JP2020068116A - Separator for power storage device, wound body employing the same, lithium ion secondary battery, and power storage device - Google Patents

Abstract

To provide a separator for power storage device, etc., capable of making blocking resistance compatible with an adhesive property to an electrode.SOLUTION: The present invention relates to a separator for power storage device comprising a substrate and a thermoplastic polymer containing layer which is formed on at least one face of the substrate. The separator meets the following expression of P1/P2≥0.5, wherein P1 is a peel strength between one face (A) of the separator for power storage device and a face (B) at an opposite side of the face (A) in a case where a wound body is formed by overlapping the face (A) and the face (B) and the wound body is pressed for five seconds under the condition that the temperature is 90°C and the pressure is 1 MPa, and P2 is a peel strength between the face (A) and the face (B) in a case where the wound body is pressed for 12 hours under the condition that the temperature is 25°C and the pressure is 5 MPa, and P1 is equal to or greater than 5 N/m.SELECTED DRAWING: None

Description

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

  BACKGROUND ART Conventionally, development of electricity storage devices represented by lithium-ion secondary batteries has been actively conducted. Usually, an electricity storage device is provided with a microporous film (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 micropores.

The separator has the characteristics of quickly stopping the battery reaction when it is abnormally heated (fuse characteristics), and the performance of maintaining the shape even at high temperatures and preventing dangerous situations in which the positive and negative electrodes directly react (short characteristics). Performance related to safety is required.
Further, for the purpose of increasing the capacity of the electricity storage device, a technique is used in which the volume of the wound body is reduced by hot pressing the wound body in which a laminated body of an electrode and a separator is wound. . 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 predetermined conditions is placed on the separator, and the adhesiveness of the separator and the electrode is improved. Techniques for improving are also used.

  Here, for example, Patent Document 1 discloses a separator for the purpose of providing a separator having excellent adhesiveness to an electrode and further excellent handling property. Such a separator includes a thermoplastic polymer-containing layer in which a thermoplastic polymer-containing portion and a thermoplastic polymer-free portion 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, and at least one of the glass transition temperatures exists in a region below 20 ° C. and at least one of the glass transition temperatures exists in a region above 20 ° C.

  Patent Document 2 discloses a lithium ion secondary battery for the purpose of improving mechanical properties and electrical properties. Such a lithium ion secondary battery has 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 Unexamined Patent Application Publication No. 2015-041603

  In recent years, regarding a separator including a thermoplastic polymer-containing layer on at least one surface of a base material, a wound body formed by stacking the separator and an electrode has a tendency of long winding from the viewpoint of improving production efficiency. The longer the wound body is, the longer the length of each of the separator and the electrode is, and the higher the pressure applied to the inner layer of the wound body is. Due to such pressure, separators adhere to each other in a stage before the wound body is produced, for example, in a normal storage stage in which the wound body in which only the separator is wound is stored, is "blocking". Is expected to occur. In such a case, when the separator is wound from the wound body in which only the separator is wound, a blocking stress between the separators is required, which makes it difficult to uniformly wind the separator having a desired length without wrinkles. .

  In addition, due to the increasing environmental awareness, electric storage devices such as electric vehicles (EV) have received more and more attention in recent years, and a lithium ion secondary battery mounted in such an electric storage device is expected to have a particularly high capacity. There is. 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, and thereby appropriately suppress the pressback of the wound body.

However, it is easy to prevent the adhesion of the separators in the normal storage stage, that is, to improve the blocking resistance, and to easily suppress the 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 adhesiveness of the.
Under the above circumstances, Patent Documents 1 and 2 have not examined how to achieve both blocking resistance and adhesiveness to an electrode.

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

The present inventors have conducted studies to solve the above problems and have found that the above problems can be solved by using a separator for an electricity storage device having the following configuration, and have completed the present invention. That is, the present invention is as follows.
[1]
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 the electricity storage device separator has the following formula:
P1 / P2 ≧ 0.5
{In the formula, P1 is a wound body formed by stacking one surface (A) of the electricity storage device separator and a surface (B) opposite to the surface (A) to form a wound body. Is the peel strength between the surface (A) and the surface (B) when pressed at a temperature of 90 ° C. and a pressure of 1 MPa for 5 seconds, and P2 is the wound body at a temperature of 25 ° C. And the peel strength between the surface (A) and the surface (B) when pressed for 12 hours under a pressure of 5 MPa. }
An electricity storage device separator satisfying the relationship represented by and having P1 of 5 N / m or more.
[2]
The electricity storage device separator according to [1], wherein the P2 is 15 N / m or less.
[3]
The electricity storage device separator according to [1] or [2], wherein P1 / P2 is 2.5 or less.
[4]
The electricity storage device separator according to any one of [1] to [3], wherein a contact angle of water with respect to a surface of the electricity storage device separator on which the thermoplastic polymer-containing layer is formed is 95 ° or less. .
[5]
The electricity storage device separator according to any one of [1] to [4], wherein a coverage of the thermoplastic polymer-containing layer with respect to the substrate is 50% or less.
[6]
The electricity storage device according to any one of [1] to [5], wherein the thermoplastic polymer contained in the thermoplastic polymer-containing layer contains a polymer unit of (meth) acrylic acid ester or (meth) acrylic acid. Separator.
[7]
The electricity storage device separator according to any one of [1] to [6], wherein the thermoplastic polymer contained in the thermoplastic polymer-containing layer has a glass transition temperature of 40 ° C. or higher.
[8]
The electricity storage device separator according to any one of [1] to [7], wherein the thermoplastic polymer-containing layer contains two or more types of thermoplastic polymers having different glass transition temperatures.
[9]
The electricity storage device separator according to any one of [1] to [8], wherein the thermoplastic polymer-containing layer contains a polyether surfactant.
[10]
The electricity storage device separator according to any one of [1] to [9], in which the electricity storage device separator is wound.
[11]
An electricity storage device including the electricity storage device separator 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 the items.

  According to the present invention, there is provided a separator for an electricity storage device, a wound body using the same, a lithium-ion secondary battery, and an electricity storage device that can achieve 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, but the present invention is not limited to the following present embodiment. The present invention can be variously modified without departing from the gist thereof.
In the present specification, "(meth) acrylic" means "acrylic" and its corresponding "methacrylic", and "(meth) acrylate" means "acrylate" and its corresponding "methacrylate". And “(meth) acryloyl” means “acryloyl” and its corresponding “methacryloyl”.
Further, in the present specification, “on” and “formed on a surface” do not mean that the positional relationship of each member is “directly above”. For example, the expressions "thermoplastic polymer-containing layer formed on a substrate" and "thermoplastic polymer-containing layer formed on the surface of a substrate" mean that between the substrate and the thermoplastic polymer-containing layer, An embodiment including an arbitrary layer (a layer having a heat resistance function, for example, an inorganic filler porous layer) is not excluded.
Furthermore, in this specification, "-" means that the numerical values described before and after the "-" are included as the upper limit value and the lower limit value, unless otherwise specified.

<Separator for electricity storage device>
The electricity storage device separator 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 surface of the separator and the aspect in which the thermoplastic polymer-containing layer is formed on both surfaces 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 stacking one surface (A) of the separator and the surface (B) opposite to the surface (A), and the wound body is heated at a temperature of 90 ° C. And the peel strength between the surface (A) and the surface (B) when pressed for 5 seconds under a pressure of 1 MPa, and P2 is 12 at a temperature of 25 ° C. and a pressure of 5 MPa. It is the peel strength between the surface (A) and the surface (B) when pressed for a time. } Is satisfied, and P1 is 5 N / m or more.
When the separator satisfies the above formula, both blocking resistance and adhesion to the electrode can be achieved.

As long as the thermoplastic polymer-containing layer is arranged between the surface (A) and the surface (B), the surface (A) and the surface (B) are overlapped with each other without departing from the scope of the present invention. The form of the wound body to be formed is not limited. Therefore, in the scope of the present invention, the thermoplastic polymer-containing layer is such that the surface (A) on which the thermoplastic polymer-containing layer is formed and the surface (B) on which it is not formed are overlapped, and the surface (A) formed and the surface (A) formed. Both the form in which B) is overlapped and the form in which the surface (A) not formed and the surface (B) formed are overlapped are included.
Hereinafter, preferred embodiments of each member that can form the separator will be described in detail.

[Base material]
The base material itself may be one conventionally used as a separator. The base material 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 has high resistance to an organic solvent. Such a porous membrane contains, for example, a polyolefin-based resin (eg, polyethylene, polypropylene, polybutene, and polyvinyl chloride), and a resin such as a mixture thereof or a copolymer of monomers thereof as a main component. Microporous membrane: Polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, etc. as a main component Microporous membrane; polyolefin fiber A woven fabric (woven fabric); a non-woven fabric of polyolefin fibers; paper; and an aggregate of insulating substance particles. These may be used alone or in combination of two or more.
Among them, a polyolefin microporous film containing a polyolefin-based resin as a main component is preferable from the viewpoint of reducing the thickness of the separator to increase the ratio of the active material in the electricity storage device and thus increase the capacity per volume. The polyolefin microporous film is excellent in coatability of the coating liquid when it undergoes the step of coating the coating liquid on the film, and is therefore advantageous in reducing the thickness of the separator.
The term “comprising a polyolefin-based resin as a main component” means that the content of the polyolefin-based resin is greater than 50% by mass with respect to the total mass of the substrate. 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. , May be 100% by 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 and the like when used as a separator, it is preferable that 50% by mass or more and 100% by mass or less of all components constituting the microporous polyolefin membrane is the 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.

  The polyolefin resin is not particularly limited, but may be a polyolefin resin that can be used for ordinary extrusion, injection, inflation, blow molding and the like. Examples of the polyolefin resin include homopolymers having ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, and two or more kinds of those monomers. Copolymers, and multistage polymers. These homopolymers, copolymers, and multistage polymers are used alone or in combination of two or more.

Representative examples of the polyolefin resin include, but are not particularly limited to, polyethylene, polypropylene, and polybutene, and more specifically, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultrahigh density. Included are molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymers, polybutene, and ethylene propylene rubber. These may be used alone 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 ultra-high-molecular-weight polyethylene is preferable from the viewpoint of shutdown characteristics in which pores are closed by heat melting. In particular, high-density polyethylene is preferable because it has a low melting point and high strength, and polyethylene having a density of 0.93 g / cm ³ or more measured according to JIS K 7112 is more preferable. The polymerization catalyst used when producing these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts.

