JP2023174383A - Separator for power storage device and power storage device including the same - Google Patents

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

The present disclosure relates to a separator for a power storage device and a power storage device including the separator.

2. Description of the Related Art Power storage devices such as lithium ion secondary batteries are actively being developed. Generally, a power storage device includes 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 electrode and the negative electrode and allowing ions to permeate through the electrolytic solution held in micropores. The separator has the property of quickly stopping the battery reaction in the event of abnormal heating (fuse property), and the property of maintaining its shape even at high temperatures to prevent a dangerous situation where the positive and negative electrodes directly react (short-circuit resistance property). ) etc. safety performance is required.

Non-aqueous secondary batteries such as lithium ion secondary batteries are on the market in various shapes such as cylindrical, square, and pouch shapes depending on their uses. The method of manufacturing batteries varies depending on the shape of the battery. For example, a method for manufacturing a prismatic battery includes the steps of pressing a laminate of electrodes and separators, or a wound body of a laminate of electrodes and separators, and inserting the pressed body into a rectangular parallelepiped exterior can.

Particularly in recent years, with the aim of increasing the capacity of power storage devices, power storage devices are Efforts are being made to reduce the volume of At that time, in order to fix the electrode and separator after heat pressing and maintain the volume at the time of pressing, a coating layer containing a thermoplastic polymer that exhibits an adhesive function under predetermined conditions is placed on the base material. , a technique for improving the adhesion between the entire separator and the electrode is known.

Patent Document 1 aims to enhance safety by increasing the bonding force between a separator and an electrode without performing a humidification phase separation process of an organic binder polymer and a secondary coating process of an adhesive layer. , describes a separator having a porous coating layer containing organic polymer particles. In the separator, the organic polymer particles protrude from the surface of the porous coating layer to a height of 0.1 μm or more and 3 μm or less.

Patent Document 2 describes a separator including a functional layer containing inorganic particles and a particulate polymer, with the aim of providing a separator that has excellent adhesiveness and heat resistance and improves electrolyte pourability. When the surface of this functional layer is viewed in plan, the ratio of the area occupied by inorganic particles per unit area of the surface of the functional layer is more than 90%, and 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 larger than the thickness of the inorganic particle layer.

Patent Document 3 has a functional layer containing inorganic particles and a particulate polymer for the purpose of providing a functional layer for an electrochemical device that has excellent process adhesion and can exhibit excellent cycle characteristics in an electrochemical device. Separators are listed. This functional layer has particle falling parts, and when the surface of the electrochemical element functional layer is viewed in plan, the ratio of the area of the particle falling parts to the total area of the particulate polymer and the particle falling parts is 0. It is 1% or more and 40.0% or less, and the volume average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing inorganic particles.

Korean Published Patent No. 10-2016-0118979 International Publication No. 2020/175079 International Publication No. 2021/085144

However, these conventional separators have the following problems. For example, in Patent Document 1, because the adhesive polymer has poor dispersibility in the paint state, parts of the adhesive polymer aggregate on the separator, causing uneven adhesive force with the electrodes and increasing the overall adhesive strength. There was a problem that the heat resistance (heat shrinkage resistance) deteriorated. In Patent Documents 2 and 3, the binding strength of the coating layer was not sufficient, and there was still room for improvement in suppressing powder falling during the manufacturing process and in terms of adhesive strength with the electrode.

Furthermore, with the improvement of electrode materials and the high-density modularization of multiple non-aqueous secondary batteries (single cells) (increasing the volumetric energy density of the module), the output characteristics (rate characteristics) of batteries including separators, There were also situations where improvements in cycle characteristics were still desired.

In view of the above circumstances, an object of the present invention is to provide a separator for a power storage device that can improve productivity of power storage devices such as cell productivity, and a power storage device including the separator.

Examples of embodiments of the present disclosure are listed below.
[1]
a base material that is a polyolefin microporous membrane containing polyolefin as a main component;
a coating layer disposed on at least one surface of the base material;
A separator for a power storage device, comprising:
The coating layer includes an inorganic filler and a particulate thermoplastic polymer,
The particulate polymer includes a particulate polymer protruding from the surface of the inorganic filler portion, and the coating layer has a static friction coefficient of 0.10 or more and less than 0.40.
Separator for power storage devices.
[2]
The separator for an electricity storage device according to item 1, wherein the volume average particle diameter (MV)/number average particle diameter (MN) expressed as the particle size distribution of the protruding particulate polymer is larger than 1.50.
[3]
The coating layer is formed in an inclined manner so as to become thicker toward the protruding particulate polymer,
When the thickness of the inorganic filler portion is L1 and the maximum distance from the substrate-coating layer boundary line to the outer surface of the inorganic filler formed in an inclined shape is L2, the slope rate of the coating layer L2 The separator for an electricity storage device according to item 1 or 2, wherein the average value of /L1 is 1.2 or more.
[4]
The coating layer is formed in an inclined manner so as to become thicker toward the protruding particulate polymer,
The thickness of the inorganic filler portion is L1, the maximum distance from the base material-coating layer boundary line to the outer surface of the inorganic filler formed in an inclined shape is L2, and from the base material-coating layer boundary line , when the maximum distance to the contour of the protruding particulate polymer is L3, the average value of the coverage ratio (L2-L1)/(L3-L1) of the protruding particulate polymer is 0.4 or more. The separator for an electricity storage device according to any one of items 1 to 3.
[5]
5. The separator for a power 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 base material.
[6]
The separator for a power storage device according to any one of items 1 to 5, wherein the coating layer has a 180° peel strength from the base material of 200 gf/cm or more.
[7]
In the surface observation of the coating layer, the coefficient of variation (cv) of the area (s _i ) of the obtained Voronoi polygon obtained by Voronoi division using the protruding particulate polymer as a generating point is 0.10 or more and 0.60 or less. A separator for an electricity storage device according to any one of items 1 to 6.
[8]
The separator for an electricity 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 included in the coating layer.
[9]
The separator for a power storage device according to any one of items 1 to 8, wherein the particulate polymer is a primary particle.
[10]
The separator for an electricity storage device according to item 9, wherein the primary particles have an average particle size of 1 μm or more and 10 μm or less.
[11]
The separator for an electricity storage device according to any one of items 1 to 10, wherein the TD has a thermal shrinkage rate of 5% or less at 130° C. for 1 hour.
[12]
The separator for an electricity storage device according to any one of items 1 to 11, wherein the TD has a heat shrinkage rate of 5% or less at 150° C. for 1 hour.
[13]
The power 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 with respect to 100 parts by mass of the inorganic filler contained in the coating layer. Separator.
[14]
The separator for an electricity storage device according to any one of items 1 to 13, wherein the protruding particulate polymer protrudes from the surface of the inorganic filler portion by 0.1 times or more the thickness of the inorganic filler portion.
[15]
The protruding particulate polymer includes at least one selected from the group consisting of a copolymer containing (meth)acrylate as a monomer, a styrene-butadiene copolymer, and a copolymer containing a fluorine atom. The separator for a power storage device according to any one of items 1 to 14.
[16]
Any of items 1 to 15, wherein the protruding particulate polymer includes a copolymer containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers. The separator for an electricity storage device according to item 1.
[17]
The separator for a power storage device according to any one of items 1 to 16, wherein the protruding particulate polymer includes a copolymer containing a polyfunctional (meth)acrylate as a monomer.
[18]
Any one of items 1 to 17, wherein the methylene chloride soluble content in the separator for electricity storage devices is 0.05 parts by mass or more and 0.80 parts by mass or less based on the total mass of the separator for electricity storage devices. A separator for an electricity storage device as described in .
[19] (Subject claim: Total amount of metal cations)
The separator for an electricity storage device 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 electricity storage device comprising the separator for an electricity storage device according to any one of items 1 to 19.

According to the present disclosure, for example, in the production of a cylindrical power storage device, it is possible to prevent pins from falling out of a wound body obtained by wrapping a separator for a power storage device around a pin, and/or to prevent a pin from coming off from a wound body obtained by wrapping a separator for a power storage device around a pin, and/or to prevent a pin from falling out of a cylindrical can, etc. Since the winding body can be easily inserted into the device exterior body, productivity of the power storage device such as cell productivity can be improved.

It is a schematic diagram of the surface of the coating layer in this embodiment. FIG. 2 is a schematic diagram of the AA cross section in FIG. 1. FIG. It is a schematic diagram of an example of observing the surface of a coating layer in this embodiment. This is an example of the results of identifying the protruding particulate polymer in FIG. 3. This is an example of the result of Voronoi division of FIG. 4. This is an example of the result of extracting Voronoi polygons corresponding to the closed region in FIG. 5. This is an example of a method for setting 10 sections including 95 fields of view.

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

In this specification, the longitudinal direction (MD) means the machine direction of continuous molding of the microporous membrane, and the transverse direction (TD) means the direction that crosses the MD of the microporous membrane at an angle of 90°.

In this specification, the upper and lower limits of each numerical range can be arbitrarily combined. Further, when a certain member contains a specific component as a main component, it means that the content of the specific component constitutes the largest mass of the mass of the member. Unless otherwise specified, the physical properties or numerical values described in this specification are measured or calculated by the methods described in Examples. The scale, shape, length, etc. of each part shown in the drawings may be exaggerated in order to further improve clarity.

《Separator for electricity storage devices》
The separator for a power storage device of this embodiment includes a base material that is a polyolefin microporous membrane containing polyolefin as a main component, and a coating layer disposed on at least one surface of the base material. The coating layer includes an inorganic filler and a particulate thermoplastic polymer.

<Amount of particulate polymer>
The amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less, preferably 3 parts by mass or more and 30 parts by mass or less, more preferably 5 parts by mass or more and 20 parts by mass or less, based on 100 parts by mass of the inorganic filler. Preferably it is 5 parts by mass or more and 15 parts by mass or less. When the amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less, the adhesive force with the electrode can be increased while maintaining ion permeability. From the viewpoint of improving heat shrinkage resistance, the amount is preferably 10 parts by mass or less.

<Protrusion amount of particulate polymer>
The particulate polymer may include a particulate polymer that protrudes by 0.1 times or more the thickness of the inorganic filler portion of the coating layer.

In this specification, the "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 (layer of inorganic filler) in which inorganic filler is laminated thereon. It is measured from a SEM image of a cross section of the coating layer. In addition, the "inorganic filler portion" is defined as a diameter of 1.5D or more in the horizontal direction (in the surface direction of the coating layer) from the center of each protruding particulate polymer, where D is the diameter of each of the protruding particulate polymers. means a separate, particulate polymer-free portion. The measurement conditions are explained in the Examples section.

When the protrusion of the particulate polymer is 0.1 times or more the thickness of the inorganic filler portion, the adhesive force with the electrode can be increased. Further, since the protrusion of the particulate polymer is 0.1 times or more the thickness of the inorganic filler portion, a gap is formed between the separator and the electrode. The voids can alleviate the effects of expansion and contraction of the electrodes due to charging and discharging of the electricity storage device, suppress distortion of the wound body, and improve cycle characteristics. From this viewpoint, the protrusion of the particulate polymer is preferably 0.2 times or more, 0.3 times or more. From the viewpoint of suppressing the particulate polymer from falling off from the separator, the protrusion of the particulate polymer is preferably 5 times or less, more preferably 4 times or less, 3 times or less, 2 times or less, 1 time or less, 0. It is 4 times or less.

As used herein, "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 parts of the particulate polymer (hereinafter referred to as "protruding parts"), a part of the protruding parts may be coated with an 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 portion of the periphery of the protruding portion be coated with an inorganic filler. Further, from the viewpoint of securing a contact area between the particulate polymer and the electrode and obtaining higher adhesive strength, it is preferable that the central portion of the protruding portion be exposed to the surface of the coating layer.

In this specification, "a state in which the particulate polymer protrudes by 0.1 times or more the thickness of the inorganic filler part" means that the thickness of the inorganic filler part measured from the SEM image of the cross section of the coating layer is L1, and the If the maximum distance from the material-coating layer boundary line to the protruding contour of the particulate polymer is L3, it means that 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 line to the protruding outline of the particulate polymer" refers to the base material-coating layer boundary line among the protruding outline of the particulate polymer. This is the distance from the farthest point.

In this specification, "a state in which the particulate polymer protrudes from the coating layer by 0.1 times or more the thickness of the inorganic filler portion of the coating layer" means, in other words, a state in which the particulate polymer protrudes from the coating layer by a distance of 0.1 times or more the thickness of the inorganic filler portion of the coating layer, as measured from an SEM image of a cross section of the coating layer. The maximum distance (L3) from the boundary between the base material and 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. means.

The number of protruding particulate polymers is preferably 50% or more of the total number of particulate polymers contained in the coating layer. According to this, the effects of the protruding particulate polymer can be suitably obtained. The ratio of the number of protruding particulate polymers to the total number of particulate polymers contained in the coating layer (number of protruding particulate polymers/total number of particulate polymers) is also expressed as the protrusion ratio. , is positioned as one of the indicators of the degree of protrusion of the particulate polymer in the coating layer. The protrusion ratio is more preferably 60% or more, 70% or more, or 80% or more, and the theoretical upper limit is 100%.

<Gradient morphology of coating layer, contact ratio between particulate polymer and base material, 180° peel strength>
The separator for a power storage device of this embodiment preferably has one or more of the following features (1) to (3).
(1) The coating layer is formed in an inclined manner so that it becomes thicker toward the protruding particulate polymer;
(2) 20% or more of the protruding particulate polymer is in contact with the surface of the substrate;
(3) The 180° peel strength (hereinafter also simply referred to as "180° peel strength") of the coating layer from the base material is 200 gf/cm or more;

Features (1):
In the separator for a power storage device, it is preferable that the coating layer is formed in an inclined shape so that it becomes thicker toward the protruding particulate polymer. This prevents the particulate polymer from slipping off the coating layer and increases the adhesive strength with the electrode. In this specification, "slanted" means that the thickness of the inorganic filler portion of the coating layer is L1, and the distance from the boundary line of the base material to the coating layer to the outer surface of the inorganic filler of the coating layer formed in a sloped shape is defined as L1. When the maximum distance is L2, it means that the average value of the slope ratio L2/L1 of the coating layer is 1.1 (for example, 1.10) or more.

Regarding the relationship between L1 and L2, please refer to the schematic diagram of FIG. 2 as an example. Preferably, the slope is such that the thickness of the coating layer changes continuously so that the coating layer gradually becomes thicker toward the protruding particulate polymer, and does not include discontinuous changes such as lack of the coating layer. is preferred. Since there is no loss of the coating layer, heat resistance and/or cycle characteristics tend to improve. The slope may be gentler as it moves away from the protruding particulate polymer, and steeper as it approaches the protruding portion of the protruding particulate polymer. Moreover, when the inorganic filler covers a part of the protruding part, the slope on the protruding part may become gentle again toward the center of the protruding part. The average value of the slope ratio L2/L1 of the coating layer is preferably 1.2 (for example, 1.20) or more, 1.3 (for example, 1.30) or more, or 1.4 (for example, 1.40) or more. , 1.5 (for example, 1.50) or more, or 1.7 (for example, 1.70) or more.

By forming the coating layer in an inclined manner so that it becomes thicker toward the protruding particulate polymer, the inorganic filler covers a part of the protruding part by riding along the contour of the particulate polymer. Good too. It is preferable that the inorganic filler covers part of the periphery of the protruding portion so as to ride along the contour of the particulate polymer. Further, it is preferable that the vicinity of the center of the protruding portion be exposed on the surface of the coating layer. The maximum distance from the substrate-coating layer boundary line to the protruding outline of the particulate polymer (distance to the point farthest from the base material-coating layer boundary line among the protruding particulate polymer outlines) Assuming L3, the average value of the coverage ratio (L2-L1)/(L3-L1) of the protruding portion is preferably 0.4 (for example, 0.40) or more.

