JP6718669B2 - Storage device separator winding body - Google Patents

Description

The present invention relates to a separator wound body that is preferably used for an electricity storage device, a method for manufacturing the same, a lithium ion secondary battery including a separator that is obtained from the separator wound body, and a method for manufacturing the same.

Microporous membranes are widely used as separation or selective permeation separation membranes for various substances, separators, etc., and examples of their applications include microfiltration membranes, fuel cell separators, condenser separators, or functional materials as base materials. The base material for the functional film, the separator for the battery, and the like for filling the inside of the hole to bring out a new function. Among them, a polyolefin microporous film is preferably used as a separator for lithium ion batteries widely used in notebook personal computers, mobile phones, digital cameras and the like.

The separator may be wound and used (see Patent Documents 1 and 2). For example, Japanese Patent Application Laid-Open No. 2004-242242 discloses a technique that maintains the film performance during winding and prevents winding deviation by increasing the mechanical strength and elastic modulus of the wound film. Patent Document 2 discloses a microporous film that is excellent in thickness uniformity and is suitable as a separator for a lithium-ion secondary battery by winding the microporous film around a core having a specific outer diameter and surface roughness. Techniques that can be obtained are disclosed.

In recent years, in particular, due to the miniaturization and thinning of portable equipment, miniaturization or thinning has been demanded for power storage devices such as lithium-ion secondary batteries. On the other hand, in order to make it possible to carry the electricity storage device for a long time, the capacity of the electricity storage device has been increased by improving the volume energy density.

Here, in the separator, there is a characteristic that the battery reaction is quickly stopped when abnormally heated (fuse characteristic), and there is a dangerous situation that the positive electrode material and the negative electrode material directly react while maintaining the shape even at high temperature. In addition to the performance related to safety that has been conventionally demanded such as prevention performance (short-circuit property), from the viewpoint of uniform charging/discharging current and suppression of lithium dendrite, improvement in adhesion with the electrode is required. There is. Under such circumstances, coating of an adhesive polymer onto a polyolefin microporous film has been performed as an attempt to provide the separator with adhesive properties (see Patent Documents 3 and 4).

JP, 10-340715, A International Publication No. 2011/024849 International Publication No. 2011/0405062 International Publication No. 2014/0176751

In recent years, due to the demand for high output of batteries and the demand for thinning of laminated batteries, there is an increasing demand for thinning the battery separator. However, in the conventional separators described in Patent Documents 1 to 4, when the separator becomes thin, the film strength of the separator becomes insufficient, the separator is deformed when the battery is wound, and the battery initial failure rate increases. There is a problem called.

In addition, the demand for thinner and thinner mobile batteries is increasing due to the demand for smaller or thinner mobile devices. However, thin laminated batteries have insufficient bending resistance and malfunction due to battery deformation. There is a problem to do.

In view of the above problems, the present invention provides a separator wound body for an electricity storage device, which suppresses an initial failure of the electricity storage device, has excellent bending resistance of a laminate type electricity storage device, and ensures adhesion between an electrode and a separator. The purpose is to do.

As a result of intensive studies, the present inventors have controlled the unwinding force when unwinding the separator from the wound body of the battery separator having the thermoplastic polymer coating layer containing the adhesive polymer within a certain range. By doing so, they have found that the above problems can be solved, and completed the present invention.
That is, the present invention is as follows.
[1]
A separator winding body for an electricity storage device comprising a winding core and an electricity storage device separator wound around the winding core,
The separator has a polyolefin microporous membrane, and a thermoplastic polymer coating layer coating at least a part of at least one surface of the polyolefin microporous membrane,
The thermoplastic polymer coating layer contains no filler, and the unwinding force when unwinding the separator from the wound body at a speed of 5 mm/sec is 10 mN/10 mm or more and 750 mN/10 mm or less,
The separator wound body for the electricity storage device.
[2]
The separator winding body for an electricity storage device according to [1], wherein the unwinding force is 10 mN/10 mm or more and 500 mN/10 mm or less.
[3]
The separator wound body for an electricity storage device according to [1] or [2], wherein the polyolefin microporous film has an average thickness of 1 μm or more and 10 μm or less.
[4]
The separator wound body for an electricity storage device according to any one of [1] to [3], wherein the polyolefin microporous film has an average thickness of 1 μm or more and 6 μm or less.
[5]
The separator wound body for an electricity storage device according to any one of [1] to [4], wherein the average particle diameter of the granular thermoplastic polymer contained in the thermoplastic polymer coating layer is 500 nm or more and less than 3000 nm.
[6]
The separator wound body for an electricity storage device according to [5], wherein the granular thermoplastic polymer has an average particle diameter of 1000 nm or more and less than 2000 nm.
[7]
The separator wound body for an electricity storage device according to [5] or [6], wherein the granular thermoplastic polymer is a polymer containing a monomer unit formed by polymerizing a (meth)acrylate monomer.
[8]
At least one of the glass transition temperatures of the granular thermoplastic polymer is present in a region of less than 20° C. when measured by a differential scanning calorimetry method, [5] to [7]. A separator wound body for an electricity storage device.
[9]
The electricity storage device separator wound body according to any one of [1] to [8], wherein the winding core has an outer diameter of 127 mm to 381 mm.
[10]
A lithium ion secondary battery comprising the separator rewound from the separator winding body for an electricity storage device according to any one of [1] to [9].

According to the present invention, it is possible to provide a separator wound body for an electricity storage device, which has a good initial failure rate of the electricity storage device, excellent bending resistance of the laminate-type electricity storage device, and ensures the adhesion between the electrode and the separator. ..

Hereinafter, modes for carrying out the present invention (hereinafter, abbreviated as “this embodiment”) will be described in detail. The present invention is not limited to the following embodiments, but can be modified in various ways within the scope of the invention.

[Separator wound body for electricity storage device]
In this embodiment, a power storage device separator (hereinafter, also simply referred to as “separator”) is wound around the winding core. The separator has a polyolefin microporous membrane (hereinafter, also simply referred to as “microporous membrane”), and a thermoplastic polymer coating layer coating at least a part of the surface of at least one of the microporous membranes. In the present embodiment, the thermoplastic polymer coating layer does not contain an inorganic filler or an organic filler (hereinafter, also simply referred to as “filler”).

Specific examples of the inorganic filler not included in the thermoplastic polymer coating layer include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide; silicon nitride, titanium nitride, boron nitride. Nitride ceramics such as; silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, seri Ceramics such as site, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; glass fiber and the like.

Specific examples of organic fillers not included in the thermoplastic polymer coating layer include crosslinked polyacrylic acid, crosslinked polyacrylic acid ester, crosslinked polymethacrylic acid, crosslinked polymethacrylic acid ester, crosslinked polymethylmethacrylate, and crosslinked polysilicone (polymethylmethacrylate). Silsesquioxane), crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, polyamideimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. crosslinked polymer fine particles; polysulfone, Examples thereof include heat-resistant polymer fine particles such as polyacrylonitrile, aramid, and polyacetal.

In the present embodiment, when the separator is unwound at a speed of 5 mm/sec from the wound body in which the separator for the electricity storage device is wound around the winding core, the unwinding force is 10 mN/10 mm or more and 750 mN/10 mm or less. is there. By adopting such a configuration, it is possible to provide a power storage device having a good initial failure rate and a laminate-type power storage device having excellent bending resistance.

Here, the "wound body" refers to a wound core on which a microporous film having a uniform width is wound by a predetermined length. The winding length and width are not particularly limited, but the winding length is usually 50 m to 10000 m, and the width is several mm to 1000 mm. When the microporous membrane is used as a separator for a lithium ion secondary battery, the winding length is usually 500 m to 5000 m and the width is about 20 mm to 500 mm.

Here, the "winding core" (hereinafter also referred to as "core") has a cylindrical outer shape such as a paper tube used for winding a microporous membrane, a cylindrical winding core made of ABS resin or phenol resin, and the like. Refers to a core that is a shape. The outer diameter of such a winding core is preferably 5 inches or more (that is, 127 mm or more), more preferably 6 inches or more, and further preferably from the viewpoint of relaxing winding tightness after winding the microporous membrane. It is at least 8 inches, particularly preferably at least 9 inches. The upper limit of the outer diameter of the winding core is not limited, but from the viewpoint of handling, the outer diameter of the winding core is preferably 20 inches or less, more preferably 15 inches or less (that is, 381 mm or less). In this embodiment, 1 inch can be converted to 25.4 mm.

The width (length) of the winding core is usually about several mm to 1000 mm, but the present invention is more effective as the width is wider. Therefore, it is preferably 10 mm or more and 1000 mm or less, more preferably 50 mm or more and 1000 mm or less, and particularly preferably. It is 100 mm or more and 1000 mm or less. This is because a wider one is more susceptible to the quality of the winding core.

Here, the "rewinding force" is the force required to rewind the separator from the wound body described above at a certain constant speed. The smaller the number, the lighter the rewinding, that is, the tape is unwound. Indicates that it is easy. The unit of the unwinding force is mN/10 mm, which is used after being converted into a 10 mm width. In the present embodiment, the rewinding force is preferably 750 mN/10 mm or less, more preferably 500 mN/10 mm or less.

When the unwinding force is 750 mN/10 mm or less, the electricity storage device formed by using the separator unwound from the separator winding body has an excellent initial failure rate. Here, the initial failure rate is evaluated by evaluating the initial charge/discharge efficiency of the electricity storage device manufactured using the separator according to the present embodiment, and the case where the initial charge/discharge efficiency is 85% or less is determined to be defective. The percentage of defective batteries in the total number of power storage devices. This defective rate is preferably less than 40%, more preferably less than 20%.

Here, it is not clear about the mechanism that the smaller the unwinding force of the separator winding body is, the better the initial failure rate of the electricity storage device produced from it is. However, when the unwinding force is large, when the electricity storage device is wound, Since the separator is pulled, it is considered that the stretching and the winding in the state where the length in the width direction is shortened have an influence. As described above, it is considered that this tendency has become more prominent in recent years because the separators have become thinner.

It is considered that the method for adjusting the unwinding force within the range described above correlates with the thermoplastic polymer coating layer that is the separator adhesive layer. In particular, the material, shape, etc. of the thermoplastic polymer coating layer are considered to be correlated with this method.
As a material for the thermoplastic polymer coating layer, a diene polymer, an acrylic polymer or a fluorine polymer is considered to be preferable.
Moreover, when the thermoplastic polymer is coated on the microporous film and then observed by an observation method using a scanning electron microscope (also referred to as SEM) described later, the shape of the thermoplastic polymer is granular and It is considered that the average particle diameter of the thermoplastic polymer is preferably 500 nm or more and less than 3000 nm, and more preferably 1000 nm or more and less than 2000 nm. Here, "granular" refers to a state in which each thermoplastic polymer has a contour in SEM measurement, and has an elongated shape, a spherical shape, a polygonal shape, or the like. Good.

The separator according to the present embodiment has a microporous film and a thermoplastic polymer coating layer that covers at least a part of at least one surface of the microporous film.

The polyolefin microporous membrane has an average thickness (hereinafter, also referred to as “film thickness”) of preferably 11 μm or less, more preferably 10 μm or less, and further preferably 6 μm or less. When the average thickness of the polyolefin microporous film is 11 μm or less, when a laminate-type electricity storage device having a constant thickness is produced using the separator, the lamination-type electricity storage device has a bending resistance of more than 11 μm in average thickness. Is superior to the case of using. The mechanism by which the bending resistance is excellent is not clear, but it is presumed that the polyolefin microporous membrane functions as a reinforcing material.
The lower limit of the average thickness of the polyolefin microporous film is preferably 1 μm or more, 1.5 μm or more, or 2 μm or more from the viewpoint of bending resistance of the laminate-type electricity storage device.

