JP6856988B2 - Separator for power storage device and laminate using it, wound body, lithium ion secondary battery or power storage device - Google Patents

Description

The present invention relates to a separator for a power storage device.

In recent years, the development of power storage devices represented by lithium ion secondary batteries has been actively carried out. Usually, the power storage device is provided with a microporous film (separator) between the 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 microporous.

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

Patent Document 1 describes polymer particles 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 resin composition containing the above is applied onto a separator to form a protective layer on the separator (Synthesis Example 6, Formulation Example 6 and Example 16).

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

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 6 and Example 16).

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

In view of the above circumstances, it is an object of the present invention to provide a separator for a power storage device capable of achieving both the rate characteristics and safety of the power storage device at a higher level than that of a conventional separator.

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 a power storage device containing a porous base material and a porous layer containing an inorganic filler and a resin binder.
The porous layer is arranged 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. The average number of repeating units (n) of the polyalkylene glycol chain of the ethylenically unsaturated monomer (P) containing the above polyalkylene glycol group is 3 or more.
The separator for the power storage device.
[2]
The copolymer is an ethylenically unsaturated monomer (P) having 2 to 50% by mass of the polyalkylene glycol group with respect to 100% by mass of the copolymer, and an ethylenically having the polyalkylene glycol group. The separator for a power storage device according to [1], which comprises, as a monomer unit, a monomer copolymerizable with an unsaturated monomer (P) and which does not have a polyalkylene glycol group.
[3]
The monomer having no polyalkylene glycol group has an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer having an amide group (b2), and a hydroxyl group. The description in [2], wherein at least one monomer selected from the group consisting of the ethylenically unsaturated monomer (b3) is contained in an amount of 0.1 to 10% by mass based on 100% by mass of the copolymer. Separator for power storage devices.
[4]
The separator for a power storage device according to [2] or [3], wherein the monomer having no polyalkylene glycol group contains a crosslinkable monomer (b4).
[5]
The monomer having no polyalkylene glycol group contains an ethylenically unsaturated monomer (A) having a cycloalkyl group and a (meth) acrylic acid ester monomer (b5).
The (meth) acrylic acid ester monomer (b5) is a (meth) acrylic acid ester 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 ester monomer (b5) is 50 to 98% by mass with respect to 100% by mass of the copolymer [2]. ] To [4]. The separator for a power storage device according to any one of the items.
[6]
The storage capacity 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. Separator for devices.
[7]
The separator for a power storage device according to [5], wherein the ethylenically unsaturated monomer (A) having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.
[8]
A laminate comprising a positive electrode, a separator for a power storage device according to any one of [1] to [7], and a negative electrode.
[9]
A wound body in which a positive electrode, a separator for a power storage device according to any one of [1] to [7], and a negative electrode are wound.
[10]
A power storage device containing the laminate according to [8] or the wound body according to [9] and an electrolytic solution.
[11]
A lithium ion secondary battery containing the laminate according to [8] or the wound body according to [9] and an electrolytic solution.

According to the present invention, there is provided a separator for a power storage device that can achieve both the rate characteristics and safety of the power storage device. By manufacturing the power storage device and the secondary battery using the separator according to the embodiment of the present invention, the battery characteristics and safety of the power storage device and the secondary battery can be improved.

<Separator for power storage device>
The separator for a power storage device of the present invention includes a porous base material and a porous layer containing an inorganic filler and a resin binder, and the porous layer is arranged on at least one surface of the porous base material. The separator for a power storage device may be composed of only a porous base material and an inorganic filler-containing porous layer, or may further have a thermoplastic polymer layer in addition to these.

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

Each member constituting the separator for a power storage device of the present invention and a preferred embodiment of a method for manufacturing a separator for a power storage device will be described in detail below.
Further, in the present specification, "(meth) acrylic" means "acrylic" and its corresponding "methacrylic", and "(meth) acrylate" means "acrylate" and its corresponding "methacrylate". "(Meta) acryloyl" means "acryloyl" and its corresponding "methacryloyl".

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

In the present embodiment, the content of the polyolefin resin in the microporous polyolefin membrane is not particularly limited, but from the viewpoint of shutdown performance when used as a separator for a power storage device, 50 of all the components constituting the porous substrate It is preferable that the porous membrane is made of a polyolefin resin composition in which the polyolefin resin accounts for 100% by mass or more and 100% by mass or less. 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, but may be a polyolefin resin used for ordinary extrusion, injection, inflation, blow molding, etc., and ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and Homopolymers such as 1-octene and copolymers, multi-stage polymers and the like can be used. In addition, polyolefins selected from the group consisting of these homopolymers, copolymers, and multistage polymers can be used alone or in combination.
Typical examples of the polyolefin resin are not particularly limited, but for example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, tactic polypropylene, ethylene-propylene. Random copolymers, polybutene, ethylene propylene rubber and the like can be mentioned.
As the material of the polyolefin porous base material used as a separator for a power storage device, it is particularly preferable to use a resin containing high-density polyethylene as a main component because it has a low melting point and high strength. Further, these polyethylenes may be mixed in two or more kinds for the purpose of imparting flexibility. The polymerization catalyst used in the production of these polyethylenes is also not particularly limited, and examples thereof include Ziegler-Natta-based catalysts, Philips-based catalysts, and metallocene-based catalysts.

In order to improve the heat resistance of the polyolefin porous substrate, it is more preferable to use a porous film composed of a resin composition containing polypropylene and a polyolefin resin other than polypropylene.
Here, the three-dimensional structure of polypropylene is not limited, and may be any of isotactic polypropylene, syndiotactic polypropylene, and tactic polypropylene.
The ratio of polypropylene to 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 also not particularly limited, and examples thereof include Ziegler-Natta-based catalysts and metallocene-based catalysts.

In this case, the polyolefin resin other than polypropylene is not limited, and is, for example, a homopolymer of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Examples include copolymers. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, ethylene-propylene random copolymer and the like.

From the viewpoint of shutdown characteristics in which the pores of the porous polyolefin substrate are closed by thermal melting, as polyolefin resins other than polypropylene, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high-density 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 of 0.93 g / cm 3 or more measured according to JIS K 7112.}

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin porous substrate is not particularly limited, but is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and further preferably 100,000. More than 1 million. When the viscosity average molecular weight is 30,000 or more, the melt tension during melt molding is increased, the moldability is improved, and the polymer tends to be entangled with each other to increase the strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12 million or less, it becomes easy to uniformly melt and knead, and the formability of the sheet, particularly the thickness stability tends to be excellent, which is preferable. Further, when the viscosity average molecular weight is less than 1,000,000, the pores are easily closed when the temperature rises, and a good shutdown function tends to be obtained, which is preferable.

For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000 and having a viscosity average molecular weight of less than 1 million is used. You may use it.
The polyolefin porous substrate in this embodiment can contain any additive. Such additives are not particularly limited, and are, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenol-based, phosphorus-based, and sulfur-based; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorption. Agents; light stabilizers; antistatic agents; antifogging agents; coloring pigments and the like.
The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin composition.
The viscosity average molecular weight (Mv) is calculated by the following formula from the ultimate viscosity [η] measured at a measurement temperature of 135 ° C. using decalin as a solvent based on ASTM-D4020.
Polyethylene: [η] = 6.77 × 10 ^-4 Mv ^0.67 (Chang's 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, and preferably 80% or less. It is preferable that the porosity is 20% or more from the viewpoint of ensuring the permeability of the separator. On the other hand, it is preferable that the porosity is 90% or less from the viewpoint of ensuring the puncture strength. Here, the porosity is determined from, for example, the volume (cm ³ ), mass (g), and film density (g / cm ³ ) of the polyolefin porous substrate sample, and the following formula:
Porosity = (volume-mass / membrane density) / volume x 100
Can be obtained by. Here, for example, in the case of a polyolefin porous substrate made of polyethylene, the calculation can be performed on the assumption that the ^{film density is 0.95 (g / cm 3).} The porosity can be adjusted by changing the draw ratio of the polyolefin porous base material.