Regarding the relationship between L1, L2, and L3, please refer to the schematic diagram of FIG. 2 as an example. When the average value of the slope ratio L2/L1 is 1.1 or more, or the average value of the coverage ratio (L2-L1)/(L3-L1) is 0.4 or more, the particulate polymer coating layer can be removed. Prevents slipping and increases adhesive strength with electrodes. The upper limit of the average value of the slope ratio L2/L1 is 5.0 or less, 4.0 or less, and 3.0 from the viewpoint of securing the adhesive area between the particulate polymer and the electrode and increasing the adhesive force with the electrode. Below, it may be 2.8 or less, 2.5 or less, 2.3 or less, 2.0 or less, or 1.8 or less. Further, the upper limit value of coverage (L2-L1)/(L3-L1) is preferably less than 1.0 (for example, 1.00), 0.9 (for example, 0.90) or less, 0.8 ( For example, it is 0.80) or less, or 0.7 (for example, 0.70) or less. A coverage ratio of 1.0 or more means that the inorganic filler on the protruding part of the particulate polymer is located at the top of the contour of the protruding particulate polymer (the point farthest from the boundary line between the base material and the coating layer). It means that it has been reached. When the coverage is less than 1.0, the contact area between the particulate polymer and the electrode is ensured, and the adhesive force with the electrode is increased. When the coverage is 0.8 or less, the contact area between the particulate polymer and the electrode becomes larger, and the adhesive force with the electrode is further increased.

Features (2):
In the separator for a power storage device, the contact ratio between the protruding particulate polymer and the surface of the base material is preferably 20% or more, more preferably 50% or more, and still more preferably 70% or more. The "contact rate" is calculated from an image obtained by observing a cross section of a coating layer of a separator for an electricity storage device using a SEM. By increasing the particulate polymer that protrudes and is in contact with the base material, the binding force between the base material and the particulate polymer is further increased, the 180° peel strength is improved, and the adhesive force with the electrode is increased. The upper limit of the contact rate between the protruding particulate polymer and the substrate surface may be less than 100% or 100%.

Features (3):
The separator for power storage devices has a 180° peel strength of preferably 200 gf/cm or more, more preferably 230 gf/cm or more, and still more preferably 250 gf/cm or more. "180° peel strength" is the strength when the covering layer is peeled off so that the surface of the covering layer facing the base material forms an angle of 180° with respect to the base material. When the 180° peel strength is 200 gf/cm or more, the adhesive force with the electrode is increased and thermal shrinkage is suppressed. The upper limit of the 180° peel strength may be 500 gf/cm or less.

The separator for a power storage device of this embodiment has any combination of the above features (1) to (3), namely: (1) and (2); (1) and (3); (2) and (3); It may have a combination of (1), (2) and (3). Among these, the combination of (1), (2), and (3), that is, the coating layer becomes thicker toward the protruding particulate polymer, from the viewpoint of higher adhesive strength and lower heat shrinkage rate. It is preferable that the contact ratio between the protruding particulate polymer formed in an inclined shape and the surface of the substrate is 20% or more, and the 180° peel strength is 200 gf/cm or more.

Here, the separator for a power storage device of the present embodiment has the following (4) and/or in addition to the above features (1) to (3) or in addition to any combination of the above features (1) to (3). Or it has the feature (5).

Features (4):
In the separator for power storage devices, when observing the surface of the coating layer, Voronoi division is performed using the protruding particulate polymer as a generating point, and the coefficient of variation (cv) of the area (s _i ) of the resulting Voronoi polygon is 0.10 or more. .60 or less. In a coating layer having a coefficient of variation (cv) within this range, the distribution of the protruding particulate polymer is highly uniform. The coefficient of variation (cv) is preferably 0.20 or more, 0.25 or more, and 0.30 or more, and preferably 0.55 or less, 0.50 or less, and 0.45 or less.

In the separator having the above feature (4), since the distribution of the protruding particulate polymers is highly uniform, the distribution of the regions between the protruding particulate polymers is also highly uniform. Therefore, by using a separator having the above feature (4), it is possible to improve the uniformity of the in-plane distribution of lithium ion movement through the region between the electrodes, and as a result, the rate characteristics and/or cycle characteristics can be improved. It is possible to improve the

In addition, the separator having the above feature (4) has a high uniformity in the distribution of the protruding particulate polymer, so that the protruding particulate polymer and the electrode can be bonded together before or after the hot pressing process. The distribution of contact areas is also highly uniform. Therefore, by using a separator having the above feature (4), it is possible to improve the uniformity of the in-plane distribution of the stress of the protruding particulate polymer applied to the electrode, and further improve the adhesiveness with the electrode. It is possible to improve the

Further, in the separator having the above characteristic (4), since the distribution of the protruding particulate polymer is highly uniform, the distribution of the proportion of the inorganic filler having a heat-resistant function is also highly uniform. Therefore, by using a separator having the feature (4) above, it is possible to improve the uniformity of the in-plane distribution of heat resistance due to the inorganic filler, and as a result, it is possible to improve the heat shrinkage resistance.

Here, it has conventionally been thought that there is a trade-off between "adhesiveness to electrodes" and "heat shrinkage resistance," and also, "adhesiveness to electrodes" and "rate characteristics" and/or " It was thought that there may be a trade-off with the cycle characteristics. Specifically, since particulate polymers do not have sufficient heat resistance, increasing the content of particulate polymers in order to improve "adhesion with electrodes" improves "heat shrinkage resistance". It was thought that it would be difficult. In addition, since the presence of particulate polymers acts as resistance to ions, it was thought that increasing the content of particulate polymers would make it difficult to improve "rate characteristics" and/or "cycle characteristics." . In view of these points, according to the present embodiment, by adjusting the coefficient of variation (cv) to a predetermined range, as described above, it is possible to improve the adhesive force with the electrode, improve the heat shrinkage resistance, and improve the storage capacity. It is possible to simultaneously improve the rate characteristics and/or cycle characteristics of the device.

The means for adjusting the coefficient of variation (cv) within the above range includes, for example, 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, and the coating method. , and by changing the coating conditions. For example, adjusting the viscosity of the coating liquid applied to the substrate within a predetermined range; reducing the particle size of the thermoplastic polymer in the coating liquid; reducing agitation due to turbulence when supplying the coating liquid to the substrate in the coating process; and performing ultrasonic treatment on the coating liquid applied onto the base material.

"Voronoi partitioning" refers to dividing multiple points (generating points) located at arbitrary positions in a metric space into regions based on which generating point other points in the same space are close to. say. A diagram including the regions obtained in this way is called a Voronoi diagram. In the Voronoi diagram, the boundaries of the plurality of regions are part of the bisector of each generating point, and each region forms a polygon (Voronoi polygon). Here, in this specification, the above-mentioned parent point is the "protruding particulate polymer", and more specifically, it is the center point of the protruding portion of the protruding particulate polymer in surface observation.

In the observation field of the coating layer, one of the protruding particulate polymers is regarded as a circle with an average diameter (l). Then, a perpendicular bisector is drawn between a plurality of adjacent protruding particulate polymers, and a polygon surrounded by the perpendicular bisector for each polymer is referred to as a "Voronoi polygon." Regions that are not closed when Voronoi partitioning is performed in the observation field of view are not handled. For example, when a polymer exists at the boundary of the observation field and the entire protruding part of the polymer is not observed, an unclosed region can be obtained by performing Voronoi partitioning on the polymer. Examples include areas.

The area of a Voronoi polygon (s _i ) can be measured using image analysis if necessary, and the total area of the Voronoi polygon (s _i ) can be divided by the total number of Voronoi polygons to be handled (n). Then, the average value (m) of the area (s _i ) is obtained. Then, from the area (s _i ) of the Voronoi polygon, the total number (n) of Voronoi polygons to be handled, and the average value (m ₎ , the standard deviation ( sd) is obtained. The coefficient of variation (cv) of the area (s _i ) of the Voronoi polygon is calculated by the following formula:
Coefficient of variation (cv) = standard deviation (sd) / mean value (m)
Calculated by

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

The means for observing the coating layer is preferably selected as appropriate depending on the dimensions or distribution state of the thermoplastic polymer. Further, as for the microscope, an electron microscope, an atomic force microscope, an optical microscope, a differential interference microscope, etc. can be used. Among these, when dealing with the distribution state of dispersed particles as in this embodiment, an electron microscope is used. Alternatively, it is preferable to use an atomic force microscope. In particular, the method shown in the Examples section is adopted as a means for observing the coating layer.

An average observation field of the coating layer should be ensured within the observation field. Further, the projected area in the observation field should be adjusted appropriately so that the average distribution state of the protruding particulate polymers can be grasped. For example, it is preferable that the number of protruding particulate polymers to be handled is about 80 to 200 per field of view. This observation field can be obtained by observing the coating layer using a preset observation means and magnification. For example, FIG. 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 1000 times. The dispersion state of such thermoplastic polymer particles can be analyzed by Voronoi partitioning.

In observation using a scanning electron microscope, an appropriate magnification for analysis by Voronoi division is set depending on the particle size of the thermoplastic polymer particles. Specifically, a magnification at which the number of thermoplastic polymer particles observed in one field of view is preferably 40 to 300, more preferably 60 to 240, even more preferably 80 to 200. Set to . This makes it possible to appropriately perform analysis using Voronoi division. For example, if the content of thermoplastic polymer particles with a particle size of about 2.0 μm is about 10 parts by mass with respect to 100 parts by mass of the inorganic filler in the coating layer, it is appropriate to set the magnification to 5000 times. If the content of thermoplastic polymer particles with a diameter of about 3.5 μm is about 10 parts by mass per 100 parts by mass of the inorganic filler in the coating layer, the magnification should be set to about 1000 times for analysis by Voronoi splitting. Appropriate.

Protruding particulate polymers included in the observation field obtained by the above observation method are identified. For example, protruding particulate polymers are identified from the observation field with the naked eye or using image processing software. FIG. 4 is an example showing the results of identifying protruding particulate polymers included in the observation field of FIG. 3 using image processing software.

Protruding particulate polymers identified by surface observation of the coating layer can be subjected to Voronoi partitioning as defined above. Specifically, an image is obtained by photographing the surface of a coating film after coating a substrate with a coating liquid containing a thermoplastic polymer. The protruding parts of the protruding particulate polymer identified in the obtained image are regarded as circles with an average diameter (L), and a Voronoi polygon can be drawn by performing Voronoi division. . For example, the Voronoi polygons may be drawn manually or using image processing software. Then, the area (si) of the drawn Voronoi polygon is calculated.

For example, FIG. 5 is an example of the results obtained by performing Voronoi division using the protruding particulate polymer identified in FIG. 4 as a generating point to obtain a Voronoi polygon. FIG. 6 shows the results of automatically extracting Voronoi polygons corresponding to closed regions among the Voronoi polygons shown in FIG. 5 using image processing software.

By the above 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 polygon can be obtained. The coefficient of variation (cv) can then be calculated according to the above. The distribution of prominent particulate polymers may vary depending on the observation field. Therefore, as the coefficient of variation (cv), it is preferable to adopt an average value of values calculated for each of a plurality of observation visual fields. The number of fields of view is preferably three or more.

Particularly preferably, the average value of the values calculated for 10 visual fields determined as follows is employed.
i) Each measurement field of view: Image taken with a scanning electron microscope ii) Field of view setting method:
a) Set the starting field of view,
b) A total of 10 visual fields consisting of the visual field of the starting point and nine visual fields consisting of areas successively adjacent in the uniaxial direction at 5 mm intervals with respect to the visual field of the starting point are set as the measurement visual field.

It is preferable that each measurement field of view is a captured image set at a magnification such that the number of protruding particulate polymers observed in one field of view is 80 or more and 200 or less.

Hereinafter, a preferred method for setting 10 visual fields in this embodiment will be explained with reference to FIG. 7.
i) As the captured image, as described above, an image captured using a scanning electron microscope with a magnification of 1000 times can be adopted. In the image of FIG. 7, first, the starting point field of view (I) is set. Since one field of view is composed of images taken with a scanning electron microscope with a magnification of 1000 times, the scale of one field of view is approximately 100 μm x 100 μm, which is suitable for Voronoi division evaluation based on protruding particulate polymers. Configure. Next, with respect to the field of view (I) at the starting point, nine fields of view (II to X) are set successively adjacent to each other in the uniaxial direction at intervals of 5 mm. These fields of view (II to X) each consist of a captured image with the same magnification as the field of view (I) at the starting point.

It is preferable that the above-mentioned observation of the surface of the coating layer is performed on a region not involved in ion conduction. For example, it is possible to observe a coating layer on a separator that has just been manufactured and has not yet been incorporated into a power storage element. When the energy storage element is in use or after use, it is also possible to observe the so-called "ears" of the separator (regions near the outer edge of the separator that are not involved in ion conduction). , is a preferred aspect of this embodiment. As understood from the above evaluation method, when observing 10 fields of view, since a separator piece with a length of about 45 mm is measured, it is possible to accurately evaluate the dispersion state of the thermoplastic polymer on its surface.

It is presumed that the fact that Voronoi partitioning is possible as described above indicates that the particulate polymers exist as single-layer particles in the coating layer without substantially overlapping each other. For example, when particulate polymers overlap each other in multiple layers in the coating layer, the concept of area occupied by a single particle does not hold, and therefore Voronoi partitioning cannot be performed.
In the separator of this embodiment, it is preferable that the particulate polymers in the coating layer are arranged so that they do not substantially overlap each other, and that the above requirements are adjusted to the above ranges.

The form (pattern) of the coating layer on the base material is preferably such that the particulate polymers are mutually dispersed over the entire surface of the base material. Although the particulate polymer may form clusters in some regions, it is preferable that the particulate polymer is suitably dispersed to the extent that the above coefficient of variation (cv) is satisfied as a whole. It is preferable that the particulate polymer is suitably dispersed to such an extent that the above coefficient of variation (cv) is satisfied as a whole.

Features (5):
In the separator for a power storage device, the coating layer has a static friction coefficient of 0.10 or more and less than 0.40. If the static friction coefficient of the coating layer is within this range, for example, in the manufacture of cylindrical power storage devices, pins may not come out of the wound body obtained by wrapping a separator for power storage devices around pins (for example, pins may not be pulled out of the wound body). This can prevent the separator from turning into a bamboo shoot-like state when removed, and/or make it easier to insert the wound body into the device exterior body such as a cylindrical can, thereby increasing the productivity of power storage devices such as cells. can be improved.

From the viewpoint of further improving the productivity of power 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, and 0. It is more preferably .24 or more and 0.39 or less, particularly preferably 0.30 or more and 0.39 or less.

In the separator for power storage devices having feature (5), the particulate polymer protruding from the surface of the inorganic filler portion included in the coating layer is composed of a thermoplastic polymer, and the shape of the protruding portion is easily maintained. is preferred. If the shape of the protrusion formed by the thermoplastic polymer is easily maintained, the particulate polymer becomes difficult to crush, and the followability of the separator to other members is suppressed. In addition, pin-out defects are less likely to occur.

From the viewpoint of easily adjusting the static friction coefficient of the coating layer within the above range, the particulate polymer obtained by dividing the volume average particle diameter MV of the protruding particulate polymer by the number average particle diameter MN. The particle size distribution MV/MN is preferably larger than 1.50, more preferably 1.51 or more, and even more preferably 1.55 or more. If MV/MN exceeds 1.50, the number of contact points of the particulate polymer with other members will decrease, or the contact point area will decrease, so the static friction coefficient of the coating layer should be adjusted to less than 0.40. It becomes easier.

