JP2013203894A - Polyolefin microporous membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for electric storage device, which is adhesive and excellent in handling property in winding and transparency.SOLUTION: A separator for electric storage device includes an adhesive polymer applied to at least one surface of a polyolefin microporous membrane, and contains 0.1 mg/mor more and 100/mor less of a surfactant.

Description

  The present invention relates to a polyolefin microporous membrane and an electricity storage device separator.

In recent years, power storage devices such as lithium ion secondary batteries and electric double layer capacitors (including those called lithium ion capacitors and non-aqueous lithium power storage elements) have been actively developed. In a power storage device, a microporous membrane (separator) is usually provided between the positive and negative electrodes. Such a separator has a function of preventing contact between positive and negative electrodes and transmitting ions.
In recent years, as portable devices have become smaller and thinner, power storage devices such as lithium ion secondary batteries have been 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.
Here, the separator has a characteristic that the battery reaction is quickly stopped if it is abnormally heated (fuse characteristic), or a dangerous situation in which the positive electrode material and the negative electrode material react directly while maintaining the shape even at high temperatures. In addition to safety-related performances that have been conventionally required, such as performance to prevent (short characteristics), improvement in adhesion to electrodes is required 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, many attempts have been made to apply an adhesive polymer to a polyolefin microporous membrane as an attempt to give the separator an adhesive property (see, for example, Patent Documents 1 and 2).

Japanese Patent No. 3839706 JP 2007-59271 A

However, the microporous membranes described in Patent Documents 1 and 2 still have room for improvement from the viewpoints of handling properties and lithium ion permeability when winding the battery.
An object of the present invention is to provide a separator for an electricity storage device having adhesiveness with excellent handling and permeability during winding.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the above problem can be solved by blending a specific amount of a surfactant in a separator for an electricity storage device having adhesiveness, and the present invention is completed. It came to.

That is, the present invention is as follows.
[1]
A separator for an electricity storage device, wherein an adhesive polymer is applied to at least one surface of a polyolefin microporous membrane, and contains 0.1 mg / m ² or more and 100 / m ² or less surfactant.
[2]
Electric storage device separator according to [1], wherein the coating basis weight of the adhesive polymer is not more than 0.05 g / m ² or more 1.0 g / m ^2.
[3]
The separator for an electricity storage device according to any one of [1] to [2], wherein the water content is 300 ppm or less.
[4]
The porosity for the polyolefin microporous membrane is 35% or more and 60% or less, and the electricity storage device separator according to any one of [1] to [3].
[5]
The electrical storage device separator according to any one of [1] to [4], wherein the thickness of all layers is 5 μm or more and 25 μm or less.
[6]
The electrical storage device separator according to any one of [1] to [5], wherein the air permeability is 40 sec or more and 1000 sec or less.

  ADVANTAGE OF THE INVENTION According to this invention, the polyolefin microporous film suitable as a separator which can improve the cycling characteristics of an electrical storage device is provided.

  Hereinafter, the best mode for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

The separator for an electricity storage device of the present embodiment is coated with an adhesive polymer on at least one surface of a polyolefin microporous membrane, and further contains a surfactant of 0.1 mg / m ² or more and 100 / m ² or less. It is characterized by that.
Here, in the present embodiment, by adopting the configuration as described above, it is not clear why the separator having good adhesiveness in handling property at the time of winding can be realized, but it is assumed as follows. Is done.

  That is, in this embodiment, the surfactant present on the surface of the separator attracts moisture in the air that is electrically conductive, so that the electrical resistance is reduced and static electricity can be removed, and the surfactant is present on the surface of the adhesive polymer. This is considered to be because the surfactant that suppresses the fusion between the adhesive polymers at room temperature and the fusion between the adhesive polymer and the polyolefin microporous film.

