JP2022157163A - Separator for power storage device - Google Patents

Abstract

To provide a separator for a power storage device and the like that can improve the cycle characteristics of a power storage device.SOLUTION: A separator for a power storage device includes a substrate, and a thermoplastic polymer-containing layer formed on at least one substrate surface of the substrate and containing a thermoplastic polymer, and satisfies a relationship represented by B90/B10<7 {B90 and B10 represent the maximum peel strength for 90% RH and maximum peel strength for 10% RH, respectively, as defined herein}.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a separator for an electric storage device, a laminate or a wound body using the separator, an electric storage device, and the like.

2. Description of the Related Art Conventionally, development of power storage devices represented by lithium ion secondary batteries has been actively carried out. Generally, an electricity storage device has a microporous membrane (separator) provided between a positive electrode and a negative electrode. The separator has the function of preventing direct contact between the positive electrode and the negative electrode and allowing ions to permeate through the electrolyte held in the micropores.

The separator has the property of quickly stopping the battery reaction when it is abnormally heated (fuse property), and the property of maintaining its shape even at high temperatures to prevent a dangerous situation in which the positive and negative electrodes react directly (short-circuit resistance). ) and other safety performance is required.

In addition, due to the growing concern for the environment, electricity storage devices for electric vehicles (EV), on-vehicle parts, etc. are attracting more and more attention. is used to reduce the volume by hot pressing. In order to fix the electrode and separator after pressing and maintain the volume at the time of pressing, a thermoplastic polymer-containing layer that exhibits an adhesive function under predetermined conditions is placed on the separator to improve the adhesion between the separator and the electrode. Techniques for improvement are also used, thereby suppressing the pressback of the laminate or the wound body.

However, it is expected that a "blocking" phenomenon, in which the separators having the thermoplastic polymer-containing layer adhere to each other, will occur. In this case, when the separator is unwound from the wound body in which only the separator is wound, a stress corresponding to the blocking force between the separators is required, and it becomes difficult to unwrinkle the separator of the desired length uniformly without wrinkles. problem can also arise. Therefore, regarding separators, consideration has been given to both blocking resistance and adhesion to electrodes.

For example, Patent Literature 1 describes a separator for a power storage device intended to achieve both blocking resistance and adhesion to an electrode, and the separator is formed on at least one side of a base material. Figure 2 specifies the ratio of two peel strengths measured under two conditions for a roll of separator comprising a thermoplastic polymer-containing layer.

Japanese Patent No. 6580234

In recent years, there has been a demand for improving the cycle characteristics of power storage devices due to the increasing concern for the environment and safety. Conventional separators for electric storage devices have room for further improvement in improving the cycle characteristics of electric storage devices, even if attention is paid to blocking resistance, adhesion to electrodes, etc., as described in Cited Document 1, for example. rice field.

The present invention has been made in view of the above circumstances, and provides a separator for an electricity storage device capable of improving the cycle characteristics of the electricity storage device, a laminate or wound body using the same, and an electricity storage device. intended to provide

The present inventors conducted studies to solve the above problems, found that the above problems can be solved by using a power storage device separator having the following configuration, and completed the present invention. That is, the present invention is as follows.
[1]
An electricity storage device separator comprising a substrate and a thermoplastic polymer-containing layer formed on at least one substrate surface of the substrate and containing a thermoplastic polymer, wherein the electricity storage device separator has the following formula: :
B90/B10<7
{Wherein, B90 and B10 are defined as follows:
After preparing two sheets of the electricity storage device separator and storing them for one day in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 90%, one surface (A) and the surface ( A) a laminate (AA) _RH90 formed by laminating each other, a laminate (AB) _RH90 formed by laminating the surface (A) and the opposite surface (B), and the above A laminate (BB) _RH90 formed by laminating the surfaces (B) was produced, and each laminate was pressed for 2 minutes at a temperature of 40 ° C. and a pressure of 1 MPa. Of the individually measured peel strengths (N / m), the maximum value is B90;
Further, after preparing two sheets of the electricity storage device separator and storing them for one day in an environment with a temperature of 35° C. and a relative humidity (RH) of 10%, one surface (A) of the electricity storage device separator and the A laminate (AA) _RH10 formed by laminating surfaces (A) together, a laminate (AB) _RH10 formed by laminating the surface (A) and the opposite surface (B), And a laminate (BB) _RH10 formed by laminating the surfaces (B) was produced, and each laminate was pressed for 2 minutes at a temperature of 40 ° C. and a pressure of 1 MPa. Of the peel strengths (N / m) measured individually for the laminate, the maximum value is B10}
A separator for an electricity storage device that satisfies the relationship represented by:
[2]
The power storage device separator has the following configuration:
(1) the substrate and the thermoplastic polymer-containing layer formed on one side of the substrate;
(2) the substrate and the thermoplastic polymer-containing layers formed on both sides of the substrate;
(3) the substrate, an inorganic coating layer formed on one side of the substrate, and the thermoplastic polymer-containing layer formed on the other side of the substrate; and (4) the substrate, the substrate The inorganic coating layer formed on one side of the material, the thermoplastic polymer-containing layer formed on the side of the inorganic coating layer opposite to the substrate, and the other side of the substrate the thermoplastic polymer-containing layer;
Item 1. The power storage device separator according to item 1, comprising at least one of
[3]
3. The electricity storage device separator according to item 1 or 2, wherein the B90 is less than 10 N/m.
[4]
A power storage device separator comprising a substrate and a thermoplastic polymer-containing layer formed on at least a portion of at least one side of the substrate and containing a thermoplastic polymer, wherein the thermoplastic polymer has the following formula:
T10-T90<10
{wherein T90 and T10 are defined as follows:
After storing the thermoplastic polymer in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 90% for 1 day, the thermoplastic polymer was sealed in an aluminum closed pan and measured by DSC (differential scanning calorimetry). The glass transition temperature (° C.) is T90,
In addition, after storing the thermoplastic polymer in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 10% for 1 day, the thermoplastic polymer was sealed in an aluminum sealed pan, and the glass transition temperature measured by DSC (°C) is T10}
A separator for an electricity storage device that satisfies the relationship represented by:
[5]
5. The electricity storage device separator according to item 4, wherein the T90 is 30° C. or higher.
[6]
The separator for the electricity storage device was subjected to the following conditions:
{Conditions: The measured value P10 is defined as follows:
Two sheets of the electricity storage device separator are prepared, and the electricity storage device separator is stored for one day in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 10%, and then one surface of the electricity storage device separator ( A) and the laminate (AA) _RH10 formed by laminating the surface (A) and the laminate (A-A) formed by laminating the surface (A) and the opposite surface (B) B) When _RH10 and a laminate (BB) _RH10 formed by laminating the surfaces (B) are laminated, each laminate is pressed for 5 seconds at a temperature of 90 ° C. and a pressure of 1 MPa. In addition, among the peel strengths measured individually for all laminates, the maximum value is P10 (N / m)}
6. The power storage device separator according to any one of items 1 to 5, wherein the measured value P10 measured in the above is 5 N/m or more.
[7]
Any one of items 1 to 6, wherein the thermoplastic polymer has a mass swelling degree with respect to the electrolytic solution (ethylene carbonate (EC)/diethyl carbonate (DEC) volume ratio = 2/3) of 2 times or more and less than 7 times. The separator for an electricity storage device according to Item 1.
[8]
8. The electricity storage device separator according to any one of items 1 to 7, wherein the coverage ratio of the thermoplastic polymer to the substrate is 5% or more and 70% or less.
[9]
9. The electricity storage device separator according to any one of items 1 to 8, wherein the thermoplastic polymer includes a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer.
[10]
the thermoplastic polymer has at least two glass transition temperatures;
Any one of items 1 to 9, wherein at least one of the glass transition temperatures is in the region of less than 20°C, and at least one of the glass transition temperatures is in the region of 20°C or higher. The separator for electrical storage devices according to 1.
[11]
The thermoplastic polymer is a water-insoluble particulate thermoplastic polymer and contains a copolymer having an aromatic vinyl compound monomer and a nitrile group-containing monomer as monomer units, and the water-insoluble particles The electricity storage device separator according to any one of items 1 to 10, wherein the ratio of the aromatic vinyl compound monomer and the nitrile group-containing monomer in the thermoplastic polymer is 10% by mass or more, respectively. .

ADVANTAGE OF THE INVENTION According to this invention, the separator for electrical storage devices which can aim at the improvement of the cycling characteristics of an electrical storage device, a laminated body or winding body using the same, and an electrical storage device can be provided.

Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail, but the present invention is not limited to the present embodiment, and various modifications can be made without departing from the gist thereof. is possible.

As used herein, "(meth)acrylic" means "acrylic" and its corresponding "methacrylic", and "(meth)acrylate" means "acrylate" and its corresponding "methacrylate". and "(meth)acryloyl" means "acryloyl" and the corresponding "methacryloyl".

In addition, the term "above" in this specification does not mean that the positional relationship of each member is "directly above". For example, the expression "a thermoplastic polymer-containing layer formed on a substrate" means that any layer (a layer having a heat-resistant function, such as an inorganic filler porous layer) is provided between the substrate and the thermoplastic polymer-containing layer. Do not exclude embodiments that include.

Furthermore, in this specification, unless otherwise specified, the term "~" includes the numerical values before and after it as upper and lower limits.

<Separator for power storage device>
One aspect of the present invention provides an electricity storage device separator (hereinafter also simply referred to as "separator") comprising a substrate and a thermoplastic polymer-containing layer formed on at least one side of the substrate and containing a thermoplastic polymer. do. Both the embodiment in which the thermoplastic polymer-containing layer is formed on only one side of the separator and the embodiment in which the thermoplastic polymer-containing layer is formed on both sides of the separator are both included in the scope of the present invention.

A separator can be placed between the positive and negative electrodes in a power storage device, such as a non-aqueous electrolyte secondary battery, a capacitor, and a capacitor. In particular, when the separator is placed between the positive and negative electrodes of the lithium ion secondary battery, it tends to be excellent in electrical insulation, ion permeability, fuse characteristics, short-circuit characteristics, power storage performance, and the like.

(Embodiment 1)
A separator according to Embodiment 1 includes a substrate and a thermoplastic polymer-containing layer formed on at least one surface of the substrate and containing a thermoplastic polymer, wherein the following formula:
B90/B10<7
{Wherein, B90 and B10 are defined as follows:
Two sheets of separators were prepared and stored for one day in an environment with a temperature of 35° C. and a relative humidity (RH) of 90%. A laminate (A-A) _RH90 , a laminate (AB) RH90 formed by laminating the surface (A) and the opposite surface (B), and a laminate (A-B) _RH90 formed by laminating the surfaces (B) Laminate (BB) _RH90 was prepared, and each laminate was pressed for 2 minutes at a temperature of 40 ° C. and a pressure of 1 MPa, and the peel strength (N / m), the maximum value is B90;
In addition, two separators were prepared and stored for one day in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 10%, and then one surface (A) of the separator and the surface (A) were laminated. A laminated body (A-A) _RH10 formed, a laminated body (AB) RH10 formed by laminating the surface (A) and the opposite side (B), and a laminated body (A-B) _RH10 formed by laminating the surfaces (B) Formed laminate (BB) _RH10 was prepared, and each laminate was pressed for 2 minutes at a temperature of 40 ° C. and a pressure of 1 MPa. N / m), the maximum value is B10}
It is characterized by satisfying the relationship represented by

By satisfying the above formula B90/B10<7, the separator according to Embodiment 1 can reduce the amount of water brought into the separator when incorporated in an electricity storage device and improve cycle characteristics. Separator blocking at can also be suppressed. Methods for measuring peel strengths B10 and B90 are detailed in the examples. Also, controlling B90/B10 as shown in the above formula is considered to contribute to suppression of blocking phenomenon when the separator roll is stored in a high-humidity environment in this technical field. Furthermore, B90 according to Embodiment 1 is preferably less than 10 N/m from the viewpoint of preventing defects during feeding out the separator in addition to improving the cycle characteristics of the electricity storage device.

In addition, although not wishing to be bound by theory, the separator satisfies the above formulas B90/B10<7 and B90<10 N/m, thereby preventing unsuccessful unwinding of the separator from the wound body, It is conceivable to reduce the amount of moisture adsorbed by the separator, or to improve the cycle characteristics or yield of the electricity storage device by reducing the amount of moisture brought into the electricity storage device in manufacturing the electricity storage device using the separator.

The separator more preferably satisfies B90<8N/m, further preferably satisfies B90<5N/m, and satisfies B90<2N/m from the viewpoint of cycle characteristics, blocking resistance, prevention of feeding failure, etc. is particularly preferred. The separator preferably satisfies B90/B10<6, more preferably B90/B10<5, from the viewpoint of reducing the amount of water brought into the electricity storage device and improving the cycle characteristics of the electricity storage device. It is more preferable to satisfy /B10<4. In addition, it is preferable that the peel strength measured as described above does not change or changes significantly due to RH during storage of the separator, so the lower limit of B90/B10 is preferably 1 or more.

B10, B90, and B90/B10 regarding the peel strength of the separator are determined by controlling the physical properties and composition of the thermoplastic polymer-containing layer, for example, using a thermoplastic polymer unit that hardly swells in the electrolytic solution, hydrophobic block or It can be adjusted within the numerical range described above by introducing a functional group, controlling the content of both the unit derived from the aromatic vinyl compound monomer and the unit derived from the nitrile group-containing monomer, or controlling the content ratio. be.

(Embodiment 2)
A separator according to Embodiment 2 comprises a substrate and a thermoplastic polymer-containing layer formed on at least a portion of at least one side of the substrate and containing a thermoplastic polymer, wherein the thermoplastic polymer has the following formula:
T10-T90<10
{wherein T90 and T10 are defined as follows:
Glass measured by DSC (differential scanning calorimetry) after storing the thermoplastic polymer in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 90% for 1 day, enclosing the thermoplastic polymer in an aluminum closed pan. The transition temperature (° C.) is T90,
In addition, after storing the thermoplastic polymer for 1 day in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 10%, the thermoplastic polymer was sealed in an aluminum sealed pan, and the glass transition temperature measured by DSC (° C. ) is T10}
It is characterized by satisfying the relationship represented by

Since the thermoplastic polymer according to Embodiment 2 satisfies the above formula T10−T90<10, it is possible to reduce the amount of water brought into the separator when incorporated in an electricity storage device and improve the cycle characteristics. Blocking resistance can also be improved. The method for measuring the glass transition temperatures T10 and T90 is detailed in item (6) of Examples. In addition, a thermoplastic polymer satisfying T10-T90<10 tends to exhibit this effect when a hydrophobic molecular skeleton or a hydrophobic functional group is introduced, and as a result, in a high humidity environment in this technical field It is thought that this contributes to the suppression of the blocking phenomenon when the separator-wound body is stored.

In addition, although not wishing to be bound by theory, the thermoplastic polymer satisfies the above formula T10-T90<10, thereby preventing the separator from being unsuccessfully drawn out from the wound body, reducing the amount of moisture adsorbed on the separator, In manufacturing an electricity storage device using a separator, it is conceivable to reduce the amount of moisture brought into the electricity storage device to improve the cycle characteristics or yield of the electricity storage device.

The thermoplastic polymer contained in the thermoplastic polymer-containing layer preferably satisfies T10-T90<9 from the viewpoint of reducing the amount of water brought from the separator into the electricity storage device and improving the cycle characteristics of the electricity storage device. More preferably, T10-T90<7, and even more preferably T10-T90<6. In addition, with respect to the glass transition temperature of the thermoplastic polymer measured as described above, there is no numerical difference due to multiple RH conditions during storage of the separator, or the more significantly the numerical difference is, the less blocking tends to occur. Therefore, T10-T90≈0 or T10-T90=0 is preferable, and T10-T90≧0 is also acceptable.

T90 according to Embodiment 2 is preferably 30° C. or higher, more preferably 31° C. or higher, from the viewpoints of reducing the amount of moisture brought into the electricity storage device by the separator and improving cycle characteristics.

