JP7057722B2 - Winding body of separator for power storage device and its manufacturing method - Google Patents

Description

The present invention relates to a wound body of a separator for a power storage device (hereinafter, also simply referred to as “separator”) and a method for manufacturing the same. More specifically, the present invention relates to a wound body of a separator having a thermoplastic polymer coating layer containing a thermoplastic polymer on at least a part of at least one side of a porous polyolefin substrate and used for a power storage device. ..

In recent years, non-aqueous electrolyte batteries, mainly lithium-ion batteries, have been actively developed. Usually, a non-aqueous electrolyte battery is provided with a separator having a porous material, for example, a microporous membrane as a substrate (also referred to as “porous substrate” in the present specification) between the positive and negative electrodes. Such a separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the microporous.

Improvements to the separator are being studied in order to improve the cycle characteristics and safety of non-aqueous electrolyte batteries. For example, in Patent Document 1, for the purpose of providing a secondary battery having excellent discharge characteristics and safety, a porous film in which a reactive polymer is applied on a porous membrane and dried to support an adhesive is used. Proposed.

In recent years, with the miniaturization and thinning of portable devices, there is a demand for miniaturization and thinning of power storage devices such as lithium ion secondary batteries. On the other hand, in order to make it possible to carry it for a long time, the capacity is also increased by improving the volumetric energy density of the power storage device.

Conventionally, the separator has a characteristic that the battery reaction is stopped promptly when abnormally heated (fuse characteristic), and a dangerous situation in which the positive electrode substance and the negative electrode substance directly react with each other while maintaining the shape even at a high temperature. There has been a demand for safety-related performance such as performance to prevent short-circuit characteristics (short-circuit characteristics). In recent years, in addition to these safety performances, it has been required to improve the adhesiveness between the separator and the electrode from the viewpoint of uniform charging / discharging current and suppression of lithium dendrite.

By improving the adhesiveness between the separator and the battery electrode, non-uniformity of the charge / discharge current is less likely to occur, and lithium dendrite is less likely to precipitate, resulting in a longer charge / discharge cycle life. Become.

For example, in Patent Documents 1 and 2, a polymer solution is further applied on a porous coating layer formed on a porous substrate to obtain a separator, and the polymer layer and the electrode of the separator are adhered and fixed. It is proposed to do.

International Publication No. 2014/017651 International Publication No. 2016/047165

However, in the case of manufacturing a wound body of a conventional separator as described in Patent Documents 1 and 2, as the number of times the separator is wound on the core increases, the pressure applied to the separator located in the inner layer of the wound body is increased. May be increased and the thermoplastic polymers and / or the thermoplastic polymer and the substrate may stick to each other. Such a phenomenon is generally called "blocking". Due to blocking, it becomes difficult to feed out the separator on the inner layer side of the wound body, and the handleability may be significantly impaired.

The present invention has been made in view of the above problems, and is a wound body of a separator having a thermoplastic polymer coating layer containing a thermoplastic polymer, without impairing the adhesiveness between the separator and the electrode. It is an object of the present invention to provide a wound body of a separator for a power storage device, which can suppress the occurrence of winding misalignment and wrinkles of the wound body and reduce blocking.

As a result of diligent studies to achieve the above problems, the present inventors have found that the innermost layer of the wound body of a separator having a thermoplastic polymer coated layer on at least a part of at least one side of the porous polyolefin substrate. It has been found that the above problems can be solved by adjusting the peel strength between the separators to a specific range. Further, they have found that the wound body can be manufactured by adjusting the winding tension to a specific range when the wound body is manufactured, and completed the present invention.

That is, the present invention is as follows.
[1]
It is a winding body of a separator for a power storage device.
The separator has a polyolefin porous substrate and a thermoplastic polymer coating layer containing a thermoplastic polymer on at least a part of at least one side of the substrate.
The wound body is a wound body of a separator for a power storage device, in which the number of windings is 1000 or more and 10000 times or less, and the peel strength between separators in the innermost layer is 0.5 mN / mm or more and 10 mN / mm or less.
[2]
The wound body of the separator for a power storage device according to item 1, wherein the thermoplastic polymer coating layer has adhesiveness.
[3]
The wound body of the separator for a power storage device according to item 1 or 2, wherein at least one of the thermoplastic polymers has a glass transition temperature of 40 ° C. or higher.
[4]
The storage device according to any one of items 1 to 3, wherein the thermoplastic polymer contained in the thermoplastic polymer coating layer has a coating weight of 0.02 g / m ² or more and 2.00 g / m ² or less. A wound body of the separator.
[5]
The storage device according to any one of items 1 to 3, wherein the thermoplastic polymer contained in the thermoplastic polymer coating layer has a coating weight of 0.02 g / m ² or more and 1.00 g / m ² or less. A wound body of the separator.
[6]
The wound body of a separator for a power storage device according to any one of items 1 to 5, wherein the thickness per one side of the thermoplastic polymer coating layer is 2.0 μm or less.
[7]
The winding of the separator for a power storage device according to any one of items 1 to 6, wherein the thermoplastic polymer comprises at least one selected from the group consisting of a conjugated diene polymer, an acrylic polymer, and a fluorine polymer. body.
[8]
The wound body of a separator for a power storage device according to any one of items 1 to 7, wherein the thermoplastic polymer contains a copolymer containing at least a (meth) acrylate monomer as a monomer unit.
[9]
It is a method of manufacturing a wound body of a separator for a power storage device, and the above method is:
A thermoplastic polymer coating layer containing a thermoplastic polymer is attached to at least a part of at least one side of the polyolefin porous substrate to obtain a separator;
A method comprising winding the separator around a core 1000 times or more and 10000 times or less with a tension of 20 N / m or more and 70 N / m or less.

According to the present invention, even in the case of a wound body of a separator provided with a thermoplastic polymer coating layer for adhering the electrode and the separator, the adhesiveness to the electrode is not impaired and blocking is eliminated. It is possible to provide a wound body of a separator for a power storage device.

Hereinafter, embodiments for carrying out the present invention (hereinafter, abbreviated as “the present embodiment”) will be described in detail. The present invention is not limited to the present embodiment, and can be variously modified and implemented within the scope of the gist thereof.

[Wrapper of separator for power storage device]
The wound body of the separator for a power storage device according to the present embodiment (hereinafter, also simply referred to as “wrapped body”) has a polyolefin porous base material and a thermoplastic polymer on at least a part of at least one side of the base material. It is a wound body of a separator having a thermoplastic polymer coating layer contained therein. The wound body of the separator for a power storage device is generally a wound body in which a separator continuously manufactured in the mechanical direction is wound around a winding core (also referred to as a "core"). The number of turns of the wound body is 1000 times or more and 10000 times or less, and the separator in the region within 10% of the number of turns (referred to as the "innermost layer" in the present specification) from the beginning of winding in which the separator is not fixed to the core. The peel strength between them is 0.5 mN / mm or more and 10 mN / mm or less. The peel strength of the innermost layer is preferably 0.5 mN / mm or more and 10.0 mN / mm or less, more preferably 0.5 mN / mm or more and 7.0 mN / mm or less, and further preferably 0.5 mN / mm or more and 3.0 mN or less. / Mm or less. When the peel strength is 0.5 mN / mm or more, an appropriate adhesive force is developed in the wound body, it is possible to suppress winding misalignment during the production of the wound body, and wrinkles are formed on the wound separator. It is less likely to occur. Further, when the peel strength is 10 mN / mm or less, the separator can be satisfactorily unwound from the wound body when the electrode-separator laminate is manufactured.

The method for manufacturing a wound body of a separator for a power storage device according to the present embodiment is to obtain a separator by attaching a thermoplastic polymer coating layer to at least a part of at least one side of a porous polyolefin substrate; It includes winding the separator around the core 1000 times or more and 10,000 times or less. The tension of the separator in the winding step is 20 N / m or more and 70 N / m or less, and more preferably 20 N / m or more and 50 N / m or less. When the winding tension is 20 N / m or more, an appropriate adhesive force is developed in the wound body, it is possible to suppress the winding deviation at the time of manufacturing the wound body, and wrinkles are generated in the wound separator. Less to do. Further, when the winding tension is 70 N / m or less, the separator can be satisfactorily unwound from the wound body when the electrode-separator laminated body is manufactured.

The winding step is performed between the time when the thermoplastic polymer coating layer is applied to at least a part of at least one side of the polyolefin porous substrate and the time before the electrode-separator laminate is produced, and the separator is wound up. It is a process.

