WO2015076571A1 - Separator coating agent composition, separator formed of coating agent composition, and battery using same - Google Patents

Abstract

The present invention relates to a separator which comprises a polyolefin-based base film, and a coating layer which is formed on one surface or both surfaces of the base film and contains an organic binder and inorganic particles, wherein the organic binder comprises an acryl-based copolymer having a (meth)acrylate monomer-derived repeat unit and an acetate group-containing monomer-derived repeat unit; to a separator coating agent composition; and to an electrochemical battery comprising the separator.

Description

Separator coating composition, separator formed of the coating composition and a battery using the same

The present invention relates to a membrane coating composition. The present invention also relates to a separator coated with the coating composition and an electrochemical cell using the same.

A separator for an electrochemical cell refers to an interlayer membrane which maintains ionic conductivity while separating an anode and a cathode from each other in a cell, thereby allowing the battery to be charged and discharged.

In recent years, as the stability of the battery has risen, the role of the separator to prevent short circuit between the anodes with respect to these characteristics has been dealt with important. In general, polyolefin-based fabrics used are severely heat-shrinkable at high temperatures and physically poor in durability. Therefore, when an abnormality occurs in the battery and the internal temperature is increased, deformation of the separator is likely to occur, and in severe cases, an explosion may occur. Therefore, improvement of heat resistance and shrinkage resistance related to high temperature stability is an important factor in the development of the separator. In relation to improving the heat resistance of the separator, a non-woven separator prepared by processing heat-resistant polymer into a fibrous shape, a ceramic separator made by connecting inorganic particles using a small amount of binder, and a coated separator coated with ceramic and binder on existing polyolefin or nonwoven fabrics. (Korean Registered Patent No. 10-0775310) and the like are in progress. Recently, since there is a limitation on the thickness of the coating layer due to the thickness limitation of the separator, a study for securing physical properties through a thinner coating layer is being conducted.

The present invention is to provide a coating separator that is prevented from shrinking in the battery and improved heat resistance and shape stability.

According to an embodiment of the present invention, an organic binder comprising an acrylic copolymer comprising a (meth) acrylate-based monomer-derived repeating unit and an acetate group-containing monomer-derived repeating unit; Inorganic particles; And there is provided a membrane coating composition comprising a solvent.

According to another embodiment of the present invention, a polyolefin-based substrate film, and a coating layer comprising an organic binder and inorganic particles, formed on one or both sides of the base film, the organic binder is a (meth) acrylate monomer-derived repeat There is provided a separator comprising an acrylic copolymer comprising a unit and a repeating unit derived from an acetate group-containing monomer.

According to another embodiment of the present invention, a separator comprising a polyolefin-based substrate film and a coating layer comprising an organic binder and inorganic particles, formed on one or both sides of the substrate film, is placed between the anode and the cathode at 100 ℃ After pressing for 10 seconds at a pressure of 20kgf / cm ² to 100kgf / cm ^2, the membrane is provided with a separation shrinkage of 10% or less in the MD and TD directions when left at 130 ° C. for 10 minutes.

According to another embodiment of the present invention, an electrochemical cell, particularly a lithium secondary battery, including the separator according to the above example is provided.

The separator according to the present invention has the effect of preventing shrinkage in the battery and improving heat resistance. In addition, the separator according to the present invention is further excellent in physical properties such as air permeability and mechanical strength.

Hereinafter, the present invention will be described in more detail. The content not described in the present specification may be sufficiently recognized and inferred by those skilled in the art or similar fields of the present invention, and thus description thereof is omitted.

The separator according to an embodiment of the present invention includes a base film, and a coating layer formed on one side or both sides of the base film.

The base film may be a polyolefin-based. The polyolefin-based substrate film has an excellent shut down function and may contribute to improvement of safety of the battery. The polyolefin-based substrate film may be selected from the group consisting of, for example, polyethylene monolayer, polypropylene monolayer, polyethylene / polypropylene double membrane, polypropylene / polyethylene / polypropylene triple membrane, and polyethylene / polypropylene / polyethylene triple membrane. . The polyolefin based film may have a thickness of 1 to 40 μm, specifically 5 μm to 15 μm. When using the base film within the thickness range, it is possible to produce a separator having a suitable thickness, thick enough to prevent a short circuit between the positive and negative electrodes of the battery, but not thick enough to increase the internal resistance of the battery.