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, and preferably 1,000 seconds / 100 cc or less. It is preferably 500 seconds / 100 cc or less. It is preferable that the air permeability is 10 seconds / 100 cc or more from the viewpoint of suppressing self-discharge of the power storage device. On the other hand, it is preferable that the air permeability is 1,000 seconds / 100 cc or less from the viewpoint of obtaining good charge / discharge characteristics. Here, the air permeability is the air permeability resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the porous substrate.

The average pore size of the polyolefin porous substrate in the present embodiment is preferably 0.15 μm or less, more preferably 0.1 μm or less, and the lower limit is preferably 0.01 μm or more. Setting the average pore diameter to 0.15 μm or less is preferable from the viewpoint of suppressing self-discharge of the power storage device and suppressing capacity reduction. The average pore size can be adjusted by changing the draw ratio when producing the porous polyolefin 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, and more preferably 1,. It is 000 g / 20 μm or less. The puncture strength of 200 g / 20 μm or more is preferable from the viewpoint of suppressing the film rupture due to the active material or the like that has fallen off when the battery is wound, and from the viewpoint of suppressing the concern of short circuit due to the expansion and contraction of the electrode due to charging and discharging. .. On the other hand, it is preferable that the puncture strength is 2,000 g / 20 μm or less from the viewpoint of reducing the width shrinkage due to the relaxation of orientation during heating. The puncture strength is measured by the method described in the examples below.
The puncture strength can be adjusted by adjusting the stretching ratio and / or the stretching temperature of the porous polyolefin 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, still more preferably 50 μm or less. .. Adjusting this thickness to 2 μm or more is preferable from the viewpoint of improving the mechanical strength. On the other hand, adjusting the film thickness to 100 μm or less is preferable because the occupied volume of the separator in the battery is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.

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

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

The inorganic filler is not particularly limited, and is, for example, oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, itria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride. Ceramics: Silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide, aluminum hydroxide, potassium titanate, talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, kaolin, and silica sand; glass fibers and the like can be mentioned. These may be used alone or in combination of two or more.

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

Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be preferably 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 an internal short circuit due to the generation of lithium dendrite. By adopting particles containing boehmite as the main component as the inorganic filler constituting the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability, and even a thinner porous layer is a porous film. The heat shrinkage at high temperature is suppressed, and it tends to exhibit excellent heat resistance. Synthetic boehmite, which can reduce ionic impurities that adversely affect the properties of electrochemical devices, is even more preferred.

As the aluminum silicate compound having no ion exchange ability, kaolin, which is mainly composed of kaolin minerals, is more preferable because it is inexpensive and easily available. As kaolin, wet kaolin and calcined kaolin obtained by calcining the wet kaolin are known. In this embodiment, calcined kaolin is particularly preferred. Calcined kaolin is particularly preferable in terms of electrochemical stability because water of crystallization is released during the calcining treatment and impurities are also removed.

The average particle size of the inorganic filler is preferably more than 0.01 μm and 4.0 μm or less, more preferably more than 0.2 μm and 3.5 μm or less, and more than 0.4 μm and 3.0 μm. The following is more preferable. Adjusting the average particle size of the inorganic filler to the above range is preferable from the viewpoint of suppressing heat shrinkage at high temperatures even when the thickness of the porous filler layer is thin (for example, 7 μm or less). Examples of the method for adjusting the particle size of the inorganic filler and its distribution include a method of pulverizing the inorganic filler using an appropriate pulverizer such as a ball mill, a bead mill, or a jet mill to reduce the particle size. ..

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

The ratio of the inorganic filler in the porous filler layer can be appropriately determined from the viewpoints of the binding property of the inorganic filler, the permeability of the separator, the heat resistance, and the like. The ratio 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)
As the resin binder, it is preferable to use a resin latex binder. When a resin latex binder is used as the resin binder, the separator having the resin binder and the filler porous layer containing the inorganic filler binds the resin binder onto the porous film through the step of applying the resin binder solution on the base material. Compared with the separated separator, the ion permeability is less likely to decrease, and there is a tendency to provide a power storage device having high output characteristics. Further, a power storage device having a separator formed by using a resin latex binder exhibits smooth shutdown characteristics even when the temperature rises rapidly at the time of abnormal heat generation, and tends to easily obtain high safety.

In the present embodiment, the resin binder may contain a resin such as a homopolymer or a copolymer, but from the viewpoint of achieving both rate characteristics and safety of the power storage device, at least one of the copolymers contained in the resin binder is used. The seed consists of a copolymer having an ethylenically unsaturated monomer (P) having a polyalkylene glycol group (also referred to as "polyoxyalkylene group") as a monomer unit, and ethylene having a polyalkylene glycol group. It is preferable that the average number of repeating units (n) of the polyalkylene glycol chain (also referred to as “alkylene glycol repeating unit”) of the sex unsaturated monomer (P) is 3 or more. The "ethylenically unsaturated monomer" means a monomer having one or more ethylenically unsaturated bonds in the molecule.

By having the copolymer contained in the resin binder as a copolymerization unit an ethylenically unsaturated monomer having an average of three or more alkylene glycol repeating units, the separator can be compared with a conventional resin binder such as an acrylic binder. Even if the amount of resin binder in the porous filler layer is increased in order to reduce the ionic resistance and further improve the strength, powder removal property or flexibility of the porous filler layer, the ionic resistance is not increased and the battery characteristics such as rate characteristics are improved. Do not sacrifice.
Further, 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, a uniform inorganic coating layer is formed on the separator base material, so that the peel strength of the coating layer is increased and the binding property between the polyolefin base material and the inorganic coating layer is also improved. This can improve the safety of the power storage device.
It is presumed that the separator in the present embodiment contributes to both the rate characteristics and the safety of the power storage device in this way.

The copolymer contained in the resin binder is also effective in improving the ion permeability of the separator because the oxygen atom in the alkylene glycol repeating unit coordinates with the lithium (Li) ion to promote the diffusion of the Li ion. 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. The oxyalkylene group constituting the polyoxyalkylene group preferably has 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, and further preferably 2 carbon atoms. The hydrocarbon group in the polyalkylene glycol group may be linear or branched.

As described above, the average number of repeating units (n) of the polyalkylene glycol chain of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group is from the viewpoint of achieving both the rate characteristics and safety of the power storage device. 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 at the time of 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 a polyalkylene glycol unit and an allyl group in the molecule. Examples thereof include monomers having a reactive substituent 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 (meth) acrylate ) Acrylate, ethoxypolyethylene glycol (meth) acrylate, butoxypolyethylene glycol (meth) acrylate, octoxypolyethylene glycol (meth) acrylate, lauroxypolyethylene glycol (meth) acrylate, stearoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol ( Examples thereof include (meth) acrylic acid ester monomers having a polyalkylene glycol group such as meth) acrylate, methoxypolypropylene glycol (meth) acrylate, and octoxypolyethylene glycol-polypropylene glycol (meth) acrylate. These are preferable from the viewpoint of effective and reliable solution.

Further, the monomer (P) also includes the 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 because it has good polymerization stability during the preparation of the copolymer.

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, and specifically, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether and the like. May be used.

From the viewpoint of the rate characteristics and safety of the power 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 0% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more. The upper limit is preferably 50% by mass or less, more preferably 40% by mass or less, further preferably 30% by mass or less, and particularly preferably 20% by mass or less. When the content ratio of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group is within the range, the ion permeability of the separator is improved, which is preferable. Furthermore, since the dispersibility of the filler and the binder in the slurry is improved, not only can a uniform coating layer having good strength of the coating layer be formed, but also the effect of the alkylene glycol group causes the connection between the base material and the coating layer. Wearability also tends to increase. When the content ratio of the ethylenically unsaturated monomer (P) having a polyalkylene glycol group is 50% by mass or less, the copolymerizability at the time of emulsion polymerization is improved, which is preferable.

The copolymer contained in the resin binder contains an ethylenically unsaturated monomer having an alkylene glycol unit repetition number of 3 or more and a polyalkylene glycol group from the viewpoint of achieving both the rate characteristics and safety of the power storage device. It is preferable that it is designed to contain a monomer that does not have it 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 above-mentioned monomer (P).