In the wound body according to the present embodiment, the material of the core for winding the separator is not particularly limited. As the material of the core, for example, paper, resin, metal, or a combination thereof can be used. The shape of the core is typically cylindrical, as long as the separator can be wound up. The diameter of the core is not particularly limited. The width of the core is not particularly limited as long as it is equal to or larger than the width of the separator.

Generally, the wound body is formed by continuously winding a separator on a core in an arbitrary number of times in a mechanical direction, and the number of times the wound body of the present embodiment is wound is 1000 times or more and 10,000 times or less. be. When the number of windings is 10,000 or less, it is possible to sufficiently reduce the occurrence of feeding defects due to sticking between the separators even at the maximum value of the winding tension (70 N / m).

[Thermoplastic polymer coating layer]
In the present embodiment, it is preferable that the thermoplastic polymer coating layer has an adhesive property that allows the electrode and the separator to be adhered to each other by undergoing a hot pressing step. That is, it is preferable that the thermoplastic polymer coating layer can function as an adhesive layer between the electrode and the separator.

The amount of the thermoplastic polymer coated layer supported on the substrate (also referred to as “coatsuke”) is preferably 0.02 g / m ² or more and 2.00 g / m ² or less as a solid content, and more preferably 0. 02 g / m ² or more and 1.50 g / m ² or less, more preferably 0.02 g / m ² or more and 1.00 g / m ² or less. By controlling the amount of the thermoplastic polymer coating layer carried on the substrate in the range of 0.02 g / m ² or more and 2.00 g / m ² or less, the cycle characteristics (permeability) are lowered due to the closure of the pores of the substrate. It is preferable from the viewpoint of exhibiting the effect of further improving the adhesion between the thermoplastic polymer coating layer and the base material while suppressing the above.
The amount of the thermoplastic polymer coating layer supported on the substrate can be adjusted, for example, by changing the content of the thermoplastic polymer in the coating liquid, the coating amount of the thermoplastic polymer solution, and the like. However, the method for adjusting the loading amount is not limited to the above.

The thermoplastic polymer coating layer is preferably present on the surface of the substrate with a surface coverage of 80% or less with respect to 100% of the total area of the substrate per one side of the substrate, more preferably 70%. Below, it is more preferably present on at least one side of the substrate with a surface coverage of 60% or less. Further, it is preferable that the thermoplastic polymer coating layer is present on the substrate with a surface coverage of 5% or more. It is preferable that the surface coverage of the thermoplastic polymer coating layer is 80% or less from the viewpoint of further suppressing the blockage of the pores of the base material by the thermoplastic polymer and improving the permeability of the separator. On the other hand, it is preferable to set the surface coverage to 5% or more from the viewpoint of further improving the adhesiveness with the electrode.

The average thickness of the thermoplastic polymer coating layer is preferably 0.1 to 2.0 μm or less on one side, more preferably 0.1 to 1.0 μm or less, still more preferably 0.1 to 0.5 μm. It is as follows. When the average thickness of the thermoplastic polymer coating layer is 2.0 μm or less, the decrease in permeability due to the thermoplastic polymer is suppressed, and the thermoplastic polymer coating layers or the base when the separator is stored as a wound body. It is preferable from the viewpoint of effectively suppressing sticking to the material. Further, from the viewpoint of achieving both adhesiveness and permeability, it is preferable that the thickness corresponds to the particle size of the thermoplastic polymer used. It is preferable that the average thickness of the thermoplastic polymer coating layer is 0.1 μm or more because it easily follows the unevenness of the electrode active material. The average thickness of the thermoplastic polymer coating layer shall be adjusted, for example, by changing the thermoplastic polymer content in the coating liquid to be applied to the substrate, the coating amount of the coating liquid, and the coating method and coating conditions. Can be done. However, the method for adjusting the average thickness of the thermoplastic polymer coating layer is not limited to these.

The thermoplastic polymer in the thermoplastic polymer coating layer preferably contains a granular thermoplastic polymer, and more preferably substantially all of the thermoplastic polymers are granular thermoplastic polymers. Since the thermoplastic polymer is granular, it tends to be more excellent in the adhesiveness between the separator and the electrode and the handleability of the separator.

<Thermoplastic polymer>
The thermoplastic polymer used in the present embodiment is not particularly limited, and is, for example, a polyolefin resin such as polyethylene, polypropylene, α-polypolymer; a fluoropolymer such as polyvinylidene fluoride and polytetrafluoroethylene, and a copolymer containing these. Conjugate diene polymers containing conjugated diene such as butadiene and isoprene as monomer units or copolymers containing these and hydrides thereof; acrylic polymers containing acrylic acid esters, methacrylic acid esters and the like as monomer units or copolymers containing these and The hydride; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, and polyamide. Examples thereof include resins having a melting point and / or a glass transition temperature of 180 ° C. or higher, such as imide, polyamide and polyester, and mixtures thereof. Further, as the 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, at least one selected from the group consisting of conjugated diene-based polymers, acrylic-based polymers, and fluoropolymers is preferable because of its excellent binding property to the electrode active material and its strength or flexibility. ..
Among these, acrylic polymers are preferable from the viewpoints of adhesiveness between the separator and the electrode and compatibility with bending stress of the laminated battery.

(Diene polymer)
The diene-based polymer is not particularly limited, and examples thereof include 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-octadien, 3-butyl-1,3-octadien and the like can be mentioned. These may be polymerized alone or copolymerized.

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

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

The "other monomer" is not particularly limited, and is, for example, an α, β-unsaturated nitrile compound such as acrylonitrile and methacrylnitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and fumaric acid; styrene. , Chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, divinylbenzene and other styrene monomers; Olefins; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl biel ether; Methyl vinyl Vinyl ketones such as ketones, ethyl vinyl ketones, butyl vinyl ketones, hexyl vinyl ketones and isopropenyl vinyl ketones; heterocyclic-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine and vinylimidazole; acrylic acids such as methyl acrylates and methyl methacrylates. Esters 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-methylolacrylamide, acrylamide-2-methylpropanesulfonic acid, etc. 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 copolymer containing a monomer unit composed of a (meth) acrylate monomer.

In the present specification, "(meth) acrylic acid" means "acrylic acid or methacrylic acid", and "(meth) acrylate" means "acrylate or methacrylate".

The (meth) acrylate monomer is not particularly limited, and is, for example, 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) acrylates, n-tetradecyl (meth) acrylates and stearyl (meth) acrylates; hydroxyethyl (meth) acrylates, hydroxypropyl (meth) acrylates, hydroxybutyl (meth) acrylates and the like. Examples thereof include hydroxy group-containing (meth) acrylates; amino group-containing (meth) acrylates such as aminoethyl (meth) acrylates; and epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylates.

The ratio of the monomer unit composed of the (meth) acrylate monomer is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, based on the mass of the total acrylic polymer. Is. Examples of the acrylic polymer include homopolymers of (meth) acrylate monomers and copolymers thereof with copolymerizable monomers.

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

(Fluorine polymer)
The fluoropolymer is not particularly limited, and examples thereof include homopolymers of vinylidene fluoride and copolymers thereof with copolymerizable monomers. Fluorine-based polymers are preferred from the viewpoint of electrochemical stability.

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

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

Among the fluoropolymers, homopolymers of vinylidene fluoride, vinylidene fluoride / tetrafluoroethylene copolymer, vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer and the like are preferable. Particularly preferred fluoropolymers are vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, the monomer composition of which is usually 30-90% by mass of vinylidene fluoride, 9-50% by mass of tetrafluoroethylene and hexafluoropropylene. It is 1 to 20% by mass. These fluororesin particles may be used alone or in combination of two or more.

Further, as the 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 also be used.

The monomer having a hydroxy group is not particularly limited, and examples thereof include vinyl-based 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-based monomers such as pentenic acid.

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

The monomer having a sulfonic acid group is not particularly limited, but for example, vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) Alice sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-sulfonic acid ethyl, 2-. Examples thereof include acrylamide-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, and N-methylolmethacrylamide.

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

The thermoplastic polymer used in the present embodiment may be used alone or in combination 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 preferably 40 ° C. or higher from the viewpoint of suppressing the blocking phenomenon between separators. Here, the glass transition temperature is determined from the 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 extending the baseline on the low temperature side of 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. More specifically, the method described in the examples can be referred to.