As a means 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, for example, in the manufacturing process of a separator for an electricity storage device, applying it to a base material is possible. Conditions of the coating/drying process in which the liquid is applied, such as the particle size, particle size distribution, and content of the thermoplastic polymer in the coating liquid applied to the substrate, the viscosity of the coating liquid, and the amount of coating, and the coating method and coating. conditions, etc., or conditions after the coating/drying process, such as the pressure applied to the coated surface, the speed of the conveyor roll that the coated surface contacts, the shape of the inorganic filler in the coating layer, and the peel strength of the coating layer, etc. .

More specifically, as means for controlling the conditions of the coating/drying process, for example, adjusting the viscosity of the coating liquid applied to the substrate within a predetermined range; increasing the particle size distribution of the thermoplastic polymer in the coating liquid; etc. Can be mentioned.

More specifically, as a means of controlling the conditions after the coating/drying process, for example, the tension applied in the direction perpendicular to the surface where the coated surface contacts the conveyance roll is controlled to be below a predetermined value; Examples include making the speed equal to the separator transport speed; increasing the peel strength of the coating layer; and so on.

<Methylene chloride soluble content>
In the separator for power storage devices of the present embodiment, the methylene chloride soluble content is preferably 0.05 parts by mass or more and 0.80 parts by mass or less, more preferably 0.10 parts by mass, based on the total mass of the separator for power storage devices. parts or more and 0.60 parts by mass or less, more preferably 0.15 parts by mass or more and 0.50 parts by mass or less. The "soluble content" of methylene chloride means a component extracted into methylene chloride when the separator is immersed in methylene chloride. Mainly, the plasticizer mixed when manufacturing the base material is extracted as a methylene chloride soluble component. By containing 0.10 parts by mass or more of methylene chloride soluble content, the binding force between the base material and the coating layer is further increased, and it is easier to adjust the 180° peel strength to 200 gf/cm or more. When the methylene chloride soluble content is 0.60 parts by mass or less, the internal resistance of the battery can be lowered. As a method for adjusting the methylene chloride soluble content to 0.05 parts by mass or more and 0.80 parts by mass or less, in the plasticizer extraction step during base material production, if it is a batch method, the extraction time, the type of extraction solvent, Examples include adjusting the temperature of the extraction solvent, the number of times of extraction, etc. In the case of a continuous type, examples include adjusting the extraction time, the type of extraction solvent, the temperature of the extraction solvent, the amount of the extraction solvent supplied, etc.

<Metal cation>
In the separator for a power storage device of the present embodiment, the total amount of metal cations contained in the coating layer is preferably 0.1 ppm or more and 100 ppm or less, more preferably 0.1 ppm or more and 70 ppm or less, based on the total mass of the coating layer. , more preferably 0.1 ppm or more and 50 ppm or less. When the total amount of metal cations is adjusted to be small, the inorganic filler and particulate polymer are easily dispersed and coated uniformly in forming the coating layer. Examples of metal cations include sodium ions (Na ⁺ ), calcium ions (Ca ²⁺ ), and magnesium ions (Mg ²⁺ ). An example of a method for adjusting the total amount of metal cations to 0.1 ppm or more and 100 ppm or less is a method of washing the filler, which is a raw material for the coating layer, with water before use. The number of washings may be once or twice or more, but the more the number of washings is, the lower the total amount of metal cations contained in the filler will be.

<Heat shrinkage rate>
In the separator for an electricity storage device of the present embodiment, the thermal contraction rate of TD at 130° C. for 1 hour is preferably 5% or less, more preferably 0% or more and 3% or less, and even more preferably 0% or more and 1% or less. . The thermal shrinkage rate of the TD at 150° C. for 1 hour is preferably 5% or less, more preferably 0% or more and 3% or less, and still more preferably 0% or more and 1% or less. Here, when the thermal contraction rate of the TD is 5% or less, it is possible to more effectively suppress the occurrence of short circuits at locations other than those to which external force is applied when heat is generated due to short circuits during a collision test. This makes it possible to more reliably prevent a rise in the temperature of the entire battery, as well as smoke and ignition that may occur as a result. The heat shrinkage rate of the separator can be adjusted by appropriately combining the stretching operation and heat treatment of the base material described above. While suppressing the heat shrinkage rate of the TD, the heat shrinkage of the MD is also preferably 5% or less, more preferably 0% or more and 3% or less, and even more preferably 0% or more and 1% or less.

<Separator air permeability>
The air permeability of the separator for electricity storage devices is preferably 10 seconds/100 cm ³ or more and 10,000 seconds/100 cm ³ or less, more preferably 40 seconds/100 cm ³ or more and 500 seconds/100 cm ³ or less, even more preferably 50 seconds/100 cm ³ or more. It is 250 seconds/100 cm ³ or less, particularly preferably 60 seconds/100 cm ³ or more and 200 seconds/100 cm ³ or less. This provides high ion permeability. Air permeability is air permeability resistance measured in accordance with JIS P-8117.

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

Aspect (1):
Although not bound by theory, a polyolefin microporous membrane can be used as a separator, for example, by having an air permeability of 500 sec/100 cm ³ or less and a porosity after compression of 30% or more within a membrane thickness range of 1 μm to 30 μm. In the production of non-aqueous secondary batteries using microporous polyolefin membranes, it is possible to reduce the electrical resistance of the microporous polyolefin membranes or suppress increases in electrical resistance after the pressing process, thereby increasing the high output of non-aqueous secondary batteries. It is believed that high cycle characteristics can be achieved. The suppression of resistance increase by polyolefin microporous membrane is remarkable when using electrodes that easily expand and contract within the cells of non-aqueous secondary batteries. ) is more noticeable when using a negative electrode containing

It is thought that the porosity after compression is related to the structure of the main component of the polyolefin microporous membrane, which is responsible for lowering the resistance and/or suppressing the increase in resistance in a non-aqueous secondary battery. From the viewpoint explained above, the porosity of the microporous polyolefin membrane after compression is preferably 31% or more, more preferably 32% or more, and even more preferably 33% or more. The upper limit of the post-compression porosity of the microporous polyolefin membrane can be determined depending on the porosity before compression, and may be, for example, preferably 60% or less, more preferably 50% or less.

The post-compression porosity of a microporous polyolefin membrane is determined by, 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, and the stretching ratio during the biaxial stretching process in the manufacturing process of the polyolefin microporous membrane. By controlling the preheating coefficient, the stretching coefficient during the biaxial stretching process, the MD/TD stretching temperature during the biaxial stretching process, the heat setting temperature, etc., the numerical value can be adjusted within the numerical range explained above. Alternatively, the porosity after compression of the microporous polyolefin membrane can be determined by 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, and the biaxial stretching process. By controlling the stretching coefficient during the process, the ratio of the preheating coefficient to the stretching coefficient, etc., the numerical value can be adjusted within the above-mentioned numerical range.

Comparing the porosity of polyolefin microporous membranes before and after compression testing can reduce resistance and/or suppress resistance increase in non-aqueous secondary batteries to achieve high output and high cycle characteristics. This is preferable from the viewpoint of specifying the structure of the main component of the film. A preferable numerical range of the porosity of the polyolefin microporous membrane before the compression test or not subjected to the compression test (hereinafter simply referred to as "porosity") will be described later.

Aspect (2):
Although not bound by theory, by having a polyolefin microporous membrane with a long crystal period of 37.0 nm or more, the structural uniformity and compression resistance of the polyolefin microporous membrane are surprisingly improved, and along with this, non-porous polyolefin membranes are improved. The reaction uniformity within the aqueous secondary battery is also improved. It is thought that this makes it possible to achieve high output and high cycle characteristics of a non-aqueous secondary battery even after the pressing step in the production of a non-aqueous secondary battery that uses a microporous polyolefin membrane as a separator, for example. The improvement in structural uniformity and compression resistance of polyolefin microporous membranes is remarkable when using electrodes that easily expand and contract within the cells of non-aqueous secondary batteries, and is suitable for high-capacity electrodes used in automotive batteries, etc. Or, it is more noticeable when using a silicon (Si)-containing negative electrode.

Although not bound by theory, it is thought that the long crystal period obtained by SAXS measurement is related to the structure of polyethylene, which improves the structural uniformity and compression resistance of the membrane and the reaction uniformity within the non-aqueous secondary battery. It will be done. Furthermore, the long crystal period of the microporous polyolefin membrane is considered to be correlated with the porosity of the membrane after compression. From the viewpoint explained above, the crystal long period of the polyolefin microporous membrane is preferably 37.0 nm to 60.0 nm, 38.0 nm to 55.0 nm, 40.0 nm to 50.0 nm, or 42.0 nm to 50 nm. .0 nm.

The crystal long period of a microporous polyolefin membrane is determined by, 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, and the preheating during the biaxial stretching process in the manufacturing process of the polyolefin microporous membrane. By controlling the coefficient, the stretching coefficient during the biaxial stretching process, the MD/TD stretching temperature during the biaxial stretching process, the heat setting temperature, etc., the numerical value can be adjusted within the numerical range explained above.

The separator for a power storage device of this embodiment has a base material that is a microporous polyolefin membrane containing polyolefin as a main component. "Contained as a main component" means that the mass of the target component (polyolefin) constitutes the largest mass of the entire base material. The content of polyolefin 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, based on the total mass of the base material. It is even more preferably 95 parts by mass or more, particularly preferably 98 parts by mass or more, and may be 100 parts by mass.

Polyolefin has excellent coating properties when a coating solution is applied onto the film, so it is advantageous for making the separator thinner, increasing the active material ratio in the energy storage device, and increasing the volume. Capacity per unit can be increased. Polyolefin microporous membranes can be used as base materials for conventional separators, and are porous with fine pores that have no electronic conductivity, ion conductivity, and high resistance to organic solvents. Preferably, it is a membrane.

The polyolefin may be a polyolefin that can be used in conventional extrusion, injection, inflation, blow molding, and the like. Examples of polyolefins include homopolymers containing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, and monomers containing two or more of these monomers. Copolymers, and multistage polymers are included. These homopolymers, copolymers, and multistage polymers may be used singly or in combination of two or more.

Examples of polyolefins include polyethylene, polypropylene, and polybutene, from the viewpoint of decreasing or suppressing the increase in electrical resistance of the membrane, compression resistance and structural uniformity of the membrane, and more specifically, 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.

These may be used alone or in combination of two or more. Among these, polyolefins are selected from the group consisting of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene, from the viewpoint of shutdown characteristics in which pores are closed by thermal melting. At least one of these is preferred. In particular, high-density polyethylene is preferred because it has a low melting point and high strength, and polyethylene whose density measured according to JIS K 7112 is 0.93 g/cm ³ or more is more preferred. Examples of the polymerization catalysts used for producing these polyethylenes include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. It is preferable that the main component of the polyolefin is polyethylene, and the content ratio of polyethylene to the total weight of the polyolefin in the base material is preferably 50 parts by mass or more.

In order to improve the heat resistance of the base material, the microporous polyolefin membrane more preferably contains polypropylene and a polyolefin other than polypropylene. Examples of polyolefin resins other than polypropylene include homopolymers containing ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, and two types of these monomers. The above copolymers and multistage polymers may be mentioned.

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

From the viewpoints of crystallinity, high strength, compression resistance, etc. when forming the polyolefin microporous membrane for non-aqueous secondary batteries, the polyolefin microporous membrane should contain at least 50% by mass or more of 100% by mass of the resin component constituting the microporous membrane. % or less is preferably a porous membrane formed by a polyethylene composition in which polyethylene accounts for less than %. The proportion of polyethylene in the resin component constituting the porous membrane is more preferably 60% by mass or more and 100% by mass or less, still more preferably 70% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less. It is.

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 still more preferably 150,000 to 2,000,000. It is preferable that the viscosity average molecular weight is 30,000 or more because the strength tends to be even higher due to the entanglement of the polymers. On the other hand, when the viscosity average molecular weight is 6 million or less, uniform melt-kneading becomes easy, which is preferable from the viewpoint of improving moldability in extrusion and stretching steps. Furthermore, it is preferable that the viscosity average molecular weight is less than 1 million, because the pores tend to be easily blocked when the temperature rises, and a better shutdown function tends to be obtained.

When the polyolefin microporous membrane contains polyethylene as a 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. This is the above, and the upper limit of Mv of polyethylene may be, for example, 2 million or less. From the same viewpoint, the proportion of polyethylene having an Mv of 700,000 or more in the polyolefin resin constituting the microporous polyolefin membrane is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more. , 100% by mass. From the viewpoint of decreasing fluidity when melting the membrane and short circuit resistance during nail penetration test, the proportion of polyethylene with an Mv of 600,000 or more in the polyolefin resin constituting the microporous polyolefin membrane is preferably 30% by mass or more, and more preferably 30% by mass or more. The content is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and may be 100% by mass.

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

For example, instead of using a single polyolefin with a viscosity average molecular weight of less than 1 million, 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, the viscosity average molecular weight of which is less than 1 million, may be used. May be used.

In addition to polyolefin, the base material may also include other resins such as polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, etc. May be contained.

The base material can contain optional additives. Such additives are not particularly limited, and include, for example, plasticizers, polymers other than polyolefins; inorganic particles; phenol-based, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate. UV absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less, based on 100 parts by mass of the polyolefin resin in the microporous polyolefin membrane.

The substrate preferably contains a plasticizer. When the base material contains a plasticizer, the binding strength between the base material and the coating layer is improved, and it is easier to control the 180° peel strength to 200 gf/cm or more. The amount of plasticizer is based on the total mass of the base material, 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 parts by mass or less. When the amount of the plasticizer is within the above range, it is possible to lower the internal resistance of the battery and improve the binding force between the base material and the coating layer. Examples of the plasticizer 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, the plasticizer is preferably liquid paraffin.

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

The air permeability of the base material is preferably 10 seconds/100 cm ³ or more and 450 seconds/100 cm ³ or less, more preferably 40 seconds/100 cm ³ or more and 300 seconds/100 cm ³ or less, and even more preferably 50 seconds/100 cm ³ or more and 250 seconds. /100 cm ³ or less, particularly preferably 60 seconds/100 cm ³ or more and 200 seconds/100 cm ³ or less. Moreover, the time can be 60 seconds/100 cm ³ or more and 150 seconds/100 cm ³ or less. Thereby, the coating layer is appropriately impregnated into the micropores of the base material, and it is easier to control the 180° peel strength to 200 gf/cm or more. Air permeability is 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 base material.

The average pore diameter of the base material is preferably 0.15 μm or less, more preferably 0.10 μm or less, and preferably 0.01 μm or more. Setting the average pore diameter to 0.15 μm or less is preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity reduction. From the viewpoint of improving denseness, the thickness is preferably 0.08 μm or less. The average pore diameter can be adjusted by changing the stretching ratio when manufacturing the base material.

The puncture strength of the base material is preferably 200 gf or more, more preferably 300 gf or more, still more preferably 400 gf or more, and preferably 2,000 gf or less, more preferably 1,000 gf or less. The puncture strength of 200 gf or more is from the viewpoint of suppressing membrane rupture due to fallen active material etc. when the separator is wound together with the electrode, and from the viewpoint of suppressing the fear of short circuit due to expansion and contraction of the electrode due to charging and discharging. It is also preferable. On the other hand, it is preferable that the puncture strength is 2,000 gf or less from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. Puncture strength is measured according to the method described in Examples. The puncture strength can be adjusted by adjusting the stretching ratio and/or stretching temperature of the base material.

The type, molecular weight, and composition of the polyolefin resin constituting the microporous polyolefin membrane are adjusted, for example, by controlling the type, molecular weight, blending ratio, etc. of the polymer raw material such as polyolefin in the manufacturing process of the microporous polyolefin membrane. be able to. Furthermore, a multilayer polyolefin resin microporous membrane 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 prepared as described above.

