WO2015009055A1

WO2015009055A1 - Porous separator and manufacturing method therefor

Info

Publication number: WO2015009055A1
Application number: PCT/KR2014/006439
Authority: WO
Inventors: 이상호; 김기욱; 이정승; 장정수; 정준호; 조재현; 홍대현
Original assignee: 삼성에스디아이 주식회사
Priority date: 2013-07-17
Filing date: 2014-07-16
Publication date: 2015-01-22
Also published as: KR20150009856A; KR101627738B1

Abstract

The present invention relates to a method for manufacturing a porous separator, a porous separator manufactured by the manufacturing method, and an electrochemical cell comprising the separator, the manufacturing method comprising: melt-mixing and extruding a composition comprising a polymer resin and a plasticizer, thereby forming a sheet solidified by cooling; drawing the solidified sheet in the length direction at a temperature of T₁ and thereafter drawing the sheet in the width direction at a temperature of T₂; and extracting the plasticizer from the drawn sheet, wherein T₂-T₁ ≥ 20 °C.

Description

Porous Membrane and Method for Manufacturing the Same

The present invention relates to a porous membrane and a method of manufacturing the same.

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

In recent years, along with the trend of lightening and miniaturization of electrochemical cells for increasing the portability of electronic devices, there is a tendency to require high output large capacity batteries for use in electric vehicles. Accordingly, in the case of the separator for an electrochemical cell, it is required to reduce the thickness and light weight, and at the same time, it is required to have excellent form stability by heat for the production of a high capacity battery. In addition, in the separation membrane, permeability, mechanical strength, heat shrinkage rate, shutdown characteristics, meltdown characteristics, and the like are required.

As a method of improving the physical properties of the separator, optimization of raw material composition, stretching conditions, heat treatment conditions, and the like have been proposed. For example, Japanese Patent Laid-Open No. 2-94356 proposes a polymer resin microporous membrane for a lithium battery separator having good assembly processability and low electrical resistance, but the separator has insufficient strength due to its excessive surface pore size. There is.

The present invention aims to provide a porous membrane having improved characteristics such as cell permeability, such as cycle characteristics, battery life, and electrolyte productivity, as well as permeability and mechanical strength of the separator.

In addition, the present invention seeks to provide a separator having satisfactory tensile strength in high-speed winding of battery production, which is carried out for the purpose of cost reduction.

In addition, the present invention is to provide a porous membrane with a small change in membrane thickness change and air permeability change rate when the separator is pressed, a fast absorption rate of the electrolyte, mechanical properties such as strength, and improved air permeability.

According to one embodiment of the present invention, by melt-kneading and extruding a composition comprising a polymer resin and a plasticizer to form a cooled solidified sheet, and biaxially stretched the solidified sheet, the sheet at a temperature T ₁ in the longitudinal direction After drawing, the film is drawn at a temperature T _{2 in} the width direction, wherein T ₁ and T ₂ are T ₂ -T ₁ ≧ 20 ° C., and a method of manufacturing a porous separator is provided, which includes extracting a plasticizer from the drawn sheet. .

According to another embodiment of the present invention, the porosity (P%) of the porous separator is 40% to 70%, the air permeability (S sec / 100cc) of the porous separator is 100 sec / 100cc to 300 sec / 100cc, A porous separator is provided in which P and S satisfy 3000 ≦ S × P ≦ 7500.

According to another embodiment of the present invention, the thickness before heat compression of the porous membrane (T ₁ ) and the compression thickness change rate of the formula (T ₂ ) of the thickness (T ₂ ) after heating and compressing the separator at 90 ° C. under 2.2 MPa pressure for 5 minutes ( A porous separator having a T) of 20% or less is provided.

[Equation 1]

T = [T ₁ -T ₂ ] / T ₁ × 100

The present invention provides a separator having a large pore and a small pore together, the change in membrane thickness and air permeability when the membrane is pressurized is small, the absorption rate of the electrolyte is fast, excellent mechanical properties, permeability and heat shrinkage characteristics.