Here, "glass transition" refers to a DSC in which a change in calorific value accompanying a change in the state of a polymer as a test piece occurs on the endothermic side. Such a calorific value change is observed in the DSC curve as a stepped change shape or a shape in which a stepped change and a peak are combined.

“Stepped change” refers to the portion of the DSC curve from the previous baseline to the transition to a new baseline. It also includes a combination of peaks and staircase changes.

The "inflection point" indicates a point where the gradient of the DSC curve of the stepped change portion is maximized. It can also be expressed as a point where an upwardly convex curve changes to a downwardly convex curve in the stepped change portion.

“Peak” refers to the portion of the DSC curve from when the curve leaves the baseline until it returns to the baseline again.

The "baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs in the test piece.

When the thermoplastic polymer is granular, it is preferable that at least one of the glass transition temperatures of the granular thermoplastic polymer is present in the region of 40 ° C. or higher as measured by the differential scanning calorimetry method.

The glass transition temperature existing in the region of 40 ° C. or higher is preferably present only in the region of 45 ° C. or higher and 100 ° C. or lower from the viewpoint of suppressing the blocking phenomenon between the separators.

In the present embodiment, the glass transition temperature of the thermoplastic polymer may be present in a region of less than 40 ° C. or may be present in a region of 40 ° C. or higher. When the glass transition temperature of the thermoplastic polymer is 40 ° C. or higher, the adhesiveness and handleability between the separator and the electrode are excellent. In addition, the adhesiveness between the electrode and the separator, which is developed by pressurization during battery production, can be enhanced.

In this embodiment, the thermoplastic polymer may have two glass transition temperatures, one in the region below 40 ° C and the other in the region above 40 ° C. This can be achieved by a method of blending two or more kinds of thermoplastic polymers, a method of using a thermoplastic polymer having a core-shell structure, or the like. The core-shell structure is a polymer in the form of a double structure in which the composition of the polymer belonging to the central portion and the polymer belonging to the outer shell portion are different.

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, and can impart multiple functions to the entire thermoplastic polymer. For example, in the case of a polymer blend, by blending two or more types of polymers having a glass transition temperature in the region of 40 ° C or higher and a polymer having a glass transition temperature in the region of less than 40 ° C, stickiness resistance and polyolefin porosity can be obtained. It is preferable from the viewpoint of achieving both applicability to a sex substrate. In the case of a core-shell structure, the adhesiveness or compatibility with other materials such as a polyolefin porous substrate can be adjusted by changing the composition of the outer shell polymer, and the polymer belonging to the central portion can be adjusted. Therefore, for example, the adhesiveness to the electrode after hot pressing can be improved. Further, the viscoelasticity can be controlled by combining a highly viscous polymer and a highly elastic polymer.

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, it is roughly estimated from the Tg of the homopolymer generally shown for each monomer used in the production of the thermoplastic polymer (for example, described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the mixing ratio of the monomers. can do. For example, a copolymer containing a high proportion of monomers such as styrene, methylmethacrylate, and acrylonitrile that give a polymer of Tg at about 100 ° C. has a high Tg. For example, copolymers containing high proportions of monomers such as butadiene, which gives a polymer of Tg at about -80 ° C, n-butylacryllate and 2-ethylhexylacrylate, which give a polymer of Tg at about -50 ° C, are low. Has Tg.

The Tg of the polymer can be estimated 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 method using the DSC is adopted.
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ + ... + Wi _i / Tg _i + ... W _n / Tg _n (1)
(In the formula (1), Tg (K) is the copolymer Tg, Tg _i (K) is the homopolymer Tg of each monomer _i , and Wi is the mass fraction of each monomer.)

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

Examples of the method for producing a granular thermoplastic polymer include synthesizing a thermoplastic polymer first, using it as a seed, and further adding a monomer, an initiator, and the like. Thereby, the shape of the thermoplastic polymer can be granulated, and the particle size of the thermoplastic polymer can be further 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 superior. Here, the area of the granular thermoplastic polymer is measured by SEM observation (magnification 30,000 times) of the outermost surface of the separator as described in Examples described later.

The average particle size of the granular thermoplastic polymer is preferably 10 nm or more and less than 2000 nm, and more preferably 100 nm or more and less than 1000 nm. The particle size of 10 nm or more is preferable because it is possible to secure a particle size such that the thermoplastic polymer does not enter the pores of the substrate when the granular thermoplastic polymer is applied to the polyolefin porous membrane substrate, and it is preferably less than 2000 nm. Is preferable from the viewpoint of adhesiveness between the separator and the electrode.

[Polyolefin porous substrate]
The porous polyolefin base material in the present embodiment is not particularly limited, but is preferably a microporous membrane composed of a polyolefin resin composition containing a polyolefin resin, and is preferably a microporous membrane containing a polyolefin resin as a main component. It is more preferably a membrane. The content of the polyolefin resin in the porous polyolefin base material in the present embodiment is not particularly limited, but the mass fraction of all the components constituting the base material is determined from the viewpoint of shutdown performance when used as a separator for a power storage device. It is preferable that the porous substrate is composed of a polyolefin resin composition in which the polyolefin resin accounts for 50% or more and 100% or less. The proportion of the polyolefin resin in the base material is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

<Polyolefin resin>
The polyolefin resin is not particularly limited, but is a polyolefin resin used for ordinary extrusion, injection, inflation, blow molding and the like, for example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and the like. And homopolymers and copolymers such as 1-octene, multistage polymers and the like can be used. In addition, polyolefins selected from the group consisting of these homopolymers, copolymers, and multistage polymers can be used alone or in admixture.

Since polyethylene has a low melting point and high strength as a base material for forming a separator for a power storage device, it is preferable to use a resin containing polyethylene as a main component in the present embodiment. In the present specification, the "main component" means a component constituting 50% by mass or more.

Typical examples of the polyolefin resin are not particularly limited, but for example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene. Examples include random copolymers, polybutene, polyethylene propylene rubber and the like.

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, more preferably 3 to 20% by mass, from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.

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

Polyethylene such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high-molecular-weight polyethylene can be used as polyolefin resins other than polypropylene from the viewpoint of shut-down characteristics in which the pores of the porous substrate are closed by thermal melting. Is preferably used. 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 K 7112.

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin porous substrate 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 100. It is less than 10,000. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding becomes large and the moldability becomes good, and the polymer tends to be entangled with each other to have high strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12 million or less, it becomes easy to uniformly melt and knead, and the formability 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 easily closed when the temperature rises, and a good shutdown function tends to be obtained, which is preferable. For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million 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, and the viscosity average molecular weight is less than 1 million. A mixture may be used.

The polyolefin porous substrate in this embodiment can contain any additive. Such additives are not particularly limited, and are, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenol-based, phosphorus-based and sulfur-based; metal soaps such as calcium stearate and zinc stearate; ultraviolet rays. Absorbents; 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 characteristics of polyolefin porous substrate>
The puncture strength of the polyolefin porous substrate 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, and 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 the film rupture due to the active material or the like that has fallen off during battery winding. It is also preferable from the viewpoint of suppressing the concern of short circuit due to expansion and contraction of the electrode due to charging and discharging. On the other hand, the value of 2000 g / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to relaxation of orientation during heating. Here, the puncture strength is measured by the method described in the examples below.
The puncture strength can be adjusted by adjusting the stretching ratio, stretching temperature, and the like.

The porosity of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, more preferably 80% or less, still more preferably. It is 70% or less. It is preferable that the porosity is 20% or more from the viewpoint of ensuring the permeability of the separator. On the other hand, 90% or less is preferable from the viewpoint of ensuring piercing strength. Here, the porosity is measured by the method described in the examples below.
The porosity can be adjusted by changing the draw ratio or the like.

The air permeability of the polyolefin porous substrate 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, and more preferably 500 sec / 100 cc. Hereinafter, it is more preferably 300 sec / 100 cc. It is preferable that the air permeability is 10 sec / 100 cc or more from the viewpoint of suppressing self-discharge of the power 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 described later.
The air permeability can be adjusted by changing the stretching temperature, stretching ratio, and the like.

The average pore size of the polyolefin porous substrate 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. It is preferable that the average pore diameter is 0.15 μm or less from the viewpoint of suppressing the self-discharge of the power storage device and suppressing the capacity decrease when the separator for the power storage device is used. The average pore size can be adjusted by changing the draw ratio when producing the porous polyolefin substrate.