  In order to improve the heat resistance of the substrate, the polyolefin microporous film more preferably contains polypropylene and a polyolefin resin other than polypropylene. Here, the three-dimensional structure of polypropylene is not limited, and may be any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Further, as the polyolefin resin other than polypropylene, for example, homopolymers of ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and the like, and monomers thereof Two or more types of copolymers and multi-stage polymers can be mentioned, and specific examples thereof include those already described above. The polymerization catalyst used for producing polypropylene is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts.

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

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 further preferably 100,000 or more and 1 million. Is less than. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding becomes large, the moldability becomes better, and the entanglement of the polymers tends to further increase the strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12,000,000 or less, it is easy to uniformly melt-knead and the moldability of the sheet, especially the thickness stability tends to be excellent, which is preferable. Furthermore, when the viscosity average molecular weight is less than 1,000,000, the pores are likely to be clogged when the temperature rises, and a better shutdown function tends to be obtained, which is preferable. The viscosity average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at 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's formula)
Polypropylene: [η] = 1.10 × 10 ⁻⁴ Mv ^0.80
Note that, for example, instead of using a polyolefin having a viscosity average molecular weight of less than 1,000,000 alone, it is a mixture of a polyolefin having a viscosity average molecular weight of 2,000,000 and a polyolefin having a viscosity average molecular weight of 270,000, and the viscosity average molecular weight of less than 1,000,000. Mixtures may be used.

  Further, the base material can contain any additive. Such additives are not particularly limited, and examples thereof include polymers other than polyolefin; inorganic particles; phenol-based, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet rays. Examples thereof include absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin in the polyolefin microporous film. Is.

The porosity of the base material 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, its porosity is preferably 90% or less, more preferably 80% or less. The porosity of 20% or more is preferable from the viewpoint of ensuring the permeability of the separator more effectively and surely. On the other hand, it is preferable to set the porosity to 90% or less from the viewpoint of more effectively and reliably ensuring the puncture strength. The porosity is calculated, for example, from the volume (cm ³ ), mass (g), and film density (g / cm ³ ) of the base material sample by the following formula:
Porosity = (volume-mass / film density) / volume × 100
Can be obtained by Here, in the case of a polyolefin microporous film made of polyethylene, for example, the film density can be calculated assuming that the film density is 0.95 (g / cm ³ ). The porosity can be adjusted by changing the stretching ratio of the polyolefin microporous film.

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. It is ³ or less. The air permeability of 10 seconds / 100 cm ³ or more is preferable from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, the air permeability of 1000 seconds / 100 cm ³ or less is preferable from the viewpoint of obtaining good charge / discharge characteristics. The air permeability is the air resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or the stretching ratio of the substrate.

  The average pore size of the substrate is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more. Setting the average pore size to 0.15 μm or less is suitable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity decrease. The average pore size can be adjusted by changing the draw ratio when manufacturing the substrate.

  The puncture strength of the base material is not particularly limited, but is preferably 200 gf / 20 μm or more, more preferably 300 gf / 20 μm or more, further preferably 400 gf / 20 μm or more, preferably 2000 gf / 20 μm or less, more preferably 1000 gf. / 20 μm or less. The puncture strength of 200 gf / 20 μm or more suppresses the rupture of the membrane due to the active material that has fallen off when the separator is wound together with the electrode, and the risk of short circuit due to expansion and contraction of the electrode due to charge / discharge. From the viewpoint of On the other hand, the puncture strength of 2000 gf / 20 μm or less is preferable from the viewpoint of reducing the 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 the stretching temperature of the substrate.

  The thickness of the base material is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, further preferably 50 μm or less. The 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 is 100 μm or less, because the volume occupied by the separator in the electricity storage device is reduced, which tends to be advantageous in increasing the capacity of the electricity storage device.

The surface tension of the base material 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 smaller than the surface tension values of the thermoplastic polymer-containing layer, for example.
When the thermoplastic polymer-containing layer is present only on a part of the surface of the base material, when only the separator is wound, another part of the exposed surface of the base material (a part where the thermoplastic polymer-containing layer does not exist) is The substrate or another thermoplastic polymer containing layer is overlaid. In such a case, it is preferable to set the surface tension to 45 mN / m or more from the viewpoint that a phenomenon such as cissing can be suppressed when the thermoplastic polymer is formed on the substrate, and the thermoplastic polymer can be uniformly formed. . On the other hand, setting the surface tension to 52 mN / m or less means a normal storage stage in which a wound body in which only the separator is wound is stored, and the base material or the thermoplastic polymer is exposed to the exposed portion of the surface of the base material. This is preferable from the viewpoint of ensuring anti-blocking property, because the containing layer becomes difficult to adhere excessively. The surface tension is measured according to the method described in the examples.

  When the base material is a polyolefin microporous membrane, the surface tension of the polyolefin microporous membrane is determined by mixing a hydrophilic polymer, for example, a polymer containing an acid group such as carboxylic acid, into the polyolefin microporous membrane; It can be adjusted by a method of applying a surface treatment to the membrane. By carrying out these methods, the chemical properties of the surface of the polyolefin microporous membrane are changed, and as a result, the surface of the polyolefin microporous membrane is easily hydrophilized. From the viewpoint of adjusting only the surface tension without changing the physical properties of the polyolefin microporous film, it is preferable to adopt a method of performing surface treatment. The method of surface treatment is not particularly limited as long as it does not significantly impair the porous structure that the base material may have, and examples thereof include corona discharge treatment method, plasma discharge treatment method, mechanical surface roughening method, and solvent treatment method. , An acid treatment method, and an ultraviolet oxidation method. Among them, the corona discharge treatment method or the plasma treatment method is preferable from the viewpoint of minimizing damage to the microporous polyolefin membrane and the viewpoint of high-speed treatment. Of course, these methods may be used together. In addition, in the case of the corona treatment or the plasma treatment, the surface tension of the polyolefin microporous film can be appropriately adjusted by the output of the processing device, the length of the processing electrode, and the transport speed of the polyolefin microporous film.

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

[The layer containing the thermoplastic polymer]
The thermoplastic polymer-containing layer contains a thermoplastic polymer. The thermoplastic polymer-containing layer may be arranged on all or part of the surface of the base material. 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 as to be directly bonded to the electrode, for example, at least a part of the base material and the electrode are bonded to each other via the thermoplastic polymer-containing layer. Preferably.

The coating amount of the thermoplastic polymer-containing layer on the base material, that is, the formation amount (arrangement amount) of the thermoplastic polymer-containing layer per one surface area of the base material is 0.03 g / m ² or more in terms of solid content. It is preferable, and it is more preferable that 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. When the coating amount is 0.03 g / m ² or more, in the obtained separator, the adhesive force between the thermoplastic polymer-containing layer and the electrode is improved, more uniform charge / discharge is realized, and device characteristics (for example, It is preferable in that the cycle characteristics of the battery are improved. On the other hand, a coating amount of 2.0 g / m ² or less is preferable from the viewpoint of further suppressing the decrease in ion permeability.

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

  When the thermoplastic polymer-containing layer is arranged only on a part of the surface of the base material, the existing form (pattern) of the thermoplastic polymer is not particularly limited, but the thermoplastic polymer is dispersed over the entire surface of the base material. It is preferable that they exist in a state of existing in the form of sea islands. When the thermoplastic polymer exists in a sea-striped pattern, examples of the arrangement pattern thereof include dot-shaped, striped, lattice-shaped, striped, hexagonal, random-shaped patterns, and combinations thereof. Among these, the dot shape is preferable from the viewpoint of more effectively and surely exhibiting the action and effect of the present invention. When the arrangement pattern has a dot shape, the dot diameter is preferably 50 μm or more, more preferably 100 μm or more, and further 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 adhered to the electrode, and the in-plane current density can be made more uniform. Furthermore, by providing a portion where the thermoplastic polymer is not applied in the dot-shaped arrangement pattern, the in-plane current density can be made more uniform.

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

  The thickness of the thermoplastic polymer-containing layer is preferably 0.01 μm or more, and more preferably 0.1 μm or more, per surface of the substrate. In addition, 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 base material. The thickness of 0.01 μm or more is preferable in that the adhesive force between the electrode and the base material is uniformly expressed, and as a result, the device characteristics can be improved. Further, it is preferable that the thickness is 5.0 μm or less in order to suppress the decrease in ion permeability. The thickness of the thermoplastic polymer-containing layer, for example, by changing the type of the particulate polymer in the coating liquid to be applied to the substrate or the concentration of the polymer or 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 Examples.

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

  Specific examples of the particulate polymer include an acrylic polymer, a conjugated diene polymer, an acrylic polymer, a polyvinyl alcohol resin, and a fluorine-containing resin. Among these, acrylic polymers are preferable from the viewpoint of more effectively and surely exhibiting the effects of the present invention. Further, 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. Further, from the viewpoint of more effectively and surely exhibiting the effects of the present invention, the particulate polymer preferably contains a particulate copolymer. The particulate polymer may be used alone or in combination of two or more.

  Further, the thermoplastic polymer contained in the thermoplastic polymer-containing layer is preferably 60% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, particularly preferably 98% by mass, based on the total amount. As described above, the particulate polymer is included. The thermoplastic polymer-containing layer may contain a thermoplastic polymer other than the particulate polymer to the 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 conjugation. Examples thereof include pentadienes, substituted, 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. Moreover, the conjugated diene-based polymer may include a (meth) acrylic compound or another monomer described below as a monomer unit. Examples of such monomers include styrene-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene-styrene copolymers, and hydrides thereof. To be

  Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol and polyvinyl acetate. As the fluorine-containing resin, for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoro An ethylene copolymer may be used.

The acrylic polymer is a polymer having a (meth) acrylic compound as a monomer unit, that is, a polymerized unit. The (meth) acrylic compound means at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester. Examples of such a compound include compounds represented by the following formulas.
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 which may be linear or branched, a cycloalkyl group, and an aryl group. Examples of the substituent include a hydroxyl group and a phenyl group, and examples of the hetero atom include a halogen atom and an oxygen atom. The (meth) acrylic compounds are used alone or in combination of two or more. Examples of such a (meth) acrylic compound 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.

As the chain alkyl group which is one type of R ^Y2 , more specifically, a chain alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group; -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. The aryl group, which is one type of R ^Y2 , includes, for example, a phenyl group. 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, 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. (Meth) acrylate having a linear 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 preferable. 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 may be used alone or in combination of two or more.