T10, T90, and T10-T90 relating to the glass transition temperature of the thermoplastic polymer are obtained by controlling the physical properties or structure of the thermoplastic polymer, for example, the property that it is difficult to swell in the electrolytic solution, the hydrophobic molecular skeleton, or the introduction of a hydrophobic functional group. It can be adjusted within the numerical range described above by controlling the content or the content ratio of both the unit derived from the aromatic vinyl compound monomer and the unit derived from the nitrile group-containing monomer.

Preferred embodiments of each member that can constitute the separator are described in detail below.

[Base material]
The substrate itself may be one that has been conventionally used as a separator. The substrate is preferably a porous membrane, and more preferably a porous membrane with a fine pore size that has no electronic conductivity but ionic conductivity and high resistance to organic solvents. Examples of such porous membranes include resins such as polyolefins (e.g., polyethylene, polypropylene, polybutene, and polyvinyl chloride), mixtures thereof, or copolymers of these monomers as main components. Microporous membrane; Microporous membrane containing resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene as a main component; Polyolefin fiber (woven fabric); non-woven fabric of polyolefin fibers; paper; and aggregates of insulating material particles. These are used individually by 1 type or in combination of 2 or more types.
Among them, a polyolefin microporous film containing a polyolefin resin as a main component is preferable from the viewpoint of increasing the active material ratio in the electricity storage device by making the thickness of the separator thinner, thereby increasing the capacity per volume. A polyolefin microporous membrane is excellent in the coating properties of a coating liquid when subjected to a step of coating the coating liquid on the membrane, and is therefore advantageous in making the thickness of the separator thinner.
In addition, "containing a polyolefin resin as a main component" means that it contains more than 50% by mass of the total mass of the base material.

When a polyolefin microporous membrane is used as the substrate, the content of the polyolefin resin in the polyolefin microporous membrane is not particularly limited. However, from the viewpoint of shutdown performance when used as a separator, it is preferable that 50% by mass or more and 100% by mass or less of all components constituting the polyolefin microporous membrane is polyolefin resin. The content of the polyolefin resin is more preferably 60% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, of all components constituting the polyolefin microporous membrane, and 75% by mass. % or more and 100 mass % or less, 85 mass % or more and 100 mass % or less, 90 mass % or more and 100 mass % or less, or 95 mass % or more and 100 mass % or less, and 98 mass % or more and 100 mass %. It is particularly preferable that the content is below, and may be 100% by mass.

Although the polyolefin resin is not particularly limited, it may be a polyolefin resin that can be used for ordinary extrusion, injection, inflation, blow molding, and the like. Polyolefin resins include, for example, homopolymers containing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, and two or more of these monomers. and multistage polymers. These homopolymers, copolymers and multistage polymers are used singly or in combination of two or more.

Representative examples of polyolefin resins include, but are not limited to, polyethylene, polypropylene, and polybutene, more specifically low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high Molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymers, polybutene, and ethylene propylene rubber. These are used individually by 1 type or in combination of 2 or more types. As the polyolefin resin, polyethylene such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high-molecular-weight polyethylene is used as the main component from the viewpoint of shutdown characteristics in which pores are closed by heat melting. Preferably. In particular, high-density polyethylene is preferable because it has a low melting point and high strength, and polyethylene having a density of 0.93 g/cm ³ or more as measured according to JIS K 7112 is more preferable. Polymerization catalysts used in the production of these polyethylenes are not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts.

In order to improve the heat resistance of the substrate, the polyolefin microporous membrane more preferably contains polypropylene and a polyolefin resin other than polypropylene. Here, the steric structure of polypropylene is not limited, and may be isotactic polypropylene, syndiotactic polypropylene, or atactic polypropylene. Further, polyolefin resins other than polypropylene include, for example, homopolymers of ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, and their monomers. Copolymers of two or more species, and multi-stage polymers may be mentioned, particular examples being those already described above. The polymerization catalyst used for producing polypropylene is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts.

The content ratio of polypropylene with respect to the total amount of polyolefin in the polyolefin microporous membrane (polypropylene/polyolefin) is preferably 1 to 35% by mass, more preferably 3 to 3, from the viewpoint of achieving both heat resistance and good shutdown function. 20% by mass, more preferably 4 to 10% by mass. From the same point of view, the content ratio of olefin resin other than polypropylene, such as polyethylene, relative to the total amount of polyolefin in the polyolefin microporous membrane (olefin resin other than polypropylene/polyolefin) is preferably 65 to 99% by mass, more preferably. is 80 to 97% by mass, more preferably 90 to 96% by mass.
Polyolefin resins other than polyethylene and polypropylene include, for example, polybutene, ethylene-propylene random copolymers, and polymethylpentene.

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably 30,000 or more and 12,000,000 or less, more preferably 50,000 or more and less than 2,000,000, and still more preferably 100,000 or more and 1,000,000. is less than When the viscosity-average molecular weight is 30,000 or more, the melt tension during melt molding is increased, resulting in better moldability, 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 sheet formability, particularly thickness stability tends to be excellent, which is preferable. Further, when the viscosity-average molecular weight is less than 1,000,000, the pores are likely to be closed when the temperature rises, and a better shutdown function tends to be obtained, which is preferable. Also, from the standpoint of moldability, the viscosity-average molecular weight is preferably less than 1,000,000. 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] = 6.80 × 10 ^-4 Mv ^0.67 (Chiang 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, which has a viscosity average molecular weight of less than 1,000,000. Mixtures may also be used.

The substrate can also contain optional additives. Such additives are not particularly limited and include, for example, polymers other than polyolefins; inorganic particles; phenolic, phosphorus, and sulfur antioxidants; metallic soaps such as calcium stearate and zinc stearate; Absorbents; light stabilizers; antistatic agents; antifogging agents; The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin in the polyolefin microporous membrane. is.

The porosity of the substrate is preferably 20-80%, more preferably 35-70%, even more preferably 40-60%, and particularly preferably 40-50%.
A porosity of the base material of 20% or more is preferable from the viewpoint of ensuring the permeability of the separator more effectively and reliably. A porosity of the base material of 80% or less is preferable from the viewpoint of ensuring the puncture strength more effectively and reliably. The porosity can be determined, for example, from the volume (cm ³ ), mass (g), and film density (g/cm ³ ) of the sample of the substrate, using the following formula:
Porosity = (volume - mass / film density) / volume x 100
can be obtained by Here, for example, in the case of a polyolefin microporous membrane made of polyethylene, the calculation can be performed assuming the membrane density to be 0.95 (g/cm ³ ). The porosity can be adjusted by changing the draw ratio of the polyolefin microporous membrane.

The air permeability of the substrate is preferably 10 sec/100 cm ³ or more, more preferably 50 sec/100 cm ³ or more, preferably 1,000 sec/100 cm ³ or less, more preferably 500 sec/100 cm ³ or less. More preferably, it is 200 seconds/100 cm ³ or less. It is preferable to set the air permeability of the substrate to 10 seconds/100 cm ³ or more from the viewpoint of suppressing self-discharge of the electricity storage device. It is preferable to set the air permeability of the substrate to 1000 seconds/100 cm ³ or less from the viewpoint of obtaining good charge/discharge characteristics. The air permeability is air resistance measured according to JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and/or stretching ratio of the base material.

The average pore size of the substrate 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 preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing decrease in capacity. The average pore diameter can be adjusted by changing the draw ratio or the like when manufacturing the base material.

The puncture strength of the substrate is preferably 200 gf/20 μm or more, more preferably 250 gf/20 μm or more, still more preferably 300 gf/20 μm or more, preferably 2,000 gf/20 μm or less, more preferably 1,000 gf/ 20 μm or less. The puncture strength of 200 gf/20 μm or more is from the viewpoint of suppressing film breakage due to fallen active material etc. when the separator is wound together with the electrode, and suppresses the concern of short circuit due to expansion and contraction of the electrode due to charging and discharging. It is also preferable from the viewpoint of A puncture strength of 2,000 gf/20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength is measured according to the method described in Examples. The puncture strength can be adjusted by adjusting the draw ratio and/or the draw temperature of the substrate.

The thickness of the substrate is preferably 2 µm or more, more preferably 5 µm or more, and preferably 100 µm or less, more preferably 60 µm or less, and even more preferably 50 µm or less. It is preferable to set the thickness of the substrate to 2 μm or more from the viewpoint of improving the mechanical strength. Setting the thickness of the substrate to 100 μm or less is preferable because the volume occupied by the separator in the electricity storage device is reduced, which tends to be advantageous in increasing the capacity of the electricity storage device.

[Thermoplastic polymer-containing layer]
The thermoplastic polymer-containing layer contains a thermoplastic polymer. The thermoplastic polymer-containing layer may be arranged on the entire surface of the base material, or may be arranged on a part thereof. It is preferable to dispose the thermoplastic polymer-containing layer only on a part of the surface of the substrate so that the resulting electricity storage device exhibits high ion permeability.

The thermoplastic polymer-containing layer is intended to be directly adhered to the electrodes. At least one thermoplastic polymer-containing layer provided in the separator is arranged so as to be directly adhered to the electrode, for example, so that at least a portion of the substrate and the electrode are adhered via the thermoplastic polymer-containing layer. preferably.

The amount of the thermoplastic polymer-containing layer applied to the base material, that is, the amount of the thermoplastic polymer-containing layer formed per area of one surface of the base material (arranged amount) is preferably 0.01 g/m ² or more. , 0.02 g/m ² or more. The coating amount is preferably 2.0 g/m ² or less, more preferably 1.5 g/m ² or less, even more preferably 1.0 g/m ² or less, and 0.5 g/m 2 or less. m ² or less is particularly preferred. A coating amount of 0.01 g/m ² or more improves the adhesive strength between the thermoplastic polymer-containing layer and the electrode by, for example, improving the measured value P10, which will be described later, in the resulting separator. , is preferable from the viewpoint of achieving more uniform charging and discharging and improving device characteristics (for example, cycle characteristics of a battery). On the other hand, setting the coating amount to 2.0 g/m ² or less is preferable from the viewpoint of power storage device characteristics (rate characteristics) and prevention of decrease in ion permeability.

In the substrate, the area ratio of the surface on which the thermoplastic polymer-containing layer is present with respect to the total area of the surface on which the thermoplastic polymer-containing layer is arranged, that is, the coverage area ratio of the thermoplastic polymer-containing layer to the substrate, It is preferably 70% or less, more preferably 50% or less, and particularly preferably 40% or less. Also, the surface coverage is preferably 5% or more, more preferably 10% or more, and even more preferably 12% or more. Setting the coverage area ratio to 70% or less suppresses clogging of the pores of the base material by the particulate polymer, improves the permeability of the separator, and in turn improves the rate characteristics of the electricity storage device provided with the separator. can. On the other hand, setting the coverage area ratio to 5% or more is preferable from the viewpoint of, for example, improving the measured value P10 described later and further improving the adhesion to the electrode. The coverage area ratio is measured by observing the surface of the obtained separator on which the thermoplastic polymer-containing layer is formed by SEM, and in detail, it is measured according to the method described in Examples. The coating area ratio is, for example, in the separator manufacturing method described later, the type of particulate polymer in the coating liquid applied to the surface of the substrate or the concentration of the polymer, the coating amount of the coating liquid, the coating method, and the coating It can be adjusted by changing the conditions. However, the method for adjusting the coating area is not limited to them.

When the thermoplastic polymer-containing layer is arranged only on a part of the surface of the substrate, the existence form (pattern) of the thermoplastic polymer is not particularly limited. It is preferable to exist in a dispersed state or in a sea-island state. When the thermoplastic polymer is present in a sea-island pattern, examples of the arrangement pattern include dots, stripes, grids, stripes, tortoise shells, random patterns, and combinations thereof. Among these, the dot shape is preferable from the viewpoint that the thermoplastic polymer-containing layers do not overlap each other when the separator is wound. Also, from the viewpoint of anti-blocking property, the dot shape is preferable to the state in which the thermoplastic polymer is dispersed over the entire surface of the substrate (for example, solid coating). When the arrangement pattern is dot-shaped, the dot diameter is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more. Also, the dot diameter is preferably 1,000 μm or less, more preferably 800 μm or less, and even more preferably 500 μm or less. When the dot diameter is 10 μm or more, the flow of ions in the electrolytic solution is further improved, and the permeability is further improved. When the dot diameter is 1,000 μm (1 mm) or less, the separator can be more uniformly adhered to the electrode, and the in-plane current density can be made more uniform. Furthermore, by providing a portion where the thermoplastic polymer is not applied in the dot-like arrangement pattern, the in-plane current density can be made even more uniform.

When the thermoplastic polymer-containing layer is partially arranged, it is desirable that the coverage area ratio is uniform within a certain area range. Specifically, when the surface of the separator is observed with an SEM, it is preferable that the change rate of the covered area ratio represented by the following formula is within ±50% in the observation field range of 10 mm×10 mm or more.
(Change rate of coverage area ratio (%)) = (C1-C2) / C1 x 100
Here, C1 indicates the covered area ratio in an arbitrary observation visual field range of 10 mm×10 mm or more, and C2 indicates the covered area ratio in the other observation visual field range of 10 mm×10 mm or more. For example, for a separator in which a thermoplastic polymer-containing layer is partially disposed, if the measured value of the coverage area ratio in an observation field range of 10 mm × 10 mm is 50%, any other part of the separator is observed Even so, it is preferable that the covered area ratio in the observation field range of 10 mm×10 mm is 25% or more and 75% or less.

The thickness of the thermoplastic polymer-containing layer is preferably 0.01 μm or more, more preferably 0.1 μm or more, and even more preferably 0.3 μm or more per side of the substrate. In addition, the thickness per surface of the substrate is preferably 5.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. A thickness of 0.01 μm or more is preferable from the viewpoint of uniform adhesion between the electrode and the substrate, and as a result, device characteristics can be improved. Moreover, it is preferable to set the thickness to 5.0 μm or less from the viewpoint of suppressing a decrease in ion permeability. The thickness of the thermoplastic polymer-containing layer can be changed, for example, by changing the type of particulate polymer in the coating liquid applied to the substrate, the concentration of the polymer, the coating amount of the coating liquid, the coating method, and the coating conditions. can be adjusted. However, this thickness adjustment method is not limited to them. The thickness of the thermoplastic polymer-containing layer is measured according to the method described in Examples.

The degree of mass swelling of the thermoplastic polymer used with respect to the electrolyte (hereinafter also referred to as "electrolyte swelling degree") is preferably 2 times or more and less than 7 times, more preferably 3 to 6 times. , more preferably 4 to 5 times. When the degree of swelling of the thermoplastic polymer in the electrolyte solution is 2 times or more, the amount of water brought into the separator or the electricity storage device can be reduced, and the cycle characteristics of the electricity storage device can be improved. If the degree of swelling of the thermoplastic polymer in the electrolytic solution is less than 7 times, an increase in electrical resistance can be suppressed. The electrolyte solution swelling degree can be measured by the method described in Examples. The electrolyte used to measure the degree of swelling of the electrolyte can be a non-aqueous solvent, can be a single or multiple carbonate-based solvents, a mixture of multiple carbonate-based solvents, etc., and can be ethylene carbonate ( A mixed solvent of EC) and diethyl carbonate (DEC) (volume ratio of EC/DEC=2/3) may be used.

(particulate polymer)
The thermoplastic polymer contained in the thermoplastic polymer-containing layer may comprise particulate polymer. The thermoplastic polymer is water-insoluble and particles from the viewpoint of adjusting B10, B90, B90/B10, T10, T90, T10-T90, etc. measured under specific conditions within the numerical ranges described above. preferably in the form of In the following description, "ethylenically unsaturated monomer" means a monomer having one or more ethylenically unsaturated bonds in the molecule. By including the particulate polymer in the thermoplastic polymer, both excellent adhesion to the electrode and ion permeability can be achieved.

