KR102208408B1 - Separator for energy storage device, and laminated body, roll and secondary battery using the same - Google Patents

Abstract

[Problem] To provide a separator for power storage devices that is excellent in a balance of peel strength between a substrate and an active layer, handling properties, cold and thermal shock properties, and low temperature cycle properties.
[Solution means] A separator for a power storage device comprising a polyolefin multilayer microporous membrane containing polyethylene and polypropylene, and an active layer disposed on at least one side of the polyolefin multilayer microporous membrane. In the polyolefin multilayer microporous membrane, the outermost polypropylene concentration is higher than the innermost polypropylene concentration, the outermost polyethylene concentration is lower than the innermost polyethylene concentration, and the active layer contains an acrylic resin.

Description

A separator for power storage devices, and a laminate using the same, a winding body, and a secondary battery TECHNICAL FIELD [SEPARATOR FOR ENERGY STORAGE DEVICE, AND LAMINATED BODY, ROLL AND SECONDARY BATTERY USING THE SAME}

The present invention relates to a separator for power storage devices, and a laminate using the same, a wound body, and a secondary battery.

Microporous membranes containing a polyolefin resin as a main component are widely used as separators in batteries, capacitors, etc. because they exhibit excellent electrical insulation or ion permeability. In addition, in recent years, with the multifunctional and lightweight electronic devices, secondary batteries of high power density and high capacity density are required as power sources thereof. Microporous membranes containing polyolefin resin as a main component are also widely used as separators for such secondary batteries.

For example, Patent Document 1 includes a first microporous layer containing a specific first polyolefin resin and a second microporous layer containing a second polyolefin resin, (I) porosity ( %)/Membrane thickness (µm), and (II) a polyolefin multilayer microporous membrane having a specific range of air permeability converted into a film thickness of 16µm is described.

Patent Document 2 is a polyolefin multilayer microporous membrane having at least a first microporous layer forming both surface layers and at least one second microporous layer provided between both surface layers, and the other side of the surface of the polyolefin multilayer microporous membrane A polyolefin multilayer microporous membrane having a static friction coefficient of 1.1 or less in the long side direction (MD) of the side and a pore density calculated from the average pore diameter and porosity measured by the mercury intrusion method is 4 or more.

Patent Document 3 is a battery separator having a laminated polyethylene microporous membrane and a modified porous layer present on at least one side thereof, and has a specific shutdown temperature and air permeation resistance increase rate, and protrusions containing polyethylene of a specific shape on the surface. And a laminated polyethylene microporous membrane having a specific tensile strength.

Patent Document 4 is a battery separator having a laminated polyethylene microporous membrane and a modified porous layer present on at least one side thereof, and has a specific meltdown temperature and air permeability resistance, and protrusions containing polyethylene of a specific shape on the surface. And a laminated polyethylene microporous membrane having a specific tensile strength.

Patent Document 5 is a battery separator in which a water-soluble resin or a water-dispersible resin and a modified porous layer containing fine particles are laminated on at least one side of a polyolefin microporous membrane base material, and the polyolefin microporous membrane base material is a surface layer composed of resin composition A. A separator for a battery, which is a base material for a polyolefin microporous membrane having a three-layer structure in which a microporous layer and a microporous layer of an intermediate layer composed of a resin composition B having a melting point lower than that of the resin composition A, are laminated is described.

International Publication No. 2015/194667 International Publication No. 2013/146403 International Publication No. 2015/190264 International Publication No. 2015/190265 Japanese Patent Publication No. 2015-50121

However, in the separator for power storage devices described in Patent Documents 1 to 5, it has been difficult to satisfy all of the peel strength, handling properties, cold and thermal shock properties, and low-temperature cycle properties between the substrate and the active layer in a balanced manner.

One of the problems to be solved by the present invention is to provide a separator for power storage devices having excellent balance of peel strength, handling property, cold thermal shock properties, and low-temperature cycle properties between a substrate and an active layer.

The inventors of the present application have repeatedly studied the above problems in order to solve the above problems, and as a result of forming an active layer containing an acrylic resin and inorganic particles as necessary on a polyolefin multilayer microporous membrane having a specific polyolefin resin, the above problems can be solved. It found out, and came to complete the present invention. That is, the present invention is as follows.

[One]

A polyolefin multilayer microporous membrane comprising polyethylene and polypropylene,

Active layer disposed on at least one side of the polyolefin multilayer microporous membrane

It is a separator for power storage devices containing,

In the polyolefin multilayer microporous membrane, the outermost polypropylene concentration is higher than the innermost polypropylene concentration, and the outermost polyethylene concentration is lower than the innermost polyethylene concentration,

The active layer contains an acrylic resin,

Separator for power storage devices.

[2]

The separator for power storage devices according to item 1, wherein the active layer further contains inorganic particles.

[3]

The polyolefin multilayer microporous membrane includes a first microporous layer and a second microporous layer,

The first microporous layer comprises a first polyolefin resin containing polyethylene and polypropylene,

The second microporous layer contains a second polyolefin resin containing polyethylene,

The separator for power storage devices according to item 1 or 2, wherein the polyolefin multilayer microporous membrane is laminated in the order of a first microporous layer, a second microporous layer, and a first microporous layer.

[4]

The separator for power storage devices according to item 3, wherein the first polyolefin resin or the second polyolefin resin further contains linear low-density polyethylene.

[5]

The separator for power storage devices according to item 3, wherein the first polyolefin resin or the second polyolefin resin further contains polypropylene having a heat of fusion of 150 J/g or less.

[6]

The separator for power storage devices according to item 4, wherein the linear low-density polyethylene is an ethylene/1-hexene copolymer.

[7]

The separator for power storage devices according to any one of items 4 to 6, wherein the second polyolefin resin further contains linear low-density polyethylene or polypropylene having a heat of fusion of 150 J/g or less.

[8]

The separator for power storage devices according to any one of items 1 to 7, wherein the acrylic resin is particulate and has a core-shell structure having a core portion and a shell portion that at least partially covers the outer surface of the core portion.

[9]

The separator for power storage devices according to any one of items 1 to 8, wherein the acrylic resin includes a copolymer having an ethylenically unsaturated monomer having a polyalkylene glycol group as a monomer unit.

[10]

Item 3, wherein the ratio of the weight average molecular weight of polyethylene contained in the first polyolefin resin to the weight average molecular weight of polypropylene (Mw (weight average molecular weight of polyethylene)/Mw (weight average molecular weight of polypropylene)) is 0.6 to 1.5 The separator for power storage devices according to any one of claims 9 to 9.

[11]

The separator for power storage devices according to any one of items 3 to 10, wherein the first microporous layer of the polyolefin multilayer microporous membrane further contains at least one or more selected from silica, alumina, and titania.

[12]

With positive pole,

The separator for power storage devices according to any one of items 1 to 11, and

Negative pole

A laminate that is laminated in this order.

[13]

A wound body in which the laminate according to item 12 is wound.

[14]

A power storage device comprising the laminate according to item 12 or the wound body according to item 13, and an electrolytic solution.

Advantageous Effects of Invention According to the present invention, it is possible to provide a separator for power storage devices that is excellent in balance between peeling strength between a substrate and an active layer, handling properties, cold and thermal shock properties, and low-temperature cycle properties. In addition, in one embodiment, the separator for power storage devices of the present invention is excellent in variation in peel strength and collision resistance between a substrate and an active layer.

1 is a schematic diagram of a crash test according to UL standard 1642 and/or 2054.

Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail for the purpose of illustrating, but the present invention is not limited to the present embodiment. In the specification of the present application, the upper and lower limits of each numerical range can be arbitrarily combined.

《Separator for power storage device》

The separator for power storage devices of the present embodiment includes a polyolefin multilayer microporous membrane and an active layer disposed on at least one side thereof.

<Polyolefin multilayer microporous membrane>

In this embodiment, the polyolefin multilayer microporous membrane contains polyethylene and polypropylene, the outermost polypropylene concentration is higher than the innermost polypropylene concentration, and the outermost polyethylene concentration is lower than the innermost polyethylene concentration. The ``outermost'' of the polyolefin multilayer microporous membrane refers to the portion of the outer two membranes when the polyolefin multilayer microporous membrane is divided into three to have the same thickness in the thickness direction, and the ``innermost'' refers to the inner membrane. Point to the part.

(Outermost)

In this embodiment, it is preferable that the outermost part contains the 1st polyolefin resin containing polyethylene and polypropylene. The first polyolefin resin is preferably composed of polyethylene and polypropylene.

By including the first polyolefin resin containing polyethylene and polypropylene as the outermost polyolefin multilayer microporous membrane, the peel strength from the active layer laminated on the outermost layer is increased. Although not limited to theory, it is believed that the coexistence of polypropylene and polyethylene compared to the case of using polyethylene alone increases the surface free energy on the surface of the layer due to the polar effect of the polypropylene, thereby increasing the adhesion with the active layer. do.

By including the first polyolefin resin containing polyethylene and polypropylene as the outermost, the low-temperature characteristics of the separator, particularly the low-temperature cycle characteristics, are improved. Although not limited to theory, it is thought that this is because the transition temperature is lowered by blending polyethylene and brittle fracture of the material is less likely to occur, compared to the case where polypropylene having a glass transition temperature of around 0°C is used alone.

The polyethylene and polypropylene contained in the first polyolefin resin are not particularly limited, but, for example, low density polyethylene, linear low density polyethylene (L-LDPE), medium density polyethylene, high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMwPE), Isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, ethylene propylene rubber, and the like. The polymerization catalyst used in the production of these polyethylene or polypropylene is not particularly limited, and examples thereof include a Ziegler-Natta catalyst, a Phillips catalyst, and a metallocene catalyst.

The polyethylene contained in the first polyolefin resin is preferably high-density polyethylene (HDPE) from the viewpoint of good melt extrusion properties and uniform stretching properties. Polyethylene may be used alone or in combination of two or more for the purpose of imparting flexibility.

The content of polyethylene in the first polyolefin resin is from the viewpoint of heat resistance, peel strength between the active layer and the substrate, etc., the total mass of the first polyolefin resin is 100% by mass, preferably 50% by mass to 99% by mass, more preferably Preferably, it is 60 mass%-95 mass %, More preferably, it is 65 mass%-85 mass %.

The polypropylene contained in the first polyolefin resin has a three-dimensional structure from the viewpoint of heat resistance of the separator and can improve the heat resistance of the separator, such as isotactic polypropylene, syndiotactic polypropylene, and atactic poly At least one selected from the group consisting of propylene is preferred. Polypropylene may be used individually by 1 type, and may be used in combination of 2 or more types.

It is preferable that the 1st polyolefin resin further contains linear low-density polyethylene in addition to the said polyethylene from the viewpoint of collision resistance of a power storage device. It is more preferable that the 1st polyolefin resin further contains linear low-density polyethylene in addition to high-density polyethylene (HDPE). It is more preferable that linear low-density polyethylene is, for example, an ethylene/1-hexene copolymer.

The first polyolefin resin preferably further contains polypropylene having a heat of fusion of 150 J/g or less in addition to the polypropylene. Polypropylene having a heat of fusion of 150 J/g or less contains a large number of amorphous portions, and the collision resistance of the power storage device is improved.

The content of polypropylene in the first polyolefin resin is from the viewpoint of peel strength between the active layer and the substrate, cold and thermal shock characteristics, and low-temperature cycle characteristics, and the total mass of the first polyolefin resin is 100% by mass, preferably 1% by mass. It is 50 mass %, more preferably 5 mass%-40 mass %, More preferably 15 mass%-35 mass %. It is particularly preferably 15 to less than 30% by mass.

