JP6739320B2 - Storage device separator - Google Patents

Description

The present invention relates to a power storage device separator.

In recent years, development of electricity storage devices such as non-aqueous electrolyte batteries has been actively conducted. Usually, in a non-aqueous electrolyte battery, a separator including a microporous membrane is provided between the positive and negative electrodes. The separator has a function of preventing direct contact between the positive and negative electrodes and a function of allowing ions to permeate through the electrolytic solution held in the micropores.

Although a microporous polyolefin membrane is an electronic insulator, it is widely used as a separator for non-aqueous electrolyte batteries because it has ion permeability due to its porous structure. The polyolefin microporous membrane also has a shutdown function to block the ionic conduction in the electrolyte and block the progress of the electrochemical reaction by blocking the pores by thermal melting when the non-aqueous electrolyte battery causes abnormal heat generation. Have.

Generally, an electricity storage device including a polyolefin microporous film as a separator has safety and reliability due to the shutdown function of the polyolefin microporous film. Attempts to provide at least one functional layer on the polyolefin microporous membrane have been reported in order to improve the safety and reliability of the electricity storage device or to provide the separator with functionality other than shutdown (Patent Document 1). ~ 3).

International Publication No. 2013/080946 International Publication No. 2015/005151 JP, 2015-28842, A

In Patent Document 1, in order to suppress an increase in the thickness of the separator and ensure heat resistance, inorganic oxide particles, expandable polymer particles, and a binder polymer such as polyvinylpyrrolidone (PVP) are provided on the polyolefin microporous film. It has been proposed to form a heat resistant porous layer containing In Patent Document 1, from the viewpoint of the shape stability of the separator, the amount of the binder polymer in the heat resistant porous layer is 0.1% by mass or more based on the total mass of the inorganic oxide particles and the expandable polymer particles. Is described.

In Patent Documents 2 and 3, a porous membrane composition or adhesive containing inorganic oxide particles, polymer particles having a core-shell structure, and a water-soluble polymer such as carboxymethyl cellulose (CMC) is applied onto a polyolefin microporous membrane. Is described.

The porous membrane composition described in Patent Document 2 is blended in order to secure the low-temperature output characteristics of the non-aqueous electrolyte solution and to prevent the porous membrane from falling out of the polyolefin microporous membrane in the electrolyte solution, From the viewpoint of the dispersibility of the porous film composition and the ionic diffusivity of the polymer particles, the amount of the water-soluble polymer in the porous film composition is 0.1% by mass based on the total mass of the inorganic oxide particles and the polymer particles. It is proposed that the content is 15% by mass or less.

The adhesive described in Patent Document 3 is blended in order to secure the low-temperature output characteristics of the non-aqueous electrolyte and the adhesiveness between the separator and the electrode, and the dispersibility and ion diffusivity of the polymer particles having a core-shell structure. From the viewpoint, it is proposed that the amount of the water-soluble polymer in the adhesive is 0.1% by mass or more and 15% by mass or less based on the mass of the polymer particles.

However, the content of each component in the functional layer formed on the polyolefin microporous film may have a trade-off relationship with the rigidity, rate characteristics, or cycle characteristics of the electricity storage device including the polyolefin microporous film and the functional layer. Therefore, the electricity storage device including the separators described in Patent Documents 1 to 3 still has room for improvement from the viewpoint of balancing rigidity, rate characteristics, and cycle characteristics.

Therefore, it is an object of the present invention to provide a separator for an electricity storage device, which can balance rigidity, rate characteristics, and cycle characteristics of the electricity storage device appropriately.

As a result of intensive studies, the present inventors have found that the above problems can be solved by the following technical means.
[1]
A separator for a power storage device comprising a porous substrate and a thermoplastic layer arranged on at least one surface of the porous substrate,
The thermoplastic layer contains an inorganic filler, a thermoplastic polymer and a water-soluble polymer,
The thermoplastic polymer is a water dispersible polymer,
The volume ratio of the inorganic filler and the thermoplastic polymer (volume of the inorganic filler:volume of the thermoplastic polymer) is 35:65 to 65:35, and the content of the water-soluble polymer in the thermoplastic layer. The amount is 0.04 mass% or more and less than 1.0 mass% with respect to the total mass of the inorganic filler and the thermoplastic polymer,
The separator for the electricity storage device.
[ 2 ]
The thermoplastic polymer is
1) a conjugated diene-based polymer,
2) Acrylic polymer,
3) Polyvinyl acetate,
4) Fluorine-containing resin
Any one or two or more of the above, The separator for electrical storage devices as described in [1].
[ 3 ]
The electricity storage device separator according to [1] or [2], wherein the water-soluble polymer is an ammonium salt or an alkali metal salt of a polycarboxylic acid, or an anionic cellulose derivative.
[ 4 ]
The heat press for the thickness (T _b ) of the thermoplastic layer before the heat pressing, when the separator for an electricity storage device is immersed in an electrolytic solution and then subjected to heat pressing at 80° C. and 1.0 MPa. after the ratio of the thickness of the thermoplastic layer _{(T a) (T a /} T b) is, Ri 0.6-0.9 der,
The electrolytic solution is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume/DEC volume=2/3, LiPF ₆ concentration: 1 M, SP value as mixture=11.6) , [1 ] The separator for electrical storage devices in any one of [3] .
[ 5 ]
The content of the water-soluble polymer in the thermoplastic layer is 0.2% by mass or more and 0.8% by mass or less with respect to the total mass of the inorganic filler and the thermoplastic polymer, [1] to [4 ] ] The separator for electricity storage devices in any one of these .
[ 6 ]
The electricity storage device separator according to any one of [ 1 ] to [5], wherein the water-soluble polymer is anionic, cationic, or amphoteric.
[ 7 ]
The water-soluble polymer is a separator for an electricity storage device according to any one of [1] to [5], which is nonionic.
[ 8 ]
The electricity storage device separator according to any one of [1] to [ 7 ], wherein the water-soluble polymer does not have an amide bond-containing cyclic structure.
[ 9 ]
A laminate comprising a positive electrode, the electricity storage device separator according to any one of [1] to [ 8 ], and a negative electrode.
[ 10 ]
A wound body in which the positive electrode, the electricity storage device separator according to any one of [1] to [ 8 ], and the negative electrode are wound.
[ 11 ]
A secondary battery comprising the laminate according to [ 9 ] or the wound body according to [ 10 ] and a non-aqueous electrolyte.

According to the present invention, there is provided a separator capable of appropriately balancing rigidity, rate characteristics, and cycle characteristics of an electricity storage device.

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

<Separator for electricity storage device>
The electricity storage device separator of the present invention (hereinafter, also simply referred to as “separator”) includes a porous substrate and a thermoplastic layer disposed on at least one surface of the porous substrate. This separator may consist of only the porous base material and the thermoplastic layer, or may have other layers. The other layer is arranged on one side or both sides of the porous base material or as an intermediate layer of the laminated porous base material layers. When the thermoplastic layer is arranged on the surface having the other layer, the mutual positional relationship between them is arbitrary, but it is preferable to expose at least a part of the thermoplastic layer from the viewpoint of adhesiveness between the separator and the electrode.

Preferred embodiments of the members constituting the electricity storage device separator of the present invention and the method for manufacturing the electricity storage device separator will be described below.
In the present specification, "(meth)acryl" means "acryl" and its corresponding "methacryl", "(meth)acrylate" means "acrylate" and its corresponding "methacrylate", “(Meth)acryloyl” means “acryloyl” and the corresponding “methacryloyl”.

[Porous substrate]
The base material used in this embodiment may itself be one that has been conventionally used as a separator. The base material is preferably a porous membrane which has no electronic conductivity but ionic conductivity, high resistance to an organic solvent, and a fine pore size.

As the porous film, for example, a microporous film containing a resin such as a polyolefin (eg, polyethylene, polypropylene, polybutene and polyvinyl chloride) and a mixture or copolymer thereof as a main component; polyethylene terephthalate, polycycloolefin, poly Microporous membrane containing resin such as ether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene as a main component; polyolefin fiber woven fabric (woven fabric); polyolefin fiber nonwoven fabric; Paper; and an aggregate of insulating material particles. Among these, when the polymer layer is obtained through the coating step, the coating property of the coating liquid is excellent, the thickness of the separator is made thinner, and the active material ratio in the electricity storage device such as a battery is increased to increase the volume per volume. From the viewpoint of increasing the capacity of, a microporous polyolefin membrane containing a polyolefin-based resin as a main component is preferable. In addition, in this specification, "containing as a main component" means containing a specific component or member in an amount of more than 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, and further preferably Is 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

In this embodiment, the content of the polyolefin resin in the polyolefin microporous membrane is not particularly limited, but from the viewpoint of shutdown performance when used as a separator, 50% by mass or more and 100% by mass of all components constituting the porous substrate. It is preferable that the porous film is made of a polyolefin resin composition in which a polyolefin resin accounts for not more than 100%. The proportion of the polyolefin resin is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

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

Typical examples of polyolefin resins include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, ethylene propylene. Examples include rubber.

As the material of the polyolefin porous substrate used as the separator, it is particularly preferable to use a resin whose main component is high-density polyethylene because it has a low melting point and high strength. Two or more kinds of these polyethylenes may be mixed in order to impart flexibility. The polymerization catalyst used in the production of these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts and metallocene catalysts.

In order to improve the heat resistance of the polyolefin porous substrate, it is more preferable to use a porous film made of a resin composition containing polypropylene and a polyolefin resin other than polypropylene. The three-dimensional structure of polypropylene is not limited and may be any of isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene.
The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is not particularly limited, but is preferably 1 to 35% by mass, and more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, and more preferably 4 to 10% by mass.
The polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts.
In this case, the polyolefin resin other than polypropylene is not limited, for example, ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, homopolymers of olefin hydrocarbons such as 1-octene or the like. Copolymers may be mentioned. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, and ethylene-propylene random copolymer.

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

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin porous substrate is not particularly limited, but is preferably 30,000 or more and 12,000,000 or less, more preferably 50,000 or more and less than 2,000,000. , And more preferably 100,000 or more and less than 1,000,000. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding increases, the moldability becomes good, and the entanglement of the polymers tends to increase the strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12,000,000 or less, uniform melt kneading is facilitated, and the moldability of the sheet, particularly the thickness stability tends to be excellent, which is preferable. Further, when the viscosity average molecular weight is less than 1,000,000, pores are likely to be clogged when the temperature rises, and a good shutdown function tends to be obtained, which is more preferable.

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

For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1,000,000 alone, a mixture of a polyolefin having a viscosity average molecular weight of 2,000,000 and a polyolefin having a viscosity average molecular weight of 270,000, wherein A mixture having a viscosity average molecular weight of less than 1,000,000 may be used.

The polyolefin porous substrate in the present embodiment can contain any additive. The additive is not particularly limited, and examples thereof include polymers other than polyolefin; inorganic particles; phenol-based, phosphorus-based, sulfur-based, etc. antioxidants; metal soaps such as calcium stearate and zinc stearate; UV absorbers; Examples include light stabilizers, antistatic agents, antifogging agents, and coloring pigments.
The total content of these additives is preferably 0.001% by mass or more and 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass with respect to 100 parts by mass of the polyolefin resin composition. Below the section.