Method for producing a porous separator according to an embodiment of the present invention, forming a solidified sheet with a composition comprising a polymer resin and a plasticizer, biaxially stretched the solidified sheet, and then extracting a plasticizer from the stretched sheet Include.

First, forming the solidified sheet specifically includes melt kneading and extruding a composition containing a polymer resin and a plasticizer to form a cooled solidified sheet.

In addition to the polyolefin resin, the composition may be used in combination with other resins (eg, polyamide (PA), polyvinylidene fluoride (PVDF), polycarbonate (PC), polysulfone (Polysulfone, PSF)). , Etc.), inorganic particles, and the like. At this time, the polyolefin resin may be contained, for example, 50% by weight or more.

Specifically, one or two or more selected from the group consisting of ultra high molecular weight polyethylene, high molecular weight polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, high crystalline polypropylene, and polyethylene-propylene copolymer as polyolefin resin Can be used. Moreover, the copolymer of polyolefin and other resin (non-olefin resin) can be used.

The viscosity average molecular weight (Mv) of the high density polyethylene may be 1 × 10 ⁵ g / mol to 9 × 10 ⁵ g / mol, for example, 3 × 10 ⁵ g / mol to 6 × 10 ⁵ g / mol have. The viscosity average molecular weight of the ultrahigh molecular weight polyethylene may be 9 × 10 ⁵ g / mol or more, specifically 9 × 10 ⁵ g / mol to 5 × 10 ⁶ g / mol. For example, the high density polyethylene may be used alone or the ultra high molecular weight polyethylene may be used alone, or both the high density polyethylene and the ultra high molecular weight polyethylene may be used.

More specifically, the ultra high molecular weight polyethylene may be used in an amount of 30 wt% or less based on the weight of the polymer resin, and for example, a viscosity average molecular weight of 1 × 10 ⁵ g / mol to 9 × 10 ⁵ g / mol A polymer resin containing 70 wt% or more of phosphorus high density polyethylene and 30 wt% or less of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 9 × 10 ⁵ g / mol or more can be used. The polymer resin is advantageous because it can prepare a high strength separator. In addition, in the case of containing two or more kinds of the polymer resin, it is preferable to mix using at least one selected from the group consisting of Henschel mixer, Bambari mixer and French mixer.

The polymer resin may be included in an amount of 10% to 80% by weight, specifically 20% to 70% by weight, based on the total weight of the composition including the polymer resin and the plasticizer.

The plasticizer may be an organic compound that forms a single phase with the polymer resin at an extrusion temperature. Examples of plasticizers usable in embodiments of the invention include aliphatic or cyclic hydrocarbons such as liquid paraffin (or paraffin oil) such as nonane, decane, decalin, liquid paraffin (LP), paraffin wax; Phthalic acid esters such as dibutyl phthalate and dioctyl phthalate; Fatty acids having 10 to 20 carbon atoms, such as palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid; C10-C20 fatty acid alcohols, such as a palmitic alcohol, a stearic acid alcohol, and an oleic acid alcohol, etc. are mentioned. These can be used individually or in mixture of 2 or more types. Among the plasticizers can be used liquid paraffin. Liquid paraffin is harmless to the human body, has high boiling point and low volatile components, making it suitable for use as a plasticizer in the wet process. The plasticizer may be included in an amount of 30 wt% to 90 wt%, and specifically 40 wt% to 90 wt%, based on the total weight of the composition including the polymer resin and the plasticizer. Melting and kneading the composition containing the polymer resin and the plasticizer in this embodiment may be a method known to those skilled in the art, it may be to melt kneading the polymer resin and the plasticizer at a temperature of 150 ℃ to 250 ℃. The melt-kneaded composition may be injected into a twin screw extruder to extrude at 150 ° C to 250 ° C. The extruded polymer resin is then cooled using a casting roll of 20 ° C. to 80 ° C. or forcedly cooled by cold air injected from an air knife to crystallize the film to form a solidified sheet. The temperature of the cool air injected from the air knife may be -20 ℃ to 40 ℃.