The outermost layer preferably contains at least one selected from the group consisting of silica, alumina, and titania in addition to the first polyolefin resin from the viewpoint of the separator's affinity with the nonaqueous electrolyte solution, power retention performance, and low-temperature cycle characteristics. Do. The ratio of silica, alumina, and titania in the outermost is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, further preferably 20 parts by mass or more, based on 100 parts by mass of the first polyolefin resin in the outermost. , Preferably it is 90 mass parts or less, More preferably, it is 80 mass parts or less, More preferably, it is 70 mass parts or less. Setting it as such a ratio is preferable from the viewpoint of obtaining good heat resistance and from the viewpoint of improving the elongation and obtaining a porous membrane having high stab strength.

(Internal)

In this embodiment, it is preferable that the innermost part contains the 2nd polyolefin resin containing polyethylene. The second polyolefin resin is preferably composed of polyethylene.

The polyethylene contained in the second polyolefin resin is not particularly limited, but examples thereof include low-density polyethylene, linear low-density polyethylene (L-LDPE), medium-density polyethylene, high-density polyethylene (HDPE), and ultra-high molecular weight polyethylene (UHMwPE). have.

The polyethylene contained in the second polyolefin resin is preferably high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMwPE) from the viewpoint of strength and heat resistance. Polyethylene may be used alone or in combination of two or more for the purpose of imparting flexibility.

The content of polyethylene in the second polyolefin resin is from the viewpoints of molding stability, mechanical strength in a thin film, and air permeability, and the total mass of the second polyolefin resin is 100% by mass, preferably 50% by mass to 100%. It is mass %, more preferably 60 mass%-100 mass %, More preferably 70 mass%-95 mass %.

It is preferable that the 2nd polyolefin resin further contains linear low-density polyethylene in addition to the said polyethylene from the viewpoint of collision resistance of an electrical storage device. In addition to the high-density polyethylene (HDPE) and/or ultra-high molecular weight polyethylene (UHMwPE), the second polyolefin resin is more preferably a linear low-density polyethylene (L-LDPE) from the viewpoint of collision resistance of the electrical storage device. It is more preferable that linear low-density polyethylene is, for example, an ethylene/1-hexene copolymer.

The second polyolefin resin may further contain polypropylene. The polypropylene that may be further included in the second polyolefin resin is preferably a polypropylene having a heat of fusion of 150 J/g or less. Polypropylene having a heat of fusion of 150 J/g or less is preferable because it contains a large number of amorphous portions and improves the collision resistance of the power storage device.

When the second polyolefin resin contains polypropylene, the content thereof is from the viewpoint of heat resistance and collision resistance of the electrical storage device, the total mass of the second polyolefin resin is 100% by mass, preferably 0% by mass to 25% by mass. %, more preferably 0% by mass to 20% by mass.

Among the first and second polyolefin resins, it is preferable that the second polyolefin resin contains the linear low-density polyethylene or polypropylene having a heat of fusion of 150 J/g or less from the viewpoint of collision resistance of the power storage device. Although the details of this mechanism are unclear, when a layer containing linear low-density polyethylene or polypropylene with a heat of fusion of 150 J/g or less is thicker than other layers, a layer containing linear low-density polyethylene or polypropylene with a heat of fusion of 150 J/g or less is When it is further away from the electrode (when another layer is interposed), it is estimated that the collision resistance of the power storage device is good.

(Other polyolefin resins)

The first and second polyolefin resins may contain polyolefin resins other than the above polyethylene and polypropylene in order to better balance the peel strength, handling properties, cold thermal shock properties, and low temperature cycle properties between the substrate and the active layer. Other olefin resins that may be included in the first and second polyolefin resins are not particularly limited, but polyolefin resins commonly used for extrusion, injection, inflation, and blow molding may be used. For example, 1-butene, 4-methyl Homopolymers and copolymers, such as 1-pentene, 1-hexene, and 1-octene, and multistage polymers can be used. Other polyolefins may be used alone or in combination.

(Weight average molecular weight)

The weight average molecular weights of polyethylene and polypropylene contained in the first and second polyolefin resins are not limited, but each independently, preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, further preferably It is more than 100,000 and less than 1 million. When the weight average molecular weight is 30,000 or more, the melt tension at the time of melt molding is large, so that the moldability becomes good, and the strength of the resulting polyolefin multilayer microporous film tends to increase due to entanglement of polymers, which is preferable. When the weight average molecular weight is 12 million or less, it becomes easy to perform melt-kneading uniformly, and the formability of the sheet, particularly, thickness stability tends to be excellent, which is preferable. When the weight average molecular weight is less than 1 million, the pores are easily clogged when the temperature rises, and good shutdown characteristics tend to be obtained, which is preferable.

The ratio (MwE/MwP) of the weight average molecular weight (MwE) of polyethylene contained in the outermost part in contact with the active layer and the weight average molecular weight (MwP) of polypropylene (MwE/MwP) is preferably 0.6 to 1.5. When MwE/MwP is 0.6 to 1.5, it is preferable from the viewpoint of reducing the variation in peel strength between the outermost and the active layer. The reason is not limited to the theory, but is estimated to be as follows. When MwE/MwP is 0.6 to 1.5 (closer to 1), the difference in molecular weight between polyethylene and polypropylene becomes small, and compatibility becomes more favorable. In that case, it becomes difficult to unevenly distribute a portion rich in polyethylene and a portion rich in polypropylene on the outermost surface. Since polypropylene is superior to polyethylene in adhesion to the modified layer, it is estimated that uneven distribution of polypropylene and polyethylene is suppressed, and the variation in peel strength between the active layer and the substrate is reduced.

In this embodiment, it is preferable that the polyolefin multilayer microporous membrane contains a 1st microporous layer and a 2nd microporous layer. These are preferably laminated in the order of a first microporous layer, a second microporous layer, and a first microporous layer from the viewpoint of securing an excellent balance of mechanical properties, shutdown properties, and meltdown properties. A separator having an active layer on at least one side of a polyolefin multilayer microporous membrane composed of three microporous layers laminated in this lamination sequence can provide a power storage device having high output characteristics and less ionic permeability. In addition, even when the temperature rises quickly, such as during abnormal heat generation, it exhibits a smooth shutdown characteristic, and thus the safety tends to be excellent. When the polyolefin multilayer microporous membrane is composed of three microporous layers, ``outermost'' refers to the two first microporous layers constituting the outside of the polyolefin multilayer microporous membrane, and the ``innermost'' refers to the inside. It refers to the 2nd microporous layer to comprise.

(1st microporous layer)

In the present embodiment, the first microporous layer contains a first polyolefin resin containing polyethylene and polypropylene. The first polyolefin resin is preferably composed of polyethylene and polypropylene. For details about the first polyolefin resin in the first microporous layer, refer to the description of "(outermost)".

(2nd microporous layer)

In this embodiment, the 2nd microporous layer contains a 2nd polyolefin resin containing polyethylene. The second polyolefin resin is preferably composed of polyethylene. For details about the second polyolefin resin in the second microporous membrane, refer to the description of "(innermost part)".

(additive)

The polyolefin multilayer microporous membrane may contain optional additives. Although it is not limited as an additive, For example, Polymer other than polyolefin; Inorganic particles; Antioxidants such as phenol, phosphorus, and sulfur; Metal soaps such as calcium stearate and zinc stearate; Ultraviolet absorbers; Light stabilizers; Antistatic agent; Antifogging agents; And colored pigments.

The content of the additive is 100 parts by mass of the total mass of the first and second polyolefin resins, preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less.

(Porosity)

The lower limit of the porosity of the polyolefin multilayer microporous membrane is not limited, but is preferably 20% or more, more preferably 35% or more, and the upper limit is preferably 90% or less, more preferably 80% or less. A porosity of 20% or more is preferable because the ion permeability of the separator becomes good. When the porosity is 90% or less, it is preferable from the viewpoint of high ion permeability. The porosity is calculated from the volume (cm 3 ), mass (g), and film density (g/cm 3) of the measurement sample of the polyolefin multilayer microporous membrane, by the following formula:

Porosity = (volume-mass/membrane density)/volume×100

It can be obtained by For example, in the case of a polyolefin multilayer microporous membrane made of polyethylene, it can be calculated by assuming a membrane density of 0.95 (g/cm 3 ). In the case of a polyolefin multilayer microporous membrane composed of polyethylene and polypropylene, it can be similarly calculated using the respective membrane densities. The porosity can be adjusted by changing the draw ratio of the polyolefin multilayer microporous membrane or the like.

(Specification)

The lower limit of the air permeability of the polyolefin multilayer microporous membrane is not limited, but is preferably 10 seconds/100 cc or more, more preferably 50 seconds/100 cc or more, and the upper limit is preferably 1,000 seconds/100 cc or less, more Preferably it is 500 seconds/100 cc or less. When the air permeability is 10 seconds/100 cc or more, self-discharge of the power storage device can be suppressed, which is preferable. When the air permeability is 1,000 seconds/100 cc or less, good charge/discharge characteristics are obtained, which is preferable. The air permeability is the air permeability resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and/or the stretching ratio of the polyolefin multilayer microporous membrane.

(Hole diameter)

It is preferable that the polyolefin multilayer microporous membrane is a porous membrane having a fine pore diameter, which has no electron conductivity, has ion conductivity, and has high resistance to organic solvents.

The upper limit of the average pore diameter of the polyolefin multilayer microporous membrane is preferably 0.15 µm or less, more preferably 0.1 µm or less, and the lower limit is preferably 0.01 µm or more. When the average pore diameter is 0.15 µm or less, self-discharge of the power storage device is suppressed and a decrease in capacity is suppressed, which is preferable. The average pore diameter can be adjusted by changing the draw ratio when producing the polyolefin multilayer microporous membrane.

(thickness)

The lower limit of the thickness of the polyolefin multilayer microporous film is not limited, but is preferably 2 µm or more, more preferably 5 µm or more, and the upper limit is preferably 100 µm or less, more preferably 60 µm or less, even more preferably Is 50 μm or less. When the thickness is 2 μm or more, it is preferable from the viewpoint of improving the mechanical strength. When the thickness is 100 µm or less, since the occupied volume of the separator in the battery decreases, it is preferable from the viewpoint of increasing the capacity of the battery.

<Active layer>

The separator for power storage devices of this embodiment has an active layer on at least one side of the polyolefin multilayer microporous membrane. In this embodiment, the active layer contains an acrylic resin and, if necessary, inorganic particles. By the active layer, the adhesive force between the active layer and the electrode (electrode active material) side becomes stronger, and the cold and heat shock characteristics are improved.

(Acrylic resin)

The acrylic resin is a polymer containing a (meth)acrylic compound as a monomer unit. The (meth)acrylic compound represents at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid ester.

As such a compound, a compound represented by the following formula (P1) is mentioned, for example.

CH ₂ =CR ^Y1 -COO-R ^Y2 (P1)

In formula (P1), 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 or may have a hetero atom in the chain. As a monovalent hydrocarbon group, a linear alkyl group, a cycloalkyl group, and an aryl group which may be linear or branched are mentioned, for example. As a substituent, a hydroxyl group and a phenyl group are mentioned, for example, As a hetero atom, a halogen atom, an oxygen atom, etc. are mentioned, for example. The (meth)acrylic compounds are used alone or in combination of two or more.

Examples of such (meth)acrylic compounds include (meth)acrylic acid, chain alkyl (meth)acrylate, cycloalkyl (meth)acrylate, (meth)acrylate having a hydroxyl group, and (meth)acrylate having a phenyl group. I can.