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

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, and adamantyl methacrylate. The (meth) acrylic acid ester monomer is preferable from the viewpoint of more effectively and surely solving the problem according to the present invention.

The ethylenically unsaturated monomer (A) having a cycloalkyl group is more preferably a (meth) acrylic acid ester monomer composed of a cycloalkyl group and a (meth) acryloyloxy group. The number of carbon atoms constituting the alicyclic of the cycloalkyl group is preferably 4 to 8, more preferably 6 and 7, and particularly preferably 6. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a tert-butyl group. Among the monomers (A), cyclohexyl acrylate and cyclohexyl methacrylate are preferable in that they have good copolymerizability during emulsion polymerization with the monomer (P). These may be used alone or in combination of two or more.

In order to improve various qualities and physical properties, the copolymer according to the present embodiment contains other monomer (B) having no polyalkylene glycol group and no cycloalkyl group. It may have as a unit. The other monomer (B) is a monomer different from the above-mentioned monomers (A) and (P) and can be copolymerized with the monomer (P). The other monomer (B) is not particularly limited, and is, for example, an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer (b2) having an amide group, and a hydroxyl group. Ethylene unsaturated monomer (b3), crosslinkable monomer (b4), (meth) acrylic acid ester monomer (b5), ethylenically unsaturated monomer having a cyano group (b6), Other examples include ethylenically unsaturated monomers.

The other monomer (B) may be used alone or in combination of two or more. Further, the other monomer (B) may belong to two or more of the above-mentioned 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.

Above all, from the viewpoint of improving the binding property with the filler, the other monomer (B) preferably contains an ethylenically unsaturated monomer (b1) having a carboxyl group. 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 may be used alone or in combination of two or more. Among them, 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 for example, acrylamide, methacrylamide, N, N-methylenebisacrylamide, diacetoneacrylamide, diacetonemethacrylamide, maleic acid amide and Maleimide can be mentioned. These may be used alone or in combination of two or more. Of these, acrylamide and methacrylamide are preferred. The use of acrylamide and / or methacrylamide tends to improve the bondability between the substrate and the coating layer.

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 may be used alone or in combination of two or more. Of these, hydroxyethyl acrylate and hydroxyethyl methacrylate are preferable. By using hydroxyethyl acrylate and / or hydroxyethyl methacrylate, the binding property with the filler tends to be improved.

Further, from the viewpoint of adjusting the insoluble content of the copolymer in the electrolytic solution to an appropriate amount, the other monomer (B) preferably contains a crosslinkable monomer (b4). The crosslinkable monomer (b4) is not particularly limited, and for example, a monomer having two or more radically polymerizable double bonds, or a functional group that gives a self-crosslinking structure during or after polymerization is used. Examples include the monomer having. These may be used alone or in combination of two or more.

Examples of the monomer having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth) acrylate. Of these, polyfunctional (meth) acrylate is preferable from the viewpoint of exhibiting better electrolyte resistance even in a small amount.

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

Examples of the monomer having a functional group that gives a self-crosslinking structure during or after the polymerization include an ethylenically unsaturated monomer having an epoxy group, an ethylenic monomer having a methylol group, and ethylene having an alkoxymethyl group. Examples thereof include sex-unsaturated monomers and ethylenically unsaturated monomers having a hydrolyzable silyl group. These may be used alone 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 may be used alone or in combination of two or more. Of these, glycidyl methacrylate is preferable.

Examples of the ethylenically unsaturated monomer having a methylol group include N-methylolacrylamide, N-methylolmethacrylamide, dimethylolacrylamide, and dimethylolmethacrylamide. These may be used alone or in combination of two or more.

Examples of the ethylenically unsaturated monomer having an alkoxymethyl group include N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide. These may be used alone or in combination of two or more.

Examples of the ethylenically unsaturated monomer having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ. − Methacryloxypropyltriethoxysilane. These may be used alone or in combination of two or more.

Among the crosslinkable monomers (b4), the polyfunctional (meth) acrylate is particularly preferable because there is little variation in the degree of crosslinkability.

Further, from the viewpoint of improving the oxidation resistance of the resin binder containing the copolymer according to the present embodiment, the other monomer (B) contains the (meth) acrylic acid ester monomer (b5). Is preferable. The (meth) acrylic acid ester monomer (b5) is a monomer different from the above-mentioned 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, and 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, lauryl methacrylate and the like (meth) acrylate having an alkyl group (more preferably, a (meth) acrylate composed of an alkyl group and a (meth) acryloyloxy group).

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 copolymerization during emulsion polymerization (meth). ) Acryloyl ester monomer is preferable, and (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 even more preferable. These (meth) acrylic acid ester monomers (b5) may be used alone 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, vinyltoluene and α-methylstyrene. Of these, styrene is preferable.

In the present embodiment, the ethylenically unsaturated monomer (P) having an average number of repeating units (n) of 3 or more in the polyalkylene glycol chain and the ethylenically unsaturated monomer (A) having a cycloalkyl group are used. By positive use, an ethylenically unsaturated monomer having an average number of repeating units of 3 or more in a polyalkylene glycol chain is generally not suitable for emulsion polymerization, but enhances the copolymerizability of a plurality of comonomer. 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 contain 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 number of repeating units (n) of the polyalkylene glycol chain of more than 1 and less than 3 include the following formula:
CH ₂ = C (R ¹ ) -CO-O- (CH _2- CH _2- O) _n- R ²
{In the formula, R ¹ and R ² are independently hydrogen atoms or methyl groups, and n is a number satisfying 3>n> 1}.
Examples thereof include compounds represented by.

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 bondability between the porous base material and the inorganic coating layer, the resin binder ( The copolymerization ratio (total content ratio) of the meta) acrylic acid ester monomer is preferably 50 to 99.9% by mass, more preferably 60 to 99.9% by mass, based on the mass of the copolymer constituting the resin binder. It is 99.9% by mass, more preferably 70 to 99.9% by mass, and even more preferably 80 to 99.9% by mass. In this paragraph, the (meth) acrylic acid ester monomer has a (meth) acrylic acid ester among ethylenically unsaturated monomers (P) having a polyalkylene glycol group and a cycloalkyl group. Among the ethylenically unsaturated monomers (A), those corresponding to the (meth) acrylic acid ester and the (meth) acrylic acid ester monomer having no polyalkylene glycol group and no cycloalkyl group (b5). ) Includes all. 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 ratio of the ethylenically unsaturated monomer (b1) having a carboxyl group in the copolymer is With respect to 100% by mass of the copolymer, it is preferably 0.1 to 10% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.1 to 3% by mass. 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 the fillers tends to be improved, and when it is 10% by mass or less, the binding property tends to be improved. The dispersion stability of the aqueous dispersion tends to improve.

The other 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 compound (b3) is contained, the total content ratio of (b1), (b2) and (b3) in the polymer is preferably 0.1 to 10% by mass with respect to 100% by mass of the copolymer. Is. When the total content ratio 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 a crosslinkable monomer (b4), the content ratio of the crosslinkable monomer (b4) in the copolymer is preferably 100% by mass of the copolymer. It is 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.1 to 3% by 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 the adhesiveness of the separator to the electrode and the ion permeability, the copolymer contained in the resin binder is ethylene having a cycloalkyl group as a monomer having no polyalkylene glycol group. It is preferable to contain the sex unsaturated monomer (A) and the (meth) acrylic acid ester monomer (b5). The total content of the ethylenically unsaturated monomer (A) having a cycloalkyl group and the (meth) acrylic acid ester monomer (b5) was 50 to 98% by mass with respect to 100% by mass of the copolymer. It is preferably 51 to 97% by mass, or 55 to 95% by mass.

The glass transition temperature of the resin binder (hereinafter, also referred to as “Tg”) is preferably −50 ° C. or higher, and 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 the DSC curve obtained by differential scanning calorimetry (DSC). Specifically, it is determined by the intersection of a straight line extending the baseline on the low temperature side of the DSC curve to the high temperature side and a tangent line at the inflection point of the stepwise change portion of the glass transition.