As the surfactant in the present embodiment, a known surfactant used in general emulsion polymerization can be used. Anionic surfactants, nonionic surfactants, amphoteric surfactants, cationic surfactants and the like can be mentioned. Examples of the anionic surfactant include alkylbenzene sulfonates, sulfate esters of higher alcohols, aliphatic sulfonates, sulfate esters of polyethylene glycol alkyl ethers, and the like. Examples of the nonionic surfactant include polyethylene glycol alkyl esters, polyethylene glycol alkyl ethers, polyethylene glycol alkyl phenyl ethers, and the like. Examples of the cationic surfactant include alkyltrimethylammonium salts and dialkyldimethylammonium salts. Examples of the amphoteric surfactant include a carboxylic acid (salt), sulfonic acid (salt), phosphoric acid (salt), etc. as an anion moiety, and an amine (salt), a quaternary ammonium salt, etc. as a cation moiety. Specifically, betaines such as lauryl betaine and stearyl betaine; lauryl β-alanine, stearyl-β-alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine, etc. These amino acids are used. These other emulsifiers can be used alone or in admixture of two or more.
The content of the surfactant is preferably from 0.1 mg / m ^{2 to} 100 mg / m ² . More preferably, 0.2 mg / m ² or more 80 mg / m ^2, further preferably 1 mg / m ² or more 75 mg / m ² or less.
When the content of the surfactant is 0.1 mg / m ² or more and 100 mg / m ² or less, the handling property at the time of winding the microporous film is improved, while the gas generation at the time of charging / discharging of the battery is performed. It is preferable from the viewpoint of suppressing.

  Specific examples of adhesive polymers include, for example, polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene. Fluorinated rubbers such as copolymers, vinylidene fluoride-hexafluoropropylene tetrafluoroethylene copolymers, ethylene-tetrafluoroethylene copolymers; styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers, and Its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, (meth) acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer , Rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, Examples thereof include resins having a melting point and / or glass transition temperature of 180 ° C. or higher, such as polyamide and polyester.

Among these, (meth) acrylic acid ester copolymers are particularly preferable from the viewpoints of productivity and safety. Monomers for obtaining a (meth) acrylic acid ester copolymer include aromatic vinyl monomers, substituted or unsubstituted alkyl (meth) acrylates, vinyl cyanide monomers, vinyl acetate, Examples thereof include ethylenically unsaturated carboxylic acid monomers, acrylamide monomers, carboxylic acid vinyl esters, vinyl halides, amino group-containing ethylenic monomers, sodium styrenesulfonate, and the like. You may use it in combination of seed | species or 2 or more types.
Among these, as the aromatic vinyl monomer, for example, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-chlorostyrene, m-chlorostyrene, p- Examples include chlorostyrene, and styrene is particularly preferable. Examples of the substituted or unsubstituted alkyl (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, and n-butyl ( (Meth) acrylate, i-butyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) Alkyl (meth) acrylates such as acrylate, benzyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate; epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate Hydroxyalkyl (meth) acrylates such as 2-hydroxypropyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; alicyclic group-containing (meth) acrylates such as isobornyl (meth) acrylate; 2-cyanoethyl (meth) ) Cyano group-containing (meth) acrylates such as acrylates; amino group-containing (meth) acrylates such as 2-dimethylaminoethyl (meth) acrylate and 2-diethylaminoethyl (meth) acrylate; preferable. Furthermore, examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, vinylidene cyanide, and acrylonitrile is particularly preferable. Examples of the ethylenically unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid. Acrylic acid, itaconic acid, and fumaric acid are particularly preferable.

Adhesion amount for the microporous polyolefin membrane of the polymer, 0.05 g / m ² or more 1.0 g / m ² is preferred. More preferably 0.07 g / m ² or more 0.8 g / m ² or less, more preferably 0.1 g / m ² or more 0.7 g / m ² or less.
Setting the adhesion amount of the polymer to the polyolefin microporous membrane to be 0.1 g / m ² or more and 1.0 g / m ² or less improves the adhesive strength on the adherend, while the pores of the polyolefin microporous membrane are reduced. This is preferable from the viewpoint of suppressing a decrease in cycle characteristics (permeability) due to clogging.
The adhesion amount of the polymer to the polyolefin microporous membrane can be adjusted by changing the polymer concentration of the liquid to be applied and the coating amount of the polymer solution.

