JP6580234B1 - Power storage device separator, wound body using the same, lithium ion secondary battery, and power storage device - Google Patents

Abstract

An object of the present invention is to provide a separator for an electricity storage device and the like capable of achieving both blocking resistance and adhesion to an electrode. A separator for an electricity storage device comprising a substrate and a thermoplastic polymer-containing layer formed on at least one surface of the substrate, wherein P1 / P2 ≧ 0.5 {wherein P1 is One surface (A) of the separator for an electricity storage device and a surface (B) opposite to the surface (A) are overlapped to form a wound body, and the wound body is subjected to conditions of a temperature of 90 ° C. and a pressure of 1 MPa. P2 is the peel strength between the face (A) and the face (B) when pressed for 5 seconds at the bottom, and P2 is pressed for 12 hours under conditions of a temperature of 25 ° C. and a pressure of 5 MPa. The peel strength between the surface (A) and the surface (B). } And P1 is 5 N / m or more. [Selection figure] None

Description

  The present invention relates to a separator for an electricity storage device, a wound body using the separator, a lithium ion secondary battery, and an electricity storage device.

  Conventionally, development of an electricity storage device represented by a lithium ion secondary battery has been actively conducted. Usually, a power storage device is provided with a microporous membrane (separator) between a positive electrode and a negative electrode. The separator has a function of preventing direct contact between the positive electrode and the negative electrode and allowing ions to permeate through the electrolytic solution held in the micropore.

The separator has a characteristic to quickly stop the battery reaction when it is abnormally heated (fuse characteristic), and maintains the shape even at high temperatures to prevent a dangerous situation where the positive and negative electrodes react directly (short characteristic) Therefore, safety-related performance is required.
In addition, for the purpose of increasing the capacity of the electricity storage device, a technique of reducing the volume of the wound body by hot pressing the wound body in which the laminated body of the electrode and the separator is wound is used. . In order to maintain the volume at the time of pressing by fixing the electrode and the separator after pressing, a thermoplastic polymer-containing layer that exhibits an adhesive function under a predetermined condition is disposed on the separator so that the adhesive property to the separator and the electrode Technology to improve is also used.

  Here, for example, Patent Document 1 discloses a separator that is intended to provide a separator that is excellent in adhesion to an electrode and that is also excellent in handling properties. Such a separator includes a thermoplastic polymer-containing layer in which a portion containing a thermoplastic polymer and a portion not containing a thermoplastic polymer are present in a sea-island shape on a polyolefin microporous film as a substrate. The thermoplastic polymer has at least two glass transition temperatures. At least one of the glass transition temperatures is present in a region below 20 ° C., and at least one of the glass transition temperatures is present in a region above 20 ° C.

  Patent Document 2 discloses a lithium ion secondary battery for the purpose of improving mechanical characteristics and electrical characteristics. Such a lithium ion secondary battery includes a predetermined adhesive layer between at least one of the positive electrode and the separator and between the negative electrode and the separator.

International Publication No. 2014/017651 Japanese Patent Laying-Open No. 2015-041603

  In recent years, with regard to a separator having a thermoplastic polymer-containing layer on at least one surface of a base material, a wound body formed by overlapping the separator and an electrode tends to have a long winding from the viewpoint of improving production efficiency. The longer the wound body, the longer the length of each of the separator and the electrode, and the higher the pressure applied to the inner layer of the wound body. Due to such pressure, “blocking” in which separators adhere to each other in a stage before producing a wound body, for example, a normal storage stage in which a wound body in which only the separator is wound is stored. Is expected to occur. In such a case, when the separator is fed out from a wound body in which only the separator is wound, a stress corresponding to the blocking between the separators is required, and it becomes difficult to feed out a separator having a desired length uniformly without wrinkles. .

  In addition, due to the increase in environmental orientation, power storage devices such as electric vehicles (EV) have attracted more attention in recent years, and high capacity is particularly expected for lithium ion secondary batteries mounted on such power storage devices. Yes. In order to increase the capacity, it is necessary to improve the adhesion between the separator and the electrode in the lithium ion secondary battery, thereby suitably suppressing the press back of the wound body.

However, it is easy to prevent adhesion between separators in the normal storage stage, that is, to improve blocking resistance, and to easily suppress press back of the wound body during pressing, that is, to the separator and the electrode. There is a so-called trade-off tendency to improve the adhesion.
In the above situation, Patent Documents 1 and 2 have not studied how to achieve both blocking resistance and adhesion to electrodes.

  The present invention has been made in view of the above circumstances, and is capable of achieving both blocking resistance and adhesion to an electrode, a separator for an electricity storage device, and a wound body using the same, lithium ion An object is to provide a secondary battery and an electricity storage device.

The present inventors have studied to solve the above-mentioned problems, and found that the above-mentioned problems can be solved by using a power storage device separator having the following configuration, and have 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 surface of the substrate, wherein the electricity storage device separator is represented by the following formula:
P1 / P2 ≧ 0.5
{Wherein P1 forms a wound body by overlapping one surface (A) of the electricity storage device separator and a surface (B) opposite to the surface (A), and the wound body Is the peel strength between the surface (A) and the surface (B) when pressed for 5 seconds under the conditions of a temperature of 90 ° C. and a pressure of 1 MPa, and P2 is a temperature of 25 ° C. for the wound body. And the peel strength between the surface (A) and the surface (B) when pressed for 12 hours under a pressure of 5 MPa. }
The separator for electrical storage devices which satisfy | fills the relationship represented by these, and said P1 is 5 N / m or more.
[2]
The separator for an electricity storage device according to [1], wherein the P2 is 15 N / m or less.
[3]
The electricity storage device separator according to [1] or [2], wherein the P1 / P2 is 2.5 or less.
[4]
[1] to [3] The storage device separator according to any one of [1] to [3], wherein a contact angle of water with respect to the surface on which the thermoplastic polymer-containing layer of the storage device separator is formed is 95 ° or less. .
[5]
The separator for an electricity storage device according to any one of [1] to [4], wherein a covering area ratio of the thermoplastic polymer-containing layer to the base material is 50% or less.
[6]
The electrical storage device according to any one of [1] to [5], wherein the thermoplastic polymer contained in the thermoplastic polymer-containing layer includes a polymerization unit of (meth) acrylic acid ester or (meth) acrylic acid. Separator.
[7]
The separator for an electricity storage device according to any one of [1] to [6], wherein a glass transition temperature of the thermoplastic polymer contained in the thermoplastic polymer-containing layer is 40 ° C. or higher.
[8]
The separator for an electricity storage device according to any one of [1] to [7], wherein the thermoplastic polymer-containing layer includes two or more types of thermoplastic polymers having different glass transition temperatures.
[9]
The electrical storage device separator according to any one of [1] to [8], wherein the thermoplastic polymer-containing layer includes a polyether surfactant.
[10]
The electrical storage device separator according to any one of [1] to [9], wherein the electrical storage device separator is wound.
[11]
An electricity storage device comprising the separator for an electricity storage device according to any one of [1] to [10].
[12]
[1] to [10] A lithium ion secondary battery including the separator for an electricity storage device according to any one of items.

  According to the present invention, there are provided a separator for an electricity storage device, a wound body using the same, a lithium ion secondary battery, and an electricity storage device capable of achieving both blocking resistance and adhesion to an electrode. be able to.

Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to the following embodiment. The present invention can be variously modified without departing from the gist thereof.
In the present specification, “(meth) acryl” means “acryl” and “methacryl” corresponding thereto, and “(meth) acrylate” means “acrylate” and “methacrylate” corresponding thereto. The term “(meth) acryloyl” means “acryloyl” and the corresponding “methacryloyl”.
In addition, “upper” and “formed on a surface” in this specification do not limit that the positional relationship of each member is “directly above”. For example, the expressions “a thermoplastic polymer-containing layer formed on a substrate” and “a thermoplastic polymer-containing layer formed on the surface of a substrate” are expressed between the substrate and the thermoplastic polymer-containing layer, An embodiment including an arbitrary layer (a layer having a heat resistance function, such as an inorganic filler porous layer) is not excluded.
Furthermore, “to” in the present specification means to include numerical values described before and after the upper and lower limits unless otherwise specified.

<Separator for electricity storage device>
The separator for an electricity storage device of the present embodiment (hereinafter also simply referred to as “separator”) includes a base material and a thermoplastic polymer-containing layer formed on at least one surface of the base material. Both the aspect in which the thermoplastic polymer-containing layer is formed only on one side of the separator and the aspect in which the thermoplastic polymer-containing layer is formed on both sides of the separator are included in the scope of the present invention.

The separator has the following formula:
P1 / P2 ≧ 0.5
{In the formula, P1 forms a wound body by overlapping one surface (A) of the separator and the surface (B) opposite to the surface (A), and the wound body is heated to 90 ° C, And P2 is the peel strength between the face (A) and the face (B) when pressed for 5 seconds under a pressure of 1 MPa, and P2 is 12 under the conditions of a temperature of 25 ° C. and a pressure of 5 MPa. The peel strength between the surface (A) and the surface (B) when pressed for a period of time. } And P1 is 5 N / m or more.
By satisfying the above formula, the separator can achieve both blocking resistance and adhesion to the electrode.

If the thermoplastic polymer-containing layer is arranged between the surface (A) and the surface (B), the surface (A) and the surface (B) are overlapped without departing from the gist of the present invention. The form of the wound body to be formed is not limited. Accordingly, the scope of the present invention includes a form in which the thermoplastic polymer-containing layer overlaps the formed surface (A) and the non-formed surface (B), the formed surface (A) and the formed surface ( Both the form of overlapping B) and the form of overlapping the surface (A) not formed and the surface (B) formed are included.
Hereinafter, preferred embodiments of each member that can constitute the separator will be described in detail.

[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 having a fine pore size, which has no electron conductivity and ionic conductivity, and is highly resistant to organic solvents. As such a porous membrane, for example, a polyolefin-based resin (for example, polyethylene, polypropylene, polybutene, and polyvinyl chloride), a mixture thereof, or a resin such as a copolymer of monomers thereof is included as a main component. Microporous membrane: Microporous membrane containing resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene as main component; polyolefin fiber Woven fabric (woven fabric); polyolefin-based nonwoven fabric; paper; and aggregates of insulating substance particles. These are used singly or in combination of two or more.
Among these, a polyolefin microporous film containing a polyolefin-based resin as a main component is preferable from the viewpoint of further reducing the thickness of the separator to increase the active material ratio in the electricity storage device and thus increase the capacity per volume. The polyolefin microporous membrane is advantageous in reducing the thickness of the separator because it is excellent in the coating property of the coating solution when the coating solution is applied onto the membrane.
Note that “including a polyolefin-based resin as a main component” means that it contains more than 50 mass% with respect to the total mass of the base material. The content of the polyolefin resin is preferably 75% by mass or more, more preferably 85% by mass or more, further preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 98% by mass or more. 100 mass%.

  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 the components constituting the polyolefin microporous membrane is a polyolefin resin. The content of the polyolefin resin is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less, based on all components constituting the polyolefin microporous membrane.

  Although it does not specifically limit as polyolefin resin, The polyolefin resin which can be used for normal extrusion, injection, inflation, blow molding, etc. may be sufficient. Examples of the polyolefin resin include, for example, homopolymers having ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like as monomers, and two or more of these monomers. And a multi-stage polymer. These homopolymers, copolymers, and multistage polymers are used singly or in combination of two or more.

Representative examples of the polyolefin resin include, but are not particularly limited to, for example, polyethylene, polypropylene, and polybutene, and more specifically, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra-high Examples include molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and ethylene propylene rubber. These are used singly or in combination of two or more. As the polyolefin resin, polyethylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene is preferable from the viewpoint of shutdown characteristics in which pores are blocked by heat melting. In particular, since it has a low melting point and high strength, high-density polyethylene is preferable, and polyethylene having a density measured according to JIS K 7112 of 0.93 g / cm ³ or more is more preferable. There is no restriction | limiting in particular in the polymerization catalyst used at the time of manufacture of these polyethylenes, For example, a Ziegler-Natta catalyst, a Philips catalyst, and a metallocene catalyst are mentioned.

