surface of the coating film to obtain an image. Regarding the protruding portions of the protruding particulate polymers identified in the obtained image, consider them as circles with an average diameter (l (ell)) and perform Voronoi division to draw Voronoi polygons. For example, Voronoi polygons may be drawn manually or using image processing software. Then, calculate the area (si) of the drawn Voronoi polygons.

[0051] For example, FIG. 5 is an example of the result of obtaining Voronoi polygons by performing Voronoi division with the protruding particulate polymers identified in FIG. 4 as seed points. FIG. 6 shows the result of automatically extracting the Voronoi polygons corresponding to the closed regions among the Voronoi polygons shown in FIG. 5 using image processing software.

[0052] By the above-described observation method and image processing method, the total number of protruding particulate polymers in the observation field and the area (s i ) of the Voronoi polygons are obtained. Then, according to the above, the coefficient of variation (cv) can be calculated. The distribution of the protruding particulate polymers may change depending on the observation field. Therefore, it is preferable to adopt the average value of the values calculated for each of a plurality of observation fields as the coefficient of variation (cv). Preferably, the number of such fields is 3 or more.

[0053] Particularly preferably, adopt the average value of the values calculated for 10 fields determined as follows. ​ ii) How to set the field of view: a) Set a starting point and field of view, b) A total of 10 fields of view are set as the measurement field, consisting of nine fields of view that are sequentially adjacent in the uniaxial direction at 5 mm intervals to the field of view of the starting point, and the field of view of the starting point.

[0054] Preferably, each of the aforementioned measurement fields is an image captured at a magnification setting such that the number of protruding particulate polymers observed in one field is between 80 and 200.

[0055] The preferred method for setting the 10 fields of view in this embodiment will be described below with reference to Figure 7. i) As described above, images captured with a scanning electron microscope at a magnification of 1000x can be used as the image to be captured. In the image in Figure 7, first, the starting field of view (I) is set. Since one field of view consists of images captured with a scanning electron microscope at a magnification of 1000x, the scale of one field of view is approximately 100 μm × 100 μm, which constitutes a field of view suitable for Voronoi resolution evaluation based on protruding particulate polymers. Next, nine fields of view (II to X) are set sequentially adjacent to the starting field of view (I) in the uniaxial direction at 5 mm intervals. Each of these fields of view (II to X) consists of an image captured at the same magnification as the starting field of view (I).

[0056] The observation of the surface of the coating layer described above is preferably performed on areas not involved in ion conduction. For example, the coating layer of a separator that has just been manufactured and has not yet been incorporated into an energy storage element can be observed. If the energy storage element is in use or has just been used, it is also a preferred embodiment in this model to observe the so-called "ear" portion of the separator (the area near the outer edge of the separator that is not involved in ion conduction). As can be understood from the evaluation method described above, when 10 fields of view are used as the observation target, a separator piece approximately 45 mm in length is used as the measurement target, so the dispersion state of the thermoplastic polymer on its surface can be accurately evaluated.

[0057] As described above, the fact that Voronoi tessellation is possible suggests that, within the coating layer, the particulate polymer exists as single layers of particles without substantially overlapping. For example, if the particulate polymer overlaps multiple times within the coating layer, the concept of area occupied by a single particle does not apply, and therefore Voronoi tessellation cannot be performed. In this embodiment, it is preferable that the separator is arranged such that the particulate polymer in the coating layer does not substantially overlap, and that the above requirements are adjusted to the ranges described above.

[0058] The preferred form (pattern) of the coating layer on the substrate is that the particulate polymer is dispersed amongst itself across the entire surface of the substrate. While the particulate polymer may form clusters in some areas, it is preferable that the particulate polymer is well dispersed overall to the extent that the coefficient of variation (cv) is satisfied.

[0059] Features (5): For separators used in energy storage devices, the static friction coefficient of the coating layer is 0.10 or more and less than 0.40. When the static friction coefficient of the coating layer is within this range, it is possible to prevent pin removal defects from the wound body obtained by winding the separator for energy storage devices around a pin, for example in the manufacture of cylindrical energy storage devices (for example, the phenomenon in which the separator becomes like a bamboo shoot when the pin is removed), and / or it is possible to easily insert the wound body into the device casing such as a cylindrical can, thereby improving the productivity of energy storage devices such as cells.

[0060] From the viewpoint of further improving the productivity of energy storage devices, the static friction coefficient of the coating layer is preferably 0.14 or more and 0.39 or less, more preferably 0.20 or more and 0.39 or less, even more preferably 0.24 or more and 0.39 or less, and particularly preferably 0.30 or more and 0.39 or less.

[0061] In a separator for an energy storage device having feature (5), it is preferable that the particulate polymer protruding from the surface of the inorganic filler portion contained in the coating layer is made of a thermoplastic polymer, and that the shape of the protruding portion is easily maintained. If the shape of the protruding portion made of a thermoplastic polymer is easily maintained, the particulate polymer becomes less likely to be crushed, and the conformability of the separator to other members is suppressed, so that, for example, when removing a pin from the separator winding body, pin removal failures are less likely to occur.

[0062] From the viewpoint of making it easier to adjust the static friction coefficient of the coating layer to within the above range, the particle size distribution MV / MN of the particulate polymer, which is obtained by dividing the volume-average particle diameter MV of the protruding particulate polymer by the number-average particle diameter MN, is preferably greater than 1.50, more preferably 1.51 or higher, and even more preferably 1.55 or higher. When MV / MN exceeds 1.50, the number of contact points of the particulate polymer with other components decreases, or the contact area of ​​the contact points decreases, making it easier to adjust the static friction coefficient of the coating layer to less than 0.40.

[0063] Means for adjusting the static friction coefficient of the coating layer to within the above range and / or for facilitating the maintenance of the shape of protruding particulate polymers include, for example, controlling the conditions of the coating and drying process in which the coating liquid is applied to the substrate in the manufacturing process of separators for energy storage devices, such as the particle size, particle size distribution and content of the thermoplastic polymer in the coating liquid applied to the substrate, the viscosity and amount of the coating liquid applied, as well as the coating method and coating conditions, or the conditions after the coating and drying process, such as the pressure applied to the coated surface, the speed of the conveying rolls in contact with the coated surface, the shape of the inorganic filler in the coating layer, and the peel strength of the coating layer.

[0064] More specifically, means of controlling the conditions of the coating and drying process include, for example, adjusting the viscosity of the coating solution applied to the substrate to a predetermined range; and increasing the particle size distribution of the thermoplastic polymer in the coating solution.

[0065] More specifically, control methods for the conditions after the coating and drying process include, for example, controlling the tension applied perpendicular to the surface of the coated surface that contacts the conveyor roll to a predetermined value or less; setting the conveyor roll speed in contact with the coated surface to the same speed as the separator conveyor speed; and increasing the peel strength of the coating layer.

[0066] <Methylene chloride soluble components> The separator for energy storage devices of this embodiment contains methylene chloride soluble content, preferably 0.05 parts by mass or more and 0.80 parts by mass or less, more preferably 0.10 parts by mass or more and 0.60 parts by mass or less, and even more preferably 0.15 parts by mass or more and 0.50 parts by mass or less, based on the total mass of the separator for energy storage devices. The "soluble content" of methylene chloride refers to the components extracted into the methylene chloride when the separator is immersed in methylene chloride. Mainly, plasticizers mixed during the manufacturing of the base material are extracted as methylene chloride soluble content. By containing 0.10 parts by mass or more of methylene chloride soluble content, the bonding strength between the base material and the coating layer is further increased, and it becomes easier to adjust the 180° peel strength to 200 gf / cm or more. By having 0.60 parts by mass or less of methylene chloride soluble content, the internal resistance of the battery can be lowered. Methods for adjusting the methylene chloride soluble content to 0.05 parts by mass or more and 0.80 parts by mass or less include adjusting the extraction time, type of extraction solvent, temperature of the extraction solvent, and number of extractions in the plasticizer extraction process during substrate manufacturing if it is a batch process, and adjusting the extraction time, type of extraction solvent, temperature of the extraction solvent, and supply amount of the extraction solvent if it is a continuous process.

[0067] <Metallic cations> In this embodiment, the separator for energy storage devices has a total amount of metal cations in the coating layer that is preferably 0.1 ppm to 100 ppm, more preferably 0.1 ppm to 70 ppm, and even more preferably 0.1 ppm to 50 ppm, based on the total mass of the coating layer. When the total amount of metal cations is adjusted to be low, the inorganic filler and particulate polymer are more easily dispersed and coated during the formation of the coating layer. Examples of metal cations include sodium ions (Na). + ), calcium ions (Ca2+ ) and magnesium ions (Mg 2+ Examples include the following. One method for adjusting the total amount of metal cations to between 0.1 ppm and 100 ppm is to wash the filler, which is the raw material for the coating layer, with water before use. The washing can be done once or two or more times, but the more times it is washed, the lower the total amount of metal cations contained in the filler becomes.

[0068] <Thermal contraction rate> In this embodiment, the separator for the energy storage device has a thermal shrinkage rate of TD of 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1% at 130°C for 1 hour. The thermal shrinkage rate of TD at 150°C for 1 hour is preferably 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1%. Here, if the thermal shrinkage rate of TD is 5% or less, it is possible to more effectively suppress the occurrence of short circuits in areas other than where external force is applied when heat is generated due to a short circuit during a collision test. This makes it possible to more reliably prevent the temperature rise of the entire battery, and the smoke and fire that may occur as a result. The thermal shrinkage rate of the separator can be adjusted by appropriately combining the stretching operation and heat treatment of the base material as described above. At the same time as suppressing the thermal shrinkage rate of TD, the thermal shrinkage of MD is also preferably 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1%.

[0069] <Air permeability of the separator> The air permeability of the separator for energy storage devices is preferably 10 seconds / 100 cm. 3 More than 10000 seconds / 100cm 3 More preferably 40 seconds / 100cm 3 More than 500 seconds / 100cm 3 More preferably, 50 seconds / 100cm 3 More than 250 seconds / 100cm 3 The following is particularly preferable: 60 seconds / 100cm 3 More than 200 seconds / 100cm 3The following applies. This results in high ion permeability. The air permeability is the air resistance measured in accordance with JIS P-8117.

[0070] <Base material> The substrate is a polyolefin microporous membrane mainly composed of polyolefin, and preferably has the following characteristics (1), (2), or a combination thereof: (1) The film thickness is 1 μm to 30 μm and the air permeability is 500 sec / 100 cm. 3 The following conditions must be met: (1) The post-compression porosity measured in a compression test under the conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes is 30% or more. (2) The crystal long period measured by small-angle X-ray scattering (SAXS) of the polyolefin microporous film is 37.0 nm or more.

[0071] Appearance (1): Although not bound by theory, polyolefin microporous membranes have a film thickness in the range of 1 μm to 30 μm, and can withstand 500 sec / 100 cm. 3 By having the following air permeability and a post-compression porosity of 30% or more, it is possible to reduce the electrical resistance of the polyolefin microporous membrane after the pressing process or suppress the increase in electrical resistance in the fabrication of a non-aqueous secondary battery using a polyolefin microporous membrane as a separator, for example, and thereby achieve high output and high cycle characteristics in a non-aqueous secondary battery. The suppression of resistance increase by the polyolefin microporous membrane is particularly noticeable when electrodes that easily expand and contract are used in the cell of a non-aqueous secondary battery, and is even more noticeable when high-capacity electrodes used in automotive batteries, etc., or when silicon (Si)-containing negative electrodes are used.

[0072] The post-compression porosity is thought to be related to the structure of the main component of the polyolefin microporous membrane, which is responsible for reducing resistance and / or suppressing resistance increase in non-aqueous secondary batteries. From the viewpoint described above, the post-compression porosity of the polyolefin microporous membrane is preferably 31% or more, more preferably 32% or more, and even more preferably 33% or more. The upper limit of the post-compression porosity of the polyolefin microporous membrane can be determined according to the porosity before compression, and may be, for example, preferably 60% or less, and even more preferably 50% or less.

[0073] The post-compression porosity of polyolefin microporous membranes can be adjusted to within the numerical range described above by controlling, for example, the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretching coefficient during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, and the heat-fixing temperature during the biaxial stretching process, in the manufacturing process of polyolefin microporous membranes. Alternatively, the post-compression porosity of polyolefin microporous membranes can be adjusted to within the numerical range described above by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretching coefficient during the biaxial stretching process, and the ratio of the preheating coefficient to the stretching coefficient.

[0074] Comparing the porosity of polyolefin microporous membranes before and after compression testing 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 non-aqueous secondary batteries, thereby achieving high power output and high cycle characteristics. The preferred numerical range of porosity (hereinafter simply referred to as "porosity") of polyolefin microporous membranes before or before compression testing will be described later.

