JP2016213019A - Separator for electricity storage device, electricity storage device, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a separator for an electricity storage device, which is high in adhesion between inorganic particles and a polyolefin microporous film and further has excellent adhesion with an electrode; and an electricity storage device and a lithium ion secondary battery which include the separator.SOLUTION: A separator for an electricity storage device includes a base material and a porous layer arranged on at least one surface of the base material. The porous layer contains inorganic particles and a copolymer binder. The swelling degree of the copolymer binder with respect to a mixed solvent is 1.5 times or less, the mixed solvent containing 2 pts.mass of ethylene carbonate and 3 pts.mass of diethyl carbonate.SELECTED DRAWING: None

Description

  The present invention relates to a power storage device separator, a power storage device, and a lithium ion secondary battery.

  In recent years, development of nonaqueous electrolyte batteries centering on lithium ion batteries has been actively conducted. Usually, in a nonaqueous electrolyte battery, a microporous membrane (separator) is provided between positive and negative electrodes. Such a separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the micropores.

  In order to improve the cycle characteristics and safety of the nonaqueous electrolyte battery, improvement of the separator has been studied. In recent years, as portable devices become smaller and thinner, power storage devices such as lithium ion secondary batteries are also required to be smaller and thinner. On the other hand, in order to be able to carry for a long time, the capacity is increased by improving the volume energy density.

  Conventional separators have a characteristic that the battery reaction is quickly stopped if the separator is abnormally heated (fuse characteristics), preventing the dangerous situation where the cathode and anode materials react directly by maintaining the shape even at high temperatures. Performance related to safety such as performance (short characteristics) is required.

  For the purpose of producing a battery with high safety, Patent Document 1 describes a technique for forming a separator having a porous layer containing inorganic particles and a resin binder on a polyolefin microporous film.

  In addition to such safety improvements, separators are also required to improve adhesion to electrodes from the viewpoint of uniform charge / discharge current and suppression of lithium dendrite.

  By improving the close contact between the separator and the battery electrode, non-uniform charge / discharge current is less likely to occur, and lithium dendrite is less likely to precipitate, resulting in longer charge / discharge cycle life. Become.

  Under such circumstances, as an attempt to impart adhesiveness to the separator, for example, Patent Document 2 proposes a technique for supporting an acrylic binder on a base material. In addition, for the purpose of enhancing safety, a technique for supporting an acrylic binder on a polyolefin microporous film having a porous layer containing inorganic particles and a resin binder is also disclosed.

Japanese Patent No. 5354735 WO2014 / 017651

  However, the polyolefin microporous membrane provided with a porous layer containing inorganic particles and a resin binder described in Patent Document 2 does not have sufficient adhesion between the inorganic particles and the polyolefin microporous membrane. Even if the polymer layer is laminated, there is a problem that the adhesion to the electrode is not sufficient.

  The present invention has been made in view of the above circumstances, and has a high adhesion between inorganic particles and a polyolefin microporous membrane, and further has an excellent adhesion to an electrode, and an electricity storage device having the separator And it aims at providing a lithium ion secondary battery.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above problems can be solved by using a copolymer binder having a predetermined degree of swelling, and have completed the present invention. .

That is, the present invention is as follows.
[1]
A base material, and a porous layer disposed on at least one side of the base material,
The porous layer includes inorganic particles and a copolymer binder,
The swelling degree of the copolymer binder with respect to the mixed solvent containing 2 parts by mass of ethylene carbonate and 3 parts by mass of diethyl carbonate is 1.5 times or less.
Electric storage device separator.
[2]
The copolymer binder includes a cycloalkyl group-containing monomer unit,
The separator for an electricity storage device according to [1] above, wherein the content of the cycloalkyl group-containing monomer unit is 15 to 50% by mass with respect to 100% by mass of the copolymer binder.
[3]
The copolymer binder includes the cycloalkyl group-containing monomer unit, a (meth) acrylic acid ester monomer unit having an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group,
The total amount of the said cycloalkyl group containing monomer unit and the said (meth) acrylic acid ester monomer unit is 80-99.9 mass% with respect to 100 mass% of said copolymer binders, the preceding clause. [1] or [2] The electrical storage device separator.
[4]
The separator for an electricity storage device according to [2] or [3], wherein the cycloalkyl group-containing monomer unit includes a cyclohexyl acrylate unit and / or a cyclohexyl methacrylate unit.
[5]
The separator for an electricity storage device according to any one of [1] to [4], wherein the degree of swelling of the copolymer binder with respect to toluene is 6 times or more.
[6]
The separator for an electricity storage device according to any one of [1] to [5], wherein the substrate is a polyolefin microporous film.
[7]
An electricity storage device comprising the separator for an electricity storage device according to any one of [1] to [6].
[8]
A lithium ion secondary battery comprising the separator for an electricity storage device according to any one of [1] to [6].

  According to the present invention, there are provided an electricity storage device separator having high adhesion between inorganic particles and a polyolefin microporous membrane and excellent adhesion to an electrode, an electricity storage device having the separator, and a lithium ion secondary battery. can do.

It is a figure which shows the example of the presence form (pattern) of the polymer layer on the separator of this embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist. In the present specification, “(meth) acryl” means “acryl” and “methacryl” corresponding thereto, “(meth) acrylate” means “acrylate” and “methacrylate” corresponding thereto, “(Meth) acryloyl” means “acryloyl” and its corresponding “methacryloyl”.

[Separator for electricity storage devices]
[First Embodiment]
A power storage device separator (hereinafter also simply referred to as “separator”) according to a first embodiment includes a base material and a porous layer disposed on at least one surface of the base material, and the porous layer is inorganic. The swelling degree of the copolymer binder with respect to a mixed solvent containing particles and a copolymer binder (hereinafter, also simply referred to as “copolymer”) and containing 2 parts by mass of ethylene carbonate and 3 parts by mass of diethyl carbonate is 1 .5 times or less.

〔Base material〕
Although it does not specifically limit as a base material, For example, the porous membrane containing resin and other arbitrary additives is mentioned. Such a base material may be one conventionally used as a separator. Among these, as the base material, a porous film that has no electron conductivity, has ion conductivity and organic solvent resistance, and has fine pores is preferable.

  The resin contained in the base material as a main component is not particularly limited. For example, polyolefin, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoro Examples include ethylene. Among these, polyolefin is preferable. “Contained as a main component” means that the resin content is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, with respect to 100% by mass of the resin component in the substrate. More preferably, it means 70 to 100% by mass.

  Additives that can be included in the substrate are not particularly limited, but include, for example, resins other than the main components; inorganic fillers; antioxidants such as phenolic compounds, phosphorus compounds, and sulfur compounds; calcium stearate, zinc stearate Metal soaps such as; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents;

  The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less with respect to 100 parts by mass of the base material.

  Moreover, although the aspect of a base material is not specifically limited, For example, a woven fabric, a nonwoven fabric, paper, and a molded object (Aggregate of insulating substance particles etc.) are mentioned.

(Physical properties of the substrate)
The film thickness of the substrate is preferably 0.5 to 40 μm, more preferably 1 to 30 μm, and still more preferably 1 to 20 μm. When the film thickness of the substrate is within the above range, the permeability of the separator tends to be further improved.

  The porosity of the substrate is preferably 20 to 90%, more preferably 30 to 90%, and still more preferably 30 to 80%. When the porosity of the substrate is within the above range, the balance between the permeability of the separator and the piercing strength tends to be further improved.

  The air permeability of the substrate is preferably 10 to 1000 s / 100 cc, more preferably 50 to 500 s / 100 cc. When the air permeability of the substrate is within the above range, the charge / discharge characteristics tend to be further improved.

The puncture strength of the substrate is preferably 200 to 2000 g / 20 μm, more preferably 200 to 1000 g / 20 μm. When the puncture strength of the base material is within the above range, the tear resistance of the separator tends to be further improved.

  In addition, about the various parameters mentioned above, it can measure according to the measuring method in the Example mentioned later.

(Polyolefin microporous membrane)
As the base material, a base material composed of a microporous film containing polyolefin as a main component (hereinafter also referred to as “polyolefin microporous film”) is preferable. By using the polyolefin microporous film, the separator can be made thinner, and the active material ratio in an electricity storage device such as a battery can be increased to increase the capacity per volume. Hereinafter, the polyolefin microporous membrane will be described.

  The content of the polyolefin is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and further preferably 70 to 100% by mass with respect to 100% by mass of the resin component in the polyolefin microporous membrane. It is. When the content of the polyolefin is within the above range, the shutdown property tends to be further improved.

  The polyolefin is not particularly limited, and polyolefins used for ordinary extrusion, injection, inflation, blow molding and the like can be used. Although it does not specifically limit as a monomer which comprises such polyolefin, For example, vinyl chloride, ethylene, propylene, 1-butene, 4-methyl-1- pentene, 1-hexene, 1-octene, etc. are mentioned. The polyolefin may be a homopolymer of these monomers, a random copolymer, a block copolymer, a multistage polymer, or the like. In addition, the stereoregularity of the polyolefin is not particularly limited, and examples thereof include isotactic polymers, syndiotactic polymers, and atactic polymers. Polyolefin may be used individually by 1 type, or may use 2 or more types together.