  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 three-dimensional structure of polypropylene is not limited, and any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene may be used. Examples of polyolefin resins other than polypropylene include homopolymers having monomers such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, and monomers thereof. Two or more kinds of copolymers and multi-stage polymers can be mentioned, and specific examples include those already described above. The polymerization catalyst used when producing polypropylene is not particularly limited, and examples thereof include a Ziegler-Natta catalyst and a metallocene catalyst.

The content ratio of polypropylene relative to the total amount of polyolefin in the polyolefin microporous membrane (polypropylene / polyolefin) is not particularly limited, but is preferably 1 to 35% by mass from the viewpoint of achieving both heat resistance and a good shutdown function, More preferably, it is 3-20 mass%, More preferably, it is 4-10 mass%. From the same viewpoint, the content ratio of olefin resin other than polypropylene, for example, polyethylene (olefin resin other than polypropylene / polyolefin) relative to the total amount of polyolefin in the polyolefin microporous membrane is preferably 65 to 99% by mass, more preferably. Is 80 to 97 mass%, more preferably 90 to 96 mass%.
Examples of polyolefin resins other than polyethylene and polypropylene include polybutene and ethylene-propylene random copolymers.

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 million or less, more preferably 50,000 or more and less than 2 million, and still more preferably 100,000 or more and 1,000,000. Is less than. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension at the time of melt molding becomes large and the moldability becomes better, and the strength tends to become higher due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12 million or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. Furthermore, when the viscosity average molecular weight is less than 1,000,000, it is preferable because the pores are likely to be blocked when the temperature rises, and a better shutdown function tends to be obtained. The viscosity average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at a measurement temperature of 135 ° C. using decalin as a solvent based on ASTM-D4020 by the following formula.
Polyethylene: [η] = 6.77 × 10 ⁻⁴ Mv ^0.67 (Chiang formula)
Polypropylene: [η] = 1.10 × 10 ⁻⁴ Mv ^0.80
For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, it is a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, and the viscosity average molecular weight is less than 1 million. Mixtures may be used.

  Moreover, the base material can contain arbitrary additives. Such additives are not particularly limited, and include, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenolic, phosphorus, and sulfur-based; metal soaps such as calcium stearate and zinc stearate; Absorbers; light stabilizers; antistatic agents; antifogging agents; and color pigments. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin in the polyolefin microporous membrane. It is.

The porosity of the substrate is not particularly limited, but is preferably 20% or more, more preferably 35% or more, and further preferably more than 40%. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less. Setting the porosity to 20% or more is preferable from the viewpoint of securing the separator permeability more effectively and reliably. On the other hand, setting the porosity to 90% or less is preferable from the viewpoint of ensuring the puncture strength more effectively and reliably. The porosity is calculated, for example, from the volume (cm ³ ), mass (g), and film density (g / cm ³ ) of the sample of the substrate:
Porosity = (volume−mass / film density) / volume × 100
It can ask for. Here, for example, in the case of a polyolefin microporous film made of polyethylene, the film density can be calculated assuming 0.95 (g / cm ³ ). The porosity can be adjusted by changing the draw ratio of the polyolefin microporous membrane.

The air permeability of the substrate is not particularly limited, but is preferably 10 seconds / 100 cm ³ or more, more preferably 50 seconds / 100 cm ³ or more, preferably 1000 seconds / 100 cm ³ or less, more preferably 500 seconds / 100 cm. ³ or less. The air permeability is preferably 10 seconds / 100 cm ³ or more from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, the air permeability is preferably set to 1000 seconds / 100 cm ³ or less from the viewpoint of obtaining good charge / discharge characteristics. The air permeability is an air resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the substrate.

  The average pore diameter 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 capacity reduction. The average pore diameter can be adjusted by changing the draw ratio when manufacturing the substrate.

  The puncture strength of the substrate is not particularly limited, but is preferably 200 gf / 20 μm or more, more preferably 300 gf / 20 μm or more, still more preferably 400 gf / 20 μm or more, preferably 2000 gf / 20 μm or less, more preferably 1000 gf. / 20 μm or less. The pin puncture strength of 200 gf / 20 μm or more suppresses the fear of short-circuiting due to expansion and contraction of the electrode due to charge and discharge, and the viewpoint of suppressing film breakage due to the dropped active material when the separator is wound together with the electrode This is also preferable. On the other hand, a puncture strength of 2000 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 the examples. The puncture strength can be adjusted by adjusting the stretching ratio and / or stretching temperature of the substrate.

  Although the thickness of a base material is not specifically limited, Preferably it is 2 micrometers or more, More preferably, it is 5 micrometers or more, Preferably it is 100 micrometers or less, More preferably, it is 60 micrometers or less, More preferably, it is 50 micrometers or less. A film thickness of 2 μm or more is preferable from the viewpoint of improving mechanical strength. On the other hand, it is preferable that the film thickness be 100 μm or less because the occupied volume of the separator in the electricity storage device is reduced, and this tends to be advantageous in increasing the capacity of the electricity storage device.

The surface tension of the substrate is not particularly limited, but is preferably 45 mN / m or more, more preferably 47 mN / m or more, preferably 54 mN / m or less, more preferably 52 mN / m or less. These surface tension values are, for example, smaller than the surface tension value of the thermoplastic polymer-containing layer.
When the thermoplastic polymer-containing layer is present only on a part of the surface of the substrate, when only the separator is wound, the exposed portion of the surface of the substrate (portion where the thermoplastic polymer-containing layer is not present) The substrate or another thermoplastic polymer-containing layer overlaps. In such a case, it is preferable that the surface tension be 45 mN / m or more from the viewpoint of suppressing the phenomenon such as repellency and forming the thermoplastic polymer uniformly when forming the thermoplastic polymer on the substrate. . On the other hand, setting the surface tension to 52 mN / m or less means that the base material or the thermoplastic polymer is applied to the exposed portion of the surface of the base material in the normal storage stage where the wound body in which only the separator is wound is stored. Since a content layer becomes difficult to adhere | attach excessively, it is preferable from a viewpoint of ensuring blocking resistance. The surface tension is measured according to the method described in the examples.

  When the substrate is a polyolefin microporous membrane, the surface tension of the polyolefin microporous membrane is determined by mixing a polyolefin polymer with a hydrophilic polymer, for example, a polymer containing an acid group such as carboxylic acid; It can be adjusted by a method of surface-treating the film. By carrying out these methods, the chemical properties of the surface of the polyolefin microporous membrane change, and as a result, the surface of the polyolefin microporous membrane becomes easily hydrophilic. From the viewpoint of adjusting only the surface tension without changing various physical properties of the polyolefin microporous membrane, it is preferable to employ a method of performing surface treatment. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure that the substrate may have. For example, corona discharge treatment method, plasma discharge treatment method, mechanical surface roughening method, solvent treatment method , Acid treatment method, and ultraviolet oxidation method. Among these, the corona discharge treatment method or the plasma treatment method is preferable from the viewpoint of minimizing damage to the polyolefin microporous membrane and the ability to process at high speed. Of course, these methods may be used in combination. In the case of the corona treatment or the plasma treatment, the surface tension of the polyolefin microporous membrane can be appropriately adjusted by the output of the processing apparatus, the length of the processing electrode, and the transport speed of the polyolefin microporous membrane.

In particular, when a hydrophilic polymer is mixed into the polyolefin microporous membrane so that the surface tension value falls within the preferred numerical range in the present embodiment, the type and amount of the polymer are adjusted, and the surface treatment is performed. When applying, it is preferable to adjust the degree of the surface treatment.
For example, a surface treatment may be applied to the substrate so that a water-based coating solution can be suitably applied to the substrate, thereby ensuring the wettability of the substrate. On the other hand, the surface treatment for ensuring the wettability is different in the degree of the surface treatment as compared with the surface treatment for keeping the value of the surface tension within a suitable numerical range in the present embodiment. In many cases, the degree of surface treatment, which is preferable in the present embodiment, is smaller than the degree of surface treatment for ensuring the wettability of the substrate.
Such a small degree of surface treatment facilitates the presence of an exposed portion (portion in which the thermoplastic polymer-containing layer does not exist) on the surface of the base material, and thus facilitates securing blocking resistance. linked.

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

  The thermoplastic polymer-containing layer is intended to be directly bonded to the electrode. The at least one thermoplastic polymer-containing layer provided in the separator is arranged so that it is directly bonded to the electrode, for example, at least a part of the substrate and the electrode are bonded via the thermoplastic polymer-containing layer. It is preferable.

The coating amount of the thermoplastic polymer-containing layer on the base material, that is, the amount of thermoplastic polymer-containing layer formed per area of one surface of the base material (arrangement amount) is 0.03 g / m ² or more in solid content. Preferably, it is 0.05 g / m ² or more. The coating amount is preferably 2.0 g / m ² or less, and more preferably 1.5 g / m ² or less. Setting the coating amount to 0.03 g / m ² or more improves the adhesive force between the thermoplastic polymer-containing layer and the electrode in the obtained separator, realizes more uniform charge and discharge, and device characteristics (for example, This is preferable in terms of improving the cycle characteristics of the battery. On the other hand, setting the coating amount to 2.0 g / m ² or less is preferable from the viewpoint of further suppressing the decrease in ion permeability.

The ratio of the area of the surface on which the thermoplastic polymer-containing layer is present to the total area of the surface on which the thermoplastic polymer-containing layer is disposed in the substrate, that is, the ratio of the area covered by the thermoplastic polymer-containing layer to the substrate is: It is preferably 80% or less, more preferably 50% or less, and particularly preferably 35% or less. The surface coverage is preferably 5% or more, more preferably 10% or more, and particularly preferably 20 or more. Setting the covering area ratio to 50% or less means that when only the separator is wound, the exposed portion of the surface of the substrate (portion where the thermoplastic polymer-containing layer does not exist) and another substrate or another thermoplastic It is preferable from the viewpoint of ensuring blocking resistance by increasing the contact area with the polymer-containing layer. Moreover, it is also preferable from the viewpoint of further suppressing the blockage of the pores of the base material by the particulate polymer and further improving the permeability of the separator. On the other hand, it is preferable that the covering area ratio is 5% or more from the viewpoint of further improving the adhesion to the electrode. The coating area ratio is measured by observing the surface on which the thermoplastic polymer-containing layer is formed in the obtained separator with an SEM, and is specifically measured according to the method described in the examples.
The coating area ratio is, for example, the type of particulate polymer in the coating solution applied to the surface of the substrate or the concentration of the polymer, the coating amount of the coating solution, the coating method, and the coating in the separator manufacturing method described later. It can be adjusted by changing the conditions. However, the method for adjusting the coating area is not limited thereto.

  When the thermoplastic polymer-containing layer is disposed only on a part of the surface of the base material, the existence form (pattern) of the thermoplastic polymer is not particularly limited, but the thermoplastic polymers are dispersed mutually over the entire surface of the base material. It is preferable to exist in the state of being present or in the form of sea islands. When the thermoplastic polymer is present in the shape of sea stripes, examples of the arrangement pattern include dot shapes, stripe shapes, lattice shapes, stripe shapes, turtle shell shapes, random shapes, and combinations thereof. Among these, the dot shape is preferable from the viewpoint of more effectively and surely achieving the effects of the present invention. When the arrangement pattern is in the form of dots, the dot diameter is preferably 50 μm or more, more preferably 100 μm or more, and more preferably 200 μm or more. Further, the dot diameter is preferably 1 mm or less, and more preferably 500 μm or less. When the dot diameter is 50 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 mm or less, the separator can be more uniformly bonded to the electrode, and the in-plane current density can be further uniformed. 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 disposed, it is desirable that the covering area ratio is uniform in a certain area range. Specifically, in the observation visual field range of 10 mm × 10 mm or more when the surface of the separator is observed with an SEM, it is preferable that the change rate of the covering area ratio represented by the following formula is within ± 50%.
(Change rate of covering area ratio (%)) = (C1-C2) / C1 × 100
Here, C1 indicates the coverage area ratio in an observation field range of 10 mm × 10 mm or more, and C2 indicates the coverage area ratio in other observation field ranges of 10 mm × 10 mm or more. For example, for a separator in which a thermoplastic polymer-containing layer is partially disposed, when the measured value of the covering area ratio in an observation visual field range of 10 mm × 10 mm is 50%, any other part of the separator is observed. Even so, the coverage area ratio in the observation field range of 10 mm × 10 mm is preferably 25% or more and 75% or less.

