JP2017103206A - Separator for power storage device and laminate arranged by use thereof, wound body, and lithium ion secondary battery or power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a power storage device which can achieve both of a satisfying rate characteristic and safety of a power storage device.SOLUTION: A separator for a power storage device comprises: a porous base; and a porous layer including an inorganic filler and a resin binder. The porous layer is disposed on at least one face of the porous base. The resin binder includes a copolymer having, as a copolymerized unit, an ethylenic unsaturated monomer (P) of which the number of repetition of an alkylene glycol unit is 3 or more.SELECTED DRAWING: None

Description

  The present invention relates to an electrical storage device separator.

  In recent years, development of power storage devices represented by lithium ion secondary batteries has been actively conducted. Usually, a power storage device is provided with a microporous membrane (separator) between positive and negative electrodes. The separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to pass through the electrolytic solution held in the micropores.

  In order to impart various properties to the separator while ensuring the electrical characteristics and safety of the lithium ion secondary battery, a layer containing an inorganic filler and a resin binder on the surface of the separator substrate (hereinafter referred to as “porous layer” or “filler porous layer”). (Also referred to as "") has been proposed (Patent Document 1).

  Patent Document 1 discloses a polymer particle and an inorganic filler formed from a first monomer having an acidic functional group, a second monomer having an amide group, and a third monomer having a polyoxyalkylene group. It is described that a protective layer is formed on a separator by applying a resin composition containing the following (Synthesis Example 6, Formulation Example 6 and Example 16).

  Conventionally, a polyalkylene glycol group is known as a functional group that enhances the ion permeability of a separator, and is generally used in an organic solvent when incorporated into a copolymer for a non-aqueous electrolyte. On the other hand, in order to obtain an aqueous copolymer, an emulsion polymerization method is generally used. Furthermore, polyalkylene glycol itself is also known as a surfactant that can be used alone. When a polyalkylene glycol group is incorporated into an aqueous copolymer, the polyalkylene glycol group is hydrophilic. Therefore, when used in a large amount, an aqueous dispersion of the particulate copolymer cannot be obtained during emulsion polymerization, or water in the drying process can be obtained. There is a problem that removal is difficult.

Japanese Patent No. 5708872

  In Patent Document 1, methoxypolyethylene glycol methacrylate (MOEMA) having a molecular weight of about 200 is used as the third monomer constituting the polymer particles, and the average number of repeating units of ethylene glycol units in MOEMA is , Approximately 2 when calculated based on molecular weight (Synthesis Example 6, Formulation Example 6 and Example 16).

  The polymer particles described in Patent Document 1 function to point-bond inorganic fillers in the resin composition, and form a protective layer for the separator. The separator described in Patent Document 1, There is still room for improvement from the viewpoint of achieving both the rate characteristics and safety of power storage devices.

  In view of the above circumstances, an object of the present invention is to provide a separator for an electricity storage device that can achieve both rate characteristics and safety of the electricity storage device at a higher level than conventional separators.

The present inventors have found that the above problems can be solved by the following technical means, and have completed the present invention.
[1]
A separator for an electricity storage device comprising a porous substrate and a porous layer containing an inorganic filler and a resin binder,
The porous layer is disposed on at least one surface of the porous substrate, and the resin binder is a copolymer having an ethylenically unsaturated monomer (P) having a polyalkylene glycol group as a monomer unit. And the average number of repeating units (n) of the polyalkylene glycol chain of the ethylenically unsaturated monomer (P) having the polyalkylene glycol group is 3 or more,
The separator for an electricity storage device.
[2]
The copolymer is ethylenically unsaturated monomer (P) having 2 to 50% by mass of the polyalkylene glycol group and 100% by mass of the copolymer and ethylenic having the polyalkylene glycol group. The separator for an electricity storage device according to [1], having as a monomer unit a monomer that does not have a polyalkylene glycol group and is copolymerizable with the unsaturated monomer (P).
[3]
The monomer having no polyalkylene glycol group has an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer (b2) having an amide group, and a hydroxyl group. [2], containing 0.1 to 10% by mass of at least one monomer selected from the group consisting of ethylenically unsaturated monomers (b3) with respect to 100% by mass of the copolymer. For electricity storage devices.
[4]
The electrical storage device separator according to [2] or [3], wherein the monomer having no polyalkylene glycol group includes a crosslinkable monomer (b4).
[5]
The monomer having no polyalkylene glycol group includes an ethylenically unsaturated monomer (A) having a cycloalkyl group and a (meth) acrylic acid ester monomer (b5),
The (meth) acrylate monomer (b5) is a (meth) acrylate monomer composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group, and has the cycloalkyl group The total content of the ethylenically unsaturated monomer (A) and the (meth) acrylic acid ester monomer (b5) is 50 to 98% by mass with respect to 100% by mass of the copolymer, [2 ] The separator for electrical storage devices of any one of [4].
[6]
The electricity storage according to [5], wherein the (meth) acrylic acid ester monomer (b5) is a (meth) acrylic acid ester monomer composed of an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group. Device separator.
[7]
The separator for an electricity storage device according to [5], wherein the ethylenically unsaturated monomer (A) having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.
[8]
The laminated body which consists of a positive electrode, the separator for electrical storage devices of any one of [1]-[7], and a negative electrode.
[9]
A wound body in which the positive electrode, the separator for an electricity storage device according to any one of [1] to [7], and the negative electrode are wound.
[10]
The electrical storage device containing the laminated body as described in [8], or the winding body as described in [9], and electrolyte solution.
[11]
The lithium ion secondary battery containing the laminated body as described in [8], or the winding body as described in [9], and electrolyte solution.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for electrical storage devices which can make the rate characteristic and safety | security of an electrical storage device compatible are provided. By manufacturing the electricity storage device and the secondary battery using the separator according to the embodiment of the present invention, the battery characteristics and safety of the electricity storage device and the secondary battery can be improved.

<Separator for electricity storage device>
The separator for an electricity storage device of the present invention includes a porous substrate and a porous layer containing an inorganic filler and a resin binder, and the porous layer is disposed on at least one surface of the porous substrate. This electricity storage device separator may consist of only a porous substrate and an inorganic filler-containing porous layer, or may further have a thermoplastic polymer layer.

  The porous layer is also called a filler porous layer because it contains an inorganic filler, and is disposed on one or both sides of the porous substrate. When the filler porous layer and the thermoplastic polymer layer are disposed on the porous substrate, their mutual positional relationship is arbitrary, but at least one of the filler porous layers is used from the viewpoint of achieving both the rate characteristics and safety of the electricity storage device. The thermoplastic polymer layer may be disposed so as to expose the portion, and is preferably disposed on the porous filler layer.

Preferred embodiments of each member constituting the electricity storage device separator of the present invention and a method for producing the electricity storage device separator will be described in detail below.
In the present specification, “(meth) acryl” means “acryl” and “methacryl” corresponding thereto, “(meth) acrylate” means “acrylate” and “methacrylate” corresponding thereto, “(Meth) acryloyl” means “acryloyl” and its corresponding “methacryloyl”.

[Porous substrate]
The substrate used in the present embodiment may itself be one that has been conventionally used as a separator. The base material is preferably a porous film having a fine pore size, having no electron conductivity, ionic conductivity, high resistance to organic solvents. As such a porous membrane, for example, a polyolefin-based (for example, polyethylene, polypropylene, polybutene and polyvinyl chloride), and a microporous membrane containing a resin such as a mixture or copolymer thereof as a main component, polyethylene terephthalate, Microporous membrane containing resin such as polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, woven polyolefin fiber (woven fabric) ), Polyolefin fiber nonwoven fabric, paper, and aggregates of insulating substance particles. Among these, when a polymer layer is obtained through a coating process, the coating solution is excellent in coating property, the separator film thickness is made thinner, and the active material ratio in an electricity storage device such as a battery is increased to increase the volume per volume. From the viewpoint of increasing the capacity, a polyolefin microporous film containing a polyolefin-based resin as a main component is preferable. Here, “include as a main component” means to contain more than 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more. More preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

  In the present embodiment, the content of the polyolefin resin in the polyolefin microporous membrane is not particularly limited, but from the viewpoint of shutdown performance when used as a separator for an electricity storage device, all the components constituting the porous substrate 50 A porous film made of a polyolefin resin composition in which the polyolefin resin occupies the mass% to 100 mass% is preferable. The proportion of the polyolefin resin 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.

The polyolefin resin is not particularly limited, and may be a polyolefin resin used for normal extrusion, injection, inflation, blow molding, and the like, and includes ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and Homopolymers and copolymers such as 1-octene, multistage polymers and the like can be used. In addition, polyolefins selected from the group consisting of these homopolymers and copolymers and multistage polymers can be used alone or in admixture.
Representative 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 Random copolymer, polybutene, ethylene propylene rubber and the like can be mentioned.
As a material for the polyolefin porous substrate used as a separator for an electricity storage device, it is preferable to use a resin mainly composed of high-density polyethylene because it has a low melting point and a high strength. These polyethylenes may be used in combination of two or more for the purpose of imparting flexibility. The polymerization catalyst used in the production of these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Philips catalysts, and metallocene catalysts.

In order to improve the heat resistance of the polyolefin porous substrate, it is more preferable to use a porous film made of a resin composition containing polypropylene and a polyolefin resin other than polypropylene.
Here, the three-dimensional structure of polypropylene is not limited, and any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene may be used.
The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is not particularly limited, but is preferably 1 to 35% by mass, 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.
The polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts.

  In this case, the polyolefin resin other than polypropylene is not limited. For example, homopolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene or the like Mention may be made of copolymers. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, and ethylene-propylene random copolymer.

From the viewpoint of shutdown characteristics in which the pores of the polyolefin porous substrate are blocked by heat melting, polyolefin resins other than polypropylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, etc. It is preferable to use polyethylene. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density measured according to JIS K 7112 of 0.93 g / cm ³ or more.

  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 still more preferably 100,000. More than 1 million. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension during melt molding increases, moldability is improved, and the strength tends to increase due to entanglement between polymers. On the other hand, when the viscosity average molecular weight is 12 million or less, it is easy to uniformly melt and knead, and it tends to be excellent in sheet formability, particularly thickness stability, which is preferable. Furthermore, when the viscosity average molecular weight is less than 1,000,000, it is preferable because pores are likely to be blocked when the temperature rises and a good shutdown function tends to be obtained.