  The polyolefin obtained from such a monomer is not particularly limited. For example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, An ethylene-propylene random copolymer, polybutene, ethylene propylene rubber, etc. are mentioned. Among these, high-density polyethylene is preferable from the viewpoint of low melting point and strength.

  The viscosity average molecular weight of the polyolefin is preferably 30,000 to 12,000,000, more preferably 50,000 to 2,000,000, and even more preferably 100,000 to 1,000,000. . When the viscosity average molecular weight of the polyolefin is 30,000 or more, the melt tension at the time of melt molding is increased, the moldability is improved, and the strength tends to be further improved by the entanglement of the polymers. On the other hand, when the viscosity average molecular weight of the polyolefin is 12,000,000 or less, uniform melt kneading becomes easier, and the formability of the sheet, particularly the thickness stability, tends to be further improved. Furthermore, when the viscosity average molecular weight is 1,000,000 or less, the shutdown property tends to be further improved. The viscosity average molecular weight of the polyolefin can be adjusted by mixing a polyolefin having a relatively low viscosity average molecular weight and a polyolefin having a relatively high viscosity average molecular weight.

  As one aspect, the polyolefin microporous membrane preferably contains polypropylene and a polyolefin resin other than the polypropylene. By using such a polyolefin microporous membrane, the heat resistance tends to be further improved.

Here, the polyolefin resin other than polypropylene is not particularly limited. For example, homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are used. A polymer is mentioned. Among these, polyethylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene is preferable from the viewpoint of improving shutdown performance. From the viewpoint of improving the strength, polyethylene having a density measured in accordance with JIS K 7112 of 0.93 g / cm ³ or more is preferable.

  The content of polypropylene is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, and further preferably 4 to 10% by mass with respect to 100% by mass of polyolefin in the polyolefin microporous membrane. is there. When the content of polypropylene is within the above range, the heat resistance and the shutdown property tend to be further improved.

[Production method of substrate]
It does not specifically limit as a manufacturing method of a base material, A well-known manufacturing method is employable. For example, a method in which a resin composition and a plasticizer are melt-kneaded and formed into a sheet, and optionally stretched, and then made porous by extracting the plasticizer; the resin composition is melt-kneaded and a high draw ratio Method of making porous by exfoliating resin crystal interface by heat treatment and stretching after extrusion; resin composition and inorganic filler are melt-kneaded and molded on a sheet; then, resin composition and inorganic filler are stretched And a method of making the substrate porous by removing the solvent at the same time as solidifying the resin by immersing it in a poor solvent for the resin after dissolving the resin composition.

(Manufacturing method of polyolefin microporous membrane)
Hereinafter, as an example of a method for producing a substrate, a melt-kneading step for obtaining a melt-kneaded product by melt-kneading a polyolefin resin composition and a plasticizer, and a molding step for obtaining a sheet-like molded body by molding the melt-kneaded product, A method for producing a polyolefin microporous membrane having an extraction step of extracting a plasticizer from a sheet-like molded body to obtain a porous membrane will be described.

(Melting and kneading process)
The melt-kneading step is a step of melt-kneading polyolefin and a plasticizer. Although it does not specifically limit as a melt-kneading method, For example, the method of using resin kneading apparatuses, such as an extruder, a kneader, a lab plast mill, a kneading roll, a Banbury mixer, is mentioned.

  Specifically, there may be mentioned a method in which polyolefin and other additives as required are introduced into a resin kneading apparatus, and a plasticizer is introduced and kneaded in an arbitrary ratio while the resin component is heated and melted. At this time, it is preferable that the polyolefin, other additives, and the plasticizer are pre-kneaded at a predetermined ratio in advance using a Henschel mixer or the like before being added to the resin kneading apparatus. More preferably, only a part of the plasticizer is added in the pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading apparatus. By doing in this way, the dispersibility of a plasticizer can be improved, and when extending | stretching a sheet-like molded object in a next process, it exists in the tendency which can suppress a film breakage and can extend | stretch at high magnification.

  Although it does not specifically limit as a plasticizer, For example, the non-volatile solvent which can form a uniform solution above melting | fusing point of polyolefin is mentioned. Examples of such non-volatile solvents include, but are not limited to, hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. Can be mentioned. Among these, liquid paraffin having high compatibility with polyolefin is preferable. By using such a plasticizer, even if a sheet-like molded product obtained in a subsequent step is stretched, the interface between the resin and the plasticizer hardly occurs, and a uniform base material tends to be obtained.

  Although content of a plasticizer is not specifically limited, For example, with respect to 100 mass% of melt-kneaded materials, Preferably it is 30-80 mass%, More preferably, it is 40-70 mass%. When the content of the plasticizer is 80% by mass or less, the melt tension at the time of melt molding is hardly insufficient and the moldability tends to be further improved. On the other hand, when the content of the plasticizer is 30% by mass or more, even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high magnification, the polyolefin chain is hardly broken, and a uniform and fine pore structure is obtained. The strength of the base material that can be formed tends to be further improved.

(Molding process)
The forming step is a step of forming a melt-kneaded product to obtain a sheet-like formed body. Examples of the molding method include a method in which the melt-kneaded material is extruded into a sheet shape via a T-die or the like, brought into contact with a heat conductor, cooled to a temperature sufficiently lower than the crystallization temperature of the resin component, and solidified. It is done.

  The die lip interval when extruding into a sheet form from a T die is preferably 400 to 3000 μm, more preferably 500 to 2500 μm. When the die lip interval is 400 μm or more, there is a tendency that the meander and the like are reduced, and there is little influence on the film quality such as streaks and defects, and film breakage and the like can be prevented in the subsequent stretching process. On the other hand, when the die lip interval is 3000 μm or less, the cooling rate is high and uneven cooling can be prevented and the thickness stability of the sheet tends to be maintained.

  As the heat conductor used for cooling and solidification, metal, water, air, the plasticizer itself, or the like can be used. Among these, a metal roll is preferable because of its high heat conduction efficiency. When contacting the metal roll, it is more preferable to sandwich the roll between the rolls, since the efficiency of heat conduction is further increased, the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is also improved.

(Stretching process)
In the manufacturing method of a base material, you may have a extending | stretching process of extending | stretching a sheet-like molded object as needed. The stretching method is not particularly limited, and examples thereof include uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple stretching. Among these, biaxial stretching is preferable from the viewpoint of the strength of the obtained base material. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained base material is not easily torn and tends to have high puncture strength. In addition, simultaneous biaxial stretching is preferable from the viewpoints of improvement of puncture strength, uniformity of stretching, and shutdown property. Here, “simultaneous biaxial stretching” means that stretching in the MD direction (machine direction of the microporous film) and stretching in the TD direction (direction crossing the MD of the microporous film at an angle of 90 °) are performed simultaneously. Refers to a stretching method. In addition, the draw ratio of each direction may be the same or different. “Sequential biaxial stretching” refers to a stretching method in which stretching in the MD direction or TD direction is independently performed. In sequential biaxial stretching, when stretching is performed in the MD direction or the TD direction, the other direction is set to an unconstrained state or a fixed state.

  The stretched plane magnification is preferably 20 to 100 times, more preferably 25 to 50 times. When the stretched surface magnification is 20 times or more, the strength of the obtained base material tends to be further improved. On the other hand, when the total area magnification is 100 times or less, film breakage in the stretching process is suppressed, and productivity tends to be further improved.

  Moreover, the draw ratio of MD direction becomes like this. Preferably it is 4-10 times, More preferably, it is 5-8 times. On the other hand, the draw ratio in the TD direction is preferably 4 to 10 times, more preferably 5 to 8 times. When the draw ratios in the MD direction and the TD direction are within the above ranges, the strength of the base material is further improved, film breakage is suppressed, and productivity tends to be further improved.

  In the stretching step, the sheet-like molded body may be rolled. Although it does not specifically limit as a rolling method, For example, the press method using a double belt press etc. is mentioned. By rolling, the resin orientation of the substrate surface layer portion tends to increase.

  The rolling surface magnification is preferably 1 to 3 times, more preferably 1 to 2 times. When the rolling ratio is larger than 1, the orientation in the surface direction of the resin increases, and the strength of the base material tends to increase. On the other hand, when the rolling ratio is 3 times or less, the orientation difference between the surface layer portion and the resin inside the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film.

(Extraction process)
An extraction process is a process of extracting a plasticizer from a sheet-like molded object, and obtaining a porous film. As a method for extracting the plasticizer, for example, a method of extracting the plasticizer by immersing the sheet-shaped molded body in an extraction solvent and sufficiently drying it can be mentioned. The extraction of the plasticizer may be either batch type or continuous type. In order to suppress the shrinkage of the porous film, it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying. Further, the residual amount of plasticizer in the porous film is preferably less than 1% by mass.

  As the extraction solvent, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the plasticizer and has a boiling point lower than the melting point of the polyolefin resin. Such an extraction solvent is not particularly limited, and examples thereof include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; hydrofluoroether and hydrofluorocarbon. Non-chlorinated halogenated solvents such as ethanol; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by an operation such as distillation.