Polyolefin microporous membranes have a porous structure in which many very small pores come together to form dense communicating pores, so they have excellent ion permeability and high strength when containing an electrolyte. .

The thickness of the base material is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 6 μm or more, particularly preferably 7 μm or more, and preferably 100 μm or less, more preferably 60 μm or less, still more preferably 50 μm or less, especially Preferably it is 16 μm or less. It is preferable that the film thickness be 2 μm or more from the viewpoint of improving mechanical strength. On the other hand, it is preferable that the film thickness be 100 μm or less, since this tends to be advantageous in terms of increasing the capacity of the electricity storage device because the volume occupied by the separator in the electricity storage device is reduced.

<Coating layer>
The separator for a power storage device of this embodiment includes a coating layer disposed on at least one surface of the base material. That is, the coating layer may be arranged only on one side of the base material, or may be arranged on both sides. "Arranged on the surface" means that it may be arranged on the entire surface of the base material or on a part thereof. The covering layer is intended to be bonded directly to the electrode. It is preferable that the base material and the electrode be arranged so that the covering layer is directly adhered to the electrode, or that the base material and the electrode are adhered to each other via the covering layer. The coating layer is preferably a coating layer formed by a method of coating a substrate with a coating liquid containing an inorganic filler and a particulate polymer.

The coating layer includes an inorganic filler and a particulate thermoplastic polymer. The coating layer may further contain a resin binder, a water-soluble polymer, other additives, and the like. The coating layer may have at least two Tg's, one based on a particulate polymer made of a thermoplastic polymer and the other based on a thermoplastic polymer as a binding binder.

(Inorganic filler)
As an inorganic filler, it has a melting point of 200°C or higher, or a thermal decomposition temperature of 200°C or higher, has high electrical insulation properties, and is electrochemically compatible within the range of use in power storage devices such as lithium ion secondary batteries. Stable ones are preferred. Examples of such inorganic fillers include inorganic oxides (oxide ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; silicon nitride, titanium nitride, and nitride. Inorganic nitrides such as boron (nitride ceramics); silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum hydroxide oxide (boehmite), potassium titanate, talc, kaolinite, Ceramics such as dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyte, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. It will be done. These may be used alone 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 preferable as the inorganic filler.

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. Hereinafter, it is 800 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, or 300 nm or less. It is preferable that the average particle size of the inorganic filler is 50 nm or more from the viewpoint of maintaining voids for ions to pass through the coating layer and improving rate characteristics. It is preferable that the average particle size of the inorganic filler is 2000 nm or less from the viewpoint of increasing the proportion of the inorganic filler in the coating layer and improving heat shrinkage resistance. It is preferable that the average particle size of the inorganic filler is, for example, 180 nm or more and 300 nm or less. This is because, especially when the thickness of the coating layer is small, a uniform coating layer thickness is formed and heat shrinkage resistance is improved. It is also preferable that the average particle size of the inorganic filler is, for example, 150 nm or more and 500 nm or less, or 200 nm or more and 450 nm or less. The reason is that it is possible to achieve a high degree of both rate characteristics and heat shrinkage resistance. The "average particle size" of the inorganic filler was measured by the method described in Examples. Examples of methods for adjusting the particle size and distribution of the inorganic filler include a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizer such as a ball mill, bead mill, jet mill, or the like. The particle size distribution of the inorganic filler can be such that there is one peak in a graph of frequency versus particle size. However, a trapezoidal chart with two peaks or no peaks may be used.

Examples of the shape of the inorganic filler include a plate, a scale, a needle, a column, a sphere, a polyhedron, and a block. You may use multiple types of inorganic fillers having these shapes in combination. A block shape is preferable from the viewpoint of improving the slope ratio of the coating layer and increasing the adhesive force with the electrode.

The aspect ratio of the inorganic filler is preferably 1.0 or more and 2.5 or less, more preferably 1.1 or more and 2.0 or less. By having an aspect ratio of 2.5 or less, the amount of moisture adsorbed by the multilayer porous membrane is suppressed, and capacity deterioration during repeated cycles is suppressed, and deformation at temperatures exceeding the melting point of the base material is suppressed. , and is preferable from the viewpoint of improving the slope ratio of the coating layer and increasing the adhesive force with the electrode. The reason why the inclination ratio increases when the aspect ratio of the inorganic filler is 1.0 or more and 2.5 or less is considered to be that since the orientation of particles in the coating layer is small, it is easy to form a laminated structure.

The particle size distribution of the inorganic filler, which is determined 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 It is 0.45 or less. It is preferable that the particle size distribution is 0.55 or less, from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the base material, and from the viewpoint of improving the slope ratio of the coating layer and increasing the adhesive force with the electrode. The reason why the gradient ratio increases when the particle size distribution of the inorganic filler is 0.55 or less is that the uniformity of the particles increases and the contact rate between particles improves, making it easier to form a laminated structure. It is believed that there is.

The amount of the inorganic filler is, for example, 20 parts by mass or more and less than 100 parts by mass, 30 parts by mass or more and 80 parts by mass, 35 parts by mass or more and 70 parts by mass, and even 40 parts by mass or more and 60 parts by mass, based on the total mass of the coating layer. Parts by mass or less.

(Particulate polymer)
Particulate polymers are particles of thermoplastic polymers. The particulate polymer preferably contains a thermoplastic polymer having a glass transition temperature or melting point of 20° C. or more and 200° C. or less, from the viewpoint of improving the adhesiveness between the separator and the electrode. The glass transition temperature refers to the midpoint glass transition temperature described in JIS K7121, and is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, for a straight line that is the same distance in the vertical axis direction from a straight line that extends the baseline on the low temperature side of the DSC curve toward the high temperature side, and a straight line that extends the baseline on the high temperature side of the DSC curve toward the low temperature side, The temperature at the point where the curve of the stepwise change portion of the glass transition intersects can be employed as the glass transition temperature. More specifically, it may be determined according to the method described in Examples. Furthermore, "glass transition" refers to a change in heat flow on the endothermic side due to a change in the state of a polymer, which is a test piece, in DSC. Such a change in heat flow rate is observed as a step-like change in the DSC curve. A "step-like change" refers to a portion of the DSC curve where the curve leaves the previous baseline on the low-temperature side and transitions to a new baseline on the high-temperature side. Note that a combination of a step-like change and a peak is also included in the step-like change. In addition, in the step-like changing portion, when the upper side is the heat generation side, it can also be expressed as a point where an upwardly convex curve changes to a downwardly convex curve. A "peak" refers to a portion of a DSC curve from when the curve departs from the baseline on the low temperature side until it returns to the same baseline again. "Baseline" refers to a DSC curve in a temperature range in which no transition or reaction occurs in the test piece.

The glass transition temperature (Tg) of the particulate polymer is preferably 10°C or higher and 110°C or lower, more preferably 45°C or higher, even more preferably 80°C or higher, even more preferably 90°C or higher, and The temperature is particularly preferably higher than 90° C. from the viewpoint of improving the subsequent adhesive strength and the blocking resistance. The temperature can be 92° C. or higher in that shape stability can be maintained up to higher temperatures. The fact that the Tg of the particulate polymer is 10°C or higher prevents adhesion (blocking) between separators that are adjacent to each other via the coating layer during storage and transportation of the separator for electricity storage devices, as well as during the manufacturing process of electricity storage devices. It is preferable from the viewpoint of On the other hand, it is preferable that the Tg of the particulate polymer is 110° C. or less from the viewpoint of obtaining good adhesive strength with the electrode. The Tg of the particulate polymer can be determined by, for example, changing the type of monomer used when producing the particulate polymer and the blending ratio of each monomer if the particulate polymer is a copolymer. It can be adjusted as appropriate. That is, for each monomer used in the production of a particulate polymer, the generally indicated Tg of the homopolymer (as described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the Tg of the monomer are determined. The glass transition temperature can be roughly estimated from the blending ratio. For example, a copolymer copolymerized with a high proportion of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid to give a homopolymer with a Tg of about 100°C has a high Tg of about -50°C. The Tg of a copolymer obtained by copolymerizing a high proportion of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate to give a homopolymer with a Tg of . Further, the Tg of the copolymer can also be approximately estimated by the FOX formula represented by the following formula.
1/Tg=W ₁ /Tg ₁ +W ₂ /Tg ₂ +...+W _i /Tg _i +...W _n /Tg _n
Here, in the formula, Tg (K) is the Tg of the copolymer, Tg _i (K) is the Tg of the homopolymer of monomer i, and W _i is the mass fraction of each monomer. . i is an integer from 1 to n, and n is the number of types of monomers constituting the copolymer. However, as the glass transition temperature Tg of the particulate polymer in this embodiment, a value measured by the method using the above-mentioned DSC is adopted.

The average particle diameter of the particulate polymer is preferably 0.5 times or more 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 from the coating layer. It is 5 times or less, more preferably 1 time or more and 2 times or less, still more preferably 1.1 times or more and less than 1.5 times, particularly preferably 1.2 times or more and 1.4 times or less. The "average particle size" of the particulate polymer means the volume average particle size measured by the measuring method described in the Examples. A "primary particle" of a particulate polymer means an independent particle held together 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."

The particulate polymer contained in the coating layer is preferably in the form of primary particles. The average particle size of the primary particles of the particulate polymer is preferably 1 μm or more and 10 μm or less, more preferably 1 μm or more and 8 μm or less, and still more preferably 2 μm or more and 5 μm or less. 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 and the adhesive force with the electrode. The thickness of the coating layer increases, thermal shrinkage is suppressed, and the uniformity of the thickness of the coating layer can be ensured. When the average particle size of the primary particles is 1 μm or more and 10 μm or less, the particulate polymer tends to form a structure protruding from the surface of the coating layer, increasing adhesive strength with the electrode and suppressing thermal shrinkage.

Examples of the thermoplastic polymer include (meth)acrylic polymers, conjugated diene polymers, polyvinyl alcohol resins, and fluororesins.

From the viewpoint of high adhesion to the electrode and low thermal shrinkage rate, the thermoplastic polymer more preferably contains a (meth)acrylic polymer. "(Meth)acrylic polymer" means a polymer or copolymer containing a (meth)acrylic compound as a monomer. The (meth)acrylic compound can be represented by the following general formula.
CH ₂ =CR ^Y1 -COO-R ^Y2
In the formula, R ^Y1 represents a hydrogen atom or a methyl group, and R ^Y2 represents a hydrogen atom or a monovalent hydrocarbon group. When R ^Y2 is a monovalent hydrocarbon group, it may have a substituent or a heteroatom. Examples of the monovalent hydrocarbon group include a linear alkyl group that may be linear or branched, a cycloalkyl group, and an aryl group. Examples of the substituent include a hydroxyl group and a phenyl group, and examples of the heteroatom include a halogen atom and an oxygen atom. The (meth)acrylic compounds may be used alone or in combination of two or more. Examples of (meth)acrylic compounds include (meth)acrylic acid, chain alkyl (meth)acrylate, cycloalkyl (meth)acrylate, (meth)acrylate having a hydroxyl group, and (meth)acrylic acid aryl ester. It will be done.

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

(Meth)acrylates include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and methyl methacrylate. , ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and (meth)acrylates having a linear alkyl group such as lauryl methacrylate; and phenyl Examples include (meth)acrylates and (meth)acrylates having an aromatic ring such as benzyl (meth)acrylate.

A conjugated diene polymer is a polymer having a conjugated diene compound as a monomer unit, and is preferred because it is easily compatible with an electrode. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated Examples include pentadienes, substituted hexadienes, and side chain conjugated hexadienes, and these may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. The conjugated diene polymer may contain a (meth)acrylic compound or other monomer described below as a monomer unit. Examples of such monomers include styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride. It will be done.

Examples of the polyvinyl alcohol resin include polyvinyl alcohol and polyvinyl acetate.

Fluorine-containing resins are preferable from the viewpoint of voltage resistance, and include, for example, polyvinylidene fluoride, polytetrafluoroethylene, and copolymers containing fluorine atoms, such as vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoride, etc. Examples include fluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer. The fluororesin is preferably a copolymer containing a fluorine atom.

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

Preferably, the particulate polymer contains a crosslinkable monomer. The crosslinking monomer is not particularly limited, but includes, for example, a monomer having two or more radically polymerizable double bonds, and a monomer having a functional group that provides a self-crosslinking structure during or after polymerization. Examples include the body. These may be used alone or in combination of two or more.

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

(resin binder)
The coating layer preferably contains a resin binder for binding the inorganic fillers and the inorganic filler and the base material. The type of resin in the resin binder is not particularly limited; Chemically stable resins can be used.

Specific examples of the resin of the resin binder include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers; Fluororubbers such as ethylene-tetrafluoroethylene copolymers; styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides Rubbers such as , methacrylic acid ester-acrylic ester copolymer, styrene-acrylic ester copolymer, acrylonitrile-acrylic ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; ethyl cellulose, methyl cellulose, hydroxy Cellulose derivatives such as ethyl cellulose and carboxymethyl cellulose; and resins with a melting point of 180°C or higher, such as polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester, or have no melting point. Examples include resins with a decomposition temperature of 200°C or higher. These may be used alone or in combination of two or more.

The resin binder can 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 with these monomers 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 , for example, styrene. Although there are no particular limitations on the method of polymerizing such a copolymer, emulsion polymerization is preferred. The emulsion polymerization method is not particularly limited, and known methods can be used. The method of adding monomers and other components is not particularly limited, and any of a batch addition method, a divided addition method, and a continuous addition method can be adopted, and the polymerization method includes one-stage polymerization, Either two-stage polymerization or multi-stage polymerization of three or more stages can be employed.

Specific examples of the resin binder include the following (1) to (7).
(1) Polyolefins, such as polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
(2) Conjugated diene polymers, such as styrene-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene-styrene copolymers, and hydrides thereof;
(3) Acrylic polymers, such as methacrylic ester-acrylic ester copolymers, styrene-acrylic ester copolymers, and acrylonitrile-acrylic ester copolymers;
(4) polyvinyl alcohol resins, such as polyvinyl alcohol and polyvinyl acetate;
(5) Fluorine-containing resins, such as 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 with a melting point and/or glass transition temperature of 180°C or higher, or resins that do not have a melting point but have a decomposition temperature of 200°C or higher. polymers such as polyphenylene ethers, polysulfones, polyethersulfones, polyphenylene sulfides, polyetherimides, polyamideimides, polyamides, and polyesters.

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

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

The volume average particle diameter (D50) of the resin binder is preferably at least 1 time, more preferably at least 2 times, and even more preferably 2.5 times the average pore diameter of the microporous polyolefin membrane from the viewpoint of improving 180° peel strength. That's more than double that. By selecting the volume average particle diameter (D50) of the resin binder in this manner, it becomes possible to hold the resin binder on the surface of the microporous polyolefin membrane, and the 180° peel strength is improved. The volume average particle diameter (D50) of the resin binder is preferably 10 times or less the average pore diameter of the microporous polyolefin membrane from the viewpoint of improving rate characteristics. From the viewpoint of maintaining low permeability and suppressing blocking, the content ratio of the resin binder in the coating layer is, for example, more than 0 parts by mass and 50 parts by mass or less, and 1 part by mass, based on the total amount of the coating layer. The amount may be greater than or equal to 20 parts by mass, less than or equal to 2 parts by mass and less than or equal to 10 parts by mass, or greater than or equal to 3 parts by mass and less than or equal to 5 parts by mass.