[Thermoplastic polymer coating layer]
In the present embodiment, the thermoplastic polymer coating layer that covers at least a part of the surface of at least one of the microporous polyolefin membranes does not contain a filler, but contains a thermoplastic polymer.

The thermoplastic polymer used in the present embodiment is not particularly limited, but examples thereof include polyolefin resins such as polyethylene, polypropylene and α-polyolefin; fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene and copolymers containing them. A diene polymer containing a conjugated diene such as butadiene or isoprene as a monomer unit or a copolymer containing the same and a hydride thereof; an acrylic polymer containing an acrylic ester, a methacrylic acid ester or the like as a monomer unit, or a copolymer containing the same Hydride; Rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; Polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide , A resin having a melting point and/or a glass transition temperature of 180° C. or higher, such as polyamide and polyester, and a mixture thereof. Further, as a monomer used when synthesizing the thermoplastic polymer, a monomer having a hydroxyl group, a sulfonic acid group, a carboxyl group, an amide group or a cyano group can also be used.

Among these thermoplastic polymers, a diene-based polymer, an acrylic-based polymer, or a fluorine-based polymer is preferable because it has excellent binding property with an electrode active material and strength or flexibility.
Among these, acrylic polymers are preferable from the viewpoints of the adhesion between the separator and the electrode and the bending stress of the laminated battery.

(Diene polymer)
The diene polymer is not particularly limited, but is a polymer containing a monomer unit formed by polymerizing a conjugated diene having two conjugated double bonds such as butadiene and isoprene. The conjugated diene monomer is not particularly limited, but for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2 -Methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene and the like. These may be polymerized alone or may be copolymerized.

The ratio of the monomer unit formed by polymerizing the conjugated diene in the diene polymer is not particularly limited, but for example, is 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more in the total diene polymer. is there.

The diene-based polymer is not particularly limited, and examples thereof include homopolymers of conjugated dienes such as polybutadiene and polyisoprene, and copolymers of the conjugated diene and a copolymerizable monomer. The copolymerizable monomer is not particularly limited, and examples thereof include the (meth)acrylate monomer described below and the following monomers (hereinafter, also referred to as “other monomers”).

The "other monomer" is not particularly limited, but examples thereof include α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and fumaric acid; styrene. Styrene-based monomers such as chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene and divinylbenzene; ethylene, propylene, etc. Olefins; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl acetates such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl beer ether; methyl vinyl Vinyl ketones such as ketones, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic ring-containing vinyl compounds such as N-vinylpyrrolidone, vinyl pyridine and vinyl imidazole; acrylic acid such as methyl acrylate and methyl methacrylate. Ester and/or methacrylic acid ester compounds; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; amide-based monomers such as acrylamide, N-methylol acrylamide and acrylamido-2-methylpropanesulfonic acid. These may be used alone or in combination of two or more.

(Acrylic polymer)
The acrylic polymer is not particularly limited, but is preferably a polymer containing a monomer unit formed by polymerizing a (meth)acrylate monomer.

In addition, in this specification, "(meth)acrylic acid" shows "acrylic acid or methacrylic acid", and "(meth)acrylate" shows "acrylate or methacrylate."

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

The proportion of monomer units formed by polymerizing a (meth)acrylate monomer is not particularly limited, but is, for example, 40 mass% or more, preferably 50 mass% or more, and more preferably 60 mass% based on the mass of the total acrylic polymer. That is all. Examples of the acrylic polymer include a homopolymer of a (meth)acrylate monomer and a copolymer of the (meth)acrylate monomer and a copolymerizable monomer.

Examples of the copolymerizable monomer include the “other monomers” listed in the item of the diene polymer, and these may be used alone or in combination of two or more.

(Fluorine-based polymer)
The fluorine-based polymer is not particularly limited, and examples thereof include a vinylidene fluoride homopolymer and a copolymer with a homopolymerizable monomer thereof. Fluorine-based polymers are preferable from the viewpoint of electrochemical stability.

The ratio of monomer units formed by polymerizing vinylidene fluoride is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably based on the mass of all the monomers forming the fluoropolymer. It is 60% by mass or more.

The monomer copolymerizable with vinylidene fluoride is not particularly limited, for example, vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, Fluorine-containing ethylenically unsaturated compounds such as fluoroalkyl esters of acrylic acid or methacrylic acid; Fluorine-free ethylenically unsaturated compounds such as cyclohexyl vinyl ether and hydroxyethyl vinyl ether; Fluorine-free diene compounds such as butadiene, isoprene and chloroprene Can be mentioned.

Among the fluorine-based polymers, vinylidene fluoride homopolymer, vinylidene fluoride/tetrafluoroethylene copolymer, vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer and the like are preferable. A particularly preferred fluorine-based polymer is vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer, and its monomer composition is usually 30 to 90% by mass of vinylidene fluoride, 9 to 50% by mass of tetrafluoroethylene and hexafluoropropylene. It is 1 to 20 mass %. You may use these fluororesin particles individually or in mixture of 2 or more types.

Further, as a monomer used when synthesizing the thermoplastic polymer, a monomer having a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, an amide group, or a cyano group can be used.

The hydroxy group-containing monomer is not particularly limited, and examples thereof include vinyl monomers such as pentenol.

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

The monomer having an amino group is not particularly limited, but examples thereof include 2-aminoethyl methacrylate and the like.

The monomer having a sulfonic acid group is not particularly limited, but examples thereof include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)alis sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, and 2-acrylamide. Examples thereof include 2-methylpropanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid.

The monomer having an amide group is not particularly limited, and examples thereof include acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide and the like.

The monomer having a cyano group is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate.

The thermoplastic polymers used in the present embodiment may be used alone or as a mixture of two or more kinds, but it is preferable to contain two or more kinds of polymers.

The thermoplastic polymer used in the present embodiment has a glass transition temperature of less than 100° C., and the glass transition temperature is more preferably less than 100° C., further less than 60° C. from the viewpoint of the adhesion between the separator and the electrode. It is preferably below 20° C. and particularly preferably below 20° C. Here, the glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). In this specification, the glass transition temperature may be expressed as Tg.
Specifically, it is determined by the intersection of a straight line obtained by extending the low temperature side baseline in the DSC curve to the high temperature side and a tangent line at the inflection point of the stepwise change portion of the glass transition. For more details, reference can be made to the methods described in the examples.

Here, “glass transition” refers to a change in the amount of heat due to a change in the state of the polymer, which is a test piece, on the endothermic side in DSC. Such a change in the amount of heat is observed in the DSC curve as a stepwise change shape or a shape in which a stepwise change and a peak are combined.

The "step change" refers to a portion of the DSC curve until the curve deviates from the baseline until then and shifts to a new baseline. It also includes a combination of peaks and step changes.

The "inflection point" refers to a point at which the gradient of the DSC curve of the stepwise change portion becomes maximum. In addition, it can be expressed as a point at which a curve that is convex upward changes to a curve that is convex downward in a stepwise change portion.

“Peak” refers to a portion of the DSC curve after the curve is separated from the baseline and returns to the baseline again.

The “baseline” refers to a DSC curve in a temperature range in which the test piece does not undergo a transition and a reaction.

When the thermoplastic polymer is granular, it is preferred that at least one of the glass transition temperatures of the granular thermoplastic polymer be in the region of less than 20°C as measured by differential scanning calorimetry.

The glass transition temperature existing in the region of less than 20° C. exists only in the region of −30° C. or higher and 15° C. or lower from the viewpoint of maintaining good handling property while enhancing the adhesiveness between the thermoplastic polymer and the microporous film. It is preferable.

In the present embodiment, the thermoplastic polymer to be used may have a glass transition temperature in the range of less than 20°C or in the range of 20°C or higher. This brings about an effect of excellent adhesiveness and handling property between the separator and the electrode. In addition, the adhesion between the electrode and the separator, which develops due to the pressure applied during the battery production, can be improved.

In this embodiment, the thermoplastic polymer over the, with fewer than 20 ° C. region, may have two glass transition temperatures in the 20 ° C. or more areas, which are two or more thermoplastic polymers It can be achieved by blending or by using a thermoplastic polymer with a core-shell structure. The core-shell structure is a polymer having a double structure in which the polymer belonging to the central portion and the polymer belonging to the outer shell have different compositions.

In particular, the polymer blend or core-shell structure can control the glass transition temperature of the entire thermoplastic polymer by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature. Also, a plurality of functions can be imparted to the whole thermoplastic polymer. For example, in the case of blending, in particular, by blending two or more kinds of polymers having a glass transition temperature in the range of 20°C or higher and polymers having a glass transition temperature in the range of lower than 20°C, stickiness resistance and polyolefin microporosity The wettability to the film can be compatible. In the case of the core-shell structure, the adhesiveness or compatibility with other materials such as a polyolefin microporous membrane can be adjusted by changing the outer shell polymer, and by adjusting the polymer belonging to the central portion, for example, after hot pressing. Can be adjusted to a polymer with improved adhesion to the electrodes. Further, viscoelasticity can be controlled by combining a polymer having high viscosity and a polymer having high elasticity.

In the present embodiment, the glass transition temperature of the thermoplastic polymer, that is, Tg, can be appropriately adjusted by, for example, changing the monomer component used for producing the thermoplastic polymer and the input ratio of each monomer. That is, to roughly estimate from the homopolymer Tg (for example, described in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) which is generally shown for each monomer used for producing a thermoplastic polymer, and the mixing ratio of the monomer You can For example, a copolymer having a high ratio of monomers such as styrene, methyl methacrylate, and acrylonitrile, which gives a polymer having a Tg of about 100° C., has a high Tg. For example, a polymer having a Tg of about −80° C. Copolymers in which a high proportion of monomers such as butadiene to give, n-butyl acrylate and 2-ethylhexyl acrylate to give polymers with a Tg of about -50° C. are obtained with a low Tg.

Further, the Tg of the polymer can be roughly calculated from the FOX formula (the following formula (1)). As the glass transition point of the thermoplastic polymer of the present application, the one measured by the above-mentioned method using DSC is adopted.
1/Tg=W ₁ /Tg ₁ +W ₂ /Tg ₂ +... +W _i /Tg _i +... W _n /Tg _n (1)
(In the formula (1), Tg(K) is the Tg of the copolymer, Tg _i (K) is the Tg of the homopolymer of each monomer i, and W _i is the mass fraction of each monomer.)

The structure of the thermoplastic polymer in the present embodiment is preferably a granular thermoplastic polymer, at least a part of which is granular.

As a method for producing the granular thermoplastic polymer, first, a thermoplastic polymer is synthesized, and then it is synthesized by using it as a seed and further adding a monomer, an initiator and the like. As a result, the shape of the thermoplastic polymer can be made granular, and the particle size of the thermoplastic polymer can be increased.

By using such a granular thermoplastic polymer, the adhesiveness between the separator and the electrode and the handleability of the separator tend to be more excellent.
Here, the area of the granular thermoplastic polymer is measured by observing the outermost surface of the separator with an SEM (magnification: 30,000 times), as described in Examples below.

The average particle diameter of the granular thermoplastic polymer is preferably 500 nm or more and less than 3000 nm, more preferably 1000 nm or more and less than 2000 nm. It is preferably 500 nm or more from the viewpoint of the initial defect rate of the battery using the separator having the granular thermoplastic polymer in the adhesive layer, and preferably less than 3000 nm from the viewpoint of the adhesion between the separator and the electrode. Further, when the content is in the above range, the dispersibility in the solution becomes good, the concentration and viscosity of the solution at the time of coating are easily adjusted, and the uniform filling layer is easily formed, which is preferable. ..