(Other processes)
In order to suppress the shrinkage of the porous film, a heat treatment such as heat fixation or heat relaxation can be performed after the stretching process or after the porous film is formed. Further, the porous film may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like, or a crosslinking treatment with ionizing radiation or the like.

(Porous layer)
The porous layer is a layer disposed on at least one surface of the substrate, and includes inorganic particles and a copolymer binder.

  The thickness of the porous layer is preferably 1 to 50 μm, more preferably 1.5 to 20 μm, further preferably 2 to 10 μm, particularly preferably 3 to 10 μm, and most preferably 3 to 7 μm. It is. When the thickness of the porous layer is 1 μm or more, the heat resistance tends to be further improved. Moreover, when the thickness of the porous layer is 50 μm or less, the capacity and ion permeability of the obtained battery tend to be further improved.

(Inorganic particles)
As the inorganic particles, those having a melting point of 200 ° C. or higher, high electrical insulating properties, and electrochemically stable within the use range of the lithium ion secondary battery are preferable. Such inorganic particles are not particularly limited. For example, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide; silicon nitride, titanium nitride, boron nitride, etc. Nitride-based ceramics: silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite , Ceramics such as mica, amicite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. An inorganic particle may be used individually by 1 type, or may use 2 or more types together. Among these, aluminum oxide compounds such as alumina and aluminum hydroxide oxide; aluminum silicate compounds having no ion exchange ability such as kaolinite, dickite, nacrite, halloysite, and pyrophyllite; calcium carbonate is preferable. By using such inorganic particles, the electrochemical stability and the heat resistance of the separator tend to be further improved.

  As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easily available. Kaolin includes wet kaolin and calcined kaolin, which is calcined. However, calcined kaolin releases crystal water during the calcining process and removes impurities. Particularly preferred.

  As the calcium carbonate, columnar, needle-shaped or spindle-shaped light calcium carbonate is particularly preferable.

  The average particle diameter of the inorganic particles is preferably 0.1 to 4.0 μm, more preferably 0.2 to 3.5 μm, and still more preferably 0.4 to 3.0 μm. When the average particle diameter of the inorganic particles is within the above range, even when the porous layer is thin (for example, 7 μm or less), thermal shrinkage at a high temperature tends to be further suppressed.

  The content of the inorganic particles having a particle size of 0.2 to 1.4 μm is preferably 2% by volume or more, more preferably 3% by volume or more, further preferably 100% by volume of the total inorganic particles. Is 5% by volume or more. Further, the content of inorganic particles having a particle size of 0.2 to 1.4 μm is preferably 90% by volume or less, more preferably 80% by volume or less with respect to 100% by volume of all inorganic particles.

  The content of the inorganic particles having a particle size of 0.2 to 1.0 μm is preferably 1% by volume or more, more preferably 2% by volume or more with respect to 100% by volume of all inorganic particles. Further, the content of inorganic particles having a particle size of 0.2 to 1.0 μm is preferably 80% by volume or less, more preferably 70% by volume or less with respect to 100% by volume of all inorganic particles.

  The content of inorganic particles having a particle size of 0.5 to 2.0 μm is preferably 8% by volume or more, more preferably 10% or more by volume with respect to 100% by volume of all inorganic particles. The content of the inorganic particles having a particle size of 0.5 to 2.0 μm is preferably 60% by volume or less, more preferably 50% by volume or less with respect to 100% by volume of all inorganic particles.

  The content of the inorganic particles having a particle size of 0.6 to 1.4 μm is preferably 1% by volume or more, more preferably 3% by volume or more with respect to 100% by volume of all inorganic particles. The content of inorganic particles having a particle size of 0.6 to 1.4 μm is preferably 40% by volume or less, more preferably 30% by volume or less with respect to 100% by volume of all inorganic particles.

  When the inorganic particles have the above particle size distribution, even when the porous layer is thin (for example, 7 μm or less), thermal shrinkage at high temperatures tends to be further suppressed.

  The method for adjusting the average particle size and particle size distribution of the inorganic particles is not particularly limited. For example, a method of pulverizing the inorganic particles using a ball mill, bead mill, jet mill or the like to reduce the particle size, etc. Can be mentioned.

  The content of the inorganic particles is preferably 50% by mass or more and less than 100% by mass with respect to 100% by mass of the porous layer, more preferably 70 to 99.99% by mass, and further preferably 80 to 99.9%. It is mass%, Most preferably, it is 90-99 mass%. When the content of the inorganic particles is within the above range, the binding properties of the inorganic particles, the permeability of the separator, the heat resistance, and the like tend to be further improved.

(Copolymer binder)
The swelling degree of the copolymer binder with respect to the mixed solvent containing 2 parts by mass of ethylene carbonate and 3 parts by mass of diethyl carbonate is 1.5 times or less, preferably 0.5 times or more and 1.5 times or less. When the swelling degree of the copolymer binder is 1.5 times or less, the adhesion between the base material and the inorganic particles and the cushioning property with the electrode are further improved. The degree of swelling with respect to the mixed solvent containing 2 parts by mass of ethylene carbonate and 3 parts by mass of diethyl carbonate can be adjusted by adjusting the monomer components constituting the copolymer. The degree of swelling can be measured by the method described in the examples.

  Moreover, the swelling degree of the copolymer binder with respect to toluene becomes like this. Preferably it is 6 times or more, More preferably, it is 8 times or more, More preferably, it is 10 times or more. When the swelling degree of the copolymer binder is 6 times or more, the cushioning property with the electrode tends to be further improved. The degree of swelling with respect to toluene can be adjusted by adjusting the monomer component. Among these, adjusting the kind and amount of the crosslinkable monomer greatly contributes to the degree of swelling with respect to toluene. The degree of swelling can be measured by the method described in the examples.

  The glass transition temperature (hereinafter also referred to as “Tg”) of the copolymer binder is preferably −50 ° C. or higher, more preferably −40 to 10 ° C. When the glass transition temperature of the copolymer binder is within the above range, the heat resistance of the separator tends to be further improved. Here, the glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, it is determined by the intersection of a straight line obtained by extending the base line on the low temperature side in the DSC curve to the high temperature side and the tangent at the inflection point of the stepped change portion of the glass transition. “Glass transition” refers to a change in calorific value associated with a change in the state of the polymer that is a test piece in DSC on the endothermic side. Such a change in heat quantity is observed as a step-like change shape in the DSC curve. The “step change” refers to a portion of the DSC curve until the curve moves away from the previous low-temperature base line to a new high-temperature base line. Note that a combination of a step change and a peak is also included in the step change. Further, the “inflection point” indicates a point at which the gradient of the DSC curve of the step-like change portion is maximized. Further, in the step-like change portion, when the upper side is the heat generation side, it can also be expressed as a point where the upward convex curve changes to the downward convex curve. “Peak” indicates a portion of the DSC curve from when the curve leaves the low-temperature side baseline until it returns to the same baseline again. “Baseline” refers to a DSC curve in a temperature region where no transition or reaction occurs in the test piece. The glass transition temperature of the copolymer binder can be measured by the method described in the examples.

  The average particle size of the copolymer particles is preferably 70 to 300 nm, more preferably 100 to 300 nm. When the average particle size of the copolymer particles is 70 nm or more, the heat resistance tends to be further improved. Further, when the average particle diameter of the copolymer particles is 300 nm or less, the falling off of the inorganic particles from the porous layer can be further suppressed, and the strength of the porous layer tends to be further improved. The average particle diameter of the copolymer particles can be measured by the method described in the examples.

(Monomer unit)
Hereinafter, the monomer unit contained in the copolymer binder will be described. The “monomer” means a compound having one or more polymerizable unsaturated bonds such as ethylenically unsaturated bonds in the molecule. The “monomer unit” refers to a structural unit derived from a monomer in a copolymer binder.

(Cycloalkyl group-containing monomer unit (A))
The copolymer binder preferably includes a cycloalkyl group-containing monomer unit (A). By using a copolymer binder having a cycloalkyl group-containing monomer unit (A), the adhesion between the inorganic particles and the substrate tends to be further improved.

  Although it does not specifically limit as a cycloalkyl group containing monomer unit (A), What has a cycloalkyl group and has one ethylenically unsaturated bond is mentioned. Such a cycloalkyl group-containing monomer unit (A) is not particularly limited, and examples thereof include a cyclohexyl acrylate unit, a cyclohexyl methacrylate unit, an isobornyl acrylate unit, an isobornyl methacrylate unit, an adamantyl acrylate unit, and an adamantyl methacrylate. Examples thereof include (meth) acrylic acid ester monomer units having a cycloalkyl group such as units. Among these, a (meth) acrylic acid ester monomer unit having a cycloalkyl group and a (meth) acryloyloxy group is preferable, and a cyclohexyl acrylate unit and a cyclohexyl methacrylate unit are more preferable. By using such a cycloalkyl group-containing monomer unit (A), the problem according to the present invention tends to be more effectively and reliably solved. Moreover, it exists in the tendency for the polymerization stability at the time of copolymer binder preparation to improve more. A cycloalkyl group containing monomer unit (A) may be used individually by 1 type, or may use 2 or more types together.