Further, "glass transition" refers to a DSC in which a change in calorific value accompanying a change in the state of a polymer, which is a test piece, occurs on the endothermic side. Such a change in calorific value is observed as a shape of a stepwise change in the DSC curve. The “step-like change” refers to the portion of the DSC curve until the curve departs from the previous baseline on the low temperature side and shifts to a new baseline on the high temperature side. In addition, the combination of the step-like change and the peak is also included in the step-like change.

Further, the "inflection point" indicates a point where the gradient of the DSC curve of the stepped change portion is maximized. Further, in the stepped change portion, when the upper side is the heat generating side, it can be expressed as a point where the upwardly convex curve changes to the downwardly convex curve. The “peak” refers to the portion of the DSC curve from when the curve leaves the baseline on the low temperature side to when it returns to the same baseline. “Baseline” refers to the DSC curve in the temperature range where no transition or reaction occurs on the test piece.

The method for obtaining the copolymer contained in the resin binder is not particularly limited, but the emulsion polymerization method is preferable for the purpose of obtaining the copolymer in the form of particles. The method of emulsion polymerization is not particularly limited, and a conventionally 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 as basic composition components in an aqueous medium, each of the above-mentioned monomers is composed. A copolymer can be obtained by polymerizing the monomer composition. At the time of polymerization, a method of making the composition of the supplied monomer composition constant in the entire polymerization process, and by sequentially or continuously changing the composition in the polymerization process, the morphological composition change of the particles of the resin dispersion produced is changed. Various methods can be used as needed, such as the method of giving. When the copolymer is obtained by emulsion polymerization, the copolymer is in the form of an aqueous dispersion (also referred to as "aqueous latex") containing, for example, water and a particulate copolymer dispersed in the water. May be good.

Surfactants are compounds 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 ester, polyoxyethylene alkyl ether sulfate ester salt, alkylbenzene sulfonate, alkylnaphthalenzulfonate, alkylsulfosuccinate, alkyldiphenyl ether disulfonate, and sodium sulfone. Anionic surfactants such as acid formalin condensates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene distyrene phenyl ether sulfates, fatty acid salts, alkyl phosphates, polyoxyethylene alkyl phenyl ether sulfates, etc. Activators and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distyrene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxy Nonionic surfactants such as ethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, and polyoxyethylene alkylphenyl ether can be mentioned. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of the surfactant having a hydrophilic group and a lipophilic group may be used.

Examples of the anionic surfactant among the reactive surfactants include sulfonic acid groups, sulfonate groups or sulfate ester groups and ethylenically unsaturated monomers having salts thereof, and examples thereof include sulfonic acid groups or sulfonic acid groups. A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) which is the ammonium salt or alkali metal salt is preferable. Specifically, for example, alkylallyl sulfosuccinate (for example, Eleminor (trademark) JS-20 manufactured by Sanyo Chemical Industries, Ltd., Latemul (trademark; the same applies hereinafter) manufactured by Kao Corporation) S-120, S-180A, S- 180 is mentioned), polyoxyethylene alkylpropenylphenyl ether sulfate ester salt (for example, Aqualon (trademark; the same applies hereinafter) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α- [1-[. (Allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adecaria soap manufactured by ADEKA Co., Ltd. (trademark; the same applies hereinafter) SE-10N), ammonium = Α-sulfonato-ω-1- (allyloxymethyl) alkyloxypolyoxyethylene (for example, Aqualon KH-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Toso Organic Chemicals Co., Ltd.) Spinomer ™ NaSS manufactured by the company can be mentioned.), Α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adecaria manufactured by ADEKA Co., Ltd.) Soap SR-10 can be mentioned), and a sulfate ester salt of polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (for example, Latemul PD-104 manufactured by Kao Corporation can be mentioned).

Examples of the nonionic surfactant among the reactive surfactants include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, ADEKA Corporation Adecaria Soap NE-20, NE-30, NE-40, etc.), Polyoxyethylene alkyl propenylphenyl ether (for example, Aqualon RN-10, RN-20 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), RN-30, RN-50, etc.), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, ADEKA Corporation Adecaria Soap ER) -10 can be mentioned), polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (for example, Latemul PD-420 manufactured by Kao Corporation can be mentioned).

Among the above-mentioned various surfactants, a reactive surfactant is preferable, an anionic reactive surfactant is more preferable, and a reactive surfactant having a sulfonic acid group is 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. The surfactant may be used alone or in combination of two or more.

The radical polymerization initiator is one that radically decomposes with a heat or a reducing substance to initiate addition polymerization of the monomer, and either an inorganic initiator or an organic initiator 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 peroxodisulfuric acid salts, peroxides, water-soluble azobis compounds, and redox systems of peroxide-reducing agents. Examples of the peroxodisulfate include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS), and examples of the peroxide include hydrogen peroxide and t-. Examples thereof include butyl hydroperoxide, t-butyl peroxymaleic acid, peroxide succinate, and benzoyl peroxide, and examples of the water-soluble azobis compound include 2,2-azobis (N-hydroxyethylisobutylamide), 2 , 2-azobis (2-amidinopropane) dihydrogen peroxide, 4,4-azobis (4-cyanopentanoic acid), and examples of the redox system of the peroxide-reducing agent include sodium in the peroxide. One or more reducing agents such as sulfooxylate formaldehyde, sodium hydrogen peroxide, sodium thiosulfate, sodium hydroxymethanesulfuric acid, L-ascorbic acid, and salts thereof, ferrous salts, and ferrous salts. A combination can be mentioned.

The radical polymerization initiator can be preferably used in an amount of 0.05 to 2 parts by mass with respect to 100 parts by mass of the monomer composition. The radical polymerization initiator may be used alone or in combination of two or more.

A single amount containing an ethylenically unsaturated monomer (P) having a polyalkylene glycol group, an ethylenically unsaturated monomer (A) having 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 preferable.

Further, it is preferable that the pH of the aqueous dispersion is adjusted in the range of 5 to 12 in order to maintain long-term dispersion stability. For adjusting the pH, it is preferable to use amines such as ammonia, sodium hydroxide, potassium hydroxide, and dimethylaminoethanol, and it is more preferable to adjust the pH with ammonia (water) or sodium hydroxide.

The aqueous dispersion contains a copolymer obtained by copolymerizing a monomer composition containing the above-mentioned 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 bactericide and the like.

The average particle size of the copolymer particles is preferably 30 to 1000 nm, more preferably 30 to 800 nm, and even more preferably 100 to 700 nm. When the average particle size of the copolymer particles is 30 nm or more, the ion permeability is unlikely to decrease, and it is easy to provide a power storage device having high output characteristics. Further, even when the temperature rises rapidly at the time of abnormal heat generation, it is easy to obtain a power storage device that exhibits smooth shutdown characteristics and has high safety. Further, it is preferable that the average particle size of the copolymer particles is 1000 nm or less from the viewpoint of ensuring the dispersion stability of the aqueous dispersion, and further, when a multilayer porous film is formed by exhibiting good binding properties. The heat shrinkage is good, and the safety tends to be excellent. The average particle size of the copolymer particles can be measured according to the method described in the following Examples.

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

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

The other polymer is not particularly limited, but it is preferable to use a polymer that is insoluble in the electrolytic solution of the lithium ion secondary battery and is electrochemically stable within the range of use of the lithium ion secondary battery.
Specific examples of other polymers include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene. Fluorine-containing rubber such as copolymers; 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 Copolymers, acrylonitrile-acrylic acid ester copolymers, rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, Examples thereof include polyetherimide, polyamideimide, polyamide and polyester.