From the viewpoint of safety when the polyolefin porous substrate in the present embodiment is used in a battery, the shutdown temperature is preferably 120 ° C. or higher and 200 ° C. or lower, more preferably 165 ° C. or lower, still more preferably 140. It is below ° C.

The short temperature, which is an index of the heat resistance of the porous polyolefin substrate in the present embodiment, is preferably 140 ° C. or higher, more preferably 150 ° C. or higher, still more preferably 160 ° C. or higher. It is preferable that the short-circuit temperature is 140 ° C. or higher from the viewpoint of safety of the power storage device when the separator for the power storage device is used.

The film thickness of the polyolefin porous substrate in this embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 3 μm or more, preferably 100 μm or less, more preferably 30 μm or less, still more preferably 20 μm or less, and further. It is preferably 10 μm or less. It is preferable that the film thickness is 2 μm or more from the viewpoint of improving the mechanical strength. On the other hand, it is preferable that the film thickness is 100 μm or less because the occupied volume of the separator in the battery is reduced, which tends to be advantageous for increasing the capacity of the battery. The film thickness can be adjusted by changing the thickness of the film after casting, the draw ratio, and the like.

<Manufacturing method of polyolefin porous base material>
The method for producing the porous polyolefin substrate 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 form a sheet, then stretched in some cases, and then made porous by extracting the plasticizer; the polyolefin resin composition is melt-kneaded and highly drawn. A method of extruding by ratio and then exfoliating the polyolefin crystal interface by heat treatment and stretching to make it porous; the polyolefin resin composition and the inorganic filler are melt-kneaded, molded on a sheet, and then stretched to form the polyolefin and the inorganic filler. A method of making the polyolefin resin porous by peeling off the interface with the polyolefin; a method of immersing the polyolefin resin composition in a poor solvent for the polyolefin to coagulate the polyolefin and at the same time removing the solvent to make the polyolefin porous.

Hereinafter, as an example of a method for producing a porous polyolefin base material, a method of melting and 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 a melt-kneading method, for example, a polyolefin resin and, if necessary, other additives are put into a resin kneading device such as an extruder, a kneader, a lab plast mill, a kneading roll, and a Banbury mixer, and the resin component is heated and melted. A method of introducing a plasticizer at the ratio of the above and kneading the plasticizer can be mentioned. At this time, it is preferable to pre-knead the polyolefin resin, other additives and the plasticizer at a predetermined ratio using a Henschel mixer or the like before putting them into the resin kneading apparatus. 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 kneader. By doing so, the dispersibility of the plasticizer is enhanced, and when the sheet-shaped molded product of the melt-kneaded product 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 capable of forming a uniform solution above the melting point of the 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; 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, so that uniform stretching tends to be easy to carry out. 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 composed of the polyolefin resin composition and the plasticizer is preferably 30 to 80% by mass, more preferably 40 to 70% by mass. When the mass fraction of the plasticizer is 80% by mass or less, the melt tension at the time of melt molding is unlikely to be insufficient, and the moldability tends to be improved. On the other hand, when the mass fraction is 30% by mass or more, even if the mixture of the polyolefin resin composition and the plasticizer is stretched at a high magnification, the polyolefin chain is not cut, a uniform and fine pore structure is formed, and the strength is also high. It is easy to increase.

Next, the melt-kneaded product is formed into a sheet. As a method for producing a sheet-shaped molded product, for example, the melt-kneaded product is extruded into a sheet shape via 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 the heat conductor used for cooling and solidification, metal, water, air, a plasticizer itself, or the like can be used, but a metal roll is preferable because of its high heat conduction efficiency. At this time, if it is sandwiched between the rolls when it is brought into contact with the metal roll, the efficiency of heat conduction is further increased, the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is also improved, which is more preferable. The die lip interval when extruded into a sheet 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. When the die lip interval is 400 μm or more, the shavings and the like are reduced, there are few defects (for example, streaks and the like) that affect the film quality, and there is a tendency that the film breakage and the like can 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, cooling unevenness 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 preferable from the viewpoint of the strength of the obtained porous membrane and the like. When the sheet-shaped molded product is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, the finally obtained porous film is less likely to tear, and the sheet-shaped molded product has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching, and simultaneous biaxial stretching can be performed from the viewpoint of improving puncture strength, stretching uniformity, and shutdown property. Stretching is preferred.

Simultaneous biaxial stretching is a stretching method in which stretching in the MD direction (mechanical direction of the porous substrate) and stretching in the TD direction (direction of crossing the MD of the porous substrate at an angle of 90 °) are performed at the same time. 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 independently performed, and when stretching in the MD direction or the TD direction, the other direction is in an unconstrained state or a constant length. It is assumed that it is fixed to.

The draw ratio is preferably in the range of 20 times or more and 100 times or less in terms of surface magnification, and more preferably in the range of 25 times or more and 50 times or less. The draw ratio in each axial direction is preferably in the range of 4 times or more and 10 times or less in the MD direction, 4 times or more and 10 times or less in the TD direction, 5 times or more and 8 times or less in the MD direction, and 5 times in the TD direction. It is more preferable that the range is 8 times or more. When the total area magnification is 20 times or more, sufficient strength tends to be imparted to the obtained porous film, while when the total area magnification is 100 times or less, film breakage in the stretching step is prevented and high productivity is achieved. It tends to be obtained.

Further, the sheet-shaped molded product may be rolled. Rolling can be carried out by, for example, a pressing method using a double belt press machine or the like. Rolling can especially increase the orientation of the surface layer portion. The rolled surface magnification is preferably greater than 1x and 3x or less, and more preferably greater than 1x and 2x or less. When the rolling ratio is larger than 1 times, the surface 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 orientation difference between the surface layer portion and the inside of 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 product to form a porous film. Examples of the method for removing the plasticizer include a method in which a sheet-shaped molded product is immersed in an extraction solvent to extract the plasticizer and sufficiently dried. The method for extracting the plasticizer may be either 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 dipping and drying steps. Further, the residual amount of the plasticizer in the porous membrane is preferably less than 1% by mass.

As the extraction solvent, it is preferable to use a solvent that is poor with respect to the polyolefin resin, is a good solvent with respect to 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 type such as hydrofluoroether and hydrofluorocarbon. Hydrocarbon solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone can be mentioned. These extraction solvents may be recovered and reused by an operation such as distillation.

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

[Poor layer]
In the present embodiment, the separator for a power storage device may include a porous layer containing an inorganic filler or an organic filler and a resin binder in addition to the polyolefin porous substrate and the thermoplastic polymer coating layer. Positions of the porous layer include at least a portion of the surface of the polyolefin porous substrate, at least a portion of the surface of the thermoplastic polymer coated layer, and / or between the polyolefin porous substrate and the thermoplastic polymer coated layer. .. The porous layer may be provided on one side or both sides of the polyolefin porous base material.

<Inorganic filler>
The inorganic filler used for the porous layer is not particularly limited, but preferably has a melting point of 200 ° C. or higher, has high electrical insulation, and is electrochemically stable within the range of use of the lithium ion secondary battery.

The inorganic filler is not particularly limited, and is, for example, oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, itria, 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, Potassium Titanium, Tarku, Kaolinite, Decite, Nacronite, Halloysite, Pyrophyllite, Montmorillonite, Sericite, Mica, Examples thereof include ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand, and glass fibers, which may be used alone or in combination of two or more. 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; or ions such as kaolinite, dekite, nacrite, halloysite and pyrophyllite. An aluminum silicate compound having no exchange ability is preferable. As the aluminum oxide compound, aluminum hydroxide oxide is particularly preferable. 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. There are wet kaolin and calcined kaolin obtained by calcining the wet kaolin. In addition to releasing water of crystallization during the calcining process, calcined kaolin removes impurities, so that it is electrochemically stable. Especially preferable.

<Organic filler>
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.), and crosslinked polystyrene. , Cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, polyamideimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. Examples thereof include heat-resistant polymer fine particles such as plastic crosslinks. Further, the organic resin (polymer) constituting these organic fine particles includes a mixture, a modified product, a derivative, and a copolymer (random copolymer, alternate copolymer, block copolymer, and graft) of the above-exemplified materials. It may be a polymer) or a crosslinked product (in the case of the above-mentioned heat-resistant polymer).
Among these, crosslinked polyacrylic acid, crosslinked polyacrylic acid ester, crosslinked polymethacrylic acid, crosslinked polymethacrylic acid ester, crosslinked polymethylmethacrylate, and crosslinked polysilicone (polymethylsilsesquioxane, etc.), polyimide, polyamideimide. , One or more resins selected from the group consisting of aramid.