Then, it is said that the biaxially oriented, comprises Specifically stretched at a temperature T ₂ in the transverse direction after stretching the sheet at a temperature T ₁ in the longitudinal direction. Here, T ₁ and T ₂ may be T ₂ -T ₁ ≥ 20 ° C. In the biaxial stretching, when the longitudinal stretching temperature (T ₁ ) is lowered by 20 ° C or more than the widthwise stretching temperature (T ₂ ), a deviation may occur in the longitudinal stretching length for each part due to the low stretching temperature. By stretching in the width direction, two or more kinds of pores having different average pore sizes can be formed in the separation membrane.

Specifically, it is possible to prepare a separator having two paper-like pores including first pores having an average pore size of 100 nm or less and second pores having an average pore size of more than 100 nm. The first pore is advantageous in terms of heat shrinkage rate, strength, electrolyte retention rate, and safety, and the second pore is advantageous in terms of electrolyte wettability and battery capacity. The separation membrane of this embodiment contains both the first pores and the second pores as described above, so that the change in membrane thickness and air permeability at the time of pressurization of the microporous membrane is small, the absorption rate of the electrolyte is fast, and the mechanical properties, permeability and heat shrinkage characteristics are excellent. Do. The longitudinal stretching temperature (T ₁₎ may be 80 ℃ to 110 ℃. Specifically, the longitudinal stretching temperature T ₁ may be 85 ° C. to 105 ° C., for example, 90 ° C. to 100 ° C.

The widthwise stretching temperature T ₂ may be 20 ° C. or more higher than the longitudinal stretching temperature T ₁ . Therefore, the widthwise stretching temperature T ₂ may be 100 ° C. to 140 ° C., specifically 105 ° C. to 135 ° C., for example, 110 ° C. to 130 ° C.

The draw ratios in the longitudinal direction and the width direction may be 5 to 10 times each independently. Specifically, the draw ratio may be 6 times to 9 times in the longitudinal direction, and 6 times to 9 times in the width direction. The draw ratios in the width direction and the longitudinal direction may be the same or different.

The plasticizer may be extracted after the biaxial stretching. The plasticizer extraction may be performed using an organic solvent, and in particular, the longitudinally stretched and widthwise stretched separators may be immersed in an organic solvent in the plasticizer extracting apparatus to extract a plasticizer. The organic solvent used for the plasticizer extraction is not particularly limited, and any solvent may be used as long as it can extract the plasticizer. Non-limiting examples of the organic solvent may be methyl ethyl ketone, methylene chloride, hexane, etc., which has high extraction efficiency and easy drying, and methylene chloride may be used as the organic solvent when liquid paraffin is used as a plasticizer.

Since the organic solvent used in the plasticizer extraction process is mostly volatile and toxic, water may be used to suppress volatilization of the organic solvent if necessary.

The manufacturing method according to another embodiment of the present invention may further include heat setting after the plasticizer extraction. The heat setting is to reduce the shrinkage of the final film by removing the residual stress of the film, it is possible to adjust the heat shrinkage, permeability, etc. of the film according to the temperature and the fixed ratio when performing the heat setting. Specifically, the heat setting includes stretching at a draw ratio of 1 to 2 times in the width direction and relaxing at 80% to 100% with respect to the stretched width direction length. The heat setting may be performed at 100 ° C to 150 ° C, for example, may be performed at 125 ° C to 145 ° C. It is effective in removing residual stress of the film in the above range, and can improve physical properties.

The present invention provides a porous separator prepared by the method of manufacturing a porous separator according to the embodiments.

In the porous separator according to the embodiments of the present invention, the compressive thickness change rate (T) expressed by Equation 1 may be 20% or less, for example, 15% or less.

[Equation 1]

T = [T ₁ -T ₂ ] / T ₁ × 100

In Equation 1, T ₁ represents the thickness before heat compression of the separator, and T ₂ represents the thickness after heat compression of the separator at 90 ° C. for 5 minutes at 2.2 MPa pressure.

When the thickness change rate before and after compression is satisfied, it is possible to prevent deterioration of the cycle characteristics of the battery due to the change in the film thickness when the separator is pressed by the expansion during charging of the electrode.