The porosity of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, preferably 80% or less. The porosity of 20% or more is preferable from the viewpoint of ensuring the ion permeability of the separator. On the other hand, the porosity of 90% or less is preferable from the viewpoint of ensuring the puncture strength. In the present specification, the porosity is calculated, for example, from the following numerical formula from the volume (cm ³ ), mass (g) and film density (g/cm ³ ) of the polyolefin porous substrate.
Porosity=(volume-mass/film density)/volume×100
Can be obtained by For example, in the case of a polyolefin porous substrate made of polyethylene, the porosity can be calculated by assuming that the film density is 0.95 (g/cm ³ ). The porosity can be adjusted by changing the stretch ratio of the polyolefin porous substrate.

The air permeability of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 10 seconds/100 cc or more, more preferably 50 seconds/100 cc or more, and preferably 1,000 seconds/100 cc or less. It is preferably 500 seconds/100 cc or less. The air permeability of 10 seconds/100 cc or more is preferable from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, the air permeability of 1,000 seconds/100 cc or less is preferable from the viewpoint of obtaining good charge/discharge characteristics. In the present specification, the air permeability is the air resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and/or the 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 preferably 0.01 μm or more. Setting the average pore size to 0.15 μm or less is suitable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity decrease. The average pore size can be adjusted by, for example, changing the draw ratio when manufacturing the polyolefin porous substrate.

The puncture strength of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 200 g/20 μm or more, more preferably 300 g/20 μm or more, preferably 2,000 g/20 μm or less, more preferably 1, It is 000 g/20 μm or less. It is preferable that the puncture strength is 200 g/20 μm or more from the viewpoint of suppressing film breakage due to the active material that has fallen off during winding of the battery and suppressing the short circuit due to expansion and contraction of the electrodes due to charge and discharge. On the other hand, the puncture strength of 2,000 g/20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength is measured by the method described in the examples. The puncture strength can be adjusted by adjusting the stretching ratio and/or the stretching temperature of the polyolefin porous substrate.

The film 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, further preferably 50 μm or less. .. It is preferable that the film thickness is 2 μm or more from the viewpoint of improving mechanical strength. On the other hand, it is preferable to set the film thickness to 100 μm or less, because the volume occupied by the separator in the battery decreases, which tends to be advantageous in increasing the capacity of the battery.

[Thermoplastic layer]
In this embodiment, the thermoplastic layer is arranged on at least one side of the porous substrate. In order to suppress press-back of the wound body after winding the separator including the thermoplastic layer together with the electrode, the thermoplastic layer is preferably arranged on both sides of the porous substrate.

The thermoplastic layer may be arranged on the entire surface of the porous substrate, or may be arranged only on a part of the substrate surface. It is preferable to dispose the thermoplastic layer only on a part of the surface of the polyolefin porous substrate so that the electricity storage device including the separator exhibits high ion permeability.

The thermoplastic layer in this embodiment contains an inorganic filler, a thermoplastic polymer, and a water-soluble polymer. The thermoplastic layer may optionally include additives. Each component contained in the thermoplastic layer will be described later.

The thermoplastic layer in the present embodiment ensures the handling property and blocking resistance of the separator before pressing, and further, when pressed to such an extent that the electric resistance does not significantly increase, the thermoplastic polymer is applied to the surface of the thermoplastic layer. It functions as an adhesive layer by migrating. As a level for appropriately expressing such a function in the thermoplastic layer, when the separator for an electricity storage device is subjected to heat press at 80° C. and 1.0 MPa after being immersed in an electrolytic solution, before the heat press. The ratio (T _a /T _b ) of the thickness (T _a ) of the thermoplastic layer after heat pressing to the thickness (T _b ) of the thermoplastic layer is preferably 0.6 to 0.9, It is more preferably 0.70 to 0.85.

The electrode used for measuring the thickness of the thermoplastic layer before and after heat pressing may be a positive electrode or a negative electrode, and may be a positive electrode current collector or a negative electrode current collector. In order to properly grasp the effect of the electricity storage device separator according to the present embodiment, a positive electrode or a positive electrode current collector is preferable. On the positive electrode current collector, a positive electrode for a lithium ion secondary battery in which a positive electrode active material layer containing a positive electrode active material is formed, or laminated so that the positive electrode active material layer faces the thermoplastic layer forming surface of the separator, Alternatively, it is appropriate to measure the thickness of the thermoplastic layer before and after heat pressing after the positive electrode current collector and the surface of the separator on which the thermoplastic layer is formed are superposed.
As a method of measuring the thickness change of the thermoplastic layer before and after heat pressing from the battery, there is a place called an ear where the positive and negative electrodes are not opposed to the end of the electrode body included in the battery and only the separator is provided. Therefore, it is possible to cut out that portion and use it for measurement.

The thickness of the thermoplastic layer arranged on the porous substrate is preferably 0.01 μm or more, and more preferably 0.1 μm or more, per one side of the substrate. Further, this thickness is preferably 5 μm or less, more preferably 4 μm or less, and further preferably 3 μm or less. It is preferable to adjust the thickness of the thermoplastic layer to 0.01 μm or more in order to allow the thermoplastic layer to function as an adhesive layer by migrating the thermoplastic polymer to the surface of the thermoplastic layer during pressing of the separator. It is possible to secure the adhesive strength between the separator and the electrode and the rigidity of the electricity storage device. It is preferable to adjust the thickness of the thermoplastic layer to 5 μm or less from the viewpoint of suppressing a decrease in ion permeability of the separator.

In the present embodiment, the thickness of the thermoplastic layer arranged on the porous substrate and the thickness of the thermoplastic layer before and after heat pressing are measured according to the method described in the following examples. Although the thickness of the thermoplastic layer is not limited, for example, the concentration of the thermoplastic polymer or copolymer in the coating liquid applied to the substrate, or the coating amount of the coating liquid, the coating method and the coating conditions are changed. It can be adjusted.

In the present embodiment, the area ratio of the thermoplastic layer to the total area of the surface of the porous substrate on which the thermoplastic layer is arranged is 100% or less, 80% or less, 75% or less, or 70%. And the area ratio is preferably 5% or more, 10% or more, or 15% or more. Setting the area ratio of the thermoplastic layer to 100% or less is preferable from the viewpoint of further suppressing the blockage of the holes of the base material by the thermoplastic polymer and further improving the permeability of the separator. On the other hand, the area ratio of 5% or more is preferable from the viewpoint of further improving the adhesiveness to the electrode. This area ratio is measured by observing the thermoplastic layer formation surface of the obtained separator with SEM.
Further, in the present embodiment, since the thermoplastic layer contains the inorganic filler, the thermoplastic polymer and the water-soluble polymer, the total area occupied by the inorganic filler, the thermoplastic polymer and the water-soluble polymer is calculated as the existing area of the thermoplastic layer. ..

Of the surface of the porous substrate, the area ratio of the thermoplastic layer to the total area of the surface on which the thermoplastic layer is arranged is not limited, for example, in the method for producing a separator described below, the substrate The concentration can be adjusted by changing the concentration of the thermoplastic polymer or copolymer in the coating liquid to be applied to the coating liquid, the coating amount of the coating liquid, the coating method and the coating conditions.

When the thermoplastic layer is arranged only on a part of the surface of the porous substrate, examples of the arrangement pattern of the thermoplastic layer include, for example, dot shape, stripe shape, lattice shape, stripe shape, hexagonal shape, random shape, and these. The combination of

(Inorganic filler)
The inorganic filler contained in the thermoplastic layer is not limited, but has a melting point of 200° C. or higher, has high electric insulation, and is electrochemically stable in the range of use of the lithium ion secondary battery. It is preferable.

The inorganic filler is not particularly limited, but examples thereof include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride. Ceramics; Silicon Carbide, Calcium Carbonate, Magnesium Sulfate, Aluminum Sulfate, Aluminum Hydroxide, Aluminum Hydroxide Oxide, Potassium Titanate, Talc, Kaolinite, Dickite, Nacrite, Halloysite, Pyrophyllite, Montmorillonite, Sericite, Mica, Ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth and silica sand; glass fibers and the like can be mentioned. These may be used alone or in combination.
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 such as kaolinite, dickite, nacrite, halloysite and pyrophyllite. Aluminum silicate compounds that have no function are preferred.

Aluminum hydroxide oxide (AlO(OH)) is particularly preferable as the aluminum oxide compound. As a specific example of aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing an internal short circuit due to the generation of lithium dendrite. The thermoplastic layer containing an inorganic filler containing boehmite as a main component, while maintaining high ion permeability, suppresses thermal contraction at high temperatures of the porous substrate even if it is made lightweight and thin, and is excellent. It tends to develop heat resistance. Synthetic boehmite is more preferable from the viewpoint of reducing ionic impurities that adversely affect the characteristics of the electricity storage device.

As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easily available. As kaolin, wet kaolin and calcined kaolin obtained by calcining the same are known. In the present embodiment, calcined kaolin is particularly preferable from the viewpoint of electrochemical stability, because water of crystallization is released and impurities are removed during the calcining treatment.

The average particle size of the inorganic filler is preferably more than 0.01 μm, more preferably more than 0.1 μm, still more preferably more than 0.3 μm. The average particle size of the inorganic filler is preferably 4.0 μm or less, more preferably 3.5 μm or less, and further preferably 3.0 μm or less. It is preferable to adjust the average particle size of the inorganic filler to more than 0.01 μm from the viewpoint of securing a specific surface area of the inorganic filler sufficient to apply the thermoplastic polymer and suppressing powder falling of the thermoplastic layer. Adjusting the average particle size of the inorganic filler to 4.0 μm or less suppresses the overlapping of the inorganic fillers in the laminating direction of the thermoplastic layer with respect to the porous substrate, so that the thermoplastic layer is crushed during pressing of the separator. This is preferable from the standpoint that it becomes easy to perform, and as a result, the rigidity of the electricity storage device including the separator can be improved.

Regarding the particle size distribution of the inorganic filler, the minimum particle size is preferably 0.001 μm or more, more preferably 0.005 μm or more, further preferably 0.01 μm or more, and the maximum particle size is 20 μm or less. The thickness is preferably 10 μm or less, more preferably 7 μm or less. Further, the ratio of maximum particle size/average particle size is preferably 50 or less, more preferably 30 or less, and further preferably 20 or less. Adjusting the particle size distribution of the inorganic filler in this manner is preferable from the viewpoint of suppressing thermal contraction of the separator at high temperatures.

While suppressing the powder falling of the thermoplastic layer, from the viewpoint of suppressing the overlap of the inorganic fillers in the laminating direction of the thermoplastic layer to the porous substrate, the average of the inorganic filler with respect to the average particle size of the thermoplastic polymer described below. The smaller the particle size ratio, the more preferable. The ratio of the average particle size of the inorganic filler to the average particle size of the thermoplastic polymer is specifically more than 0 and 12 or less, 0.5 or more and 10 or less, or 1 or more and 8 or less. Good.