The Tg of the resin binder is determined by the wettability to the base material, the binding property between the base material and the particulate polymer, the binding property between the coating layer and the particulate polymer, the binding property between the base material and the coating layer, From the viewpoint of adhesion to electrodes, the temperature is preferably lower than 40°C. The Tg of the resin binder is more preferably -100°C or higher, still more preferably -50°C or higher, particularly preferably -40°C or higher, from the viewpoint of ion permeability, and the Tg of the resin binder is more preferably -100°C or higher, still more preferably -50°C or higher, and particularly preferably -40°C or higher, and the Tg of the resin binder is such that the bonding between the base material and the particulate polymer is From the viewpoint of performance, the temperature is more preferably less than 20°C, still more preferably less than 15°C, particularly preferably less than 0°C.

(Water-soluble polymer)
The coating layer may further contain a water-soluble polymer in addition to the inorganic filler and the particulate thermoplastic polymer. The water-soluble polymer may be incompatible with the thermoplastic polymer that constitutes the particulate polymer. In general, a water-soluble polymer functions as a dispersant in a coating solution for forming a coating layer containing an inorganic filler and a particulate thermoplastic polymer, and when the coating solution is a water-based coating, it functions as a dispersant and/or a dispersant. Or it functions as a water retention agent.

The content of the 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, based on 100 parts by mass of the inorganic filler. , more preferably 0.1 part by mass or more and 1 part by mass or less. When the content of the water-soluble polymer is 0.04 parts by mass or more, the binding property between the inorganic components increases and thermal shrinkage can be further suppressed. Further, it is possible to suppress sedimentation of the components during preparation of the slurry for the coating layer and to stably disperse the components. When the content of the water-soluble polymer is 5 parts by mass or less, it is possible to suppress streaks and unevenness during formation of the coating layer.

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

Water-soluble polymers may be polymers derived from natural products, synthetic products, semi-synthetic products, etc.; Nonionic polymers are preferred, and anionic, cationic, or amphoteric polymers are more preferred.

Examples of anionic polymers include modified starches such as carboxymethyl starch and starch phosphate; anionic cellulose derivatives such as carboxymethyl cellulose; ammonium salts or alkali metal salts of polyacrylic acid; gum arabic; carrageenan; chondroitin sulfate sodium Sulfonic acid compounds such as polystyrene sodium sulfonate, polyisobutylene sodium sulfonate, and naphthalene sulfonic acid condensate salts; and polyethyleneimine xanthate salts. Among these, from the viewpoint of achieving an appropriate balance between rigidity, rate characteristics, and cycle characteristics for power storage devices, anionic polymers containing metal salts as countercations are preferred; anionic cellulose derivatives, and polyacrylics. Ammonium salts or alkali metal salts of acids are also preferred; from the viewpoint of the balance between heat resistance and rate characteristics, alkali metal salts of polyacrylic acid are more preferred, and sodium polyacrylate is even more preferred.

The ammonium salt or alkali metal salt of polyacrylic acid refers to a polymer in which at least one of the -COO 2 ^- moieties derived from a plurality of carboxylic acid groups forms a salt with an ammonium ion or an alkali metal ion. Examples of the alkali metal ions include sodium ions (Na ⁺ ), potassium ions (K ⁺ ), and the like.

The ammonium salt or alkali metal salt of polyacrylic acid may be at least one of the following (I) to (III):
(I) A homopolymer of a monomer (C _i ) having one ammonium salt or alkali metal salt of a carboxylic acid, or a copolymer of a plurality of monomers (C _i ) and other monomers;
(II) A homopolymer of monomer (C _ii ) having a plurality of ammonium salts or alkali metal salts of carboxylic acid, or a copolymer of monomer (C _ii ) and other monomers; and (III) having one or more carboxylic acids. Ammonium salts or alkali metal salts of polymers or copolymers obtained by polymerizing or copolymerizing monomers.

Examples of the monomer (C _i ) having one ammonium salt or alkali metal salt of carboxylic acid include sodium (meth)acrylate and ammonium (meth)acrylate.

Examples of monomers (C _ii ) having multiple ammonium salts or alkali metal salts of carboxylic acids include ammonium salts or sodium salts of 11-(methacryloyloxy)undecane-1,1-dicarboxylic acid; fumaric acid, maleic acid, itacon; Examples include ammonium salts, monosodium salts, or disodium salts of ethylenically unsaturated dicarboxylic acids such as citraconic acid; and alicyclic polycarboxylic acids having a (meth)acryloyl group.

Examples of monomers copolymerizable with monomer (C _i ) or monomer (C _ii ) include (meth)acrylamide; ethylenically unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and citraconic acid; and anhydride. Examples include ethylenically unsaturated dicarboxylic anhydrides such as maleic acid, itaconic anhydride, and citraconic anhydride.

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.

The structures of the ammonium salt or alkali metal salt of polyacrylic acid explained in (I) to (III) above may overlap with each other. The ammonium salt or alkali metal salt of polyacrylic acid described in (I) to (III) above desirably has a low content of polyvalent cations when dissolved in water. Examples of polyvalent cations include magnesium ions, calcium ions, and iron ions. By reducing the content of these ions, the dispersibility of the particulate polymer in the mixed slurry with the particulate polymer is stabilized.

Examples of cationic polymers include cationic starch; chitosan; gelatin; homopolymer or copolymer of dimethylaminoethyl (meth)acrylate quaternary salt; homopolymer or copolymer of dimethylallylammonium chloride; polyamidine and its copolymer; polyvinylimidazoline; dicyandiamide Examples include epichlorohydrin/dimethylamine condensates; and polyethyleneimine.

Examples of the amphoteric polymer include dimethylaminoethyl (meth)acrylate quaternary salt-acrylic acid copolymer, Hofmann decomposition product of polyacrylamide, and the like.

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 modified products thereof; and polyvinyl alcohol and polyvinyl alcohol. Examples include synthetic polymers such as acrylamide, polyethylene glycol, polymethyl vinyl ether, polyisopropylacrylamide, copolymers of vinyl alcohol and other monomers, and modified products thereof.

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

The group having an amide bond-containing cyclic structure is represented by the following formula (2):
Examples include groups represented by: Specific examples of water-soluble polymers having an amide bond-containing cyclic structure include poly(N-vinylcaprolactam), which is a homopolymer of N-vinylcaprolactam, and polyvinylpyrrolidone (PVP), which is a homopolymer of vinylpyrrolidone. Homopolymers of monomers having a group having a bond-containing cyclic structure and a polymerizable double bond; homopolymers of monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.) A copolymer of two or more types; and one or more types of monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond (N-vinyl caprolactam, vinyl pyrrolidone, etc.), and another polymerizable double bond. Examples include copolymers of one or more monomers having a bond (monomers other than monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond).

Monomers that can be copolymerized with a monomer having a group having 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 vinyl imidazole and vinyl pyridine 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.

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

Specific examples of antifoaming agents include the following formula (A):
{In the formula, R ⁵ to R ⁸ each independently represent an alkyl group having 1 to 10 carbon atoms, and n and m independently represent an integer of 0 or more, but n+m=0 or more 40 or less. } It is preferable to use a surfactant containing an ethoxylated acetylene glycol (acetylene surfactant).

Specific examples of alkyl groups having 1 to 10 carbon atoms may be linear, branched, or cyclic, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, Examples include sec-butyl group, tert-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, and n-decyl group.

Specific examples of acetylene glycol represented by formula (A) include 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 5,8-dimethyl-6-dodecyne-5,8 -diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 4,7-dimethyl-5-decyne-4,7-diol, 2,3,6,7-tetramethyl -4-octyne-3,6-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,4,7,9 - Ethoxylated product of tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 1.3), 2,4,7,9-tetramethyl-5-decyne-4,7-diol Ethoxylated product (number of moles of ethylene oxide added: 4), ethoxylated product of 3,6-dimethyl-4-octyne-3,6-diol (number of moles of ethylene oxide added: 4), 2,5,8,11- Ethoxylated product of tetramethyl-6-dodecyne-5,8-diol (number of moles of ethylene oxide added: 6) Ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol ( Number of moles of ethylene oxide added: 10), ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 30), and 3,6-dimethyl- Examples include ethoxylated 4-octyne-3,6-diol (number of moles of ethylene oxide added: 20). The antifoaming agents may be used alone or in combination of two or more.

Acetylene surfactants can also be obtained as commercial products, such as Olfine SPC (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 80 parts by mass, pale yellow liquid), Olfine SPC AF-103 (manufactured by Nissin Chemical Industry Co., Ltd., light brown liquid), Olfin AF-104 (manufactured by Nissin Chemical Industry Co., Ltd., light brown liquid), Olfin SK-14 (manufactured by Nissin Chemical Industry Co., Ltd.) , short yellow viscous liquid), Olfin AK-02 (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin AF-201F (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin D-10PG (manufactured by Nissin Chemical Industry Co., Ltd., 50 parts by mass of active ingredient, pale yellow liquid), Olfin E-1004 (manufactured by Nissin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1010 (manufactured by Nissin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1020 (manufactured by Nissin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1030W (manufactured by Nissin Chemical Industry Co., Ltd., 75 parts by mass of active ingredient, pale yellow liquid), Surfynol 420 (manufactured by Nissin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow viscous substance), Surfy Nol 440 (manufactured by Nissin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow viscous substance), and Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd., 50 parts by mass of active ingredient, pale yellow viscous substance) ) etc.

As the additive surfactant, a polyether surfactant and/or a silicone surfactant can also be used instead of or together with the acetylene surfactant. Typical examples of polyether surfactants include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene dodecyl ether, and polyoxyethylene. Examples include nonylphenyl ether, polyoxyethylene octylphenyl ether, and polyoxyethylene/polyoxypropylene block copolymer. Among these, polyethylene glycol is particularly preferred. Note that these surfactants may be used alone or in combination of two or more.

Polyether surfactants can also be obtained as commercial products, and examples of such commercial products include E-D052, E-D054, and E-F010 (manufactured by San Nopco Co., Ltd.).

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

Silicone surfactants can also be obtained as commercial products, such as BYK-300, BYK-301, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-320BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349 (all product names, manufactured by BYK Chemie Japan Co., Ltd.), KM-80 , KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, 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 Industries, Ltd.) Polyflow KL-245, Polyflow KL-270, Polyflow KL-100 (manufactured by Kyoeisha Chemical Co., Ltd.), Silface SAG002, Silface SAG005, and Silface SAG0085 (product names above) (manufactured by Nissin Chemical Industry Co., Ltd.), etc.

(Amount of coating layer)
The amount of the coating layer relative to the base material, that is, the amount of the coating layer per unit area of one surface of the base material, in terms of weight, is preferably 0.5 g/m ² or more, more preferably 1.0 g/m ² or more. The volume is preferably 0.15 cm ³ /m ² or more, more preferably 0.30 cm ³ /m ² or more. The upper limit of the amount of the coating layer is preferably 10.0 g/m ² or less, more preferably 7.0 g/m ² or less in terms of weight, and preferably 3.50 cm ³ /m ² or less in volumetric amount. Preferably it is 2.50 cm ³ /m ² or less. It is preferable that the amount of the coating layer is equal to or greater than the lower limit value from the viewpoint of improving the adhesive force between the coating layer and the electrode and suppressing thermal shrinkage. It is preferable that the amount of the coating layer be less than or equal to the above upper limit value from the viewpoint of suppressing a decrease in ion permeability.

(Thickness of coating layer)
The thickness of either one of the coating layers disposed on at least one of the base materials (thickness of the inorganic filler portion) 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 further Preferably it is 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, and the adhesive force between the electrode and the base material can be easily made uniform, and as a result, the characteristics of the electricity storage device can be improved. I can do it. It is preferable that the thickness is 1.3 μm or less because it is possible to suppress a decrease in ion permeability and to obtain a thin film separator for an electricity storage device. That is, by reducing the thickness of the separator, it is possible to manufacture an electricity storage device with a large capacity per volume. On the other hand, from the viewpoint of further suppressing thermal shrinkage and preventing the particulate polymer from slipping off from 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 the particulate polymer in the coating solution applied to the substrate, the amount of the coating solution, the coating method, the coating conditions, etc. However, the method for adjusting the thickness of the coating layer is not limited to these methods.

FIG. 1 is a schematic diagram of the surface of the coating layer of the separator for a power storage device according to the present embodiment. As schematically shown in FIG. 1, on the surface of the coating layer (10), there are an inorganic filler (1) and a particulate thermoplastic polymer (2) protruding from the inorganic filler portion. In FIG. 1, the particulate polymer exists in the state of primary particles without agglomerating with other particulate polymers.

FIG. 2 is a sectional view taken along line AA of the separator for an electricity storage device shown in FIG. As schematically shown in FIG. 2, the coating layer (20) consists of particles protruding from an inorganic filler portion that is 1.5D or more away from the volume center of each particulate polymer in the horizontal direction (in the plane direction of the coating layer). It is formed in an inclined shape so that it becomes continuously thicker as it approaches the shaped polymer (2). The slope of the sloped coating layer becomes gentler as it moves away from the protruding particulate polymer, and becomes steeper as it approaches the protruding particulate polymer. The inorganic filler (1) covers a part of the periphery of the protruding part so as to ride along the contour of the particulate polymer, and the vicinity of the center of the protruding part is exposed on the surface of the coating layer.

《Method for manufacturing separators for power storage devices》
<Method for manufacturing base material>
A known manufacturing method can be employed as a method for manufacturing the base material, and for example, either a wet porous method or a dry porous method may be employed. For example, when the base material is a microporous polyolefin membrane, a polyolefin resin composition and a plasticizer are melt-kneaded and formed into a sheet, optionally stretched, and then the plasticizer is added. A method of making porous by extracting polyolefin; after melt-kneading a polyolefin resin composition containing polyolefin resin as the main component and extruding it at a high draw ratio, making it porous by exfoliating the polyolefin crystal interface by heat treatment and stretching. A method of melt-kneading a polyolefin resin composition and an inorganic filler, forming it into a sheet, and then making it porous by peeling off the interface between the polyolefin and the inorganic filler by stretching; and a method of dissolving the polyolefin resin composition. After that, a method of making the polyolefin porous by coagulating the polyolefin by immersing it in a poor solvent for the polyolefin and simultaneously removing the solvent can be mentioned.

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 method in which hot-melt fibers are mixed into the web and the fibers are partially melted to bond the fibers together. Bond method; Needle punch method, in which the web is repeatedly punctured with barbed needles to mechanically entangle the fibers; and Water entanglement method, in which high-pressure water is sprayed from a nozzle onto the web through a net (screen) to entangle the fibers. Can be mentioned.

Hereinafter, as an example of a method for manufacturing a polyolefin microporous membrane, a method will be described in which a polyolefin resin composition and a plasticizer are melt-kneaded, molded into a sheet shape, and then the plasticizer is extracted. A polyolefin resin composition and a plasticizer are melt-kneaded. As a melt-kneading method, for example, a polyolefin resin and other additives as necessary are put into a resin kneading device such as an extruder, a kneader, a laboplast mill, a kneading roll, or a Banbury mixer, and the resin components are heated and melted. An example of this method is to introduce a plasticizer in an arbitrary ratio and knead the mixture. At this time, 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 introducing the polyolefin resin, other additives, and plasticizer into the resin kneading device. More preferably, only a part of the plasticizer is added during preliminary kneading, and the remaining plasticizer is kneaded while being side-fed to the resin kneading device.

As the plasticizer, a nonvolatile solvent capable of forming a homogeneous solution at a temperature equal to or higher than the melting point of the polyolefin can be used. Examples of the plasticizer 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.

The ratio of the polyolefin resin composition to the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and molded into a sheet. For example, the mass fraction of the plasticizer in a composition consisting of a polyolefin resin composition and a 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 formability of a uniform and fine pore structure.