In addition, the porous separator according to the embodiments of the present invention is the difference between the air permeability (P ₂ ) and the heat compression electric permeability (P ₁ ) after heating and compressing the separator for 5 minutes at 90 ℃ under 2.2 MPa pressure 400 sec / 100cc It may be: More specifically, the difference in air permeability after and before the heat compression may be 300 sec / 100 cc or less. Within this range, the air permeability to the pressure due to the expansion of the battery when the battery is charged, the cycle characteristics of the battery can be improved. In the porous separator according to the embodiments of the present invention, an electrolyte absorption amount when the separator is immersed in an electrolyte solution at 18 ° C. for 60 minutes may be 400 mg or more per 1 g of the separator, and specifically, 500 mg or more per 1 g of the separator. Separation membrane according to embodiments of the present invention can be improved by the absorption rate of the electrolyte by including pores of different pore size.

In addition, the porous membrane according to the embodiments of the present invention has a porosity ( P %) of 40 to 70%, air permeability ( S sec / 100cc) of 100 sec / 100cc to 300 sec / 100cc, the P and S The product may be 3000 ≦ S × P ≦ 7500, specifically 3000 ≦ S × P ≦ 7000.

When P and S satisfy the above-mentioned ranges, pores having different pore sizes have lower air permeability values than conventional separators having the same porosity. This can be improved.

The porous separator according to the embodiments of the present invention may have an average thickness of 7 μm to 20 μm and a variation in thickness may be less than 4% of the average thickness.

The porous separator according to the embodiments of the present invention may have an average puncture strength of 300 gf or more, and specifically 400 gf or more.

The porous membrane according to the embodiment of the present invention may have a longitudinal average tensile strength of 1600 kgf / cm ² or more and a width average tensile strength of 1800 kgf / cm ^{2 or} more, the longitudinal average tensile strength is specifically 1700 kgf / cm ^{2 or} more.

Porous separator according to the embodiments of the present invention by cutting the prepared membrane into a size of 50 × 50 mm and put in an oven at 120 ℃ shrinkage for 1 hour, after that by measuring the size of the shrinked separator to reflect the reduced size When measuring the shrinkage rate, the longitudinal shrinkage may be 5% or less, the widthwise shrinkage may be 3% or less, and more specifically, the longitudinal shrinkage may be 4% or less and the widthwise shrinkage may be 2% or less.

According to another example of the present invention, it may include a coating layer formed on one or both sides of the separator or porous separator prepared by the above-described manufacturing method.

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

Specifically, as the organic binder, polyvinylidene fluoride (PVdF) homopolymer, polyvinylidene fluoride-hexaxafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate ( polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate , Cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan ( pullulan), carboxyl methyl cell It may be used alone or as a mixture thereof selected from the group consisting of butadiene copolymers (acrylonitrilestyrene-butadiene copolymer) - Lawrence's (carboxyl methyl cellulose), and styrene acrylonitrile.

Molecular weight, content, etc. of the organic binder can be appropriately adjusted by the choice of those skilled in the art, non-limiting example, when using a PVdF-based binder, the adhesion between the coating layer and the separator can be enhanced, thereby improving the heat shrinkage rate By providing a separator having improved electrolyte impregnation, there is an advantage in that a battery in which electrical output can be efficiently produced can be produced.

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 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.

Inorganic particles in the coating layer may be included in 70% to 95% by weight, specifically 75% to 95% by weight, more specifically 80% to 95% 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 this example include dimethyl formamide, dimethyl sulfoxide, dimethyl acetamide, dimethyl carbonate, or N-methylpyrrolidone. (N-methylpyrrolydone) etc. are mentioned.

The content of the solvent may be 20 wt% to 99 wt%, specifically 50 wt% to 95 wt%, and more specifically 70 wt% to 95 wt%, 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.

Method for producing a coating separator according to the present example is an organic binder; Inorganic particles; And forming a coating composition comprising a solvent, and forming a coating layer with the coating composition on one or both surfaces of the separator described in another example of the present invention.