The coating layer may be formed of a coating composition, the coating composition may include an organic binder, inorganic particles, and a solvent.

Specifically, the organic binder may be an acrylic copolymer, and for example, may be an acrylic copolymer including a (meth) acrylate-based monomer-derived repeating unit and an acetate group-containing monomer-derived repeating unit. By using an acrylic copolymer having a (meth) acrylate-based monomer-derived repeating unit and an acetate group-containing monomer-derived repeating unit as a binder, it is possible to prevent shrinkage of the membrane and improve heat resistance in a battery in which the separator is actually used. have. In general, the heat resistance of the separator is applied to the separator itself under constant conditions, and in each of the longitudinal direction (hereinafter referred to as 'MD direction') and width direction (hereinafter referred to as 'TD direction') of the separator before and after heating. The degree of shrinkage is evaluated. However, the heat resistance evaluated as described above does not properly reflect the heat shrinkage stability in the environment in which the actual separator is used, and does not match the actual shape stability of the separator in the battery. Therefore, it is necessary to arrange the separator between the electrodes in the battery and to evaluate the heat resistance and shrinkage in the compressed state. When an acrylic copolymer including a (meth) acrylate-based monomer-derived repeating unit and an acetate group-containing monomer-derived repeating unit is used as a binder, the acrylic copolymer improves the adhesion between the electrode and the separator, and the adhesive strength increases the heat resistance. There is an effect to promote and prevent the shrinkage of the separator. That is, the shape stability of the separator in the battery is improved, thereby improving the safety of the battery.

The glass transition temperature (Tg) of the acrylic copolymer may be less than 100 ℃, for example, 20 to 60 ℃. Within this range, the separator may be positioned between the electrodes and formed to have good adhesion at a temperature at which the separator is pressed, thereby improving the shrinkage rate and improving heat resistance.

The acrylic copolymer having a (meth) acrylate-based monomer-derived repeating unit and an acetate group-containing monomer-derived repeating unit which can be used herein may be capable of forming a good adhesive force at a temperature compressed between the anode and the cathode as described above. Although not particularly limited, for example, the acrylic copolymer may include at least one selected from the group consisting of butyl (meth) acrylate, propyl (meth) acrylate, ethyl (meth) acrylate and methyl (meth) acrylate ( It may be a copolymer produced by polymerizing a meth) acrylate-based monomer and at least one acetate group-containing monomer selected from the group consisting of vinyl acetate and allyl acetate.

The acetate group-containing monomer-derived repeating unit may be a repeating unit of Formula 1:

 [Formula 1]

In Chemical Formula 1,

R ₁ is a single bond, straight or branched alkyl of 1 to 6 carbon atoms, R ₂ is hydrogen or methyl, and l is an integer between 1 and 100, respectively.

The acrylic copolymer is a (meth) acrylate monomer and an acetate group-containing monomer, for example, vinyl acetate and / or allyl acetate in a molar ratio of 3: 7 to 7: 3, specifically 4: 6 to 6: 4 More specifically, by polymerization in a ratio of about 5: 5. The acrylic copolymer may include, for example, a butyl (meth) acrylate monomer, a methyl (meth) acrylate monomer, and a vinyl acetate and / or allyl acetate monomer, in a weight ratio of 3 to 5: 0.5 to 1.5: 4 to 6, specifically It may be prepared by a polymerization reaction of 4: 1: 5.

The inorganic particles used in the present invention are not particularly limited and may be inorganic particles commonly used in the art. Non-limiting examples of the inorganic particles usable in the present invention include Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Ga ₂ O ₃ , TiO ₂ , SnO ₂ , and the like. These can be used individually or in mixture of 2 or more types. As the inorganic particles used in the present invention, for example, Al ₂ O ₃ (alumina) can be used.