[0075] Appearance (2): Although not bound by theory, polyolefin microporous membranes, by having a crystal period of 37.0 nm or longer, surprisingly exhibit improved structural uniformity and compressibility, and consequently, improved reaction uniformity within non-aqueous secondary batteries. This suggests that, for example, high power output and high cycle characteristics can be achieved even after the pressing process in the fabrication of non-aqueous secondary batteries using polyolefin microporous membranes as separators. The improvement in structural uniformity and compressibility of polyolefin microporous membranes is particularly noticeable when using electrodes that are prone to expansion and contraction within the cell of a non-aqueous secondary battery, and is even more pronounced when using high-capacity electrodes or silicon (Si)-containing negative electrodes used in automotive batteries, etc.

[0076] While not bound by theory, the crystal period obtained by SAXS measurement is thought to be related to the structure of polyethylene, which improves the structural uniformity and compressibility of the film and the reaction uniformity in non-aqueous secondary batteries. Furthermore, the crystal period of polyolefin microporous films is thought to correlate with the post-compression porosity of the film. From the viewpoint described above, the crystal period of polyolefin microporous films 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.

[0077] The crystal length period of a polyolefin microporous film can be adjusted to within the numerical range described above by controlling, for example, the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretching coefficient during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, and the heat setting temperature during the biaxial stretching process, in the manufacturing process of the polyolefin microporous film.

[0078] The separator for the energy storage device of this embodiment has a substrate which is a polyolefin microporous membrane containing polyolefin as the main component. "Containing as the main component" means that the mass of the component in question (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 be 100 parts by mass, based on the total mass of the substrate.

[0079] Polyolefins are advantageous for reducing the thickness of separators because they exhibit excellent coating properties when a coating solution is applied to their film, thereby increasing the active material ratio in energy storage devices and increasing the capacity per unit volume. The polyolefin microporous film can be the same material used as the substrate for conventional separators, and it is preferable that it is a porous film with fine pores that is ionically conductive but not electrically conductive, and has high resistance to organic solvents.

[0080] The polyolefin may be any polyolefin that can be used in conventional extrusion, injection, inflation, and blow molding processes. Examples of polyolefins include homopolymers using ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, as well as copolymers of two or more of these monomers, and multi-stage polymers. These homopolymers, copolymers, and multi-stage polymers may be used individually or in combination of two or more.

[0081] Polyolefins, in particular, include polyethylene, polypropylene, and polybutene, from the viewpoint of suppressing the decrease or increase in the electrical resistance of the membrane, the compressive resistance of the membrane, and structural uniformity. More specifically, 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.

[0082] These can be used individually or in combination of two or more. Among these, at least one polyolefin 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 is preferred from the viewpoint of shutdown characteristics where pores are closed by thermal melting. In particular, high-density polyethylene is preferred because it has a low melting point and high strength, and its density measured according to JIS K 7112 is 0.93 g / cm³. 3 Polyethylene meeting the above criteria is even more preferable. Polymerization catalysts used in the production of these polyethylenes include, for example, Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. It is preferable that the main component of the polyolefin is polyethylene, and that the polyethylene content relative to the total mass of polyolefin in the substrate is 50 parts by mass or more.

[0083] To improve the heat resistance of the substrate, the polyolefin microporous film more preferably contains polypropylene and a polyolefin other than polypropylene. Examples of polyolefin resins other than polypropylene include homopolymers using ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, as well as copolymers of two or more of these monomers, and multi-stage polymers.

[0084] 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 or more and 35 parts by mass or less, more preferably 3 parts by mass or more and 20 parts by mass or less, and even more preferably 4 parts by mass or more and 10 parts by mass or less. From a similar viewpoint, the content ratio of olefin resins 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 or more and 99 parts by mass or less, more preferably 80 parts by mass or more and 97 parts by mass or less, and even more preferably 90 parts by mass or more and 96 parts by mass or less.

[0085] From the viewpoint of crystallinity, high strength, and compressive resistance when forming a polyolefin microporous membrane for non-aqueous secondary batteries, it is preferable that the porous membrane is formed from a polyethylene composition in which 50% to 100% by mass of the resin component constituting the porous membrane is polyethylene. More preferably, the proportion of polyethylene in the resin component constituting the porous membrane is 60% to 100% by mass, even more preferably 70% to 100% by mass, and even more preferably 90% to 100% by mass.

[0086] 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 preferable because it tends to result in even higher strength due to the entanglement of polymers. On the other hand, a viscosity-average molecular weight of 6,000,000 or less is preferable because it facilitates uniform melt-kneading, improving moldability in the extrusion and stretching processes. Furthermore, a viscosity-average molecular weight of less than 1,000,000 is preferable because it tends to easily clog pores when the temperature rises, resulting in a better shutdown function.

[0087] When a polyolefin microporous membrane contains polyethylene as its main component, the lower limit of the weight-average molecular weight (Mv) of at least one type of polyethylene is preferably 600,000 or more, more preferably 700,000 or more, from the viewpoint of membrane orientation and rigidity, and the upper limit of the Mv of polyethylene may be, for example, 2,000,000 or less. From a similar 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 also be 100% by mass. From the viewpoint of reduced fluidity when the membrane melts and short-circuit resistance during nail penetration tests, 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, and even more preferably 70% by mass or more, and may also be 100% by mass.

[0088] The viscosity-average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at a measurement temperature of 135°C using decalin, 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

[0089] For example, instead of using a polyolefin with a viscosity-average molecular weight of less than 1 million alone, a mixture of a polyolefin with a viscosity-average molecular weight of 2 million and a polyolefin with a viscosity-average molecular weight of 270,000, where the viscosity-average molecular weight of the mixture is less than 1 million, may be used.

[0090] The base material may contain other resins besides polyolefins, such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimidamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, and other resins.

[0091] The base material may contain any additives. Such additives are not particularly limited and include, for example, plasticizers, polymers other than polyolefins, inorganic particles, antioxidants such as phenolic, phosphorus-based, and sulfur-based antioxidants, metal soaps such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging 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 polyolefin resin in the polyolefin microporous film.

[0092] The substrate preferably contains a plasticizer. When the substrate contains a plasticizer, the bonding strength between the substrate and the coating layer is improved, making it easier to control the 180° peel strength to 200 gf / cm or higher. The amount of plasticizer is preferably 0.1 parts by mass or more and 1.6 parts by mass or less, more preferably 0.2 parts by mass or more and 1.2 parts by mass or less, and even more preferably 0.3 parts by mass or more and 1.0 part by mass or less, based on the total mass of the substrate. By having the amount of plasticizer within the above range, it is possible to improve the bonding strength between the substrate and the coating layer while lowering 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 as the plasticizer.

[0093] The porosity of the substrate is preferably 30% to 65%, more preferably 35% to 60%. Even more preferably, it is 35% to 50%, and may be 40% to 50%. This allows the coating layer to be adequately impregnated into the micropores of the substrate, making it easier to control the 180° peel strength to 200 gf / cm or higher. The porosity is measured by the volume (cm³) of the substrate sample. 3 ), mass (g), membrane density (g / cm 3 ) From the following formula: Porosity = (Volume - Mass / Membrane Density) / Volume × 100 This is how it is determined. Here, for example, in the case of a polyolefin microporous membrane made of polyethylene, the membrane density is 0.95 g / cm³. 3 This can be assumed and calculated. Porosity can be adjusted by changing the stretching ratio of the polyolefin microporous membrane, etc.

[0094] The air permeability of the substrate is preferably 10 seconds / 100 cm. 3 More than 450 seconds / 100cm 3 More preferably 40 seconds / 100cm 3 More than 300 seconds / 100cm 3 More preferably, 50 seconds / 100cm 3 More than 250 seconds / 100cm 3 The following is particularly preferable: 60 seconds / 100cm 3 More than 200 seconds / 100cm 3 The following applies. Also, 60 seconds / 100cm 3 More than 150 seconds / 100cm 3 The following is possible. This allows the coating layer to be adequately impregnated into the micropores of the substrate, making it easier to control the 180° peel strength to 200 gf / cm or higher. The air permeability is the air permeability resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the substrate.

[0095] 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 preferable from the viewpoint of suppressing self-discharge of the energy storage device and preventing capacity degradation. From the viewpoint of improving density, an average pore size of 0.08 μm or less is preferable. The average pore size can be adjusted by changing the stretching ratio during the manufacturing of the substrate.

[0096] The puncture strength of the substrate is preferably 200 gf or more, more preferably 300 gf or more, even more preferably 400 gf or more, preferably 2,000 gf or less, and more preferably 1,000 gf or less. A puncture strength of 200 gf or more is preferable from the viewpoint of suppressing film rupture due to detached active material, etc., when the separator is wound together with the electrode, and from the viewpoint of suppressing concerns about short circuits due to the expansion and contraction of the electrode accompanying charging and discharging. On the other hand, a puncture strength of 2,000 gf or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength is measured according to the method described in the examples. The puncture strength can be adjusted by adjusting the stretching ratio and / or stretching temperature of the substrate.

[0097] 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 polyolefins during the manufacturing process of the polyolefin microporous membrane. Furthermore, multilayer polyolefin resin microporous membranes having a structure in which two or more layers of the same or different types of polyolefin resin microporous membranes are laminated can also be adjusted as described above.

[0098] Polyolefin microporous membranes have a porous structure in which a large number of very small pores come together to form dense interconnected pores. As a result, they exhibit excellent ion permeability and high strength when containing electrolytes.

[0099] The thickness of the substrate 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, preferably 100 μm or less, more preferably 60 μm or less, even more preferably 50 μm or less, and particularly preferably 16 μm or less. A film thickness of 2 μm or more is preferable from the viewpoint of improving mechanical strength. On the other hand, a film thickness of 100 μm or less is preferable because it tends to be advantageous in terms of increasing the capacity of the energy storage device, as it reduces the volume occupied by the separator in the energy storage device.

[0100] <Coating layer> The separator for the energy 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 side of the substrate or on both sides. "Disposed on the surface" means that it may be disposed on all of the surface of the substrate or on part of it. The coating layer is intended to be directly bonded to the electrodes. It is preferable that the substrate and the electrodes are bonded via the coating layer so that the coating layer is directly bonded to the electrodes. The coating layer is preferably a coated layer formed by applying a coating solution containing an inorganic filler and a particulate polymer to the substrate.

[0101] The coating layer comprises an inorganic filler and a particulate polymer of a thermoplastic polymer. The coating layer may further contain a resin binder, a water-soluble polymer, and other additives. The coating layer may have at least two Tgs, consisting of a Tg based on the particulate polymer composed of a thermoplastic polymer and a Tg based on the thermoplastic polymer that acts as a binding binder.

[0102] (Inorganic filler) Preferably, the inorganic filler has a melting point of 200°C or higher, or a thermal decomposition temperature of 200°C or higher, high electrical insulation properties, and is electrochemically stable within the range of use for energy storage devices such as lithium-ion secondary batteries. Examples of such inorganic fillers include inorganic oxides (oxide-based ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride-based 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 hydroxide oxide (boehmite), potassium titanate, talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyst, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These can be used individually or in combination of two or more. Among these, at least one selected from the group consisting of alumina, barium sulfate, and aluminum hydroxide oxide (boehmite) is preferred as the inorganic filler.

[0103] 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 50 nm or more for the inorganic filler is preferable from the viewpoint of maintaining voids for ions to permeate the coating layer and improving rate characteristics. An average particle size of 2000 nm or less for the inorganic filler is preferable from the viewpoint of increasing the weight ratio of the 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, especially when the thickness of the coating layer is small, it forms a uniform coating layer thickness and improves heat shrinkage resistance. The average particle size of the inorganic filler is preferably, for example, between 150 nm and 500 nm, or between 200 nm and 450 nm. This is because it allows for a high degree of compatibility between rate characteristics and heat shrinkage resistance. The "average particle size" of the inorganic filler was measured by the method described in the examples. As a method for adjusting the particle size and distribution of the inorganic filler, for example, a method of reducing the particle size by grinding the inorganic filler using an appropriate grinding device such as a ball mill, bead mill, or jet mill. The particle size distribution of the inorganic filler can be such that there is one peak in the frequency graph relative to particle size. However, it is also acceptable to have two peaks or a trapezoidal chart without any peaks.

[0104] Examples of inorganic filler shapes include plate-like, flaky, needle-like, columnar, spherical, polyhedral, and lumpy (block-like) shapes. Multiple types of inorganic fillers having these shapes may be used in combination. Block-like shapes are preferred from the viewpoint of improving the gradient of the coating layer and increasing the adhesion strength with the electrode.

[0105] The aspect ratio of the inorganic filler is preferably 1.0 to 2.5, more preferably 1.1 to 2.0. An aspect ratio of 2.5 or less is preferable from the viewpoint of suppressing the amount of moisture adsorption of the multilayer porous film and suppressing capacity degradation when repeated cycles are performed, suppressing deformation at temperatures exceeding the melting point of the substrate, and improving the gradient of the coating layer and increasing the adhesion strength to the electrode. The reason why the gradient increases when the aspect ratio of the inorganic filler is 1.0 to 2.5 is thought to be because the orientation of the particles in the coating layer is small, making it easier to form a laminated structure.