As a chain alkyl group which is one type of R ^Y2 , More specifically, a chain alkyl group having 1 to 3 carbon atoms which is a methyl group, an ethyl group, an n-propyl group and an isopropyl group; and chain alkyl groups having 4 or more carbon atoms such as n-butyl group, isobutyl group, t-butyl group, n-hexyl group, 2-ethylhexyl group and lauryl group. As an aryl group which is 1 type of R ^Y2 , a phenyl group is mentioned, for example.

As specific examples of such a (meth)acrylic acid ester monomer having R ^{Y 2} , for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, (meth)acrylates having a chain alkyl group such as t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate; (Meth)acrylates having an aromatic ring, such as phenyl (meth)acrylate and benzyl (meth)acrylate.

Among these, excessive swelling in the electrolyte is suppressed by appropriately separating the dissolution parameter (SP value) of the polymer and the SP value of the polymer from the viewpoint of improving the adhesion with the electrode (electrode active material) and collision of the power storage device. From the viewpoint of achieving balance between resistance and resistance, a monomer having a chain alkyl group having 4 or more carbon atoms, more specifically, a (meth)acrylic acid ester monomer wherein R ^Y2 is a chain alkyl group having 4 or more carbon atoms 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 for example, it may be 14 or less, preferably 7 or less. These (meth)acrylic acid ester monomers are used alone or in combination of two or more.

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

As a monomer having such a cycloalkyl group, more specifically, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, etc. are mentioned, for example. The number of carbon atoms constituting the alicyclic ring of the cycloalkyl group is preferably 4 to 8, more preferably 6 and 7, and particularly preferably 6. The cycloalkyl group may or may not have a substituent. As a substituent, a methyl group and a t-butyl group are mentioned, for example. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferable from the viewpoint of good polymerization stability when producing an acrylic resin. These are used alone or in combination of two or more.

It is preferable that the acrylic resin, as a (meth)acrylic acid ester monomer, contains a crosslinkable monomer instead of or in addition to the above, preferably in addition to the above. Although it does not specifically limit as a crosslinkable monomer, For example, a monomer which has two or more radical polymerizable double bonds, a monomer which has a functional group which imparts a self-crosslinking structure during or after polymerization, etc. are mentioned. These are used alone or in combination of two or more.

Examples of the monomer having two or more radical polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylate. The polyfunctional (meth)acrylate may be at least one selected from the group consisting of bifunctional (meth)acrylate, trifunctional (meth)acrylate, and (4) functional (meth)acrylate. Specifically, for example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacryl Rate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, and the like. These are used alone or in combination of two or more. Among them, at least one selected from the group consisting of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferable from the viewpoint of good polymerization stability when producing an acrylic resin.

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

As a monomer having a methylol group, N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, dimethylol methacrylamide, etc. are mentioned, for example.

The monomer having an alkoxymethyl group is preferably an ethylenically unsaturated monomer having an alkoxymethyl group, and specifically, for example, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacryl Amide, N-butoxymethyl methacrylamide, and the like.

As the monomer having a hydrolyzable silyl group, for example, vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryl And oxypropyl triethoxysilane. These are used alone or in combination of two or more.

The acrylic resin may further have a monomer other than the above as a monomer unit in order to improve various qualities and physical properties. Such monomers include, for example, a monomer having a carboxyl group (excluding (meth)acrylic acid), a monomer having an amide group, a monomer having a cyano group, a monomer having a hydroxyl group, a monomer forming a urethane group, and an aromatic vinyl monomer. And the like.

Various vinyl monomers having functional groups such as sulfonic acid group and phosphoric acid group, and vinyl acetate, vinyl propionate, vinyl versatate, vinylpyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, vinyl chloride, vinylidene chloride, etc. Can be used.

These are used alone or in combination of two or more. The other monomers may belong to two or more types of the respective monomers at the same time.

As a monomer which has an amide group, (meth)acrylamide etc. are mentioned, for example. As the monomer having a cyano group, an ethylenically unsaturated monomer having a cyano group is preferable, and specifically, (meth)acrylonitrile, etc. are mentioned. As a monomer having a hydroxyl group, 2-hydroxyethyl (meth)acrylate, etc. are mentioned, for example.

As an aromatic vinyl monomer, styrene, vinyl toluene, α-methylstyrene, etc. are mentioned, for example. Preferably it is styrene.

Acrylic resins are obtained, for example, by an ordinary emulsion polymerization method. There is no restriction|limiting in particular about the method of emulsion polymerization, A well-known method can be used.

For example, in an aqueous medium, in a dispersion system containing the above-described monomer, surfactant, radical polymerization initiator, and other additive components used as necessary as a basic composition component, by polymerizing a monomer composition containing each of the above monomers, an acrylic resin is Is obtained. During polymerization, a method of making the composition of the supplied monomer composition constant during the entire polymerization process, a method of giving a change in the morphological composition of the particles of the resin dispersion produced by sequentially or continuously changing the polymerization process, etc. Method can be used.

The surfactant is a compound having at least one hydrophilic group and at least one lipophilic group per molecule. Various surfactants include non-reactive surfactants and reactive surfactants, preferably reactive surfactants, more preferably anionic reactive surfactants, and still more preferably reactive surfactants having a sulfonic acid group.

It is preferable to use 0.1-5 mass parts of the said surfactant with respect to 100 mass parts of a monomer composition. Surfactants are used alone or in combination of two or more.

As the radical polymerization initiator, it is radically decomposed by heat or a reducing substance to initiate addition polymerization of a monomer, and both inorganic initiators and organic initiators can be used. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used.

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

From the viewpoint of ion permeability, the acrylic resin preferably contains a copolymer having an ethylenically unsaturated monomer having a polyalkylene glycol group as a monomer unit. The ethylenically unsaturated monomer having a polyalkylene glycol group can be copolymerized with a monomer not having a polyalkylene glycol group. The polyalkylene glycol group is also called a polyoxyalkylene group, and may be, for example, a polyoxymethylene group, a polyoxyethylene group, a polyoxypropylene group, a polyoxybutylene group, or the like. The number of carbon atoms of the oxyalkylene group constituting the polyoxyalkylene group is preferably 1 to 6, more preferably 1 to 3, and still more preferably 2). The hydrocarbon group in the polyalkylene glycol group may be linear or branched.

The average repetition number (n) of the alkylene glycol unit in the ethylenically unsaturated monomer having a polyalkylene glycol group is not particularly limited, but 1 or more is preferable, 3 or more is more preferable, 100 or less is preferable, and 30 or less is It is more preferable, 15 or less are still more preferable, and 8 or less are especially more preferable. When the average repetition number n is 3 or more, the ionic permeability of the copolymer tends to increase. When the average repetition number n is 15 or less, the copolymerization during emulsion polymerization with a monomer not having a polyalkylene glycol group tends to be improved.

As an ethylenically unsaturated monomer (P2) having a polyalkylene glycol group, for example, polyalkylene glycol mono(meth)acrylate, polyalkylene glycol di(meth)acrylate, or polyalkylene glycol unit and allyl in the molecule And a monomer having a reactive substituent such as a group.

As polyalkylene glycol mono(meth)acrylate, for example, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, polyethylene glycol-polypropylene glycol (meth)acrylate, polyethylene glycol-polybutylene Glycol (meth)acrylate, polypropylene glycol-polybutylene glycol (meth)acrylate, 2-ethylhexyl polyethylene glycol mono (meth)acrylate, phenoxydiethylene glycol mono (meth)acrylate, phenoxy polyethylene glycol mono (Meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxydiethylene glycol mono (meth)acrylate, ethoxy polyethylene glycol (meth)acrylate, butoxy polyethylene glycol (meth)acrylate, octoxy polyethylene Glycol (meth)acrylate, lauroxy polyethylene glycol (meth)acrylate, stearoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, octoxy (Meth)acrylic acid ester monomers having a polyalkylene glycol group such as polyethylene glycol-polypropylene glycol (meth)acrylate, and the like, from the viewpoint of more effective and reliably solving the problem of the present invention, these are preferred. In addition, as the monomer (P2), it is a reactive surfactant and includes those having a polyalkylene glycol chain. Among the monomers (P2), methoxydiethylene glycol mono (meth) acrylate, methoxy polyethylene glycol mono (meth) acrylate, butoxy polyethylene glycol mono (meth) acrylate, 2-ethylhexyl polyethylene glycol mono (meth) Acrylate and methoxypolypropylene glycol mono(meth)acrylate are preferred in view of good polymerization stability during the production of the copolymer.

As polyalkylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polyethylene glycol-polypropylene glycol di(meth)acrylate, etc. are mentioned.

Examples of the monomer having a polyalkylene glycol unit and an allyl group in the molecule include polyalkylene glycol monoallyl ether, and specifically, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, and the like may be used. .

The acrylic resin may have a core/shell structure. The core/shell structure is a polymer in the form of a double structure, in which a polymer belonging to a central portion and a polymer belonging to an outer portion have different compositions. In the core shell structure, by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature, the glass transition temperature of the entire acrylic resin can be controlled. Specifically, the handling property of the separator can be improved (refer to the comparison between Example 2 and Example 9 described later). A plurality of functions can be imparted to the entire thermoplastic polymer.

As the acrylic resin, a commercially available acrylic resin can also be used. As commercially available ones, for example, "POVACOAT" (registered trademark) manufactured by Nisshin Kasei Co., Ltd., "Jurimer" manufactured by Toa Kosei Corporation (registered trademark) AT-510, ET-410, FC- 60, SEK-301, Daisei Fine Chemical Co., Ltd. UW-223SX, UW-550CS, DIC Co., Ltd. WE-301, EC-906EF, CG-8490, etc. are mentioned. Among these, POVACOAT and WE-301 are preferable from the viewpoint of both the peel strength of the active layer and the substrate and ion permeability.

The active layer may contain other resins other than the acrylic resin as long as the various characteristics expressed by the separator according to the present embodiment are not impaired. As other resins, for example, polyvinylidene fluoride, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, ethylene vinyl acetate copolymer, polyimide, polyethylene oxide, etc. Can be lifted. The other resins may be used alone or in combination of two or more of them, and are not limited thereto.

(Weapon particles)

Although it is not limited as an inorganic particle, it has a melting|fusing point of 200 degreeC or more, electrical insulation is high, and it is preferable that it is electrochemically stable in the use range of a lithium ion secondary battery.

Although it is not limited as an inorganic particle, For example, Oxide ceramics, such as alumina (Al ₂ O ₃ ), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; Nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride; Silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide (AlO(OH)), potassium titanate, talc, kaolinite, decite, nacrite, haloysite, pyrophyllite, montmorillonite, serie Ceramics such as site, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; Glass fiber, etc. are mentioned. These may be used independently and may use multiple together.

Among these, examples of the inorganic particles include aluminum oxide compounds such as alumina and aluminum hydroxide from the viewpoint of improving electrochemical stability and heat resistance of the separator; And an aluminum silicate compound having no ion exchange ability, such as kaolinite, decite, nachrite, halosite, and pyrophilite.

In alumina, there are many crystalline forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and all of them can be used. Among these, α-alumina is preferable because it is thermally and chemically stable.

As the aluminum oxide compound, aluminum hydroxide (AlO(OH)) is preferable. As aluminum hydroxide, boehmite is more preferable from the viewpoint of preventing an internal short circuit caused by the generation of lithium dendrites. By using boehmite as the inorganic particles, it is possible to provide a very lightweight active layer while maintaining high permeability, and even when the thickness of the active layer is thin, heat shrinkage at high temperature can be suppressed, and excellent heat resistance tends to be obtained. Synthetic boehmite, which can reduce ionic impurities that adversely affect the characteristics of the electrical storage device, is more preferable.