The (meth) acrylic acid ester monomer contains 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 adhesiveness of the separator to the electrode. More specifically, examples of the monomer having a cycloalkyl group include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and adamantyl (meth) acrylate. 4-8 are preferable, as for the number of carbon atoms which comprise the alicyclic ring of a cycloalkyl group, 6-7 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 during preparation of the acrylic polymer. These may be used alone or in combination of two or more.

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

  Examples of the monomer having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth) acrylate. The polyfunctional (meth) acrylate may be at least one selected from the group consisting of bifunctional (meth) acrylate, trifunctional (meth) acrylate, and tetrafunctional (meth) acrylate. Specifically, for example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol. Mention may be made of dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. Among them, at least one kind of trimethylolpropane triacrylate or trimethylolpropane trimethacrylate is preferable from the same viewpoint as above.

  Examples of the monomer having a functional group that gives a self-crosslinking structure during or after the polymerization include a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, and hydrolysis. And a monomer having a silyl group. As the monomer having an epoxy group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable, and 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, and specifically, for example, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide. , And N-butoxymethylmethacrylamide. Examples of the monomer having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyl. Examples include triethoxysilane. These may be used alone or in combination of two or more.

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

  Examples of the amide group-containing monomer 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. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate.

  Examples of aromatic vinyl monomers include styrene, vinyltoluene, and α-methylstyrene. Preferred is styrene.

  The ratio of the acrylic polymer having a (meth) acrylic compound as a monomer unit, that is, a polymerized unit is preferably 5% by mass or more and 95% by mass or less with respect to 100% by mass of the acrylic polymer. The lower limit value is more preferably 15% by mass, further 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, the more preferable upper limit value is 92% by mass, the still more preferable upper limit value is 80% by mass, and the particularly preferable upper limit value is 60% by mass. When the content ratio of the monomer is 95% by mass or less, the adhesiveness to the substrate is improved, which is preferable.

  When the acrylic polymer has a chain alkyl (meth) acrylate or a cycloalkyl (meth) acrylate as a monomer unit, the total content ratio thereof is preferably 100% by mass of the acrylic polymer. 3 mass% or more and 92 mass% or less, more preferably 10 mass% or more and 90 mass% or less, still more preferably 15 mass% or more and 75 mass% or less, and particularly preferably 25 mass% or more and 55 mass% or less. It is the following. When the content of these monomers is 3% by mass or more, it is preferable from the viewpoint of improving the oxidation resistance, and when it is 92% by mass or less, the binding property with the base material is improved, which is preferable.

  When the acrylic polymer has (meth) acrylic acid as a monomer unit, the content ratio thereof is preferably 0.1% by mass or more and 5% by mass or less based on 100% by mass of the acrylic polymer. . When the content ratio of the above monomer is 0.1% by mass or more, the separator tends to have improved cushioning properties in a swollen state, and when it is 5% by mass or less, polymerization stability tends to be good. is there.

  When the acrylic polymer has a crosslinkable monomer as a monomer unit, the content ratio of the crosslinkable monomer in the acrylic polymer is preferably 0.1% with respect to 100% by mass of the acrylic polymer. The content is 01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, and further preferably 0.1% by mass or more and 3% by mass or less. When the content ratio of the above-mentioned monomer is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when it is 10% by mass or less, the deterioration of the cushioning property in a swollen state can be further suppressed.

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

  The copolymer of (2) above preferably has a hydrocarbon ester of (meth) acrylic acid 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. When the copolymer (2) has a monomer having an amide group, the copolymerization ratio is preferably 0.1% by mass or more and 5% by mass or less. Further, 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.

  The copolymer of (3) above may contain, as the (meth) acrylic acid ester monomer, at least one selected from the group consisting of chain alkyl (meth) acrylate and 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 or more and 95% by mass or less, more preferably 3% by mass or more and 90% by mass or less, It is more preferable that the content is 5% by mass or more and 85% by mass or less. The upper limit of this copolymerization ratio may be 60% by weight, in particular 40% by weight or 30% by weight, and particularly preferably 20% by weight. 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. It is more preferable that the content 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. When the copolymer (3) has a monomer having an amide group, the copolymerization ratio is preferably 0.1% by mass or more and 10% by mass or less, and 2% by mass or more and 10% by mass or more. % Or less is more preferable. Further, 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. It is more preferably 10% by mass or less.

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

  For example, in a dispersion system containing the above-mentioned monomer, a surfactant, a radical polymerization initiator, and optionally other additive components used as a basic composition component in an aqueous medium, each monomer is contained. An acrylic polymer is obtained by polymerizing the monomer composition. In the polymerization, a method of making the composition of the supplied monomer composition constant in the whole polymerization process, or changing the morphological composition of the particles of the resin dispersion produced by changing it sequentially or continuously in the polymerization process Various methods such as a method can be used as needed. When the acrylic polymer is obtained by emulsion polymerization, it may be in the form of an aqueous dispersion (latex) containing water and the particulate acrylic polymer dispersed in the water.

The surfactant is a compound having at least one hydrophilic group and one or more lipophilic group 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 will be omitted here.
Further, the radical polymerization initiator is one which initiates the addition polymerization of monomers by radical decomposition by heat or a reducing substance. Since the radical polymerization initiator will be described later, the description thereof will be omitted here.

  Among the forms of the thermoplastic polymer, the monomer from the viewpoint of improving the adhesiveness between the separator and the electrode, the high temperature storage property of the electricity storage device, and the cycle property, and achieving the thinning 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 preferable.

  The glass transition temperature (Tg) of the particulate polymer is preferably −50 ° C. or higher, more preferably −30 ° C. or higher, and more preferably 20 ° C., from the viewpoint of adhesion to electrodes and ion permeability. The above is more preferable, and 40 ° C. or more is still more preferable. The glass transition temperature of the particulate polymer is preferably 200 ° C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the temperature at the intersection of the straight line obtained by extending the low temperature side baseline in the DSC curve to the high temperature side and the tangent line at the inflection point of the stepwise change portion of the glass transition may be adopted as the glass transition temperature. it can. More specifically, it may be determined according to the method described in the examples. Further, "glass transition" refers to a change in the amount of heat caused by a change in the state of a polymer as a test piece on the endothermic side in DSC. Such a change in the amount of heat is observed as a step-like change shape in the DSC curve. The “stepwise change” refers to a part of the DSC curve from the baseline on the low temperature side until the curve moves to a new baseline on the high temperature side. Note that a combination of a step change and a peak is also included in the step change. Furthermore, the "inflection point" refers to a point at which the slope of the DSC curve in the stepwise change portion becomes maximum. Further, in the stepwise change portion, when the upper side is the heat generating side, it can be expressed as a point where the upward convex curve changes to the downward convex curve. “Peak” refers to a portion of the DSC curve from the time when the curve leaves the baseline on the low temperature side until it returns to the same baseline again. The “baseline” refers to a DSC curve in a temperature range in which no transition or reaction occurs on the test piece.

The glass transition temperature Tg of the particulate polymer is, for example, the kind of monomer used in producing the particulate polymer, and when the particulate polymer is a copolymer, the compounding ratio of each monomer. It can be appropriately adjusted by changing it. That is, for each monomer used in the production of the particulate polymer, the Tg of the homopolymer that is generally shown (for example, described in “Polymer Handbook” (A WILEY-INTERSCIENCE PUBLICATION)) and the monomer An approximate glass transition temperature can be estimated from the blending ratio. For example, a copolymer obtained by copolymerizing a monomer such as methyl methacrylate, acrylonitrile, and methacrylic acid in a high ratio to give a homopolymer having a Tg of about 100 ° C. has a high Tg of about −50 ° C. The copolymers obtained by copolymerizing monomers such as n-butyl acrylate and 2-ethylhexyl acrylate in a high proportion to give a homopolymer having a Tg of 2 are lower in Tg.
The Tg of the copolymer can also be roughly estimated by the FOX formula represented by the following 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 the 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 above-mentioned method using DSC is adopted.

  From the viewpoint of wettability to the base material, binding property between the base material and the thermoplastic polymer-containing layer, and adhesiveness to the electrode, the thermoplastic polymer-containing layer contains a polymer having a glass transition temperature of less than 40 ° C. Preferably. The glass transition temperature of the polymer having a glass transition temperature of lower than 40 ° C. is preferably −100 ° C. or higher, more preferably −50 ° C. or higher, further preferably −40 ° C. or higher from the viewpoint of ion permeability, and the polyolefin microporous film From the viewpoint of the binding property between the thermoplastic polymer-containing layer and the thermoplastic polymer-containing layer, the temperature is preferably lower than 20 ° C, more preferably lower than 15 ° C, and further preferably lower 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 of allowing the particulate polymer to have at least two glass transition temperatures is not limited, but a method of blending two or more types of particulate polymers, and a particulate polymer having a core-shell structure The method of using is mentioned. The core-shell structure is a structure having a central portion and an outer shell portion covering the central portion, and is a polymer having a double structure in which the types or compositions of polymers constituting the respective portions are different from each other. . In particular, in the blend of polymers and the core-shell structure, the glass transition temperature of the entire particulate polymer can be controlled by combining the polymer having a high glass transition temperature and the polymer having a low glass transition temperature. Further, it is possible to impart a plurality of functions to the entire particulate polymer.

  For example, in the case of blending two or more kinds of particulate polymers, one or more polymers existing in a region having a glass transition temperature of 20 ° C. or more and one or more polymers existing in a region having a glass transition temperature of less than 20 ° C. By blending with the above polymer, the stickiness resistance and the wettability on the base material can be more favorably achieved. The blending ratio of each polymer in the case of blending is 0.1: 99 as a ratio of a polymer existing in a region having a glass transition temperature of 20 ° C. or higher to a polymer existing in a region having a glass transition temperature of less than 20 ° C. It is preferably in the range of 9.9 to 99.9: 0.1, more preferably 5:95 to 95: 5, further preferably 50:50 to 95: 5, and particularly preferably 60 :. It is 40 to 90:10.

  When a particulate polymer having a core-shell structure is used, the adhesion and compatibility of the thermoplastic polymer-containing layer with other members (such as a base material) can be adjusted by selecting the type of polymer of the outer shell portion. it can. Also, by selecting the type of polymer in the central portion, for example, the adhesiveness to the electrode after hot pressing can be enhanced. Alternatively, it is also possible to control the viscoelasticity of the thermoplastic polymer-containing layer by combining a highly viscous polymer and a highly elastic polymer.