In the present embodiment, the glass transition temperature Tg of the polymer contained in the resin binder can be appropriately adjusted by, for example, changing the monomer component used in producing the polymer and the input ratio of each monomer. That is, for each monomer used in the production of the polymer, from the generally shown homopolymer Tg (for example, described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the compounding ratio of the monomer. , The outline of the glass transition temperature can be estimated. For example, a copolymer obtained by copolymerizing a monomer such as methyl methacrylate, acrylonitrile, methacrylic acid, etc., which gives a homopolymer of Tg at about 100 ° C. at a high ratio, has a high Tg; for example, Tg at about -50 ° C. The Tg of the copolymer obtained by copolymerizing a monomer such as n-butylacrylonitrile or 2-ethylhexylacrylonitrile which gives the homopolymer of the above in a high ratio is low.
The Tg of the copolymer is calculated by the following mathematical formula (1):
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ + ... + _Wi / 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 the monomer i, _{W i} is the weight fraction of each monomer. } Can also be estimated by the FOX formula.
However, as the glass transition temperature Tg of the polymer in the present embodiment, the value measured by the method using the DSC is adopted.

The thickness of the porous filler layer is preferably 0.5 μm or more from the viewpoint of improving heat resistance and insulating properties, and preferably 50 μm or less from the viewpoint of improving the capacity and permeability of the battery.
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 to at least one surface of the base material. In this case, the coating liquid may contain a solvent, a dispersant, etc. in order to improve the dispersion stability and the coatability.
The method of applying the coating liquid to the base material 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 raw material may be laminated and extruded by a coextrusion method, or the base material and the filler porous membrane may be individually prepared and then bonded together.

[Thermoplastic polymer layer]
If desired, the separator for a power storage device may have a thermoplastic polymer layer in addition to the porous base material and the filler porous layer. The thermoplastic polymer layer may be arranged on one or both sides of the porous substrate or on the porous filler layer, and it is preferable that the thermoplastic polymer layer is arranged so that at least a part of the porous filler layer is exposed.

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 arranged among the surfaces of the porous substrate is 100% or less, 80% or less, 75% or less, or It is preferably 70% or more, and the area ratio is preferably 5% or more, 10% or more, or 15% or more. It is preferable that the coating area of the thermoplastic polymer layer is 100% or less 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, it is preferable that the coating area is 5% or more from the viewpoint of further improving the adhesiveness with the electrode. This area ratio is measured by observing the thermoplastic polymer layer forming surface of the obtained separator with SEM.
When the thermoplastic polymer layer is a layer mixed with the inorganic filler, the existing area of the thermoplastic polymer is calculated with the total area of the thermoplastic polymer and the inorganic filler as 100%.

When the thermoplastic polymer layer is arranged only on a part of the surface of the porous substrate and the inorganic filler layer, the arrangement pattern of the thermoplastic polymer layer is, for example, dot-like, striped, lattice-like, striped, or hexagonal. , Random, etc., and combinations thereof.
The thickness of the thermoplastic polymer layer arranged on the polyolefin porous substrate is preferably 0.01 μm to 5 μm, more preferably 0.1 μm to 3 μm, and 0. It is more preferably 1 to 1 μm.

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

Examples of the thermoplastic polymer include:
Polyolefin resins such as polyethylene, polypropylene and α-polyolefin;
Fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, or copolymers containing them;
Diene-based polymers containing conjugated diene such as butadiene and isoprene as monomer units, copolymers containing them, or hydrides 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 Acrylic polymers with, or copolymers containing them, or hydrides 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 that do not have polymerizable functional groups, such as polyethylene glycol and polypropylene glycol;
Resins such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester;
A copolymer having an ethylenically unsaturated monomer having 3 or more repetitions of an alkylene glycol unit as a copolymerization unit, which has been described above as a resin binder for forming a porous filler layer; and a combination thereof;
Can be mentioned.
Among these, a diene polymer, an acrylic polymer or a fluorine polymer is preferable from the viewpoint of adhesiveness to the 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, and more preferably in the range of −50 ° C. to 150 ° C. from the viewpoint of adhesion to the electrode and ion permeability. ..

From the viewpoint of wettability to the polyolefin microporous film, adhesion between the polyolefin microporous film and the thermoplastic polymer layer, and adhesion to the electrode, the thermoplastic polymer layer is a polymer having a glass transition temperature of less than 20 ° C. Is preferably blended, and from the viewpoint of blocking resistance and ion permeability, it is preferable that a polymer having a glass transition temperature of 20 ° C. or higher is also blended.

Having at least two glass transition temperatures of a thermoplastic polymer can be achieved by, but is not limited to, a method of blending two or more kinds of thermoplastic polymers, a method of using a thermoplastic polymer having a core-shell structure, and the like.
The core-shell structure is a polymer in the form of a double structure in which a polymer belonging to the central portion and a polymer belonging to the outer shell portion have different compositions.
In particular, in polymer blends and core-shell structures, the glass transition temperature of the entire thermoplastic polymer can be controlled by combining a polymer with a high glass transition temperature and a polymer having a low glass transition temperature. In addition, a plurality of functions can be imparted to the entire thermoplastic polymer.

In the present embodiment, from the viewpoint of the blocking inhibitory property and ion permeability of the separator, the thermoplastic copolymer is in the form of particles when the glass transition temperature is, for example, 20 ° C. or higher, 25 ° C. or higher, or 30 ° C. or higher. Is preferable.
By incorporating the particulate thermoplastic copolymer in the thermoplastic polymer layer, the porosity of the thermoplastic polymer layer arranged on the substrate and the blocking resistance of the separator can be ensured.

The average particle size 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. It is ~ 800 nm, most preferably 200 ~ 750 nm. Setting the average particle size to 10 nm or more ensures that the size of the particulate thermoplastic polymer does not enter the pores of the substrate when the particulate thermoplastic polymer is applied to the substrate including at least the porous membrane. Means to be done. Therefore, in this case, it is preferable from the viewpoint of improving the adhesiveness between the electrode and the separator and the cycle characteristics of the power storage device. Further, setting the average particle size to 2,000 nm or less means that an amount of particulate thermoplastic polymer required to achieve both the adhesiveness between the electrode and the separator and the cycle characteristics of the power storage device is placed on the base material. 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 examples below.

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

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

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

<Manufacturing method of separator for power storage device>
[Manufacturing method of polyolefin porous base material]
The method for producing the porous polyolefin substrate in the present embodiment is not particularly limited, and a known production method can be adopted. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded to form a sheet, stretched in some cases, and then made porous by extracting the plasticizer, or a polyolefin resin composition is melt-kneaded and highly drawn. A method of extruding by ratio and then peeling the polyolefin crystal interface by heat treatment and stretching to make the polyolefin porous. The polyolefin resin composition and the inorganic filler are melt-kneaded, molded on a sheet, and then stretched to form the polyolefin and the inorganic filler. Examples thereof include a method of making the polyolefin resin composition porous by peeling off the interface with the polyolefin, and a method of immersing the polyolefin resin composition in a poor solvent for the polyolefin to solidify the polyolefin and at the same time removing the solvent to make the polyolefin porous.

Further, a method for producing a non-woven fabric or paper as a base material may be known. As a manufacturing method thereof, for example, a chemical bond method in which a web is immersed in a binder, dried and bonded between fibers; a thermal bond method in which heat-meltable fibers are mixed with the web and the fibers are partially melted and bonded between the fibers. A needle punching method in which a needle with a piercing in the web is repeatedly pierced and the fibers are mechanically entangled; a water flow entanglement method in which a high-pressure water stream is jetted from a nozzle to the web through a net (screen) and entwined between the fibers can be mentioned.

Hereinafter, as an example of a method for producing a porous polyolefin base material, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded, molded into a sheet, and then the plasticizer is extracted will be described.
First, the polyolefin resin composition and the plasticizer are melt-kneaded. As a melt-kneading method, for example, a polyolefin resin and, if necessary, other additives are put into a resin kneading device such as an extruder, a kneader, a lab plast mill, a kneading roll, or a Banbury mixer, and the resin components are heated and melted. There is a method of introducing a plasticizer at the ratio of and kneading. At this time, it is preferable to pre-knead the polyolefin resin, other additives and the plasticizer at a predetermined ratio using a Henschel mixer or the like before putting them into the resin kneading apparatus. More preferably, in the pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is kneaded while side-feeding the resin kneader.