The water content of the microporous membrane is preferably 300 ppm or less, more preferably 250 ppm or less, and even more preferably 200 ppm or less.
The moisture content of the microporous membrane is preferably 300 ppm or less from the viewpoint of suppressing gas generation during charging / discharging of the battery.

  The method for applying the coating solution to the porous film 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 thereof include a coater method, a die coater method, a screen printing method, a spray coating method, and an ink jet coating.

  When the adhesive polymer is applied to the polyolefin microporous membrane, if the coating solution gets into the microporous membrane, the adhesive polymer fills the surface and the inside of the pores, resulting in a decrease in permeability. . Therefore, it is preferable to use a medium containing water as a main component as a medium for the coating solution. When water is used as the medium of the coating solution, the coating solution does not enter the inside of the microporous membrane, and the adhesive polymer is mainly present on the surface of the microporous membrane, so that the decrease in permeability is suppressed. It is preferable from the viewpoint. Moreover, ethanol, methanol, etc. can be mentioned as a medium which can be used together with water.

  Furthermore, it is preferable to perform a surface treatment on the surface of the porous film prior to coating, since it becomes easy to apply the coating liquid and the adhesion between the porous layer and the adhesive polymer is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous film. For example, corona discharge treatment method, plasma treatment method, mechanical surface roughening method, solvent treatment method, acid treatment method And an ultraviolet oxidation method.

  The method for removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film. For example, a method of drying at a temperature below the melting point while fixing the porous film, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for the adhesive polymer to coagulate the adhesive polymer and extracting the solvent at the same time, etc. Is mentioned.

Next, the porous film which has polyolefin resin as a main component is demonstrated.
In the porous film mainly composed of polyolefin resin, the polyolefin resin occupies 50% or more and 100% or less of the mass fraction of the resin component constituting the porous film from the viewpoint of shutdown performance when used as a separator for an electricity storage device. A porous film made of a polyolefin resin composition is preferred. The proportion of the polyolefin resin is more preferably 60% or more and 100% or less, and still more preferably 70% or more and 100% or less.

  The polyolefin resin refers to a polyolefin resin used for normal extrusion, injection, inflation, blow molding and the like, such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Homopolymers and copolymers, multistage polymers, and the like can be used. In addition, polyolefins selected from the group consisting of these homopolymers, copolymers and multistage polymers can be used alone or in combination.

  Representative examples of the polymer include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene. And ethylene propylene rubber.

When a polyolefin microporous membrane is used as a battery separator, it is particularly preferable to use a resin mainly composed of high-density polyethylene because of its low melting point and high strength.
Moreover, it is more preferable to use the porous film which consists of the resin composition containing the heat resistance improvement of a porous film, polypropylene, and polyolefin resin other than a polypropylene.

Here, the three-dimensional structure of polypropylene is not limited, and any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene may be used.
The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, and still more preferably from the viewpoint of achieving both heat resistance and a good shutdown function. It is 4-10 mass%.
In this case, the polyolefin resin other than polypropylene is not limited, and examples thereof include homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Can be mentioned. Specific examples include polyethylene, polybutene, and ethylene-propylene random copolymer.

When a polyolefin microporous membrane is used as a separator for an electricity storage device, etc., it is necessary to shut down due to thermal melting of the pore, and as a polyolefin resin other than polypropylene, low density polyethylene, linear low density polyethylene can be used. It is preferable to use polyethylene such as medium density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density measured according to JIS K 7112 of 0.93 g / cm ³ or more.