From the viewpoint of battery characteristics such as cycle characteristics, the thermoplastic polymer in the present embodiment preferably has a swelling property in an electrolytic solution. The dried thermoplastic polymer (or thermoplastic polymer dispersion) is impregnated with the electrolytic solution for 3 hours, and the weight of the thermoplastic polymer (A) after washing is W _a , and A is stored in an oven at 150° C. for 1 hour. When the weight after placement is W _b , the electrolytic solution can be calculated by the following formula. The swelling degree is preferably 5 times or less, more preferably 4.5 times or less, still more preferably 4 times or less. The swelling degree is preferably 1 time or more, more preferably 2 times or more.
Swelling degree (times) of the thermoplastic polymer with respect to the electrolytic solution=(W _a −W _b )÷W _b

The degree of swelling of the thermoplastic polymer in the present embodiment with respect to the electrolytic solution can be adjusted by, for example, changing the monomer component to be polymerized and the input ratio of each monomer.

In the present embodiment, the gel fraction of the thermoplastic polymer is not particularly limited, but is preferably 80% or more from the viewpoint of suppressing dissolution in the electrolytic solution or maintaining the strength of the thermoplastic polymer inside the battery, and It is preferably 85% or more, more preferably 90% or more. Here, the gel fraction is determined by measuring the toluene insoluble content, as described in Examples below.
The gel fraction can be adjusted by changing the monomer component to be polymerized, the input ratio of each monomer, and the polymerization conditions.

Although the content of the thermoplastic polymer in the present embodiment is not particularly limited, while improving the adhesive force in the polyolefin microporous membrane, cycle characteristics (permeability) by clogging the pores of the polyolefin microporous membrane reducing the suppression of the 0.05 g / ^{m 2} or more 1.0 g / ^{m 2} or less is preferred. It is more preferably 0.07 g/m ² or more and 0.8 g/m ² or less, and even more preferably 0.1 g/m ² or more and 0.7 g/m ² or less.
The content of the thermoplastic polymer can be adjusted by changing the polymer concentration of the coating liquid or the coating amount of the polymer solution.

The average thickness of the thermoplastic polymer coating layer in the present embodiment is preferably 1.5 μm or less on one side, more preferably 1.0 μm or less, still more preferably 0.5 μm or less. When the average thickness of the thermoplastic polymer is 1.5 μm or less, it is preferable from the viewpoint of effectively suppressing the decrease in permeability due to the thermoplastic polymer and the sticking between the thermoplastic polymers or between the thermoplastic polymer and the polyolefin microporous film.

The average thickness of the thermoplastic polymer can be adjusted by changing the polymer concentration of the coating liquid or the coating amount of the polymer solution, the coating method, and the coating conditions.

The thickness of the thermoplastic polymer coating layer can be measured by observing the cross section of the separator using a scanning electron microscope (SEM).

The separator of the present embodiment has a thermoplastic polymer on at least a part of at least one side of a microporous polyolefin membrane. The area ratio (%) of the polyolefin microporous membrane covered with the thermoplastic polymer coating layer is preferably 95% or less, preferably 70% or less, and more preferably 50%, based on 100% of the total area of the polyolefin microporous membrane. % Or less, more preferably 45% or less, still more preferably 40% or less. The area ratio (%) is preferably 5% or more. When the area ratio is 95% or less, the clogging of the pores of the polyolefin microporous film by the thermoplastic polymer is further suppressed, and the permeability tends to be further improved. Further, when the area ratio is 5% or more, the adhesiveness tends to be further improved. Here, the area ratio is calculated by the method described in Examples below.

The area ratio can be adjusted by changing the polymer concentration of the coating liquid or the coating amount of the polymer solution, the coating method, and the coating conditions.

[Polyolefin microporous membrane]
The polyolefin microporous membrane in the present embodiment is not particularly limited, but includes, for example, a porous membrane composed of a polyolefin resin composition containing polyolefin, and it is a porous membrane containing a polyolefin resin as a main component. preferable. The polyolefin microporous film in the present embodiment, the content of the polyolefin resin is not particularly limited, from the viewpoint of shutdown performance when used as a separator for an electricity storage device, the mass fraction of all components constituting the porous film. The porous film is preferably made of a polyolefin resin composition in which the polyolefin resin occupies 50% or more and 100% or less. The proportion of the polyolefin resin is more preferably 60% or more and 100% or less, and further preferably 70% or more and 100% or less.

The polyolefin resin is not particularly limited, but refers to a polyolefin resin used for ordinary extrusion, injection, inflation, blow molding and the like, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and Homopolymers and copolymers such as 1-octene, multistage polymers and the like can be used. Further, a polyolefin selected from the group consisting of these homopolymers and copolymers and multistage polymers can be used alone or in combination.

Representative examples of the polyolefin resin include, but are not particularly limited to, 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 copolymers, polybutene, ethylene propylene rubber and the like can be mentioned.

In the present embodiment, as a material for forming the electricity storage device separator, it is particularly preferable to use a resin containing high-density polyethylene as a main component because it has a low melting point and high strength.

It is more preferable to improve the heat resistance of the porous film and use a porous film made of a resin composition containing polypropylene and a polyolefin resin other than polypropylene.

Here, the three-dimensional structure of polypropylene is not limited, and any of isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene may be used.

The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is not particularly limited, but is preferably 1 to 35% by mass, and more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, and more preferably 4 to 10% by mass.

In this case, the polyolefin resin other than polypropylene is not limited, and examples thereof include homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene. Specific examples include polyethylene, polybutene, and ethylene-propylene random copolymer.

From the viewpoint of shutdown characteristics in which pores are blocked by heat fusion, it is preferable to use polyethylene such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high-molecular-weight polyethylene as the polyolefin resin other than polypropylene. .. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density of 0.93 g/cm ³ or more measured according to JIS K7112.

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and further preferably 100,000 or more and 1 million. Is less than. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding increases, the moldability becomes good, and the entanglement of the polymers tends to increase the strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12 million or less, uniform melt kneading becomes easy, and the moldability of the sheet, particularly the thickness stability tends to be excellent, which is preferable. Further, when the viscosity average molecular weight is less than 1,000,000, the pores are likely to be clogged when the temperature rises, and a good shutdown function tends to be obtained, which is preferable. Note that, for example, instead of using a polyolefin having a viscosity average molecular weight of less than 1,000,000 alone, it is a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the viscosity average molecular weight of which is less than 1 million. Mixtures may be used.

The polyolefin microporous membrane in the present embodiment can contain any additive. Such additives are not particularly limited and include, for example, polymers other than polyolefins; inorganic particles; phenol-based, phosphorus-based, sulfur-based antioxidants, etc.; metal soaps such as calcium stearate and zinc stearate; UV absorption. Agents; light stabilizers; antistatic agents; antifogging agents; coloring pigments and the like.

The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin composition.

(Physical properties of polyolefin microporous membrane)
The puncture strength of the polyolefin microporous membrane in the present embodiment is not particularly limited, but is preferably 200 g/20 μm or more, more preferably 300 g/20 μm or more, preferably 2000 g/20 μm or less, more preferably 1000 g/20 μm or less. Is. It is preferable that the puncture strength is 200 g/20 μm or more from the viewpoint of suppressing film breakage due to the active material that has fallen off when the battery is wound. It is also preferable from the viewpoint of suppressing the risk of short circuit due to expansion and contraction of the electrodes due to charge and discharge. On the other hand, it is preferably 2000 g/20 μm or less from the viewpoint of reducing the width shrinkage due to orientation relaxation during heating. Here, the puncture strength is measured by the method described in Examples below.
The puncture strength can be adjusted by adjusting the draw ratio and the draw temperature.

The porosity of the polyolefin microporous membrane in the present embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, preferably 80% or less. The porosity of 20% or more is preferable from the viewpoint of ensuring the permeability of the separator. On the other hand, 90% or less is preferable from the viewpoint of ensuring the puncture strength. Here, the porosity is measured by the method described in Examples below.
The porosity can be adjusted by changing the draw ratio.

The air permeability of the microporous polyolefin membrane in the present embodiment is not particularly limited, but is preferably 10 sec/100 cc or more, more preferably 50 sec/100 cc or more, preferably 1000 sec/100 cc or less, more preferably 500 sec/100 cc. It is as follows. The air permeability of 10 sec/100 cc or more is preferable from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, 1000 sec/100 cc or less is preferable from the viewpoint of obtaining good charge/discharge characteristics. Here, the air permeability is measured by the method described in Examples below.
The air permeability can be adjusted by changing the stretching temperature and the stretching ratio.

The average pore size of the polyolefin microporous membrane in the present embodiment is preferably 0.15 μm or less, more preferably 0.1 μm or less, and the lower limit is preferably 0.01 μm or more. When the average pore diameter is 0.15 μm or less, it is suitable from the viewpoint of suppressing self-discharge of the power storage device and suppressing a decrease in capacity when used as a power storage device separator. The average pore diameter can be adjusted by, for example, changing the draw ratio when producing the polyolefin microporous membrane.

The short-circuit temperature, which is an index of heat resistance of the polyolefin microporous film in the present embodiment, is preferably 140° C. or higher, more preferably 150° C. or higher, still more preferably 160° C. or higher. The short-circuit temperature of 140° C. or higher is preferable from the viewpoint of the safety of the electricity storage device when it is used as an electricity storage device separator.

(Method for producing microporous polyolefin membrane)
The method for producing the polyolefin microporous membrane in the present embodiment is not particularly limited, and a known production method can be adopted. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded to be molded into a sheet, and optionally stretched, and then made to be porous by extracting the plasticizer, and the polyolefin resin composition is melt-kneaded to form a high draw. After extruding in a ratio, a method of making it porous by peeling the polyolefin crystal interface by heat treatment and stretching, melt-kneading the polyolefin resin composition and the inorganic filler into a sheet, and then stretching the polyolefin and the inorganic filler. And the like, and a method of dissolving the polyolefin resin composition and then immersing it in a poor solvent for the polyolefin to coagulate the polyolefin and at the same time remove the solvent to make it porous.

Hereinafter, as an example of a method for producing a porous film, a method of melt-kneading a polyolefin resin composition and a plasticizer to form a sheet and then extracting the plasticizer will be described.

First, the polyolefin resin composition and the plasticizer are melt-kneaded. As the melt-kneading method, for example, a polyolefin resin and, if necessary, other additives are charged into a resin kneading apparatus such as an extruder, a kneader, a Labo Plastomill, a kneading roll, a Banbury mixer, and the like, while heating and melting the resin components. A method in which a plasticizer is introduced at a ratio of and kneading is included. At this time, it is preferable to pre-knead the polyolefin resin, other additives, and the plasticizer in a predetermined ratio using a Henschel mixer or the like before introducing them into the resin kneading device. More preferably, in the pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is kneaded while side-feeding the resin kneading device. By doing so, the dispersibility of the plasticizer is enhanced, and when the sheet-shaped molded product of the melt-kneaded mixture of the resin composition and the plasticizer is stretched in a later step, it is stretched at a high magnification without breaking the film. can do.

As the plasticizer, a non-volatile solvent that can form a uniform solution at a temperature equal to or higher than the melting point of polyolefin can be used. Specific examples of such a non-volatile solvent 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 has high compatibility with polyethylene or polypropylene, and even if the melt-kneaded product is stretched, interfacial peeling between the resin and the plasticizer is unlikely to occur, and therefore uniform stretching tends to be easily performed. Therefore, it is preferable.