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. Adjusting the average particle size of the filler to the above range is preferable from the viewpoint of suppressing heat shrinkage at high temperatures 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, still more 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 entire 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 2.0 μm or less in the entire filler is preferably 8% by volume or more, more preferably 10% by volume or more, and the upper limit is preferably. It is 60% by volume or less, more preferably 50% by volume or less.

Further, 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 entire filler is preferably 1% by volume or more, more preferably 3% by volume or more, and the upper limit is It is preferably 40% by volume or less, more preferably 30% by volume or less.

Adjusting the particle size distribution of the filler to the above range is preferable from the viewpoint of suppressing heat shrinkage at high temperatures even when the thickness of the porous layer is thin (for example, 7 μm or less). As a method for adjusting the ratio of the particle size of the filler, for example, a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill, or the like to reduce the particle size 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, a lump shape, and the like, and a plurality of types of fillers having the above shapes may be used in combination. The shape of the filler is not particularly limited as long as it is possible to suppress the heat shrinkage at 150 ° C. described later to 10% or less when the multilayer porous membrane is formed, but it is composed of a plurality of surfaces from the viewpoint of improving permeability. Polyhedral, columnar, and spindle-shaped are preferable.

The proportion of the filler in the porous layer can be appropriately determined from the viewpoints of filler binding, permeability of the multilayer porous film, heat resistance, etc., and is preferably 50% by mass or more and less than 100% by mass. , 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 resin binder is not particularly limited, but when the separator for a power storage device is used as a separator for a lithium ion secondary battery in the present embodiment, it is insoluble in the electrolytic solution of the lithium ion secondary battery. Moreover, it is preferable to use an electrochemically stable lithium ion secondary battery within the range of use.

Specific examples of the resin binder include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetra. Fluorohydrate-containing rubber such as fluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, methacrylic acid ester- Acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, etc. Cellulose derivatives; Examples thereof include resins 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 short-circuit temperature (short-circuit temperature) is improved, and better safety performance tends to be obtained, which is preferable. The degree of saponification 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 degree of polymerization 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 degree of polymerization is 200 or more, an inorganic filler such as calcined kaolin can be firmly bound to the porous membrane with a small amount of polyvinyl alcohol, and the air permeability of the multilayer porous membrane by forming the porous layer while maintaining the mechanical strength of the porous layer. It is preferable because it tends to suppress the increase in degree. Further, when the degree of polymerization is 5000 or less, gelation or the like when preparing the coating liquid tends to be prevented, which is preferable.

As the resin binder, a resin latex binder is preferable. When a resin latex binder is used, when a porous layer containing a filler and a binder is laminated on at least one side of the polyolefin porous film, a solution obtained after dissolving a part or all of the resin binder in a solvent. Is laminated on at least one side of the polyolefin porous film, and the ion permeability is less likely to decrease and the output is high as compared with the case where the resin binder is bound to the porous film by dipping in a poor solvent or removing the solvent by drying. There is a tendency for the characteristics to be easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics and tends to provide high safety.

As the resin latex binder, from the viewpoint of improving electrochemical stability and binding property, an aliphatic conjugated diene-based monomer and an unsaturated carboxylic acid monomer, and other single amounts copolymerizable with these are used. Those obtained by emulsion polymerization of the body are preferable. The method of emulsion polymerization is not particularly limited, and a conventionally known method can be used. The method for adding the monomer and other components is not particularly limited, and any of a batch addition method, a split addition method, and a continuous addition method can be adopted, and one-stage polymerization, two-stage polymerization, or multiple addition methods can be adopted. Any of step polymerization and the like can be adopted.

The aliphatic conjugated diene-based monomer is not particularly limited, and is, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3butadiene, 2-chlor-1. , 3-butadiene, substituted linear conjugated pentadiene, substituted and side chain conjugated hexadiene, etc., 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 (anhydrous) 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.

The other monomer copolymerizable with these is not particularly limited, and for example, an aromatic vinyl-based monomer, a cyanide vinyl-based monomer, an unsaturated carboxylic acid alkyl ester monomer, and a hydroxyalkyl group. Examples thereof include unsaturated monomers and unsaturated carboxylic acid amide monomers containing the above, and these may be used alone or in combination of two or more. Among the above, unsaturated carboxylic acid alkyl ester monomers are particularly preferable. The unsaturated carboxylic acid alkyl ester monomer is not particularly limited, and for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl. Examples thereof include maleate, dimethylitaconate, monomethylfumarate, monoethylfumarate, 2-ethylhexyl acrylate and the like, and 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, monomer components other than the above can be further used in order to improve various qualities and physical properties.

The average particle size of the resin binder is preferably 50 to 500 nm, more preferably 60 to 460 nm, and even more preferably 80 to 250 nm. When the average particle size of the resin binder is 50 nm or more, when the porous layer containing the inorganic filler and the binder is laminated on at least one surface of the polyolefin porous membrane, the ion permeability does not easily decrease and high output characteristics can be easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics and is easy to obtain high safety. When the average particle size of the resin binder is 500 nm or less, good binding property is exhibited, and when a multilayer porous film is used, heat shrinkage is good and the safety tends to be excellent.

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

The thickness of the porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulating properties, and preferably 50 μm or less from the viewpoint of improving the capacity and permeability of the battery. The 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.

The layer density of the porous layer is preferably 0.5 to 2.0 g / cm ³ , and more preferably 0.7 to 1.5 cm ³ . When the layer density of the porous layer is 0.5 g / cm ³ or more, the heat shrinkage rate at high temperature tends to be good, and when it is 2.0 g / cm ³ or less, the air permeability tends to decrease. be.

<Method of forming a porous layer>
Examples of the method for forming the porous layer include a method of applying a coating liquid containing an inorganic filler and a resin binder to at least one surface of a porous substrate containing a polyolefin resin as a main component to form the porous layer. Can be done.

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

In the coating liquid, various additives such as a dispersant such as a surfactant; a thickener; a wetting agent; an antifoaming agent; and a pH adjuster containing an acid and an alkali are used to stabilize the dispersion or improve the coatability. May be added. These additives are preferably those that can be removed when the solvent is removed, but are porous if they are electrochemically stable in the range of use of the lithium ion secondary battery, do not inhibit the battery reaction, and are stable up to about 200 ° C. 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 can realize the dispersion characteristics of the coating liquid required for the coating step. Examples thereof include ball mills, bead mills, planetary ball mills, vibration ball mills, sand mills, colloidal 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 liquid to the porous membrane is not particularly limited as long as it can realize the required layer thickness or coating area. For example, the gravure coater method, the small diameter gravure coater method, the reverse roll coater method, and the transfer roll. Examples include the coater method, the kiss coater method, the dip coater method, the knife coater method, the air doctor coater method, the blade coater method, the rod coater method, the squeeze coater method, the cast coater method, the die coater method, the screen printing method, and the spray coating method. ..

It is preferable to apply a surface treatment to the surface of the porous film prior to the application of the coating liquid because the coating liquid can be easily applied and the adhesion between the inorganic filler-containing porous layer after coating and the surface of the porous film is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous membrane. For example, a corona discharge treatment method, a mechanical roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method. And so on.

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 fixing the porous film and drying it at a temperature below its melting point, or at a low temperature. Examples thereof include a method of drying under reduced pressure. From the viewpoint of controlling the shrinkage stress of the porous membrane and the multilayer porous membrane in the MD direction, it is preferable to appropriately adjust the drying temperature, winding tension and the like.

[Separator]
In the present embodiment, the separator has an excellent adhesiveness to the electrode active material by having a thermoplastic polymer coating layer containing a thermoplastic polymer on at least a part of at least one side of the porous polyolefin substrate.

When the aluminum foil is pressed against the outermost surface of the separator in which the thermoplastic polymer coating layer is present for 3 minutes under the conditions of a temperature of 80 ° C. and a pressure of 10 MPa, the peel strength between the separator and the aluminum foil is obtained. (Hereinafter also referred to as "heat peel strength") is preferably 9.8 N / m (10 gf / cm) or more, more preferably 15 gf / cm or more, and further preferably 20 gf / cm or more. ..

Since the aluminum foil is generally used as an electrode current collector, the adhesiveness of the separator to the electrode during heating can be easily confirmed by measuring the heat peeling strength. When the heat peeling strength is 10 gf / cm or more, the peeling of the electrode and the separator is reduced during the assembly process or use of the power storage device, and the performance of the power storage device is further improved. The normal temperature peel strength and the heat peel strength are measured by the methods described in Examples.