For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the mixture having a viscosity average molecular weight of less than 1 million It may be used.
The polyolefin porous substrate in the present embodiment can contain any additive. Such additives are not particularly limited, and include, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenols, phosphoruss, and sulfurs; metal soaps such as calcium stearate and zinc stearate; Agents; light stabilizers; antistatic agents; antifogging agents; colored 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 still more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin composition.
The viscosity average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at a measurement temperature of 135 ° C. using decalin as a solvent based on ASTM-D4020 by the following formula.
Polyethylene: [η] = 6.77 × 10 ⁻⁴ Mv ^0.67 (Chiang formula)
Polypropylene: [η] = 1.10 × 10 ⁻⁴ Mv ^0.80

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, preferably 80% or less. Setting the porosity to 20% or more is preferable from the viewpoint of securing the permeability of the separator. On the other hand, setting the porosity to 90% or less is preferable from the viewpoint of securing the puncture strength. Here, the porosity is calculated, for example, from the volume (cm ³ ), mass (g), and membrane density (g / cm ³ ) of the polyolefin porous substrate sample:
Porosity = (volume−mass / film density) / volume × 100
It can ask for. Here, in the case of a polyolefin porous substrate made of, for example, polyethylene, the film density can be calculated assuming 0.95 (g / cm ³ ). The porosity can be adjusted by changing the draw ratio of the polyolefin porous substrate.

  The air permeability of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 10 seconds / 100 cc or more, more preferably 50 seconds / 100 cc or more, preferably 1,000 seconds / 100 cc or less, more Preferably, it is 500 seconds / 100 cc or less. The air permeability is preferably 10 seconds / 100 cc or more from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, setting the air permeability to 1,000 seconds / 100 cc or less is preferable from the viewpoint of obtaining good charge / discharge characteristics. Here, the air permeability is an air resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the porous substrate.

  The average pore diameter 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. Setting the average pore size to 0.15 μm or less is preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity reduction. The average pore diameter can be adjusted by changing the draw ratio when producing a 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 2,000 g / 20 μm or less, more preferably 1, 000 g / 20 μm or less. It is preferable that the puncture strength is 200 g / 20 μm or more from the viewpoint of suppressing film breakage due to the dropped active material or the like during battery winding, and from the viewpoint of suppressing the concern of short-circuiting due to expansion and contraction of the electrode accompanying charge / discharge. . On the other hand, a puncture strength of 2,000 g / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength is measured by the method described in Examples below.
The puncture strength can be adjusted by adjusting the draw ratio and / or the draw temperature of the polyolefin porous substrate.

  The thickness of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. . It is preferable to adjust the thickness to 2 μm or more from the viewpoint of improving the mechanical strength. On the other hand, it is preferable to adjust the film thickness to 100 μm or less because the occupied volume of the separator in the battery is reduced, and this tends to be advantageous in increasing the capacity of the battery.

[Filler porous layer]
The filler porous layer includes an inorganic filler and a resin binder.

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

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

  Among these, from the viewpoint of improving the electrochemical stability and the heat resistance of the separator, aluminum oxide compounds such as alumina and aluminum hydroxide oxide; and ion exchange such as kaolinite, dickite, nacrite, halloysite, and pyrophyllite. An aluminum silicate compound having no function is preferred.

  Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Among these, α-alumina is preferable because it is thermally and chemically stable.

  As the aluminum oxide compound, aluminum hydroxide oxide (AlO (OH)) is particularly preferable. As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing internal short circuit due to generation of lithium dendrite. By adopting particles mainly composed of boehmite as the inorganic filler constituting the porous layer, it is possible to realize a very light porous layer while maintaining high permeability, and even in a thinner porous layer, a porous film The thermal contraction at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of the electrochemical device is more preferred.

  As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easily available. Known kaolins include wet kaolin and calcined kaolin obtained by calcining this. In the present embodiment, calcined kaolin is particularly preferable. The calcined kaolin is particularly preferable from the viewpoint of electrochemical stability because crystal water is released during the calcining process and impurities are also removed.

  The average particle size of the inorganic filler is preferably more than 0.01 μm and not more than 4.0 μm, more preferably more than 0.2 μm and not more than 3.5 μm, more than 0.4 μm and 3.0 μm. More preferably, it is as follows. Adjusting the average particle size of the inorganic filler to the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperature even when the filler porous layer is thin (for example, 7 μm or less). Examples of the method for adjusting the particle size and distribution of the inorganic filler include a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizer such as a ball mill, a bead mill, or a jet mill. .

  Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a columnar shape, a spherical shape, a polyhedral shape, and a lump shape. A plurality of inorganic fillers having these shapes may be used in combination.

  The proportion of the inorganic filler in the filler porous layer can be appropriately determined from the viewpoints of the binding properties of the inorganic filler, the permeability of the separator, and the heat resistance. The proportion of the inorganic filler in the filler porous layer is preferably 20% by mass or more and less than 100% by mass, more preferably 50% by mass or more and 99.99% by mass or less, and further preferably 80% by mass or more and 99.9% by mass. % Or less, particularly preferably 90% by mass or more and 99% by mass or less.

(Resin binder)
A resin latex binder is preferably used as the resin binder. When a resin latex binder is used as the resin binder, the separator having a filler porous layer containing a resin binder and an inorganic filler binds the resin binder onto the porous film through a process of coating the resin binder solution on the substrate. Compared to the separator, the ion permeability is less likely to decrease, and there is a tendency to provide an electricity storage device with high output characteristics. Furthermore, an electricity storage device having a separator formed using a resin latex binder exhibits smooth shutdown characteristics even when the temperature rise during abnormal heat generation is fast, and tends to provide high safety.

  In the present embodiment, the resin binder may include a resin such as a homopolymer or a copolymer, but at least one of the copolymers included in the resin binder from the viewpoint of achieving both rate characteristics and safety of the electricity storage device. The seed is composed of a copolymer having, as a monomer unit, an ethylenically unsaturated monomer (P) having a polyalkylene glycol group (also referred to as “polyoxyalkylene group”) and having a polyalkylene glycol group. The average number of repeating units (n) of the polyalkylene glycol chain (also referred to as “alkylene glycol repeating unit”) of the polymerizable unsaturated monomer (P) is preferably 3 or more. The “ethylenically unsaturated monomer” means a monomer having one or more ethylenically unsaturated bonds in the molecule.

The copolymer contained in the resin binder has an ethylenically unsaturated monomer having an average of three or more alkylene glycol repeating units as a copolymer unit, so that the separator can be compared with a conventional resin binder such as an acrylic binder. In order to reduce the ionic resistance and further improve the strength, powder-off property or flexibility of the filler porous layer, increasing the amount of the resin binder in the filler porous layer does not increase the ionic resistance, and battery characteristics such as rate characteristics Don't sacrifice.
Furthermore, the copolymer contained in the resin binder improves the dispersibility of the coating slurry containing the inorganic filler and the resin binder by the surface activity of three or more alkylene glycol repeating units on average. As a result, since a uniform inorganic coating layer is formed on the separator substrate, the peel strength of the coating layer can be increased, and the binding property between the polyolefin substrate and the inorganic coating layer can be improved. This improves the safety of the electricity storage device.
The separator in the present embodiment is thus presumed to contribute to both the rate characteristics and safety of the electricity storage device.

  The copolymer contained in the resin binder is effective in improving the ion permeability of the separator because the oxygen atom in the alkylene glycol repeating unit coordinates with lithium (Li) ions to promote the diffusion of Li ions. is there.

  The ethylenically unsaturated monomer (P) having a polyalkylene glycol group can be copolymerized with a monomer having no polyalkylene glycol group. The polyalkylene glycol group is also called a polyoxyalkylene group, and may be, for example, a polyoxymethylene group, a polyoxyethylene group, a polyoxypropylene group, a polyoxybutylene group, or the like. Carbon number of the oxyalkylene group which comprises a polyoxyalkylene group becomes like this. Preferably it is 1-6, More preferably, it is 1-3, More preferably, it is 2. The hydrocarbon group in the polyalkylene glycol group may be linear or branched.

  The average number of repeating units (n) of the polyalkylene glycol chain of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group, as described above, is a viewpoint of achieving both rate characteristics and safety of the electricity storage device. To 3 or more, preferably 100 or less, more preferably 30 or less, further preferably 15 or less, and most preferably 8 or less. When the average number of repeating units (n) is 8 or less, the copolymerizability during emulsion polymerization with a monomer having no polyalkylene glycol group tends to be improved.

  Examples of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group include polyalkylene glycol mono (meth) acrylate, polyalkylene glycol di (meth) acrylate, or polyalkylene glycol unit and allyl group in the molecule. And monomers having reactive substituents such as:

  Examples of the polyalkylene glycol mono (meth) acrylate include polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, polyethylene glycol-polypropylene glycol (meth) acrylate, polyethylene glycol-polybutylene glycol (meth) acrylate, and polypropylene glycol. -Polybutylene glycol (meth) acrylate, 2-ethylhexyl polyethylene glycol mono (meth) acrylate, phenoxydiethylene glycol mono (meth) acrylate, phenoxypolyethylene glycol mono (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxydiethylene glycol mono (meta) ) Acrylate, ethoxypolyethylene Glycol (meth) acrylate, butoxy polyethylene glycol (meth) acrylate, octoxy polyethylene glycol (meth) acrylate, lauroxy polyethylene glycol (meth) acrylate, stearoxy polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, Examples include (meth) acrylic acid ester monomers having a polyalkylene glycol group such as methoxypolypropylene glycol (meth) acrylate, octoxypolyethylene glycol-polypropylene glycol (meth) acrylate, and more effectively and reliably solve the problems of the present invention. From the viewpoint of solving, these are preferable.

  Furthermore, examples of the monomer (P) include reactive surfactants described in the following paragraphs having a polyalkylene glycol chain.

  Among the monomers (P), methoxydiethylene glycol mono (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, butoxypolyethylene glycol mono (meth) acrylate, 2-ethylhexyl polyethylene glycol mono (meth) acrylate, and methoxypolypropylene Glycol mono (meth) acrylate is preferable in that the polymerization stability at the time of preparing the copolymer is good.