  The thickness of the thermoplastic polymer-containing layer is preferably 0.01 μm or more and more preferably 0.1 μm or more per one surface of the substrate. Further, the thickness is preferably 5.0 μm or less, more preferably 3.0 μm or less, and further preferably 2.0 μm or less per one surface of the substrate. Setting the thickness to 0.01 μm or more is preferable in that the adhesive force between the electrode and the substrate is uniformly expressed, and as a result, device characteristics can be improved. Moreover, it is preferable that the thickness is 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 determined, for example, by changing the type of particulate polymer in the coating liquid applied to the substrate or the concentration of the polymer, the coating amount of the coating liquid, the coating method, and the coating conditions. Can be adjusted. However, the adjustment method of this thickness is not limited to them. The thickness of the thermoplastic polymer-containing layer is measured according to the method described in the examples.

(Particulate polymer)
The thermoplastic polymer contained in the thermoplastic polymer-containing layer contains a particulate polymer. In the following description, “ethylenically unsaturated monomer” means a monomer having one or more ethylenically unsaturated bonds in the molecule. When the thermoplastic polymer contains a particulate polymer, both excellent adhesion to the electrode and ion permeability can be achieved.

  Specific examples of the particulate polymer include acrylic polymers, conjugated diene polymers, acrylic polymers, polyvinyl alcohol resins, and fluorine-containing resins. Among these, an acrylic polymer is preferable from the viewpoint of more effectively and reliably achieving the effects of the present invention. An acrylic polymer and a fluorine-containing resin are also preferable from the viewpoint of voltage resistance, and a conjugated diene polymer is also preferable from the viewpoint of easy compatibility with the electrode. Furthermore, it is preferable that the particulate polymer contains a particulate copolymer from the viewpoint of more effectively and reliably achieving the effects of the present invention. A particulate polymer is used individually by 1 type or in combination of 2 or more types.

  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, and particularly preferably 98% by mass, based on the total amount. As mentioned above, a particulate polymer is included. The thermoplastic polymer-containing layer may contain a thermoplastic polymer other than the particulate polymer to such an extent that the effects of the present invention are not impaired.

  The conjugated diene polymer is a polymer having a conjugated diene compound as a monomer unit. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and substituted linear conjugates. Examples include pentadienes, substitutions, 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 preferable. Further, the conjugated diene polymer may contain a (meth) acrylic compound or other monomer described later as a monomer unit. Such monomers include, for example, styrene-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene copolymers, and hydrides thereof, acrylonitrile-butadiene-styrene copolymers, and hydrides thereof. It is done.

  Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol and polyvinyl acetate. Examples of the fluorine-containing resin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoro. An ethylene copolymer is mentioned.

The acrylic polymer is a polymer having a (meth) acrylic compound as a monomer unit, that is, a polymerization unit. The (meth) acrylic compound indicates at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester. An example of such a compound is a compound represented by the following formula.
CH ₂ = CR ^Y1 -COO-R ^Y2
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 hetero atom in the chain. Examples of the monovalent hydrocarbon group include a linear alkyl group, a cycloalkyl group, and an aryl group which may be linear or branched. Examples of the substituent include a hydroxyl group and a phenyl group, and examples of the hetero atom include a halogen atom and an oxygen atom. A (meth) acrylic compound is used alone or in combination of two or more. Such (meth) acrylic compounds include (meth) acrylic acid, chain alkyl (meth) acrylate, cycloalkyl (meth) acrylate, (meth) acrylate having a hydroxyl group, and phenyl group-containing (meth) acrylate. Is mentioned.

More specifically, as the chain alkyl group which is one kind of R ^Y2 , a chain alkyl group having 1 to 3 carbon atoms such as methyl group, ethyl group, n-propyl group, and isopropyl group; n Examples include -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. Moreover, as an aryl group which is 1 type of R ^<Y2>, a phenyl group is mentioned, for example. Specific examples of the (meth) acrylic acid ester monomer having R ^Y2 include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, and 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 A (meth) acrylate having an alkyl group; and phenyl (meth) acrylate, and Having an aromatic ring such as Njiru (meth) acrylate (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 which 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 preferable. The upper limit of the number of carbon atoms in the chain alkyl group having 4 or more carbon atoms is not particularly limited, and may be 14, for example, but 7 is preferable. These (meth) acrylic acid ester monomers are used singly or in combination of two or more.

The (meth) acrylic acid ester monomer includes a monomer having a cycloalkyl group as R ^Y2 instead of or in addition to the monomer having a chain alkyl group having 4 or more carbon atoms. Is also preferable. This also improves the adhesion of the separator to the electrode. More specifically, examples of such a monomer having a cycloalkyl group include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and adamantyl (meth) acrylate. 4-8 are preferable, as for the number of the carbon atoms which comprise the alicyclic ring of a cycloalkyl group, 6-7 are more preferable, and 6 is especially preferable. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a t-butyl group. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferable in terms of good polymerization stability when preparing an acrylic polymer. These are used singly or in combination of two or more.

  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. For example, a monomer having two or more radical polymerizable double bonds, a single monomer having a functional group that gives a self-crosslinking structure during or after polymerization. Examples include the body. These are used singly or in combination of two or more.

  Examples of the monomer having two or more radical polymerizable double bonds include divinylbenzene and polyfunctional (meth) acrylate. The polyfunctional (meth) acrylate may be at least one selected from the group consisting of a bifunctional (meth) acrylate, a trifunctional (meth) acrylate, and a tetrafunctional (meth) acrylate. Specifically, for example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol Examples include dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These are used singly or in combination of two or more. Especially, at least 1 sort (s) of a trimethylol propane triacrylate or a trimethylol propane trimethacrylate is preferable from a viewpoint similar to the above.

  Examples of the monomer having a functional group that gives a self-crosslinking structure during or after polymerization include, for example, a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, and hydrolysis. And monomers having a functional 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 are mentioned.

  Examples of the monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. As the monomer having an alkoxymethyl group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable. Specific examples thereof include N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, and N-butoxymethylacrylamide. , And N-butoxymethyl methacrylamide. Examples of the monomer having a hydrolyzable silyl group include vinyl silane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyl. A triethoxysilane is mentioned. These are used singly or in combination of two or more.

  The acrylic polymer may further have other monomers as monomer units in order to improve various qualities and physical properties. Examples of such a monomer include a monomer having a carboxyl group (excluding (meth) acrylic acid), a monomer having an amide group, a monomer having a cyano group, and a hydroxyl group. And aromatic vinyl 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 versatic acid, vinyl pyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, chloride Vinyl and vinylidene chloride are also used as necessary. These are used singly or in combination of two or more. Further, such other monomers may belong to two or more of the above monomers at the same time.

  Examples of the monomer having an amide group include (meth) acrylamide. The monomer having a cyano group is preferably an ethylenically unsaturated monomer having a cyano group, and specific examples thereof include (meth) acrylonitrile. As a monomer which has a hydroxyl group, 2-hydroxyethyl (meth) acrylate is mentioned, for example.

  Examples of the aromatic vinyl monomer include styrene, vinyl toluene, and α-methylstyrene. Styrene is preferred.

  The proportion of the acrylic polymer having the (meth) acrylic compound as a monomer unit, that is, a polymer 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. When the content ratio of the monomer unit is 5% by mass or more, it is preferable in terms of binding property to the base material and oxidation resistance. On the other hand, a more preferred upper limit is 92% by mass, a still more preferred upper limit is 80% by mass, and a particularly preferred upper limit is 60% by mass. When the monomer content is 95% by mass or less, the adhesion 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 thereof is preferably 100% by mass of the acrylic polymer. 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 as follows. The content of these monomers is preferably 3% by mass or more from the viewpoint of improving oxidation resistance, and the content of 92% by mass or less is preferable because the binding property to the substrate is improved.

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

  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. 0% with respect to 100% by mass of the acrylic polymer. It is 01 mass% or more and 10 mass% or less, More preferably, it is 0.1 mass% or more and 5 mass% or less, More preferably, it is 0.1 mass% or more and 3 mass% or less. When the content ratio of the monomer is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when it is 10% by mass or less, a decrease in cushioning property in the swollen state can be further suppressed.

As the acrylic polymer, any of the following embodiments is preferable. The following copolymerization ratios are values based on 100% by mass of the copolymer.
(1) A copolymer having a (meth) acrylic acid ester as a monomer unit (excluding the copolymer (2) and the copolymer (3) below). Preferably, (meth) acrylic acid is 5% by mass or less (more preferably 0.1% by mass or more and 5% by mass or less) and (meth) acrylic acid ester monomer is 3% by mass or more and 92% by mass or less (more preferably). 10 mass% or more and 90 mass% or less, more preferably 15 mass% or more and 75 mass% or less, particularly preferably 25 mass% or more and 55 mass% or less), a monomer having an amide group, a monomer having a cyano group And at least one selected from the group consisting of monomers having a hydroxyl group, 15% by mass or less (more preferably 10% by mass or less) and a crosslinkable monomer 10% by mass or less (more preferably 0.01% or less). A copolymer of from 5% by mass to 5% by mass, and more preferably from 0.1% by mass to 3% by mass.
(2) A copolymer having an aromatic vinyl monomer and a (meth) acrylic acid ester monomer as monomer units. Preferably, the aromatic vinyl monomer is 5% by mass or more and 95% by mass or less (more preferably 10% by mass or more and 92% by mass or less, still more preferably 25% by mass or more and 80% by mass or less, and particularly preferably 40% by mass or more and 60% by mass or less. Mass% or less), (meth) acrylic acid 5 mass% or less (more preferably 0.1 mass% or more and 5 mass% or less), and (meth) acrylic acid ester monomer 5 mass% or more and 95 mass% or less ( More preferably 15% by mass or more and 85% by mass or less, further preferably 20% by mass or more and 80% by mass or less, and particularly preferably 30% by mass or more and 75% by mass or less), a monomer having an amide group, and a cyano group. 10% by mass or less (more preferably 5% by mass or less) selected from the group consisting of a monomer and a monomer having a hydroxyl group, and 10% by mass or less (more preferably 5% by mass or less). Preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 3% by mass or less); and (3) a monomer having a cyano group and (meth) acrylic A copolymer having an acid ester monomer as a monomer unit. Preferably, the monomer having a cyano group is 1% by mass to 95% by mass (more preferably 5% by mass to 90% by mass, and still more preferably 50% by mass to 85% by mass), and (meth) acrylic acid. 5 mass% or less (preferably 0.1 mass% or more and 5 mass% or less), and (meth) acrylic acid ester monomer 1 mass% or more and 95 mass% or less (more preferably 5 mass% or more and 85 mass% or less, And more preferably 10% by mass or more and 50% by mass or less) and at least one selected from the group consisting of monomers having an amide group, monomers having a cyano group, and monomers having a hydroxyl group. % Or less (more preferably 5% by mass or less) and a crosslinkable monomer 10% by mass or less (more preferably 0.01% by mass or more and 5% by mass or less, and further preferably 0.1% by mass or more and 3% by mass or less). )When, Copolymer.

  The copolymer (2) preferably has a (meth) acrylic acid hydrocarbon ester as the (meth) acrylic acid ester monomer. In this case, the copolymerization ratio of the hydrocarbon ester of (meth) acrylic acid is preferably 0.1% by mass or more and 5% by mass or less. Moreover, when the copolymer of said (2) has a monomer which has an amide group, it is preferable that the copolymerization ratio is 0.1 to 5 mass%. Furthermore, when the copolymer (2) has a monomer having a hydroxyl group, the copolymerization ratio is preferably 0.1% by mass or more and 5% by mass or less.