Specific examples of particulate polymers include acrylic polymers, conjugated diene polymers, acrylic polymers, polyvinyl alcohol resins, and fluorine-containing resins. Among these, from the viewpoint of polymer stability in the electricity storage device, the thermoplastic polymer is preferably an acrylic polymer, and contains a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer. is more preferred. Acrylic polymers and fluorine-containing resins are also preferred from the viewpoint of voltage resistance, and conjugated diene polymers are also preferred from the viewpoint of compatibility with electrodes. Furthermore, from the viewpoint of more effectively and reliably exhibiting the effects of the present invention, the particulate polymer preferably contains a particulate copolymer. A particulate polymer is used individually by 1 type or in combination of 2 or more types.

Further, the thermoplastic polymer contained in the thermoplastic polymer-containing layer is preferably 60% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass, based on the total amount. The above includes a particulate polymer. The thermoplastic polymer-containing layer may contain a thermoplastic polymer other than the particulate polymer to the extent that the effect of the present invention is not impaired.

A conjugated diene-based polymer is a polymer having a conjugated diene compound as a monomer unit. Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and substituted linear conjugated Examples include pentadienes, substituted hexadienes, and side chain conjugated hexadienes, and these may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. Moreover, the conjugated diene-based polymer may contain a (meth)acrylic compound or other monomer described later as a monomer unit. Examples of such monomers include styrene-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene-styrene copolymers and hydrides thereof. be done.

Polyvinyl alcohol-based resins include, for example, polyvinyl alcohol and polyvinyl acetate. Examples of fluorine-containing resins include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene. Ethylene copolymers are mentioned.

An acrylic polymer is a polymer having a (meth)acrylic compound as a monomer unit, that is, a polymerization unit. The (meth)acrylic compound means at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters. Examples of such compounds include compounds represented by the following formulas.
_CH2 = ^CRY1 -COO- ^RY2
In the formula, R ^Y1 represents a hydrogen atom or a methyl group, and R ^Y2 represents a hydrogen atom or a monovalent hydrocarbon group. When R ^Y2 is a monovalent hydrocarbon group, it may have a substituent and may have a heteroatom in the chain. Monovalent hydrocarbon groups include, for example, linear or branched chain alkyl groups, cycloalkyl groups, and aryl groups. Substituents include, for example, hydroxyl groups and phenyl groups, and heteroatoms include, for example, halogen atoms and oxygen atoms. A (meth)acrylic compound is used individually by 1 type or in combination of 2 or more types. Examples of such (meth)acrylic compounds include (meth)acrylic acid, chain alkyl (meth)acrylates, cycloalkyl (meth)acrylates, hydroxyl group-containing (meth)acrylates, and phenyl group-containing (meth)acrylates. is mentioned.

The chain alkyl group, which is one type of R ^Y2 , more specifically, a chain alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group; n -butyl group, isobutyl group, t-butyl group, n-hexyl group, 2-ethylhexyl group; and chain alkyl groups having 4 or more carbon atoms such as lauryl group. Further, examples of the aryl group, which is one type of R ^Y2 , include a phenyl group. Specific examples of (meth)acrylate monomers having such R ^Y2 include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl Chains such as 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, and lauryl methacrylate and (meth)acrylates having an aromatic ring such as phenyl (meth)acrylate and benzyl (meth)acrylate.

Among these, from the viewpoint of improving the adhesion of the separator to the electrode (electrode active material), a monomer having a chain alkyl group having 4 or more carbon atoms, more specifically, R ^Y2 is a carbon atom A (meth)acrylic acid ester monomer that is a chain alkyl group having a number of 4 or more is preferred. More specifically, at least one selected from the group consisting of butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate is preferred. 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, for example, 14, but preferably 7. These (meth)acrylic acid ester monomers may be used singly or in combination of two or more.

The (meth)acrylic acid ester monomer contains a monomer having a cycloalkyl group as R ^Y2 in place of or in addition to a monomer having a chain alkyl group having 4 or more carbon atoms. is also preferred. This also further improves the adhesion of the separator to the electrode. More specific examples of monomers having such cycloalkyl groups include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantyl (meth)acrylate. The number of carbon atoms constituting the alicyclic ring of the cycloalkyl group is preferably 4-8, more preferably 6-7, and particularly preferably 6. Moreover, the cycloalkyl group may or may not have a substituent. Substituents include, for example, methyl groups and t-butyl groups. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferable from the viewpoint of good polymerization stability during preparation of the acrylic polymer. These are used individually by 1 type or in combination of 2 or more types.

The acrylic polymer preferably contains a crosslinkable monomer as a (meth)acrylic acid ester monomer instead of or in addition to the above, preferably in addition to the above. The crosslinkable monomer is not particularly limited, but for example, a monomer having two or more radically polymerizable double bonds, a monomer having a functional group that gives a self-crosslinking structure during or after polymerization. A body etc. are mentioned. These are used individually by 1 type or in combination of 2 or more types.

Examples of monomers having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylates. 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. Specifically, for example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol Dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These are used individually by 1 type or in combination of 2 or more types. Among them, at least one of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferable from the same viewpoint as above.

Examples of the monomer having a functional group that provides a self-crosslinking structure during or after polymerization include a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, and a monomer having a hydrolyzed and a monomer having a silyl group. As the monomer having an epoxy group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable. Specifically, for example, glycidyl (meth)acrylate, 2,3-epoxycyclohexyl (meth)acrylate, 3, 4-epoxycyclohexyl (meth)acrylate, and allyl glycidyl ether.

Monomers having a methylol group include, for example, N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. As the monomer having an alkoxymethyl group, ethylenically unsaturated monomers having an alkoxymethyl group are preferred, and specific examples include N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, and N-butoxymethylacrylamide. , and N-butoxymethyl methacrylamide. Examples of monomers having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyl. Triethoxysilane can be mentioned. These are used individually by 1 type or in combination of 2 or more types.

In addition, the acrylic polymer may further contain monomers other than those described above as monomer units in order to improve various qualities and physical properties. Examples of such monomers include monomers having a carboxyl group (excluding (meth)acrylic acid), monomers having an amide group, nitrile group-containing monomers, and hydroxyl group-containing monomers. monomers, and aromatic vinyl compound monomers (excluding divinylbenzene). Furthermore, various vinyl monomers having functional groups such as sulfonic acid groups or phosphoric acid groups, and vinyl acetate, vinyl propionate, vinyl versatate, vinyl pyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, chloride Vinyl and vinylidene chloride are also optionally used. These are used individually by 1 type or in combination of 2 or more types. Also, such other monomers may belong to two or more of the above monomers at the same time.

Examples of monomers having an amide group include (meth)acrylamide. Monomers having a hydroxyl group include, for example, 2-hydroxyethyl (meth)acrylate.

Examples of nitrile group-containing monomers include acrylic nitrile group-containing monomers such as (meth)acrylonitrile, cyano nitrile group-containing monomers such as α-cyanoacrylate and dicyanovinylidene, and fumaronitrile. A fumaric nitrile group-containing monomer or the like can be used. Among these, the viewpoint of adjusting B10, B90, B90/B10, T10, T90, T10-T90, etc. measured under specific conditions within the numerical range described above, the polymerizability of the monomer And from the viewpoint of economy, cyclization during heating or the hydrophobicity of the obtained copolymer, an ethylenically unsaturated monomer having a cyano group is preferable, (meth) acrylonitrile is more preferable, acrylonitrile and / or methacrylonitrile is more preferred.

Aromatic vinyl monomers include, for example, styrene, styrenesulfonic acid, butoxystyrene, vinyltoluene, vinylnaphthalene, and α-methylstyrene. Among them, the viewpoint of adjusting B10, B90, B90/B10, T10, T90, T10-T90, etc. measured under specific conditions within the numerical range described above, the hydrophobicity of the resulting copolymer From the point of view, styrene is preferable.

The proportion of the acrylic polymer containing the (meth)acrylic compound as a monomer unit, ie, polymerized unit, is preferably 5% by mass or more and 95% by mass or less with respect to 100% by mass of the acrylic polymer. The lower limit is more preferably 15% by mass, still more preferably 20% by mass, and particularly preferably 30% by mass. A monomer unit content of 5% by mass or more is preferable from the standpoint of adhesion to substrates and oxidation resistance. On the other hand, a more preferable upper limit is 92% by mass, a still more preferable upper limit is 80% by mass, and a particularly preferable upper limit is 60% by mass. When the content of the monomer is 95% by mass or less, the adhesiveness to the substrate is improved, which is preferable.

When the acrylic polymer has a chain alkyl (meth)acrylate or cycloalkyl (meth)acrylate as a monomer unit, the total content of these is preferably , 3% by mass or more and 92% by mass or less, more preferably 10% by mass or more and 90% by mass or less, still more preferably 15% by mass or more and 75% by mass or less, and particularly preferably 25% by mass or more and 55% by mass or less It is below. When the content of these monomers is 3% by mass or more, it is preferable from the viewpoint of improving oxidation resistance.

When the acrylic polymer has (meth)acrylic acid as a monomer unit, the content is preferably 0.1% by mass or more and 5% by mass or less with respect to 100% by mass of the acrylic polymer. . When the content of the monomer is 0.1% by mass or more, the cushioning property of the separator in a swollen state tends to be improved, and when it is 5% by mass or less, the polymerization stability tends to be good. be.

When the acrylic polymer has a crosslinkable monomer as a monomer unit, the content of the crosslinkable monomer in the acrylic polymer is preferably 0.00% with respect to 100% by mass of the acrylic polymer. 01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, and still more preferably 0.1% by mass or more and 3% by mass or less. When the content of the monomer is 0.01% by mass or more, the electrolytic solution resistance is further improved.

In the case of water-insoluble particulate thermoplastic polymers, B10, B90, B90/B10, T10, T90, T10-T90, etc. measured under specific conditions are adjusted within the numerical ranges described above. From a viewpoint, the particulate polymer includes or is a copolymer having one or both of an aromatic vinyl compound monomer and a nitrile group-containing monomer as monomer units. Preferably, it contains an acrylic copolymer having a (meth) acrylic acid ester monomer, an aromatic vinyl compound monomer and a nitrile group-containing monomer as monomer units, or such an acrylic More preferably, it is a system copolymer. Furthermore, from the viewpoint of reducing the amount of moisture brought into the separator into the electricity storage device and improving the cycle characteristics, the ratio of the aromatic vinyl compound monomer and the nitrile group-containing monomer in the water-insoluble thermoplastic polymer are each preferably 10% by mass or more, and in the water-insoluble particulate thermoplastic polymer, the proportion of the aromatic vinyl compound monomer is 12 to 30% by mass, and the proportion of the nitrile group-containing monomer is 15 It is more preferably up to 60% by mass, more preferably 14 to 25% by mass of the aromatic vinyl compound monomer and 20 to 55% by mass of the nitrile group-containing monomer.

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

For example, in an aqueous medium, the above-mentioned monomers, surfactants, radical polymerization initiators, and other additive components used as necessary in a dispersion system as basic composition components, containing each of the above-mentioned monomers An acrylic polymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the supplied monomer composition is kept constant throughout the polymerization process, and the morphological composition of the particles of the resin dispersion produced is changed by sequentially or continuously changing the composition during the polymerization process. Various methods can be used as necessary. When the acrylic polymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and particulate acrylic polymer dispersed in the water.

A surfactant is a compound having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. The surfactant is not particularly limited, but polyether-based surfactants are preferred. Since the surfactant will be described later, the description is omitted here.
The radical polymerization initiator is one that initiates addition polymerization of monomers by radical decomposition with heat or a reducing substance. Since the radical polymerization initiator will be described later, description thereof is omitted here.

Among the forms of thermoplastic polymers, from the viewpoint of improving the adhesiveness between the separator and the electrode, the high-temperature storage characteristics and cycle characteristics of the electrical storage device, and achieving a thinner adhesive between the electrode and the separator, a monomer An acrylic copolymer latex formed from an emulsion comprising an emulsifier, an initiator, and water is preferred.

The glass transition temperature Tg of the particulate polymer (but different from T10 and T90 described above) is preferably −50° C. or higher from the viewpoint of adhesion to the electrode and ion permeability, It is more preferably -30°C or higher, even more preferably 20°C or higher, and even more preferably 40°C or higher. Also, the glass transition temperature of the particulate polymer is preferably 200° C. or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the temperature at the intersection of a straight line obtained by extending the base line on the low temperature side of the DSC curve to the high temperature side and the tangent line at the inflection point of the stepwise change portion of the glass transition can be used as the glass transition temperature. can. More specifically, it may be determined according to the method described in item (5) of Examples. "Glass transition" refers to a change in the amount of heat generated on the endothermic side due to a change in the state of the polymer, which is the test piece, in DSC. Such a heat quantity change is observed as a shape of step-like change in the DSC curve. A “step-like change” refers to a portion of a DSC curve from a baseline on the low temperature side to a transition to a new baseline on the high temperature side. A combination of a stepped change and a peak is also included in the stepped change. Furthermore, the “point of inflection” indicates the point at which the gradient of the DSC curve of the stepwise change portion is maximized. In addition, in the stepwise change portion, when the upper side is the heat generation side, it can be expressed as a point at which the upwardly convex curve changes to the downwardly convex curve. "Peak" refers to the portion of the DSC curve from when the curve departs from the baseline on the low temperature side to when it returns to the same baseline again. "Baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs in the specimen.

The glass transition temperature Tg of the particulate polymer is determined, for example, by the type of monomer used in producing the particulate polymer, and when the particulate polymer is a copolymer, the blending ratio of each monomer. By changing it, it can be adjusted as appropriate. That is, for each monomer used in the production of the particulate polymer, the generally indicated Tg of the homopolymer (for example, described in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)), The approximate glass transition temperature can be estimated from the blending ratio. For example, a copolymer obtained by copolymerizing a high proportion of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid to give a homopolymer with a Tg of about 100° C. has a high Tg of about −50° C. The Tg of a copolymer obtained by copolymerizing a high proportion of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate, which gives a homopolymer with a Tg of , is low.
The Tg of the copolymer can also be roughly estimated by the FOX formula represented by the following formula (1).
₁ /Tg ₌ W1/Tg1 ₊ W2/Tg2+...+ _Wi /Tg1+... _Wn / _{Tgn ( 1} )
where Tg(K) is the Tg of the copolymer, Tg _i (K) is the Tg of the homopolymer of monomer i, and W _i is the mass fraction of each monomer .
However, as the glass transition temperature Tg of the particulate polymer in the present embodiment, the value measured by the above-described method using DSC is employed.

From the viewpoint of wettability to the substrate, binding property between the substrate and the thermoplastic polymer-containing layer, and adhesiveness to the electrode, the thermoplastic polymer-containing layer contains a polymer having a glass transition temperature of less than 40°C. From the viewpoint of ion permeability, the glass transition temperature is more preferably -100 ° C. or higher, still more preferably -50 ° C. or higher, and particularly preferably -40 ° C. or higher. From the viewpoint of binding properties with the containing layer, the temperature is more preferably less than 20°C, still more preferably less than 15°C, and particularly preferably less than 0°C.

The particulate polymer preferably has at least two glass transition temperatures from the viewpoint of the adhesion of the thermoplastic polymer-containing layer to the electrode and the resistance to powder falling off. It preferably contains two or more thermoplastic polymers having transition temperatures, more preferably at least one of the glass transition temperatures is in the region below 20°C, and at least one of the glass transition temperatures is , above 20°C.

When the particulate polymer has a glass transition temperature (Tg) of less than 20°C and a Tg of 20°C or more, the former Tg is preferably -100°C or more, or more, from the viewpoint of blocking resistance. It is preferably -50°C or higher, more preferably -40°C or higher, and from the viewpoint of binding strength and powder fall resistance, preferably lower than -20°C, more preferably lower than -15°C, and even more preferably lower than -10°C. and the Tg of the latter is preferably 20° C. or higher, more preferably 40° C. or higher, and still more preferably 50° C. or higher from the viewpoint of blocking resistance, and preferably less than 100° C. from the viewpoint of adhesive strength. It is more preferably less than 90°C, still more preferably less than 80°C.