  The viscosity average molecular weight of the polyolefin resin is preferably from 30,000 to 12 million, more preferably from 50,000 to less than 2 million, and still more preferably from 100,000 to less than 1 million. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension during melt molding increases, moldability is improved, and the strength tends to increase due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12 million or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. Furthermore, when the multilayer porous membrane of the present embodiment is used as a separator for an electricity storage device, if the viscosity average molecular weight is less than 1 million, it tends to close a hole when the temperature rises and a good shutdown function tends to be obtained. preferable. For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the viscosity average molecular weight being less than 1 million Mixtures may be used.

Arbitrary additives can be contained in the polyolefin resin composition. Examples of such additives include polymers other than polyolefins; inorganic particles; antioxidants such as phenolic, phosphorous, and sulfur; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; Stabilizers; antistatic agents; antifogging agents; colored pigments and the like.
The total amount of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin composition.

  There is no restriction | limiting in the method of manufacturing the said porous film, A well-known manufacturing method is employable. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded and formed into a sheet shape, optionally stretched and then made porous by extracting the plasticizer, and a polyolefin resin composition is melt-kneaded to obtain a high draw rate. After extruding at a ratio, the polyolefin crystal interface is peeled off by heat treatment and stretching, the polyolefin resin composition and the inorganic filler are melt-kneaded and molded on a sheet, and then the polyolefin and inorganic filler are stretched And a method of making the structure porous by removing the solvent at the same time as solidifying the polyolefin by dissolving it in a poor solvent for the polyolefin after dissolving the polyolefin resin composition.

Hereinafter, as an example of a method for producing a porous film, a method for extracting a plasticizer after melting and kneading a polyolefin resin composition and a plasticizer to form a sheet will be described.
First, a polyolefin resin composition and a plasticizer are melt-kneaded. As the melt-kneading method, for example, polyolefin resin and other additives as required may be added to a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc. A method of introducing a plasticizer at a ratio of kneading and kneading. At this time, it is preferable that the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being added to the resin kneading apparatus. More preferably, only a part of the plasticizer is added in the pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading apparatus. By doing so, the dispersibility of the plasticizer is increased, and when stretching a sheet-like molded product of the melt-kneaded mixture of the resin composition and the plasticizer in the subsequent step, the film is stretched at a high magnification without breaking. can do.

  As the plasticizer, a non-volatile solvent capable of forming a uniform solution at a melting point or higher of the polyolefin can be used. Specific examples of such a non-volatile solvent include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin has high compatibility with polyethylene and polypropylene, and even when the melt-kneaded product is stretched, the interface peeling between the resin and the plasticizer does not easily occur. Therefore, uniform stretching tends to be easily performed. Therefore, it is preferable.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30 to 80 mass%, more preferably 40 to 70 mass%. When the mass fraction 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 improved. On the other hand, when the mass fraction is 30% by mass or more, even if the mixture of the polyolefin resin composition and the plasticizer is stretched at a high magnification, the polyolefin chain is not broken, and a uniform and fine pore structure is formed and the strength is also improved. Easy to increase.

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. As the heat conductor used for cooling and solidification, metal, water, air, plasticizer itself, or the like can be used. However, a metal roll is preferable because of high heat conduction efficiency. At this time, it is more preferable that the metal roll is sandwiched between the rolls, since the efficiency of heat conduction is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved. The die lip interval when extruding into a sheet form from a T die is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less. When the die lip interval is 400 μm or more, the mess and the like are reduced, and there is little influence on the film quality such as streaks and defects, and there is a tendency that film breakage and the like can be prevented in the subsequent stretching step. 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.