  In the copolymer of (3), the (meth) acrylic acid ester monomer contains at least one selected from the group consisting of a chain alkyl (meth) acrylate and a cycloalkyl (meth) acrylate. preferable. As the chain alkyl (meth) acrylate, a (meth) acrylic acid ester having a chain alkyl group having 6 or more carbon atoms is preferable. The copolymerization ratio of the chain alkyl (meth) acrylate in the copolymer (3) is preferably 1% by mass to 95% by mass, more preferably 3% by mass to 90% by mass, More preferably, it is 5 mass% or more and 85 mass% or less. The upper limit of the copolymerization ratio may be 60% by mass, particularly 40% by mass or 30% by mass, and particularly preferably 20% by mass. The copolymerization ratio of cyclohexylalkyl (meth) acrylate in the copolymer (3) is preferably 1% by mass or more and 95% by mass or less, more preferably 3% by mass or more and 90% by mass or less. More preferably, it is at least 85% by mass. The upper limit of the copolymerization ratio may be 60% by mass, particularly 50% by mass, and particularly preferably 40% by mass. Moreover, when the copolymer of said (3) has a monomer which has an amide group, it is preferable that the copolymerization ratio is 0.1 to 10 mass%, and is 2 to 10 mass. % Or less is more preferable. Furthermore, when the copolymer (3) has a monomer having a hydroxyl group, the copolymerization ratio is preferably 0.1% by mass or more and 10% by mass or less, and preferably 1% by mass or more. More preferably, it is 10 mass% or less.

  The acrylic polymer is obtained, for example, by a usual emulsion polymerization method. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-known method can be used.

  For example, in a dispersion system containing the above-mentioned monomer, surfactant, radical polymerization initiator, and other additive components used as necessary in an aqueous medium as a basic composition component, each of the above monomers is included. An acrylic polymer is obtained by polymerizing the monomer composition. In the polymerization, a method of making the composition of the monomer composition to be supplied constant throughout the entire polymerization process, and changing the morphological composition of the particles of the resin dispersion produced by sequentially or continuously changing the polymerization process Various methods can be used as needed. 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 a particulate acrylic polymer dispersed in the water.

The 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 a polyether surfactant is preferable. Since the surfactant will be described later, the description thereof 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, the description thereof is omitted here.

  Among the thermoplastic polymer forms, from the viewpoint of improving the adhesion between the separator and the electrode, the high-temperature storage characteristics of the electricity storage device, and the cycle characteristics, and achieving a thin film of the adhesive body between the electrode and the separator. An acrylic copolymer latex formed from an emulsion containing an emulsifier, an initiator, and water is preferred.

  The glass transition temperature (Tg) of the particulate polymer is preferably −50 ° C. or higher, more preferably −30 ° C. or higher, and 20 ° C. from the viewpoints of adhesion to electrodes and ion permeability. More preferably, it is more preferably 40 ° C. or higher. Moreover, it is preferable that the glass transition temperature of a particulate polymer is 200 degrees C or less. 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 baseline on the low temperature side in the DSC curve to the high temperature side and the tangent at the inflection point of the stepwise change portion of the glass transition may be adopted as the glass transition temperature. it can. More specifically, it may be determined according to the method described in the examples. “Glass transition” refers to a change in calorific value associated with a change in the state of the polymer that is a test piece in DSC on the endothermic side. Such a change in heat quantity is observed as a step-like change shape in the DSC curve. The “step change” refers to a portion of the DSC curve until the curve moves away from the previous low-temperature base line to a new high-temperature base line. Note that a combination of a step change and a peak is also included in the step change. Further, the “inflection point” indicates a point at which the gradient of the DSC curve at the step-like change portion is maximized. Further, in the step-like change portion, when the upper side is the heat generation side, it can also be expressed as a point where the upward convex curve changes to the downward convex curve. “Peak” indicates a portion of the DSC curve from when the curve leaves the low-temperature side baseline until it returns to the same baseline again. The “baseline” indicates a DSC curve in a temperature region where no transition or reaction occurs in the test piece.

The glass transition temperature Tg of the particulate polymer is, for example, the type of monomer used when producing the particulate polymer, and the blending ratio of each monomer when the particulate polymer is a copolymer. It can adjust suitably by changing. That is, for each monomer used in the production of the particulate polymer, the Tg of the homopolymer generally shown (for example, described in “A WILEY-INTERSCIENCE PUBLICATION”) and the monomer The outline of the glass transition temperature can be estimated from the blending ratio. For example, a copolymer with a high proportion of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid that gives a homopolymer with a Tg of about 100 ° C. has a high Tg and is about -50 ° C. Tg of a copolymer obtained by copolymerizing monomers such as n-butyl acrylate and 2-ethylhexyl acrylate in a high ratio to give a homopolymer of Tg is low.
Moreover, Tg of a copolymer can be estimated also by the formula of FOX represented by following Numerical formula (1).
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ +... + W _i / Tg _i +... W _n / Tg _n (1)
Here, in the formula, 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, a value measured by the method using the DSC is adopted.

  From the viewpoints of wettability to the substrate, binding property between the substrate and the thermoplastic polymer-containing layer, and adhesion to the electrode, the thermoplastic polymer-containing layer contains a polymer having a glass transition temperature of less than 40 ° C. It is preferable that From the viewpoint of ion permeability, the glass transition temperature of the polymer having a glass transition temperature of less than 40 ° C. is preferably −100 ° C. or higher, more preferably −50 ° C. or higher, and further preferably −40 ° C. or higher. From the viewpoint of the binding property between the thermoplastic polymer-containing layer and the thermoplastic polymer-containing layer, it is preferably less than 20 ° C, more preferably less than 15 ° C, and still more preferably less than -10 ° C.

  The particulate polymer preferably has at least two glass transition temperatures. That is, it is preferable that the thermoplastic polymer-containing layer contains two or more types of thermoplastic polymers having different glass transition temperatures. The method for causing the particulate polymer to have at least two glass transition temperatures is not limited, but includes a method of blending two or more types of particulate polymers, and a particulate polymer having a core-shell structure. The method using is mentioned. The core-shell structure is a structure having a center part and an outer shell part covering the center part, and is a polymer having a dual structure form in which the types or compositions of the polymers constituting each part are different from each other. . In particular, the glass transition temperature of the whole particulate polymer can be controlled by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature in the polymer blend and the core-shell structure. 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 present in a region where the glass transition temperature is 20 ° C. or higher and one or more polymers present in a region where the glass transition temperature is less than 20 ° C. By blending with the polymer, it is possible to achieve both better anti-stickiness and better coatability to the substrate. The blend ratio of each polymer in the case of blending is 0.1: 99 as a ratio of the polymer existing in the region where the glass transition temperature is 20 ° C. or more and the polymer existing in the region where the glass transition temperature is less than 20 ° C. Is preferably in the range of 9.9 to 99.9: 0.1, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and particularly preferably 60: 40-90: 10.

  In the case of using a particulate polymer having a core-shell structure, the adhesiveness and compatibility of the thermoplastic polymer-containing layer to other members (for example, a substrate) can be adjusted by selecting the type of polymer in the outer shell portion. it can. Further, by selecting the type of polymer in the central portion, for example, the adhesion to the electrode after hot pressing can be improved. Alternatively, the viscoelasticity of the thermoplastic polymer-containing layer can be controlled 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 to 15 ° C. More preferably, it is as follows. 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 50 ° C or higher and 200 ° C or lower. preferable.

  The arithmetic average particle size of the particulate polymer is preferably 10 nm or more, more preferably 100 nm or more, and further preferably 200 nm or more. The arithmetic average particle size of the particulate polymer is preferably 1000 nm or less, more preferably 800 nm or less, and still more preferably 700 nm or less. By making this arithmetic average particle size 10 nm or more, the ion permeability of the separator can be maintained higher. Therefore, in this case, it is preferable from the viewpoint of improving the adhesion between the electrode and the separator, the cycle characteristics of the electricity storage device, and the rate characteristics. In addition, it is preferable that the arithmetic average particle diameter be 1000 nm or less from the viewpoint of securing the dispersion stability when the thermoplastic polymer-containing layer containing the particulate polymer is formed from an aqueous dispersion. It is preferable from the viewpoint that the thickness of the plastic polymer-containing layer can be flexibly controlled. From these viewpoints, the arithmetic average particle size of the particulate polymer is particularly preferably 200 nm or more and 1000 nm or less. The arithmetic average particle diameter of the particulate polymer is measured according to the method described in the following examples.

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

  The particulate polymer described above can be produced by a known polymerization method except that the monomer described above is used. As a polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization or the like can be employed. In particular, an emulsion polymerization method is preferred for the purpose of obtaining a particle-shaped dispersion. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-known method can be used. For example, in a dispersion system containing the above-mentioned monomer, surfactant, radical polymerization initiator, and other additive components used as necessary in an aqueous medium, the above-mentioned monomers. A polymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the supplied monomer composition is made constant throughout the entire polymerization process, and the morphological composition change of the particles of the resin dispersion to be produced is changed by sequentially or continuously changing the polymerization process. Various methods can be used as needed, such as a giving method. When the polymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and a particulate polymer dispersed in the water.

  The 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, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ethers. Disulfonate, naphthalenesulfonic acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene distyrenated phenyl ether sulfate, fatty acid salt, alkyl phosphate, and polyoxyethylene alkylphenyl ether sulfate Anionic surfactants such as ester salts; and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, Oxyethylene distyrenated phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, and polyoxyethylene Nonionic surfactants such as alkylphenyl ethers can be mentioned. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

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

  Examples of the nonionic surfactant in the reactive surfactant include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) RN-30 and RN-50), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap ER manufactured by ADEKA Corporation) -10), and polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) Ether (for example, Kao Corp. LATEMUL PD-420.) And the like. The surfactant is preferably used in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the monomer composition. Surfactant is used individually by 1 type or in combination of 2 or more types.

The surfactant can be added later after the polymerization reaction in combination with the method of adding it as a raw material for the polymerization reaction of the particulate polymer. By adding a surfactant after the polymerization reaction, the surface energy of the thermoplastic polymer layer formed on the surface of the substrate can be adjusted. By adjusting the surface energy of the thermoplastic polymer layer, the contact angle of the separator surface on which the thermoplastic polymer is formed can be adjusted. Post-addition of the surfactant is preferable from the viewpoint that the surface energy of the thermoplastic polymer layer can be adjusted without being influenced by the conditions of the polymerization reaction. By adding the surfactant later, a large amount of the free surfactant is present in the slurry, and it is considered 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 than the method of adding 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, but since the polymerization reaction has already been completed when the addition is performed after the polymerization reaction, It is preferable to use a surfactant that is not a surfactant. Among these, it is easy to suppress foaming of the slurry, and further, the dispersion effect becomes larger as it is added, and it is easy to ensure dispersibility, and there is an effect of greatly changing the surface tension of the polyolefin microporous membrane with a small amount. From the viewpoint, the polyether-based surfactant or the anionic surfactant is preferable.
The post-added surfactant is preferably used in an amount of 0.05 to 20 parts by mass with respect to 100 parts by mass of the monomer composition.
When the amount is 0.05 parts by weight or more, it is possible to sufficiently adjust the surface energy. When the amount is 20 parts by weight or less, the surface energy of the thermoplastic polymer layer becomes too high and can be prevented from being easily blocked.

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

  The radical polymerization initiator is preferably used in an amount of 0.05 part 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.

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

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

[Any layer]
An embodiment including an arbitrary layer, for example, an inorganic filler porous layer, between the base material and the thermoplastic polymer-containing layer is also included in the scope of the present invention. The inorganic filler porous layer includes an inorganic filler and has a plurality of pores. In this section, it is assumed that the inorganic filler porous layer is included between the base material and the thermoplastic polymer-containing layer, and such an inorganic filler porous layer will be described. The layers can be omitted.

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

  Examples of the inorganic filler include, but are not limited to, inorganic oxides (oxide 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, dickite, nacrite, halloysite And ceramics such as pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These are used singly or in combination of two or more.

The average particle diameter D50 of the inorganic filler is, for example, 0.01 μm or more, 0.2 μm or more, and further 0.5 μm or more. The average particle diameter D50 is 4.0 μm or less, 3.5 μm or less, and further less than 1.0 μm. Examples of the method for adjusting the particle size and distribution of the inorganic filler include a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizing apparatus such as a ball mill, a bead mill, or a 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, it may be a trapezoidal chart that has two peaks or no peak.