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

  The arithmetic mean 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 mean particle size of the particulate polymer is preferably 1000 nm or less, more preferably 800 nm or less, and further preferably 700 nm or less. By setting the arithmetic average particle size to 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 adhesiveness between the electrode and the separator and the cycle characteristics and rate characteristics of the electricity storage device. In addition, it is preferable that the arithmetic average particle diameter is 1000 nm or less from the viewpoint of ensuring the dispersion stability when the thermoplastic polymer-containing layer containing the particulate polymer is formed from the aqueous dispersion. It is preferable from the viewpoint that the thickness of the plastic polymer-containing layer can be flexibly controlled. From these viewpoints, it is particularly preferable that the arithmetic mean particle size of the particulate polymer is 200 nm or more and 1000 nm or less. The arithmetic mean particle size of the particulate polymer is measured according to the method described in the following examples.

  Two or more types of particulate polymers each having a different arithmetic mean particle size may 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 , "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 the polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization and the like can be adopted. The emulsion polymerization method is preferable for the purpose of obtaining a dispersion in the form of particles. The emulsion polymerization method is not particularly limited, and a conventionally known method can be used. For example, in a dispersion system having the above-mentioned monomer, a surfactant, a radical polymerization initiator, and optionally other additive components used as a basic composition component in an aqueous medium, A polymer is obtained by polymerizing the monomer composition. At the time of polymerization, a method of keeping the composition of the monomer composition to be constant in the entire polymerization process, or by sequentially or continuously changing the composition of the resin composition to change the morphological composition of the particles of the resulting resin dispersion. Various methods such as a giving method can be used as necessary. When the polymer is obtained by emulsion polymerization, it may be in the form of an aqueous dispersion (latex) containing, for example, water and a particulate polymer dispersed in the water.

  The surfactant is a compound having at least one hydrophilic group and one or more lipophilic group in one molecule. Examples of the surfactant include polyether surfactants; non-reactive alkyl sulfates, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ethers. Disulfonic acid salt, naphthalenesulfonic acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate ester salt, polyoxyethylene distyrenated phenyl ether sulfate ester salt, fatty acid salt, alkyl phosphate salt, and polyoxyethylene alkylphenyl ether sulfate Anionic surfactants such as ester salts; as well as non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, and 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 Examples include nonionic surfactants such as alkylphenyl ether. 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 sulfuric acid ester group, and salts thereof, a sulfonic acid group or A compound having a group that is an ammonium salt or an alkali metal salt (ammonium sulfonate group or alkali metal sulfonate group) is preferable. Specifically, for example, alkylallyl sulfosuccinate (for example, Elyominol (trademark) JS-20 manufactured by Sanyo Kasei Co., Ltd., Latemur (trademark; the same applies hereinafter) manufactured by Kao Co., Ltd. S-120, S-180A, S-). 180), polyoxyethylene alkylpropenyl phenyl ether sulfate ester salt (for example, Aqualon (trademark; the same applies hereinafter) HS-10 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), α- [1- [. (Allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-polyoxyethylene sulfuric acid ester salt (for example, ADEKA CORPORATION ADEKA REASOAP (trademark; the same applies hereinafter) SE-10N) and ammonium. = Α-sulfonato-ω-1- (allyloxymethyl) alkyloxypolyoxyethylene (for example, Ichikogyo Seiyaku Co., Ltd., Aqualon KH-10), styrene sulfonate (for example, Tosoh Organic Chemical Co., Ltd., Spinomer (trademark) NaSS), and α- [2-[(allyloxy)-. 1- (alkyloxymethyl) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, ADEKA CORPORATION ADEKA REASOAP SR-10 is mentioned), and polyoxyethylene polyoxybutylene (3-methyl-3). -Sulfonate salt of butenyl) ether (for example, Latemur PD-104 manufactured by Kao Corporation is mentioned).

  Further, as the nonionic surfactant in the reactive surfactants, for example, α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, ADEKA CORPORATION ADEKA REASOAP NE-20, NE-30, NE-40 are mentioned.), Polyoxyethylene alkyl propenyl phenyl ether (for example, Aqualon RN-10, RN-20, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). RN-30, RN-50, etc.), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, ADEKA Corporation ADEKA rear soap ER). -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 part by mass or more and 5 parts by mass or less based on 100 parts by mass of the monomer composition. The surfactants may be used alone or in combination of two or more.

The surfactant can also be added after the polymerization reaction, in combination with the method of adding the surfactant as a raw material for the polymerization reaction of the particulate polymer. The surface energy of the thermoplastic polymer layer formed on the surface of the substrate can be adjusted by adding a surfactant after the polymerization reaction. By adjusting the surface energy of the thermoplastic polymer layer, it is possible to adjust the contact angle of the separator surface on which the thermoplastic polymer is formed. Post-addition of a surfactant is preferable from the viewpoint that the surface energy of the thermoplastic polymer layer can be adjusted without being affected by the conditions of the polymerization reaction. By adding the surfactant afterwards, a large amount of the surfactant is released 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 as compared with the method of adding it as a raw material for the polymerization reaction.
As the surfactant to be added after the polymerization reaction of the particulate polymer, the same surfactant as the surfactant to be added during the polymerization reaction can be used, but the polymerization reaction has already been completed when the addition is performed, so the reaction It is preferable to use a surfactant that is not a cationic surfactant. Of these, it is easy to suppress foaming of the slurry, and further, the dispersion effect increases as it is added, it is easy to secure the dispersibility, and a small amount has the effect of greatly changing the surface tension of the microporous polyolefin membrane. From the viewpoint, the polyether-based surfactant or the anionic surfactant is preferable.
The surfactant to be added afterwards is preferably used in an amount of 0.05 parts by mass or more and 20 parts by mass or less based on 100 parts by mass of the monomer composition.
When the amount is 0.05 parts by weight or more, sufficient surface energy can be adjusted, and when the amount is 20 parts by weight or less, it is possible to prevent the surface energy of the thermoplastic polymer layer from becoming too high and easily blocking.

  The radical polymerization initiator is one that radically decomposes by heat or a reducing substance to initiate addition polymerization of a monomer, and both an inorganic initiator and an organic initiator can be used. 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), and examples of the peroxide include hydrogen peroxide and t-. Butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide can be mentioned. Examples of the water-soluble azobis compound include 2,2-azobis (N-hydroxyethylisobutyramide), 2 , 2-azobis (2-amidinopropane) hydrogen dichloride, and 4,4-azobis (4-cyanopentanoic acid). Examples of the peroxide-reducing agent redox system include the above-mentioned peroxides. Sodium sulfoxylate formaldehyde, sodium hydrogen sulfite, thiosulfate 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 can be preferably used in an amount of 0.05 parts by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the monomer composition. The radical polymerization initiator may be used alone or in combination of two or more.

  A unit amount containing the ethylenically unsaturated monomer (P) having a polyalkylene glycol group, the ethylenically unsaturated monomer (A) having 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 is 30% by mass or more and 70% by mass or less. preferable. The pH of the dispersion is preferably adjusted to a range of 5 to 12 in order to maintain long-term dispersion stability. For adjusting the pH, it is preferable to use ammonia, sodium hydroxide, potassium hydroxide, and amines such as dimethylaminoethanol, and it is more preferable to adjust the pH with ammonia (water) or sodium hydroxide.

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

[Any layer]
The aspect including an optional 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 contains an inorganic filler and has a plurality of pores. In this column, an aspect including an inorganic filler porous layer is assumed between the base material and the thermoplastic polymer-containing layer, and the inorganic filler porous layer will be described. However, in the present invention, an optional inorganic filler porous layer such as the inorganic filler porous layer is used. Layers can be omitted.

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

  The inorganic filler is not particularly limited, and examples thereof include 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-based 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. Ceramics such as pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These may be used alone 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 a method for adjusting the particle size of the inorganic filler and its distribution include a method of crushing the inorganic filler using an appropriate crushing device such as a ball mill, a bead mill, a jet mill or the like to reduce the particle size.
The particle size distribution of the inorganic filler can be such that there is one peak in the graph of frequency against particle size. However, a trapezoidal chart having two peaks or no peaks may be used.

  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. It is 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. 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% by volume with respect to the total amount of the inorganic filler porous layer. % Or less.

When measuring the average pore diameter of the inorganic filler porous layer, the observation of the cross section of the separator may be performed on the region of the cross section of the separator that is not involved in ionic conduction. The average pore diameter of the inorganic filler porous layer may be measured, for example, for a separator that has just been manufactured and has not yet been incorporated into an electricity storage device. Alternatively, when the separator is installed in the electricity storage device, the so-called "ears" of the separator (a region near the outer edge of the separator and not involved in ion conduction) is measured. 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, in the inorganic filler porous layer formed on at least one surface of the substrate, preferably an index representing the size of the void portion formed by the inorganic fillers bound by the resin binder. is there. The average pore diameter of the inorganic filler porous layer is determined by the method of forming the inorganic filler porous layer, and therefore, for example, the properties of the inorganic filler used, the properties of the slurry for the inorganic filler porous layer for forming the inorganic filler porous layer, and the inorganic filler porosity. It can be adjusted according to the forming method when forming the layer.

Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a column shape, a spherical shape, a polyhedral shape, and a lump shape (block shape). A plurality of types 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 or more and less than 100% by mass, 30% by mass or more and 80% by mass or less, 35% by mass or more and 70% by mass with respect to the total amount of the inorganic filler porous layer. Hereafter, it is 40% by mass or more and 60% by mass or less.

(Resin binder)
The type of resin of the resin binder contained in the inorganic filler porous layer is not particularly limited, but it is insoluble in the electrolyte solution of the electricity storage device such as the lithium-ion secondary battery, and is similar to the lithium-ion secondary battery. A resin that is electrochemically stable can be used in the range of use of various electricity storage devices. As the resin of the resin binder, 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 binder is contained in the thermoplastic polymer-containing layer and is in the form of particles. A binding binder (C) that binds the polymer (B) to the substrate or the inorganic filler porous layer may be used. The resin binder (A) and 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 resin binder (A) and a resin different from the binder binder (C).

  Specific examples of such resins include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene 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. Melts; Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; and melting point and / or glass transition of polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester, etc. A resin having a temperature of 180 ° C. or higher can be used. These may be used alone 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-based monomer include butadiene and isoprene, examples of the unsaturated carboxylic acid monomer include (meth) acrylic acid, and examples of the other monomer include , For example, styrene. The polymerization method of such a copolymer is not particularly limited, but emulsion polymerization is preferable. The emulsion polymerization method is not particularly limited, and a known method can be used. The addition method of the monomer and other components is not particularly limited, and any one of a batch addition method, a divided addition method, and a continuous addition method can be adopted, and the polymerization method is a one-step polymerization, Either two-step polymerization or multi-step polymerization of three or more steps can be adopted.