In the present embodiment, the thickness of the separator for a power storage device (that is, the thickness of the entire separator including the polyolefin porous substrate, the thermoplastic polymer coating layer, an arbitrary porous layer, etc.) is preferably 2 μm or more, more preferably. Is 5 μm or more, and the upper limit is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 30 μm or less. It is preferable that the thickness is 2 μm or more from the viewpoint of ensuring the strength of the separator for a power storage device. On the other hand, it is preferable that the thickness is 100 μm or less from the viewpoint of obtaining good charge / discharge characteristics.

The air permeability of the separator for a power storage device 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 10000 sec / 100 cc or less, more preferably 1000 sec / 100 cc or less. It is preferable that the air permeability is 10 sec / 100 cc or more from the viewpoint of further suppressing the self-discharge of the power storage device when the separator for the power storage device is used. On the other hand, the value of 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 a power storage device can be adjusted by changing the stretching temperature, the stretching ratio, the area ratio of the thermoplastic polymer, the existence form, etc. when producing the porous polyolefin base material.

The separator for a power storage device has a short-circuit temperature, which is an index of heat resistance, 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 the safety of the power storage device when the separator for the power storage device is used.

[Method for forming a thermoplastic polymer coating layer]
The method for forming the thermoplastic polymer on the polyolefin porous substrate is not particularly limited, and examples thereof include a method of applying a coating liquid containing the thermoplastic polymer to the polyolefin porous substrate.

The method of applying the coating liquid containing the thermoplastic polymer to the porous membrane is not particularly limited as long as it can realize 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. Of these, the gravure coater method or the spray coating method is preferable because the degree of freedom in the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

As the medium of the coating liquid, a poor solvent of a thermoplastic polymer is preferable. When a poor solvent of the thermoplastic polymer is used as the medium of the coating liquid, when the thermoplastic polymer is applied to the polyolefin porous base material, the coating liquid penetrates into the inside of the porous base material and the thermoplastic polymer. Can effectively prevent the surface and the inside of the hole from being filled and the permeability from being lowered. 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.

It is preferable to surface-treat the surface of the porous film prior to coating because the coating liquid can be easily applied and the adhesion between the porous layer and the adhesive polymer is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous membrane. For example, a corona discharge treatment method, a plasma treatment method, a mechanical roughening method, a solvent treatment method, and an acid treatment method. , Ultraviolet oxidation method and the like.

The method for 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 fixing a porous film and drying it at a temperature below its melting point, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for an adhesive polymer to coagulate the adhesive polymer, and a method of extracting a solvent at the same time. Can be mentioned.

The separator for a power storage device is excellent in handleability at the time of winding and rate characteristics of the power storage device, and is also excellent in adhesion and permeability between the thermoplastic polymer and the porous polyolefin substrate. Therefore, the use of the separator for a power storage device is not particularly limited, but it can be suitably used, for example, for a battery such as a non-aqueous electrolyte secondary battery, a capacitor, a separator for a power storage device such as a capacitor, and separation of substances.

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

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 and evaluating various physical properties used in the following production examples, examples, and comparative examples are as follows. Unless otherwise specified, various measurements and evaluations were carried out under the conditions of room temperature of 23 ° C., 1 atm and relative humidity of 50%.

[Measurement and evaluation method]
(1) Viscosity average molecular weight of polyolefin (hereinafter, also referred to as "Mv")
The ultimate viscosity [η] (dl / g) at 135 ° C. in a decalin solvent was determined according to ASRM-D4020.
The Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ^-4 Mv ^0.67
The Mv of polypropylene was calculated from the following equation.
[Η] = 1.10 × 10 ^-4 Mv ^0.80

(2) Film thickness (μm)
(2-1) Film thickness (μm) of polyolefin porous substrate and separator for power storage device
A sample of 10 cm x 10 cm is cut out from the polyolefin porous substrate and the separator for the power storage device, 9 points (3 points x 3 points) are selected in a grid pattern, and the film thickness is measured by a micro-thickening instrument (Toyo Seiki Seisakusho). It was measured at room temperature 23 ± 2 ° C. using Type KBM Co., Ltd. The average value of the measured values at each of the nine points was taken as the film thickness (μm) of the polyolefin porous substrate and the separator for the power storage device.
(2-2) Thickness of thermoplastic polymer 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, Ltd.". The separator of the sample was cut to a size of about 1.5 mm × 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen in liquid nitrogen, and then the sample was cut with a hammer. The sample was vapor-deposited with osmium, observed at an acceleration voltage of 1.0 kV and 30,000 times, and the thickness of the thermoplastic polymer coated layer was calculated. The outermost surface region where the porous structure of the cross section of the polyolefin porous substrate cannot be seen in the SEM image was defined as the region of the thermoplastic polymer coating layer.

(3) Porosity (%) of the porous polyolefin substrate
A 10 cm × 10 cm square sample was cut from a porous polyolefin substrate, and its volume (cm ³ ) and mass (g) were determined, and the film density was 0.95 (g / cm ³ ), which was calculated using the following equation.
Porosity = (1-mass / volume / 0.95) x 100
The film density was calculated as 0.95 (g / cm ³ ).

(4) Air permeability (sec / 100cc)
It was measured by GB2 ™, a Garley type air permeability meter manufactured by Toyo Seiki Co., Ltd., in accordance with JIS P-8117.

(5) Puncture strength (g)
A polyolefin porous substrate was fixed with a sample holder having an opening diameter of 11.3 mm using a handy compression tester KES-G5 ™ manufactured by Kato Tech. Next, the central portion of the fixed polyolefin porous substrate was subjected to a puncture test at a needle tip with a radius of curvature of 0.5 mm and a piercing speed of 2 mm / sec in an atmosphere of 25 ° C. to obtain a raw maximum piercing load. The puncture strength (g) was obtained.

(6) Glass transition temperature of thermoplastic polymer A suitable amount of the coating liquid of the thermoplastic polymer (nonvolatile content = 38 to 42%, pH = 9.0) is placed in an aluminum dish and dried in a hot air dryer at 130 ° C. for 30 minutes. bottom. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DSC curve under a nitrogen atmosphere were obtained with a DSC measuring device (DSC6220 manufactured by Shimadzu Corporation). The measurement conditions were as follows.
(1st stage temperature rise program)
The temperature rises from 70 ° C to 15 ° C per minute. Maintained for 5 minutes after reaching 110 ° C.
(2nd stage temperature lowering program)
The temperature drops from 110 ° C to 40 ° C per minute. Maintain for 5 minutes after reaching -50 ° C.
(3rd stage temperature rise program)
The temperature rises from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data are acquired when the temperature rises in the third stage.
Then, the intersection of the baseline (a straight line extending the baseline of the obtained DSC curve to the high temperature side) and the tangent line at the inflection point (the point where the upward convex curve changes to the downward convex curve) is transferred to the glass. The temperature (Tg) was used.

(7) Gel fraction of thermoplastic polymer (toluene insoluble content)
A thermoplastic polymer coating liquid (nonvolatile content = 38 to 42%, pH = 9.0) is dropped on a Teflon (registered trademark) plate with a dropper (diameter 5 mm or less), and 30 in a hot air dryer at 130 ° C. Dry for minutes. After drying, about 0.5 g of the dry film was precisely weighed (a), taken in a 50 mL polyethylene container, 30 mL of toluene was poured into the container, and the mixture was shaken at room temperature for 3 hours. Then, the contents were filtered through a 325 mesh, and the toluene insoluble content remaining on the mesh was dried together with the mesh in a hot air dryer at 130 ° C. for 1 hour. The dry weight of the 325 mesh used here was measured in advance.
Then, after the toluene was volatilized, the dry weight of the toluene insoluble matter (b) was obtained by subtracting the weight of the 325 mesh weighed in advance from the weight of the dried toluene insoluble matter and the 325 mesh. The gel fraction (toluene insoluble matter) was calculated by the following formula.
Gel fraction of thermoplastic polymer (toluene insoluble) = (b) / (a) x 100 [%]

(8) Degree of swelling (double) of the thermoplastic polymer with respect to the electrolytic solution
The thermoplastic polymer or the solution in which the thermoplastic polymer was dispersed was allowed to stand in an oven at 130 ° C. for 1 hour, and then the dried thermoplastic polymer was cut to 0.5 g, and ethylene carbonate: ethylmethyl carbonate = 1. : A 50 mL vial was placed with 10 g of a mixed solvent of 2 (volume ratio), soaked for 3 hours, the sample was taken out, washed with the above mixed solvent, and the weight (Wa) was measured. Then, after allowing it to stand in an oven at 150 ° C. for 1 hour, the weight (Wb) was measured, and the degree of swelling of the thermoplastic polymer with respect to the electrolytic solution was measured from the following formula.
Swelling degree (double) of thermoplastic polymer with respect to electrolytic solution = (Wa-Wb) ÷ (Wb)

(9) Average particle size (nm) of thermoplastic polymer
The average particle size of the thermoplastic polymer was measured using a particle size measuring device (Microtrac UPA150 manufactured by Nikkiso Co., Ltd.). The measurement conditions were a loading index of 0.15 to 0.3 and a measurement time of 300 seconds, and the numerical value of the 50% particle size in the obtained data was described as the particle size.