  The arithmetic average particle diameter of the particulate polymer may be larger than the average pore diameter of the inorganic filler porous layer. For example, the arithmetic average particle diameter of the particulate polymer is, for example, 1.2 times or more, 1.5 times or more, and further 1.8 times or more with respect to the average pore diameter of the inorganic filler porous layer. 0 times or less, and further 3.0 times or less. The average pore diameter 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. Further, 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, and further 5% with respect to the total amount of the inorganic filler porous layer. % Or less.

When measuring the average pore size of the porous inorganic filler layer, the cross section of the separator is preferably observed in a region of the separator cross section that is not involved in ion conduction. The average pore diameter of the inorganic filler porous layer may be measured, for example, on a separator that has just been manufactured and is not yet incorporated into an electricity storage device. Alternatively, after the separator is incorporated in the electricity storage device, measure the so-called “ear” portion of the separator (the region near the outer edge of the separator and not involved in ion conduction). Also good.
The average pore diameter 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. The average pore diameter 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 the void portion formed by inorganic fillers preferably bound by a resin binder in the inorganic filler porous layer formed on at least one side of the substrate. is there. 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 It can adjust with the formation method at the time of forming a layer.

Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a columnar shape, a spherical shape, a polyhedral shape, and a block shape. A plurality of inorganic fillers having these shapes may be used in combination.
The content ratio of the inorganic filler in the inorganic filler porous layer is, for example, 20% by mass to less than 100% by mass, 30% by mass to 80% by mass, 35% by mass to 70% by mass with respect to the total amount of the inorganic filler porous layer. Hereinafter, it is 40 mass% or more and 60 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 is insoluble in the electrolyte solution of an electricity storage device such as a lithium ion secondary battery, and like a lithium ion secondary battery. In addition, an electrochemically stable resin can be used within the range of use of a simple electricity storage device. 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, the resin contained in the thermoplastic polymer-containing layer as a resin of the resin binder A binding binder (C) for binding the polymer (B) to the base material or the inorganic filler porous layer may be used. The resin binder (A) and the binder binder (C) are usually not in the form of particles 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 binder binder (C).

  Specific examples of such a resin include, for example, polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer; and Fluorine-containing rubber such as ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and hydride thereof, acrylonitrile-butadiene copolymer, and hydride thereof, acrylonitrile-butadiene-styrene copolymer, and hydride thereof , Methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, etc. Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; and melting points and / or glass transitions of polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester Examples thereof include resins having a temperature of 180 ° C. or higher. These are used singly or in combination of two or more.

  The resin binder can include, for example, a resin latex binder. As the resin latex binder, for example, a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable therewith can be used. Here, examples of the aliphatic conjugated diene monomer include butadiene and isoprene, examples of the unsaturated carboxylic acid monomer include (meth) acrylic acid, and examples of other monomers. Examples thereof include styrene. There is no particular limitation on the polymerization method of such a copolymer, but emulsion polymerization is preferred. There is no restriction | limiting in particular as a method of emulsion polymerization, A known method can be used. The addition method of the monomer and other components is not particularly limited, and any of a batch addition method, a divided addition method, and a continuous addition method can be adopted, and the polymerization method is a one-stage polymerization, Either two-stage polymerization or three-stage or more multi-stage polymerization can be employed.

Specific examples of the resin binder include the following 1) to 7).
1) Polyolefin: For example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
2) Conjugated diene polymer: for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer, and its hydride, acrylonitrile-butadiene-styrene copolymer, and its hydride;
3) Acrylic polymer: For example, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, and acrylonitrile-acrylic acid ester copolymer;
4) Polyvinyl alcohol resin: For example, polyvinyl alcohol and polyvinyl acetate;
5) Fluorine-containing resin: 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 having a melting point and / or glass transition temperature of 180 ° C. or higher, or polymers having no melting point but a decomposition temperature of 200 ° C. or higher: For example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

When the resin binder is a resin latex binder, the average particle diameter (D50) is, for example, 50 to 500 nm, 60 to 460 nm, and further 80 to 250 nm. The average particle diameter 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 ratio 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 to 20% by mass, and 2% by mass to 10% by mass with respect to the total amount of the inorganic filler porous layer. % Or less, and further 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, and 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 can be, for example, 10.0 μm or less, and further 6.0 μm or less. Moreover, the thickness of the inorganic filler porous layer can be set to be 0.5 μm or more, for example. The layer density of the inorganic filler porous layer is, for example, 0.5 g / (m ² · μm) or more and 3.0 g / (m ² · μm) or less, and further 0.7 to 2.0 cm ^3. Can do.

(Optional component)
The thermoplastic polymer-containing layer may contain only the thermoplastic polymer, or may contain other optional components in addition to the thermoplastic polymer. Examples of the optional component include the inorganic filler described above for forming the inorganic filler porous layer. The content of the thermoplastic polymer 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, based on the total amount of the thermoplastic polymer-containing layer. Especially preferably, it is 98 mass% or more.

(Various properties related to separators)
The separator has the following formula:
P1 / P2 ≧ 0.5
And P1 is 5 N / m or more. P1 and P2 are as described above.

  The above formula means that the separator can achieve both blocking resistance and adhesion to the electrode. Among these, P1 is corresponded to the peeling strength of a separator and an electrode after pressing the winding body which piles up and forms a separator and an electrode. The larger P1 is, the higher the adhesion between the separator and the electrode is, and it is advantageous for suppressing the press back. P1 is the kind of the thermoplastic polymer contained in the thermoplastic polymer-containing layer, the other components including the surfactant contained in the thermoplastic polymer layer, the presence form of the thermoplastic polymer on the substrate, and the thermoplastic polymer It can be adjusted as appropriate by adjusting the thickness of the containing layer. Basically, P1 tends to increase as the thermoplastic polymer-containing layer is more likely to exhibit an adhesive function during the pressing of the wound body formed by stacking the separator and the electrode. P1 is measured according to the method described in the Examples.

  Moreover, P2 is corresponded to the peeling strength of separators in the winding body which wound only the separator. As P2 is smaller, blocking when the separator is fed out from the wound body in which only the separator is wound is reduced, and a separator having a desired length can be easily fed out without wrinkles. P2 can be appropriately adjusted by adjusting the resin type of the base material, the surface tension of the base material, the ratio of the area covered with the thermoplastic polymer-containing layer to the base material, the configuration of the thermoplastic polymer-containing layer, and the like. Basically, in a normal storage stage in which a rolled body in which only the separator is wound is stored, P2 tends to be smaller as the thermoplastic polymer-containing layer is less likely to exhibit an adhesive function. P2 is measured according to the method described in the Examples.

Here, in order for the separator to achieve both blocking resistance and adhesion to the electrode, the relationship formed by P1 and P2 is P1 / P2 ≧ 0.5 and P1 is 5 N / m as described above. Above (P1 ≧ 5 N / m). When P1 / P2 <0.5, a desired effect cannot be obtained for either or both of the blocking resistance and the adhesion to the electrode. Further, even if P1 / P2 ≧ 0.5, if P1 is less than 5 N / m (P1 <5 N / m), the adhesiveness to the electrode is low and the pressback amount is large, It cannot be used as a separator. Therefore, when the separator satisfies the above relationship, both blocking resistance and adhesion to the electrode can be achieved. The preferable range of P1 is 5 N / m or more, more preferably 10 N / m or more, and further preferably 15 N / m or more.
Being able to achieve both blocking resistance and adhesion to the electrode, it can meet both expectations for higher capacity lithium ion secondary batteries and improvements in manufacturing handling for separators. it can.

  P1 / P2 is preferably 5 or less from the viewpoint of achieving both blocking resistance and adhesion to the electrode. Further, P1 / P2 is preferably 0.5 or more, preferably 1.0 or more, and preferably 1.4 or more from the viewpoint of achieving both blocking resistance and adhesion to the electrode. preferable.

  Further, P2 is preferably 15 N / m or less, and more preferably 10 N / m or less. The fact that P2 is 15 N / m or less means that, for example, in a normal storage stage in which a wound body in which only the separator is wound is stored, the separators are more difficult to adhere to each other, and thus sufficient locking resistance is ensured. Is advantageous.

The upper limit of P1 is preferably, for example, 35 N / m. The upper limit of P1 is 35 N / m, so that the adhesive function at the time of pressing the thermoplastic polymer-containing layer is excessively increased, and at the time of lamination with the electrode It becomes easy to prevent the thermoplastic polymer layer from deeply biting into the electrode and deteriorating the electrical resistance.
However, the values of P1 and P2 are not limited to the above example as long as the relationship of P1 / P2 ≧ 0.5 and P1 ≧ 5 N / m is satisfied.

  The contact angle of water with the surface on which the thermoplastic polymer-containing layer of the separator is formed is preferably 95 ° or less, and more preferably 90 ° or less. It is preferable that the contact angle of water is 95 ° or less from the viewpoint of securing the adhesion of the separator to the electrode. Basically, the smaller the contact angle of water, the higher the surface energy of the thermoplastic polymer-containing layer and the easier it is for the thermoplastic polymer-containing layer and its bonding object to adhere. As a method for reducing the contact angle of water, a method of mixing a hydrophilic polymer into the thermoplastic polymer-containing layer; a method of adding a predetermined surfactant to the thermoplastic polymer-containing layer; and an exposed portion of the substrate surface Adjusting the area of (the portion where the thermoplastic polymer-containing layer does not exist) may be mentioned. The contact angle of water is measured according to the method described in the examples.

  From the viewpoint of improving safety during a collision test, the separator preferably has a thermal shrinkage ratio at TD of 120 ° C. of less than 15.0%, more preferably 0% or more and 10% or less. More preferably, it is 0% or more and 5.0% or less. Here, when the thermal contraction rate at TD is less than 15.0%, occurrence of a short circuit other than a portion where an external force is applied when heat is generated by a short circuit during a collision test is more effectively suppressed. Thereby, the temperature rise of the whole battery, the smoke which may arise with it, and ignition can be prevented more reliably. The adjustment of the thermal shrinkage rate of the separator can be performed by appropriately combining the above-described stretching operation of the substrate and heat treatment.

The air permeability of the separator is preferably 10 seconds / 100 cm ³ or more and 10,000 seconds / 100 cm ³ or less, more preferably 10 seconds / 100 cm ³ or more and 1000 seconds / 100 cm ³ or less, and further preferably 50 seconds / 100 cm ^3. The time is 500 seconds / 100 cm ³ or less. Thus, when the separator is applied to an electricity storage device, good high ion permeability is exhibited. This air permeability is the air resistance measured according to JIS P-8117, similar to the air permeability of the polyolefin porous substrate.

<Manufacturing method of separator>
[Manufacturing method of substrate]
The method for producing the substrate is not particularly limited, and a known production method can be adopted. For example, any of a wet porosity method and a dry porosity method may be employed. For example, when the base material is a polyolefin microporous film, the polyolefin resin composition and a plasticizer are melt-kneaded and molded into a sheet, and optionally stretched, and then the plasticizer A method of making it porous by extracting it; after melting and kneading a polyolefin resin composition containing a polyolefin resin as a main component and extruding it at a high draw ratio, it is made porous by exfoliating the polyolefin crystal interface by heat treatment and stretching A method in which a polyolefin resin composition and an inorganic filler are melt-kneaded and formed on a sheet, and then the surface is made porous by peeling the interface between the polyolefin and the inorganic filler by stretching; and the polyolefin resin composition is dissolved Then, it is immersed in a poor solvent for polyolefin to coagulate the polyolefin and at the same time solvent Method for pore formation and the like by removing.

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

  Hereinafter, as an example of a method for producing a polyolefin microporous film, a method for extracting a plasticizer after melting and kneading a polyolefin resin composition and a plasticizer to form a sheet will be described. First, a polyolefin resin composition and a plasticizer are melt-kneaded. As the melt-kneading method, for example, a polyolefin resin and, if necessary, other additives are put into a resin kneading apparatus such as an extruder, a kneader, a lab plast mill, a kneading roll, and a Banbury mixer, and the resin component is heated and melted. However, a method of introducing a plasticizer at an arbitrary ratio and kneading can be mentioned. At this time, it is preferable that the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being added to the resin kneading apparatus. More preferably, only a part of the plasticizer is added in the pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading apparatus.