As the aluminum silicate compound having no ion exchange ability, kaolin composed of a kaolin mineral is more preferable from the viewpoint of cost and availability. Examples of kaolin include wet kaolin and calcined kaolin obtained by calcining the same, and calcined kaolin is more preferable. The calcined kaolin is particularly preferable from the viewpoint of electrochemical stability because crystal water has already been released by the calcining treatment and there are few impurities.

The average particle diameter of the inorganic particles is preferably more than 0.01 µm and not more than 4.0 µm, more preferably more than 0.2 µm and not more than 3.5 µm, and still more preferably more than 0.4 µm and not more than 3.0 µm. When the average particle diameter of the inorganic particles is more than 0.01 µm and not more than 4.0 µm, it is preferable because heat shrinkage at high temperature can be suppressed even when the thickness of the active layer is thin (for example, 7 µm or less). As a method of adjusting the particle size and particle size distribution of the inorganic particles, for example, a method of pulverizing the inorganic particles using an appropriate pulverizing device such as a ball mill, a bead mill, and a jet mill to reduce the particle size is mentioned.

Examples of the shape of the inorganic particles include a plate shape, a scale shape, a needle shape, a column shape, a spherical shape, a polyhedron shape, and a block shape. As for the shape of an inorganic filler, one type of these may be used and may be used in combination of 2 or more types.

The content of the inorganic particles in the active layer can be appropriately determined from the viewpoints of the binding properties of the inorganic particles, the permeability of the separator, and heat resistance. The content of the inorganic particles in the active layer is preferably 50% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, still more preferably 60% by mass or more, based on the total mass of the active layer. It is 90 mass% or less. When the content of the inorganic particles is 50% by mass or more and 95% by mass or less, the adhesion between the separator and the electrode and the reduction in the resistance of the film resistance of the separator can be achieved both and are preferable.

The mass ratio of the acrylic resin and the inorganic particles in the active layer is preferably 5/95 to 50/50 of the acrylic resin/inorganic particles, more preferably 10/90 to 50/50, even more preferably 10/90 to It is 40/60. When the mass ratio of the acrylic resin/inorganic particles is 5/95 to 50/50, the peel strength of the active layer/substrate and the handling property of the separator can be made compatible, which is preferable.

(thickness)

The thickness of the active layer is preferably 0.5 µm or more from the viewpoint of heat resistance and insulation, and preferably 50 µm or less from the viewpoint of increasing the battery capacity and improving ion permeability.

(Bulk density)

The layer density of the active layer is preferably 0.5 g/cm 3 to 3.0 g/cm 3, more preferably 0.7 g/cm 3 to 2.0 g/cm 3. When the layer density of the active layer is 0.5 g/cm 3 or more, the thermal contraction rate at high temperature tends to be good, and when it is 3.0 g/cm 3 or less, the air permeability tends to decrease.

<Physical properties of the separator for power storage devices>

The air permeability of the power storage device separator is preferably 10 seconds / 100 cc or more and 650 seconds / 100 cc or less, more preferably 20 seconds / 100 cc or more and 500 seconds / 100 cc or less, even more preferably 30 seconds / 100 It is more than or equal to 450 sec/100 cc or less, particularly preferably less than or equal to 50 sec/100 cc and less than 400 sec/100 cc. The air permeability is the air permeability resistance measured in accordance with JIS P-8117, similar to the air permeability of the polyolefin porous substrate.

When the air permeability of the electrical storage device separator is 10 seconds/100 cc or more, self-discharge tends to decrease, and when it is 650 seconds/100 cc or less, favorable charge/discharge characteristics tend to be obtained. In one embodiment, since the separator for power storage devices exhibits such a very large air permeability, it can exhibit high ion permeability when applied to a lithium ion secondary battery.

The thickness of the separator for power storage devices (that is, the total thickness including the polyolefin multilayer microporous membrane and the active layer) is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, even more preferably It is 7 μm or more and 30 μm or less. When this thickness is 2 µm or more, mechanical strength can be sufficiently secured, and when it is 200 µm or less, the occupied volume of the separator decreases, which is preferable from the viewpoint of increasing the capacity of the battery.

《Method of manufacturing separator for power storage device》

<Method for producing polyolefin multilayer microporous membrane>

The method of manufacturing the first and second microporous membranes is not particularly limited, and a known manufacturing method may be employed. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded, molded into a sheet, stretched, if necessary, and then made porous by extracting the plasticizer; A method in which the polyolefin resin composition is melt-kneaded and extruded at a high draw ratio, and then the polyolefin crystal interface is peeled off by heat treatment and stretching to make it porous; A method in which the polyolefin resin composition and the inorganic filler are melt-kneaded and molded into a sheet, and then the interface between the polyolefin and the inorganic filler is peeled off by stretching to make it porous; After dissolving the polyolefin resin composition, a method of making the polyolefin porous by removing the solvent while solidifying the polyolefin by immersing it in a poor solvent for the polyolefin may be mentioned.

The first and second microporous membranes may be produced in the form of a nonwoven fabric or paper, and examples of the method include a chemical bonding method in which a web is immersed in a binder and dried to bond between fibers; A thermal bonding method in which hot meltable fibers are incorporated into a web, and the fibers are partially melted to bond between fibers; A needle punching method in which a needle with thorns in the web is repeatedly stabbed and the fibers are mechanically tied; A water flow entanglement method in which a high-pressure water flow is sprayed from a nozzle to a web through a net (screen) to bind the fibers can be mentioned.

Hereinafter, as an example of a method for producing a polyolefin multilayer microporous membrane, through an operation of melt-kneading a polyolefin resin composition and a plasticizer to form the sheet-like first and second microporous layers, and to extract the plasticizer, the first and second A method of laminating the microporous layer will be described.

First, the polyolefin resin composition and the raw material composition containing a plasticizer are melt-kneaded. As a melt-kneading method, for example, polyolefin resin and other additives as necessary are introduced into a resin kneading apparatus such as an extruder, kneader, laboplasto mill, kneading roll, and Banbury mixer, and the resin component is heated and melted. A method of kneading by introducing a plasticizer at a ratio is mentioned. Before introducing the polyolefin resin, plasticizer, and other additives into the resin kneading apparatus, it is preferable to pre-knead the raw materials in a predetermined ratio using a Henschel mixer or the like. More preferably, in pre-kneading, a part of the plasticizer is added, and the remaining plasticizer is kneaded while side-feeding the resin kneading device.

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

The ratio of the polyolefin resin composition and the plasticizer in the raw material composition is not particularly limited as long as it is a range in which they can be uniformly melt-kneaded and molded into a sheet. For example, the content of the plasticizer is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, based on the total mass of the raw material composition. When the content of the plasticizer is 30 to 80% by mass, the melt tension at the time of melt molding and the formability of a uniform and fine pore structure can be made compatible, which is preferable.

Then, the obtained melt-kneaded product is molded into a sheet shape. As a method of manufacturing a sheet-shaped molded article, for example, a method of extruding a melt-kneaded product into a sheet through a T-die, contacting a heat conductor, cooling to a temperature sufficiently lower than the crystallization temperature of the resin component, and solidifying it. I can. Examples of the heat conductor used for cooling and solidification include metal, water, air, and a plasticizer itself. From the viewpoint of high efficiency of heat conduction, it is preferably a metal roll. When the melt-kneaded product is brought into contact with a metal roll, it is more preferable because it is sandwiched between metallic rolls, because heat can be conducted more efficiently, the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is improved. Do. When the melt-kneaded product is extruded into a sheet through a T-die, the die lip interval is preferably 400 µm or more and 3,000 µm or less, and more preferably 500 µm or more and 2,500 µm or less.

In this way, the first microporous layer and the second microporous layer can be obtained. As a method of laminating the obtained microporous layer in the order of the first microporous layer, the second microporous layer, and the first microporous layer, for example, a three-layer batch lamination method of manufacturing and laminating three layers in parallel, and And a method of laminating after each of the two first microporous layers and the second microporous layer is produced.

Hereinafter, a three-layer batch lamination method will be described. The raw material composition of the first microporous layer and the raw material composition of the second microporous layer are melt-kneaded in parallel using each twin-screw extruder, and each melt-kneaded product is fed from each twin-screw extruder into a single three-layer T While supplying to the die and adjusting the layer thickness ratio of each layer molded from each melt-kneaded product (first melt-kneaded material layer/second melt-kneaded material layer/first melt-kneaded material layer) to a desired range, while taking out at a predetermined winding speed It can be cooled and formed as a gel-like three-layer sheet.

Next, it is preferable to stretch the obtained gel-like three-layer sheet. As the stretching treatment, either uniaxial stretching or biaxial stretching can be used. Biaxial stretching is preferable from the viewpoint of strength of the obtained polyolefin multilayer microporous membrane. By stretching the sheet-like molded body at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the resulting polyolefin multilayer microporous membrane becomes difficult to tear, which is preferable. Examples of the method of biaxial stretching include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple times stretching. Simultaneous biaxial stretching is preferable from the viewpoint of improvement in strength, uniformity of stretching, and shutdown characteristics.

The draw ratio is preferably 20 times or more and 100 times or less, and more preferably 25 times or more and 50 times or less in terms of the surface ratio. The draw ratio in each axis direction is preferably in the range of 4 times or more and 10 times or less in the MD direction, 4 times or more and 10 times or less in the TD direction, and 5 times or more and 8 times or less in the MD direction, and 5 times or more in the TD direction. It is more preferable that it is in the range of 8 times or less. By setting it as the total area magnification of this range, while being able to provide sufficient strength, it is preferable from the viewpoint that a film breakage in a stretching process can be prevented and high productivity can be obtained.

The stretched sheet-shaped molded body may be further rolled. Rolling can be performed by, for example, a press method using a double belt press machine or the like. Rolling can increase the orientation of the surface portion. The rolling surface magnification is preferably greater than 1 times and 3 times or less, more preferably greater than 1 times and less than 2 times. By setting it as the rolling ratio in this range, the film strength of the polyolefin multilayer microporous film finally obtained increases, and it is preferable from the point which can form a uniform porous structure in the thickness direction of a film.

Subsequently, a plasticizer can be removed from the stretched or stretched and rolled sheet-like molded body to obtain a polyolefin multilayer microporous membrane. As a method of removing the plasticizer, a method of extracting the plasticizer by immersing the sheet-shaped molded body in an extraction solvent and drying it sufficiently is mentioned, for example. The method of extracting the plasticizer may be either a batch type or a continuous type. In order to suppress the shrinkage of the polyolefin multilayer microporous membrane, it is preferable to restrain the end of the sheet-like molded body between the immersion and drying operations. It is preferable that the residual amount of the plasticizer in the polyolefin multilayer microporous membrane is less than 1% by mass.

As an extraction solvent, it is preferable to use a solvent which is poor with respect to a polyolefin resin, and is a good solvent with respect to a plasticizer, and a boiling point is lower than the melting point of a polyolefin resin. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; Halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; Non-chlorine-based halogenated solvents such as hydrofluoroether and hydrofluorocarbon; Alcohols such as ethanol and isopropanol; Ethers such as diethyl ether and tetrahydrofuran; Ketones, such as acetone and methyl ethyl ketone, are mentioned. The extraction solvent may be recovered and reused by an operation such as distillation.