Examples of the method of adjusting the particle size and distribution of the inorganic filler include a method of pulverizing the inorganic filler with a pulverizing device such as a ball mill, a bead mill and a jet mill.

Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a column shape, a spherical shape, a polyhedral shape, and a lump shape. A plurality of types of inorganic fillers having these shapes may be used in combination. In the thermoplastic layer containing the spherical inorganic filler, the inorganic fillers are easily separated from each other in the laminating direction of the thermoplastic layer with respect to the porous substrate, as a result, the thermoplastic layer tends to be crushed during pressing of the separator. is there. On the other hand, in the thermoplastic layer containing an inorganic filler having a shape other than spherical, the voids between the inorganic fillers tend to be adjusted to the extent that the surface of the thermoplastic polymer is exposed when the separator is pressed. In this embodiment, it is preferable to select the shape of the inorganic filler from such a viewpoint.

(Thermoplastic polymer)
In the present embodiment, the thermoplastic polymer contained in the thermoplastic layer contributes to at least one of adhesion between the thermoplastic layer and the porous substrate, adhesion between the separator and the electrode, and adhesion between the inorganic fillers in the thermoplastic layer. To do.

In the present embodiment, the volume ratio of the inorganic filler and the thermoplastic polymer in the thermoplastic layer (that is, the volume of the inorganic filler:the volume of the thermoplastic polymer) is 35:65 to 65:35 and 36:64 to 63. : 37 is preferable. When this volume ratio is 35 or more:65, the safety of the electricity storage device tends to be improved. On the other hand, when the volume ratio is 65 or less: 35, when the thermoplastic layer is pressed, a sufficient amount of the thermoplastic polymer for securing the adhesive area with the electrode migrates to the surface of the thermoplastic layer. The laminate or wound body including the separator and the electrode has rigidity, that is, has resistance to external stress, and as a result, contributes to the rigidity of the electricity storage device (particularly, the pouch-type electricity storage device). Furthermore, when this volume ratio is 65 or less:35, voids between the inorganic fillers in the thermoplastic layer are secured, so that the rigidity and resistance of the electricity storage device can be balanced.
The calculation method of the volume ratio is not limited, but it can be calculated by the following method, for example.
The paint can be converted into volume by dividing the weight of the inorganic filler and the thermoplastic polymer by the specific gravity. As a general method, the inorganic filler can be identified by XRD measurement, and the thermoplastic polymer can be identified by IR measurement and GC-MS measurement.
As the separator, the surface of the coating layer is scraped off, and the scraped coating layer is subjected to TG measurement (500° C., 2 hours or more) to measure the weight reduction, and the weight ratio can be calculated by the following formula. The calculated weight ratio can be converted into a volume ratio by dividing each by the specific gravity.
Thermoplastic polymer weight ratio in coating layer = TG measurement weight reduction ratio Inorganic filler weight ratio in coating layer = 1-TG measurement weight reduction ratio

Specific examples of the thermoplastic polymer include the following 1) to 4).
1) a conjugated diene-based polymer,
2) Acrylic polymer,
3) Polyvinyl alcohol intermediate, and 4) Fluorine-containing resin.

1) The conjugated diene polymer is a polymer containing a conjugated diene compound as a monomer unit. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and substituted linear conjugation. Examples include pentadienes, substituted and side chain conjugated hexadienes, and the like. These may be used alone or in combination of two or more.

The conjugated diene-based polymer may contain a (meth)acrylic compound or another monomer described below as a monomer unit. Specifically, for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, and the like.

2) The acrylic polymer is a polymer containing a (meth)acrylic compound as a monomer unit. The (meth)acrylic compound means at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid ester. Examples of such a compound include the following formula (P1):
_{^{CH 2 = CR Y1 -COO-R}} Y2 (P1)
{In the formula, R ^Y1 represents a hydrogen atom or a methyl group, R ^Y2 represents a hydrogen atom or a monovalent hydrocarbon group, and when R ^Y2 is a monovalent hydrocarbon group, it has a substituent. And may have a heteroatom in the chain. }
The compound represented by

In the formula (P1), examples of the monovalent hydrocarbon group include a chain alkyl group which may be linear or branched, a cycloalkyl group, and an aryl group. Further, examples of the substituent include a hydroxyl group and a phenyl group, and examples of the hetero atom include a halogen atom and an oxygen atom.

The (meth)acrylic compounds are used alone or in combination of two or more. Specific examples of the (meth)acrylic compound include (meth)acrylic acid, chain alkyl (meth)acrylate, cycloalkyl (meth)acrylate, hydroxyl group-containing (meth)acrylate, and phenyl group-containing (meth)acrylate. Are listed.

In the formula (P1), the chain alkyl group, which is one type of the group R ^Y2 , more specifically has a carbon number of 1 to 3 such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. A chain alkyl group having 4 or more carbon atoms, such as an n-butyl group, an isobutyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group and a lauryl group. As the aryl group which is one type of R ^Y2 , for example, a phenyl group can be mentioned.

Specific examples of the (meth)acrylic acid ester monomer having the group R ^Y2 include, for example,
Methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate , Isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, and other (meth)acrylates having a chain alkyl group; and phenyl (meth)acrylate, benzyl (meth)acrylate, and other aromatic compounds. (Meth)acrylate having a ring;
Are listed.
Among these, from the viewpoint of improving the adhesion with the electrode (electrode active material) and suppressing the excessive swelling of the thermoplastic polymer in the electrolytic solution and achieving a balance between rigidity and resistance, carbon atoms A monomer having a chain alkyl group of 4 or more, more specifically, a (meth)acrylic acid ester monomer in which the group R ^Y2 is a chain alkyl group of 4 or more carbon atoms is preferable, and butyl acrylate and butyl methacrylate. And at least one selected from the group consisting of 2-ethylhexyl acrylate are more preferable. The upper limit of the number of carbon atoms in the chain alkyl group having 4 or more carbon atoms is not particularly limited and may be 14, for example, but 7 is preferable. These (meth)acrylic acid ester monomers are used alone or in combination of two or more.

It is also preferable that the (meth)acrylic acid ester monomer contains a monomer having a cycloalkyl group as the group R ^Y2 instead of or in addition to the monomer having a chain alkyl group having 4 or more carbon atoms. Due to the presence of the cycloalkyl group having a high degree of swelling, excessive swelling in the electrolytic solution can be suppressed, and this also further improves the adhesion to the electrode.

Specific examples of the monomer having a cycloalkyl group include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantyl (meth)acrylate. 4-8 are preferable, as for the number of carbon atoms which comprise the alicyclic ring of a cycloalkyl group, 6 and 7 are more preferable, and 6 is especially preferable. The cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a t-butyl group. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferable because it has good polymerization stability during preparation of the acrylic polymer. These may be used alone or in combination of two or more.

Further, the acrylic polymer preferably contains a crosslinkable monomer as the (meth)acrylic acid ester monomer instead of or in addition to the above-listed monomers, preferably in addition to the above-listed monomers. The crosslinkable monomer is not particularly limited, and examples thereof include a monomer having two or more radically polymerizable double bonds, and a monomer having a functional group that provides a self-crosslinking structure during or after polymerization. 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. The polyfunctional (meth)acrylate may be at least one selected from the group consisting of bifunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional (meth)acrylate.

Specific examples of polyfunctional (meth)acrylates include polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol. Examples thereof include diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. Among them, at least one selected from the group consisting of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferable from the viewpoint of polymerization stability when preparing an acrylic polymer.

Examples of the monomer having a functional group that gives a self-crosslinking structure during or after the polymerization include a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, a monomer having a hydrolyzable silyl group, and the like. To be

As the monomer having an epoxy group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable, and specifically, glycidyl (meth)acrylate, 2,3-epoxycyclohexyl (meth)acrylate, 3,4-epoxycyclohexyl ( Examples thereof include (meth)acrylate and allyl glycidyl ether.

Examples of the monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide.

As the monomer having an alkoxymethyl group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable, and specific examples thereof include N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide and N-butoxymethyl. Methacrylamide and the like can be mentioned.

Examples of the monomer having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxysilane. Etc.

The monomer having a functional group that provides a self-crosslinking structure during or after the polymerization may be used alone or in combination of two or more.

The acrylic polymer may further have a monomer unit other than the above-listed monomers as a monomer unit in order to improve various qualities and physical properties. Examples of such a monomer include a monomer having a carboxyl group (excluding (meth)acrylic acid), a monomer having an amide group, a monomer having a cyano group, a monomer having a hydroxyl group, an aromatic vinyl monomer and the like. Can be mentioned.
Further, various vinyl-based monomers having functional groups such as sulfonic acid group and phosphoric acid group, and vinyl acetate, vinyl propionate, vinyl versatic acid, methyl vinyl ketone, butadiene, ethylene, propylene, vinyl chloride, vinylidene chloride, etc. Can be used as needed.
These may belong to two or more of the respective monomers at the same time, and may be used alone or in combination of two or more.

Examples of the amide group-containing monomer include (meth)acrylamide.
As the monomer having a cyano group, an ethylenic unsaturated monomer having a cyano group is preferable, and specific examples thereof include (meth)acrylonitrile.
Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate.
Examples of the aromatic vinyl monomer include styrene, vinyltoluene and α-methylstyrene, and styrene is preferable.

The acrylic polymer is obtained, for example, by a usual emulsion polymerization method. The emulsion polymerization method is not particularly limited, and a known method can be used.

For example, an acrylic polymer is obtained by polymerizing a monomer composition containing each of the above-mentioned monomers in a dispersion system containing the above-mentioned monomer, a surfactant, a radical polymerization initiator, and optionally other additives in an aqueous medium. can get. Various methods such as a method for making the composition of the monomer composition to be supplied constant throughout the entire polymerization process, a method for changing the morphological composition of the particles of the resin dispersion produced by changing the composition sequentially or continuously during the polymerization process, etc. Legality may be used as needed.

The surfactant may be used in an amount of 0.1 to 5 parts by mass based on 100 parts by mass of the monomer composition. As the surfactant, a compound having a sulfonic acid group or a group that is an ammonium salt or an alkali metal salt thereof (for example, an ammonium sulfonate group or an alkali metal sulfonate group) is preferable.

The radical polymerization initiator is one that radically decomposes by heat or a reducing substance to initiate addition polymerization of a monomer, and both an inorganic initiator and an organic initiator can be used. The radical polymerization initiator may be water-soluble or oil-soluble. The radical polymerization initiator may be used in an amount of 0.05 to 2 parts by mass with respect to 100 parts by mass of the monomer composition.

3) Examples of polyvinyl alcohol intermediates include polyvinyl acetate.

4) Examples of the fluorine-containing resin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer. To be

In order to balance the strength of the thermoplastic layer, the crushability of the thermoplastic polymer at the time of pressing the thermoplastic layer, and the ease of passage of the thermoplastic polymer between the inorganic fillers, the rigidity required for the electricity storage device is adjusted. Accordingly, it is preferable to control the degree of swelling of the thermoplastic polymer in the electrolytic solution. In the present embodiment, an appropriate degree of swelling of the thermoplastic polymer in the electrolytic solution is obtained when a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume:DEC volume=2:3) is used as the electrolytic solution. It is preferably 0.1 to 12 times, more preferably 1 to 11 times, still more preferably 2 to 10 times.