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

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30% by mass to 80% by mass, and more preferably 40% by mass to 70% by mass. By setting the mass fraction of the plasticizer within this range, it is preferable from the viewpoint of achieving both melt tension at the time of melt molding and formability of 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 shape. As a method for producing a sheet-like molded product, for example, the melt-kneaded product is extruded into a sheet shape via a T-die or the like, and is brought into contact with a heat conductor and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. Examples of the heat conductor used for cooling and solidification include metal, water, air, and the plasticizer itself, but a metal roll is preferable because of high heat conduction efficiency. In this case, when the molten kneaded material is sandwiched between the rolls when being brought into contact with the metal roll, the efficiency of heat conduction is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved. Therefore, it is more preferable. The die lip interval when extruding into a sheet form from the T die is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less.

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

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

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

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

  As the extraction solvent, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the plasticizer and has a boiling point lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; hydrofluoroethers, hydrofluorocarbons and the like. Non-chlorinated halogenated solvents; 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 and reused by an operation such as distillation.

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

  The example by the dry-type porosity method different from the said wet-type porosity method is given. First, a film that is directly stretched and oriented after melt-kneading in an extruder without using a solvent is produced, and then a microporous film is produced through an annealing process, a cold stretching process, and a hot stretching process in this order. In the dry porosification method, a method of stretching and aligning a molten resin from an extruder through a T die, an inflation method, and the like can be used, and the method is not particularly limited.

[Method of arranging thermoplastic polymer-containing layer]
A thermoplastic polymer-containing layer is disposed on at least one side of the substrate produced as described above. When the inorganic filler porous layer is disposed on the surface of the base material, a thermoplastic polymer-containing layer is disposed on all 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 surface of the substrate that is not. The method of disposing 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 the substrate.

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

  The method for applying the coating solution containing the particulate polymer on the substrate is not particularly limited as long as it can realize a desired coating pattern, coating film 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, cast Examples include a coater method, a die coater method, a screen printing method, a spray coating method, and an ink jet coating method. Among these, the gravure coater method or the spray coating method is preferable from the viewpoint that the degree of freedom of the coating shape of the particulate polymer is high and a preferable area ratio can be easily obtained.

  As a medium for the coating solution, water or a mixed solvent composed of water and a water-soluble organic medium is preferable. Although it does not specifically limit as a water-soluble organic medium, For example, ethanol, methanol, etc. can be mentioned. Among these, water is more preferable. When applying the coating liquid to the base material, if the coating liquid gets into the inside of the base material, the particulate polymer containing the polymer closes the surface of the pores of the base material and the inside, and is permeable. It tends to decrease. In this regard, when water is used as the solvent or dispersion medium of the coating solution, it becomes difficult for the coating solution to enter the substrate, and the particulate polymer containing the polymer is present mainly on the outer surface of the substrate. Since it becomes easy, the fall of permeability can be controlled more effectively, and is preferred. Examples of the solvent or dispersion medium that can be used in combination with water include ethanol and methanol.

  About the method of removing a solvent from a coating film after application | coating, if it is a method which does not have a bad influence on a base material and a thermoplastic polymer content layer, there will be no limitation in particular. For example, a method of drying at a temperature below the melting point while fixing the substrate, a method of drying under reduced pressure at a low temperature, and dipping in a poor solvent for the particulate polymer to coagulate the particulate polymer at the same time Examples include a method of extracting a solvent.

[Method for forming porous inorganic filler layer]
When disposing an inorganic filler porous layer on at least one surface of the substrate, the method for forming the inorganic filler porous layer is not particularly limited, and can be formed by a known method. For example, the method of apply | coating the coating liquid containing an inorganic filler and a resin binder as needed to a base material is mentioned. When the base material contains a resin like a polyolefin microporous membrane, the raw material containing the inorganic filler and the resin binder and the raw material of the base material containing the resin may be laminated and extruded by a co-extrusion method. And the inorganic filler porous layer (film) may be prepared separately and then bonded together.

  As the solvent of the coating solution, those capable of uniformly and stably dispersing or dissolving the inorganic filler and, if necessary, the resin binder are preferable. For example, N-methylpyrrolidone, N, N-dimethylformamide, 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; and a PH preparation containing acid and alkali may be added to the coating solution.

  Examples of the method for dispersing or dissolving the inorganic filler and, if necessary, the resin binder in the coating solution medium 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. , A disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring by a stirring blade.

  As for the method of applying the coating liquid to the substrate, 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 Examples include 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.

  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. 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, and immersing in a poor solvent for the resin binder to solidify the resin binder while simultaneously removing the solvent The method of extracting is mentioned. Further, a part of the solvent may be left as long as the device characteristics are not significantly affected.

  When removing the coating solution 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 made stronger and the drying speed is increased, it is considered that the average pore size is increased as a result of fixing the inorganic filler as it is without adjusting the shape from a sufficiently dispersed state. On the other hand, when the drying conditions are more relaxed, the dispersed inorganic filler tries to take 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. Moreover, if the viscosity of a coating liquid is low, it will become easy to take a stable structure and the average hole diameter of an inorganic filler porous layer will become smaller. Furthermore, the dispersion state of the inorganic filler is also affected by the type of the inorganic filler, the type of the solvent, the presence or absence of the added surfactant, and the type of the 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. There is no particular limitation on the calendering method, and a method of transporting the coating liquid while applying pressure with a nip roll after drying the coating solution may be used.

<Power storage device>
The electricity storage device including the separator may be the same as a conventionally known one except that the electricity storage device separator is provided. Although it does not specifically limit as an electrical storage device, For example, batteries, such as a non-aqueous electrolyte secondary battery, a capacitor | condenser, and a capacitor are mentioned. Among these, from the viewpoint of more effectively obtaining the benefits of the effects of the present invention, a battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is still more preferable. Since the separator according to this embodiment is provided, the power storage device is excellent in device characteristics such as power storage performance. Moreover, the lithium ion secondary battery is excellent in battery characteristics.

  The electrode used for measuring the peel strength with the electrode may be either a positive electrode or a negative electrode, but in order to properly grasp the effect of the separator, it is appropriate to use the positive electrode. In particular, when the electricity 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 appropriate that the measurement is carried out after the layers are laminated so as to face the formation surface of the thermoplastic polymer-containing layer and hot-pressed as described above.

When manufacturing a lithium ion secondary battery using a separator, there is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, Each known thing can be used, respectively.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be suitably used. Examples of the positive electrode current collector include an aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel-type LiMnO ₄ , and olivine-type LiFePO ₄ . In addition to the positive electrode active material, the positive electrode active material layer may appropriately include 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 suitably used. Examples of the negative electrode current collector include copper foil. Examples of the negative electrode active material include carbon materials such as graphitic materials, non-graphitizable carbon materials, graphitizable carbon materials, and composite carbon bodies; and 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. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

<Method for manufacturing power storage device>
The method for manufacturing the electricity storage device using the separator is not particularly limited. For example, the following method can be illustrated. 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. Subsequently, it laminates | stacks in order of a positive electrode-separator-negative electrode-separator, or a negative electrode-separator-positive electrode-separator, and it winds in a circle or a flat spiral shape, and obtains a winding body. It can manufacture by accommodating the winding body in a device can (for example, battery can), and also inject | pouring electrolyte solution. Alternatively, the electrode and the separator may be folded to form a wound body, and may be manufactured by a method of pouring the electrolytic solution into a device container (for example, an aluminum film).

  At this time, pressing can be performed on the wound body. Specifically, the separator, the current collector, and the electrode having the active material layer formed on at least one surface of the current collector are arranged so that the former thermoplastic polymer-containing layer and the active material layer face each other. An example of the method is to perform pressing by superimposing.

  The press temperature is preferably 20 ° C. or higher, for example, as a temperature at which adhesiveness can be effectively expressed. Moreover, it is preferable that the press temperature is lower than the melting point of the material contained in the substrate, and 120 ° C. or less is more preferable in terms of suppressing clogging or thermal shrinkage of the holes in the separator by hot pressing. The press pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of holes in the separator. The press time may be 1 second or less when a roll press is used, or may be a surface press for several hours, but 2 hours or less is preferable from the viewpoint of productivity. When the power storage device separator of the present embodiment is used and the manufacturing process described above is performed, press back when the wound body including the electrode and the separator is press-molded can be suppressed. Therefore, it is preferable because the yield reduction in the device assembly process can be suppressed and the production process time can be shortened.

  The electricity storage device manufactured as described above, particularly the lithium ion secondary battery, has a separator having high adhesiveness and reduced ionic resistance, and therefore has excellent battery characteristics (rate characteristics) and long-term continuity. Excellent operating durability (cycle characteristics).

  The physical properties described in this Example column were evaluated according to the following methods.

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

(2) Average particle diameter of particulate polymer (D50)
The average particle diameter (D50) of the particulate polymer was measured using a particle diameter measuring device (product name “Microtrac UPA150” manufactured by Nikkiso Co., Ltd.). As the measurement conditions, the loading index = 0.20, the measurement time was 300 seconds, and the value of 50% particle diameter (D50) in the obtained data was described as the average particle diameter.

(3) Average pore diameter of thermoplastic polymer-containing layer It is known that the fluid inside the capillary follows a Knudsen flow when the mean free path of the fluid is larger than the pore diameter of the capillary, and a Poiseuille flow when it is small. Therefore, it is assumed that the air flow in the air permeability measurement of the thermoplastic polymer-containing layer follows the Knudsen flow, and the water flow in the water permeability measurement of the substrate follows the Poiseuille flow.

The average pore diameter d (μm) of the thermoplastic polymer-containing layer is such that the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)), the water permeation rate constant R _liq (m ³ / (m ² · sec · Pa)), air molecular velocity ν (m / sec), water viscosity η (Pa · sec), standard pressure Ps (= 101325 Pa), porosity ε (%), film thickness L (μm), It calculated | required using following Formula.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶

Here, R _gas was calculated | required from the air permeability (sec) using the following Formula.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ⁻⁴ ) × (0.01276 × 101325))

R _liq was determined from the water permeability (cm ³ / (cm ² · sec · Pa)) using the following equation.
R _liq = water permeability / 100

The water permeability was determined as follows. A thermoplastic polymer-containing layer previously immersed in ethanol is set in a stainless steel liquid-permeable cell having a diameter of 41 mm. After the ethanol in this layer is washed with water, water is allowed to permeate at a differential pressure of about 50000 Pa for 120 sec. The water permeability per unit time, unit pressure, and unit area was calculated from the water permeability (cm ³ ) when the time passed, and this was defined as the water permeability.

Ν is a gas constant R (= 8.314), an absolute temperature T (K), a circumference ratio π, and an average molecular weight M of air (= 2.896 × 10 ⁻² kg / mol), using the following formula. Asked.
ν = ((8R × T) / (π × M)) ^1/2

(4) Base material thickness (μm)
A sample of 10 cm × 10 cm square is cut out from the base material, nine locations (3 points × 3 points) are selected in a lattice shape, and the room temperature is 23 ± 2 using a microthickness meter (Toyo Seiki Seisakusho Co., Ltd., type KBM). The thickness was measured at ° C. The average value of the nine measured values obtained was calculated as the thickness of the substrate.

(5) Thickness of thermoplastic polymer-containing layer The separator was frozen and cut, and the cross section was confirmed by SEM (model S-4800, manufactured by HITACHI). From the obtained field of view, the thickness of the thermoplastic polymer-containing layer was measured. Specifically, a separator sample was cut to about 1.5 mm × 2.0 mm and stained with ruthenium. The dyed sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then cleaved with a hammer. The cleaved sample was osmium-deposited and observed at an acceleration voltage of 1.0 kV and 30000 times, and the thickness of the thermoplastic polymer-containing layer was calculated. It should be noted that the boundary line between the portion where the porous structure of the cross section of the base material can be seen and the portion where it cannot be seen in the SEM image, and the shortest distance from the farthest base material to the thermoplastic polymer-containing layer in parallel with this It was set as the area | region of the thickness of a plastic polymer content layer.
In addition, when 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 base material to the thermoplastic polymer-containing layer is the thickness of the thermoplastic polymer-containing layer. can do.