Methods for making the particulate polymer have at least two glass transition temperatures include, but are not limited to, a method of blending two or more types of particulate polymers, and a particulate polymer having a core-shell structure. A method using A core-shell structure is a structure having a central portion and an outer shell portion covering the central portion, and is a polymer having a double structure in which the type or composition of the polymer constituting each portion is different from each other. . In particular, in polymer blends and core-shell structures, by combining a polymer with a high glass transition temperature and a polymer with a low glass transition temperature, the glass transition temperature of the entire particulate polymer can be controlled. Moreover, a plurality of functions can be imparted to the entire particulate polymer.

For example, when blending two or more types of particulate polymers, in particular, one or more polymers having a glass transition temperature (Tg) present in a region of 20 ° C. or higher and a glass transition temperature present in a region of less than 20 ° C. By blending with one or more polymers, it is possible to achieve a better balance between anti-stickiness and wettability to substrates. From the viewpoint of compatibility between adhesion and blocking resistance, the mixing ratio of each polymer when blending is such that a polymer having a glass transition temperature of 20°C or higher and a polymer having a glass transition temperature of less than 20°C are mixed. The ratio of the polymer to the to 95:5, particularly preferably 60:40 to 90:10.

Further, when two or more types of particulate polymers having Tg are present in the thermoplastic polymer-containing layer, the average particle diameter (D50) of the particulate polymer with the higher Tg is From the viewpoint of suppressing the amount, it is preferably 10 to 1000 nm, more preferably 100 to 800 nm, still more preferably 200 to 700 nm. The average particle size (D50) of the particulate polymer is measured according to the method described in Examples below.

Two or more types of particulate polymers each having a different average particle size (D50) can also be contained in the thermoplastic polymer-containing layer. For example, a particulate polymer having an arithmetic average particle diameter of 10 nm or more and 300 nm or less (hereinafter referred to as "small particle diameter particles") and a particulate polymer having an arithmetic average particle diameter of more than 100 nm and 2000 nm or less (hereinafter , referred to as "large particle size particles").

Moreover, from the viewpoint of blocking resistance and powder-off resistance, two or more kinds of particulate polymers may exist not only separately in the thermoplastic polymer-containing layer but also as a core-shell structure. When a particulate polymer having a core-shell structure is used, the adhesiveness and compatibility of the thermoplastic polymer-containing layer with other members (for example, substrates, etc.) can be adjusted by selecting the type of polymer for the outer shell portion. can. Also, by selecting the type of polymer for the central portion, it is possible to enhance the adhesion to the electrode after hot pressing, for example. Alternatively, it is possible to control the viscoelasticity of the thermoplastic polymer-containing layer by combining a highly viscous polymer and a highly elastic polymer.

The glass transition temperature of the outer shell portion (shell) of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably less than 20°C, more preferably 15°C or less, and -30°C or more and 15°C. It is more preferable in it being below. The glass transition temperature of the central portion (core) of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably 20°C or higher, more preferably 20°C or higher and 200°C or lower, and further preferably 50°C or higher and 200°C or lower. preferable.

The particulate polymer described above can be produced by known polymerization methods, except that the monomers described above are used. As the polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization, or the like can be adopted. Especially for the purpose of obtaining a dispersion in the form of particles, an emulsion polymerization method is preferred. The emulsion polymerization method is not particularly limited, and conventionally known methods can be used. For example, in an aqueous medium, the above-mentioned monomers, surfactants, radical polymerization initiators, and other additive components used as necessary in a dispersion system as basic composition components, consisting of each of the above-mentioned monomers A polymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the monomer composition to be supplied is kept constant during the entire polymerization process, and the morphological composition change of the particles of the resin dispersion to be generated is controlled by changing the composition sequentially or continuously during the polymerization process. Various methods, such as the method of giving, can be used as needed. When the polymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and particulate polymer dispersed in the water.

A surfactant is a compound having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. Examples of surfactants include polyether surfactants; non-reactive alkyl sulfates, polyoxyethylene alkyl ether sulfates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkylsulfosuccinates, alkyldiphenyl ethers. Disulfonates, naphthalenesulfonic acid formalin condensates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene distyrenated phenyl ether sulfates, fatty acid salts, alkyl phosphates, and polyoxyethylene alkylphenyl ether sulfates anionic surfactants such as ester salts; Nonionic surfactants such as ethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, alkylalkanolamides, and polyoxyethylene alkylphenyl ethers. In addition to these surfactants, so-called reactive surfactants in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

Anionic surfactants among reactive surfactants include, for example, ethylenically unsaturated monomers having a sulfonic acid group, a sulfonate group or a sulfate ester group, and salts thereof, and a sulfonic acid group or A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) that is its ammonium salt or alkali metal salt is preferred. Specifically, for example, alkyl allyl sulfosuccinate (e.g., Sanyo Chemical Co., Ltd. Eleminol (trademark) JS-20, Kao Corporation Latemul (trademark, hereinafter the same.) S-120, S-180A, S- 180.), polyoxyethylene alkylpropenylphenyl ether sulfate (for example, Daiichi Kogyo Seiyaku Co., Ltd. Aqualon (trademark, the same shall apply hereinafter) HS-10.), α-[1-[ (allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate (for example, Adekariasoap (trademark, hereinafter the same) SE-10N manufactured by ADEKA Co., Ltd.), ammonium =α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (for example, Aqualon KH-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Tosoh Organic Chemical Co., Ltd.) Spinomer (trademark) NaSS manufactured by the company), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-polyoxyethylene sulfate (for example, Adekaria manufactured by ADEKA Co., Ltd.) Soap SR-10), and sulfuric acid ester salts of polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (for example, latemul PD-104 manufactured by Kao Corporation). .

Examples of nonionic surfactants among reactive surfactants include α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene (e.g., Adekaria Soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., RN-30 and RN-50.), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-hydroxypolyoxyethylene (for example, Adekaria Soap ER manufactured by ADEKA Co., Ltd. -10.), and polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (eg, Latemul PD-420 manufactured by Kao Corporation). The surfactant is preferably used in an amount of 0.1 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the monomer composition. Surfactants are used singly or in combination of two or more.

The surfactant can also be added after the polymerization reaction, in combination with the method of adding it as a raw material when the particulate polymer is polymerized. By adding a surfactant after the polymerization reaction, the surface energy of the thermoplastic polymer layer formed on the substrate surface can be adjusted. By adjusting the surface energy of the thermoplastic polymer layer, it is possible to adjust the contact angle of the separator surface on which the thermoplastic polymer is formed. The post-addition of the surfactant is preferable from the viewpoint of being able to adjust the surface energy of the thermoplastic polymer layer without being affected by the conditions of the polymerization reaction. It is believed that the post-addition of the surfactant results in the presence of a large amount of free surfactant in the slurry, and that a large amount of the surfactant is present on the outermost surface of the binder when the slurry is dried. As a result, the surface energy of the thermoplastic polymer layer can be adjusted with a smaller amount compared to the method of adding it as a raw material for the polymerization reaction.
As the surfactant to be added after the polymerization reaction of the particulate polymer, the same surfactant as that added during the polymerization reaction can be used. It is preferred to use surfactants that are not toxic surfactants. Among these, it is said that it is easy to suppress the foaming of the slurry, and furthermore, the more it is added, the greater the dispersion effect becomes, making it easier to ensure dispersibility, and the effect of greatly changing the surface tension of the polyolefin microporous membrane with a small amount. From the point of view, the polyether surfactant or the anionic surfactant is preferable.
The surfactant to be added later is preferably used in an amount of 0.05 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the monomer composition.
When the amount is 0.05 parts by weight or more, the surface energy can be sufficiently adjusted, and when the amount is 20 parts by weight or less, the surface energy of the thermoplastic polymer layer becomes too high and blocking is easily prevented.

The radical polymerization initiator is one that is radically decomposed by heat or a reducing substance to initiate addition polymerization of monomers, and both inorganic initiators and organic initiators can be used. A water-soluble or oil-soluble polymerization initiator can be used as the radical polymerization initiator. Water-soluble polymerization initiators include, for example, peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems. Peroxodisulfates include, for example, potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS), and peroxides include, for example, hydrogen peroxide, t- butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide; , 2-azobis(2-amidinopropane) hydrogen dichloride, and 4,4-azobis(4-cyanopentanoic acid), and the peroxide-reducing agent redox system includes, for example, the above peroxide One or more of reducing agents such as sodium sulfoxylate formaldehyde, sodium bisulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid and salts thereof, cuprous salts, and ferrous salts A combination of

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

Incidentally, a monomer containing an ethylenically unsaturated monomer (P) having a polyalkylene glycol group, an ethylenically unsaturated monomer (A) having a cycloalkyl group, and another monomer (B) When the polymer composition is emulsion-polymerized to form a dispersion in which polymer particles are dispersed in a solvent (water), the solid content of the obtained dispersion is 30% by mass or more and 70% by mass or less. preferable. The dispersion preferably has a pH of 5 to 12 in order to maintain long-term dispersion stability. For adjustment of pH, it is preferable to use ammonia, sodium hydroxide, potassium hydroxide, and amines such as dimethylaminoethanol, and it is more preferable to adjust pH with ammonia (water) or sodium hydroxide.

The aqueous dispersion contains a polymer obtained by polymerizing a monomer composition containing the specific monomer as particles (polymer particles) dispersed in water. The aqueous dispersion may contain a solvent such as methanol, ethanol, or isopropyl alcohol, a dispersant, a lubricant, a thickener, a bactericide, or the like, in addition to water and the polymer. Since the thermoplastic polymer-containing layer can be easily formed by coating, it is preferable to form a particulate polymer by emulsion polymerization and use the resulting particulate polymer emulsion as an aqueous latex.

(Other Ingredients in Thermoplastic Polymer-Containing Layer)
In addition to the thermoplastic polymer, the thermoplastic polymer-containing layer may optionally contain other ingredients, such as inorganic substances. Examples of inorganic substances include inorganic oxides (oxide-based ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; Nitrides (nitride ceramics); silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dikite, nacrite, halloysite, pyrophyllite, montmorillonite , sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; You may use it in combination of 2 or more types. The content of the inorganic substance in the thermoplastic polymer-containing layer may be 5% by mass or less, and should exceed 0% by mass, based on the total amount of the thermoplastic polymer-containing layer so as not to cause cohesive failure of the inorganic substance. can also

[Arbitrary layer]
As long as the separator can exhibit the effects of B10, B90, B90/B10, T10, T90, T10-T90, etc. adjusted within the numerical ranges described above, the substrate and the thermoplastic polymer-containing layer other than An optional layer, an inorganic filler porous layer may be included. The inorganic filler porous layer can be disposed, for example, on one side of the substrate, on both sides of the substrate, between the substrate and the thermoplastic polymer-containing layer, or to form at least one outer surface of the separator. can be done. The inorganic filler porous layer contains an inorganic filler and a resin binder and has a plurality of pores.

(Inorganic filler)
The inorganic filler is not particularly limited, but it should have a melting point of 200° C. or higher, have high electrical insulation, and be electrochemically stable within the range of use of an electricity storage device such as a lithium ion secondary battery. can be done.

Examples of inorganic fillers include, but are not limited to, inorganic oxides (oxide-based ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; silicon nitride, titanium nitride, and inorganic nitrides (nitride ceramics) such as boron nitride; silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dakite, nacrite, halloysite , pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These are used individually by 1 type or in combination of 2 or more types.

The average particle size D50 of the inorganic filler is preferably 0.01 µm or more, more preferably 0.2 µm or more, and still more preferably 0.4 µm or more. Also, the average particle diameter D50 of the inorganic filler is preferably 4.0 μm or less, more preferably 3.5 μm or less, and even more preferably less than 1.0 μm. The average particle diameter D50 of the inorganic filler of 0.01 μm or more is preferable from the viewpoint of reducing the amount of water adsorbed by the separator. The average particle diameter D50 of the inorganic filler of 4.0 μm or less is preferable from the viewpoint of the heat resistance of the separator. Methods for adjusting the particle size and distribution of the inorganic filler include, for example, a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizing device such as a ball mill, bead mill, or jet mill.
The particle size distribution of the inorganic filler can be such that there is one peak in the graph of frequency versus particle size. However, a trapezoidal chart with two peaks or no peaks may be used.

The average particle size of the particulate polymer may be larger than the average pore size of the inorganic filler porous layer. For example, the average particle diameter of the particulate polymer is, for example, 1.2 times or more, 1.5 times or more, further 1.8 times or more, the average pore diameter of the inorganic filler porous layer, and 6.0 times or less, or even 3.0 times or less. The average pore size of the inorganic filler porous layer quantitatively defines the gap between the inorganic filler and the inorganic filler, the inorganic filler and the binder, or the binder and the binder in the inorganic filler porous layer. In addition, the content of the particulate polymer contained in the inorganic filler porous layer is, for example, 20% by volume or less, 15% by volume or less, 10% by volume or less, or even 5% by volume with respect to the total amount of the inorganic filler porous layer. % or less.

When measuring the average pore diameter of the inorganic filler porous layer, it is preferable to observe the cross section of the separator in a region not involved in ion conduction in the cross section of the separator. The average pore size of the inorganic filler porous layer may be measured, for example, on a separator that has just been manufactured and has not yet been incorporated into an electricity storage device. Alternatively, after the separator has been incorporated into the electricity storage device, the so-called "ear" portion of the separator (the region near the outer edge of the separator and not involved in ion conduction) is measured. good too.
The average pore size of the inorganic filler porous layer is, for example, 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, and further 0.2 μm or more. Also, the average pore size is 5 μm or less, 3 μm or less, 0.7 μm or less, and further 0.5 μm or less.

The average pore diameter of the inorganic filler porous layer is an index representing the size of voids formed by the inorganic fillers preferably bound together by a resin binder in the inorganic filler porous layer formed on at least one side of the substrate. be. Since the average pore diameter of the inorganic filler porous layer is determined by the method of forming the inorganic filler porous layer, for example, the properties of the inorganic filler used, the properties of the inorganic filler porous layer slurry for forming the inorganic filler porous layer, and the inorganic filler porous layer It can be adjusted by the forming method when forming the layer.

Examples of the shape of the inorganic filler include plate-like, scale-like, needle-like, columnar, spherical, polyhedral, and massive (block-like) shapes. A plurality of types of inorganic fillers having these shapes may be used in combination.
The content of the inorganic filler in the inorganic filler porous layer is, for example, 20% by mass or more and less than 100% by mass, 30% by mass or more and 80% by mass or less, or 35% by mass or more and 70% by mass with respect to the total amount of the inorganic filler porous layer. 40% by mass or more and 60% by mass or less.

(resin binder)
The type of resin of the resin binder contained in the inorganic filler porous layer is not particularly limited, but it is insoluble in the electrolytic solution of an electricity storage device such as a lithium ion secondary battery and is insoluble in the electrolyte such as a lithium ion secondary battery. An electrochemically stable resin can be used in the range of use of the electricity storage device. As the resin binder resin, in addition to the resin binder (A) contained in the inorganic filler porous layer and the particulate polymer (B) contained in the thermoplastic polymer-containing layer, A binding binder (C) that binds the polymer (B) to the substrate or the inorganic filler porous layer may be used. The resin binder (A) and binding binder (C) are generally not particulate in the separator. On the other hand, the particulate polymer (B) is particulate in the separator, and the particulate polymer (B) can contain a different type of resin from the resin binder (A) and the binding binder (C).

Specific examples of such resins include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers; Fluorine-containing rubber such as ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride , methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate rubbers; ethyl cellulose, methyl cellulose, hydroxy Cellulose derivatives such as ethyl cellulose and carboxymethyl cellulose; and resins having a melting point and/or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester. is mentioned. These are used individually by 1 type or in combination of 2 or more types.