From the viewpoint of the adhesiveness between the separator and the electrode and the rigidity of the electricity storage device, it is also preferable that the thermoplastic polymer has an appropriate degree of swelling in the electrolytic solution. If the degree of swelling of the thermoplastic polymer is too low, the affinity with the electrolytic solution deteriorates and the battery characteristics also deteriorate. On the other hand, when the degree of swelling of the monomer is too high, the polymer cannot maintain its strength in the electrolytic solution, so that the rigidity of the polymer in the electrolytic solution decreases.

The degree of swelling of the thermoplastic polymer with respect to the electrolytic solution is measured by the method described in Examples. When two or more copolymers are used as the thermoplastic polymer, the degree of swelling is a weighted average of the degree of swelling of each copolymer.

As long as the thermoplastic polymer is distinguished from the water-soluble polymer described below, even if it is a polymer that can be dissolved or dispersed in a solvent (hereinafter referred to as “solvent-based polymer”), a polymer that is dispersible in water (hereinafter referred to as “aqueous dispersion A “polymer”).
As the solvent-based polymer, among thermoplastic polymers, a polymer having solubility in an organic solvent and/or a polymer having dispersibility in an organic solvent may be used.
The water-dispersible polymer is in the form of an aqueous dispersion (hereinafter referred to as “latex”) containing water and a granular polymer dispersed in water, or a form in which the polymer itself has a site having a high affinity with water. Good.
Of these, water-dispersible polymers are preferable, and latex is more preferable, from the viewpoint of coatability of the polymer or electric characteristics of the electricity storage device. The latex can be formed, for example, when the thermoplastic polymer is obtained by emulsion polymerization.

As the polymer in the latex, it is preferable to use at least one selected from the group consisting of acrylic polymers, fluorine-containing resins and styrene-butadiene rubber.

When the thermoplastic polymer is a water-dispersible polymer consisting only of an acrylic polymer, the degree of swelling of the acrylic polymer with respect to the electrolytic solution depends on the mixed solvent of EC and DEC (EC volume:DEC volume=2:3) as the electrolytic solution. ) Is used, it is preferably in the range of 1.5 times to 10 times, more preferably 3 times to 10 times.

When the water-dispersible polymer contains a fluororesin and/or styrene-butadiene rubber, the degree of swelling of the fluororesin with respect to the electrolytic solution and the degree of swelling of the styrene-butadiene rubber with respect to the electrolytic solution are EC and DEC. When the mixed solvent (EC volume:DEC volume=2:3) is used, it is preferably in the range of 0.1 to 5 times, more preferably 0.3 to 3 times.

When the water-dispersible polymer contains a fluorine-containing resin, among the above 4) fluorine-containing resins, polyvinylidene fluoride or a copolymer containing vinylidene fluoride and hexafluoropropylene as a copolymerization component is preferable, and vinylidene fluoride-hexafluoropropylene. More preferred are copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers and the like.

In order to improve the rigidity of the fluororesin in the electrolytic solution, the copolymerization ratio of hexafluoropropylene in the fluororesin is, for example, preferably in the range of 0.5 mol% to 15 mol %. More preferably, it is in the range of mol% to 10 mol %. It is also preferable to increase the molecular weight of the fluororesin, and the weight average molecular weight (Mw) of the fluororesin is preferably 100,000 or more, more preferably 300,000 or more, still more preferably 500,000 or more. The higher the crystallinity of the fluorine-containing resin, the more preferable it is, more preferably 15% or more, further preferably 20% or more, particularly preferably 25% or more.

When the water-dispersible polymer contains styrene-butadiene rubber, it is preferable to adjust the degree of crosslinking of the styrene-butadiene rubber within an appropriate range in order to improve the rigidity of the styrene-butadiene rubber in the electrolytic solution. Since the strength of the styrene-butadiene rubber may decrease if the degree of crosslinking is excessively increased, the gel fraction of the styrene-butadiene rubber is preferably 90% to 99%, and 95% to 99%. Is more preferable.

The glass transition temperature (Tg) of the thermoplastic polymer may be -50°C or higher, preferably -40°C to 120°C, more preferably -30°C to 100°C. When the Tg of the thermoplastic polymer is −40° C. to 120° C., the thermoplastic polymer on the porous substrate is likely to form a film, whereby the adhesion between the porous substrate and the thermoplastic layer or the separator and the electrode. It is presumed that the adhesiveness is secured.

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 obtained by extending the low temperature side baseline in the DSC curve to the high temperature side and a tangent line at the inflection point of the stepwise change portion of the glass transition.
Further, the “glass transition” refers to a change in the amount of heat caused by the change in the state of the polymer as the test piece on the endothermic side in DSC. Such a change in the amount of heat is observed in the DSC curve as a stepwise change. The “stepwise change” refers to a part of the DSC curve from the baseline on the low temperature side until then to a new baseline on the high temperature side. Note that a combination of a step change and a peak is also included in the step change.
Further, the "inflection point" refers to a point at which the gradient of the stepwise change portion of the DSC curve becomes maximum. Further, in the stepwise changing portion, when the upper side is the heat generating side, it can be expressed as a point where an upward convex curve changes to a downward convex curve. “Peak” refers to a portion of the DSC curve from the time when the curve leaves the baseline on the low temperature side until it returns to the same baseline again. The “baseline” refers to a DSC curve in a temperature range in which the test piece does not undergo a transition and a reaction.

The Tg of the thermoplastic polymer can be appropriately adjusted by, for example, changing the type of monomer used for producing the thermoplastic polymer and the compounding ratio of each monomer. The Tg of the thermoplastic polymer is calculated from the homopolymer Tg (for example, described in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) generally shown for each monomer used in the production thereof and the compounding ratio of the monomer, It can be roughly estimated. For example, thermoplastic polymers that incorporate high proportions of monomers such as styrene, methylmethacrylate, and acrylonitrile that give polymers with a Tg of about 100° C. have a high Tg. Further, for example, a thermoplastic polymer prepared by blending a high proportion of monomers such as butadiene which gives a polymer having a Tg of about -80°C, n-butyl acrylate and 2-ethylhexyl acrylate which gives a polymer having a Tg of about -50°C. Has a low Tg.
Further, the Tg of the polymer can be roughly calculated from the FOX equation (Equation 1 below). As the glass transition temperature of the thermoplastic polymer, the one measured by the above-mentioned method using DSC is adopted.
1/Tg=W ₁ /Tg ₁ +W ₂ /Tg ₂ +...+W _i /Tg _i +...W _n /Tg _n (1)
{In the formula, Tg(K) represents the Tg of the copolymer, Tg _i (K) represents the Tg of the homopolymer of each monomer i, and W _i represents the mass fraction of each monomer}.

It is also preferable that the thermoplastic layer formed on the porous substrate has at least two glass transition temperatures from the viewpoint of appropriately balancing the rigidity, rate characteristics, and cycle characteristics of the electricity storage device.

When the thermoplastic layer has at least two glass transition temperatures, at least one of Tg of the thermoplastic polymer is preferably less than 20°C, more preferably 15°C or less, further preferably -30°C or more 15 It exists in the region below ℃. As a result, the thermoplastic layer is more excellent in the adhesiveness with the porous substrate, and as a result, the separator is more excellent in the adhesiveness with the electrodes, so that the rigidity of the electricity storage device is also improved. In order to improve the adhesion between the thermoplastic polymer and the porous substrate and the handleability of the separator, and/or to suppress the powder falling off of the thermoplastic layer, Tg existing in the region of less than 20°C is -30°C or more. It is particularly preferred that it exists only in the region of 15°C or lower.

When the thermoplastic layer has at least two glass transition temperatures, at least one of Tg of the thermoplastic polymer is preferably 20° C. or higher, more preferably 20° C. or higher and 120° C. or lower, further preferably 50° C. It exists in the region of not less than 120°C and not more than 120°C. Accordingly, the thermoplastic layer can maintain the handleability of the separator and the adhesion between the electrode and the separator when the separator is heated or pressed for the production of the electricity storage device. In order to improve the handling property of the separator and the adhesion between the electrode and the separator, it is particularly preferable that Tg existing in the region of 20°C or higher exists only in the region of 50°C or higher and 120°C or lower.

The fact that the thermoplastic polymer has at least two glass transition temperatures can be achieved by, for example, a method of blending two or more kinds of thermoplastic polymers, a method of using a thermoplastic polymer having a core-shell structure, or the like. In the present specification, the core-shell structure means that the polymer has a morphology of a double structure and the polymer composition of the central portion and the polymer composition of the outer shell portion are different.
In particular, in a polymer blend and a core-shell structure, by combining a polymer having a high Tg and a polymer having a low Tg, it is possible to control the glass transition temperature of the entire thermoplastic polymer and impart a plurality of functions to the entire thermoplastic polymer. it can.

For example, in the case of a polymer blend, the stickiness resistance is improved by blending two or more kinds of a polymer having a glass transition temperature of 20° C. or more and a polymer having a glass transition temperature of less than 20° C. And the wettability to the base material can both be achieved. As a mixing ratio in the case of blending, the mass ratio of the polymer existing in the region where the glass transition temperature is 20° C. or higher and the polymer existing in the region where the glass transition temperature is lower than 20° C. is 0.1:99.9. To 99.9:0.1, more preferably 5:95 to 95:5, even more preferably 50:50 to 95:5, and particularly preferably 60:40 to. It is 90:10.

In the case of the core-shell structure, the adhesiveness and compatibility with other materials (for example, a polyolefin microporous film) can be adjusted by changing the type of the outer shell polymer. Further, by changing the type of the polymer belonging to the central portion, for example, the adhesiveness of the polymer to the electrode after hot pressing can be adjusted.
In the case of the core-shell structure, viscoelasticity can be controlled by combining a polymer having high viscosity and a polymer having high elasticity.
Regarding the thermoplastic polymer having a core-shell structure, the glass transition temperature of the shell is not particularly limited, but is preferably lower than 20°C, more preferably 15°C or lower, still more preferably -30°C or higher and 15°C or lower. Regarding the thermoplastic polymer having a core-shell structure, the glass transition temperature of the core is not particularly limited, but is preferably 20° C. or higher, more preferably 20° C. or higher and 120° C. or lower, still more preferably 50° C. or higher and 120° C. or lower.

The thermoplastic polymer may be granular, more particularly particles composed of one thermoplastic polymer or a mixture of thermoplastic polymers, or may have the core-shell structure described above.
As used herein, the term "granular" of a thermoplastic polymer refers to the state in which individual polymers have a contour when observed under a scanning electron microscope (SEM). Therefore, the granular thermoplastic polymer may have, for example, a flat shape, a spherical shape, a polygonal shape, or the like.