There is no limitation on the method of forming the coating layer on the separator, and may be performed by an appropriate method according to the choice of those skilled in the art.

Hereinafter, an electrochemical cell according to an embodiment of the present invention will be described. The electrochemical cell according to the embodiment of the present invention also includes a porous separator, a positive electrode, a negative electrode and an electrolyte prepared according to the above-described embodiments. The type of electrochemical cell is not particularly limited and may be a battery of a kind known in the art. For example, it 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 manufacturing the electrochemical cell of the present embodiment 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 separator comprising a separator according to embodiments of the present invention or a coating layer according to other embodiments of the present invention is disposed between the cathode and the cathode of the cell. After positioning, the battery may be manufactured by filling the electrolyte therein. 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 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. Specifically, the positive electrode includes a positive electrode active material capable of reversibly inserting and detaching lithium ions, and the positive electrode active material may be at least one selected from cobalt, manganese, nickel, and a composite metal oxide with lithium. . The solid solution ratio between the metals may be various, and in addition to these metals, Mg, Al, Co, Ni, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, An element selected from the group consisting of Fe, Sr, V, and rare earth elements may be further included. The anode may be, for example, a composite metal oxide of a metal selected from the group consisting of lithium and Co, Ni, Mn, Al, Si, Ti, and Fe, and specifically, lithium cobalt oxide (LCO.) For example LiCoO ₂ ), lithium nickel manganese cobalt oxide, NCM. For example Li [Ni (x) Co (y) Mn (z)] O ₂ ), lithium manganese oxide (Lithium manganese oxide, LMO, for example LiMn ₂ O ₄ , LiMnO ₂ ), lithium iron phosphate (LFP. For example LiFePO ₄ ), lithium nickel oxide (LNO, for example LiNiO ₂ ) and the like can be used. The negative electrode includes a negative electrode active material capable of inserting and desorbing lithium ions, and the negative electrode active material includes crystalline or amorphous carbon, or a carbon-based negative electrode active material (thermally decomposed carbon, coke, graphite) and combustion of a carbon composite. Organic polymer compounds, carbon fibers, tin oxide compounds, lithium metal or alloys of lithium and other elements can be used. For example, amorphous carbons include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1,500 ° C or lower, and mesophase pitch-based carbon fibers (MPCF). The crystalline carbon includes a graphite material, and specific examples thereof include natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. The negative electrode may include, for example, crystalline or amorphous carbon.

The positive electrode or the negative electrode may be prepared by dispersing a binder, a conductive material, and, if necessary, a thickener in a solvent in addition to an electrode active material to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector. The binder, the conductive material and the thickener may be used as commonly used in the art. For example, as the binder, polyvinylidene-fluoride (PVdF), styrene-butadiene rubber (SBR), and the like, carbon black as a conductive material, and carbonate methyl cellulose as a thickener (Carbonate methyl cellulose, CMC) can be used.

The electrode current collector used in the present embodiment is not particularly limited, and an electrode current collector commonly used in the art 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, a copper alloy or a combination thereof.

The positive electrode current collector and the negative electrode current collector may be in the form of a foil or a mesh.

The electrolyte solution used in the present embodiment 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), dimethylformamide (Dimethylformamide, DMF), Dipropyl carbonate (DPC), Dimethyl sulfoxide (DMSO), Acetonitrile, Dimethoxyethane, Diethoxyethane, Tetrahydrofuran ( Tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC) or gamma-butyrolactone (-Butyrolactone, GBL) Can be 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.

실시예 Example

실시예 1: 다공성 분리막의 제조Example 1 Preparation of Porous Membranes

70% by weight of high-density polyethylene (HDPE; manufactured by Mitsui Chemical) with a viscosity average molecular weight of 350,000 g / mol and ultra high molecular weight polyethylene (UHMWPE; UHMWPE; Mitsui with a viscosity average molecular weight of 1,000,000 g / mol); 30 wt% of Chemical Co., Ltd. was supplied to a twin screw extruder, and the liquid paraffin (Far East Emulsification) was injected into the twin screw extruder in an amount such that the weight ratio of the polyethylene to the polyethylene 30 to the liquid paraffin 70 was extruded.