Resin binders can include, for example, resin latex binders. As the resin latex binder, for example, a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable therewith can be used. Examples of aliphatic conjugated diene monomers include butadiene and isoprene; examples of unsaturated carboxylic acid monomers include (meth)acrylic acid; , for example, styrene. Although there are no particular restrictions on the method of polymerizing such copolymers, emulsion polymerization is preferred. The emulsion polymerization method is not particularly limited, and known methods can be used. The method of adding the monomers and other components is not particularly limited, and any of a batch addition method, a divisional addition method, and a continuous addition method can be employed. Either two-stage polymerization or multi-stage polymerization of three or more stages can be employed.

Specific examples of the resin binder include the following 1) to 7).
1) Polyolefins: such as polyethylene, polypropylene, ethylene propylene rubber, and modifications thereof;
2) conjugated diene-based polymer: for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride;
3) acrylic polymers: such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers;
4) polyvinyl alcohol-based resins: for example, polyvinyl alcohol and polyvinyl acetate;
5) fluorine-containing resins: for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer;
6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and 7) Resins with a melting point and/or glass transition temperature above 180°C or polymers without a melting point but with a decomposition temperature above 200°C: For example, polyphenylene ethers, polysulfones, polyethersulfones, polyphenylene sulfides, polyetherimides, polyamideimides, polyamides, and polyesters.

When the resin binder is a resin latex binder, its average particle size (D50) is, for example, 50-500 nm, 60-460 nm, and further 80-250 nm. The average particle size of the resin binder can be controlled, for example, by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, and the like.
The content of the resin binder in the inorganic filler porous layer is, for example, more than 0% by mass and 80% by mass or less, 1% by mass or more and 20% by mass or less, 2% by mass or more and 10% by mass, relative to the total amount of the inorganic filler porous layer. % or less, more preferably 3% by mass or more and 5% by mass or less.
The content of the particulate polymer contained in the inorganic filler porous layer is, for example, less than 5% by volume, less than 3% by volume, or even less than 2% by volume of the content of the particulate polymer contained in the separator. can be

The thickness of the inorganic filler porous layer is preferably 0.5 μm or more, more preferably 1.0 μm or more from the viewpoint of heat resistance, and preferably 10.0 μm or less from the viewpoint of suppressing the amount of water adsorbed by the separator. More preferably, it is 6.0 μm or less. In addition, the layer density of the inorganic filler porous layer may be, for example, 0.5 g/(m ² ·μm) or more and 3.0 g/(m ² ·μm) or less, further 0.7 to 2.0 cm ³ . Furthermore, the peel strength between the substrate and the inorganic filler porous layer is not particularly limited, but can be determined so as to prevent cohesive failure of the inorganic material due to blocking.

(Laminate of substrate and inorganic filler porous layer)
The laminate of the substrate and the inorganic filler porous layer may, for example, have a thickness of 2.5 to 110.0 μm, an air permeability of 50 to 400 sec/100 cm ³ and/or a heat treatment of 130° C. in TD. Shrinkage may be 1.0 to 5.0%.

<Various characteristics of the separator>
Separators are subject to the following conditions:
{Conditions: The measured value P10 is defined as follows:
Two separators were prepared and stored for 1 day in an environment with a temperature of 35° C. and a relative humidity (RH) of 10%. A laminate (A-A) _RH10 , a laminate (AB) RH10 formed by laminating the surface (A) and the opposite surface (B), and a laminate (A-B) _RH10 formed by laminating the surfaces (B) Laminate (BB) _RH10 was produced, and each laminate was pressed for 5 seconds at a temperature of 90 ° C. and a pressure of 1 MPa. Of the peel strengths measured individually for all laminates, Let the maximum value be P10 (N/m)}
It is preferable that the measured value P10 measured in is 5 N/m or more.

A method for measuring the value P10 is detailed in the Examples. When the measured value P10 of the separator measured under the above conditions is 5 N/m or more, the adhesiveness between the separator and the electrode tends to be secured or improved. Further, when a separator having a P10 of 5 N/m or more is used for lamination with electrodes, winding, assembly, etc., assembly speed and productivity are improved, leading to so-called tact-up. From this point of view, the measured value P10 of the separator is more preferably over 5 N/m, still more preferably over 10 N/m, and particularly preferably over 15 N/m. The upper limit of the measured value P10 is not particularly limited, and may be, for example, 30 N/m or less, 25 N/m or less, or 20 N/m or less.

The measured value P10 for the peel strength of the separator can be adjusted within the numerical range described above by controlling the physical properties and composition of the thermoplastic polymer-containing layer, for example, by controlling the glass transition temperature of the thermoplastic polymer. In addition, the measured value P10 is determined not only by the control of the glass transition temperature of the thermoplastic polymer, but also by the use of a thermoplastic polymer unit that is difficult to swell in the electrolytic solution, the introduction of a hydrophobic block or functional group, and the aromatic vinyl compound monomer. It can also be adjusted by controlling the content of both the derived unit and the unit derived from the nitrile group-containing monomer or by controlling the content ratio.

The air permeability of the separator is preferably 10 sec/100 cm ³ or more and 10,000 sec/100 cm ³ or less, more preferably 10 sec/100 cm ³ or more and 1000 sec/100 cm ³ or less, and still more preferably 50 sec/ It is 100 cm ³ or more and 500 sec/100 cm ³ or less, and particularly preferably 100 sec/100 cm ³ or more and 300 sec/100 cm ³ or less. As a result, when the separator is applied to an electricity storage device, it exhibits good high ion permeability. This air permeability is the air resistance measured according to JIS P-8117, like the air permeability of the polyolefin porous substrate.

The puncture strength of the separator is preferably 200 g/20 μm or more, more preferably 250 g/20 μm or more, still more preferably 300 g/20 μm or more, preferably 2000 g/20 μm or less, more preferably 1000 g/20 μm or less. The puncture strength of 200 g/20 μm or more is from the viewpoint of suppressing film breakage due to fallen active material etc. when the separator is wound together with the electrode, and suppresses the concern of short circuit due to expansion and contraction of the electrode due to charging and discharging. It is also preferable from the viewpoint of A puncture strength of 2000 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 according to the method described in Examples. The puncture strength can be adjusted by adjusting the draw ratio and/or the draw temperature of the substrate.

The total thickness of the separator is preferably 2 μm or more, more preferably 5 μm or more, and preferably 80 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less. A total thickness of 2 μm or more is preferable from the viewpoint of improving the mechanical strength. A total thickness of 100 μm or less is preferable because the volume occupied by the separator in the electricity storage device is reduced, which tends to be advantageous in increasing the capacity of the electricity storage device.

<Preparing two separators and stacking them>
The values B10, B90, and P10 for the peel strength of the separator are measured by preparing two sheets of the separator and forming a stack of them, as described for the formula above. Preparing two separators in the measurement of the values B10, B90, and P10 means forming a laminate using two equal-area members derived from the same separator.

In the measurement of the values B10, B90, and P10 relating to the peel strength of the separator, it is preferable to press the laminate while maintaining the relative humidity (RH) environment corresponding to each value. If it is difficult to control the humidity of the laminate and press at the same time, depending on the storage, lamination equipment, press equipment, surrounding environment, etc., store the laminate in a humidity control device such as an oven and adjust the humidity to a predetermined level. Immediately after this, the laminate may be placed in a container such as an aluminum pouch, sealed, and then transferred to press equipment to quickly press the laminate.

In determining the values B10, B90 and P10, the formation of the laminate may be the method detailed in the Examples, for example the following method;
(a) A method of forming a laminate by cutting out two sheets having the same area from a sheet-like or leaf-like separator and laminating them;
(a) A method of folding a sheet-like or single-leaf separator in half; and (c) A method of folding a sheet-like or single-leaf separator and then cutting it into an arbitrary size;
can be performed by at least one selected from the group consisting of

<Layer structure of separator>
The separator according to embodiments 1 and 2 comprises a substrate and a thermoplastic polymer-containing layer disposed on at least one substrate surface of the substrate, more particularly the substrate on one or both sides of the substrate. It has a layer structure in which a thermoplastic polymer-containing layer is arranged on the surface of the material. Due to such a layer structure, the separator exhibits remarkable effects such as B10, B90, B90/B10, T10, T90, T10-T90, P10 adjusted within the numerical ranges described above.

More specifically, the separators according to Embodiments 1 and 2, or the separators whose measured value P10 satisfies the conditions described above, improve the cycle characteristics of the electricity storage device, achieve both adhesion and blocking resistance, and From the viewpoint of preventing misalignment and reducing the amount of water brought into the storage device, the following configuration:
(1) a substrate and a thermoplastic polymer-containing layer formed on one side of the substrate;
(2) a substrate and thermoplastic polymer-containing layers formed on both sides of the substrate;
(3) a substrate, an inorganic coating layer formed on one side of the substrate, and a thermoplastic polymer-containing layer formed on the other side of the substrate; and (4) a substrate, formed on one side of the substrate an inorganic coating layer, a thermoplastic polymer-containing layer formed on the surface of the inorganic coating layer opposite to the substrate, and a thermoplastic polymer-containing layer formed on the other surface of the substrate;
It is preferred to have at least one of Each layer configuration and a laminate formed from separators having the same will be described below.

(1) Substrate and thermoplastic polymer-containing layer formed on one side of the substrate In the layer configuration (1), it is assumed that the thermoplastic polymer-containing layer side of the separator is the surface (B), and the thermoplastic polymer-containing layer is formed. If the side that is not coated is the surface (A), there is almost no adhesiveness between the surfaces (A) that are the substrate exposed surfaces, so the laminate (BB) between the surfaces (B), or the surface (A) A laminate (AB) of the surface (B) and the surface (B) is preferred. More specifically, in the measurement of B90, B10 or P10 of the separator of the layer configuration (1), the peel strength of the pressed body of the laminate (BB) _{RH90, RH10} or the laminate (AB) _{RH90, RH10} is , is preferably the maximum value.

(2) Substrate and Thermoplastic Polymer-Containing Layers Formed on Both Sides of the Substrate In the layer configuration (2), thermoplastic polymer-containing layers are arranged on both sides of the separator (that is, on both sides (A, B)). , due to the adhesive strength of the thermoplastic polymer-containing layer, the laminate (A-A) between surfaces (A), the laminate (B-B) between surfaces (B), or the surface (A) and surface (B) ) and the laminate (AB) are both preferred. More specifically, in the measurement of B90, B10 or P10 of the separator of the layer configuration (2), the laminate (AA) _{RH90, RH10} , the laminate (BB) _{RH90, RH10} or the laminate (AB ) The peel strength of both _{RH90 and RH10} presses can reach the maximum value.

(3) substrate, an inorganic coating layer formed on one side of the substrate, and a thermoplastic polymer-containing layer formed on the other side of the substrate In the layer configuration (3), the inorganic coating layer of the separator When the side is the surface (A) and the thermoplastic polymer-containing layer side is the surface (B), there is generally no adhesion between the surfaces (A), which are the inorganic coated surfaces, and peeling between the substrate and the inorganic layer and separation of the inorganic layer. From the viewpoint of observing peeling between a plurality of thermoplastic polymer-containing layers rather than cohesive failure, a laminate (BB) between surfaces (B) is preferable. More specifically, in the measurement of B90, B10 or P10 of the separator of the layer configuration (3), it is preferable that the peel strength of the pressed body of the laminate (BB) _{RH90, RH10} becomes the maximum value. The inorganic coating layer may be, for example, an inorganic filler porous layer formed by a coating method.

(4) a base material, an inorganic coating layer formed on one side of the base material, a thermoplastic polymer-containing layer formed on the side of the inorganic coating layer opposite to the base material, and the other side of the base material; In the layer configuration (4) of the thermoplastic polymer-containing layer formed in the separator, the thermoplastic polymer-containing layer side formed in contact with the inorganic coating layer of the separator is assumed to be the surface (A), and is formed in contact with the substrate surface. If the thermoplastic polymer-containing layer side is the surface (B), the peeling between the thermoplastic polymer-containing layers is observed rather than the peeling between the substrate and the inorganic layer and the cohesive failure of the inorganic layer. A laminate (BB) of each other is preferred. More specifically, in the measurement of B90, B10 or P10 of the separator of the layer configuration (4), it is preferable that the peel strength of the pressed body of the laminate (BB) _{RH90, RH10} becomes the maximum value. The inorganic coating layer may be, for example, an inorganic filler porous layer formed by a coating method.

<Separator manufacturing method>
[Method for manufacturing base material]
The method for producing the base material is not particularly limited, and known production methods can be employed. For example, either a wet porosification method or a dry porosification method may be employed. To give an example of a wet porosification method, for example, when the base material is a polyolefin microporous film, the polyolefin resin composition and the plasticizer are melt-kneaded to form a sheet, optionally stretched, and then the plasticizer A method of making porosity by extracting: After melt-kneading a polyolefin resin composition containing a polyolefin resin as a main component and extruding at a high draw ratio, the polyolefin crystal interface is peeled off by heat treatment and stretching to make porosity. a method in which a polyolefin resin composition and an inorganic filler are melt-kneaded to form a sheet, and then the interface between the polyolefin and the inorganic filler is exfoliated by stretching to make the sheet porous; and a method in which the polyolefin resin composition is dissolved. After that, the polyolefin is immersed in a poor solvent for the polyolefin to solidify the polyolefin, and at the same time, the solvent is removed to make it porous.

Also, the method of making the nonwoven fabric or paper as the substrate may be known. Examples of manufacturing methods include a chemical bond method in which a web is immersed in a binder and dried to bond between fibers; a thermal bond method in which heat-fusible fibers are mixed into a web and partially melted to bond between fibers. A needle punch method in which a needle with thorns is repeatedly pierced into the web to mechanically entangle the fibers; and a hydroentanglement method in which the fibers are entangled by jetting a high-pressure water stream from a nozzle through a net (screen) to the web. .

As an example of a method for producing a polyolefin microporous membrane, a method of melt-kneading a polyolefin resin composition and a plasticizer to form a sheet, and then extracting the plasticizer will be described below. First, a polyolefin resin composition and a plasticizer are melt-kneaded. As a melt-kneading method, for example, a polyolefin resin and, if necessary, other additives are put into a resin-kneading device such as an extruder, a kneader, a Laboplastomill, a kneading roll, and a Banbury mixer, and the resin component is heated and melted. while introducing a plasticizer in an arbitrary ratio and kneading. At this time, it is preferable to knead the polyolefin resin, other additives, and the plasticizer in advance at a predetermined ratio using a Henschel mixer or the like before charging the resin kneading device. More preferably, only a portion of the plasticizer is added during pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading device.

As the plasticizer, a non-volatile solvent capable of forming a homogeneous solution above the melting point of the polyolefin can be used. Specific examples of such nonvolatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred.

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

Next, the melt-kneaded product obtained by heat-melting and kneading as described above is formed into a sheet. As a method for producing a sheet-shaped molding, for example, the melt-kneaded product is extruded into a sheet through a T-die or the like, brought into contact with a heat conductor, and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. and solidification. Heat conductors used for cooling and solidification include metal, water, air, and the plasticizer itself, but metal rolls are preferred because of their high heat conduction efficiency. In this case, when the melt-kneaded product is sandwiched between rolls when it is brought into contact with metal rolls, the heat conduction efficiency is further increased, the sheet is oriented, the film strength is increased, and the surface smoothness of the sheet is also improved. Therefore, it is more preferable. The die lip interval when the sheet is extruded from the T-die is preferably 400 μm or more and 3000 μm or less, more preferably 500 μm or more and 2500 μm or less.

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

The draw ratio is preferably in the range of 20 times or more and 100 times or less, more preferably in the range of 25 times or more and 50 times or less. The draw ratio in each axial direction is preferably in the range of 4 times to 10 times in the MD direction, 4 times to 10 times in the TD direction, 5 times to 8 times in the MD direction, and 5 times in the TD direction. More preferably, it is in the range of 8 times or less. By setting the draw ratio within this range, more sufficient strength can be imparted, film breakage in the drawing step can be prevented, and high productivity can be obtained.
The MD direction means the machine direction when, for example, a polyolefin microporous membrane is continuously molded, and the TD direction means the direction crossing the MD direction at an angle of 90°.