The average particle size of the granular thermoplastic polymer is preferably 50 nm or more, more preferably 75 nm or more, even more preferably 100 nm or more, and preferably 1,000 nm or less, more preferably 800 nm or less, further preferably 700 nm or less. .. The average particle size of 1,000 nm or less is preferable from the viewpoint of ensuring the dispersion stability of the aqueous dispersion for forming the thermoplastic layer and the viewpoint of flexibly controlling the thickness of the thermoplastic layer. When the average particle size is 50 nm or more, the following (i) to (iii):
(I) Since the size of the granular thermoplastic polymer that is easily crushed during pressing of the thermoplastic layer is ensured, the thermoplastic polymer is present on the surface of the thermoplastic layer (the surface of the separator), whereby the adhesion between the separator and the electrode. And the rigidity of the electricity storage device including the separator are improved;
(Ii) The granular thermoplastic polymer is likely to intervene between the inorganic fillers in the thermoplastic, so that the ion permeability of the thermoplastic layer itself is maintained; and (iii) to the extent that it does not enter the pores of the porous substrate. The size of the particulate thermoplastic polymer is ensured so that the ion permeability of the separator comprising the thermoplastic layer is maintained;
It is speculated that at least one of The average particle size of the granular thermoplastic polymer is measured according to the method described in the examples below.

In order to balance the adhesiveness and blocking resistance of the separator, it is also preferable to include two or more types of thermoplastic polymer particles having different average particle sizes in the thermoplastic layer. More preferably, a combination of two or more kinds of thermoplastic polymer particles having an average particle diameter of 10 nm to 300 nm (hereinafter referred to as "small particle diameter particles"); heat having an average particle diameter of more than 300 nm and 2,000 nm or less. A combination of two or more kinds of plastic polymer particles (hereinafter referred to as “large particle size particles”); or a combination of at least one small particle size particle and at least one large particle size particle is used.

(Water-soluble polymer)
In this embodiment, known water-soluble polymers can be included in the thermoplastic layer as long as the water-soluble polymers are distinguished from the thermoplastic polymers described above. More specifically, the water soluble polymer may be incompatible with the thermoplastic polymer.

Generally, the water-soluble polymer functions as a dispersant in a resin composition containing an inorganic filler or a granular thermoplastic polymer, and further as a dispersant and/or a water retention agent when the resin composition is an aqueous paint.

The water-soluble polymer used in the present embodiment may be a polymer derived from a natural product, a synthetic product, a semi-synthetic product, or the like, but from the viewpoint of forming an inorganic filler and a thermoplastic polymer into a paint, particularly an aqueous paint, it is anionic. It is preferably cationic, amphoteric, or nonionic, and more preferably anionic, cationic, or amphoteric.

Examples of the anionic polymer include modified starches such as carboxymethyl starch and starch phosphate; anionic cellulose derivatives such as carboxymethyl cellulose; ammonium salts or alkali metal salts of polycarboxylic acids; gum arabic; carrageenan; sodium chondroitin sulfate; Examples thereof include sulfonic acid compounds such as sodium polystyrene sulfonate, sodium polyisobutylene sulfonate, and naphthalene sulfonic acid condensate salts; and polyethyleneimine xanthate salt. Among these, anionic cellulose derivatives and ammonium salts of polycarboxylic acids or alkali metal salts are preferable from the viewpoint of appropriately balancing rigidity, rate characteristics, and cycle characteristics of the electricity storage device, and ammonium salts of polycarboxylic acids or Alkali metal salts are more preferred.

In the present specification, the ammonium salt or alkali metal salt of polycarboxylic acid means a polymer in which at least one of —COO ⁻ moieties derived from a plurality of carboxylic acid groups forms a salt with an ammonium ion or an alkali metal ion. .. Examples of the alkali metal ion include Na ⁺ , K ^{+ and the} like.

The ammonium or alkali metal salt of polycarboxylic acid may be at least one of the following (I) to (III):
(I) a homopolymer of a monomer (C _i ) having one ammonium salt or an alkali metal salt of a carboxylic acid, or a copolymer of a plurality of monomers (C _i ) and another monomer;
(II) a homopolymer of a monomer (C _ii ) having a plurality of ammonium salts or alkali metal salts of a carboxylic acid, or a copolymer of a monomer (C _ii ) and another monomer; and (III) having a carboxylic acid or carboxylic acids. An ammonium salt or an alkali metal salt of a polymer or copolymer obtained by polymerizing or copolymerizing monomers.

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

Examples of the monomer ( _Cii ) having a plurality of ammonium salts or alkali metal salts of carboxylic acids include ammonium salts or sodium salts of 11-(methacryloyloxy)undecane-1,1-dicarboxylic acid; fumaric acid, maleic acid, itacone. Examples thereof include ammonium salt, monosodium salt or disodium salt of ethylenically unsaturated dicarboxylic acid such as acid and citraconic acid; and alicyclic polyvalent carboxylic acid having a (meth)acryloyl group.

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

Examples of the ammonium salt or alkali metal salt of a polymer or copolymer obtained by polymerizing or copolymerizing a monomer having one or more carboxylic acids include sodium polyacrylate, ammonium polyacrylate and the like.

The structures of the ammonium salt or the alkali metal salt of the polycarboxylic acid described in (I) to (III) above may overlap each other.

Examples of the cationic polymer include cationic starch; chitosan; gelatin; dimethylaminoethyl (meth)acrylate quaternary salt homopolymers or copolymers; dimethylallylammonium chloride homopolymers or copolymers; polyamidine and its copolymers; polyvinyl imidazoline; dicyandiamide. System condensates; epichlorohydrin-dimethylamine condensates; and polyethyleneimine.

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

Examples of the nonionic polymer include starch and its derivatives; cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose, and ammonium salts or alkali metal salts thereof; gums such as guar gum and modified products thereof; and polyvinyl alcohol and poly Examples thereof include acrylamide, polyethylene glycol, polymethyl vinyl ether, polyisopropyl acrylamide, synthetic polymers such as copolymers of vinyl alcohol and other monomers, and modified products thereof.

The water-soluble polymer used in this embodiment more preferably does not have an amide bond-containing cyclic structure.

In the present specification, the water-soluble and nonionic polymer having an amide bond-containing cyclic structure refers to a homopolymer or a copolymer having a group having an amide bond-containing cyclic structure and a skeleton derived from a polymerizable double bond. The water-soluble and nonionic polymers having an amide bond-containing cyclic structure may have one or more amide bond-containing cyclic structures.

で表される基等が挙げられる。アミド結合含有環状構造を有する水溶性及び非イオン性ポリマーの具体例としては、Ｎ−ビニルカプロラクタムのホモポリマーであるポリ（Ｎ−ビニルカプロラクタム）、ビニルピロリドンのホモポリマーであるポリビニルピロリドン（ＰＶＰ）等の、アミド結合含有環状構造を有する基と重合性二重結合とを有するモノマーのホモポリマー；アミド結合含有環状構造を有する基と重合性二重結合とを有するモノマー（Ｎ−ビニルカプロラクタム、ビニルピロリドン等）２種以上のコポリマー；及びアミド結合含有環状構造を有する基と重合性二重結合とを有するモノマー（Ｎ−ビニルカプロラクタム、ビニルピロリドン等）の１種又は２種以上と、他の重合性二重結合を有するモノマー（アミド結合含有環状構造を有する基と重合性二重結合とを有するモノマー以外のモノマー）の１種又は２種以上とのコポリマーが挙げられる。 The group having an amide bond-containing cyclic structure is represented by the following formula (2):

And the like. Specific examples of the water-soluble and nonionic polymers having an amide bond-containing cyclic structure include poly(N-vinylcaprolactam), which is a homopolymer of N-vinylcaprolactam, and polyvinylpyrrolidone (PVP), which is a homopolymer of vinylpyrrolidone. A homopolymer of a monomer having a group having an amide bond-containing cyclic structure and a polymerizable double bond; a monomer having a group having an amide bond-containing cyclic structure and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone Etc.) Two or more kinds of copolymers; and one or more kinds of monomers (N-vinylcaprolactam, vinylpyrrolidone, etc.) having a group having an amide bond-containing cyclic structure and a polymerizable double bond, and another polymerizable Examples thereof include a copolymer with one or more monomers having a double bond (monomers other than the monomer having a group having an amide bond-containing cyclic structure and a polymerizable double bond).

Examples of the monomer copolymerizable with the monomer having a group having an amide bond-containing cyclic structure and a polymerizable double bond include vinyl acyclic amides; (meth)acrylic acid and its esters; (meth)acrylamide and its derivatives. Styrene and its derivatives; vinyl esters such as vinyl acetate; α-olefins; basic unsaturated compounds such as vinylimidazole and vinylpyridine and their derivatives; unsaturated compounds containing a carboxyl group and their acid anhydrides; vinyl sulfonic acid And its derivatives; vinyl ethylene carbonate and its derivatives; and vinyl ethers.

In the present embodiment, the content of the water-soluble polymer in the thermoplastic layer is 0.04 mass% or more and less than 1.0 mass% with respect to the total mass of the inorganic oxide particles and the thermoplastic polymer. This content is 0.04 mass% or more as the amount of the water-soluble polymer necessary for forming a resin composition containing an inorganic filler and a thermoplastic polymer as a coating liquid, particularly as a water-based paint. On the other hand, this content is less than 1.0% by mass from the viewpoint that the water-soluble polymer partially covers the surface of the thermoplastic polymer in the thermoplastic layer, so that the thermoplastic polymer is appropriately swollen in the electrolytic solution. Is. This content is preferably 0.05% by mass or more and 0.9% by mass or less, more preferably 0.1% by mass or more and 0.85% by mass or less, and further preferably 0.2% by mass or more and 0.8% by mass. It is as follows.

(Additive)
In the present embodiment, the thermoplastic layer may be composed only of the inorganic filler, the thermoplastic polymer and the water-soluble polymer, or may contain an additive other than the inorganic filler, the thermoplastic polymer and the water-soluble polymer. Examples of the additives include low molecular weight dispersants other than the water-soluble polymers described above; thickeners; and pH adjusters such as ammonium hydroxide. Specific examples of the low molecular weight dispersant include monomers (C _ii ) having a plurality of ammonium salts or alkali metal salts of carboxylic acids, non-polymerizable compounds having a plurality of ammonium salts or alkali metal salts of carboxylic acids (for example, sodium alginate, And sodium hyaluronate) and the like.

[Arrangement Method of Thermoplastic Layer]
One embodiment of the method of disposing the thermoplastic layer on the porous substrate includes a step of applying a coating liquid containing an inorganic filler, a thermoplastic polymer, a water-soluble polymer and optionally additives to the porous substrate.

As the coating liquid, a dispersion prepared by dispersing a thermoplastic polymer in a solvent in which the thermoplastic polymer is insoluble can be preferably used. It is preferable to synthesize a thermoplastic polymer by emulsion polymerization and use the emulsion obtained by emulsion polymerization as it is as a coating liquid.