(6) Thermal contraction rate (%) of laminate of separator and substrate at 120 ° C
A sample obtained by cutting the laminate to 100 mm in the TD direction and 100 mm in the MD direction was left in an oven at 120 ° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the hot air did not directly hit the sample. After the sample was taken out of the oven and cooled, its length (mm) was measured, and the thermal contraction rate of TD was calculated by the following formula.
TD heat shrinkage rate (%) = 100-length in TD after heating (mm)

(7) Measurement of glass transition temperature of thermoplastic polymer An appropriate amount of an aqueous dispersion (solid content = 38 to 42% by mass, pH = 9.0) containing a thermoplastic polymer is placed in an aluminum dish and heated at 130 ° C. And dried for 30 minutes to obtain a dry film. About 17 mg of the dried film was filled in an aluminum container for measurement, and a DSC curve and a DSC curve in a nitrogen atmosphere were obtained with a DSC measuring device (manufactured by Shimadzu Corporation, model name “DSC6220”). The measurement conditions were as follows.
First stage temperature increase program: Start at 70 ° C., increase temperature at a rate of 15 ° C. per minute. Maintained for 5 minutes after reaching 110 ° C.
Second stage temperature drop program: temperature drop from 110 ° C. at a rate of 40 ° C. per minute. Maintained for 5 minutes after reaching -50 ° C.
Third stage temperature increase program: Temperature is increased from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data are acquired when the temperature rises at the third stage.
The intersection of the base line (the straight line obtained by extending the base line in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to the downward convex curve) is defined as the glass transition temperature ( Tg).

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

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

(10) Air permeability (seconds / 100 cm ³ )
About the base material, based on JISP-8117, the air resistance measured by the Gurley type air permeability meter G-B2 (model name) by Toyo Seiki Co., Ltd. was made into the air permeability. If 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)
Using a handy compression tester KES-G5 (model name) manufactured by Kato Tech, the substrate was fixed with a sample holder having a diameter of 11.3 mm at the opening. Next, a maximum puncture load is obtained by performing a puncture test in a 25 ° C atmosphere at a puncture speed of 2 mm / sec using a needle with a radius of curvature of 0.5 mm at the center of the fixed substrate. Was measured. The value obtained by converting the maximum puncture load per 20 μm thickness was defined as the puncture strength (gf / 20 μm). If the thermoplastic polymer is present only on one side of the substrate, the needle can be pierced from the side where the thermoplastic polymer is present.

(12) Surface tension of base material and separator The surface tension of the base material or the separator was determined from a Zisman plot. Specifically, using a contact angle meter (CA-V) (model name) manufactured by Kyowa Interface Science Co., Ltd., a liquid mixture for wetting tension test having a surface tension of 40, 46, 50, 58, and 65 mN / m ( 2 μl) (manufactured by Kanto Chemical Co., Inc.) was dropped onto a substrate or a separator in an environment of 25 ° C., and the contact angle 40 seconds after dropping in each wetting reagent was measured. In addition, the base material or the separator measured the contact angle of MD direction and each TD direction 3 times, and employ | adopted the average value. The obtained data was plotted on a graph with the surface tension on the horizontal axis and the contact angle on the vertical axis to obtain a linear first-order approximation straight line. The approximate straight line was extrapolated, and the value of the horizontal axis when intersecting the horizontal axis was taken as the surface tension of the substrate or separator.

(13) Contact angle of water Using a contact angle meter (CA-V) (model name) manufactured by Kyowa Interface Science Co., Ltd., 2 μl of ion-exchanged water was dropped on the surface of the clean thermoplastic polymer-containing layer, and after 40 seconds had elapsed. The contact angle was measured. As the water contact angle, an average value measured three times in the MD and TD directions was used.

(14) Rate characteristics a. Production of positive electrode 90.4% by mass of nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) as a positive electrode active material, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) as conductive aid, and acetylene black powder (AB) (density 1.95 g / cm ³ , number An average particle diameter of 48 nm) was mixed with 3.8% by mass, and polyvinylidene fluoride (PVdF) (density 1.75 g / cm ³ ) as a binder at a ratio of 4.2% by mass, and these were mixed with N-methylpyrrolidone (NMP). ) To prepare a slurry. This slurry was applied to one side of a 20 μm-thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then subjected to compression molding using a roll press to obtain a positive electrode. Produced. The coating amount of the positive electrode active material at this time was 109 g / m ² .

b. Graphite powder A (density 2.23 g / cm ^3, number average particle diameter of 12.7 [mu] m) as prepared negative active material of the negative electrode of 87.6 wt%, and graphite powder B (density 2.27 g / cm ^3, the number average particle 9.7% by mass of 6.5 μm in diameter), 1.4% by mass of ammonium salt of carboxymethylcellulose as a binder (solid content conversion) (solid content concentration 1.83% by mass aqueous solution), and 1.7% by mass of diene rubber latex % (Solid content conversion) (solid content concentration 40 mass% aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press to produce a negative electrode. The coating amount of the negative electrode active material at this time was 5.2 g / m ² .

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

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

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

Evaluation criteria for rate characteristic (%) A (good): rate characteristic exceeds 85% B (possible): rate characteristic exceeds 80% and 85% or less C (defect): rate characteristic is 80% or less

(15) Peel strength P2
The separator was cut into a width of 20 mm and a length of 70 mm, and one surface (A) of the separator and the surface (B) opposite to the surface (A) were overlapped to form a wound body. In the examples and comparative examples, since the thermoplastic polymer-containing layer was formed on both the surface (A) and the surface (B) of the base material, the thermoplastic polymer-containing layer on the surface (A) and the surface (B) The overlapping wound body is configured such that the thermoplastic polymer-containing layer faces the layer. The wound body was pressed under the following conditions.
Temperature: 25 ° C
Press pressure: 5 MPa
Press time: 12h
Using a force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd., the peel strength between the face (A) and the face (B) of the separator after pressing was set to 50 mm / min. A 90 ° peel test was conducted to measure the peel strength. At this time, the average value of the peel strength in a peel test for 40 mm in length performed under the above conditions was adopted as the peel strength. Further, the obtained peel strength value was set as P2 and used for calculation of the peel strength ratio (P1 / P2).

(16) Covering area ratio of thermoplastic polymer-containing layer The covering area ratio of the thermoplastic polymer-containing layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by HITACHI). The separator which is a sample was vapor-deposited on osmium, and observed under conditions of an acceleration voltage of 1.0 kV and 50 times, and the surface coverage was calculated from the following formula. In addition, the area | region where the porous structure of a base-material surface is not visible in a SEM image was made into the thermoplastic polymer content layer area | region.
Covering area ratio (%) of thermoplastic polymer-containing layer = Area of thermoplastic polymer-containing layer ÷ (Area including pore portion of substrate + Area of thermoplastic polymer-containing layer) × 100
The covering area ratio in each sample was measured three times to obtain an arithmetic average value.

(17) Peel strength P1
The separator was cut into a rectangular shape having a width of 20 mm and a length of 70 mm, and one surface (A) of the separator and a surface (B) opposite to the surface (A) were overlapped to form a wound body. In the examples and comparative examples, since the thermoplastic polymer-containing layer was formed on the surface (A) and the surface (B) of the substrate, the thermoplastic polymer-containing layer on the surface (A) and the thermoplasticity on the surface (B). The overlapping wound body is configured so that the polymer-containing layer faces the polymer-containing layer. The wound body was pressed under the following conditions.
Temperature: 90 ° C
Press pressure: 1 MPa
Press time: 5 seconds Peeling strength between the face (A) and the face (B) of the separator after pressing was peeled using Force Gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. A 90 ° peel test was conducted at a speed of 50 mm / min, and the peel strength was measured. At this time, the average value of the peel strength in a peel test for 40 mm in length performed under the above conditions was adopted as the peel strength. Further, the obtained peel strength value was set as P1, and used for calculation of the peel strength ratio (P1 / P2).

(18) Pressback amount of wound body Each of the separator and the electrode was cut into a length of 30 mm wide by 200 mm long, and a laminate was produced by stacking the separator, the negative electrode, the separator, and the positive electrode in this order. The laminate was wound around a support having a width of 15 mm and a thickness of 1 mm. After winding to the end, the support was taken out to prepare a separator and electrode winding body. After measuring the thickness (the length in the radial direction) of the formed wound body, the wound body was pressed under the following conditions.
Temperature: 90 ° C
Press pressure: 1 MPa
Press time: 2 min
After pressing, the thickness of the wound body was measured in the same manner, and the press back amount of the wound body was evaluated based on the following criteria. The thickness of the wound body was measured with a ruler.
Pressback amount of wound body (%) = “(thickness of wound body after pressing) − (total thickness of laminated separator and electrode)” / “(thickness of wound body before pressing) − (Total thickness of stacked separators and electrodes) ”× 100
Evaluation criteria for rollback pressback amount A (very good): rollback pressback amount of 0% or more and less than 10% B (good): rollback pressback amount of 10% or more, Less than 50% C (possible): The rollback has a pressback amount of 50% or more and less than 95%. D (Poor): The rollback has a pressback amount of 95%.

(19) Blocking resistance A separator having a rectangular shape with 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 fed out uniformly and without wrinkles within 20 m from the inner layer of the wound body is measured. Based on the following evaluation criteria, anti-blocking Sex was evaluated.
Evaluation criteria for blocking resistance A (very good): Uniform and wrinkle-free separator length is over 1 m B (good): Uniform and wrinkle-free separator length is over 95 cm and over 1 m C (defect): Uniform and wrinkle-free separator length is 95m or less

(20) Coated surface Confirm the surface of the 0.5m2 separator coated with the thermoplastic polymer layer, measure the number of repels that can completely cover the 2mm x 2mm square, and based on the following evaluation criteria The coated surface was evaluated.
○ (Good): Number of repellants on one side of the separator is less than 4 × (Not possible): Number of cissings on one side of the separator is 5 or more

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

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

  About the obtained polyolefin microporous film B1, the physical property was measured by the said method. Further, the obtained polyolefin microporous film was used as a separator as it was and evaluated by the above method. The obtained results are shown in Table 1.

[Production Example 1-2] (Production of polyolefin microporous membrane B2)
Except having changed the temperature and relaxation rate in the case of extending | stretching, it carried out similarly to manufacture example 1-1, and obtained polyolefin microporous film B2 as a base material. The obtained polyolefin microporous membrane B2 was evaluated in the same manner as in Production Example 1-1. The obtained results are shown in Table 1.
[Production Example 1-3] (Production of polyolefin microporous membrane B3)
25 parts by mass of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 2 million, 15 parts by mass of high-density polyethylene having a viscosity average molecular weight of 700,000, 30 parts by mass of high-density polyethylene having a viscosity average molecular weight of 250,000, and a viscosity average molecular weight of 12 Ten parts by weight of copolymer polyethylene having a propylene unit content of 1 mol% was dry blended using a tumbler blender. 0.3 parts by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 parts by mass of the obtained polymer mixture. Then, again by dry blending using a tumbler blender, a polymer mixture was obtained. The obtained mixture of polymers and the like was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Liquid paraffin was injected into the extruder cylinder by a plunger pump. They were melt-kneaded, and the feeder and the pump were adjusted so that the ratio of liquid paraffin in the total mixture to be extruded was 65 mass%, that is, the ratio of the resin composition was 35 mass%. The obtained melt-kneaded product was extruded and cast on a cooling roll through a T-die to obtain a sheet-like molded product. Then, except having changed the extending | stretching temperature and the relaxation rate, it carried out similarly to manufacture example 1-1, and obtained polyolefin microporous film B3 as a base material. The obtained polyolefin microporous membrane B3 was evaluated in the same manner as in Production Example 1-1. The obtained results are shown in Table 1.