[0106] The particle size distribution of the inorganic filler, obtained by dividing the standard deviation (SD) of the volume-average particle size of the inorganic filler by the value of 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 ratio of the coating layer and increasing the adhesion strength to the electrode. The reason why the gradient ratio increases when the particle size distribution of the inorganic filler is 0.55 or less is thought to be that the uniformity of the particles increases and the contact rate between particles improves, making it easier to form a laminated structure.

[0107] The amount of inorganic filler is, for example, 20 parts by mass or more but less than 100 parts by mass, 30 parts by mass or more but 80 parts by mass or less, 35 parts by mass or more but 70 parts by mass or less, and 40 parts by mass or more but 60 parts by mass or less, relative to the total mass of the coating layer.

[0108] (particulate polymer) Particulate polymers are particles of thermoplastic polymers. From the viewpoint of improving adhesion between the separator and the electrode, it is preferable that the particulate polymer contains a thermoplastic polymer with 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 described in JIS K7121 and is determined from the DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the temperature at the point where the curve of the stepwise transition portion intersects a straight line extending the low-temperature baseline in the DSC curve toward the high-temperature side and a straight line equidistant in the vertical axis direction from the straight line extending the high-temperature baseline in the DSC curve toward the low-temperature side can be adopted as the glass transition temperature. More specifically, it can be determined according to the method described in the examples. Furthermore, "glass transition" refers to the change in heat flow that occurs on the endothermic side due to the change in state of the polymer test specimen in DSC. Such a change in heat flow is observed as a stepwise change in the shape of the DSC curve. A "stepwise change" refers to the portion of the DSC curve from the previous low-temperature baseline to a new high-temperature baseline. Furthermore, a combination of a stepwise change and a peak is also included in the definition of a stepwise change. In addition, in the stepwise change portion, if the upper side is considered the exothermic side, it can also be described as the point where the curve changes from an upward-convex curve to a downward-convex curve. A "peak" in the DSC curve refers to the portion where the curve moves away from the low-temperature baseline and then returns to the same baseline. A "baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs in the test specimen.

[0109] The glass transition temperature (Tg) of the particulate polymer is preferably 10°C to 110°C, more preferably 45°C or higher, even more preferably 80°C or higher, and even more preferably 90°C or higher. From the viewpoint of improving adhesion after electrolyte injection and enhancing blocking resistance, it is particularly preferable to have a Tg greater than 90°C. It can be 92°C or higher in that it can maintain shape stability up to higher temperatures. A Tg of 10°C or higher for the particulate polymer is preferable from the viewpoint of suppressing adhesion (blocking) between adjacent separators via the coating layer during storage and transportation of separators for energy storage devices, and during the manufacturing process of energy storage devices. On the other hand, a Tg of 110°C or lower for the particulate polymer is preferable from the viewpoint of obtaining good adhesion to electrodes. The Tg of the particulate polymer can be appropriately adjusted, for example, by changing the type of monomer used when manufacturing the particulate polymer, and, if the particulate polymer is a copolymer, by changing the blending ratio of each monomer. In other words, for each monomer used in the production of particulate polymers, the approximate glass transition temperature can be estimated from the generally available Tg of the homopolymer (for example, as listed in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the monomer blending ratio. For example, copolymers obtained by copolymerizing monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid in high proportions, which give homopolymers with a Tg of approximately 100°C, will have a high Tg, while copolymers obtained by copolymerizing monomers such as n-butyl acrylate and 2-ethylhexyl acrylate in high proportions, which give homopolymers with a Tg of approximately -50°C, will have a low Tg. Furthermore, the Tg of a copolymer can also be estimated using the FOX formula, which is shown below. 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + W i / Tg i +···W n / Tg n Here, in the formula, Tg(K) is the Tg of the copolymer, and Tg i (K) is the Tg of the homopolymer of monomer i, and W iis the mass fraction of each monomer. i is an integer from 1 to n, and n is the number of types of monomers that make up the copolymer. However, in this embodiment, the glass transition temperature Tg of the particulate polymer is the value measured by the method using DSC described above.

[0110] 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, relative to the thickness of the coating layer, from the viewpoint of adhesion between the separator and the electrode and preventing the particulate polymer from falling off the coating layer. The "average particle size" of the particulate polymer refers to the volume average particle diameter measured by the measurement method described in the examples. The "primary particles" of the particulate polymer refer to independent particles that are united by covalent bonds. On the other hand, a form in which two or more primary particles are in contact and form an aggregate is called a "secondary particle."

[0111] 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 to 10 μm, more preferably 1 μm to 8 μm, and even more preferably 2 μm to 5 μm. The fact that the particulate polymer is 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 adhesion to the electrode, suppresses thermal shrinkage, and ensures uniformity of the thickness of the coating layer. When the average particle size of the primary particles is 1 μm to 10 μm, the particulate polymer is more likely to form a structure that protrudes from the surface of the coating layer, which increases the adhesion to the electrode and suppresses thermal shrinkage.

[0112] Examples of thermoplastic polymers include (meth)acrylic polymers, conjugated diene polymers, polyvinyl alcohol resins, and fluororesins.

[0113] From the viewpoint of high adhesion to electrodes and low thermal shrinkage, it is more preferable that the thermoplastic polymer contains a (meth)acrylic polymer. "(meth)acrylic polymer" means a polymer or copolymer containing a (meth)acrylic compound as a monomer. A (meth)acrylic compound can be represented by the following general formula. CH2=CR Y1 -COO-R Y2 In the formula, R Y1 R represents a hydrogen atom or a methyl group. Y2 R represents a hydrogen atom or a monovalent hydrocarbon group. Y2 If the group is a monovalent hydrocarbon group, it may have substituents and may also have heteroatoms. Examples of monovalent hydrocarbon groups include linear alkyl groups, cycloalkyl groups, and aryl groups, which may be linear or branched. Examples of substituents include hydroxyl groups and phenyl groups, and examples of heteroatoms include halogen atoms and oxygen atoms. (meth)acrylic compounds can be used individually 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 hydroxyl groups, and aryl esters of (meth)acrylates.

[0114] More specifically, examples of linear alkyl (meth)acrylates include linear alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, n-propyl, and isopropyl groups; linear alkyl groups having 4 or more carbon atoms, such as n-butyl, isobutyl, t-butyl, n-hexyl, 2-ethylhexyl groups; and lauryl groups. An example of an aryl (meth)acrylate is phenyl (meth)acrylate.

[0115] Examples of (meth)acrylates 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; as well as (meth)acrylates having an aromatic ring, such as phenyl (meth)acrylate and benzyl (meth)acrylate.

[0116] Conjugated diene polymers are polymers that have a conjugated diene compound as a monomer unit and are preferred because they are easily compatible with electrodes. Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side-chain conjugated hexadienes, which may be used individually or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. Conjugated diene polymers may also contain (meth)acrylic compounds or other monomers as monomer units, as described later. Examples of such monomers include styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, and acrylonitrile-butadiene-styrene copolymers and their hydrides.

[0117] Examples of polyvinyl alcohol-based resins include polyvinyl alcohol and polyvinyl acetate.

[0118] Fluorine-containing resins are preferred from the viewpoint of dielectric strength, and examples include polyvinylidene fluoride, polytetrafluoroethylene, and copolymers containing fluorine atoms, such as vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer. Fluorine-containing resins are preferably copolymers containing fluorine atoms.

[0119] 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. More preferably, the copolymer containing (meth)acrylate as a monomer contains 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 energy storage devices that has higher adhesion to electrodes and a lower thermal shrinkage rate.

[0120] The particulate polymer preferably contains a crosslinkable monomer. The crosslinkable monomer is not particularly limited, but examples include monomers having two or more radically polymerizable double bonds, and monomers having functional groups that give a self-crosslinking structure during or after polymerization. These can be used individually or in combination of two or more.

[0121] 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 difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional (meth)acrylates. Specifically, 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 can be used individually or in combination of two or more. In particular, from the same viewpoint as above, at least one of trimethylolpropane triacrylate or trimethylolpropane trimethacrylate is preferred.

[0122] (Resin binder) The coating layer preferably includes a resin binder for bonding the inorganic fillers together and between the inorganic fillers and the substrate. The type of resin used for the resin binder is not particularly limited, but any resin that is insoluble in the electrolyte of an energy storage device such as a lithium-ion secondary battery and is electrochemically stable within the operating range of such an energy storage device can be used.

[0123] Specific examples of resins used in resin binders include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; fluororubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, methacrylic acid ester-acrylic acid ester copolymer, etc. Examples include rubbers such as ethylene-acrylic acid copolymers, acrylonitrile-acrylic acid 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, or resins without a melting point but with a decomposition temperature of 200°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester. These can be used individually or in combination of two or more.

[0124] The resin binder may include, for example, a resin latex binder. As the resin latex binder, for example, a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable thereto can be used. Here, examples of aliphatic conjugated diene monomers include butadiene and isoprene, examples of unsaturated carboxylic acid monomers include (meth)acrylic acid, and examples of other monomers include styrene. There are no particular restrictions on the polymerization method of such copolymers, but emulsion polymerization is preferred. There are no particular restrictions on the emulsion polymerization method, and known methods can be used. There are no particular restrictions on the method of adding monomers and other components, and any of a single addition method, a divided addition method, or a continuous addition method can be employed, and the polymerization method can be a one-step polymerization, a two-step polymerization, or a multi-step polymerization of three or more steps.

[0125] Specific examples of resin binders include the following (1) to (7). (1) Polyolefins, such as polyethylene, polypropylene, ethylene propylene rubber, and modified versions thereof; (2) Conjugated diene polymers, for example, styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides; (3) Acrylic polymers, for example, methacrylic acid ester-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, and acrylonitrile-acrylic acid ester copolymers; (4) Polyvinyl alcohol-based resins, for example, polyvinyl alcohol and polyvinyl acetate; (5) Fluorine-containing resins, for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; (6) Cellulose derivatives, such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; and (7) Resins having a melting point and / or glass transition temperature of 180°C or higher, or polymers that do not have a melting point but have a decomposition temperature of 200°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0126] When the resin binder is a resin latex binder, its volume-average particle size (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 size of the resin binder can be controlled by adjusting, for example, the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, and pH.

[0127] From the viewpoint of improving 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 permeability, the glass transition temperature of the resin binder is preferably -60°C or higher.

[0128] From the viewpoint of improving 180° peel strength, the volume average particle size (D50) of the resin binder is preferably 1 or more times, more preferably 2 or more times, and even more preferably 2.5 or more times, the average pore size of the polyolefin microporous film. By selecting the volume average particle size (D50) of the resin binder in this way, it becomes possible to retain the resin binder on the surface of the polyolefin microporous film, thereby improving 180° peel strength. From the viewpoint of improving rate characteristics, the volume average particle size (D50) of the resin binder is preferably 10 times or less of the average pore size of the polyolefin microporous film. From the viewpoint of maintaining low permeability and suppressing blocking, the content ratio of the resin binder in the coating layer may be, for example, more than 0 parts by mass and 50 parts by mass or less, 1 part by mass and 20 parts by mass or less, 2 parts by mass and 10 parts by mass or less, or 3 parts by mass and 5 parts by mass or less, relative to the total amount of the coating layer.

[0129] 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. From the viewpoint of ion permeability, 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, and from the viewpoint of adhesion between the substrate and the particulate polymer, it is more preferably less than 20°C, even more preferably less than 15°C, and particularly preferably less than 0°C.

[0130] (Water-soluble polymer) The coating layer may further contain a water-soluble polymer in addition to the inorganic filler and particulate polymer of the thermoplastic polymer. The water-soluble polymer may be incompatible with the thermoplastic polymer constituting the particulate polymer. Generally, the water-soluble polymer functions as a dispersant in the coating solution for forming the coating layer containing the inorganic filler and particulate polymer of the thermoplastic polymer, and functions as a dispersant and / or water-retaining agent when the coating solution is a water-based paint.

[0131] The content of water-soluble polymer in the coating layer is preferably 0.04 parts by mass or more and less than 2 parts by mass, more preferably 0.04 parts by mass or more and 1.5 parts by mass or less, and even more preferably 0.1 parts by mass or more and 1 part by mass or less, per 100 parts by mass of inorganic filler. A water-soluble polymer content of 0.04 parts by mass or more increases the binding properties between inorganic components, further suppressing thermal shrinkage. It also suppresses sedimentation of components during slurry preparation of the coating layer, enabling stable dispersion. A water-soluble polymer content of 5 parts by mass or less suppresses streaks and unevenness during coating layer formation.

[0132] Water-soluble polymers also contribute to the bonding of inorganic fillers within the coating layer. From the viewpoint of suppressing thermal shrinkage of the separator, the water-soluble polymer preferably has a weight loss rate of less than 10% at 150°C, when the weight at 50°C is taken as 100% in thermogravimetric measurements.

[0133] The water-soluble polymer may be a polymer derived from natural products, a synthetic product, a semi-synthetic product, etc., but from the viewpoint of paint formulation of inorganic and organic components, particularly water-based paint formulation, it is preferable that it be an anionic, cationic, amphoteric, or nonionic polymer, and more preferably an anionic, cationic, or amphoteric polymer.