The method of applying the coating liquid on the porous substrate is not particularly limited as long as it is a method capable of realizing a desired coating pattern, coating film thickness, and coating area, for example, a gravure coater method, a small diameter gravure coater method, Reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, A spray coating method, an inkjet coating method and the like can be mentioned. Among them, the gravure coater method or the spray coating method is preferable from the viewpoint that the flexibility of the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

As a medium for the coating liquid, it is preferable to use a poor solvent for the thermoplastic polymer. As such a medium, water or a mixed solvent of water and a water-soluble organic medium is preferable. Examples of the water-soluble organic medium include ethanol and methanol. Of these, water is more preferable. Generally, when the coating liquid enters the inside of the substrate when the coating liquid is applied to the substrate, the thermoplastic polymer containing the copolymer blocks the surface and the inside of the pores of the substrate to reduce the permeability. Easier to do. On the other hand, when water is used as the solvent or dispersion medium for the coating liquid, the coating liquid is less likely to enter the inside of the base material, and the thermoplastic polymer containing the copolymer is likely to be present on the outer surface of the base material. Therefore, the decrease in permeability can be suppressed more effectively, which is preferable.

It is preferable to subject the surface of the porous substrate to a surface treatment prior to coating, because the coating liquid can be easily coated and the adhesion between the porous substrate and the thermoplastic polymer is improved. Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

The method of removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous substrate or the thermoplastic layer. For example, a method of drying the porous substrate at a temperature below its melting point while fixing it, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for the thermoplastic polymer to coagulate the thermoplastic polymer into particles, and at the same time a solvent And a method of extracting

<Separator for electricity storage device>
The electricity storage device separator according to the present embodiment is provided with a specific thermoplastic layer on a porous base material, and has ion permeability, and adhesiveness with an electrode active material, particularly electrode activity when pressed with an electrode. Excellent adhesion to substances.

The separator for an electricity storage device according to this embodiment has a peel strength of 2N when pressed under the conditions of a temperature of 100° C., a pressure of 1.0 MPa, and a pressing time of 2 minutes, which is superposed on an electrode and wetted with an electrolytic solution. /M or more is preferable. As the electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume:DEC volume=2:3) containing 1 mol/L of LiPF ₆ is used. This means that the separator according to this embodiment has adhesiveness to the electrodes. By setting the peeling strength within this range, sufficient adhesiveness between the separator and the electrode can be ensured, and peeling between the separator and the electrode due to expansion and contraction of the electrode due to charge/discharge and an increase in battery thickness can be suppressed. As a result, it is possible to uniformly transfer lithium ions, suppress the generation of lithium dendrites, and achieve good cycle characteristics.

The electrode used for measuring the peel strength may be either a positive electrode or a negative electrode, but the positive electrode is preferable in order to properly understand the effect of the separator for an electricity storage device according to the present embodiment. On the positive electrode current collector, a positive electrode active material layer containing a positive electrode active material positive electrode for a lithium ion secondary battery, the positive electrode active material layer is laminated so as to face the thermoplastic layer forming surface of the separator, It is appropriate to measure the peel strength after roll pressing as described above.

The air permeability of the electricity storage device separator according to the present embodiment is preferably 10 to 10,000 seconds/100 cc, more preferably 10 to 1,000 seconds/100 cc, and further preferably 50 to 500 seconds/. It is 100 cc. As a result, when the separator is applied to a lithium ion secondary battery, it exhibits large ion permeability. The air permeability is the air resistance measured in accordance with JIS P-8117, like the air permeability of the porous substrate.

<Power storage device>
The electricity storage device including the electricity storage device separator according to the present embodiment is not particularly limited, and examples thereof include batteries such as non-aqueous electrolyte secondary batteries, capacitors, and capacitors. Among them, the battery is preferable, the non-aqueous electrolyte secondary battery is more preferable, and the lithium ion secondary battery is still more preferable, from the viewpoint of more effectively obtaining the benefit of the action and effect of the present invention.

The configuration of the electricity storage device according to the present embodiment may be as conventionally known, except that the electricity storage device separator described above is provided. A preferred embodiment in the case where the electricity storage device is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery will be described below.

When a lithium ion secondary battery is manufactured using the separator according to this embodiment, the positive electrode, the negative electrode, and the non-aqueous electrolytic solution are not limited, and known ones can be used.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be preferably used. Examples of the positive electrode current collector include aluminum foil and the like; 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. it can. The positive electrode active material layer may include a binder, a conductive material, and the like in addition to the positive electrode active material.

As the negative electrode, a negative 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. As the negative electrode current collector, for example, copper foil or the like; as the negative electrode active material, for example, carbon material such as graphite, non-graphitizable carbonaceous material, easily graphitizable carbonaceous material, composite carbon body; silicon, tin, metallic lithium , Various alloy materials and the like;

The non-aqueous electrolytic solution is not particularly limited, but an electrolytic solution 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 .

A method for manufacturing an electricity storage device using the electricity storage device separator according to the present embodiment will be exemplified below.
The separator according to 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). Positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator are laminated in this order and wound into a circular or flat spiral to obtain a wound body, and the wound body is housed in a battery can. An electric storage device can be manufactured by injecting the electrolytic solution. Alternatively, a laminate composed of a sheet-shaped separator and an electrode (for example, a positive electrode-separator-negative electrode-separator-positive electrode, or a negative electrode-separator-positive electrode-separator-negative electrode laminated in the order of a flat plate), or The separator may be folded into a wound body, and the wound body may be put into a battery container (for example, a film made of aluminum) and the electrolytic solution may be injected.

In any case, pressing can be performed on the laminate or the wound body. Specifically, the electricity storage device separator according to the present embodiment, and a current collector and an electrode having an active material layer formed on at least one surface of the current collector, a thermoplastic layer of the separator and an active material of the electrode. It is possible to exemplify a method of stacking and pressing so that the layers face each other.

The pressing temperature is preferably, for example, 20° C. or higher as a temperature at which adhesiveness can be effectively exhibited. In addition, the pressing temperature is preferably lower than the melting point of the polyolefin porous substrate, and more preferably 120° C. or lower, from the viewpoint of suppressing clogging of separator holes or thermal shrinkage due to hot pressing. The pressing pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of separator holes. The pressing time may be 1 second or less when a roll press is used, or a surface press for several hours. When the electricity storage device separator according to the present embodiment is used and the above manufacturing process is performed, it is possible to suppress pressback when the wound body including the electrode and the separator is press-molded. It is also possible to prevent peeling and misalignment after press-molding a laminated body including a sheet-shaped electrode and a sheet-shaped separator. Therefore, it is possible to suppress a decrease in yield in the battery assembly process and shorten the production process time, and thus the above-described manufacturing process is preferable.

It is also possible to perform hot pressing after injecting the electrolytic solution into the laminate or wound body described above. In that case, the pressing temperature is preferably 20° C. or higher as the temperature at which adhesiveness can be effectively exhibited, and is preferably 120° C. or lower from the viewpoint of suppressing clogging of separator holes or thermal shrinkage due to hot pressing. The pressing pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of separator holes. The pressing time is preferably 2 hours or less from the viewpoint of productivity.

The electricity storage device such as the lithium-ion secondary battery manufactured as described above has a separator having a high adhesive property and a reduced ionic resistance, so that the rigidity, the battery characteristics (rate characteristics), and the long-term continuity are maintained. Excellent operation resistance (cycle characteristics).

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

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

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

(3) Swelling degree to electrolyte solution After allowing the polymer or polymer dispersion solution to stand in an oven at 130° C. for 1 hour, the dried polymer was cut to a weight of 0.5 g, and ethylene carbonate:diethyl carbonate=2. : 3 (mass ratio) of the mixed solvent was put in a 50 mL vial. After allowing the sample in the vial to permeate for 3 hours, the sample was taken out, washed with the above mixed solvent, and the weight (W _a ) was measured. After allowing the sample to stand in an oven at 150° C. for 1 hour, the weight (W _b ) was measured, and the swelling degree of the polymer with respect to the electrolytic solution was measured by the following formula.
Degree of swelling electrolyte of the thermoplastic polymer _{(times) = (W a -W b)} ÷ (W b)

(4) Measurement of glass transition temperature An appropriate amount of an aqueous dispersion (solid content=38 to 42 mass%, pH=9.0) containing thermoplastic polymer particles is placed in an aluminum dish, and a hot air dryer at 130° C. is used for 30 minutes. Dried. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve under a nitrogen atmosphere were obtained with a DSC measuring device (manufactured by Shimadzu Corporation, DSC6220). The measurement conditions were as follows.
1st stage heating program: 70°C start, heating at a rate of 15°C/min. Hold for 5 minutes after reaching 110°C.
Second stage cooling program: 110°C to 40°C/min. Hold for 5 minutes after reaching -50°C.
3rd stage heating program: Temperature rising from -50°C to 130°C at a rate of 15°C per minute. Data of DSC and DDSC were acquired when the temperature was raised in the third step.
The intersection of the baseline (a straight line obtained by extending the baseline in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to the downward convex curve) is taken to be the glass transition temperature ( Tg).

(5) Viscosity average molecular weight Mv
In accordance with ASRM-D4020, the intrinsic viscosity [η] at 135°C in a decalin solvent was determined. Using this [η] value, the viscosity average molecular weight Mv was calculated from the relationship of the following mathematical formula.
In the case of polyethylene: [η]=0.00068×Mv0.67
In the case of polypropylene: [η]=1.10×Mv0.80

(6) Film thickness (μm)
Cut out a 10 cm x 10 cm square sample from the base material, select 9 points (3 points x 3 points) in a grid pattern, and use a micro thickness gauge (Toyo Seiki Seisakusho Type KBM) at room temperature 23 ± 2°C. The film thickness was measured. The average value of the obtained measured values at 9 points was calculated as the film thickness of the substrate.

(7) Porosity A 10 cm×10 cm square sample was cut out from the base material, and its volume (cm ³ ) and mass (g) were determined. Using these values, the density of the substrate is set to 0.95 (g/cm ³ ), and the porosity is calculated by the following mathematical formula:
Porosity (%)=(1-mass/volume/0.95)×100
Calculated by

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

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

(10) Thickness of Electrolytic Solution Immersed Sample After Heat Press A separator and an aluminum foil (UACJ foil, alloy number 1085, thickness: 20 μm) were cut into a width of 20 mm and a length of 40 mm. After stacking the separator and the aluminum foil, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume/DEC volume=2/3, LiPF ₆ concentration: 1M, SP value as mixture=11.6) The separator was soaked. This laminate was placed in an aluminum laminate film (trade name SPAL manufactured by Showa Denko), the four corners were sealed with a heating sealer, and then pressed at 80° C. and 1.0 MPa for 60 minutes, and then the laminate was taken out. A separator sample was obtained by washing with ethanol.

The cross section of the washed laminate was processed by a broad ion beam (BIB). During processing, the sample was allowed to cool to just before to prevent thermal damage. Specifically, the separator sample was left to stand overnight in a cooling device at -40°C. As a result, a smooth separator cross section was obtained. The obtained separator cross-section was subjected to conduction treatment with C paste and Os coating, and then photographed using "HITACHI S-4700" (manufactured by Hitachi High-Tech Fielding), and the obtained cross-section SEM image was used for heat treatment. The thickness ( _Ta ) of the coating layer after pressing was measured.