The melt-kneaded product obtained by heating, melting, and kneading as described above is formed into a sheet shape. As a method for manufacturing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet-like form through a T-die, etc., and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component by contacting with a heat conductor. An example of this method is to solidify the material. Thermal conductors used for cooling and solidification include metals, water, air, and plasticizers themselves, but metal rolls are preferred because of their high heat conduction efficiency. In this case, if the molten mixture is sandwiched between the rolls when it comes into contact with the metal rolls, the heat conduction efficiency will be further increased, the sheet will be oriented, the film strength will be increased, and the surface smoothness of the sheet will also be improved. Therefore, it is more preferable. The die lip interval when extruding into a sheet form from a T-die is preferably 400 μm or more and 3000 μm or less, more preferably 500 μm or more and 2500 μm or less.

It is preferred that the sheet-like molded product thus obtained is then stretched. As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used. Biaxial stretching is preferred from the viewpoint of the strength of the resulting microporous membrane. When a sheet-like molded product is stretched biaxially at a high magnification, the molecules are oriented in the plane direction, and the porous base material finally obtained becomes difficult to tear and has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoint of improving puncture strength, uniformity of stretching, and shutdown properties.

The stretching ratio is preferably in the range of 20 times or more and 100 times or less, more preferably 25 times or more and 50 times or less in area magnification. The stretching ratio in each axial direction is preferably in the range of 4 times or more and 10 times or less in the MD direction, 4 times or more and 10 times or less in the TD direction, 5 times or more and 8 times or less in the MD direction, and 5 times or more and 8 times in the TD direction. The following ranges are more preferable. Setting the stretching ratio within this range is preferable because more sufficient strength can be imparted, film breakage in the stretching process can be prevented, and high productivity can be obtained. Note that the MD direction means, for example, the machine direction when continuously molding a polyolefin microporous membrane, and the TD direction means a direction that crosses the MD direction at an angle of 90°.

The sheet-like molded product obtained as described above may be further rolled. Rolling can be carried out, for example, by a pressing method using a double belt press machine or the like. By rolling, the orientation of the surface layer portion of the sheet-like molded product can be increased. The rolling surface magnification is preferably greater than 1 time and less than 3 times, more preferably greater than 1 time and less than 2 times. By setting the rolling ratio in this range, the membrane strength of the porous base material finally obtained is increased, and a more uniform porous structure in the thickness direction of the membrane can be formed, which is preferable.

Next, the plasticizer is removed from the sheet-like molded body to obtain a porous base material. As a method for removing the plasticizer, for example, a method of immersing the sheet-shaped molded body in an extraction solvent to extract the plasticizer, and thoroughly drying the molded body is exemplified. The method for extracting the plasticizer may be either a batch method or a continuous method. In order to suppress shrinkage of the porous base material, it is preferable to restrain the ends of the sheet-like molded body during the series of steps of dipping and drying. In removing the plasticizer, 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, based on the total mass of the obtained base material. It can be controlled to be 0.3 parts by mass or more and 1.0 parts by mass or less. When the amount of the plasticizer is within the above range, it is possible to lower the internal resistance of the battery and improve the binding force between the base material and the coating layer.

As the extraction solvent, it is preferable to use one that is a poor solvent for the polyolefin resin, a good solvent for the plasticizer, and has a boiling point lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; hydrofluoroethers and hydrofluorocarbons; Non-chlorinated halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. Note that these extraction solvents may be recovered and reused by operations such as distillation.

In order to suppress shrinkage of the porous base material, heat treatment such as heat setting or thermal relaxation may be performed after the stretching step or after the formation of the porous base material. The porous base material may be subjected to post-treatments such as hydrophilization treatment using a surfactant or the like, crosslinking treatment using ionizing radiation or the like.

An example of a dry porosification method, which is different from the wet porosification method described above, will be given. First, a film is produced by directly stretching and orienting the film in an extruder without using a solvent after being melt-kneaded, and then an annealing process, a cold stretching process, and a hot stretching process are performed in order to produce a microporous membrane. Examples of the dry porosification method include a method in which a molten resin is stretched and oriented from an extruder through a T-die, an inflation method, and the like, and the method is not particularly limited.

<How to arrange the coating layer>
A coating layer is disposed on at least one side of the base material produced as described above. Examples of the method for arranging the coating layer include a method in which a coating liquid containing an inorganic filler and a particulate thermoplastic polymer is applied to the substrate, and the medium is removed.

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

The medium for the coating solution is preferably one that can uniformly and stably disperse or dissolve the inorganic filler, particulate polymer, and water-soluble polymer if necessary, such as N-methylpyrrolidone, N,N-dimethylformamide, etc. , N,N-dimethylacetamide, water, ethanol, methanol, toluene, hot xylene, methylene chloride, and hexane. The medium for the coating liquid is preferably water or a mixed medium consisting of water and a water-soluble organic medium. Examples of the water-soluble organic medium include, but are not limited to, ethanol, methanol, and the like. Among these, water is more preferred. When applying the coating liquid to the base material, if the coating liquid penetrates into the inside of the base material, the particulate polymer containing the polymer will block the surface and inside of the pores of the base material, reducing permeability. It becomes easier to decrease. In this regard, in the case of an aqueous dispersion that uses water as a medium for the coating liquid, it is difficult for the coating liquid to enter the inside of the substrate, and the particulate polymer containing the polymer is mainly present on the outer surface of the substrate. This is preferable because it makes it easier to prevent the permeability from decreasing.

The volume average particle diameter (D50) of the particulate polymer in the coating liquid may be, for example, 1.0 μm or more and 12 μm or less. From the viewpoint of obtaining a suitable distribution state of the protruding particulate polymer in the coating layer, the volume average particle diameter (D50) is preferably 1.5 μm or more, and preferably 10 μm or less, 7.5 μm. Hereinafter, it is 5.0 μm or less, 3.0 μm or less, or 2.5 μm or less. When the volume average particle diameter (D50) is equal to or larger than the above lower limit value, aggregation of particulate polymers can be suitably prevented. In addition, if the volume average particle diameter (D50) is below the above upper limit value, the difference in particle diameter from the inorganic filler can be kept within a predetermined range, thereby causing precipitation of the particulate polymer in the coating liquid. can be easily controlled. The volume average particle diameter of the particulate polymer can be controlled, for example, by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, pH, etc. for obtaining the particulate polymer.

The coating liquid may optionally contain additives. Examples of additives for the coating solution include various additives such as dispersants such as surfactants; thickeners; wetting agents; antifoaming agents; and PH adjusting agents containing acids and alkalis.

Examples of methods for dispersing or dissolving the inorganic filler, particulate polymer, and optionally a water-soluble polymer in the medium of the coating solution include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, and atomizers. Examples include mechanical stirring using lighters, roll mills, high-speed impeller dispersion, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and stirring blades.

As a procedure for preparing a coating liquid, it is preferable to first add a water-soluble polymer to a coating liquid in which an inorganic filler is dispersed, and then add a resin binder and a particulate polymer. By preparing the coating liquid in this order, the metal ions contained in the inorganic filler are adsorbed and protected by the water-soluble polymer, and aggregation of the resin binder and particulate polymer can be prevented.

In order to obtain a suitable distribution state of the protruding particulate polymer in the coating layer, the viscosity of the coating liquid is preferably 10 mPa·s or more, or 20 mPa·s or more, and preferably 100 mPa·s or less, It is 80 mPa·s or less, 60 mPa·s or less, or 40 mPa·s or less. In this embodiment, the thermoplastic polymer contained in the coating liquid preferably has a large particle size of 1 μm to 10 μm. Therefore, when the viscosity of the coating liquid is 10 mPa·s or more, it is possible to prevent the thermoplastic polymer from settling in the coating liquid. On the other hand, if the viscosity of the coating liquid is 100 mPa・s or less, turbulent flow of the liquid will easily occur during stirring, and the dispersion of the particulate polymer in the coating liquid flow will be good, resulting in fluctuations in the area (si) of the Voronoi polygon. It is easier to control the coefficient (CV) within the above range. In addition, the viscosity of the coating liquid is 10 mPa·s or more and 100 mPa·s or less, from the viewpoint of suitably controlling sedimentation of the particulate polymer in the process of removing the solvent from the coating film and forming the coating layer after coating. , is preferable from the viewpoint of increasing the slope ratio of the coating layer and increasing the contact ratio between the particulate polymer and the surface of the substrate.

The substrate may be surface treated before coating. Surface treatment is preferable because it makes it easier to apply the coating liquid, improves the adhesion between the base material and the thermoplastic polymer, and makes it easier to control the 180° peel strength to 200 gf/cm or more. Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method. As the surface treatment, a corona discharge treatment method can be mentioned.

The method of applying the coating liquid onto the substrate is not particularly limited as long as it is a method that can achieve a desired coating pattern, coating thickness, and coating area. Examples of the coating method include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, Examples include squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, and inkjet coating method. Among these, the gravure coater method or the spray coating method is preferable from the viewpoint that the degree of freedom in the coating shape of the particulate polymer is high and a preferable area ratio can be easily obtained.

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

The coating solution may be stirred before or during coating. As a stirring method,
A method of stirring the coating solution using turbulent flow in the supply tank;
A method in which the coating liquid is subjected to ultrasonic treatment (vibration and stirring treatment using ultrasonic waves) immediately before coating;
etc. Suitable stirring is advantageous from the viewpoint 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 within the above range. .

The method for removing the medium from the coating film after coating is not particularly limited as long as it does not adversely affect the base material and the coating layer. For example, methods include drying at a temperature below the melting point of the base material while fixing it, drying under reduced pressure at low temperatures, and solidifying the particulate polymer into particles by immersing it in a medium that is a poor solvent for the particulate polymer. Examples include a method of extracting the medium at the same time.

From the viewpoint of adjusting the static friction coefficient of the coating layer within the above range and/or from the viewpoint of making it easier to maintain the shape of the protruding particulate polymer, the conditions after the coating and drying steps were controlled as follows. It is preferable to:
- Control the tension applied in the direction perpendicular to the surface where the coated surface contacts the conveyance roll to a predetermined value or less, for example, 40 N/m or less;
・Make the speed of the conveyance roll that the coated surface contacts the same as the separator conveyance speed. Specifically, for example, set the speed of the conveyance roll that the coated surface touches after the coating process to be greater than 0.999 times and 1.001 times the separator conveyance speed. etc.

<Preparation of separator winding body>
It is preferable that the obtained separator for an electricity storage device is wound into a form of a wound body. By using the separator as a wound body, it can be easily fed out at high speed, and productivity can be increased in the production process of electricity storage devices.

《Electricity storage device》
The power storage device of this embodiment includes the separator for power storage devices of this embodiment. Examples of power storage devices include, but are not particularly limited to, batteries such as non-aqueous electrolyte secondary batteries, capacitors, and capacitors. Among them, in order to take advantage of the advantages of the separator for power storage devices of this embodiment, batteries are preferred, non-aqueous electrolyte secondary batteries are more preferred, and lithium ion secondary batteries are even more preferred. The lithium ion secondary battery includes a positive electrode, a negative electrode, the separator for an electricity storage device of the present embodiment disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The electricity storage device of this embodiment includes a separator for an electricity storage device, so it has excellent characteristics such as electricity storage performance, and in the case of a lithium ion secondary battery, it has excellent battery characteristics.

When the electricity storage device of this embodiment is a lithium ion secondary battery, there are no limitations on the positive electrode, negative electrode, and nonaqueous electrolyte, and known ones can be used for each. 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 can be suitably used. Examples of the positive electrode current collector include aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel-type LiMnO ₄ , and olivine-type LiFePO ₄ . The positive electrode active material layer may appropriately contain a binder, a conductive material, etc. in addition to the positive electrode active material.

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 the negative electrode current collector include copper foil. Examples of negative electrode active materials include carbon materials such as graphite, non-graphitizable carbon materials, easily graphitizable carbon materials, and composite carbon bodies, as well as silicon, tin, metallic lithium, and various alloy materials.

The nonaqueous electrolyte is not particularly limited, but an electrolyte in which an electrolyte is dissolved in an organic solvent can be used. Examples of organic solvents include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

《Method for manufacturing electricity storage device》
A method for manufacturing an electricity 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 or more and 500 mm or less, preferably 80 mm or more and 500 mm or less, and a length of 200 m or more and 10,000 m or less, preferably 1,000 m or more and 6,000 m or less. Next, the layers are laminated in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator and wound into a circular or flat spiral shape to obtain a wound body. It can be manufactured by housing the wound body in a device can (for example, a battery can) and further injecting an electrolyte. Alternatively, the electrode and the separator may be folded to form a wound body, which is then placed in a device container (for example, an aluminum film), and an electrolyte solution may be poured into the device container.

At this time, the wound body can be pressed. Specifically, 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 so that the coating layer and the active material layer face each other, and then pressed. An example of how to do this can be given.

The pressing temperature is preferably T _1.00 or higher, which is a temperature at which adhesiveness can be effectively developed. In addition, _T1.00 indicates the minimum value of DDSC from 0°C to 150°C when DDSC is the value obtained by differentiating the heat flow difference per unit time measured by DSC (differential scanning calorimetry) with temperature. It's temperature. By pressing at a temperature of T _1.00 or higher, the coating layer is sufficiently deformed and good adhesive strength can be obtained. For example, the temperature is preferably 35°C or higher. In order to suppress clogging of holes or thermal shrinkage in the separator caused by hot pressing, the pressing temperature is preferably lower than the melting point of the material contained in the base material, and more preferably 130° C. or lower. From the viewpoint of suppressing clogging of holes in the separator, the press pressure is preferably 20 MPa or less. The pressing time may be 1 second or less when using a roll press, and may be several hours when using a surface press, and is preferably 2 hours or less from the viewpoint of productivity. By using the separator for an electricity storage device of this embodiment and going through the above manufacturing process, pressback can be suppressed when a wound body consisting of an electrode and a separator is press-molded. Therefore, it is possible to suppress a decrease in yield in the device assembly process and shorten the production process time.

Adhesiveness may be imparted to the wound body without pressing. Specifically, the wound body is housed in a device can and an electrolytic solution is injected, and the pressure generated in the device can when manufacturing an electricity storage device, or due to the expansion and contraction of the electrode due to charging and discharging of the electricity storage device. An example of a method of imparting adhesiveness between the covering layer of the separator and the opposing electrodes by applying pressure can be exemplified.

The electricity storage device manufactured as described above, especially the lithium ion secondary battery, has excellent battery characteristics (rate characteristics) and long-term continuous operation durability (cycle characteristics).

Hereinafter, embodiments of the present disclosure will be specifically described using Examples and Comparative Examples, but the present disclosure is not limited to these Examples and Comparative Examples.

《Measurement and evaluation method》
<Thickness of the inorganic filler portion of the coating layer, slope ratio of the coating layer, and protrusion amount of the particulate polymer>
The separator was freeze-fractured, and its cross section was confirmed using a SEM (model S-4800, manufactured by HITACHI). From the obtained visual field, the thickness of the inorganic filler portion of the coating layer, the slope ratio of the coating layer, and the amount of protrusion of the particulate polymer were measured. Specifically, a sample of the separator was cut into a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The dyed sample and ethanol were placed in a gelatin capsule, and after freezing with liquid nitrogen, the sample was cut with a hammer. Osmium was deposited on the cut sample and observed at an acceleration voltage of 1.0 kV and a magnification of 5000 times. As schematically shown in Figure 2, in the SEM image of the cross section of the cut sample, the distance from the substrate-coating layer boundary line to the outer surface of the coating layer in the inorganic filler part of the coating layer is The thickness L1 (μm) of the filler portion was measured. In addition, the maximum distance L2 (μm) from the substrate-coating layer boundary line to the outer surface of the inorganic filler of the coating layer formed in an inclined manner, and the maximum distance L3 ( μm), and the slope 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 slope ratio L2/L1 of the coating layer, the coverage ratio (L2-L1)/(L3-L1) of the protruding portion, and the protrusion amount L3-L1 of the particulate polymer were measured at 200 points, and the average value was determined. .