  The number of carbon atoms constituting the alicyclic ring of the cycloalkyl group is preferably 4-8, more preferably 6-7, and even more preferably 6. Further, the cycloalkyl group may or may not have a substituent. Although it does not specifically limit as a substituent, For example, a methyl group and a tertiary butyl group are mentioned.

  The content of the cycloalkyl group-containing monomer unit (A) is preferably 15% by mass or more, more preferably 20% by mass or more, and further preferably 30% with respect to 100% by mass of the copolymer binder. It is at least mass%. The content of the cycloalkyl group-containing monomer unit (A) is preferably 50% by mass or less with respect to 100% by mass of the copolymer binder. When the content of the cycloalkyl group-containing monomer unit (A) is 15% by mass or more, the degree of swelling of the copolymer with respect to the electrolytic solution tends to decrease. On the other hand, when the content of the cycloalkyl group-containing monomer unit (A) is 50% by mass or less, the polymerization stability at the time of preparing the copolymer tends to be improved.

  The fact that the copolymer has a cycloalkyl group-containing monomer unit (A) can be confirmed by pyrolysis gas chromatography. More specifically, a homopolymer of a cycloalkyl group-containing monomer is measured by pyrolysis gas chromatography, and the retention time of the pyrolyzate is determined in advance. Next, when the copolymer is measured under the same conditions by pyrolysis gas chromatography and has a peak of pyrolysis product at the same retention time, a cycloalkyl group-containing monomer is used as the copolymer monomer unit. It can be estimated that it has. It is also possible to determine the ratio of the cycloalkyl group-containing monomer in the copolymer monomer unit by using a homopolymer of the cycloalkyl group-containing monomer as an internal standard.

(Monomer unit (B))
The said copolymer binder may have other monomer units (B) other than a cycloalkyl group containing monomer unit (A) as needed. Although it does not specifically limit as a monomer unit (B), For example, a carboxyl group-containing monomer unit (b1), an amide group-containing monomer unit (b2), a hydroxyl group-containing monomer unit (b3), Crosslinkable monomer unit (b4), (meth) acrylate monomer unit (b5), cyano group-containing monomer unit (b6), aromatic group-containing monomer unit (b7), other ethylene Unsaturated unsaturated monomer units. A monomer unit (B) may be used individually by 1 type, or may use 2 or more types together. Moreover, the monomer unit (B) may belong to two or more of the above monomers at the same time. That is, the monomer unit (B) is an ethylenically unsaturated monomer unit having two or more groups selected from the group consisting of a carboxyl group, an amide group, a hydroxyl group, a cyano group, and an aromatic group. Alternatively, it may be a crosslinkable monomer unit having two or more groups selected from the group consisting of a carboxyl group, an amide group, a hydroxyl group, a cyano group and an aromatic group together with an ethylenically unsaturated bond.

  In addition, the total content of the monomer (B) is preferably 50% by mass or more with respect to 100% by mass of the copolymer binder. Further, the total content of the monomer (B) is preferably 85% by mass or less, more preferably 80% by mass or less, and further preferably 70% by mass with respect to 100% by mass of the copolymer binder. It is as follows.

(Carboxyl group-containing monomer unit (b1))
When the copolymer binder contains the carboxyl group-containing monomer unit (b1), the heat resistance of the separator tends to be further improved. The monomer that can constitute the carboxyl group-containing monomer unit (b1) is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, itaconic acid half ester, maleic acid half ester, and fumaric acid half ester. And monocarboxylic acid monomers such as itaconic acid, fumaric acid and maleic acid. Of these, acrylic acid, methacrylic acid and itaconic acid are preferred, and acrylic acid and methacrylic acid are more preferred from the viewpoint of improving the heat resistance of the separator. These may be used alone or in combination of two or more.

  The content of the carboxyl group-containing monomer unit (b1) is preferably 0.1 to 5% by mass and more preferably 1 to 5% by mass with respect to 100% by mass of the copolymer. When the content of the carboxyl group-containing monomer unit (b1) is 0.1% by mass or more, the heat resistance of the separator tends to be further improved. Moreover, it exists in the tendency which the polymerization stability at the time of preparing a copolymer binder improves more because content of a carboxyl group-containing monomer unit (b1) is 5 mass% or less.

(Amide group-containing monomer unit (b2))
When the copolymer binder contains the amide group-containing monomer unit (b2), the heat resistance of the separator tends to be further improved. The monomer that can constitute the amide group-containing monomer unit (b2) is not particularly limited, and examples thereof include acrylamide, methacrylamide, N, N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, and maleic acid amide. And maleimide. Among these, acrylamide and methacrylamide are preferable from the viewpoint of improving the heat resistance of the separator. These may be used alone or in combination of two or more.

  The content of the amide group-containing monomer unit (b2) is preferably 0.1 to 5% by mass with respect to 100% by mass of the copolymer. When the content of the amide group-containing monomer unit (b2) is 0.1% by mass or more, the heat resistance with the electrode (electrode active material) tends to be further improved. Moreover, when content of an amide group containing monomer unit (b2) is 5 mass% or less, it exists in the tendency which the polymerization stability at the time of preparing a copolymer binder improves more.

(Hydroxyl group-containing monomer unit (b3))
When the copolymer binder contains the hydroxyl group-containing monomer unit (b3), the polymerization stability when preparing the copolymer binder tends to be further improved. Examples of the monomer that can constitute the hydroxyl group-containing monomer unit (b3) include hydroxyl groups such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, polyethylene glycol acrylate, and polyethylene glycol methacrylate ( And (meth) acrylate. Of these, hydroxyethyl acrylate and hydroxyethyl methacrylate are preferred from the viewpoint of improving the polymerization stability of the copolymer. These may be used alone or in combination of two or more.

  The content of the hydroxyl group-containing monomer unit (b3) is preferably 0.1 to 10% by mass, more preferably 1 to 10% by mass, further preferably 100% by mass of the copolymer. Is 1-7 mass%. When the content of the hydroxyl group-containing monomer unit (b3) is within the above range, the polymerization stability when preparing the copolymer tends to be further improved.

(Crosslinkable monomer unit (b4))
From the viewpoint of making the insoluble content in the electrolytic solution an appropriate amount, the crosslinkable monomer (b4) may be included. The monomer that can form the crosslinkable monomer unit (b4) is not particularly limited. For example, a monomer having two or more radical polymerizable double bonds, self-crosslinking during or after polymerization Examples thereof include monomers having a functional group that gives a structure. These may be used alone or in combination of two or more.

  Although it does not specifically limit as a monomer which has two or more radically polymerizable double bonds, For example, polyfunctional aromatic compounds, such as divinylbenzene; Bifunctional (meth) acrylate, Trifunctional (meth) Polyfunctional (meth) acrylates such as acrylate and tetrafunctional (meth) acrylate are exemplified. Among these, polyfunctional (meth) acrylates are preferable from the viewpoint of better electrolytic solution resistance even in a small amount.

  Although it does not specifically limit as polyfunctional (meth) acrylate, For example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol diacrylate, for example Examples include methacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more.

  The monomer having a functional group that gives a self-crosslinking structure during or after polymerization is not particularly limited. For example, an epoxy group-containing monomer, a methylol group-containing monomer, an alkoxymethyl group-containing monomer, and Examples thereof include hydrolyzable silyl group-containing monomers. These may be used alone or in combination of two or more.

  The epoxy group-containing monomer is not particularly limited, and examples thereof include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate. Of these, glycidyl methacrylate is preferred. These may be used alone or in combination of two or more.

  Although it does not specifically limit as a methylol group containing monomer, For example, N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide are mentioned. These may be used alone or in combination of two or more.

  Although it does not specifically limit as an alkoxymethyl group containing monomer, For example, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-butoxymethyl acrylamide, and N-butoxymethyl methacrylamide are mentioned. These may be used alone or in combination of two or more.

  Although it does not specifically limit as a hydrolysable silyl group containing monomer, For example, vinylsilane, (gamma) -acryloxypropyltrimethoxysilane, (gamma) -acryloxypropyltriethoxysilane, (gamma) -methacryloxypropyl trimethoxysilane, and (gamma) -Methacryloxypropyltriethoxysilane. These may be used alone or in combination of two or more.

  Among the crosslinkable monomers (b4), polyfunctional (meth) acrylates are particularly preferable in that there is little variation in the degree of crosslinking.

  The content of the crosslinkable monomer unit (b4) is preferably 0.0 to 5% by mass, more preferably 0.0 to 2.0% by mass with respect to 100% by mass of the copolymer. More preferably, it is 0.0-1.0 mass%, More preferably, it is 0.0-0.5 mass%. When the content of the crosslinkable monomer (b4) is 0.5% by mass or less, the degree of swelling of the copolymer with respect to toluene tends to increase, and at the same time, the adhesion between the separator and the electrode tends to improve. is there.