It is preferable to stretch the sheet-like molded body thus obtained. As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used, but biaxial stretching is preferred from the viewpoint of the strength of the porous film to be obtained. 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 porous film is not easily torn and has a high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, multiple stretching, and the like, and simultaneous biaxial from the viewpoint of improvement of puncture strength, uniformity of stretching, and shutdown property Stretching is preferred.
Here, simultaneous biaxial stretching means stretching in which stretching in the MD direction (machine direction of the microporous membrane) and stretching in the TD direction (direction crossing the MD of the microporous membrane at an angle of 90 °) are performed simultaneously. It refers to a method, and the draw ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching in the MD direction or TD direction is independently performed. When stretching is performed in the MD direction or TD direction, the other direction is unconstrained or constant length. It is assumed that it is fixed to

  The draw ratio is preferably in the range of 20 times or more and 100 times or less, more preferably in the range of 25 times or more and 50 times or less in terms of surface magnification. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction, preferably in the range of 4 to 10 times in the TD direction, 5 to 8 times in the MD direction, and 5 times in the TD direction. More preferably, it is in the range of 8 times or less. When the total area magnification is 20 times or more, there is a tendency that sufficient strength can be imparted to the resulting porous film. On the other hand, when the total area magnification is 100 times or less, film breakage in the stretching process is prevented, and high productivity is achieved. It tends to be obtained.

  Moreover, you may roll a sheet-like molded object. Rolling can be performed, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion. The rolling surface magnification is preferably greater than 1 and 3 or less, more preferably greater than 1 and 2 or less. When the rolling ratio is larger than 1, the plane orientation increases and the film strength of the finally obtained porous film tends to increase. On the other hand, a rolling ratio of 3 or less is preferable because the orientation difference between the surface layer portion and the center is small and a uniform porous structure tends to be formed in the thickness direction of the film.

  Next, the plasticizer is removed from the sheet-like molded body to form a porous film. As a method for removing the plasticizer, for example, a method of extracting the plasticizer by immersing the sheet-like molded body in an extraction solvent and sufficiently drying it can be mentioned. The method for extracting the plasticizer may be either a batch type or a continuous type. In order to suppress the shrinkage of the porous 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. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine such as hydrofluoroether and hydrofluorocarbon. Halogenated solvents; 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.

  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 formation of the porous film. 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.

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 .

About the separator for electrical storage devices of this embodiment, the puncture strength is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, and the upper limit is preferably 2000 g / 20 μm or less, more preferably 1000 g / 20 μm or less. . It is preferable to set the puncture strength to 240 g / 20 μm or more from the viewpoint of suppressing film breakage due to the dropped active material or the like during battery winding. Moreover, it is preferable also from a viewpoint of suppressing the concern which short-circuits by the expansion / contraction of the electrode accompanying charging / discharging. On the other hand, setting it to 2000 g / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating.
The puncture strength can be adjusted by adjusting the draw ratio and the draw temperature.

The porosity of the polyolefin microporous membrane serving as a substrate is preferably 20% or more, more preferably 35% or more, and the upper limit is preferably 90% or less, preferably 80% or less. Setting the porosity to 20% or more is preferable from the viewpoint of ensuring the permeability of the separator. On the other hand, it is preferable to set it as 90% or less from a viewpoint of ensuring piercing strength.
The porosity can be adjusted by changing the draw ratio.

The average pore diameter of the microporous membrane is preferably 0.1 μm or less, more preferably 0.09 μm or less, and the lower limit is preferably 0.01 μm or more. Setting the average pore diameter to 0.1 μm or less is preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity reduction.
The average pore diameter can be adjusted by changing the draw ratio.

  The thickness of the microporous membrane is preferably 2 μm or more, more preferably 5 μm or more, and the upper limit is preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. Setting the film thickness to 2 μm or more is preferable from the viewpoint of improving the mechanical strength. On the other hand, a thickness of 100 μm or less is preferable because the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.

The air permeability of the microporous membrane is preferably 10 Sec / 100 cc or more, more preferably 50 Sec / 100 cc or more, and the upper limit is preferably 1000 Sec / 100 cc or less, more preferably 500 Sec / 100 cc or less. Setting the air permeability to 10 sec / 100 cc or more is preferable from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, setting it to 1000 sec / 100 cc or less is preferable from the viewpoint of obtaining good charge / discharge characteristics.
The air permeability can be adjusted by changing the stretching temperature and the stretching ratio.