The ratio of the polyolefin resin composition and 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 the composition comprising the polyolefin resin composition and the plasticizer is preferably 30 to 80 mass%, more preferably 40 to 70 mass%. When the mass fraction of the plasticizer is 80% by mass or less, melt tension during melt molding does not easily become insufficient, and moldability tends to be improved. On the other hand, when the mass fraction is 30% by mass or more, the polyolefin chain is not broken even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high ratio, and a uniform and fine pore structure is formed and the strength is also high. Easy to increase.

Next, the melt-kneaded product is formed into a sheet. As a method for producing a sheet-shaped molded article, for example, a melt-kneaded product is extruded into a sheet through a T-die or the like, brought into contact with a heat conductor and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. There is a method of solidifying. As a heat conductor used for cooling and solidification, metal, water, air, or a plasticizer itself can be used, but a metal roll is preferable because of high heat conduction efficiency. At this time, it is more preferable to sandwich it between the rolls when the rolls are made to contact with each other, because the efficiency of heat conduction is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved. The die lip interval when extruded into a sheet form from the T die is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less. If the die lip interval is 400 μm or more, the dents and the like are reduced, there are few defects (for example, streaks and the like) that affect the film quality, and the film breakage and the like tend to be prevented in the subsequent stretching step. On the other hand, when the die lip interval is 3000 μm or less, the cooling rate is high and uneven cooling can be prevented, and the thickness stability of the sheet tends to be maintained.

It is preferable to stretch the sheet-shaped molded product thus obtained. As the stretching treatment, either uniaxial stretching or biaxial stretching can be preferably used, but biaxial stretching is preferred from the viewpoint of the strength of the obtained porous membrane. When the sheet-shaped molded product is biaxially stretched at a high ratio, the molecules are oriented in the plane direction, the final porous film becomes difficult to tear, and high puncture strength is obtained. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple stretching, and simultaneous biaxial stretching from the viewpoint of puncture strength improvement, stretching uniformity, and shutdown property. Stretching is preferred.

Here, the simultaneous biaxial stretching is a stretching in which the stretching in MD direction (machine direction of microporous membrane) and the stretching in TD direction (direction crossing MD of microporous membrane at an angle of 90°) are simultaneously performed. Method, and the draw ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching in the MD direction or the TD direction is performed independently, and when stretching is performed in the MD direction or the TD direction, the other direction is unrestrained or has a constant length. It should be fixed to.

The stretch ratio is preferably in the range of 20 times to 100 times in terms of surface magnification, and more preferably in the range of 25 times to 50 times. The draw ratio in each axial direction is preferably 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, and 5 times or more and 8 times or less in the MD direction and 5 times in the TD direction. It is more preferable that the range is 8 times or less. When the total area ratio is 20 times or more, sufficient strength tends to be imparted to the obtained porous film, while when the total area ratio is 100 times or less, film breakage in the stretching step is prevented and high productivity is obtained. It tends to be obtained.

Further, the sheet-shaped compact may be rolled. The rolling can be carried out by a pressing method using, for example, a double belt press. Rolling can especially increase the orientation of the surface layer portion. The rolling surface magnification is preferably more than 1 time and not more than 3 times, more preferably more than 1 time and not more than 2 times. If the rolling ratio is larger than 1, the plane orientation tends to increase and the film strength of the finally obtained porous film tends to increase. On the other hand, when the rolling ratio is 3 times or less, the difference in orientation between the surface layer portion and the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film, which is preferable.

Next, the plasticizer is removed from the sheet-shaped molded body to form a porous film. As a method of removing the plasticizer, for example, a method of immersing the sheet-shaped molded article in an extraction solvent to extract the plasticizer and sufficiently drying it can be mentioned. The method for extracting the plasticizer may be a batch method or a continuous method. In order to suppress the shrinkage of the porous film, it is preferable to restrain the end portion of the sheet-shaped molded product during a series of steps of immersion and drying. The residual amount of plasticizer in the porous film is preferably less than 1% by mass.

As the extraction solvent, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the plasticizer and has a boiling point lower than the melting point of the polyolefin resin. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine solvents such as hydrofluoroether and hydrofluorocarbon. Examples thereof include halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone. In addition, these extraction solvents may be recovered and reused by an operation such as distillation.

In order to suppress shrinkage of the porous film, heat treatment such as heat fixation or thermal relaxation can be performed after the stretching step or after the formation of the porous film. Further, the porous membrane may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like and a crosslinking treatment with an ionizing radiation or the like.

(Porous layer)
In the present embodiment, the electricity storage device separator may include a porous layer containing an inorganic filler or an organic filler and a resin binder in addition to the polyolefin microporous film and the thermoplastic polymer coating layer. The position of the porous layer includes at least a part of the surface of the polyolefin microporous film, at least a part of the surface of the thermoplastic polymer coating layer, and/or between the polyolefin microporous film and the thermoplastic polymer coating layer. The porous layer may be provided on one side or both sides of the microporous polyolefin membrane.
(Inorganic filler)
The inorganic filler used in the porous layer is not particularly limited, but it is preferable that the inorganic filler has a melting point of 200° C. or higher, has high electric insulation, and is electrochemically stable in the usage range of the lithium ion secondary battery.

The inorganic filler is not particularly limited, but examples thereof include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride. Ceramics; silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dikite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, ceramics such as silica sand, glass fibers and the like, may be used alone or in combination. Good.

Among the above, from the viewpoint of improving electrochemical stability and heat resistance of the multilayer porous film, aluminum oxide compounds such as alumina and aluminum hydroxide oxide; or ions such as kaolinite, dikite, nacrite, halloysite, and pyrophyllite. Aluminum silicate compounds having no exchange ability are preferred. Aluminum hydroxide oxide is particularly preferable as the aluminum oxide compound. As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin minerals is more preferable because it is inexpensive and easily available. Kaolin includes wet kaolin and calcined kaolin obtained by calcining it, but calcined kaolin releases crystal water during the calcining process and also removes impurities, which results in electrochemical stability. Particularly preferred.

Examples of the organic filler include crosslinked polyacrylic acid, crosslinked polyacrylic acid ester, crosslinked polymethacrylic acid, crosslinked polymethacrylic acid ester, crosslinked polymethylmethacrylate, crosslinked polysilicone (polymethylsilsesquioxane, etc.), crosslinked polystyrene. , Cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked product, polyimide, polyamide imide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate and other various cross-linked polymer particles; polysulfone, polyacrylonitrile, aramid, polyacetal, heat Examples of such particles include heat-resistant polymer particles such as plastic polyimide. The organic resin (polymer) constituting these organic fine particles is a mixture of the materials exemplified above, a modified product, a derivative, a copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer). It may be a polymer) or a crosslinked body (in the case of the above-mentioned heat resistant polymer).
Among them, crosslinked polyacrylic acid, crosslinked polyacrylic acid ester, crosslinked polymethacrylic acid, crosslinked polymethacrylic acid ester, crosslinked polymethylmethacrylate, and crosslinked polysilicone (polymethylsilsesquioxane, etc.), polyimide, polyamideimide, aramid It is preferably one or more resins selected from the group consisting of

The average particle size of the filler is preferably more than 0.1 μm and 4.0 μm or less, more preferably more than 0.2 μm and 3.5 μm or less, and more than 0.4 μm and 3.0 μm or less. Is more preferable. It is preferable to adjust the average particle size of the filler within the above range from the viewpoint of suppressing thermal contraction at high temperature even when the thickness of the porous layer is thin (for example, 7 μm or less).

In the filler, the proportion of particles having a particle size of more than 0.2 μm and 1.4 μm or less in the entire filler is preferably 2% by volume or more, more preferably 3% by volume or more, further preferably 5% by volume or more. The upper limit is preferably 90% by volume or less, more preferably 80% by volume or less.

In the filler, the proportion of particles having a particle size of more than 0.2 μm and 1.0 μm or less in the whole inorganic filler is preferably 1% by volume or more, more preferably 2% by volume or more, and the upper limit is: It is preferably 80% by volume or less, more preferably 70% by volume or less.

In the filler, the proportion of particles having a particle size of more than 0.5 μm and not more than 2.0 μm in the entire filler is preferably 8% by volume or more, more preferably 10% by volume or more, and the upper limit is: It is preferably 60% by volume or less, more preferably 50% by volume or less.

Furthermore, in the filler, the proportion of particles having a particle size of more than 0.6 μm and 1.4 μm or less in the whole filler is preferably 1% by volume or more, more preferably 3% by volume or more, and the upper limit is , Preferably 40 vol% or less, more preferably 30 vol% or less.

It is preferable to adjust the particle size distribution of the filler within the above range from the viewpoint of suppressing heat shrinkage at high temperature even when the thickness of the porous layer is thin (for example, 7 μm or less). As a method of adjusting the particle size ratio of the filler, for example, a method of reducing the particle size by pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill or the like can be mentioned.

Examples of the shape of the filler include a plate shape, a scale shape, a needle shape, a columnar shape, a spherical shape, a polyhedral shape, and a lump shape, and a plurality of fillers having the above shapes may be used in combination. The shape of the filler is not particularly limited as long as the heat shrinkage at 150° C. described later can be suppressed to 10% or less in the case of the multilayer porous film, but it is composed of a plurality of surfaces from the viewpoint of improving the permeability. Polyhedral shape, columnar shape, and spindle shape are preferable.

The proportion of the filler in the porous layer can be appropriately determined from the viewpoints of the binding property of the filler, the permeability of the multilayer porous membrane, the heat resistance, etc., but it is preferably 50% by mass or more and less than 100% by mass. It is more preferably 70% by mass or more and 99.99% by mass or less, further preferably 80% by mass or more and 99.9% by mass or less, and particularly preferably 90% by mass or more and 99% by mass or less.

(Resin binder)
The type of the resin binder is not particularly limited, but when using the electricity storage device separator as the lithium ion secondary battery separator in the present embodiment, it is insoluble in the electrolyte solution of the lithium ion secondary battery. It is preferable to use a lithium ion secondary battery that is electrochemically stable in the range of use.

Specific examples of the resin binder include, for example, polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene. Fluorine-containing rubber such as fluoroethylene copolymer; styrene-butadiene copolymer and hydride thereof, acrylonitrile-butadiene copolymer and hydride thereof, acrylonitrile-butadiene-styrene copolymer and hydride thereof, methacrylic acid ester- Acrylic ester copolymers, styrene-acrylic acid ester copolymers, acrylonitrile-acrylic acid ester copolymers, rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, etc. And a resin having a melting point and/or a glass transition temperature of 180° C. or higher such as polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

When polyvinyl alcohol is used as the resin binder, the saponification degree is preferably 85% or more and 100% or less. When the saponification degree is 85% or more, when the multilayer porous membrane is used as a battery separator, the temperature at which a short circuit occurs (short circuit temperature) is improved, and more favorable safety performance tends to be obtained, which is preferable. The saponification degree is more preferably 90% or more and 100% or less, further preferably 95% or more and 100% or less, and particularly preferably 99% or more and 100% or less. The polymerization degree of polyvinyl alcohol is preferably 200 or more and 5000 or less, more preferably 300 or more and 4000 or less, and further preferably 500 or more and 3500 or less. When the polymerization degree is 200 or more, a small amount of polyvinyl alcohol can firmly bind the inorganic filler such as calcined kaolin to the porous film, and the air permeability of the multi-layer porous film by forming the porous layer while maintaining the mechanical strength of the porous layer. This is preferable because it tends to suppress the increase in temperature. A degree of polymerization of 5000 or less is preferable because it tends to prevent gelation and the like when preparing a coating solution.