After the extrusion, the gel phase obtained through the T-die was used to form a sheet using a cooling roll. The sheet was stretched in the longitudinal direction (Machine Direction, MD) at 90 ° C. and in the transverse direction (TD) at 110 ° C. (stretch ratio: 7 × 7).

The stretched sheet was immersed in methylene chloride (Samsung Fine Chemicals) and a water-methylene chloride zone (Water-MC zone) in which a water layer was formed on top of the methylene chloride to extract liquid paraffin, and then moved to a drying roll to dry.

Then, the dried sheet was heat-set in the transverse direction in the secondary stretching (lateral stretching ratio: 1.0 → 1.4 → 1.2, stretching temperature 128 ° C.) to prepare a porous separator having a thickness of 12 m.

실시예 2: 다공성 분리막의 제조Example 2 Preparation of Porous Membrane

In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the widthwise stretching temperature was 120 ° C and the longitudinal stretching temperature was 90 ° C.

실시예 3: 다공성 분리막의 제조Example 3 Preparation of Porous Membrane

In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the widthwise stretching temperature was 120 ° C and the longitudinal stretching temperature was 100 ° C.

실시예 4: 다공성 분리막의 제조Example 4 Preparation of Porous Membrane

In Example 3, the separator was manufactured in the same manner as in Example 3, except that polyethylene 27 was used to form liquid paraffin 73.

비교예 1: 다공성 분리막의 제조Comparative Example 1: Preparation of Porous Membrane

In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the longitudinal stretching temperature was 100 ° C and the widthwise stretching temperature was 110 ° C.

비교예 2: 다공성 분리막의 제조Comparative Example 2: Preparation of Porous Membrane

In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the longitudinal stretching temperature was 110 ° C and the widthwise stretching temperature was 120 ° C.

The composition of each separator according to Examples 1 to 4 and Comparative Examples 1 and 2 and the preparation conditions of each separator are shown in Table 1 below.

Table 1

		Example 1	Example 2	Example 3	Example 4	Comparative Example 1	Comparative Example 2
Raw material	HDPE	70 (wt%)	70 (wt%)	70 (wt%)	70 (wt%)	70 (wt%)	70 (wt%)
	UHMWPE	30 (wt%)	30 (wt%)	30 (wt%)	30 (wt%)	30 (wt%)	30 (wt%)
	LP viscosity @ 40 ℃	68cSt	68cSt	68cSt	68cSt	68cSt	68cSt
	PE / LP	30/70	30/70	30/70	27/73	30/70	30/70
Stretch	Drawing method	rotor	rotor	rotor	rotor	rotor	rotor
	Draw ratio	7 × 7	7 × 7	7 × 7	7 × 7	7 × 7	7 × 7
	Longitudinal drawing temperature	90 ℃	90 ℃	100 ℃	100 ℃	100 ℃	110 ℃
	Lateral stretching temperature	110 ℃	120 ℃	120 ℃	120 ℃	110 ℃	120 ℃
Heat setting	Lateral draw ratio	1.0 → 1.4 → 1.2	1.0 → 1.4 → 1.2	1.0 → 1.4 → 1.2	1.0 → 1.4 →→ 1.2	1.0 → 1.4 →→ 1.2	1.0 → 1.4 → 1.2
Heat setting	Temperature	128 ℃	128 ℃	128 ℃	128 ℃	128 ℃	128 ℃

HDPE High Density Polymer Resin (Mitsui chemical): Mv35 only

UHMWPE Ultra High Molecular Weight Polyethylene (Mitsui chemical): Mv1 million

PE polyethylene (Prime polymer)

LP: Liquid Paraffin, Methylene Chloride, Samsung Fine Chemicals

실험예 Experimental Example

For the separators prepared in Examples 1 to 4 and Comparative Examples 1 to 2, the porosity, air permeability, sticking strength, tensile strength, shrinkage, electrolyte absorption amount, film thickness change and heat permeability after heat compression were measured. It measured and the result is shown in Table 2.