In order to suppress the shrinkage of the polyolefin multilayer microporous film, heat treatment such as heat fixation or heat relaxation may be performed after the stretching step or after the polyolefin multilayer microporous film is formed.

The obtained polyolefin multilayer microporous membrane may be subjected to surface treatment such as hydrophilization treatment with a surfactant or the like, crosslinking treatment with ionizing radiation or the like. If surface treatment is performed, it is preferable to apply the coating liquid of the active layer after that, and the adhesion between the polyolefin and the active layer is improved. Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

<Formation method of active layer>

The method of forming the active layer is not particularly limited as long as the required layer thickness and coating area can be realized. For example, the active layer is a polyolefin multilayer microporous membrane (hereinafter also referred to as a ``substrate'') using a coating liquid containing an additional component such as an acrylic resin, arbitrary inorganic particles, and, if desired, a solvent such as water and a dispersant. It can be formed by coating it on at least one surface of (ham).

The method of applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. As a coating method, 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 A method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, a spray coating method, an inkjet coating method, and the like are mentioned. Among these, the gravure coater method is preferable because the degree of freedom of the coating shape is high.

Alternatively, the raw material for the active layer and the raw material for the polyolefin multilayer microporous membrane may be collectively extruded and laminated by coextrusion, or the polyolefin multilayer microporous membrane and the active layer may be separately produced and then bonded.

The method of removing the solvent from the coating film after coating is not limited as long as it does not adversely affect the substrate and the porous layer. For example, a method of drying at a temperature equal to or lower than the melting point of the substrate while fixing the substrate, a method of drying under reduced pressure at a low temperature, and the like may be mentioned.

《Power storage device》

The separator for power storage devices of the present embodiment can provide a stacked body and a wound body that can be used for power storage devices by combining this with a positive electrode, a negative electrode, and a nonaqueous electrolyte. As a power storage device, a secondary battery, for example, a lithium ion secondary battery can be mentioned, for example. Hereinafter, for the purpose of illustration, a lithium ion secondary battery having the separator for power storage devices of the present embodiment will be described.

As the positive electrode, the negative electrode, and the non-aqueous electrolyte, a known one can be used, respectively.

As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be used. As a positive electrode current collector, aluminum foil etc. are mentioned, for example. Examples of the positive electrode active material include lithium-containing complex oxides such as LiCoO ₂ , LiNiO ₂ , spinel LiMnO ₄ , and olivine LiFePO ₄ . In addition to the positive electrode active material, the positive electrode active material layer may contain a binder, a conductive material, and the like.

As the negative electrode, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector can be used. As a negative electrode current collector, copper foil etc. are mentioned, for example. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitized carbonaceous, easily graphitized carbonaceous, and composite carbonaceous material; Silicon, tin, metallic lithium, and various alloy materials.

Although it does not specifically limit as a non-aqueous electrolytic solution, an electrolytic solution obtained by dissolving an electrolyte in an organic solvent can be used. As an organic solvent, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc. are mentioned, for example. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ and LiPF ₆ .

The method of manufacturing the power storage device using the separator for power storage devices of the present embodiment is not particularly limited. For example, the following method can be illustrated.

The separator for power storage devices of the present embodiment is preferably manufactured in a lengthwise shape having a width of 10 to 500 mm, a length of 200 to 4,000 m, more preferably a width of 80 to 500 mm, and a length of 1,000 to 4,000 m. A layered product can be obtained by laminating the separator in the order of a positive electrode-separator-negative electrode-separator, or a negative electrode-separator-positive electrode-separator. The obtained laminate may be wound in a circular or flat winding shape to obtain a wound body. A power storage device can be manufactured by accommodating the obtained laminated body or wound body together with an electrolytic solution in an exterior body. As the exterior body, a metal can and a laminate film, for example, an aluminum film, etc. are mentioned, for example.

It is also preferable to press the laminated body or the wound body. Specifically, the separator for power storage devices of the present embodiment, the current collector and the electrode having an active material layer formed on at least one surface of the current collector can be overlapped and pressed. The press temperature may be, for example, 25°C or more and 120°C or less, or 50°C to 100°C. Pressing can be performed using a known press device such as a roll press or a surface press.

Example

Hereinafter, embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples.

《Measurement method and evaluation method》

(1) Peel strength between active layer and substrate

To the active layer of the separator obtained in Examples and Comparative Examples, a tape having a width of 12 mm x a length of 100 mm (manufactured by 3M, product name: Scotch (registered trademark) 600) was attached parallel to the length direction of the separator. The force when the tape was peeled from the active layer at a rate of 50 mm/min was measured using a 90° peel strength measuring instrument (manufactured by IMADA, product name IP-5N). Five points were measured, and the average value of the obtained peel strength was made into the peel strength of an adhesive layer and a base material, and evaluated by the following evaluation criteria.

(Evaluation standard)

A: Peel strength is 50 N/m or more

B: Peel strength is 40 N/m or more and less than 50 N/m

C: Peel strength is less than 40 N/m

(2) Separator handling properties (blocking resistance; room temperature peel strength test)

Two samples were prepared by cutting the separators obtained in Examples and Comparative Examples into 20 mm×100 mm. After superimposing these, it pressed for 3 minutes under the conditions of a temperature of 25 degreeC and a pressure of 5 MPa. The 90° peeling strength between the separators in the sample after pressing was measured at a tensile speed of 50 mm/min using force gauges ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. Based on the value of the peel strength, it evaluated according to the following evaluation criteria.

(Evaluation standard)

A: Peel strength is less than 30 N/m

B: Peel strength is 30 N/m or more and less than 40 N/m

C: Peel strength is 40 N/m or more

(3) cold and heat shock characteristics

Using the separators obtained in Examples and Comparative Examples, for each of the secondary batteries assembled as follows a to d, the cold and heat shock characteristics (cooling and heat resistance cycle characteristics) were evaluated.

a. Production of positive pole

96 parts by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, ₂ parts by mass of carbon black powder as a positive electrode conductive agent, and 2 parts by mass of polyvinylidene fluoride as a positive electrode binder (binder) were dry-mixed, and N -Disperse in methylpyrrolidone (NMP) to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was applied to both surfaces of an aluminum foil having a thickness of 13 μm to be a positive electrode current collector, dried, and then rolled to produce a positive electrode. The packing density and thickness of the positive electrode active material layer at this time were 3.95 g/cc and 140 µm in the portion in which the positive electrode active material layer was formed on both surfaces of the current collector.

b. Production of negatives

97 parts by mass of a carbon-based active material (artificial graphite) and 3 parts by mass of a silicon-based active material (SiO _x ) (x=1.05) were mixed. 98 parts by mass of the obtained mixture, 1 part by mass of sodium carboxymethylcellulose (CMC-Na), and 1 part by mass of fine particles of polyvinylidene fluoride (PVDF) were mixed, and these were dispersed in water to obtain a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both surfaces of a copper foil having a thickness of 8 μm to be a negative electrode current collector, dried, and then rolled. Next, the negative electrode mixture after rolling was heated to 170°C, which is a temperature equal to or higher than the melting point of PVDF. Thereby, PVDF fine particles were fused to the surfaces of the carbon-based active material and the silicon-based active material. A negative electrode was produced by the above process. The packing density and thickness of the negative electrode active material layer at this time were 1.75 g/cc and 137 μm in the portion where the negative electrode active material layer was formed on both surfaces of the current collector.

c. Preparation of non-aqueous electrolyte

A non-aqueous electrolyte was prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate:diethyl carbonate=3:7 (mass ratio) so that the concentration became 1.2 mol/L.

d. Battery assembly

The positive electrode produced in a., the negative electrode produced in b., and the separators obtained in Examples and Comparative Examples were cut and superimposed, respectively, and then wound in the direction of the long side at room temperature and crushed to form a flat winding body (battery element ) Was produced. This battery element was inserted into a laminate film having a thickness of 120 µm consisting of three layers of polypropylene/aluminum/nylon from the inside to the outside, and thermally fused while leaving one side of the exterior member. The non-aqueous electrolyte solution adjusted in c. was injected into the exterior member containing the battery element, and the remaining one side of the exterior member was thermally fused under reduced pressure to seal under reduced pressure. This was heated between metal plates at 80° C. for 3 minutes to obtain a secondary battery having a thickness of 2 mm x a width of 30 mm x a height of 30 mm.

The obtained secondary battery was charged to 4.35 V with a constant current of 56 mA at 25° C., and then constant voltage charging was performed to a charging current of 14 mA. After constant voltage charging, the secondary battery resistance (1 kHz AC impedance: Ω) in the charged state was measured, and this resistance was taken as the initial resistance.

Then, using a thermal shock tester (TSA-71H-W manufactured by SPEC), the temperature was raised to 70°C and maintained for 4 hours. Thereafter, the cycle of maintaining the battery at 20°C for 2 hours and then at -40°C for 4 hours was repeated 50 times. In the same manner as in the above d, the resistance (1 kHz AC impedance: Ω) of the secondary battery was measured. From this result and the initial resistance measured in d above, the amount of change in resistance before and after the cooling and heating cycle (resistance after the cooling and heating cycle-initial resistance) was calculated, and evaluated according to the following criteria.

(Evaluation standard)

A: The amount of resistance change before and after cold and heat shock is 0Ω or more and less than 20Ω

B: The amount of resistance change after a cold shock shock is 20Ω or more and less than 40Ω

C: The amount of change in resistance before and after cold shock is 40Ω or more

(4) Low temperature cycle characteristics

Using the separators obtained in Examples and Comparative Examples, low-temperature cycle characteristics were measured for each of the rechargeable batteries assembled as follows a to c.

a. Production of positive pole

100 parts by weight of lithium cobaltate as a positive electrode active material, 2 parts by weight of acetylene black as a conductive agent, and 2 parts by weight of polyvinylidene fluoride as a binding agent are twin-armed with an appropriate amount of N-methyl-2-pyrrolidone By stirring and kneading in a machine, a positive electrode mixture coating was produced. A positive electrode active material layer was formed by applying and drying the obtained positive electrode mixture paint on both surfaces of an Al foil having a thickness of 20 μm as a positive electrode current collector. This was pressed with a pair of rollers and rolled to obtain a positive electrode having a total thickness of 120 µm. Further, an exposed portion of the positive electrode current collector in which the positive electrode active material layer was not formed was provided on one side of the positive electrode current collector in the short side direction.

b. Production of negatives

100 parts by volume of artificial graphite as a negative electrode active material, 2.3 parts by volume of styrene-butadiene copolymer rubber particle dispersion as a binder in terms of the solid content of the binder, 1.4 parts by volume of carboxymethylcellulose as a thickener, and a predetermined amount of water Was stirred in a twin arm kneader to prepare a negative electrode mixture coating having a volume solid fraction of 55%. The volume solid fraction is the volume concentration of the solid content contained in the mixture coating material. The obtained negative electrode mixture coating was applied to both surfaces of a 15 μm-thick copper foil as a negative electrode current collector, dried, and then rolled to obtain a negative electrode having a total thickness of 185 μm. Further, an exposed portion of the negative electrode current collector in which the negative electrode active material layer was not formed was provided on one side of the negative electrode current collector in the short side direction.

c. Production of batteries

The positive electrode produced in a., the separator obtained in Examples and Comparative Examples, and the negative electrode produced in b. were stacked and wound to obtain a wound body, and the wound body was inserted into a cylindrical battery case. 5.5 g of an electrolytic solution obtained by dissolving 1 M of LiPF ₆ and 3 parts by weight of VC in a mixed solvent of EC (ethylene carbonate), DMC (dimethyl carbonate) and MEC (methyl ethyl carbonate) was placed in a cylindrical battery case and sealed. Thus, a cylindrical 18650 non-aqueous secondary battery having a design capacity of 2000 mAh was produced.

d. Measurement of low temperature cycle characteristics

The capacity retention rate at the time of 100 cycles at low temperature was measured by the following method. The battery after sealing was subjected to break-in charging and discharging twice, and after being stored for 7 days in a 45°C environment, the following charging and discharging cycles were repeated 100 times at -30°C. Regarding charging, charging is performed at a constant voltage of 4.2 V and 1400 mA, charging is terminated when the charging current is reduced to 100 mA, and discharging is discharged to the end voltage (3 V) at a constant current of 2000 mA as one cycle, 1 The ratio of the discharge capacity at the 100th cycle to the cycleth was measured as the 100 cycle capacity retention rate. And the low-temperature cycle characteristics were evaluated based on the following criteria.