[0134] Examples of anionic polymers include starch modifiers such as carboxymethyl starch and starch phosphate; anionic cellulose derivatives such as carboxymethylcellulose; ammonium salts or alkali metal salts of polyacrylic acid; gum arabic; carrageenan; chondroitin sulfate sodium; sulfonic acid compounds such as polystyrene sulfonate sodium, polyisobutylene sulfonate sodium, and naphthalene sulfonic acid condensate salts; and polyethylene iminzanate salts. Among these, from the viewpoint of achieving an appropriate balance between rigidity, rate characteristics, and cycle characteristics for energy storage devices, anionic polymers containing metal salts as countercations are preferred; anionic cellulose derivatives and ammonium salts or alkali metal salts of polyacrylic acid are also preferred; from the viewpoint of balancing heat resistance and rate characteristics, alkali metal salts of polyacrylic acid are even more preferred, and sodium polyacrylate is even more preferred.

[0135] Ammonium salts or alkali metal salts of polyacrylic acid are derived from multiple carboxylic acid groups -COO - This refers to a polymer in which at least one of its parts forms a salt with an ammonium ion or an alkali metal ion. Examples of alkali metal ions include sodium ions (Na). + ), potassium ions (K + Examples include:

[0136] The ammonium salt or alkali metal salt of polyacrylic acid may be at least one of the following (I) to (III): (I) A monomer having one ammonium salt or alkali metal salt of a carboxylic acid (C i ) homopolymer, or multiple monomers (C i ) and copolymers with other monomers; (II) A monomer having multiple ammonium salts or alkali metal salts of carboxylic acids (C ii ) homopolymer or monomer (C ii ) copolymers with 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.

[0137] A monomer having one ammonium salt or alkali metal salt of a carboxylic acid (C i Examples of such substances include sodium (meth)acrylate and ammonium (meth)acrylate.

[0138] A monomer having multiple ammonium salts or alkali metal salts of carboxylic acids (C ii Examples of these include ammonium or sodium salts of 11-(methacryloyloxy)undecane-1,1-dicarboxylic acid; ammonium, monosodium, or 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.

[0139] Monomer (C i ) or monomer (C ii Examples of monomers copolymerizable with ) 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.

[0140] Examples of ammonium salts or alkali metal salts of polymers or copolymers obtained by polymerizing or copolymerizing monomers having one or more carboxylic acids include sodium polyacrylate and ammonium polyacrylate.

[0141] The structures of the ammonium salts or alkali metal salts of polyacrylic acid described in (I) to (III) above may overlap. It is desirable that the ammonium salts or alkali metal salts of polyacrylic acid described in (I) to (III) above 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.

[0142] 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; polyvinylimidazolines; dicyandiamide condensates; epichlorohydrin-dimethylamine condensates; and polyethyleneimines.

[0143] Examples of amphoteric polymers include dimethylaminoethyl (meth)acrylate quaternary salt-acrylic acid copolymers and Hoffmann decomposition products of polyacrylamide.

[0144] Examples of nonionic polymers include starch and its derivatives; cellulose derivatives such as methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, and their ammonium salts or alkali metal salts; gums such as guar gum and their modified forms; and synthetic polymers such as polyvinyl alcohol, polyacrylamide, polyethylene glycol, polymethyl vinyl ether, polyisopropylacrylamide, and copolymers of vinyl alcohol and other monomers, and their modified forms.

[0145] Water-soluble polymers may or may not have amide bond-containing cyclic structures. A 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. A water-soluble polymer having an amide bond-containing cyclic structure may have one or more amide bond-containing cyclic structures.

[0146] Groups having an amide bond-containing cyclic structure include the following formula (2): [ka] Examples of groups represented by include the following. Specific examples of water-soluble polymers having an amide bond-containing cyclic structure include homopolymers of monomers having a group with an amide bond-containing cyclic structure and a polymerizable double bond, such as poly(N-vinylcaprolactam), a homopolymer of N-vinylcaprolactam, and polyvinylpyrrolidone (PVP), a homopolymer of vinylpyrrolidone; copolymers of two or more monomers (N-vinylcaprolactam, vinylpyrrolidone, etc.) having a group with an amide bond-containing cyclic structure and a polymerizable double bond; and copolymers of one or more monomers (N-vinylcaprolactam, vinylpyrrolidone, etc.) having a group with an amide bond-containing cyclic structure and a polymerizable double bond, and one or more monomers having other polymerizable double bonds (monomers other than monomers having a group with an amide bond-containing cyclic structure and a polymerizable double bond).

[0147] Examples of monomers copolymerizable with monomers having a group with an amide bond-containing cyclic structure and a polymerizable double bond include vinyl acyclic amides; (meth)acrylic acid and its esters; (meth)acrylamide and its derivatives; styrene and its derivatives; vinyl esters such as vinyl acetate; α-olefins; basic unsaturated compounds such as vinylimidazole and vinylpyridine and their derivatives; carboxyl group-containing unsaturated compounds and their acid anhydrides; vinyl sulfonic acid and its derivatives; vinyl ethylene carbonate and its derivatives; and vinyl ethers.

[0148] (Additives) The coating layer may consist only of inorganic fillers, particulate polymers of thermoplastic polymers, and any water-soluble polymers, or it may further contain other additives. Examples of additives include low molecular weight dispersants other than water-soluble polymers; thickeners; defoamers; 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 Examples include nonpolymerizable compounds having multiple ammonium salts or alkali metal salts of carboxylic acids (e.g., sodium alginate and sodium hyaluronate).

[0149] A specific example of an antifoaming agent is the following formula (A): [ka] {where, R 5 ~R 8 It is preferable to use a surfactant (acetylene-based surfactant) containing an ethoxylated acetylene glycol represented by}, where n and m are independent of each other and represent alkyl groups having 1 to 10 carbon atoms, and n and m are independent of each other and represent integers of 0 or more, but n + m = 0 to 40.

[0150] Specific examples of alkyl groups having 1 to 10 carbon atoms include linear, branched, and cyclic 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 groups.

[0151] Specific examples of acetylene glycol represented by formula (A) include 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, 5,8-dimethyl-6-dodecine-5,8-diol, 2,4,7,9-tetramethyl-5-decine-4,7-diol, 4,7-dimethyl-5-decine-4,7-diol, 2,3,6,7-tetramethyl-4-octin-3,6-diol, 3,6-dimethyl-4-octin-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, ethoxylated derivative of 2,4,7,9-tetramethyl-5-decine-4,7-diol (number of moles of ethylene oxide added: 1.3), and 2,4,7,9-tetramethyl-5-decine-4,7-diol. Examples include ethoxylated compounds (4 moles of ethylene oxide added), ethoxylated compounds of 3,6-dimethyl-4-octyne-3,6-diol (4 moles of ethylene oxide added), ethoxylated compounds of 2,5,8,11-tetramethyl-6-dodecine-5,8-diol (6 moles of ethylene oxide added), ethoxylated compounds of 2,4,7,9-tetramethyl-5-decine-4,7-diol (10 moles of ethylene oxide added), ethoxylated compounds of 2,4,7,9-tetramethyl-5-decine-4,7-diol (30 moles of ethylene oxide added), and ethoxylated compounds of 3,6-dimethyl-4-octyne-3,6-diol (20 moles of ethylene oxide added). The defoaming agent may be used alone or in combination of two or more types.

[0152] Acetylene-based surfactants can also be obtained commercially. Examples of such commercially available products include Olfin SPC (manufactured by Nisshin Chemical Industry Co., Ltd., 80 parts by mass of active ingredient, pale yellow liquid), Olfin AF-103 (manufactured by Nisshin Chemical Industry Co., Ltd., pale brown liquid), Olfin AF-104 (manufactured by Nisshin Chemical Industry Co., Ltd., pale brown liquid), Olfin SK-14 (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin AK-02 (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin AF-201F (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin D-10PG (manufactured by Nisshin Chemical Industry Co., Ltd., 50 parts by mass of active ingredient, pale yellow liquid), Olfin E- Examples include 1004 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1010 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1020 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1030W (manufactured by Nisshin Chemical Industry Co., Ltd., 75 parts by mass of active ingredient, pale yellow liquid), Surfinol 420 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow viscous substance), Surfinol 440 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow viscous substance), and Surfinol 104E (manufactured by Nisshin Chemical Industry Co., Ltd., 50 parts by mass of active ingredient, pale yellow viscous substance).

[0153] As an additive surfactant, polyether surfactants and / or silicone surfactants can be used in place of or in combination with acetylene surfactants. Typical 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 copolymer. Among these, polyethylene glycol is particularly preferred. These surfactants may be used individually or in combination of two or more.

[0154] Polyether surfactants are also available commercially, and examples of such commercially available products include E-D052, E-D054, and E-F010 (manufactured by Sunopco Co., Ltd.).

[0155] Silicone-based surfactants may be linear, branched, or cyclic, as long as they contain at least a silicone chain, and may contain either a hydrophobic group or a hydrophilic group. Specific examples of hydrophobic groups 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 groups; cyclic alkyl groups such as cyclohexyl groups; and aromatic hydrocarbon groups such as phenyl groups. Specific examples of hydrophilic groups include amino groups, thiol groups, hydroxyl groups, alkoxy groups, carboxylic acids, sulfonic acids, phosphoric acid, nitric acid, and their organic and inorganic salts, ester groups, aldehyde groups, glycerol groups, and heterocyclic groups. Representative examples of silicone-based 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.

[0156] Silicone-based surfactants are also available commercially. 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, BYK-349 (all product names, manufactured by Big Chemie Japan Co., Ltd.), KM-80, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, and KF-640. Examples include KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (all product names, manufactured by Shin-Etsu Chemical Co., Ltd.), SH-28PA, SH8400, SH-190, SF-8428 (all product names, manufactured by Toray Dow Corning Co., Ltd.), Polyflow KL-245, Polyflow KL-270, Polyflow KL-100 (all product names, manufactured by Kyoeisha Chemical Co., Ltd.), Silface SAG002, Silface SAG005, and Silface SAG0085 (all product names, manufactured by Nisshin Chemical Industry Co., Ltd.).

[0157] (Amount of coating layer) The amount of coating layer relative to the substrate, that is, the amount of coating layer per unit area of ​​one surface of the substrate, is preferably 0.5 g / m² by weight. 2 Above all, a comfortable 1.0 g / m 2 The above is true, and the volume is preferably 0.15 cm³. 3 / m 2 More preferably 0.30 cm 3 / m 2 That concludes the explanation. The upper limit of the amount of the coating layer is preferably 10.0 g / m² by weight. 2 More preferably, 7.0 g / m 2 The following is the volume, preferably 3.50 cm³. 3 / m 2 More preferably 2.50 cm 3 / m 2The following applies: It is preferable for the amount of the coating layer to be greater than or equal to the lower limit above, in terms of improving the adhesion between the coating layer and the electrode and suppressing thermal shrinkage. It is preferable for the amount of the coating layer to be less than or equal to the upper limit above, from the viewpoint of suppressing a decrease in ion permeability.

[0158] (Thickness of the coating layer) The thickness of either one of the coating layers (thickness of the inorganic filler portion) disposed on at least one of the substrates is preferably 0.3 μm or more and 5.0 μm or less, more preferably 0.5 μm or more and 2.5 μm or less, and even more preferably 0.7 μm or more and 1.3 μm or less. When the thickness of the coating layer is 0.3 μm or more, thermal shrinkage can be further suppressed, the adhesive force between the electrode and the substrate can be made uniform, and as a result the characteristics of the energy storage device can be improved. When the thickness is 1.3 μm or less, a decrease in ion permeability can be suppressed, and it is preferable in that a thin film separator for energy storage devices can be obtained. That is, by making the separator thinner, it is possible to manufacture an energy storage device with a large capacity per unit volume. On the other hand, from the viewpoint of further suppressing thermal shrinkage and from the viewpoint of preventing the particulate polymer from sliding off the coating layer, it is preferably 1.6 μm or more, or 2.1 μm or more. The above thickness can be adjusted, for example, by changing the type or concentration of particulate polymer in the coating solution applied to the substrate, the amount of coating solution applied, the application method, and the application conditions. However, the method for adjusting the thickness of the coating layer is not limited to these methods.

[0159] Figure 1 is a schematic diagram of the surface of the coating layer of the separator for the energy storage device of this embodiment. As schematically shown in Figure 1, the surface of the coating layer (10) contains an inorganic filler (1) and particulate polymers (2) of thermoplastic polymer protruding from the inorganic filler portion. In Figure 1, the particulate polymers exist in a primary particle state without agglomerating with other particulate polymers.

[0160] Figure 2 is a cross-sectional view of the separator for the energy storage device shown in Figure 1. As schematically shown in Figure 2, the coating layer (20) is formed in a sloping manner, starting from an inorganic filler portion located at least 1.5D horizontally (in the surface direction of the coating layer) from the volume center of each particulate polymer, and becoming continuously thicker as it approaches the protruding particulate polymer (2). The slope of the sloping coating layer is gentler as it moves away from the protruding particulate polymer and steeper as it approaches the protruding particulate polymer. The inorganic filler (1) covers a portion of the periphery of the protruding portion by resting along the contour of the particulate polymer, while the area near the center of the protruding portion is exposed on the surface of the coating layer.