TABLE 2

		Example 1	Example 2	Example 3	Example 4	Comparative Example 1	Comparative Example 2
Thickness (㎛)		12	12	12	12	12	12
Porosity (%)		42.3	42.0	42.2	51.2	41.6	43.0
Air permeability (sec / 100cc)		158	152	155	100	230	200
Sting strength (gf)		485	488	480	450	488	479
Tensile strength (kgf / cm ² )	MD	1,801	1,795	1,788	1,714	1,799	1,849
Tensile strength (kgf / cm ² )	TD	2,200	2,155	2,167	1,833	2,252	2,198
Shrinkage (105 ℃, 1 hr)	MD	3.0	3.0	3.0	2.5	2.5	3.0
Shrinkage (105 ℃, 1 hr)	TD	0.0	0.0	0.0	0.5	0.0	0.0
Electrolyte uptake per sample mass (mg / g)		567.7	545.9	545.8	779.7	218.3	327.5
% Change in film thickness after heat compression		14	15	15	18	21	21
Air compression after heat compression (sec / 100cc)		350	376	422	309	664	633

1. Porosity

Samples of 10 cm × 10 cm of each separator prepared in Examples and Comparative Examples were cut out to obtain their volume (cm 3) and mass (g), and the volume and mass and density of membrane (g / cm 3) The porosity was calculated from the following equation.

Porosity (%) = (volume-mass / sample density) / volume 100

Density of sample = density of polyethylene

2. Speculation

Each of the separators prepared in the above Examples and Comparative Examples was prepared to cut 10 samples cut from 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 to obtain air permeability.

3. Sticking strength

Each of the separators prepared in Examples and Comparative Examples was made of 10 samples cut at 10 different points in width (MD) 50 mm × length (TD) 50 mm, and then using GATO Tech G5 equipment. The sample was placed on a 10 cm hole and the punching force was measured while pressing with a 1 mm probe. The puncture strength of each sample was measured three times, and then the average value was calculated.

4. Tensile Strength

Each of the separators prepared in Examples and Comparative Examples was made of 10 samples cut at 10 different points in the form of a rectangle 10 mm x 50 mm TD, and then each sample was prepared. It was mounted on a UTM (tension tester) and bitten to have a measurement length of 20 mm, and then the sample was pulled to measure average tensile strength in the MD direction and the TD direction.

5. Shrinkage

Each of the separators prepared in Examples and Comparative Examples was prepared with 10 samples cut at 10 different points with a width of 50 mm and a length of 50 mm of TD. The samples were left in an oven at 105 ° C. for 1 hour, and then the average thermal shrinkage was calculated by measuring the shrinkage in the MD and TD directions of each sample.

6. Electrolyte Absorption

The microporous membrane was immersed for 1 hour in an electrolyte solution (electrolyte: LiBF ₄ , electrolyte concentration: 1mo1 / L, solvent: propylene carbonate) in which each of the separators prepared in Examples and Comparative Examples was kept at 18 ° C., and the mass was increased. Was investigated to calculate the amount of absorption per sample mass [increase in membrane mass (g) / mass of mass before absorption (g)].

7. Film thickness change rate and air permeability after heat compression

Each of the separators prepared in Examples and Comparative Examples was sandwiched between a pair of press plates having a smooth surface and heated by a press machine at 90 ° C. for 5 minutes under a pressure of 2.2 MPa (22 kgf / cm ² ). It was compressed and the film thickness was measured using a Litematic thickness meter (Model: VL-50) manufactured by Mitutoyo. The compression thickness change rate (T) of the following formula 1 was calculated.

[Equation 1]

_{_{T = [T 1 -T 2]}} / T 1 × 100

In addition, the air permeability was measured in the same manner as described in the air permeability of the separation membrane heat-compressed under the above conditions.