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

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

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

In order to suppress the shrinkage of the porous substrate, heat treatment such as heat setting or thermal relaxation may be performed after the stretching step or after the formation of the porous substrate. The porous substrate may be subjected to a post-treatment such as a hydrophilization treatment using a surfactant or the like, or a cross-linking treatment using ionizing radiation or the like.

An example of a dry porosification method, which is different from the wet porosification method, will be given. First, a film is directly drawn and oriented after melt-kneading in an extruder without using a solvent, and then an annealing step, a cold drawing step, and a hot drawing step are sequentially performed to prepare a microporous membrane. In the dry porosification method, a method in which a molten resin is stretched and oriented through a T-die from an extruder, an inflation method, or the like can be used, and the method is not particularly limited.

[Method for Arranging Thermoplastic Polymer-Containing Layer]
A thermoplastic polymer-containing layer is disposed on at least one substrate surface of the substrate produced as described above. When the inorganic filler porous layer is arranged on the surface of the substrate, the thermoplastic polymer-containing layer is arranged on the whole or part of the surface of the inorganic filler porous layer, or the inorganic filler porous layer is formed. A thermoplastic polymer-containing layer is disposed on the side of the substrate that is not exposed. The method for arranging the thermoplastic polymer-containing layer is not particularly limited, and examples thereof include a method of applying a coating liquid containing a particulate polymer to the inorganic filler porous layer or substrate.

As the coating liquid, a dispersion in which a particulate polymer is dispersed in a solvent that does not dissolve the polymer can be preferably used. Particularly preferably, the particulate polymer is synthesized by emulsion polymerization, and the emulsion obtained by the emulsion polymerization can be used as the coating liquid as it is.

The shape of the application of the thermoplastic polymer to the substrate can be determined so as to obtain the placement pattern of the thermoplastic polymer described above. The amount of the thermoplastic polymer applied to the substrate can be determined according to the coating shape. For example, the amount of the thermoplastic polymer-containing layer formed per area of one surface of the substrate described above can be the same as

The method of applying the coating liquid containing the particulate polymer onto the substrate is not particularly limited as long as it is a method capable of realizing a desired coating pattern, coating thickness and coating area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, casting A coater method, a die coater method, a screen printing method, a spray coating method, an inkjet coating method, and the like can be mentioned. Among these, the gravure coater method and the spray coating method are preferable from the viewpoints that the coating shape of the particulate polymer has a high degree of freedom and that a preferable area ratio can be easily obtained.

As a medium for the coating liquid, water or a mixed solvent composed of water and a water-soluble organic medium is preferable. Examples of the water-soluble organic medium include, but are not particularly limited to, ethanol, methanol, and the like. Among these, water is more preferable. When the coating liquid is applied to the substrate, if the coating liquid penetrates into the interior of the substrate, the particulate polymer containing the polymer blocks the surface and interior of the pores of the substrate, resulting in poor permeability. easy to decline. In this regard, when water is used as the solvent or dispersion medium for the coating liquid, the coating liquid becomes difficult to enter the interior of the substrate, and the particulate polymer containing the polymer is mainly present on the outer surface of the substrate. This is preferable because it is possible to more effectively suppress the decrease in permeability. Solvents or dispersion media that can be used in combination with water include, for example, ethanol and methanol.

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

The drying temperature during or after coating of the thermoplastic polymer-containing layer is preferably 30°C to 80°C, more preferably 35°C to 60°C, still more preferably 40°C to 60°C. A drying temperature of 30° C. or higher is preferable from the viewpoint of reliable drying and suppression of the amount of moisture carried from the thermoplastic polymer-containing layer to the separator or the electricity storage device. A drying temperature of 80° C. or less is preferable from the viewpoint of suppressing changes in the physical properties of the separator due to heat, such as wrinkles and sagging.

[Method for Forming Inorganic Filler Porous Layer]
When the inorganic filler porous layer is arranged on at least one surface of the substrate, the method for forming the inorganic filler porous layer is not particularly limited, and it can be formed by a known method. For example, there is a method of coating a substrate with a coating liquid containing an inorganic filler and, if necessary, a resin binder. When the base material contains a resin such as a polyolefin microporous film, a raw material containing an inorganic filler and a resin binder and a base material containing a resin may be laminated and extruded by a coextrusion method, or the base material may be extruded. and the inorganic filler porous layer (membrane) may be prepared separately and then bonded together.

The solvent for the coating liquid is preferably one that can uniformly and stably disperse or dissolve the inorganic filler and, if necessary, the resin binder. Examples include N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide. , water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

Various additives such as a dispersant such as a surfactant; a thickener; a wetting agent; an antifoaming agent;

Methods for dispersing or dissolving the inorganic filler and optionally the resin binder in the medium of the coating liquid include, for example, a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, and a high-speed impeller dispersion. , dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and mechanical agitation such as agitating blades.

The method of applying the coating liquid to the substrate includes, for example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade A coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, and a spray coating method can be mentioned.

The method for removing the solvent from the coating film after coating is not particularly limited as long as it is a method that does not adversely affect the substrate. For example, a method of drying at a temperature below the melting point of the material constituting the substrate while fixing the substrate, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for the resin binder to solidify the resin binder and removing the solvent at the same time. A method of extracting is mentioned. Part of the solvent may also remain as long as it does not significantly affect the device characteristics.

When the coating liquid is removed from the coating film by drying, the average pore size of the inorganic filler porous layer can be adjusted by changing the drying conditions. If the drying conditions are strengthened and the drying rate is increased, the inorganic fillers are fixed in a sufficiently dispersed state without adjusting the shape, and as a result, the average pore size is considered to increase. On the other hand, if the drying conditions are relaxed, the dispersed inorganic filler tries to adopt a more energetically stable structure in the process of drying the solvent, resulting in a smaller average pore size of the inorganic filler porous layer. It is considered to be. Further, when the viscosity of the coating liquid is low, it becomes easier to obtain a stable structure, and the average pore size of the inorganic filler porous layer becomes smaller. Furthermore, the dispersed state of the inorganic filler is also affected by the type of inorganic filler, the type of solvent, the presence or absence of added surfactant, and the type of surfactant.

By calendering the laminate of the inorganic filler porous layer and the substrate, the average pore size of the inorganic filler porous layer can be reduced. The calendering method is not particularly limited, and after drying the coating liquid, a method of conveying the coating liquid while applying pressure with nip rolls may be used.

<Power storage device>
The electricity storage device provided with the separator may be the same as conventionally known devices, except that the electricity storage device separator is provided. Examples of the electric storage device include, but are not particularly limited to, batteries such as non-aqueous electrolyte secondary batteries, condensers, and capacitors. Among them, batteries are preferred, non-aqueous electrolyte secondary batteries are more preferred, and lithium ion secondary batteries are even more preferred, from the viewpoint of more effectively obtaining benefits from the effects of the present invention. Since the separator of the present embodiment is provided, the electricity storage device is excellent in device characteristics such as electricity storage performance. In addition, lithium ion secondary batteries are excellent in battery characteristics.

Either the positive electrode or the negative electrode may be used for measuring the peel strength from the electrode, but it is appropriate to use the positive electrode in order to properly grasp the effect of the separator. In particular, when the power storage device is a lithium ion secondary battery, 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 on a positive electrode current collector, and the positive electrode active material layer is a separator. It is suitable to measure after superimposing so as to face the formation surface of the thermoplastic polymer-containing layer and hot-pressing as described above.

When manufacturing a lithium ion secondary battery using a separator, the positive electrode, the negative electrode, and the non-aqueous electrolyte 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 positive electrode current collectors include aluminum foil. Examples of positive electrode active materials include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel-type LiMnO ₄ , and olivine-type LiFePO ₄ . In addition to the positive electrode active material, the positive electrode active material layer may appropriately contain a binder, a conductive material, and the like.

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

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

<Method for manufacturing power storage device>
A method for manufacturing an electricity storage device using a separator is not particularly limited. For example, the following method can be exemplified. First, a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) is manufactured. Next, the positive electrode-separator-negative electrode-separator or the negative electrode-separator-positive electrode-separator are laminated in this order, and wound in a circular or flat spiral shape to obtain a wound body. It can be manufactured by housing the wound body in a device can (for example, a battery can) and further injecting an electrolytic solution. Alternatively, the electrode and the separator may be folded to form a wound body, which is put into a device container (for example, an aluminum film), and an electrolytic solution may be poured into the device container.

At this time, the wound body can be pressed. Specifically, a separator, a current collector, and an electrode having an active material layer formed on at least one side of the current collector are arranged so that the former thermoplastic polymer-containing layer and the active material layer face each other. A method of overlapping and pressing can be exemplified.

The press temperature is preferably, for example, 20° C. or higher as a temperature capable of effectively exhibiting adhesiveness. In order to suppress clogging of pores in the separator or heat shrinkage due to hot pressing, the pressing temperature is preferably lower than the melting point of the material contained in the substrate, and more preferably 120° C. or lower. The press pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of pores in the separator. The press time may be 1 second or less when a roll press is used, or may be several hours for a surface press, but is preferably 2 hours or less from the viewpoint of productivity. By using the power storage device separator of the present embodiment and going through the above manufacturing process, it is possible to suppress pressback when the wound body composed of the electrodes and the separator is press-molded. Therefore, it is possible to suppress the yield reduction in the device assembly process and shorten the production process time, which is preferable.

The electrical storage device produced as described above, particularly a lithium ion secondary battery, has high adhesiveness and has a separator with reduced ionic resistance, so it has excellent battery characteristics (rate characteristics) and long-term continuity. Excellent operational durability (cycle characteristics).

The evaluation of physical properties described in the Examples column was performed according to the following methods.

(1) Solid content About 1 g of a thermoplastic polymer aqueous dispersion was accurately weighed onto an aluminum dish, and the weight of the aqueous dispersion thus weighed was defined as (a) g. It was dried in a hot air dryer at 130° C. for 1 hour, and the dry mass of the thermoplastic polymer after drying was defined as (b) g. Solid content was calculated by the following formula.
Solid content = (b) / (a) × 100 [%]

(2) Average particle size of particulate polymer (D50)
The average particle size (D50) of the particulate polymer was measured using a particle size measuring device (manufactured by Nikkiso Co., Ltd., product name "Microtrac UPA150"). The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds.

(3) Base material thickness (μm)
The thickness of the substrate was measured by observing the cross section of the substrate with an SEM (model S-4800, manufactured by HITACHI).

(4) Thickness of Layer Containing Thermoplastic Polymer The separator was freeze-fractured, and its cross section was confirmed by SEM (model S-4800, manufactured by HITACHI). The thickness of the thermoplastic polymer-containing layer was measured from the resulting field of view. Specifically, a sample of about 1.5 mm×2.0 mm and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then cut with a hammer. Osmium vapor deposition was applied to the cut sample, and the sample was observed at an acceleration voltage of 1.0 kV and a magnification of 30,000 to calculate the thickness of the thermoplastic polymer-containing layer. In the SEM image, the boundary line between the part where the porous structure of the cross section of the substrate is visible and the part where it is not visible, and the shortest distance from the farthest line parallel to this and in contact with the thermoplastic polymer-containing layer are the thermoplastic The region of the thickness of the polymer-containing layer was taken.
In the case where there is a thermoplastic polymer-containing layer on the inorganic filler porous layer, the distance obtained by subtracting the thickness of the inorganic filler porous layer from the distance from the substrate to the thermoplastic polymer-containing layer is the thickness of the thermoplastic polymer-containing layer. can do.

(5) Glass transition temperature Tg of thermoplastic polymer
An appropriate amount of an aqueous dispersion containing a thermoplastic polymer (solid content = 38 to 42 mass%, pH = 9.0) was placed in an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes to obtain a dry film. About 10 mg of the dry film was filled in an aluminum container for measurement, and a DSC curve under a nitrogen atmosphere and a DSC curve were obtained with a DSC measurement device (manufactured by Shimadzu Corporation, model name "DSC6220"). The measurement conditions were as follows.
1st stage heating program: Start at 70°C and raise the temperature at a rate of 15°C per minute. Maintain for 5 minutes after reaching 110°C.
2nd stage temperature decreasing program: Temperature decreased from 110°C at a rate of 40°C per minute. Hold for 5 minutes after reaching -50°C.
3rd step temperature raising program: Temperature was raised from -50°C to 130°C at a rate of 15°C per minute. Acquire DSC and DDSC data during this 3rd stage temperature rise.
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 line at the inflection point (the point where the upwardly convex curve changes to the downwardly convex curve) is the glass transition temperature ( Tg). The Tg explained in this item is shown in Tables 3 and 5 as the glass transition temperature Tg of the particulate polymer.

(6) Glass transition temperature T10, T90 after storage for 1 day of thermoplastic polymer
The glass transition temperatures T10 and T90 of the thermoplastic polymer after storage for 1 day were measured as follows.
A thermoplastic polymer (a mixture of multiple types of thermoplastic polymers may also be used) was stored for 1 day at a temperature of 35°C and a relative humidity (RH) of 10%, and then placed in an aluminum closed pan (Hitachi High Tech Co., Ltd.). Science Co., Ltd., K-YSSC000E031) was sealed with 10 mg. After that, the glass transition temperature T10 (° C.) was measured by DSC (differential scanning calorimetry) under the following conditions.
Heating program: Start at 0°C, heat up to 100°C at a rate of 3°C per minute

A thermoplastic polymer (a mixture of multiple types of thermoplastic polymers may also be used) was stored for 1 day at a temperature of 35°C and a relative humidity (RH) of 90%, and then placed in an aluminum closed pan (Hitachi High Tech Co., Ltd.). Science, K-YSSC000E031, volume 15 μL) was sealed and sealed. After that, the glass transition temperature T90 (° C.) was measured by DSC (differential scanning calorimetry) under the following conditions.
Heating program: Start at 0°C, heat up to 100°C at a rate of 3°C per minute

Table 5 shows the measurement results of T10 and T90, and the value obtained by subtracting T90 from T10 (T10-T90).

(7) Degree of swelling of the thermoplastic polymer with respect to the electrolytic solution (times)
A thermoplastic polymer or a latex containing it (a mixture of a plurality of thermoplastic polymers, or a latex containing the same may be used) is allowed to stand in an oven at 80°C for 9 hours, and then vacuum-dried at 80°C for 12 hours. was performed to obtain a dried polymer. About 0.5 g of the dried product was weighed and used as the weight before immersion (W _A ). This dried product is placed in a 50 mL vial bottle with 10 g of a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC) = 2: 3 (volume ratio) at 25 ° C. and immersed for 24 hours. Immediately after wiping off with paper, the mass was measured and taken as the mass after immersion (W _B ).
The electrolytic solution swelling degree of the thermoplastic polymer was calculated from the following formula.
Degree of swelling (times) = W _B /W _A
In the above formula, when the polymer sample neither swells nor dissolves in the mixed solvent, the degree of swelling is 1-fold.

(8) Viscosity average molecular weight Mv
The intrinsic viscosity [η] at 135°C in decalin solvent was determined according to ASTM-D4020. Using this [η] value, the viscosity-average molecular weight Mv was calculated from the following formula.
For polyethylene: [η] = 0.00068 x Mv ^0.67
For polypropylene: [η] = 1.10 × 10 ^-4 × Mv ^0.80

(9) Porosity (%)
A 10 cm×10 cm square sample was cut from the base material, and its volume (cm ³ ) and mass (g) were determined. Using these values and setting the density of the substrate to 0.95 (g/cm ³ ), the porosity was obtained from the following formula.
Porosity (%) = (1-mass/volume/0.95) x 100

(10) Air permeability (sec/100 cm ³ )
Regarding the base material, the laminate of the base material and the inorganic filler porous layer, or the separator, in accordance with JIS P-8117, Gurley type air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd. The air permeation resistance measured by was taken as the air permeability. When the thermoplastic polymer-containing layer is present only on one side of the substrate, the needle can be pierced from the side where the thermoplastic polymer-containing layer is present.