The size of the inorganic particles used in the present invention is not particularly limited, but the average particle diameter may be 1 nm to 2,000 nm, for example, 100 to 1,000 nm, 300 nm to 500 nm. In the case of using the inorganic particles in the size range, it is possible to prevent the dispersibility and coating processability of the inorganic particles in the coating liquid to be lowered and the thickness of the coating layer is appropriately adjusted to prevent the reduction of mechanical properties and increase of electrical resistance. Can be. In addition, the size of the pores generated in the separator is appropriately adjusted, there is an advantage that can lower the probability of the internal short circuit occurs during the charge and discharge of the battery.

In preparing the coating composition, the inorganic particles may be used in the form of an inorganic dispersion in which it is dispersed in a suitable solvent. The appropriate solvent is not particularly limited and may be a solvent commonly used in the art. Acetone can be used as a suitable solvent for dispersing the inorganic particles, for example. The inorganic dispersion may be prepared by a conventional method without any particular limitation. For example, Al ₂ O ₃ may be added to acetone in an appropriate amount, and the inorganic dispersion may be milled and dispersed using a bead mill. Dispersions can be prepared.

The inorganic particles in the coating layer may be included in 70 to 99% by weight, specifically 75 to 95% by weight, more specifically 80 to 90% by weight based on the total weight of the coating layer. When the inorganic particles are contained within the above range, the heat dissipation characteristics of the inorganic particles may be sufficiently exhibited, and when the separator is coated using the inorganic particles, heat shrinkage of the separator may be effectively suppressed.

Non-limiting examples of the solvent usable in the present invention include dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), dimethyl carbonate (Dimethyl carbonate, DMC). ) Or N-methylpyrrolidone (N-Methyl pyrrolydone, NMP). The content of the solvent may be 20 to 99% by weight, specifically 50 to 95% by weight, and more specifically 70 to 95% by weight based on the weight of the coating composition. When the solvent is contained in the above range, the coating agent may be easily prepared, and the drying process of the coating layer may be performed smoothly.

Hereinafter, a separator and a coating composition according to another embodiment of the present invention will be described. The coating layer and the coating composition according to the present embodiment is distinguished from the embodiment of the present invention in that another binder is added in addition to the acrylic copolymer. By including another binder in addition to the acrylic copolymer, the adhesive force and heat resistance can be further improved. This will be described below with reference to other binders added.

Examples of binders added in addition to the acrylic copolymers include polyvinylidene fluoride (PVdF) homopolymers, polyvinylidene fluoride-Hexafluoropropylene copolymers (PVDF-HFP), and polymethyl Methacrylate (polymethylmethacrylate, PMMA), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyvinylacetate (PVAc), polyethylene oxide (PEO), cellulose acetate (cellulose acetate, CA), cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), cyanoethylpullulan (CYEPL), cyanoethylpolyvinyl alcohol ( cyanoethylpolyvinylalcohol (CR-V), cyanoethylcellulose (CEC), Single or a mixture thereof selected from the group consisting of cynoethylsucrose, pullulan, carboxyl methyl cellulose (CMC), and acrylonitrilestyrene-butadiene copolymer Can be mentioned. The weight ratio of the acrylic copolymer and the added binder may be 9: 1 to 3: 7, specifically 9: 1 to 5: 5, and more specifically 8: 2 to 6: 4. Within this range, the shape stability may be further improved, and thus manufacturing of a battery having high efficiency charge and discharge characteristics may be possible. For example, when the PVdF-based binder is further included, the PVdF-based binder may have a weight average molecular weight (Mw) of 500,000 to 1,500,000 (g / mol). In addition, the PVdF-based binder may use, for example, PVdF-HFP or PVdF homopolymer. In addition, the PVdF-based binder may use a weight average molecular weight of 1,000,000 g / mol or more. Moreover, you may mix and use 2 or more types from which a weight average molecular weight differs. For example, one or more types of weight average molecular weights of 1,000,000 g / mol or less and one or more types of 1,000,000 g / mol or more can be mixed and used. The use of the PVdF-based binder within the above molecular weight range enhances the adhesion between the coating layer and the polyolefin-based substrate film, thereby effectively suppressing shrinkage of the polyolefin-based substrate film, which is weak to heat, and further improving the separation membrane with sufficient electrolyte impregnation. It can be manufactured and by using this has the advantage that can produce a battery with efficient electrical output.