As a method of measuring L1, L2, and/or L3, it is also possible to use a method of determining each L1 value while polishing a cross section to be observed by SEM.

<180° peel strength>
Attach the side of the separator cut out to 2 mm x 7 mm opposite the coating layer to be measured to a glass plate with double-sided tape, and attach tape (product name "Mending Tape MP-12", manufactured by 3M Company) to the coating layer. Ta. Peel off 5 mm of the tip of the tape, and use a tensile testing machine (Model: AG-IS, SLBL-1kN, manufactured by Shimadzu Corporation) to chuck the tip of the tape so that the tape is peeled off at an angle of 180° to the surface direction of the separator. A tensile test was conducted at a tensile speed of 50 mm/sec, a temperature of 25 degrees, and a relative humidity of 40%, and the tensile strength (gf/cm) was measured.

<Friction test>
The static friction coefficient of the surface of the separator sample on which the coating layer was formed was determined using an MH-3 friction tester manufactured by Toyo Seiki Seisakusho, using table material SKD61 (surface roughness Ra: 0.4 μm), thread mass 200 g, Measured twice in TD under the conditions of load range 2N, contact area 63mm x 63mm (felt material), contact feeding speed 100mm/min, measurement distance 30mm, temperature 23℃, and humidity 50%, and the average of them. It was calculated by determining the value.

<Contact ratio between protruding particulate polymer and base material>
The separator was freeze-fractured, and its cross section was confirmed using a 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 a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The dyed sample and ethanol were placed in a gelatin capsule, and after freezing with liquid nitrogen, the sample was cut with a hammer. Osmium was deposited on the cut sample and observed at an acceleration voltage of 1.0 kV and a magnification of 5000 times. Among the particulate polymers protruding from the thickness of the inorganic filler part in the SEM image, the number of particles in contact with the base material was counted for 200 particulate polymers with a fractured surface, and the protruding particles were It was defined as the contact ratio between the polymer and the base material.

<Ratio of the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer>
The separator was freeze-fractured, and its cross section was confirmed using a 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 a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The dyed sample and ethanol were placed in a gelatin capsule, and after freezing with liquid nitrogen, the sample was cut with a hammer. Osmium was deposited on the cut sample and observed at an acceleration voltage of 1.0 kV and a magnification of 5000 times. Using the SEM image, we observed 200 particulate polymers present on the cut surface, and counted the number of particulate polymers that protruded from the thickness of the inorganic filler part of the coating layer. It was taken as the ratio of the number of particulate polymers protruding from the thickness.

<Methylene chloride soluble content>
The methylene chloride soluble content in the base material and separator was measured by the following method. The base material or separator sampled in a size of 100 x 100 mm was neutralized and weighed using a precision balance (W ₀ (g)). Subsequently, 200 ml of methylene chloride was added to the sealed container, and the separator was immersed at room temperature for 15 minutes. Thereafter, the separator was taken out, dried at room temperature for 3 hours, static electricity removed in the same manner as above, and weighed using a precision balance (W ₁ (g)). The methylene chloride soluble content was determined using the following formula.
Methylene chloride soluble content (mass%) = {(W ₀ - W ₁ )/W ₀ }×100

<Total amount of metal cations>
0.60 g of the separator was placed in a Teflon (registered trademark) pressure decomposition container, 10 ml of sulfuric acid was added thereto, the container was sealed, and the container was 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 diluted to obtain a sample solution. The sample solution was measured using 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 created from the standard solution. .

<Heat shrinkage rate>
As a sample, a multilayer porous membrane was cut to a length of 100 mm in MD and 100 mm in TD, and left in an oven at 130° C. or 150° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the hot air did not directly hit the sample. After taking out the sample from the oven and cooling it, the length (mm) was measured, and the heat shrinkage rate was calculated using the following formula. Measurements were performed in MD and TD, and TD was expressed as the heat shrinkage rate.
Heat shrinkage rate (%) = {(100-length after heating)/100} x 100

<Weight (g/m ² )>
The basis weight is the weight (g) of the polyolefin microporous membrane per unit area (1 m ² ). After sampling to a size of 1 m x 1 m, the weight was measured using an electronic balance (AUW120D) manufactured by Shimadzu Corporation. In addition, when it was not possible to sample 1 m x 1 m, a suitable area was cut out, the weight was measured, and then the weight was converted to the weight (g) per unit area (1 m ² ).

<Thickness of base material or separator>
Cut a 10 cm x 10 cm square sample from the base material or separator, select 9 points (3 points x 3 points) in a grid pattern, and heat it to room temperature using a micro-thickness meter (Toyo Seiki Seisakusho Co., Ltd., type KBM). Thickness (μm) was measured at 23±2°C. The average value of the obtained measured values at nine locations was calculated as the thickness of the base material or separator.

<Porosity of base material>
A 10 cm x 10 cm square sample was cut from the base material, and its volume (cm ³ ) and mass (g) were determined. Using these values and assuming the density of the base material to be 0.95 (g/cm ³ ), the porosity was determined from the following formula.
Porosity (%) = (1-mass/volume/0.95) x 100

<Density (g/ ^cm3 )>
The density of the sample was measured by the density gradient tube method (23° C.) according to JIS K7112:1999.

<Air permeability>
Regarding the base material and the separator for power storage devices, the air permeability is measured by the Gurley air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd. in accordance with JIS P-8117. did. If the coating layer is present on only one side of the substrate, the needle can be inserted from the side where the coating layer is present.

<Piercing strength>
Using a handy compression tester KES-G5 (model name) manufactured by Kato Tech, the substrate was fixed with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the central part of the fixed base material using a needle with a tip radius of curvature of 0.5 mm at a puncture speed of 2 mm/sec in an atmosphere of 25°C to determine the maximum puncture load. was measured and defined as puncture strength (gf). If the coating layer is present on only one side of the substrate, the needle can be inserted from the side where the coating layer is present.

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

The average pore diameter d (μm) of the polyolefin microporous membrane is determined by the air permeation rate constant R _gas (m ³ /(m ² sec Pa)) and the water permeation rate constant R _liq (m ³ /(m ² sec Pa)).・Pa)), air molecular velocity ν (m/sec), water viscosity η (Pa・sec), standard pressure Ps (=101325Pa), porosity ε (%), film thickness L (μm), the following It was calculated using the formula.
d=2ν×(R _liq /R _gas )×(16η/3Ps)×10 ⁶

Here, R _gas was determined from the air permeability (sec) using the following formula.
R _gas =0.0001/(air permeability x (6.424 x 10 ^-4 ) x (0.01276 x 101325))

Further, R _liq was determined from the water permeability (cm ³ /(cm ² ·sec · Pa)) using the following formula.
R _liq = water permeability/100

The water permeability was determined as follows. A thermoplastic polymer-containing layer soaked in ethanol in advance was set in a stainless steel cell with a diameter of 41 mm, and after washing the ethanol in this layer with water, water was allowed to permeate with a pressure difference of about 50,000 Pa for 120 seconds. The amount of water permeable per unit time, unit pressure, and unit area was calculated from the amount of water permeable (cm ³ ) after the passage of time, and this was defined as the water permeability.

In addition, ν is calculated from the gas constant R (=8.314), absolute temperature T (K), pi, and average molecular weight of air M (=2.896×10 ⁻² kg/mol) using the following formula. I asked for it.
ν=((8R×T)/(π×M)) ^1/2

<Glass transition temperature of thermoplastic polymer>
An appropriate amount of an aqueous dispersion containing a thermoplastic polymer (solid content = 38 parts by mass or more and 42 parts by mass or less, pH = 9.0) was placed in an aluminum dish and allowed to stand at room temperature for 24 hours to obtain a dry film. Approximately 17 mg of the dried film was filled into an aluminum container for measurement, and a DSC curve and a DSC curve in a nitrogen atmosphere were obtained using a DSC measuring device (manufactured by Shimadzu Corporation, model name: "DSC6220"). The measurement conditions were as follows.
1st stage heating program: Start at 30°C, raise the temperature at a rate of 10°C per minute. After reaching 150°C, maintain for 5 minutes.
Second stage temperature reduction program: The temperature is lowered from 110℃ at a rate of 10℃ per minute. After reaching -50°C, maintain for 5 minutes.
Third stage heating program: Raise the temperature from -50°C to 150°C at a rate of 10°C per minute. DSC and DDSC data were acquired during this third stage of temperature rise.

The glass transition temperature was determined for the obtained DSC curve by the method described in JIS-K7121. Specifically, for a straight line that is the same distance in the vertical axis direction from a straight line that extends the baseline on the low temperature side of the DSC curve toward the high temperature side, and a straight line that extends the baseline on the high temperature side of the DSC curve toward the low temperature side, The temperature at the point where the curve of the stepwise change portion of the glass transition intersects was defined as the glass transition temperature (Tg).

<Aspect ratio of inorganic filler in coating layer>
The surface of the osmium-deposited separator for electricity storage devices was measured by observing it using a scanning electron microscope (SEM) (model "S-4800", manufactured by HITACHI) at an acceleration voltage of 1.0 kV and a magnification of 10,000 times. The aspect ratio was determined by image processing the inorganic filler in the coating layer using a SEM image. Even when the inorganic fillers were bonded to each other, the vertical and horizontal lengths of the inorganic filler alone could be clearly recognized, and the aspect ratio was calculated based on these. Specifically, 10 inorganic fillers were selected whose vertical and horizontal lengths could be clearly recognized, and the average value of the long axis of each inorganic filler divided by the short axis length was taken as the aspect ratio. . If there were fewer than 10 objects whose vertical and horizontal lengths could be clearly recognized in one field of view, 10 objects were selected from images of multiple fields of view.

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

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

<Particle size distribution of particulate polymer in coating layer>
The cross section of the osmium-deposited separator for a power storage device was measured by observing it using a scanning electron microscope (SEM) (model "S-4800", manufactured by HITACHI) at an acceleration voltage of 1.0 kV and a magnification of 10,000 times. Specifically, the area circle equivalent diameter is measured for 200 arbitrary particulate polymers, the number average particle diameter MN and the volume average particle diameter MV are determined from these values, and the particle size distribution of the particulate polymer is determined. was calculated as MV/MN.

<Surface observation of coating layer and Voronoi division>
The surface of the osmium-deposited separator for power storage devices was examined using a scanning electron microscope (SEM) (model "SU-8220", manufactured by HITACHI) and energy dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", manufactured by Oxford). At this time, the SEM detector selected secondary electrons, the acceleration transmission was 3 kV, the number of mapping integrations was 20 times, and the magnification was 500 times depending on the particle size of the particulate polymer. Alternatively, mapping measurements of carbon atoms on the surface of the coating layer on the separator at 3000 times were carried out in 10 fields of view as shown in Figure 7.The Voronoi The area of the polygon (s _i ), the total number of Voronoi polygons (n), the mean value (m), the standard deviation (sd), and the coefficient of variation (cv) were each obtained as the average value of 10 visual fields. After performing Gaussian Blur processing (Sigma = 5) on the carbon atom mapping image using image processing software (ImageJ), it was binarized using the Threshold function (Auto), and further watershed processing was performed. This processed image was subjected to Voronoi division using the cv2.Subdiv2D.getVoronoiFacetList method of the opencv-python library (version 4.5.4.60) of the Python programming language. Areas that were not defined were not used to calculate the area of the Voronoi polygon.

<Rate characteristics>
a. Preparation of positive electrode As a positive electrode active material, 90.4 parts by mass of nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (element ratio), density 4.70 g/cm ³ ), 1.6 parts by mass of graphite powder (KS6) (density 2.26 g/cm ³ , number average particle diameter 6.5 μm) and acetylene black powder (AB) (density 1.95 g/cm ³ , number average particle size 6.5 μm) as conductive additives. 3.8 parts by mass of polyvinylidene fluoride (PVdF) (average particle diameter 48 nm) and 4.2 parts by mass of polyvinylidene fluoride (PVdF) (density 1.75 g/cm ³ ) as a binder were mixed, and these were mixed with N-methylpyrrolidone (NMP). ) to prepare a slurry. This slurry was applied using a die coater to one side of an aluminum foil with a thickness of 20 μm, which will serve as the positive electrode current collector. After drying at 130°C for 3 minutes, the positive electrode was formed by compression molding using a roll press machine. Created. The amount of positive electrode active material applied at this time was 109 g/m ² .

b. Preparation of Negative Electrode 87.6 parts by mass of graphite powder A (density 2.23 g/cm ³ , number average particle size 12.7 μm) and graphite powder B (density 2.27 g/cm ³ , number average particle size) were used as negative electrode active materials. 9.7 parts by mass of ammonium salt of carboxymethyl cellulose as a binder (in terms of solid content) (solid content concentration 1.83 parts by mass aqueous solution), and 1.7 parts by mass of diene rubber latex. (solid content equivalent) (solid content concentration 40 parts by mass aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was coated on one side of a 12 μm thick copper foil serving as a negative electrode current collector using a die coater, dried at 120° C. for 3 minutes, and then compression molded using a roll press to produce a negative electrode. The amount of negative electrode active material applied at this time was 5.2 g/m ² .

c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte is prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1:2 (volume ratio) to a concentration of 1.0 mol/L. Prepared.

d. Battery Assembly A separator or base material was cut out into a circle with a diameter of 24 mm, and a positive electrode and a negative electrode were each cut into a circle with a diameter of 16 mm. The negative electrode, the separator or base material, and the positive electrode were stacked in this order so that the active material surfaces of the positive electrode and negative electrode faced each other, and the mixture was housed in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil serving as the negative electrode, and the lid was in contact with the aluminum foil serving as the positive electrode. A battery was assembled by injecting 0.4 ml of the non-aqueous electrolyte into this container and sealing it.

e. Evaluation of rate characteristics d. After charging the simple battery assembled at 25°C with a current value of 3 mA (approximately 0.5 C) to a battery voltage of 4.2 V, the current value is started to be reduced from 3 mA while maintaining 4.2 V. The first charge after the battery was made was carried out for a total of about 6 hours. Thereafter, the battery was discharged to a voltage of 3.0 V at a current value of 3 mA. Next, at 25°C, charge the battery to a voltage of 4.2V with a current value of 6mA (approximately 1.0C), and then start reducing the current value from 6mA while maintaining 4.2V. Charged for hours. Thereafter, the discharge capacity when the battery was discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1C discharge capacity (mAh). Next, at 25°C, charge the battery to a voltage of 4.2V with a current value of 6mA (approximately 1.0C), and then start reducing the current value from 6mA while maintaining 4.2V. Charged for hours. Thereafter, the discharge capacity when the battery was discharged to a battery voltage of 3.0 V at a current value of 12 mA (approximately 2.0 C) was defined as 2C discharge capacity (mAh). Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was taken as the rate characteristic.
Rate characteristics (%) = (2C discharge capacity/1C discharge capacity) x 100
Evaluation criteria for rate characteristics (%) A (good): Rate characteristics are over 85% B (fair): Rate characteristics are over 80% and 85% or less C (poor): Rate characteristics are 80% or less