Similarly, for the separator before heat pressing, the thickness (T _b ) of the coating layer before heat pressing was measured from the cross-sectional SEM image after the cross-section processing was performed with BIB.

(11) Cell rigidity evaluation method Aluminum laminate (St ON25/AL40/OPP40 manufactured by Showa Denko Packaging Co., Ltd.) was cut into a width of 60 mm and a length of 80 mm, and three sides were sealed with a heat sealer, and a storage body Got

Positive electrode (manufactured by enertech, positive electrode material: LiCoO ₂ , positive electrode potential: 4.35 V, L/W: 36 mg/cm ² on both sides, density: 3.9 g/cc) and a separator prepared in Examples or Comparative Examples Were cut into a width of 30 mm and a length of 180 mm, and the cut positive electrode and separator were stacked to obtain a laminate.

The laminated body was wound under the condition that the number of windings was 3 times so that the length was about 27 mm and the width was 30 mm to obtain a wound body.
The wound body was placed in the container prepared above, and as an electrolyte, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume/DEC volume=2/3, LiPF ₆ concentration: 1M, as a mixture). 0.5 ml of SP value=11.6) was sealed, sealed with a heat sealer, and allowed to stand for 12 hours to obtain a pressed body.
The pressed body was pressed for 60 minutes under conditions of a temperature of 80° C. and a pressure of 1 MPa to obtain a pressed body.

Digital force gauge "DS2-50N" (product name, made by Imada Co., Ltd.) equipped with a piercing jig (A type A-4), and a notch (upper cut width: about 27 mm, lower cut width: about 15 mm) ) And the pedestal to be stabbed are attached to an electric measurement stand “MX2-500N” (product name, manufactured by Imada Co., Ltd.).

The press body is pierced so that the piercing direction is perpendicular to the winding direction of the winding body and the tip of the pressing jig can contact the center of the winding body housed in the housing body. I set it on the pedestal.

The individually set press bodies were subjected to a 3-point bending strength test at a bending speed of 50 mm/min, and the maximum value (N) of stress was measured as the 3-point bending strength (rigidity value).

(12) Rate characteristics a. Production of Positive Electrode 90.4% by mass of nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (element ratio), density 4.70 g/cm ³ ) as a positive electrode active material, 1.6 mass% of graphite powder (KS6) (density 2.26 g/cm ³ , number average particle size 6.5 μm) and acetylene black powder (AB) (density 1.95 g/cm ³ , number average) as a conduction aid. 3.8% by mass of particle diameter 48 nm, and polyvinylidene fluoride (PVDF) (density 1.75 g/cm ³ ) as a binder were mixed in a ratio of 4.2% by mass, and these were mixed with N-methylpyrrolidone (NMP). A slurry was prepared by dispersing the slurry therein. This slurry was applied to one side of an aluminum foil having a thickness of 20 μm to be a positive electrode current collector using a die coater, dried at 130° C. for 3 minutes, and then compression-molded using a roll press machine to form a positive electrode. It was made. The amount of the positive electrode active material applied 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), and as a binder, 1.4% by mass of ammonium salt of carboxymethyl cellulose (as solid content) (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass of diene rubber-based latex ( A slurry was prepared by dispersing (in terms of solid content) (solid content of 40 mass% aqueous solution) in purified water. This slurry was applied to one surface of a copper foil having a thickness of 12 μm, which is a negative electrode current collector, by a die coater, dried at 120° C. for 3 minutes, and then compression-molded with a roll press machine to prepare a negative electrode. The amount of the negative electrode active material applied at this time was 5.2 g/m ² .

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

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

e. Evaluation of rate characteristics d. By charging the simple battery assembled in above at 25°C with a current value of 3mA (about 0.5C) to a battery voltage of 4.2V, and then starting to squeeze the current value from 3mA so as to maintain 4.2V. The first charge after the battery was made was carried out for a total of about 6 hours. Then, 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 voltage was charged to 4.2 V at a current value of 6 mA (about 1.0 C), and then the current value was started to be reduced from 6 mA so as to maintain 4.2 V. Charged for an hour. 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 voltage was charged to 4.2 V at a current value of 6 mA (about 1.0 C), and then the current value was started to be reduced from 6 mA so as to maintain 4.2 V. Charged for an hour. 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)×100

(13) Cycle characteristics The cycle characteristics were evaluated using the simple batteries assembled as described in (12) a to d above.
After constant current charging the above battery to a voltage of 4.2V with a current value of 1/3C, constant voltage charging of 4.2V was performed for 8 hours, and then discharged to a final voltage of 3.0V with a current of 1/3C. I went. Next, constant current charging was performed at a current value of 1 C to a voltage of 4.2 V, constant voltage charging at 4.2 V was performed for 3 hours, and discharging was further performed at a current of 1 C to a final voltage of 3.0 V. Finally, constant current charging was performed at a current value of 1 C up to 4.2 V, and then constant voltage charging at 4.2 V was performed for 3 hours to obtain pretreatment. In addition, 1C represents the electric current value which discharges the reference capacity of a battery in 1 hour.

The battery subjected to the above pretreatment was discharged at a discharge current of 1 A to a discharge end voltage of 3 V at a temperature of 25° C., and then at a charge current of 1 A to a charge end voltage of 4.2 V. This was set as one cycle, and charging/discharging was repeated. Then, the capacity retention rate (%) after 200 cycles with respect to the initial capacity (the capacity in the first cycle) was calculated.

[Rigidity, rate characteristics and cycle characteristics evaluation criteria]
Table 1 shows the evaluation criteria of rigidity, rate characteristics and cycle characteristics.

<Synthesis of thermoplastic polymer particles>
[Thermoplastic polymer particles A1 to A6, B1, C1, C2]
According to the formulation shown in Table 2, ion-exchanged water and an emulsifier were put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer, and the reaction vessel internal temperature was raised to 80° C. The initiator was added while maintaining the temperature of °C.

Five minutes after the addition of the initiator, an emulsion prepared by mixing the components described in the "Emulsion" column of Table 2 for 5 minutes with a homomixer was started to be dropped into the reaction vessel from the dropping tank, and 150 minutes later. Then, the whole amount was dropped.

After the completion of dropping the emulsion, the internal temperature of the reaction vessel was maintained at 80° C. for 90 minutes and then cooled to room temperature to obtain an emulsion. An ammonium hydroxide aqueous solution (25% by mass aqueous solution) was added to the obtained emulsion to adjust the pH to 9.0, whereby a latex containing 40% by mass of thermoplastic polymer particles was obtained. The physical properties of the latex are shown in Table 2.

[Thermoplastic polymer particles A7]
As the thermoplastic polymer particles A7, an aqueous dispersion (solid content: 40 mass) of crosslinked polymethylmethacrylate (crosslinked PMMA) fine particles (D ₅₀ =0.5 μm, Tg _{shell part} =105° C., Tg _{core part} =−40° C.). %) was prepared.

(Absorption amount of non-aqueous electrolyte solution of thermoplastic polymer particles A7 at 25° C.)
The thermoplastic polymer particles A7 were dried at room temperature for 1 day and sufficiently pulverized with a mortar and pestle to obtain a powder. 0.3 g of this powder was placed in a glass container, and 5 mL of a nonaqueous electrolytic solution (a solvent in which ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate were mixed at a volume ratio of 2:4:4 was added with LiPF _{6 )} . A solution dissolved at a concentration of 1 mol/L) was added, and the powder was immersed in the non-aqueous electrolytic solution at 25° C. for 24 hours. Then, the powder and the non-aqueous electrolytic solution were separated by filtering through a 25 μm metal mesh, the amount of the obtained non-aqueous electrolytic solution (non-aqueous electrolytic solution which was not absorbed by the powder) was measured, and the resulting non-aqueous electrolytic solution was placed in a glass container. From the difference with the amount of the non-aqueous electrolyte, the amount of the non-aqueous electrolyte absorbed by the thermoplastic polymer particles A7 at 25° C. was 0.7 mL per 1 g of the thermoplastic polymer particles A7.

(Absorption amount of non-aqueous electrolyte solution of thermoplastic polymer particles A7 at 130° C.)
0.3 g of powder of thermoplastic polymer particles A7 obtained in the same manner as in the case of measuring the amount of absorption at 25° C. was placed in a glass container, and the same nonaqueous electrolysis as in the case of measuring the amount of absorption at 25° C. was placed therein. 5 mL of the liquid is added, and the powder is immersed in the non-aqueous electrolytic solution at 25° C. for 24 hours. After that, the non-aqueous electrolytic solution in the glass container is heated to 130° C., and the powder and the non-aqueous electrolytic solution are separated by filtering with a 25 μm metal mesh while maintaining the temperature at 130° C. The amount of (non-aqueous electrolyte that was not absorbed by the powder) was measured, and the amount of the non-aqueous electrolyte of the thermoplastic polymer particles A7 at 130° C. The amount of absorption was determined to be 2.0 mL per 1 g of the thermoplastic polymer particles A7.

[Thermoplastic polymer particles A8]
According to the formulation shown in Table 3, a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer was used as a monomer composition used for the production of the core part, and 75 parts by mass of methyl methacrylate (MMA) was used. , 4 parts by weight of methacrylic acid (MAA) and 1 part by weight of ethylene dimethacrylate (EDMA); 1 part by weight of sodium dodecylbenzenesulfonate as an emulsifier; 150 parts by weight of deionized water; and 0.5 parts of potassium persulfate as a polymerization initiator. The mass part was put and fully stirred. Then, it heated at 60 degreeC and started superposition|polymerization. By continuing the polymerization until the polymerization conversion rate reached 96%, an aqueous dispersion containing a particulate polymer forming the core portion was obtained.

To this aqueous dispersion, 20 parts by mass of styrene (ST) as a monomer composition used for producing the shell part was added all at once, and the mixture was heated to 70° C. to continue the polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to prepare an aqueous dispersion containing a particulate polymer as the thermoplastic polymer particles A8. The average particle diameter D ₅₀ of the obtained particulate polymer was 0.45 μm.

From the volume average particle diameter of the particulate polymer after forming the shell portion, the particulate polymer before forming the shell portion obtained in the production process of the particulate polymer (that is, the particulate polymer constituting the core portion The thickness of the shell portion was measured by subtracting the average particle diameter of the polymer). The core-shell ratio of the thermoplastic polymer particles A8 was calculated by dividing the measured thickness of the shell portion by the average particle diameter of the particulate polymer.
The average particle diameter is the particle diameter at which the cumulative volume calculated from the small diameter side is 50% in the particle diameter distribution measured by the laser diffraction particle diameter distribution measuring device “SALD-3100 (manufactured by Shimadzu Corporation)”. did.