((Meth) acrylic acid ester monomer (b5))
Moreover, it exists in the tendency for oxidation resistance to improve more because a copolymer binder contains a (meth) acrylic acid ester monomer (b5). The (meth) acrylic acid ester monomer (b5) is a monomer different from the monomers (b1) to (b4).

  Although it does not specifically limit as (meth) acrylic acid ester monomer (b5), For example, (meth) acrylic acid ester which has one ethylenically unsaturated bond is mentioned, More specifically, 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 acrylate, butyl methacrylate, isobutyl methacrylate , Alkyl such as t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate (Meth) acrylate having a ring (more preferably (meth) acrylate having an alkyl group and a (meth) acryloyloxy group); (meth) acrylate having an aromatic ring such as benzyl acrylate, phenyl acrylate, benzyl methacrylate, and phenyl methacrylate ( More preferred is (meth) acrylate having an aromatic ring and a (meth) acryloyloxy group. Among these, from the viewpoint of improving adhesion to the electrode (electrode active material), a (meth) acrylate monomer unit (b5) having an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group. Is preferred. More specifically, 2-ethylhexyl acrylate is preferable. These (meth) acrylic acid ester monomers (b5) may be used alone or in combination of two or more.

  The content of the (meth) acrylic acid ester monomer (b5) is preferably 50 to 99.9% by mass and more preferably 70 to 99.9% by mass with respect to 100% by mass of the copolymer. More preferably, it is 80-99.9 mass%. When the content of the (meth) acrylic acid ester monomer (b5) is 99.9% by mass or less, the heat resistance of the separator tends to be improved.

  The total content of the cycloalkyl group-containing monomer unit (A) and the (meth) acrylate monomer (b51) is preferably 80 to 99.9% by mass with respect to 100% by mass of the copolymer. Yes, more preferably 85-99.9% by mass. When the total content of the cycloalkyl group-containing monomer unit (A) and the (meth) acrylate monomer unit (b5) is within the above range, the separator is used in a non-aqueous electrolyte secondary battery. In this case, the oxidation resistance of the copolymer binder tends to be further improved.

(Cyano group-containing monomer unit (b6))
When the copolymer binder has the cyano group-containing monomer unit (b6), the oxidation resistance of the copolymer tends to be further improved. Although it does not specifically limit as a cyano group containing monomer unit (b6), For example, an acrylonitrile and a methacrylonitrile are mentioned. The cyano group-containing monomer unit (b6) may be used alone or in combination of two or more.

(Aromatic group-containing monomer unit (b7))
When the copolymer binder has the aromatic group-containing monomer unit (b7), the electrolytic solution resistance of the copolymer tends to be further improved. The aromatic group-containing monomer unit (b7) is not particularly limited, and examples thereof include styrene, vinyl toluene, and α-methylstyrene. Of these, styrene is preferable. The aromatic group-containing monomer unit (b7) may be used alone or in combination of two or more.

(Method for producing copolymer binder)
The copolymer binder is obtained, for example, by a usual emulsion polymerization method. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-known method can be used. For example, in a dispersion system containing the above-mentioned monomer, surfactant, radical polymerization initiator, and other additive components used as necessary in an aqueous medium as a basic composition component, each of the above monomers is included. A copolymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the monomer composition to be supplied is made constant throughout the entire polymerization process, or the morphological composition change of the particles of the resin dispersion to be produced is changed sequentially or continuously in the polymerization process. Various methods can be used as necessary, such as a method of giving When the copolymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and a particulate copolymer dispersed in the water.

  The surfactant is a compound having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. Examples of the surfactant include non-reactive alkyl sulfate, polyoxyethylene alkyl ether sulfate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, naphthalene sulfone. Anionic interfaces such as acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene distyrenated phenyl ether sulfate, fatty acid salt, alkyl phosphate, polyoxyethylene alkylphenyl ether sulfate Activators and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene disty Phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, polyoxyethylene alkylphenyl ether, etc. Nonionic surfactants. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

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

  Examples of the nonionic surfactant in the reactive surfactant include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) RN-30 and RN-50), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap ER manufactured by ADEKA Corporation) -10)), polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) A Le (for example, Kao Corp. LATEMUL PD-420.) And the like.

  Among the above-mentioned various surfactants, reactive surfactants are preferable, anionic reactive surfactants are more preferable, and reactive surfactants having a sulfonic acid group are more preferable. The surfactant is preferably used in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the monomer composition. Surfactant may be used individually by 1 type, or may use 2 or more types together.

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

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

  In addition, emulsion polymerization of a monomer composition containing a monomer that can constitute the cycloalkyl group-containing monomer unit (A) and a monomer that can constitute the other monomer unit (B) And when forming the dispersion which polymer particles disperse | distributed in the solvent (water), it is preferable that it is 30 mass%-70 mass% as solid content of the obtained dispersion.

  The dispersion is preferably adjusted to have a pH in the range of 5 to 12 in order to maintain long-term dispersion stability. For pH adjustment, amines such as ammonia, sodium hydroxide, potassium hydroxide, and dimethylaminoethanol are preferably used, and pH is more preferably adjusted with ammonia (water) or sodium hydroxide.

  The aqueous dispersion in the first embodiment includes a copolymer obtained by copolymerizing a monomer composition containing the specific monomer as particles (copolymer particles) dispersed in water. In addition to water and the copolymer, the aqueous dispersion may contain a solvent such as methanol, ethanol, isopropyl alcohol, a dispersant, a lubricant, a thickener, a bactericide, and the like.

[Method for forming porous layer]
The method for forming the porous layer is not particularly limited, and examples thereof include a method in which a porous layer is formed by applying a coating liquid containing inorganic particles and a copolymer binder on at least one surface of a substrate.

  As the solvent for the coating solution, those capable of uniformly or stably dispersing or dissolving the inorganic particles and the copolymer binder are preferable. For example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water , Ethanol, toluene, hot xylene, methylene chloride, hexane and the like.

  Various additives such as surfactants, thickeners, wetting agents, antifoaming agents, PH preparations containing acids and alkalis are added to the coating solution in order to stabilize dispersion and improve coating properties. May be added. These additives are preferably those that can be removed when the solvent is removed, but are porous if they are electrochemically stable in the range of use of the lithium ion secondary battery, do not inhibit the battery reaction, and are stable up to about 200 ° C. It may remain in the layer.

  The method for dissolving or dispersing the inorganic particles and the polymer particles in the solvent of the coating solution is not particularly limited as long as it can achieve the dissolution or dispersion characteristics of the coating solution necessary for the coating step. Examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade.

  The method for applying the coating solution to the substrate is not particularly limited as long as it can achieve the required layer thickness and coating area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples include a coater method, a die coater method, a screen printing method, and a spray coating method.

  Furthermore, it is preferable to perform a surface treatment on the surface of the substrate prior to coating because the coating liquid can be easily applied and the adhesion between the inorganic particle-containing porous layer after coating and the substrate surface is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the substrate. For example, corona discharge treatment method, mechanical surface roughening method, solvent treatment method, acid treatment method, ultraviolet oxidation method Etc.

  The method for removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the substrate. For example, a method of drying at a temperature below its melting point while fixing the substrate, a method of drying under reduced pressure at a low temperature, dipping in a poor solvent for the copolymer binder to solidify the copolymer binder and extracting the solvent at the same time Methods and the like.

  Next, the case where the electricity storage device separator of the present embodiment is used for a lithium ion battery will be described.

There is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, A well-known thing can be used.
Examples of the positive electrode material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ , and examples of the negative electrode material include graphite, non-graphitizable carbonaceous, and easy graphite. Carbonaceous materials such as carbonaceous carbonaceous and composite carbon bodies; silicon, tin, metallic lithium, various alloy materials, and the like.

As the non-aqueous electrolyte, an electrolyte in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples thereof include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

[Physical properties of separator]
The air permeability of the 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, and further preferably 30 seconds / 100 cc or more and 450 seconds / 100 cc. Or less, and particularly preferably 50 seconds / 100 cc or more and 400 seconds / 100 cc or less. When the separator has an air permeability of 10 seconds / 100 cc or more, self-discharge when used as a battery separator tends to be further reduced. Moreover, when the air permeability of the separator is 650 seconds / 100 cc or less, the charge / discharge characteristics tend to be further improved.

  Further, the increase rate of the air permeability of the separator due to the formation of the porous layer is preferably 0% or more and 200% or less, more preferably 0% or more and 100% or less, and further preferably 0% or more and 50% or less. Or less, particularly preferably 0% or more and 30% or less. When the increase rate of the air permeability of the separator is within the above range, the permeability tends to be further improved. However, when the air permeability of the base material is less than 100 seconds / 100 cc, the increase in the air permeability of the separator after forming the porous layer can be preferably used if it is 0% or more and 500% or less.

  The thickness of the separator is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, and further preferably 7 μm or more and 30 μm or less. When the thickness of the separator is 2 μm or more, the mechanical strength tends to be further improved. Moreover, since the separator occupied volume is reduced when the film thickness of the separator is 200 μm or less, the battery tends to have a higher capacity.