As the resin binder, a resin latex binder is preferable. When using a resin latex binder, when a porous layer containing a filler and a binder is laminated on at least one side of a polyolefin porous membrane, after dissolving a part or all of the resin binder in a solvent, the obtained solution Is laminated on at least one surface of a polyolefin porous membrane, and compared with the case where a resin binder is bound to the porous membrane by solvent removal by immersion in a poor solvent or drying, ion permeability is less likely to decrease, and high output is obtained. The characteristics tend to be easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited, and high safety tends to be obtained.

As the resin latex binder, from the viewpoint of improving electrochemical stability and binding property, an aliphatic conjugated diene monomer and an unsaturated carboxylic acid monomer, and another monomer copolymerizable therewith Those obtained by emulsion polymerization of the body are preferred. The emulsion polymerization method is not particularly limited, and a conventionally known method can be used. The addition method of the monomer and other components is not particularly limited, and any one of a batch addition method, a divided addition method, and a continuous addition method can be adopted, and one-step polymerization, two-step polymerization or multi-step polymerization can be adopted. Any of step polymerization and the like can be adopted.

The aliphatic conjugated diene-based monomer is not particularly limited, and examples thereof include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3 butadiene and 2-chloro-1. , 3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like, and these may be used alone or in combination of two or more. Among the above, 1,3-butadiene is particularly preferable.

The unsaturated carboxylic acid monomer is not particularly limited, and examples thereof include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. May be used alone or in combination of two or more. Among the above, acrylic acid and methacrylic acid are particularly preferable.

Other monomers copolymerizable with these are not particularly limited, and examples thereof include aromatic vinyl-based monomers, vinyl cyanide-based monomers, unsaturated carboxylic acid alkyl ester monomers, and hydroxyalkyl groups. And unsaturated carboxylic acid amide monomers, and the like. These may be used alone or in combination of two or more. Among the above, an unsaturated carboxylic acid alkyl ester monomer is particularly preferable. The unsaturated carboxylic acid alkyl ester monomer is not particularly limited, and examples thereof include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl. Examples thereof include maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. These may be used alone or in combination of two or more. Among the above, methyl methacrylate is particularly preferable.

In addition to these monomers, in order to improve various qualities and physical properties, monomer components other than the above may be further used.

The average particle size of the resin binder is preferably 50 to 500 nm, more preferably 60 to 460 nm, and further preferably 80 to 250 nm. When the average particle diameter of the resin binder is 50 nm or more, when a porous layer containing an inorganic filler and a binder is laminated on at least one surface of the polyolefin porous membrane, ion permeability is unlikely to be lowered and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited, and high safety is easily obtained. When the average particle size of the resin binder is 500 nm or less, good binding properties are exhibited, and when a multilayer porous film is formed, heat shrinkage tends to be good and safety tends to be excellent.

The average particle size of the resin binder can be controlled by adjusting the polymerization time, the polymerization temperature, the raw material composition ratio, the raw material charging order, the pH and the like.

The layer thickness of the porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulating properties, and is preferably 50 μm or less from the viewpoint of improving battery capacity and permeability. The layer thickness of the porous layer is more preferably 1.5 μm or more and 20 μm or less, further preferably 2 μm or more and 10 μm or less, still more preferably 3 μm or more and 10 μm or less, and particularly preferably 3 μm or more and 7 μm or less.

Layer density of the porous layer is preferably from 0.5 to 2.0 g / cm ^3, more preferably 0.7~1.5cm ^3. If the layer density of the porous layer is 0.5 g/cm ³ or more, the heat shrinkage ratio at high temperature tends to be good, and if it is 2.0 g/cm ³ or less, the air permeability tends to decrease. is there.

Examples of the method of forming the porous layer include a method of forming a porous layer by applying a coating liquid containing an inorganic filler and a resin binder on at least one surface of a porous film containing a polyolefin resin as a main component. ..

The solvent of the coating liquid is preferably one that can uniformly and stably disperse the inorganic filler and the resin binder, and examples thereof include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol and toluene. , Hot xylene, methylene chloride, hexane and the like.

Various additives such as a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent, a pH adjusting agent containing an acid or an alkali are added to the coating liquid in order to stabilize dispersion or improve coatability. May be added. These additives are preferably those which can be removed at the time of removing the solvent, but if they are electrochemically stable in the usage range of the lithium ion secondary battery, do not inhibit the battery reaction, and are stable up to about 200° C., they are porous. It may remain in the layer.

The method of dispersing the filler and the resin binder in the solvent of the coating liquid is not particularly limited as long as it is a method that can realize the dispersion characteristics of the coating liquid necessary for the coating step. Examples thereof include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high-speed impeller dispersions, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersions, mechanical stirring with stirring blades and the like.

The method of applying the coating solution to the porous film is not particularly limited as long as it can realize the required layer thickness or coating area, and examples thereof include a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, and a transfer roll. Examples include coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, and the like. ..

Furthermore, it is preferable to perform a surface treatment on the surface of the porous membrane prior to applying the coating solution, because the coating solution can be easily applied and the adhesion between the inorganic filler-containing porous layer and the porous membrane surface after application is improved. The method of surface treatment is not particularly limited as long as it does not significantly impair the porous structure of the porous film, and examples thereof include corona discharge treatment method, mechanical roughening method, solvent treatment method, acid treatment method, and ultraviolet oxidation method. Etc.

The method of removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film, for example, a method of drying at a temperature below its melting point while fixing the porous film, at a low temperature. Examples thereof include a method of drying under reduced pressure. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous film and the multilayer porous film, it is preferable to appropriately adjust the drying temperature, the winding tension, and the like.

[Separator]
In the present embodiment, the separator has a thermoplastic polymer on at least a portion of at least one surface of the microporous polyolefin membrane.

In the present embodiment, the film thickness of the electricity storage device separator is preferably 2 μm or more, more preferably 5 μm or more, and the upper limit is preferably 100 μm or less, more preferably 50 μm or less, further preferably 30 μm or less. The film thickness of 2 μm or more is suitable from the viewpoint of ensuring the strength of the separator for an electricity storage device. On the other hand, the thickness of 100 μm or less is preferable from the viewpoint of obtaining good charge/discharge characteristics.

The air permeability of the electricity storage device separator in the present embodiment is preferably 10 sec/100 cc or more, more preferably 50 sec/100 cc or more, and the upper limit is preferably 10,000 sec/100 cc or less, more preferably 1000 sec/100 cc or less. .. The air permeability of 10 sec/100 cc or more is suitable from the viewpoint of further suppressing the self-discharge of the electricity storage device when the electricity storage device separator is used. On the other hand, setting to 10,000 sec/100 cc or less is preferable from the viewpoint of obtaining good charge/discharge characteristics. The air permeability of the separator for an electricity storage device can be adjusted by the stretching temperature, the stretching ratio, the area ratio of the thermoplastic polymer, the existing form, etc. when the polyolefin microporous film is manufactured.

The short-circuit temperature, which is an index of heat resistance, of the electricity storage device separator is preferably 140° C. or higher, more preferably 150° C. or higher, and further preferably 160° C. or higher. It is preferable that the short-circuit temperature is 160° C. or higher from the viewpoint of safety of the electricity storage device when it is used as the electricity storage device separator.

(Method for manufacturing separator and its wound body)
The method of forming the thermoplastic polymer on the polyolefin microporous film is not particularly limited, and examples thereof include a method of applying a coating solution containing the thermoplastic polymer to the polyolefin microporous film.

The method of applying the coating liquid containing the thermoplastic polymer to the porous film is not particularly limited as long as it can achieve the required layer thickness or coating area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples thereof include a coater method, a die coater method, a screen printing method, a spray coating method, a spray coater coating method, and an inkjet coating method. Of these, the gravure coater method or the spray coating method is preferable because the thermoplastic polymer has a high degree of freedom in the coating shape and a preferable area ratio can be easily obtained.

When the thermoplastic polymer is applied to the polyolefin microporous film, if the coating liquid enters the inside of the microporous film, the adhesive resin fills the surface and the inside of the pores, resulting in a decrease in permeability. Therefore, a poor solvent for the thermoplastic polymer is preferable as the medium for the coating liquid. When the poor solvent of the thermoplastic polymer is used as the medium of the coating liquid, the coating liquid does not enter the inside of the microporous membrane, and the adhesive polymer is mainly present on the surface of the microporous membrane, so that the permeability is low. Is preferable from the viewpoint of suppressing a decrease in Water is preferred as such a medium. The medium that can be used in combination with water is not particularly limited, and examples thereof include ethanol and methanol.

Further, it is preferable to perform surface treatment on the surface of the porous membrane prior to coating, because the coating liquid can be easily coated and the adhesion between the porous layer and the adhesive polymer is improved. The method of surface treatment is not particularly limited as long as it does not significantly impair the porous structure of the porous film, and examples thereof include corona discharge treatment method, plasma treatment method, mechanical roughening method, solvent treatment method, and acid treatment method. , An ultraviolet oxidation method and the like.

The method of removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film. For example, a method of drying at a temperature below its melting point while fixing the porous membrane, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for the adhesive polymer to coagulate the adhesive polymer and at the same time extract the solvent. Are listed.

The electricity storage device separator is excellent in handleability during winding and rate characteristics of the electricity storage device, and is also excellent in adhesiveness and permeability between the thermoplastic polymer and the polyolefin microporous film. Therefore, the use of the electricity storage device separator is not particularly limited, but it can be suitably used for, for example, batteries such as non-aqueous electrolyte secondary batteries or capacitors, electricity storage device separators such as capacitors, and separation of substances.

The separator wound body according to the present embodiment is manufactured by slitting the separator obtained by the above method, if necessary, and winding the separator around a predetermined winding core. The separator unwound from the separator winding body can also be used for manufacturing a laminate or a battery described later.

[Laminate]
The laminate according to the present embodiment is a laminate of the separator and the electrode. The separator of this embodiment can be used as a laminate by being bonded to an electrode. Here, “adhesion” means that the above heat peeling strength between the separator and the electrode is preferably 10 gf/cm or more, more preferably 15 gf/cm or more, still more preferably 20 gf/cm or more.

The laminate is excellent in handleability during winding and rate characteristics of the electricity storage device, and is also excellent in adhesiveness and permeability between the thermoplastic polymer and the microporous polyolefin membrane. Therefore, the use of the laminate is not particularly limited, but the laminate can be suitably used, for example, in a battery such as a non-aqueous electrolyte secondary battery or a power storage device such as a capacitor or a capacitor.

As the electrodes used in the laminate of the present embodiment, those described in the item of the electricity storage device described later can be used.

The method for producing a laminate using the separator of the present embodiment is not particularly limited, but, for example, the separator of the present embodiment and the electrode are stacked, and if necessary, heated and/or pressed to produce. You can The above heating and/or pressing can be performed when the electrode and the separator are stacked. It can also be produced by heating and/or pressing a wound body obtained by winding the electrode and the separator on top of each other and winding them in a circular or flat spiral shape.

Moreover, the laminated body can be manufactured by laminating in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator in a flat plate shape and heating and/or pressing as necessary.

More specifically, the separator of the present embodiment is prepared as a vertically elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m), and the separator is The positive electrode-separator-negative electrode-separator or the negative electrode-separator-positive electrode-separator may be stacked in this order, and heated and/or pressed as necessary to manufacture.

The heating temperature is preferably 40 to 120°C. The heating time is preferably 5 seconds to 30 minutes. The pressure during pressing is preferably 1 to 30 MPa. The pressing time is preferably 5 seconds to 30 minutes. The order of heating and pressing may be such that heating is followed by pressing, pressing is followed by heating, or pressing and heating are performed simultaneously. Among these, it is preferable to perform pressing and heating at the same time.