As the plasticizer, a non-volatile solvent capable of forming a uniform solution above the melting point of polyolefin can be used. Specific examples of such non-volatile solvents 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. For example, the mass fraction of the plasticizer in the composition composed of the polyolefin resin composition and the plasticizer is preferably 30 to 80% by mass, more preferably 40 to 70% by mass. 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. As a method for producing a sheet-shaped molded product, for example, the melt-kneaded product is extruded into a sheet shape via a T-die or the like, brought into contact with a heat conductor, and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. There is a method of solidifying. As the heat conductor used for cooling and solidification, metal, water, air, a plasticizer itself, or the like can be used, but a metal roll is preferable because of its high heat conduction efficiency. At this time, if it is sandwiched between the rolls when it is brought into contact with the metal roll, the efficiency of heat conduction is further increased, the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is also improved, which is more preferable. The die lip interval when extruded into a sheet from the T die is preferably 400 μm or more and 3,000 μm or less, and more preferably 500 μm or more and 2,500 μm or less.

It is preferable that the sheet-shaped molded product thus obtained is then stretched. As the stretching treatment, either uniaxial stretching or biaxial stretching can be preferably used. Biaxial stretching is preferable from the viewpoint of the strength of the obtained porous substrate. When the sheet-shaped molded product is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, the finally obtained porous base material is hard to tear, and the sheet-shaped molded product has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple stretching. Simultaneous biaxial stretching is preferable from the viewpoint of improving puncture strength, stretching uniformity, and shutdown property.

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

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

Next, the plasticizer is removed from the sheet-shaped molded product to obtain a porous base material. Examples of the method for removing the plasticizer include a method in which a sheet-shaped molded product is immersed in an extraction solvent to extract the plasticizer and sufficiently dried. The method for extracting the plasticizer may be either a batch method or a continuous method. In order to suppress the shrinkage of the porous base material, it is preferable to restrain the end portion of the sheet-shaped molded product during a series of steps of dipping and drying. Further, the residual amount of the 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 poor with respect to the polyolefin resin, is a good solvent with respect to the plasticizer, and has a boiling point lower than the melting point of the polyolefin resin. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine type such as hydrofluoroether and hydrofluorocarbon. Hydrocarbon solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone can be mentioned. These extraction solvents may be recovered and reused by an operation such as distillation.

In order to suppress the shrinkage of the porous substrate, 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 post-treatment such as hydrophilization treatment with a surfactant or the like, cross-linking treatment with ionizing radiation or the like.

If the surface of the polyolefin porous substrate is surface-treated, it becomes easier to apply the coating liquid thereafter, and the adhesiveness 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 roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

[Arrangement method of filler porous layer]
The filler porous layer is formed on the base material by applying a coating liquid containing, for example, an inorganic filler, a resin binder, and optionally additional components such as a solvent (for example, water) and a dispersant, on at least one surface of the base material. Can be placed in. The resin binder may be synthesized by emulsion polymerization, and the obtained emulsion may be used as it is as a coating liquid.

The method of applying the coating liquid to the base material is not particularly limited as long as the required layer thickness and coating area can be realized. Examples of the coating method include a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, a knife coater method, an air doctor coater method, a blade coater method, and a rod coater method. , Squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, inkjet coating method and the like. Above all, the gravure coater method is preferable because it has a high degree of freedom in coating shape.
Further, the filler raw material containing the resin binder and the polymer base material raw material may be laminated and extruded by a coextrusion method, or the base material and the filler porous membrane may be individually prepared and then 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 base material and the porous layer. For example, a method of drying at a temperature equal to or lower than the melting point of the base material while fixing the base material, a method of drying under reduced pressure at a low temperature, and the like can be mentioned.

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

The method of applying a coating liquid containing a thermoplastic polymer on a porous polyolefin substrate is particularly limited as long as it can achieve a desired coating pattern, coating film thickness, and coating area. Absent. For example, the coating method described above may be used to coat the coating liquid containing an inorganic filler. 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 fixing a polyolefin porous substrate and drying it at a temperature below its melting point, a method of drying under reduced pressure at a low temperature, or a method of immersing the thermoplastic polymer in a poor solvent for the thermoplastic polymer to solidify the thermoplastic polymer into particles. Examples thereof include a method of extracting the solvent at the same time.

<Physical characteristics of separator for power storage device>
In the present embodiment, the air permeability of the separator for a power storage device 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, and further preferably 30 seconds. / 100 cc or more and 450 seconds / 100 cc or less, particularly preferably 50 seconds / 100 cc or more and 400 seconds / 100 cc or less. This air permeability is the air permeability resistance measured in accordance with JIS P-8117, like 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 separator for a power storage device of the present embodiment exhibits a large ion permeability when applied to a lithium ion secondary battery by exhibiting such a very large air permeability.

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. If the thickness is 2 μm or more, the mechanical strength tends to be sufficient, and if it is 200 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.

<Power storage device>
The separator for a power storage device of the present embodiment can be suitably applied as a separator for a power storage device by combining the positive electrode, the negative electrode, and the non-aqueous electrolytic solution. Examples of this power storage device include a lithium ion secondary battery.
When the lithium ion secondary battery is manufactured as the separator of the present embodiment, the positive electrode, the negative electrode, and the non-aqueous electrolytic solution are not limited, and known ones can be used for each.
As the positive electrode, a positive electrode formed by forming a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector can be preferably 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. .. The positive electrode active material layer may contain a binder, a conductive material, or the like in addition to the positive electrode active material.

As the negative electrode, a positive electrode formed by forming a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector can be preferably used. The negative electrode current collector is, for example, copper foil, and the negative electrode active material is, for example, a carbon material such as graphite, non-graphitizable carbon, easily graphitized carbon, or composite carbon; silicon, tin, metallic lithium. , Various alloy materials, etc. can be mentioned respectively.

The non-aqueous 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, ethyl methyl carbonate and the like. Examples of the electrolyte include lithium salts such as _{LiClO 4} , LiBF ₄ , and LiPF _6.

The method for manufacturing a power storage device using the power storage device separator of the present embodiment is not particularly limited. For example, the following method can be exemplified.
The separator of the present embodiment is manufactured as a vertically elongated 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). The positive electrode-separator-negative electrode-separator or the negative electrode-separator-positive electrode-separator are laminated in this order and wound in a circular or flat spiral shape to obtain a wound body, and the wound body is stored in a battery can. It can be produced by further injecting an electrolytic solution. Alternatively, a laminated body composed of a sheet-shaped separator and an electrode, or a wound body obtained by folding the electrode and the separator is placed in a battery container (for example, an aluminum film) and an electrolytic solution is injected. You may.

At this time, it is also preferable to press the laminated body or the wound body. Specifically, the separator for a power storage device of the present embodiment and the current collector and an electrode having an active material layer formed on at least one surface of the current collector are provided with the former thermoplastic polymer layer and active material layer. The press can be performed by superimposing them so that they face each other. The press temperature may be 25 ° C. or higher and 120 ° C. or lower, or 50 ° C. to 100 ° C. The press can be performed by appropriately using a known press device such as a roll press or a surface press.

The lithium-ion secondary battery manufactured as described above has a coating layer having excellent heat resistance and strength, and is provided with a separator having reduced ion resistance, so that it has excellent safety and battery characteristics (particularly rate). Characteristics) are shown. Further, when a thermoplastic polymer is provided on the outermost surface of the separator, since it exhibits excellent adhesiveness to the electrode, peeling between the electrode and the separator due to charge / discharge is suppressed, and uniform charge / discharge is achieved. Therefore, it has excellent long-term continuous operation resistance.

The physical characteristics of 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 plate, and the mass of the aqueous dispersion weighed at this time was defined as (a) g. It was dried in a hot air dryer at 130 ° C. for 1 hour, and the dry mass of the copolymer after drying was defined as (b) g. The solid content was calculated by the following formula.
Solid content = (b) / (a) x 100 [%]

(2) Measurement of Polymer Particle Size The average particle size of the polymer particles was measured using a particle size measuring device (Microtrac UPA150 manufactured by Nikkiso Co., Ltd.). As the measurement conditions, the loading index was 0.15 to 0.3 and the measurement time was 300 seconds, and the value of 50% particle size in the obtained data was described as the particle size.