  The thermal shrinkage rate in the MD direction and TD direction at 150 ° C. of the separator is preferably 0% or more and 15% or less, more preferably 0% or more and 10% or less, and further preferably 0% or more and 5% or less. . When the thermal contraction rate in the MD direction and the TD direction is 15% or less, the film breakage of the separator at the time of abnormal heat generation of the battery is suppressed, and a short circuit tends not to occur.

  The shutdown temperature of the separator is preferably 120 ° C. or higher and 160 ° C. or lower, more preferably 120 ° C. or higher and 150 ° C. or lower. When the shutdown temperature is 160 ° C. or lower, even when the battery generates heat, current interruption is promptly promoted, and the safety performance tends to be further improved. On the other hand, when the shutdown temperature is 120 ° C. or higher, the safety when the battery is used at around 100 ° C. tends to be improved.

  The short-circuit temperature of the separator is preferably 180 ° C. or higher and 1000 ° C. or lower, more preferably 200 ° C. or higher and 1000 ° C. or lower. When the short circuit temperature is 180 ° C. or higher, even if abnormal heat generation occurs in the battery, a short circuit does not occur immediately, so heat can be dissipated during that time, and safety performance tends to be further improved.

  The short temperature is a desired value by adjusting the content of polypropylene in the substrate, the type of polyolefin other than polypropylene in the substrate, the type of inorganic particles in the porous layer, the thickness of the inorganic particle-containing layer, etc. Can be controlled.

  In addition, about the various parameters mentioned above, unless otherwise indicated, it measures according to the measuring method in the Example mentioned later.

[Second Embodiment]
The separator of the second embodiment further has a polymer layer on at least one surface of the separator of the first embodiment, and the polymer layer contains a thermoplastic polymer. By having a polymer layer, an electrode and a separator can be adhered through a hot press process.

(Polymer layer)
(Thermoplastic polymer)
Although it does not specifically limit as a thermoplastic polymer, For example, fluorine-type copolymers, such as a polyvinylidene fluoride, and an acrylic copolymer are mentioned. Among these, an acrylic copolymer is more preferable from the viewpoint of adhesion to the electrode.

(Amount of polymer layer supported on the separator of the first embodiment)
Loading of the polymer layer to the separator of the first embodiment, the solid content, preferably at 0.05 g / m ² or more 1.0 g / m ² or less, more preferably 0.07 g / m ² or more 0. 80 g / m ² or less, more preferably 0.1 g / m ² or more and 0.70 g / m ² or less. By loading amount of the polymer layer is 0.05 g / m ² or more 1.0 g / m ² or less, the adhesion strength between the polymer layer and the separator of the first embodiment is further improved, in the first embodiment There is a tendency to further suppress a decrease in cycle characteristics (permeability) due to the plugging of the pores of the separator with the thermoplastic polymer.

  The amount of the polymer layer supported on the separator of the first embodiment can be adjusted, for example, by changing the concentration of the thermoplastic polymer or copolymer in the coating solution or the amount of coating of the thermoplastic polymer solution. However, the method for adjusting the carrying amount is not limited to the above.

(Surface coverage)
The surface coverage of the polymer layer with respect to the separator surface of the first embodiment is preferably 70% or less, more preferably 50% or less, and even more preferably 45% or less, with respect to the surface area per side of the separator. And particularly preferably 40% or less. In addition, the surface coverage of the polymer layer with respect to the separator surface of the first embodiment is preferably 5% or more with respect to the surface area per surface of the separator. When the surface coverage of the polymer layer is 70% or less, the pores of the separator due to the thermoplastic polymer are further suppressed, and the permeability of the separator tends to be further improved. On the other hand, when the surface coverage of the polymer layer is 5% or more, the adhesion with the electrode tends to be further improved.

  The surface coverage of the polymer layer is, for example, changing the concentration of the thermoplastic polymer or copolymer in the coating liquid applied to the separator, the coating amount of the coating liquid, the coating method, and the coating conditions in the separator manufacturing method described later. Can be adjusted. However, the method for adjusting the surface coverage is not limited thereto. Moreover, the surface coverage of the polymer layer in this embodiment is measured according to the method as described in the following Example.

(Average thickness of polymer layer)
The average thickness of the polymer layer is preferably 2.0 μm or less, more preferably 1.0 μm or less, and further preferably 0.5 μm or less. When the average thickness of the polymer layer is 2.0 μm or less, it is possible to suppress a decrease in permeability due to the polymer layer and to effectively adhere the polymer layers to each other or the polymer layer and the separator when the separator is stored as a roll. It tends to be suppressed.

  The average thickness of the polymer layer can be adjusted, for example, by changing the thermoplastic polymer or copolymer concentration in the coating liquid applied to the separator, the coating amount of the coating liquid, the coating method, and the coating conditions. However, the adjustment method of the average thickness of a polymer layer is not limited to them.

(Existence form of the polymer layer on the separator of the first embodiment)
The presence form (pattern) of the polymer layer on the separator according to the first embodiment is not particularly limited, and may have, for example, a planar shape shown in black in FIG. That is, the polymer layer has, for example, a dot shape (for example, FIG. 1A), a lattice shape (for example, FIG. 1B), a linear shape (for example, FIG. 1C), a stripe shape (for example, FIG. 1 (D)), a tortoiseshell pattern (for example, (E) in FIG. 1), and the like may exist.

  In these, it is preferable that a polymer layer exists in the dot form on the at least single side | surface of a separator from a viewpoint of ensuring permeability | transmittance and a further improving uniform adhesiveness with an electrode. “Dot-like” indicates a state of a sea-island structure in which a polymer layer is present in an island shape on a separator and a portion where the polymer layer is not present is in a sea shape. Although the polymer layer may exist independently in an island shape, a part of the polymer layer may form a continuous surface, but the polymer layer is continuous in most parts, and most of the separator is the polymer layer. It is not included when it is covered with (when the sea of the sea-island structure is a polymer layer).

  When the polymer layer exists independently in an island shape, the distance between the island dots (the distance between the ends of the adjacent island dots) is 5 μm to 500 μm. It is preferable from the point of coexistence. The average long diameter of the dots (the longest diameter of one dot; the long diameter) is preferably 20 μm or more and 1000 μm or less, more preferably 30 μm or more and 800 μm or less, and further preferably 50 μm or more and 500 μm or less. When the average major axis of the dots of the polymer layer is 20 μm or more and 1000 μm or less, the adhesion with the electrode tends to be further improved.

  The average major axis of the dots of the polymer layer can be adjusted, for example, by changing the copolymer or thermoplastic polymer concentration of the coating liquid, the coating amount of the coating liquid, the coating method, and the coating conditions. However, the method of adjusting the average major axis of the dots of the polymer layer is not limited to them.

  Moreover, it is preferable that the separator of 2nd Embodiment is 50% or more of adhesiveness with the electrode measured by the below-mentioned method.

[Method for Producing Separator of Second Embodiment]
Although the manufacturing method of the separator of 2nd Embodiment is not specifically limited, For example, the application process which apply | coats the coating liquid containing a thermoplastic polymer to the at least single side | surface of the separator of 1st Embodiment, and as needed And a drying step of removing the solvent or dispersion medium of the coating solution.

(Coating process)
The coating step is a step of coating a coating liquid containing a thermoplastic polymer on at least one surface of the separator of the first embodiment. The coating liquid contains a thermoplastic polymer and a solvent or a dispersion medium.

  Although it does not specifically limit as a solvent or a dispersion medium contained in a coating liquid, Water is preferable. When the coating liquid is applied to the separator when the coating liquid is applied to the separator, the thermoplastic polymer containing the copolymer closes the surface and the inside of the pores of the separator, and the permeability tends to decrease. . In this regard, when water is used as the solvent or dispersion medium of the coating solution, the coating solution is difficult to enter the separator, and the thermoplastic polymer including the copolymer is likely to be mainly present on the outer surface of the separator. Therefore, it is preferable because a decrease in permeability can be more effectively suppressed. Examples of the solvent or dispersion medium that can be used in combination with water include ethanol and methanol.

  The application method of the coating solution is not particularly limited as long as the required layer thickness and application area can be realized. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater Method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method and spray coating method.

(Surface treatment process)
You may have the surface treatment process which performs a surface treatment on the separator surface before an application | coating process. By having the surface treatment step, it becomes easier to apply the coating liquid and the adhesiveness between the separator and the thermoplastic polymer tends to be improved. The surface treatment method is not particularly limited as long as the structure of the separator (for example, the porous structure of the polyolefin microporous membrane) is not significantly impaired. For example, the corona discharge treatment method, the plasma treatment method, the mechanical surface roughening method. , Solvent treatment method, acid treatment method, and ultraviolet oxidation method.

(Drying process)
A drying process is a process of removing the solvent or dispersion medium of a coating liquid. The method for removing the solvent or dispersion medium from the coating liquid applied to the separator is not particularly limited as long as it does not adversely affect the separator. For example, when a polyolefin microporous membrane is used as a separator, a method of drying at a temperature below the melting point while fixing the separator, a method of drying under reduced pressure at a low temperature, or immersing in a poor solvent for the copolymer to solidify the copolymer And a method of extracting the solvent at the same time.