[Production Example 1-4] (Production of polyolefin microporous membrane B4)
A separator manufactured by Celgard Co., Ltd., H1609 (model name) was used as a polyolefin microporous membrane B4 and evaluated in the same manner as in Production Example 1. The obtained results are shown in Table 1.

  The values in the column of surface tension in Table 1 are subjected to corona treatment on the base material so that the surface tension value falls within the numerical range in terms of achieving both blocking resistance and adhesion to the electrode. This is the value before application.

<Synthesis of particulate polymer>
(Production Example A1) Aqueous dispersion (indicated as “raw polymer” in the table; the same applies hereinafter) A1 synthesis A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with ion-exchanged water 70. 4 parts by mass, “AQUALON KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., indicated as “KH1025” in the table, the same applies hereinafter), and “Adekaria soap SR1025” ( (Registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution, indicated as “SR1025” in the table, the same applies hereinafter.) Thereafter, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (indicated as “APS (aq)” in the table, the same applies hereinafter) was added while maintaining the internal temperature of the container at 80 ° C.

On the other hand, 46 parts by weight of methyl methacrylate, 20 parts by weight of n-butyl acrylate, 20 parts by weight of 2-ethylhexyl acrylate, 2 parts by weight of methacrylic acid, 2 parts by weight of acrylic acid, aromatic vinyl monomer, ie styrene, “Aqualon KH1025 "(registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 2.0 parts by mass, 1.0 part by mass of trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.), γ-methacryloxypropyltrimethoxy A mixture of 0.5 part by mass of silane, 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes with a homomixer to prepare an emulsion.
The obtained emulsion was dropped from the dropping tank into the reaction vessel. The dropping was started 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of the emulsion was dropped over 150 minutes. The container internal temperature was maintained at 80 ° C. during the dropping of the emulsion.

  After completion of the dropwise addition of the emulsion, the reaction container was maintained at an internal temperature of 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 aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40% by mass (raw polymer A1). The obtained raw material polymer (aqueous dispersion) A1 was evaluated by the above method. The obtained results are shown in Table 3.

(Production Examples A2 to A6) Synthesis of Aqueous Dispersions A2 to A6 The raw material polymer (aqueous dispersion), except that the composition of the monomer and other raw materials was changed as shown in Tables 3 to 5, respectively. In the same manner as A1, copolymer latexes (raw polymers A2 to A6) were obtained. About the obtained raw material polymer (water dispersion) A2-A6, it evaluated by the said method, respectively. The obtained results are shown in Table 2.

Abbreviations of raw material names in Table 2 and Tables 3 to 4 described later have the following meanings, respectively.
<Emulsifier>
KH1025: “AQUALON KH1025” registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: “ADEKA rear soap SR1025” registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution NaSS: sodium p-styrenesulfonate <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 BMA: n-butyl methacrylate EHA: 2-ethylhexyl acrylate CHMA: cyclohexyl methacrylate (aromatic vinyl monomer)
St: Styrene (cyano group-containing monomer)
AN: Acrylonitrile (other functional group-containing monomer)
HEMA: 2-hydroxyethyl methacrylate AM: Acrylamide (crosslinkable monomer)
GMA: Glycidyl methacrylate A-TMPT: Trimethylolpropane triacrylate AcSi: γ-methacryloxypropyltrimethoxysilane

(Production Example A1-1)
An aqueous dispersion A1-1 was synthesized by taking a part of the aqueous dispersion A1 obtained in Production Example A1 and performing multi-stage polymerization using this as a seed polymer. Specifically, first, in a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, the aqueous dispersion A1 is 16 parts by mass in terms of solid content, and Aqualon KH1025 (registered trademark) 0.5 mass. Part, Adekaria soap SR1025 (registered trademark) 0.5 part by mass, and 70.4 parts by mass of ion-exchanged water were added, and the internal temperature of the reaction vessel was raised to 80 ° C. Thereafter, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added while maintaining the internal temperature of the container at 80 ° C. The above is the initial preparation.

  Meanwhile, 46 parts by weight of methyl methacrylate, 20 parts by weight of n-butyl acrylate, 20 parts by weight of 2-ethylhexyl acrylate, 2 parts by weight of methacrylic acid, 2 parts by weight of acrylic acid, 10 parts by weight of aromatic vinyl monomer, that is, styrene , “AQUALON KH1025” (registered trademark, 25% aqueous solution) 2.0 parts by mass, 1.0 part by mass of trimethylolpropane triacrylate, 0.5 part by mass of γ-methacryloxypropyltrimethoxysilane, ammonium persulfate (2% aqueous solution) ) A mixture of 7.5 parts by mass and 52 parts by mass of ion-exchanged water was mixed with a homomixer for 5 minutes to prepare an emulsion. The obtained emulsion was dropped from the dropping tank into the reaction vessel. The dropping was started 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of the emulsion was dropped over 150 minutes. The container internal temperature was maintained at 80 ° C. during the dropping of the emulsion.

  After completion of the dropwise addition of the emulsion, the reaction container was maintained at an internal temperature of 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 aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40% by mass (raw polymer A1-1). The obtained raw material polymer A1-1 was evaluated by the above method.

(Production Examples A1-2 to A5-2)
Each copolymer latex is subjected to multistage polymerization in the same manner as the raw material polymer (aqueous dispersion) A1-1 except that the composition of the seed polymer, monomer, and other raw materials is changed as shown in Table 3, respectively. Got. About the obtained raw material polymer (water dispersion), it evaluated by the said method, respectively.

[Example 1]
An aqueous dispersion A1-2 having a solid content of 80 parts by mass and an aqueous dispersion A6 having a solid content of 20 parts by mass are uniformly dispersed in water, and a coating liquid containing a thermoplastic polymer (solid content of 5% by mass) ) Was prepared. At this time, as the post-added surfactant, polyoxyethylene alkyl ether, which is a polyether surfactant, was added so as to be 0.005% by mass with respect to the coating solution. further. Carboxymethylcellulose was added as a thickener so that it might become 1 mass% with respect to a coating liquid, and the viscosity of the coating liquid was adjusted to 30 mPa * s. Prior to application of the coating solution, the substrate was subjected to corona treatment for the purpose of adjusting the surface tension of the substrate within a predetermined range. Then, the coating liquid was apply | coated to the single side | surface (surface (A)) of polyolefin microporous film B1 using the gravure coater. At this time, the coating area ratio of the thermoplastic polymer to the polyolefin microporous film was 20%. Then, the coating liquid after application | coating was dried at 40 degreeC, and water was removed.
Furthermore, the coating liquid was similarly applied to the surface (surface (B)) opposite to the surface (A) of the polyolefin microporous membrane B1, and dried again in the same manner as described above. Thus, a separator having a thermoplastic polymer-containing layer formed on both surfaces of the polyolefin microporous membrane B1 was obtained.

[Example 2]
A separator was obtained in the same manner as in Example 1 except that the substrate was subjected to plasma treatment for the purpose of adjusting the surface tension of the substrate within a predetermined range.

[Example 3]
A separator was obtained in the same manner as in Example 1 except that an anionic surfactant alkylsulfosuccinic acid was used instead of the polyoxyethylene alkyl ether.

[Example 4]
A separator was obtained in the same manner as in Example 1 except that polyoxyethylene alkyl sulfate, which is an anionic surfactant, was used instead of polyoxyethylene alkyl ether.

[Examples 5 to 15]
A separator was obtained in the same manner as in Example 1 except that the polyolefin microporous film, the composition of the coating solution, and the presence of the thermoplastic polymer were changed as shown in Table 4, respectively.

[Example 16]
A separator was obtained in the same manner as in Example 1 except that PVdF-HFP latex Solef 21216 (Solvey) was used instead of the aqueous dispersion A1-2.

[Comparative Examples 1-3]
A separator was obtained in the same manner as in Example 1 except that the polyolefin microporous film, the composition of the coating solution, the presence of the thermoplastic polymer, and the presence or absence of surface treatment were changed as shown in Table 4. .

  The results obtained in the above production examples, examples, and comparative examples are shown in Tables 3-4.

As can be seen from Table 4, in Examples 1 to 13, as compared with Comparative Examples 1 to 3, the evaluation of the amount of press back of the wound body is C evaluation or more, and the blocking resistance (in the table, “Separator Since the evaluation of “position shift amount at the time of feeding” is not less than B evaluation, it was confirmed that both blocking resistance and adhesion to the electrode can be achieved.
In Comparative Examples 1 and 3, since P1 is less than 5 N / m, the evaluation result of the press back amount of the wound body was D evaluation. In Comparative Example 2, although P1 is 5 N / m or more, P1 / P2 ≧ 0.5 is not satisfied, and the evaluation result of blocking resistance is C evaluation, and the blocking resistance and adhesion to the electrode are I was unable to achieve both.
Also, Example 6 in which no polyether surfactant was added, Example 7 in which the covering area ratio of the thermoplastic polymer-containing layer to the substrate was 5%, and Example 13 in which PVdF was used as the polymer Compared with the other Examples, the evaluation of the press back amount of the wound body was C evaluation. About Examples other than these Examples 6, 7, and 13, all evaluations of the press back amount and blocking resistance of the wound body are B evaluation or more, and it was confirmed that this is a particularly preferable embodiment. .

  When the blocking force is increased, the binder component applied on the substrate is displaced, and the displaced binder component is rubbed against the portion of the substrate where the thermoplastic polymer-containing layer is not disposed, thereby blocking the hole. It is also considered that the rate characteristics deteriorate. However, in all of Examples 1 to 13, it was confirmed that the evaluation of the rate characteristic was B evaluation or more, and therefore both the blocking resistance and the rate characteristic can be achieved.

  The electricity storage device separator of the present invention can achieve both blocking resistance and adhesion to electrodes. Therefore, the separator for an electricity storage device of the present invention can be suitably mounted on various kinds of electricity storage devices including lithium ion batteries mounted on electric vehicles (EV), for which a particularly high capacity is desired in recent years.

Claims (12)

An electricity storage device separator comprising a substrate and a thermoplastic polymer-containing layer formed on at least one surface of the substrate, wherein the electricity storage device separator is represented by the following formula:
P1 / P2 ≧ 0.5
{Wherein P1 forms a wound body by overlapping one surface (A) of the electricity storage device separator and a surface (B) opposite to the surface (A), and the wound body Is the peel strength between the surface (A) and the surface (B) when pressed for 5 seconds under the conditions of a temperature of 90 ° C. and a pressure of 1 MPa, and P2 is a temperature of 25 ° C. for the wound body. And the peel strength between the surface (A) and the surface (B) when pressed for 12 hours under a pressure of 5 MPa. }
The separator for electrical storage devices which satisfy | fills the relationship represented by these, and said P1 is 5 N / m or more.   The electricity storage device separator according to claim 1, wherein the P2 is 15 N / m or less.   The electrical storage device separator according to claim 1 or 2, wherein the P1 / P2 is 2.5 or less.   The electrical storage device separator of any one of Claims 1-3 whose contact angle of water with respect to the surface in which the said thermoplastic polymer content layer of the said electrical storage device separator is formed is 95 degrees or less.   The electrical storage device separator according to any one of claims 1 to 4, wherein a covering area ratio of the thermoplastic polymer-containing layer to the base material is 50% or less.   The separator for electrical storage devices of any one of Claims 1-5 in which the thermoplastic polymer contained in the said thermoplastic polymer content layer contains the polymerization unit of (meth) acrylic acid ester or (meth) acrylic acid.   The separator for electrical storage devices of any one of Claims 1-6 whose glass transition temperature of the thermoplastic polymer contained in the said thermoplastic polymer content layer is 40 degreeC or more.   The electrical storage device separator according to any one of claims 1 to 7, wherein the thermoplastic polymer-containing layer includes two or more types of thermoplastic polymers having different glass transition temperatures.   The power storage device separator according to claim 1, wherein the thermoplastic polymer-containing layer includes a polyether surfactant.   The electricity storage device separator according to any one of claims 1 to 9, wherein the electricity storage device separator is wound.   An electrical storage device provided with the separator for electrical storage devices of any one of Claims 1-10.   A lithium ion secondary battery provided with the separator for electrical storage devices of any one of Claims 1-10.