Membrane in accordance with embodiments of the present invention is to position the membrane between the anode and the cathode, when On the 100 ℃ 10 chogan pressure pressed into the 20kgf / cm ² to 100kgf / cm ² eseo 130 ℃ to stand for 10 minutes MD and TD Directional compression shrinkage may be less than 10% each. Specifically, it may be 5% or less, and more specifically 3% or less. Since the compression shrinkage rate is low, heat resistance and shrinkage of the separator are improved in an environment in which the separator is used, thereby improving the safety of the battery. That is, it is possible to provide a separation membrane having excellent shape stability.

The method of measuring the compression shrinkage of the separator is as follows:

Membrane samples were prepared in 50 mm x 50 mm lengths, and the positive and negative electrodes were cut into 55 mm x 55 mm, respectively, and the aluminum pouches used for cell production were cut into 6 cm x 6 cm. do. The anodes, separators, and cathodes are then placed in order and placed in half folded aluminum pouches. The sample is pressed at 100 ° C. for 10 seconds at a pressure of 20 kgf / cm ² to 100 kgf / cm ² , and then left at 130 ° C. for 10 minutes to obtain shrinkage.

Separation membrane according to embodiments of the present invention may be less than 500 sec / 100cc, specifically 50 to 400 sec / 100cc, more specifically 50 to 300 sec / 100cc. The tensile strength in the MD direction of the separator according to the embodiments of the present invention may be 1750 kg / cm ² or more, and the tensile strength in the TD direction may be 1650 kg / cm ² or more, specifically 1700 kg / cm ^{2 or} more.

Separation membrane according to the embodiments of the present invention is excellent in mechanical properties without lowering the air permeability despite excellent compression shrinkage.

Hereinafter, a method of manufacturing a separator according to an embodiment of the present invention will be described. Method for producing a separator according to an embodiment of the present invention is a repeating unit derived from the (meth) acrylate monomers on one or both sides of the polyolefin-based substrate film, and repeating units derived from an acetate group-containing monomer, such as vinyl acetate or allyl acetate monomer A binder comprising an acrylic copolymer having a; Inorganic particles; And forming a coating layer with a coating composition comprising a solvent.

First, forming the coating composition may include mixing a binder, a solvent, and an inorganic particle including an acrylic copolymer and stirring at 10 to 40 ° C. for 30 minutes to 5 hours. At this time, the content of the solid content may be 10 to 20 parts by weight based on the coating composition, the weight ratio of the binder and the inorganic particles in the solid content may be 3: 7 to 0.1: 9.9.

Alternatively, a coating composition may be prepared by preparing an inorganic dispersion in which the inorganic particles are dispersed in a dispersion medium, and mixing the mixture with a polymer solution containing a binder and a solvent including an acrylic copolymer. When the inorganic dispersion is prepared separately as described above, the dispersibility and crude liquid stability of the inorganic particles and the binder may be improved. Thus, in another embodiment, in preparing the coating composition of the present invention, the binder component and the inorganic particles may each be prepared and mixed in a dissolved or dispersed state in a suitable solvent.

For example, an acrylic copolymer, a polyvinylidene fluoride homopolymer, and / or a polyvinylidene fluoride-hexafluoropropylene copolymer are prepared by dissolving each in an appropriate solvent, and an inorganic dispersion in which inorganic particles are dispersed. The coating composition can then be prepared by mixing them with a suitable solvent. A ball mill, a beads mill, a screw mixer, or the like may be used for the mixing.

Subsequently, a coating layer is formed of the coating composition on one or both surfaces of the polyolefin-based substrate film.