[0161] Manufacturing method for separators for energy storage devices <Method for manufacturing the base material> The method for manufacturing the substrate can employ known manufacturing methods, for example, either a wet porosization method or a dry porosization method may be used. Examples of wet porosization methods include, for example, when the substrate is a polyolefin microporous film, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded together to form a sheet, and optionally stretched, after which the plasticizer is extracted to create porosity; a method in which a polyolefin resin composition mainly containing a polyolefin-based resin is melt-kneaded together, extruded at a high draw ratio, and then porosized by peeling off the polyolefin crystal interface by heat treatment and stretching; a method in which a polyolefin resin composition and an inorganic filler are melt-kneaded together to form a sheet, and then porosized by peeling off the interface between the polyolefin and the inorganic filler by stretching; and a method in which a polyolefin resin composition is dissolved, immersed in a poor solvent for polyolefin, and the polyolefin is solidified while the solvent is removed to create porosity.

[0162] Methods for producing the base material include, for example, the chemical bonding method, in which the web is immersed in a binder and dried to bond the fibers together; the thermal bonding method, in which heat-meltable fibers are mixed into the web and the fibers are partially melted to bond them together; the needle punching method, in which a needle with thorns is repeatedly pierced into the web to mechanically entangle the fibers; and the water entanglement method, in which a high-pressure water stream is sprayed onto the web through a net (screen) from a nozzle to entangle the fibers.

[0163] The following describes an example of a method for producing a polyolefin microporous membrane, which involves melt-kneading a polyolefin resin composition with a plasticizer to form a sheet, followed by extraction of the plasticizer. The polyolefin resin composition and plasticizer are melt-kneaded. As a melt-kneading method, for example, the polyolefin resin and, if necessary, other additives are put into a resin mixing device such as an extruder, kneader, laboplast mill, kneading roll, and Banbury mixer, and the plasticizer is introduced and kneaded in an arbitrary ratio while the resin components are heated and melted. In this case, it is preferable to pre-knead the polyolefin resin, other additives, and plasticizer in a predetermined ratio using a Henschel mixer or the like before putting them into the resin mixing device. More preferably, only a portion of the plasticizer is added during the pre-kneading, and the remaining plasticizer is kneaded while being fed to the side of the resin mixing device.

[0164] As a plasticizer, a non-volatile solvent capable of forming a homogeneous solution above 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. Among these, liquid paraffin is preferred.

[0165] The ratio of the polyolefin resin composition to the plasticizer is not particularly limited, as long as they can be uniformly melt-mixed 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. Setting the mass fraction of the plasticizer within this range is preferable from the viewpoint of achieving both melt tension during melt molding and the formation of a uniform and fine pore structure.

[0166] The molten mixture obtained by heating, melting, and kneading as described above is formed into a sheet. One method for producing a sheet-shaped molded body is to extrude the molten mixture into a sheet shape through a T-die or the like, and then cool and solidify it by contacting it with a heat conductor to a temperature sufficiently lower than the crystallization temperature of the resin components. Examples of heat conductors used for cooling and solidification include metal, water, air, and the plasticizer itself, but metal rolls are preferred because they have high heat conduction efficiency. In this case, it is even more preferable to sandwich the molten mixture between the metal rolls when contacting it, as this further increases the heat conduction efficiency, aligns the sheet, increases film strength, and improves the surface smoothness of the sheet. The die lip spacing when extruding the mixture into a sheet shape from the T-die is preferably 400 μm to 3000 μm, more preferably 500 μm to 2500 μm.

[0167] It is preferable to then stretch the sheet-like molded article obtained in this manner. Either uniaxial stretching or biaxial stretching can be suitably used as the stretching process. Biaxial stretching is preferred from the viewpoint of the strength of the resulting microporous film. When the sheet-like molded article is stretched at high magnification in the biaxial direction, the molecules become oriented in the planar direction, and the resulting porous substrate becomes less prone to tearing and possesses high puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple-pass stretching. Simultaneous biaxial stretching is preferred from the viewpoint of improving puncture strength, stretching uniformity, and shutdown properties.

[0168] The stretching ratio is preferably in the range of 20 to 100 times, more preferably in the range of 25 to 50 times, in terms of surface magnification. 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, and more preferably in the range of 5 to 8 times in the MD direction and 5 to 8 times in the TD direction. Setting the stretching ratio within this range is preferable because it allows for more sufficient strength to be imparted, prevents film breakage during the stretching process, and enables high productivity. The MD direction refers to the machine direction when, for example, a polyolefin microporous film is continuously molded, and the TD direction refers to the direction that intersects the MD direction at a 90° angle.

[0169] 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. Rolling can increase the orientation of the surface layer of the sheet-like molded article in particular. The rolling ratio is preferably greater than 1 and 3 or less, and more preferably greater than 1 and 2 or less. A rolling ratio within this range is preferable because it increases the film strength of the porous substrate obtained in the end and allows for the formation of a more uniform porous structure in the thickness direction of the film.

[0170] Next, the plasticizer is removed from the sheet-like molded body to obtain a porous substrate. Methods for removing the plasticizer include, for example, immersing the sheet-like molded body in an extraction solvent to extract the plasticizer and then thoroughly drying it. The extraction method can be either batch or continuous. To suppress 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 removal of the plasticizer can be controlled so that the amount of plasticizer is preferably between 0.1 parts by mass and 1.6 parts by mass, more preferably between 0.2 parts by mass and 1.2 parts by mass, or between 0.3 parts by mass and 1.0 part by mass, based on the total mass of the obtained substrate. By keeping the amount of plasticizer within the above range, it is possible to improve the bonding strength between the substrate and the coating layer while lowering the internal resistance of the battery.

[0171] It is preferable to use an extraction solvent that is a poor solvent for polyolefin resins and a good solvent for plasticizers, and whose boiling point is 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-chlorinated 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.

[0172] To suppress shrinkage of the porous substrate, heat treatment such as thermal fixation or thermal relaxation may be performed after the stretching process or after the formation of the porous substrate. Post-treatment such as hydrophilization treatment with surfactants or crosslinking treatment with ionizing radiation may also be performed on the porous substrate.

[0173] An example of a dry porosification method, which differs from the wet porosification method described above, is given. First, a film is prepared by melting and kneading in an extruder without using a solvent and then directly stretching and oriented. Subsequently, a microporous membrane is prepared by sequentially going through an annealing process, a cold stretching process, and a hot stretching process. Examples of dry porosification methods include stretching and oriented molten resin from an extruder via a T-die, and the inflation method, and there are no particular limitations on the method.

[0174] <Method of arranging the coating layer> A coating layer is placed on at least one side of the substrate manufactured as described above. One method for placing the coating layer is to apply a coating solution containing an inorganic filler and a particulate polymer of a thermoplastic polymer to the substrate and then remove the medium.

[0175] As the coating solution, a dispersion can be used 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. Preferably, the particulate polymer is synthesized by emulsion polymerization, and the emulsion obtained by the emulsion polymerization can be used as is as the coating solution.

[0176] The coating medium is preferably one that can uniformly and stably disperse or dissolve inorganic fillers, particulate polymers, and optionally water-soluble polymers. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, methanol, toluene, hot xylene, methylene chloride, and hexane. The coating medium 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 include ethanol and methanol. Among these, water is more preferred. When the coating liquid is applied to a substrate, if the coating liquid penetrates into the interior of the substrate, the particulate polymers containing the polymer tend to clog the surface and interior of the pores of the substrate, easily reducing permeability. In this respect, an aqueous dispersion using water as the coating medium is preferable because it makes it difficult for the coating liquid to penetrate into the interior of the substrate, and the particulate polymers containing the polymer tend to remain mainly on the outer surface of the substrate, thus more effectively suppressing the reduction in permeability.

[0177] The volume-average particle size (D50) of the particulate polymer in the coating solution may be, for example, 1.0 μm or more and 12 μm or less. From the viewpoint of obtaining a suitable distribution state of protruding particulate polymer in the coating layer, the volume-average particle size (D50) is preferably 1.5 μm or more, and more preferably 10 μm or less, 7.5 μm or less, 5.0 μm or less, 3.0 μm or less, or 2.5 μm or less. If the volume-average particle size (D50) is above the lower limit, aggregation of particulate polymers can be suitably prevented. Also, if the volume-average particle size (D50) is below the upper limit, the particle size difference with the inorganic filler can be kept within a predetermined range, thereby making it easier to suitably control the sedimentation of particulate polymer in the coating solution. The volume-average particle size of the particulate polymer can be controlled, for example, by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, and pH for obtaining the particulate polymer.

[0178] The coating solution may optionally contain additives. Examples of additives to the coating solution include dispersants such as surfactants; thickeners; wetting agents; defoaming agents; and various other additives such as pH adjusters containing acids and alkalis.

[0179] Methods for dispersing or dissolving inorganic fillers, particulate polymers, and optionally water-soluble polymers in a coating medium include, for example, ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloidal mills, attritors, roll mills, high-speed impeller dispersion, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and mechanical stirring using stirring blades, etc.

[0180] The preferred procedure for preparing the coating solution is to first add a water-soluble polymer to a coating solution containing dispersed inorganic fillers, and then add a resin binder and particulate polymer. By preparing the coating solution in this order, the water-soluble polymer adsorbs and protects the metal ions contained in the inorganic fillers, preventing aggregation of the resin binder and particulate polymer.

[0181] To obtain a suitable distribution state of protruding particulate polymer in the coating layer, the viscosity of the coating solution is preferably 10 mPa·s or more, or 20 mPa·s or more, and more 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 solution is preferably particles having a large particle size of 1 μm to 10 μm. Therefore, if the viscosity of the coating solution is 10 mPa·s or more, it is possible to prevent the thermoplastic polymer from settling in the coating solution. On the other hand, if the viscosity of the coating solution is 100 mPa·s or less, turbulence of the liquid is more likely to occur during stirring, the dispersion of particulate polymer in the coating solution flow will be better, and it will be easier to control the coefficient of variation (CV) of the area (si) of the Voronoi polygon to the above range. Furthermore, a viscosity of 10 mPa·s or more and 100 mPa·s or less for the coating solution is preferable from the viewpoint of suitably controlling the sedimentation of particulate polymers during the process in which the solvent is removed from the coating film after coating and a coating layer is formed, from the viewpoint of increasing the gradient of the coating layer, and from the viewpoint of increasing the contact ratio between the particulate polymers and the substrate surface.

[0182] The substrate may be surface-treated before coating. Surface treatment is preferable because it makes it easier to apply the coating solution, improves the 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 surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation. Corona discharge treatment is one example of a surface treatment method.

[0183] The method for applying the coating solution onto the substrate is not particularly limited as long as it can achieve the desired coating pattern, coating film thickness, and coating area. Examples of coating methods include gravure coater, small-diameter gravure coater, reverse roll coater, transfer roll coater, kiss coater, dip coater, knife coater, air doctor coater, blade coater, rod coater, squeeze coater, cast coater, die coater, screen printing, spray coating, and inkjet coating. Of these, the gravure coater or spray coating method is preferred from the viewpoint of providing a high degree of freedom in the coating shape of the particulate polymer and easily obtaining a desirable area ratio.

[0184] The coating method is preferably one in which the coating is applied at a high shear rate, such as by a gravure coater, and the shear rate is preferably 40,000 sec. -1 Over 120,000 seconds -1 The following is true: When the shear rate is within this range, the dispersion of the particulate polymer as primary particles is good, and it becomes easier to control the 180° peel strength to 200 gf / cm or higher.

[0185] The coating solution may be stirred before or during coating. Stirring methods include: A method of agitating the coating solution in a supply tank by turbulence; A method of applying ultrasonic treatment (vibration and agitation treatment using ultrasonic waves) to the coating solution immediately before application; These are some examples. Performing these stirring methods appropriately is advantageous in terms of obtaining a suitable particle size distribution state of the protruding particulate polymer in the coating layer and adjusting the static friction coefficient of the coating layer to within the above range.

[0186] There are no particular limitations on the method for removing the medium from the coating film after application, as long as it does not adversely affect the substrate and the coating layer. For example, methods include drying at a temperature below the melting point while fixing the substrate, drying under reduced pressure at low temperatures, and immersing the particulate polymer in a medium that is a poor solvent for particulate polymers to solidify the particulate polymer into particles while simultaneously extracting the medium.

[0187] From the viewpoint of adjusting the static friction coefficient of the coating layer within the above range, and / or making it easier to maintain the shape of the protruding particulate polymer, it is preferable to control the conditions after the coating and drying process as follows: • The tension applied to the coated surface in a direction perpendicular to the surface in contact with the conveyor roll is controlled to a predetermined value or less, for example, 40 N / m or less. - The conveyor roll speed in contact with the coated surface should be equal to the separator conveyor speed. Specifically, for example, the conveyor roll speed in contact with the coated surface after the coating process should be greater than 0.999 times the separator conveyor speed but less than 1.001 times.