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 derivative: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and 7) a resin having a melting point and / or a glass transition temperature of 180 ° C. or higher, or a polymer having a melting point of 200 ° C. or higher but having no melting point: For example, polyphenylene ether, polysulfone, polyether sulfone, 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 size of the resin binder can be controlled by adjusting, for example, the polymerization time, the polymerization temperature, the raw material composition ratio, the raw material charging order, and the pH.
The content ratio of the resin binder in the inorganic filler porous layer is, for example, more than 0 mass% and 80 mass% or less, 1 mass% or more and 20 mass% or less, and 2 mass% or more and 10 mass% with respect to the total amount of the inorganic filler porous layer. % Or less, more preferably 3% by mass or more and 5% by mass or less.
The content of the particulate polymer contained in the inorganic filler porous layer is, for example, less than 5% by volume, less than 3% by volume, or even less than 2% by volume of the content of the particulate polymer contained in the separator. Can be

The thickness of the inorganic filler porous layer 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, for example, 0.5 μm or more. 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. You can

(Arbitrary component)
The thermoplastic polymer-containing layer may contain only the thermoplastic polymer, or may contain other optional components in addition to the thermoplastic polymer. The optional components include, for example, the inorganic fillers described above to form the inorganic filler porous layer. The content of the thermoplastic polymer in the thermoplastic polymer-containing layer, based on the total amount of the thermoplastic polymer-containing layer, preferably 60 mass% or more, more preferably 90 mass% or more, more preferably 95 mass% or more, It is particularly preferably 98% by mass or more.

(Various characteristics related to separator)
The separator has the following formula:
P1 / P2 ≧ 0.5
The relationship represented by is satisfied, 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. Of these, P1 corresponds to the peel strength between the separator and the electrode after pressing the wound body formed by stacking the separator and the electrode. The larger P1 is, the higher the adhesiveness between the separator and the electrode is, which is advantageous in suppressing pressback. P1 is a type of the thermoplastic polymer contained in the thermoplastic polymer-containing layer, other components such as a surfactant contained in the thermoplastic polymer layer, the existing form of the thermoplastic polymer on the substrate, and the thermoplastic polymer. It can be appropriately adjusted 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 pressing of the wound body formed by stacking the separator and the electrode. P1 is measured according to the method described in the examples.

  Further, P2 corresponds to the peel strength between the separators in the wound body in which only the separator is wound. The smaller P2 is, the smaller the blocking is when the separator is wound from the wound body in which only the separator is wound, and the separator having a desired length is easily wound uniformly 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 coating area of the thermoplastic polymer-containing layer to the base material, the configuration of the thermoplastic polymer-containing layer, and the like. Basically, P2 tends to be smaller as the thermoplastic polymer-containing layer is less likely to exhibit the adhesive function in the normal storage stage in which the wound body in which only the separator is wound is stored. P2 is measured according to the method described in the examples.

Here, in order for the separator to have both blocking resistance and adhesiveness 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). If P1 / P2 <0.5, desired effects cannot be obtained with respect to either or both of blocking resistance and adhesiveness to the electrode. Further, even if P1 / P2 ≧ 0.5, if P1 is less than 5 N / m (P1 <5 N / m), the adhesion to the electrode is low and the pressback amount is large, so 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.
By being able to achieve both blocking resistance and adhesiveness to the electrode, it is possible to meet both the expectation for higher capacity of the lithium ion secondary battery and the expectation for improvement in handleability in manufacturing the separator. 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, 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. When P2 is 15 N / m or less, for example, the separators are more difficult to adhere to each other in the normal storage stage in which the wound body in which only the separator is wound is stored, and therefore sufficient locking resistance is ensured. Means to be advantageous to.

The upper limit of P1 is, for example, preferably 35 N / m. The upper limit of P1 is 35 N / m, whereby the adhesive function of the thermoplastic polymer-containing layer during pressing is excessively increased, and when laminated with the electrode. It is easy to prevent the thermoplastic polymer layer from deeply digging into the electrode and deteriorating the electric resistance.
However, the values of P1 and P2 are not limited to the above examples as long as the relationship of P1 / P2 ≧ 0.5 and P1 ≧ 5 N / m is satisfied.

  The contact angle of water with respect to the surface of the separator on which the thermoplastic polymer-containing layer is formed is preferably 95 ° or less, and more preferably 90 ° or less. Setting the contact angle of water to 95 ° or less is preferable from the viewpoint of ensuring the adhesiveness 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 the adhesion between the thermoplastic polymer-containing layer and the object to be bonded. As a method of 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 surface of the base material Examples include adjusting the area of (the portion where the thermoplastic polymer-containing layer does not exist). 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 heat shrinkage ratio in TD is less than 15.0%, the occurrence of a short circuit in a portion other than the portion to which the external force is applied when heat is generated due to the short circuit in the collision test is more effectively suppressed. As a result, it is possible to more reliably prevent the temperature rise of the entire battery, and the smoke and ignition that may occur with it. The heat shrinkage of the separator can be adjusted by appropriately combining the above-described base material stretching operation and heat treatment.

The air permeability of the separator is preferably 10 seconds / 100 cm ³ or more and 10000 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. It is 500 seconds / 100 cm ³ or less. As a result, when the separator is applied to an electricity storage device, it exhibits good high ion permeability. This air permeability is the air resistance measured in accordance with JIS P-8117, like the air permeability of the polyolefin porous substrate.

<Method of manufacturing separator>
[Method of manufacturing base material]
The method for producing the base material is not particularly limited, and a known production method can be adopted. For example, either a wet porosification method or a dry porosification method may be adopted. For example, when the substrate is a microporous polyolefin film, the polyolefin resin composition and the plasticizer are melt-kneaded to form a sheet, and optionally stretched, and then the plasticizer. Of the polyolefin resin composition containing the polyolefin-based resin as the main component is melt-kneaded and extruded at a high draw ratio, and then the polyolefin crystal interface is peeled by heat treatment and stretching to make it porous. Method of melt-kneading the polyolefin resin composition and the inorganic filler to form a sheet, and then making the interface porous by peeling the polyolefin and the inorganic filler by stretching; and dissolving the polyolefin resin composition Then, it is immersed in a poor solvent for the polyolefin to coagulate the polyolefin and at the same time the solvent Method for pore formation and the like by removing.

  Further, a known method may be used for producing the non-woven fabric or paper as the base material. Examples of the manufacturing method include a chemical bond method in which a web is immersed in a binder and dried to bond the fibers to each other; a thermal bond method in which heat-fusible fibers are mixed into the web and the fibers are partially melted to bond the fibers to each other. A needle punching method in which fibers having a spine are repeatedly stabbed to mechanically entangle fibers; and a hydroentangling method in which high-pressure water streams are jetted from a nozzle to a web through a net (screen) to entangle fibers. .

  Hereinafter, as an example of a method for producing a microporous polyolefin membrane, a method of melt-kneading a polyolefin resin composition and a plasticizer to form a sheet and then extracting the plasticizer will be described. First, the polyolefin resin composition and the plasticizer are melt-kneaded. As the melt-kneading method, for example, a polyolefin resin, and optionally other additives, are charged into a resin kneading device such as an extruder, a kneader, a Labo Plastomill, a kneading roll, and a Banbury mixer, and the resin components are heated and melted. However, a method in which a plasticizer is introduced at an arbitrary ratio and kneading is used. At this time, it is preferable to pre-knead the polyolefin resin, other additives, and the plasticizer in a predetermined ratio using a Henschel mixer or the like before introducing them into the resin kneading device. More preferably, in the pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is kneaded while side-feeding the resin kneading device.

  As the plasticizer, a non-volatile solvent capable of forming a uniform solution at a temperature equal to or higher than the melting point of 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 molded into a sheet. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less. Setting the mass fraction of the plasticizer within this range is preferable from the viewpoint of achieving both melt tension during melt molding and formability of a uniform and fine pore structure.

  Next, the melt-kneaded product obtained by heating and melting and kneading as described above is formed into a sheet. As a method for producing a sheet-shaped molded product, for example, a melt-kneaded product is extruded into a sheet form through a T-die or the like, brought into contact with a heat conductor, and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. There is a method of solidifying. 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 melt-kneaded product is sandwiched between rolls when brought into contact with a 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 distance when extruded into a sheet 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 that the sheet-shaped molded product thus obtained is then stretched. As the stretching treatment, either uniaxial stretching or biaxial stretching can be preferably used. Biaxial stretching is preferable from the viewpoint of the strength of the obtained microporous membrane. When the sheet-shaped molded product is stretched in the biaxial direction at a high ratio, the molecules are oriented in the plane direction, the porous substrate finally obtained is less likely to tear, and the sheet has a high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improvement in puncture strength, uniformity of stretching, and shutdown property.

The stretch ratio is preferably in the range of 20 times to 100 times in terms of surface magnification, and more preferably in the range of 25 times to 50 times. The draw ratio in each axial direction is preferably 4 times or more and 10 times or less in the MD direction, 4 times or more and 10 times or less in the TD direction, and 5 times or more and 8 times or less in the MD direction and 5 times in the TD direction. More preferably, the range is 8 times or less. It is preferable that the stretching ratio is within this range, because more sufficient strength can be imparted, film breakage in the stretching process can be prevented, and high productivity can be obtained.
The MD direction means, for example, a 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-shaped molded product obtained as described above may be further rolled. The rolling can be performed by a pressing method using, for example, a double belt press. By rolling, the orientation of the surface layer portion of the sheet-shaped molded product can be increased. The rolling surface magnification is preferably more than 1 time and not more than 3 times, more preferably more than 1 time and not more than 2 times. A rolling ratio in this range is preferable because the film strength of the finally obtained porous substrate is increased and a more uniform porous structure can be formed in the film thickness direction.

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

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

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

  An example of a dry porosification method different from the above-mentioned wet porosification method will be given. First, a film that has been melt-kneaded in an extruder without using a solvent and directly stretched and oriented is produced, and then a microporous membrane is produced through an annealing step, a cold stretching step, and a hot stretching step in this order. In the dry porosification method, a method of stretching and orienting a molten resin from an extruder through a T-die, an inflation method or the like can be used, and the method is not particularly limited.