[battery]
The separator of this embodiment can be used for a separator in a battery, a capacitor, a capacitor, or the like, or for separating substances. In particular, when used as a separator for a non-aqueous electrolyte battery, it is possible to impart adhesion to electrodes and excellent battery performance.

Hereinafter, a suitable mode in the case where the battery is a non-aqueous electrolyte secondary battery will be described.
When a non-aqueous electrolyte secondary battery is manufactured using the separator of the present embodiment, the positive electrode, the negative electrode, and the non-aqueous electrolyte are not limited, and known ones can be used.
The positive electrode material is not particularly limited, and examples thereof include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ .

The negative electrode material is not particularly limited, but examples thereof include carbon materials such as graphite, non-graphitizable carbonaceous material, graphitizable carbonaceous material, and composite carbon body; silicon, tin, metallic lithium, various alloy materials, and the like.

The non-aqueous electrolytic solution is not particularly limited, but an electrolytic solution obtained by dissolving an electrolyte in an organic solvent can be used, and as the organic solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

A method of manufacturing a battery using the separator of the present embodiment is not particularly limited, but when the electricity storage device is a secondary battery, for example, the separator of the present embodiment has a width of 10 to 500 mm (preferably 80 to 500 mm). Prepared as a vertically elongated separator having a length of 200 to 4000 m (preferably 1000 to 4000 m), and the separators are stacked in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, and have a circle or a flat shape. It can be manufactured by winding in a spiral shape to obtain a wound body, housing the wound body in a battery can, and further injecting an electrolytic solution. At this time, the above-mentioned laminated body may be formed by heating and/or pressing the wound body. It is also possible to manufacture the above-mentioned wound body by using the above-mentioned laminated body wound in a circular or flat spiral shape. In addition, the battery is a step in which a positive electrode-separator-negative electrode-separator or a negative electrode-separator-positive electrode-separator is laminated in the order of a flat plate, or the above laminate is laminated with a bag-shaped film, and an electrolyte solution is injected In some cases, it can be manufactured through a step of heating and/or pressing. The step of performing the heating and/or pressing described above can be performed before and/or after the step of injecting the electrolytic solution.

In addition, the measured values of the above-mentioned various parameters are values measured according to the measuring methods in Examples described later, unless otherwise specified.

Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples, but the present invention is not limited to the Examples. The methods for measuring or evaluating various physical properties used in the following Production Examples, Examples, and Comparative Examples are as follows. Unless otherwise stated, various measurements and evaluations were carried out under conditions of room temperature of 23° C., 1 atmospheric pressure, and relative humidity of 50%.

[Measuring method]
<Viscosity average molecular weight (hereinafter, also referred to as “Mv”)>
Based on ASRM-D4020, the intrinsic viscosity [η] at 135°C in a decalin solvent was determined, and the Mv of polyethylene was calculated by the following formula.
[Η]=0.00068×Mv ^0.67
The Mv of polypropylene was calculated by the following formula.
[Η]=1.10× 10 ⁻⁴ × Mv ^0.80

<Basis weight of polyolefin microporous membrane>
A 10 cm×10 cm square sample was cut from the polyolefin microporous film, and the weight was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. The basis weight (g/m ² ) of the membrane per 1 m ² was calculated by multiplying the obtained weight by 100 times.

<Porosity of polyolefin microporous membrane (%)>
A 10 cm×10 cm square sample was cut out from the polyolefin microporous membrane, its volume (cm ³ ) and mass (g) were determined, and the film density was calculated as 0.95 (g/cm ³ ) using the following equation.
Porosity=(volume-mass/film density)/volume×100

<Air permeability (sec/100cc)>
Based on JIS P-8117, the air permeability resistance was measured by a Gurley type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd.

<Puncture strength (g) of polyolefin microporous membrane>
Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, the microporous polyolefin membrane was fixed with a sample holder having a diameter of 11.3 mm at the opening. Then, the center portion of the fixed polyolefin microporous membrane was subjected to a puncture test in a 25°C atmosphere at a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm/sec to obtain a maximum puncture load as puncture strength ( g) was obtained.

<Average pore size (μm)>
It is known that the fluid inside the 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 small. Therefore, it is assumed that the air flow in the permeability measurement of the microporous membrane follows the Knudsen flow, and the water flow in the permeability measurement of the microporous membrane follows the Poiseuille flow.

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

Here, R _gas is calculated from the air permeability (sec) using the following equation.
Rgas=0.0001/(air permeability×(6.424×10 ⁻⁴ )×(0.01276×101325))

Further, R _liq is obtained from the water permeability (cm ³ /(cm ² ·sec·Pa)) using the following equation.
R _liq =water permeability/100

The water permeability is calculated as follows. A microporous membrane preliminarily dipped in ethanol was set in a 41 mm diameter stainless steel liquid permeation cell, the ethanol in the membrane was washed with water, and then water was permeated at a differential pressure of about 50,000 Pa for 120 seconds. From the water permeation amount (cm ³ ) at that time, the water permeation amount per unit time, unit pressure, and unit area was calculated, and this was taken as the water permeability.

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

<Thickness (μm)>
(1) Film thickness (μm) of polyolefin microporous film and separator for electricity storage device
A 10 cm x 10 cm sample was cut out from each of the polyolefin microporous film and the separator for an electricity storage device, and nine points (3 points x 3 points) were selected in a grid pattern to measure the film thickness with a micro thickness gauge (Toyo Seiki Seisakusho Ltd. ) Type KBM) at room temperature 23±2° C. The average value of the measured values at 9 points was taken as the film thickness (μm) of the polyolefin microporous film and the electricity storage device separator.

(2) Thickness of coating layer (μm)
The thickness of the thermoplastic polymer coating layer was measured by observing the cross section of the separator using a scanning electron microscope (SEM) “Model S-4800, manufactured by HITACHI”. The sample separator was cut to a size of about 1.5 mm×2.0 mm and stained with ruthenium. The dyed sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was cut with a hammer. The sample was vapor-deposited with osmium and observed at an accelerating voltage of 1.0 kV and 30,000 times to calculate the thickness of the thermoplastic polymer layer. The outermost surface region where the porous structure of the cross-section of the microporous polyolefin film was not visible in the SEM image was defined as the region of the thermoplastic polymer coating layer.

(3) Thickness of filler porous layer (μm)
By subtracting the film thickness of the polyolefin microporous film and the thermoplastic polymer coating layer from the film thickness of the electricity storage device separator, or by subtracting the film thickness of the polyolefin microporous film from the film thickness of the electricity storage device separator, the filler porosity is reduced. The layer thickness was calculated.

<Glass transition temperature of thermoplastic polymer>
An appropriate amount of the thermoplastic polymer coating liquid (nonvolatile content=38 to 42%, pH=9.0) was placed in an aluminum dish and dried in a hot air dryer at 130° C. for 30 minutes. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve under a nitrogen atmosphere were obtained with a DSC measuring device (manufactured by Shimadzu Corporation, DSC6220). The measurement conditions were as follows.
(1st stage heating program)
Start at 70°C and raise the temperature at a rate of 15°C per minute. Hold for 5 minutes after reaching 110°C.
(Second stage cooling program)
Temperature drops from 110°C to 40°C per minute. Hold for 5 minutes after reaching -50°C.
(3rd stage heating program)
The temperature is raised from -50°C to 130°C at a rate of 15°C per minute. Data of DSC and DDSC were acquired when the temperature was raised in the third step.

The intersection of the baseline (the straight line obtained by extending the baseline in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to the downward convex curve) is the glass transition temperature ( Tg).

<Gel Fraction of Thermoplastic Polymer (Toluene Insoluble Content)>
On a Teflon (registered trademark) plate, a coating solution of a thermoplastic polymer (nonvolatile content=38 to 42%, pH=9.0) was dropped with a dropper (diameter 5 mm or less), and a hot air dryer at 130° C. was used. It was dried for 30 minutes. After drying, about 0.5 g of the dried film was precisely weighed (a), taken into a 50 mL polyethylene container, 30 mL of toluene was poured therein, and shaken at room temperature for 3 hours. Then, the content was filtered through 325 mesh, and the toluene-insoluble matter remaining on the mesh was dried together with the mesh for 1 hour in a hot air dryer at 130°C. The dry weight of the 325 mesh used here was measured in advance.

After the toluene was volatilized, a dry weight (b) of the toluene insoluble matter was obtained by subtracting the previously measured 325 mesh weight from the dry matter of the toluene insoluble matter and the weight of 325 mesh. The gel fraction (toluene-insoluble matter) was calculated by the following calculation formula.
Gel fraction of thermoplastic polymer (toluene insoluble matter)=(b)/(a)×100 [%]

<Average particle size (nm) of granular thermoplastic polymer>
The average particle diameter of the granular thermoplastic polymer was determined by using an osmium vapor-deposited electricity storage device separator with a scanning electron microscope (SEM) “Model S-4800, manufactured by HITACHI” at an acceleration voltage of 1.0 kV and 30,000 times. It was measured by observing. The part of the granular thermoplastic polymer having the largest diameter was defined as the particle size, and the average value of 20 particles was defined as the average particle size.

<Swelling degree of thermoplastic polymer in electrolyte solution (swelling degree of electrolyte solvent) (times)>
After leaving the thermoplastic polymer or the solution in which the thermoplastic polymer is dispersed in an oven at 130° C. for 1 hour, the dried thermoplastic polymer is cut into 0.5 g, and ethylene carbonate:ethyl methyl carbonate=1 : 2 (volume ratio) together with 10 g of mixed solvent was placed in a 50 mL vial and allowed to infiltrate for 3 hours, then a sample was taken out, washed with the above mixed solvent, and the weight (W _a ) was measured. Then, after standing still in an oven at 150° C. for 1 hour, the weight (W _b ) was measured, and the swelling degree of the thermoplastic polymer in the electrolytic solution was measured by the following formula.
Degree of swelling electrolyte of the thermoplastic polymer _{(times) = (W a -W b)} ÷ (W b)

[Evaluation method]
<Adhesion between separator and electrode>
The adhesion between the separator and the electrode was evaluated by the following procedure.

(Preparation of negative electrode)
96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of ammonium salt of carboxymethylcellulose and 1.7% by mass of styrene-butadiene copolymer latex as a binder were dispersed in purified water to prepare a slurry. This slurry was applied on one surface of a copper foil having a thickness of 12 μm to be a negative electrode current collector by a die coater, dried at 120° C. for 3 minutes, and then compression molded by a roll press. At this time, the amount of active material applied to the negative electrode was 106 g/m ² , and the bulk density of the active material was 1.35 g/cm ³ .

(Evaluation of adhesion with electrode)
The negative electrode obtained by the above method was cut into a width of 20 mm and a length of 40 mm. An electrolytic solution (manufactured by Toyama Yakuhin Kogyo Co., Ltd.) in which ethylene carbonate and diethyl carbonate were mixed in a ratio of 2:3 (volume ratio) was placed on the electrode to such an extent that the negative electrode was immersed therein, and a separator was placed thereon. This laminate was put into an aluminum zip and pressed at 80° C. and 10 MPa for 2 minutes, then the laminate was taken out and the separator was peeled off from the electrode.
(Evaluation criteria)
◯: When the negative electrode active material adheres to an area of 30% or more of the separator.
B: When the negative electrode active material adheres to the area of 10% or more and less than 30% of the separator.
X: When the negative electrode active material adheres to an area of less than 10% of the separator.