[0188] <Fabrication of the separator coil> The obtained separator for energy storage devices is preferably wound into a wound body. By winding the separator into a wound body, it can be easily and quickly unwound, thereby increasing productivity in the production process of energy storage devices.

[0189] Energy storage devices The energy storage device of this embodiment includes the separator for the energy storage device of this embodiment. The energy storage device is not particularly limited, but examples include batteries such as non-aqueous electrolyte secondary batteries, capacitors, and condensers. Among these, batteries are preferred in order to take advantage of the benefits of the separator for the energy storage device of this embodiment, non-aqueous electrolyte secondary batteries are more preferred, and lithium-ion secondary batteries are even more preferred. A lithium-ion secondary battery has a positive electrode, a negative electrode, the separator for the energy storage device of this embodiment disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The energy storage device of this embodiment, by including the separator for the energy storage device, has excellent characteristics such as energy storage performance, and in the case of a lithium-ion secondary battery, it has excellent battery characteristics.

[0190] When the energy 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 ones can be used. As the positive electrode, a positive electrode having a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector is preferably used. Examples of positive electrode current collectors include aluminum foil. Examples of positive electrode active materials include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4. The positive electrode active material layer may appropriately contain a binder, conductive material, etc., in addition to the positive electrode active material.

[0191] As the negative electrode, a negative electrode having a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector can be suitably used. Examples of negative electrode current collectors include copper foil. Examples of negative electrode active materials include carbon materials such as graphite, non-graphitizable carbonaceous materials, easily graphitizable carbonaceous materials, and composite carbonaceous materials; as well as silicon, tin, metallic lithium, and various alloy materials.

[0192] The non-aqueous electrolyte is not particularly limited, but an electrolyte in which the electrolyte is dissolved in an organic solvent can be used. Examples of organic solvents include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of electrolytes include lithium salts such as LiClO4, LiBF4, and LiPF6.

[0193] Manufacturing method for energy storage devices The method for manufacturing an energy storage device using the separator of this embodiment is not particularly limited. For example, the following method can be exemplified. First, the separator of this embodiment is manufactured by the method described above. 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 stacked in that order and wound into a circular or flat spiral shape to obtain a wound body. The wound body can be placed in a device container (e.g., a battery container) and then injected with an electrolyte to manufacture the device. Alternatively, the electrodes and separator may be folded to form a wound body, which can then be placed in a device container (e.g., an aluminum film) and injected with an electrolyte to manufacture the device.

[0194] At this time, the wound body can be pressed. Specifically, an example can be given of a method in which a separator, a current collector, and an electrode having an active material layer formed on at least one side of the current collector are stacked and pressed together so that the coating layer and the active material layer face each other.

[0195] The pressing temperature is the temperature at which adhesion can be effectively achieved. 1.00 It is preferable to carry out the procedure at the above temperature. 1.00 T is the temperature at which the minimum value of DDSC (Differential Scanning Calorimetry) is obtained, where DDSC is the derivative of the heat transfer rate per unit time measured by DSC with respect to temperature, is observed between 0°C and 150°C. 1.00Pressing at the above temperature allows the coating layer to deform sufficiently, resulting in good adhesion. For example, 35°C or higher is preferred. To suppress clogging of holes or thermal shrinkage in the separator due to hot pressing, the press temperature is preferably lower than the melting point of the material contained in the base material, and more preferably 130°C or lower. The press pressure is preferably 20 MPa or lower from the viewpoint of suppressing clogging of holes in the separator. The press time may be 1 second or less when using a roll press, and several hours when using a surface press, and preferably 2 hours or less from the viewpoint of productivity. By using the separator for energy storage devices of this embodiment and going through the above manufacturing process, press back when the wound body consisting of electrodes and separators is press-molded can be suppressed. Therefore, yield reduction in the device assembly process can be suppressed and production process time can be shortened.

[0196] Adhesion may be imparted to the wound material without pressing. Specifically, an example is a method in which the wound material is placed in a device can, an electrolyte is injected, and adhesion is imparted between the separator coating layer and the opposing electrode by the pressure generated inside the device can when manufacturing the energy storage device, or by the pressure associated with the expansion and contraction of the electrodes due to the charging and discharging of the energy storage device.

[0197] The energy storage devices manufactured as described above, particularly lithium-ion secondary batteries, possess the separator of this embodiment, which has high adhesion to electrodes and a low thermal shrinkage rate, and therefore exhibit excellent battery characteristics (rate characteristics) and long-term continuous operation resistance (cycle characteristics). [Examples]

[0198] The embodiments of this disclosure will be specifically described below with reference to examples and comparative examples, but this disclosure is not limited to these examples and comparative examples.

[0199] Measurement and Evaluation Methods <Thickness of the inorganic filler portion of the coating layer, gradient of the coating layer, and amount of particulate polymer protrusion> The separator was frozen and fractured, and its cross-section was examined using a scanning electron microscope (SEM, model S-4800, Hitachi). 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 amount of particulate polymer protrusion were measured. Specifically, a sample of the separator was cut to approximately 1.5 mm × 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 coated with osmium and observed at an acceleration voltage of 1.0 kV and magnification of 5000x. As schematically shown in Figure 2, the distance from the substrate-coating layer boundary to the outer surface of the coating layer in the inorganic filler portion of the coating layer was measured from the SEM image of the fractured sample cross-section, and the thickness L1 (μm) of the inorganic filler portion of the coating layer was measured. Furthermore, the maximum distance L2 (μm) from the substrate-coating layer boundary to the outer surface of the inorganic filler in the inclined coating layer, and the maximum distance L3 (μm) to the contour of the protruding particulate polymer were measured, and the inclination ratio L2 / L1 of the coating layer, the coverage ratio of the protruding portion (L2-L1) / (L3-L1), and the protrusion amount L3-L1 of the particulate polymer were calculated. The inclination ratio L2 / L1 of the coating layer, the coverage ratio of the protruding portion (L2-L1) / (L3-L1), and the protrusion amount L3-L1 of the particulate polymer were measured at 200 points, and the average value was calculated.

[0200] As a method for measuring L1, L2, and / or L3, one can also use a method in which the L1 values ​​are determined while polishing the cross section being observed with SEM.

[0201] <180° peel strength> A separator cut to 2mm x 7mm was attached to a glass plate with double-sided tape on the side opposite to the coating layer to be measured, and tape (product name "Mending Tape MP-12", manufactured by 3M) was applied to the coating layer. 5mm of the tape tip was peeled off, and the tape tip was clamped in a chuck on a tensile testing machine (model "AG-IS, SLBL-1kN", manufactured by Shimadzu Corporation) so that the tape peeled off at a 180° angle to the surface direction of the separator. A tensile test was performed at a tensile speed of 50mm / sec, a temperature of 25°C, and a relative humidity of 40%, and the tensile strength (gf / cm) was measured.

[0202] 〈Friction Test〉 Regarding the surface on which the coating layer of the separator sample was formed, the static friction coefficient was measured twice at TD under the conditions of using an MH-3 friction tester manufactured by Toyo Seiki Seisakusho Co., Ltd., table material SKD61 (surface roughness Ra: 0.4 μm), thread mass 200 g, load range 2 N, contactor area 63 mm × 63 mm (felt material), contactor feed speed 100 mm / min, measurement distance 30 mm, temperature 23°C, and humidity 50%, and calculated by obtaining their average value.

[0203] 〈Contact Ratio of Projected Particle状Polymer and Substrate〉 The separator was cryo-sectioned, and its cross-section was confirmed by SEM (model S-4800, manufactured by Hitachi, Ltd.). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a separator sample was cut into pieces of about 1.5 mm × 2.0 mm and ruthenium-stained. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was sectioned with a hammer. The sectioned sample was osmium-evaporated and observed at an acceleration voltage of 1.0 kV and 5000 times magnification. In the SEM image, for 200 particle状polymers with a cross-section among the particle状polymers protruding from the thickness of the inorganic filler part of the coating layer, the number of particles in contact with the substrate was counted, and the contact ratio of the protruding particle状polymer and the substrate was determined.

[0204] 〈Ratio of the Number of Particle状Polymers Protruding from the Thickness of the Inorganic Filler Part of the Coating Layer〉 The separator was cryo-sectioned, and its cross-section was examined using 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 sample of the separator was cut into pieces of about 1.5 mm × 2.0 mm, and ruthenium staining was performed. The stained sample and ethanol were placed in a gelatin capsule and frozen with liquid nitrogen, and then the sample was sectioned with a hammer. The sectioned sample was osmium-deposited and observed at an acceleration voltage of 1.0 kV and a magnification of 5000 times. In the SEM image, 200 particulate polymers present in the cross-section were observed, and the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer was counted, and the ratio of the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer was determined.

[0205] 〈Methylene chloride soluble content〉 The methylene chloride soluble content in the base material and the separator was measured by the following method. A base material sampled to 100 × 100 mm or the separator was discharged from static electricity and weighed using a precision balance (W0 (g)). Subsequently, 200 ml of methylene chloride was added to a sealed container, and the above separator was immersed at room temperature for 15 minutes. Then, the separator was taken out, dried at room temperature for 3 hours, discharged from static electricity as above, and weighed using a precision balance (W1 (g)). The methylene chloride soluble content was determined by the following formula. Methylene chloride soluble content (mass%) = {(W0 - W1) / W0} × 100

[0206] 〈Total amount of metal cations〉 0.60 g of the separator was placed in a pressure decomposition container made of Teflon (registered trademark), 10 ml of sulfuric acid was added, sealed, and heat-treated in an air bath at 200 °C for 15 hours. After cooling, the solution in the container was transferred to a 100 ml volumetric flask made of resin and made up to volume to obtain a sample solution. The sample solution was measured by 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 a standard solution.

[0207] 〈Thermal shrinkage rate〉 As a sample, a multilayer porous membrane was cut into 100 mm sections on the medium diameter (MD) and 100 mm sections on the torso diameter (TD), and left to stand in an oven at 130°C or 150°C for 1 hour. During this time, the sample was sandwiched between two sheets of paper to prevent direct contact with the hot air. After removing the sample from the oven and allowing it to cool, its length (mm) was measured, and the thermal shrinkage rate was calculated using the following formula. Measurements were performed on both the MD and TD sections, and the TD value is shown as the thermal shrinkage rate. Thermal shrinkage rate (%) = {(100 - length after heating) / 100} × 100

[0208] <Weight (g / m 2 )〉 Basis is measured per unit area (1 m²). 2 This is the weight (g) of the polyolefin microporous membrane per unit area (1m x 1m). After sampling a 1m x 1m area, the weight was measured using a Shimadzu Corporation electronic balance (AUW120D). If sampling a 1m x 1m area is not possible, the weight was measured by cutting out an appropriate area and then measured per unit area (1m). 2 The weight was converted to grams per unit.

[0209] <Thickness of the base material or separator> A 10cm x 10cm square sample was cut from the substrate or separator, and nine locations (3 points x 3 points) were selected in a grid pattern. The thickness (μm) was measured at room temperature (23±2℃) using a microthickness gauge (Toyo Seiki Seisakusho Co., Ltd., Type KBM). The average of the obtained measurements from the nine locations was calculated as the thickness of the substrate or separator.

[0210] <Porosity of the substrate> A 10cm x 10cm square sample is cut from the substrate, and its volume (cm³) 3 The saturation (g) and mass (g) were determined. Using these values, the density of the substrate was calculated to be 0.95 (g / cm³). 3 The porosity was calculated using the following formula. Porosity (%) = (1 - mass / volume / 0.95) × 100

[0211] 〈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.

[0212] 〈Air permeability〉 For the base material and the separator for the power storage device, the air permeability resistance measured by a Gurley type air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd. in accordance with JIS P-8117 was defined as the air permeability. When the coating layer exists only on one side of the base material, the needle can be pierced from the surface where the coating layer exists.

[0213] 〈Puncture strength〉 Using a handy compression tester KES-G5 (model name) manufactured by Kato Tech Co., Ltd., the base material was fixed with a sample holder having a diameter of 11.3 mm at the opening. Next, with respect to the central part of the fixed base material, a needle with a tip curvature radius of 0.5 mm was used, and a puncture test was performed at a puncture speed of 2 mm / sec in an atmosphere of 25°C to measure the maximum puncture load, which was defined as the puncture strength (gf). When the coating layer exists only on one side of the base material, the needle can be pierced from the surface where the coating layer exists.

[0214] 〈Average pore diameter of the polyolefin microporous membrane〉 It is known that the fluid inside the capillary follows Knudsen flow when the mean free path of the fluid is larger than the pore diameter of the capillary, and Poiseuille flow when it is smaller. Therefore, it is assumed that the air flow in the air permeability measurement of the thermoplastic polymer-containing layer follows Knudsen flow, and the water flow in the water permeability measurement of the base material follows Poiseuille flow.