  The short circuit temperature, which is an index of heat resistance of the microporous membrane, is preferably 160 ° C. or higher, more preferably 160 ° C. or higher. Setting the short-circuit temperature to 160 ° C. or higher is preferable from the viewpoint of battery safety.

The microporous membrane is particularly useful as a power storage device separator using a non-aqueous electrolyte. An electricity storage device usually uses the above-described microporous membrane as a separator, and includes a positive electrode, a negative electrode, and an electrolytic solution.
In the electricity storage device, for example, the microporous membrane is prepared as a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m). -Separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are stacked in this order and wound into a circular or flat spiral shape to obtain a wound body, which is then housed in a battery can and further electrolyzed. It can be manufactured by injecting a liquid. In addition, the electricity storage device is manufactured through a process of laminating a flat plate in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, laminating with a bag-like film, and injecting an electrolyte solution. You can also.

  In addition, about the measured value of various parameters mentioned above, unless there is particular notice, it is a value measured according to the measuring method in the Example mentioned later.

  Next, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist. In addition, the physical property in an Example was measured with the following method.

(1) Viscosity average molecular weight (Mv)
Based on ASRM-D4020, the intrinsic viscosity [η] at 135 ° C. in a decalin solvent was determined, and Mv of polyethylene was calculated by the following equation.
[Η] = 0.00068 × Mv ^0.67
Mv of polypropylene was calculated from the following formula.
[Η] = 1.10 × Mv ^0.80
The Mv of the layer was calculated using the polyethylene equation.

(2) Film thickness (μm)
A 10cm x 10cm sample was cut out from the porous film or multilayer porous film, nine locations (3 points x 3 points) were selected in a lattice shape, and the film thickness was measured using a microthickness meter (Toyo Seiki Seisakusho Co., Ltd. type KBM). And measured at room temperature 23 ± 2 ° C. As for the film thickness, the average value of the measured values at nine locations was the film thickness (μm) of the porous film and multilayer porous film.

(3) Porosity (%)
A sample of 10 cm × 10 cm square was cut from the microporous membrane, its volume (cm ³ ) and mass (g) were determined, and calculated from these and the film density (g / cm ³ ) using the following formula.
Porosity (%) = (volume-mass / density of mixed composition) / volume × 100
In addition, the value calculated | required by calculation from the density and mixing ratio of each used polyolefin resin and an inorganic particle was used for the density of a mixed composition.

(4) Air permeability (sec / 100cc)
It measured with the Gurley type air permeability meter (made by Toyo Seiki) based on JIS P-8117.

(5) Puncture strength (g)
A piercing test was conducted under the conditions of a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec using a trademark, KES-G5 handy compression tester manufactured by Kato Tech, and the maximum piercing load was defined as the piercing strength (N). .

(6) Content of surfactant (mg / m ² )
Ten samples cut into 10 cm × 10 cm are immersed in 100 mL of purified water for 3 days, filtered, and the filtrate is collected. The water in the filtrate was completely dried, the weight of the residue was measured, and the content of the surfactant in the sample was measured from the following calculation formula.
Surfactant content (mg / m ² ) = weight of residue × 10

(7) Water content (ppm)
About 0.3 g was weighed and a sample placed in a glass bottle and allowed to stand for one day in a constant temperature and humidity state was measured using a Karl Fischer (MKA-610, manufactured by Kyoto Electronics Industry Co., Ltd.). Each sample was measured three times, and the average value was taken as the water content.

(8) Handling property Two samples were cut out so that the coated surfaces face each other and pressed at 25 ° C. and 1 MPa for 2 minutes. The pressed sample was cut into a width of 2 cm and a length of 5 cm, and the 180 ° peeling adhesive strength with a width of 20 mm was measured according to JIS Z 0237. A sample having a peel strength between samples of 5 kgf / cm ² or more was evaluated as “handling property ×× 5 kgf / cm ^2” .