(3) Measurement of glass transition temperature An appropriate amount of an aqueous dispersion containing a copolymer (solid content = 38 to 42% by mass, pH = 9.0) is placed in an aluminum dish and dried in a hot air dryer at 130 ° C. for 30 minutes. did. Approximately 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 under a nitrogen atmosphere were obtained with a DSC measuring device (DSC6220 manufactured by Shimadzu Corporation). The measurement conditions were as follows.
1st stage temperature rise program: Start at 70 ° C and heat at a rate of 15 ° C per minute. Maintained for 5 minutes after reaching 110 ° C.
Second stage temperature lowering program: The temperature is lowered from 110 ° C to 40 ° C per minute. Maintain for 5 minutes after reaching -50 ° C.
Third stage temperature rise program: The temperature is raised from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data are acquired when the temperature rises in the third stage.
The intersection of the baseline (a straight line extending the baseline of the obtained DSC curve to the high temperature side) and the tangent point at the inflection point (the point where the upward convex curve changes to the downward convex curve) is the glass transition temperature (the glass transition temperature). Tg).

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

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

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

(7) Air permeability (seconds / 100cc)
The air permeability was defined as the air permeability resistance measured by the Garley type air permeability meter GB2 (trademark) manufactured by Toyo Seiki Co., Ltd. in accordance with JIS P-8117.

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

(9) Inorganic filler particle size (μm)
For the coating liquid containing the inorganic filler, the particle size distribution was measured using a laser particle size distribution measuring device (Microtrac MT3300EX manufactured by Nikkiso Co., Ltd.), and the particle size at which the cumulative frequency was 50% was the average particle size (μm). ).

(10) Thickness of coating layer (μm)
A sample of MD10 cm x TD10 cm was cut out from the coating film and the polyolefin microporous membrane base material, 9 points (3 points x 3 points) were selected in a grid pattern, and the film thickness was set to a dial gauge (Ozaki Seisakusho PEACOCK No. 25 (registered trademark). )) Was measured, and the average value of the measured values at 9 points was taken as the film thickness (μm) of the coating film and the base material. Further, the difference in film thickness between the coating film and the base material 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 base material is expressed as "single-sided coating thickness (μm)", and the total thickness of the coating layers formed on both sides of the base material is "both sides". It was expressed as "coating thickness (μm)".

(11) Peeling strength of the 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 on the slide glass 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 ° peeling test is performed at a peeling speed of 300 mm / min. The intensity was measured. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength and evaluated according to the following criteria.
◎ (Remarkably good): Peeling strength is 2.0 N / cm or more ○ (Good): Peeling strength is 1.0 N / cm or more and less than 2.0 N / cm Δ (Allowable): Peeling strength is 0.45 N / cm or more 1 Less than 0.0 N / cm × (defective): Peeling strength is less than 0.45 N / cm

(12) AC electrical resistance Six measurement samples cut out to 22 mmφ were sufficiently immersed in an electrolytic solution (1 M lithium perchlorate propylene carbonate / dimethyl carbonate = 1/1), and one of them was a stainless metal container with a lid. Contained in. The container and lid were insulated without direct contact by Teflon® packing and a 15.95 mmφ Teflon® guide, and only by SUS electrode retainers. The lid was closed using a torque wrench (tightening torque: 0.8 Nm). Using a "3522-50 LCR high tester" manufactured by Hioki E.E., a measuring cell was installed in a constant temperature bath at −30 ° C. under the conditions of a frequency of 100 Hz and an open circuit voltage of 0.01 V for measurement. The resistance values obtained here to R _1. Next, the measuring container was disassembled, the remaining 5 impregnated samples were stacked and set in the container, reassembled, and then the resistance of 6 samples was measured under the same conditions. The resulting membrane resistance herein and R _6. From the obtained R ₁ and R ₆ , the film 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 From the electrical resistance R _{b, the} resistance increase rate was calculated according to the following equation (3).
Resistance increase rate (%) = {(R _b- R _a ) / R _a } x 100 (3)
The resistance increase rate 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% × (Defective): Resistance increase rate is 100% or more

(13) Rate characteristics a. Preparation of positive electrode As the positive electrode active material, nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) was 90.4% by mass. As a conductive auxiliary 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) Particle size 48 nm) was mixed at a ratio of 3.8% by mass, and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder was mixed at a ratio of 4.2% by mass, and these were mixed with N-methylpyrrolidone (NMP). A slurry was prepared by dispersing in the mixture. This slurry is applied to 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 to obtain a positive electrode. Was produced. The amount of the positive electrode active material coated 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) was 9.7% by mass, and 1.4% by mass (solid content equivalent) of ammonium salt of carboxymethyl cellulose (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass of diene rubber-based latex as a binder. A slurry was prepared by dispersing (in terms of solid content) (an aqueous solution having a solid content concentration of 40% by mass) in purified water. This slurry was applied to one side of a copper foil having a thickness of 12 μm to be 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 prepare a negative electrode. The amount of the negative electrode active material coated at this time was 5.2 g / m ² .

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

d. Battery assembly The separators for power storage devices obtained in each Example and Comparative Example were cut out 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 faced each other, pressed or heat-pressed, and housed in a stainless metal container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode and the lid was in contact with the aluminum foil of the positive electrode. A battery was assembled by injecting 0.4 ml of the non-aqueous electrolytic solution into this container and sealing the container.

e. Evaluation of rate characteristics d. After charging the simple battery assembled in step 1 at 25 ° C. with a current value of 3 mA (about 0.5 C) to a battery voltage of 4.2 V, the current value is started to be throttled from 3 mA so as to maintain 4.2 V. The first charge after the battery was made was carried out for a total of about 6 hours. After that, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, 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 a 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) x 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 (defective): The rate characteristic is less than 85%.

[Synthesis Example 1]
(Aqueous dispersion a1)
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer, 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, Notated as "KH1025" in the table. The same shall apply hereinafter.) 0.5 parts by mass and "Adecaria soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd., expressed as "SR1025" in the table. The same shall apply hereinafter) 0 .5 parts by mass was charged. Next, the temperature inside the reaction vessel was raised to 80 ° C., and while maintaining the temperature of 80 ° C., a 2% aqueous solution of ammonium persulfate (indicated as “APS (aq)” in the table; the same applies hereinafter) was added to 7.5. By mass was added. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

The emulsion contains 25 parts by mass of cyclohexyl methacrylate (indicated as "CHMA" in the table; the same applies hereinafter) as a monomer constituting the cycloalkyl group-containing monomer unit (A), and a carboxyl group-containing monomer. 1 part by mass of methacrylic acid (indicated as "MAA" in the table; the same shall apply hereinafter) and 1 part by mass of acrylic acid (indicated as "AA" in the table; the same shall apply hereinafter) as the monomer constituting the unit (b1). , 0.1 part by mass of acrylamide (indicated as "AM" in the table; the same applies hereinafter) as a monomer constituting the amide group-containing monomer unit (b2), and a hydroxyl group-containing monomer unit (b3). 2-Hydroxyethyl methacrylate (indicated as "2HEMA" in the table; the same applies hereinafter) as a constituent monomer, and trimethylpropantriacrylate as a monomer constituting a crosslinkable monomer unit (b4). (A-TMPT, trade name manufactured by Shin-Nakamura Chemical Industry Co., Ltd., indicated as "A-TMPT" in the table. The same shall apply hereinafter.) 0.5 parts by mass, (meth) acrylic acid ester monomer unit other than the above ( As the monomer constituting b5), methyl methacrylate (indicated as "MMA" in the table; the same applies hereinafter) 4.9 parts by mass, butyl methacrylate (indicated as "BMA" in the table; the same applies hereinafter) 1.5. By mass, butyl acrylate (indicated as "BA" in the table; the same shall apply hereinafter) 1.0 part by mass, 2-ethylhexyl acrylate (indicated as "2EHA" in the table; the same shall apply hereinafter) 60 parts by mass, as an emulsion " Aqualon KH1025 (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 3 parts by mass, "Adecaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) 3 parts by mass, sodium p-styrene sulfonate (Indicated as "NaSS" in the table. The same shall apply hereinafter.) A mixture of 0.05 parts by mass, 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 for 5 minutes. Prepared.