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

<Adhesion strength with electrode (after electrolyte injection)>
Cut the separator into a rectangular shape with a width of 20 mm x length of 70 mm, overlap it with a positive electrode cut into a size of 15 mm x 60 mm to form a laminate of the separator and electrode, insert this laminate into an aluminum laminate film, and add the electrolyte ( 0.4 ml of EC/DEC=1/2 mixture containing 1 mol/L of LiPF6 was added. After this was sealed, it was allowed to stand for 12 hours and pressed under the following conditions.
Temperature: 90℃
Press pressure: 1MPa
Press time: 1 minute The peel strength of the separator and electrode after pressing was determined by a 90° peel test at a peel rate of 50 mm/min using force gauges ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. , the peel strength was measured. At this time, the average value of the peel strength in the peel test over a length of 40 mm conducted under the above conditions was adopted as the peel strength.
Evaluation criteria for adhesion A (good): Peel strength is 5 N/m or more B (fair): Peel strength is 2 N/m or more, less than 5 N/m C (poor): Peel strength is 1 N/m or more, 2 N/m Less than D (unacceptable): Peel strength is less than 1 N/m

<Powder removal property>
A tape (manufactured by 3M Company) having a width of 12 mm and a length of 100 mm was attached to the coating layer surface of the separator. The force when peeling the tape from the sample at a speed of 50 mm/min was measured using a 90° peel strength meter (manufactured by IMADA, product name: IP-5N). Based on the obtained measurement results, the adhesive strength was evaluated using the following evaluation criteria.
A (good): 59 N/m (6 gf/mm) or more B (acceptable): 40 N/m or more and less than 59 N/m C (bad): less than 40 N/m

<Cycle characteristics>
a. Preparation of positive electrode 100 parts by mass of nickel, cobalt, aluminum composite oxide (NCA) (Ni:Co:Al=90:5:5 (element ratio), density 3.50 g/cm ³ ) as a positive electrode active material, a conductive material 1.25 parts by mass of acetylene black powder (AB) as a binder and 1.0 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and these were dispersed in N-methylpyrrolidone (NMP) to form a slurry. was prepared. This slurry was applied using a die coater to both sides of an aluminum foil with a thickness of 15 μm, which will serve as the positive electrode current collector. After drying at 130°C for 3 minutes, the positive electrode was formed by compression molding using a roll press machine. Created. The amount of positive electrode active material applied at this time was 456 g/m ² .

b. Preparation of Negative Electrode 86.0 parts by mass of graphite powder and 4.5 parts by mass of silicon oxide (SiO) were used as negative electrode active materials, and 1 part by mass of sodium salt of carboxymethyl cellulose and 1.0 parts by mass of styrene-butadiene rubber (SBR) were used as binders. A slurry was prepared by dispersing 0 parts by mass in purified water. This slurry was applied with a die coater to both sides of a 7.5 μm thick copper foil serving as a negative electrode current collector, dried at 120° C. for 3 minutes, and then compression molded with a roll press to produce a negative electrode. The amount of negative electrode active material applied at this time was 266 g/m ² .

c. Preparation of non-aqueous electrolyte By dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 25:70:5 (weight ratio) to a concentration of 1.4 mol/L, A non-aqueous electrolyte was prepared.

d. Battery Assembly A positive electrode (width 63 mm), a negative electrode (width 64 mm), and a separator (width 67 mm) were laminated and spirally wound to create a wound body. This wound body was housed in a cylindrical battery can with an outer diameter of 21 mm and a height of 70 mm, and the non-aqueous electrolyte was poured into the can and sealed to assemble a battery.

e. Evaluation of cycle characteristics d. The assembled battery was charged at 25°C with a current value of 3 mA (approximately 0.5 C) until the battery voltage reached 4.2 V, and then the battery was charged while maintaining 4.2 V until the current value reached 50 mA. Ta. Thereafter, the battery was discharged at 0.2C to a battery voltage of 2.5V, and the initial capacity was determined. Next, the battery was charged at 0.3C to a voltage of 4.2V, and then held at 4.2V until the current value reached 50mA, and then discharged at 1C to a battery voltage of 2.5V. . This was regarded as one cycle, and charging and discharging were repeated. Then, the cycle characteristics were evaluated based on the following criteria using the capacity retention rate after 500 cycles with respect to the initial capacity (capacity in the first cycle).
A: Capacity retention rate of 80% or more B: Capacity retention rate of 75% or more but less than 80% C: Capacity retention rate of less than 75%

《Example of manufacturing base material》
<Manufacture of polyolefin microporous membrane B1>
Mv is 700,000 and 45 parts by mass of homopolymer high-density polyethylene, Mv is 300,000 and 45 parts by mass of homopolymer high-density polyethylene, and Mv is 400,000 and homopolymer polypropylene and Mv is 15. 10 parts by mass of a homopolymer and polypropylene (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 obtained polyolefin mixture, and the mixture was again blended in a tumbler blender. A mixture was obtained by dry blending. The resulting mixture was fed to a twin-screw extruder by a feeder under a nitrogen atmosphere. Additionally, liquid paraffin (kinematic viscosity 7.59×10 ⁻⁵ m ² /s at 37.78° C.) 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 extruded mixture was 65 parts by mass, that is, the proportion of the resin composition was 35 parts by mass.

Next, they were melt-kneaded in a twin-screw extruder while heating to 230°C, and the obtained melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 80°C, and the extrudate was A sheet-like molded product with a thickness of 1.5 mm was obtained by molding (casting) in contact with a cooling roll and cooling and solidifying it. This sheet was stretched with a simultaneous biaxial stretching machine at a magnification of 7 x 6.4 times at a temperature of 20°C, then immersed in methylene chloride to extract and remove liquid paraffin, dried, and then stretched with a tenter stretching machine at a temperature of 20°C. It was stretched 1.8 times in the transverse direction at 130°C. Thereafter, this stretched sheet was relaxed by about 10% in the width direction and heat treated to obtain a polyolefin microporous membrane B1 as a base material. The obtained microporous polyolefin membrane was evaluated according to the above method. The evaluation results are shown in the table below.

<Manufacture of polyolefin microporous membrane B2>
A microporous polyolefin membrane B2 was produced in the same manner as the microporous polyolefin membrane B1 except that the thickness of the sheet-like molded product was changed to 0.5 mm. Table 1 shows the results of measurement and evaluation of polyolefin microporous membrane B2 in the same manner.

《Example of preparation of water dispersion of particulate polymer》
<Preparation of aqueous dispersion A1 of particulate polymer>
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., table) 0.5 part by mass (indicated as "KH1025" in the table. The same applies hereinafter) and "Adekaria Soap SR1025" (registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution, indicated as "SR1025" in the table. The same applies hereinafter) 0 .5 parts by mass were added, and the internal temperature of the reaction vessel was raised to 95°C. Thereafter, while maintaining the internal temperature of the container at 95° C., 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (denoted as “APS (aq)” in the table, the same applies hereinafter) was added.

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), and 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), trimethylolpropane triacrylate. (A-TMPT) (manufactured by Shin Nakamura Chemical Co., Ltd.) 0.4 parts by mass, γ-methacryloxypropyltrimethoxysilane (AcSi) 0.3 parts by mass, KH1025 3.0 parts by mass, SR1025 3.0 parts by mass , 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 were mixed for 5 minutes using a homomixer to emulsify. A liquid was prepared. The obtained emulsion was dropped into the reaction vessel from the dropping tank. Dripping started 5 minutes after adding the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the dropping of the emulsion, the internal temperature of the container was maintained at 80°C. At this time, the stirring bar placed in the reaction vessel was constantly stirred using a magnetic stirrer.

After the emulsion was added dropwise, the internal temperature of the reaction vessel was maintained at 80° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. The resulting emulsion was adjusted to pH = 9.0 using an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex with a concentration of 40 parts by mass (aqueous dispersion (particulate polymer) A1 ). Regarding the obtained aqueous dispersion A1, the glass transition temperature (Tg) and volume average particle diameter (D50) of the thermoplastic polymer contained therein were evaluated by the above method. The results obtained are shown in the table below.

<Preparation of water dispersions A2 to A5 of particulate polymer>
Aqueous dispersions A2 to A5 were obtained in the same manner as aqueous dispersion A1, except that the composition of the emulsion was changed as shown in the table below, and their physical properties were evaluated. The results obtained are shown in the table below.

<Preparation of water dispersion A1-1 of particulate polymer>
Aqueous dispersion A1-1 was synthesized by taking a portion of aqueous dispersion A1 and performing multistage polymerization using this as a seed polymer. Specifically, first, 20 parts by mass of water dispersion A1 in terms of solid content and 70.4 parts by mass of ion-exchanged water were placed in a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer. The mixture was added, and the internal temperature of the reaction vessel was raised to 80°C. Thereafter, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added while maintaining the internal temperature of the container at 80°C. The above is the initial preparation.

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), and 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), trimethylolpropane triacrylate. (A-TMPT) 0.4 parts by mass, γ-methacryloxypropyltrimethoxysilane (AcSi) 0.3 parts by mass, KH1025 3 parts by mass, SR1025 3 parts by mass, sodium p-styrenesulfonate (NaSS) 0.05 A mixture of 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes using a homomixer to prepare an emulsion. The obtained emulsion was dropped into the reaction vessel from the dropping tank. Dripping started 5 minutes after adding the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the dropping of the emulsion, the internal temperature of the container was maintained at 80°C. At this time, the stirring bar placed in the reaction vessel was constantly stirred using a magnetic stirrer.

After the emulsion was added dropwise, the internal temperature of the reaction vessel was maintained at 80°C for 90 minutes with stirring, and then cooled to room temperature to obtain an emulsion. The resulting emulsion was adjusted to pH=9.0 using an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40 parts by mass (aqueous dispersion A2-1). The obtained aqueous dispersion A2-1 was evaluated by the above method. The results obtained are shown in Table 2.

<Preparation of water dispersions A2-1, A3-1 to A3-11, A4-1 and A5-1>
Copolymer latex (water dispersions A2-1, A3-1 ~A3-11, A4-1 and A5-1) were obtained. Each of the obtained aqueous dispersions was evaluated by the above method. The results obtained are shown in Table 2.

<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 Co., Ltd., 25% aqueous solution NaSS: Sodium p-styrene sulfonate

・Initiator APS (aq): Ammonium persulfate (2% aqueous solution)

・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

《Separator manufacturing example》
<Example 1>
0.3 parts by mass of an ammonium polycarboxylate aqueous solution (SN Dispersant 5468 manufactured by San Nopco) and 100 parts by mass of aluminum hydroxide oxide (boehmite, average particle size 450 nm) as an inorganic filler were mixed with 100 parts by mass of water, and treated with a bead mill. A pre-coating dispersion was obtained. 0.2 parts by mass of carboxymethylcellulose (CMC) as a water-soluble polymer component was mixed with 100 parts by mass of inorganic filler in the pre-coating dispersion, and then an acrylic latex suspension (solid content concentration 40%) was added as a resin binder. %, volume average particle diameter 150 nm, Tg-10°C) as solid content and 10 parts by mass of water dispersion A3-5 were mixed and uniformly dispersed to contain a thermoplastic polymer. A coating liquid (solid content: 40 parts by mass) was prepared.

Both surfaces of the polyolefin microporous membrane B1 were surface-treated by corona discharge treatment. Thereafter, a coating liquid was applied to one side of the microporous polyolefin membrane B1 using a gravure coater. In the coating liquid supply tank, the coating liquid was stirred using a Bernoulli style agitator BEAG (manufactured by Medec), and the shear rate by the gravure coater was 80,000 sec ^-1 . At this time, the coverage area ratio of the coating layer to the polyolefin microporous membrane was 100%. Thereafter, the coating liquid after coating was dried at 60° C. to remove water, thereby obtaining a separator in which a coating layer was formed on one side of the microporous polyolefin membrane B1.

<Examples 2 to 13 and Comparative Examples 1 to 5>
Separators of Examples and Comparative Examples were obtained in the same manner as in Example 1, except that the microporous polyolefin membrane, the composition of the coating liquid, the coating conditions, etc. were changed as shown in the table below.
In Comparative Example 1, an inclined paddle agitator was used to agitate the coating solution.
In the separators of Examples 2 to 13 and Comparative Examples 1, 2, and 5, the particulate polymer was dispersed in the form of primary particles, and in the separator of Comparative Example 4, the particulate polymer was dispersed in the form of secondary particles. It was dispersed.
In addition, from the 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 base material, the coefficient of variation of the Voronoi region, etc. The polymer did not protrude from the surface of the inorganic filler portion.
Moreover, in Comparative Example 5, an aqueous dispersion containing a particulate polymer was not used.

<Poor pin removal>
When producing an electrode winding body, the pin removal property after winding was determined as follows, and the pin removal failure was evaluated by the number of items that were evaluated as failure.
After the pins were removed, those in which the separator did not change the shape of the electrode-wound body were considered to be passed, and those in which the separator became bamboo-shaped were judged to be rejected. The evaluation criteria are as follows.
(Evaluation criteria for defective rate)
A: Pin removal failure rate: 0 cells/10 cells B: Pin removal failure rate: 1 cell/10 cells C: Pin removal failure rate: 2 cells or more/10 cells

The measurement results and evaluation results of Examples and Comparative Examples are shown in the table below.

The separator for power storage devices of the present disclosure can be suitably used in various power storage devices, preferably lithium ion secondary batteries.

1 Inorganic filler 2 Particulate polymer 10 Base material (base material that is a polyolefin microporous membrane)
20 Covering layer

Claims (13)

a base material that is a polyolefin microporous membrane containing polyolefin as a main component;
a coating layer disposed on at least one surface of the base material;
A separator for a power storage device, comprising:
The coating layer includes an inorganic filler and a particulate thermoplastic polymer,
The particulate polymer includes a particulate polymer protruding from the surface of the inorganic filler portion, and the coating layer has a static friction coefficient of 0.10 or more and less than 0.40.
Separator for power storage devices. The separator for an electricity storage device according to claim 1, wherein a volume average particle diameter (MV)/number average particle diameter (MN) expressed as a particle size distribution of the protruding particulate polymer is larger than 1.50. The coating layer is formed in an inclined manner so as to become thicker toward the protruding particulate polymer,
When the thickness of the inorganic filler portion is L1 and the maximum distance from the substrate-coating layer boundary line to the outer surface of the inorganic filler formed in an inclined shape is L2, the slope rate of the coating layer L2 The separator for an electricity storage device according to claim 1, wherein the average value of /L1 is 1.2 or more. The coating layer is formed in an inclined manner so as to become thicker toward the protruding particulate polymer,
The thickness of the inorganic filler portion is L1, the maximum distance from the base material-coating layer boundary line to the outer surface of the inorganic filler formed in an inclined shape is L2, and from the base material-coating layer boundary line , when the maximum distance to the contour of the protruding particulate polymer is L3, the average value of the coverage ratio (L2-L1)/(L3-L1) of the protruding particulate polymer is 0.4 or more. The separator for an electricity storage device according to claim 1. The separator for a power storage device according to claim 1, wherein 20% or more of the protruding particulate polymer is in contact with the surface of the base material. The separator for an electricity storage device according to claim 1, wherein the 180° peel strength of the coating layer from the base material is 200 gf/cm or more. In the surface observation of the coating layer, the coefficient of variation (cv) of the area (s _i ) of the obtained Voronoi polygon obtained by Voronoi division using the protruding particulate polymer as a generating point is 0.10 or more and 0.60 or less. The separator for an electricity storage device according to claim 1. The separator for an electricity storage device according to claim 1, wherein the number of the protruding particulate polymers is 50% or more of the total number of particulate polymers included in the coating layer. The separator for a power storage device according to claim 1, wherein the particulate polymer is a primary particle. The separator for an electricity storage device according to claim 9, wherein the primary particles have an average particle size of 1 μm or more and 10 μm or less. The separator for an electricity storage device according to claim 1, wherein the TD has a thermal shrinkage rate of 5% or less at 130° C. for 1 hour. The separator for an electricity storage device according to claim 1, wherein the TD has a thermal shrinkage rate of 5% or less at 150° C. for 1 hour. An electricity storage device comprising the separator for an electricity storage device according to any one of claims 1 to 12.

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