[0215] The average pore diameter d (μm) of the polyolefin microporous membrane is calculated from the air permeation rate constant R gas (m 3 / (m 2 ·sec·Pa)), the water permeation rate constant R liq (m 3 / (m 2 ·sec·Pa)), the molecular velocity ν (m / sec) of air, the viscosity η (Pa·sec) of water, the standard pressure Ps (= 101325 Pa), the porosity ε (%), and the film thickness L (μm) using the following formula. d = 2ν × (Rliq / R gas ) × (16η / 3Ps) × 10 6

[0216] Here, R gas was determined from the air permeability (sec) using the following equation. R gas = 0.0001 / (air permeability × (6.424 × 10 -4 )) × (0.01276 × 101325))

[0217] Also, R liq was determined from the water permeability (cm 3 / (cm 2 ·sec·Pa)) using the following equation. R liq = water permeability / 100

[0218] The water permeability was determined as follows. A thermoplastic polymer-containing layer previously immersed in ethanol was set in a liquid-permeable cell made of stainless steel with a diameter of 41 mm. After washing the ethanol in this layer with water, water was permeated under a differential pressure of about 50000 Pa, and the amount of water permeated (cm 3 ) when 120 seconds had elapsed was used to calculate the amount of water permeated per unit time, unit pressure, and unit area, which was taken as the water permeability.

[0219] Also, ν was determined from the gas constant R (= 8.314), absolute temperature T (K), pi π, and average molecular weight of air M (= 2.896 × 10 -2 kg / mol) using the following equation. ν = ((8R × T) / (π × M)) 1 / 2

[0220] 〈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 taken in an aluminum dish and left standing at room temperature for 24 hours to obtain a dried film. Approximately 17 mg of the dried film was filled into a measurement aluminum container, and DSC curves and DSC curves in a nitrogen atmosphere were obtained using a DSC measuring device (manufactured by Shimadzu Corporation, model name "DSC6220"). The measurement conditions were as follows. First stage heating program: Starts at 30°C, heating increases at a rate of 10°C per minute. After reaching 150°C... Hold for 5 minutes. Second stage cooling program: Cools down from 110°C at a rate of 10°C per minute. Maintains at -50°C for 5 minutes after reaching -50°C. Third stage heating program: Heat from -50°C to 150°C at a rate of 10°C per minute. DSC and DDSC data are acquired during this third stage heating.

[0221] The glass transition temperature was determined from the obtained DSC curve using the method described in JIS-K7121. Specifically, the glass transition temperature (Tg) was defined as the temperature at the point where the curve representing the stepwise transition intersects a straight line obtained by extending the low-temperature baseline of the DSC curve toward the high-temperature side, and a straight line equidistant in the vertical direction from the straight line obtained by extending the high-temperature baseline of the DSC curve toward the low-temperature side, with the curve representing the stepwise transition portion.

[0222] <Aspect ratio of inorganic fillers in the coating layer> The surface of an osmium-deposited separator for energy storage devices was observed using a scanning electron microscope (SEM) (model "S-4800", manufactured by Hitachi) at an acceleration voltage of 1.0 kV and magnification of 10,000x. The aspect ratio was determined by image processing of the inorganic fillers in the coating layer using SEM images. Even when inorganic fillers were bonded to each other, those with clearly discernible vertical and horizontal lengths were selected, and the aspect ratio was calculated based on these. Specifically, 10 objects with clearly discernible vertical and horizontal lengths were selected, and the average value obtained by dividing the major axis of each inorganic filler by the minor axis was used as the aspect ratio. If there were fewer than 10 objects with clearly discernible vertical and horizontal lengths in one field of view, 10 were selected from images of multiple fields of view.

[0223] <Particle size distribution and average particle size of inorganic fillers> The particle size distribution of inorganic fillers was measured using a particle size analyzer (Nikkiso Co., Ltd., product name "Microtrac UPA150"). The sample solution used for measurement was the pre-coating dispersion, 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 fillers was calculated by dividing the standard deviation (SD) of the volume-average particle size (D50) obtained in the data by the value of D50.

[0224] <Volume-average particle size (D50) of thermoplastic polymer in aqueous dispersion, and volume-average particle size (D50) of resin binder> The volume-average particle size (D50) of thermoplastic polymers in aqueous dispersions and the volume-average particle size (D50) of resin binders were measured using a particle size analyzer (Nikkiso Co., Ltd., product name "Microtrac UPA150"). The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds. The volume-average particle size (D50) value at which the cumulative volume in the obtained data reached 50% was recorded.

[0225] <Particle size distribution of particulate polymer in the coating layer> The cross-section of an osmium-deposited separator for an energy storage device was observed using a scanning electron microscope (SEM) (model "S-4800", manufactured by Hitachi) at an acceleration voltage of 1.0 kV and magnification of 10,000x. Specifically, the area circle equivalent diameter was measured for 200 arbitrary particulate polymer particles, and the number-average particle diameter MN and volume-average particle diameter MV were determined from these values. The particle size distribution of the particulate polymer was then calculated as MV / MN.

[0226] <Surface observation of the coating layer and Voronoi tessellation> Elemental mapping was performed on the surface of an osmium-deposited separator for energy storage devices using a scanning electron microscope (SEM) (model "SU-8220", Hitachi Corporation) and energy-dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", Oxford University Press). The SEM detector was set to secondary electrons, with an acceleration transfer of 3kV and 20 mapping integrations. As shown in Figure 7, carbon atom mapping measurements were performed in 10 fields of view on the coating layer of the separator at magnifications of 500x or 3000x depending on the particle size of the particulate polymer. The area of ​​the Voronoi polygon (s) of the protruding particulate polymer within these 10 fields of view was then calculated. i The total number of Voronoi polygons (n), mean (m), standard deviation (sd), and coefficient of variation (cv) were obtained as the average values ​​for 10 fields of view. Specifically, from the carbon atom mapping images, Gaussian Blur processing (Sigma=5) was performed using image processing software (ImageJ), followed by binarization using the Threshold function (Auto), and then watershed processing. This processed image was then subjected to Voronoi tessellation using the cv2.Subdiv2D.getVoronoiFacetList method of the opencv-python library (version 4.5.4.60) in the programming language Python. Furthermore, when Voronoi tessellation was performed in the observed field of view, regions that were not closed were not included in the calculation of the area of ​​the Voronoi polygon.

[0227] <Rate Characteristics> a. Fabrication of the positive electrode The positive electrode active material is nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (elemental ratio), density 4.70 g / cm³). 3 ) is added in 90.4 parts by mass, and graphite powder (KS6) (density 2.26 g / cm³) is added as a conductive additive. 3 1.6 parts by mass of (number average particle size 6.5 μm), and acetylene black powder (AB) (density 1.95 g / cm³). 3 3.8 parts by mass of (number average particle size 48 nm), and polyvinylidene fluoride (PVdF) (density 1.75 g / cm³) as a binder. 3A slurry was prepared by mixing ) in a ratio of 4.2 parts by mass and dispersing them in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil, which would serve as the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, the positive electrode was fabricated by compression molding using a roll press. The amount of positive electrode active material applied at this time was 109 g / m². 2 That was the case.

[0228] b. Fabrication of the negative electrode Graphite powder A (density 2.23 g / cm³) is used as the negative electrode active material. 3 87.6 parts by mass of (number average particle size 12.7 μm), and graphite powder B (density 2.27 g / cm³) 3 A slurry was prepared by dispersing 9.7 parts by mass of (number average particle size 6.5 μm), 1.4 parts by mass (solid content equivalent) of ammonium carboxymethylcellulose (solid content concentration 1.83 parts by mass aqueous solution) and 1.7 parts by mass (solid content equivalent) of diene rubber latex (solid content concentration 40 parts by mass aqueous solution) in purified water as binders. This slurry was applied to one side of a 12 μm thick copper foil, which would serve as the negative electrode current collector, using a die coater. After drying at 120°C for 3 minutes, the negative electrode was manufactured by compression molding with a roll press. The amount of negative electrode active material applied at this time was 5.2 g / m². 2 That was the case.

[0229] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute to a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:2.

[0230] d. Battery assembly The separator or substrate was cut into a 24mm diameter circle, and the positive and negative electrodes were each cut into 16mm diameter circles. The negative electrode, separator or substrate, and positive electrode were stacked in that order so that the active material surfaces of the positive and negative electrodes faced each other, and then placed in a stainless steel container with a lid. The container and the lid were insulated from each other, and the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode. The battery was assembled by pouring 0.4 ml of the non-aqueous electrolyte into this container and sealing it.

[0231] e. Evaluation of rate characteristics The simple battery assembled in d. was charged at 25°C with a current of 3mA (approximately 0.5C) until the battery voltage reached 4.2V, and then the current was gradually reduced from 3mA to maintain the 4.2V voltage, for a total of approximately 6 hours. After that, it was discharged at a current of 3mA until the battery voltage reached 3.0V. Next, at 25°C, it was charged at a current of 6mA (approximately 1.0C) until the battery voltage reached 4.2V, and then the current was gradually reduced from 6mA to maintain the 4.2V voltage, for a total of approximately 3 hours. After that, the discharge capacity when discharged at a current of 6mA until the battery voltage reached 3.0V was defined as the 1C discharge capacity (mAh). Next, at 25°C, it was charged at a current of 6mA (approximately 1.0C) until the battery voltage reached 4.2V, and then the current was gradually reduced from 6mA to maintain the 4.2V voltage, for a total of approximately 3 hours. Subsequently, the discharge capacity when the battery was discharged to a voltage of 3.0V at a current of 12mA (approximately 2.0C) was defined as the 2C discharge capacity (mAh). Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was defined as the rate characteristic. Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) × 100 Evaluation Criteria for Rate Characteristics (%) A (Good): Rate characteristics are over 85% B (Acceptable): Rating characteristics are between 80% and 85%. C (Poor): Rate characteristics are 80% or less.

[0232] <Adhesion to electrodes (before electrolyte injection)> The separator was cut into a rectangle measuring 20 mm wide x 70 mm long, and this was placed on top of a positive electrode cut to a size of 15 mm x 60 mm to form a laminate of separator and electrode. This laminate was then 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 using IMADA Corporation's Force Gauge ZP5N and MX2-500N (product name) at a peel speed of 50 mm / min during a 90° peel test. The average peel strength over a 40 mm length under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Good): Peel strength of 5 N / m or more B (Acceptable): Peel strength of 2 N / m or more, and less than 5 N / m C (Defective): Peel strength of 1 N / m or more, but less than 2 N / m. D (Not acceptable): Peel strength less than 1 N / m

[0233] <Adhesion strength to electrodes (after electrolyte injection)> The separator was cut into a rectangle measuring 20 mm wide x 70 mm long, and this was placed on top of a positive electrode cut to a size of 15 mm x 60 mm to form a laminate of separator and electrode. This laminate was then inserted into an aluminum laminate film, and 0.4 ml of electrolyte (a mixture containing 1 mol / L of LiPF6 with an EC / DEC ratio of 1 / 2) was added. After sealing, it was left to stand for 12 hours and then 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 using IMADA Corporation's Force Gauge ZP5N and MX2-500N (product name) at a peel speed of 50 mm / min during a 90° peel test. The average peel strength over a 40 mm length under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Good): Peel strength of 5 N / m or more B (Acceptable): Peel strength of 2 N / m or more, and less than 5 N / m C (Defective): Peel strength of 1 N / m or more, but less than 2 N / m. D (Not acceptable): Peel strength less than 1 N / m

[0234] <Powder-shedding> A 12mm wide x 100mm long tape (manufactured by 3M) was applied to the coating surface of the separator. The force required to peel the tape from the sample at a speed of 50mm / min was measured using a 90° peel strength meter (IMADA Corporation, product name IP-5N). Based on the obtained measurement results, the adhesive strength was evaluated according to the following evaluation criteria. A (good): 59N / m (6gf / mm) or more B (Allowable): 40 N / m or more and less than 59 N / m C (Defective): Less than 40 N / m

[0235] <Cycle Characteristics> a. Fabrication of the positive electrode The positive electrode active material is nickel, cobalt, and aluminum composite oxide (NCA) (Ni:Co:Al = 90:5:5 (elemental ratio), density 3.50 g / cm³). 3 A slurry was prepared by mixing 100 parts by mass of () as the conductive material, 1.25 parts by mass of acetylene black powder (AB) as the conductive material, and 1.0 part by mass of polyvinylidene fluoride (PVdF) as the binder, and dispersing these in N-methylpyrrolidone (NMP). This slurry was applied to both sides of a 15 μm thick aluminum foil, which would serve as the positive electrode current collector, using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to produce the positive electrode. The amount of positive electrode active material applied at this time was 456 g / m². 2 That was the case.

[0236] b. Fabrication of the negative electrode A slurry was prepared by dispersing 86.0 parts by mass of graphite powder and 4.5 parts by mass of silicon dioxide (SiO) as the negative electrode active material, and 1 part by mass of sodium carboxymethylcellulose and 1.0 part by mass 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, which would serve as the negative electrode current collector, using a die coater. After drying at 120°C for 3 minutes, the negative electrode was fabricated by compression molding using a roll press. The amount of negative electrode active material applied at this time was 266 g / m². 2 That was the case.