<Measurement of rewinding force of wound body>
The unwinding force of the separator wound body was measured based on JIS-Z0237 as follows. For the measurement of the unwinding force of the wound body, the wound body manufactured in the evaluation of the initial defective rate of the battery described later was used. Using a tensile tester (Model 5544, manufactured by Instron), the wound body was fixed to a rewinding fixture, and a separator having a width of 10 to 50 mm was rewound at a speed of 5 mm/sec. The measurement was carried out in an environment of 23° C.×50% RH by rewinding so that the angle between the rewinding separator and the surface of the wound body was perpendicular, and the number of tests n=5 or more. The rewinding force (mN/10 mm) of Examples and Comparative Examples is shown in Tables 5-9.

<Evaluation of initial defective rate of battery>
(Preparation of battery)
In this evaluation, a cylindrical lithium ion battery was prepared as described below, and the evaluation was performed using it.
For the positive electrode, a positive electrode mixture containing a lithium-transition metal composite oxide as a positive electrode active material was applied almost uniformly to an aluminum foil current collector having a thickness of 15 μm, and this was cut into strips having a width of 51 mm and a length of about 750 mm. did.
For the negative electrode, a copper foil current collector having a thickness of 10 μm was coated almost uniformly with a negative electrode mixture containing a carbon powder material such as graphite capable of reversibly storing and releasing lithium ions as a negative electrode active material. Was cut into a strip having a width of 54 mm and a length of about 800 mm. These strip-shaped positive and negative electrodes are ultrasonically welded with conductive leads for applying current to the current collector that is not coated with the electrode mixture at the end of the electrode so that the conductive leads come to the predetermined positions after winding. Installed by machine.
The separators of Examples and Comparative Examples were used after being cut into strips having a width of 57 mm and a length of about 900 mm.

For the winding operation of these members, a winding device having a diameter of about 4 mm and a winding shaft having a half-split structure was used. Two separators wound in a roll shape are drawn out, sandwiched between the half-split portions of the winding shaft, and the winding shaft is rotated several times for winding, and the positive electrode and the negative electrode are inserted between the separator and the winding. .. A tension of 0.5 to 1.5 kgf/cm ² (0.05 to 0.15 MPa) is applied to the positive electrode, the negative electrode, and the separator in the direction opposite to the rotating direction of the winding shaft, and the winding misalignment during winding or Prevented loosening. After winding the positive electrode and the negative electrode, the separator was further wound several times and cut.

An insulating plate was attached to the wound body manufactured as described above, with the negative electrode side facing down and the positive electrode side facing up, and the insulating plate was housed in a battery can whose surface was nickel-plated. The electrode rod of the welding resistor was inserted into the hole in the center of the electrode, and the negative electrode lead was welded to the bottom of the battery can. Next, a groove for attaching the battery lid was formed on the upper part of the battery can, and a gasket was put on the upper side of the groove, and then the positive electrode lead and the battery lid were welded. The assembly thus obtained was placed in a vacuum dryer and kept in a vacuum atmosphere at 60° C. for about 16 hours to remove the attached water.

Next, the dried assembly was transferred into a glove box in an argon gas atmosphere, and a predetermined amount of electrolytic solution was injected. As the electrolytic solution, a solution prepared by dissolving lithium hexafluorophosphate at a concentration of 1 mol/L in a mixed solvent of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. was used. After injecting the electrolytic solution, the battery lid was lightly put in the gasket on the upper part of the battery can and mounted on the caulking machine to crimp and seal the battery can.
(Evaluation of initial defective rate of battery)
Five batteries were prepared as described above using the separators obtained in Examples or Comparative Examples, and the defective rate was evaluated based on the following criteria from the initial charge/discharge efficiency.
Battery defect rate (%)=[number of batteries having initial charge/discharge efficiency of 85% or less]/evaluated battery (5)×100
The defective rate of the battery was evaluated according to the following criteria. The evaluation results are shown in Tables 5-9.
◯: Battery defective rate is 0% or more and less than 20% Δ: Battery defective rate is 20% or more and less than 40% ×: Battery defective rate is 40% or more

<Evaluation of bending stress of laminated battery>
In this evaluation, a laminated battery (hereinafter, also referred to as a lamellar cell) was prepared as described below, and the evaluation was performed using it.

(Production of Slurry Composition for Positive Electrode and Positive Electrode)
100 parts of lithium cobalt oxide LCO (LiCoO ₂ ) (particle diameter: 12 μm) as a positive electrode active material, and acetylene black (AB35, Denka Black powder product manufactured by Denki Kagaku Kogyo KK: particle diameter 35 nm, specific surface area 68 m ² ) as a positive electrode conductive material. /G) 2.0 parts and 1.6 parts of mixed polyvinylidene fluoride (1:1 mixture of KYNAR HSV900 and KYNAR720 manufactured by Arkema) as a fluorine-containing polymer for the binder for the positive electrode and a nitrile group-containing acrylic polymer. As 0.4 parts of the polymer B1-1 in terms of solid content and an appropriate amount of NMP were stirred by a planetary mixer to prepare a slurry composition for a positive electrode.

An aluminum foil having a thickness of 15 μm was prepared as a current collector. The above positive electrode slurry composition was applied onto both sides of an aluminum foil so that the applied amount after drying was 25 mg/cm ² , dried at 60° C. for 20 minutes and 120° C. for 20 minutes, and then heat treated at 150° C. for 2 hours. Then, a positive electrode raw material was obtained. This positive electrode raw material was rolled by a roll press to prepare a sheet-shaped positive electrode composed of a positive electrode active material layer having a density of 3.9 g/cm ³ and an aluminum foil. This was cut into a width of 4.8 mm and a length of 50 cm, and an aluminum lead was connected.

(Production of Negative Electrode Slurry Composition and Negative Electrode)
90 parts of spherical artificial graphite (particle size: 12 μm) and 10 parts of SiO _x (particle size: 10 μm) as a negative electrode active material, 1 part of styrene-butadiene rubber (particle size: 180 nm, glass transition temperature: −40° C.) as a binder Then, 1 part of carboxymethyl cellulose as a thickener and an appropriate amount of water were stirred by a planetary mixer to prepare a slurry composition for a negative electrode.

A copper foil having a thickness of 15 μm was prepared as a current collector. The slurry composition for a negative electrode was applied on both sides of a copper foil so that the applied amount after drying was 10 mg/cm ₂ , dried at 60° C. for 20 minutes and 120° C. for 20 minutes, and then heat-treated at 150° C. for 2 hours. Then, a negative electrode raw material was obtained. This negative electrode raw material was rolled by a roll press to prepare a sheet-shaped negative electrode composed of a negative electrode active material layer having a density of 1.8 g/cm ³ and a copper foil. This was cut into a width of 5.0 mm and a length of 52 cm, and a nickel lead was connected.

(Manufacture of laminated battery)
The obtained sheet-shaped positive electrode and sheet-shaped negative electrode were wound using a core having a diameter of 20 mm with the separators of Examples and Comparative Examples interposed, to obtain a wound body. The wound body was compressed from one direction at a speed of 10 mm/sec until the thickness became 4.5 mm. The ratio of the major axis to the minor axis of the substantially ellipse was 7.7.

5% by mass of fluoroethylene carbonate was mixed with a mixture of ethylene carbonate and ethyl methyl carbonate in a ratio of 3 to 7 (weight ratio), and lithium hexafluorophosphate (LiPF ₆ ) was dissolved to a concentration of 1 mol/liter. Then, 2% by volume of vinylene carbonate was added to prepare a non-aqueous electrolyte.

The sheet-shaped positive electrode and the sheet-shaped negative electrode were housed in a predetermined aluminum laminate case together with 3.2 g of a non-aqueous electrolyte. After connecting the negative electrode lead and the positive electrode lead to predetermined places, the opening of the case was sealed with heat to complete the non-aqueous electrolyte battery. As described above, a laminated battery having a width of 35 mm, a height of 48 mm and a thickness of 5 mm was manufactured.

(Bending stress evaluation)
The bending stress of the laminated battery was measured using a bending tester (AG-10FD manufactured by Shimadzu Corporation). In the bending test, the laminate type battery was supported with a fulcrum interval of 10 cm, the center of the fulcrum interval was pushed from above, and the pushing speed was 1 mm/min.
The bending stress was evaluated according to the following criteria. The evaluation results are shown in Tables 5-9.
◯: Bending stress is 100 MPa or more Δ: Bending stress is 75 MPa or more and less than 100 MPa X: Bending stress is less than 75 MPa

[Production Example 1-1] (Production of microporous membrane 1A)
A homopolymer having a viscosity average molecular weight of 700,000, 45 parts by mass of homopolymer high-density polyethylene and Mv of 300,000, and 45 parts by mass of homopolymer high-density polyethylene, and a viscosity average molecular weight of 400,000. Was mixed with 10 parts by mass of a mixture of polypropylene and a homopolymer polypropylene having a viscosity average molecular weight of 150,000 (mass ratio=4:3) using a tumbler blender. To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane was added as an antioxidant, and the tumbler blender was added again. A mixture was obtained by dry blending with. The obtained mixture was fed by a feeder into a twin-screw extruder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78° C. 7.59×10 −5 m ² /s) was injected into the extruder cylinder by a plunger pump. The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the entire mixture extruded was 65 parts by mass, that is, the polymer concentration was 35 parts by mass.

Then, they are melt-kneaded in a twin-screw extruder while being heated to 230° C., and the resulting melt-kneaded product is extruded through a T-die onto a cooling roll whose surface temperature is controlled to 80° C., and the extruded product is extruded. A sheet-like molded article was obtained by bringing the sheet into contact with a cooling roll and casting to solidify by cooling. This sheet was stretched with a simultaneous biaxial stretching machine at a magnification of 7×6.4 times at a temperature of 112° C., immersed in methylene chloride to extract and remove liquid paraffin, and then dried. The film was stretched 2 times in the transverse direction at 0°C. Thereafter, this stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin microporous membrane 1A shown in Table 1.

The physical properties of the obtained polyolefin microporous film 1A were measured by the methods described above. The results obtained are shown in Table 1.

[Production Examples 1-2 to 1-9] (Production of microporous membranes 2A to 8A and 17A)
Polyolefin microporous membranes 2A to 8A and 17A were obtained by the same operations as in Production Example 1-1, except that the stretching temperature and the relaxation rate were adjusted. The obtained polyolefin microporous membranes 2A to 8A and 17A were evaluated in the same manner as in Production Example 1 by the above method.