[Arrangement Method of Thermoplastic Polymer-Containing Layer]
The thermoplastic polymer-containing layer is arranged on at least one surface of the substrate produced as described above. When the inorganic filler porous layer is disposed on the surface of the base material, the 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. The thermoplastic polymer-containing layer is disposed on the surface of the base material that is not yet covered. The method for disposing the thermoplastic polymer-containing layer is not particularly limited, and examples thereof include a method in which a coating liquid containing the particulate polymer is applied to the inorganic filler porous layer or the substrate.

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

  The method of applying the coating liquid containing the particulate polymer onto the substrate is not particularly limited as long as it can achieve 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 thereof include a coater method, a die coater method, a screen printing method, a spray coating method, and an inkjet coating method. Of these, the gravure coater method or the spray coating method is preferable from the viewpoints that the coating shape of the particulate polymer has a high degree of freedom and a preferable area ratio can be easily obtained.

  As the medium of the coating liquid, water or a mixed solvent of water and a water-soluble organic medium is preferable. The water-soluble organic medium is not particularly limited, and examples thereof include ethanol and methanol. Of these, water is more preferable. When the coating liquid enters the inside of the base material when the coating liquid is applied to the base material, the particulate polymer containing the polymer blocks the surface and the inside of the pores of the base material, and the permeability is increased. It tends to decrease. In this respect, when water is used as a solvent or a dispersion medium for the coating liquid, the coating liquid is less likely to enter the inside of the substrate, and the particulate polymer containing the polymer is mainly present on the outer surface of the substrate. Since it is easy to do so, it is possible to suppress the decrease in permeability more effectively, which is preferable. Examples of the solvent or dispersion medium that can be used in combination with water include ethanol and methanol.

  The method of removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the substrate and the thermoplastic polymer-containing layer. For example, a method of drying at a temperature below its melting point while fixing the base material, a method of drying under reduced pressure at a low temperature, and immersing 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 of forming inorganic filler porous layer]
When the inorganic filler porous layer is arranged on at least one surface of the base material, the method for forming the inorganic filler porous layer is not particularly limited, and it can be formed by a known method. For example, a method of applying a coating liquid containing an inorganic filler and, if necessary, a resin binder to a base material can be mentioned. When the base material contains a resin such as a polyolefin microporous film, a raw material containing an inorganic filler and a resin binder, and a raw material of the base material containing a resin may be laminated by a coextrusion method and extruded. The inorganic porous layer (membrane) and the inorganic filler porous layer may be separately prepared and then bonded together.

  The solvent of the coating liquid is preferably one that can uniformly or stably disperse or dissolve the inorganic filler and the resin binder as required, and examples thereof include N-methylpyrrolidone, N, N-dimethylformamide, and N, N-dimethylacetamide. , Water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

  Various additives such as a dispersant such as a surfactant; a thickener; a wetting agent; an antifoaming agent; a pH adjusting agent containing an acid or an alkali may be added to the coating liquid.

  As a method of dispersing or dissolving the inorganic filler and the resin binder as necessary in the medium of the coating liquid, for example, ball mill, bead mill, planetary ball mill, vibrating ball mill, sand mill, colloid mill, attritor, roll mill, high-speed impeller dispersion , A disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring with a stirring blade or the like.

  Regarding 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 thereof 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 of 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, while fixing the base material, a method of drying at a temperature equal to or lower than the melting point of the material constituting the base material, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for the resin binder to coagulate the resin binder and at the same time to remove the solvent The method of extracting is mentioned. The solvent may be partially left as long as it does not significantly affect the device characteristics.

  When the coating liquid is removed from the coating film by drying, the average pore diameter of the inorganic filler porous layer can be adjusted by changing the drying conditions. It is considered that when the drying conditions are made stronger and the drying speed is increased, the inorganic filler is fixed in the state where the inorganic filler is sufficiently dispersed without adjusting the shape, and as a result, the average pore diameter is increased. On the other hand, if the drying conditions are more relaxed, in the process of drying the solvent, the dispersed inorganic filler tries to have a more energetically stable structure, resulting in a smaller average pore diameter of the inorganic filler porous layer. It is considered to be. Further, if the viscosity of the coating liquid is low, a stable structure will be more easily obtained, and the average pore diameter of the inorganic filler porous layer will be smaller. Furthermore, the dispersion state of the inorganic filler is also affected by the type of inorganic filler, the type of solvent, the presence or absence of added surfactant, and the type of surfactant.

  By calendering the laminate of the inorganic filler porous layer and the substrate, the average pore diameter of the inorganic filler porous layer can be reduced. The calendering method is not particularly limited, and a method in which the coating liquid is dried and then conveyed while applying pressure with a nip roll may be used.

<Power storage device>
The electricity storage device including the separator may be the same as the conventionally known one except that the electricity storage device separator is included. The electricity storage device is not particularly limited, but examples thereof include batteries such as non-aqueous electrolyte secondary batteries, capacitors, and capacitors. Among them, the battery is preferable, the non-aqueous electrolyte secondary battery is more preferable, and the lithium ion secondary battery is still more preferable, from the viewpoint of more effectively obtaining the benefit of the action and effect of the present invention. Since the separator of the present embodiment is provided, the electricity storage device has excellent device characteristics such as electricity storage performance. In addition, the lithium-ion secondary battery has excellent battery characteristics.

  The electrode used for measuring the peel strength with the electrode may be either a positive electrode or a negative electrode, but it is appropriate to use the positive electrode in order to properly grasp the effect of the separator. In particular, when the electricity storage device is a lithium-ion secondary battery, a positive electrode for lithium-ion secondary battery in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector, and the positive electrode active material layer is a separator. It is suitable that the measurement is carried out after being laminated so as to face the surface on which the thermoplastic polymer-containing layer is formed and hot-pressed as described above.

When a lithium ion secondary battery is manufactured using a separator, the positive electrode, the negative electrode, and the non-aqueous electrolytic solution are not limited, and known ones can be used.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be preferably used. Examples of the positive electrode current collector include aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ . The positive electrode active material layer may appropriately contain a binder, a conductive material and the like in addition to the positive electrode active material.

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

The non-aqueous electrolytic solution is not particularly limited, but an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 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 of 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. Then, the positive electrode-separator-negative electrode-separator or the negative electrode-separator-positive electrode-separator is laminated in this order and wound in a circular or flat spiral shape to obtain a wound body. It can be manufactured by housing the wound body in a device can (for example, a battery can) and further injecting an electrolytic solution. Alternatively, the electrode and the separator may be folded to form a wound body, and the wound body may be placed in a device container (for example, a film made of aluminum) to inject the electrolytic solution.

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

  The pressing temperature is preferably 20 ° C. or higher as a temperature at which adhesiveness can be effectively exhibited. Further, the pressing temperature is preferably lower than the melting point of the material contained in the base material, and more preferably 120 ° C. or lower, from the viewpoint of suppressing clogging of holes or thermal shrinkage in the separator due to hot pressing. The pressing pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of holes in the separator. The pressing time may be 1 second or less when a roll press is used, or a surface press for several hours, but is preferably 2 hours or less from the viewpoint of productivity. When the electricity storage device separator of the present embodiment is used and the above manufacturing process is performed, it is possible to suppress pressback when the wound body including the electrode and the separator is press-molded. Therefore, it is possible to suppress a decrease in yield in the device assembly process and shorten the production process time, which is preferable.

  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 continuous operation. Excellent operation resistance (cycle characteristics).

  The evaluation of physical properties described in this Example section was performed 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 hot air dryer at 130 ° C., and the dry mass of the thermoplastic polymer after drying was defined as (b) g. The solid content was calculated by the following formula.
Solid content = (b) / (a) × 100 [%]

(2) Average particle size of particulate polymer (D50)
The average particle diameter (D50) of the particulate polymer was measured using a particle diameter measuring device (manufactured by Nikkiso Co., Ltd., product name "Microtrac UPA150"). The measurement conditions were a loading index = 0.20 and a measurement time of 300 seconds, and the numerical 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 the Knudsen flow when the mean free path of the fluid is larger than the pore diameter of the capillary, and follows the 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 substrate water permeability measurement follows the Poiseuille flow.

The average pore diameter d (μm) of the thermoplastic polymer-containing layer is determined by the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)) and 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 was calculated using the following formula.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶

Here, R _gas was calculated 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 calculated from the water permeability (cm ³ / (cm ² · sec · Pa)) using the following formula.
R _liq = water permeability / 100

The water permeability was determined as follows. A thermoplastic polymer-containing layer previously dipped in ethanol was set in a 41 mm diameter stainless-steel permeable cell, and after ethanol of this layer was washed with water, water was permeated at a differential pressure of about 50,000 Pa for 120 sec. The amount of water per unit time, unit pressure, and area per unit area was calculated from the amount of water permeation (cm ³ ) after a lapse of time, and this was taken as the water permeability.

Further, ν is calculated from the gas constant R (= 8.314), the absolute temperature T (K), the circular constant π, and the average molecular weight M of air (= 2.896 × 10 ^-2 kg / mol) using the following formula. I asked.
ν = ((8R × T) / (π × M)) ^1/2

(4) Base material thickness (μm)
Cut out a 10 cm × 10 cm square sample from the base material, select 9 points (3 points × 3 points) in a grid pattern, and use a micro thickness gauge (Toyo Seiki Seisakusho Co., Ltd., type KBM) at room temperature 23 ± 2. Thickness was measured at ° C. The average value of the obtained measured values at 9 locations was calculated as the thickness of the base material.

(5) Thickness of Thermoplastic Polymer-Containing Layer The separator was freeze-fractured and its cross section was confirmed by SEM (model S-4800, manufactured by HITACHI). The thickness of the thermoplastic polymer-containing layer was measured from the obtained visual field. Specifically, a sample of the separator was cut into pieces each having a size of 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 the sample was cut with a hammer. The cleaved sample was vapor-deposited with osmium and observed at an acceleration voltage of 1.0 kV and 30,000 times to calculate the thickness of the thermoplastic polymer-containing layer. In the SEM image, the boundary line between the part where the porous structure of the base material cross section can be seen and the part where it is not visible, and the shortest distance from the line farthest from the base material that is in parallel with and is in contact with the thermoplastic polymer-containing layer are It was defined as the region of the thickness of the layer containing the plastic polymer.
Incidentally, 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 substrate to the thermoplastic polymer-containing layer is the thickness of the thermoplastic polymer-containing layer. can do.