  Examples of the polyalkylene glycol di (meth) acrylate include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, and polyethylene glycol-polypropylene glycol di (meth) acrylate.

  Examples of the monomer having a polyalkylene glycol unit and an allyl group in the molecule include polyalkylene glycol monoallyl ether and the like, specifically, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether and the like. May be used.

  From the viewpoint of rate characteristics and safety of the electricity storage device, the lower limit of the copolymerization ratio of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group is preferably 2 with respect to 100% by mass of the copolymer. It is at least mass%, more preferably at least 5 mass%, even more preferably at least 10 mass%. The upper limit is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, and particularly preferably 20% by mass or less. It is preferable that the content ratio of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group is in this range because the ion permeability of the separator is improved. Furthermore, since the dispersibility of the filler and binder in the slurry is improved, not only can a uniform coating layer with good strength of the coating layer be formed, but also the bonding between the substrate and the coating layer due to the effect of the alkylene glycol group. The wearability is also increasing. It is preferable for the content of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group to be 50% by mass or less since the copolymerization during emulsion polymerization is improved.

  The copolymer contained in the resin binder includes an ethylenically unsaturated monomer having a repeating number of alkylene glycol units of 3 or more and a polyalkylene glycol group from the viewpoint of achieving both the rate characteristics and safety of the electricity storage device. It is preferably designed to include a monomer that does not have as a copolymerization component.

  As the monomer having no polyalkylene glycol group, an ethylenically unsaturated monomer having a cycloalkyl group is preferable from the viewpoint of improving the copolymerizability with the monomer (P). The ethylenically unsaturated monomer (A) having a cycloalkyl group is a monomer different from the monomer (P).

  Examples of the alicyclic group include a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, an adamantyl group, and an isobornyl group.

  Specific examples of the ethylenically unsaturated monomer (A) having a cycloalkyl group include a cycloalkyl group such as cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, adamantyl acrylate, adamantyl methacrylate and the like. A (meth) acrylic acid ester monomer is preferable from the viewpoint of more effectively and reliably solving the problems according to the present invention.

  The ethylenically unsaturated monomer (A) having a cycloalkyl group is more preferably a (meth) acrylic acid ester monomer comprising a cycloalkyl group and a (meth) acryloyloxy group. 4-8 are preferable, as for the number of the carbon atoms which comprise the alicyclic ring of a cycloalkyl group, 6 and 7 are more preferable, and 6 is especially preferable. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a tertiary butyl group. Among the monomers (A), cyclohexyl acrylate and cyclohexyl methacrylate are preferable in terms of good copolymerizability at the time of emulsion polymerization with the monomer (P). These are used singly or in combination of two or more.

  In order to improve various qualities and physical properties, the copolymer according to this embodiment is a monomer other than the monomer (B) that does not have a polyalkylene glycol group and does not have a cycloalkyl group. You may have as a unit. The other monomer (B) is a monomer different from the monomers (A) and (P) and can be copolymerized with the monomer (P). The other monomer (B) is not particularly limited, and examples thereof include an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer (b2) having an amide group, and a hydroxyl group. Ethylenically unsaturated monomer (b3), crosslinkable monomer (b4), (meth) acrylic acid ester monomer (b5), ethylenically unsaturated monomer (b6) having a cyano group, Other ethylenically unsaturated monomers can be mentioned.

  Another monomer (B) is used individually by 1 type or in combination of 2 or more types. The other monomer (B) may belong to two or more of the monomers (b1) to (b6) at the same time. That is, the other monomer (B) may be an ethylenically unsaturated monomer having two or more groups selected from the group consisting of a carboxyl group, an amide group, a hydroxyl group, and a cyano group, It may be a crosslinkable monomer having two or more groups selected from the group consisting of a carboxyl group, an amide group, a hydroxyl group, and a cyano group together with an ethylenically unsaturated bond.

  Especially, it is preferable that another monomer (B) contains the ethylenically unsaturated monomer (b1) which has a carboxyl group from a viewpoint of a binding improvement with a filler. Examples of the ethylenically unsaturated monomer (b1) having a carboxyl group include monocarboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid half ester, maleic acid half ester, and fumaric acid half ester. And dicarboxylic acid monomers such as itaconic acid, fumaric acid and maleic acid. These are used singly or in combination of two or more. Among these, from the same viewpoint, acrylic acid, methacrylic acid and itaconic acid are preferable, and acrylic acid and methacrylic acid are more preferable.

  Similarly, from the viewpoint of improving the binding property with the filler, the other monomer (B) preferably contains an ethylenically unsaturated monomer (b2) having an amide group. The ethylenically unsaturated monomer (b2) having an amide group is not particularly limited, and examples thereof include acrylamide, methacrylamide, N, N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, maleic amide and Maleimide is mentioned. These are used singly or in combination of two or more. Of these, acrylamide and methacrylamide are preferable. By using acrylamide and / or methacrylamide, the binding property between the substrate and the coating layer tends to be improved.

  Similarly, from the viewpoint of improving the binding property with the filler, the other monomer (B) preferably contains an ethylenically unsaturated monomer (b3) having a hydroxyl group. Examples of the ethylenically unsaturated monomer (b3) having a hydroxyl group include (meth) acrylates having a hydroxyl group such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate. These are used singly or in combination of two or more. Of these, hydroxyethyl acrylate and hydroxyethyl methacrylate are preferred. By using hydroxyethyl acrylate and / or hydroxyethyl methacrylate, the binding property with the filler tends to be improved.

  Moreover, from a viewpoint of making the insoluble content of the copolymer with respect to the electrolytic solution an appropriate amount, the other monomer (B) preferably contains a crosslinkable monomer (b4). The crosslinkable monomer (b4) is not particularly limited. For example, a monomer having two or more radical polymerizable double bonds, a functional group that gives a self-crosslinking structure during or after polymerization. The monomer which has. These are used singly or in combination of two or more.

  Examples of the monomer having two or more radical polymerizable double bonds include divinylbenzene and polyfunctional (meth) acrylate. Of these, polyfunctional (meth) acrylates are preferred from the viewpoint that better electrolytic solution resistance can be achieved even with a small amount.

  Examples of the polyfunctional (meth) acrylate include bifunctional (meth) acrylate, trifunctional (meth) acrylate, and tetrafunctional (meth) acrylate. For example, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol di Examples include acrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These are used singly or in combination of two or more. Of these, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are preferable from the same viewpoint as described above.

  Examples of the monomer having a functional group that gives a self-crosslinking structure during or after polymerization include, for example, an ethylenically unsaturated monomer having an epoxy group, an ethylenic monomer having a methylol group, and an ethylene having an alkoxymethyl group And an ethylenically unsaturated monomer having a hydrolyzable silyl group. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having an epoxy group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate. These are used singly or in combination of two or more. Among these, glycidyl methacrylate is preferable.

  Examples of the ethylenically unsaturated monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having an alkoxymethyl group include N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-butoxymethyl acrylamide, and N-butoxymethyl methacrylamide. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having a hydrolyzable silyl group include vinyl silane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ. -Methacryloxypropyltriethoxysilane. These are used singly or in combination of two or more.

  Among the crosslinkable monomers (b4), polyfunctional (meth) acrylates are particularly preferable in that there is little variation in the degree of crosslinking.

  Moreover, from a viewpoint of making the oxidation resistance of the resin binder containing the copolymer which concerns on this embodiment favorable, another monomer (B) contains a (meth) acrylic acid ester monomer (b5). Is preferred. The (meth) acrylic acid ester monomer (b5) is a monomer different from the monomers (b1) to (b4). Examples of the (meth) acrylic acid ester monomer (b5) include (meth) acrylic acid ester having one ethylenically unsaturated bond, and more specifically, methyl acrylate, ethyl acrylate, propyl acrylate. , Isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate , N-hexyl methacrylate, 2-ethylhexyl methacrylate, (meth) aldehyde having an alkyl group such as lauryl methacrylate Relate like (more preferably consisting of an alkyl group and a (meth) acryloyloxy group-containing (meth) acrylate) is.

  Among these, the (meth) acrylic acid ester monomer (b5) is composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group from the viewpoint of improving the copolymerizability during emulsion polymerization (meta). ) Acrylic acid ester monomer is preferable, and a (meth) acrylic acid ester monomer composed of an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group is more preferable. More specifically, methyl methacrylate, butyl acrylate, butyl methacrylate and 2-ethylhexyl acrylate are preferable, butyl acrylate, butyl methacrylate and 2-ethylhexyl acrylate are more preferable, and 2-ethylhexyl acrylate is still more preferable. These (meth) acrylic acid ester monomers (b5) are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer (b6) having a cyano group include acrylonitrile and methacrylonitrile. Examples of the ethylenically unsaturated monomer having an aromatic group include styrene, vinyl toluene, and α-methyl styrene. Of these, styrene is preferable.

  In this embodiment, the ethylenically unsaturated monomer (A) having a cycloalkyl group is used together with the ethylenically unsaturated monomer (P) having an average number of repeating units (n) of the polyalkylene glycol chain of 3 or more. By actively using, an ethylenically unsaturated monomer having an average number of repeating units of polyalkylene glycol chain of 3 or more is generally not suitable for emulsion polymerization. The obtained copolymer can be easily dispersed in a dispersion medium such as water.

The ethylenically unsaturated monomer (P) having a polyalkylene glycol group may include a (meth) acrylate monomer having an average number of repeating units (n) of the polyalkylene glycol chain of more than 1 and less than 3. Good. Examples of the (meth) acrylate monomer having an average repeating unit number (n) of the polyalkylene glycol chain of more than 1 and less than 3 include, for example, the following formula:
^{_{CH 2 = C (R 1)}} -CO-O- (CH 2 -CH 2 -O) n -R 2
{Wherein, R ¹ and R ² are each independently a hydrogen atom or a methyl group, and n is a number satisfying 3>n> 1}
The compound etc. which are represented by these are mentioned.