(Evaluation standard)

A: The capacity retention rate at the time of 100 cycles at low temperature is 70% or more

B: The capacity retention rate at the time of 100 cycles at low temperature is 60% or more and less than 70%

C: The capacity retention rate at the time of 100 cycles at low temperature is less than 60%

(5) Variation in peel strength between active layer and substrate

Similar to the above "(1) Peel strength between the active layer and the substrate", for the separators having a width of 600 mm obtained in Examples and Comparative Examples, a tape having a width of 12 mm x a length of 100 mm (manufactured by 3M, product name: Scotch (registered trademark) ) 600) were attached at 5 points parallel to the length direction of the separator (TD direction) with an interval of 100 mm. Similarly, five points of the tapes were attached at a distance of 500 mm perpendicular to the longitudinal direction of the separator (MD direction). The force at the time of peeling the attached tape from the sample at a rate of 50 mm/min was measured using a 90° peel strength meter (manufactured by IMADA, product name IP-5N). And based on the following equation, the variation [%] of the peel strength was calculated from the standard deviation and the average value of the peel strength, and the following criteria were evaluated.

In the formula, x represents the average value of the peel strength, and n represents the number of measurements.

(Evaluation standard)

A: The variation in the peel strength of the active layer/substrate is less than 15%

B: The variation in the peel strength of the active layer/substrate is 15% or more and less than 25%

C: variation in the peel strength of the active layer/substrate is 25% or more

(6) Collision resistance (collision test)

1 is a schematic diagram of a crash test according to UL standard 1642 and/or 2054. In UL standard 1642 and/or 2054, a round bar is placed on a sample placed on a test bench so that the sample and the round bar (φ = 15.8 mm) are approximately perpendicular to each other, and on the upper surface of the round bar at a height of 610±25 mm from the round bar. By dropping a 9.1 kg (approximately 20 pounds) weight, observe the impact of the impact on the sample. With reference to Fig. 1 and UL standards 1642 and 2054, the procedure of the crash test in the embodiment will be described below.

a. Production of positive pole

As a positive electrode active material, a nickel, manganese, cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (elemental ratio), density 4.70g/cm3, capacity density 175㎃h/g) is 90.4% by mass, conductive As auxiliary material, graphite powder (KS6) (density 2.26 g/cm 3, number average particle diameter of 6.5 μm) was 1.6 mass% and acetylene black powder (AB) (density 1.95 g/cm 3, number average particle diameter of 48 nm) was 3.8 mass% And polyvinylidene fluoride (PVDF) (density 1.75 g/cm 3) as a binder was mixed at a ratio of 4.2% by mass, and these were dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of an aluminum foil having a thickness of 20 μm to be a positive electrode current collector using a die coater, dried at 130° C. for 3 minutes, and then rolled using a roll press. The thing after rolling was slit to 57.0 mm width, and the positive electrode was obtained. The applied amount of the positive electrode active material at this time was 109 g/m 2.

b. Production of negatives

As a negative electrode active material, graphite powder A (density 2.23 g/cm 3, number average particle diameter 12.7 μm) was 87.6 mass%, graphite powder B (density 2.27 g/cm 3, number average particle diameter 6.5 μm) was 9.7 mass %, and as a binder 1.4 mass% (solid content conversion) (solid content concentration 1.83 mass% aqueous solution) and diene rubber latex 1.7 mass% (solid content conversion) (solid content 40 mass% aqueous solution) of carboxymethylcellulose were dispersed in purified water to prepare a slurry. The slurry was applied with a die coater on one side of a 12 µm-thick copper foil serving as a negative electrode current collector, dried at 120° C. for 3 minutes, and then rolled using a roll press. The thing after rolling was slit to 58.5 mm width, and the negative electrode was obtained. The applied amount of the negative electrode active material at this time was 5.2 g/m 2.

c. Preparation of non-aqueous electrolyte

In a mixed solvent (Lithium Battery Grade manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:2, make LiPF ₆ to 1 mol/L. It dissolved and obtained the electrolytic solution which is a non-aqueous electrolyte.

d. Battery assembly

The produced positive electrode and negative electrode were superimposed on both sides of the separator in Examples, and a cylindrical wound body was inserted into a stainless steel cylindrical battery case (outer body). Next, 5 mL of the electrolytic solution was injected thereto, and the wound body was immersed in the electrolytic solution, and then the battery case was sealed to produce a nonaqueous electrolyte secondary battery.

e. Heat treatment

The nonaqueous electrolyte secondary battery obtained in d. was stored for 48 hours in an environment at 60°C.

f. Initial charge and discharge

The nonaqueous electrolyte secondary battery obtained in e. was charged with a constant current of 0.3C under an environment of 25°C, reached 4.2V, charged with a constant voltage of 4.2V, and discharged to 3.0V with a constant current of 0.3C. The sum of the charging time at constant current and charging time at constant voltage was 8 hours. In addition, 1C is a current value at which the battery is discharged in 1 hour.

Next, the battery was charged with a constant current of 1C, reached 4.2V, charged with a constant voltage of 4.2V, and discharged to 3.0V with a constant current of 1C. The sum of the charging time at constant current and charging time at constant voltage was set to 3 hours. Further, the capacity at the time of discharging with a 1C constant current was taken as 1C discharge capacity (mAh).

In an environment of 25° C., the non-aqueous electrolyte secondary battery obtained in f. was charged with a constant current of 1 C, reached 4.2 V, and then charged at a constant voltage of 4.2 V for a total of 3 hours. Next, in an environment of 25°C, the battery was placed in a horizontal direction on a flat surface, and a stainless steel round bar having a diameter of 15.8 mm was placed in the center of the battery so as to traverse the battery. A 9.1 kg weight was dropped from a height of 61±2.5 cm so that an impact was applied at right angles to the longitudinal axis direction of the battery from the round bar placed in the center of the battery. Thereafter, the exterior temperature of the battery was measured, and the presence or absence of gas ejection from the battery and the presence or absence of ignition of the battery were observed. In addition, the exterior temperature of a battery is a temperature measured by a thermocouple (K-type seal type) at a position 1 cm from the bottom side of the exterior body of the battery. The crash test was evaluated based on the following criteria.

(Evaluation standard)

A: Battery exterior temperature less than 60°C

B: Battery exterior temperature 60°C or more and less than 80°C

C: battery exterior temperature of 80°C or higher, and no gas ejection or ignition

D: There is gas ejection or there is ignition

<< Production of acrylic resin >>

<Acrylic resin 1>

(Manufacture of the core)

In a reaction vessel equipped with a stirrer, reflux cooler, dropping tank, and thermometer, according to the column of 1A ``mixture'' in Table 1, 70.4 parts by mass of ion-exchanged water and ``Aqualon KH1025'' (registered trademark, Daiichi Kogyo Seiyaku 0.5 parts by mass of "Adecaria Soap SR1025" (registered trademark, manufactured by ADEKA, 25% by mass aqueous solution) was added. The internal temperature of the reaction vessel was raised to 80° C., and 7.5 parts by mass of ammonium persulfate (APS(aq)) (2% by mass aqueous solution) was added while maintaining the temperature at 80° C. to obtain a mixture.

Separately from the mixture in the reaction vessel, according to the column of 1A "emulsion" in Table 1, monomers other than the crosslinking agent and the silicone compound, and other raw materials used were mixed for 5 minutes by a homomixer to prepare an emulsion 1A.

After 5 minutes of adding the aqueous ammonium persulfate solution to the reaction vessel, the emulsion 1A was started dropping into the reaction vessel from the dropping tank, and the entire amount was added dropwise over 150 minutes. After completion of the dropwise addition of the emulsion 1A, the internal temperature of the reaction vessel was maintained at 80° C. over 90 minutes, and then cooled to room temperature to obtain an emulsion. Then, in the reaction vessel, 7.5 parts by mass of the monomers and other raw materials described in the column of 1A ``emulsion solution'' in Table 1, and ammonium persulfate (APS(aq)) (2% by mass aqueous solution) as an initiator, and ions 52 parts by mass of exchanged water was added, stirred at 35°C for 12 hours, and then cooled to room temperature to obtain an emulsion. An aqueous solution of ammonium hydroxide (25% by mass aqueous solution) was added to the obtained emulsion to adjust the pH to 9.0 to obtain an emulsion containing 40% by mass of core polymer particles 1A.

(Manufacture of the shell)

A thermoplastic polymer particle having a core/shell structure was prepared by using an emulsion containing the core polymer particles 1A as a seed polymer, and performing polymerization in the second stage as follows in the presence of the seed polymer to synthesize the shell portion.

Into a reaction vessel equipped with a stirrer, reflux cooler, dropping tank, and thermometer, the seed polymer emulsion, and the ion exchange water and emulsifier described in the column of 1B “mixture” in Table 1 were added, and the temperature in the reaction vessel was maintained at 30°C. Then, a 2% by mass aqueous solution of the initiator described in the column of 1B "mixture" in Table 1 was further added to obtain a mixture.

Separately from the mixture in the reaction vessel, the monomers listed in the column 1B "Emulsion" in Table 1 and other raw materials to be used were mixed for 5 minutes by a homomixer to prepare emulsion 1B.

The emulsion 1B was started dropping from the dropping tank into the reaction vessel, and the entire amount was added dropwise over 150 minutes. In this state, stirring was continued for 30 minutes, and the monomer was absorbed into the seed polymer.

Next, while maintaining the pH of the reaction system to 4 or less, the internal temperature of the reaction vessel was raised to 80°C, stirring was continued over 120 minutes, and then cooled to room temperature. After cooling, an emulsion containing an acrylic resin (Tg: 60°C, average particle diameter: 500 nm) was obtained by filtering through a 200 mesh metal net to remove aggregates and the like.

After filtering the obtained emulsion, the above acrylic resin adjusted to pH = 8 and solid content = 40 mass% by adding 25 mass% aqueous ammonia and water, and acrylic resin 3 to be described later are polymers based on their total mass. The mixture was mixed so that the blending amount was 10% by mass to obtain a mixed solution. This mixed solution was uniformly dispersed in water at a polymer concentration of 10% by mass to prepare an acrylic resin 1.

<Acrylic resin 2>

In a reaction vessel equipped with a stirrer, reflux cooler, dropping tank, and thermometer, according to the column of acrylic resin 2 ``mixture'' in Table 1, 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of ``Aqualon KH1025'' as an emulsifier, and 0.5 parts by mass of "Adecariathorpe SR1025" was added. Next, the temperature inside the reaction vessel was raised to 80° C., while maintaining the temperature at 80° C., a 2% aqueous solution of ammonium persulfate ("APS(aq)" 7.5 parts by mass was added to obtain a mixture.