The method of coating the polyolefin-based substrate film using the coating agent is not particularly limited, and a method commonly used in the art may be used. Non-limiting examples of the coating method may include a dip coating method, a die coating method, a roll coating method, or a comma coating method. These may be applied alone or in combination of two or more methods. The coating layer of the separator of the present invention may be formed by, for example, a dip coating method.

The coating layer may have a thickness of 0.01 μm to 20 μm, specifically 1 μm to 10 μm, and more specifically 1 μm to 5 μm. Within the thickness range, it is possible to form a coating layer having a suitable thickness to obtain excellent thermal stability and adhesion, and to prevent the thickness of the entire separator from being too thick to suppress the increase in the internal resistance of the battery.

In the present invention, the coating layer may be dried by hot air, hot air, low humidity, vacuum drying, or a method of irradiating far infrared rays or electron beams. And the drying temperature is different depending on the type of the solvent, but can be dried at a temperature of approximately 60 ℃ to 120 ℃. The drying time also varies depending on the type of solvent, but may generally be dried for 1 minute to 1 hour. In embodiments, it may be dried for 1 minute to 30 minutes, or 1 minute to 10 minutes at a temperature of 90 ℃ to 120 ℃.

According to another aspect of the present invention, an electrochemical cell including a polyolefin-based porous separator including the coating layer and an anode and a cathode and filled with an electrolyte is provided.

The kind of the electrochemical cell is not particularly limited, and may be a battery of a kind known in the art.

Specifically, the electrochemical cell of the present invention may be a lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

The method for producing the electrochemical cell of the present invention is not particularly limited, and a method commonly used in the art may be used.

A non-limiting example of a method of manufacturing the electrochemical cell is as follows: A polyolefin-based separator comprising the coating layer of the present invention is placed between a positive electrode and a negative electrode of the battery, and then the battery is filled in such a manner as to fill an electrolyte solution. It can manufacture.

The electrode constituting the electrochemical cell of the present invention can be produced in a form in which the electrode active material is bound to the electrode current collector by a method commonly used in the technical field of the present invention.

Among the electrode active materials used in one embodiment of the present invention, the cathode active material is not particularly limited, and a cathode active material commonly used in the technical field of the present invention may be used. Non-limiting examples of the positive electrode active material include lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or a lithium composite oxide in combination thereof.

The negative electrode active material of the electrode active material used in one embodiment of the present invention is not particularly limited and may be a negative electrode active material commonly used in the technical field of the present invention.

Non-limiting examples of the negative electrode active material include lithium adsorption materials such as lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite (graphite) or other carbons, and the like. . The electrode current collector used in one embodiment of the present invention is not particularly limited, and an electrode current collector commonly used in the technical field of the present invention may be used.

Non-limiting examples of the positive electrode current collector material of the electrode current collector may be a foil made of aluminum, nickel or a combination thereof. Non-limiting examples of the negative electrode current collector material of the electrode current collector may be a foil produced by copper, gold, nickel, copper alloy or a combination thereof.

The electrolyte solution used in the present invention is not particularly limited and may be used an electrochemical cell electrolyte solution commonly used in the technical field of the present invention.

The electrolyte solution may be one in which a salt having a structure such as A ⁺ B ⁻ is dissolved or dissociated in an organic solvent. Non-limiting examples of A ⁺ include a cation consisting of an alkali metal cation such as Li ⁺ , Na ⁺ or K ⁺ , or a combination thereof. The B ^- Non-limiting examples of _{^{the, PF 6 -, BF 4 -}} , Cl -, Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF ₃ SO _{2) 2} ^- or _{C (CF 2 SO 2) 3} - anions, such as, or may be an anion consisting of a combination thereof. Non-limiting examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (Dipropyl carbonate, DPC), dimethyl sulfoxide (DMSO), acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran (Tetrahydrofuran, THF), N-methyl- 2-pyrrolidone (N-methyl-2-pyrrolidone, NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-Butyrolactone, GBL), etc. are mentioned. These may be used alone or in combination of two or more thereof.