(6) Thermal contraction rate (%) of the laminate of the separator and the base material at 120 ° C
A sample obtained by cutting the above laminate to 100 mm in the TD direction and 100 mm in the MD direction was allowed to stand in an oven at 120 ° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the warm air did not hit the sample directly. After the sample was taken out of the oven and cooled, its length (mm) was measured, and the heat shrinkage rate of TD was calculated by the following formula.
TD heat shrinkage (%) = 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 mass%, pH = 9.0) containing a thermoplastic polymer was placed in an aluminum dish, and a hot air dryer at 130 ° C was used. And dried for 30 minutes to obtain a dry film. About 17 mg of the dried film was filled in a measuring aluminum container, and a DSC curve in a nitrogen atmosphere and a DSC curve were obtained by a DSC measuring device (manufactured by Shimadzu Corporation, model name “DSC6220”). The measurement conditions were as follows.
1st stage heating program: 70 ° C start, heating at a rate of 15 ° C / min. Hold for 5 minutes after reaching 110 ° C.
Second stage cooling program: 110 ° C to 40 ° C / min. Hold for 5 minutes after reaching -50 ° C.
3rd stage heating program: Temperature rising from -50 ° C to 130 ° C at a rate of 15 ° C / min. Data of DSC and DDSC were acquired during the temperature rise of the third stage.
The intersection of the baseline (a straight line obtained by extending the baseline in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to the downward convex curve) is taken to be the glass transition temperature ( Tg).

(8) Viscosity average molecular weight Mv
In accordance with ASTM-D4020, the intrinsic viscosity [η] at 135 ° C in a decalin solvent was determined. Using this [η] value, the viscosity average molecular weight Mv was calculated from the relationship of the following mathematical formula.
For 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 base material, and its volume (cm ³ ) and mass (g) were determined. Using these values, the density of the base material was set to 0.95 (g / cm ³ ) and the porosity was calculated from the following formula.
Porosity (%) = (1-mass / volume / 0.95) × 100

(10) Air permeability (sec / 100 cm ³ )
Regarding the base material, the air permeability was measured by the air permeability resistance measured by Gurley type air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd. according to JIS P-8117. When the thermoplastic polymer-containing layer is present on only 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 with a needle having a radius of curvature of 0.5 mm at the center of the fixed base material. Was measured. The value obtained by converting the maximum puncture load per thickness of 20 μm was defined as the puncture strength (gf / 20 μm). If the thermoplastic polymer is present on only one side of the substrate, the needle can be pierced from the side on which the thermoplastic polymer is present.

(12) Surface Tension of Base Material and Separator The surface tension of the base material or separator was determined from 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, 65 mN / m ( 2 μl (manufactured by Kanto Chemical Co., Inc.) was dropped onto the substrate or the separator in an environment of 25 ° C., and the contact angle of each wetting reagent 40 seconds after the dropping was measured. For the base material or the separator, the contact angles in the MD direction and the TD direction were measured three times, and the average value was adopted. The obtained data was plotted on a graph in which the horizontal axis represents the surface tension and the vertical axis represents the contact angle to obtain a linear first-order approximation line. This approximate straight line was extrapolated, and the value of the horizontal axis when intersecting with 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 40 seconds later The contact angle was measured. As the contact angle of water, an average value measured three times in each of the MD and TD directions was adopted.

(14) Rate characteristics a. Preparation of positive electrode 90.4% by mass of nickel, manganese, and cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) as a positive electrode active material, 1.6 mass% of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle size 6.5 μm) as a conduction 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 ) was mixed 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 surface of an aluminum foil having a thickness of 20 μm, which was a positive electrode current collector, using a die coater, dried at 130 ° C. for 3 minutes, and then compression-molded using a roll press machine to give a positive electrode. It was made. The amount of the positive electrode active material applied at this time was 109 g / m ² .

b. Production of Negative Electrode Graphite powder A (density 2.23 g / cm ³ , number average particle size 12.7 μm) was used as a negative electrode active material in an amount of 87.6% by mass, and graphite powder B (density 2.27 g / cm ³ , number average particle). 9.5 mass% of diameter 6.5 μm, 1.4 mass% of ammonium salt of carboxymethyl cellulose as a binder (solid content conversion) (solid content concentration 1.83 mass% aqueous solution), and diene rubber latex 1.7 mass % (Solid content conversion) (solid content concentration 40 mass% aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was applied to one surface of a copper foil having a thickness of 12 μm, which was a negative electrode current collector, by a die coater, dried at 120 ° C. for 3 minutes, and compression-molded with a roll press machine to prepare a negative electrode. The amount of negative electrode active material applied at this time was 5.2 g / m ² .

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

d. Battery Assembly The separator or the base material was cut into a circle of 24 mmφ, and the positive electrode and the negative electrode were each cut into a circle of 16 mmφ. The negative electrode, the separator or the base material, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode faced each other, and they were housed 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 the container.

e. Evaluation of rate characteristics d. By charging the simple battery assembled in above at 25 ° C with a current value of 3mA (about 0.5C) to a battery voltage of 4.2V, and then starting to squeeze the current value from 3mA so as to maintain 4.2V. The first charging after the battery was manufactured was performed for a total of about 6 hours. Then, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., a battery voltage of 4.2 mA was charged at a current value of 6 mA (about 1.0 C), and then a current value of 6 mA was started so as to maintain 4.2 V. Charged for an hour. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, at 25 ° C., a battery voltage of 4.2 mA was charged at a current value of 6 mA (about 1.0 C), and then a current value of 6 mA was started so as to maintain 4.2 V. Charged for an hour. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 12 mA (about 2.0 C) was defined as a 2 C discharge capacity (mAh).
Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic.
Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) × 100

Evaluation criteria for rate characteristics (%) A (good): rate characteristics are over 85% B (possible): rate characteristics are over 80% 85% or less C (bad): rate characteristics are 80% or less

(15) Peel strength P2
The separator was cut into a piece having 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 the comparative examples, since the thermoplastic polymer-containing layer was formed on both the surface (A) and the surface (B) of the substrate, the thermoplastic polymer-containing layer on the surface (A) and the surface (B) were formed. An overlapped wound body is formed so that the thermoplastic polymer-containing layer faces it. The wound body was pressed under the following conditions.
Temperature: 25 ° C
Pressing pressure: 5MPa
Press time: 12h
The peel strength between the surface (A) and the surface (B) of the pressed separator was set to 50 mm / min using a force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. A 90 ° peel test was performed to measure the peel strength. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength. Further, the obtained peel strength value was set as P2 and used for calculating 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 osmium vapor-deposited 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. The region where the porous structure on the surface of the base material was not visible in the SEM image was defined as the thermoplastic polymer-containing layer region.
Percentage of covered area of thermoplastic polymer-containing layer (%) = area of thermoplastic polymer-containing layer / (area including pores of base material + area of thermoplastic polymer-containing layer) × 100
The covered area ratio in each sample was obtained by performing the above measurement three times and taking the arithmetic mean value thereof.

(17) Peel strength P1
The separator was cut into a rectangular shape with 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 the 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 thermoplastic polymer on the surface (B) were formed. An overlapped wound body is formed so that the polymer-containing layer faces it. The wound body was pressed under the following conditions.
Temperature: 90 ℃
Pressing pressure: 1MPa
Pressing time: 5 seconds The peeling strength between the surface (A) and the surface (B) of the separator after pressing was peeled off using Force Gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. A 90 ° peel test was performed at a speed of 50 mm / min to measure the peel strength. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength. Further, the obtained peel strength value was set as P1 and was used for calculation of the peel strength ratio (P1 / P2).

(18) Press-back amount of wound body Each of the separator and the electrode was cut into a length of 30 mm in width and 200 mm in length, and the separator, the negative electrode, the separator, and the positive electrode were stacked in this order to form a laminate. The laminated body was wound around a support having a width of 15 mm and a thickness of 1 mm, and after being wound to the end, the support was taken out to prepare a wound body of a separator and an electrode. After measuring the thickness (radial length) of the formed wound body, the wound body was pressed under the following conditions.
Temperature: 90 ℃
Pressing pressure: 1MPa
Press time: 2min
After pressing, the thickness of the wound body was similarly measured, and the pressback amount of the wound body was evaluated based on the following criteria. The thickness of the wound body was measured with a ruler.
Press-back 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 laminated separators and electrodes) × 100
Evaluation criteria for press-back amount of wound body A (extremely good): Press-back amount of wound body is 0% or more and less than 10% B (Good): Press-back amount of wound body is 10% or more, Less than 50% C (possible): The pressback amount of the wound body is 50% or more and less than 95% D (defective): The pressback amount of the wound body is 95%

(19) Blocking resistance A rectangular separator having a width of 30 mm and a length of 2000 m was wound to form a wound body. The formed wound body was stably stored at 35 ° C. for 30 days. The wound body after storage is installed in an automatic winding device, and the length of the separator within 20 m from the inner layer of the wound body is uniformly and wrinkle-free, the separator length is measured, and the blocking resistance is based on the following evaluation criteria. The sex was evaluated.
Criteria for evaluation of blocking resistance A (extremely good): Separation length that is uniform and can be extended without wrinkles is more than 1 m B (Good): Separator length that is uniform and can be extended without wrinkles is more than 95 cm and 1 m or less C (Poor): Separator length that is even and wrinkle-free, 95m or less

(20) Coated surface The surface of the separator having an area of 0.5 m2 coated with the thermoplastic polymer layer was confirmed, the number of cissings large enough to completely cover the 2 mm x 2 mm square was measured, and based on the following evaluation criteria: The coated surface was evaluated.
Good (good): The number of cissings on one side of the separator is less than 4 × (Not possible): The 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, polypropylene of homopolymer having Mv of 400,000 and Mv of 15 10 parts by mass of a mixture of various homopolymers with polypropylene (mass ratio = 4: 3) was dry-blended using a tumbler blender. To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis- [methylene- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane was added as an antioxidant, and the tumbler blender was added again. A mixture was obtained by dry blending with. The obtained mixture was fed by a feeder into a twin-screw extruder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78 ° C. 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump. The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin to 100 parts by mass of the entire mixture extruded was 65 parts by mass, that is, the ratio of the resin composition was 35 parts by mass.

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

  The physical properties of the obtained polyolefin microporous film B1 were measured by the methods described above. The obtained polyolefin microporous membrane was used as a separator as it was, and evaluated by the above method. The results obtained are shown in Table 1.