(9) Gas generation test A laminate sheet was cut into a certain size and packed into a pack (6 cm × 8 cm) using an impulse sealer. Three samples cut to 10 cm × 10 cm were folded, inserted into a Lamipack, and vacuum-dried at 80 ° C. for 12 hours. An electrolytic solution (LIPASTE-E2MEC / PF1: manufactured by Toyama Pharmaceutical Co., Ltd.) (0.4 mL) was added and the opening of the Lamipack was sealed with a sealer.
This was stored in an oven set at 85 ° C. for 3 days, the weight before and after the test was measured, and the volume was calculated by the Archimedes method. The weight was converted by the density of water (20 ° C .: 0.9982 g / cm 3). (Archimedes method: F = -ρVg)
Gas generation amount = volume after test-volume before test Each sample was measured twice, and the average value of the gas generation amount was 1 mL or more and x was 1 mL or less.

a. 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 polyvinylidene fluoride (PVDF) 3 as a binder A slurry was prepared by dispersing 2% by mass 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 .
b. 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 ammonium salt of carboxymethyl cellulose and 1.7% by mass of styrene-butadiene copolymer latex as a binder in purified water. did. 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 .

(10) Adhesion test The positive electrode and the negative electrode are cut into a width of 20 mm and a length of 40 mm. An electrolyte 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 placed on this electrode to such an extent that the electrode was immersed, and a separator was stacked thereon. This laminated body is put in an aluminum zip and pressed at 80 ° C. and 10 MPa for 2 minutes, and then the laminated body is taken out and the separator is peeled off from the electrode. At this time, the case where the active material of the electrode adhered to the separator in an area of 30% or more was defined as adhesion ○, and the case where it was less than 30% was evaluated as x.

(11) Manufacturing example of coating liquid <Manufacture of acrylic emulsion>
[Production Example 1]
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 64 parts of water and 0.25 part of Perex SS-L (Sodium alkyldiphenyl ether disulfonate 45% manufactured by Kao) were charged. Furthermore, 0.15 parts of ammonium persulfate (2% aqueous solution) was added to the reaction vessel while maintaining the reaction vessel temperature at 80 ° C.
Five minutes after the addition, an emulsion prepared as follows was dropped from the dropping tank to the reaction vessel over 150 minutes.
Preparation of emulsion:
Methyl methacrylate (MMA) 24 parts, butyl acrylate (BA) 34 parts, acrylic acid (AA) 1.5 parts, n-dodecyl mercaptan (nDDM) 0.1 part, Plex SS-L 1.5 parts, ammonium persulfate An emulsion was prepared by mixing 0.15 part and 69 parts of water with a homomixer at 6000 rpm for 5 minutes.
After completion of the emulsified droplet dropping, the reaction vessel temperature was maintained at 80 ° C. for 60 minutes and then cooled to room temperature. Next, a 25% aqueous ammonia solution was added to the reaction vessel to adjust the pH to 8.0, water was further added to adjust the solid content to 40% by mass, and the resulting acrylic emulsion was used as a coating solution 1. . The calculated values of the glass transition temperature (Tg) of the acrylic resin in the obtained acrylic emulsion are shown in Table 1.

[Production Examples 2 to 14]
Except having set it as the kind and usage-amount of the raw material shown in Table 1, it carried out similarly to [Manufacture example 1], and obtained each coating liquid 2-14.

[Example 1]
14.25 parts by mass of high density polyethylene 1 having a viscosity average molecular weight of 250,000 and a melting point of 137 ° C., 14.25 parts by mass of high density polyethylene 2 having a viscosity average molecular weight of 700,000 and a melting point of 137 ° C., a viscosity average molecular weight of 400,000, a melting point of 163 1.5 parts by mass of polypropylene at 0 ° C. and 0.2 parts by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant are blended as raw materials. It was adjusted.
Each blend was charged through a twin screw extruder feeder with a caliber of 25 mL / D = 48. Furthermore, 68 parts by mass of liquid paraffin was injected into each extruder by side feed, adjusted so that the extrusion amount was 16 kg per hour, kneaded under the conditions of 200 ° C. and 200 rpm, Extruded under conditions. Immediately, the sheet was cooled and solidified with a cast roll adjusted to 40 ° C. to form a sheet having a desired thickness. This sheet was stretched 7 × 7 times at the same time as in Table 3 under the conditions shown in Table 3, and then immersed in methylene chloride to extract and dry the liquid paraffin, and stretched in the transverse direction by a tenter stretching machine. Thereafter, the stretched sheet was relaxed in the width direction and heat-treated to obtain a polyolefin microporous film. Table 3 shows the physical properties of the obtained microporous membrane.