  From the viewpoint of achieving both the ion permeability of the separator and the adhesiveness between the inorganic fillers in the filler porous layer, and further from the viewpoint of enhancing the binding property between the porous substrate and the inorganic coating layer, The copolymerization ratio (total content ratio) of the meth) acrylate monomer is preferably 50 to 99.9% by mass, more preferably 60 to 60%, based on the mass of the copolymer constituting the resin binder. It is 99.9 mass%, More preferably, it is 70-99.9 mass%, Still more preferably, it is 80-99.9 mass%. In this paragraph, the (meth) acrylic acid ester monomer has a cycloalkyl group and an ethylenically unsaturated monomer (P) having a polyalkylene glycol group that corresponds to a (meth) acrylic acid ester. Among the ethylenically unsaturated monomers (A), those corresponding to (meth) acrylic acid esters, and (meth) acrylic acid ester monomers having no polyalkylene glycol group and no cycloalkyl group (b5) ). When the content ratio of the (meth) acrylic acid ester monomer is within the above range, the oxidation resistance of the resin binder tends to be better when the separator is used in a non-aqueous electrolyte secondary battery.

  When the other monomer (B) contains an ethylenically unsaturated monomer (b1) having a carboxyl group, the content of the ethylenically unsaturated monomer (b1) having a carboxyl group in the copolymer is The amount is preferably 0.1 to 10% by mass, more preferably 0.1 to 5% by mass, and still more preferably 0.1 to 3% by mass with respect to 100% by mass of the copolymer. When the content ratio of the ethylenically unsaturated monomer (b1) having a carboxyl group is 0.1% by mass or more, the binding property between fillers tends to be improved, and when it is 10% by mass or less, The dispersion stability of the aqueous dispersion tends to be improved.

  Another monomer (B) is an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer (b2) having an amide group, or an ethylenically unsaturated monomer having a hydroxyl group When the body (b3) is included, the total content of (b1), (b2) and (b3) in the copolymer is preferably 0.1 to 10% by mass with respect to 100% by mass of the copolymer. It is. When the total content of the above three types is 0.1% by mass or more, the binding property between the fillers tends to be improved, and when it is 10% by mass or less, water is removed from the aqueous dispersion. It tends to be easier.

  When the other monomer (B) contains the crosslinkable monomer (b4), the content of the crosslinkable monomer (b4) in the copolymer is preferably 100% by mass of the copolymer. It is 0.01-10 mass%, More preferably, it is 0.1-5 mass%, More preferably, it is 0.1-3 mass%. When the content ratio of the crosslinkable monomer (b4) is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when it is 10% by mass or less, the decrease in the binding property between the fillers can be further suppressed. it can.

  In the present embodiment, from the viewpoint of adhesion to the separator electrode and ion permeability, the copolymer contained in the resin binder is an ethylene having a cycloalkyl group as a monomer having no polyalkylene glycol group. It is preferable that a polymerizable unsaturated monomer (A) and a (meth) acrylic acid ester monomer (b5) are included. The total content of the ethylenically unsaturated monomer (A) having a cycloalkyl group and the (meth) acrylic acid ester monomer (b5) is 50 to 98% by mass with respect to 100% by mass of the copolymer, It is preferable that it is 51-97 mass% or 55-95 mass%.

  The glass transition temperature (hereinafter also referred to as “Tg”) of the resin binder is preferably −50 ° C. or higher, more preferably −40 to 10 ° C. When the glass transition temperature of the copolymer binder is within the above range, the heat resistance of the separator tends to be further improved.

  Here, the glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, it is determined by the intersection of a straight line obtained by extending the base line on the low temperature side in the DSC curve to the high temperature side and the tangent at the inflection point of the stepped change portion of the glass transition.

  “Glass transition” refers to a change in calorific value associated with a change in the state of the polymer that is a test piece in DSC on the endothermic side. Such a change in heat quantity is observed as a step-like change shape in the DSC curve. The “step change” refers to a portion of the DSC curve until the curve moves away from the previous low-temperature base line to a new high-temperature base line. Note that a combination of a step change and a peak is also included in the step change.

  Further, the “inflection point” indicates a point at which the gradient of the DSC curve of the step-like change portion is maximized. Further, in the step-like change portion, when the upper side is the heat generation side, it can also be expressed as a point where the upward convex curve changes to the downward convex curve. “Peak” indicates a portion of the DSC curve from when the curve leaves the low-temperature side baseline until it returns to the same baseline again. “Baseline” refers to a DSC curve in a temperature region where no transition or reaction occurs in the test piece.

  The method for obtaining the copolymer contained in the resin binder is not particularly limited, but the emulsion polymerization method is preferred for the purpose of obtaining a particle-shaped dispersion. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-known method can be used. For example, in a dispersion system containing the above-mentioned monomer, surfactant, radical polymerization initiator, and other additive components used as necessary in an aqueous medium as a basic composition component, each of the above monomers. A copolymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the supplied monomer composition is made constant throughout the entire polymerization process, and the morphological composition change of the particles of the resin dispersion to be produced is changed by sequentially or continuously changing the polymerization process. Various methods can be used as required, such as a giving method. When the copolymer is obtained by emulsion polymerization, the copolymer is, for example, in the form of an aqueous dispersion (also referred to as “aqueous latex”) containing water and a particulate copolymer dispersed in the water. Also good.

  The surfactant is a compound having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. Examples of the surfactant include non-reactive alkyl sulfate, polyoxyethylene alkyl ether sulfate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, naphthalene sulfone. Anionic interfaces such as acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene distyrenated phenyl ether sulfate, fatty acid salt, alkyl phosphate, polyoxyethylene alkylphenyl ether sulfate Activators and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distiles Phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, polyoxyethylene alkylphenyl ether, etc. Nonionic surfactant is mentioned. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

  Examples of the anionic surfactant in the reactive surfactant include an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group or a sulfate ester group and a salt thereof, and a sulfonic acid group, or A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) which is an ammonium salt or an alkali metal salt thereof is preferable. Specifically, for example, alkylallylsulfosuccinate (for example, Eleminol (trademark) JS-20 manufactured by Sanyo Chemical Co., Ltd., Latemuru (trademark; manufactured by Kao Corporation), S-120, S-180A, S- 180), polyoxyethylene alkylpropenyl phenyl ether sulfate ester salt (for example, Aqualon (trademark; the same shall apply hereinafter) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α- [1- [ (Allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, ADEKA Corporation soap (trademark; the same shall apply hereinafter) SE-10N manufactured by ADEKA Corporation), ammonium. = Α-sulfonato-ω-1- (allyloxymethyl) alkyloxypolyoxyethylene (eg, Aquaron KH-10 manufactured by Ichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Spinomer (trademark) NaSS manufactured by Tosoh Organic Chemical Co., Ltd.), α- [2-[(allyloxy)- 1- (alkyloxymethyl) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adeka Soap SR-10 manufactured by ADEKA Corporation), polyoxyethylene polyoxybutylene (3-methyl-3- Butenyl) ether sulfate (for example, LATEMUL PD-104 manufactured by Kao Corporation) may be mentioned.

  Examples of the nonionic surfactant in the reactive surfactant include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) RN-30 and RN-50), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap ER manufactured by ADEKA Corporation) -10)), polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) A Le (for example, Kao Corp. LATEMUL PD-420.) And the like.

  Among the above-mentioned various surfactants, reactive surfactants are preferable, anionic reactive surfactants are more preferable, and reactive surfactants having a sulfonic acid group are more preferable. The surfactant is preferably used in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the monomer composition. Surfactant is used individually by 1 type or in combination of 2 or more types.

  The radical polymerization initiator is one that initiates addition polymerization of monomers by radical decomposition with heat or a reducing substance, and any of inorganic initiators and organic initiators can be used. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used. Examples of the water-soluble polymerization initiator include peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems. Examples of the peroxodisulfate include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS). Examples of the peroxide include hydrogen peroxide, t- Examples thereof include butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide. Examples of water-soluble azobis compounds include 2,2-azobis (N-hydroxyethylisobutyramide), 2 And 2-azobis (2-amidinopropane) dichloride and 4,4-azobis (4-cyanopentanoic acid). Examples of the redox system of the peroxide-reducing agent include sodium peroxide and sodium peroxide. Sulfooxylate formaldehyde, sodium bisulfite, sodium thiosulfate Um, sodium hydroxymethanesulfinic acid, L- ascorbic acid, and its salts, cuprous salts, and include those that combine one or more reducing agents such as ferrous salts.

  The radical polymerization initiator is preferably used in an amount of 0.05 to 2 parts by mass with respect to 100 parts by mass of the monomer composition. A radical polymerization initiator is used individually by 1 type or in combination of 2 or more types.

  In addition, the single quantity containing the ethylenically unsaturated monomer (P) which has a polyalkylene glycol group, the ethylenically unsaturated monomer (A) which has a cycloalkyl group, and another monomer (B). When the body composition is emulsion-polymerized to form an aqueous dispersion in which the copolymer particles are dispersed in a solvent (water), the solid content of the obtained aqueous dispersion is 30% by mass to 70% by mass. Is preferred.

  The aqueous dispersion is preferably adjusted to have a pH in the range of 5 to 12 in order to maintain long-term dispersion stability. For pH adjustment, amines such as ammonia, sodium hydroxide, potassium hydroxide, and dimethylaminoethanol are preferably used, and pH is more preferably adjusted with ammonia (water) or sodium hydroxide.

  The aqueous dispersion contains a copolymer obtained by copolymerizing the monomer composition containing the specific monomer as particles (copolymer particles) dispersed in water. In addition to water and the copolymer, the aqueous dispersion may contain a solvent such as methanol, ethanol, isopropyl alcohol; a dispersant, a lubricant, a thickener, a disinfectant, and the like.

  The average particle size of the copolymer particles is preferably 30 to 1000 nm, more preferably 30 to 800 nm, and still more preferably 100 to 700 nm. When the average particle diameter of the copolymer particles is 30 nm or more, the ion permeability is difficult to decrease, and an electricity storage device having high output characteristics is easily provided. Furthermore, even when the temperature rises rapidly during abnormal heat generation, it is easy to obtain an electricity storage device that exhibits smooth shutdown characteristics and high safety. In addition, it is preferable that the average particle diameter of the copolymer particles is 1000 nm or less from the viewpoint of securing the dispersion stability of the aqueous dispersion, and further, when a good binding property is expressed and a multilayer porous membrane is obtained. Thermal shrinkage becomes good and tends to be excellent in safety. The average particle diameter of the copolymer particles can be measured according to the method described in the following examples.