Hereinafter, the present invention will be described in more detail by describing Examples, Comparative Examples, and Experimental Examples. However, the following Examples, Comparative Examples and Experimental Examples are merely examples of the present invention and should not be construed as being limited thereto.

Example

Example 1 Preparation of Coating Membrane

Acetone is an acrylic copolymer binder in which butyl methacrylate (BMA), methyl methacrylate (MMA), and vinyl acetate (Vinyl Acetate, VAc) are polymerized at a 4/1/5 molar ratio. Dissolved in the first binder solution of 5% by weight of solids and PVdF-based binder KF9300 (Kurehasa, Mw: 1,200,000 g / mol) in acetone and DMAc mixed solvent to dissolve a second binder solution of 7% by weight of solids, respectively. Prepared. Alumina dispersion was prepared by adding alumina (LS235, Nippon Light Metal) to acetone at 25% by weight and dispersing the beads for 3 hours. The first and second binder solutions and the alumina dispersion were mixed so that the weight ratio of the binder solid content and the alumina solid content was 1/6 so that the weight ratio of the acrylic binder and the PVdF binder was 7/3, and the total solid content was 10 weight. Acetone was added to make the coating solution. 12 μm thick polyethylene fabric (SK, Inc.) was coated on both sides of the coating solution with a thickness of 2 μm, respectively, to prepare a coating separator having a total thickness of about 16 μm.

Example 2: Preparation of Coating Membrane

5 wt% solution of an acrylic binder in which butyl methacrylate (BMA), methyl methacrylate (MMA) and vinyl acetate (VAc) were polymerized at a 4/1/5 molar ratio in acetone, and a PVdF binder KF9300 7 wt% solution dissolved in acetone, DMAc mixed solvent, and 10 wt% solution in which PVdF-HFP binder (21216 (Solbay), weight average molecular weight: 700,000 g / mol) were dissolved in acetone were prepared, respectively. Alumina dispersion was prepared by adding alumina (LS235, Nippon Light Metal) to acetone at 25% by weight and dispersing the beads for 3 hours. The binder solution and the alumina dispersion were mixed so that the weight ratio of the binder solid content and the alumina solid content was 1/5 such that the weight ratio of the acrylic binder and the KF9300, 21216 binder was 5/3/2, and the total solid content was 10% by weight. Acetone was added to prepare a coating solution. A coating separator of about 16 μm in total thickness was prepared by coating 2 μm thick with the coating solution on both sides of a 12 μm thick polyethylene fabric (SK).

Example 3: Preparation of Coating Membrane

Example 1, except that butyl methacrylate (BMA), methyl methacrylate (MMA) and allyl acetate (Allyl Acetate) as the acrylic binder was used in a molar ratio of 4/1/5. In the same manner as in the production of a coating separator having a total thickness of about 16 ㎛.

Example 4: Preparation of Coating Membrane

In Example 1, except that the molar ratio of butyl methacrylate (BMA), acrylonitrile (AN), and vinyl acetate 4/1/5 was used as the acrylic binder in the same manner as in Example 1 A coating separator having a total thickness of about 16 μm was prepared.

Example 5: Preparation of Coating Membrane

A separator was manufactured in the same manner as in Example 1, except that the weight ratio of the binder solids to the alumina solids was 1/6 by using only the acrylic copolymer binder without using the PVdF-based binder.

Comparative Example 1: Preparation of Coating Separator

A 7 wt% solution in which KF9300, a PVdF-based binder, was dissolved in acetone and DMAc mixed solvent, and a 10 wt% solution, in which 21216 binder was dissolved in acetone, were prepared. Alumina dispersion was prepared by adding alumina (LS235, Nippon Light Metal) to acetone at 25% by weight and dispersing the beads for 3 hours. The binder solution and the alumina dispersion were mixed so that the weight ratio of the binder solid content and the alumina solid content was 1/6 so that the weight ratio of the KF9300 and 21216 binders was 5/5, and acetone was added so that the total solid content was 11% by weight. A coating solution was prepared. A coating separator having a total thickness of about 16 μm was prepared using a coating solution of polyethylene fabric (SK) having a thickness of 12 μm.