Separately from the mixture in the reaction vessel, according to the column of acrylic resin 2 ``emulsion'' in Table 1, monomers and other raw materials used, 3 parts by mass of ``Aqualon KH1025'' as emulsifier, and ``Adecariasorb SR1025'' A mixture of 3 parts by mass, 0.05 parts by mass of "NaSS", 7.5 parts by mass of APS(aq), and 52 parts by mass of ion-exchanged water was mixed with a homomixer for 5 minutes to prepare an emulsion.

5 minutes after the aqueous ammonium persulfate solution was added, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

Next, while maintaining the pH of the reaction system to 4 or less, the internal temperature of the reaction vessel was raised to 80°C, stirring was continued over 120 minutes, and then cooled to room temperature. After cooling, an emulsion containing an acrylic resin (Tg: -20°C, average particle diameter: 160 nm) was obtained by filtration through a 200 mesh metal net to remove aggregates and the like.

After filtering the obtained emulsion, the above acrylic resin adjusted to pH = 8 and solid content = 40 mass% by adding 25 mass% aqueous ammonia and water, and acrylic resin 3 to be described later are polymers based on their total mass. The mixture was mixed so that the blending amount was 10% by mass to obtain a mixed solution. This mixed solution was uniformly dispersed in water at a polymer concentration of 10% by mass to prepare an acrylic resin 2.

<Acrylic resin 3>

Acrylic resin 3 (Tg: -30°C) under the same conditions as the production of acrylic resin 2 before mixing with acrylic resin 3, except that the raw materials used for acrylic resin 2 shown in Table 1 were replaced with the raw materials used for acrylic resin 3 , Average particle diameter: 160 nm) was prepared.

<< Example 1 >>

(1) Preparation of the first polyolefin solution

20 mass% of polypropylene (PP: melting point 162°C) having a weight average molecular weight (Mw) of 1.2×10 ⁶ and 80 mass of high-density polyethylene (HDPE: density 0.955 g/cm 3, melting point 135°C) having a Mw of 0.74×10 ⁶ % To 100 parts by mass of the first polyolefin resin containing 0.2 parts by mass of tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane as an antioxidant, , A mixture was prepared.

25 parts by mass of the obtained mixture was put into a strong kneading type twin-screw extruder (inner diameter 58 mm, L/D = 42), and 75 parts by mass of liquid paraffin (35 cst (40°C)) was supplied from the side feeder of the twin-screw extruder, It melt-kneaded under conditions of 210 degreeC and 250 rpm, and the 1st polyolefin solution was prepared.

(2) Preparation of the second polyolefin solution

100 parts by mass of a second polyolefin resin containing 40 mass% of ultra-high molecular weight polyethylene (UHMwPE) having Mw of 2.0×10 ⁶ and 60 mass% of high-density polyethylene (HDPE: density 0.955 g/cm 3) having Mw of 5.6×10 ⁵ And 0.2 parts by mass of tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane as an antioxidant were blended to prepare a mixture.

25 parts by mass of the obtained mixture was put into another twin-screw extruder of the same type as above, 75 parts by mass of liquid paraffin (35 cSt (40°C)) was supplied from the side feeder of the twin-screw extruder, and melt-kneaded under the same conditions as above, A second polyolefin solution was prepared.

(3) extrusion

The first and second polyolefin solutions were supplied from each twin screw extruder to a three-layer T die, and extruded so that the layer thickness ratio of the first polyolefin solution/second polyolefin solution/first polyolefin solution was 10/80/10. The extruded body was cooled while taking-up with a cooling roll controlled at 30°C at a take-up speed of 2 m/min, thereby forming a gel-like three-layer sheet.

(4) 1st stretching, removal of film forming solvent, drying

The gel-like three-layer sheet was simultaneously biaxially stretched (first stretched) at 116° C. in both the MD direction and the TD direction 5 times by a tenter stretching machine. The stretched gel-like three-layer sheet was fixed to an aluminum frame plate of 20 cm×20 cm, immersed in a methylene chloride bath controlled at 25°C, and shaken at 100 rpm for 3 minutes to remove liquid paraffin, and air-dried at room temperature.

(5) Second stretching, heat fixing

The dried film was stretched 1.4 times (second stretching) in the TD direction at 126°C using a batch-type stretching machine. Next, this film was subjected to a heat setting treatment at 126°C by a tenter method.

(6) formation of active layer

80.0 parts by mass of aluminum oxide (Al ₂ O ₃ , average particle diameter of 0.6 µm) as inorganic particles, 20.0 parts by mass of acrylic resin 1 as an acrylic resin, and an aqueous solution of polycarboxylic acid ammonium (SN dispersant manufactured by Sannofuco) as a dispersant Persant 5468) was uniformly dispersed in 100 parts by mass of water to prepare a coating liquid.

After dip coating the three-layer microporous membrane prepared in (5) in the coating solution thus prepared, using a wire bar having a wire size of 0.5 mm, respectively, the thickness of the slurry coating layer applied on both sides was adjusted. , The solvent was dried. The thickness of each active layer formed on both sides of the porous membrane was 4.0 μm.

Tables 2 and 4 show the blending ratios, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane with an active layer produced as described above.

<< Example 2 >>

In ``(2) Preparation of the second polyolefin solution'' of Example 1, instead of the mixture of Example 1, 17.5% by mass of ultrahigh molecular weight polyethylene (UHMwPE) having Mw of 2.0 × 10 ⁶ and Mw of 3.0 × 10 ⁵ A second polyolefin resin comprising 57.5% by mass of high-density polyethylene (HDPE: density 0.955 g/cm 3) and 25% by weight of linear low-density polyethylene (ethylene 1-hexene copolymer) having an MFR of 135 g/10 min and a melting point of 124° C. To 100 parts by mass, 0.2 parts by mass of tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane as an antioxidant was added to prepare a mixture.

In the same manner as in Example 1 except for the above, a polyolefin 3-layer microporous membrane with an active layer formed thereon was prepared. Tables 2, 3, and 4 show the blending ratio of each component, production conditions, and evaluation results.

<< Example 3 >>

In ``(2) Preparation of the second polyolefin solution'' of Example 1, instead of the mixture of Example 1, 16 mass% of ultra-high molecular weight polyethylene (UHMwPE) having Mw of 2.0 × 10 ⁶ and Mw of 3.0 × 10 ⁵ In 100 parts by mass of a second polyolefin resin containing 66% by mass of high-density polyethylene (HDPE: density 0.955 g/cm 3) and 18% by weight of polypropylene having a heat of fusion of 96 J/g, tetrakis[methylene-3-( 0.2 parts by mass of 3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane were blended to prepare a mixture.

In the same manner as in Example 1 except for the above, a polyolefin 3-layer microporous membrane with an active layer was prepared, and the blending ratio of each component of the polyolefin 3-layer microporous membrane with an active layer, production conditions, evaluation results, etc. are shown in Tables 2 and 4. .

<< Example 4 >>

In "(6) Formation of active layer" in Example 2, as a coating liquid, 95.0 parts by mass of aluminum oxide (average particle diameter 0.6 µm), 5.0 parts by mass of acrylic resin 1, and an aqueous solution of ammonium polycarboxylic acid ( A coating liquid prepared by uniformly dispersing 1.0 parts by mass of SN Dispersant 5468) manufactured by Sanno Fuco in 100 parts by mass of water was used.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 5 >>

In "(6) Formation of active layer" in Example 2, as a coating liquid, 50.0 parts by mass of aluminum oxide (average particle diameter 0.6 µm), 50.0 parts by mass of acrylic resin 1, and an aqueous solution of ammonium polycarboxylic acid ( A coating liquid prepared by uniformly dispersing 1.0 parts by mass of SN Dispersant 5468) manufactured by Sanno Fuco in 100 parts by mass of water was used.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 6 >>

In "(6) formation of an active layer" of Example 2, an acrylic resin 2 was used instead of the acrylic resin 1 as an acrylic resin.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 7 >>

On one side of the polyolefin three-layer microporous membrane with an active layer prepared in Example 6, acrylic resin 2 was applied to the entire surface so that the coating area ratio was 60% and the weight per coating unit area was 0.5 g/m 2 using a gravure coater. Applied. Subsequently, by heating and drying at 50 degreeC for 1 minute, the separator in which the thermoplastic polymer particle layer was formed was obtained. Table 2 shows the evaluation results.

<< Example 8 >>

In ``(6) formation of an active layer'' in Example 2, a two-component curable aqueous acrylic urethane resin (WE-301 manufactured by DIC Corporation, solid content concentration) containing an aqueous acrylic polyol and a water dispersible polyisocyanate (curing agent) 45% by mass), alumina particles having an average particle diameter of 0.6 μm, and ion-exchanged water, respectively, at a weight ratio of 10:40:50 (the weight ratio of the aqueous acrylic urethane resin and alumina is 20/80), and 6 hours Dispersed. Then, it filtered with a filter of 5 micrometers of filtration limits, and obtained the coating liquid.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 9 >>

In "(6) formation of an active layer" in Example 2, a copolymer of polyvinyl alcohol, acrylic acid, and methyl methacrylate ("POVACOAT" (registered trademark) manufactured by Nisshin Kasei Co., Ltd.) and an average particle diameter of 0.6 μm Of the alumina particles and the solvent (ion-exchanged water: ethanol = 70:30) were each blended in a weight ratio of 5:45:50 (the weight ratio of the copolymer and the alumina particles was 10/90), and dispersed for 6 hours. . Then, it filtered with a filter of 5 micrometers of filtration limits, and obtained the coating liquid.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 10 >>

In "(6) formation of an active layer" of Example 2, AlO(OH) powder (aluminum hydroxide, average particle diameter: 1.0 µm) was used instead of Al ₂ O ₃ powder as the inorganic particles.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 11 >>

In "(6) Formation of Active Layer" in Example 2, BaTiO ₃ powder (barium titanate, average particle diameter: 0.6 µm) was used instead of Al ₂ O ₃ powder as inorganic particles.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 12 >>

In the "(1) Preparation of the first polyolefin solution" of Example 2, as a mixture, 16% by mass of polypropylene (PP: melting point 162°C) having a Mw of 1.2×10 ⁶ and a high density having a Mw of 0.74×10 ⁶ 100 parts by mass of the first polyolefin resin containing 64 mass% of polyethylene (HDPE: density 0.955 g/cm 3, melting point 135° C.), 20 mass% of silica powder (average particle diameter: 15 nm), and tetrakis[methylene-] as an antioxidant 0.2 parts by mass of 3-(3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane was added. In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

《Comparative Example 1》

In Example 1, except not performing "(6) formation of an active layer", it was prepared in the same manner as in Example 1, and the blending ratio of each component of the polyolefin three-layer microporous membrane, production conditions, evaluation results, etc. are shown in Table 2. Described.

《Comparative Example 2》

In the "(1) Preparation of the first polyolefin solution" of Example 1, 20% by mass of polypropylene (PP: melting point 162°C) having a Mw of 1.2×10 ⁶ and high-density polyethylene (HDPE) having a Mw of 0.74×10 ⁶ Containing high-density polyethylene (HDPE: density 0.955 g/cm 3, melting point 135° C.) having a Mw of 0.74×10 ⁶ instead of 100 parts by mass of the first polyolefin resin containing 80 mass% of density 0.955 g/cm 3, melting point 135° C. 100 parts by mass of the first polyolefin resin was used.