  An adhesive separator was prepared using the base material A described in Table 2. A coating solution was prepared by uniformly dispersing 7.5 parts by mass of the coating solution shown in Table 1 in 92.5 parts by mass of water, and applied to the surface of the polyolefin resin porous film using a gravure coater. Water was removed by drying at 60 ° C. Furthermore, the other side was similarly coated with a coating solution and dried to obtain an electricity storage device separator. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Examples 2 to 6]
An electricity storage device separator was produced in the same manner as in Example 1 except that the coating liquids 2 to 6 in Table 1 were used. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Example 7]
A separator for an electricity storage device was produced in the same manner as in Example 1 except that the base material B and the coating liquid 7 shown in Table 2 were used. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Example 8]
The coating liquid 8 described in Table 1 was applied to the substrate A described in Table 2 by spraying. Water was removed by drying at 60 ° C. Furthermore, the other side was similarly coated with the coating liquid 8 and dried to obtain a separator for an electricity storage device. The physical properties of the obtained separator are shown in Table 1. When the coating state was confirmed with an electron microscope, the average particle size was 30 μm. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Example 9]
A separator for an electricity storage device was produced in the same manner as in Example 1 except that the coating 9 shown in Table 1 was used for the substrate C shown in Table 2. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Example 10]
A separator for an electricity storage device was produced in the same manner as in Example 1 except that the coating liquid 10 shown in Table 1 was used for the substrate D shown in Table 2. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Example 11]
A separator for an electricity storage device was produced in the same manner as in Example 1 except that the coating liquid 11 shown in Table 1 was used for the substrate E shown in Table 2. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Example 12]
A separator for an electricity storage device was produced in the same manner as in Example 1 except that the coating liquid 12 shown in Table 1 was used for the substrate F shown in Table 2. The physical properties and evaluation results of the obtained separator are shown in Table 3.

[Comparative Example 1]
The coating liquid 13 shown in Table 1 was extracted with flowing water for 7 days with a semipermeable membrane (Visking tube (pore diameter 5 nm)) to separate and remove aqueous substances, thereby obtaining an aqueous dispersion of polymer particles. Using this coating liquid, an electricity storage device separator was produced in the same manner as in Example 1. Table 4 shows the physical properties and evaluation results of the separators obtained.

[Comparative Example 2]
A separator for an electricity storage device was produced in the same manner as in Example 1 except that the coating liquid 14 shown in Table 1 was used for the substrate A shown in Table 2. Table 4 shows the physical properties and evaluation results of the separators obtained.

Claims (6)

A separator for an electricity storage device, wherein an adhesive polymer is applied to at least one surface of a polyolefin microporous membrane, and contains 0.1 mg / m ² or more and 100 / m ² or less surfactant. The separator for an electricity storage device according to claim 1, the coating basis weight of the adhesive polymer is characterized in that it is 0.05 g / m ² or more 1.0 g / m ² or less.   The separator for an electricity storage device according to claim 1, wherein the moisture content is 300 ppm or less.   The electrical storage device separator according to any one of claims 1 to 3, wherein the polyolefin microporous membrane has a porosity of 35% to 60%.   The electrical storage device separator according to any one of claims 1 to 4, wherein the thickness of all layers is 5 µm or more and 25 µm or less.   The separator for an electricity storage device according to any one of claims 1 to 5, wherein the air permeability is 40 sec or more and 1000 sec or less.