(10) Metsuke of the thermoplastic polymer coating layer (the amount of the thermoplastic polymer coating layer supported on the substrate)
A 10 cm × 10 cm square sample was cut from a base material (polyolefin porous base material or polyolefin porous base material + inorganic filler porous layer), and the weight was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. .. By multiplying the obtained weight by 100, the basis weight (g / m ² ) of the substrate film per 1 m ² was calculated. Next, a 10 cm × 10 cm square sample was cut from a separator (thermoplastic polymer coating layer + base material), and the mass was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. By multiplying the obtained mass by 100, the basis weight (g / m ² ) of the separator per 1 m ² was calculated. By subtracting the basis weight of the substrate per 1 m ² (g / m ² ) from the basis weight of the separator per 1 m ² (g / m ² ), the basis weight of the thermoplastic polymer coating layer per 1 m ² (thermoplastic polymer). The amount of the coating layer carried on the substrate, g / m ² ) was calculated.

(11) Handleability of the wound body (peeling strength of the innermost layer)
The handleability of the wound body was evaluated by the peel strength of the innermost layer. The wound body was unwound to the innermost layer, and cut out in a state where the innermost separator and the separator wound on the innermost separator were overlapped to obtain a sample. The obtained sample was cut out to 75 mm in the MD direction and 20 mm in the TD direction to prepare a measurement sample. For the measurement sample, the 90 ° peel strength between the separators was measured at a tensile speed of 50 mm / min using a force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd., and evaluated according to the following criteria.
◎ (Good): The peel strength of the innermost layer is less than 3.0 mN / mm ○ (Allowable): The peel strength of the innermost layer is 3.0 mN / mm or more and less than 7.0 mN / mm △ (Evil): The peel strength of the innermost layer Is 7.0 mN / mm or more and less than 10.0 mN / mm × (impossible): The peel strength of the innermost layer is 10.0 mN / mm or more.

(12) Heat peeling strength A separator and a positive current collector as an adherend (UACJ Foil Corporation, alloy number A1085, thickness: 20 μm) were cut into 30 mm × 150 mm, respectively, and laminated to obtain a laminated body. Later, the laminate was sandwiched between Teflon (registered trademark) sheets (Nachias Corporation Naflon (trademark) PTFE sheet TOMBO-No. 9000) to obtain samples. Each of the obtained samples was pressed in the stacking direction for 3 minutes under the conditions of a temperature of 80 ° C. and a pressure of 1 MPa to obtain a test press.
The peel strength between the base material or separator of each test press obtained and the positive electrode current collector is based on JIS K6854-2 using Autograph AG-IS type (trademark) manufactured by Shimadzu Corporation. The measurement was performed at a tensile speed of 200 mm / min. Based on the value of the peel strength, the adhesiveness with the electrode was evaluated according to the following evaluation criteria.
Evaluation Criteria ◎ (Excellent): 15 N / m or more ○ (Good): 9.8 N / m or more and less than 15 N / m △ (Allowable): 5 N / m or more and less than 9.8 N / m × (Defective): Less than 5 N / m

When the peel strength of the test press body pressed in the stacking direction for 1 minute under the conditions of a temperature of 80 ° C. and a pressure of 1 MPa is 5 N / m or more, it is preferable in terms of producing a device with good productivity.

(13) Adhesion to the electrode The adhesiveness between the separator and the electrode was also evaluated by the following procedure.

(Manufacturing of negative electrode)
A slurry was prepared by dispersing 96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of an ammonium salt of carboxymethyl cellulose and 1.7% by mass of a styrene-butadiene copolymer latex as a binder in purified water. This slurry was applied to one side of a copper foil having a thickness of 12 μm as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression-molded with a roll press machine. At this time, the amount of the 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 adhesiveness with electrodes)
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 Tomiyama Pure Chemical Industries, Ltd.), which was a mixture of ethylene carbonate and diethyl carbonate at a ratio of 2: 3 (volume ratio), was poured onto this electrode to the extent that the negative electrode was immersed, and a separator was placed on top of this. This laminate was placed in an aluminum zip, pressed at 80 ° C. and 1 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 100% of the area of the separator.
◯: When the negative electrode active material adheres to an area of 30% or more and less than 100% of the separator.
Δ: When the negative electrode active material adheres to an area of 10% or more and less than 30% of the separator.
X: When the negative electrode active material adheres to an area less than 10% of the separator.

(14) Adhesiveness to the Substrate A tape (manufactured by 3M) having a width of 12 mm and a length of 100 mm was attached to the thermoplastic polymer coating layer of the separator. The force when the tape was peeled off from the substrate (polyolefin microporous film) together with the thermoplastic polymer coating layer at a speed of 50 mm / min was measured using a 90 ° peel strength measuring device (product name IP-5N manufactured by IMADA). .. Based on the obtained measurement results, the adhesive strength with the substrate was evaluated according to the following evaluation criteria.
⊚: 6 gf / mm or more ○: 2 gf / mm or more and less than 6 gf / mm Δ: less than 2 gf / mm

[Production Example 1-1A] (Production of Polyolefin Microporous Membrane 1A)
45 parts by mass of high-density polyethylene, which is a homopolymer having a viscosity average molecular weight (Mv) of 700,000, 45 parts by mass of high-density polyethylene, which is a homopolymer having an Mv of 300,000, and a homopolymer having a viscosity average molecular weight of 400,000. 5 parts by mass of polypropylene was dry blended using a tumbler blender. To 99 parts by mass of the obtained polyolefin mixture, add 1 part by mass of tetrakis- [methylene- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane as an antioxidant, and tumbler again. The mixture was obtained by dry blending using a blender. The obtained mixture was fed to a twin-screw extruder under a nitrogen atmosphere by a feeder. Further, 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 pump were adjusted so that the proportion of liquid paraffin in the total extruded mixture was 65 parts by mass, that is, the polymer concentration was 35 parts by mass.

Then, they were melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product was extruded through a T-die onto a cooling roll controlled to a surface temperature of 80 ° C. to extrude the extruded product. A sheet-shaped molded product was obtained by contacting with a cooling roll and molding (casting) to cool and solidify. This sheet was stretched at a magnification of 7 × 6.4 times with a simultaneous biaxial stretching machine at a temperature of 112 ° C., then immersed in methylene chloride to extract and remove liquid paraffin, dried, and then dried with a tenter stretching machine at a temperature of 130. It was stretched twice in the transverse direction at ° C. Then, this stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain the polyolefin microporous film 1A shown in Table 1.

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

[Production Example 1-2A] (Production of Polyolefin Microporous Membrane 2A)
As the polyolefin microporous film 2A, a model number "CG2500" (manufactured by Asahi Kasei Corporation) of Cellguard, which is a polypropylene single layer film, was prepared. The base materials used are shown in Table 1.

[Production Example 1-3A] (Production of Polyolefin Microporous Membrane 3A)
96.0 parts by mass of aluminum hydroxide (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 formation temperature 0 ° C or less), and polycarboxylic acid. A coating solution was prepared by uniformly dispersing 1.0 part by mass of an aqueous ammonium acid solution (SN Dispersant 5468 manufactured by Sannopco) in 100 parts by mass of water. The obtained coating liquid was applied to the surface of the polyolefin resin porous film 4A using a microgravure coater. It was dried at 60 ° C. to remove water, and a porous layer was formed to a thickness of 2 μm to obtain a microporous membrane 3A. The obtained polyolefin microporous membrane 3A was evaluated by the above method in the same manner as in Production Example 1-1A. The results obtained are shown in Table 1.