In the same manner as in Example 1 except for the above, a polyolefin 3-layer microporous membrane with an active layer formed thereon was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

《Comparative Example 3》

In the "(1) Preparation of the first polyolefin solution" of Example 1, 20% by mass of polypropylene (PP: melting point 162°C) having a Mw of 1.2×10 ⁶ and high-density polyethylene (HDPE) having a Mw of 0.74×10 ⁶ 100 mass of first polyolefin resin containing polypropylene (PP: melting point 162° C.) having a Mw of 1.2×10 ⁶ instead of 100 parts by mass of the first polyolefin resin containing 80 mass% of density 0.955 g/cm 3, melting point 135° C.) Wealth was used.

In the same manner as in Example 1 except for the above, a polyolefin 3-layer microporous membrane with an active layer formed thereon was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 13 >>

In the "(1) Preparation of the first polyolefin solution" of Example 2, 20% by mass of polypropylene (PP: melting point 162°C) having a Mw of 2.0×10 ⁶ and high-density polyethylene (HDPE) having a Mw of 0.56×10 ⁶ Tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl) as an antioxidant in 100 parts by mass of the first polyolefin resin containing 80 mass% of density 0.955 g/cm 3 and melting point 135°C) )-Propionate] methane 0.2 parts by mass were blended to prepare a mixture.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 3 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 14 >>

In the "(1) Preparation of the first polyolefin solution" of Example 2, 20% by mass of polypropylene (PP: melting point 162°C) having a Mw of 0.6×10 ⁶ and high-density polyethylene (HDPE) having a Mw of 0.86×10 ⁶ Tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl) as an antioxidant in 100 parts by mass of the first polyolefin resin containing 80 mass% of density 0.955 g/cm 3 and melting point 135°C) )-Propionate] methane 0.2 parts by mass were blended to prepare a mixture.

In the same manner as in Example 2 except for the above, a polyolefin three-layer microporous membrane with an active layer was prepared. Table 3 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 15 >>

In the "(1) Preparation of the first polyolefin solution" of Example 1, 20% by mass of polypropylene (PP: melting point 162°C) having a Mw of 1.2×10 ⁶ and high-density polyethylene (HDPE) having a Mw of 0.74×10 ⁶ Density 0.955 g/cm 3, melting point 135°C) 55% by mass, MFR 135g/10min, melting point 124°C Linear low density polyethylene (ethylene 1-hexene copolymer) 25% by weight of the first polyolefin resin 100 mass To the part, 0.2 parts by mass of tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane as an antioxidant was blended to prepare a mixture.

In the same manner as in Example 1 except for the above, a polyolefin 3-layer microporous membrane with an active layer formed thereon was prepared. Table 4 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 16 >>

In the "(1) Preparation of the first polyolefin solution" of Example 1, 82 mass% of high-density polyethylene (HDPE: density 0.955 g/cm 3, melting point 135°C) having a Mw of 0.74×10 ⁶ and a heat of fusion of 96 J/g 0.2 mass of antioxidant tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane to 100 parts by mass of the first polyolefin resin containing 18 mass% of polypropylene The parts were blended to prepare a mixture.

In the same manner as in Example 1 except for the above, a polyolefin 3-layer microporous membrane with an active layer formed thereon was prepared. Table 4 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 17 >>

In "(1) Preparation of the first polyolefin solution" of Example 1, 35% by mass of polypropylene (PP: melting point 162°C) having a weight average molecular weight (Mw) of 1.2×10 ⁶ and Mw were 0.74×10 ⁶ It was set as 100 parts by mass of the first polyolefin resin containing 65% by mass of phosphorus high-density polyethylene (HDPE: density 0.955 g/cm 3, melting point 135°C). In the same manner as in Example 1 except for the above, a polyolefin 3-layer microporous membrane with an active layer formed thereon was prepared. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

<< Example 18 >>

In the same manner as in Example 1 except that the active layer did not contain inorganic particles, a polyolefin three-layer microporous membrane with an active layer was produced. Table 2 shows the mixing ratio of each component, production conditions, and evaluation results.

The abbreviations in Table 1 are as follows, respectively.

(1) emulsifier

KH1025: Aqualon KH1025, manufactured by Daiichi Kogyo Seiyaku

SR1025: Adecaria soap SR1025, manufactured by ADEKA Co., Ltd.

NaSS: p-styrene sulfonic acid sodium, manufactured by Tosoh Corporation

(2) initiator

APS(aq): ammonium persulfate aqueous solution

(3) (meth)acrylic acid ester

MMA: methyl methacrylate

BA: butyl acrylate

CHMA: cyclohexyl methacrylate

EHA: ethylhexyl acrylate

BMA: butyl methacrylate

(4) acid monomer

MAA: methacrylic acid

AA: acrylic acid

(5) functional group-containing monomer

HEMA: hydroxyethyl methacrylate

AM: acrylamide

GMA: Glycidyl methacrylate

(6) Polyalkylene glycol group-containing monomer

M-40G: Acrylate monomer, manufactured by Shinnakamura Chemical Industry Co., Ltd.

(7) crosslinking agent

A-TMPT: Trimethylolpropane triacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd.

EDMA: Ethylene dimethacrylate

《Consideration on the evaluation results》

(1) On the peel strength between the active layer and the substrate

Comparing Example 1 and Comparative Example 2, it was found that the peel strength tends to be superior to the case where the first microporous layer does not contain PP (only PE), but the one containing PP and PE tends to be superior. The reason is not limited to the theory, but it is considered that PP has a higher polarity (surface free energy) than PE, so that the intermolecular force with the active layer increases, and the peel strength between the active layer and the substrate increases.

(2) Separator handleability

Comparing Example 2 and Example 9, it was found that compared with the example in which the aqueous binder contained PVA, the example not containing PVA tended to be superior in the handling properties of the separator. The reason is not limited to the theory, but it is considered that PVA has an absorbent hydroxyl group, so that the stickiness tends to occur by adsorbing moisture in the atmosphere.

(3) About cold and heat shock characteristics

Comparing Example 4 and Example 2, it was found that the lower the number of inorganic particles in the active layer has excellent cold and thermal shock properties. The reason is not limited to the theory, but it is considered that the less inorganic particles have higher adhesion between the electrode and the separator, and delamination is less likely to occur in a cooling/heat cycle.

Comparing Example 2 and Example 9, it was found that compared to the example in which the aqueous binder contained PVA, the example not containing PVA tended to have excellent cold and thermal shock characteristics. The reason for this is not limited to theory, but it is considered that PVA has greater expansion and contraction at the time of cold heat than acrylic resin, so that peeling between the active layer and other layers becomes difficult to occur due to the small amount of PVA.

Comparing Example 1 and Comparative Example 1, it was found that the one having the active layer on the base material has better cold-heat impact characteristics than the case where the active layer is not provided. The reason is not limited to the theory, but it is considered that the adhesion between the electrode and the separator is improved, so that interfacial deviation is unlikely to occur during a cooling/heat cycle, and resistance does not deteriorate even in a cooling/heat-resistant cycle.

(4) Low temperature cycle characteristics

Comparing Example 1 and Comparative Example 3, it was found that the low-temperature cycle characteristics of the first microporous layer containing PE and PP were superior to those of PE alone. The reason is not limited to theory, but since the glass transition temperature of PP is around 0°C, in the low-temperature cycle test, when the battery becomes 0°C or less, PP becomes brittle, and the state of the pores of the porous membrane, and Li ions I think it is because it affects the delivery.

Comparing Example 2 and Example 12, it was found that the low-temperature cycle characteristics were superior to those in which the first microporous layer contained silica. The reason is not limited to theory, but it is considered that the affinity of the first microporous layer with the electrolyte is improved by containing silica, and the low-temperature cycle characteristics are improved.

Comparing Example 2 and Example 7, it was found that when the acrylic resin of the active layer was a copolymer having an ethylenically unsaturated monomer having a polyalkylene glycol group as a monomer unit, the low-temperature cycle characteristics were excellent. The reason is not limited to the theory, but it is considered that the latter has a smaller film resistance of the separator and improves the low-temperature cycle characteristics.

(5) On the variation of the peel strength between the active layer and the substrate

Comparing Examples 2, 13, and 14, it was found that when the Mw ratio of PE/PP in the first microporous layer is within the range of 0.6 to 1.5, the variation in peel strength tends to be small. The reason is not limited to the theory, but if the Mw ratio of PE/PP of the first microporous layer is out of the range, the compatibility between PE and PP deteriorates. In addition, the PE-rich portion and the PP-rich portion exist in the first microporous layer. Since PP is superior to PE in adhesion to the active layer, it is considered that the variation in the peel strength of the adhesion to the active layer increases.

(6) About collision tolerance

As other components, it was found that collision resistance tends to be improved by using component A (linear low-density polyethylene) and component B (polypropylene having a heat of fusion of 96 J/g) in the first or second microporous layer. The reason is not limited to theory, but component A has many amorphous parts because it is difficult to crystallize compared to HDPE and UHMwPE, whereas component B has many amorphous parts because it is difficult to crystallize compared to PP with Mw 1.2×10 ⁶ , and It is thought that this is because the amorphous portion has a shock absorbing action and thus the collision resistance tends to be improved.

It was found that the second polyolefin resin containing the A component or B component is more preferable than the first polyolefin resin from the viewpoint of collision resistance of the power storage device. The reason is not limited to theory, but when the layer containing the A component or the B component is thicker than the other layers, when the layer containing the A component or B component is farther away from the electrode (when other layers are interposed ), it is estimated that the collision resistance of the power storage device is good.

The separator for power storage devices of the present invention can be suitably used as a separator for power storage devices, for example, secondary batteries, particularly lithium ion secondary batteries.

20: pendulum
21: round bar
22: sample

Claims (9)

A polyolefin multilayer microporous membrane comprising polyethylene and polypropylene,
Active layer disposed on at least one side of the polyolefin multilayer microporous membrane
It is a separator for power storage devices containing,
In the polyolefin multilayer microporous membrane, the outermost polypropylene concentration is higher than the innermost polypropylene concentration, and the outermost polyethylene concentration is lower than the innermost polyethylene concentration,
The outermost portion contains a first polyolefin resin containing polyethylene and polypropylene, and the content of polypropylene in the first polyolefin resin is 1 to 30% by mass, with the total mass of the first polyolefin resin being 100% by mass. ,
The innermost portion contains a second polyolefin resin containing polyethylene,
In the active layer, the water-based binder includes an acrylic resin, and the mass ratio of the acrylic resin and the inorganic particles in the active layer is 10/90 to 50/50,
Separator for power storage devices. The separator for an electrical storage device according to claim 1, wherein the innermost portion of the polyolefin multilayer microporous membrane contains a second polyolefin resin containing polyethylene and polypropylene. The separator for power storage devices according to claim 1, wherein the second polyolefin resin further contains linear low-density polyethylene or polypropylene having a heat of fusion of 150 J/g or less. The separator for power storage device according to claim 1, wherein the acrylic resin is particulate and has a core-shell structure having a core portion and a shell portion that at least partially covers an outer surface of the core portion. The separator for an electrical storage device according to claim 1, wherein the acrylic resin contains a copolymer having an ethylenically unsaturated monomer having a polyalkylene glycol group as a monomer unit. The separator for an electrical storage device according to claim 1, wherein the outermost portion of the polyolefin multilayer microporous membrane further contains at least one or more selected from silica, alumina, and titania. With positive pole,
The separator for power storage devices according to any one of claims 1 to 6, and
Negative pole
A laminate that is laminated in this order. The wound body in which the laminated body according to claim 7 is wound. A power storage device comprising the laminate according to claim 7 or a wound body on which the laminate is wound, and an electrolyte.

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