  The content of the copolymer having an ethylenically unsaturated monomer having an average number of repeating units (n) of the polyalkylene glycol chain of 3 or more as a copolymer unit in the filler porous layer is based on the mass of the filler porous layer. As 0.1% by weight or more, 1% by weight or more, 2% by weight or more, 5% by weight or more, or 10% by weight or more, and the content is less than 80% by weight, 70% by weight or less, 60% by weight. Or 50% by mass or less.

  In the resin binder, other polymers may be blended together with a copolymer having an ethylenically unsaturated monomer having three or more alkylene glycol repeating units as a copolymer unit.

Although it does not specifically limit as another polymer, It is preferable to use the polymer which is insoluble with respect to the electrolyte solution of a lithium ion secondary battery, and is electrochemically stable in the use range of a lithium ion secondary battery.
Specific examples of other polymers include, for example, polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene Fluorine-containing rubber such as 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, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate Gums; cellulose, methyl cellulose, hydroxyethyl cellulose, cellulose derivatives such as carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester or the like.

In the present embodiment, the glass transition temperature Tg of the polymer contained in the resin binder can be adjusted as appropriate by changing, for example, the monomer components used when producing the polymer and the charging ratio of each monomer. That is, for each monomer used in the production of the polymer, from the generally indicated homopolymer Tg (for example, described in “A WILEY-INTERSCIENCE PUBLICATION”) and the blending ratio of the monomers The outline of the glass transition temperature can be estimated. For example, a copolymer having a high proportion of monomers such as methyl methacrylate, acrylonitrile, methacrylic acid, etc., giving a homopolymer with a Tg of about 100 ° C. has a high Tg; for example, a Tg of about −50 ° C. The Tg of a copolymer obtained by copolymerizing monomers such as n-butyl acrylate and 2-ethylhexyl acrylate at a high ratio is low.
Moreover, Tg of a copolymer is following numerical formula (1):
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ +... + W _i / Tg _i +... W _n / Tg _n (1)
{Wherein Tg (K) is the Tg of the copolymer, Tg _i (K) is the Tg of the homopolymer of monomer i, and W _i is the mass fraction of each monomer. } Can also be approximated by the formula of FOX represented by:
However, as the glass transition temperature Tg of the polymer in this embodiment, a value measured by the method using DSC is adopted.

The thickness of the filler porous layer is preferably 0.5 μm or more from the viewpoint of improving heat resistance and insulation, and is preferably 50 μm or less from the viewpoint of increasing the capacity and permeability of the battery.
Layer density of the filler porous layer ^is preferably ^{0.5g / cm 3 ~3.0g / cm 3} , more preferably ^{0.7g / cm 3 ~2.0g / cm 3} . When the layer density of the filler 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 3.0 g / cm ³ or less, the air permeability tends to decrease. It is in.

Examples of the method for forming the porous filler layer include a method of applying a coating liquid containing an inorganic filler and a resin binder on at least one surface of a substrate. In this case, the coating liquid may contain a solvent, a dispersing agent, and the like in order to improve dispersion stability and coating property.
The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. For example, a filler raw material containing a resin binder and a polymer base material may be laminated and extruded by a co-extrusion method, or the base material and the filler porous film may be separately produced and bonded.

[Thermoplastic polymer layer]
The electricity storage device separator may have a thermoplastic polymer layer in addition to the porous substrate and the filler porous layer, if desired. The thermoplastic polymer layer may be disposed on one or both surfaces of the porous substrate or on the filler porous layer, and it is preferable that at least a part of the filler porous layer is disposed.

In the present embodiment, the area ratio of the thermoplastic polymer layer to the total area of the surface on which the thermoplastic polymer layer is disposed in the surface of the porous substrate is 100% or less, 80% or less, 75% or less, or The area ratio is preferably 70%, and the area ratio is preferably 5% or more, 10% or more, or 15% or more. Setting the coating area of the thermoplastic polymer layer to 100% or less is preferable from the viewpoint of further suppressing the blockage of the pores of the base material by the thermoplastic polymer and further improving the permeability of the separator. On the other hand, setting the coating area to 5% or more is preferable from the viewpoint of further improving the adhesion to the electrode. This area ratio is measured by observing the thermoplastic polymer layer forming surface of the obtained separator with an SEM.
Further, when the thermoplastic polymer layer is a layer mixed with an inorganic filler, the total area of the thermoplastic polymer and the inorganic filler is taken as 100% to calculate the existing area of the thermoplastic polymer.

When the thermoplastic polymer layer is arranged only on a part of the surface of the porous base material and the inorganic filler layer, examples of the arrangement pattern of the thermoplastic polymer layer include a dot shape, a stripe shape, a lattice shape, a stripe shape, and a turtle shell shape. , Random shapes, and combinations thereof.
The thickness of the thermoplastic polymer layer disposed on the polyolefin porous substrate is preferably 0.01 μm to 5 μm, more preferably 0.1 μm to 3 μm per side of the substrate. More preferably, it is 1-1 micrometer.

(Thermoplastic polymer)
The thermoplastic polymer layer includes a thermoplastic polymer. The thermoplastic polymer layer may contain 60% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more of the thermoplastic polymer, based on the total amount of the thermoplastic polymer layer. . The thermoplastic polymer layer may contain other components in addition to the thermoplastic polymer.

Examples of the thermoplastic polymer include the following:
Polyolefin resins such as polyethylene, polypropylene and α-polyolefin;
Fluoropolymers such as polyvinylidene fluoride and polytetrafluoroethylene or copolymers containing these;
A diene polymer containing a conjugated diene such as butadiene or isoprene as a monomer unit, a copolymer containing these, or a hydride thereof;
Acrylic polymer containing (meth) acrylate or the like as a monomer unit and not having a polyalkylene glycol unit, (meth) acrylate or the like as a monomer unit, and one or two polyalkylene glycol units An acrylic polymer or a copolymer containing these or a hydride thereof;
Rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate;
Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose;
Polyalkylene glycols having no polymerizable functional group, such as polyethylene glycol and polypropylene glycol;
Resins such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester;
A copolymer having, as a copolymerization unit, an ethylenically unsaturated monomer having 3 or more repeating alkylene glycol units, as described above as a resin binder for forming a filler porous layer; and combinations thereof;
Is mentioned.
Among these, a diene polymer, an acrylic polymer, or a fluorine polymer is preferable from the viewpoints of adhesion to an electrode active material, flexibility, and ion permeability of the polymer.

  The glass transition temperature (Tg) of the thermoplastic polymer is preferably −50 ° C. or higher, more preferably in the range of −50 ° C. to 150 ° C., from the viewpoints of adhesion to the electrode and ion permeability. .

  From the viewpoint of wettability to the polyolefin microporous membrane, the binding property between the polyolefin microporous membrane and the thermoplastic polymer layer, and the adhesion to the electrode, the thermoplastic polymer layer has a glass transition temperature of less than 20 ° C. Are preferably blended, and a polymer having a glass transition temperature of 20 ° C. or higher is preferably blended from the viewpoint of blocking resistance and ion permeability.

The thermoplastic polymer having at least two glass transition temperatures can be achieved by, for example, a method of blending two or more thermoplastic polymers, a method of using a thermoplastic polymer having a core-shell structure, and the like.
The core-shell structure is a polymer having a dual structure in which the polymer belonging to the central portion and the polymer belonging to the outer shell portion are composed of different compositions.
In particular, in a polymer blend and a core-shell structure, the glass transition temperature of the entire thermoplastic polymer can be controlled by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature. Moreover, a plurality of functions can be imparted to the entire thermoplastic polymer.

In the present embodiment, from the viewpoint of blocking suppression and ion permeability of the separator, the thermoplastic copolymer is particulate when the glass transition temperature is, for example, 20 ° C. or higher, 25 ° C. or higher, or 30 ° C. or higher. It is preferable.
By including the particulate thermoplastic copolymer in the thermoplastic polymer layer, the porosity of the thermoplastic polymer layer disposed on the substrate and the blocking resistance of the separator can be ensured.

  The average particle diameter of the particulate thermoplastic copolymer is preferably 10 nm to 2,000 nm, more preferably 50 nm to 1,500 nm, still more preferably 100 nm to 1,000 nm, particularly preferably 130 nm to 800 nm, and particularly preferably 150 nm. It is -800 nm, Most preferably, it is 200-750 nm. Setting the average particle size to 10 nm or more ensures that the size of the particulate thermoplastic polymer is such that it does not enter the pores of the substrate when at least the particulate thermoplastic polymer is applied to the substrate including the porous film. Means that Therefore, in this case, it is preferable from the viewpoint of improving the adhesion between the electrode and the separator and the cycle characteristics of the electricity storage device. In addition, when the average particle diameter is 2,000 nm or less, an amount of the particulate thermoplastic polymer necessary for achieving both the adhesion between the electrode and the separator and the cycle characteristics of the electricity storage device is formed on the substrate. It is preferable from the viewpoint of coating. The average particle size of the particulate thermoplastic polymer can be measured according to the method described in the following examples.

  The particulate thermoplastic polymer described above can be produced by a known polymerization method using the corresponding monomer or comonomer. As a polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization or the like can be employed.

  In this embodiment, since the thermoplastic polymer layer can be easily formed by coating, a particulate thermoplastic polymer is formed by emulsion polymerization, and the resulting thermoplastic polymer emulsion is used as an aqueous latex. It is preferable.

(Optional component)
The thermoplastic polymer layer in the present embodiment may contain only the thermoplastic polymer, or may contain other optional components in addition to the thermoplastic polymer. Examples of the optional component include the inorganic filler described above for forming a filler porous layer.

<Method for producing separator for power storage device>
[Method for producing polyolefin porous substrate]
The method for producing the polyolefin porous 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 and formed into a sheet shape, optionally stretched and then made porous by extracting the plasticizer, and a polyolefin resin composition is melt-kneaded to obtain a high draw rate. After extruding at a ratio, the polyolefin crystal interface is peeled off by heat treatment and stretching, the polyolefin resin composition and the inorganic filler are melt-kneaded and molded on a sheet, and then the polyolefin and inorganic filler are stretched And a method of making the structure porous by removing the solvent at the same time as solidifying the polyolefin by dissolving it in a poor solvent for the polyolefin after dissolving the polyolefin resin composition.