[Production Example 2-1] (Production of microporous membrane 9A)
96.0 parts by mass of aluminum hydroxide oxide (average particle size 1.0 μm), 4.0 parts by mass of acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film forming temperature 0° C. or lower), and polycarboxylic acid. 1.0 part by mass of ammonium acid aqueous solution (SN Dispersant 5468 manufactured by San Nopco) is uniformly dispersed in 100 parts by mass of water to prepare a coating solution, which is coated on the surface of the polyolefin resin porous membrane 4A using a microgravure coater. did. Water was removed by drying at 60° C., and coating layer 1B was formed to a thickness of 2 μm to obtain microporous membrane 9A. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

[Production Example 2-2] (Production of microporous membrane 10A)
A coating layer 2B having a thickness of 3 μm was formed on one surface of the polyolefin microporous film 4A in the same manner as in Production Example 9A to obtain a microporous film 10A. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

[Production Example 2-3] (Production of microporous membrane 11A)
A coating layer 3B having a thickness of 4 μm was formed on one surface of the polyolefin microporous film 4A in the same manner as in Production Example 9A to obtain a microporous film 11A. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

[Production Example 2-4] (Production of microporous membrane 12A)
A coating layer 4B having a thickness of 7 μm was formed on one surface of the polyolefin microporous film 4A in the same manner as in Production Example 9A to obtain a microporous film 12A. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

[Production Example 2-5] (Production of microporous membrane 13A)
95.0 parts by weight of calcined kaolin (high-temperature calcined wet kaolin containing kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ) as the main component, average particle size of 1.8 μm) and acrylic latex (solid content) A concentration of 40%, an average particle size of 220 nm, a minimum film formation temperature of 0° C. or lower) 5.0 parts by mass, and an ammonium polycarboxylate aqueous solution (SN Dispersant 5468 manufactured by San Nopco Ltd.) 0.5 parts by mass in 180 parts by mass of water A coating liquid was prepared by uniformly dispersing it, and was coated on the surface of the polyolefin microporous film 4A using a microgravure coater. Water was removed by drying at 60° C., and coating layer 5B was formed to a thickness of 6 μm to obtain microporous membrane 13A. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

[Production Example 2-6] (Production of microporous membrane 14A)
Polyvinylidene fluoride resin (VdF-HFP resin) (hereinafter referred to as resin A), vinylidene fluoride/hexafluoropropylene (99/1 mol%, weight average molecular weight 350,000), and polyvinylidene fluoride resin (VdF) -HFP resin) (hereinafter referred to as resin B), vinylidene fluoride/hexafluoropropylene copolymer (95.2/4.8 mol%, weight average molecular weight 270,000), and resin A/resin B= Mixing was performed at 60/40 (mass ratio) to obtain a mixed resin.

A mixed resin of Resin A and Resin B was dissolved at a concentration of 5 mass% in a mixed solvent of dimethylacetamide/tripropylene glycol=7/3 mass ratio to prepare a coating liquid.
The obtained coating liquid was applied to both surfaces of the microporous polyolefin membrane 4A in an equal amount and a thickness of 12 μm. Then, the VdF resin and the VdF-HFP resin are solidified by immersing the polyethylene microporous membrane in a coagulation liquid (40° C.) of water/dimethylacetamide/tripropylene glycol=57/30/13 (mass ratio), Microporous film 14A was obtained. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

[Production Example 2-7] (Production of microporous membrane 15A)
As a polyvinylidene fluoride-based resin, a vinylidene fluoride/hexafluoropropylene copolymer (molar ratio 98.9/1.1, weight average molecular weight 1.95 million) was prepared.
The resin is dissolved in a mixed solvent of dimethylacetamide and tripropylene glycol (dimethylacetamide/tripropylene glycol=7/3 [mass ratio]) so that the concentration becomes 5% by mass, and a crosslinked methyl methacrylate resin filler ( A volume average particle diameter of 1.8 μm and D90-D10 of 1.3 μm) were dispersed to prepare a coating liquid. In this coating liquid, the content of the filler was 5% by mass with respect to the total amount of the polyvinylidene fluoride resin and the filler.
This coating solution is applied to both sides of the polyolefin microporous film 4A in an equal amount and a thickness of 3 μm, and a coagulating solution at 40° C. (water/dimethylacetamide/tripropylene glycol=57/30/13 [mass ratio]) Then, the microporous film 15A was obtained by immersing it in a solidified state. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

[Production Example 2-8] (Production of microporous membrane 16A)
Using VINYCOAT PVDF AQ360 (manufactured by East Japan Paint Co., Ltd.), which is an aqueous emulsion (aqueous dispersion) containing fine particles of polyvinylidene fluoride (PVdF)-based resin, this is diluted and the coating has a fine particle concentration of 3.7% by mass. A working solution was prepared. The average particle diameter of the fine particles made of polyvinylidene fluoride resin is 250 nm (0.25 μm), and the resin is vinylidene fluoride/acrylic acid copolymer (vinylidene fluoride: 70 mol %). This coating solution and magnesium hydroxide are mixed, and the resulting mixture is applied on both sides of the polyolefin microporous film 4A in an equal amount using a #6 bar coater and dried at 60° C. Layer 8B was formed to a thickness of 5 μm to obtain microporous film 16A. The obtained microporous membrane was evaluated by the above method in the same manner as in Production Example 1.

The evaluation results of the microporous membranes 1A to 17A are shown in Table 1 below.

[Production Example 3-1]
(Production of Raw Polymer 1C to 8C for Thermoplastic Polymer Coating Layer)
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 Dai-ichi Kogyo Seiyaku Co., Ltd.) were used. 5 parts by mass and 0.5 parts by mass of “ADEKA REASOAP SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA CORPORATION) were charged, and the internal temperature of the reaction vessel was raised to 80° C. to a temperature of 80° C. While maintaining the above, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added.
Five minutes after adding the ammonium persulfate aqueous solution, 38.5 parts by mass of methyl methacrylate, 19.6 parts by mass of n-butyl acrylate, 31.9 parts by mass of 2-ethylhexyl acrylate, 0.1 parts by mass of methacrylic acid, and acrylic Acid 0.1 parts by mass, 2-hydroxyethyl methacrylate 2 parts by mass, acrylamide 5 parts by mass, glycidyl methacrylate 2.8 parts by mass, trimethylolpropane triacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd.) 0 .7 parts by mass, "Aqualon KH1025" (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 25% aqueous solution) 3 parts by mass, "Adecaria Soap SR1025" (registered trademark, manufactured by ADEKA 25% aqueous solution) 3 parts by mass, A mixture of 0.05 part by mass of sodium p-styrenesulfonate, 7.5 parts by mass of ammonium persulfate (2% aqueous solution), 0.3 part by mass of γ-methacryloxypropyltrimethoxysilane, and 52 parts by mass of ion-exchanged water, The mixture was mixed with a homomixer for 5 minutes to prepare an emulsion. The obtained emulsion was added dropwise from the dropping tank to the reaction container over 150 minutes.
After the addition of the emulsion was completed, the internal temperature of the reaction vessel was maintained at 80° C. for 90 minutes and then cooled to room temperature. The obtained emulsion was adjusted to pH=9.0 with an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40% (raw polymer 1C). The resulting raw material polymer 1C was evaluated by the above method. The obtained results are shown in Table 2.

Acrylic copolymer latexes were obtained in the same manner as polymer 1C except that the compositions of the monomers and other raw materials used were changed as shown in Table 2 (raw polymers 2C to 8C). The obtained raw material polymers 2C to 8C were evaluated by the above method. The obtained results are shown in Table 2.

The Tg values of the raw material polymers 1C to 8C shown in Table 2 are all approximate values based on the FOX equation.
(Note) Raw material names in Table 2 MMA: methyl methacrylate BA: n-butyl acrylate EHA: 2-ethylhexyl acrylate MAA: methacrylic acid AA: acrylic acid HEMA: 2-hydroxyethyl methacrylate AM: acrylamide GMA: methacrylic Acid glycidyl NaSS: sodium p-styrenesulfonate A-TMPT: trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.)
KH1025: Aqualon KH1025 (registered trademark, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)
SR1025: ADEKA rear soap SR1025 (registered trademark, manufactured by ADEKA Corporation)
APS: Ammonium persulfate

[Production Example 3-2]
(Method for producing granular thermoplastic polymer 1C1-8C4)
65 parts by mass of water, 16 parts by mass of seed particles, 0.5 parts by mass of KH1025, 0.5 parts by mass of SR1025, and ion exchange were initially charged into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer. 70.4 parts by mass of water was added, the temperature in the reaction vessel was maintained at 30° C., and 7.5 parts by mass of APS was added.

Five minutes after the addition of APS, MMA38.5 parts by mass, BA19.6 parts by mass, EHA31.9 parts by mass, MAA0.1 parts by mass, AA0.1 parts by mass, HEMA2 parts by mass, AM5 parts by mass, GMA2.8 parts by mass. Parts, 3 parts by mass of KH1025, 3 parts by mass of SR1025, NaSS 0.05 parts by mass, A-TMPT 0.7 parts by mass, γ-methacryloxypropyltrimethoxysilane 0.3 parts by mass, APS 7.5 parts by mass, ion exchange. The emulsified mixed solution containing 52 parts by mass of water was charged into the reaction vessel from the dropping tank over 150 minutes. In this state, stirring was continued for another 30 minutes to allow the seed particles to absorb the monomer. Next, while maintaining the pH of the reaction system at 4 or less, the temperature of the reaction vessel was raised to 80° C., and stirring was continued for 120 minutes. Then, it cooled to room temperature.

After cooling, filtration was performed with a 200-mesh wire net to remove aggregates and the like. After filtration, the pH was adjusted to 8 with 25% ammonia water, and then water was added to adjust the solid content to 50% to obtain granular thermoplastic polymer 1C1. The obtained granular thermoplastic polymer was evaluated by the above method. The results obtained are shown in Table 3.

Granular thermoplastic polymers 1C2 to 8C4 were obtained in the same manner as the polymer 1C1 except that the compositions of the monomers and other raw materials used were changed as shown in Table 3 or 4. The obtained granular thermoplastic polymer was evaluated by the above method. The obtained results are shown in Table 3 or 4.

Note: See footnotes in Table 2 for raw material names in Tables 3 and 4.

[Example 1]
The granular thermoplastic polymer 1C5 shown in Table 5 was weighed out in a solid content of 2.4 parts by mass and uniformly dispersed in 92.5 parts by mass of water to prepare a coating solution containing the thermoplastic polymer. Next, the coating liquid was applied to one surface of the microporous membrane 1A shown in Table 1 using a gravure coater. The coating solution was dried to remove water. Further, the coating liquid was applied on the other surface in the same manner and dried again to obtain a separator for an electricity storage device having a thermoplastic polymer on both surfaces of the microporous film. The obtained separator was evaluated by the above method. The results obtained are shown in Table 5.

[Examples 2 to 43 (however, Examples 5 to 8, 17 to 24, 30 to 38 , 40 to 43 are reference examples), Comparative Examples 1 to 5]
In the same manner as in Example 1 except that the coating liquid containing the thermoplastic polymer was applied to both surfaces of the microporous membrane by various methods (spray, gravure) in the combinations described in any of Tables 5 to 9. A separator for a power storage device was produced. The physical properties and evaluation results of the obtained separator are shown in any of Tables 5 to 9.

Claims (5)

A separator winding body for an electricity storage device comprising a winding core and an electricity storage device separator wound around the winding core,
The separator has a polyolefin microporous membrane, and a thermoplastic polymer coating layer coating at least a part of at least one surface of the polyolefin microporous membrane,
The average thickness of the polyolefin microporous membrane is 1 μm or more and 6 μm or less,
The thermoplastic polymer coating layer contains no filler,
The average particle diameter of the granular thermoplastic polymer included in the thermoplastic polymer coating layer is less than 1050nm or more and 2 000Nm,
At least one of the glass transition temperatures of the granular thermoplastic polymer exists in a region of 15° C. or less when measured by a differential scanning calorimetry method, and the separator is moved from the wound body at a speed of 5 mm/sec. The rewinding force when rewound with is 10 mN/10 mm or more and 750 mN/10 mm or less,
The separator wound body for the electricity storage device. The separator winding body for an electricity storage device according to claim 1, wherein the unwinding force is 10 mN/10 mm or more and 500 mN/10 mm or less. The separator wound body for an electricity storage device according to claim 1 or 2 , wherein the granular thermoplastic polymer is a polymer containing a repeating unit obtained by polymerizing a (meth)acrylate monomer. The winding outer diameter of the core is 127Mm～381mm, wound separator device according to any one of claims 1 to 3 Kaitai. Lithium-ion secondary battery using a separator unwound from the separator wound body for an electricity storage device according to any one of claims 1-4.