(Binder for thermoplastic polymer particles A8)
In a reactor equipped with a stirrer, 70 parts by mass of ion-exchanged water, 0.15 parts by mass of sodium lauryl sulfate (manufactured by Kao Chemical Co., product name "Emar 2F") as an emulsifier, and ammonium persulfate (APS) of 0. 5 parts by mass of each was supplied, the gas phase part was replaced with nitrogen gas, and the temperature was raised to 60°C.
On the other hand, according to the formulation shown in Table 3, 50 parts by mass of ion-exchanged water in another container, 0.5 part by mass of sodium dodecylbenzenesulfonate as a dispersant, and n-butyl acrylate as a polymerizable monomer. 94 parts by mass of (BA), 2 parts by mass of acrylonitrile (AN), 2 parts by mass of methacrylic acid (MAA), 1 part by mass of N-methylolacrylamide (NMA) and 1 part by mass of acrylamide (AM) are mixed to prepare a monomer mixture. Got The monomer mixture was continuously added to the reactor for 4 hours to carry out polymerization. During the addition, the reaction was carried out at 60°C. After the addition was completed, the reaction was further completed by stirring at 70° C. for 3 hours to prepare an acrylic polymer-containing aqueous dispersion as a binder for thermoplastic polymer particles A8. The average particle diameter D ₅₀ of the obtained acrylic polymer was 0.36 μm, and the glass transition temperature was −45° C.
Note that 6 parts by mass (based on the solid content) of the binder for the thermoplastic polymer particles A8 is used with respect to 100 parts by mass of the thermoplastic polymer particles A8.

<Production of polyolefin porous substrate>
[Polyolefin porous substrate S1]
45 parts by mass of a homopolymer high-density polyethylene having an Mv of 700,000,
45 parts by mass of homopolymer high-density polyethylene having an Mv of 300,000,
5 parts by mass of homopolymer polypropylene having an Mv of 400,000,
Were 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 added again. A mixture was obtained by dry blending with.
The obtained mixture was fed by a feeder into a twin-screw extruder under a nitrogen atmosphere.
Liquid paraffin (kinematic viscosity at 37.78° C. 7.59×10 ⁻⁵ m ² /s) was injected into the extruder cylinder by a plunger pump.
The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the entire mixture extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.

Then, they are melt-kneaded in a twin-screw extruder while being heated to 230° C., and the resulting melt-kneaded product is extruded through a T-die onto a cooling roll whose surface temperature is controlled to 80° C., and the extruded product is extruded. A sheet-like molded article was obtained by bringing the sheet into contact with a cooling roll and casting to solidify by cooling.
This sheet was stretched at a temperature of 112° C. with a simultaneous biaxial stretching machine at a magnification of 7×6.4 times. 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 substrate S1. Table 5 shows the physical properties of the obtained substrate S1.

Polyolefin porous substrate S2
The following materials:
SiO ₂ “DM10C” (trademark, manufactured by Tokuyama Corporation,
High-density polyethylene with a viscosity average molecular weight of 700,000,
High-density polyethylene with a viscosity average molecular weight of 250,000,
Homopolypropylene having a viscosity average molecular weight of 400,000,
Liquid paraffin as a plasticizer, and pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as an antioxidant.
Was premixed with a super mixer to prepare a raw material for the first microporous polyolefin layer.
The following ingredients:
High density polyethylene with a viscosity average molecular weight of 700,000, high density polyethylene with a viscosity average molecular weight of 250,000,
Homopolypropylene having a viscosity average molecular weight of 400,000,
Liquid paraffin as a plasticizer, and pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as an antioxidant.
Was premixed with a super mixer to prepare a raw material for the second microporous polyolefin layer.

Each of the above raw materials was supplied to two twin-screw same-direction screw type extruder feed ports by a feeder. At this time, liquid paraffin was side-fed with each raw material into a twin-screw extruder cylinder so that the ratio of the amount of the plasticizer in the entire mixture melt-kneaded and extruded was 60% by mass.

Subsequently, the melt-kneaded product is extruded between a pair of rolls through a gear pump, a conduit, and a T-die capable of coextruding two types of three layers to form a first layer made of the raw material of the first microporous layer. A sheet-shaped composition for the surface layer was obtained. Then, a polyolefin porous substrate B2 was obtained by performing the same operation as in the production example of the polyolefin porous substrate S1 except that the stretching temperature and the relaxation rate were adjusted.

Polyolefin porous substrate S3
As the polyolefin porous substrate S3, a Celgard model number "CG2500" which is a polypropylene single layer film was prepared.

<Examples 1 to 20 and Comparative Examples 1 to 4, 7 to 10>
According to the types and blending amounts of the porous substrate, the inorganic oxide particles, the thermoplastic polymer particles, and the water-soluble polymer shown in Table 6 or 7, using a gravure coater, the inorganic oxide particles, the thermoplastic polymer particles and the water-soluble polymer are used. A coating solution containing a hydrophilic polymer is applied on both surfaces of the porous substrate S1 so as to cover all of the surfaces, and then heated at 50° C. for 1 minute to dry, thereby forming a coating on the polyolefin porous substrate. A thermoplastic layer was formed to obtain an electricity storage device separator.

<Comparative Example 5>
In 600 g of water, ₅₀ g of polyhedral shaped boehmite synthetic product (aspect ratio 1.4, D ₅₀ =0.63 μm) which is heat-resistant fine particles, and PVP (heat-resistant fine particles and thermoplastic polymer particles A7) which is a binder are added together. And 1.0% by mass relative to the mass) is stirred and dispersed for 1 hour by using a three-one motor, and the thermoplastic polymer particles A7 are mixed in a volume ratio of the thermoplastic polymer particles A7 and the boehmite synthetic product. A coating liquid was prepared by adding 50:50 and uniformly dispersing. The PVP used was “K-90 (trade name)” manufactured by ISP Japan, having a weight average molecular weight of 1,600,000 and a Tg of 174° C. The coating liquid is applied on both surfaces of the porous base material S1 so as to cover all of the respective surfaces, and then heated at 50° C. for 1 minute and dried to form a thermoplastic layer on the polyolefin porous base material. Then, a separator for a power storage device was obtained.

<Comparative example 6>
Alumina particles (manufactured by Sumitomo Chemical Co., Ltd., product name “AKP-3000”, average particle diameter D ₅₀ =0.45 μm, tetrapot-like particles, specific gravity=3.9), 50 parts by mass, and degree of etherification 0.8 to 1 0.3 parts by mass of 0.0 carboxymethyl cellulose (manufactured by Daicel Finechem, product name “Daicel 1220”, viscosity of 1% aqueous solution=10 Pa·s to 20 mPa·s, abbreviated as “CMC” in Table 7) of 0.0 Part by mass of the thermoplastic polymer particles A8 and 6 parts by mass of the binder for thermoplastic polymer particles A8 were mixed, ion-exchanged water was further added, and the alumina particles were dispersed to obtain a coating liquid. The coating liquid is applied on both surfaces of the porous base material S1 so as to cover all of the respective surfaces, and then heated at 50° C. for 1 minute and dried to form a thermoplastic layer on the polyolefin porous base material. Then, a separator for a power storage device was obtained.

<Evaluation result>
A lithium ion secondary battery was assembled as described above using the obtained separator, and various evaluations were performed. The evaluation results are shown in Table 6 or 7. Regarding the volume ratio (inorganic oxide particles/thermoplastic polymer particles) in Table 6 or 7, aluminum hydroxide oxide (boehmite) has a specific gravity of 3.0, and alumina (Al ₂ O ₃ ) has a specific gravity of 3.9. In addition, it is a value calculated with the specific gravity of the acrylic polymer being 1.0. In Comparative Example 3, it was not possible to apply the coating liquid uniformly to the base material, so evaluation of rigidity, rate characteristics and cycle characteristics was omitted.

As is clear from Tables 6 and 7, in Comparative Example 1 in which the proportion of the inorganic filler was high, the rigidity of the film was lowered. In Comparative Example 2 in which the proportion of the inorganic filler was small, the thickness ratio before and after pressing was small, and the rate characteristics and cycle characteristics of the battery were also poor. In Comparative Example 3 containing no water-soluble polymer, the coating liquid could not be applied uniformly. In Comparative Example 4 in which the content of the water-soluble polymer was large, the rigidity of the film was lowered. In Comparative Example 6 in which the thickness ratio before and after pressing was small, the rate characteristics and cycle characteristics of the battery were poor.
Similarly, when S2 and S3 are used as the base material, in Comparative Examples 7 and 8 in which the proportion of the inorganic oxide particles is high and in Comparative Examples 9 and 10 in which the content of the water-soluble polymer is high, the rigidity of the film is poor. It was
On the other hand, the volume of the inorganic filler: the volume of the thermoplastic polymer is 35:65 to 65:35, and the content of the water-soluble polymer in the thermoplastic layer is the total mass of the inorganic filler and the thermoplastic polymer. On the other hand, the separators of Examples 1 to 20 having a content of 0.04% by mass or more and less than 1.0% by mass have strong rigidity, and have good rate characteristics and cycle characteristics when used as a battery.

Claims (11)

A separator for a power storage device comprising a porous substrate and a thermoplastic layer arranged on at least one surface of the porous substrate,
The thermoplastic layer contains an inorganic filler, a thermoplastic polymer and a water-soluble polymer,
The thermoplastic polymer is a water dispersible polymer,
The volume ratio of the inorganic filler and the thermoplastic polymer (volume of the inorganic filler:volume of the thermoplastic polymer) is 35:65 to 65:35, and the content of the water-soluble polymer in the thermoplastic layer. The amount is 0.04 mass% or more and less than 1.0 mass% with respect to the total mass of the inorganic filler and the thermoplastic polymer,
The separator for the electricity storage device. The thermoplastic polymer is
1) a conjugated diene-based polymer,
2) Acrylic polymer,
3) Polyvinyl acetate,
4) Fluorine-containing resin
2. The separator for an electricity storage device according to claim 1, which is any one or two or more of the above. The separator for an electricity storage device according to claim 1 or 2, wherein the water-soluble polymer is an ammonium salt or an alkali metal salt of a polycarboxylic acid, or an anionic cellulose derivative. The heat press for the thickness (T _b ) of the thermoplastic layer before the heat pressing, when the separator for an electricity storage device is immersed in an electrolytic solution and then subjected to heat pressing at 80° C. and 1.0 MPa. after the ratio of the thickness of the thermoplastic layer _{(T a) (T a /} T b) is, Ri 0.6-0.9 der,
The electrolyte solution is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume/DEC volume=2/3, LiPF ₆ concentration: 1 M, SP value as mixture=11.6). The separator for an electricity storage device according to any one of 1 to 3 . The content of the water-soluble polymer in the thermoplastic layer is 0.2% by mass or more and 0.8% by mass or less based on the total mass of the inorganic filler and the thermoplastic polymer . The separator for an electricity storage device according to any one of items . The water-soluble polymer may be anionic, cationic, or amphoteric, electric storage device separator as claimed in any one of claims 1 to 5. The electricity storage device separator according to claim 1, wherein the water-soluble polymer is nonionic. The water-soluble polymer does not have an amide bond-containing cyclic structure, separator device according to any one of claims 1-7. Stack of the electric storage device separator and the negative electrode according to any one of the positive electrode and the claims 1-8. The positive electrode as defined in Claim 1 and a separator for an electricity storage device according to any one of 8 and the negative electrode are wound rolled body. A secondary battery comprising the laminate according to claim 9 or the wound body according to claim 10 and a non-aqueous electrolyte.