Comparative Example 2: Preparation of Separator

In Example 1, except that polybutyl methacrylate (PBMA) was used as the acrylic binder was carried out in the same manner as in Example 1 to prepare a coating separator having a total thickness of about 16 ㎛.

Comparative Example 3: Preparation of Separator

In Comparative Example 3, a polyethylene fabric (SK company) having a thickness of 12 um which was the same as that used in Comparative Example 1 was used without coating.

The composition of each membrane or membrane coating according to Examples 1 to 5 and Comparative Examples 1 to 3 is shown in Table 1 below.

Table 1

	Fabric / thickness (㎛)	Binder composition		Inorganic Particle Content in Coating Layer
Example 1	PE / 12	Acrylic / PVdF binder, 70/30%	BMA + MMA + VAc	86 wt%
Example 2	PE / 12	Acrylic / PVdF binder + PVdF-HFP, 50/50%	BMA + MMA + VAc	83% by weight
Example 3	PE / 12	Acrylic / PVdF binder, 70/30%	BMA + MMA + allyl Ac	86 wt%
Example 4	PE / 12	Acrylic / PVdF binder, 70/30%	BMA + AN + VAc	86 wt%
Example 5	PE / 12	Acrylic, 100%	BMA + MMA + VAc	86 wt%
Comparative Example 1	PE / 12	PVdF binder + PVdF-HFP, 100%		86 wt%
Comparative Example 2	PE / 12	PBMA / PVdF binder, 70/30%		86 wt%
Comparative Example 3	PE / 12	-		-

Experimental Example

Air permeability by the measurement method described below for the separator prepared in Examples 1 to 5 and Comparative Examples 1 to 3; The tensile strength; Shrinkage in the cathode, separator and cathode structures during non-compression and compression was measured and the results are shown in Table 2.

TABLE 2

		Example 1	Example 2	Example 3	Example 4	Example 5	Comparative Example 1	Comparative Example 2	Comparative Example 3
Thickness (㎛)		16	16	16	16	16	16	16	12
Breathability (sec / 100cc)		198	195	291	202	183	209	1320	140
Tensile strength (kgf / cm 2 )	MD	1790	1794	1786	1803	1750	1807	1792	1765
	TD	1713	1705	1698	1712	1684	1709	1713	1680
Non-compression shrinkage%) (130 ° C, left for 10 minutes)	MD	16	15	17	18	19	13	16	24
	TD	11	10	12	12	15	8	11	23
Crimp shrinkage (%) (100 ℃, 10 seconds, 20kgf / cm 2 compression, 130 ℃, left for 10 minutes)	MD	2	One	2	2	2	15	4	24
	TD	2	One	One	2	One	8	2	22

1. Breathability

Each of the separators prepared in the above Examples and Comparative Examples was prepared to cut 10 samples cut at 10 different points to a size of 1 inch (1 inch) in diameter, and then the air permeability measuring device (Asahi Seiko) G) was used to measure the time for passage of 100 cc of air in each sample. The time was measured five times each, and then the average value was calculated as air permeability.

2. Tensile Strength

Each of the separators prepared in Examples and Comparative Examples was cut into five pieces in a rectangular shape of 50 mm long by 150 mm long by 150 mm long by MD, and 150 mm long by 50 mm wide by 50 mm TD. Ten samples were prepared, and each sample was mounted on a UTM (tension tester) to bite to a measurement length of 20 mm, and then the sample was pulled to measure average tensile strength in the MD and TD directions.

3. Compression and non-compression shrinkage in anode, separator and cathode structures

Each of the separators prepared in Examples and Comparative Examples was 50 mm long by 50 mm long by TD. The positive electrode (lithium cobalt oxide) cathode / binder styrene-butadiene rubber (SBR) + carboxymethyl cerule Rhodes (CMC) / conductor (carbon black) = 95 / 2.5 / 2.5) and cathode (natural graphite, cathode active material / binder (styrenebutadiene rubber (SBR) + carboxymethylcellulose (CMC) 5%) Cut carbon black = 98/1/1) into 55 mm × 55 mm each and prepare. The aluminum pouches used for battery production are cut into 6 cm x 6 cm and prepared. The anodes, separators, and cathodes are then placed in order and placed in half folded aluminum pouches.