(Use)
The separator of 1st Embodiment and 2nd Embodiment can be used suitably as separators, such as an electrical storage device and a lithium ion secondary battery. The electricity storage device of this embodiment includes the separator of the first embodiment or the second embodiment, and the lithium ion secondary battery of this embodiment includes the separator of the first embodiment or the second embodiment. .

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to an Example. The measurement methods and evaluation methods for various physical properties used in the following synthesis examples, production examples, examples and comparative examples are as follows.

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

(2) Average particle diameter of copolymer particles Using a light-scattering particle diameter measuring apparatus (LEED & NORTH UP, trade name “MICROTRAC UPA150”), 50% particle diameter (nm) was measured and used as the average particle diameter. .

(3) Weight of base material (polyolefin microporous film) A 10 cm × 10 cm square sample was cut from the base material, and mass was measured using an electronic balance AEL-200 (trade name) manufactured by Shimadzu Corporation. Is multiplied by the resulting mass 100 was calculated 1 m ² per layer of basis weight (g / m ²⁾ in.

(4) Film thickness of base material (polyolefin microporous film) A sample of MD 10 mm × TD 10 mm was cut out from the base material, nine locations (3 points × 3 points) were selected in a lattice shape, and the film thickness was dial gauge (manufactured by Ozaki Mfg. Co., Ltd.) PEACOCK No. 25 (registered trademark)) was used, and the average value of the nine measured values was defined as the film thickness (μm) of the substrate.

(5) Porosity of substrate (polyolefin microporous membrane) A 10 cm x 10 cm square sample was cut from the substrate, its volume (cm ³ ) and mass (g) were determined, and the membrane density was 0.95 (g / cm ³ ) The porosity was calculated using the following formula.
Porosity = (1−mass / volume / 0.95) × 100

(6) Air Permeability of Substrate (Polyolefin Microporous Membrane) Air permeation resistance measured by Gurley type air permeance meter, G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. according to JIS P-8117 Was the air permeability.

(7) Puncture strength of base material (polyolefin microporous membrane) Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, the base material was fixed with a sample holder having a diameter of 11.3 mm. Next, by performing a piercing test in a 25 ° C. atmosphere at a piercing speed of 2 mm / sec using a needle having a radius of curvature of 0.5 mm at the center of the fixed substrate. The puncture strength (g) was obtained as the maximum puncture load.

(8) The average pore size of the substrate (polyolefin microporous membrane) It is known that the fluid inside the capillary follows the Knudsen flow when the fluid mean free path is larger than the capillary pore size, and the Poiseuille flow when it is small. Yes. Therefore, it was assumed that the air flow in the air permeability measurement of the base material follows the Knudsen flow, and the water flow in the base material permeability measurement follows the Poiseuille flow.

The average pore diameter d (μm) is the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)), the water permeation rate constant R _liq (m ³ / (m ² · sec · Pa)), From the air molecular velocity ν (m / sec), water viscosity η (Pa · sec), standard pressure P _s (= 101325 Pa), porosity ε (%), and film thickness L (μm), the following equation is used. Asked.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶

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

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

The water permeability was determined as follows. A base material previously immersed in ethanol is set in a stainless steel liquid-permeable cell having a diameter of 41 mm, and after the ethanol of the base material is washed with water, water is permeated through the base material with a differential pressure of about 50000 Pa, From the water permeability (cm ³ ) when 120 seconds passed, the water permeability per unit time, unit pressure, and unit area was calculated and used as the water permeability.

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

(9) Glass transition temperature of copolymer An appropriate amount of an aqueous dispersion (solid content = 38 to 42% by mass, pH = 9.0) containing a copolymer is placed in an aluminum dish and heated with a hot air dryer at 130 ° C. Dried for minutes. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve in a nitrogen atmosphere were obtained with a DSC measuring apparatus (manufactured by Shimadzu Corporation, model number: DSC6220). The measurement conditions were as follows.
(First stage temperature rise program)
Starting at 70 ° C., the temperature was increased at a rate of 15 ° C. per minute. After reaching 110 ° C., the temperature was maintained for 5 minutes.
(Second stage temperature drop program)
The temperature was lowered from 110 ° C. at a rate of 30 ° C. per minute. After reaching −50 ° C., the temperature was maintained for 4 minutes.
(Third-stage temperature rising program)
The temperature was raised from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data were acquired during the third stage of temperature increase.

  The intersection of the straight line obtained by extending the base line in the obtained DSC curve to the high temperature side and the tangent at the inflection point was defined as the glass transition temperature (Tg).

(10) Swelling degree of copolymer with respect to electrolyte solution The aqueous dispersion containing the copolymer was allowed to stand in an oven at 130 ° C. for 1 hour and dried. The copolymer film obtained by drying was cut to 0.5 g. The cut sample is put in a 50 mL vial together with 10 g of a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (mass ratio), and the mixed solvent is infiltrated for 1 day. And the mass (Wa: g) was measured. Thereafter, the sample was allowed to stand in an oven at 150 ° C. for 1 hour, the mass was measured (Wb: g), and the degree of swelling of the copolymer with respect to the electrolytic solution was calculated from the following formula.
Swelling degree of copolymer to electrolyte (times) = (Wa−Wb) ÷ (Wb)

(11) Swelling degree of copolymer with respect to toluene The aqueous dispersion containing the copolymer was left to stand in an oven at 130 ° C. for 1 hour and dried. The copolymer film obtained by drying was cut to 0.5 g. The cut sample was put into a 50 mL vial together with 30 g of toluene, and the mixed solvent was infiltrated for one day. Then, the sample was taken out, washed with the mixed solvent, and the mass (Wa: g) was measured. Thereafter, the sample was allowed to stand in an oven at 150 ° C. for 1 hour, the mass was measured (Wb: g), and the degree of swelling of the copolymer with respect to the electrolytic solution was calculated from the following formula.
Swelling degree of copolymer to electrolyte (times) = (Wa−Wb) ÷ (Wb)

[Evaluation method]
(12) Adhesiveness between separator and electrode The adhesiveness between the separator and the electrode was evaluated by the following procedure.
(Preparation of positive electrode)
92.2% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 2.3% by mass of flake graphite and acetylene black as a conductive material, and 3.2% by mass of polyvinylidene fluoride (PVDF) as a binder A slurry was prepared by dispersing in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material coating amount of the positive electrode was 250 g / m ² , and the active material bulk density was 3.00 g / cm ³ .

(Preparation of negative electrode)
A slurry was prepared by dispersing 96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of an ammonium salt of carboxymethyl cellulose and 1.7% by mass of a styrene-butadiene copolymer aqueous dispersion as a binder in purified water. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material application amount of the negative electrode was set to 106 g / m ² , and the active material bulk density was set to 1.35 g / cm ³ .

(Electrolytic solution immersion test)
The separator obtained by the above method was cut into a width of 20 mm and a length of 40 mm. This separator was transferred to a plastic container, and an electrolytic solution (manufactured by Toyama Pharmaceutical Co., Ltd.) in which ethylene carbonate and diethyl carbonate were mixed at a ratio (volume ratio) of 2: 3 was dropped until the separator was sufficiently immersed. A cover was attached so as not to volatilize and shaken for 24 hours.
After shaking for 24 hours, the cover was removed, the state of the coating layer was observed, and the adhesion between the inorganic particles and the substrate was evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: Even if the coating layer is traced with a spatula, the coating layer does not break.
○: Trace the coating layer with a spatula to break the coating layer.
X: Destruction of the coating layer is observed before tracing with a spatula.

(Cushion test)
The electrode obtained by the above method was cut into a width of 20 mm and a length of 40 mm. An electrolytic solution (manufactured by Toyama Pharmaceutical Co., Ltd.) in which ethylene carbonate and diethyl carbonate are mixed at a ratio (volume ratio) of 2: 3 is dropped onto this electrode until it is immersed in the electrode active material. A separator (size: width 30 mm, length 50 mm) was overlaid so that the electrode covered the entire surface of the substrate or the separator. The obtained laminate was put in an aluminum zip bag and hot pressed under the conditions of pressing conditions (80 ° C., 10 MPa, 3 minutes). Thereafter, the laminate was removed from the bag, and the substrate or separator was peeled off from the electrode. In the cushioning test, a positive electrode was used as the electrode, and a laminate was prepared so that the separator was in contact with the electrode on the side where the inorganic particles were present.
The cushioning properties were evaluated according to the following evaluation criteria. The peel strength was measured at a tensile speed of 200 mm / min according to JIS K6854-2 using an autograph AG-IS type (trademark) manufactured by Shimadzu Corporation.
<Evaluation criteria>
◎: When a peel strength of 2 N / m or more is shown. ○: When a peel strength of 1 N / m or more and less than 2 N / m is shown. △: When a peel strength of 0.1 N / m or more and less than 1 N / m is shown. : When the peel strength is less than 0.1 N / m

[Synthesis Example 1]
(Water dispersion A1)
In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank and thermometer, 70.4 parts by mass of ion-exchanged water and “AQUALON KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier In the table, indicated as “KH1025”. The same shall apply hereinafter.) 0.5 part by mass, “ADEKA rear soap SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, indicated as “SR1025” in the table, and so on) 0 And 5 parts by mass were charged. Next, the temperature inside the reaction vessel was raised to 80 ° C., and while maintaining the temperature at 80 ° C., a 2% aqueous solution of ammonium persulfate (indicated as “APS (aq) in the table, the same shall apply hereinafter)” 7.5. Part by mass was added. Five minutes after the completion of the addition of the ammonium persulfate aqueous solution, the emulsion was dropped from the dropping tank into the reaction vessel over 150 minutes.