  Moreover, a well-known thing may be sufficient as the method of producing the nonwoven fabric or paper as a base material. The production method includes, for example, a chemical bond method in which a web is dipped in a binder, dried, and bonded between fibers; a heat-bondable fiber is mixed into the web, and the fibers are partially melted to bond between fibers. A needle punch method in which a needle having a stab is repeatedly stabbed into the web and mechanically entangled with the fiber; a high-pressure water flow is entangled between the fibers by jetting a high-pressure water stream from the nozzle through the net (screen).

Hereinafter, as an example of a method for producing a polyolefin porous substrate, a method for melt-kneading a polyolefin resin composition and a plasticizer to form a sheet and then extracting the plasticizer will be described.
First, a polyolefin resin composition and a plasticizer are melt-kneaded. As the melt-kneading method, for example, polyolefin resin and other additives as required may be added to a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc. A method of introducing a plasticizer at a ratio of kneading and kneading. At this time, it is preferable that the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being added to the resin kneading apparatus. More preferably, only a part of the plasticizer is added in the pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading apparatus.

  As the plasticizer, a non-volatile solvent capable of forming a uniform solution at a melting point or higher 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. Of these, liquid paraffin is preferred.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30 to 80 mass%, more preferably 40 to 70 mass%. By setting the mass fraction of the plasticizer within this range, it is preferable from the viewpoint of achieving both melt tension during melt molding and formability of a uniform and fine pore structure.

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. As the heat conductor used for cooling and solidification, metal, water, air, plasticizer itself, and the like can be used, but a metal roll is preferable because of high heat conduction efficiency. In this case, it is more preferable that the metal roll is sandwiched between the rolls, since the efficiency of heat conduction is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved. The die lip interval when extruding from a T-die into a sheet is preferably from 400 μm to 3,000 μm, and more preferably from 500 μm to 2,500 μm.

  It is preferable to subsequently stretch the sheet-like molded body thus obtained. As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used. Biaxial stretching is preferred from the viewpoint of the strength of the resulting porous substrate. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the porous substrate finally obtained is difficult to tear and has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improvement of puncture strength, uniformity of stretching, and shutdown property.

  The draw ratio is preferably in the range of 20 times to 100 times, more preferably in the range of 25 times to 50 times in terms of surface magnification. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction, preferably in the range of 4 to 10 times in the TD direction, 5 to 8 times in the MD direction, and 5 times in the TD direction. More preferably, it is in the range of 8 times or less. By setting the total area magnification within this range, it is preferable in that sufficient strength can be imparted, film breakage in the stretching step can be prevented, and high productivity can be obtained.

  The sheet-like molded body obtained as described above may be further rolled. Rolling can be performed, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion. The rolling surface magnification is preferably greater than 1 and 3 or less, more preferably greater than 1 and 2 or less. By setting the rolling magnification within this range, it is preferable in that the film strength of the porous substrate finally obtained can be increased and a uniform porous structure can be formed in the film thickness direction.

  Next, the plasticizer is removed from the sheet-like molded body to obtain a porous substrate. As a method for removing the plasticizer, for example, a method of extracting the plasticizer by immersing the sheet-like molded body in an extraction solvent and sufficiently drying it can be mentioned. The method for extracting the plasticizer may be either a batch type or a continuous type. In order to suppress the shrinkage of the porous substrate, it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying. Further, the residual amount of plasticizer in the porous substrate is preferably less than 1% by mass.

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

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

  If the surface treatment is performed on the surface of the polyolefin porous substrate, it becomes easier to apply the coating liquid thereafter, and the adhesion between the polyolefin porous substrate and the filler porous layer or the thermoplastic polymer layer is improved. preferable. Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

[Method for arranging filler porous layer]
The filler porous layer is formed on the substrate by applying a coating liquid containing an inorganic filler, a resin binder, and, if desired, an additional component such as a solvent (for example, water) and a dispersant to at least one surface of the substrate. Can be arranged. A resin binder may be synthesized by emulsion polymerization, and the obtained emulsion may be used as it is as a coating solution.

The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. Coating methods include, 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 coater method, die coater method, screen printing method, spray coating method, ink jet coating method and the like. Among these, the gravure coater method is preferable because the degree of freedom of the coating shape is high.
Furthermore, the filler raw material containing the resin binder and the polymer base material may be laminated and extruded by a co-extrusion method, or the base material and the filler porous film may be individually produced and bonded.

  The method for removing the solvent from the coating film after coating is not limited as long as it does not adversely affect the substrate and the porous layer. For example, a method of drying at a temperature lower than the melting point of the substrate while fixing the substrate, a method of drying under reduced pressure at a low temperature, and the like can be mentioned.

[Method of arranging thermoplastic polymer layer]
A thermoplastic polymer can be arrange | positioned on a base material by applying the coating liquid containing a thermoplastic polymer to a base material, for example. A thermoplastic polymer may be synthesized by emulsion polymerization, and the resulting emulsion may be used as it is as a coating solution. The coating liquid preferably contains a poor solvent such as water, a mixed solvent of water and a water-soluble organic medium (for example, methanol or ethanol).

  Regarding the method of applying a coating liquid containing a thermoplastic polymer on a polyolefin porous substrate, there is no particular limitation as long as it can realize a desired coating pattern, coating film thickness, and coating area. Absent. For example, the coating method described above may be used to apply the inorganic filler-containing coating solution. The gravure coater method or the spray coating method is preferable from the viewpoint that the degree of freedom of the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

  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 substrate and the polymer layer. For example, a method of drying at a temperature below its melting point while fixing a polyolefin porous substrate, a method of drying under reduced pressure at a low temperature, and dipping in a poor solvent for a thermoplastic polymer to solidify the thermoplastic polymer into particles The method of extracting a solvent simultaneously is mentioned.

<Physical properties of separator for electricity storage device>
In the present embodiment, the air permeability of the electricity storage device separator is preferably 10 seconds / 100 cc or more and 650 seconds / 100 cc or less, more preferably 20 seconds / 100 cc or more and 500 seconds / 100 cc or less, more preferably 30 seconds. / 100 cc to 450 seconds / 100 cc, particularly preferably 50 seconds / 100 cc to 400 seconds / 100 cc. This air permeability is the air resistance measured according to JIS P-8117, similar to the air permeability of the polyolefin porous substrate.
When the air permeability is 10 seconds / 100 cc or more, self-discharge tends to decrease when used as a battery separator, and when it is 650 seconds / 100 cc or less, good charge / discharge characteristics tend to be obtained.
The electricity storage device separator according to the present embodiment exhibits a very large air permeability, and thus exhibits a large ion permeability when applied to a lithium ion secondary battery.

  The final thickness of the separator is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, and further preferably 7 μm or more and 30 μm or less. When the thickness is 2 μm or more, the mechanical strength tends to be sufficient, and when the thickness is 200 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the battery capacity.

<Power storage device>
The separator for an electricity storage device of this embodiment can be suitably applied as a separator for an electricity storage device by combining this with a positive electrode, a negative electrode, and a non-aqueous electrolyte. An example of the electricity storage device is a lithium ion secondary battery.
When manufacturing a lithium ion secondary battery using the separator of this embodiment, there is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, Each can use a well-known thing.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be suitably used. Examples of the positive electrode current collector include aluminum foil, and examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO _4. . In addition to the positive electrode active material, the positive electrode active material layer may include a binder, a conductive material, and the like.

  As the negative electrode, a positive electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector can be suitably used. Examples of the negative electrode current collector include copper foil, and examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, and metallic lithium. And various alloy materials.

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

The method for producing the electricity storage device using the electricity storage device separator of the present embodiment is not particularly limited. For example, the following method can be illustrated.
The separator of this embodiment is manufactured as a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4,000 m (preferably 1,000 to 4,000 m). Laminated in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, wound into a circular or flat spiral shape to obtain a wound body, and the wound body is housed in a battery can, Furthermore, it can manufacture by inject | pouring electrolyte solution. Alternatively, it is manufactured by a method in which a laminate composed of a sheet-like separator and an electrode, or a wound body obtained by folding an electrode and a separator is placed in a battery container (for example, an aluminum film) and an electrolyte is injected. May be.

  At this time, it is also preferable to press the laminated body or the wound body. Specifically, the separator for an electricity storage device of the present embodiment, an electrode having a current collector and an active material layer formed on at least one surface of the current collector, the former thermoplastic polymer layer and the active material layer It is possible to perform pressing in such a manner that they face each other. The pressing temperature may be 25 ° C. or higher and 120 ° C. or lower, or 50 ° C. to 100 ° C. The press can be performed using a known press device such as a roll press or a surface press as appropriate.

  The lithium ion secondary battery manufactured as described above has a coating layer with excellent heat resistance and strength and a separator with reduced ionic resistance. Therefore, it has excellent safety and battery characteristics (especially rate Characteristic). In addition, when a separator is provided with a thermoplastic polymer on the outermost surface, it exhibits excellent adhesion to the electrode, so that peeling between the electrode and the separator accompanying charging / discharging is suppressed, and uniform charging / discharging is achieved. Therefore, it has excellent long-term continuous operation resistance.

  The physical properties in the following experimental examples were evaluated according to the following methods.

<Evaluation>
(1) Solid content About 1 g of the obtained aqueous dispersion of the copolymer was precisely weighed on an aluminum dish, and the mass of the aqueous dispersion weighed at this time was defined as (a) g. It was dried for 1 hour with a hot air dryer at 130 ° C., and the dry mass of the dried copolymer was (b) g. The solid content was calculated by the following formula.
Solid content = (b) / (a) × 100 [%]

(2) Measurement of polymer particle diameter The average particle diameter of the polymer particles was measured using a particle diameter measuring apparatus (Nikkiso Co., Ltd., Microtrac UPA150). As the measurement conditions, the loading index = 0.15 to 0.3, the measurement time was 300 seconds, and the numerical value of the 50% particle diameter in the obtained data was described as the particle diameter.

(3) Measurement of glass transition temperature An appropriate amount of an aqueous dispersion (solid content = 38 to 42% by mass, pH = 9.0) containing a copolymer is placed in an aluminum dish and dried in a hot air dryer at 130 ° C. for 30 minutes. did. About 17 mg of the dried film sample after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve in a nitrogen atmosphere were obtained with a DSC measurement apparatus (Shimadzu Corporation, DSC 6220). The measurement conditions were as follows.
First stage temperature increase program: Start at 70 ° C., increase temperature at a rate of 15 ° C. per minute. Maintained for 5 minutes after reaching 110 ° C.
Second stage temperature drop program: temperature drop from 110 ° C. at a rate of 40 ° C. per minute. Maintained for 5 minutes after reaching -50 ° C.
Third stage temperature increase program: Temperature is increased from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data are acquired at the third stage of temperature rise.
The intersection of the base line (the straight line obtained by extending the base line in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to the downward convex curve) is defined as the glass transition temperature ( Tg).