[0237] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute to a concentration of 1.4 mol / L in a mixed solvent of ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 25:70:5 (by weight ratio).

[0238] d. Battery assembly A positive electrode (63 mm wide), a negative electrode (64 mm wide), and a separator (67 mm wide) were stacked and wound into a spiral to create a coiled body. This coiled body was placed inside a cylindrical battery case with an outer diameter of 21 mm and a height of 70 mm, and the non-aqueous electrolyte was then injected and sealed to assemble the battery.

[0239] e. Evaluation of cycle characteristics The battery assembled in d. was charged at 25°C with a current of 3mA (approximately 0.5C) until the battery voltage reached 4.2V. Then, while maintaining the 4.2V voltage, it was charged until the current reached 50mA. After that, it was discharged at 0.2C until the battery voltage reached 2.5V, and the initial capacity was determined. Next, it was charged at 0.3C until the battery voltage reached 4.2V. Then, while maintaining the 4.2V voltage, it was charged until the current reached 50mA, and then discharged at 1C until the battery voltage reached 2.5V. This constituted one cycle, and the charge-discharge cycle was repeated. The cycle characteristics were then evaluated using the capacity retention rate after 500 cycles relative to the initial capacity (capacity in the first cycle) according to the following criteria. A: Over 80% capacity retention rate B: Volume retention rate of 75% or more but less than 80% C: Volume retention rate of less than 75%

[0240] Examples of substrate manufacturing <Manufacturing of polyolefin microporous membrane B1> 45 parts by mass of homopolymer high-density polyethylene with an Mv of 700,000, 45 parts by mass of homopolymer high-density polyethylene with an Mv of 300,000, and 10 parts by mass of a mixture of homopolymer polypropylene with an Mv of 400,000 and homopolymer polypropylene with an Mv of 150,000 (mass ratio = 4:3) were dry-blended using a tumbler blender. 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant was added to 99 parts by mass of the resulting polyolefin mixture, and the mixture was dry-blended again using a tumbler blender to obtain a mixture. The obtained mixture was fed to a twin-screw extruder via a feeder under a nitrogen atmosphere. Furthermore, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 × 10⁻⁶) was used. -5 m 2 The mixture ( / 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., the proportion of the resin composition was 35 parts by mass.

[0241] Next, these materials were melt-kneaded in a twin-screw extruder while being heated to 230°C. The resulting molten mixture was extruded through a T-die onto a cooling roll with a surface temperature controlled to 80°C. The extruded material was then cast in contact with the cooling roll and cooled and solidified to obtain a sheet-like molded product with a thickness of 1.5 mm. This sheet was stretched in a simultaneous twin-screw stretcher at a magnification of 7 × 6.4 times and a temperature of 20°C. After that, it was immersed in methylene chloride to extract and remove the liquid paraffin, dried, and then stretched in a tenter stretcher at a temperature of 130°C and a transverse magnification of 1.8 times. Subsequently, this stretched sheet was relaxed by approximately 10% in the width direction and heat-treated to obtain a polyolefin microporous membrane B1 as a base material. The obtained polyolefin microporous membrane was evaluated according to the method described above. The evaluation results are shown in the table below.

[0242] <Manufacturing of polyolefin microporous membrane B2> Polyolefin microporous membrane B2 was manufactured in the same manner as polyolefin microporous membrane B1, except that the thickness of the sheet-like molded material was changed to 0.5 mm. The results of the measurement and evaluation of polyolefin microporous membrane B2, performed in the same manner, are shown in Table 1.

[0243] [Table 1]

[0244] 《Examples of preparation of aqueous dispersions of particulate polymers》 <Preparation of aqueous dispersion A1 of particulate polymer> In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, 70.4 parts by mass of deionized water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., indicated as "KH1025" in the table; the same applies hereinafter), and 0.5 parts by mass of "Adekaria Soap SR1025" (registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution, indicated as "SR1025" in the table; the same applies hereinafter) were added, and the internal temperature of the reaction vessel was raised to 95°C. Then, while maintaining the internal temperature of the vessel at 95°C, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (indicated as "APS(aq)" in the table; the same applies hereinafter) were added.

[0245] 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 Industry Co., Ltd.), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane (AcSi), 3.0 parts by mass of KH1025, and SR1025. A mixture of 3.0 parts by mass of sodium p-styrenesulfonate (NaSS), 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 deionized water was mixed in a homomixer for 5 minutes to prepare an emulsion. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. Dropping began 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of emulsion was added dropwise over 150 minutes. The internal temperature of the vessel was maintained at 80°C during the addition of the emulsion. At this time, a stirring bar placed in the reaction vessel was continuously stirred using a magnetic stirrer.

[0246] After the addition of the emulsifier dropwise was complete, the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH=9.0 using an aqueous solution of ammonium hydroxide (25% aqueous solution) to obtain 40 parts by mass of acrylic copolymer latex (aqueous dispersion (particulate polymer) A1). The glass transition temperature (Tg) and volume-average particle size (D50) of the thermoplastic polymer contained in the obtained aqueous dispersion A1 were evaluated by the method described above. The results are shown in the table below.

[0247] <Preparation of aqueous dispersions A2-A5 of particulate polymers> 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 their physical properties were evaluated. The results obtained are shown in the table below.

[0248] <Preparation of aqueous dispersion A1-1 of particulate polymer> Aqueous dispersion A1-1 was synthesized by taking a portion of aqueous dispersion A1 and performing multi-stage polymerization using this as a seed polymer. Specifically, first, a mixture of 20 parts by mass of aqueous dispersion A1 (in terms of solid content) and 70.4 parts by mass of deionized water was 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 constitutes the initial preparation.

[0249] On the other hand, an emulsion was prepared by mixing 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-styrene sulfonate (NaSS), 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water in a homomixer for 5 minutes. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. Dropping began 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of emulsion was added dropwise over 150 minutes. The internal temperature of the vessel was maintained at 80°C during the addition of the emulsion. At this time, a stirring bar placed inside the reaction vessel was continuously stirred using a magnetic stirrer.

[0250] After the addition of the emulsifier dropwise was complete, the reaction vessel was kept at a temperature of 80°C and stirred for 90 minutes, then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH=9.0 using an aqueous solution of ammonium hydroxide (25% aqueous solution) to obtain 40 parts by mass of acrylic copolymer latex (aqueous dispersion A2-1). The obtained aqueous dispersion A2-1 was evaluated using the method described above. The results are shown in Table 2.

[0251] <Preparation of aqueous dispersions A2-1, A3-1 to A3-11, A4-1 and A5-1> Copolymer latexes (aqueous dispersions A2-1, A3-1 to A3-11, A4-1, and A5-1) were obtained in the same manner as aqueous dispersion A1-1, except that the composition of the seed polymer, monomer, and other raw materials was changed as shown in Table 2. Each of the obtained aqueous dispersions was evaluated using the method described above. The results are shown in Table 2.

[0252] [Table 2-1]

[0253] [Table 2-2]

[0254] <Explanation of Abbreviations> ·emulsifier KH1025: "Aqualon KH1025" registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "Adekaria Soap SR1025" registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution NaSS: Sodium p-styrene sulfonate

[0255] Initiator APS(aq): Ammonium persulfate (2% aqueous solution)

[0256] • 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

[0257] Examples of separator manufacturing <Example 1> To 100 parts by mass of water, 0.3 parts by mass of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by Sunopco) and 100 parts by mass of aluminum hydroxide oxide (boehmite, average particle size 450 nm) as an inorganic filler were mixed and treated with a bead mill to obtain a pre-coating dispersion. To the pre-coating dispersion, 0.2 parts by mass of carboxymethylcellulose (CMC) as a water-soluble polymer component was mixed with 100 parts by mass of inorganic filler. Subsequently, 4 parts by mass of an acrylic latex suspension (solid content concentration 40%, volume average particle size 150 nm, Tg -10℃) as a resin binder and 10 parts by mass of aqueous dispersion A3-5 were mixed and uniformly dispersed to prepare a coating solution (solid content 40 parts by mass) containing a thermoplastic polymer.

[0258] Both sides of the polyolefin microporous membrane B1 were surface-treated by corona discharge. Then, a coating solution was applied to one side of the polyolefin microporous membrane B1 using a gravure coater. The coating solution was agitated in the supply tank using a Bernoulli flow agitator BEAG (manufactured by Medic), and the shear rate of the gravure coater was 80,000 sec. -1 The coating layer covered 100% of the polyolefin microporous membrane. The coating solution was then dried at 60°C to remove water. Thus, a separator was obtained in which a coating layer was formed on one side of the polyolefin microporous membrane B1.

[0259] <Examples 2-13 and Comparative Examples 1-5> Separators for the example and comparative example were obtained in the same manner as in Example 1, except that the composition of the polyolefin microporous membrane, the coating solution, and the coating conditions were changed as shown in the table below. In Comparative Example 1, an inclined paddle agitator was used to stir the coating solution. In the separators of Examples 2-13 and Comparative Examples 1, 2, and 5, 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. Furthermore, from surface observation of the separator obtained in Comparative Example 4, L2 / L1, (L2-L1) / (L3-L1), the contact ratio between the particulate polymer and the substrate, and the coefficient of variation of the Voronoi region, it was determined that the particulate polymer did not protrude from the surface of the inorganic filler portion. In Comparative Example 5, an aqueous dispersion containing particulate polymer was not used.

[0260] <Pin missing> When fabricating the electrode windings, the pin release properties after winding were evaluated as follows, and the number of items evaluated as unacceptable was used to assess the pin release defects. After removing the pins, those that did not deform the shape of the electrode coil were deemed acceptable, while those that became shoot-shaped were deemed unacceptable. The evaluation criteria were as follows: (Criteria for evaluating defect rates) A: Pin removal failure rate: 0 cells / 10 cells B: Pin removal failure rate per 1 cell / 10 cells C: Pin-out failure rate of 2 or more cells per 10 cells

[0261] The measurement and evaluation results for the examples and comparative examples are shown in the table below.

[0262] [Table 3-1]

[0263] [Table 3-2]

[0264] [Table 4] [Industrial applicability]

[0265] The separator for energy storage devices of this disclosure can be suitably used in various energy storage devices, preferably lithium-ion secondary batteries. [Explanation of Symbols]

[0266] 1. Inorganic filler 2 Particulate polymer 10. Substrate (a substrate that is a polyolefin microporous film) 20 Covering layer

Claims

1. A substrate which is a polyolefin microporous film containing polyolefin as the main component, A coating layer disposed on at least one surface of the substrate, A separator for energy storage devices, including, The coating layer comprises 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 particulate polymer is a primary particle, and the volume-average particle diameter (D50) of the primary particle is 1 μm or more and 5 μm or less. The volume-average particle size (MV) / number-average particle size (MN) shown as the particle size distribution of the aforementioned protruding particulate polymer is 1.50 or greater than 1.50, and The static friction coefficient of the coating layer is 0.10 or more and less than 0.

40. Separator for energy storage devices.

2. The separator for an energy storage device according to claim 1, wherein the volume-average particle diameter (MV) / number-average particle diameter (MN), which is shown as the particle size distribution of the protruding particulate polymer, is greater than 1.

50.

3. The coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer. A separator for an energy storage device according to claim 1, wherein the thickness of the inorganic filler portion is L1, and the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inclined inorganic filler is L2, and the average value of the inclination ratio L2 / L1 of the coating layer is 1.2 or more.

4. The coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer. A separator for an energy storage device according to claim 1, wherein the thickness of the inorganic filler portion is L1, the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inclined inorganic filler is L2, and the maximum distance from the boundary line between the substrate and the coating layer to the contour of the protruding particulate polymer is L3, and the average value of the coverage rate of the protruding particulate polymer (L2-L1) / (L3-L1) is 0.4 or more.

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

6. The separator for an energy storage device according to claim 1, wherein the 180° peel strength of the coating layer from the substrate is 200 gf / cm or more.

7. In the surface observation of the coating layer, the protruding particulate polymer is used as the parent point for Voronoi tessellation, and the area of ​​the resulting Voronoi polygon (s) is determined. ｉ A separator for an energy storage device according to claim 1, wherein the coefficient of variation (cv) of ) is 0.10 or more and 0.60 or less.

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

9. The separator for an energy storage device according to claim 1, wherein the particulate polymer is a primary particle.

10. The separator for an energy storage device according to claim 9, wherein the volume-average particle diameter (D50) of the primary particles is 1.5 μm or more and 5 μm or less.

11. A separator for an energy storage device according to claim 1, wherein the thermal shrinkage rate of TD at 130°C for 1 hour is 5% or less.

12. A separator for an energy storage device according to claim 1, wherein the thermal shrinkage rate of TD at 150°C for 1 hour is 5% or less.

13. A storage device comprising a separator for a storage device according to any one of claims 1 to 12.

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