(11) puncture strength (gf/20 μm, or g/20 μm)
Using a handy compression tester KES-G5 (model name) manufactured by Kato Tech Co., Ltd., the substrate or separator was fixed with a sample holder having an opening with a diameter of 11.3 mm. Next, using a needle with a tip radius of curvature of 0.5 mm, a puncture test was performed in an atmosphere of 25° C. at a puncture speed of 2 mm/sec against the central portion of the fixed base material or separator. The puncture load was measured. A value obtained by converting the maximum puncture load per 20 μm thickness was taken as puncture strength (gf/20 μm or g/20 μm). If the thermoplastic polymer is present on only one side of the substrate, the needle can be pierced through the side on which the thermoplastic polymer is present.

(12) Average particle size D50 (μm) of inorganic filler
The average particle size of the inorganic filler was measured together with the particle size distribution using a particle size measuring device (manufactured by Nikkiso Co., Ltd., product name: "Microtrac UPA150"). The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds.

(13) Thickness of inorganic filler porous layer (μm)
The difference between the thickness of the substrate obtained by the method described in the "thickness of the substrate" column above and the thickness of the multilayer porous membrane obtained by the method described in the "thickness of the multilayer porous membrane" column described later is Calculated.

(14) Thickness (μm) of laminate (multilayer porous membrane) of substrate and inorganic filler porous layer
A multi-layer porous film was used as a measurement object, and the thickness was measured by the same method as described in the section "Thickness of base material".

(15) 130 ° C. heat shrinkage rate (%) of laminate (multilayer porous membrane) of base material and inorganic filler porous layer
A sample obtained by cutting the above laminate to 100 mm in the TD direction and 100 mm in the MD direction was allowed to stand in an oven at 130° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the warm air would not hit the sample directly. After the sample was taken out of the oven and cooled, its length (mm) was measured, and the thermal shrinkage rate of TD was calculated by the following formula.
TD heat shrinkage rate (%) = 100 - length in TD after heating (mm)

(16) Total thickness of separator (μm)
A separator was used as an object to be measured, and the thickness was measured by the same method as described in the "Thickness of base material" section above. The total thickness of the separator may be equal to the thickness of the substrate or multilayer porous membrane depending on the presence or absence of pattern coating or the inorganic filler porous layer.

(17) Covered area ratio of thermoplastic polymer-containing layer (%)
The coverage area ratio of the thermoplastic polymer-containing layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by HITACHI). Osmium was vapor-deposited on the separator sample, which was then observed under conditions of an acceleration voltage of 1.0 kV and a magnification of 50 times, and the surface coverage was calculated from the following formula. In addition, the area|region where the porous structure of the base-material surface was not visible by the SEM image was made into the thermoplastic polymer content layer area|region.
Covered area ratio (%) of thermoplastic polymer-containing layer = area of thermoplastic polymer-containing layer / (area including hole portion of substrate + area of thermoplastic polymer-containing layer) x 100
The coating area ratio in each sample was obtained by performing the above measurements three times and taking the arithmetic mean value.

(18) Peel strength B10 (N/m)
Two rectangular separator test pieces with a width of 20 mm and a length of 70 mm are cut from the separator, and the two cut separator test pieces are stored in a test box at a temperature of 35 ° C. and a relative humidity (RH) of 10% for 1 day. did. The following laminates were then made using the two stored separator specimens:
(AA) _RH10 : Laminate formed by laminating the surface (A) of one test piece and the surface (A) of another test piece;
(AB) _RH10 : A laminate formed by laminating the surface (A) of one test piece and the surface (B) opposite to the surface (A) of another test piece;
(BB) _RH10 : A laminate formed by laminating the surface (B) of one test piece opposite to the surface (A) and the surface (B) of another test piece.

Each laminate was pressed under the following conditions.
temperature 40°C
Press pressure: 1MPa
Press time: 2 minutes

For each of the laminated body (AA) _RH10 , the laminated body (AB) _RH10 , and the laminated body (BB) _RH10 after pressing, a force gauge ZP5N manufactured by Imada Co., Ltd. was used to measure the peeling speed. A 90° peel test was performed at 50 mm/min to measure the peel strength. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength. Next, among the peel strengths (N/m) individually measured for all laminates, the maximum value was adopted as B10 (N/m).

(19) Peel strength B90 (N/m)
Two rectangular separator test pieces with a width of 20 mm and a length of 70 mm are cut from the separator, and the two cut separator test pieces are stored in a test box at a temperature of 35 ° C. and a relative humidity (RH) of 90% for 1 day. did. The following laminates were then made using the two stored separator specimens:
(AA) _RH90 : A laminate formed by laminating the surface (A) of one test piece and the surface (A) of another test piece;
(AB) _RH90 : A laminate formed by laminating the surface (A) of one test piece and the surface (B) opposite to the surface (A) of another test piece;
(BB) _RH90 : A laminate formed by laminating the surface (B) of one test piece opposite to the surface (A) and the surface (B) of another test piece.

Each laminate was pressed under the following conditions.
Temperature: 40°C
Press pressure: 1 MPa
Press time: 2 minutes

For each of the laminated body (AA) _RH90 , the laminated body (AB) _RH90 , and the laminated body (BB) _RH90 after pressing, a force gauge ZP5N manufactured by Imada Co., Ltd. was used to measure the peeling speed. A 90° peel test was performed at 50 mm/min to measure the peel strength. At this time, the average peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength. Next, among the peel strengths (N/m) individually measured for all laminates, the maximum value was adopted as the peel strength B90 (N/m). Moreover, the ratio B90/B10 of B90 to the peel strength B10 laminated above was also calculated.

(20) Peel strength P10 (N/m)
Laminate (AA) _RH10 , Laminate (AB) _RH10 , and Laminate (BB) prepared using two separator test pieces for measurement of peel strength B10 (N / m) ) For _RH10 , each laminate was prepared before being pressed for measurement of peel strength B10 (N/m).

Next, each laminate was pressed under the following conditions.
Temperature: 90°C
Press pressure: 1 MPa
Press time: 5 seconds

For each of the laminated body (AA) _RH10 , the laminated body (AB) _RH10 , and the laminated body (BB) _RH10 after pressing, the peel speed was measured using a force gauge ZP5N manufactured by Imada Co., Ltd. A 90° peel test was performed at 50 mm/min to measure the peel strength. At this time, the average peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength. Next, among the peel strengths individually measured for all laminates, the maximum value was adopted as the peel strength P10 (N/m).

(21) Blocking resistance (positional deviation amount when separator is fed out)
A rectangular separator having a width of 30 mm and a length of 2000 m was wound to form a wound body. The formed wound body was stably stored at 35° C. for 30 days. The wound body after storage is installed in an automatic winding device, and the length of the separator that can be drawn out uniformly and without wrinkles is measured within 20 m from the inner layer of the wound body, and the blocking resistance is evaluated based on the following evaluation criteria. The properties (indicated in the table as "the amount of positional deviation during feeding out the separator") were evaluated.
Evaluation criteria for blocking resistance ○ (extremely good): The length of the separator that can be drawn out uniformly and without wrinkles is more than 1 m △ (Good): The length of the separator that can be drawn out uniformly and without wrinkles is more than 95 cm and 1 m or less × (Poor): The length of the separator that can be pulled out evenly and without wrinkles is 95m or less.

(22) Adhesion to Electrode Substrate, multilayer porous film, or separator, and positive electrode as adherend (manufactured by enertech, positive electrode material: LiCoO ₂ , conductive aid: acetylene black, binder: PVdF, LiCoO ₂ / Acetylene black/PVdF (mass ratio) = 95/2/3, L/W: 36 mg/cm ² on both sides, density: 3.9 g/cm ³ , thickness of Al current collector: 15 µm, thickness of positive electrode after pressing : 107 μm) was cut into a rectangular shape with a width of 15 mm and a length of 60 mm, and the thermoplastic polymer layer of the separator and the positive electrode active material were laminated so as to face each other to obtain a laminate. Pressed under the following conditions. The room temperature during the evaluation was 23° C. and the humidity was 30%.
Press pressure: 1MPa
Temperature: 100°C
Press time: 5 seconds

For the laminate after pressing, the electrodes are fixed using force gauge ZP-5N and MX2-500N (product name) manufactured by Imada Co., Ltd., and the substrate, multilayer porous membrane, or separator is gripped and pulled. Depending on the method, a 90° peel test was performed at a peel speed of 50 mm/min to measure the peel strength. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength, and the adhesion to the electrode was evaluated according to the following criteria.
○ (Good): The peel strength is 5 N/m or more.
Δ (somewhat poor): The peel strength is 3 N/m or more and less than 5 N/m.
x (defective): The peel strength is less than 3 N/m.

Regarding the above "adhesion to the electrode" test, Table 1 shows the test results when the substrate was used instead of the above separator, and Table 2 shows the results of the multilayer instead of the above separator. Test results when using a porous membrane are shown. As can be seen from Tables 1 and 2, the polyolefin microporous membrane or multi-layer porous membrane alone, ie without the thermoplastic polymer layer, does not exhibit significant adhesion to the electrode.

(23) Powder fall-off property A 10 cm x 10 cm square sample was cut from the power storage device separator, and the mass (g) was weighed. After fixing one side to the cardboard, the inorganic filler porous layer side (however, if there is no inorganic filler porous layer, either the substrate exposed side or the thermoplastic polymer containing layer side is fine) with a cotton cloth. A weight of 900 g with a diameter of 5 cm covered was put on and these were rubbed against each other for 10 minutes at a rotation speed of 50 rpm. After that, the mass (g) was accurately measured again, and the powder removal property was measured by the following formula.
Powder removal (mass%) = {(mass before rubbing (g) - mass after rubbing (g)) / mass before rubbing} x 100
Next, the powder removal property was ranked according to the following evaluation criteria.
◯ (Good) Powder removal property is less than 2%.
(triangle|delta) (acceptable) powder falling property is 2% or more and less than 10%.
× (Poor) The powder falling property exceeds 10%.

(24) Rate Characteristics a. Preparation of positive electrode Nickel, manganese, cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (element ratio), density: 4.70 g/cm ³ ) was used as a positive electrode active material in an amount of 90.4% by mass, Graphite powder (KS6) (density: 2.26 g/cm ³ , number average particle size: 6.5 µm) was used as a conductive additive in an amount of 1.6% by mass, and acetylene black powder (AB) (density: 1.95 g/cm ³ , number 3.8% by mass of average particle diameter 48 nm) and 4.2% by mass of polyvinylidene fluoride (PVdF) (density 1.75 g/cm ³ ) as a binder, and N-methylpyrrolidone (NMP ) to prepare a slurry. This slurry is applied to one side of an aluminum foil having a thickness of 20 μm as a positive electrode current collector using a die coater, dried at 130° C. for 3 minutes, and then compression-molded using a roll press to form a positive electrode. made. The amount of the positive electrode active material applied at this time was 109 g/m ² .

b. Preparation of Negative Electrode Graphite powder A (density: 2.23 g/cm ³ , number average particle size: 12.7 μm) was used as the negative electrode active material in an amount of 87.6% by mass, and graphite powder B (density: 2.27 g/cm ³ , number average particle size: 87.6% by mass). diameter 6.5 μm), 1.4% by mass of ammonium salt of carboxymethyl cellulose as a binder (in terms of solid content) (solid content concentration 1.83% by mass aqueous solution), and 1.7 mass% of diene rubber latex % (in terms of solid content) (aqueous solution with a solid content concentration of 40% by mass) was dispersed in purified water to prepare a slurry. This slurry was applied to one side of a copper foil having a thickness of 12 μm as a negative electrode current collector with a die coater, dried at 120° C. for 3 minutes, and then compression-molded with a roll press to prepare a negative electrode. At this time, the coating amount of the negative electrode active material was 5.2 g/m ² .

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

d. Battery Assembly A separator, a base material, or a multilayer porous film was cut into a circular shape of 24 mmφ, and a positive electrode and a negative electrode were each cut into a circular shape of 16 mmφ. Negative electrode--separator or base material or multi-layer porous film--positive electrode were stacked in this order so that the active material surfaces of the positive electrode and the negative electrode faced each other, and placed in a lidded stainless steel container. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode. A battery was assembled by injecting 0.4 ml of the non-aqueous electrolyte into the container and sealing the container.

e. Evaluation of rate characteristics d. After charging the simple battery assembled in 25 ° C. with a current value of 3 mA (about 0.5 C) to a battery voltage of 4.2 V, the current value is reduced from 3 mA while maintaining 4.2 V. , the first charge after battery preparation was performed for a total of about 6 hours. After that, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., after charging to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), the current value was reduced from 6 mA while maintaining 4.2 V. Time charging. After that, the discharge capacity when the battery was discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as a 1C discharge capacity (mAh).
Next, at 25 ° C., after charging to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), the current value was reduced from 6 mA while maintaining 4.2 V. Time charging. After that, the discharge capacity when the battery was discharged to a battery voltage of 3.0 V at a current value of 12 mA (approximately 2.0 C) was defined as a 2C 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 characteristics (%) = (2C discharge capacity/1C discharge capacity) x 100

Evaluation Criteria for Rate Characteristics (%) ⊚ (remarkably good): Rate characteristics are 95% or more.
◯ (Good): The rate characteristic is 85% or more and less than 95%.
Δ (Acceptable): The rate characteristic is 80% or more and less than 85%.
x (defective): Rate characteristics are less than 80%.

(25) Cycle characteristics Cycle characteristics were also evaluated using the simple batteries assembled as in items a to d of the above “rate characteristics”.
After charging the above battery with a constant current of 1/3 C to a voltage of 4.2 V, the battery was charged with a constant voltage of 4.2 V for 8 hours, and then discharged at a current of 1/3 C to a final voltage of 3.0 V. did Next, after constant-current charging to a voltage of 4.2V at a current value of 1C, constant-voltage charging at 4.2V was performed for 3 hours, and then discharging was performed to a final voltage of 3.0V at a current of 1C. Finally, after constant-current charging to 4.2 V at a current value of 1 C, constant-voltage charging at 4.2 V was performed for 3 hours as pretreatment. Note that 1C represents the current value for discharging the standard capacity of the battery in one hour.
The pretreated battery was discharged at a discharge current of 1 A to a discharge cut-off voltage of 3 V at a temperature of 25° C., and then charged at a charge current of 1 A to a charge cut-off voltage of 4.2 V. This cycle was defined as one cycle, and charging and discharging were repeated. Then, using the capacity retention after 200 cycles with respect to the initial capacity (capacity in the first cycle), the cycle characteristics were evaluated according to the following criteria.
<Evaluation Criteria for Cycle Characteristics>
◎ (extremely good): capacity retention rate of 90% or more and 100% or less ○ (good): capacity retention rate of 85% or more and less than 90% △ (acceptable): capacity retention rate of 80% or more and less than 85% × (defective) : capacity retention rate less than 80%

[Production Example 1] (Production of polyolefin microporous membrane B1)
45 parts by mass of homopolymer high-density polyethylene with Mv of 700,000, 45 parts by mass of homopolymer high-density polyethylene with Mv of 300,000, and homopolymer polypropylene with Mv of 400,000 and Mv of 15 10 parts by mass of a mixture of a homopolymer of 10,000 and polypropylene (mass ratio=4:3) was dry blended using a tumbler blender. 1 part by mass of tetrakis-[methylene-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane as an antioxidant was added to 99 parts by mass of the resulting polyolefin mixture, and the mixture was again tumble blended. A mixture was obtained by dry blending using The resulting mixture was fed through a feeder to a twin-screw extruder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78° C. 7.59×10 ⁻⁵ m ² /s) was also injected into the extruder cylinder by means of a plunger pump. The operating conditions of the feeder and the pump were adjusted so that the proportion of liquid paraffin in 100 parts by mass of the total mixture to be extruded was 65 parts by mass, that is, the proportion of the resin composition was 35 parts by mass.