The compression shrinkage is indicated by 5 points at regular intervals on the membrane, pressurized at 20 kgf / cm ² for 10 seconds at 100 ° C., left at 130 ° C. for 10 minutes, and then measured by the contracted length between the gaps. The compression shrinkage was obtained.

The non-compression shrinkage was measured for 10 minutes after leaving the membrane sample in an oven at 130 ℃ to measure the shrinkage of the membrane.

As can be seen in Table 2, in the case of Comparative Example 3, which is a membrane fabric without a coating layer formed, it shows a large shrinkage regardless of the presence or absence of compression, and in Comparative Example 1 or 2, the degree of shrinkage at the time of compression and non-compression is Similar. On the other hand, in the case of the separation membrane of Examples 1 to 5 containing the (meth) acrylate-based repeating unit and the acryl-based copolymer containing an acetate group-containing monomer derived repeating unit, the compression shrinkage is significantly reduced compared to the non-compression shrinkage rate Can be.

Claims (13)

1. Polyolefin base film, and

   It includes a coating layer comprising an organic binder and inorganic particles, formed on one side or both sides of the base film,

   The organic binder comprises a (meth) acrylate monomer-derived repeating unit, and an acrylic copolymer comprising an acetate group-containing monomer-derived repeating unit, separation membrane.
2. The separation membrane according to claim 1, wherein the acetate group-containing monomer-derived repeating unit is a single unit derived from one or more monomers of vinyl acetate and allyl acetate.
3. The separation membrane according to claim 1 or 2, wherein the glass transition temperature of the acrylic copolymer is less than 100 ° C.
4. The separator according to any one of claims 1 to 3, wherein the inorganic particles are 70 to 99% by weight based on the total weight of the coating layer.
5. The polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethylmethacrylate, polyacrylonitrile according to any one of claims 1-4. , Polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose Separation membrane further comprises a binder selected from the group consisting of pullulan, carboxyl methyl cellulose, and acrylonitrile styrenebutadiene copolymer.
6. The repeating unit derived from the (meth) acrylate monomer is butyl (meth) acrylate, propyl (meth) acrylate, ethyl (meth) acrylate and methyl according to any one of claims 1 to 5. Separation membrane which is a repeating unit derived from at least one monomer selected from the group consisting of (meth) acrylates.
7. The said acrylic copolymer is manufactured by superposing | polymerizing the said (meth) acrylate type monomer and the said acetate group containing monomer in molar ratio 3: 7-7: 3. , Separator.
8. Polyolefin base film, and

   It includes a coating layer comprising an organic binder and inorganic particles, formed on one or both sides of the base film,

   When the separator between the positive electrode and the negative electrode was pressed at 100 ° C. for 10 seconds at a pressure of 20 kgf / cm ² to 100 kgf / cm ² , and then left at 130 ° C. for 10 minutes, the compression shrinkage was 10% or less in the length and width directions of the separator, respectively. ,

   Separation membrane of the separation membrane is less than 500 sec / 100cc.
9. The separator according to claim 8, wherein the tensile strength in the MD direction of the separator is 1750 kg / cm ² or more, and the tensile strength in the TD direction is 1650 kg / cm ² or more.
10. The separation membrane according to claim 8 or 9, wherein the organic binder comprises an acrylic copolymer comprising a (meth) acrylate-based repeating unit and an acetate group-containing monomer-derived repeating unit.
11. The polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethylmethacrylate, polyacrylonitrile according to any one of claims 8 to 10. , Polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose Separation membrane further comprises a binder selected from the group consisting of pullulan, carboxyl methyl cellulose, and acrylonitrile styrenebutadiene copolymer.
12. An electrochemical cell comprising the separator according to any one of claims 1 to 11.
13. The electrochemical cell of claim 12, wherein the electrochemical cell is a lithium secondary battery.