[Production Example 1-2] (Production of polyolefin microporous membrane B2)
A polyolefin microporous film B2 as a substrate was obtained in the same manner as in Production Example 1-1, except that the temperature and relaxation rate during stretching were changed. The obtained polyolefin microporous film B2 was evaluated in the same manner as in Production Example 1-1. The results obtained are shown in Table 1.
[Production Example 1-3] (Production of polyolefin microporous membrane B3)
25 parts by mass of ultra-high molecular weight polyethylene having a viscosity average molecular weight of 2,000,000, 15 parts by mass of homopolymer 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 Then, 30 parts by mass of copolymerized 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] was added as an antioxidant to 99 parts by mass of the obtained polymer mixture. Then, a polymer mixture was obtained by dry blending again using a tumbler blender. The obtained mixture of polymers and the like was replaced with nitrogen and then fed to a twin-screw extruder by a feeder under a nitrogen atmosphere. Liquid paraffin was injected into the extruder cylinder by a plunger pump. The feeder and the pump were adjusted so that the ratio of the liquid paraffin in the entire mixture extruded by melt-kneading was 65% by mass, that is, the ratio of the resin composition was 35% by mass. The obtained melt-kneaded product was extruded and cast onto a cooling roll through a T-die to obtain a sheet-shaped molded product. Then, a polyolefin microporous film B3 as a substrate was obtained in the same manner as in Production Example 1-1 except that the stretching temperature and the relaxation rate were changed. The obtained polyolefin microporous film B3 was evaluated in the same manner as in Production Example 1-1. The results obtained 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 the polyolefin microporous film B4 and evaluated in the same manner as in Production Example 1. The results obtained are shown in Table 1.

  In addition, the value in the column of surface tension in Table 1 is corona-treated on the base material so that the surface tension value falls within a numerical range from the viewpoint of achieving both blocking resistance and adhesion to the electrode. It is the value before applying.

<Synthesis of particulate polymer>
(Production Example A1) Aqueous Dispersion (Indicated as "raw material polymer" in the table. The same shall apply hereinafter.) Synthesis of A1 A reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer was charged with 70. 4 parts by mass, "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., written as "KH1025" in the table, the same applies hereinafter), and "Adecaria Soap SR1025" ( A registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution, written as “SR1025” in the table. The same applies hereinafter.) 0.5 parts by mass was 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) (indicated as “APS (aq)” in the table. The same applies hereinafter) was added while maintaining the temperature inside the container at 80 ° C.

On the other hand, 46 parts by mass of methyl methacrylate, 20 parts by mass of n-butyl acrylate, 20 parts by mass of 2-ethylhexyl acrylate, 2 parts by mass of methacrylic acid, 2 parts by mass of acrylic acid, an aromatic vinyl monomer, that is, styrene, "Aqualon KH1025 "(registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 2.0 parts by mass, trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) 1.0 part by mass, γ-methacryloxypropyltrimethoxy A mixture of 0.5 parts 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 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 aqueous ammonium persulfate solution was added to the reaction vessel, and the whole amount of the emulsion was dropped over 150 minutes. The temperature inside the container was maintained at 80 ° C. during the dropping of the emulsion.

  After the dropping of the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH = 9.0 with an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40 mass% (raw material polymer A1). The obtained raw material polymer (water dispersion) A1 was evaluated by the above method. The results obtained are shown in Table 3.

(Production Examples A2 to A6) Synthesis of Water Dispersions A2 to A6 Raw materials polymers (water dispersions) except that the compositions of the monomers and other raw materials are changed as shown in Tables 3 to 5, respectively. Copolymer latexes (raw material polymers A2 to A6) were obtained in the same manner as in A1. Each of the obtained raw material polymers (aqueous dispersions) A2 to A6 was evaluated by the above method. The obtained results are shown in Table 2.

Abbreviations for raw material names in Table 2 and Tables 3 to 4 described below have the following meanings.
<Emulsifier>
KH1025: "Aqualon KH1025" registered trademark, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "ADEKA REASORP 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)
A part of the aqueous dispersion A1 obtained in Production Example A1 was taken and multistage polymerization was carried out using this as a seed polymer to synthesize an aqueous dispersion A1-1. Specifically, first, in a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 16 parts by mass of water dispersion A1 in terms of solid content, 0.5 part by mass of Aqualon KH1025 (registered trademark). Parts, 0.5 parts by mass of Adecaria Soap SR1025 (registered trademark), 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. Then, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added while maintaining the temperature inside the container at 80 ° C. The above is the initial preparation.

  On the other hand, 46 parts by mass of methyl methacrylate, 20 parts by mass of n-butyl acrylate, 20 parts by mass of 2-ethylhexyl acrylate, 2 parts by mass of methacrylic acid, 2 parts by mass of acrylic acid, that is, 10 parts by mass of styrene, an aromatic vinyl monomer. , "Aqualon KH1025" (registered trademark, 25% aqueous solution) 2.0 parts by mass, trimethylolpropane triacrylate 1.0 part by mass, γ-methacryloxypropyltrimethoxysilane 0.5 part by mass, 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 aqueous ammonium persulfate solution was added to the reaction vessel, and the whole amount of the emulsion was dropped over 150 minutes. The temperature inside the container was maintained at 80 ° C. during the dropping of the emulsion.

  After the dropping of the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH = 9.0 with an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40 mass% (raw material polymer A1-1). The obtained raw material polymer A1-1 was evaluated by the above method.

(Production Example A1-2 to A5-2)
Each copolymer latex was subjected to multi-stage polymerization in the same manner as the raw material polymer (water dispersion) A1-1 except that the compositions of the seed polymer, the monomer, and the other raw materials were changed as shown in Table 3. Got Each of the obtained raw material polymers (aqueous dispersion) was evaluated by the above method.

[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 to obtain a coating solution containing a thermoplastic polymer (solid content: 5% by mass). ) Was prepared. At this time, as a post-added surfactant, polyoxyethylene alkyl ether, which is a polyether-based surfactant, was added so as to be 0.005 mass% with respect to the coating liquid. further. Carboxymethyl cellulose was added as a thickener so that the content of carboxymethyl cellulose was 1% by mass with respect to the coating liquid, and the viscosity of the coating liquid was adjusted to 30 mPa · s. Then, prior to the application of the coating liquid, 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 applied to one surface (surface (A)) of the polyolefin microporous film B1 using a gravure coater. At this time, the area coverage of the polyolefin microporous film with the thermoplastic polymer was 20%. Then, the coating liquid after coating was dried at 40 ° C. to remove water.
Further, the coating liquid was similarly applied to the surface (surface (B)) opposite to the surface (A) of the polyolefin microporous film B1 and dried again in the same manner as above. Thus, a separator was obtained in which the thermoplastic polymer-containing layer was formed on both surfaces of the polyolefin microporous film B1.

[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 that was 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 composition of the polyolefin microporous film, the composition of the coating liquid, and the existence form 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 Solef21216 (Solvey) was used instead of the water dispersion A1-2.

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

  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 pressback amount of the wound body was C evaluation or more, and the blocking resistance (in the table, "separator" It is confirmed that both the blocking resistance and the adhesiveness to the electrode can be achieved at the same time, since the evaluation of the “positional deviation amount at the time of feeding” ”is B evaluation or more.
In Comparative Examples 1 and 3, since P1 was less than 5 N / m, the evaluation result of the pressback amount of the wound body was D evaluation. Further, in Comparative Example 2, although P1 is 5 N / m or more, P1 / P2 ≧ 0.5 is not satisfied, the evaluation result of the blocking resistance is C evaluation, and the blocking resistance and the adhesion to the electrode are I could not achieve both.
In addition, Example 6 in which no polyether surfactant was added, Example 7 in which the ratio of the coating area of the thermoplastic polymer-containing layer to the substrate was 5%, and Example 13 in which PVdF was used as the polymer In comparison with other examples, the evaluation of the pressback amount of the wound body was C evaluation. In Examples other than Examples 6, 7 and 13, the evaluation of the press-back amount of the wound body and the blocking resistance was B evaluation or more, and it was confirmed that this is a particularly preferable embodiment. .

  Incidentally, when the blocking force becomes high, the binder component applied on the base material is displaced, and the displaced binder component is rubbed on a portion of the base material where the thermoplastic polymer-containing layer is not arranged, thereby closing the hole. It is also considered that the rate characteristic deteriorates. 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 at the same time.

  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 installed in various electricity storage devices including a lithium-ion battery to be installed in an electric vehicle (EV) for which a particularly high capacity is desired in recent years.

Claims (12)

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 the electricity storage device separator has the following formula:
P1 / P2 ≧ 0.5
{In the formula, P1 is a wound body formed by stacking one surface (A) of the electricity storage device separator and a surface (B) opposite to the surface (A) to form a wound body. Is the peel strength between the surface (A) and the surface (B) when pressed at a temperature of 90 ° C. and a pressure of 1 MPa for 5 seconds, and P2 is the wound body at a temperature of 25 ° C. And the peel strength between the surface (A) and the surface (B) when pressed for 12 hours under a pressure of 5 MPa. }
An electricity storage device separator satisfying the relationship represented by and having P1 of 5 N / m or more.   The electricity storage device separator according to claim 1, wherein the P2 is 15 N / m or less.   The electricity storage device separator according to claim 1, wherein the P1 / P2 is 2.5 or less.   The separator for an electricity storage device according to any one of claims 1 to 3, wherein a contact angle of water with respect to a surface of the electricity storage device separator on which the thermoplastic polymer-containing layer is formed is 95 ° or less.   The electricity storage device separator according to any one of claims 1 to 4, wherein a coverage area ratio of the thermoplastic polymer-containing layer to the base material is 50% or less.   The electricity storage device separator according to claim 1, wherein the thermoplastic polymer contained in the thermoplastic polymer-containing layer contains a polymer unit of (meth) acrylic acid ester or (meth) acrylic acid.   The electricity storage device separator according to claim 1, wherein the thermoplastic polymer contained in the thermoplastic polymer-containing layer has a glass transition temperature of 40 ° C. or higher.   The electricity storage device separator according to any one of claims 1 to 7, wherein the thermoplastic polymer-containing layer contains two or more kinds of thermoplastic polymers having different glass transition temperatures.   The electricity storage device separator according to claim 1, wherein the thermoplastic polymer-containing layer contains a polyether surfactant.   The separator for an electricity storage device according to claim 1, wherein the electricity storage device separator is wound.   An electricity storage device comprising the electricity storage device separator according to claim 1.   A lithium ion secondary battery comprising the electricity storage device separator according to any one of claims 1 to 10.