Then, they are melt-kneaded while being heated to 230°C in a twin-screw extruder, 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 extrudate is obtained. A sheet-like molded product was obtained by contacting with a cooling roll, molding (casting), and solidifying by cooling. This sheet was stretched by a simultaneous biaxial stretching machine at a magnification of 7×6.4 at a temperature of 112° C., then immersed in methylene chloride to remove liquid paraffin by extraction, dried, and then stretched by a tenter stretching machine at a temperature of 130° C. °C, and stretched twice in the transverse direction. After that, the stretched sheet was relaxed about 10% in the width direction and heat-treated to obtain a polyolefin microporous membrane B1 as a base material.

The physical properties of the obtained polyolefin microporous membrane B1 were measured by the methods described above. The obtained polyolefin microporous membrane was used as a separator as it was and evaluated by the above method. Table 1 shows the results obtained. In addition, when using the base material B1, the base material B1 was subjected to corona treatment for the purpose of adjusting the surface tension.

[Production Example 2] (Production of polyolefin microporous membrane B2)
A Celgard separator H1609 (model name) was used as the polyolefin microporous membrane B2 and evaluated in the same manner as in Production Example 1. Table 1 shows the results obtained.

[Production Example 1-1] (Formation of multilayer porous membrane B1-1)
An acrylic latex used as a resin binder for the inorganic particle layer was produced by the following method. 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as an emulsifier were added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank and thermometer. 0.5 part by mass and 0.5 part by mass of "ADEKARI SOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added. Next, the temperature inside the reaction vessel was raised to 80° C., and while maintaining the temperature at 80° C., 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. Five minutes after the completion of the addition of the aqueous ammonium persulfate solution, the emulsified liquid was dropped from the dropping tank into the reaction vessel over 150 minutes. The above emulsion contains 70 parts by mass of butyl acrylate, 29 parts by mass of methyl methacrylate, 1 part by mass of methacrylic acid, and "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier. A mixture of 3 parts by mass, 3 parts by mass of "ADEKARI SOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation), 7.5 parts by mass of 2% aqueous solution of ammonium persulfate, and 52 parts by mass of ion-exchanged water was prepared. was prepared by mixing for 5 minutes with a homomixer. After the dropwise addition of the emulsified liquid was completed, the temperature inside the reaction vessel was maintained at 80° C. for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH=8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex having a solid content of 40%. The obtained acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -23°C.

95 parts by mass of aluminum hydroxide oxide (block-shaped, average particle size 1.4 μm) as an inorganic filler, and 0.4 parts by mass (in terms of solid content) of an aqueous ammonium polycarboxylate solution (manufactured by San Nopco Co., Ltd.) as an ionic dispersant. SN Dispersant 5468, solid concentration 40%) was uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion is pulverized with a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles is adjusted to D50 = 0.7 μm. A particle-containing slurry was prepared. 2.0 parts by mass (in terms of solid content) of the acrylic latex produced above as the resin binder was added to the dispersion liquid with the adjusted particle size distribution to obtain an inorganic particle-containing slurry. Substrate B1 was continuously fed out from the mother roll, and the inorganic particle-containing slurry was coated on one side of substrate B1 with a gravure reverse coater. The coated base material was dried in a drier at 60° C. to remove water, thereby obtaining a multilayer porous membrane B1-1 having an inorganic filler porous layer on one side of the base material B1. This was wound up to obtain a mother roll. The aluminum hydroxide oxide contained in the inorganic filler porous layer was 95% by mass, and the thickness of the inorganic filler porous layer was 4.0 μm per side. According to the method described above, the physical properties of the multilayer porous membrane B1-1 were measured and evaluated, and the results are shown in Table 2.

[Production Example 1-2] (Formation of multilayer porous membrane B1-2)
A multilayer porous membrane B1-2 was formed in the same manner as in Production Example 1-1, except that the inorganic filler material was changed as shown in Table 2. Table 2 shows the measurement and evaluation results of the multilayer porous membrane B1-2.

[Production Example 1-3] (Formation of multilayer porous membrane B1-3)
A multilayer porous membrane B1-3 was formed in the same manner as in Production Example 1-1, except that the shape of the inorganic filler and the average particle diameter D50 were changed as shown in Table 2. Table 2 shows the measurement and evaluation results of the multilayer porous membrane B1-3.

<Synthesis of Particulate Polymer>

(Production Example A1) Aqueous Dispersion (referred to as “raw polymer” in the table, the same shall apply hereinafter) Synthesis of A1 70.4 parts by mass, "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., indicated as "KH1025" in the table. The same applies hereinafter.) 0.5 parts by mass, and "Adekari Soap SR1025 (registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution, abbreviated as "SR1025" in the table. The same shall apply hereinafter.) 0.5 parts by mass were added, and the internal temperature of the reaction vessel was raised to 80°C. After that, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (indicated as “APS (aq)” in the table, the same shall apply hereinafter) was added while maintaining the container internal temperature of 80°C.

On the other hand, 38.5 parts by weight of methyl methacrylate, 19.6 parts by weight of n-butyl acrylate, 31.9 parts by weight of 2-ethylhexyl acrylate, 0.1 parts by weight of methacrylic acid, 0.1 parts by weight of acrylic acid, methacrylic 2 parts by weight of 2-hydroxyethyl acid, 5 parts by weight of acrylamide, GMA: 2.8 parts by weight of glycidyl methacrylate, 0.7 parts by weight of trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.), γ-methacryloxypropyl 0.3 parts by weight of trimethoxysilane, 3 parts by weight of "Aqualon KH1025", 3 parts by weight of "Adekari Soap SR1025", 0.05 parts by weight of sodium p-styrenesulfonate, 7.5 parts by weight of ammonium persulfate (2% aqueous solution) and 52 parts by mass of ion-exchanged water were mixed for 5 minutes with a homomixer to prepare an emulsified liquid.

The obtained emulsified liquid was dropped from the dropping tank into the reaction vessel. Dropping was started 5 minutes after the aqueous ammonium persulfate solution was added to the reaction vessel, and the entire amount of the emulsified liquid was dropped over 150 minutes. The internal temperature of the container was maintained at 80° C. during the dropwise addition of the emulsified liquid.

After the dropwise addition of the emulsified liquid was completed, 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. The obtained emulsion was adjusted to pH=9.0 using an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain a copolymer latex having a concentration of 40% by mass (raw material polymer A1). The obtained raw material polymer (aqueous dispersion) A1 was evaluated by the above method. Table 3 shows the results obtained.

(Production Examples A2 to A12) Synthesis of water dispersions A2 to A12 Except for changing the composition of the monomer and other raw materials as shown in Table 3 or Table 4, the raw material polymer (water dispersion Body) Copolymer latexes (raw material polymers A2 to A12) were obtained in the same manner as in the synthesis of A1. The obtained raw material polymers (aqueous dispersions) A2 to A12 were each evaluated by the above method. The results obtained are shown in Table 3 or Table 4.

The abbreviations of raw material names in Tables 3 and 4 have the following meanings.
<Emulsifier>
KH1025: "Aqualon KH1025" registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "Adekari Soap SR1025" registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution NaSS: sodium p-styrene sulfonate <initiator ＞
APS: ammonium persulfate (2% aqueous solution)
<monomer>
((meth)acrylic acid monomer)
MAA: methacrylic acid AA: acrylic acid ((meth)acrylic acid ester)
MMA: methyl methacrylate BA: n-butyl acrylate EHA: 2-ethylhexyl acrylate CHMA: cyclohexyl methacrylate (aromatic vinyl compound monomer)
St: styrene (nitrile group-containing monomer)
AN: acrylonitrile (other functional group-containing monomers)
HEMA: 2-hydroxyethyl methacrylate AM: acrylamide (crosslinking monomer)
GMA: glycidyl methacrylate A-TMPT: trimethylolpropane triacrylate AcSi: γ-methacryloxypropyltrimethoxysilane

<Example 1>
Aqueous Dispersion A1 with a solid content of 10 parts by mass and Aqueous Dispersion A2 with a solid content of 90 parts by mass were uniformly dispersed in water to prepare a thermoplastic polymer-containing coating liquid (solid content: 5 mass %). At this time, polyoxyethylene alkyl ether, which is a polyether-based surfactant, was added as a surfactant so as to be 0.005% by mass with respect to the coating liquid. moreover. Carboxymethyl cellulose was added as a thickener to the coating liquid so as to be 1% by mass, and the viscosity of the coating liquid was adjusted to 30 mPa·s.

Thereafter, using a gravure coater, the coating solution was applied to both surfaces of the multilayer porous membrane B1-1 with a thermoplastic polymer coating amount of 0.15 g/m ² . At this time, the coating area ratio of one surface of the polyolefin porous substrate B1 with the thermoplastic polymer was 20%, and the coating shape was dot-like. After that, the coating liquid after coating is dried at 40 ° C. to remove water, and the polyolefin porous substrate B1 has an inorganic filler porous layer and a thermoplastic polymer layer thereon on one side, and B1 on the other side. A separator having a thermoplastic polymer layer was obtained.

<Examples 2 to 21>
As shown in Table 5, the composition of the thermoplastic polymer-containing coating liquid, the conditions for forming the thermoplastic polymer-containing layer, the multilayer porous film, the physical properties of the separator, etc. were changed in the same manner as in Example 1. manufactured. In Example 7, the entire surface of the multilayer porous membrane B1-1 was coated with the thermoplastic polymer-containing coating liquid so that 50% of the surface of the multilayer porous membrane B1-1 opposite to the inorganic filler porous layer was covered with the thermoplastic polymer-containing layer. Therefore, the coating shape in Table 5 is indicated as "uniform dispersion". Moreover, in Examples 18 and 19, the thermoplastic polymer-containing coating liquid was applied to both surfaces of the polyolefin porous substrates B1 and B2 without using the multi-layer porous membrane.

<Comparative Examples 1 to 3, Examples 22 to 25>
As shown in Table 5, the composition of the thermoplastic polymer-containing coating liquid, the conditions for forming the thermoplastic polymer-containing layer, the multilayer porous film, the physical properties of the separator, etc. were changed in the same manner as in Example 1. manufactured. In Example 23, the thermoplastic polymer-containing coating liquid was applied solidly so that 50% of the surface of the multilayer porous membrane B1-1 opposite to the inorganic filler porous layer was covered with the thermoplastic polymer-containing layer. Therefore, the coating shape in Table 5 is indicated as "uniform dispersion".

The thermoplastic polymer-containing coating liquids, thermoplastic polymer-containing layers, separators, and batteries formed in Examples and Comparative Examples were evaluated by the methods described above. Table 5 shows the evaluation results.

Claims (11)

An electricity storage device separator comprising a substrate and a thermoplastic polymer-containing layer formed on at least one substrate surface of the substrate and containing a thermoplastic polymer, wherein the electricity storage device separator has the following formula: :
B90/B10<7
{Wherein, B90 and B10 are defined as follows:
Two sheets of the electricity storage device separator are prepared and stored for one day in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 90%, and then one surface (A) and the surface ( A) a laminate (AA) _RH90 formed by laminating each other, a laminate (AB) _RH90 formed by laminating the surface (A) and the opposite surface (B), and the above A laminate (BB) _RH90 formed by laminating the surfaces (B) was produced, and each laminate was pressed for 2 minutes at a temperature of 40 ° C. and a pressure of 1 MPa. Of the individually measured peel strengths (N / m), the maximum value is B90;
Further, after preparing two sheets of the electricity storage device separator and storing them for one day in an environment with a temperature of 35° C. and a relative humidity (RH) of 10%, one surface (A) of the electricity storage device separator and the A laminate (AA) _RH10 formed by laminating surfaces (A) together, a laminate (AB) _RH10 formed by laminating the surface (A) and the opposite surface (B), And a laminate (BB) _RH10 formed by laminating the surfaces (B) was produced, and each laminate was pressed for 2 minutes at a temperature of 40 ° C. and a pressure of 1 MPa. Of the peel strengths (N / m) measured individually for the laminate, the maximum value is B10}
A separator for an electricity storage device that satisfies the relationship represented by: The power storage device separator has the following configuration:
(1) the substrate and the thermoplastic polymer-containing layer formed on one side of the substrate;
(2) the substrate and the thermoplastic polymer-containing layers formed on both sides of the substrate;
(3) the substrate, an inorganic coating layer formed on one side of the substrate, and the thermoplastic polymer-containing layer formed on the other side of the substrate; and (4) the substrate, the substrate The inorganic coating layer formed on one side of the material, the thermoplastic polymer-containing layer formed on the side of the inorganic coating layer opposite to the substrate, and the other side of the substrate the thermoplastic polymer-containing layer;
The power storage device separator according to claim 1, comprising at least one of The electricity storage device separator according to claim 1 or 2, wherein said B90 is less than 10 N/m. A power storage device separator comprising a substrate and a thermoplastic polymer-containing layer formed on at least a portion of at least one side of the substrate and containing a thermoplastic polymer, wherein the thermoplastic polymer has the following formula:
T10-T90<10
{wherein T90 and T10 are defined as follows:
After storing the thermoplastic polymer in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 90% for 1 day, the thermoplastic polymer was sealed in an aluminum closed pan and measured by DSC (differential scanning calorimetry). The glass transition temperature (° C.) is T90,
In addition, after storing the thermoplastic polymer in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 10% for 1 day, the thermoplastic polymer was sealed in an aluminum sealed pan, and the glass transition temperature measured by DSC (°C) is T10}
A separator for an electricity storage device that satisfies the relationship represented by: The power storage device separator according to claim 4, wherein the T90 is 30°C or higher. The separator for the electricity storage device was subjected to the following conditions:
{Conditions: The measured value P10 is defined as follows:
Two sheets of the electricity storage device separator are prepared, and the electricity storage device separator is stored for one day in an environment with a temperature of 35 ° C. and a relative humidity (RH) of 10%, and then one surface of the electricity storage device separator ( A) and the laminate (A-A) _RH10 formed by laminating the surface (A) and the laminate (A-A) formed by laminating the surface (A) and the opposite surface (B) B) When _RH10 and a laminate (BB) _RH10 formed by laminating the surfaces (B) are produced, and each laminate is pressed for 5 seconds at a temperature of 90 ° C. and a pressure of 1 MPa. In addition, among the peel strengths measured individually for all laminates, the maximum value is P10 (N / m)}
The power storage device separator according to any one of claims 1 to 5, wherein the measured value P10 measured at is 5 N/m or more. Any one of claims 1 to 6, wherein the thermoplastic polymer has a mass swelling degree of 2 times or more and less than 7 times with respect to the electrolytic solution (ethylene carbonate (EC) / diethyl carbonate (DEC) volume ratio = 2/3). 2. The electricity storage device separator according to item 1. The power storage device separator according to any one of claims 1 to 7, wherein the thermoplastic polymer has a coverage area ratio of 5% or more and 70% or less with respect to the base material. The electricity storage device separator according to any one of claims 1 to 8, wherein the thermoplastic polymer comprises a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer. the thermoplastic polymer has at least two glass transition temperatures;
Any one of claims 1 to 9, wherein at least one of the glass transition temperatures is in the region below 20°C, and at least one of the glass transition temperatures is in the region of 20°C or higher. The separator for an electricity storage device according to Item 1. The thermoplastic polymer is a water-insoluble particulate thermoplastic polymer and contains a copolymer having an aromatic vinyl compound monomer and a nitrile group-containing monomer as monomer units, and the water-insoluble particles The ratio of the aromatic vinyl compound monomer and the nitrile group-containing monomer in the thermoplastic polymer is 10% by mass or more, respectively, for an electricity storage device according to any one of claims 1 to 10 separator.