[Production Example 1-4A] (Production of Polyolefin Microporous Membrane 4A)
The polyolefin microporous membrane 4A was obtained by performing the same operation as the polyolefin microporous membrane 1A except that the extrusion amount was changed to 1/2. The physical characteristics of the obtained polyolefin microporous membrane 4A are shown in Table 1.

[Production Example 1-5A] (Production of Polyolefin Microporous Membrane 5A)
The following materials:
SiO ₂ "DM10C" (trademark, manufactured by Tokuyama Corporation),
High-density polyethylene with a viscosity average molecular weight of 700,000,
High-density polyethylene with a viscosity average molecular weight of 250,000,
Homopolypropylene with an average molecular weight of 400,000,
Liquid paraffin as a plasticizer, and pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate as an antioxidant]
Was premixed with a super mixer to prepare a first raw material.

The following ingredients:
High-density polyethylene with an average viscosity molecular weight of 700,000, high-density polyethylene with an average viscosity molecular weight of 250,000,
Homopolypropylene with an average molecular weight of 400,000,
Liquid paraffin as a plasticizer, and pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate as an antioxidant]
Was premixed with a super mixer to prepare a second raw material.

The first and second raw materials were individually supplied to the feed ports of two twin-screw codirectional screw extruders by a feeder. At this time, the liquid paraffin is sided to each twin-screw extruder cylinder so that the amount ratio of the plasticizer (liquid paraffin) in the total melt-kneaded product extruded by melt-kneading together with each raw material is 60% by mass. Feeded.

Subsequently, the melt-kneaded products of the first and second raw materials were extruded between a pair of rolls through a T-die capable of co-extrusion of two types and three layers, respectively, via a gear pump and a conduit. In this way, a sheet-like composition (first layer-second layer-first layer) in which the first layer made of the first raw material is a surface layer and the second layer made of the second raw material is an intermediate layer. Got After that, the polyolefin microporous film 5A was obtained by performing the same operation as in the production example of the polyolefin microporous film 1A except that the stretching temperature and the relaxation rate were adjusted.

[Production Examples 2-1B-4B] (Production of Acrylic Emulsion Coating Liquid)
70.4 parts of ion-exchanged water and 0.34 parts of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) in a reaction vessel equipped with a stirrer, reflux cooler, dropping tank and thermometer. And "Adecaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation), 0.34 part was added, the temperature inside the reaction vessel was raised to 80 ° C, and ammonium persulfate was maintained at 80 ° C. 7.5 parts (2% aqueous solution) was added to obtain an initial mixture.

5 minutes after the addition of aqueous ammonium persulfate solution (APS), 71.5 parts of methyl methacrylate (MMA), 18.9 parts of n-butyl acrylate (BA), 2 parts of 2-ethylhexyl acrylate (EHA), methacrylic acid. 0.1 part of (MAA), 0.1 part of acrylic acid (AA), 2 parts of 2-hydroxyethyl methacrylate (HEMA), 5 parts of acrylamide (AM), 0.4 part of glycidyl methacrylate (GMA), trimethylol Propanetriacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) 0.4 parts, "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) 3 parts, "Adecaria Soap SR1025" ( Registered trademark, ADEKA Co., Ltd. 25% aqueous solution) 3 parts, p-styrene sodium sulfonate (NaSS) 0.05 parts, ammonium persulfate (2% aqueous solution) 7.5 parts, γ-methacrylic acid propyltrimethoxysilane 0. The emulsion prepared by mixing 3 parts and 52 parts of ion-exchanged water with a homomixer for 5 minutes was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

After the addition of the emulsion was completed, the temperature inside 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 aqueous solution of ammonium hydroxide (25% aqueous solution) to obtain a coating liquid 1B containing a thermoplastic polymer.

Acrylic copolymer latex was obtained in the same manner as in 2-1B except that the compositions of the monomers and other raw materials used were changed as shown in Table 2 (2-2B to 4B). The obtained 1B to 4B were evaluated by the above method. The results obtained are shown in Table 2.

[Manufacturing Example 2-5B]
A polyvinylidene fluoride-hexafluoropropylene copolymer (HFP7 mL%, Tg: -30 ° C., 50% average particle size: 150 nm) (hereinafter, also referred to as aqueous PVdF) on a water-dispersed latex has a polymer concentration of 30%. The raw material polymer 5B uniformly dispersed in water was prepared.

The Tg of the raw material polymers 1B to 4B shown in Table 2 are all approximate values according to the FOX formula.
The abbreviations in Table 2 mean the following materials, respectively.
MMA: Methyl methacrylate BA: n-butyl EHA acrylate: 2-ethylhexyl acrylate MAA: AA methacrylic acid: HEMA acrylate: 2-hydroxyethyl methacrylate AM: acrylamide GMA: glycidyl acrylate NaSS: p-styrene sulfonic acid Sodium A-TMPT: Trimethylol Propanetriacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.)
KH1025: Aqualon KH1025 (registered trademark, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)
SR1025: Adecaria Soap SR1025 (registered trademark, manufactured by ADEKA CORPORATION)
APS: Ammonium persulfate

[Example 1]
The raw material polymer 1B shown in Table 2 is coated with a coating liquid on one surface of the polyolefin microporous film 1A shown in Table 1 using a gravure coater, and dried at 60 ° C. to remove water from the coating liquid. bottom. Further, the other side was similarly coated with the coating liquid and dried again to obtain a wound body (Example 1A) of a separator having a thermoplastic polymer on both sides of the microporous polyolefin membrane. The obtained separator was evaluated by the above method. The results obtained are shown in Tables 3 and 4.

[Examples 2A to 14A and 16A to 18A, and Comparative Examples 1A to 2A]
Further, in the same manner, wound bodies of Examples 2A to 14A and 16A to 18A and Comparative Example 1A were obtained. In Comparative Example 2A, a wound body could not be obtained. The results obtained are shown in Tables 3 and 4.

[Example 15A]
The same as in Example 1 except that the slurry was adjusted so that the solid content ratio of the raw material polymers 1B and 4B shown in Table 2 was 1B: 4B = 80: 20, and the slurry was applied to the polyolefin microporous film 1A. A wound body of the separator (Example 15A) was obtained. The obtained separator was evaluated by the above method. The results obtained are shown in Tables 3 and 4.

The use of the porous film according to the present embodiment is not particularly limited, but the handling property at the time of winding and the rate characteristic of the energy storage device when used as a separator for an energy storage device are excellent, and further, a thermoplastic polymer and a polyolefin porous group are excellent. Since it has excellent adhesion and permeability to materials, it can be suitably used, for example, for batteries such as non-aqueous electrolyte secondary batteries, capacitors, separators for power storage devices such as capacitors, and separation of substances.

Claims (8)

It is a winding body of a separator for a power storage device.
The separator has a polyolefin porous substrate and a thermoplastic polymer coating layer containing a thermoplastic polymer on at least a part of at least one side of the substrate.
The wound body is a wound body of a separator for a power storage device, in which the number of windings is 1000 or more and 10000 times or less, and the peel strength between separators in the innermost layer is 0.5 mN / mm or more and 10 mN / mm or less. The wound body of the separator for a power storage device according to claim 1, wherein the thermoplastic polymer coating layer has adhesiveness. The wound body of the separator for a power storage device according to claim 1 or 2, wherein the glass transition temperature of at least one of the thermoplastic polymers is 40 ° C. or higher. The power storage device according to any one of claims 1 to 3, wherein the coating texture of the thermoplastic polymer contained in the thermoplastic polymer coating layer is 0.02 g / m ² or more and 2.00 g / m ² or less. For separator winding body. The power storage device according to any one of claims 1 to 3, wherein the coating texture of the thermoplastic polymer contained in the thermoplastic polymer coating layer is 0.02 g / m ² or more and 1.00 g / m ² or less. For separator winding body. The wound body of a separator for a power storage device according to any one of claims 1 to 5, wherein the thickness of the thermoplastic polymer coated layer per one side is 2.0 μm or less. The winding of the separator for a power storage device according to any one of claims 1 to 6, wherein the thermoplastic polymer comprises at least one selected from the group consisting of a conjugated diene polymer, an acrylic polymer, and a fluorine polymer. Polymer. The wound body of the separator for a power storage device according to any one of claims 1 to 7, wherein the thermoplastic polymer contains a copolymer containing at least a (meth) acrylate monomer as a monomer unit.