Having described the specific parts of the present invention in detail, it will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments, and thus the scope of the present invention is not limited thereto. will be. Thus, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims

Melt kneading and extruding a composition comprising a polymer resin and a plasticizer to form a cooled solidified sheet,

The solidified sheet is stretched at a temperature T 1 in the longitudinal direction and then stretched at a temperature T 2 in the width direction,

Extracting a plasticizer from the stretched sheet,

T 2 -T 1 ≥ 20 ℃ a method of producing a porous separator.
The method according to claim 1, wherein the T 1 is 80 ℃ to 110 ℃.
The manufacturing method of Claim 1 whose draw ratio of the said longitudinal direction is 5 times-10 times, and the draw ratio of the said width direction is 5 times-10 times.
The manufacturing method of Claim 3 whose draw ratio of the said longitudinal direction and the said width direction is 6 times-9 times, respectively, and the draw ratio of the said longitudinal direction and the draw ratio of the said width direction are the same.
The method of claim 1, wherein the polymer resin, the viscosity average molecular weight of a 1 × 10 5 g / mol to about 9 × 10 5 g / mol of high density polyethylene and ultra high molecular weight polyethylene having a viscosity-average molecular weight of not less than 9 × 10 5 g / mol It is a single or a mixture thereof selected from the group consisting of.
The method of claim 5, wherein the ultra high molecular weight polyethylene is included in an amount of 30 wt% or less based on the weight of the polymer resin.
The manufacturing method according to any one of claims 1 to 6, further comprising heat setting after the plasticizer extraction.
8. The method according to claim 7, wherein the heat setting comprises stretching at a draw ratio of 1 to 2 times in the width direction and relaxing at 80% to 100% with respect to the stretched width direction length.
The method according to any one of claims 1 to 6, wherein the porous separator has a compression thickness change rate (T) of 20% or less.

[Equation 1]

T = [T 1 -T 2 ] / T 1 × 100

In Equation 1, T 1 represents the thickness before heat compression of the separator, and T 2 represents the thickness after heat compression of the separator at 90 ° C. for 5 minutes at 2.2 MPa pressure.
Porosity (P%) is 40 to 70%,

Air permeability (S sec / 100cc) is 100 sec / 100cc to 300 sec / 100cc,

Wherein P and S satisfies 3000 ≦ S × P ≦ 8500, porous separator.
The porous membrane of claim 10, wherein the porous membrane has a compressive thickness change rate (T) of 20% or less.

[Equation 1]

T = [T 1 -T 2 ] / T 1 × 100

In Equation 1, T 1 represents the thickness before heat compression of the separator, and T 2 represents the thickness after heat compression of the separator at 90 ° C. for 5 minutes at 2.2 MPa pressure.
The thickness before heat compression of the porous separator of Formula 1 (T 1 ) and the compression thickness change rate (T) of the following formula 1 of the thickness (T 2 ) of the thickness (T 2 ) after heating and compressing the separator at 90 ° C. for 5 minutes at 2.2 MPa pressure is 20%. Less than, porous separator.

[Equation 1]

T = [T 1 -T 2 ] / T 1 × 100
The porous separator according to claim 10 or 12, wherein an electrolyte absorption amount when the separator is immersed in an electrolyte at 18 ° C. for 60 minutes is 400 mg or more per gram of the separator.
The porous membrane according to claim 10 or 12, wherein the separator has a difference between air permeability (P 2 ) and heat compression pre-air permeability (P 1 ) after heating and compression at 90 ° C. for 5 minutes at 2.2 MPa pressure of 400 sec / 100 cc or less. Separator.
The high-density polyethylene according to claim 10 or 12, wherein the polymer resin has a viscosity average molecular weight of 1 × 10 5 g / mol to 9 × 10 5 g / mol, and a viscosity average molecular weight of 9 × 10 5 g / mol. Porous separation membrane which is selected from the group consisting of ultra-high molecular weight polyethylene or more or a mixture thereof.
The porous membrane of claim 15, wherein the ultra high molecular weight polyethylene is included in an amount of 30 wt% or less based on the weight of the polymer resin.
An electrochemical cell comprising the porous separator according to claim 10.
18. The electrochemical cell of claim 17, wherein said electrochemical cell is a lithium secondary battery.