(4) Viscosity average molecular weight Mv
Based on ASRM-D4020, the intrinsic viscosity [η] at 135 ° C. was determined in a decalin solvent. Using this [η] value, the viscosity average molecular weight Mv was calculated from the relationship of the following mathematical formula.
In the case of polyethylene: [η] = 0.00068 × Mv ^0.67
In the case of polypropylene: [η] = 1.10 × Mv ^0.80

(5) Thickness (μm)
A sample of MD10 cm × TD10 cm square is cut out from a polyolefin porous substrate or separator, and 9 points (3 points × 3 points) are selected in a lattice shape, and a dial gauge (Ozaki Seisakusho PEACOCK No, 25 (registered trademark)) is used. The film thickness was measured at room temperature 23 ± 2 ° C. The average value of the nine measured values obtained was calculated as the film thickness of the sample.

(6) Porosity A 10 cm × 10 cm square sample was cut from the polyolefin porous substrate, and its volume (cm ³ ) and mass (g) were determined. Using these values, the density of the porous substrate was 0.95 (g / cm ³ ), and the porosity was expressed by the following formula:
Porosity (%) = (1−mass / volume / 0.95) × 100
Calculated by

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

(8) Puncture strength (g)
Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, a polyolefin porous substrate was fixed with a sample holder having a diameter of 11.3 mm at the opening. Next, a maximum piercing load is obtained by performing a piercing test in a 25 ° C. atmosphere at a piercing speed of 2 mm / sec. As a result, puncture strength (g) was obtained.

(9) Inorganic filler particle size (μm)
About the coating liquid containing an inorganic filler, a particle size distribution is measured using a laser type particle size distribution measuring device (Microtrack MT3300EX manufactured by Nikkiso Co., Ltd.), and the particle size at which the cumulative frequency is 50% is determined as the average particle size (μm ).

(10) Coating layer thickness (μm)
A sample of MD 10 cm × TD 10 cm was cut out from the coated membrane and the polyolefin microporous membrane substrate, nine locations (3 points × 3 points) were selected in a lattice shape, and the film thickness was measured with a dial gauge (Ozaki Mfg. PEACOCK No. 25 (registered trademark). )), And the average value of the measured values at the nine locations was defined as the film thickness (μm) of the coating film and the substrate. Further, the difference in film thickness between the coating film and the substrate measured in this way was defined as the thickness (μm) of the coating layer. In Table 12, the thickness of the coating layer formed on one side of the substrate is expressed as “single-sided coating thickness (μm)”, and the total thickness of the coating layer formed on both sides of the substrate is expressed as “double-sided”. It was expressed as “coating thickness (μm)”.

(11) Peel strength of coating layer (N / cm)
A double-sided tape was attached to a slide glass having a width of 26 mm and a length of 76 mm, and a separator was attached thereon so that the coated surface was on the double-sided tape side. Using a force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd., a slide glass is fixed, a separator is gripped and pulled, and a 180 ° peel test is performed at a peel rate of 300 mm / min. The strength was measured. At this time, the average value of the peel strength in a peel test for 40 mm in length performed under the above conditions was adopted as the peel strength, and evaluation was performed according to the following criteria.
◎ (Remarkably good): Peel strength is 2.0 N / cm or more ○ (Good): Peel strength is 1.0 N / cm or more and less than 2.0 N / cm △ (Acceptable): Peel strength is 0.45 N / cm or more 1 Less than 0.0 N / cm x (defect): Peel strength is less than 0.45 N / cm

(12) AC electric resistance Six measurement samples cut into 22 mmφ were sufficiently immersed in an electrolytic solution (1M lithium perchlorate, propylene carbonate / dimethyl carbonate = 1/1), and one of them was a stainless steel container with a lid. Housed in. The container and the lid were insulated by Teflon (registered trademark) packing and 15.95 mmφ Teflon (registered trademark) guide without being in direct contact with each other, and were in contact only with a SUS electrode restraint. The lid was closed using a torque wrench (tightening torque: 0.8 Nm). Using a “3522-50 LCR high tester” manufactured by Hioki Electric Co., Ltd., measurement was performed by installing a measurement cell in a thermostatic bath at −30 ° C. under conditions of a frequency of 100 Hz and an open circuit voltage of 0.01 V. The resistance values obtained here to R _1. Next, the measurement container was disassembled, and the remaining five impregnated samples were stacked and set in the container, reassembled, and then the resistance of the six sheets was measured under the same conditions. The film resistance obtained here is R ₆ . From the obtained R ₁ and R ₆ , the membrane resistance R (Ω · cm ² ) per sample was calculated according to the following formula (2).
_{R = (R 6 -R 1)} / 5 (2)
Calculating equation (2) AC electrical resistance of the separator obtained from (Omega / cm ²⁾ as a resistance value in terms of 20μm thickness, alternating after coating an AC electrical resistance R _a of the coating before the substrate The rate of increase in resistance was determined from the electric resistance _Rb according to the following equation (3).
Resistance increase rate (%) = {(R _b −R _a ) / R _a } × 100 (3)
The rate of increase in resistance was ranked according to the following evaluation criteria.
◎ (Remarkably good): Resistance increase rate is less than 50% ○ (Good): Resistance increase rate is 50% or more and less than 100% x (Bad): Resistance increase rate is 100% or more

(13) Rate characteristics a. Production of positive electrode 90.4% by mass of nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) as a positive electrode active material, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) and acetylene black powder (AB) (density 1.95 g / cm ³ , number average) as conductive aids 3.8% by mass of particle diameter 48 nm) and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder at a ratio of 4.2% by mass, and these are mixed with N-methylpyrrolidone (NMP). A slurry was prepared by dispersing in the slurry. This slurry was coated on one side of a 20 μm thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then compression molded using a roll press machine. Was made. The coating amount of the positive electrode active material at this time was 109 g / m ² .

b. Graphite powder A as prepared negative active material of the negative electrode (density 2.23 g / cm ^3, number average particle diameter 12.7 [mu] m) 87.6% by weight and graphite powder B (density 2.27 g / cm ^3, number average particle diameter 6.5 μm) is 9.7% by mass, and the ammonium salt of carboxymethyl cellulose as a binder is 1.4% by mass (in terms of solid content) (solid content concentration is 1.83% by mass aqueous solution) and the diene rubber latex is 1.7% by mass ( (Solid content conversion) (solid content concentration 40 mass% aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12 μm thick copper foil serving 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 to produce a negative electrode. The negative electrode active material coating amount at this time was 5.2 g / m ² .

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

d. Battery assembly The separator for the electricity storage device obtained in each Example and Comparative Example was cut into a circle of 24 mmφ, and the positive electrode and the negative electrode were each cut into a circle of 16 mmφ. The negative electrode, the separator, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode were opposed to each other, pressed, or heat pressed, and accommodated in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the negative electrode copper foil and the lid was in contact with the positive electrode aluminum foil. A battery was assembled by injecting 0.4 ml of the non-aqueous electrolyte into the container and sealing it.

e. Evaluation of rate characteristics d. After charging the simple battery assembled in step 3 at 25 ° C. to a battery voltage of 4.2 V at a current value of 3 mA (about 0.5 C), the current value starts to be reduced from 3 mA so as to maintain 4.2 V. The first charge after the battery was made was performed for a total of about 6 hours. Thereafter, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, after charging to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C) at 25 ° C., the current value starts to be reduced from 6 mA so as to hold 4.2 V, so that a total of about 3 Charged for hours. Thereafter, the discharge capacity when discharging to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, after charging to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C) at 25 ° C., the current value starts to be reduced from 6 mA so as to hold 4.2 V, so that a total of about 3 Charged for hours. Thereafter, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 12 mA (about 2.0 C) was defined as 2 C discharge capacity (mAh).
Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic.
Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) × 100
The evaluation criteria for rate characteristics (%) were as follows.
(Remarkably good): The rate characteristic is 95% or more.
○ (Good): The rate characteristic is 85% or more and less than 95%.
X (defect): Rate characteristics are less than 85%.

[Synthesis Example 1]
(Water dispersion a1)
In a reaction vessel equipped with a stirrer, reflux condenser, dripping tank and thermometer, 70.4 parts by mass of ion-exchanged water and “AQUALON KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier In the table, indicated as “KH1025”. The same shall apply hereinafter.) 0.5 part by mass, “ADEKA rear soap SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, indicated as “SR1025” in the table, and so on) 0 And 5 parts by mass were charged. Next, the temperature inside the reaction vessel was raised to 80 ° C., and while maintaining the temperature at 80 ° C., a 2% aqueous solution of ammonium persulfate (indicated as “APS (aq) in the table, the same shall apply hereinafter)” 7.5. Part by mass was added. Five minutes after the completion of the addition of the ammonium persulfate aqueous solution, the emulsion was dropped from the dropping tank into the reaction vessel over 150 minutes.

  In the emulsion, 25 parts by mass of cyclohexyl methacrylate (indicated in the table as “CHMA”, the same applies hereinafter) as a monomer constituting the cycloalkyl group-containing monomer unit (A), a carboxyl group-containing monomer As a monomer constituting the unit (b1), 1 part by mass of methacrylic acid (in the table, expressed as “MAA”, the same shall apply hereinafter), acrylic acid (in the table, indicated as “AA”, the same shall apply hereinafter) 1 part by mass As a monomer constituting the amide group-containing monomer unit (b2), 0.1 part by mass of acrylamide (denoted as “AM” in the table, the same shall apply hereinafter), and a hydroxyl group-containing monomer unit (b3) 2-hydroxyethyl methacrylate (indicated in the table as “2HEMA”; the same shall apply hereinafter) as a constituent monomer, 5 parts by mass, and a trimethylolpropane triacrylic monomer as a monomer constituting a crosslinkable monomer unit (b4) (A-TMPT, trade name of Shin-Nakamura Chemical Co., Ltd., listed as “A-TMPT” in the table, the same shall apply hereinafter) 0.5 parts by mass, (meth) acrylic acid ester monomers other than the above As a monomer constituting the unit (b5), methyl methacrylate (denoted as “MMA” in the table, the same applies hereinafter) 4.9 parts by mass, butyl methacrylate (denoted as “BMA” in the table, the same applies hereinafter) 1 0.5 parts by mass, butyl acrylate (in the table, expressed as “BA”, the same applies hereinafter) 1.0 part by mass, 2-ethylhexyl acrylate (in the table, expressed as “2EHA”, the same applies hereinafter) 60 parts by mass, emulsifier 3 parts by weight of “AQUALON KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 3 parts by weight of “ADEKA rear soap SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation), p A mixture of 0.05 part by mass of sodium styrenesulfonate (in the table, expressed as “NaSS”, the same applies hereinafter), 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate, and 52 parts by mass of ion-exchanged water was mixed with a homomixer. Prepared by mixing for minutes.