  In the emulsion, 15 parts by mass of cyclohexyl methacrylate (shown as “CHMA” in the table, the same shall apply hereinafter) as a monomer constituting the cycloalkyl group-containing monomer unit (A), a carboxyl group-containing monomer unit ( As a monomer constituting b1), 1 part by mass of methacrylic acid (in the table, expressed as “MAA”, the same shall apply hereinafter), acrylic acid (in the table, indicated as “AA”, the same shall apply hereinafter), 1 part by mass, containing an amide group Acrylamide (denoted as “AM” in the table, the same shall apply hereinafter) as a monomer constituting the monomer unit (b2), 0.1 part by mass, and a monomer constituting the hydroxyl group-containing monomer unit (b3) as 2-monomer Hydroxyethyl methacrylate (in the table, expressed as “2HEMA”, the same applies hereinafter) 5 parts by mass, trimethylolpropane as a monomer constituting the crosslinkable monomer unit (b4) Reacrylate (A-TMPT, trade name manufactured by Shin-Nakamura Chemical Co., Ltd., listed as “A-TMPT” in the table, the same shall apply hereinafter) 1.0 part by mass, (meth) acrylic acid ester monomers other than the above As a monomer constituting the unit (b5), methyl methacrylate (in the table, expressed as “MMA”, the same applies hereinafter) 4.9 parts by mass, butyl methacrylate (in the table, expressed as “BMA”, the same applies hereinafter) 1.0 1 part by mass, butyl acrylate (in the table, expressed as “BA”, the same applies hereinafter) 1.0 part by mass, 2-ethylhexyl acrylate (in the table, expressed as “2EHA”, the same applies hereinafter) 70 parts by mass, 3 parts by weight of Aqualon KH1025 "(registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)," Adekaria soap SR1025 "(registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) Part by mass, sodium p-styrenesulfonate (expressed as “NaSS” in the table, the same shall apply hereinafter) 0.05 part by mass, 3.75 parts by mass of a 2% aqueous solution of ammonium persulfate, and 52 parts by mass of ion-exchanged water Was prepared by mixing for 5 minutes with a homomixer.

  After completion of dropping of the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature. The obtained emulsion was adjusted to pH = 9.0 with an aqueous ammonium hydroxide solution (25% aqueous solution), and a small amount of water was added to obtain an aqueous dispersion having a solid content of 40% (aqueous dispersion A1). About the copolymer in obtained water dispersion A1, Tg, average particle diameter, and the swelling degree with respect to electrolyte solution were measured with the said method. The obtained results are shown in Table 1.

[Synthesis Examples 2 to 26]
(Water dispersions A2 to A26)
Aqueous dispersions A2 to A26 were obtained in the same manner as in Synthesis Example 1 except that the types and mixing ratios of the raw materials were changed as shown in Tables 1 to 4.

  In the table, “IBXA” means isobornyl acrylate which is one kind of cycloalkyl group-containing monomer (A), and “IA” is one kind of carboxyl group-containing monomer (b1). "GMA" means glycidyl methacrylate which is one kind of the crosslinkable monomer (b4), and "MAPTMS" is one kind of the crosslinkable monomer (b4). It means γ-methacryloxypropyltrimethoxysilane. Further, in the table, “OTP” means a 25% aqueous solution of sodium dialkylsulfosuccinate (registered trademark, Perex-OTP manufactured by Kao Corporation), which is one kind of emulsifier, and “STA” is stearin, which is one kind of emulsifier. It means a 25% aqueous solution of ammonium acid.

  About the copolymer in obtained water dispersion A2-26, the swelling degree with respect to Tg, a particle diameter, and electrolyte solution was measured with the said method. The obtained results are shown in Tables 1 to 4. In the table, the composition of raw materials is based on mass.

[Production Example 1]
(Manufacture of base material B1)
45 parts by mass of homopolymer high-density polyethylene having an Mv of 700,000, 45 parts by mass of homopolymer high-density polyethylene having an Mv of 300,000, and a homopolymer polypropylene having an Mv of 400,000 10 parts by mass of a homopolymer having a Mv of 150,000 with polypropylene (mass ratio = 4: 3) was dry blended using a tumbler blender. 1 part by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and again a tumbler blender. Was used for dry blending to obtain a mixture. The obtained mixture was supplied to the twin screw extruder by a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump. The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the total mixture to be extruded was 65 parts by mass, that is, the polymer concentration was 35 parts by mass.

  Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll controlled at a surface temperature of 80 ° C. A sheet-like molded product was obtained by bringing into contact with a cooling roll and molding by cooling. The sheet was stretched by a simultaneous biaxial stretching machine at a magnification of 7 × 6.4 and a temperature of 112 ° C., then immersed in methylene chloride, extracted by removing liquid paraffin and dried, and then a temperature of 130 by a tenter stretching machine. The film was stretched 2 times in the transverse direction at ° C. Thereafter, the stretched sheet was relaxed by about 10% in the width direction and subjected to heat treatment to obtain a base material B1 shown in Table 5.

  About the obtained base material B1, various physical properties were measured by the said method. Moreover, about the obtained base material B1, adhesiveness and cushioning property were evaluated by the said method. The results obtained are shown in Table 5.

[Examples and Comparative Examples]
(Separator S1)
96.0 parts by mass of aluminum hydroxide oxide (average particle size: 1.0 μm), 4.0 parts by mass of aqueous dispersion A1, and 1.0 part by mass of aqueous ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) Were uniformly dispersed in 100 parts by mass of water to prepare a coating solution, and coated on the surface of the polyolefin resin porous membrane B1 using a micro gravure coater. Water was removed by drying at 60 ° C., and a porous layer was formed with a thickness of 2 μm to obtain a separator S1.

(Separators S2 to S26)
Separators S2 to S26 were obtained in the same manner as the separator S1, except that the aqueous dispersion was changed as shown in Table 6.

(Separator T1)
A water dispersion A4 was applied to the surface of the separator S1 on which inorganic particles were present with a micro gravure coater at 60 ° C., and then dried to remove water to obtain a separator T1. In this separator, the surface coverage of the polymer layer was 30%, and the basis weight of the polymer layer was 1 g / m ² .

(Separators T2 to T26)
Similarly to the separator T1, the aqueous dispersion A4 was applied to the separators S2 to S26 to obtain separators T2 to T26.

  Table 6 shows the evaluation results of the separators.

(Evaluation results)
As shown in the table, the separators T1 to T24 obtained using the separators S1 to S24 have higher adhesion between the inorganic particles and the substrate than the separators T25 and T26 obtained using the separators S25 and S26. And high adhesion to the electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for electrical storage devices which is excellent also in the outstanding adhesiveness between a base material and inorganic particle, and also the adhesiveness with an electrode can be provided. Therefore, the present invention is useful as a separator for an electricity storage device such as a battery such as a non-aqueous electrolyte secondary battery, a capacitor, and a capacitor, and has industrial applicability in these fields.

Claims (8)

A base material, and a porous layer disposed on at least one side of the base material,
The porous layer includes inorganic particles and a copolymer binder,
The swelling degree of the copolymer binder with respect to the mixed solvent containing 2 parts by mass of ethylene carbonate and 3 parts by mass of diethyl carbonate is 1.5 times or less.
Electric storage device separator. The copolymer binder includes a cycloalkyl group-containing monomer unit,
The separator for an electricity storage device according to claim 1, wherein the content of the cycloalkyl group-containing monomer unit is 15 to 50% by mass with respect to 100% by mass of the copolymer binder. The copolymer binder includes the cycloalkyl group-containing monomer unit, a (meth) acrylic acid ester monomer unit having an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group,
The total content of the cycloalkyl group-containing monomer unit and the (meth) acrylic acid ester monomer unit is 80 to 99.9% by mass with respect to 100% by mass of the copolymer binder. Item 3. The electricity storage device separator according to Item 1 or 2.   The separator for an electricity storage device according to claim 2 or 3, wherein the cycloalkyl group-containing monomer unit includes a cyclohexyl acrylate unit and / or a cyclohexyl methacrylate unit.   The electrical storage device separator according to any one of claims 1 to 4, wherein the degree of swelling of the copolymer binder with respect to toluene is 6 times or more.   The electrical storage device separator according to any one of claims 1 to 5, wherein the substrate is a polyolefin microporous membrane.   An electrical storage device provided with the electrical storage device separator of any one of Claims 1-6.   A lithium ion secondary battery provided with the separator for electrical storage devices of any one of Claims 1-6.

Images