After the completion of dropping 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). For the obtained copolymer in the aqueous dispersion a1, the average particle size and the glass transition temperature (Tg) were measured by the above method. The results obtained are shown in Table 1.

[Synthesis Examples 2-31]
(Aqueous 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 compounding ratios of the raw materials were changed as shown in Tables 1 to 5.

For the obtained copolymers of the aqueous dispersions A1 to A27 and a2 to a4, the particle size and the glass transition temperature (Tg) were measured by the above method. The obtained results are shown in Tables 1 to 5. In the table, the composition of raw materials is based on mass.

The abbreviations of the raw materials used in Tables 1 to 5 have the following meanings, respectively.
(emulsifier)
KH1025: Aqualon KH1025, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., 25% by mass aqueous solution SR1025: Adecaria Soap SR1025, trade name, manufactured by ADEKA Corporation, 25% by mass aqueous solution,
NaSS: Sodium p-styrene sulfonate (initiator)
APS: Ammonium persulfate (2% by mass aqueous solution)
(Neutralizer)
AW: Ammonia hydroxide

(Polymer)
Polyalkylene glycol group-containing monomer: Polyester shown in Table 6 below

Cycloalkyl group-containing monomer CHMA: Cyclohexyl methacrylate Carboxyl group-containing monomer MAA: Methacrylic acid AA: Acrylic acid Amid group-containing monomer AM: acrylamide hydroxyl group-containing monomer HEMA: 2-hydroxyethyl methacrylate Cross-linking property Monomer GMA: Glycidyl methacrylate A-TMPT: Trimethylol propantriacrylate MAPTMS: Methacrylicoxypropyltrimethoxysilane Other (meth) acrylate MMA: Methyl methacrylate BMA: Butyl methacrylate BA: n-butyl acrylate 2EHA: 2 -Ethethylhexyl acrylate

<Manufacturing of Polyolefin Porous Base Material>
Polyolefin porous base material B1
Homopolymer high-density polyethylene with Mv of 700,000 was added to 45 parts by mass.
Homopolymer high-density polyethylene with Mv of 300,000 was added to 45 parts by mass.
5 parts by mass of polypropylene of homopolymer having Mv of 400,000 and
Was dry-blended using a tumbler blender.
To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis- [methylene- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane was added as an antioxidant, and the tumbler blender was used again. The mixture was obtained by dry blending using.
The resulting mixture was fed to a twin-screw extruder under a nitrogen atmosphere by a feeder.
Further, liquid paraffin (kinematic viscosity at 37.78 ° C. 7.59 × ^10-5 m ² / s) was injected into the extruder cylinder by a plunger pump.
The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the total mixture 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 whose surface temperature is controlled to 80 ° C., and the extruded product is extruded. A sheet-shaped molded product was obtained by contacting with a cooling roll and molding (casting) to cool and solidify.
This sheet was stretched at a temperature of 112 ° C. at a magnification of 7 × 6.4 times by a simultaneous biaxial stretching machine. Then, the stretched product was immersed in methylene chloride to extract and remove liquid paraffin, dried, and further stretched twice in the transverse direction at a temperature of 130 ° C. using a tenter stretching machine.
Then, this stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin porous base material B1. The physical characteristics of the obtained base material B1 are shown in Table 7 below.

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

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

Subsequently, the melt-kneaded product is extruded between a pair of rolls whose surface temperature is controlled to 30 ° C. via a gear pump and a conduit whose temperature is set to 220 ° C. and a T-die capable of co-extruding two types and three layers, respectively. , A sheet-like composition having the first layer made of the raw material of the first microporous layer as a surface layer was obtained. After that, the polyolefin porous base material B2 was obtained by performing the same operation as in the production example of the polyolefin porous base material B1 except that the stretching temperature and the relaxation rate were adjusted. The physical characteristics of the obtained base material B2 are shown in Table 7 below.

Base material B3
A cell guard model number "CG2500" was prepared as the base material B3.

<Separator No. S1>
Aluminum hydroxide (average particle size 1.0 μm) 96.0 parts by mass, resin binder A1 3.0 parts by mass, and ammonium polycarboxylic acid aqueous solution (SN Dispersant 5468 manufactured by San Nopco) 1.0 parts by mass 100 parts. A coating solution was prepared by uniformly dispersing in a mass of water. Subsequently, the coating liquid was applied to the surface of the polyolefin porous base material B1 using a gravure coater. Then, it was dried at 60 ° C. to remove water. In this way, the separator S1 was obtained by forming an aluminum hydroxide oxide layer (a porous layer of an inorganic filler) having a thickness of 4 μm on the polyolefin porous base material B1.

<Separator No. S2 to S53>
Separator S2 to S53 were prepared according to Tables 8 to 13 in the same manner as 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 further applied to the other side to coat both sides of the base material B1 with an inorganic filler layer. It was manufactured as a separator.

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

Claims (9)

A separator for a power storage device containing a porous base material and a porous layer containing an inorganic filler and a resin binder.
The porous layer is arranged 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. hints, and Ri der average number of repeating units of the polyalkylene glycol chain (n) is 3 or more of said ethylenically unsaturated monomers having a polyalkylene glycol group (P),
The copolymer is an ethylenically unsaturated monomer (P) having 2 to 50% by mass of the polyalkylene glycol group with respect to 100% by mass of the copolymer, and an ethylenically having the polyalkylene glycol group. A monomer copolymerizable with an unsaturated monomer (P) and having no polyalkylene glycol group, and having as a monomer unit,
The monomer having no polyalkylene glycol group has an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer having an amide group (b2), and a hydroxyl group. A separator for a power storage device containing at least one monomer selected from the group consisting of ethylenically unsaturated monomers (b3) in an amount of 0.1 to 10% by mass based on 100% by mass of the copolymer. A separator for a power storage device containing a porous base material and a porous layer containing an inorganic filler and a resin binder.
The porous layer is arranged 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. hints, and Ri der average number of repeating units of the polyalkylene glycol chain (n) is 3 or more of said ethylenically unsaturated monomers having a polyalkylene glycol group (P),
The copolymer is an ethylenically unsaturated monomer (P) having 2 to 50% by mass of the polyalkylene glycol group with respect to 100% by mass of the copolymer, and an ethylenically having the polyalkylene glycol group. A monomer copolymerizable with an unsaturated monomer (P) and having no polyalkylene glycol group, and having as a monomer unit,
A separator for a power storage device , wherein the monomer having no polyalkylene glycol group contains a crosslinkable monomer (b4). A separator for a power storage device containing a porous base material and a porous layer containing an inorganic filler and a resin binder.
The porous layer is arranged 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. hints, and Ri der average number of repeating units of the polyalkylene glycol chain (n) is 3 or more of said ethylenically unsaturated monomers having a polyalkylene glycol group (P),
The copolymer is an ethylenically unsaturated monomer (P) having 2 to 50% by mass of the polyalkylene glycol group with respect to 100% by mass of the copolymer, and an ethylenically having the polyalkylene glycol group. It has, as a monomer unit, a monomer copolymerizable with an unsaturated monomer (P) and which does not have a polyalkylene glycol group.
The monomer having no polyalkylene glycol group contains an ethylenically unsaturated monomer (A) having a cycloalkyl group and a (meth) acrylic acid ester monomer (b5).
The (meth) acrylic acid ester monomer (b5) is a (meth) acrylic acid ester monomer composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group, and
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. %, Separator for power storage device. The storage capacity according to claim 3 , 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. Separator for devices. The separator for a power storage device according to claim 3 or 4 , wherein the ethylenically unsaturated monomer (A) having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate. A laminate comprising a positive electrode, a separator for a power storage device according to any one of claims 1 to 5, and a negative electrode. A wound body in which a positive electrode, a separator for a power storage device according to any one of claims 1 to 5, and a negative electrode are wound. A power storage device containing the laminate according to claim 6 or the wound body according to claim 7 and an electrolytic solution. A lithium ion secondary battery containing the laminate according to claim 6 or the wound body according to claim 7 and an electrolytic solution.