  After completion of dropping of the emulsion, 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 = 8.0 with an aqueous ammonium hydroxide solution (25% aqueous solution), and a small amount of water was added to obtain an aqueous dispersion having a solid content of 40% (aqueous dispersion a1). About the copolymer in the obtained water dispersion a1, the average particle diameter and the glass transition temperature (Tg) were measured by the said method. The obtained results are shown in Table 1.

[Synthesis Examples 2-31]
(Water dispersions A1 to A27, a2 to a4)
Aqueous dispersions A1 to A27 and a2 to a4 were obtained in the same manner as in Synthesis Example 1 except that the types and mixing ratios of the raw materials were changed as shown in Tables 1 to 5.

  About the obtained water dispersion A1-A27 and the copolymer of a2-a4, the particle diameter and the glass transition temperature (Tg) were measured by the said method. The obtained results are shown in Tables 1 to 5. In the table, the composition of raw materials is based on mass.

Abbreviations of the raw materials used in Tables 1 to 5 have the following meanings, respectively.
(emulsifier)
KH1025: Aqualon KH1025, trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% by mass aqueous solution SR1025: Adekaria soap SR1025, trade name, manufactured by ADEKA Co., Ltd., 25% by mass aqueous solution,
NaSS: Sodium p-styrene sulfonate (initiator)
APS: ammonium persulfate (2% by weight aqueous solution)
(Neutralizer)
AW: Ammonium hydroxide

(Monomer)
Polyalkylene glycol group-containing monomer: monomers shown in Table 6 below

Cycloalkyl group-containing monomer CHMA: Cyclohexyl methacrylate Carboxyl group-containing monomer MAA: Methacrylic acid AA: Acrylic acid Amide group-containing monomer AM: Acrylamide Hydroxyl group-containing monomer HEMA: 2-hydroxyethyl methacrylate Crosslinkable Monomer GMA: Glycidyl methacrylate A-TMPT: Trimethylolpropane triacrylate MAPTMS: Methacryloxypropyltrimethoxysilane Other (meth) acrylates MMA: Methyl methacrylate BMA: Butyl methacrylate BA: n-butyl acrylate 2EHA: 2 -Ethylhexyl acrylate

<Manufacture of polyolefin porous substrate>
Polyolefin porous substrate B1
45 parts by mass of a homopolymer high-density polyethylene having an Mv of 700,000,
45 parts by mass of a homopolymer high-density polyethylene having an Mv of 300,000,
5 parts by mass of a homopolymer polypropylene having an Mv of 400,000,
Was dry blended using a tumbler blender.
1 part by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and again a tumbler blender. Was used for dry blending to obtain a mixture.
The obtained mixture was supplied to the twin screw extruder by a feeder under a nitrogen atmosphere.
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 the pump were adjusted so that the ratio of liquid paraffin in the total mixture to be extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.

Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll controlled at a surface temperature of 80 ° C. A sheet-like molded product was obtained by bringing into contact with a cooling roll and molding by cooling.
This sheet was stretched by a simultaneous biaxial stretching machine at a temperature of 112 ° C. and a magnification of 7 × 6.4. Thereafter, the stretched product was immersed in methylene chloride, and the liquid paraffin was extracted and dried, and then dried, and further stretched twice in the transverse direction at a temperature of 130 ° C. using a tenter stretching machine.
Thereafter, the stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin porous substrate B1. The physical properties of the obtained substrate B1 are shown in Table 7 below.

Polyolefin porous substrate B2
The following materials:
6.4 parts by mass of SiO ₂ “DM10C” (trademark, manufactured by Tokuyama Corporation)
12.2 parts by mass of high density polyethylene having a viscosity average molecular weight of 700,000,
12.2 parts by mass of high-density polyethylene having a viscosity average molecular weight of 250,000,
1.3 parts by mass of homopolypropylene having a viscosity average molecular weight of 400,000
Liquid paraffin 37.1 parts by mass as a plasticizer, and pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 0.3 parts by mass as an antioxidant The raw material of the polyolefin 1st microporous layer was prepared by premixing addition with a super mixer.
The following ingredients:
10.8 parts by mass of high density polyethylene having a viscosity average molecular weight of 700,000, 10.8 parts by mass of high density polyethylene having a viscosity average molecular weight of 250,000,
1.1 parts by weight of homopolypropylene having a viscosity average molecular weight of 400,000
As plasticizer, liquid paraffin 46.3 parts by mass, and as antioxidant, pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 0.3 part by mass Were premixed with a super mixer to prepare a raw material for the polyolefin second microporous layer.

Each of the above raw materials was supplied to two twin-screw co-directional screw extruder feed ports by a feeder. At this time, liquid paraffin was side-fed to the twin screw extruder cylinder so that the amount ratio of the plasticizer in the total mixture extruded by melt kneading together with each raw material was 60% by mass.
The melt kneading conditions in the extruder are as follows.
Raw material for the first microporous layer Setting temperature: 200 ° C
Screw rotation speed: 100rpm
Discharge rate: 5kg / h
Raw material for the second microporous layer Setting temperature: 200 ° C
Screw rotation speed: 120rpm
Discharge rate: 16kg / h

  Subsequently, the melt-kneaded material was extruded between a pair of rolls controlled at a surface temperature of 30 ° C. through a gear pump set at a temperature of 220 ° C., a conduit, and a T-die capable of co-extrusion of two types and three layers. A sheet-like composition having a first layer made of the raw material of the first microporous layer as a surface layer was obtained. Then, except having adjusted the extending | stretching temperature and the relaxation rate, polyolefin porous base material B2 was obtained by performing operation similar to the manufacture example of polyolefin porous base material B1. The physical properties of the obtained substrate B2 are shown in Table 7 below.

Base material B3
Celgard's model number “CG2500” was prepared as the base material B3.

<Separator No. S1>
100 parts by mass of 96.0 parts by mass of aluminum hydroxide oxide (average particle size: 1.0 μm), 3.0 parts by mass of resin binder A1, and 1.0 part by mass of ammonium polycarboxylate aqueous solution (SN Dispersant 5468 manufactured by San Nopco) A coating solution was prepared by uniformly dispersing in mass parts of water. Then, the coating liquid was apply | coated to the surface of polyolefin porous base material B1 using the gravure coater. Then, it dried at 60 degreeC and removed water. Thus, separator S1 was obtained by forming the aluminum hydroxide oxide layer (porous layer of an inorganic filler) with a thickness of 4 μm on the polyolefin porous substrate B1.

<Separator No. S2 to S53>
Separators S2 to S53 were produced according to Tables 8 to 13 in the same manner as for the separator S1.
In the separators S42 to S46, the coating liquid is applied to one side of the base material B1 and dried, and then the coating liquid is applied to the other side, whereby the inorganic filler layer is applied to both sides of the base material B1. As a separator.

  A lithium ion secondary battery was assembled as described above using the obtained separator, and various evaluations were performed. The evaluation results are shown in Tables 8-13.

Claims (11)

A separator for an electricity storage device comprising a porous substrate and a porous layer containing an inorganic filler and a resin binder,
The porous layer is disposed on at least one surface of the porous substrate, and the resin binder is a copolymer having an ethylenically unsaturated monomer (P) having a polyalkylene glycol group as a monomer unit. And the average number of repeating units (n) of the polyalkylene glycol chain of the ethylenically unsaturated monomer (P) having the polyalkylene glycol group is 3 or more,
The separator for an electricity storage device.   The copolymer is ethylenically unsaturated monomer (P) having 2 to 50% by mass of the polyalkylene glycol group and 100% by mass of the copolymer and ethylenic having the polyalkylene glycol group. The separator for electrical storage devices of Claim 1 which has as a monomer unit the monomer which does not have a polyalkylene glycol group which can be copolymerized with an unsaturated monomer (P).   The monomer having no polyalkylene glycol group has an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer (b2) having an amide group, and a hydroxyl group. The at least 1 sort (s) of monomer selected from the group which consists of an ethylenically unsaturated monomer (b3) is contained 0.1-10 mass% with respect to 100 mass% of said copolymers. For electricity storage devices.   The electrical storage device separator according to claim 2 or 3, wherein the monomer having no polyalkylene glycol group contains a crosslinkable monomer (b4). The monomer having no polyalkylene glycol group includes an ethylenically unsaturated monomer (A) having a cycloalkyl group and a (meth) acrylic acid ester monomer (b5),
The (meth) acrylate monomer (b5) is a (meth) acrylate monomer composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group, and has the cycloalkyl group The total content of the ethylenically unsaturated monomer (A) and the (meth) acrylic acid ester monomer (b5) is 50 to 98% by mass with respect to 100% by mass of the copolymer. The separator for electrical storage devices of any one of 2-4.   The electricity storage according to claim 5, wherein the (meth) acrylate monomer (b5) is a (meth) acrylate monomer composed of an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group. Device separator.   The separator for an electricity storage device according to claim 5, wherein the ethylenically unsaturated monomer (A) having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.   The laminated body which consists of a positive electrode, the separator for electrical storage devices of any one of Claims 1-7, and a negative electrode.   A wound body in which the positive electrode, the electricity storage device separator according to any one of claims 1 to 7, and the negative electrode are wound.   The electrical storage device containing the laminated body of Claim 8, or the winding body of Claim 9, and electrolyte solution.   The lithium ion secondary battery containing the laminated body of Claim 8, or the winding body of Claim 9, and electrolyte solution.